Electrophysiological effects of serotonin in the solitary tract nucleus of the rat

Abstract

The nucleus tractus solitarius (nTS) is an important site for the integration of visceral information and its modification by afferent neural systems. One such afferent system arises from the raphe nuclei. This study investigated the electrophysiological effects of the primary transmitter of the raphe nuclei, serotonin (5-HT), on neurones in the nTS of the rat. Extracellular single unit recordings were made of the spontaneous activity of nTS neurones in isolated, superfused brainstem slices during bath-application of 5-HT (50, 100, 250, 500, 1000 nM). Twenty-seven of 46 neurones studied (approximately 59%) showed concentration-dependent decreases of firing rate, with a calculated EC50 of 261 nM. An additional 3 neurones displayed excitatory responses, while the remaining 16 were unaffected. The broad-spectrum 5-HT1 antagonist methysergide (200 nM) was highly effective in producing blockade of 5-HT-evoked depressions of neuronal activity (4 of 4), whereas the 5-HT1A receptor-selective antagonist spiroxatrine (5 nM) and the 5-HT2-selective antagonist mianserin (200 nM) were considerably less effective (1 of 5 and 2 of 5, respectively). Seven additional neurones were examined during exposure to the 5-HT1-selective agonist 5-carboxamidotryptamine (5-CT) or the 5-HT2-selective agonist DOI. 5-CT depressed the activity of three of the four neurones tested, the remaining neurone being unresponsive at concentrations up to 50 nM. DOI at concentrations up to 100 nM failed to affect the activity of two of the three neurones tested, and depressed the activity of the third at a concentration of 50 nM.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Stem Control of Swallowing: Neuronal Network and Cellular Mechanisms

“…Local applications of serotonin have been reported to have either inhibitory or excitatory effects on swallowing (123,175). One should note, however, that ionophoretic application of serotonin or serotonergic agents to NTS neurons, particularly the reflex neurons, consistently inhibits the neuronal activity (100,297,298). The antagonistic effects on swallowing are certainly due to differences in the neuronal sensitivity to serotonin and are therefore likely to have resulted from different receptor subsets being activated.…”

Vagal control of the heart: central serotonergic (5‐HT) mechanisms

“…Variable effects of DOI, as seen in vivo , have also been reported by authors performing in vitro studies. Brooks & Albert (1995) reported that activating 5‐HT 2 receptors evoked a depolarization and increases in both the amplitude and frequency of synaptic noise but Feldman (1994) could find no evidence for an excitatory effect. More recent in vivo studies to define more clearly the responses to activation of 5‐HT 2 receptors have demonstrated several important points and may account for the contradictory in vitro data (Sévoz‐Couche et al 2000 a,b ).…”

Preclinical Neuropharmacology of Naratriptan

“…Binding studies with the triptans: sumatriptan and zolmitriptan, showed high intensities of binding sites in the NTS of cats (69,141) or humans (19,163). In an in vitro study, application of 5-HT in the region of neurons in the NTS had an inhibitory effect on their spontaneous firing rate (52). Work from our own laboratory (87) demonstrated that neurons in the NTS can be activated by electrical stimulation of the dura mater, via what appeared to be a monosynaptic input and that this activation was suppressed by iontophoretic application or intravenous injection of naratriptan.…”