EFFECTS OF CENTRAL GABA RECEPTORS ACTIVATION ON CATECHOLAMINE SECRETION IN RATS

We investigated the effects of muscimol, the GABA(A) receptor agonist, and baclofen, the GABA(B) receptor agonist, injected into the third c erebral ventricle on plasma epinephrine (E) and norepinephrine (NE) le vels in anesthetized rats. Baclofen (0.4-5 nmol) increased plasma NE l evels in a dose dependent manner but did not affect plasma E levels. M uscimol (2.5 nmol) affected neither plasma E nor NE levels. Concomitan t injection of muscimol (2.5 nmol) with baclofen (5 nmol) attenuated t he baclofen (5 nmol)-induced NE secretion. These findings suggest that activation of GABAB receptors in the central nervous system (CNS) sti mulates the sympathetic nervous system but not the adrenal medullary r esponse. In contrast, activation of GABA(A) receptors in the CNS affec ts neither the sympathetic nervous system nor the adrenal medullary re sponse, but inhibits the sympathetic neural activity induced by activa tion of GABA(B) receptors in anesthetized rats.