SYNAPTIC CONTACTS BETWEEN CHOLINERGIC AFFERENTS AND SUPRACHIASMATIC NEURONS OF THE RAT

The relationship between cholinergic fibres in the suprachiasmatic nuc leus (SCN) and neurones of the cell group was investigated at the ligh t and electron microscopic level using choline acetyltransferase (ChAT ) immunocytochemistry for the identification of cholinergic elements. Axosomatic and axodendritic synaptic contacts were found between ChAT- immunopositive axon terminals and SCN neurones. These synapses were as ymmetrical. The observations provide the final morphological basis for the view already suggested by neuroanatomical, electrophysiological a nd pharmacological findings that the cholinergic elements in the SCN m ay act directly on the neurones of the nucleus.