We acknowledge the audiovisual technician and video producer Rebeca De las Heras Ponce as well as the head veterinarian Gonzalo Moreno del Val, for the supervision of good practice during mouse experimentation.&#160;Work was funded by grants from the GVA Excellence Program (2022/8) and the Spanish Research Agency (PID2022143237OB-I00) to Isabel P&#233;rez-Ota&#241;o.

In the current study, adult (2-3 months old) C57BL/6J mice of both sexes were used. Animals were housed two to five per cage with ad libitum access to food and water in an animal unit under observation and maintained in a temperature-controlled environment on a 12 h dark/light cycle. All procedures were conducted in accordance with the European and Spanish regulations (2010/63/UE; RD 53/2013) and were approved by the Ethical Committee of the Generalitat Valenciana and the animal welfare committee of the Universidad Miguel Hern&#225;ndez.
1. Behavioral room setup
<ol>
	<li>Reserve the behavioral testing room every day at the same time and establish the list and order of mice to be used, as well as arrangements for their hosting.</li>
	<li>Keep the experimental mice outside the testing room so they do not hear the sounds of the air compressor and Erasmus Ladder tones when not being tested.</li>
	<li>Check that all components of the Erasmus Ladder system are in order and ready to use: the network router, the computer with the software (see Table of Materials), the air compressor, two goal boxes, and the ladder with the rungs properly positioned.</li>
	<li>Extensively clean the goal boxes, ladder, and rungs with water after each animal and with water and 70% ethanol at the end of each training day.</li>
</ol>
2. Behavioral test protocol
<ol>
	<li>Create an experiment and enter the protocol into the software (Supplementary Figure S1).
	<ol>
		<li>Turn on the software.</li>
		<li>To create an experiment, choose File | New experiment | New or Set up | Experiment protocol. 
		NOTE: The default protocol, used in this study, is named EMC and was designed at Erasmus University Medical Center, Rotterdam.</li>
		<li>Give the experiment a name and click OK.</li>
		<li>Check that the default EMC protocol selected consists of 4 days of undisturbed sessions (42 undisturbed trials per day) and 4 days of challenge sessions (42 daily mixed trials: undisturbed, CS-only (tone), US-only (obstacle), Paired (obstacle announced by tone) (see Figure 1B). In the right side panel, also check the light cue (3 s maximum duration), air cue (45 s maximum duration), and tailwind (Yes in all the trial types), used to encourage the mouse to cross the ladder, and the tone (250 ms, Yes only in CS-only and Paired trials).</li>
		<li>To create a different protocol, choose Set up | Experiment protocol | New | From scratch or Copy from the EMC protocol and simply modify it, editing the table lines related to number of sessions (days of experiment) and number and type of trials per day. 
		NOTE: Resting time, cues type and activation, duration, intensity, and interval can also be adapted according to the experimental questions.</li>
		<li>To open the session list and name the subjects, choose Setup | Session List.</li>
		<li>Click on Add Subjects and Variables.</li>
		<li>Enter each specific Mouse Identifier, Birth Date, Sex, Genotype, and relevant categories, following the ordered list of mice.</li>
	</ol>
	</li>
	<li>Start the session (Supplementary Figure S2).
	<ol>
		<li>Before starting, check that the software is open, then turn on the Ladder.</li>
		<li>Check that the air compressor is connected and switched on.</li>
		<li>To open the Acquisition window, open the Experiment created.</li>
		<li>Choose Acquisition | Open Acquisition.</li>
		<li>Place the mouse with the identifier indicated by the software in the starting goal box (right side of the ladder).</li>
		<li>Select the mouse identifier to acquire in the first session.</li>
		<li>Click on Start Acquisition.</li>
		<li>Press the red ladder menu knob 3x. Check that the session starts and automatically controls and records mouse movements until the end of the last trial of the session.</li>
	</ol>
	</li>
	<li>End the session.
	<ol>
		<li>Check that at the end of the 42nd trial, the display shows the messages Sending Data and Acquired.</li>
		<li>Return the mouse to the home cage.</li>
		<li>Clean the ladder and the goal boxes.</li>
		<li>Place the next mouse and repeat from step 2.2.6 onwards.</li>
	</ol>
	</li>
	<li>Perform the selected type of session every day until the end of the protocol. Repeat steps 2.2 and 2.3 every day according to the selected protocol.</li>
	<li>Export the data (Supplementary Figure S2).
	<ol>
		<li>To visualize the recorded data, choose from the Analysis menu, Trial Statistics, Session statistics, and Group Statistic &#38; Charts. 
		NOTE: Data can be downloaded as a spreadsheet with data for individual trials and the means of the same trial types within a session. Sessions can also be filtered by variables chosen for specific analysis.</li>
		<li>Click on the Export button at the top-right corner choosing the file format (spreadsheet) and folder location.</li>
		<li>Right-click on the automatically generated charts and select Save to File as *.jpg.</li>
	</ol>
	</li>
</ol>
3. Data analysis
NOTE: A list of parameters is automatically measured by the Erasmus Ladder based on the instantaneous recording of the activities of the touch-sensitive sensors. For analysis, output parameters selected by the user are organized and processed in the spreadsheets. Along with the software-generated graphs, users can generate graphs using the graphing software of choice to visualize specific changes in different parameters over sessions.
<ol>
	<li>Choose specific parameters to analyze basal motivation or anxiety states, sensory responses, motor performance, and fine motor learning over the first 4 days.
	<ol>
		<li>Select and plot control parameters, including resting time in the goal box and time to exit the goal box after the resting period in response to light and air cues (Figure 2A). 
		NOTE: Resting times or response to cues are relatively constant in WT mice. Other parameters such as frequency of exits are basically negligible in WT mice-the animals rarely leave the rest box without the cues or come back once in the ladder, resulting in frequencies of exit equal to 1 per trial. If an animal goes out before cues are applied, an airflow gets activated forcing the mouse to return to the goal box; this is not counted as a trial by the software.</li>
		<li>Select and plot the time on ladder after cues, measured as the time spent crossing the ladder once the mouse leaves the goal box (Figure 2B). 
		NOTE: A power non-linear regression is a robust method for evaluating learning. The Pearson or Spearman coefficients (R) will provide a measure of whether the data fitting is good (R values close to one when the animals learn/improve over sessions; R values close to 0 imply that the data are constant and mice do not learn).</li>
		<li>Select and plot stepping pattern parameters such as the percentage of trials with missteps as a sensitive learning parameter (Figure 2C).
		<ol>
			<li>Define a correct step as a step from a high rung to another high rung (H-H), irrespective of the length of the step. Consider step types that involve a lower rung as&#160;missteps.</li>
			<li>Divide correct steps and missteps into short and long steps, backsteps, and jumps depending on the length and directionality of the step between the rungs pressed (see Figure 1A).</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Select and plot specific parameters to evaluate challenged motor learning (US-only trials) and associative learning (paired trials) over the last 4 days.
	<ol>
		<li>Select and plot the time on ladder after cues (Figure 3).</li>
		<li>Select and plot the percentage of trials with missteps (Figure 4A).</li>
		<li>Select and plot the pre and post perturbation step times, defined as a ms precision difference between rung activation just before (control step) and after the obstacle (adapted step) on the same side of the ladder (Figure 4B). 
		NOTE: Pre vs post-perturbation step times analysis should be performed to compare data inside each type of session. The parameter measures the ability of the mice to predict and overcome the obstacles during associative learning.</li>
	</ol>
	</li>
	<li>Analyze the data with dedicated statistical software (e.g., SigmaPlot). Perform a power non-linear regression analysis of data collected from the same trial type across sessions to describe the learning process more efficiently and use Two-Way Repeated Measures (RM) ANOVA to compare between trial types.</li>
</ol>

Automated Assessment of Fine Motor Performance in Mice Using the Erasmus Ladder

<ol>
	<li>Brooks, S. P., Dunnett, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tests+to+assess+motor+phenotype+in+mice:+a+user's+guide.">Tests to assess motor phenotype in mice: a user's guide.</a> Nat. Rev. Neurosci. 10 (7), 519-529 (2009).</li><li>. Available from: <a target="_blank" href="https://www.noldus.com/erasmusladder">https://www.noldus.com/erasmusladder</a> (2023)</li><li>Cupido, 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=.">.</a> Detecting cerebellar phenotypes with the Erasmus ladder[dissertation]. , (2009).</li><li>Van Der Giessen, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+olivary+electrical+coupling+in+cerebellar+motor+learning.">Role of olivary electrical coupling in cerebellar motor learning.</a> Neuron. 58 (4), 599-612 (2008).</li><li>Vinueza Veloz, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+an+mGluR5+inhibitor+on+procedural+memory+and+avoidance+discrimination+impairments+in+Fmr1+KO+mice.">The effect of an mGluR5 inhibitor on procedural memory and avoidance discrimination impairments in Fmr1 KO mice.</a> Genes Brain Behav. 11 (3), 325-331 (2012).</li><li>Vinueza Veloz, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cerebellar+control+of+gait+and+interlimb+coordination.">Cerebellar control of gait and interlimb coordination.</a> Brain Struct. Funct. 220 (6), 3513-3536 (2015).</li><li>Sathyanesan, A., Kundu, S., Abbah, J., Gallo, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neonatal+brain+injury+causes+cerebellar+learning+deficits+and+Purkinje+cell+dysfunction.">Neonatal brain injury causes cerebellar learning deficits and Purkinje cell dysfunction.</a> Nat. Commun. 9 (1), 3235 (2018).</li><li>Sathyanesan, A., Gallo, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cerebellar+contribution+to+locomotor+behavior:+A+neurodevelopmental+perspective.">Cerebellar contribution to locomotor behavior: A neurodevelopmental perspective.</a> Neurobiol. Learn Mem. 165, 106861 (2019).</li><li>McKenzie, I. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Motor+skill+learning+requires+active+central+myelination.">Motor skill learning requires active central myelination.</a> Science. 346 (6207), 318-322 (2014).</li><li>Xiao, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+production+of+new+oligodendrocytes+is+required+in+the+earliest+stages+of+motor-skill+learning.">Rapid production of new oligodendrocytes is required in the earliest stages of motor-skill learning.</a> Nat. Neurosci. 19 (9), 1210-1217 (2016).</li></ol>

The authors have no conflicts of interest to disclose.

The Erasmus Ladder presents major advantages for motor phenotype assessment beyond current approaches. Testing is easy to conduct, automated, reproducible, and allows researchers to assess various aspects of motor behavior separately using a single mouse cohort. In the current study, reproducibility allowed the generation of robust data with a small number of WT mice taking advantage of the features of the device, experimental design, and analysis methods. For instance, when compared to traditional beam-walk assays, the ...

A variety of tests have been developed to assess motor phenotypes in mice. Each test gives information on a specific aspect of motor behavior1. For example, the open field test informs on general locomotion and anxiety state; the rotarod and walking beam tests on coordination and balance; footprint analysis is about gait; the treadmill or running wheel on forced or voluntary physical exercise; and the complex wheel is about motor skill learning. To analyze mouse motor phenotypes, investigators must perform these tests sequentially, which involves a lot of time and effort and often several animal cohorts. If there is information at the cellular or circuitry level, the investigator normally opts for a test that monitors a related aspect and follows from there. However, paradigms that discriminate different aspects of motor behavior in an automated way are lacking.
This article describes a protocol to use the Erasmus Ladder2,3, a system that allows comprehensive assessment of a variety of motor learning features in mice. The main advantages are the reproducibility and sensitivity of the method, along with the ability to titrate motor difficulty and to separate deficits in motor performance from impaired associative motor learning. The main component consists of a horizontal ladder with alternate high (H) and low (L) rungs equipped with touch-sensitive sensors that detect the position of the mouse on the ladder. The ladder is made of 2 x 37 rungs (L, 6 mm; H, 12 mm) spaced 15 mm apart from each other and positioned in a left-right alternating pattern with 30 mm gaps (Figure 1A). Rungs can be moved individually to generate various levels of difficulty, that is, creating an obstacle (raising the high rungs by 18 mm). Coupled with an automated recording system and associating modifications of the rung pattern with sensory stimuli, the Erasmus ladder tests for fine motor learning and adaptation of motor performance in response to environmental challenges (appearance of a higher rung to simulate an obstacle, an unconditioned stimulus [US]) or association with sensory stimuli (a tone, a conditioned stimulus [CS]). Testing involves two distinct phases, each assessing improvement in motor performance over 4 days, during which mice undergo a session of 42 consecutive trials per day. In the initial phase, mice are trained to navigate the ladder to assess &#34;fine&#34; or &#34;skilled&#34; motor learning. The second phase consists of interleaved trials where an obstacle in the form of a higher rung is presented in the path of the moving animal. The perturbation can be unexpected to assess &#34;challenged&#34; motor learning (US-only trials) or announced by an auditory tone to assess &#34;associative&#34; motor learning (Paired trials).
The Erasmus ladder has been developed relatively recently2,3. It has not been extensively used because setting up and optimizing the protocol required focused effort and was specifically designed to assess cerebellar-dependent associative learning without exploring in detail its potential to reveal other motor deficits. To date, it has been validated for its ability to unveil subtle motor impairments linked to cerebellar dysfunction in mice3,4,5,6,7,8. For instance, connexin36 (Cx36) knockout mice, where gap junctions are impaired in olivary neurons, display firing deficits due to lack of electrotonic coupling but the motor phenotype had been hard to pinpoint. Testing using the Erasmus ladder suggested that the role of inferior olivary neurons in a cerebellar motor learning task is to encode precise temporal coding of stimuli and facilitate learning-dependent responses to unexpected events3,4. Fragile X Messenger Ribonucleoprotein 1 (Fmr1) knockout mouse, a model for Fragile-X-Syndrome (FXS), exhibits a well-known cognitive impairment along with milder defects in procedural memory formation. Fmr1 knockouts showed no significant differences in step times, missteps per trial, or motor performance improvement over sessions in the Erasmus Ladder but failed to adjust their walking pattern to the suddenly appearing obstacle compared to their wild-type (WT) littermates, confirming specific procedural and associative memory deficits3,5. Furthermore, cell-specific mouse mutant lines with defects in cerebellar function, including impaired Purkinje cell output, potentiation, and molecular layer interneuron or granule cell outputs, exhibited problems in motor coordination with altered acquisition of efficient step patterns and in the number of steps taken to cross the ladder6. Neonatal brain injury causes cerebellar learning deficits and Purkinje cell dysfunction that could also be detected with the Erasmus Ladder7,8.
In this video, we present a comprehensive step-by-step guide, which details the setup of the behavioral room, the behavioral test protocol, and subsequent data analysis. This report is crafted to be accessible and user-friendly and is designed specifically to assist newcomers. This protocol provides insight into different phases of motor training and expected motor patterns that mice adopt. Finally, the article proposes a systematic workflow for data analysis using a powerful non-linear regression approach, complete with valuable recommendations and suggestions for adapting and applying the protocol in other research contexts.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>C57BL/6J mice (Mus musculus)</td>
			<td>Charles Rivers</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Erasmus Ladder device</td>
			<td>Noldus, Wageningen, Netherlands</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Erasmus Ladder 2.0 software</td>
			<td>Noldus, Wageningen, Netherlands</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Excel software</td>
			<td>Microsoft&#160;</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sigmaplot software</td>
			<td>Systat Software, Inc.</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

monitoring fine and associative motor learning in mice using the erasmus ladder

Behavior is shaped by actions, and actions necessitate motor skills such as strength, coordination, and learning. None of the behaviors essential for sustaining life would be possible without the ability to transition from one position to another. Unfortunately, motor skills can be compromised in a wide array of diseases. Therefore, investigating the mechanisms of motor functions at the cellular, molecular, and circuit levels, as well as understanding the symptoms, causes, and progression of motor disorders, is crucial for developing effective treatments. Mouse models are frequently employed for this purpose.
This article describes a protocol that allows the monitoring of various aspects of motor performance and learning in mice using an automated tool called the Erasmus Ladder. The assay involves two phases: an initial phase where mice are trained to navigate a horizontal ladder built of irregular rungs (&#34;fine motor learning&#34;), and a second phase where an obstacle is presented in the path of the moving animal. The perturbation can be unexpected (&#34;challenged motor learning&#34;) or preceded by an auditory tone (&#34;associative motor learning&#34;). The task is easy to conduct and is fully supported by automated software.
This report shows how different readouts from the test, when analyzed with sensitive statistical methods, allow fine monitoring of mouse motor skills using a small cohort of mice. We propose that the method will be highly sensitive to evaluate motor adaptations driven by environmental modifications as well as early-stage subtle motor deficits in mutant mice with compromised motor functions.

The Erasmus Ladder device, setup, and protocol applied are presented in Figure 1. The protocol consists of four undisturbed and four challenge sessions (42 trials each). Each trial is one run on the ladder between the starting and ending goal boxes. At the beginning of the session, a mouse is placed in one of the starting boxes. After a set time of 15 &#177; 5 s (&#34;resting&#34; state), the light is turned on (cue 1, for a maximum of 3 s). A light air cue (cue 2, 45 s maximum) is then appl...

Watch this Scientific Journal Video about Unveiling Neural Mechanisms Through Automated Evaluation of Motor Learning and Myelin Plasticity Studies Using the Erasmus Ladder at JoVE.com

Author Spotlight: Unveiling Neural Mechanisms Through Automated Evaluation of Motor Learning and Myelin Plasticity Studies Using the Erasmus Ladder 

This article presents a protocol that allows a non-invasive and automated assessment of fine motor performance, as well as adaptive and associative motor learning upon challenges, using a device called the Erasmus Ladder. Task difficulty can be titrated to detect motor impairment ranging from major to subtle degrees.

Monitoring Fine and Associative Motor Learning in Mice Using the Erasmus Ladder

Behavior is shaped by actions, and actions necessitate motor skills such as strength, coordination, and learning. None of the behaviors essential for ...

monitoring-fine-associative-motor-learning-mice-using-erasmus

Research

JoVE Journal

Neuroscience

1.1K Views.  Spain - Consejo Superior de Investigaciones Científicas and Universidad Miguel Hernández. This article presents a protocol that allows a non-invasive and automated assessment of fine motor performance, as well as adaptive and associative motor learning upon challenges, using a device called the Erasmus Ladder. Task difficulty can be titrated to detect motor impairment ranging from major to subtle degrees. 

Video: Author Spotlight: Unveiling Neural Mechanisms Through Automated Evaluation of Motor Learning and Myelin Plasticity Studies Using the Erasmus Ladder 

Low-stress Route Learning Using the Lashley III Maze in Mice

Many behavior tests designed to assess learning and memory in rodents, particularly mice, rely on visual cues, food and/or water deprivation, or other aversive stimuli to motivate task acquisition. As animals age, sensory modalities deteriorate. For example, many strains of mice develop hearing deficits or cataracts. Changes in the sensory systems required to guide mice during task acquisition present potential confounds in interpreting learning changes in aging animals. Moreover, the use of aversive stimuli to motivate animals to learn tasks is potentially confounding when comparing mice with differential sensitivities to stress. To minimize these types of confounding effects, we have implemented a modified version of the Lashley III maze. This maze relies on route learning, whereby mice learn to navigate a maze via repeated exposure under low stress conditions, e.g. dark phase, no food/water deprivation, until they navigate a path from the start location to a pseudo-home cage with 0 or 1 error(s) on two consecutive trials. We classify this as a low-stress behavior test because it does not rely on aversive stimuli to encourage exploration of the maze and learning of the task. The apparatus consists of a modular start box, a 4-arm maze body, and a goal box. At the end of the goal box is a pseudo-home cage that contains bedding similar to that found in the animal&#x2019;s home cage and is specific to each animal for the duration of maze testing. It has been demonstrated previously that this pseudo-home cage provides sufficient reward to motivate mice to learn to navigate the maze1. Here, we present the visualization of the Lashley III maze procedure in the context of evaluating age-related differences in learning and memory in mice along with a comparison of learning behavior in two different background strains of mice. We hope that other investigators interested in evaluating the effects of aging or stress vulnerability in mice will consider this maze an attractive alternative to behavioral tests that involve more stressful learning tasks and/or visual cues.

The Lashley III maze is a route-learning task that does not rely on aversive stimuli or visual cues. It is thus a highly attractive option for evaluating learning and memory, especially in aging mice or otherwise where stress is a consideration.

Many behavior tests designed to assess learning and memory in rodents, particularly mice, rely on visual cues, food and/or water deprivation, or other ...

Assessment of Motor Balance and Coordination in Mice using the Balance Beam

Brain injury, genetic manipulations, and pharmacological treatments can result in alterations of motor skills in mice. Fine motor coordination and balance can be assessed by the beam walking assay. The goal of this test is for the mouse to stay upright and walk across an elevated narrow beam to a safe platform. This test takes place over 3 consecutive days: 2 days of training and 1 day of testing. Performance on the beam is quantified by measuring the time it takes for the mouse to traverse the beam and the number of paw slips that occur in the process. Here we report the protocol used in our laboratory, and representative results from a cohort of C57BL/6 mice. This task is particularly useful for detecting subtle deficits in motor skills and balance that may not be detected by other motor tests, such as the Rotarod.

Deficits in fine motor coordination can be assessed with the balance beam test. Performance on the beam is quantified by the speed at which the beam is traversed and the number of times the mouse slips on the beam.

Brain injury, genetic manipulations, and pharmacological treatments can result in alterations of motor skills in mice.  Fine motor coordination and ...

C. elegans Positive Butanone Learning, Short-term, and Long-term Associative Memory Assays

The memory of experiences and learned information is critical for organisms to make choices that aid their survival. C. elegans navigates its environment through neuron-specific detection of food and chemical odors1, 2, and can associate nutritive states with chemical odors3, temperature4, and the pathogenicity of a food source5.
Here, we describe assays of C. elegans associative learning and short- and long-term associative memory. We modified an aversive olfactory learning paradigm6 to instead produce a positive response; the assay involves starving ~400 worms, then feeding the worms in the presence of the AWC neuron-sensed volatile chemoattractant butanone at a concentration that elicits a low chemotactic index (similar to Toroyama et al.7). A standard population chemotaxis assay1 tests the worms' attraction to the odorant immediately or minutes to hours after conditioning.
After conditioning, wild-type animals' chemotaxis to butanone increases ~0.6 Chemotaxis Index units, its "Learning Index". Associative learning is dependent on the presence of both food and butanone during training. Pairing food and butanone for a single conditioning period ("massed training") produces short-term associative memory that lasts ~2 hours. Multiple conditioning periods with rest periods between ("spaced training") yields long-term associative memory (&lt;40 hours), and is dependent on the cAMP Response Element Binding protein (CREB),6 a transcription factor required for long-term memory across species.8
Our protocol also includes image analysis methods for quick and accurate determination of chemotaxis indices. High-contrast images of animals on chemotaxis assay plates are captured and analyzed by worm counting software in MatLab. The software corrects for uneven background using a morphological tophat transformation.9 Otsu's method is then used to determine a threshold to separate worms from the background.10 Very small particles are removed automatically and larger non-worm regions (plate edges or agar punches) are removed by manual selection. The software then estimates the size of single worm by ignoring regions that are above a specified maximum size and taking the median size of the remaining regions. The number of worms is then estimated by dividing the total area identified as occupied by worms by the estimated size of a single worm.
We have found that learning and short- and long-term memory can be distinguished, and that these processes share similar key molecules with higher organisms.6,8 Our assays can quickly test novel candidate genes or molecules that affect learning and short- or long-term memory in C. elegans that are relevant across species.

C. elegans Positive Butanone Learning, Short-term, and Long-term Associative Memory Assays

Here we describe methods to test C. elegans associative learning and short- and long-term associative memory. These population assays employ the worms abilities to chemotax toward volatile odorants, and form positive associations upon pairing food with the chemoattractant butanone. Increasing the number of conditioning periods induces long-term memory.

The memory of experiences and learned information is critical for organisms to make choices that aid their survival. C. elegans navigates its environment ...

Measuring Motor Coordination in Mice

Mice are increasingly being used in behavioral neuroscience, largely replacing rats as the behaviorist's animal of choice. Before aspects of behavior such as emotionality or cognition can be assessed, however, it is vital to determine whether the motor capabilities of e.g. a mutant or lesioned mouse allow such an assessment. Performance on a maze task requiring strength and coordination, such as the Morris water maze, might well be impaired in a mouse by motor, rather than cognitive, impairments, so it is essential to selectively dissect the latter from the former. For example, sensorimotor impairments caused by NMDA antagonists have been shown to impair water maze performance2. 
Motor coordination has traditionally been assessed in mice and rats by the rotarod test, in which the animal is placed on a horizontal rod that rotates about its long axis; the animal must walk forwards to remain upright and not fall off. Both set speed and accelerating versions of the rotarod are available.
The other three tests described in this article (horizontal bar, static rods and parallel bars) all measure coordination on static apparatus. The horizontal bar also requires strength for adequate performance, particularly of the forelimbs as the mouse initially grips the bar just with the front paws. 
Adult rats do not perform well on tests such as the static rods and parallel bars (personal observations); they appear less well coordinated than mice. I have only tested male rats, however, and male mice seem generally less well coordinated than females. Mice appear to have a higher strength:weight ratio than rats; the Latin name, Mus musculus, seems entirely appropriate. The rotarod, the variations of the foot fault test12 or the Catwalk (Noldus)15 apparatus are generally used to assess motor coordination in rats.

Protocols are presented for two established motor coordination tasks, the accelerating rotarod and horizontal bar, also two tests developed in Oxford recently, the static rods and parallel bars. These tests can detect motor impairments potentially of interest in their own right, as well as being possible variables in tests of other areas of behavior.

Mice are increasingly being used in behavioral neuroscience, largely replacing rats as the behaviorist's animal of choice. Before aspects of behavior such ...

Video-oculography in Mice

Eye movements are very important in order to track an object or to stabilize an image on the retina during movement. Animals without a fovea, such as the mouse, have a limited capacity to lock their eyes onto a target. In contrast to these target directed eye movements, compensatory ocular eye movements are easily elicited in afoveate animals1,2,3,4. Compensatory ocular movements are generated by processing vestibular and optokinetic information into a command signal that will drive the eye muscles. The processing of the vestibular and optokinetic information can be investigated separately and together, allowing the specification of a deficit in the oculomotor system. The oculomotor system can be tested by evoking an optokinetic reflex (OKR), vestibulo-ocular reflex (VOR) or a visually-enhanced vestibulo-ocular reflex (VVOR). The OKR is a reflex movement that compensates for "full-field" image movements on the retina, whereas the VOR is a reflex eye movement that compensates head movements. The VVOR is a reflex eye movement that uses both vestibular as well as optokinetic information to make the appropriate compensation. The cerebellum monitors and is able to adjust these compensatory eye movements. Therefore, oculography is a very powerful tool to investigate brain-behavior relationship under normal as well as under pathological conditions (f.e. of vestibular, ocular and/or cerebellar origin).
Testing the oculomotor system, as a behavioral paradigm, is interesting for several reasons. First, the oculomotor system is a well understood neural system5. Second, the oculomotor system is relative simple6; the amount of possible eye movement is limited by its ball-in-socket architecture ("single joint") and the three pairs of extra-ocular muscles7. Third, the behavioral output and sensory input can easily be measured, which makes this a highly accessible system for quantitative analysis8. Many behavioral tests lack this high level of quantitative power. And finally, both performance as well as plasticity of the oculomotor system can be tested, allowing research on learning and memory processes9.
Genetically modified mice are nowadays widely available and they form an important source for the exploration of brain functions at various levels10. In addition, they can be used as models to mimic human diseases. Applying oculography on normal, pharmacologically-treated or genetically modified mice is a powerful research tool to explore the underlying physiology of motor behaviors under normal and pathological conditions. Here, we describe how to measure video-oculography in mice8.

Video-oculography is a very quantitative method to investigate ocular motor performance as well as motor learning. Here, we describe how to measure video-oculography in mice. Applying this technique on normal, pharmacologically-treated or genetically modified mice is a powerful research tool to explore the underlying physiology of motor behaviors.

Eye movements are very important in order to track an object or to stabilize an image on the retina during movement. Animals without a fovea, such as the ...

Optical Recording of Suprathreshold Neural Activity with Single-cell and Single-spike Resolution

Signaling of information in the vertebrate central nervous system is often carried by populations of neurons rather than individual neurons. Also propagation of suprathreshold spiking activity involves populations of neurons. Empirical studies addressing cortical function directly thus require recordings from populations of neurons with high resolution. Here we describe an optical method and a deconvolution algorithm to record neural activity from up to 100 neurons with single-cell and single-spike resolution. This method relies on detection of the transient increases in intracellular somatic calcium concentration associated with suprathreshold electrical spikes (action potentials) in cortical neurons. High temporal resolution of the optical recordings is achieved by a fast random-access scanning technique using acousto-optical deflectors (AODs)1. Two-photon excitation of the calcium-sensitive dye results in high spatial resolution in opaque brain tissue2. Reconstruction of spikes from the fluorescence calcium recordings is achieved by a maximum-likelihood method. Simultaneous electrophysiological and optical recordings indicate that our method reliably detects spikes (&gt;97% spike detection efficiency), has a low rate of false positive spike detection (&lt; 0.003 spikes/sec), and a high temporal precision (about 3 msec) 3. This optical method of spike detection can be used to record neural activity in vitro and in anesthetized animals in vivo3,4.

Understanding the function of the vertebrate central nervous system requires recordings from many neurons because cortical function arises on the level of populations of neurons. Here we describe an optical method to record suprathreshold neural activity with single-cell and single-spike resolution, dithered random-access scanning. This method records somatic fluorescence calcium signals from up to 100 neurons with high temporal resolution. A maximum-likelihood algorithm deconvolves the underlying suprathreshold neural activity from the somatic fluorescence calcium signals. This method reliably detects spikes with high detection efficiency and a low rate of false positives and can be used to study neural populations in vitro and in vivo.

Signaling of information in the vertebrate central nervous system is often carried by populations of neurons rather than individual neurons. Also ...

Appetitive Associative Olfactory Learning in Drosophila Larvae

In the following we describe the methodological details of appetitive associative olfactory learning in Drosophila larvae. The setup, in combination with genetic interference, provides a handle to analyze the neuronal and molecular fundamentals of specifically associative learning in a simple larval brain.
Organisms can use past experience to adjust present behavior. Such acquisition of behavioral potential can be defined as learning, and the physical bases of these potentials as memory traces1-4. Neuroscientists try to understand how these processes are organized in terms of molecular and neuronal changes in the brain by using a variety of methods in model organisms ranging from insects to vertebrates5,6. For such endeavors it is helpful to use model systems that are simple and experimentally accessible. The Drosophila larva has turned out to satisfy these demands based on the availability of robust behavioral assays, the existence of a variety of transgenic techniques and the elementary organization of the nervous system comprising only about 10,000 neurons (albeit with some concessions: cognitive limitations, few behavioral options, and richness of experience questionable)7-10.
Drosophila larvae can form associations between odors and appetitive gustatory reinforcement like sugar11-14. In a standard assay, established in the lab of B. Gerber, animals receive a two-odor reciprocal training: A first group of larvae is exposed to an odor A together with a gustatory reinforcer (sugar reward) and is subsequently exposed to an odor B without reinforcement 9. Meanwhile a second group of larvae receives reciprocal training while experiencing odor A without reinforcement and subsequently being exposed to odor B with reinforcement (sugar reward). In the following both groups are tested for their preference between the two odors. Relatively higher preferences for the rewarded odor reflect associative learning - presented as a performance index (PI). The conclusion regarding the associative nature of the performance index is compelling, because apart from the contingency between odors and tastants, other parameters, such as odor and reward exposure, passage of time and handling do not differ between the two groups9.

Appetitive Associative Olfactory Learning in Drosophila Larvae

Drosophila larvae are able to associate odor stimuli with gustatory reward. Here we describe a simple behavioral paradigm that allows the analysis of appetitive associative olfactory learning.

In the following we describe the methodological  details of appetitive associative olfactory learning in Drosophila larvae. The setup, in combination with ...

The Neuromuscular Junction: Measuring Synapse Size, Fragmentation and Changes in Synaptic Protein Density Using Confocal Fluorescence Microscopy

The neuromuscular junction (NMJ) is the large, cholinergic relay synapse through which mammalian motor neurons control voluntary muscle contraction. Structural changes at the NMJ can result in neurotransmission failure, resulting in weakness, atrophy and even death of the muscle fiber. Many studies have investigated how genetic modifications or disease can alter the structure of the mouse NMJ. Unfortunately, it can be difficult to directly compare findings from these studies because they often employed different parameters and analytical methods. Three protocols are described here. The first uses maximum intensity projection confocal images to measure the area of acetylcholine receptor (AChR)-rich postsynaptic membrane domains at the endplate and the area of synaptic vesicle staining in the overlying presynaptic nerve terminal. The second protocol compares the relative intensities of immunostaining for synaptic proteins in the postsynaptic membrane. The third protocol uses Fluorescence Resonance Energy Transfer (FRET) to detect changes in the packing of postsynaptic AChRs at the endplate. The protocols have been developed and refined over a series of studies. Factors that influence the quality and consistency of results are discussed and normative data are provided for NMJs in healthy young adult mice.

The neuromuscular junction (NMJ) is altered in a variety of conditions that can sometimes culminate in synaptic failure. This report describes fluorescence microscope-based methods to quantify such structural changes.

The neuromuscular junction (NMJ) is the large, cholinergic relay synapse through which mammalian motor neurons control voluntary muscle contraction. ...

Electrophysiological Method for Recording Intracellular Voltage Responses of Drosophila Photoreceptors and Interneurons to Light Stimuli In Vivo

Voltage responses of insect photoreceptors and visual interneurons can be accurately recorded with conventional sharp microelectrodes. The method described here enables the investigator to measure long-lasting (from minutes to hours) high-quality intracellular responses from single Drosophila R1-R6 photoreceptors and Large Monopolar Cells (LMCs) to light stimuli. Because the recording system has low noise, it can be used to study variability among individual cells in the fly eye, and how their outputs reflect the physical properties of the visual environment. We outline all key steps in performing this technique. The basic steps in constructing an appropriate electrophysiology set-up for recording, such as design and selection of the experimental equipment are described. We also explain how to prepare for recording by making appropriate (sharp) recording and (blunt) reference electrodes. Details are given on how to fix an intact fly in a bespoke fly-holder, prepare a small window in its eye and insert a recording electrode through this hole with minimal damage. We explain how to localize the center of a cell's receptive field, dark- or light-adapt the studied cell, and to record its voltage responses to dynamic light stimuli. Finally, we describe the criteria for stable normal recordings, show characteristic high-quality voltage responses of individual cells to different light stimuli, and briefly define how to quantify their signaling performance. Many aspects of the method are technically challenging and require practice and patience to master. But once learned and optimized for the investigator's experimental objectives, it grants outstanding in vivo neurophysiological data.

Electrophysiological Method for Recording Intracellular Voltage Responses of Drosophila Photoreceptors and Interneurons to Light Stimuli In Vivo

Sharp microelectrodes enable accurate electrophysiological characterization of photoreceptor and visual interneuron output in living Drosophila. Here we show how to use this method to record high-quality voltage responses of individual cells to controlled light stimulation. This method is ideal for studying neural information processing in insect compound eyes.

Voltage responses of insect photoreceptors and visual interneurons can be accurately recorded with conventional sharp microelectrodes. The method ...

An Objective and Reproducible Test of Olfactory Learning and Discrimination in Mice

Olfaction is the predominant sensory modality in mice and influences many important behaviors, including foraging, predator detection, mating, and parenting. Importantly, mice can be trained to associate novel odors with specific behavioral responses to provide insight into olfactory circuit function. This protocol details the procedure for training mice on a Go/No-Go operant learning task. In this approach, mice are trained on hundreds of automated trials daily for 2&#8211;4 weeks and can then be tested on novel Go/No-Go odor pairs to assess olfactory discrimination, or be used for studies on how odor learning alters the structure or function of the olfactory circuit. Additionally, the mouse olfactory bulb (OB) features ongoing integration of adult-born neurons. Interestingly, olfactory learning increases both the survival and synaptic connections of these adult-born neurons. Therefore, this protocol can be combined with other biochemical, electrophysiological, and imaging techniques to study learning and activity-dependent factors that mediate neuronal survival and plasticity.

Here, we train mice on an associative learning task to test odor discrimination. This protocol also allows for studies on learning-induced structural changes in the brain.