No abstract available.
Animals ; Corticotropin-Releasing Hormone* ; Dogs* ; Hypothalamus* ; Neurons* ; Somatostatin*

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.

Ultrastructures of the neurohypophysis in the rats have been studied by means of electron microscopy. Besides identifying the fact that the neurosecretory substances store in the nerve terminals and release into the blood, there are also axo-axonic synaptoid structures existed between neurosecretory terminals and neuro-glial synaptoid contacts between neurosecretory terminals and pituicytes. The characteristics of these contacts mentioned above are as follows: (1) the pre-and postsynaptic membranes are insignificantly thickened; (2) clustered microvesicles are close to and attach to the presynaptic membrane; (3) the synaptic cleft is about 20 nm wide and contains various amount of electron dense materials. The authors suggest that the two kinds of synaptoid structures and pituicytes are all involved in the regulation for the releasing of the neurosecretory substances.

Using the immunohistochemical and immunoelectron microscopic methods, the localization and pattern of vasoactive intestinal polypeptidergic nerves in the wall of cerebral vessels were investigated. The results revealed that the VIP-like immunoreactive (VIPLI) fibres were located in the adventitia or at the adventitia-media border. No synaptic contacts were identified among the nerve terminals or between nerve terminal and smooth muscle cell. VIPLI terminals directly apposed to the smooth muscle cells with a distance of 100 nm.The observations mentioned above indicate that there is peptidergic innervation in the wall of the cerebral vessels besides traditional adrenergic and cholinergic innervations. The regulatory function of VIP-containing nerves to the cerebral vessels may be performed by affecting the smooth muscle directly through the nonsynaptic release. In addition, present study identified and discussed the distribution and function of substance P(SP) in the cerebral vessels.