Effect of cooling on supraoptic neurohypophysial neuronal activity and on urine flow in the rat

Peptidergic excitation of supraoptic nucleus neurons: involvement of stretch-inactivated cation channels

Although the primary stimulus regulating vasopressin (VP) release is a change in systemic osmolality, other physiological parameters are known to affect VP secretion or modulate the osmotic control over its release. Neuropeptides feature prominently in afferents underlying the central regulation of the VP-releasing magnocellular neurosecretory cells (MNCs). Although little is yet known of the circumstances under which peptides are released onto MNCs, previous studies have shown that a common response profile to exogenous peptide application is a slow excitation that seems to result from the activation of a nonselective cation conductance. In this paper we review the basis for the excitatory effects of angiotensin II, cholecystokinin, and neurotensin in MNCs acutely isolated from the supraoptic nucleus of adult rats. Saturating concentrations of these three peptides evoked nonadditive increases in macroscopic cation conductance. During single-channel recordings Ang II, CCK, and NT caused kinetically identical increases in the probability of opening of 35-pS nonselective cation channels. Patches containing only one channel further revealed that the activity of single channels could be regulated by separate applications of all three peptides. Peptide-stimulated channels were also found to be inactivated by increases in membrane stretch and to be blocked by low concentrations of gadolinium (Gd(3+)). It is concluded that many excitatory peptides depolarize MNCs by stimulating the stretch-inactivated cation channels underlying osmoreception. Convergent regulation of these channels provides a potentially powerful mechanism for integrating signals derived from the various afferents involved in the regulation of MNCs.

Thermosensitivity of neurons in the paraventricular nucleus of the rat slice preparation

The thermosensitivity of 65 spontaneously active neurons in the paraventricular nucleus (PVN) was investigated by extracellular recording in the rat hypothalamic slice preparation. The firing rate of these cells was comparatively low, ranging from 0.03 to 10.0 (mean 2.46) impulses/s at 37 degrees C, and only a minority showed a phasic firing pattern. Of 65 neurons tested, 23 (35%) increased their firing rate when the slice was warmed (warm-sensitive neurons) and 9 (14%) showed the opposite response (cold-sensitive neurons). Thermosensitivity was also tested in solutions with reduced [Ca2+] and high [Mg2+]. Eight out of 10 warm-sensitive neurons and 5 of 7 cold-sensitive neurons retained thermosensitivity after synaptic blockade. Out of 6 phasic firing neurons tested, one showed warm-sensitivity and another one showed cold-sensitivity. The thermosensitive neurons were diffusely distributed throughout the PVN and were not located in particular areas of the nucleus. Thus a group of cells in the PVN, including probably both magno- and parvocellular neurons, showed an inherent thermosensitivity, which suggests an important role for the PVN in thermoregulation.