The ultrastructure of rat rod synaptic terminals: effects of dark-adaptation.
The ultrastructure of synaptic terminals of rat rod photoreceptors was studied in light-adapted and dark-adapted states. In the light-adapted state, horizontal cell processes embedded in the photoreceptor terminal show smooth surface contours and are ovoid in cross section. In the dark-adapted state, fingerlike protrusions of photoreceptor cytoplasm extend into the horizontal cell processes on either side of the synaptic ribbon. An electron-dense structure lies under the horizontal cell membrane that surrounds these fingerlike protrusions. This submembrane specialization is generally associated with areas of concavity of the horizontal cell membrane; it occurs in goldfish rods as well as rat rods. The protrusions and the horizontal cell specialization may be involved in membrane dynamics during synaptic activity.
D000818:Animals; D003530:Cyprinidae / Q000033:anatomy & histology*; D003623:Dark Adaptation; D004705:Endocytosis; D006054:Goldfish / Q000033:anatomy & histology*; D008297:Male; D008854:Microscopy, Electron; D010786:Photoreceptor Cells / Q000502:physiology / Q000648:ultrastructure*; D051381:Rats; D013569:Synapses / Q000648:ultrastructure; D013570:Synaptic Membranes / Q000648:ultrastructure