Effects of concurrent access to multiple ethanol concentrations and repeated deprivations on alcohol intake of high-alcohol-drinking (HAD) rats.

High-alcohol-drinking rats, given access to 10% ethanol, expressed an alcohol deprivation effect (ADE) only after multiple deprivations. In alcohol-preferring (P) rats, concurrent access to multiple ethanol concentrations combined with repeated cycles of EtOH access and deprivation produced excessive ethanol drinking. The current study was undertaken to examine the effects of repeated alcohol deprivations with concurrent access to multiple concentrations of ethanol on ethanol intake of HAD replicate lines of rats. HAD-1 and HAD-2 rats received access to 10, 20 and 30% (v/v) ethanol for 6 weeks. Rats from each replicate line were assigned to: (1) a non-deprived group; (2) a group initially deprived of ethanol for 2 weeks; or (3) a group initially deprived for 8 weeks. Following the restoration of the ethanol solutions, cycle of 2 weeks of ethanol exposure and 2 weeks of alcohol deprivation was repeated three times for a total of four deprivations. Following the initial ethanol deprivation period, deprived groups significantly increased ethanol intakes during the initial 24-hour re-exposure period. Multiple deprivations increased ethanol intakes, shifted preference to higher ethanol concentrations and prolonged the duration of the elevated ethanol intakes for up to 5 days. In addition, repeated deprivations increased ethanol intake in the first 2-hour re-exposure period as high as 5-7 g/kg (which are equivalent to amounts consumed in 24 hours by HAD rats), and produced blood ethanol levels in excess of 150 mg%. The results indicate that HAD rats exhibit 'loss-of-control' of alcohol drinking with repeated deprivations when multiple ethanol concentrations are available.

Effects of alcohol and saccharin deprivations on concurrent ethanol and saccharin operant self-administration by alcohol-preferring (P) rats.

Consumption of sweet solutions has been associated with a reduction in withdrawal symptoms and alcohol craving in humans. The objective of the present study was to determine the effects of ethanol and saccharin (SACC) deprivations on operant oral self-administration. Alcohol-preferring (P) rats were allowed to lever press concurrently self-administer ethanol (15% vol/vol) and SACC (0.0125% g/vol) for 8 weeks. Rats were then maintained on daily operant access (nondeprived), deprived of both fluids (2 weeks), deprived of SACC and given 2 ml of ethanol daily, or deprived of ethanol and given 2 ml of SACC daily. All groups were then given 2 weeks of daily operant access to ethanol and SACC, followed by an identical second deprivation period. P rats responded more for ethanol than SACC. All deprived groups increased responding on the ethanol lever, but not on the SACC lever. Daily consumption of 2 ml ethanol decreased the duration of the alcohol deprivation effect (ADE). Home cage access to 2 ml of SACC also decreased the ADE but to a lesser extent than access to ethanol. A second deprivation period further increased and prolonged the expression of an ADE. These results show ethanol is a more salient reinforcer than SACC. With concurrent access to ethanol and SACC, P rats do not display a saccharin deprivation effect. Depriving P rats of both ethanol and SACC had the most pronounced effect on the magnitude and duration of the ADE, suggesting that there may be some interactions between ethanol and SACC in their CNS reinforcing effects.

Effects of multiple alcohol deprivations on operant ethanol self-administration by high-alcohol-drinking replicate rat lines.

Previously, we reported that the expression of an alcohol deprivation effect (ADE) under 24-h free-choice alcohol-drinking access in high-alcohol-drinking (HAD) replicate lines of rats is dependent upon repeated cycles of alcohol access and forced abstinence. In the present study, operant techniques (including progressive ratio measures) were used to examine the effects of initial deprivation length and number of deprivation cycles on the magnitude and duration of the ADE in HAD rats to test the hypothesis that repeated deprivations increase the reinforcing effects of ethanol. Adult male HAD-1 and HAD-2 rats were trained in two-lever operant chambers to concurrently self-administer 15% ethanol (v/v) on a fixed-ratio (FR)-5 schedule and water on an FR-1 schedule of reinforcement in daily 1-h sessions. Following 10 weeks of daily 1-h sessions, the HAD-1 and HAD-2 rats were randomly assigned to one of four groups (n=6-8/group/line): nondeprived, or deprived of alcohol for 2, 5, or 8 weeks. Following this initial period, the deprived groups were given 15% ethanol again in the operant chambers for a 2-week period, following which they were deprived again for 2 weeks (all three deprived groups). Following the fifth deprivation, the rats underwent a progressive ratio test to determine the breakpoints for the nondeprived and deprived groups. The expression of an ADE under operant conditions in HAD rats was dependent upon exposure to repeated cycles of ethanol access and abstinence. Additionally, repeated deprivations increased both the magnitude and the duration of the ADE as indicated by increased responding on the ethanol lever for more sessions. Breakpoint values for the deprived groups were 1.5-fold and twofold higher than the value for the nondeprived group for the HAD-1 and HAD-2 rats, respectively. The results suggest that repeated alcohol deprivations increased the expression of an ADE and the reinforcing effects of ethanol in both HAD replicate lines of rats, and these effects were more pronounced in the HAD-2 line than the HAD-1 line.

Intracranial self-administration of cocaine within the posterior ventral tegmental area of Wistar rats: evidence for involvement of serotonin-3 receptors and dopamine neurons.

The rewarding properties of cocaine have been postulated to be regulated, in part, by the mesolimbic dopamine (DA) system. The present study assessed whether adult female Wistar rats would self-administer cocaine directly into the ventral tegmental area (VTA). Following guide cannulae surgery aimed at either the posterior or anterior VTA, subjects were placed in an operant box equipped with an active lever that caused the delivery of the infusate and an inactive lever that did not. Posterior and anterior VTA subjects were randomly assigned to one of six groups that self-administered either artificial cerebrospinal fluid (aCSF) or 25 to 400 pmol cocaine/100 nl in aCSF for the first four sessions, aCSF in sessions 5 and 6, and the acquisition dose of infusate during session 7. Additionally, the effects of increasing the time-out period, higher concentrations of cocaine, coadministration of a 5HT3 antagonist, and coadministration of a D2/3 agonist on self-infusion of cocaine were determined. Self-infusions were maintained when the time-out period was extended from 5 to 25 s. Coinfusion of a 5HT3 antagonist or D2/3 agonist blocked the self-infusion of cocaine. In contrast, rats did not self-administer 25 to 400 pmol/100 nl cocaine into the anterior VTA. Additionally, rats did not self-administer either 800 or 1600 pmol/100 nl cocaine into the posterior or anterior VTA. Overall, the data indicate that the VTA is functionally heterogeneous with regard to the rewarding actions of cocaine and that the reinforcing effects of cocaine within the posterior VTA are mediated by activation 5-HT3 receptors and DA neurons.

Comparison of intracranial self-administration of ethanol within the posterior ventral tegmental area between alcohol-preferring and Wistar rats.

BACKGROUND: A previous study indicated that selectively bred alcohol-preferring (P) rats self-administered ethanol (EtOH) directly into the ventral tegmental area (VTA), whereas the alcohol-nonpreferring line did not. Wistar rats will also self-administer EtOH directly into the posterior VTA. Because Wistar rats also have a low preference for EtOH solutions but self-inject EtOH into the VTA, this study was undertaken to test the hypothesis that there is an association between EtOH preference and sensitivity of the VTA to the reinforcing effects of EtOH. METHODS: Adult P and Wistar rats were assigned to groups that received one of the following concentrations of EtOH: 0, 50, 75, 100, 150, or 200 mg/100 ml. Rats were connected to the microinjection system, placed into two-lever (active and inactive) experimental chambers, and given EtOH for the first four sessions (acquisition), artificial cerebrospinal fluid for sessions 5 and 6 (extinction), and EtOH again in session 7 (reinstatement). Responding on the active lever produced a 100-nl injection of the infusate. RESULTS: P rats self-infused 75 to 200 mg/100 ml EtOH and demonstrated lever discrimination, whereas Wistar rats reliably self-infused only 150 and 200 mg/100 ml EtOH. Both P and Wistar rats reduced responding on the active lever when artificial cerebrospinal fluid (aCSF) was substituted for EtOH and reinstated responding in session 7 when EtOH was restored, although P rats demonstrated a very robust enhancement of responding for 100 and 150 mg/100 ml EtOH, and this was not found for Wistar rats. CONCLUSIONS: These results suggest that, compared with Wistar rats, the posterior VTA of P rats was more sensitive to the reinforcing effects of EtOH. Furthermore, the reinstatement data suggest that the posterior VTA of P rats underwent neuronal alterations as a result of prior EtOH exposure and extinction that changed the reinforcing effects of EtOH within this region.

Intracranial self-administration of ethanol within the ventral tegmental area of male Wistar rats: evidence for involvement of dopamine neurons.

Previous work from our laboratory indicated that female Wistar rats will self-administer ethanol (EtOH) directly into the posterior ventral tegmental area (VTA). These results suggested that VTA dopamine (DA) neurons might be involved in mediating the reinforcing actions of EtOH within this region. The objectives of this study were to determine (1) the dose-response effects for the self-administration of EtOH into the VTA of male Wistar rats, and (2) the involvement of VTA DA neurons in the reinforcing actions of EtOH within the VTA. Adult male Wistar rats were implanted stereotaxically with guide cannulas aimed at the posterior or anterior VTA. After 1 week, rats were placed in standard two-lever (active and inactive) experimental chambers for a total of seven to eight sessions. The first experiment determined the intracranial self-administration of EtOH (0-400 mg%) into the posterior and anterior VTA. The second experiment examined the effects of coadministration of the D2/3 agonist quinpirole on the acquisition and maintenance of EtOH self-infusions into the posterior VTA. The final experiment determined the effects of a D2 antagonist (sulpiride) to reinstate self-administration behavior in rats given EtOH and quinpirole to coadminister. Male Wistar rats self-infused 100-300 mg% EtOH directly into the posterior, but not anterior, VTA. Coadministration of quinpirole prevented the acquisition and extinguished the maintenance of EtOH self-infusion into the posterior VTA, and addition of sulpiride reinstated EtOH self-administration. The results of this study indicate that EtOH is reinforcing within the posterior VTA of male Wistar rats and suggest that activation of VTA DA neurons is involved in this process.

Effects of repeated alcohol deprivations on operant ethanol self-administration by alcohol-preferring (P) rats.

We reported that repeated alcohol deprivations prolonged the expression of an alcohol-deprivation effect (ADE) under 24-h free-choice alcohol-drinking access and that the duration of the initial deprivation period had a positive effect of prolonging the duration of the ADE. In the present study, operant techniques (including progressive ratio measures) were used to examine the effects of initial deprivation length and number of deprivation cycles on the magnitude and duration of the ADE in alcohol-preferring (P) rats to test the hypothesis that repeated deprivations can increase the reinforcing effects of ethanol (ETOH). Adult male P rats were trained in two-lever operant chambers to self-administer 15% ETOH (v/v) on a fixed-ratio 5 (FR-5) and water on a FR-1 schedule of reinforcement in daily 1-h sessions. Following 6 weeks of daily 1-h sessions, the P rats were randomly assigned to one of four groups (n=10/group): nondeprived or deprived of alcohol for 2, 5, or 8 weeks. Following this initial period, the deprived groups were given 15% ETOH again in the operant chambers for a 2-week period, following which they were deprived again for 2 weeks (all three deprived groups). Following the fourth deprivation, the rats underwent a progressive ratio test to determine the breakpoints (FR values) for the nondeprived and the deprived groups. Repeated deprivations increased both the magnitude and duration of the ADE as indicated by increased responding on the ETOH lever. However, the length of the initial deprivation had little effect on expression of the ADE except following the first deprivation, where an ADE was not observed for the 8-week group. Breakpoint values for responding on the ETOH lever for all three deprived groups were two-fold higher than the value for the nondeprived group. The results suggest that repeated cycles of alcohol deprivation and alcohol access increased the reinforcing effects of ETOH in the P rats.

Effects of concurrent access to a single concentration or multiple concentrations of ethanol on the intake of ethanol by male and female periadolescent alcohol-preferring (P) rats.

The objectives of this study were to assess the effects of access to different concentrations of ethanol and sex of the animal on ethanol consumption during periadolescence [postnatal days (PNDs) 30-60] in alcohol-preferring (P) rats. On PND 28, female and male P pups were single housed in hanging stainless steel cages with ad libitum access to water and food. Beginning on PND 30, the rats were also given access to either a single concentration [15% volume/volume (vol./vol.)] or multiple concentrations [10%, 20%, and 30% (vol./vol.)] of ethanol. Differences between sex (male vs. female) and ethanol conditions (single concentration vs. multiple concentrations), for the average amount of ethanol consumed for each week (starting on PND 33) of access, were examined. Analyses of the data for ethanol drinking revealed significant (P<.025) main effects of week and ethanol condition, as well as a significant weekxethanol condition interaction. For the first week, both male and female P pups consumed more ethanol under the multiple-ethanol-concentration condition than under the single-ethanol-concentration condition. However, across the second through fourth weeks, this pattern was seen only in female P pups. When preference for one concentration of ethanol over the other concentrations was assessed, it was found that male P pups tended to choose the 30% concentration over the 10% and 20% concentrations, whereas female P pups did not display a preference. The findings of this study corroborate previous work indicating that periadolescent P rats readily acquire high-ethanol-drinking behavior and that, similar to adult P rats, concurrent access to multiple concentrations of ethanol further enhances ethanol intake. These findings suggest to us that innate genetically influenced mechanisms promoting high ethanol intake are present at this stage of development.

Effects of ethanol exposure on subsequent acquisition and extinction of ethanol self-administration and expression of alcohol-seeking behavior in adult alcohol-preferring (P) rats: I. Periadolescent exposure.

BACKGROUND: The current study examined the effects of ethanol (EtOH) drinking during periadolescence on the subsequent acquisition and extinction of operant self-administration of EtOH and expression of alcohol-seeking behavior in adult alcohol-preferring (P) rats to test the hypothesis that alcohol drinking during periadolescence produces enduring alterations that enhance the reinforcing properties of EtOH. METHODS: Periadolescent female P rats were given 24 hr free-choice access to 15% (v/v) EtOH starting at postnatal day (PND) 30 and ending on PND 60 or were similarly housed and received water only. On PND 75, without any prior training, periadolescent alcohol-drinking and periadolescent alcohol-naïve rats were placed in standard two-lever (15% EtOH and water) chambers to examine acquisition of EtOH self-administration with a fixed ratio (FR) 1 schedule of reinforcement. After the acquisition phase and after stable responding was established on an FR5 for EtOH and FR1 for water, P rats underwent extinction training for both EtOH and water rewards. After extinction training and a 2 week home cage period, rats were returned to the operant chambers in the absence of reward for seven consecutive sessions (Pavlovian spontaneous recovery). After this testing period, animals were maintained in their home cage for a week before being returned to the operant chambers and allowed to respond for EtOH and water (reacquisition). RESULTS: Compared with periadolescent alcohol-naïve rats, periadolescent alcohol-drinking rats acquired EtOH responding sooner (i.e., in the first acquisition session), displayed a greater resistance to extinguish EtOH responding (i.e., higher levels of responding in sessions 4-6), had higher responding for more sessions on the EtOH lever in the absence of reward after a prolonged home cage rest period, and had a more prolonged elevated level of EtOH responding during reacquisition (four sessions versus one session). CONCLUSIONS: Overall, the results suggest that periadolescent EtOH drinking by P rats produced long-lasting alterations in the reinforcing effects of alcohol, which increased the likelihood that alcohol drinking would be initiated in adulthood, decreased the likelihood that once adult alcohol drinking began it could be extinguished easily, and increased the potential for relapse.

Effects of ethanol exposure on subsequent acquisition and extinction of ethanol self-administration and expression of alcohol-seeking behavior in adult alcohol-preferring (P) rats: II. Adult exposure.

BACKGROUND: In a preceding study, we reported that ethanol (EtOH) consumption during periadolescence in alcohol-preferring (P) rats produced significant effects on the acquisition, extinction, Pavlovian spontaneous recovery (PSR), and reacquisition of operant self-administration of EtOH. The objective of the present study was to determine if EtOH consumption during adulthood produced similar effects on subsequent operant behaviors. METHODS: Adult female P rats (>135 days of age) were given 24 hr free-choice access to 15% EtOH for 30 days or were similarly housed and received water only. After a 15 day period of no EtOH access and without any prior training, adult alcohol drinking and adult alcohol-naïve rats were placed in standard two-lever (15% EtOH and water) chambers to examine acquisition of EtOH self-administration. After stable responding was established on a concurrent fixed ratio (FR) 5 FR1 schedule for EtOH versus water, the P rats underwent extinction training for nine sessions. After extinction and a 2 week home cage period (with no operant sessions or access to EtOH), rats were returned to the operant chambers in the absence of reward for seven consecutive sessions to test for PSR. After PSR testing, animals were maintained in their home cage for a week, before being reintroduced to the operant chambers and allowed to respond for EtOH and water. RESULTS: Both the adult alcohol-drinking and adult alcohol-naïve groups rapidly acquired EtOH self-administration, expressed a pronounced PSR, which was augmented by EtOH priming and the presence of a discriminative stimulus (odor cue), and increased responding when EtOH was reinstated. Adult pre-exposure to EtOH did not alter any of the operant measures. CONCLUSIONS: The results of this study suggest that, unlike the results with EtOH pre-exposure during periadolescence, chronic alcohol drinking by P rats in adulthood did not produce sufficient long-lasting changes in neuronal function to alter subsequent operant acquisition of alcohol self-administration, alcohol relapse, or alcohol-seeking behavior.