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Neuropeptide-Y innervation of beta-endorphin-containing cells in the rat mediobasal hypothalamus: a light and electron microscopic double immunostaining analysis.
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1992
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Synaptic TransmissionNeuroendocrinologyPeripheral Nervous SystemPituitary GlandElectron MicroscopyBeta-endorphin-containing CellsRat Mediobasal HypothalamusNeuroendocrine MechanismPituitary Lh ReleaseHypothalamic PeptideHypothalamic FunctioningHealth SciencesCentral AdministrationEndocrine MechanismHypothalamusNeuropharmacologyNeuropeptide-y InnervationNervous SystemEndocrinologyPharmacologyOvarian HormoneNeurophysiologyNeuroanatomyPhysiologyNeuropeptide ReceptorNeuroscienceCentral Nervous SystemMedicineNeuropeptides
Neuropeptide‑Y centrally inhibits LH release in ovariectomized rats but stimulates it in intact or steroid‑pretreated rats, and this dual effect is thought to involve interaction with the hypothalamic beta‑endorphin system, though the precise neural mechanism remains unclear. This study aimed to investigate the morphological basis of the interaction between hypothalamic NPY and beta‑endorphin systems. Colchicine‑pretreated female rats’ mediobasal hypothalamus sections were double‑immunostained for NPY and beta‑endorphin using light‑brown DAB and dark blue nickel‑enhanced DAB, then examined by light and electron microscopy. Light microscopy revealed a dense network of NPY‑positive axons closely apposed to beta‑endorphin neurons, and electron microscopy showed NPY boutons forming predominantly asymmetrical axosomatic and axodendritic synapses with beta‑endorphin cells, implying that NPY’s dual effects on LH secretion involve both direct modulation of LHRH neurons and indirect influence via the beta‑endorphin system.
Central administration of neuropeptide-Y (NPY) inhibits pituitary LH release in ovariectomized rats and stimulates LH release in intact and ovariectomized rats pretreated with ovarian steroids. Although the precise neural mechanism of this dual effect of NPY is not known, experimental evidence suggests an underlying interaction between hypothalamic NPY and the inhibitory beta-endorphin (beta END) systems in the neuroendocrine regulation of pituitary LH release in the rat. The present study was undertaken to examine the morphological basis of the interaction between these two peptidergic systems in the hypothalamus. Sections of the mediobasal hypothalamus of colchicine-pretreated female rats were double immunostained for NPY and beta END and examined by light and electron microscopy. The light brown diaminobenzidine reaction was used to visualize beta END cells, while NPY neurons were labeled with a dark blue nickel ammonium sulfate-intensified diaminobenzidine reaction. Under the light microscope, a dense network of NPY-immunoreactive axons and axon terminals was observed in close apposition with beta END-immunoreactive neurons throughout the medial basal hypothalamus. Electron microscopic examination revealed that NPY-immunoreactive boutons formed axosomatic and axo-dendritic synaptic connections with beta END cells. A majority of these synaptic membrane specializations appeared asymmetrical [corrected]. In light of the previous evidence of excitatory and inhibitory effects on LH release and the existence of direct synaptic connections between NPY and LHRH neurons in the hypothalamus, the current results imply that the dual effects of NPY on LH secretion may involve modulation of LHRH secretion, both by the direct route and indirectly through the hypothalamic beta END system.