Brain Research Bulletin, Vol. 5, pp. 745-749. Printed in the U.S.A. Activation and Lateralization of Sensorimotor Field for Perioral Biting Reflex by Intranigral GABA Agonist and by Systemic Apomorphine in the Rat J. P. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA HUSTON,’ B. NEF, G. PAPADOPOULOS2 AND H. WELZL zyxwvutsrqponmlkjihgfedcba Institute of Psychology ZZZ,University of Diissefdor- Universittitsstrasse 1, D-4000 Diksefdorf Federal Republic of Germany Received 6 June 1980 HUSTON, J. P., B. NEF, G. PAPADGPGULOS AND H. WELZL. Activation and luteralization ofsensorimotorfieldfor period biting reflex by intranigral GABA agonist and by systemic apomorphine in the rat. BRAIN RES. BULL. 5(6) ‘745-749, 1980.- In Experiment 1 unilateral injection of the GABA agonist, muscimol (20 ng in 0.1 .pl saline) into the substantia nigra (SN) of rats elicited con&aversive turning and a correlated transient asymmetry in responsiveness to tactile stimulation of the mouth area. On the side of the face contralateral to the injected SN they responded stronger than on the ipsilateral side, and, furthermore, they responded to tactile stimulation with a withdraws of the lip, folIowed by a vigorous biting of the probe. In Experiment 2, systemic injection of apomorphine also sensitized the periorai biting response to tactile stimulation. Unilateral injection into the SN of 8 pg 6-OHDA blocked this response to stimulation of the side of the face ipsilateral to the lesion. The experiments demonstrate: (1) pharmacological control of sensory-motor neglect, the asymmetry being determined by the direction of turning; and (2) a possible neuropharmacological basis of the perioral biting reflex, which may be related to certain types of aggressive behaviors. GABA Muscimol Picrotoxin Apomorphine Amphetamine Substantia nigra ~Hydroxydopamine Turning behavior Biting Aggressive behavior Sensory-motor neglect UNILATERAL destruction of the nigro-striatal dopamine system by injection of 6-hydroxydopamine into the substan- tia nigra (SN) leads to the well known syndrome of ipsiversive turning (to the lesioned side) [26,28] accompanied by sensory inattention or neglect to tactile and other stimulation ad- ministered to the face and body contralateral to the lesioned side [4, 10, 13, 22, 291. The present study was designed to investigate the rela- tionship between direction of turning and the lateralized sensory-motor neglect, the hypothesis being that the sen- sory-motor deficit is directly related to the postural asym- metry and direction of turning, and, therefore, might be brought under ph~acologic~ control insofar as transient ipsi- and contraversive turning can be induced by various pharmacological manipulations of the substantia nigra [ 181. We expected, for example, to find an ipsiversive sensory neglect during the period of contraversive turning induced by the unilateral intranigral injection of the GABA agonist muscimol [15, 16, 17, 201. Experiment 1 examined and con- firms this prediction along with our chance finding [P] that unilateral intranigral injection of muscimol sensitizes the rat to respond to tactile stimulation of the vibrissae and mouth region on the side of the face contralateral to the injected SN with biting of the probe. Systemic injection of apomorphine reverses the direction of turning in rats with unilateral 6-OHDA lesion of the ni- grostriatal dopamine neurons from ipsi- to contraversive, presumably as a result of a supersensitivity of denervated dopamine receptors 1271. Experiment 2 was designed to examine the possibility of a transient reversal in the sen- sory-motor inattention (from the contra- to the ipsilateral side of the face) concomitant with the reversal in direction of turning. This possibility was considered particularly promis- ing since Marshall [12] has already reported that sensory neglect produced by bilateral nigral 6-OHDA lesions is at- tenuated by systemic injection of apomo~hine. Secondly, since apomo~hine also is known to induce biting behavior [l, 6, 19, 241, it was of interest in light of the resuits of Experiment 1 to determine whether apomorphine-induced biting would be lateralized by a unilateral 6-OHDA lesion of SN catecholamine neurons. EXPERIMENT 1: EFFECTS OF UNILATERAL INJECTION OF MUSCIMOL AND PICROTOXIN INTO SUBSTANTIA NIGRA The intent of this study was to assess the behavioral ef- fects of injecting the GABA agonist muscimol and the GABA ‘This study was supported by a grant from the Ministry of Science of the State of Nosh-Rhine Westphalia (G.F.R.). *Now at the Department of Experimental Pharmacology, University of Athens, Greece. Copyright o 1980 ANKHO International Inc .-0361-9230/80/060745-05$01.00/O