Central effects of 5‐HT on respiratory rhythm in newborn rats in vivo

Abstract

The role of 5-HT in inducing apnoeas (a major element in sudden infant death syndrome) is controversial because while 5-HT is a respiratory depressant in vivo, it evokes respiratory analeptic effects when applied to the isolated brainstem of the newborn rat. In decerebrate newborn rats, the electrical activity of the diaphragm and that of a hypoglossally innervated tongue muscle, as well as the cardiac frequency (Fc), were recorded before and after the application of 5-HT and related agents to the floor of the IVth ventricle. To assess the spontaneous variability in inspiratory frequency (Fi) and Fc, a sham group was studied. A decrease in Fi was observed in response to 5-HT. This respiratory depressant effect was associated with an activation of the tongue muscle, but there was no change in Fc. Application of agonists elicited a small increase in Fi linked to activation of 5-HT1A receptors, and decreases in both Fi and the activity of the tongue muscle resulting predominantly from activation of 5-HT2 receptors. The decrease in Fi was much smaller in newborn rats than that reported in newborn kittens. Indeed, in newborn rats, we did not observe long-lasting apnoeas. Our results differ from those obtained from the newborn rat in vitro, inasmuch as in vivo 5-HT essentially depressed the respiratory rhythm generator. The role of the afferent system appears to be crucial in modulating the action of 5-HT.

Differential respiratory control of the upper airway and diaphragm muscles induced by 5-HT1A receptor ligands

“…These studies were performed in vivo in anesthetized or decerebrate animals [23,24], in conscious animals [38,39], or in vitro [40,41]. As in our previous work [26], this study also confirms that 8-OHDPAT decreased RF in rats under liquid anesthesia.…”

“…5-HT also directly influences respiratory activities of the DIA and UAM [19][20][21][22][23][24]. In addition, electrical activity of brainstem serotonergic neurons located in the raphe nuclei depends on sleep-wake states, and 5-HT neurons play a role in controlling the sleep-wake cycle [18,25].…”

5-HT2 receptor subtypes mediate different long-term changes in GABAergic activity to parasympathetic cardiac vagal neurons in the nucleus ambiguus

“…In decerebrate adult cats (Rose et al, 1995), anesthetized adult rats (Fenik and Veasey, 2003), and decerebrate newborn rats ((Khater-Boidin et al, 1999;Glerant et al, 2005) 5-HT induced an increase in hypoglossal activity due to activation of 5-HT 2 receptors. The results in this study are in agreement with most other studies since a single application of the 5-HT 2 receptor agonist α-Me-5-HT produced a significant increase in fictive inspiratory burst frequency, similar to that observed in a majority of other studies (Schwarzacher et al, 2002).…”

Time- and dose-related effects of three 5-HT receptor ligands on the genioglossus activity in anesthetized and conscious rats

“…The whole of the studies in anesthetized animals reported an increase in the respiratory rate [9,30,31] supported by in vitro [32], decerebrated [33], or conscious animals [34,35]. However, none of the studies in intact anesthetized animals [9,30,31] used ketamine known as a blocker of the glutamate NMDA receptors.…”