Role of GABA(A) receptors in the retrorubral field and ventral pallidum in rat jaw movements elicited by dopaminergic stimulation of the nucleus accumbens shell.

The role of gamma-aminobutyric acid (GABA)(A) receptors in the retrorubral field in the production of rat repetitive jaw movements was examined, as this nucleus receives a GABAergic, inhibitory input from the nucleus accumbens and is connected with the parvicellular reticular formation, a region that is directly connected with the orofacial motor nuclei. The GABA(A) receptor antagonist bicuculline (150 ng/0.2 microl per side) significantly produced repetitive jaw movements when injected bilaterally into the retrorubral field, but not the ventral pallidum. The effects of bicuculline were GABA(A) receptor specific, because the effects were abolished by muscimol, a GABA(A) receptor agonist, given into the same site. The bicuculline-induced jaw movements differed qualitatively from those elicited by injection of a mixture of (+/-)-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol (SKF 82958; 5 microg) and quinpirole (10 microg), agonist at dopamine D1 and D2 receptors respectively, into the nucleus accumbens shell. Nevertheless, bilateral injections of muscimol (10 ng, 25 ng and 50 ng/0.2 microl per side) into the retrorubral field significantly inhibited jaw movements evoked by the dopamine D1/D2 receptor stimulation in the nucleus accumbens shell. Bilateral injections of bicuculline (50 ng and 150 ng/0.2 microl per side) also reduced the dopamine D1/D2 receptor-mediated jaw movements. Essentially similar effects were obtained when muscimol and bicuculline were given into the ventral pallidum, a region that is also known to receive GABAergic inhibitory inputs from the nucleus accumbens. In conclusion, GABA(A) receptor blockade in the retrorubral field elicits characteristic repetitive jaw movements, and the GABA(A) receptors in that region as well as in the ventral pallidum modulate the accumbens-specific, dopamine D1/D2 receptor-mediated jaw movements.