Osmosensitive single neurones in the hypothalamus of unanaesthetized monkeys

Abstract

SUMMARY1. We recorded with tungsten micro-electrodes the activity of single neurones in the supraoptic nucleus (NSO) and adjacent regions of the hypothalamus while repeatedly injecting solutions of varying tonicity into the common carotid artery of trained, unanaesthetized monkeys who accepted the experimental restraints without anxiety.2. Intracarotid injections of mildly hypertonic solutions of sodium chloride produced a characteristic behavioural response during and immediately after injection: e.e.g. 'arousal,' lip and tongue smacking, chewing, irregular sniffing respiration and associated mildly increased movement of face, eyes and body.3. Of the 130 cells analysed during hypertonic intracarotid injections, 105 (81 %) were osmosensitive. Twenty-five (19 %) of the cells studied during similar injections were non-osmosensitive. On the basis of the anatomical location of the cells, the pattern of discharge to intracarotid osmotic stimuli and the response to arousing sensory stimuli, we divided the osmosensitive cells into two major groups, 'specific' and 'non-specific' osmosensitive cells.4. Fifty-two (50 %) of the osmosensitive cells we labelled 'specific' because they responded to an intracarotid injection of hypertonic sodium chloride, generally did not respond to non-noxious arousing sensory stimuli and were located in or near the supraoptic nucleus. We found two subtypes of these 'specific' osmosensitive cells: (a) twenty-one (20 %) NSO cells with 'biphasic' responses, that is, acceleration followed by inhibition; (b) thirty-one (30 %) cells in the immediate perinuclear zone of the NSO with 'monophasic' responses, subdivided into twenty-one (20 %) cells that accelerated and ten (10 %) that were inhibited. lateral hypothalamus, were 'non-specific', responding both to intracarotid injections of hypertonic sodium chloride and also to sensory stimuli that were mildly arousing. Two groups of 'non-specific' osmosensitive cells showed monophasic responses; thirty-five (34 %) cells accelerated and seventeen (16 %) of them were inhibited.6. The 'monophasic' specific osmosensitive neurones lying in the immediate perinuclear zone of the supraoptic nucleus in the primate could conceivably be the 'osmoreceptors' of Verney. The 'biphasic' specific osmosensitive neurones in the NSO may well represent the secretary cells of this system. From our data, the 'non-specific' osmosensitive neurones, scattered diffusely in the anterolateral hypothalamus, have little to do with osmoregulation. Some of these cells located in the perinuclear zone of the NSO could act as interneurones, however, conveying afferent input to the osmoreceptor-secretory complex of the supraoptic nucleus.

GABA-T-positive neurons in the rat supraoptic nucleus as revealed by a pharmaco-histochemical method with gabaculine.

“…Further critical studies are needed to settle this problem. The essentially negative result within the SO is consistent also with some electrophysiological studies (3,7,10,26) . Kelly and Dreifuss (7) ruled out the possibility of the presence of inhibitory interneurons in the recurrent collateral system of the rat SO, although their presence was found in the dog and cat (8).…”

“…However, monophasic specific osmonsensitive cells in the perinuclear zone around the SO have been classified into excitatory and inhibitory neurons in the unanesthetized monkey (3).…”

The activity of identified supraoptic neurones and their response to acetylcholine applied by iontophoresis

“…It has been proposed that both the silence of some neurones and the episodic behaviour of others occurs as a result of a functionally active negative feed-back loop from intensely excited supraoptic neurones (Hayward & Vincent, 1970;Dyball, 1971). Negative feed-back could be mediated synaptically by the recurrent inhibitory pathway to supraoptic neurones described in the companion paper (Dreifuss & Kelly, 1971).…”

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

“…input (Hayward, 1972c(Hayward, , d, 1974 and send axonal processes along the hypothalamo-hypophysial tract to the median eminence (birds, Oksche, 1966;sheep, Parry & Livett, 1973), the pars intermedia (cat, Bargmann, 1968;teleost, Knowles & Vollrath, 1966;Perks, 1969; Zambrano, Nishioka & Bern, 1972) and to the neurohypophysial terminal neurohemal gland. Despite considerable anatomical (Bargmann, 1968;Cajal, 1911;Christ, 1966; Szentagothai, Flerko, Mess & Halasz, 1968), electrophysiological (Cross, 1973;Findlay & Hayward, 1969;Hayward, 1972cHayward, , d, 1974Hayward & Jennings, 1973a, b, c, d;Hayward & Vincent, 1970; Kandel, 1964) and chemical-pharmacological data (Ginsburg, 1968) on these magnocellular neuroendocrine cells only the classical Golgi study of Leontovich (1969) has provided some evidence about the morphology of dendritic arborization, the configuration of the somata and the numbers and types of axonal processes of these neurosecretory neurons. Now with the recent development of the fluorescent dye-marking technique (Stretton & Kravitz, 1968) a more precise delineation of different cell types, of connexions between dendrites of particular cells and the third ventricle, of the presence or absence of axone branching and collaterals and of the connexions between magnocellular neuroendocrine cells in the supraoptic and paraventricular nuclei and the extent to which magnocellular neuroendocrine cells send their axones to the median eminence, pars intermedia and pars distalis seemed possible.…”