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Topic:Nerves
The study of nerves in horses encompasses the structure, function, and disorders of the equine nervous system. This system is responsible for transmitting signals between different parts of the body and coordinating actions and sensory information. Key components include the central nervous system, consisting of the brain and spinal cord, and the peripheral nervous system, which includes nerves extending throughout the body. Research in this area investigates the role of nerves in equine behavior, movement, and response to stimuli, as well as conditions such as neuropathies and nerve injuries. This topic includes a collection of peer-reviewed research studies and scholarly articles that explore the anatomy, physiology, and clinical implications of the nervous system in horses.
Perineural and spinal anesthesia. Local and regional anesthetic techniques are useful tools for the equine practitioner. These techniques allow surgery to be performed without the risk and cost of general anesthesia. There are, however, risks associated with the local and regional techniques. Neurotoxicity, although rare, may occur when 200 mL or more of a local anesthetic are infiltrated in a short period of time to a 450-kg horse. More likely, horses may become ataxic after nerve blockade in the limbs. This ataxia may lead to self trauma because the horse may not know where the limbs are actually being placed. Although local...
Chronic cervical compressive myelopathy in horses: clinical correlations with spinal cord alterations. Histological examination was performed on the cervical spinal cord from 13 horses with chronic cervical compressive myelopathy of 4 to 29 months duration. Structural alterations were correlated with clinical features. At the level of compression, the spinal cord was grossly deformed. Histological alterations included nerve fibre swelling and degeneration, occasional spheroids, astrocytic gliosis, increased macrophage activity and increased perivascular collagen. Myelin degeneration or loss at the level of the compressive lesion was greatest in the ventral and lateral funiculi and less consiste...
Treatment of left laryngeal hemiplegia in standardbreds, using a nerve muscle pedicle graft. The efficacy of a nerve muscle pedicle (NMP) graft in restoring upper airway function was evaluated in exercising horses with induced left laryngeal hemiplegia. The NMP graft was created from the first cervical nerve and the omohyoideus muscle and transplanted into the left cricoarytenoideus dorsalis muscle. Seven adult Standardbreds were trained to exercise on a treadmill inclined at 6.38 degrees. With the horses at rest and exercising at 4.2 and 7.0 m/s, the following variables were recorded: peak inspiratory and expiratory transupper airway pressures (defined as the pressure difference betw...
Sarcocystis neurona n. sp. (Protozoa: Apicomplexa), the etiologic agent of equine protozoal myeloencephalitis. Sarcocystis neuronan n. sp. is proposed for the apicomplexan taxon associated with myeloencephalitis in horses. Only asexual stages of this parasite presently are known, and they are found within neuronal cells and leukocytes of the brain and spinal cord. The parasite is located in the host cell cytoplasm, does not have a parasitophorous vacuole, and divides by endopolygeny. Schizonts are 5-35 microns x 5-20 microns and contain 4-40 merozoites arranged in a rosette around a prominent residual body. Merozoites are approximately 4 x 1 micron, have a central nucleus, and lack rhoptries. Schizonts...
Proliferation of chick embryo neuroblasts grown in the presence of horse serum requires exogenous transferrin. We have previously shown that neuroblasts from cerebral hemispheres of 6-day-old chick embryos are able to proliferate when grown in the presence of fetal calf serum. We report here that in the presence of horse serum alone the proliferative rate of neuroblasts is strongly reduced. A high proliferative rate is restored upon the addition of bovine transferrin and to a lesser extent with added FeSO4 or hemin. These findings suggest that the transferrin of horse serum cannot be used by chick neuroblasts in vitro, while bovine transferrin exogenously added is active in promoting cell proliferation...
Preferential denervation of the adductor muscles of the equine larynx. I: Muscle pathology. The laryngeal muscles of 18 horses were examined histologically. The neurogenic changes found in each muscle were scored by four reviewers and the results evaluated statistically. Fifteen of these horses had endoscopic evidence of abnormal laryngeal function, three of which were defined as having adductor paralysis. Measurement of muscle fibre area in two horses with idiopathic laryngeal hemiplegia (ILH) was performed. In the quantitative study of neurogenic change, the adductor muscles were more significantly affected than the abductor muscle. This was also true in the clinical cases of ILH w...
Preferential denervation of the adductor muscles of the equine larynx. II: Nerve pathology. The terminal branches of the recurrent laryngeal nerve (RLN) of three normal ponies and six horses with sub-clinical laryngeal disease were examined qualitatively and quantitatively in an attempt to explain the preferential denervation of the laryngeal adductor muscles in the neuropathy of idiopathic laryngeal hemiplegia (ILH). The myelinated fibre spectra of all the motor nerve fibres in the left and right abductor and adductor branches of the RLN in three normal ponies were measured. The density of myelinated fibres was also calculated. There was no significant difference between the larger ...
Effects of increased end-expiratory lung volume on breathing in awake ponies. We studied the changes in breathing and respiratory muscle electromyograms (EMG) during passively induced increases in end-expiratory lung volume (EELV) in awake normal (N), hilar nerve-denervated (HND), carotid body-denervated (CBD), and HND + CBD ponies. EELV was increased by applying continuous negative pressure (-10 and -20 cmH2O) around the torso of the standing pony. In all groups, negative pressure produced sustained increases in EELV that were linearly related to the degree of negative pressure. Elevated EELV decreased breathing frequency (f) in N and CBD ponies but increased f in HND ...
Ultrastructure of the red pulp in spleen innervation in horse and pig. The innervation of the red pulp in the spleen of horse and pig was investigated by electron microscopy. In addition, the neurilemma was studied by immunohistochemistry specific for S-100 protein. In the pig, a large population of smooth-muscle cells extending from the smooth-muscle trabeculae was present in the red pulp. The cytoplasmic processes of reticular cells enwrapped the smooth-muscle cells, and nerve fibres were distributed between the smooth-muscle cells and the reticular cells. The nerve terminals clustered toward the facing of the smooth-muscle cells. Nerve fibres and terminals wer...
Neuromuscular blocking agents in equine anesthesia. In summary, neuromuscular blocking agents can be used safely and to advantage in equine anesthesia. Muscle-relaxant use in equine anesthesia has been helped by the development of new relaxants such as atracurium, which has a reliable and reproducible duration of action. There are certain cases that benefit particularly by the use of relaxants but their use is not limited to these cases. These cases involve horses that experience persistent movement and hypotension during anesthesia, are undergoing ophthalmic or abdominal surgery or fracture repair, or are severely ill. Horses receiving muscle ...
Leukoencephalomalacia in two horses induced by oral dosing of fumonisin B1. Leukoencephalomalacia (LEM) was induced by the oral administration of fumonisin B1 (FB1) to 2 horses: a filly received 59.5 mg/kg of a 50% preparation of FB1, administered in 21 doses of 1.25-4 mg/kg over 33 days; a colt, 44.3 mg/kg of 95% pure FB1 in 20 doses of 1-4 mg/kg in 29 days. Both animals developed nervous signs such as apathy, changes in temperament, inco-ordination, walking into objects, and one showed paralysis of the lips and tongue. Characteristic lesions of LEM were present in the brains. These trials proved conclusively that FB1 can induce LEM in horses.
Attenuated Hering-Breuer inflation reflex 4 years after pulmonary vagal denervation in ponies. The purpose of this study was to determine whether there was any recovery of the Hering-Breuer inflation reflex in ponies between 2-4 wk and 3-4 yr after hilar nerve denervation (HND). Under anesthesia and before HND, airway occlusion after a 3-liter lung inflation lengthened the subsequent occluded breath by nearly 10 times the control breath duration. Between 2 wk and 3-4 yr after HND, this maneuver increased the duration of the occluded breath by only 2.5 times the control breath duration. Also under anesthesia, the airway was occluded at end expiration. This maneuver increased the duration...
A method of assessing auditory and brainstem function in horses. Brainstem auditory evoked potential (BAEP) waveforms were recorded as a means of objectively evaluating auditory and brainstem function in horses. BAEP recordings were readily and repeatably recorded from horses, under minimal restraint, using signal averaging equipment. Clearly identified BAEP waveforms were obtained with compression clicks of 30-100 dB (HHL) at 10 Hz applied in the external auditory meatus of one ear and masking white noise (10 dB lower) in the other ear. Vertex positive (upwards) waveforms I through V were obtained with an active, subdermal electrode over the ipsilateral an...
Infarction of the pons and medulla oblongata caused by arteriolar thrombosis in a horse. Infarction of the pons and rostral medulla secondary to arteriolar thrombosis was documented histologically in a 17-year-old mixed-Arabian female horse. Clinically, the animal experienced a sudden onset of a head tilt and subsequent non-controllable seizures. There was no historical, clinical or histological evidence to suggest the presence of infection of Equine Herpesvirus-1 or the feeding of corn contaminated by Fusarium moniliforme.
Intracranial schwannoma in a horse. A case of intracranial schwannoma is described in a young horse. Clinical signs developed slowly and were suggestive of a lesion involving the left cerebrum. The filly exhibited a change in mentation, and circled to the left. Visual impairment and decreased facial sensation were noted on the right side. A solitary schwannoma which compressed the left cerebrum was found at necropsy.
An immunohistochemical study of various peptide-containing endocrine cells and neurones at the equine ileocaecal junction. The ileocaecal junctions of 5 horses and 2 donkeys were examined by using antisera to the following peptides: somatostatin, glucagon, gastrin, neurotensin, vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI), calcitonin gene-related peptide (CGRP), substance P (SP) and neuropeptide Y (NPY). Antisera to somatostatin, neurotensin and NPY demonstrated endocrine cells in the ileal- and caecal parts of the ileocaecal junction, while immunoreactivity for glucagon was demonstrated in endocrine cells of the ileal part only. Nerve cell bodies showing immunoreactivity to SP, VIP, CGR...
Effects of left recurrent laryngeal neurectomy, prosthetic laryngoplasty, and subtotal arytenoidectomy on upper airway pressure during maximal exertion. Upper airway pressure was measured with a nasotracheal catheter system and a portable pressure transducer in 10 normal horses during maximal exercise before and after left recurrent laryngeal neurectomy. Measurements were repeated 16 weeks after prosthetic laryngoplasty (5 horses) or subtotal arytenoidectomy (5 horses). During maximal exertion, prosthetic laryngoplasty was more effective than subtotal arytenoidectomy in reversing the increases in upper airway pressure that followed left recurrent laryngeal neurectomy.
Respiratory muscle electromyogram responses to acute hypoxia in awake ponies. We determined the effect of acute hypoxia on the ventilatory (VE) and electromyogram (EMG) responses of inspiratory (diaphragm) and expiratory (transversus abdominis) muscles in awake spontaneously breathing ponies. Eleven carotid body-intact (CBI) and six chronic carotid body-denervated (CBD) ponies were studied during normoxia (fractional inspired O2 concn [FIO2] = 0.21) and two levels of hypoxia (FIO2 approximately 0.15 and 0.12; 6-10 min/period). Four CBI and five CBD ponies were also hilar nerve (pulmonary vagal) denervated. Mean VE responses to hypoxia were greater in CBI ponies (delta a...
Effect of age on sensory nerve conduction velocity in the horse. This study aimed to establish a clinically reproducible method of evaluation of sensory nerve conduction in the horse and to provide reference values in a group of normal horses. Age-related changes in the sensory nerve conduction velocity were of particular interest. Sensory nerve conduction was performed in the lateral palmar nerve. The results revealed an increase in velocity over the first year of life and a subsequent decrease in velocity in older horses. The effect of age must be considered if results from horses in which peripheral nerve disease is suspected are to be interpreted correc...
Clinical evaluation of laryngeal sensation in horses. Sensory innervation of the larynx was examined by tactile stimulation with a blunt biopsy forceps passed through a flexible videoendoscope. Twenty horses with no evidence of laryngeal motor deficit were stimulated on 10 sites by touch with the forceps. Unilateral neurectomies of the internal branch of the left cranial laryngeal nerve were performed on 5 other horses. These horses were stimulated by touch on the same sites preoperatively and up to 1 week postoperatively. In all 25 horses the motor response of the larynx was recorded on videotape and evaluated by 2 observers blind as to treatmen...
On the collateral sesamoidean (suspensory navicular) ligament of equines: topographic relations and sensitive innervation. The origin and course of the collateral sesamoidean (suspensory navicular) ligament of the horse and ass and its attachment to the distal sesamoid bone were studied by means of dissection. Particular attention was given to the topographic relations between this ligament and the deep digital flexor tendon. Numerous sensitive nerve endings are present in this anatomical district. The free and encapsulated nerve endings, displayed by impregnating techniques, are mostly concentrated in the ligament tract connected to the above-named tendon and close to its attachment to the distal sesamoid angle. ...
Multifocal innervation and muscle length. A morphological study on the role of myo-myonal junctions, fiber branching and multiple innervation in muscles of different size and shape. The dependence of the inner organisation and innervation of a skeletal muscle on its size was studied at the level of single muscle fiber architecture and motor endplate topography in muscles of different size, all of them lacking a tendinous scaffolding. The muscles evaluated in this study were: Mm. sternomastoideus, gracilis and latissimus dorsi of the rat and the M. sternocephalicus of the horse. In these muscles a subdivision into two or more 'innervation-compartments' becomes obvious in fascicles reaching a certain length. This provides the possibility of an almost synchronous activation ...
The immunocytochemical distribution of seven peptides in the spinal cord and dorsal root ganglia of horse and pig. The distribution of calcitonin gene-related peptide (CGRP), enkephalin, galanin, neuropeptide Y (NPY), somatostatin, tachykinins and vasoactive intestinal polypeptide (VIP) was compared in cervical, thoracic, lumbar and sacral segmental levels of spinal cord and dorsal root ganglia of horse and pig. In both species, immunoreactivity for the peptides under study was observed at all segmental levels of the spinal cord. Peptide-immunoreactive fibres were generally concentrated in laminae I-III, the region around the central canal, and in the autonomic nuclei. A general increase in the number of i...
Influence of limb temperature on sensory nerve conduction velocity in horses. Sensory nerve conduction velocity was measured in the lateral palmar nerve of 8 horses. The limb temperature was manipulated by external means and monitored. Alterations in the nerve conduction velocity related to limb temperature variation were identified at both increased and decreased temperatures. These were quantified and a mean value of 2.15 +/- 0.2 m/s/degree Celsius was determined. The effect of altered limb temperature should be considered in nerve conduction velocity determinations.
Bilateral colobomas in a horse. Bilateral true colobomas with retrobulbar cysts located over the optic nerves are described in an 8-year-old Quarterhorse mare with a history of progressive blindness. Colobomas result from the failure of an embryonic fissure to close and retrobulbar cysts result from eversion of the neuroectoderm through the colobomas. It could not be determined whether the small optic nerves and the scars, rosettes and disorganization of the cell layers in the retina were the result of concurrent dysplasia or were secondary to degeneration.
Attempts to restore abduction of the paralyzed equine arytenoid cartilage. III. Nerve anastomosis. The purpose of this project was to attempt restoration of abduction of a recently denervated left dorsal cricoarytenoid muscle in the horse by anastomosing the first cervical nerve to the abductor branch of the left recurrent laryngeal nerve. Ten horses were used in the study. In six horses the left recurrent laryngeal nerve was transected and ligated while the ventral branch of the left first cervical nerve was anastomosed to the abductor branch of the left recurrent laryngeal nerve. The remaining four horses also had the left recurrent laryngeal nerve transected and ligated but had no nerve ...
Attempts to restore abduction of the paralyzed equine arytenoid cartilage. II. Nerve implantation (pilot study). The purpose of this project was to attempt restoration of abduction of a recently experimentally denervated left dorsal cricoarytenoid muscle by implanting a transected nerve-end into the paralyzed muscle. In six ponies the cut end of the second cervical nerve was implanted into a slit made in the left dorsal cricoarytenoid muscle. The nerve end was secured in place with one 5-0 polypropylene suture connecting the epineurium to the epimysium. The left recurrent laryngeal nerve was transected during this procedure. All six ponies showed signs of complete left laryngeal hemiplegia immediately af...
