GABA Modulates Baroreflex in the Ventral Tegmental Area in Rat

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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 GABAA, GABAB 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 GABAA antagonist, into the VTA strongly decreased the Phe-induced hypertension, indicating that GABA itself attenuated the baroreflex. Muscimol, a GABAA agonist (30 mM, 100 nl), produced no significant changes. Baclofen, a GABAB receptor agonist (1000 pmole/100 nl), moderately attenuated the baroreflex, however phaclofen, a GABAB receptor antagonist (1000 pmole/100 nl), had no significant effect. In conclusion, for the first time, we demonstrated that GABAA receptors of the VTA strongly attenuate and GABAB receptors of the VTA moderately attenuate baroreflex in rat. Synapse 69:592–599, 2015. © 2015 Wiley Periodicals, Inc.

The figure shows that the hypertension induced by i.v. injection of phenylephrine before and minutes after GABAA receptor antagonist (BMI) injection into the VTA. BMI strongly augments baroreflex by decreasing the hypertension induced by phenylephrine. Overall, activation of GABAA and GABAB receptors of the VTA attenuates baroreflex.

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