EVIDENCE FOR A DOUBLY INNERVATED SECRETORY UNIT IN ANURAN PARS INTERMEDIA .2. ELECTRON MICROSCOPIC STUDIES

Two types of nerve endings were found in synaptic contact with secretory cells of the pars intermedia of Rana pipiens. One type contains relatively large granules 1000 to 1700 Å in diameter. The other type, more numerous and more broadly distributed, contains vesicles 600 to 1000 Å in diameter with a dark core. One example was found of a single secretory cell on which two synapses of the two types occurred in the same plane of section. Several examples were found of single nerve endings in presynaptic contact with a secretory cell and another neuron. This information is considered in relation to a hypothesis of opposed double innervation of the pars intermedia cell. © 1969.