Paternal alcohol exposure reduces acquisition of operant alcohol self-administration and affects Bdnf DNA methylation in male and female offspring.

Familial transmission of alcohol use disorder reflects genetic and environmental factors. Paternal alcohol exposure may affect rodent offspring via epigenetic modifications transmitted through the male germ line. While such exposure alters alcohol sensitivity in mouse offspring, no studies examined if it impacts the development of operant alcohol self-administration in rats. We exposed male (sires) Wistar rats to chronic intermittent ethanol in vapour chambers (16 h/day; 5 days/week) or to air for 6 weeks. Eight weeks later, rats were mated with alcohol-naive females. Adult alcohol- and control-sired F1 offspring were assessed in acquisition of alcohol self-administration in which increasing alcohol concentrations (2.5%, 5% and 10%, v/v) were delivered after one lever press (fixed ratio 1 or FR1). Prior to alcohol sessions, rats were trained to lever press for food delivery under an FR1 schedule of reinforcement. DNA methylation levels of the brain derived neurotrophic factor (Bdnf) gene were measured in sperm, nucleus accumbens (NAc) and medial prefrontal cortex (mPFC) in sires and in offspring. Alcohol-exposed sires had lower Bdnf DNA methylation levels in NAc and greater methylation levels in mPFC. Although this pattern was not recapitulated in offspring, alcohol-sired offspring of both sexes did show aberrant Bdnf DNA methylation patterns compared to control-sired offspring. Alcohol-sired offspring self-administered less alcohol (5% and 10%) with no group differences in food responding. Results indicate that paternal alcohol exposure prior to conception protects against alcohol's initial reinforcing effects but the pattern of dysregulated Bdnf methylation in reward-related circuitry did not mimic changes seen in sires.

Equal response rates maintained by concurrent drug and nondrug reinforcers: a design for treatment evaluation.

During daily 3-h sessions, four rhesus monkeys had concurrent access to 16% alcohol (w/v) and saccharin. A response occurred when a monkey made mouth contact with the metal spout and thereby completed a drinkometer circuit. The liquids were available under concurrent nonindependent fixed-ratio 32 schedules. With these schedules, responses on the right spout decremented both the right and left fixed-ratio counters and vice versa. Responding was well maintained by both alcohol and saccharin. Increases in saccharin concentration produced increases in saccharin responding to the point that saccharin responding exceeded alcohol responding. Responses per saccharin delivery were also a direct function of the saccharin concentration. In contrast, responses per alcohol delivery generally decreased as the saccharin concentration became greater. Changeover or switching responses were also a direct function of the saccharin concentration. Relative reinforcing effects of each combination of liquid pairs were measured for each monkey. For all monkeys, it was possible to establish equal rates of responding for both reinforcers and frequent switching between reinforcers. The balanced responding can serve as a baseline for the evaluation of potential treatments that may alter relative reinforcing effects.

Drug self-administration studies: a novel reinforcement schedule enhances choice.

Relative reinforcing effects of different ethanol and different cocaine doses were studied under concurrent independent fixed-ratio (FR) schedules and concurrent nonindependent FR schedules with rhesus monkeys. Nonindependent FR schedules differed from independent FR schedules in that responses on either side counted towards the FR requirements of two concurrently presented choices. Thus, responses on the right operandum counted toward completion of both right and left FR schedules and, symmetrically, responses on the left did the same. Nonindependent schedules allow the number of responses per drug delivery to vary considerably, unlike independent schedules, thereby making the number of responses per delivery a sensitive dependent variable. In contrast, standard independent schedules do not allow responses per drug delivery to vary; the required number of responses is an independent variable. Three rhesus monkeys were subjects, and choices between different doses of ethanol or cocaine were studied. Larger doses maintained higher response rates than smaller doses - consistent with previous choice studies. By using nonindependent schedules, however, graded responses per drug delivery and increased switching between sides were obtained, providing additional data and useful measures of choice.

Concurrent nonindependent fixed-ratio schedules of alcohol self-administration: Effects of schedule size on choice.

Choice behavior was studied under concurrent nonindependent fixed-ratio fixed-ratio (nFR) schedules of reinforcement, as these schedules result in frequent changeover responses. With these schedules, responses on either operandum count toward the completion of the ratio requirements of both schedules. Five monkeys were subjects, and two pairs of liquid reinforcers were concurrently available: 16% (w/v) and 0% ethanol or 16% and 8% ethanol. For each pair of reinforcers, the nFR sizes were systematically altered across sessions while keeping the schedule size equal for both liquids. Responding varied as a function of reinforcer pair and nFR size. With the 16% and 0% pair, higher response rates were maintained by 16% and were an inverted U-shape function of nFR size. With 16% and 8%, a greater number of responses initially occurred on the schedule that delivered 8% ethanol. However, as nFR size increased, preference reversed such that responses that delivered 16% ethanol were greater. When the nFR size was subsequently decreased, preference reverted back to 8%. Number of responses emitted per delivery was a dependent variable and, in behavioral economic terms, was the price paid for each liquid delivery. With 16% and 0%, changeover responses initially increased and then decreased as schedule size became larger. In contrast, with the 16% and 8% pair, changeover responses increased directly with schedule size. Responding under nFR schedules is sensitive to differences in reinforcer magnitude and demonstrates that relative reinforcing effects can change as a function of schedule size.

Methadone and nicotine self-administration in humans: a behavioral economic analysis.

RATIONALE: Prior research has revealed inconsistencies in the behavioral relations between nicotine and opiates among methadone-maintained patients. OBJECTIVES: The current study examined whether the drug reinforcers cigarette puffs and methadone were economic complements or substitutes. METHODS: Five methadone-maintained, nicotine-dependent participants were trained to self-administer methadone, cigarette puffs, or concurrently available methadone and puffs. Following training, the fixed ratio (FR) value ("price") was increased across sessions (FR 32, 64, 128, 256, and 512), first for methadone and then for puffs. Subsequently, methadone and puffs were concurrently available, and the price of each drug was increased independently, while the price of the alternative (puffs or methadone) remained constant at FR 32. RESULTS: Demand for methadone and cigarette puffs decreased as a function of increases in methadone and cigarette puff prices, respectively. When methadone and puffs were concurrently available, an increase in methadone's price decreased puff consumption, and demand for methadone was less elastic than when puffs were not concurrently available. An increase in puff price decreased puff and methadone demand, but the elasticity of puff demand was unaffected. The concurrent presence of methadone had no effect on the elasticity of demand for cigarette puffs. CONCLUSIONS: Methadone and cigarette puffs appear to be asymmetric economic complements.

Relation between choice of ethanol concentration and response rates under progressive- and fixed-ratio schedules: studies with rhesus monkeys.

RATIONALE: A fundamental problem in the study of drugs as reinforcers is the evaluation of a drug's relative reinforcing effects and changes in such effects. Relative reinforcing effects can be measured by determining the preference for one drug dose relative to another drug dose. However, in IV drug self-administration studies technical limitations make direct comparisons between drug doses difficult. An alternative procedure is to measure the relative persistence of behavior across increases in schedule size. OBJECTIVE: To develop a more rapid method to measure the relative persistence of behavior. Instead of increasing the schedule size across sessions, schedule size was increased within sessions by use of a progressive-ratio schedule (PR). METHODS: Male rhesus monkeys orally self-administered ethanol during daily 3-h sessions. At each concentration responding was measured with fixed-ratio (FR) 8 schedules to obtain baseline values. Subsequently behavior was studied with a PR schedule. Relative persistence of behavior was calculated by dividing the mean response rate under the PR schedule by the mean response rate under the FR8 schedules. To compare these findings with results of choice between concentrations, monkeys were given concurrent access to pairs of ethanol concentrations. RESULTS: The relative persistence of behavior increased with increases in drug concentration. When two concentrations were concurrently available, the higher concentration maintained higher response rates. CONCLUSIONS: The relative persistence of behavior can be efficiently measured by dividing the response rate under the PR schedule by the response rate under the FR schedule. Measures of relative persistence corresponded well with measures of choice and show that relative reinforcing effects increase as dose increases.

Relative reinforcing effects of different benzodiazepine doses for rhesus monkeys.

The relative reinforcing effects of different doses of benzodiazepines were determined by giving rhesus monkeys concurrent access to different diazepam and midazolam concentrations. For each monkey a dose response function was obtained using three drug concentrations: low (L), intermediate (I), and high (H). The benzodiazepine and the water vehicle were concurrently available under independent fixed-ratio (FR) schedules. After establishing that each concentration was a reinforcer in comparison to vehicle, relative preference for the different concentrations was examined by making pairs of concentrations concurrently available under independent FR schedules. Three pairs were studied (H vs. L, H vs. I, and I vs. L). With both drugs, higher concentrations maintained greater response rates than lower concentrations. Thus, relative reinforcing effects increased with dose. These findings are similar to those obtained with other reinforcing drugs and provide further evidence that benzodiazepines share significant characteristics with other drug reinforcers. Importantly, absolute response rates (responses per session) obtained when only one drug dose was present were not reliably predictive of subsequent preferences for the dose. Both benzodiazepines served as effective reinforcers in that consistent levels of responding were maintained across doses and above vehicle levels under concurrent FR 32 schedules. As with other reinforcing drugs, the reinforcing effects of benzodiazepines increase with increases in dose over a broad range of values.

Direct relation between etonitazene dose and response rate: responding under a single FI per session.

Response-contingent injections of etonitazene (ETZ) have been shown to reinforce rats' lever pressing behavior. The objective of the present study was to determine the relation between response rate and ETZ dose when ETZ was administered subcutaneously once per session by the experimenter contingent upon completion of a 10-min fixed-interval (FI) schedule. When injections of the saline vehicle replaced drug injections, response rates dropped to low levels; rates subsequently increased above saline levels when drug injections were reintroduced, demonstrating that ETZ was serving as a reinforcer. A range of ETZ doses (0.01, 0.1, 1, 5.7, and 10 microg/kg) was administered subcutaneously to six rats, resulting in response rates that were directly related to drug dose. These findings are consistent with other studies that have found an increase in reinforcing effects with increases in drug dose. Thus, studies in which drug is administered once per session may be used to measure the reinforcing effects of drugs directly from rate measures, as the response rate in these studies is unaffected by satiation or direct drug effects.

Relative reinforcing effects of different oral ethanol doses in rhesus monkeys.

The relative reinforcing effects of different doses of orally delivered ethanol were evaluated. Mouth-contact responding by rhesus monkeys was measured under concurrent fixed-ratio fixed-ratio schedules of liquid delivery (0.67 ml/delivery) from each of two spouts during daily 3-hr sessions. Experiment 1 examined persistence of responding with ethanol (2%, 8%, and 32% wt/vol) and water available. When fixed-ratio values from 8 to 128 were tested, the number of ethanol deliveries obtained per session decreased as the response requirement increased. The decrease in deliveries was less at higher than at lower ethanol concentrations, however. Experiment 2 examined choice between two ethanol concentrations under concurrent fixed-ratio 16 schedules (4% vs. 8%, 4% vs. 16%, 8% vs. 16%, 2% vs. 8%, 2% vs. 32%, 8% vs. 32%). Higher concentrations (16%, 32%) generally maintained more responding than concurrently available concentrations of 8% or less. An exception was the observation of a preference for 8% over 32% ethanol. When the fixed-ratio value was increased, however, the relative preference for these two doses was reversed so that 32% ethanol maintained more responding than 8% ethanol. Thus, the direction of the preference depended on the size of the response requirement. These results indicate that the reinforcing effects of ethanol increase with dose.

Predicting extinction and reinstatement of alcohol and sucrose self-administration in outbred rats.

Preventing relapse to drinking or escalation to excessive drinking could be aided by identifying factors that predict these behaviors. Animal models, particularly those that utilize operant self-administration techniques, can be useful. In a prior operant study, we noted a good deal of variability in behaviors during training and test sessions. We utilized data obtained from that study of two groups of rats, trained and tested identically except one responded for alcohol and the other for sucrose, to explore for associations related to relapse (reinstatement) or to excessive drinking (maintenance). Data were obtained from sessions conducted under fixed- and progressive-ratio schedules as well as from extinction and reinstatement sessions. Variables assessed included active and inactive presses, head entries into the dipper trough, and automated recordings of body movements during these sessions as well as alcohol preference before training. First, using multiple regression, we examined whether alcohol preference before training associated with any response variable among alcohol-responding rats. Second, using factor analysis, we identified a training variable, body movements, that associated with responses during tests. Using this measure, rats were divided into low- and high-response groups and compared on active lever presses and head entries across test sessions. Results show that among alcohol-responding rats, alcohol preference predicted head entries during extinction. High-body-movement rats emitted significantly fewer active lever presses and had fewer head entries across test sessions, particularly during reinstatement, compared with low-body-movement rats. Results from this exploratory study provide clues for future experimental studies.