The Effect Of Acute Alcohol Exposure On The Response Properties Of A17 Neurons

Physiological and behavioral studies have demonstrated that a number of visual functions such as visual acuity, contrast sensitivity, and motion perception can be impaired by acute alcohol exposure. The orientation-and direction-selective responses of cells in primary visual cortex are thought to participate in the perception of form and motion, while spatial response properties are thought to play an important role in many aspects of spatial vision. Thus, investigation on the effect of alcohol to the response properties of primary visual cortex (A 17) neurons could help us better understanding the psycophysical mechanism mediating many aspects of alcohol-induced changes observed in behavioral studies.In this experiment, we used the extracellular single-unit recording technique to examine the response properties of neurons in A17 neurons of adult cats.1.The effect of acute alcohol exposure on the spontaneous activity, visual evoked unit resonse and the signal-to-noise ratio of A17 neuronsThe spontaneous activity and visual evoked response reflect the neuronal activity with and without visual stimuli; while the signal-to-noise ratio indicates the ability of the cell to retrieve signals from noisy backgrounds.We found that acute administration of alcohol results in decreased stimulus driven and spontaneous activity. The proportionally greater decrease in peak response resulted in a reduced signal-to-noise ratio, indicating a reduced signaling capacity of A17 cells in general, which may be partially involved in the impaired information processing after the administration of alcohol.2.The effect of acute alcohol exposure on the orientation selectivity and direction selectivity of A17 neuronsOrientation selectivity and direction selectivity, which refer to the selective response to both the angular orientation and the direction of motion of lines, bars, and edges, are fundamental properties of most neurons in the primary visual cortex and are thought to participate in the perception of form and motion. We found that high concentration alcohol reduces the orientation selectivity of A17 cells. In addition, our results suggest that the changes of orientation selectivity during the administration of alcohol were due to the changes in both bandwidth and orthogonal/optimal responses. The direction selectivity for the whole population exhibited a tendency of decreased selectivity, however, did not approach the statistical significance. The direction selelctivity of strongly direction selective neurons was significantly reduced after acute alcohol administration. Detectable changes in both the preferred orientation/direction and the bandwidth of the orientation tuning curve of strongly orientation-biased A17 cells were also observed after acute alcohol administration.Our results suggest that despite the effect of the enhanced GABA-mediated inhibition, the decreased excitatory input from LGN and/or other cortical cells may have a major role in reducing the orientation selectivity of A17 neurons in overall. Our findings may provide physiological evidence for some alcohol-related deficits in visual function observed in behavioral studies.3.The effect of acute alcohol on the spatial properties of A17 neuronsThe detection of repetitive patterns such as gratings may be achieved by neurons which selectively sensitive to a limited band of spatial frequencies. The spatial frequency selectivity of cortical cell is thought to play an important role in many aspects of spatial vision. In this experiment, we found that alcohol could significantly decrease the spatial frequency selectivity A17 neurons. No significant changes were observed in optimal spatial frequency after acute alcohol exposure. Moreover, the cells that had relatively higher optimal spatial frequencies were more severely affected by alcohol than that had relatively lower optimal spatial frequencies. Considering that the origin of cortical spatial frequency selectivity involves a mechanism similar to that of orientation selectivity in terms of the balance of excitation and inhibition, the predominant mechanism mediating such changes could alco be attributed to the alcohol-induced reduction of the excitotary neurotransmitter system. Our results suggest an additional mechanism by which alcohol impaired some aspects of spatial vision.Conclusion:Acute alcohol exposure could alter the spontaneous, visually evoked response, orientation/direction selectivity and spatial frequency selectivity of A17 neurons. The reduced response to the optimal stimulus may play an important role in mediating such changes. Our research may provide a possible physiological explanation for the alcohol-related deficits in many aspects of visual function observed in behavioral studies.