Physiological and morphological identification of hypothalamic magnocellular neuroendocrine cells in goldfish preoptic nucleus*

Abstract

SUMMARY1. Intracellular recordings were made from antidromically identified neurones in the goldfish preoptic nucleus and Procion Yellow was ejected from the recording pipette, marking these magnocellular neuroendocrine cells diffusely, for histological identification.2. In confirmation of earlier studies these preoptic neuroendocrine cells showed resting membrane potentials of 47 mV, action potentials up to 85 mV, action potentials of long duration (3.9 msec) occurring in two steps, long-lasting hyperpolarizing after-potentials and orthodromic driving from olfactory input.3. Magnocellular neuroendocrine cells exhibited all-or-none jumps to shorter antidromic latencies as pituitary stimulus strength increased, suggesting multiple branching of the 'axones' either near the preoptic nucleus or within the neural lobe.4. I find three morphological types of neuroendocrine cells throughout the magnocellular part of the preoptic nucleus. Cell Type I is a large (37 jtm), multipolar neurone, 48 stm from the ependyma, with fine 'dendrites' projecting into the lateral hypothalamus and within the preoptic nucleus, with multiple branched 'axones'. Cell Type II is a large (31 Itm), multipolar neurone, 24 Itm from the ependyma, with a coarse 'dendrite' to the ependyma and fine 'dendrites' within the preoptic nucleus, with limited 'axonal' branching. Cell Type III is a small (18 ,um), multipolar neurone, 46 /tm from the ependyma, with fine 'dendritic ' processes distributed within the preoptic nucleus, with limited 'axonal' branching.

Intracellular dye-marked enkephalin neurons in the magnocellular preoptic nucleus of the goldfish hypothalamus.

“…The electrophysiological properties of enkephalin neurons from this study are consistent with previous findings of MgC of the goldfish (3,4,11,14) and mammalian hypothalamus (18) and in other mammalian central neurons (19). On the basis of these initial electrophysiological and morphological data, enkephalin neurons cannot be distinguished either functionally or structurally from the isotocin or vasotocin MgC also present in the NPO of the goldfish (2,4,20).…”

“…Adult goldfish (Carassius auratus), weighing 290-850 g and measuring 25-35 cm, were anesthetized, immobilized, suspended, and perfused with water, and the brain was exposed according to earlier methods (11,14).…”

“…12) and beveled (15) to impedances of 6-40 MQ for intracellular recordings. Electrophysiological recording and stimulating apparatus and the pituitary stimulating electrodes have been described (11). Intracellular electrophoretic injection (5-10 nA of hyperpolarizing dc current, 0.3-6 min) of LY (an anionic fluorescent dye) marked the physiologically studied, antidromically identified preoptic neurons for subsequent localization.…”

“…The recent discovery of enkephalin in the magnocellular nuclei, the hypothalamus, and the pituitary gland of the goldfish (2-5) confirms earlier studies in mammals (6)(7)(8)(9)(10) and suggests a role for endogenous opioid peptides in neurohypophyseal regulation in fish and mammals. The combination of cell identification by immunocytochemistry with a previously developed intracellular dye-injecting approach in the goldfish (11) provides a working model for chemical typing of single cells. This investigation offers an approach to the analysis of neural networks by use of the current technology of cell identification by dye marking (12), peptide biochemistry (13), and immunocytochemistry (6) for the study of single, electrophysiologically defined, morphologically reconstructed magnocellular neurons that contain enkephalin.…”

Osmoreceptors or sodium receptors: an investigation into ADH release in the rhesus monkey.

“…Scanning electron microscopic observations have shown that the surface of the choroid plexus and distinct areas known as the circumventricular 80 PRIMATE OSMORECEPTOR AND ADH RELEASE organs are free of cilia, while major parts of the ventricular ependyma are covered by a dense layer of cilia in rabbit, cat and squirrel monkey (Weindl & Joynt, 1972). Many workers have attributed a sensory function to the processes of magnocellular neurosecretory cells ending freely in the ependyma of the third ventricle of fishes and amphibia (Dierickx, 1962;Smoller, 1965;Hayward, 1974). On the basis of the present data as well as the considerable histological evidence (see above), it is proposed that the osmoreceptors of Verney are sodium sensitive elements composed of the ependymal dendrites alone or specialized ependymal cells plus the dendrites in the anterior third ventricle.…”