Neurons in the caudal ventrolateral medulla mediate the somato-sympathetic inhibitory reflex response via GABA receptors in the rostral ventrolateral medulla.
In urethane-anesthetized rabbits, stimulation of the sural nerve, consisting of cutaneous afferents (A-fibers), evoked reflex responses consisting of an early small excitatory component followed by a prolonged inhibitory component in renal sympathetic nerve activity. Bilateral injections of GABA antagonist, bicuculline (4 nmol/site), into the rostral ventrolateral medulla (RVLM), where sympatho-excitatory reticulospinal neurons are located, attenuated the inhibitory component in a dose-dependent manner as well as the inhibition evoked by stimulation of the aortic nerve A-fibers (baroreceptor afferents). Bilateral injections of a neurotoxic agent, kainic acid (4 nmol/site, 3 sites/side), into the caudal ventrolateral medulla (CVLM), where sympatho-inhibitory neurons with axonal projection to the RVLM are located, diminished these sympatho-inhibitory responses. Therefore it is concluded that the sympatho-inhibition evoked by activation of somatic afferents was mediated by neurons in the CVLM and by GABA receptors in the RVLM, as was the sympatho-inhibition associated with the arterial baroreceptor reflex. Bilateral injections of kynurenic acid (4 nmol/site, 3 sites/side) into the CVLM did not affect the somato-sympathetic reflex response, but diminished the sympatho-inhibition produced by activation of the baroreceptor afferents. Sympatho-inhibitory neurons in the CVLM were activated by glutamate when baroreceptor afferents were activated, but another excitatory transmitter may participate in the somato-sympathetic reflex in the CVLM.
Masuda
N
N
Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki, Japan.
Ootsuka
Y
Y
Terui
N
N
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D007608:Kainic Acid / Q000494:pharmacology; D007736:Kynurenic Acid / Q000494:pharmacology; D008297:Male; D008526:Medulla Oblongata / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects*; D009475:Neurons, Afferent; D011817:Rabbits; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D005680:gamma-Aminobutyric Acid; D007736:Kynurenic Acid; D007608:Kainic Acid; D001640:Bicuculline