1-Methyl-4-phenyl-1,2,5,6- tetrahydropyri dine ( MPTP ) is known to cause an irreversible destruction of the dopaminergic nigrostriatal pathway and symptoms of parkinsonism in humans and in monkeys. However, MPTP has been reported to act only minimally or not at all in several other animal species. When MPTP (30 milligrams per kilogram of body weight) was administered parenterally to mice, a decrease in concentrations of neostriatal dopamine and its metabolites, a decrease in the capacity of neostriatal synaptosomal preparations to accumulate [3H]dopamine, and a disappearance of nerve cells in the zona compacta of the substantia nigra were observed. In contrast, MPTP administration had no effect on neostriatal concentrations of serotonin and its metabolites. MPTP administration thus results in biochemical and histological changes in mice similar to those reported in humans and monkeys and similar to those seen in Parkinson's disease in humans. The mouse should prove to be a useful small animal with which to study the mode of action of MPTP .

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Electron micrographs, stained Epon-embedded sections, and silver stains of the ciliary ganglion of chickens 19 days prehatched, 4 days, 5 weeks, 6 months, and 1 to 2 years of age were studied. The majority of ganglion cells are large neurons; smaller cells are restricted to a dorsal, distal part of the ganglion. The following description applies to the large neurons. Three to twenty lamellae of loose, semicompact, and compact myelin ensheathe virtually every neuron. All these types of myelin form the sheath of a single neuron. The lamellae greatly increase in number and in compactness during the period between the 19-day embryo and the 4-day-old chick. During the period between the 4-day chick and the adult chicken, the myelin becomes only slightly thicker and denser. The calyx is a large synaptic terminal encircling virtually every neuron in the ganglion up to 5 weeks of age. At 6 months of age, the calyx appears to break up; only about half the number of neurons in the ganglion have this large terminal, while the remaining neurons have numerous relatively small, boutonlike synapses. This rather remarkable transformation in the structure of the calyx is virtually complete in the 1- to 2-year-old chickens. In these older chickens all the cells have boutons, and calyces are no longer present. The entering preterminal fiber, the calyx, the neuron, and the axon hillock can all have myelin lamellae on them. It is possible that this entire complex is effectively insulated by the myelin sheath. No synaptic discs or fusion of the membranes of the preterminal fiber and the postganglionic neuron are seen. The chick ciliary ganglion cells are the only myelinated neurons so far described which receive synapses. The neurons in the small-cell part of the ganglion do not have calyces and are not ensheathed by myelin lamellae at any age.