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Hypothalamic neuroendocrine neurons: endocrine and central effects

المؤلف:  Wass, J. A. H., Arlt, W., & Semple, R. K. (Eds.).

المصدر:  Oxford Textbook of Endocrinology and Diabetes

الجزء والصفحة:  3rd edition , p115-116

2026-01-21

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For this volume it is particularly important to consider the neuro endocrine neurones. These form two major groups: magnocellular neurons of the supraoptic and paraventricular nuclei which project to the posterior pituitary and release oxytocin or vasopressin into the systemic circulation; and the more scattered parvocellular neurosecretory neurons which produce the releasing- and release- inhibiting factors and project to the capillaries of the median eminence where they release their signalling molecules to control the anterior pituitary endocrine cells via the hypothalamo– pituitary portal veins. Although vasopressin and oxytocin in peripheral blood can be assayed for diagnostic purposes, the concentrations of the parvocellular releasing and release- inhibiting factors are normally too low for assay, and such measurements are useful only when investigating ectopic secretion by tumours.

Most magnocellular and parvocellular neurosecretory neurons secrete peptides. These are produced from larger precursors and packaged into DCV in the cell bodies. The DCV are transported along varicose axons of the neurosecretory neurons to their neurohaemal contacts (indeed, this defines the neurons as ‘neuro endocrine’). The role of DCV in the dendrites of neurosecretory neurons was not understood until it was shown that they can be released from the dendrites and that dendritic release into the hypo thalamus is controlled separately from neurohaemal axonal release and that the released peptides have important local autocrine and paracrine physiological effects. This has been demonstrated most clearly for magnocellular neurons secreting oxytocin or vasopressin, but it seems likely that it applies more generally to peptidergic neurons. Indeed, the two long processes of GnRH neurons both contain GnRH DCV and are contacted by synaptic boutons along their length, making them intermediate between axons and dendrites (‘dendrons’). There is also now evidence that the oxytocinergic neurons of the posterior part of the paraventricular nucleus that project varicose axons down the spinal cord release oxytocin from non- synaptic varicosities to influence the lumbar gastrin- releasing peptide (GRP) neurons to facilitate male reproductive activity. It is clear, therefore, that peptidergic neuroendocrine neurons can have much more widespread effects in the CNS than those caused by the neurohaemal release of their products. This is consistent with the widespread distribution of receptors for the peptides, often far dis tant from relevant peptidergic axons. Neuroendocrine neurons are only one subset of peptidergic neurons— the extent to which these considerations apply generally to all peptidergic neurons remains to be determined.