The experimental induction of leukoencephalomyelopathy in cats.

Leukoencephalomyelopathy of undetermined etiology has been described in specific pathogen-free cats. A study was established to assess if the long-term feeding of a gamma-irradiated diet could induce this disease. Cats fed exclusively on diet irradiated at 25.7-38.1 kGy ("typical" dose) and 38.1-53.6 kGy (high-end dose), respectively, developed typical lesions with attendant, progressively severe ataxia between study days 140 and 174. The onset of ataxia at day 140 and the number of animals affected at this time were similar in animals fed each ration. A maximum ataxia "score" was first reached by an animal on the high-end dose diet on day 167 and by 2 cats fed the "typical-end" dose diet 21 days later. Ataxic cats and 1 animal euthanized on day 93 prior to the onset of ataxia exhibited varying degrees of Wallerian degeneration in the spinal cord and brain, similar to the spontaneous disease. The elevated total antioxidant status of spinal cord segments and hepatic superoxide dismutase concentration of cats fed typical and high-end treated diets suggested free-radical involvement in the pathogenesis. The significantly elevated peroxide concentrations of the irradiated diets (1,040% and 6,440% of untreated values) may have resulted in increased oxidative insult, a factor possibly exacerbated by the treated diets' reduced vitamin A content. This study has reproduced leukoencephalomyelopathy in cats similar to spontaneous outbreaks by feeding a gamma-irradiated dry diet with elevated peroxide and reduced vitamin A concentrations.

Corticosterone and serotonin similarly influence GABAergic and purinergic pathways to affect cortical inhibitory networks.

Both serotonin (5-HT) and stress exert changes in cortical inhibitory tone to shape the activity of cortical networks. Because astrocytes are also known to affect inhibition through established purinergic pathways, we assessed the role of GABA and purinergic pathways with respect to the effects of rapid corticosterone (CORT) and 5-HT on cortical inhibition. We used a paired-pulse paradigm (P1 and P2) in acutely isolated mouse brain slices to evaluate changes in cortical evoked inhibition. Normally, 5-HT decreases the amplitude of the first pulse P1, whereas it increases the amplitude of P2 (increasing frequency transmission). Interestingly, it was observed that CORT application decreased P1 and increased P2 similar to that of 5-HT application. Given that CORT and 5-HT are known to modulate inhibition, we applied the GABAA antagonist bicuculline in the presence of both and found that the increase in P2 and the P2/P1 was lost, providing evidence for a common mechanism involving GABAA receptor signalling. Additional occlusion experiments (ie, 5-HT in presence of CORT and CORT in presence of 5-HT) provide further support for a common mechanism. Because both 5-HT and CORT blocked the increase in P2 and P2/P1 with respect to the other, we suggest 5-HT/CORT already utilise the shared mechanism to affect cortical inhibition. Using low concentrations of the GAPDH inhibitor iodoacetate, as commonly used to selectively disrupt astrocyte metabolism, we found that the increase in P2 and P2/P1 was similarly blocked in response to both CORT and 5-HT. Because astrocyte signalling depends in large part on purinergic pathways, the purinergic contribution was assessed using Ab129 (P2Y antagonist) and SCH 58261 (A2A antagonist). Once again, P2Y and A2A receptor blockade similarly disrupted 5-HT- or CORT-mediated increases in P2 and P2/P1. Taken together, these results support the common involvement of GABAergic and purinergic pathways in the effects of CORT and 5-HT that may also involve astrocytes.

Pontine infarction in a dog with unilateral involvement of the trigeminal motor nucleus and pyramidal tract.

An unusual case of unilateral trigeminal neuronopathy in a dog is reported, in which the motor nucleus of the trigeminal nerve and the ipsilateral corticospinal tract were destroyed, apparently by a cerebrovascular accident (stroke). Hemiplegia did not occur. Neuropathological changes are described, including remyelination by Schwann cells in the central nervous system. The case illustrates the importance of central nervous system post-mortem examination when establishing causes of cranial nerve paralysis.

Sex differences in the early life correlates of natural antibody concentrations.

Innate-like B1a lymphocytes arise from long-lived progenitors produced exclusively by fetal stem cells. Any insults coinciding with this early lymphopoietic wave could have a permanent impact on the B1a population and its unique protein products, the natural antibodies (NAb). We investigated early life nutritional influences on NAb concentrations of pre-adolescent children (n=290) in rural Nepal for whom we had extensive information on exposures from pregnancy and early infancy. Infant size and growth were strongly associated with NAb concentrations at 9-13 years of age among males (e.g., for neonatal weight: ßBOYS=0.43; P<0.001), but not females (e.g., for neonatal weight: ßGIRLS=-0.16; P=0.26). In females, season of birth was associated with NAb concentrations, with marked reductions among girls born during the pre-monsoon (March-May; ßGIRLS=-0.39; P=0.01) and pre-harvest (September-November; ßGIRLS=-0.35; P=0.03) seasons. Our findings suggest that nutritional or other environmental influences on immune development may vary by sex, with potential consequences for immune function during infancy and long-term risk of immune-mediated disease.

Inhibition of recombinant human cardiac L-type Ca2+ channel alpha1C subunits by 3-isobutyl-1-methylxanthine.

Inhibition of ion channels by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) and related compounds has been demonstrated in various cell types, including the neuromuscular junction, GH3 cells and vascular smooth muscle cells. These effects may be unrelated to the actions of these compounds on cellular metabolism, intracellular Ca2+ stores and phosphodiesterase inhibition. In this study, the inhibition of recombinant human cardiac L-type Ca2+ channel alpha1C subunits by IBMX was examined using the whole-cell configuration of the patch clamp technique. Inhibition was repeatable, voltage-independent and associated with increased apparent channel inactivation. The actions of IBMX were unaffected in the presence of inhibitors of protein kinases A and G. The non-xanthine phosphodiesterase inhibitor rolipram had a small inhibitory effect on currents, but this was also unaffected by a protein kinase A inhibitor. These effects of IBMX could not be attributed to release of Ca2+ from intracellular stores. Our findings indicate that methylxanthines can inhibit the cardiac L-type Ca2+ channel alpha1C subunit in the absence of auxiliary subunits by an undetermined, possibly direct mechanism.

The effect of the angiotensin II (AT1A) receptor stably transfected into human neuroblastoma SH-SY5Y cells on noradrenaline release and changes in intracellular calcium.

A stable cell line expressing the angiotensin II (AII) receptor has been obtained by transfecting the human neuroblastoma SH-SY5Y with the plasmid pCEP4 containing the entire coding region of the rat angiotensin AII receptor AT1A. Angiotensin II (AII; 1-100 nM) evokes the release of [3H]noradrenaline ([3H]NA) in this cell line. Pretreatment with 100 nM 12-O-tetradecanoylphorbol-13-acetate (TPA) enhances the AII-evoked release of [3H]NA approximately two-fold. Removal of extracellular Ca2+ ([Ca2+]o) decreases 100 nM AII-evoked release of [3H]NA by over 50% both in the presence and absence of TPA. AII increases intracellular Ca2+ ([Ca2+]i) in this cell line which is consistent with the AT1A receptor being coupled to phospholipase C. Pretreatment with 100 nM TPA for 8 min attenuated the effect of AII on [Ca2+]i. The effects of AT1A receptor stimulation are therefore regulated differently in this cell line by activation of protein kinase C (PKC). Thus a useful cell line has been obtained from the human neuroblastoma SH-SY5Y in which to study at the molecular level the mechanism(s) by which AII regulates NA release.

Morphometric analysis of white matter lesions in MR images: method and validation.

The analysis of MR images is evolving from qualitative to quantitative. More and more, the question asked by clinicians is how much and where, rather than a simple statement on the presence or absence of abnormalities. The authors present a study in which the results obtained with a semiautomatic, multispectral segmentation technique are quantitatively compared to manually delineated regions. The core of the semiautomatic image analysis system is a supervised artificial neural network classifier augmented with dedicated preand postprocessing algorithms, including anisotropic noise filtering and a surface-fitting method for the correction of spatial intensity variations. The study was focused on the quantitation of white matter lesions in the human brain. A total of 36 images from six brain volumes was analyzed twice by each of two operators, under supervision of a neuroradiologist. Both the intra- and interrater variability of the methods were studied in terms of the average tissue area detected per slice, the correlation coefficients between area measurements, and a measure of similarity derived from the kappa statistic. The results indicate that, compared to a manual method, the use of the semiautomatic technique not only facilitates the analysis of the images, but also has similar or lower intra- and interrater variabilities.

Ultrastructure of motor endplates in canine congenital myasthenia gravis.

Morphometric analysis was carried out on electron micrographs of motor endplates from three Jack Russell terriers affected with congenital myasthenia gravis (CMG) aged 10 weeks, 12 weeks and 22 weeks, respectively. Control endplates from age-matched pups and an adult Jack Russell were also examined. The results showed that postsynaptic membrane density was significantly increased in affected animals and secondary fold length was decreased. The ratio of postsynaptic to presynaptic membrane length was normal in the 10 and 12-week-old pups, but reduced in the 22-week-old CMG animal. These changes were unrelated to muscle fibre diameter and there was no evidence of a destructive process. It is suggested that the alteration in membrane folding pattern in this condition may be related to abnormal trophic influences during synaptogenesis.

Neuropathological changes associated with the neonatal maladjustment syndrome in the thoroughbred foal.

A neuropathological investigation was carried out on the brains of 18 foals suffering from the neonatal maladjustment syndrome and results were compared with those obtained from the brains of nine foals dying from other causes. Necrosis of the cerebral cortex of an ischaemic nature was found in nine of the neonatal maladjustment foals, frequently accompanied by local haemorrhage. In three of this group of foals there was also necrosis in the diencephalon and brain stem. In the brains of the nine other affected foals there was haemorrhage in the cerebrum and sometimes in the brain stem and cerebellum; in four animals there was also brain swelling or oedema. In the control gorup, significant haemorrhage in the brain was the only finding in two foals, one premature and one stillborn apart from minimal ischaemic damage in the latter. The nature of the CNS damage in the neonatal maladjustment syndrome is considered in the light of recent experimental evidence. Although the cause is unknown it may be related to circulatory disturbances induced in the foal at the time of birth.

An investigation into the genetics of 'wobbler disease' in thoroughbred horses in Britain.

Sixty-seven TB horses in Britain suffering from clinical wobbler disease were divided into 5 groups, based on the presence or absence of pathological lesions and their nature. These groups were compared genetically with a control group of 67 TBs known not to exhibit signs of wobbling. Though analysed for both simple and complex modes of inheritance no evidence of a genetic basis was found in any group. The high breed incidence in TBs may be real or apparent. Considerably more male than female wobblers are reported. Other forms of possibly inherited ataxia in equidae are reviewed and reference is made to pathologically comparable conditions occurring in man and in the large breeds of dogs.

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 gestation. Subarachnoid haemorrhage was also present in some pony and Thoroughbred foals born after 301 days gestation; the incidence usually appeared greater in those pony foals which survived for the shortest periods. Haemorrhage also occurred elsewhere in the brains, including the cerebral white matter, the molecular layer of the cerebellum and the medulla, but the intensity could not be related to either length of gestation or duration of survival. No other neuropathological changes were found that could account for the functional state of the animals, whether they were pre-viable, premature, dysmature or convulsive.

Myasthenia gravis.

Myasthenia gravis is characterized by muscle weakness, which is alleviated by rest and by anticholinesterase drugs. There are two forms of the disease in the dog, acquired and congenital. The acquired form occurs either in young adults, or in older animals that have developed mediastinal tumors. Clinically, there is weakness of the muscles of the limbs, neck, and head, together with dilatation of the esophagus. In some cases, circulating antibody to acetylcholine receptor is present and the amount of receptor in the end-plates is decreased. It is thought to be an autoimmune disease. The congenital form of canine myasthenia gravis occurs most frequently in Jack Russell terriers from six to eight weeks of age. The clinical manifestations are similar to those accompanying acquired myasthenia, although dilatation of the esophagus is not a feature. Raised antibody levels to acetylcholine receptor have not been noted, although the amount of receptor in the end-plates is decreased. Thus, the congenital form does not appear to be an autoimmune disease and the pathophysiology has yet to be established. Both forms of canine myasthenia gravis provide useful models analogous to the disease in man.

Concussion: the result of impact injury to the brain.

The pathogenesis of impact injuries to the brain is reviewed and hypotheses accepted in human medicine are compared with results of experimental work in animals. When treating concussed animals, attention should be directed to the control of both brain ischaemia and raised intracranial pressure, features which exacerbate the consequences of direct injury to the brain.

Hearing in the dog as assessed by auditory brainstem evoked potentials.

Auditory brainstem evoked potentials were used to test hearing in dogs. A technique is described which can be carried out normally on conscious or sedated animals. Eleven normal adults, eight normal puppies and four deaf animals were rested. Reproducible brainstem evoked potentials were readily obtained from the normal adult dogs except when they became fractious (unsedated animals only). Usually the evoked waveform consisted of four peaks (I to IV) occurring in the first five milliseconds after the delivery of an auditory stimulus. In adults, the brainstem threshold for clicks varied between 5 and 25 dB normal hearing level. Brainstem evoked potentials were not detected in puppies at two weeks old but occurred at three weeks old. Between three and seven weeks of age the latencies of waves I and IV and the interval between these waves became shorter, to resemble the adult waveform. No brainstem evoked potentials were detected in the four deaf animals.

Stenosis of the cervical vertebral canal in a yearling ram.

Stenosis of the cervical vertebral canal in a 10 1/2-month-old Suffolk ram is described. The vertebral canal was narrowed in a dorsoventral direction at the anterior and posterior ends of the cervical vertebral C3 and C4, at the posterior end of C2 and the anterior end of C5. The body of C3 was wedge-shaped in a longitudinal plane. The vertebral abnormalities are believed to have resulted from instability, perhaps exacerbated by fighting. There was a region of necrosis of the spinal cord at junction of C1-2. The animal showed sudden onset of quadriplegia from which it gradually recovered. The rams in the group were on a high plane of nutrition and two others were probably affected.

Histological diagnosis of mucopolysaccharidosis IIIA in a wire-haired dachshund.

A four-year-old wire-haired dachshund developed progressive neurological signs of ataxia, intention tremor and finally dysuria. Two years later, histopathology showed that neurons throughout the brain and spinal cord were distended with lipopigment which was also present in macrophages. Ultrastructurally, the pigment in the neurons occurred predominantly as electron-dense membranous whorls and stacks. There were a few vacuolated macrophages in the meninges. Hepatocytes were highly vacuolated and electron microscopy suggested that they were empty membrane-bound vesicles. The disease was diagnosed as mucopolysaccharidosis IIIA because of its similarity to other biochemically confirmed cases in the same breed and in a New Zealand huntaway dog. Additional lesions included calcium oxalate uroliths, severe secondary calcification of tissues including the brain and storage deposits in some neurons, and lesions which may have been associated with high levels of the substrate, heparan sulphate.

Ataxia and spinal cord degeneration in llama, wildebeeste and camel.

Clinical and pathological findings from instances of ataxia in a group of wildebeeste (Connochaetes taurinus), two llamas (Llama glama) and one Arabian camel (Camelus dromedarius) are presented. Clinically, all the affected animals showed a non-febrile, progressive ataxia. Neuropathologically, Wallerian degeneration was diffuse in the spinal cord of the camel and llamas but was focal in the wildebeeste. Degeneration was present in the cervical dorsal roots in the wildebeeste and in the ventral nerve roots at all levels of the cord in the llamas. Peripheral nerve were affected in all the species. The possible roles of copper deficiency and plant poisons in the aetiology of the condition are discussed.

Recognition of 'trembler', a hypomyelinating condition in the Bernese mountain dog.

An account is given of a hypomyelinating condition, 'trembler', in the Bernese mountain dog. The condition is manifested clinically as a tremor of the limbs and head which becomes more intense with excitement or stress and which disappears with sleep. The tremor, which is first noticeable between two and eight weeks old, may persist throughout life but decline with age. Examination of plastic embedded tissue obtained post mortem from two, nine-week-old animals showed hypomyelination of the spinal cord. Preliminary examination of breeding data suggests that the condition may be inherited as an autosomal recessive.

Progressive encephalomyelopathy and cerebellar degeneration in 10 captive-bred cheetahs.

Progressive ataxia, with head tremor, developed in 10 captive-born cheetah cubs under six months of age. The condition was usually preceded by coryza and an ocular discharge. Initially the ataxia and weakness affected the hindquarters, then the forelegs, and head tremor developed later. Significant pathological changes were confined to the central nervous system. There was widespread Wallerian degeneration in the funiculi of the spinal cord (except those in the dorsal columns), in the medulla and in the cerebellum. In the cerebellum there was degeneration of Purkinje cells and of the molecular and granular cell layers. There was chromatolysis in the Purkinje cells, the ventral horn cells of the spinal cord and in the neurons of the lateral vestibular nucleus. The olivary nucleus was necrotic. There were foci of inflammatory cells in the molecular layer of the cerebellum and in the medulla. The cause of the disease remains unknown.

Paralysis in hedgehogs (Erinaceus europaeus) associated with demyelination.

Paraplegia affected 14 hedgehogs (Erinaceus europaeus) in a wildlife rescue hospital over a period of six months. Postmortem examination revealed demyelination in the brain and spinal cord and an inflammatory response in the meninges, choroid plexus and CNS. The peripheral nervous system was not affected. In the spleen, lungs and liver there was an accumulation of megakaryocytes and other evidence of extramedullary haemopoiesis, but there was no haematological evidence of anaemia. The pattern of disease incidence and the nature of the changes in the CNS suggest they were of viral origin, but no causal agent was isolated and the possibility of a neurotoxin cause cannot be ruled out.