Genetic basis for the psychostimulant effects of nicotine: a quantitative trait locus analysis in AcB/BcA recombinant congenic mice

Genetic differences in sensitivity to nicotine have been reported in both animals and humans. The present study utilized a novel methodology to map genes involved in regulating both the psychostimulant and depressant effects of nicotine in the AcB/BcA recombinant congenic strains (RCS) of mice. Locomotor activity was measured in a computerized open-field apparatus following subcutaneous administration of saline (days 1 and 2) or nicotine on day 3. The phenotypic measures obtained from this experimental design included total basal locomotor activity, as well as total nicotine activity, nicotine difference scores, nicotine percent change and nicotine regression residual scores. The results indicated that the C57BL/6J (B6) were insensitive to nicotine over the entire dose-response curve (0.1, 0.2, 0.4 and 0.8 mg/kg). However, the 0.8-mg/kg dose of nicotine produced a significant decrease in the locomotor activity in the A/J strain and a wide and continuous range of both locomotor excitation and depression among the AcB/BcA RCS. Single-locus association analysis in the AcB RCS identified quantitative trait loci (QTL) for the psychostimulant effects of nicotine on chromosomes 11, 12, 13, 14 and 17 and one QTL for nicotine-induced depression on chromosome 11. In the BcA RCS, nicotine-induced locomotor activation was associated with seven putative regions on chromosomes 2, 7, 8, 13, 14, 16 and 17. There were no overlapping QTL and no genetic correlations between saline- and nicotine-related phenotypes in the AcB/BcA RCS. A number of putative candidate genes were in proximity to regions identified with nicotine sensitivity, including the alpha2 subunit of the nicotinic acetylcholine receptor and the dopamine D3 receptor.

Sensitivity of AXB/BXA recombinant inbred lines of mice to the locomotor activating effects of cocaine: a quantitative trait loci analysis

The present study was conducted in order to characterize putative quantitative trait loci (QTL) for cocaine-induced activation in the AXB/BXA recombinant inbred (RI) lines of mice. Locomotor activity was measured in the AXB/BXA and progenitor A/J and C57BL/6J strains using a computerized open-field apparatus following saline or cocaine (0, 5, 10, 20 mg/kg) administration (i.p.). Analyses were conducted on phenotypes including both novelty (responses under initial saline conditions) and cocaine-induced locomotor activity. Significant differences were observed across RI lines on all measures. Gender differences in sensitivity to the activating effects of cocaine were not observed. The wide and continuous distributions of phenotypic responses in the AXB/BXA RI lines suggested polygenic regulation. Initial basal locomotor activity was significantly correlated with cocaine-induced activation (raw scores) (r = 0.60, P = 0.0021) but not with cocaine difference scores (r = 0.370, P = 0.082). Simple regression and interval mapping were used to initially identify significant gene markers associated with novelty and cocaine-induced activation. Subsequently, composite interval mapping was used to increase the accuracy in mapping individual loci. QTL analysis of cocaine-induced activation (difference scores--20 mg/kg dose) identified significant loci on chromosomes 12 (23 cM), and 15 (46.8 cM). The significant QTLs were identified on chromosomes 12 and 15 map to regions in proximity to genes for the somatostatin 1 (Smstr1 -23 cM) and 3 (Smstr3 -46.3 cM) receptors, respectively. Further research employing AcB/BcA recombinant congenic lines of mice will be employed to confirm the QTL on chromosomes 12 and 15 identified in the present study.

The effects of the GABA(B) agonist baclofen on the temporal and structural characteristics of ethanol intake

The present study examined the behavioral processes mediating the influence of the GABA(B) agonist baclofen on the maintenance of voluntary ethanol intake. Long-Evans rats were randomly assigned to two groups, one receiving baclofen (10 mg/kg, IP) and the other an equal volume of saline. Subjects were presented with a free choice of ethanol (10% v/v) and water immediately following drug injections, which occurred every other day. The results demonstrated that baclofen treatment resulted in an overall increase in the intake of absolute ethanol but failed to influence the intake of water. In contrast, food intake was substantially attenuated as evidenced by a decrease in the number of pellets consumed in subjects treated with baclofen. A microanalysis of the patterns of food and fluid bouts indicated that the enhanced ethanol intake was primarily a function of an increase in the frequency of ethanol bouts. In contrast, the decrease in food intake appeared to be a reflection of a decrease in the size of the food meals but not their frequency. An analysis of the temporal pattern of intake over the 23-h test sessions indicated that baclofen treatment produced a biphasic effect on ethanol intake with a slight decrease in intake during the first hour following treatment. Baclofen-treated animals then were observed to consume greater amounts of ethanol than did saline controls throughout the remainder of the dark cycle as well as into the light cycle. Although ethanol intake gradually decreased in controls throughout the light cycle, baclofen-treated subjects maintained a consistent level of intake throughout this period. Furthermore, there was a clear dissociation between the temporal pattern of ethanol intake and that of food and water, as intake of the latter substances was shown to decrease during the first hour following injection, but unlike with ethanol, no increase in intake was observed during the remainder of the test session. The nature of the effects of baclofen observed in the present study would suggest that the GABA(B) receptor system may not play a central role in the mediation of voluntary ethanol intake.

Effects of acute and chronic doses of naltrexone on ethanol self-administration in rhesus monkeys

The effects of acute and chronic administration of intramuscular naltrexone (0.1, 0.3, 1.0, and 3.0 mg/kg) on oral ethanol (8%) self-administration were examined. Naltrexone (1.0 mg/kg) effects on the self-administration of ethanol concentrations ranging from 0.5 to 8% (w/v) were also investigated. Rhesus monkeys with substantial histories of drug and ethanol drinking served as subjects. During daily 3-hr sessions, monkeys were presented with ethanol solutions, concurrently available with water, under fixed-ratio reinforcement schedules. Naltrexone decreased the consumption of ethanol (g/kg). Biphasic temporal effects were observed within sessions. Naltrexone dose-dependently decreased the number of ethanol deliveries by a maximum of 56% (n = 18; 3 monkeys x 6 sessions) during the first hour of the session. During the second and third hours, however, ethanol intake recovered such that maximum decreases over the 3-hr session were approximately 27% (n = 18), and the mean decrease was 16% (n = 18). Often marked tolerance was observed, such that the effects of acute naltrexone administration were greater than effects after chronic administration. The self-administration of low ethanol concentrations (< or =2% w/v) was increased in several monkeys, by up to 340%, after naltrexone pretreatment. In summary, the effects of naltrexone on ethanol self-administration, in drug- and alcohol-experienced rhesus monkeys, are not characterized by unitary decreases in measures of ethanol self-administration. Rather, differential naltrexone effects were a function of experimental parameters, including the dose and number of naltrexone injections, the ethanol concentration, and the time point of measurement.

A descriptive analysis of the structure and temporal pattern of voluntary ethanol intake within an acquisition paradigm

OBJECTIVE

The present experiment examined the microstructure and temporal pattern of consummatory behavior to provide insight into the behavioral processes that regulate the acquisition of voluntary oral ethanol intake.

METHOD

A microcomputer-controlled data acquisition system was used to dynamically monitor food, water and ethanol intake in Long Evans rats across acquisition of ethanol drinking initiated through the presentation of a sequence of increasing concentrations of ethanol solutions in a free choice with water.

RESULTS

The results showed a biphasic pattern of ethanol intake as a function of presentation of increasing concentrations of ethanol. Total ethanol intake decreased as the ethanol concentration was increased from 2% to 6%, while, inversely, ethanol intake was significantly increased as the concentration went from 6% to 10%. The initial decrease in ethanol intake, across 2% to 6% ethanol, was a function of decreases in both frequency and size of ethanol bouts. The increase in ethanol intake observed following presentation of higher ethanol presentations was solely a function of increased size of ethanol bouts. The increased size of ethanol bouts was paralleled by an increase in the rate of intake which was not evident across presentation of concentrations below 6%. The pattern of intake across the 23-hour daily sessions exhibited no differences across the dark/light cycle in ethanol or water intake as the concentrations of ethanol were increased. The results indicated, however, that food intake was characterized by increases in consumption during the first hour following the presentation of fluids and the night portion of the dark/light cycle.

CONCLUSIONS

The present study revealed, for the first time, the involvement of differential, concentration dependent, behavioral processes in the mediation of the acquisition of voluntary ethanol intake.

Effectiveness of Trimming and/or Washing on Microbiological Quality of Beef Carcasses

Beef carcass sides (n = 48) were selected randomly on three different days in a commercial processing facility and microbiologically analyzed before being moved to the cooler. Four types of samples were obtained per side from the inside round area: no trim and no wash (NTNW); trim, but no wash (TNW); trim and wash (TW), and no trim but wash (NTW). A flame-sterilized knife, forceps, and scalpel were used for each trimming treatment and sampling. Significant differences (P < 0.05) were observed in mean aerobic plate counts (APCs) between treatments. The greatest reduction in APC (log₁₀ colony forming units [CFU] per cm²) was observed in TNW samples followed by TW and NTW, with the corresponding mean APC reductions relative to NTNW being 3.0, 0.9, and 0.3, respectively, indicating that trimming can be an effective control point in reducing bacterial contamination in the slaughter process. Although TNW samples, had the lowest counts, samples from the same location after wash (TW) had counts 2 log cycles higher than TNW samples. These results indicate that washing spreads contamination to adjacent carcass sites. However, washing of carcasses was effective in lowering microbial populations relative to the NTNW treatment. Escherichia coli and coliform counts in all samples were low (0.03 to 0.4 log₁₀ CFU/cm²); however, the mean E. coli or coliform count in NTNW samples was higher (P < 0.05) than those in the rest of the treatments.

Bidirectional effects of GABAergic agonists and antagonists on maintenance of voluntary ethanol intake in rats

The effects of THIP (GABAA agonist) and picrotoxin (GABA antagonist) on the maintenance of voluntary ethanol ingestion were examined. Thirty-three male Long-Evans rats were initially exposed to a screening procedure in which increasing concentrations of ethanol (from 2% to 9%) were presented in a free choice with water, on an alternate day schedule. Following the screening procedure, the rats were exposed to five ethanol presentations at a concentration of 9%, which constituted the baseline period, and five additional ethanol presentations during which the effects of the GABAergic manipulations were determined (test period). During the test period, the animals received IP injections of either 16 mg/kg of THIP, 2 mg/kg of picrotoxin or saline. The results suggested that the differential GABA manipulations resulted in bidirectional effects on the consumption of ethanol. More specifically, the GABAA agonist THIP increased the intake of ethanol as compared to baseline measures, while the GABA antagonist picrotoxin decreased ethanol intake. Similarly, the administration of THIP increased ethanol preference. In contrast, preference for ethanol over water was decreased following the administration of picrotoxin. It appears that the effects of these GABAergic manipulations are specific to ethanol, since total fluid intake was not influenced by the administration of either drug (i.e., THIP or picrotoxin). In light of the literature suggesting that THIP and picrotoxin are active at different sites within the GABAA chloride-ionophore receptor complex, the present findings would suggest that the GABAA receptor may play a role in regulating the voluntary intake of ethanol.

Microstructural analysis of the effects of THIP, a GABAA agonist, on voluntary ethanol intake in laboratory rats

The effects of GABAA agonist THIP on the acquisition of voluntary ethanol intake and the pattern of food and water consumption were examined through the use of a computer-controlled data acquisition system. Twenty male Long-Evans rats were randomly assigned to two groups, one of which received THIP (16 mg/kg, IP) and the other an equal volume of saline. Subjects were presented with a free choice of ethanol and water immediately following drug injections, which occurred every other day. The initial concentration of ethanol presented was 2% and was increased by increments of 2% following the second presentation of each concentration, up to a maximum concentration of 10%. Subjects treated with THIP consumed significantly greater amounts of ethanol than did saline controls. A microstructural analysis of bout patterns suggested that the increased consumption of ethanol was a function of an increase in the size, duration, and frequency of ethanol drinking bouts. Food intake was also attenuated by THIP treatment. The results indicated that the decrease in total food intake was a function of a decrease in the frequency of the food bouts. However, in contrast to that observed for ethanol intake, the size and duration of the food bouts were unchanged. The qualitatively different patterns in the microstructure of consummatory behavior for ethanol and food following THIP treatment would suggest that differential mechanisms may mediate the food and ethanol effects observed in the present study. In addition, the differential effects of THIP on ethanol consumption relative to water would suggest that GABAA manipulations may play a role in influencing the acquisition of voluntary ethanol drinking.

Differential effects of an early housing manipulation on cocaine-induced activity and self-administration in laboratory rats

Several reports in the literature suggested that environmental influences which are reflected in the social housing conditions of the rat may play a role in the expression of individual differences in drug self-administration. The present experiments were performed in order to further examine the effects of early housing manipulations, as reflected by grouped or isolation housing, on cocaine-induced behavioral responding. The first study examined the effects of this manipulation on the locomotor stimulant properties of cocaine. The results suggested that grouped housing produced a significantly greater increase in cocaine-induced locomotion than was observed in animals housed in isolation. Experiment 2 examined the effects of housing manipulations on the self-administration of cocaine under a continuous reinforcement schedule. Differences in the rate of cocaine self-administration were only observed at the lowest dose tested. Responding at all other doses was equivalent, including the optimal dose for both groups, suggesting that the housing manipulations failed to affect the reinforcing efficacy of cocaine. The present investigation suggests that, while the early housing manipulation produced a differential sensitivity in rats to the stimulant properties of cocaine, the same manipulation failed to alter the sensitivity of rats to the reinforcing properties of cocaine as assessed through self-administration.