The ultrastructure of the substantia nigra and caudate nucleus of the mouse and the cellular localization of catecholamines.

The fine structure of the substantia nigra and caudate nucleus of the mouse is studied by electron microscopy. The structure of neurones in both regions confirm the general contention that catecholamines are produced in the perikaryon. In the substantia nigra two structurally distinct types of synaptic junctions are observed; namenly an 'encircled type' by which a dentrite is surrounded by three or more axon terminals, containing granulate and/or synaptic vesicles, and a 'sandwich type' which is characterized by a dendrite interposed between two axon terminals, which contain only synaptic vesicles. The bouton containing both granulate and synaptic vesicles is considered aminergic (type A), whereas that having only synaptic vesicles is regarded cholinergic (type C) in nature. The caudate nucleus does not show the regional specialization of synaptic junctions, and its junctions are composed of simple appositions of dendrites and axon terminals, which contain a limited number of granulate vesicles. Treatment with reserpine depletes the dense core of granulate vesicles, while injections of iproniazid increase the relative number of granulate vesicles in axon terminals. The relative number of granulate vesicles is not affected by oxypertin. These observations are discussed in light of currently available information on the anatomy, chemistry and physiology of amine-containing brain regions. It is suggested that there might be two functionally different types of boutons (types A and C) in the substantia nigra, and that granulate vesicles of axon terminals of the substantia nigra and caudate nucleus might contain dopamine, which may act as a transmitter. [ABSTRACT FROM AUTHOR]