Systemic Administration of Serotonin Reduces the Excitability of the Raphé Pallidus‐Brown Adipose Tissue Sympathetic Nerve Pathway

Abstract

Activation of 5‐HT1A receptors in the raphé pallidus (RPa) inhibits the skin cooling‐evoked increases in brown adipose tissue (BAT) sympathetic nerve activity (SNA). Our aim was to determine whether intravenous (iv) 5‐HT would affect BAT SNA and if 5‐HT1A receptors in the RPa play a role in mediating any of the effects of iv 5‐HT. In urethane/α‐chloralose anesthetized, neuromuscularly blocked, ventilated rats, electrical stimulation (100–150 μA, single 1 ms pulses) of the RPa evoked compound potentials in BAT SNA. Iv infusion of 5‐HT (500 μg/h) reduced the amplitude of the RPa‐evoked compound potentials in BAT SNA. Skin cooling‐evoked increases in BAT SNA were also inhibited by the iv infusion of 5‐HT, and by an iv bolus of the 5‐HT1A/7 receptor agonist, 8‐OHDPAT (100 μg in 50 μl). Nanoinjection of the 5‐HT1A receptor antagonist, WAY100635 (10 mM, 100 nl), in the RPa completely prevented the iv 8‐OHDPAT‐induced inhibition of BAT SNA, but not that following iv 5‐HT. In conclusion, iv 5‐HT reduces the excitability of the sympathetic pathway from the RPa to BAT, but this effect is not mediated by activation of 5‐HT1A receptors in the RPa. In contrast, activation of 5‐HT1A receptors in the RPa plays a key role in the inhibition of cold‐evoked BAT SNA by iv administration of 8‐OHDPAT.Support or Funding InformationSupported by São Paulo Research Foundation (FAPESP) grant #2017/24232‐9 (C.M.D.M.) and by NIH R01‐NS091066 (S.F.M.).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.