The ultrastructural localization of peptide substances——VP,SP,ENK,SRIFand distribution of peptidergic nerves in rat neurohypophysis were studied by elect-ron microscopy.The results showed that VP,SP,ENK and SRIF immunoreactiveproducts located in large granular vesicles(110-150 nm in diameter),at the surfaceof microvesicles and outer membrane of mitochondria.The VP-,SP-,ENK- andSRIF-containing nerve fibers distributed at periphery of capillaries and vicinity ofpituicytes.VP- and ENK- positive nerve terminals formed axo-axonic synapses withnegative terminals.Axo-axonic synapses also existed between two SRIF-positive ter-minals.In addition,ENK- and SP-positive terminals formed synaptoid structureswith pituicytes.The authors have discovered the VP-positive pituicytes for the firsttime.The scientific significances of present paper are as follows:(1)Several kinds ofpeptide such as VP,SP,ENK and SRIF have been identified in neurohypophysis atultrastructural level;(2)The discovery of VP-positive pituicytes and their peptide-rgic innervation imply that these structures probably participate in the regulation ofneurohormone releasing;(3)New morphological bases have been provided for theregulation of neurohormone releasing.

6-OHDA was injected into the third cerebroventricle of rats.24 hours later,thanimals were sacrificed and the degeneration of catecholaminergic (CA) nerve term-inals were studied by electron microscopic cytochemical method.The results showedthat there were a number of degenerated nerve terminals in the arcuate nucleus.Thecharacteristics of these terminals were as follows:enhanced axoplasmic electron opa-sity,destroyed mitochondria and synaptic vesicles and the formation of dense bodies.The multilocular forms were commonly encountered.Most of degenerated terminalswere surrouded by processes of glial cells.The degnerated perikarya of the neuronsin arcuate nucleus with decreased RER,destroyed mitochondria and dense bodieswere also observed.Based on the characteristics of degenerated features the authorsbelieved that these damaged terminals should mainly belong to DA fibers.Theymight regulate or control the function of the arcuate nucleus by means of differentkinds of synaptic mechanisms.The source of DA nerve fibers may originate from A_(12)A_(14) or A_(15) cell groups of the hypothalamus.