[Roles of vagal projection areas afferents on vagal input-evoked depressor response]

Vagal afferents project directly or indirectly to several brain areas. In urethane-anesthetized and bilaterally vagotomized rats, either procaine injection into the nucleus tractus solitarii (NTS) or beta-endorphin antiserum injection into the rostral ventrolateral medulla (RVL) markedly decreased the depressor (DpV) and bradycardia response to stimulation of cervical vagal afferents, while propranolol (or beta-endorphin antiserum) injection into the nucleus paraventricularis and procaine injection into the area postrema had no significant effect. In left vagotomized rats, the DpV remained unchanged after methyl atropine (i.v), but the bradycardia response during the DpV was attenuated. Since our previous study has shown the NTS can induce a depressor response via its beta-endorphinergic projections to RVL, the above results suggest that the inhibitory effect of vagal afferents on the RVL-sympathoexcitatory neurons via NTS beta-endorphinergic neurons represents one aspect of the mechanism underlying DpV.