Cytoplasmic peptide content and nuclear estrogen binding of magnocellular neurons in the hypothalamus of Long-Evans and Brattleboro rats

Comparison of the number of vasopressin-producing hypothalamic neurons in rats and humans

The aim of this study was to assess the number and proportion of vasopressin-producing neurons in the hypothalamic magnocellular nuclei in rats and humans. Accurate and unbiased neuronal counts were estimated using the optical disector method. Arginine vasopressin-containing neurons were immunohistochemically visualized in formalin-fixed tissue sections. The magnocellular neurons were similar in size and morphology in both species. While the human hypothalamus contained significantly more vasopressin-containing neurons compared with the rat (36-fold increase), the proportion of vasopressin-containing neurons between species was similar. In both species, the majority of supraoptic neurons contained vasopressin, however the proportion of vasopressin-containing neurons in the human paraventricular nucleus was double that of the rat (nearly a 100-fold increase in number). These results suggest that the paraventricular nucleus contributes significantly to the release of vasopressin from the posterior pituitary in humans, whereas in rats vasopressin is mainly released by supraoptic neurons.

Neuroendocrine anatomy of the hypothalamus

The hypothalamus is a most complex part of the CNS having rich interconnections with forebrain, limbic and brainstem structures. Its outflow is directed in such a way as to influence the endocrine system (via the neurohypophyseal and adenohypophyseal neurosecretory systems), the autonomic nervous system (via projections to preganglionic cell groups in brainstem and spinal cord) and behavioural responses to physiological and environmental cues via its interaction with limbic and somatomotor systems. The chemical identity of many of its neuronal messengers and those of some of its important afferents, such as the monoaminergic neurons, has opened the way to a form of systematic experimental investigation with chemical tools more powerful than those available to neuroendocrinologists in the past. Much of the information which follows has accrued very rapidly through the use of these methods to reveal the rich complexities of neuroendocrine integration.