The superior colliculus contains a discrete region involved in the control of jaw movements:: role of GABAA receptors

The role of GABA(A) receptors in the superior colliculus in the production of rat repetitive jaw movements was examined, as this nucleus receives tonic GABAergic inhibitory inputs from the dorsolateral part of the substantia nigra pars reticulata and the entopeduncular nucleus. Both regions are also connected with the ventrolateral striatum where stimulation of either dopamine or acetylcholine receptors has been found to elicit distinct types of jaw movements in rats. The GABA(A) receptor antagonist bicuculline (50 and 150 ng/0.2 mul per side) dose-dependently produced repetitive jaw movements only when injected bilaterally into a circumscribed region (A 3.0) of the lateral deeper layers of the superior colliculus; this region is known to receive input predominantly from the dorsolateral part of the substantia nigra pars reticulata. 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 (SYF 82958; 5 mug) and quinpirole (10 mug), agonist at dopamine D1 and D2 receptors, respectively, or carbachol (2.5 mug), an acetylcholine receptor agonist, into the ventrolateral striatum. Nevertheless, injection of muscimol into the lateral deeper layers of the superior colliculus (A 3.0) inhibited jaw movements evoked by the dopamine D1/D2 receptor stimulation. Conversely, the jaw movements evoked by acetylcholine receptor stimulation were enhanced by injection of muscimol into the superior colliculus. In conclusion, GABA(A) receptor blockade in a circumscribed region (A 3.0) of the lateral deeper layers of the superior colliculus elicits characteristic repetitive jaw movements, and the GABA(A) receptors in that region modulate the dopamine D1/D2 receptor-mediated and acetylcholine receptor-mediated jaw movements in an opposite manner. (C) 2003 Elsevier Science B.V. All rights reserved.