There are some reports demonstrating the cardiovascular functions of the ventral tegmental area (VTA). About 20-30% of the VTA neurons are GABAergic, which might play a role in baroreflex modulation. This study was performed to find the effects of
GABA(A),
GABA(B) receptors and reversible synaptic blockade of the VTA on baroreflex. Drugs were microinjected into the VTA of
urethane anesthetized rats, and the maximum change of blood pressure and the gain of the reflex
bradycardia in response to intravenous
phenylephrine (Phe) injection were compared with the preinjection and the control values. Microinjection of
bicuculline methiodide (BMI, 100 pmol/100 nl), a
GABA(A) antagonist, into the VTA strongly decreased the Phe-induced
hypertension, indicating that
GABA itself attenuated the baroreflex.
Muscimol, a
GABA(A) agonist (30 mM, 100 nl), produced no significant changes.
Baclofen, a
GABA(B) receptor agonist (1000 pmole/100 nl), moderately attenuated the baroreflex, however
phaclofen, a
GABA(B) receptor antagonist (1000 pmole/100 nl), had no significant effect. In conclusion, for the first time, we demonstrated that
GABA(A) receptors of the VTA strongly attenuate and
GABA(B) receptors of the VTA moderately attenuate baroreflex in rat.