C-FOS INDUCTION IN THE ROSTROVENTROLATERAL MEDULLA BY 5-HT3 RECEPTOR ACTIVATION IN THE NUCLEUS-TRACTUS-SOLITARIUS

THE nucleus tractus solitarius (NTS) plays a crucial role in the refle x control of sympathetic tone through direct projections to the caudal and rostral regions of the ventrolateral medulla (CVLM and RVLM respe ctively). 5-HT3 receptor stimulation in the NTS increases both blood p ressure and sympathetic tone. In order to investigate whether the vent rolateral medulla participates in these effects, the expression of c-F os protein, a marker of neuronal activation, was examined at this leve l after intra-NTS microinjections of 1-(m-chlorophenyl)biguanide, a se lective 5-HT3 receptor agonist. A marked increase (93%) in the density of c-Fos-immunoreactive neurons was restricted to the most rostral pa rt of the RVLM after this treatment. This effect could be prevented by prior intra-NTS microinjection of ondansetron, a selective 5-HT3 anta gonist. These results suggest the participation of sympathoexcitatory neurons in the rostral RVLM in the presser response to 5-HT3 receptor stimulation in the NTS. (C) 1998 Rapid Science Ltd.