A comparison of GABAergic influences on the analgesic responses to morphine and pentazocine.

1. The interactions of three GABAergic compounds, gamma-acetylenic GABA, gamma-vinyl GABA and ethylenediamine with the analgesic effects of morphine and pentazocine were examined in mice using the hot plate and tail immersion tests. 2. A significant increase in reaction time induced by morphine was noted in the tail immersion test after pretreatment with the drugs acting through GABA functions. 3. The inhibitors of GABA transaminase, gamma-acetylenic GABA and gamma-vinyl GABA, and the GABAmimetic ethylenediamine did not significantly change the analgesic action induced by pentazocine. 4. In the hot plate test the three GABAergic compounds antagonized the analgesic effects of pentazocine in contraposition with previous results indicating that morphine-induced analgesia is increased by pretreatment with those agents. 5. These findings suggest that GABAergic and opiopeptidergic systems are interconnected through mu receptors, whereas the kappa opiate systems seem to be unrelated to GABA functions.