title: Plasma leptin inhibits the response of nucleus of the solitary tract neurons to aortic baroreceptor stimulation.
abstract: Leptin receptors have been identified within the nucleus of the solitary tract (NTS) and leptin injections into the caudal NTS inhibit the baroreceptor reflex. However, whether plasma leptin alters the discharge of NTS neurons mediating aortic baroreceptor reflex activity is not known. A series of electrophysiological single unit recording experiments was done in the urethane-chloralose anesthetized, paralyzed and artificially ventilated Wistar and Zucker obese rat with either their neuroaxis intact or with mid-collicular transections. Single units in NTS antidromically activated by electrical stimulation of depressor sites in the caudal ventrolateral medulla (CVLM) were found to display a cardiac cycle-related rhythmicity. These units were tested for their responses to stimulation of the aortic depressor nerve (ADN) and intra-carotid injections of leptin (50-200ng/0.1ml). Of 63 single units tested in NTS, 33 were antidromically activated by stimulation of CVLM depressor sites and 18 of these single units responded with a decrease in discharge rate after intracarotid injections of leptin. Thirteen of these leptin responsive neurons (∼72%) were excited by ADN stimulation. Furthermore, the excitatory response of these single units to ADN stimulation was attenuated by about 50% after the intracarotid leptin injection. Intracarotid injections of leptin (200ng/0.1ml) in the Zucker obese rat did not alter the discharge rate of NTS-CVLM projecting neurons. These data suggest that leptin exerts a modulatory effect on brainstem neuronal circuits that control cardiovascular responses elicited during the reflex activation of arterial baroreceptors.
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada N6A 5C1. john.ciriello@schulich.uwo.ca
authors.forename: John
authors.initials: J
authors.lastname: Ciriello
mesh_terms: D000818:Animals; D001011:Aorta / Q000294:innervation; D017704:Baroreflex; D004558:Electric Stimulation; D020738:Leptin / Q000008:administration & dosage / Q000097:blood / Q000502:physiology*; D008297:Male; D009433:Neural Inhibition; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D011924:Rats, Zucker; D017552:Solitary Nucleus / Q000502:physiology*
chemical_list: D020738:Leptin
keywords: 12M; 4V; 4th ventricle; ADN; ANOVA; AP; Amb; Aortic depressor nerve; CVLM; Cardiovascular reflex pathways; Com; Cu; DMV; Gr; ION; LRN; Leptin; Leptin receptors; MdV; NTS; Obesity; Ob–Rb; ROb; RPa; Sdl; Sg; Slt; Sm; Sp5C; St; analysis of variance; aortic depressor nerve; ap; area postrema; arterial pressure; caudal ventrolateral medulla; cc; central canal; commissural nucleus of the NTS complex; cu; cuneate fasciculus; dorsal motor nucleus of the vagus; dorsolateral nucleus of the NTS complex; hypoglossal motor nucleus; inferior olivary nucleus; lateral nucleus of the NTS complex; lateral reticular nucleus; long form of leptin receptor; medial longitudinal fasciculus; medial nucleus of the NTS complex; medullary reticular nucleus, ventral component; mlf; nucleus ambiguus; nucleus cuneatus; nucleus gelantinous of the NTS complex; nucleus gracilis; nucleus of the solitary tract; py; pyramidal decussation; pyramidal tract; pyx; raphe obscurus; raphe pallidus; solitary tract; spinal trigeminal nucleus