Canine models for human genetic neurodegenerative diseases

Lessons learnt from animal models: pathophysiology of neuropathic lysosomal storage disorders

Approximately 50 inborn errors of metabolism known as lysosomal storage disorders have been discovered to date, most of which are due to a single mutation in a gene encoding a soluble lysosomal enzyme. Consequently, inadequate enzyme activity results in the accumulation of substrates for that enzyme, invariably accompanied by a wide variety of secondary pathological changes. Many of these conditions remain untreatable, and therefore, research into pathogenic processes and potential treatment strategies is intense. A key tool for researchers in this area is the availability of clinically relevant animal models in which to study disease manifestation and evaluate therapeutic outcomes. Large numbers of both naturally occurring and genetically modified animal models of neurodegenerative lysosomal storage disorders are in existence, with spontaneous models occurring in both large domestic (e.g., cat, dog, sheep) and small (e.g., mouse) animal species. Many have undergone rigorous phenotypic characterization and are now providing us with insights into neurological disease processes. The purpose of this review is to highlight some of the major lessons learnt from these studies.

Beta-amyloid cortical deposits are accompanied by the loss of serotonergic neurons in the dog

Dogs may naturally suffer an age-related cognitive impairment that has aroused a great deal of interest, even beyond the field of the veterinary clinic. This canine senile dementia reproduces several key aspects of Alzheimer's disease (AD), including the presence of beta-amyloid (A beta) deposits in the cerebral cortex, neurodegeneration, and learning and memory impairments. In the present study, we have used unbiased stereological procedures to estimate the number of the dorsal and median raphe nuclei (DRN and MRN, respectively) serotonergic neurons immunolabeled with an anti-tryptophan hydroxylase (TrH) monoclonal antibody in young and aged dogs without A beta cortical deposits and in aged dogs with A beta cortical deposits. The estimated total number of TrH-labeled neurons (mean +/- SD) was 94,790 +/- 26,341 for the DRN and 40,404 +/- 8,692 for the MRN. The statistical analyses revealed that aged dogs with A beta cortical pathology had 33% fewer serotonergic neurons in the DRN and MRN than aged dogs without A beta cortical deposits (108,043 +/- 18,800 vs. 162,242 +/- 39,942, respectively; P = 0.01). In contrast, no significant variations were found between young and aged dogs without A beta cortical deposits. These results suggest that degeneration of the serotonergic neurons could be involved in the cognitive damage that accompanies A beta cortical pathology in the dog and reinforce the use of the canine model for exploring the potential mechanisms linking the cortical A beta pathology and serotonergic neurodegeneration that occurs during the course of AD.

Distribution of ACTH immunoreactivity in the diencephalon and the brainstem of the dog

The present work describes for the first time the anatomical distribution of adrenocorticotropic hormone (ACTH) in the diencephalon and the brainstem of the dog by means of the indirect immunoperoxidase technique. The distribution found in this species agrees well with the pattern found in other mammals and particularly confirms much of the findings reported in the cat. An exception to that concordance is the presence of ACTH perikarya in the nucleus of the solitary tract of the dog, a population that has been described in the rat but not in the cat, and in the ventral mesencephalon. This last population spread across the ventral tegmental area from the raphe to the cerebral peduncle and appeared to be a specific feature of the canine brain. On the other hand, we can not see ACTH fibers in the substantia nigra of the dog which could be a characteristic of the domestic carnivores, opposite to rodents, since these fibers appeared to be also lacking in the cat. Nevertheless, the widespread distribution of ACTH fibers in the brain of the dog included many other nuclei containing monoaminergic neurons which supported a possible role for ACTH in the regulation of these neurotransmitter systems.