Pro- and anticonvulsant actions of morphine and the endogenous opioids: involvement and interactions of multiple opiate and non-opiate systems.
The proconvulsant actions of high doses of systemic morphine are probably mediated by 3 different systems. One of them produces non-convulsant electrographic seizures and can be activated separately from the others both by intracerebroventricular injections as well as microinjections into discrete subcortical areas. The enkephalins and beta-endorphin, when administered to the same loci, produce similar effects. Pharmacological evidence suggests that specific opiate receptors of the delta-subtype mediate the epileptiform effects produced by this system. The second system mediating proconvulsant effects of systemic morphine is not mediated by stereo-specific opiate receptors. It produces behavioral convulsions, and the GABA-ergic system has been implicated in its action. A third proconvulsant action of systemic morphine can be activated separately from the other two systems by administering this compound with other convulsive agents or manipulations. Specific mu-type opiate receptors are implicated in this effect. In addition to potent proconvulsant effects, systemic morphine also has anticonvulsant properties which are mediated by specific opiate mu-receptors. The conditions under which morphine acts as a proconvulsant rather than an anticonvulsant agent are, as yet, not understood.
D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology* / Q000502:physiology; D001696:Biomechanical Phenomena; D003292:Convulsants / Q000494:pharmacology*; D004347:Drug Interactions; D004361:Drug Tolerance; D004723:Endorphins / Q000008:administration & dosage / Q000494:pharmacology*; D004827:Epilepsy / Q000503:physiopathology; D006801:Humans; D007276:Injections, Intraventricular; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology; D009294:Narcotics / Q000502:physiology; D011957:Receptors, Opioid / Q000502:physiology; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology
D000927:Anticonvulsants; D003292:Convulsants; D004723:Endorphins; D009292:Narcotic Antagonists; D009294:Narcotics; D011957:Receptors, Opioid; D009020:Morphine