The neurons and the synaptic endings in the primate basilar pontine gray.

Two types of neurons, projection and intrinsic, previously identified in Golgi preparations of the adult monkey (Macaca mulatta) basilar pontine gray (Cooper and Fox, '76) were observed electronmicroscopically in Macaca mulatta and the squirrel monkey Saimiri sciureus. The cell body of the projection neuron measures up to 37 micrometer and its cytoplasm is rich in organelles. The Goli apparatus, ribosomes, and mitochondria are disposed around the nucleus, while rough endoplasmic reticulum though abundant is usually confined to one half of the cell body. The cell body of the intrinsic neuron measures less than 20 micrometer and its cytoplasm displays prominent ribosomes, but a paucity of other organelles. Five types of synaptic profiles have been identified in the neuropil of the basilar pons; one measures up to 5 micrometer and the rest 2 micrometer or less. They are: (1) a large profile (MSV) containing medium size vesicles (500A) and a central core of mitochondria and neurofilaments; (2) a profile (SSV) containing small round vesicles (250-500 A) which is the most abundant and ubiquitous; (3) a profile (F) containing flattened or pleomorphic vesicles; (4) a profile (LSV) containing large oval egg shaped vesicles (750 A); and (5) a pale profile (PP) that contains oval and occasionally pleomorphic vesicles. MSV, SSV, and LSV terminals form asymmetrical contacts and F terminals form symmetrical contacts with both dendritic and vesicle-containing, pale profiles. The vesicle-containing, pale profile is both pre- and post-synaptic and participates in serial synapses. Following unilateral cortical ablations both dark and filamentous degeneration were observed in the ipsilateral basilar pontine gray.