Characterization of hypothalamic noradrenaline receptors in the supraoptic nucleus and periventricular region of the paraventricular nucleus of mice in vitro

Angiotensin II sensitive neurons in the supraoptic nucleus, subfornical organ and anteroventral third ventricle of rats in vitro

The angiotensin II (AII) sensitivity of neurons in the supraoptic nucleus (SON), subfornical organ (SFO) and the region near the anteroventral part of the third ventricle (AV3V) was investigated using extracellular recording in the rat brain slice preparation by adding AII (10(-10)-10(-6) M) to the perfusion medium. Forty seven (44%) of 106 SON neurons, 62 (66%) of 94 SFO neurons and 28 (33%) of 86 AV3V neurons were excited by AII. One cell was inhibited by AII in the SON and one in the SFO. The threshold concentration to evoke responses in the SON neurons was approximately 10(-9) M, but neurons in the SFO and AV3V showed clear excitatory responses to AII at 10(-10) M. In the SON, 18 (40%) of 45 phasic firing neurons (putative vasopressin neurons) and 29 (48%) of 61 nonphasic firing neurons (including putative oxytocin neurons) were excited by AII. The excitatory effect of AII was reversibly antagonized by a specific antagonist saralasin and persisted after synaptic blockade in medium with low [Ca2+] and high [Mg2+]. We conclude that AII can stimulate both vasopressin and oxytocin release, acting directly upon SON neurons and also that both the SFO and AV3V are important receptive sites for AII (although the SFO is relatively more sensitive) which contributes SON input and modulates release of these hormones.

Chronic methamphetamine and its withdrawal modify behavioral and neuroendocrine circadian rhythms

Chronic methamphetamine (MA) administration via the drinking water not only induced hyperactivity, but phase delayed the rat rest-activity cycle under entrained conditions. The minimum and/or maximum of the rhythms in eating, drinking, body weight, core body temperature and plasma/urine corticosterone were delayed. The different phase shifts of peak and trough values can also be a result of modulation in the wave form of the rhythms. The fall, but not the rise, of nocturnal pineal melatonin secretion occurred 4 hours earlier in MA-treated rats than in controls: this pattern was still present 1 week after withdrawal, but no longer after 4 weeks withdrawal. Neither chronic MA nor its withdrawal had any effect on plasma thyrotropin. These patterns after chronic MA intake fall into two groups: those rhythms whose peak and/or trough are delayed and those that are not. We thus interpret chronic MA application as modulating the eating rhythm (though not directly through rhythmic MA levels in the CNS), and that this in turn changes all food-dependent rhythms. In contrast, the circadian rhythms of melatonin and thyrotropin remain independent.

Electrophysiological properties of neurons in the caudal ventrolateral medulla projecting to the paraventricular nucleus of the hypothalamus in rats

Extracellular recordings were made from neurons in the caudal ventrolateral medulla in urethane-chloralose-anesthetized rats. Stimulation of the paraventricular nucleus (PVN) in the hypothalamus evoked antidromic action potentials in 71 neurons. On the basis of antidromic spike latencies, these neurons could be divided into fast- (24 neurons) and slow-conducting cell groups (47 neurons). Slow-conducting cells showed irregular and slow spontaneous discharges, while a majority of the fast-conducting cells did not show spontaneous discharges. The spontaneous activity of slow-conducting cells was suppressed by i.v. clonidine administration. The effects of clonidine could be consistently reversed by administration of the alpha 2-adrenergic antagonist, yohimbine. The responses by clonidine and yohimbine remained unimpaired in baroreceptor-denervated rats. Vagus nerve stimulation produced an excitation in 80% of slow-conducting cells tested. Baroreceptor activation induced by i.v. administration of phenylephrine inhibited about half of slow-conducting cells tested. Similar elevation of blood pressure in baroreceptor-denervated rats did not show any effect. These physiological and pharmacological properties of slow-conducting cells were similar to those previously reported for catecholaminergic cells in other parts of the brain. The results show the existence of two different populations among neurons in the caudal ventrolateral medulla which project directly to the PVN, and suggest that the presumed A1 catecholaminergic cells are involved in the afferent pathway from cardiovascular baroreceptors and the vagus nerve to the PVN.