COMPULSIVE GNAWING IN RATS AFTER IMPLANTATION OF DRUGS INTO THE VENTRAL THALAMUS. A CONTRIBUTION TO THE MECHANISM OF MORPHINE ACTION

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Abstract
1 Implantation of morphine into various parts of the corpus striatum of rats evokes only weak gnawing responses. 2 Deposition of apomorphine, morphine or methadone in the region of the nucleus ventralis thalami produces a biphasic response, i.e. general excitation, followed by a period of intense gnawing. 3 The effect of both apomorphine and morphine is blocked by chlorpromazine, haloperidol and pimozide. However, pretreatment with α-methyltyrosine methyl ester or α-methyldopa prevents only the gnawing response to morphine, but not to apomorphine. 4 Systemic nalorphine, morphine or pethidine suppress the gnawing response, evoked by thalamic implants of apomorphine or morphine. 5 Systemic amphetamine potentiates the effect of thalamic deposits of morphine. 6 Compulsive gnawing, following implantation of morphine into the ventral region of the thalamus, probably results from enhanced production and release of catecholamines.