Ethanol modulation of excitatory and inhibitory synaptic transmission in rat and monkey dentate granule neurons

The physiological mechanisms underlying the behavioral and cognitive effects of ethanol are not fully understood. However, there is now compelling evidence that ethanol acts, at least in part, by modulating the function of a small group of proteins that mediate excitatory and inhibitory synaptic transmission. For example, intoxicating concentrations of ethanol have been shown to enhance GABAergic synaptic inhibition and depress glutamatergic excitatory neurotransmission in a number of brain regions. Because all of these electrophysiological studies have been performed in rodent brain slice or neuronal culture preparations, direct evidence that ethanol exerts similar effects on synaptic transmission in the primate central nervous system is lacking.

We have therefore developed methods to perform patch-clamp electrophysiological recordings from neurons in acutely prepared monkey (Macaca fascicularis) hippocampal slices. We have used these methods to compare the acute effects of ethanol on excitatory and inhibitory synaptic transmission in rat and monkey dentate granule neurons.

Under our recording conditions, ethanol significantly potentiated gamma-aminobutyric acid type A inhibitory postsynaptic currents in both rat and monkey neurons. In addition, ethanol significantly inhibited NMDA, but not AMPA, excitatory postsynaptic currents in dentate granule neurons from both species. Notably, no significant differences were observed in any of the pharmacological properties of inhibitory or excitatory synaptic responses recorded from rat and monkey neurons.

These data suggest that the differences in the behavioral effects of ethanol that have been observed between rats and higher-order mammals, such as monkeys and humans, may not reflect differences in the sensitivity of some of the major synaptic sites of ethanol action. Moreover, our results provide empirical evidence for the use of rodent brain slice preparations in elucidating synaptic mechanisms of ethanol action in the primate central nervous system.