Volume and dose effects of experimenter-administered ethanol preloads on ethanol seeking and self-administration

Abstract

The present experiment used a behavioral model developed to separate the initial behavior required to obtain access to ethanol (appetitive responding or lever presses) from the actual self-administration (consummatory responding or intake) to test the hypothesis that these responses are under the control of different behavioral/physiological processes, and therefore differentially affected by an ethanol priming dose. In male, Long Evans rats, "preload" volume (0.5 and 2.0ml) and dose (approximately 10%, 25%, and 50% of the total normally consumed in nontreatment sessions translating to 0.1, 0.25, and 0.5g/kg) of ethanol were varied and administered by the experimenter via oral gavage prior to an operant session. Overall, there were no priming effects, or increases, in ethanol-reinforced responding resulting from the ethanol preloads. The findings showed that the low preload volume produced linear, dose-dependent decreases in both intake and seeking. However, while the high volume also produced a linear dose-dependent decrease in ethanol seeking, there was a decrease in intake at every dose. That is, ethanol seeking was insensitive to preload volume, while intake was affected in a dose-dependent manner except at the lowest dose when preload volume did play a role in intake regulation. These findings indicate that "fullness" and pharmacological cues differentially impact the appetitive and consummatory behaviors reinforced by ethanol solutions, with intake being more sensitive to preload volume and seeking being more sensitive to preload pharmacology.

Fig. 1

Mean (±SEM) number of lever-press responses during the 20-min extinction sessions (no ethanol made available) following either the sham gavage or the ethanol preloads (administered 15 min prior to the session) that varied by volume (low volume: lighter bars; high volume: darker bars) and dose as indicated. Asterisks indicate significant difference from sham gavage when analyzed within both volume and dose.

Fig. 2

Mean (±SEM) ethanol intake (g/kg) in reinforced sessions (response requirement of 20) following either the sham gavage or the ethanol preloads (administered 15 min prior to the session) that varied by volume (low volume: lighter bars; high volume: darker bars) and dose as indicated. Asterisks indicate significant difference from sham gavage when analyzed within both volume and dose; plus sign indicates significant difference from sham when analyzed within dose only.