GABA- and glutamate-gated ion channels as molecular sites of alcohol and anesthetic action.

The evidence presented above indicates that GABA- and glutamate-activated ion channels are molecular sites of alcohol and anesthetic action. In view of the important role that these channels play in CNS excitability, it seems likely that the actions of alcohol and anesthetics on these channels contribute significantly to the behavioral effects of these agents. Although the behavioral effects of alcohol and anesthetics may well result from a combination of actions on different ion channels and other molecular sites in the CNS, it is of interest to consider whether the actions of these agents on particular types of ion channels may contribute to particular behavioral effects. In this regard, it should be noted that benzodiazepines potentiate GABAA responses, but do not produce intoxication or general anesthesia in their clinical dose range. Benzodiazepines are widely used clinically, primarily for their anxiolytic actions (26), suggesting that the potentiation of GABAA responses by ethanol and barbiturates may contribute to the anxiolytic effects of these agents. Since kainate and quisqualate channels mediate fast excitatory transmission in the CNS, inhibition of kainate and quisqualate receptor-activated responses would be expected to result in general CNS depression. This suggests that inhibition of kainate and quisqualate receptor-mediated responses may contribute to the general anesthetic effects of ethanol, trichloroethanol and barbiturates. NMDA channels are thought to mediate complex excitatory neural phenomena and cognitive function. In view of this, the observation that ethanol inhibits NMDA receptor-mediated responses over the concentration range that produces intoxication and the correlation between the potency of different alcohols for inhibiting NMDA-activated current and their potency for producing intoxication suggest that ethanol-induced inhibition of NMDA receptor-mediated responses may contribute to the intoxicating effects of ethanol. Although these speculations are no doubt oversimplifications, the recognition that GABA- and glutamate-gated ion channels are molecular sites of alcohol and anesthetic action provides a basis for investigating the molecular mechanisms involved in the action of these agents and the behavioral significance of those actions.