GABAergic systems in the nucleus tractus solitarius regulate noradrenaline release in the subfornical organ area in the rat.
Previous studies have shown that catecholaminergic neurons in the nucleus tractus solitarius (NTS) with ascending projections to the subfornical organ (SFO) are highly sensitive to gamma-aminobutyric acid (GABA). To clarify the role of the GABAergic system in the NTS in the regulation of the activity of noradrenergic NTS projections to the SFO, the present study was carried out to investigate the effects of local administration (50 nl) of GABA, the GABA(A) agonist muscimol, the GABA(B) agonist baclofen, the GABA(A) antagonist bicuculline or the GABA(B) antagonist phaclofen into the NTS on the release of noradrenaline (NA) in the region of the SFO using microdialysis techniques in rats under urethane anesthesia. Microinjections of GABA (10(-4) - 10(-2) M) into the region of the NTS significantly decreased the NA release in the SFO area. Injections of either muscimol (10(-4) - 10(-2) M) or baclofen (10(-5) - 10(-3) M) into the NTS region significantly attenuated the NA release in the SFO area. Injections of bicuculline (10(-5) and 10(-4) M), but not phaclophen (10(-6) - 10(-4) M), into the NTS region significantly enhanced the NA release in the SFO area, suggesting that the GABAergic system in the NTS may tonically inhibit the NA release in the SFO area through a GABA(A) receptor mechanism. Neither injection of these drugs in any of the doses used in this study into the NTS region caused any significant changes in the NA release in the sites away from the SFO. Injections of vehicle (50 nl) into the NTS region had no significant effect on the NA release in either the SFO area or the sites away from the SFO. These results suggest that the GABAergic system in the NTS may serve to decrease the release of NA in the SFO area and the two types of GABA receptors are involved in the modulation of the NA release.
Tanaka
Junichi
J
Neuroscience Program, Teaching and Memory, Naruto University of Education, Tokushima, Japan. tanakaj@naruto-u.ac.jp
Mashiko
Norifumi
N
Kawakami
Ayako
A
Ushigome
Akihiko
A
Nomura
Masahiko
M
D000704:Analysis of Variance; D000818:Animals; D001418:Baclofen / Q000031:analogs & derivatives* / Q000494:pharmacology; D001640:Bicuculline / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D008297:Male; D017551:Microdialysis / Q000379:methods; D009118:Muscimol / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017552:Solitary Nucleus / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D013356:Subfornical Organ / Q000187:drug effects / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D018755:GABA Agonists; D018756:GABA Antagonists; C052329:phaclofen; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; D001418:Baclofen; D009638:Norepinephrine; D001640:Bicuculline