PARTICIPATION OF ENDOGENOUS GALANIN IN THE SUPPRESSION OR BARORECEPTOR REFLEX RESPONSE BY LOCUS-COERULEUS IN THE RAT

We evaluated the potential participation of endogenous brain galanin ( GAL) in tile suppression of baroreceptor reflex (BRR) response by locu s coeruleus (LC), using adult male Sprague-Dawley rats anesthetized wi th pentobarbital sodium (40 mg/kg, i.p., with 15 mg/kg/h i.v. infusion supplements). Our physiologic and pharmacologic results demonstrated that bilateral microinjection of GAL antiserum (1:20, 20 nl) into the nucleus tractus solitarii (NTS), the terminal site for baroreceptor af ferent fibers, significantly attenuated the suppressive effect of LC o n the ERR response. Pretreatment with the same amount of normal rabbit serum (1:20) or heat-inactivated GAL antiserum (1:20), oil the other hand, was ineffective. Microinjection of GAL (100 pmol) into the bilat eral NTS also appreciably depressed the ERR response. Histochemically, retrogradely labeled neurons were distributed in the LC following mic roinjection of fast blue into the NTS. Immunofluorescent staining furt her revealed that some of these fast blue labeled LC neurons also show ed positive immunoreactivity to GAL. These results suggest that a dire ct galaninergic projection to the NTS may participate in the suppressi on of BRR response by the LC.