Sham ingestion of alcohol in rats

Silencing the insular-striatal circuit decreases alcohol self-administration and increases sensitivity to alcohol

Internal drug states/cues can impact drug taking, as pretreatment with a moderate to high alcohol dose (i.e., loading dose) can decrease subsequent alcohol self-administration, alcohol-seeking, and relapse-like drinking. The insular cortex (IC) is implicated in processing information about internal states and findings show that silencing the IC and its projections to the nucleus accumbens core (AcbC) enhance sensitivity to the interoceptive effects of alcohol. Therefore, the goal of the present work was to determine the functional role of IC-AcbC projections in modulating the effects of alcohol pretreatment on operant alcohol self-administration. Long-Evans rats were trained to self-administer a sweetened alcohol solution (15% alcohol (v/v) + 2% sucrose (w/v)) and on test sessions received pretreatment with an alcohol loading dose. A chemogenetic strategy (i.e., hM4D Designer Receptors Exclusively Activated by Designer Drugs [DREADDs]) was implemented to silence the IC-AcbC projections and test the functional role of the insular-striatal circuitry in regulating self-administration following the alcohol loading doses. Alcohol self-administration decreased following pre-session treatment with alcohol, confirming titration of alcohol drinking following a loading dose of alcohol. Chemogenetic silencing of IC-AcbC projections decreased alcohol self-administration under baseline conditions (i.e., water loading dose) and the reduction in self-administration of an alcohol loading dose, implicating a role for this circuit in the maintenance of alcohol self-administration and suggesting increased sensitivity to the alcohol loading dose. These findings provide evidence for the critical nature of insular-striatal circuitry in ongoing alcohol self-administration, and specifically in relation to interoceptive/internal cues that can impact alcohol drinking.

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.

Effects of ethanol on energy balance of rats and the inappropriateness of intraperitoneal injection

Energy balance of female rats that were either injected daily with ethanol or received the alcohol by gavage was determined and the results compared with saline animals. Food intake, feces elimination, and body weight were recorded daily. After a 20-day period of treatment the animals were sacrificed and the energy content of the carcasses and feces was determined by bomb calorimetry. The results indicated that ethanol-injected animals underwent an impairment in the energy balance, with losses in body weight and body energy. Also, there was a decrease in metabolized energy intake. The results of a group of saline rats pair-fed to alcohol-injected rats showed that the impairment of the energy balance was not only a consequence of the decreased energy intake, because the ethanol-fed animals had an energy balance that was worse than the one of the pair-fed rats, even though both had eaten the same amount of food. Nevertheless, when alcohol was given by gavage, no alteration in the energy balance parameters was detected. Macroscopic observation of the abdominal cavity showed adherences in the gut of the alcohol-injected animals. It is concluded that the ethanol by itself does not alter the energy balance; however, depending on the route of administration it could indirectly impair the energy balance.

Preference for NaCl solutions in sham drinking Sprague-Dawley rats: water deprivation, sodium depletion, and angiotensin II

Male Sprague-Dawley rats were fitted with closable gastric fistulas and were then tested under closed fistula (real intake) and open fistula (sham intake--fluids drain from the stomach without appreciable absorption) conditions in one of three states: fluid deprivation, sodium depletion, and infusion of angiotensin (Ang) II. Water and various concentrations of NaCl were offered to drink in 1-h one- or two-bottle intake tests. In Experiment 1, water-deprived rats with closed fistulas drank more 0.15 M NaCl than either water or 0.3 M NaCl, offered in one-bottle tests. In sham drinking tests, the intake decreased monotonically as NaCl concentration increased. In two-bottle tests, water was greatly preferred over NaCl solutions. In Experiment 2, sodium-depleted rats preferred NaCl over water, again demonstrating a peak intake at 0.15 M in closed fistula conditions. However, with the fistula open the intakes of 0.05 and 0.15 M were similar, and 0.45 M considerably lower. In Experiment 3, Ang II-infused rats consumed both water and NaCl in two-bottle tests in both open and closed fistula trials. The quantity ingested on sham trials was only modestly elevated over real intake trials with Ang II compared with sham tests in Experiments 1 and 2.

Sham intake of ethanol in "P" rats

Alcohol-preferring (P) rats were surgically fitted with gastric fistulas, and intakes of 10% ethanol solution were measured in 1-h sessions either with the fistula closed (normal drinking) or open (sham drinking). In water-replete P rats in which ethanol access was limited to 1 h/day, no increase in intake was noted in the sham compared with normal drinking tests in the day. A small increase was seen when the sham drinking test was conducted at night. In water-deprived P rats, sham intake of ethanol was elevated over intakes in closed fistula trials. However, in comparison with water intake on separate test days, sham intake of ethanol by P rats was lower and satiated after 15-30 min. The absence of robust sham alcohol drinking in P rats is similar to what we have previously reported in normal Sprague-Dawley rats, suggesting that preabsorptive factors alone do not account for the strain differences in ethanol preference.