Sham intake of ethanol in "P" rats

Early ethanol and water consumption: accumulating experience differentially regulates drinking pattern and bout parameters in male alcohol preferring (P) vs. Wistar and Sprague Dawley rats

Alcohol-preferring (P) rats develop high ethanol intake over several weeks of water/10% ethanol (10E) choice drinking. However, it is not yet clear precisely what components of drinking behavior undergo modification to achieve higher intake. Our concurrent report compared precisely measured daily intake in P vs. non-selected Wistar and Sprague Dawley (SD) rats. Here we analyze their drinking patterns and bouts to clarify microbehavioral components that are common to rats of different genetic backgrounds, vs. features that are unique to each. Under sole-fluid conditions P, Wistar and SD rats all consumed water at a high initial rate followed by a slow maintenance phase, but 10E - in a distinctly different step-like pattern of evenly distributed bouts. During choice period, 10E vs. water patterns for P rat appeared as an overlap of sole-fluid patterns. The SD rat choice patterns resembled sole-fluid patterns but were less regular. Choice patterns in Wistar differed from both P and SD rats, by consisting of intermixed small frequent episodes of drinking both 10E and water. Wistar and SD rats increased choice ethanol intake by elevating the number of bouts. A key finding was that P rat increased choice ethanol intake through a gradual increase of the bout size and duration, but kept bout number constant. This supports the hypothesis that genetic selection modifies microbehavioral machinery controlling drinking bout initiation, duration, and other pattern features. Precision analysis of drinking patterns and bouts allows differentiation between genetic lines, and provides a venue for study of localized circuit and transmitter influences mediating mesolimbic control over ethanol consumption.

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

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.

Alcohol place preference conditioning in high- and low-alcohol preferring selected lines of mice

High- and low-alcohol preferring (HAP and LAP) selected lines of mice diverge greatly in free-choice alcohol consumption. This study investigated whether the lines differ in a measure of alcohol reward not dependent on drinking, specifically place conditioning. Mice were subjected to a differential conditioning procedure in which four alcohol-paired CS+ trials on one floor cue (0, 1.5, 3, or 4 g/kg; ns=20-24) alternated with four saline-paired CS- trials on a different floor cue. Testing was on a split floor, half CS+ and half CS-. HAP and LAP mice showed no preference at 0 g/kg, and equivalent, moderate preference at 1.5 and 3 g/kg alcohol. At 4 g/kg, LAP, but not HAP mice showed an increase in preference. The present findings imply greater efficacy of alcohol preference conditioning in LAP mice, but do not speak for line differences in sensitivity. Results do not support the hypothesis that selection for high drinking yields greater efficacy of alcohol as a reinforcer when reward is measured using a technique that does not rely on drinking. Low drinking in LAP mice may emerge from innate taste avoidance of alcohol as a result of selective breeding for low preference, which prevents them from encountering alcohol's rewarding, pharmacological effects.

Pregastric and postabsorptive inhibitory effects of water on angiotensin-induced Fos in rat brain

Intraventricularly (ICV)-injected Ang II activates cells in several forebrain structures of rats, including SFO, OVLT, PVN and SON, and produces a spectrum of physiological and behavioral responses. It has been reported that the Fos-like immunoreactivity (FLI; a marker of cell activation) that is induced in PVN and SON by exogenous Ang II is prevented by allowing rats to ingest water after injection. The present study tests whether this inhibitory effect of water is due to either preabsorptive (oral) or postingestive factors, or both. Rats received cerebroventricular injection of Ang II (100 ng) and were killed 1 h later. One group received no water after the injection, another group drank water, a third group drank water but had it drain from a gastric fistula (sham drinking), and a fourth group received an intragastric infusion of water. In confirmation of a previous study, rats allowed to drink water after Ang II showed an almost complete absence of FLI in SON and PVN, compared with those not allowed access to water. Both sham drinking and intragastrically-infused rats showed less FLI in SON and PVN than nondrinkers. The reduction was greater in the infused group than the sham drinkers, but was not as great as in those allowed to drink water and absorb it. This suggests that both orally-mediated as well as postabsorptive factors can inhibit Ang II-induced FLI by impinging upon cells in the SON and PVN. In contrast, Ang II-induced FLI in OVLT and SFO was not affected by any of the oral or gastric water conditions.