Retinal afferents form Gray-type-I and type-II synapses in the suprachiasmatic nucleus (rat)

Abstract

The synapses of optic nerve afferents in the suprachiasmatic nucleus (SCN) usually form Gray type I (asymmetrical) synapses, but about 13% show clear-cut Gray type II (symmetrical) active zones. Some presynaptic elements form a Gray type I—active zone with one dendrite and a Gray type II—active zone with another postsynaptic element at the same time. It is discussed whether this variability is related to a simultaneous excitatory and inhibitory action, to a variable activity or efficiency of the synapses or to various stages of maturation.