Ultrastructural observations on intercellular contacts of nigral dendrites.

Possible morphological correlates of dendritic release sites for dopamine have been investigated in the rat substantia nigra. Electronmicroscopic and freeze etching studies show that nigral dendrites fail to form dendrodendritic contacts but on the contrary are always separated by glial elements, which in turn are connected by multiple gap junctions. No dendro-axonic synapses are present but large specialized symmetrical junctions could provide a possible morphological specialization for a dopamine transfer from presynaptic dendrites to axon endings.