Catecholamine modulation of enkephalin-induced electrophysiological responses in cerebral cortex

The interaction between locally applied D-Ala2-methionine enkephalinamide (2dA) and catecholamine inputs to frontal cortex was investigated in rats. Parenteral administration of antipsychotic agents known to block catecholamines receptors, such as spiroperidol, alpha-flupenthixol and (+)-butaclamol, reversibly antagonized enkephalin-induced depressions. The biochemically inactive isomers of these antipsychotics, beta-flupenthixol and (-)-butaclamol, manifested no such activity. Unilateral lesions of the catecholaminergic projections to frontal cortex, produced by interstitial injection of 6-hydroxydopamine, resulted in an ipsilateral decrease in 2dA efficacy and in an elimination of the antagonisms of 2dA depressions by antipsychotic agents. The depressions caused by 2dA were not antagonized by iontophoretically applied Mg++. It is concluded that intact catecholaminergic transmission is required for the full expression of enkephalin-induced depressions in frontal cortex and that this mechanism probably does not involve presynaptic release. Taken together with other recently published data, these results suggest that catecholamines may act as postsynaptic modulators to augment responsiveness to enkephalins.