Acute effects of ethanol on recurrent inhibitory circuits of CA1 neurons in vivo

Centrally-mediated sensory information processing is impacted with increased alcohol consumption in college-aged individuals

Alcohol consumption can have an impact on a variety of centrally-mediated functions of the nervous system, and some aspects of sensory perception can be altered as a result of long-term alcohol use. In order to assess the potential impact of alcohol intake on sensory information processing, metrics of sensory perception (simple and choice reaction time; static and dynamic threshold detection; amplitude discrimination with and without pre-exposure to conditioning stimulation) were tested in college-aged subjects (18 to 26 years of age) across a broad range of levels of alcohol consumption. The analysis indicated no detectable associations between reaction time and threshold measures with alcohol consumption. However, measures of adaptation to short duration (0.5s) conditioning stimuli were significantly associated with alcohol consumption: the impact of a confounding conditioning stimulus on amplitude discriminative capacity was comparable to values reported in previous studies on healthy controls (28.9±8.6) for light drinkers while the same adaptation metric for heavy drinkers (consuming greater than 60 drinks per month) was significantly reduced (8.9±7.1). The results suggest that while some of the sensory perceptual metrics which are normally impacted in chronic alcoholism (e.g., reaction time and threshold detection) were relatively insensitive to change with increased alcohol consumption in young non-alcoholic individuals, other metrics, which are influenced predominantly by centrally-mediated mechanisms, demonstrate a deviation from normative values with increased consumption. Results of this study suggest that higher levels of alcohol consumption may be associated with alterations in centrally-mediated neural mechanisms in this age group.

electrophysiology and immunohistochemistry in the hippocampal ca1 and the dentate gyrus of rats chronically exposed to 1-bromopropane, a substitute for specific chlorofluorocarbons

1-Bromopropane is a newly introduced substitute for specific chlorofluorocarbons whose production was prohibited because of depletion of ozone layers. In this study, we analyzed disinhibitory effects induced by repetitive inhalation of 1-bromopropane for 12 weeks in the hippocampal CA1 and the dentate gyrus. In addition, reversal of the disinhibitory effects was examined 4 weeks after 1-bromopropane inhalation ceased. Exposure rats were placed in a stainless steel inhalation chamber at a concentration of 700 ppm, while the control group was provided only room air in the same type of chamber. Paired-pulse inhibition of population spike was considerably decreased (P<0.05) at 5 ms interpulse intervals in the CA1, and at 10 and 20 ms (P<0.05) interpulse intervals in the dentate gyrus in slices obtained from exposed rats following 4-, 8- and 12-week inhalation periods. The paired-pulse inhibition was decreased at 5 ms interpulse intervals in the dentate gyrus after 12 weeks of inhalation. These changes were not associated with the paired-pulse ratio of field excitatory postsynaptic potentials, suggesting a reduction of recurrent inhibition. The disinhibition was counteracted with the N-methyl-d-aspartate receptor antagonist dl-2-amino-5-phosphonopentameric acid in the dentate gyrus, whereas it was unchanged in the CA1. Tiagabine, a selective inhibitor of GABA transporter GAT1, increased the paired-pulse inhibition in the dentate gyrus, and the increase was less in the exposed rats compared with control rats (P<0.0003). The changes in both areas recovered to control levels 4 weeks after cessation of inhalation. Our electrophysiological studies suggest differential and reversible disinhibitory effects in the dentate gyrus and the CA1. 1-Bromopropane-induced disinhibition was further analyzed by immunohistochemical methods. There were no apparent morphological defects in either excitatory or inhibitory neuronal components, supporting the reversibility of physiological changes. In conclusion, chronic inhalation of 1-bromopropane induces a disinhibition in the CA1 and dentate gyrus that is reversible following cessation of exposure.