Non-stereospecific excitatory actions of morphine may be due to GABA-A receptor blockade.

An explosive motor behavior (EMB) similar to that seen following morphine injection into the rat periaqueductal gray (PAG) was observed following an injection of GABA-A receptor antagonists into the rat PAG. In general, the potencies of certain opiates and known GABA-A antagonists in producing EMB following their injections into the PAG paralleled their potencies as GABA antagonists in a radioreceptor assay. We suggest that one of the dual actions of morphine in the CNS may be GABA blockade.