The work is supported by grants to M.F. from the Japanese government MEXT KAKENHI (24592560, 15H04991, and 15K15624) and the Takeda Science Foundation to M.F. and the Jikei University Strategic Prioritizing Research Fund to H.J.O.

All experimental procedures were performed at the Jikei University, Tokyo Japan. Animal handling and experimental procedures were approved by The Institutional Animal Care and Use Committee of The Jikei University (Approval no: 26-060) and performed in accordance with the Institutional guidelines for use of laboratory animals at the Jikei University, which agree with the Guidelines for Proper Conduct of Animal Experiments by the Science Council of Japan (2006). Animal care was conducted in accordance with the recommendations of the Guide for the Care and Use of Laboratory Animals (Institute of Laboratory Animal Resources, 1996).
1. Preoperative Examination
<ol>
	<li>Take a cranial Computed Tomography (CT) scan of animals (common marmosets) in order to facilitate the identification of individual anatomical structures at least one month before surgery.</li>
	<li>Carry out an audiometric test at least one month before surgery. 
	NOTE: Here, we used the ABR to assess hearing status. Briefly, a positive electrode was subcutaneously placed at the vertex and a reference negative electrode at the dorsal base of the stimulated ear. The ground electrode was subcutaneously placed at the dorsal part of the neck.17,18 ABRs were evoked with tone burst (1.0 ms tone burst duration with 0.1 ms rise and fall time). The sound level was then reduced in 10 dB steps from its maximum amplitude. At each sound level, 512 responses were averaged (with stimulus polarity alternated). ABR threshold was defined as the lowest sound pressure level (SPL) at which any wave could be detected.</li>
</ol>
2. Anesthesia
<ol>
	<li>Fast animals from the night before surgery under general anesthesia.</li>
	<li>Administer 4% isoflurane and ambient air at 5 - 6 mL/min with mask-to-face ventilation or in an induction chamber for slow induction (Figure 1A). Confirm that the animal does not respond to painful stimuli, such as the toe pinch.</li>
	<li>Anesthestize common marmosets with intramuscular injection (into the femoral muscle) of a combination of medetomidine (0.04 mg/kg), midazolam (0.4 mg/kg), and butorphanol (0.4 mg/kg).</li>
	<li>Inject ampicillin (0.08 mg/g) subcutaneously 30 min or more&#160;prior to skin incision as a preoperative antibiotic.</li>
	<li>Place the marmoset in the supine position with its head toward the top, and extend the head and neck. Fix the maxilla to the table with a nylon thread, and pull up the tongue to obtain a good view, or use a laryngoscope to visualize the epiglottis and the entry of the larynx alternatively (Figure 1B).</li>
	<li>Insert an endotracheal tube along the laryngeal surface of the epiglottis. 
	NOTE: It is possible to use a 16-gauge intravenous catheter, or 6-French gauge feeding tube, as an endotracheal tube (Figure 1C).</li>
	<li>Check the EtCO2 from the endotracheal tube in order to confirm that it has been properly placed into the trachea. After the tube has been positioned and respiratory gas movement has been checked, fix the endotracheal tube to the marmoset&#39;s face with tape.</li>
	<li>Maintain anesthesia between 1-3% Isoflurane during the operation.</li>
	<li>Monitor the SpO2, EtCO2, body temperature and rectal temperature during operations. Perform all procedures on a heating mat to prevent a reduction in body temperature.</li>
</ol>
3. Preoperative Preparation
<ol>
	<li>Prepare the marmoset in a supine position, and incline the head to a 30 - 45 degree angle to the non-operative side (Figure 2A).</li>
	<li>Shave the post-auricular region of the operative side.</li>
	<li>Disinfect the surgical area with alcohol and povidone iodine, both in the post-auricular region and the external auditory canal.</li>
	<li>Place a surgical drape sheet with a round hole onto the marmoset (Figure 2B).</li>
</ol>
4. Surgical Procedures
<ol>
	<li>Inject 1% of lidocaine hydrochloride (with 1:100,000 epinephrine, 0.1-0.2 mL) subcutaneously into the skin incision site. Make an incision in the postauricular skin with a No.15 round-shaped blade.</li>
	<li>For hemostasis, apply pressure to the bleeding area using a gauze soaked in 1:5,000 diluted epinephrine. Bipolar cauterization is also effective (Figure 2C).</li>
	<li>Open up the soft tissue of the post-auricular region so that auricular cartilage (c) and post-auricular muscle (m) can be recognized. Expose the external auditory canal bone that should be visible deep in the cartilage (Figure 3A).</li>
	<li>To confirm the depth of the tympanic membrane, expose the bony part of the tympanic rim which can be recognized as the adhesion of skin and bone in the deepest part of the posterior ear canal. 
	NOTE: This step allows us to recognize how deep the lateral part of the middle ear cavity is (Figure 3A).</li>
	<li>Peel the post-auricular muscles (sternocleidomastoid muscle, splenius capitis muscle, and posterior belly of digastric muscle) toward the caudal aspect, separated from the temporal bone. Then expose the lateral surface of the temporal bone (asterisk in Figure 3B).</li>
	<li>Make a hole approximately 5 mm behind the external auditory canal with a 1.0 mm diamond bur. (Figure 3C). Use a drill speed of 1,000 - 8,000 rpm depending on the drilling site. 
	NOTE: A slow speed is adequate for delicate manipulation near the semicircular canal or the facial nerve.&#160;Drip the saline in drilling site properly to prevent the thermal injury.</li>
	<li>Enlarge the hole by drilling and confirm the position of the horizontal semicircular canal (HSC), which bulges toward the mastoid cavity (Figure 3D).</li>
	<li>Confirm the position of the facial nerve whose vertical part runs anterior of HSC. Drill and remove all the bone septa, if they exist, to obtain a clear view of the facial recess, which is located at the center of the triangular area between the facial nerve and the chorda tympani.</li>
	<li>Make a small hole by drilling in between the vertical part of the facial nerve and the tympanic rim (asterisk in Figure 4A) with a 0.6 mm diameter diamond bur at 1,000 rpm.</li>
	<li>Move the bur parallel to the posterior canal wall to prevent damage to the facial nerve, which can be seen as a pink line through the thinned bone. Stop the drilling immediately before the nerve is exposed as a white line structure (Figure 4B).</li>
	<li>Ensure the round window niche can be visualized through the hole (Figure 4C). Then, administrate drugs into the niche with a 25-gauge or thinner needle. In order to retain drugs in the round window niche, place a viscous solution on the niche (Figure 4D).</li>
	<li>After confirming that hemostasis is securely controlled, close the layers (epidermal layer and dermal layer) with simple interrupted suture using 6-0 absorbent threads.</li>
	<li>Fix gauze on the surgical wound and affix a bandage.</li>
</ol>
5. Postoperative Care
<ol>
	<li>Administrate atipamezole hydrochloride (0.15 mg/kg) intramuscularly into the femoral muscle to antagonize medetomidine.</li>
	<li>When spontaneous breathing starts, remove the endotracheal tube.</li>
	<li>Maintain the common marmoset in an intensive care unit at 30% O2, 29 &#8451; until anesthesia wears off to complete arousal.</li>
	<li>Confirm that there are no findings suggestive of vestibular dysfunction such as nystagmus, and return the animal to the breeding cage.</li>
</ol>

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The authors have nothing to disclose.

The volume of cochlear blood flow is extremely small, estimated to be in the order of 1/1,000,000 of the total cardiac output in humans, and access is limited by the presence of the blood-cochlea barrier which separates the inner ear from the general circulation19,20. For these reasons, drug or viral vector administration into the inner ear is favorable, not via systemic administration but rather by direct administration. In mouse and guinea pig experiments, vari...

Sensorineural hearing loss (SNHL) arises predominantly from damage or deficiency in the cochlea. Common causes of SNHL include aging (e.g. presbycusis), genetic defects, exposure to loud noise, infection, and ototoxic drugs1. The World Health Organization (WHO) estimated that over 360 million people, representing 5.3% of the world&#39;s population, suffer from hearing loss2. It is also estimated that 1 in 900 to 1 in 2,500 newborns have moderate, severe, and profound congenital permanent hearing loss, and around one in three adults older than 65 years have some degree of hearing loss3. However, there is no effective clinical treatment of hearing loss for these patients.
Hearing research has long been performed using rodent or guinea pig models, and many approaches, such as gene therapy and regenerative therapy, have been suggested as a new treatment for hearing loss. However, there is a large difference between humans and rodents in terms of the auditory system, and it is very difficult to translate animal models to human applications. The common marmoset (C. jacchus), a New World monkey originating from the Amazon, has become an attractive non-human primate model for various basic research studies for several reasons. First, its anatomy and physiology are more similar to those of the humans rather than rodents. Second, the basic biological information about this species, including diseases, neural networks, behavior, and the genome, is well characterized. Auditory and vocal processing, the cortical coding of periodicity, the representation of pitch, and the auditory-vocal interactions of common marmosets have also been reported4,5,6,7,8,9,10. In recent histological studies, researchers identified distinctive expression patterns of 20 deafness genes and anion exchangers in the cochlea of the common marmoset and found that five genes that are causative of progressive deafness, and three anion exchangers, had different expression patterns from those of rodents11,12. These profiles lead us to believe that the common marmoset is a powerful tool for hearing research.
The most marked attributes of the common marmoset as an experimental animal are as follows:
<ul>
	<li>Easy handling with a small body size compared to some species of Old World monkeys: Adult marmosets weigh 300 - 400 g and are approximately 60 cm in height, which is similar to rats.</li>
	<li>Highly reproductive primate: Marmosets attain sexual maturity at an age of 18 months and are able to bear twice a year and produce 4 to 6 offspring annually.</li>
	<li>Genetic modifications are available: Sasaki E et al. succeeded in creating transgenic13 and knock-out14 primates using marmosets by genetic modifications implicated in neurological disorders (e.g., Parkinson&#39;s disease and Alzheimer&#39;s disease).</li>
	<li>Both embryonic stem (ES) cells and induced pluripotent stem (iPS) cells have been established15,16. Though it is rather difficult to keep the same number of marmosets compared to rodents, the availability of stem cells or iPS cells provides in vitro assays which will reduce the number of in vivo assays required.</li>
</ul>
To facilitate better translational research in the field of deafness and its potential therapy, we established an imaging study protocol using CT and MRI, general anesthesia and hearing tests using auditory brain stem responses (ABRs). These experimental systems may provide us with better opportunities to obtain pre-clinical proof of concept studies which are essential for bridging the gaps between rodent studies and clinical trials. Here, we report a surgical method to administrate drugs to the inner ear of the common marmoset through the round window membrane. To obtain a clear view around the round window, without manipulating the tympanic membrane which might cause a conductive hearing loss, it is useful to approach from the mastoid cavity. Clinically, this approach, referred to as &#34;posterior tympanotomy&#34; is well established and usually used for cochlear implantation and cholesteatoma surgery. We believe that posterior tympanotomy allows us to perform the accurate administration of drugs without inducing hearing loss.

<table><tbody><tr><td>common marmoset</td><td>CLEA Japan</td><td>EDM:C.Marmoset(Jic)</td><td></td></tr><tr><td>isoflurane</td><td>Phizer</td><td></td><td></td></tr><tr><td>medetomidine</td><td>ZENOAQ</td><td></td><td></td></tr><tr><td>midazolam</td><td>astellas</td><td></td><td></td></tr><tr><td>butorphanol</td><td>Meiji Seika</td><td></td><td></td></tr><tr><td>ampicillin</td><td>Meiji Seika</td><td></td><td></td></tr><tr><td>lidocaine hydrochloride</td><td>AstraZeneca</td><td></td><td></td></tr><tr><td>&amp;nbsp;6-0 absorbent thread</td><td>ETHICON</td><td>RD-1</td><td></td></tr><tr><td>atipamezole hydrochloride</td><td>ZENOAQ</td><td></td><td></td></tr><tr><td>phosphate buffered saline</td><td>Wako</td><td>045-29795</td><td></td></tr><tr><td>Surge Wave</td><td>Morita</td><td>TR-900-OR</td><td></td></tr><tr><td>Diamond Bar 006</td><td>Morita</td><td>14070057</td><td></td></tr><tr><td>Diamond Bar 010</td><td>Morita</td><td>14070081</td><td></td></tr><tr><td>intensive care unit</td><td>Menix</td><td>P-100</td><td></td></tr></tbody></table>

a surgical procedure for the administration of drugs to the inner ear in a non-human primate common marmoset (callithrix jacchus)

Hearing research has long been facilitated by rodent models, although in some diseases, human symptoms cannot be recapitulated. The common marmoset (Callithrix jacchus) is a small, easy-to-handle New World monkey which has a similar anatomy of the temporal bone, including the middle ear ossicular chains and inner ear to humans, than in comparison with that of rodents. Here, we report a reproducible, safe, and rational surgical approach to the cochlear round window niche for the drug delivery to the inner ear of the common marmoset. We adopted posterior tympanotomy, a procedure used clinically in human surgery, to avoid manipulation of the tympanic membrane that may cause conductive hearing loss. This surgical procedure did not lead to any significant hearing loss. This approach was possible due to the large bulla structure of the common marmoset, although the lateral semicircular canal and vertical portion of the facial nerve should be carefully considered. This surgical method allows us to perform the safe and accurate administration of drugs without hearing loss, which is of great importance in obtaining pre-clinical proof of concept for translational research.

Posterior tympanotomy was performed without any complication such as surgical site infection, bleeding with vascular injury, or vestibular dysfunction, which sometimes occurs with middle ear manipulation. We performed posterior tympanotomy on the right ear of 7-year-old common marmoset and administered 1 &#181;L of phosphate buffered saline to the round window niche. ABRs were measured before and two months after surgery (Figure 5A-B). Wavefo...

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A Surgical Procedure for the Administration of Drugs to the Inner Ear in a Non-Human Primate Common Marmoset Callithrix jacchus

We report a surgical method to administrate drugs to the inner ear of a non-human primate, the common marmoset (Callithrix jacchus), via the round window membrane.

A Surgical Procedure for the Administration of Drugs to the Inner Ear in a Non-Human Primate Common Marmoset (Callithrix jacchus)

Hearing research has long been facilitated by rodent models, although in some diseases, human symptoms cannot be recapitulated. The common marmoset ...

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Research

JoVE Journal

Medicine

8.6K Views.  Jikei University School of Medicine. Een chirurgische methode te beheren van drugs aan het binnenoor van een niet-menselijke primaten, de gemeenschappelijke Hapalomys (Callithrix jacchus), rapporteren we via het membraan van het ronde venster.

Video: A Surgical Procedure for the Administration of Drugs to the Inner Ear in a Non-Human Primate Common Marmoset Callithrix jacchus

A Strategy to Identify de Novo Mutations in Common Disorders such as Autism and Schizophrenia

There are several lines of evidence supporting the role of de novo mutations as a mechanism for common disorders, such as autism and schizophrenia. First, the de novo mutation rate in humans is relatively high, so new mutations are generated at a high frequency in the population. However, de novo mutations have not been reported in most common diseases. Mutations in genes leading to severe diseases where there is a strong negative selection against the phenotype, such as lethality in embryonic stages or reduced reproductive fitness, will not be transmitted to multiple family members, and therefore will not be detected by linkage gene mapping or association studies. The observation of very high concordance in monozygotic twins and very low concordance in dizygotic twins also strongly supports the hypothesis that a significant fraction of cases may result from new mutations. Such is the case for diseases such as autism and schizophrenia. Second, despite reduced reproductive fitness1 and extremely variable environmental factors, the incidence of some diseases is maintained worldwide at a relatively high and constant rate. This is the case for autism and schizophrenia, with an incidence of approximately 1% worldwide. Mutational load can be thought of as a balance between selection for or against a deleterious mutation and its production by de novo mutation. Lower rates of reproduction constitute a negative selection factor that should reduce the number of mutant alleles in the population, ultimately leading to decreased disease prevalence. These selective pressures tend to be of different intensity in different environments. Nonetheless, these severe mental disorders have been maintained at a constant relatively high prevalence in the worldwide population across a wide range of cultures and countries despite a strong negative selection against them2. This is not what one would predict in diseases with reduced reproductive fitness, unless there was a high new mutation rate. Finally, the effects of paternal age: there is a significantly increased risk of the disease with increasing paternal age, which could result from the age related increase in paternal de novo mutations. This is the case for autism and schizophrenia3. The male-to-female ratio of mutation rate is estimated at about 4&#x2013;6:1, presumably due to a higher number of germ-cell divisions with age in males. Therefore, one would predict that de novo mutations would more frequently come from males, particularly older males4. A high rate of new mutations may in part explain why genetic studies have so far failed to identify many genes predisposing to complexes diseases genes, such as autism and schizophrenia, and why diseases have been identified for a mere 3% of genes in the human genome. Identification for de novo mutations as a cause of a disease requires a targeted molecular approach, which includes studying parents and affected subjects. The process for determining if the genetic basis of a disease may result in part from de novo mutations and the molecular approach to establish this link will be illustrated, using autism and schizophrenia as examples.

Molecular genetic strategy for finding de novo mutations causing common disorders such as autism and schizophrenia.

There are several lines of evidence supporting the role of de novo mutations as a mechanism for common disorders, such as autism and schizophrenia. First, ...

Canalostomy As a Surgical Approach to Local Drug Delivery into the Inner Ears of Adult and Neonatal Mice

Local delivery of therapeutic drugs into the inner ear is a promising therapy for inner ear diseases. Injection through semicircular canals (canalostomy) has been shown to be a useful approach to local drug delivery into the inner ear. The goal of this article is to describe, in detail, the surgical techniques involved in canalostomy in both adult and neonatal mice. As indicated by fast-green dye and adeno-associated virus serotype 8 with the green fluorescent protein gene, the canalostomy facilitated broad distribution of injected reagents in the cochlea and vestibular end-organs with minimal damage to hearing and vestibular function. The surgery was successfully implemented in both adult and neonatal mice; indeed, multiple surgeries could be performed if required. In conclusion, canalostomy is an effective and safe approach to drug delivery into the inner ears of adult and neonatal mice and may be used to treat human inner ear diseases in the future.

Here we describe canalostomy procedure which allows local drug delivery into the inner ears of adult and neonatal mice through the semicircular canal with minimum damage to hearing and vestibular function. This method can be used to inoculate viral vectors, pharmaceuticals, and small molecules into the mouse inner ear.

Local delivery of therapeutic drugs into the inner ear is a promising therapy for inner ear diseases. Injection through semicircular canals (canalostomy) ...

Genetics

A Novel Surgical Approach for Intratracheal Administration of Bioactive Agents in a Fetal Mouse Model

Prenatal pulmonary delivery of cells, genes or pharmacologic agents could provide the basis for new therapeutic strategies for a variety of genetic and acquired diseases. Apart from congenital or inherited abnormalities with the requirement for long-term expression of the delivered gene, several non-inherited perinatal conditions, where short-term gene expression or pharmacological intervention is sufficient to achieve therapeutic effects, are considered as potential future indications for this kind of approach. Candidate diseases for the application of short-term prenatal therapy could be the transient neonatal deficiency of surfactant protein B causing neonatal respiratory distress syndrome1,2 or hyperoxic injuries of the neonatal lung3. Candidate diseases for permanent therapeutic correction are Cystic Fibrosis (CF)4, genetic variants of surfactant deficiencies5 and &alpha;1-antitrypsin deficiency6.
Generally, an important advantage of prenatal gene therapy is the ability to start therapeutic intervention early in development, at or even prior to clinical manifestations in the patient, thus preventing irreparable damage to the individual. In addition, fetal organs have an increased cell proliferation rate as compared to adult organs, which could allow a more efficient gene or stem cell transfer into the fetus. Furthermore, in utero gene delivery is performed when the individual's immune system is not completely mature. Therefore, transplantation of heterologous cells or supplementation of a non-functional or absent protein with a correct version should not cause immune sensitization to the cell, vector or transgene product, which has recently been proven to be the case with both cellular and genetic therapies7.
In the present study, we investigated the potential to directly target the fetal trachea in a mouse model. This procedure is in use in larger animal models such as rabbits and sheep8, and even in a clinical setting9, but has to date not been performed before in a mouse model. When studying the potential of fetal gene therapy for genetic diseases such as CF, the mouse model is very useful as a first proof-of-concept because of the wide availability of different transgenic mouse strains, the well documented embryogenesis and fetal development, less stringent ethical regulations, short gestation and the large litter size.
Different access routes have been described to target the fetal rodent lung, including intra-amniotic injection10-12, (ultrasound-guided) intrapulmonary injection13,14 and intravenous administration into the yolk sac vessels15,16 or umbilical vein17. Our novel surgical procedure enables researchers to inject the agent of choice directly into the fetal mouse trachea which allows for a more efficient delivery to the airways than existing techniques18.

We developed a novel surgical approach for intratracheal administration of bioactive agents into the mouse fetus. The delivery route is more efficient in targeting the fetal mouse lungs than the commonly used intra-amniotic injection. This procedure has to date not been described in a mouse model.

Prenatal pulmonary delivery of cells, genes or pharmacologic agents could provide the basis for new therapeutic strategies for a variety of genetic and ...

Surgical Method for Virally Mediated Gene Delivery to the Mouse Inner Ear through the Round Window Membrane

Gene therapy, used to achieve functional recovery from sensorineural deafness, promises to grant better understanding of the underlying molecular and genetic mechanisms that contribute to hearing loss. Introduction of vectors into the inner ear must be done in a way that widely distributes the agent throughout the cochlea while minimizing injury to the existing structures. This manuscript describes a post-auricular surgical approach that can be used for mouse cochlear therapy using molecular, pharmacologic, and viral delivery to mice postnatal day 10 and older via the round window membrane (RWM). This surgical approach enables rapid and direct delivery into the scala tympani while minimizing blood loss and avoiding animal mortality. This technique involves negligible or no damage to essential structures of the inner and middle ear as well as neck muscles while wholly preserving hearing. To demonstrate the efficacy of this surgical technique, the vesicular glutamate transporter 3 knockout (VGLUT3 KO) mice will be used as an example of a mouse model of congenital deafness that recovers hearing after delivery of VGLUT3 to the inner ear using an adeno-associated virus (AAV-1).

The described post-auricular surgical approach allows rapid and direct delivery into the mouse cochlear scala tympani while minimizing blood loss and animal mortality. This method can be used for cochlear therapy using molecular, pharmacologic and viral delivery to postnatal mice through the round window membrane.

Gene therapy, used to achieve functional recovery from sensorineural deafness, promises to grant better understanding of the underlying molecular and ...

Neuroscience

Chronic Implantation of Whole-cortical Electrocorticographic Array in the Common Marmoset

Electrocorticography (ECoG) allows the monitoring of electrical field potentials from the cerebral cortex with high spatiotemporal resolution. Recent development of thin, flexible ECoG electrodes has enabled conduction of stable recordings of large-scale cortical activity. We have developed a whole-cortical ECoG array for the common marmoset. The array continuously covers almost the entire lateral surface of cortical hemisphere, from the occipital pole to the temporal and frontal poles, and it captures whole-cortical neural activity in one shot. This protocol describes a chronic implantation procedure of the array in the epidural space of the marmoset brain. Marmosets have two advantages regarding ECoG recordings, one being the homologous organization of anatomical structures in humans and macaques, including frontal, parietal, and temporal complexes. The other advantage is that the marmoset brain is lissencephalic and contains a large number of complexes, which are more difficult to access in macaques with ECoG, that are exposed to the brain surface.These features allow direct access to most cortical areas beneath the surface of the brain. This system provides an opportunity to investigate global cortical information processing with high resolutions at a sub-millisecond order in time and millimeter order in space.

We have developed a whole-cortical electrocorticographic array for the common marmoset that continuously covers almost the entire lateral surface of cortex, from the occipital pole to the temporal and frontal poles. This protocol describes a chronic implantation procedure of the array in the epidural space of the marmoset brain.

Electrocorticography (ECoG) allows the monitoring of electrical field potentials from the cerebral cortex with high spatiotemporal resolution. Recent ...

Stereotaxic Surgery for Implantation of Microelectrode Arrays in the Common Marmoset (Callithrix jacchus)

Marmosets (Callithrix jacchus) are small non-human primates that are gaining popularity in biomedical and preclinical research, including the neurosciences. Phylogenetically, these animals are much closer to humans than rodents. They also display complex behaviors, including a wide range of vocalizations and social interactions. Here, an effective stereotaxic neurosurgical procedure for implantation of recording electrode arrays in the common marmoset is described. This protocol also details the pre- and postoperative steps of animal care that are required to successfully perform such a surgery. Finally, this protocol shows an example of local field potential and spike activity recordings in a freely behaving marmoset 1 week after the surgical procedure. Overall, this method provides an opportunity to study the brain function in awake and freely behaving marmosets. The same protocol can be readily used by researchers working with other small primates. In addition, it can be easily modified to allow other studies requiring implants, such as stimulating electrodes, microinjections, implantation of optrodes or guide cannulas, or ablation of discrete tissue regions.

Stereotaxic Surgery for Implantation of Microelectrode Arrays in the Common Marmoset Callithrix jacchus

This work presents a protocol to perform a stereotaxic, neurosurgical implantation of&#160;microelectrode arrays in the common marmoset. This method specifically enables electrophysiological recordings in freely behaving animals but can be easily adapted to any other similar neurosurgical intervention in this species (e.g., cannula for drug administration or electrodes for brain stimulation).

Marmosets (Callithrix jacchus) are small non-human primates that are gaining popularity in biomedical and preclinical research, including the ...

Development of an X-Y Electrode Stage for Precise Neural Recording in Marmosets

Electrophysiology of Laminar Cortical Activity in the Common Marmoset

The marmoset monkey provides an ideal model for examining laminar cortical circuits due to its smooth cortical surface, which facilitates recordings with linear arrays. The marmoset has recently grown in popularity due to its similar neural functional organization to other primates and its technical advantages for recording and imaging. However, neurophysiology in this model poses some unique challenges due to the small size and lack of gyri as anatomical landmarks. Using custom-built micro-drives, researchers can manipulate linear array placement to sub-millimeter precision and reliably record at the same retinotopically targeted location across recording days. This protocol describes the step-by-step construction of the micro-drive positioning system and the neurophysiological recording technique with silicon linear electrode arrays. With precise control of electrode placement across recording sessions, researchers can easily traverse the cortex to identify areas of interest based on their retinotopic organization and the tuning properties of the recorded neurons. Further, using this laminar array electrode system, it is possible to apply a current source density analysis (CSD) to determine the recording depth of individual neurons. This protocol also demonstrates examples of laminar recordings, including spike waveforms isolated in Kilosort, which span multiple channels on the arrays.

Author Spotlight: Optimizing Micro-Drive Systems for Precise Electrode Positioning in Marmoset

Custom-built micro-drives enable the sub-millimeter targeting of cortical recording sites with linear silicon arrays.

The marmoset monkey provides an ideal model for examining laminar cortical circuits due to its smooth cortical surface, which facilitates recordings with ...

A Comparative Study of Drug Delivery Methods Targeted to the Mouse Inner Ear: Bullostomy Versus Transtympanic Injection

We present two minimally invasive microsurgical techniques in rodents for specific drug delivery into the middle ear so that it may reach the inner ear. The first procedure consists of perforation of the tympanic bulla, termed bullostomy; the second one is a transtympanic injection. Both emulate human clinical intratympanic procedures.
Chitosan-glycerophosphate (CGP) and Ringer&#180;s Lactate buffer (RL) were used as biocompatible vehicles for local drug delivery. CGP is a nontoxic biodegradable polymer widely used in pharmaceutical applications. It is a viscous liquid at RT&#160;but it congeals to a semi solid phase at body temperature. RL is an isotonic solution used for intravenous administrations in humans. A small volume of this vehicle is precisely placed on the Round Window (RW) niche by means of a bullostomy. A transtympanic injection fills the middle ear and allows less control but broader access to the inner ear.
The safety profiles of both techniques were studied and compared by using functional and morphological tests. Hearing was evaluated by registering the Auditory Brainstem Response (ABR) before and several times after microsurgery. The cytoarchitecture and preservation level of cochlear structures were studied by conventional histological techniques in paraformaldehyde-fixed and decalcified cochlear samples. In parallel, unfixed cochlear samples were taken and immediately frozen to analyze gene expression profiles of inflammatory markers by quantitative Reverse Transcriptase Polymerase Chain Reaction (qRT-PCR).
Both procedures are suitable as drug delivery methods into the mouse middle ear, although transtympanic injection proved to be less invasive compared to bullostomy.

A Comparative Study of Drug Delivery Methods Targeted to the Mouse Inner Ear: Bullostomy Versus Transtympanic Injection

Two microsurgery approaches for local drug delivery to the inner ear are described here and compared in terms of impact on hearing parameters, cochlear cytoarchitecture and expression of inflammatory markers.

We present two minimally invasive microsurgical techniques in rodents for specific drug delivery into the middle ear so that it may reach the inner ear. ...

Biology

Noninvasive EEG for Comparative Studies of Vocal Perception in Marmosets

Electroencephalography Measurements in Awake Marmosets Listening to Conspecific Vocalizations

Vocal communication plays a crucial role in the social interactions of primates, particularly in survival and social organization. Humans have developed a unique and advanced vocal communication strategy in the form of language. To study the evolution of human language, it is necessary to investigate the neural mechanisms underlying vocal processing in humans, as well as to understand how brain mechanisms have evolved by comparing them with those in nonhuman primates. Herein, we developed a method to noninvasively measure the electroencephalography (EEG) of awake nonhuman primates. This recording method allows for long-term studies without harming the animals, and, importantly, allows us to directly compare nonhuman primate EEG data with human data, providing insights into the evolution of human language. In the current study, we used the scalp EEG recording method to investigate brain activity in response to species-specific vocalizations in marmosets. This study provides novel insights by using scalp EEG to capture widespread neural representations in marmosets during vocal perception, filling gaps in existing knowledge.

Author Spotlight: Investigating Vocal Information Representation in Small Primates and Its Alteration by Psychiatric Disorders Using Noninvasive EEG

To study the evolution of language, comparing brain mechanisms in humans with those in nonhuman primates is important. We developed a method to noninvasively measure the electroencephalography (EEG) of awake animals. It allows us to directly compare EEG data between humans and animals for the long term without harming them.

Vocal communication plays a crucial role in the social interactions of primates, particularly in survival and social organization. Humans have developed a ...

Canalostomy for Local Drug Delivery into the Inner Ear of an Adult Mouse

Source: Guo, J. et al., <a href="https://app.jove.com/v/57351">Canalostomy as a Surgical Approach to Local Drug Delivery into the Inner Ears of Adult and Neonatal Mice.</a>&#160;J. Vis. Exp. (2018)
This video showcases canalostomy, a procedure that allows local drug delivery into the inner ear of a mouse through the semicircular canal with minimal damage to hearing and vestibular function. This method enables the inoculation of viral vectors, pharmaceuticals, and small molecules into the mouse&#39;s inner ear.

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.
1. Device ...

A Surgical Procedure for the Administration of Drugs to the Inner Ear in a Non-Human Primate Common Marmoset (Callithrix jacchus)

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