Oral self-administration of ethanol and cocaine in rats

Most laboratory animal studies on self-administration of drugs of abuse use only one drug, whereas humans frequently engage in polydrug use. For this reason, we studied oral self-administration of ethanol (E) and cocaine (C) with the free choice bottle method using a single drug alone, a combination (E and C in separate bottles) or a mixture of both drugs in a single bottl e. Young female rats (45 days) consumed similar amounts of C if offered alo ne (12.4 +/- 7.5 mg/kg/day), in the presence of ethanol (10.6 +/- 3.5) or a s E/C mixture (8.0 +/- 4.0). They also consumed similar amounts of E if off ered alone (3.8 +/- 1.6 ml/kg/day), in the presence of C (2.3 +/- 0.8) or E /C mixture (2.4 +/- 1.1). Voluntary consumption of both drugs varied marked ly among animals but was consistent in a given rat. No correlation occurred between consumption of E and C. Young male rats behaved similarly and cons umed similar amounts of E and C alone, in combination and as mixture. While E consumption was similar, C consumption was higher in female rats. Old ma le rats (180 days) were similar to young male rats. The presence of a sacch arin solution as a distracter had no effect on intake of E or C in young fe males but reduced E intake only in young male rats. In young animals, prior voluntary consumption of either E or C had no effect on subsequent volunta ry consumption of the same or other drug offered in combination. These resu lts indicate that this model may be useful to study polydrug use in humans, that consumption of both E and C is strongly controlled by an individual a nimal, that prior exposure to one drug had no or little effect on a subsequ ent consumption of the same or other drug in combination and that intake of E or C seems to be independent of each other suggesting two independent re ward centers. Copyright (C) 2001 S, Karger AG, Basel.