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 γ-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 μl 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-1 H-3-benzazepine-7,8-diol (SKF 82958; 5 μg) and quinpirole (10 μg), 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 μl 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 μl 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.