Responses of supraoptic neurones in the intact and deafferented rat hypothalamus to injections of hypertonic sodium chloride.

Abstract

SUMMARY1. Recordings were made from a total of fifty-three neurones in the supraoptic nuclei of four groups of rats: intact rats, animals in which the hypothalamus had been partly denervated by anteriorly or posteriorly placed semicircular cuts, and rats with a totally deafferented hypothalamus. 4. The results imply that under the conditions ofthese experiments the spontaneous activity of the supraoptic nucleus in intact animals was maintained by an extrahypothalamic excitatory input, that partial hypothalamic isolation reduced its intensity, possibly by unmasking an inhibitory input, and that total isolation reduced it to an even greater extent. Osmotic activation of supraoptic cells was only possible when the anterior connexions of the hypothalamus were intact. Thus the cerebral osmoreceptors for vasopressin release may be situated outside the supraoptic nuclei.

Ibotenate Lesions of the Diagonal Band of Broca Attenuate Baroreceptor Sensitivity of Rat Supraoptic Vasopressin Neurons

“…Previous work in this laboratory showed that acute electrolytic lesions of the DBB markedly reduced the spontaneous activity of SON vasopressin-secreting neurons making it difficult to assess the effects of this maneuver on baroreceptor-induced inhibition (Jhamandas and Renaud, unpublished observations). Similar changes in the spontaneous activity of SON neurons have also been observed after acute lesions of the anteroventral region of the third ventricle (15) and knife cuts between the ventral lamina terminalis and the SON (16). In this study, chronic Diagonal band and baroreflex inhibition of supraoptic neurons 307 ibotenic acid lesions appear to circumvent these changes in neural activity that are associated with acute electrolytic lesions of these forebrain regions, in addition to their ability to destroy neural perikarya with little effect on fibers of passage.…”

Cerebral Metabolic and Vasopressin and Oxytocin Responses During Osmotic Stimulation in Conscious Rats

“…This implicates some supraoptic neurons themselves as transducers of osmotic stimuli. However, Dyball and Prilusky (24) showed that the normal response of the supraoptic neurons to osmotic stimulation depended upon an afferent input from the hypothalamus. As lesions of the OVLT and the anteroventral region of the third ventricle (AV3V) area interfere with the release of vasopressin and water balance (25), and injection of hypertonic solution into the AV3V area excites magnocellular neurons in the supraoptic nucleus, it has been suggested that osmosensitive neurons in this area provide the osmotic drive to the supraoptic nucleus.…”

Regulation of spontaneous phasic firing of rat supraoptic vasopressin neurones in vivo by glutamate receptors.

“…6C Bourque & Renaud, 1990;Renaud & Bourque, 1991 for review). Deafferentation studies suggest that afferent connections are important for sustaining the excitability of supraoptic neurones (Dyball & Prilusky, 1981), but direct physiological evidence linking a particular neurotransmitter system to the genesis of patterned electrical activity of supraoptic neurones has not been obtained in intact animals. Our study now indicates that the initiation and maintenance of spontaneous phasic activity in putative VP-secreting cells in vivo require extrinsic excitatory drive that is predominantly provided through activation of glutamate receptors.…”

“…The phasic activity patterns displayed by VP-secreting MNCs are deemed to arise from an intrinsic membrane conductance, the post-spike depolarizing after-potential (DAP), which succeeds each action potential, and firing during a phasic burst is sustained by depolarizing plateaux potentials that develop from the summation of individual DAPs (Andrew & Dudek, 1983;Bourque, 1986 (Day & Renaud, 1985), whereas interruption of afferent pathways arising from the area of the anteroventral third ventricle (AV3V) produces a marked acute reduction in their excitability and spontaneous activity (Dyball & Prilusky, 1981;Leng, Blackburn, Dyball & Russell, 1989;Chaudry, Dyball, Honda & Wright, 1989). It was proposed earlier (Dyball & Prilusky, 1981) (Yang, Senatorov & Renaud, 1994). Supraoptic MNCs possess both N-methyl-D-aspartate (NMDA) and non-NMDA glutamatergic receptors (Gribkoff & Dudek, 1990;Gribkoff, 1991;Hu & Bourque, 1991).…”