Operant behavior in conditions of activation and blockade of neostriatal muscarinic receptors.

Chronic experiments were performed on four dogs using a model of an operant defensive reflex associated with maintaining a flexion posture to study the effects of bilateral intraneostriatal microinjection of the non-selective muscarinic receptor agonist carbachol, the selective D2 dopamine receptor blocker raclopride, and the selective M1 muscarinic receptor blocker pirenzipine on the performance of the operant defensive reflex and differentiation of signals. The results show that microinjection of carbachol induced increases in the tonic component and inhibition of the phasic component of the reflex, an ordering rearrangement of the posture, and increases in the amplitudes of its components. Raclopride microinjection gave similar but less marked results. The greatest effects with both substances were seen using differential stimuli. There were sharp increases in the process of differentiation of sound signals. Pirenzipine microinjections gave the opposite result. These data are assessed on the basis of concepts of the existence of two efferent outputs from the neostriatum with opposite effects on their targets and the roles of muscarinic and dopamine receptors in triggering and blocking these effects.