Two types of dopaminergic nerve terminals in the rat neostriatum. An ultrastructural study.

In the neostriatum 7.7% of all boutons absorbed alpha-methylnoradrenaline, thus staining their synaptic vesicles profiles granular. These presumably monoaminergic synapses were divided into two types according to ultrastructural features. Type A was composed of a relatively large axon terminal and a dendritic spine with postsynaptic membrane thickening. The axon terminal of type B, that is a bouton en passant, was smaller than the postsynaptic profile, while the synaptic contact was symmetrical. Following nigral coagulation, both types of synapse degenerated. It is concluded that both types of synapse are dopaminergic.