Acute ethanol effects on sensory responses of single units in the somatosensory cortex of rats during different behavioral states.

We have investigated the dose-dependence and time-course of ethanol effects on the activity of single neurons in the somatosensory (SI) cortex of behaving, unanesthetized rats. Sensory responses of neurons recorded in the forepaw area of the SI cortex were quantitatively measured by constructing post-stimulus histograms to repetitive stimulation through electrodes chronically implanted in the forepaw. Single units were isolated and held throughout a protocol involving: (1) a control period, (2) intoxication produced by a single dose of ethanol administered IP or IV and (3) recovery for 60 minutes or more. Post-stimulus histograms were generated during three standard behaviors: (1) REST, (2) IMMOBILE AROUSAL (produced by holding the animal), and (3) MOVEMENT (running on a treadmill). In pre-ethanol controls, the immobile arousal condition slightly increased both excitatory and inhibitory components of the sensory response, while the movement condition strongly inhibited them. Ethanol reduced both of these types of behavioral modulation of sensory responses by abolishing the facilitation normally seen during immobile arousal, as well as the inhibitory gating normally seen during movement. Different latency response epochs of post-stimulus histograms were also used to compare the effect of ethanol on fast vs. slow conducting pathways to the SI cortex. Ethanol at low doses (0.3 g/kg bw, IP) was found to selectively reduce the longer latency excitatory response peaks, while sparing the shortest latency response peak. At moderate doses (1.0 g/kg), however, the shortest latency response peak was also reduced. This contrasted with the effects of halothane which, at anesthetic doses, exerted a much more selective reduction of the longer latency responses.(ABSTRACT TRUNCATED AT 250 WORDS)