On the interaction of drugs with the cholinergic nervous system. II. Cross-tolerance between phencyclidine derivatives and cholinergic drugs.

A symmetrical cross-tolerance was found between two phencyclidine derivatives--phencyclidine and cyclohexamine--and also between two cholinergic drugs--physostigmine and oxotremorine. On the other hand, mice rendered tolerant to the phencyclidine derivatives showed cross-tolerance to these cholinergic drugs, but no cross-tolerance was observed in the opposite direction. The applicability of such experiments to the elucidation of neurochemical interactions of centrally acting drugs is discussed.