Effect of morphine and morphine-like drugs on carbachol-induced fighting in cats

In the present experiments, morphine, methadone or pethidine was injected into the cerebral ventricle of the unanesthetized cat after fighting was induced with carbachol injected previously. The fighting evoked by carbachol was sensitive to the depressant action of morphine or pethidine but not to the depressant effect of methadone. The most likely explanation of the depressant effects of the former compounds is that they act on the postsynaptic receptors of central cholinergic neurons.