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Topic:Brain
The equine brain is a complex organ responsible for processing sensory information, regulating behavior, and controlling motor functions in horses. It plays a part in cognitive processes such as learning, memory, and decision-making. The equine brain is divided into several regions, each with distinct functions, including the cerebrum, cerebellum, and brainstem. Research in this area often focuses on understanding the neurological pathways and mechanisms that underlie equine behavior and performance. This topic encompasses studies that explore brain anatomy, neurophysiology, and the effects of various factors such as stress, training, and disease on brain function in horses. This page compiles peer-reviewed research studies and scholarly articles that investigate the structure, function, and health of the equine brain.
Dysplastic disease of the cerebellum of an adult horse. A 4-year-old horse was evaluated at the Colorado State University Veterinary Teaching Hospital for rapidly progressing cerebellar disease. Euthanasia was elected and at postmortem examination a proliferative mass encompassing the right side of the cerebellum was discovered. The lesion was characterized by large, convoluted, vascular folia and absence of the core of central white matter. Histologically, there was a diminution or loss of the internal granule cell layer, cavitation of the central white matter, and absence of Purkinje cells. The molecular layer was thickened with myelinated axons ...
Aggressive behavior problems. Accurate diagnosis of the cause of aggression in horses is essential to determining the appropriate course of action. The affective forms of aggression include fear-induced, pain-induced, intermale, dominance, protective, maternal, learned, and redirected aggressions. Non-affective aggression includes play and sex-related forms. Irritable aggression and hypertestosteronism in mares are medical problems, whereas genetic factors, brain dysfunction, and self-mutilation are also concerns.
Equine protozoal myeloencephalitis in a pony. A 10-year-old pony died 5 days after the onset of a nervous disorder. Necropsy revealed a yellowish area of discoloration (1.5 by 1 cm) in the medulla oblongata. Microscopically, necrosis and nonsuppurative myeloencephalitis were found in the medulla oblongata. Immature and mature meronts (25 by 10 microns) were seen in neural tissue and in capillaries of the brain stem. Organisms were similar structurally to those seen in equine protozoal myeloencephalitis of horses.
Regional brain blood flow and O2 delivery during severe exertion in the pony. Regional distribution of brain blood flow (radionuclide labelled 15 microns diameter microspheres) and O2 supply were studied in 11 healthy adult grade ponies at rest and during severe exercise (SE) performed on a treadmill (heart rate = 220 +/- 4 beats X min-1; VO2 = 126 +/- 9 ml X min-1 X kg-1). During SE, the mean aortic pressure increased to 169 +/- 4 mm Hg and the pHa, PaCO2 and PaO2 were 7.213 +/- 0.010, 30 +/- 1 mm Hg and 85 +/- 4 mm Hg, respectively. The hemoglobin concentration increased by 59.6% with SE. Whereas blood flow increased in the cerebellar gray matter (96%), pons (39.5%) a...
Occurrence and distribution of 5-S-cysteinyl derivatives of dopamine, dopa and dopac in the brains of eight mammalian species. The 5-S-cysteinyl derivatives of dopamine, dopa (3,4-dihydroxyphenylalanine) and dopac (3,4-dihydroxyphenylacetic acid) were synthesized and used as reference compounds in high performance liquid chromatography analyses of extracts from various brain regions of eight mammalian species. All three metabolites were detected in the brains of all the species studied. The regional distribution of the metabolites was similar to that of dopamine; the metabolite concentrations ranged from less than 0.1 percent to more than 1 percent of the dopamine level, the highest ratios generally being found in sub...
Hindlimb hyperesthesia associated with rabies in two horses. Rabies was diagnosed in 2 adult Quarter Horses with hindlimb hyperesthesia and progressive weakness. Microscopic examination of the cord and brain of the first horse revealed nonsuppurative meningomyelitis and ganglioneuritis in the cord extending cranially to the 6th cervical segment. Fluorescent antibody test results of both horses were positive for rabies in hindlimb peripheral nerve specimens, but negative in sections of the upper lip. Salivary gland, cerebrum, cerebellum, hippocampus, musculocutaneous nerve, cornea, and optic nerve specimens were tested for rabies by fluorescent antibody ...
Four cases of traumatic optic nerve blindness in the horse. Traumatic optic nerve atrophy is characterised clinically by a unilateral or bilateral sudden onset of blindness. Dilated, fixed pupils and a lack of a menace reflex are the only abnormalities noted soon after the trauma. Within three to four weeks the optic disc becomes paler and the retinal vasculature is markedly decreased. The pathological lesion is a rupture of the nerve axons from stretching forces produced by the posterior movement of the brain against the fixed canalicular portion of the optic nerves. Medical therapy has not been successful.
Localization of tones by horses: use of binaural cues and the role of the superior olivary complex. The ability of horses to use binaural time and intensity difference cues to localize sound was assessed in free-field localization tests by using pure tones. The animals were required to discriminate the locus of a single tone pip ranging in frequency from 250 Hz to 25 kHz emitted by loudspeakers located 30 degrees to the left and right of the animals' midline (60 degrees total separation). Three animals were tested with a two-choice procedure; 2 additional animals were tested with a conditioned avoidance procedure. All 5 animals were able to localize 250 Hz, 500 Hz, and 1 kHz but were complet...
Paralysis and lipofuscin-like pigmentation of farm stock caused by the plant, Trachyandra laxa var. laxa. A paralytic condition of farm stock in South West Africa, characterized by prominent neuronal and some mild extraneuronal pigmentation, is described. The distribution of the pigment, which was mainly located in the larger neurones of the brain and spinal cord, is given. Experimental evidence, obtained by feeding the plant, is presented that the condition is caused by Trachyandra laxa var. laxa. The histochemical features of the pigment proved to be compatible with a lipofuscin.
Cerebral, renal, adrenal, intestinal, and pancreatic circulation in conscious ponies and during 1.0, 1.5, and 2.0 minimal alveolar concentrations of halothane-O2 anesthesia. Blood flow to the brain, kidneys, adrenal glands, pancreas, and small intestine was studied in 8 healthy ponies while awake (control) and during 1.0, 1.5, and 2.0 minimal alveolar concentrations (MAC) of anesthesia produced, using halothane vaporized in oxygen. During the anesthesia steps, intermittent positive-pressure ventilation was used to ensure isocapnia. Organ blood flow was determined with 15-micron (diameter) radionuclide-labeled microspheres, after allowing 30 minutes of equilibration at each of the 3 preestablished end-tidal halothane concentrations. The sequence of 1.0, 1.5, and 2....
Solubilization and characterization of [3H] 5HT high affinity binding sites (5HT1 and 5HT3). The solubilization of the serotonergic 5HT1 and 5HT3 sites was performed with digitonin and sodium cholate at 1% (final concentration). Two binding sites for [3H]5HT were observed on rat or horse brain synaptosomal membranes solubilized with these detergents. The corresponding dissociation constants (KD) were 1-3 nM and 13-30 nM respectively. These values were closely similar to those corresponding to 5HT1 and 5HT3 sites located in intact membranes. The solubilized sites specifically bound 5HT. The effect of GTP decreasing the binding to 5HT1 sites was lost on solubilized 5HT1 sites; it was re...
Brain stem auditory-evoked response in the nonanesthetized horse and pony. The brain stem auditory-evoked response (BAER) was measured in 10 horses and 7 ponies under conditions suitable for clinical diagnostic testing. Latencies of 5 vertex-positive peaks and interpeak latency and amplitude ratio on the 1st and 4th peaks were determined. Data from horses and ponies were analyzed separately and were compared. The stimulus was a click (n = 3,000) ranging from 10- to 90-dB hearing level (HL). Neither horses nor ponies responded with a BAER at 10 dB nor did they give reliable responses at less than 50 dB. The 2nd of the BAER waves appeared in the record at lower stimulu...
Spontaneous craniofacial malformations and central nervous system defects in an aborted equine foetus. Developmental defects are rarely reported in the horse. Severe craniofacial and central nervous system defects in an equine foetus are described and their possible causation and pathogenesis are suggested.
Clinical and pathological studies of brain injuries in horse-riding accidents: a description of cases and review with a warning to the unhelmeted. We present a clinical and pathological study of brain injuries in horse-riding accidents. Among six fatal cases, all experienced riders varying in age and sex, two were not wearing helmets and four had inadequate protective headgear. Among five non-fatal cases, four wore adequate helmets and only one of these suffered permanent neurological damage. The fifth was not wearing a helmet and although he eventually returned to work, a CT scan following the fall showed a deep-seated perithalamic hematoma. These findings are consistent with those of virtually all other studies in that they suggest tha...
The distribution and origin of a novel brain peptide, neuropeptide Y, in the spinal cord of several mammals. The distribution of neuropeptide Y [NPY]-immunoreactive material was examined in the spinal cord and dorsal root ganglia of rat, guinea-pig, cat, marmoset, and horse. Considerable concentrations of NPY and similar distribution patterns of immunoreactive nerve fibres were found in the spinal cord of all species investigated. The dorsal root ganglia of the cat and the horse contained numerous immunoreactive nerve fibres, but in these species, as in the other three studied [rat, guinea-pig, marmoset], no positively stained cell bodies were found. Neuropeptide Y-immunoreactive nerves were observed...
Intracranial haemorrhage in pre-viable, premature and full term foals. A neuropathological examination was carried out on the brains of 58 foals. Forty-two were pony foals induced at various periods of gestation from 200 days onwards. Two were pre-viable pony foals delivered by caesarean section and 14 were Thoroughbred foals (one set of twins, two stillborn, five premature, two dysmature, two convulsive and one induced). The only significant pathological change involved intracranial haemorrhage. Subarachnoid haemorrhage occurred in all of 10 pony foals induced before 301 days of gestation and in two pony foals born by caesarean section at 270 and 280 days gestat...
Borna disease of horses. An immunohistological and virological study of naturally infected animals. The brains of eight horses that had suffered from natural Borna disease were examined with virologic, immunohistological, and electron-microscopic methods. All brains harbored infectious virus as shown by inoculation of experimental animals. Regional assessment of the infectivity exhibited the highest titers in the hippocampus and piriform cortex and the lowest in the cerebellum. Conventional histology yielded pathologic alterations very similar to those of the classical description of the disease. Immunohistology demonstrated the highest amounts of Borna disease virus-specific antigen in the ...
Cerebrovascular response to acute decreases in arterial PO2. The purpose of these studies was to examine the time course of the cerebrovascular response to acute hypoxia in unanesthetized ponies. An electromagnetic flow transducer chronically placed on the internal carotid artery of the pony allowed continuous recording of internal carotid artery blood flow (ICBF) which has been shown to be representative of cerebral blood flow (CBF). The ponies were subjected to three levels of acute isocapnic hypoxia (PaO2 = 62, 44, and 39 mm Hg for hypoxia level I, II, and III, respectively), and the temporal and steady-state cerebrovascular response was examined. IC...
Carotid and cerebral angiography in the horse. Carotid and cerebral angiography has been found to be a relatively simple technique to carry out in the horse. At most it involves a cutdown approach to the carotid artery, followed by catheterisation of the artery and selective catheterisation, if necessary, of one of its three branches. The technique can be carried out with standard equipment normally available within equine hospital facilities. The authors have employed angiography as a routine aid to diagnosis over the past nine years, without encountering any serious complications or adverse reactions. Carotid angiography has been especia...
Distribution of blood flow during moderate and strenuous exercise in ponies (Equus caballus). Blood flow to the brain, heart, kidneys, diaphragm, and skeletal muscles was studied at rest and during graded treadmill exercise, using radionuclide-labeled microspheres (15 microns diameter), in 11 healthy adult ponies. Hemodynamic changes brought about by exercise included marked increases in cardiac output, mean aortic pressure, left ventricular end-diastolic pressure, and right ventricular systolic and end-diastolic pressures. Blood flow to the brain stem and cerebral hemispheres was unchanged during both moderate exercise (heart rate = 154 +/- 3 beats/min) and severe exercise (heart rate...
The pathogenicity in mice of respiratory, abortion and paresis isolates of equine herpesvirus-1. Eleven isolates of equine herpesvirus-1 (subtype 1) all infected the brain following intracerebral inoculation of 2 d.o. mice. Most isolates were from cases of paresis, abortion or respiratory disease in the U.K., but established strains were also included. They divided into two subgroups. The 5 less pathogenic isolates were characterized by being restricted predominantly to the olfactory lobes. The 6 pathogenic isolates included the three known to cause equine paresis and were detected in neurones throughout the brain as well as giving rise to viraemia and infecting bronchial and renal epithe...
Distribution of internal carotid artery blood flow in the pony. This study determined whether blood flow through the internal carotid artery (ICA) could be used to sample total cerebral blood flow in the pony. To answer this question we considered both the anatomic arrangement of the ICA in cadavers and the relative distribution of ICA blood flow to cerebral and extracerebral tissue using radioactive microspheres. Acrylic corrosion casts of the ICA indicated that this vessel traveled directly to the base of the brain, contributing to the formation of the circle of Willis, and did not send any significant branches to other tissues. Two vessels (internal eth...
Observations on the isoenzymes of creatine kinase in equine serum and tissues. The isoenzymes of creatine kinase have been measured in serum and selected tissues from horses. The distribution followed that reported in other species in that the MM dimer of the isoenzyme was present in voluntary and non-voluntary muscle, thyroid, liver, spleen, lung and intestine. The BB dimer of the isoenzyme was predominant in brain, pancreas, kidney, intestine, lung, spleen, liver and thyroid. In contrast, in 4 hearts examined less than 1.5 per cent of the total creatine kinase activity was attributable to the MB form of the isoenzyme. The MB isoenzyme was, however, present in intestine...
Migration of a spiruroid nematode through the brain of a horse. A pregnant 10-year-old Paint mare was examined because of an acute neurologic disturbance. Physical examination revealed signs consistent with extensive, asymmetric brain stem disease. The hemogram, serum chemical panel, and results of lumbosacral spinal fluid analysis were within normal limits. A primary diagnosis of equine protozoal myeloencephalitis was considered, and the mare was placed on treatment with trimethoprim-sulfadiazine. After 5 weeks of steady improvement, an acute exacerbation of neurologic signs necessitated euthanasia of the mare. At necropsy, large, malacic tracts were foun...
Brain abscess in three horses. Three horses with brain abscesses had different clinical manifestations: 1 had a protracted clinical course whereas 2 had a short clinical course. Clinical signs in 2 horses (1 acute case, 1 chronic case) included unilateral loss of vision, head tilt, circling, abnormal mental status, and ataxia. The 3rd horse had bilateral loss of vision, altered mental status, and apparent deafness. Results of cerebrospinal fluid analysis were inconsistent. The horse with the protracted clinical course had paradoxic central vestibular disease.
