RECOVERY AFTER INTERRUPTED EXPOSURE DURING INDUCTION OF EXPERIMENTAL ALCOHOLISM IN THE RAT

A model of alcoholism founded on a long-term treatment with intermitte nt weekly ethanol exposures [each week a voluntary choice between 10% (w/v) ethanol and water for 24 hr followed by an intraperitoneal (i.p. ) injection of 2.0 g/kg ethanol] was used to test the effect of a 10-w eek interruption of the treatment. Three groups were tested. Group CT had 65 weeks of treatment with no interruption. Group BT started the t reatment at the same time as group CT, but no treatment was given in w eeks 33-42. In group LS, the treatment started at the same time as it was restarted in group BT (week 43). An evaluation period with a conti nuous choice between ethanol and water was started in week 66. During the evaluation period dependence, defined as a voluntary ethanol intak e not influenced by changes in ethanol concentration, was determined b y comparing the intake of a 10% (w/v) reference solution with that of a 5% (w/v) test solution. At the start of the treatment the 24 hr volu ntary ethanol intake in group CT and BT was inhibited maximally after 6-7 weeks of treatment. When group LS was started in week 43, a simila r, but more marked, inhibition developed. In all groups, ethanol intak e rose again after the inhibition. After restarting the treatment in g roup BT, the rats could be divided into two subgroups. Group BT;LI wit h a low intake of ethanol in week 32 had voluntary ethanol intake afte r restarting the treatment which was similar to corresponding data rec orded in group LS when starting the treatment. In group BT;HI with a h igh intake of ethanol in week 32 there was no influence of the break i n the treatment. The voluntary ethanol intake was similar to the corre sponding intake in group CT and not to that seen in group LS. During t he evaluation period, a marked dependence was recorded as a strong cor relation between voluntary intake of ethanol as a 5 and a 10% solution in group CT (r = 0.93; N = 11, P < 0.001). A similar dependence but w ith a lower daily ethanol intake was recorded in group LS (r = 0.88, N = 9, P < 0.01) after a treatment lasting for 22 instead of 65 weeks. A dependence was recorded in group BT;HI (r = 0.97; N = 4, P < 0.05) b ut not in group BT;LI (r = 0.63, N = 7, NS). Thus rats with a low inta ke before the break of the treatment behaved as naive rats starting th e treatment but did not show dependence, while rats with a high intake before the break behaved in the same way as rats continuously exposed to ethanol with regard to the development of dependence.