Research reported in this publication was supported by an NSF Graduate Research Fellowship (RJW) and by the National Institute on Drug Abuse of the National Institutes of Health and FDA Center for Tobacco Products (CTP) under Award Number P50DA036151(EJN and NAA). The content is solely the responsibility of the authors and does not necessarily represent the official view of the National Institutes of Health.

All experiments were conducted according to the National Institutes of Health (NIH) Guide for the Care and Use of Laboratory Animals and were approved by the Yale University Institutional Animal Care and Use Committee (IACUC).
1) Pre-surgical Preparations
<ol>
	<li>Oral solution preparation
	<ol>
		<li>Create solutions of 10% sucrose and 0.005% L-menthol in deionized water (pH 7.4). Store these solutions in closed containers, at RT, and remake every 2 weeks, to prevent degradation.</li>
	</ol>
	</li>
	<li>Electrode calibration solutions
	<ol>
		<li>Make Tris buffer (pH 7.4) at any time prior to calibration. The solution consists of 12.0 mM Tris-HCl, 140 mM NaCl, 3.25 mM KCl, 1.20 mM CaCl2, 1.25 mM NaH2PO4, 1.20 mM MgCl2, and 2.00 mM Na2SO4.</li>
		<li>Create a stock solution of 10 mM dopamine (DA; dopamine hydrochloride) in 0.1 M perchloric acid. The perchloric acid helps prevent oxidation of dopamine. Store this stock solution at -20 &#176;C and use for up to 6 months. Make several aliquots of the DA stock solution for storage to use each aliquot only once.</li>
		<li>From the 10 mM DA stock, dilute solutions in Tris buffer to concentrations of 1 &#956;M, 500 nM, 250 nM, 125 nM, 62.5 nM, and 31.25 nM.</li>
		<li>For pH calibration, prepare solutions of Tris buffer with the pH of 7.2, 7.3, 7.5, and 7.6. This will provide solutions that mimic pH shifts that may occur during the in vivo experiment.</li>
	</ol>
	</li>
	<li>Electrode fabrication
	<ol>
		<li>By vacuum suction, aspirate a T-650 carbon fiber (7 &#956;m diameter) into a borosilicate glass capillary (length 10 mm, outside diameter 0.6 mm, inside diameter 0.4 mm).</li>
		<li>Place glass capillary filled with carbon fiber into a vertical electrode puller. For initial parameters, set the heater to 55.0 and turn off the magnet. However, further optimization may be necessary as both heater and magnetic settings vary from lab to lab. 
		Note: The electrode should be at least 5.5 cm long (including taper) so that it can easily fit into the micromanipulator and be inserted at least 6.9 mm below dura in the rat brain. If the electrode is too short, recordings from ventral portion of the nucleus accumbens will not be achievable. On the other hand, the total electrode length should not exceed 6.5 cm otherwise it will be too long to fit into the micromanipulator.</li>
		<li>Using a light microscope, cut the exposed carbon-fiber so that it extends 75-100 &#956;m beyond the end of the glass. Verify that the electrode has a very tight, barely discernible, seal between the glass electrode and carbon fiber, which will produce minimal noise during subsequent recording. Discard the electrode if there are any noticeable cracks in the glass or if the seal is loose, which is indicative of a poor seal. For more detailed instructions see [12] and [13].</li>
	</ol>
	</li>
	<li>Assembling the electrode into the micromanipulator
	<ol>
		<li>Obtain a 3 in, 30G&#160;wire that is insulated along half the length of the wire and use a small brush to apply a thin layer of silver paint directly to the wire. Immediately after applying silver paint, insert the wire into the hole on the top of the electrode to provide a physical and electrical connection to the carbon fiber. Under a microscope, ensure that the silver wire makes contact with the carbon fiber.</li>
		<li>Secure the silver wire and electrode to the micromanipulator using heat shrink.</li>
		<li>Place the prepared carbon-fiber electrode into purified isopropyl alcohol (IPA) for at least 10 min to clean the electrode surface and to increase subsequent sensitivity to dopamine. After soaking in IPA, rinse the carbon fiber with tap water to remove the IPA.</li>
	</ol>
	</li>
	<li>Reference electrode fabrication
	<ol>
		<li>Take a 13 mm silver wire containing an approximately 6 mm Ag/Ag Cl mesh (7 mm silver wire alone, 6 mm mesh, 0.4 mm diameter), cut the silver portion down to approximately half its original length and solder the silver portion of the wire to a gold pin.</li>
		<li>Apply epoxy over the solder on the pin.</li>
		<li>Dip the Ag/Ag Cl mesh end into a copolymer of 5% polytetrafluroethylene and perfluoro-3,6-dioxa-4-methyl-7octene-sulfonic acid 5 times, with 30 min&#160;air drying periods between each dip.</li>
		<li>Allow the coated Ag/Ag Cl mesh to air dry O/N.</li>
		<li>Cure in oven at 120 &#186;C for 1 hr.</li>
	</ol>
	</li>
</ol>
&#160;2) Combined Intraoral Surgery and Intracranial Cannulation Surgery (Approximately 75 min)
<ol>
	<li>Oral catheter fabrication
	<ol>
		<li>Make the oral catheter, and sterilize by ethylene oxide sterilization, at least 10 days prior to surgery.</li>
		<li>Cut PE 100 tubing into 6 cm long segments.</li>
		<li>Using a soldering iron, melt one end of the PE tubing and immediately press against a solid surface to cool the PE tubing. The result should create a small, flat disc at one end of the PE tubing and should not be flanged. Use a needle (18 G) or push pin to create a hole in the center of this disc.</li>
		<li>On the other end of the PE tubing, snugly insert the blunt end of a 18 G needle into the tube.</li>
		<li>Using a standard paper hole puncher, punch several circular pieces of a polytetrafluroethylene sheet (3.18 mm thick, 6 mm in diameter) to create polytetrafluroethylene washers.</li>
		<li>Create a hole in the center of the washer. Take the needle attached to the PE tubing and push it completely through the washer. Once the needle is through, slide the washer to the bottom of the PE tubing so that it is flush against the washer.</li>
	</ol>
	</li>
	<li>Oral surgery
	<ol>
		<li>After sterilizing the surgical tools, cannula (trimmed to 2.5 mm below the pedestal before sterilization), and reference electrode, anesthetize the rat with an intraperitoneal injection of ketamine (100 mg/kg) and xylazine (10 mg/kg).
		<ol>
			<li>After 5 min, apply a noxious stimulus test (foot or tail pinch) to assess the level of anesthesia. If the subject shows any physical reaction to the noxious stimulus test (flinch response, increase in respiratory or heart rate), administer a ketamine boost of 10% to 15% of the original dose and repeat the noxious stimulus protocol above.</li>
		</ol>
		</li>
		<li>After the rat is fully anesthetized and shows no reaction to the noxious stimulus test, use animal hair clippers to shave the rat&#39;s fur from the eyes to about 2 mm behind the ears. Then place the rat on a thin water recirculating heating pad to maintain body temperature during surgery. Apply eye lubricant. Administer the non-steroidal anti-inflammatory (NSAID) drug, Carprofen (5 mg/kg), by intraperitoneal injection prior to performing any incisions and prior to inserting intraoral cannulas. Use aseptic technique at all times.</li>
		<li>Apply betadine followed by 70% ethanol to clean the skin. Repeat 3 times.</li>
		<li>Place the rat on its back, and open the mouth using a sterile cotton swab. Find the first upper molar.</li>
		<li>Insert the needle into the tissue between the cheek and the first upper molar until the needle exits just behind and medial to the ears.</li>
		<li>Pierce the needle through the skin until the PE tubing exits the skin and is accessible.</li>
		<li>Pull up on the cannula (gripping by the cannula itself and not the needle) and secure the polytetrafluroethylene washer into the molars so that the catheter remains in place. 
		Note: Cutting the washer into a trapezoid shape and securing it against the molars with the flat side facing the cheek makes this step easier.</li>
		<li>Take another polytetrafluroethylene washer and slide it over the exposed needle, down the plastic tubing, and abut against the incision.</li>
		<li>To secure the polytetrafluroethylene washer, use sterilized tape to create a triangular &#34;flag&#34; so that the washer does not slide up. Secure the washer against the rat&#39;s skin and the sterilized tape.</li>
		<li>Cut the exposed catheter to allow 2-4 cm of tubing to be exposed above the rat&#39;s head.</li>
		<li>Repeat steps 2.2.1 through 2.2.10 for the other side of the mouth.</li>
	</ol>
	</li>
	<li>Intracranial surgery for voltammetry
	<ol>
		<li>Place the rat in the stereotaxic frame and clean the animal&#8217;s scalp using a two stage scrub (a betadine scrub followed by a 70% ethanol scrub, perform with a 3 cycle repetition).</li>
		<li>Use sterilized needle nose tweezers and surgical scissors to cut away a 15 x 15 mm section of scalp tissue.</li>
		<li>Gently clean the surface of the skull using sterilized cotton tip applicators. Further clean the skull by applying 2 to 3 drops of 3% hydrogen peroxide.</li>
		<li>Use a stereotaxic drill to make 3 small (1 mm diameter) holes in the skull for subsequent insertion of screws, 1 hole for the guide cannula, 1 hole for the stimulating electrode, and 1 hole for the reference electrode.</li>
		<li>For recordings in the NAc core, position the guide cannula at 1.2 mm anterior and 1.4 mm lateral to Bregma. Lower the cannula apparatus until the plastic base is flush with the skull.</li>
		<li>Place the sterilized reference electrode in the hemisphere contralateral to the guide cannula. Lower the reference approximately 2 mm below the dura.</li>
		<li>Position the stimulating electrode at 5.2 mm posterior and 1.0 mm lateral to Bregma and lowered 8.0 mm below dura to target the ventral tegmental area (VTA).</li>
		<li>Use a sterilized small surgical screwdriver to secure screws to the skull. Then, insert the reference electrode, stimulating electrode, and guide cannula. Finally, secure all components using cranioplastic cement.</li>
		<li>For the first 48 hours of post-operative care, administer the non-steroidal anti-inflammatory drug (NSAID) Carprofen by subcutaneous injection (5 mg/kg). Allow at least 1 week for complete surgical recovery prior to performing voltammetry recording.
		<ol>
			<li>During post-operative care, flush oral catheters daily with water. Provide food saturated in water for 2 days to aid the animal in chewing and eating.&#160; Provide daily monitoring for potential signs of stress of pain (due to mild infection or dehydration) and provide appropriate interventions as necessary (including administration of fluids, topical administration of antiseptics, and or NSAID Carprofen administration at 5 mg/kg).</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
3) Voltammetric Recordings in Awake, Freely Moving Rat
<ol>
	<li>Lowering the electrode and acquiring a DA training set.
	<ol>
		<li>On the day of the experiment, check the patency of the oral cannula by infusing 200 &#956;l of water and observing orofacial responses (to verify that the rat is tasting the water).</li>
		<li>Attach the FSCV headstage to the rat by inserting the stimulating electrode (on the headstage) into the bipolar stimulating electrode cannula (on the rat). Thus, the headstage (miniaturized current-to-voltage converter) connects directly to the bipolar stimulating electrode.</li>
		<li>Remove the dummy cannula from the cannula apparatus and apply two drops of 50% heparin solution into the cannula. Then gently insert a dummy cannula (slightly longer that the dummy cannula that was previously removed) to clear any blood clots or glial scarring that may have occurred, which will break carbon fiber electrodes that will subsequently be inserted during the experiment. Extend the cannula used for clearing clots 3-4 mm below the skull (at least 2 mm above the recording site).</li>
		<li>Insert the micromanipulator, with electrode, into the guide cannula and place the omega ring in a &#34;locked&#34; position.</li>
		<li>Connect the reference electrode wire from the headstage to the appropriate pin. Then connect the working electrode wire from the micromanipulator to the appropriate wire on the headstage.</li>
		<li>Lower the electrode to approximately 4-4.5 mm below skull.</li>
		<li>Use a potentiostat to apply a triangular waveform (400 V/s, -0.4 to +1.3 V). Apply the waveform to the electrode at 60 Hz for at least 10 min, then change the waveform application frequency to 10 Hz for subsequent experimental recordings. 
		Note: The 60 Hz waveform application step produces a stable carbon fiber surface and will help prevent electrical drift</li>
		<li>Apply electrical stimulation to the VTA using various frequencies (10 to 60 Hz) pulses (10 to 30 pulses) and currents (50 to 150 &#956;A) all with a pulse width of 2 ms/phase, to evoke different concentrations of DA release and pH shifts. Acquire at least 5 different concentrations of DA release and 5 different pH shifts. Wait (2 - 3 min&#160;minimum) between stimulations to allow for vesicular reloading[14]. 
		Note: It is important to obtain stimulations that produce DA concentrations across the entire range that will be collected during the subsequent experiment since they will be used as a training set for Principal Component Analysis (see section 5.1).</li>
		<li>Lower the electrode into the NAc core (6.3 mm ventral to dura). Subsequently lower the electrode in 100 &#956;m increments within the NAc core until transient DA release events are observed at frequencies of at least 1 per min.</li>
		<li>Connect the tubing (inner diameter 1/32&#34;, outer diameter 3/32&#34;) to a 20 ml syringe, attached to a syringe pump. On the other end of the tube, use a beveled 23 G needle to connect the tubing to the rat&#39;s cannula. Ensure that the tubing is filled completely with the desired tastant and verify that no bubbles exist in the tubing. 
		Note: Typically, administer a small amount of tastant into the mouth of the rat prior to recording to ensure that the first infusion for recording delivers the full infusion amount and not any residual water or air in the tubing. Moreover, this allows the animal to have some prior experience with the tastant since novel tastants, even appetitive ones, can be aversive initially due to its novelty.</li>
		<li>For data collection, infuse 200 &#956;l of tastant (6.5 sec using a pump and previously described tubing). Infuse the tastant every 1-3 min. Infuse a total of 25 times per tastant. Each infusion delivers 200 &#956;l of solution.</li>
		<li>If multiple tastants are being delivered in a single experiment, flush the oral catheter with water after collecting data for one tastant and wait at least 20 min&#160;before infusing the new tastant.</li>
		<li>After the DA recording session, prepare for histological verification by creating a small lesion at the recording site. To preserve the carbon fiber electrode for subsequent calibration, first retract the electrode and remove the micromanipulator. Then use a new micromanipulator with a glass microelectrode and a tungsten wire (extending 100&#160;&#956;m beyond the glass tip) to the same depth (below dura) as the original carbon fiber microelectrode.</li>
		<li>For histological verification, create a small lesion by applying 3 V at the tungsten wire and increasing the voltage at 1 V increments, every 10 sec, until the 10 V setting is reached.</li>
		<li>If a standard concentration curve has already been created using multiple carbon fiber electrodes, perform the lesion step above (3.1.14) by applying the potential directly the carbon fiber electrode. 
		Note: This lesion method will damage the carbon fiber and prevent subsequent calibration with that specific electrode.</li>
		<li>Euthanize the animal using a lethal injection pentobarbital (150 mg/kg, i.p.).</li>
		<li>Dislodge the headcap with the cannulae using pliers by pulling directly upward on the headcap. Do not twist the headcap since this will cause unnecessary damage to the brain and make it challenging to identify the location of the electrode during histology.
		<ol>
			<li>Remove the brain and place in 4% formalin for 3 days followed by 30% sucrose for 1 week. Create 30 &#956;m slices using a cryostat, mount on cover slips and examine slices under a light microscope to identify the location of the carbon fiber or tungsten lesion. 
			Note: Perfusion is optional for 3.1.17.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
4) Electrode Calibration
<ol>
	<li>Using the flow cell to create a current-concentration conversion factor.
	<ol>
		<li>In order to determine electrode sensitivity, calibrate electrodes after each experiment using a flow &#34;t-cell&#34; apparatus. Lower the electrode into the &#34;t-cell&#34; while Tris buffer, pH solutions, or DA solutions are washed over the electrode surface (at a rate of 2 ml/min). Use a six-position air solenoid actuator to switch back and forth between buffer and pH or DA solution.</li>
		<li>For each calibration, collect voltammetric data during 5 sec application of Tris buffer (baseline) followed by 5 sec application of pH or DA solution, followed by 20 sec application of Tris buffer (30 sec total file). Repeat each run 3 times for each calibration standard concentration, counterbalancing between different concentrations of each standard.</li>
		<li>For each sample collection, measure the peak DA or pH-evoked current. Average the peak current across each trial to obtain a concentration versus peak current relationship. For more detailed instructions see [12] and [13].</li>
	</ol>
	</li>
</ol>
5) Data Analysis
<ol>
	<li>Using a training set in principal component analysis (PCA) 
	Note: During a voltammetry experiment, output is produced as current, which is the result of dopamine oxidation and reduction, pH shifts, and electrochemical noise. PCA allows separation of these factors so that one can isolate the desired components (DA and pH) and remove additional components that might distort the desired signals (for a more detailed description, see 15, 16).
	<ol>
		<li>Assign a calibration factor to the output current (approximately 5-10 nA/&#956;M) after PCA to allow concentration values of the analytes to be determined.</li>
		<li>Use the training set obtained during an experiment to &#34;train&#34; the PCA model to separate out DA, pH, and other factors. PCA takes the training set cyclic voltammograms (collected in section 3.1.8) and determines which essential characteristics of the voltammogram can be used to identify each analyte collected during in vivo voltammetry recordings.</li>
		<li>To determine the number of principal components to keep, use a Malinowski F-test. Typically, keep only 2 or 3 principal components which normally explain about 95-99% of the variance in the data. For further discussion on implementing the Malinowski F-test, see17. 
		Note: Once the number of components are determined, the PCA analysis effectively will project the measured voltammograms from DA and pH training sets onto the principal components that have been retained. The result is a data set that has been filtered so that only DA (or pH) data remains and the residual data that does not resemble DA or pH is removed (See Representative Results for expected output). For a further detailed explanation and step by step instruction for using PCA for voltammetric analysis see Materials sheet and16, 17.</li>
	</ol>
	</li>
</ol>

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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+neuroscience+of+pleasure.+Focus+on+'Ventral+pallidum+firing+codes+hedonic+reward:+when+a+bad+taste+turns+good.">The neuroscience of pleasure. Focus on 'Ventral pallidum firing codes hedonic reward: when a bad taste turns good.</a> J Neurophysiol. 96 (5), 2175-2176 (2006).</li><li>Bunin, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Release+and+uptake+rates+of+5-hydroxytryptamine+in+the+dorsal+raphe+and+substantia+nigra+reticulata+of+the+rat+brain.">Release and uptake rates of 5-hydroxytryptamine in the dorsal raphe and substantia nigra reticulata of the rat brain.</a> J Neurochem. 70 (3), 1077-1087 (1998).</li><li>Zimmerman, J. B., Wightman, R. 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The authors have nothing to disclose.

Intraoral tastant delivery combined with FSCV permits analysis of &#8220;real-time&#8221; DA responses to oral flavorants. There are three critical steps in the protocol that are required for successful DA measurements. First, proper implantation of the oral catheter is critical for delivery of flavorants. Ensuring that the catheter is inserted behind the first molar and wedged into place prevents the catheter from losing patency and prevents accidental removal by the animal. Flushing the catheter during the first few da...

Erratum: Examination of Rapid Dopamine Dynamics with Fast Scan Cyclic Voltammetry During Intra-oral Tastant Administration in Awake Rats

Phasic DA release plays an important role in mediating reward-directed behavior [1-3]. However, isolating and studying how a primary reward alters phasic DA release is often complicated by co-occurring behavioral or cognitive processes that are also capable of altering phasic DA release - such as decision making processes or reward-directed motor behavior to acquire the reward. In the current work, we isolate phasic DA responses to tastants through the use of in vivo fast-scan cyclic voltammetry (FSCV) combined with tastant delivery through intraoral cannulae. This technique bypasses choice and action and allows us to examine extracellular DA release during direct infusion of a tastant to the palate of a rat.
FSCV is an electrochemical technique with high temporal and spatial resolution, permitting measurements of DA release in a discrete local area (approximately 100 &#181;m) on a sub-second scale (10 Hz resolution). The combination of intra-oral delivery and FSCV provides the advantage of observing rapid, 'real-time' DA responses to a tastant, which cannot be examined using conventional microdialysis methods. Furthermore, phasic DA release in response to either rewards or reward-associated cues occurs at concentrations between 20-100 nM, which is above the 10-20 nM detection threshold for FSCV [4]. The high spatial resolution of FSCV also permits recording from sub-regions of small brain areas, such as the nucleus accumbens core (NAc). Thus, FSCV combined with intraoral infusions of tastants is an ideal model for studying how tastants or other stimuli alter phasic DA release in an awake, behaving animals. Indeed, these techniques have permitted experiments investigating how rewarding and aversive tastants alter extracellular DA release [5]. 
Over the last decade, FSCV analyses have been successfully combined with intravenous drug delivery [6] and rat self-administration paradigms [7, 8] to identify the role of phasic DA mechanisms in drug addiction models. In addition, combined intraoral delivery with FSCV has been used to examine how tastant cues paired with cocaine availability modulate phasic DA release and behavioral responses that reflect emotional affect [3]. This combined intraoral and FSCV methodology can also be powerfully utilized to examine phasic DA responses to flavorants, such as menthol and oral sweeteners, that are added to cigarettes and dissolvable tobacco products [9-11]. Although many of the flavorants added to tobacco products are appetitive [9-11], it is unknown if these flavorants increase phasic DA release in a manner consistent with a rewarding hedonic valence. Indeed, flavorants added to cigarettes and to dissolvable tobacco products may have direct effects on the DA reward system and may act through dopaminergic mechanisms to influence the rewarding valence of cigarettes and other tobacco products. Thus, intraoral delivery combined with FSCV can provide new understanding on how flavorants modulate rapid DA release. The use of combined intra-oral and in vivo FSCV methodology, and the data obtained from such studies, can also facilitate future studies to determine how flavorants and nicotine interact to alter DA signaling and to potentially modulate nicotine reinforcement. Further, the data gained from such studies can be used to inform regulatory decisions about tobacco product flavorants.

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examination of rapid dopamine dynamics with fast scan cyclic voltammetry during intra-oral tastant administration in awake rats

Rapid, phasic dopamine (DA) release in the mammalian brain plays a critical role in reward processing, reinforcement learning, and motivational control. Fast scan cyclic voltammetry (FSCV) is an electrochemical technique with high spatial and temporal (sub-second) resolution that has been utilized to examine phasic DA release in several types of preparations. In vitro experiments in single-cells and brain slices and in vivo experiments in anesthetized rodents have been used to identify mechanisms that mediate dopamine release and uptake under normal conditions and in disease models. Over the last 20 years, in vivo FSCV experiments in awake, freely moving rodents have also provided insight of dopaminergic mechanisms in reward processing and reward learning. One major advantage of the awake, freely moving preparation is the ability to examine rapid DA fluctuations that are time-locked to specific behavioral events or to reward or cue presentation. However, one limitation of combined behavior and voltammetry experiments is the difficulty of dissociating DA effects that are specific to primary rewarding or aversive stimuli from co-occurring DA fluctuations that mediate reward-directed or other motor behaviors. Here, we describe a combined method using in vivo FSCV and intra-oral infusion in an awake rat to directly investigate DA responses to oral tastants. In these experiments, oral tastants are infused directly to the palate of the rat &#8211; bypassing reward-directed behavior and voluntary drinking behavior &#8211; allowing for direct examination of DA responses to tastant stimuli.

FSCV combined with intraoral catheter implantation was used to examine how sucrose, an appetitive tastant, modulates phasic DA release in the NAc core. Prior to tastant infusion, electrical stimulation (150 &#181;A, 60 Hz, 24 pulses; indicated by the red bar) of the VTA produces robust increases in phasic DA release in the NAc (Figure 1). Figure 1 shows a color plot with potential on the y-axis, time on the x-axis, and current (represented as false color) on the z-axis. Below the color p...

Watch this Scientific Journal Video about Examination of Rapid Dopamine Dynamics with Fast Scan Cyclic Voltammetry During Intra-oral Tastant Administration in Awake Rats at JoVE.com

Examination of Rapid Dopamine Dynamics with Fast Scan Cyclic Voltammetry During Intra-oral Tastant Administration in Awake Rats

Rapid fluctuations in extracellular dopamine (DA) mediate both reward processing and motivated behavior in mammals. This manuscript describes the combined use of fast scan cyclic voltammetry (FSCV) and intra-oral tastant administration to determine how tastants alter rapid dopamine release in awake, freely moving rats.

Rapid, phasic dopamine (DA) release in the mammalian brain plays a critical role in reward processing, reinforcement learning, and motivational control. ...

examination-rapid-dopamine-dynamics-with-fast-scan-cyclic-voltammetry

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12.6K Views.  Yale University. Rapid fluctuations in extracellular dopamine (DA) mediate both reward processing and motivated behavior in mammals. This manuscript describes the combined use of fast scan cyclic voltammetry (FSCV) and intra-oral tastant administration to determine how tastants alter rapid dopamine release in awake, freely moving rats.

Video: Examination of Rapid Dopamine Dynamics with Fast Scan Cyclic Voltammetry During Intra-oral Tastant Administration in Awake Rats

Creating Dynamic Images of Short-lived Dopamine Fluctuations with lp-ntPET:  Dopamine Movies of Cigarette Smoking

We describe experimental and statistical steps for creating dopamine movies of the brain from dynamic PET data. The movies represent minute-to-minute fluctuations of dopamine induced by smoking a cigarette. The smoker is imaged during a natural smoking experience while other possible confounding effects (such as head motion, expectation, novelty, or aversion to smoking repeatedly) are minimized.
We present the details of our unique analysis. Conventional methods for PET analysis estimate time-invariant kinetic model parameters which cannot capture short-term fluctuations in neurotransmitter release. Our analysis - yielding a dopamine movie - is based on our work with kinetic models and other decomposition techniques that allow for time-varying parameters 1-7. This aspect of the analysis - temporal-variation - is key to our work. Because our model is also linear in parameters, it is practical, computationally, to apply at the voxel level. The analysis technique is comprised of five main steps: pre-processing, modeling, statistical comparison, masking and visualization. Preprocessing is applied to the PET data with a unique 'HYPR' spatial filter 8 that reduces spatial noise but preserves critical temporal information. Modeling identifies the time-varying function that best describes the dopamine effect on 11C-raclopride uptake. The statistical step compares the fit of our (lp-ntPET) model 7 to a conventional model 9. Masking restricts treatment to those voxels best described by the new model. Visualization maps the dopamine function at each voxel to a color scale and produces a dopamine movie. Interim results and sample dopamine movies of cigarette smoking are presented.

We present a novel PET imaging approach for capturing dopamine fluctuations induced by cigarette smoking. Subjects smoke in the PET scanner. Dynamic PET images are modeled voxel-by-voxel in time by lp-ntPET, which includes a time-varying dopamine term. The results are 'movies' of dopamine fluctuations in the striatum during smoking.

We describe experimental and statistical steps for creating dopamine movies of the brain from dynamic PET data. The movies represent minute-to-minute ...

Construction of Microdrive Arrays for Chronic Neural Recordings in Awake Behaving Mice

State-of-the-art electrophysiological recordings from the brains of freely behaving animals allow researchers to simultaneously examine local field potentials (LFPs) from populations of neurons and action potentials from individual cells, as the animal engages in experimentally relevant tasks. Chronically implanted microdrives allow for brain recordings to last over periods of several weeks. Miniaturized drives and lightweight components allow for these long-term recordings to occur in small mammals, such as mice. By using tetrodes, which consist of tightly braided bundles of four electrodes in which each wire has a diameter of 12.5 &mu;m, it is possible to isolate physiologically active neurons in superficial brain regions such as the cerebral cortex, dorsal hippocampus, and subiculum, as well as deeper regions such as the striatum and the amygdala. Moreover, this technique insures stable, high-fidelity neural recordings as the animal is challenged with a variety of behavioral tasks. This manuscript describes several techniques that have been optimized to record from the mouse brain. First, we show how to fabricate tetrodes, load them into driveable tubes, and gold-plate their tips in order to reduce their impedance from M&Omega; to K&Omega; range. Second, we show how to construct a custom microdrive assembly for carrying and moving the tetrodes vertically, with the use of inexpensive materials. Third, we show the steps for assembling a commercially available microdrive (Neuralynx VersaDrive) that is designed to carry independently movable tetrodes. Finally, we present representative results of local field potentials and single-unit signals obtained in the dorsal subiculum of mice. These techniques can be easily modified to accommodate different types of electrode arrays and recording schemes in the mouse brain.

The design and assembly of microdrives for in vivo electrophysiological recordings of brain signals from the mouse is described. By attaching microelectrode bundles to sturdy driveable carriers, these techniques allow for long-term and stable neural recordings. The lightweight design allows for unrestricted behavioral performance by the animal following drive implantation.

State-of-the-art electrophysiological recordings from the brains of freely behaving animals allow researchers to simultaneously examine local field ...

A Procedure to Study the Effect of Prolonged Food Restriction on Heroin Seeking in Abstinent Rats

In human drug addicts, exposure to drug-associated cues or environments that were previously associated with drug taking can trigger relapse during abstinence. Moreover, various environmental challenges can exacerbate this effect, as well as increase ongoing drug intake.
The procedure we describe here highlights the impact of a common environmental challenge, food restriction, on drug craving that is expressed as an augmentation of drug seeking in abstinent rats.
Rats are implanted with chronic intravenous i.v. catheters, and then trained to press a lever for i.v. heroin over a period of 10-12 days. Following the heroin self-administration phase the rats are removed from the operant conditioning chambers and housed in the animal care facility for a period of at least 14 days. While one group is maintained under unrestricted access to food (sated group), a second group (FDR group) is exposed to a mild food restriction regimen that results in their body weights maintained at 90% of their nonrestricted body weight. On day 14 of food restriction the rats are transferred back to the drug-training environment, and a drug-seeking test is run under extinction conditions (i.e.&#160;lever presses do not result in heroin delivery).
The procedure presented here results in a highly robust augmentation of heroin seeking on test day in the food restricted rats. In addition, compared to the acute food deprivation manipulations we have used before, the current procedure is a more clinically relevant model for the impact of caloric restriction on drug seeking. Moreover, it might be closer to the human condition as the rats are not required to go through an extinction-training phase before the drug-seeking test, which is an integral component of the popular reinstatement procedure.

A procedure that allows a demonstration of robust augmentation of drug seeking in food-restricted rats is described. Following heroin self-administration training, rats go through an abstinence period, in a drug-free environment, during which they are mildly food restricted. Drug seeking is then tested in the drug-associated environment.

In human drug addicts, exposure to drug-associated cues or environments that were previously associated with drug taking can trigger relapse during ...

A Novel Procedure for Evaluating the Reinforcing Properties of Tastants in Laboratory Rats: Operant Intraoral Self-administration

This paper describes a novel method for studying the bio-behavioral basis of addiction to food. This method combines the surgical component of taste reactivity with the behavioral aspects of operant self-administration of drugs. Under very brief general anaesthesia, rats are implanted with an intraoral (IO) cannula that allows delivery of test solutions directly in the oral cavity. Animals are then tested in operant self-administration chambers whereby they can press a lever to receive IO infusions of test solutions. IO self-administration has several advantages over experimental procedures that involve drinking a solution from a spout&#160;or operant responding for solid pellets or solutions delivered in a receptacle. Here, we show that IO self-administration can be employed to study self-administration of high fructose corn syrup (HFCS). Rats were first tested for self-administration on a progressive ratio (PR) schedule, which assesses the maximum amount of operant behavior that will be emitted for different concentrations of HFCS (i.e.&#160;8%, 25%, and 50%). Following this test, rats self-administered these concentrations on a continuous schedule of reinforcement (i.e.&#160;one infusion for each lever press) for 10 consecutive days (1 session/day; each lasting 3 hr), and then they were retested on the PR schedule. On the continuous reinforcement schedule, rats took fewer infusions of higher concentrations, although the lowest concentration of HFCS (8%) maintained more variable self-administration. Furthermore, the PR tests revealed that 8% had lower reinforcing value than 25% and 50%. These results indicate that IO self-administration can be employed to study acquisition and maintenance of responding for sweet solutions. The sensitivity of the operant response to differences in concentration and schedule of reinforcement makes IO self-administration an ideal procedure to investigate the neurobiology of voluntary intake of sweets.

The current study evaluates a novel procedure for assessing the reinforcing effects of palatable solutions in laboratory rats: intraoral self-administration. To this end, operant responding (i.e.&#160;lever pressing) for intraoral infusions of sweet solutions at different concentrations was measured on continuous and progressive ratios schedules of reinforcement.

This paper describes a novel method for studying the bio-behavioral basis of addiction to food. This method combines the surgical component of taste ...

Barnes Maze Testing Strategies with Small and Large Rodent Models

Spatial learning and memory of laboratory rodents is often assessed via navigational ability in mazes, most popular of which are the water and dry-land (Barnes) mazes. Improved performance over sessions or trials is thought to reflect learning and memory of the escape cage/platform location. Considered less stressful than water mazes, the Barnes maze is a relatively simple design of a circular platform top with several holes equally spaced around the perimeter edge. All but one of the holes are false-bottomed or blind-ending, while one leads to an escape cage. Mildly aversive stimuli (e.g.&#160;bright overhead lights) provide motivation to locate the escape cage. Latency to locate the escape cage can be measured during the session; however, additional endpoints typically require video recording. From those video recordings, use of automated tracking software can generate a variety of endpoints that are similar to those produced in water mazes (e.g.&#160;distance traveled, velocity/speed, time spent in the correct quadrant, time spent moving/resting, and confirmation of latency). Type of search strategy (i.e.&#160;random, serial, or direct) can be categorized as well. Barnes maze construction and testing methodologies can differ for small rodents, such as mice, and large rodents, such as rats. For example, while extra-maze cues are effective for rats, smaller wild rodents may require intra-maze cues with a visual barrier around the maze. Appropriate stimuli must be identified which motivate the rodent to locate the escape cage. Both Barnes and water mazes can be time consuming as 4-7 test trials are typically required to detect improved learning and memory performance (e.g.&#160;shorter latencies or path lengths to locate the escape platform or cage) and/or differences between experimental groups. Even so, the Barnes maze is a widely employed behavioral assessment measuring spatial navigational abilities and their potential disruption by genetic, neurobehavioral manipulations, or drug/ toxicant exposure.

The dry-land Barnes maze is widely used to measure spatial navigation ability in response to mildly aversive stimuli. Over consecutive days, performance (e.g.&#160;latency to locate escape cage) of control subjects improves, indicative of normal learning and memory. Differences between rats and mice necessitate apparatus and methodology changes that are detailed here.

Spatial learning and memory of laboratory rodents is often assessed via navigational ability in mazes, most popular of which are the water and dry-land ...

Flat-floored Air-lifted Platform: A New Method for Combining Behavior with Microscopy or Electrophysiology on Awake Freely Moving Rodents

It is widely acknowledged that the use of general anesthetics can undermine the relevance of electrophysiological or microscopical data obtained from a living animal&#8217;s brain. Moreover, the lengthy recovery from anesthesia limits the frequency of repeated recording/imaging episodes in longitudinal studies. Hence, new methods that would allow stable recordings from non-anesthetized behaving mice are expected to advance the fields of cellular and cognitive neurosciences. Existing solutions range from mere physical restraint to more sophisticated approaches, such as linear and spherical treadmills used in combination with computer-generated virtual reality. Here, a novel method is described where a head-fixed mouse can move around an air-lifted mobile homecage and explore its environment under stress-free conditions. This method allows researchers to perform behavioral tests (e.g., learning, habituation or novel object recognition) simultaneously with two-photon microscopic imaging and/or patch-clamp recordings, all combined in a single experiment. This video-article describes the use of the awake animal head fixation device (mobile homecage), demonstrates the procedures of animal habituation, and exemplifies a number of possible applications of the method.

This method creates a tangible, familiar environment for the mouse to navigate and explore during microscopic imaging or single-cell electrophysiological recordings, which require firm fixation of the animal&#8217;s head.

It is widely acknowledged that the use of general anesthetics can undermine the relevance of electrophysiological or microscopical data obtained from a ...

A Procedure to Observe Context-induced Renewal of Pavlovian-conditioned Alcohol-seeking Behavior in Rats

Environmental contexts in which drugs of abuse are consumed can trigger craving, a subjective Pavlovian-conditioned response that can facilitate drug-seeking behavior and prompt relapse in abstinent drug users. We have developed a procedure to study the behavioral and neural processes that mediate the impact of context on alcohol-seeking behavior in rats. Following acclimation to the taste and pharmacological effects of 15% ethanol in the home cage, male Long-Evans rats receive Pavlovian discrimination training (PDT) in conditioning chambers. In each daily (Mon-Fri) PDT session, 16 trials each of two different 10 sec auditory conditioned stimuli occur. During one stimulus, the CS+, 0.2 ml of 15% ethanol is delivered into a fluid port for oral consumption. The second stimulus, the CS-, is not paired with ethanol. Across sessions, entries into the fluid port during the CS+ increase, whereas entries during the CS- stabilize at a lower level, indicating that a predictive association between the CS+ and ethanol is acquired. During PDT each chamber is equipped with a specific configuration of visual, olfactory and tactile contextual stimuli. Following PDT, extinction training is conducted in the same chamber that is now equipped with a different configuration of contextual stimuli. The CS+ and CS- are presented as before, but ethanol is withheld, which causes a gradual decline in port entries during the CS+. At test, rats are placed back into the PDT context and presented with the CS+ and CS- as before, but without ethanol. This manipulation triggers a robust and selective increase in the number of port entries made during the alcohol predictive CS+, with no change in responding during the CS-. This effect, referred to as context-induced renewal, illustrates the powerful capacity of contexts associated with alcohol consumption to stimulate alcohol-seeking behavior in response to Pavlovian alcohol cues.

A procedure to study the capacity of an alcohol associated environmental context to trigger the renewal of alcohol-seeking behavior in rats is described.

Environmental contexts in which drugs of abuse are consumed can trigger craving, a subjective Pavlovian-conditioned response that can facilitate ...

Measuring Neural and Behavioral Activity During Ongoing Computerized Social Interactions: An Examination of Event-Related Brain Potentials

Social exclusion is a complex social phenomenon with powerful negative consequences. Given the impact of social exclusion on mental and emotional health, an understanding of how perceptions of social exclusion develop over the course of a social interaction is important for advancing treatments aimed at lessening the harmful costs of being excluded. To date, most scientific examinations of social exclusion have looked at exclusion after a social interaction has been completed. While this has been very helpful in developing an understanding of what happens to a person following exclusion, it has not helped to clarify the moment-to-moment dynamics of the process of social exclusion. Accordingly, the current protocol was developed to obtain an improved understanding of social exclusion by examining the patterns of event-related brain activation that are present during social interactions. This protocol allows greater precision and sensitivity in detailing the social processes that lead people to feel as though they have been excluded from a social interaction. Importantly, the current protocol can be adapted to include research projects that vary the nature of exclusionary social interactions by altering how frequently participants are included, how long the periods of exclusion will last in each interaction, and when exclusion will take place during the social interactions. Further, the current protocol can be used to examine variables and constructs beyond those related to social exclusion. This capability to address a variety of applications across psychology by obtaining both neural and behavioral data during ongoing social interactions suggests the present protocol could be at the core of a developing area of scientific inquiry related to social interactions.

Research on social exclusion has grown tremendously in recent years. As the field expands, it is imperative to develop sophisticated methodologies allowing for the simultaneous measurement of neural and behavioral outcomes during social exclusion. This protocol utilizes event-related brain potentials to record ongoing neural activity during computerized social interactions.

Social exclusion is a complex social phenomenon with powerful negative consequences. Given the impact of social exclusion on mental and emotional health, ...

The Modified Hole Board - Measuring Behavior, Cognition and Social Interaction in Mice and Rats

This protocol describes the modified hole board (mHB), which combines features from a traditional hole board and open field and is designed to measure multiple dimensions of unconditioned behavior in small laboratory mammals (e.g., mice, rats, tree shrews and small primates). This paradigm is a valuable alternative for the use of a behavioral test battery, since a broad behavioral spectrum of an animal&#8217;s behavioral profile can be investigated in one single test.
The apparatus consists of a box, representing the &#8216;protected&#8217; area, separated from a group compartment. A board, on which small cylinders are staggered in three lines, is placed in the center of the box, representing the &#8216;unprotected&#8217; area of the set-up. The cognitive abilities of the animals can be measured by baiting some cylinders on the board and measuring the working and reference memory. Other unconditioned behavior, such as activity-related-, anxiety-related- and social behavior, can be observed using this paradigm. Behavioral flexibility and the ability to habituate to a novel environment can additionally be observed by subjecting the animals to multiple trials in the mHB, revealing insight into the animals&#8217; adaptive capacities.
Due to testing order effects in a behavioral test battery, na&#239;ve animals should be used for each individual experiment. By testing multiple behavioral dimensions in a single paradigm and thereby circumventing this issue, the number of experimental animals used is reduced. Furthermore, by avoiding social isolation during testing and without the need to food deprive the animals, the mHB represents a behavioral test system, inducing if any, very low amount of stress.

This protocol describes the modified hole board, which is a behavioral test set-up that comprises the characteristics of an open field and a traditional hole board. This set-up enables the differential analysis of unconditioned behavior of small laboratory mammals as well as the analysis of cognitive abilities.

This protocol describes the modified hole board (mHB), which combines features from a traditional hole board and open field and is designed to measure ...

Pavlovian Conditioned Approach Training in Rats

Cues that are contingently paired with unconditioned, rewarding stimuli can acquire rewarding properties themselves through a process known as the attribution of incentive salience, or the transformation of neutral stimuli into attractive, &#34;wanted&#39; stimuli capable of motivating behavior. Pavlovian conditioned approach (PCA) develops after the response-independent presentation of a conditioned stimulus (CS; e.g., a lever) that predicts the delivery of an unconditioned stimulus (US; e.g., a food pellet) and can be used to measure incentive salience. During training, three patterns of conditioned responses (CRs) can develop: sign-tracking behavior (CS-directed CR), goal-tracking behavior (US-directed CR), and an intermediate response (both CRs). Sign-trackers attribute incentive salience to reward-related cues and are more vulnerable to cue-induced reinstatement of drug-seeking as well as other addiction-related behaviors, making PCA a potentially valuable procedure for studying addiction vulnerability. Here, we describe materials and methods used to elicit PCA behavior from rats as well as analyze and interpret PCA behavior in individual experiments.

Here, we present a protocol to elicit Pavlovian conditioned approach behavior in rats. This procedure can be used to measure individual differences in the tendency to approach and attribute incentive salience to reward-related cues and investigate addiction vulnerability.