This study was funded by grants from the National Natural Science Foundation of China (Nos. 81970890) and the Chongqing Scientific Research Institution Performance incentive project (Nos. 19540). We thank Anandhan Dhanasingh and Zhi Shu from the MED-EL company for their support.

All procedures and animal surgeries were conducted according to the guidelines of the Ethics Committee of the PLA General Hospital and were approved.
1. Anesthesia and surgical preparation
<ol>
	<li>Inject the pig (male, 2 months old, 5 kg) muscularly with tiletamine and zolazepam with a dosage of 10-15 mg/kg and intubate it with a 5.5-French endotracheal tube. Maintain anesthesia by ventilator-assisted respiration with isofluorane inhalation. Monitor the oxygen saturation (&#62;90%), breathing (15-20/min), and heart rate (60-120 beats/min) using the pulse oximetry clamp of an ECG monitor, which is connected to the pig&#39;s tongue.</li>
	<li>Put the mini-pig in a left lateral position (when the right side is to be implanted) on&#160;a thermostatically regulated heating pad to prevent&#160;hypothermia. Confirm the pig is adequately anesthetized using various stimuli. Ensure the absence of all responses (e.g., toe pinch&#160;reflex). Apply artificial tear ointment to the eyes of the minipig to keep the cornea from drying. Keep the eyes closed using a medical patch.</li>
	<li>Shave the surgical area around the earlobe, keeping it 10 cm in diameter&#160;(Figure 1) and disinfect&#160;it with three alternating swabs of iodine&#160;and alcohol in a circular motion from the center toward the outside. Cover the surgical area with sterile surgical drapes.</li>
	<li>Cover the microscope with a sterile plastic sleeve and remove the parts covering the eyepieces and objective.</li>
</ol>
2. Surgical procedure
<ol>
	<li>Locate the surface projection site of the cochlea 1 cm behind the posterior auricular sulcus at the level of the earlobe. Make a postauricular incision about 5 cm long with the projection site as the center using a #15 scalpel. Divide the subcutaneous tissue, parotid gland, and sternocleidomastoid muscle with micro-scissors to expose the surface of the mastoid bone (Figure 2A). Use bipolar cautery when necessary to minimize bleeding.</li>
	<li>Cortical mastoidectomy
	<ol>
		<li>Drill the mastoid at the surface projection of the cochlea on the mastoid bone (Figure 2B) to the external auditory canal (EAC), which is dense and pale blue (Figure 2C). Be careful not to damage the pale or reddish vertical segment of the facial nerve dorsal to the EAC to avoid bleeding (Figure 2C). 
		NOTE: If the facial nerve is damaged, bipolar cautery is a good choice to stop bleeding.</li>
	</ol>
	</li>
	<li>Expose the tympanum by drilling the bone surrounding the posterior bony EAC (Figure 2D). Separate the skin of the EAC and the facial nerve with a hypodermic needle to avoid damaging the facial nerve. Carefully push the skin of the EAC away to expose the tympanum (including the ossicular chain) and round window niche (Figure 3A).</li>
	<li>Expose the round window membrane. Remove the round window niche with a small diamond burr, and keep continuous suction-irrigation to expose the basal turn of the cochlea and round window membrane (Figure 3B).</li>
	<li>Fix the receiver package. Separate the cranial parietal muscle to form a pocket just large enough for the receiver. Place the internal receiver package in the muscular pocket and fix it with a fixation suture.</li>
	<li>Insert the electrode array, which is connected to a receiver fixed in a muscular pocket, by opening the round window membrane with a sharp microsurgical knife and inserting the array using micro forceps slowly, steadily, and continuously in relationship to the modiolus of the cochlea (Figure 3C). Suture the surgical incision with an absorbable&#160;suture 2-0.</li>
	<li>ECAP measurements 
	NOTE: The setup is composed of a PC with MAESTRO Software connected to the patient&#39;s cochlear implant (CI) through the stimulation device (MAX Programming Interface) and the CI coil.
	<ol>
		<li>Magnetically connect the CI coil to the CI receiver through the skin. Confirm the integrity of the CI and check the electrode impedance for all channels before ECAP measurements using the telemetry function of the CI, which is conducted by MAESTRO Software automatically (Figure 4A,B).</li>
		<li>Conduct the ECAP measurements as described previously19. Select the ECAP module, choose all 12 electrodes for stimulation, and wait for the ECAP tests of the electrodes to be completed. See the Table of Materials for the software and stimulation device used to measure ECAP responses. Stimulate all 12 electrodes for ECAP measurements using biphasic stimuli of 30 &#181;s phase duration, with an alternating-polarity paradigm, averaging over 25 iterations, and a stimulation rate of 45.1 pulses/s.</li>
	</ol>
	</li>
</ol>
3. Postoperative care
<ol>
	<li>Keep monitoring the mini-pig to avoid harm due to unconscious movement until it has regained sufficient consciousness to maintain sternal recumbency. Put&#160;the minipig on the thermostatically regulated heating pad to prevent&#160;hypothermia.</li>
	<li>Place the mini-pig back into its home cage alone.</li>
	<li>Inject antibiotics to prevent postoperative infection for 7 days.</li>
	<li>Check the mini-pig for symptoms of vestibular injury such as nystagmus, circling, or rolling over.</li>
</ol>
4. Postoperative CT scan
<ol>
	<li>&#160;Administer intramuscular injection of 3% sodium pentobarbital 1 ml/kg, and 0.1 ml/kg of Sulforaphane to minipig to induce anesthesia. Use&#160;a 37&#8451; warming plate to keep it warm. After&#160;3 or 5 minutes,&#160;a CT scan can be&#160;conducted.&#160;</li>
	<li>To confirm the correct position of the electrode array, narcotize the mini-pig with tiletamine and zolazepam 1 week after the operation. Perform the CT scan and 3D reconstruction20 using the 3D slicer image computing platform (see the Table of Materials). Import DICOM data of the CT and conduct the Volume rendering module to achieve 3D images of the CI.</li>
</ol>

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	<li>World report on hearing. World Health Organization Available from: <a target="_blank" href="https://www.who.int/publications/i/item/world-report-on-hearing">https://www.who.int/publications/i/item/world-report-on-hearing</a> (2021)</li><li>Lee, S. Y., 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=Natural+course+of+residual+hearing+preservation+with+a+slim,+modiolar+cochlear+implant+electrode+array.">Natural course of residual hearing preservation with a slim, modiolar cochlear implant electrode array.</a> American Journal of Otolaryngology. 43 (2), 103382 (2022).</li><li>Lorens, 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=Binaural+advantages+in+using+a+cochlear+implant+for+adults+with+profound+unilateral+hearing+loss.">Binaural advantages in using a cochlear implant for adults with profound unilateral hearing loss.</a> Acta Oto-Laryngologica. 139 (2), 153-161 (2019).</li><li>Lally, J. W., Adams, J. K., Wilkerson, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+cochlear+implantation+in+the+elderly.">The use of cochlear implantation in the elderly.</a> Current Opinion in Otolaryngology &amp; Head and Neck Surgery. 27 (5), 387-391 (2019).</li><li>Rhodes, R. M., Tsai Do, B. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Future+of+implantable+auditory+devices.">Future of implantable auditory devices.</a> Otolaryngologic Clinics of North America. 52 (2), 363-378 (2019).</li><li>Colesa, D. 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The authors declare that they have no conflicts of interest.

Around 15% of the world's population have some degree of hearing loss, and over 5% have disabling hearing loss21. CI provision is the most efficient treatment for both adult and pediatric patients with severe and profound sensorineural hearing loss. As the first successful implantable cranial nerve stimulator, over the past 2 decades, CIs have offered thousands of people with hearing loss the opportunity to return to the world of sound and (re)integrate into mainstream society. Even though CIs are...

According to the World Health Organization (WHO), over 1 billion people are at risk of hearing loss globally, and it is estimated that, by 2050, one out of four people will suffer hearing loss1. Over the last 2 decades, CIs have been the most effective intervention for people with permanent severe and profound sensorineural hearing loss (SNHL). A CI converts physical signals of sound into bioelectrical signals that stimulate the spiral ganglion neurons (SGNs), bypassing hair cells. Over time, the indications for a CI have been broadened so that they now include people with residual hearing, unilateral hearing loss, and very old or young people2,3,4. Meanwhile, totally implantable CIs and advanced arrays have been developed5. There is, however, no economically feasible large animal model for investigating the electrophysiology and histopathology of the inner ear with a CI. This lack of a large animal model limits research seeking to improve CIs and gain insights into the electrophysiological impact of CIs on the inner ear.
Several rodent animal models have been applied in CI research, such as mouse6, gerbil7, rat8, and guinea pig9; however, the characteristics of morphology and electrophysiological responses are different from that in humans. Cochlear structures of animal models traditionally used for CI studies, such as cats, guinea pigs, and other animals, differ greatly from those of human cochlear structures10. Although array insertion has been conducted on cats11 and rabbits12, because of their smaller cochleae, this was done with arrays that were not designed for use in humans. Several large animal models have also been explored for CI. Lambs are well suited as a training model for atraumatic cochlear implantation, but the smaller size of the cochlea makes full array insertion impossible13. Primates might be the most suitable animals for CI research because of their anatomical similarity to humans14,15; however, the sexual maturity of monkeys is delayed (4-5 years), the gestation period is up to about 165 days, and each female usually produces only one offspring per year16. These reasons, and the expensive cost, hinder the extensive application of primates in CI research.
In contrast, pigs reach sexual maturity at 5-8 months and have a gestation period of ~114 days, making pigs more accessible for CI research as a large animal model16. Bama mini pigs (mini-pigs) originated from a small-sized pig species in China in 1985, whose genetic background is well understood. They are characterized by an inherent small size, early sexual maturity, rapid breeding, and ease of management17. The mini-pig is an ideal model for otology and audiology because of its similarity to humans in morphology and electrophysiology18. The scala tympani length of a Bama mini-pig is 38.58 mm, which is close to the 36 mm length in humans10. The mini-pig cochlea has 3.5 turns, which is similar to the 2.5-3 turns seen in humans10. In addition to morphology, the electrophysiology of Bama mini-pigs is also highly similar to that of humans18. Therefore, in the present study, we inserted arrays designed for human use into the mini-pig cochlea via the round window membrane and followed a similar surgical approach to that used in human CI recipients. Intraoperative ECAP measurements were applied to evaluate the procedure. The process we describe herein could be used both for preclinical translational research associated with CIs and as a platform for resident training.

<table><tbody><tr><td>0.5 mm diamond burr</td><td></td><td></td><td></td></tr><tr><td>1 mm diamond burr</td><td></td><td></td><td></td></tr><tr><td>5 mm diamond burr</td><td></td><td></td><td></td></tr><tr><td>2-0 suture silk</td><td></td><td></td><td></td></tr><tr><td>3D Slicer image computing platform</td><td></td><td></td><td>3D reconstruction of CT image</td></tr><tr><td>Alcohol</td><td></td><td></td><td></td></tr><tr><td>Bipolar cautery</td><td></td><td></td><td></td></tr><tr><td>Bipolar electrocoagulation</td><td></td><td></td><td>Stop bleeding</td></tr><tr><td>CI designed for human use (CONCERTO FLEX28)</td><td>MED-EL</td><td>&amp;nbsp;Concerto F28</td><td></td></tr><tr><td>Dressing forceps</td><td></td><td></td><td></td></tr><tr><td>ECG monitor</td><td></td><td></td><td></td></tr><tr><td>Iodine tincture</td><td></td><td></td><td></td></tr><tr><td>Isoflurane</td><td></td><td></td><td>3.6 mL/h</td></tr><tr><td>Laryngoscope</td><td></td><td></td><td></td></tr><tr><td>MAESTRO Software</td><td>MED-EL</td><td></td><td>Measure ECAP responses</td></tr><tr><td>Micro forceps</td><td></td><td></td><td></td></tr><tr><td>Micro spatula</td><td></td><td></td><td></td></tr><tr><td>Mosquito forceps</td><td></td><td></td><td></td></tr><tr><td>Needle holder</td><td></td><td></td><td></td></tr><tr><td>Needle probe</td><td></td><td></td><td></td></tr><tr><td>Negative pressure suction device</td><td></td><td></td><td></td></tr><tr><td>Otological surgical instruments&amp;nbsp;</td><td></td><td></td><td></td></tr><tr><td>Respiratory Anesthesia Machine</td><td></td><td></td><td></td></tr><tr><td>Scalpel with blade No. 15</td><td></td><td></td><td></td></tr><tr><td>Scissors</td><td></td><td></td><td></td></tr><tr><td>Shaver</td><td></td><td></td><td></td></tr><tr><td>Stimulation device (MAX Programming Interface)</td><td>MED-EL</td><td></td><td>Measure ECAP responses</td></tr><tr><td>Surgery microscope</td><td>Leica</td><td></td><td></td></tr><tr><td>Surgical drill</td><td></td><td></td><td></td></tr><tr><td>Surgical Power Device</td><td></td><td></td><td></td></tr><tr><td>Tiletamine and zolazepan</td><td></td><td></td><td>10-15 mg/kg</td></tr><tr><td>Tissue forceps</td><td></td><td></td><td></td></tr><tr><td>Trachea cannula</td><td></td><td></td><td></td></tr></tbody></table>

the miniature pig: a large animal model for cochlear implant research

Cochlear implants (CI) are the most effective method to treat people with severe-to-profound sensorineural hearing loss. Although CIs are used worldwide, no standard model exists for investigating the electrophysiology and histopathology in patients or animal models with a CI or for evaluating new models of electrode arrays. A large animal model with cochlea characteristics similar to those of humans may provide a research and evaluation platform for advanced and modified arrays before their use in humans. 
To this end, we established standard CI methods with Bama mini-pigs, whose inner ear anatomy is highly similar to that of humans. Arrays designed for human use were implanted into the mini pig cochlea through a round window membrane, and a surgical approach followed that was similar to that used for human CI recipients. Array insertion was followed by evoked compound action potential (ECAP) measurements to evaluate the function of the auditory nerve. This study describes the preparation of the animal, surgical steps, array insertion, and intraoperative electrophysiological measurements. 
The results indicated that the same CI used for humans could be easily implanted in mini-pigs via a standardized surgical approach and yielded similar electrophysiological outcomes as measured in human CI recipients. Mini-pigs could be a valuable animal model to provide initial evidence of the safety and potential performance of novel electrode arrays and surgical approaches before applying them to human beings.

The integrity (Figure 4A)&#160;and impedances (Figure 4B) of the CI were confirmed by MAESTRO Software. ECAP results showed that all 12 electrodes demonstrated good neural responses (Figure 4C), meaning the electrode array was well attached to the cochlear axis and stimulated the auditory nerve. Figure 5 demonstrates postoperative 3D reconstructed electrode coils in the right cochlea. The array did not ...

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The Miniature Pig: A Large Animal Model for Cochlear Implant Research

Miniature pigs (mini-pigs) are an ideal large animal model for research into cochlear implants. Cochlear implantation surgery in mini-pigs can be utilized to provide initial evidence of the safety and potential performance of novel electrode arrays and surgical approaches in a living system similar to human beings.

Cochlear implants (CI) are the most effective method to treat people with severe-to-profound sensorineural hearing loss. Although CIs are used worldwide, ...

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2.7K Views.  Chinese PLA General Hospital. Miniature pigs (mini-pigs) are an ideal large animal model for research into cochlear implants. Cochlear implantation surgery in mini-pigs can be utilized to provide initial evidence of the safety and potential performance of novel electrode arrays and surgical approaches in a living system similar to human beings.

Video: The Miniature Pig: A Large Animal Model for Cochlear Implant Research

Use of a Piglet Model for the Study of Anesthetic-induced Developmental Neurotoxicity (AIDN): A Translational Neuroscience Approach

Anesthesia cannot be avoided in many cases when surgery is required, particularly in children. Recent investigations in animals have raised concerns that anesthesia exposure may lead to neuronal apoptosis, known as anesthesia-induced developmental neurotoxicity (AIDN). Furthermore, some clinical studies in children have suggested that anesthesia exposure may lead to neurodevelopmental deficits later in life. Nonetheless, an ideal animal model for preclinical study has yet to be developed. The neonatal piglet represents a valuable model for preclinical study, as they share a striking number of developmental similarities with humans.
The anatomy and physiology of piglets allow for implementation of rigorous human perioperative conditions in both survival and non-survival procedures. Femoral artery catheterization allows for close monitoring, thus enabling prompt correction of any deviation of the piglet's vital signs and chemistries. In addition, there are multiple developmental similarities between piglets and human neonates. The techniques required to use piglets for experimentation will require experience to master. A pediatric anesthesiologist is a critical member of the investigative team. We describe, in a general sense, the appropriate use of a piglet model for neurodevelopmental study.

Use of a Piglet Model for the Study of Anesthetic-induced Developmental Neurotoxicity AIDN: A Translational Neuroscience Approach

Anesthesia-induced developmental neurotoxicity (AIDN) research has focused on rodents, which are not broadly applicable to humans. Non-human primate models are more relevant, but are cost-prohibitive and difficult to use for experimentation. The piglet, in contrast, is a clinically relevant, practical animal model ideal for the study of anesthetic neurotoxicity.

Anesthesia cannot be avoided in many cases when surgery is required, particularly in children.  Recent investigations in animals have raised concerns that ...

Adaptation of Microelectrode Array Technology for the Study of Anesthesia-induced Neurotoxicity in the Intact Piglet Brain

Every year, millions of children undergo anesthesia for a multitude of procedures. However, studies in both animals and humans have called into question the safety of anesthesia in children, implicating anesthetics as potentially toxic to the brain in development. To date, no studies have successfully elucidated the mechanism(s) by which anesthesia may be neurotoxic. Animal studies allow investigation of such mechanisms, and neonatal piglets represent an excellent model to study these effects due to their striking developmental similarities to the human brain.
This protocol adapts the use of enzyme-based microelectrode array (MEA) technology as a novel way to study the mechanism(s) of anesthesia-induced neurotoxicity (AIN). MEAs enable real-time monitoring of in vivo neurotransmitter activity and offer exceptional temporal and spatial resolution. It is hypothesized that anesthetic neurotoxicity is caused in part by glutamate dysregulation and MEAs offer a method to measure glutamate. The novel implementation of MEA technology in a piglet model presents a unique opportunity for the study of AIN.

This study explores the novel use of enzyme-based microelectrode array (MEA) technology to monitor in vivo neurotransmitter activity in piglets. The hypothesis was that glutamate dysregulation contributes to the mechanism of anesthetic neurotoxicity. Here, we present a protocol to adapt MEA technology to study the mechanism of anesthesia-induced neurotoxicity.

Every year, millions of children undergo anesthesia for a multitude of procedures. However, studies in both animals and humans have called into question ...

Neuroscience

Cochlear Implant Surgery and Electrically-evoked Auditory Brainstem Response Recordings in C57BL/6 Mice

Cochlear implants (CIs) are neuroprosthetic devices that can provide a sense of hearing to deaf people. However, a CI cannot restore all aspects of hearing. Improvement of the implant technology is needed if CI users are to perceive music and perform in more natural environments, such as hearing out a voice with competing talkers, reflections, and other sounds. Such improvement requires experimental animals to better understand the mechanisms of electric stimulation in the cochlea and its responses in the whole auditory system. The mouse is an increasingly attractive model due to the many genetic models available. However, the limited use of this species as a CI model is mainly due to the difficulty of implanting small electrode arrays. More details about the surgical procedure are therefore of great interest to expand the use of mice in CI research.
In this report, we describe in detail the protocol for acute deafening and cochlear implantation of an electrode array in the C57BL/6 mouse strain. We demonstrate the functional efficacy of this procedure with electrically-evoked auditory brainstem response (eABR) and show examples of facial nerve stimulation. Finally, we also discuss the importance of including a deafening procedure when using a normally hearing animal. This mouse model provides a powerful opportunity to study genetic and neurobiological mechanisms that would be of relevance for CI users.

Animal models of cochlear implants can advance knowledge of the technological bases of treating permanent sensorineural hearing loss with electrical stimulation. This study presents a surgical protocol for acute deafening and cochlear implantation of an electrode array in mice as well as the functional assessment with auditory brainstem response.

Cochlear implants (CIs) are neuroprosthetic devices that can provide a sense of hearing to deaf people. However, a CI cannot restore all aspects of ...

Cochlear Implantation in the Guinea Pig

Cochlear implants are highly efficient devices that can restore hearing in subjects with profound hearing loss. Due to improved speech perception outcomes, candidacy criteria have been expanded over the last few decades. This includes patients with substantial residual hearing that benefit from electrical and acoustical stimulation of the same ear, which makes hearing preservation during cochlear implantation an important issue. Electrode impedances and the related issue of energy consumption is another major research field, as progress in this area could pave the way for fully implantable auditory prostheses. To address these issues in a systematic way, adequate animal models are essential. Therefore, the goal of this protocol is to provide an animal model of cochlear implantation, which can be used to address various research questions. Due to its large tympanic bulla, which allows easy surgical access to the inner ear, as well as its hearing range which is relatively similar to the hearing range of humans, the guinea pig is a commonly used species in auditory research. Cochlear implantation in the guinea pig is performed via a retroauricular approach. Through the bullostomy a cochleostomy is drilled and the cochlear implant electrode is inserted into the scala tympani. This electrode can then be used for electrical stimulation, determination of electrode impedances and the measurement of compound action potentials of the auditory nerve. In addition to these applications, cochlear implant electrodes can also be used as drug delivery devices, if a topical delivery of pharmaceutical agents to the cells or fluids of the inner ear is intended.

The goal of this protocol is to provide an animal model of cochlear implantation, which can be used to address a multitude of research questions. Potential applications include the evaluation of pharmaceutical interventions or electrical stimulation for beneficial effects on hearing thresholds or electrode impedances.

Cochlear implants are highly efficient devices that can restore hearing in subjects with profound hearing loss. Due to improved speech perception ...

Subretinal Implantation of RPE on a Carrier in Minipigs: Guidelines for Preoperative Preparations, Surgical Techniques, and Postoperative Care

Degenerative disorders of the retina (including age-related macular degeneration), which originate primarily at or within the retinal pigmented epithelial (RPE) layer, lead to a progressive disorganization of the retinal anatomy and the deterioration of visual function. The substitution of damaged RPE cells (RPEs) with in vitro cultured RPE cells using a subretinal cell carrier has shown potential for re-establishing the anatomical structure of the outer retinal layers and is, therefore, being further studied. Here, we present the principles of a surgical technique that allows for the effective subretinal transplantation of a cell carrier with cultivated RPEs into minipigs. The surgeries were performed under general anesthesia and included a standard lens-sparing three-port pars plana vitrectomy (PPV), subretinal application of a balanced salt solution (BSS), a 2.7 mm retinotomy, implantation of a nanofibrous cell carrier into the subretinal space through an additional 3.0 mm sclerotomy, fluid-air exchange (FAX), silicone oil tamponade, and closure of all the sclerotomies. This surgical approach was used in 29 surgeries (18 animals) over the past 8 years with a success rate of 93.1%. Anatomic verification of the surgical placement was carried out using in vivo fundus imaging (fundus photography and optical coherence tomography). The recommended surgical steps for the subretinal implantation of RPEs on a carrier in minipig eyes can be used in future preclinical studies using large-eye animal models.

The subretinal implantation of retinal pigmented epithelium (RPE) is one of the most promising approaches for the treatment of degenerative retinal diseases. However, the performance of preclinical studies on large-eye animal models remains challenging. This report presents guidelines for the subretinal transplantation of RPE on a cell carrier into minipigs.

Degenerative disorders of the retina (including age-related macular degeneration), which originate primarily at or within the retinal pigmented epithelial ...

Bioengineering

Subdural Soft Electrocorticography (ECoG) Array Implantation and Long-Term Cortical Recording in Minipigs

Neurological impairments and diseases can be diagnosed or treated using electrocorticography (ECoG) arrays. In drug-resistant epilepsy, these help delineate the epileptic region to resect. In long-term applications such as brain-computer interfaces, these epicortical electrodes are used to record the movement intention of the brain, to control the robotic limbs of paralyzed patients. However, current stiff electrode grids do not answer the need for high-resolution brain recordings and long-term biointegration. Recently, conformable electrode arrays have been proposed to achieve long-term implant stability with high performance. However, preclinical studies for these new implant technologies are needed to validate their long-term functionality and safety profile for their translation to human patients. In this context, porcine models are routinely employed in developing medical devices due to their large organ sizes and easy animal handling. However, only a few brain applications are described in the literature, mostly due to surgery limitations and integration of the implant system on a living animal.
Here, we report the method for long-term implantation (6 months) and evaluation of soft ECoG arrays in the minipig model. The study first presents the implant system, consisting of a soft microfabricated electrode array integrated with a magnetic resonance imaging (MRI)-compatible polymeric transdermal port that houses instrumentation connectors for electrophysiology recordings. Then, the study describes the surgical procedure, from subdural implantation to animal recovery. We focus on the auditory cortex as an example target area where evoked potentials are induced by acoustic stimulation. We finally describe a data acquisition sequence that includes MRI of the whole brain, implant electrochemical characterization, intraoperative and freely moving electrophysiology, and immunohistochemistry staining of the extracted brains.
This model can be used to investigate the safety and function of novel design of cortical prostheses; mandatory preclinical study to envision translation to human patients.

Subdural Soft Electrocorticography ECoG Array Implantation and Long-Term Cortical Recording in Minipigs

Here, we present a method for the long-term performance and safety assessment of soft subdural electrode arrays in a minipig model, describing surgical method and tools, postoperative magnetic resonance imaging, electrophysiology of the auditory cortex, electrochemical properties of the implant, and postmortem immunochemistry.

Neurological impairments and diseases can be diagnosed or treated using electrocorticography (ECoG) arrays. In drug-resistant epilepsy, these help ...

Pupillometry to Assess Auditory Sensation in Guinea Pigs

Noise exposure is a leading cause of sensorineural hearing loss. Animal models of noise-induced hearing loss have generated mechanistic insight into the underlying anatomical and physiological pathologies of hearing loss. However, relating behavioral deficits observed in humans with hearing loss to behavioral deficits in animal models remains challenging. Here, pupillometry is proposed as a method that will enable the direct comparison of animal and human behavioral data. The method is based on a modified oddball paradigm - habituating the subject to the repeated presentation of a stimulus and intermittently presenting a deviant stimulus that varies in some parametric fashion from the repeated stimulus. The fundamental premise is that if the change between the repeated and deviant stimulus is detected by the subject, it will trigger a pupil dilation response that is larger than that elicited by the repeated stimulus. This approach is demonstrated using a vocalization categorization task in guinea pigs, an animal model widely used in auditory research, including in hearing loss studies. By presenting vocalizations from one vocalization category as standard stimuli and a second category as oddball stimuli embedded in noise at various signal-to-noise ratios, it is demonstrated that the magnitude of pupil dilation in response to the oddball category varies monotonically with the signal-to-noise ratio. Growth curve analyses can then be used to characterize the time course and statistical significance of these pupil dilation responses. In this protocol, detailed procedures for acclimating guinea pigs to the setup, conducting pupillometry, and evaluating/analyzing data are described. Although this technique is demonstrated in normal-hearing guinea pigs in this protocol, the method may be used to assess the sensory effects of various forms of hearing loss within each subject. These effects may then be correlated with concurrent electrophysiological measures and post-hoc anatomical observations.

Pupillometry, a simple and non-invasive technique, is proposed as a method to determine hearing-in-noise thresholds in normal hearing animals and animal models of various auditory pathologies.

Noise exposure is a leading cause of sensorineural hearing loss. Animal models of noise-induced hearing loss have generated mechanistic insight into the ...

Sterile Pericarditis in Aachener Minipigs As a Model for Atrial Myopathy and Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia caused by structural remodeling of the atria, also called atrial myopathy. Current therapies only target the electrical abnormalities and not the underlying atrial myopathy. For the development of novel therapies, a reproducible large animal model of atrial myopathy is necessary. This paper presents a model of sterile pericarditis-induced atrial myopathy in Aachener minipigs. Sterile pericarditis was induced by spraying sterile talcum and leaving a layer of sterile gauze over the atrial epicardial surface. This led to inflammation and fibrosis, two crucial components of the pathophysiology of atrial myopathy, making the atria susceptible to the induction of AF. Two pacemaker electrodes were positioned epicardially on each atrium and connected to two pacemakers from different manufacturers. This strategy allowed for repeated non-invasive atrial programmed stimulation to determine the inducibility of AF at specified time points after surgery. Different protocols to test AF inducibility were used. The advantages of this model are its clinical relevance, with AF inducibility and the rapid induction of inflammation and fibrosis-both present in atrial myopathy-and its reproducibility. The model will be useful in the development of novel therapies targeting atrial myopathy and AF.

We describe a sterile pericarditis model in minipigs to study atrial myopathy and atrial fibrillation (AF). We present surgical and anesthetic techniques, strategies for vascular access, and a protocol to study the inducibility of AF.

Atrial fibrillation (AF) is the most common arrhythmia caused by structural remodeling of the atria, also called atrial myopathy. Current therapies only ...

A Surgical Model of Heart Failure with Preserved Ejection Fraction in Tibetan Minipigs

More than half of heart failure (HF) cases are classified as heart failure with preserved ejection fraction (HFpEF) worldwide. Large animal models are limited for investigating the fundamental mechanisms of HFpEF and identifying potential therapeutic targets. This work provides a detailed description of the surgical procedure of descending aortic constriction (DAC) in Tibetan minipigs to establish a large animal model of HFpEF. This model used a precisely controlled constriction of the descending aorta to induce chronic pressure overload in the left ventricle. Echocardiography was used to evaluate the morphological and functional changes in the heart. After 12 weeks of DAC stress, the ventricular septum was hypertrophic, but the thickness of the posterior wall was significantly reduced, accompanied by dilation of the left ventricle. However, the LV ejection fraction of the model hearts was maintained at &gt;50% during the 12-week period. Furthermore, the DAC model displayed cardiac damage, including fibrosis, inflammation, and cardiomyocyte hypertrophy. Heart failure marker levels were significantly elevated in the DAC group. This DAC-induced HFpEF in minipigs is a powerful tool for investigating molecular mechanisms of this disease and for preclinical testing.

The present protocol describes a step-by-step procedure to establish a minipig model of heart failure with preserved ejection fraction using descending aortic constriction. The methods for evaluating cardiac morphology, histology, and function of this disease model are also presented.

More than half of heart failure (HF) cases are classified as heart failure with preserved ejection fraction (HFpEF) worldwide. Large animal models are ...

Endoscopic Balloon Dilatation of the Eustachian Tube via the Soft Palate Approach in Miniature Pigs

The eustachian tube (ET) is one of the most complex organs in the human body, and its dysfunction may lead to a variety of diseases. In recent years, an increasing number of scholars have opted to conduct ET-related studies using large experimental animals such as miniature pigs or sheep, yielding promising results. Typically, conventional endoscopic procedures are performed through the nasal approach for large experimental animals. However, due to the elongated and narrow nasal cavity in these animals, transnasal surgeries are challenging. 
To address this issue, we explored an ET surgery approach via the soft palate. The animal was placed in a supine position. After endotracheal intubation under general anesthesia, a mouth opener was used to fully expose the upper palate. Local infiltration with diluted adrenal fluid was performed for anesthesia of the area. A sickle knife was then used to make a longitudinal soft palate incision at the junction of the soft and hard palates. After hemostasis, an endoscope was inserted into the nasopharynx cavity, allowing the visualization of the pharyngeal opening of the ET on the posterior lateral wall of the nasal cavity. 
Subsequently, a specialized pusher was used to insert a balloon into ET. The balloon was inflated, maintained at 10 bar for 2 min, and then removed. The incision in the soft palate was then sutured to ensure proper alignment. The soft palate healed well after the operation. This surgical approach is suitable for ET-related procedures in large experimental animals (e.g., miniature pigs, sheep, and dogs). The surgical procedure is simple, with a short surgical time, and wound healing is rapid. Under endoscopy, the pharyngeal opening of the ET is visible, and it is thus a good choice for procedures such as balloon dilation of the ET.

In this study, we present a protocol to explore an eustachian tube surgery approach via the soft palate in miniature pigs. The surgical procedure is simple, with short surgical time, and wound healing is rapid; it is thus a good choice for procedures such as balloon dilation of the eustachian tube.

The eustachian tube (ET) is one of the most complex organs in the human body, and its dysfunction may lead to a variety of diseases. In recent years, an ...