Effects of an alcohol diet on locomotor activity and the acquisition of brain self-stimulation in rats

Effects of chronic ethanol consumption on rat GABA(A) and strychnine-sensitive glycine receptors expressed by lateral/basolateral amygdala neurons

It is well known that the anxiolytic potential of ethanol is maintained during chronic exposure. We have confirmed this using a light-dark box paradigm following chronic ethanol ingestion via a liquid diet. However, cessation from chronic ethanol exposure is known to cause severe withdrawal anxiety. These opposing effects on anxiety likely result from neuro-adaptations of neurotransmitter systems within the brain regions regulating anxiety. Recent work highlights the importance of amygdala ligand-gated chloride channels in the expression of anxiety. We have therefore examined the effects of chronic ethanol exposure on GABA(A) and strychnine-sensitive glycine receptors expressed by acutely isolated adult rat lateral/basolateral amygdala neurons. Chronic ethanol exposure increased the functional expression of GABA(A) receptors in acutely isolated basolateral amygdala neurons without altering strychnine-sensitive glycine receptors. Neither the acute ethanol nor benzodiazepine sensitivity of either receptor system was affected. We explored the likelihood that subunit composition might influence each receptor's response to chronic ethanol. Importantly, when expressed in a mammalian heterologous system, GABA(A) receptors composed of unique alpha subunits were differentially sensitive to acute ethanol. Likewise, the presence of the beta subunit appeared to influence the acute ethanol sensitivity of glycine receptors containing the alpha(2) subunit. Our results suggest that the facilitation of GABA(A) receptors during chronic ethanol exposure may help explain the maintenance of ethanol's anti-anxiety effects during chronic ethanol exposure. Furthermore, the subunit composition of GABA(A) and strychnine-sensitive glycine receptors may ultimately influence the response of each system to chronic ethanol exposure.

Housing conditions alter the acquisition of brain self-stimulation and locomotor activity in adult rats

Rats were implanted with stimulating electrodes in the medial forebrain bundle-lateral hypothalamus (MFB-LH). After recovery from surgery, they were assigned to one of two groups equalized for body weight. One group was housed four animals to a cage and animals in the other group were housed individually. After four weeks in these housing conditions, animals were tested during the fifth week for locomotor activity in five daily 15-min sessions, and their reactivity to handling was also measured. During the sixth and seventh weeks, animals were allowed to self-train for brain stimulation (ICSS) during daily 15-min sessions. Animals housed in groups had higher levels of locomotor activity and were less reactive to handling than were animals housed individually. When tested for the acquisition of ICSS, animals housed as a group made more responses than did animals housed individually. These results indicate that, within the time frame of a few weeks, the housing conditions of adult animals caused differences in both unconditioned behavior, such as locomotor activity, and in the acquisition of a highly reinforcing brain self-stimulation task.