Animal models of degenerative neurological disease

Amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and Alzheimer's disease (AD) are human neurological disorders which occur in middle and late life. These three diseases share certain features: they are slowly progressive; transmitter-specific groups of neurons are selectively affected by disease processes; and affected nerve cells exhibit cytoskeletal pathology. The causes and mechanisms of cell injury are unknown, and there are no treatments which directly affect the disease process. Dysfunction and death of these specific cell groups account for different clinical syndromes. In ALS, patients become paralyzed, at-risk cholinergic motor neurons in the spinal cord develop neurofilamentous swellings of proximal axons, and distal axons atrophy. In PD, affected individuals show slowed movements, tremor, and rigidity. These clinical findings are attributed to regeneration of dopaminergic neurons of the substantia nigra, a cell group showing abnormal accumulations of neurofilament antigens in the form of Lewy bodies. In AD, patients develop dementia (a syndrome of cognitive and memory impairment), and cholinergic neurons of the basal forebrain and certain other populations of nerve cells develop abnormalities of the cytoskeleton. These include perikaryal neurofibrillary tangles and enlarged distal axons which appear as neurites in senile plaques. Certain features of ALS, PD, and AD are recapitulated in three animal models described in this review. Hereditary Canine Spinal Muscular Atrophy (HCSMA), a dominantly inherited motor neuron disease, shows many clinical and pathological features in common with ALS. Affected dogs are clinically weak, have denervation atrophy of muscles, and develop neurofilamentous swellings of proximal axons, atrophy of distal axons, and degeneration of motor neurons. These abnormalities of axonal caliber are associated with impaired transport of the neurofilament triplet proteins and a maldistribution of phosphorylated neurofilaments. Intoxication of macaques with 1-methyl-4-]henyl-1,2,3,6,tetrahydropyridine (MPTP) produces a Parkinsonian syndrome due to selective injury of dopaminergic neurons in the substantia nigra and associated denervation of the striatum. Finally, aged rhesus monkeys (older than 23 years of age) show cognitive and memory deficits and exhibit senile plaques whose neurites are derived from cholinergic and other transmitter systems. Although these macaques do not have AD, they do provide a model for examining the relationships between age-associated cognitive deficits and pathological changes occurring in certain transmitter systems of primates.(ABSTRACT TRUNCATED AT 400 WORDS)