Ethanol (0.75, 1.5, 2.0 g/kg ethyl alcohol) consistently and profoundly narrowed three independent dimensions of behavioral variability (BV) exhibited by rats in an eight-arm radial maze. Thie was true for all doses except the lowest. Rats were run with a replacement procedure wherein rewards (two food pellets) were replaced after they were taken. With no constraints against where, how, or by what route rewards could be taken, the three indices of spontaneous BV recorded were the number of different arms chosen, the sequence of visitation, and instances of deviations from goal-directed activity. The behavior of saline and low-dose groups was widely variable in form and place; and the sequence of behavior was relatively unpredictable from trial to trial and from session to session. Medium and high doses of ethanol exerted a marked organizing influence on behavior. Superfluous topographies were eliminated, sequences became highly, and in many cases perfectly predictable, and spatial BV declined. The considerable promotion of stereotypy by ethanol helps to explain many effects of the drug, e.g., how the drug can in some instances impair, and in others facilitate performance. We propose that the scores from tasks whose mastery entails repetition, few topographies, and rigid structure will be improved by ethanol, but that those requiring change and the sampling of new strategies will be impaired.
Naloxone hydrochloride, in doses of .5 to 10 mg /kg intraperitoneally, reduced water consumption by rats fluid deprived for 24 h. Administered intracerebroventricularly, 100 micrograms of naloxone produced similar effects while doses of 50 micrograms or less had no effect. Naloxone (10 mg /kg) also reduced consumption of a palatable solution (10% sucrose, weight/volume I by nondeprived rats. Morphine sulfate (.5 to 2 mg/kg) failed to increase consumption. twice under morphine sulfate (.5 mg/kg), and once under morphine sulfate (.25 mg/kg). On other days, all rats received placebo injections of physiological saline, the carrier of naloxone and morphine .
PL MS.25
Albino rats implanted with intracerebroventricular (lCV) cannulae were used to investigate the effects of ICV administration of d-alavmethionine enkephalin. Potentially positive affective consequences were assessed by observing rats' movements in an alley, one compartment of which had previously been paired with drug administration. Like morphine (10 mg/kg, intraperitoneally-IP), this enkephalin analogue (10 lAg, ICV) produced a tendency for rats to move toward the place where they had previously experienced the drug's effects. In another experiment, the same dose of d-alavmethionine enkephalin was not sufficient to produce a conditioned taste aversion, as did the lO·mg/kg IP dose of morphine. Rats with a prior history of administration of either d-ala--methionine enkephalin or systemic morphine subsequently consumed significantly more sweetened morphine solution than control animals in a voluntary oral consumption situation with tap water also available. Collectively , these results suggest that enkephalin administration may produce a positive affective state without aversive components and potentiate voluntary consumption of morphine.
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