Differential modulation of sympathetic and respiratory activities by cholinergic mechanisms in the nucleus of the solitary tract in rats

Abstract

The contribution of cholinergic mechanisms of the nucleus of the solitary tract (NTS) to cardiorespiratory control is not completely clear. In the present study, we investigated the involvement of the cholinergic mechanisms in the intermediate NTS (iNTS) and commissural NTS (cNTS) on the control of sympathetic (SNA) and phrenic nerve activity (PNA). Decorticated, arterially perfused in situ preparations of male juvenile rats (60-100g) were used. Acetylcholine (10mm, 60nl) injected into the iNTS reduced SNA (-54±4%, versus vehicle -5±3%; P<0.001) and PNA (-30±4%, versus vehicle -5±6%; P<0.001), whereas injections of ACh into the cNTS increased PNA (30±6%, versus vehicle 5±3%; P<0.001), without changing SNA. Pretreatment with mecamylamine (nicotinic antagonist; 5mm) abolished all the effects of ACh injected into the iNTS or the cNTS, whereas atropine (muscarinic antagonist; 5mm) reduced only the effects of ACh injected into the cNTS. Mecamylamine injected into the cNTS also reduced the tachypnoea in response to peripheral chemoreflex activation. The baroreflex was unaltered by injections of atropine or mecamylamine into the NTS. The results suggest that ACh and mainly nicotinic receptors in the NTS are involved in the modulation of SNA and PNA, with distinct functions between the iNTS and the cNTS. An involvement of the nicotinic receptors in the cNTS in the tachypnoea in response to peripheral chemoreflex activation is also suggested.