Sex differences in the effect of wheel running on subsequent nicotine-seeking in a rat adolescent-onset self-administration model

Rationale

Wheel running attenuates nicotine-seeking in male adolescent rats; however, it is not known if this effect extends to females.

Objective

To determine if wheel running during abstinence would differentially attenuate subsequent nicotine-seeking in male and female rats that had extended access to nicotine self-administration during adolescence.

Methods

Male (n?=?49) and female (n?=?43) adolescent rats self-administered saline or nicotine (5 μg/kg) under an extended access (23-h) paradigm. Following the last self-administration session, rats were moved to polycarbonate cages for an abstinence period where they either had access to a locked or unlocked running wheel for 2 h/day. Subsequently, nicotine-seeking was examined under a within-session extinction/cue-induced reinstatement paradigm. Due to low levels of nicotine-seeking in females in both wheel groups, additional groups were included that were housed without access to a running wheel during abstinence.

Results

Females self-administered more nicotine as compared to males; however, within males and females, intake did not differ between groups prior to wheel assignment. Compared to saline controls, males and females that self-administered nicotine showed a significant increase in drug-seeking during extinction. Wheel running during abstinence attenuated nicotine-seeking during extinction in males. In females, access to either locked or unlocked wheels attenuated nicotine-seeking during extinction. While responding was reinstated by cues in both males and females, levels were modest and not significantly affected by exercise in this adolescent-onset model.

Conclusions

While wheel running reduced subsequent nicotine-seeking in males, access to a wheel, either locked or unlocked, was sufficient to suppress nicotine-seeking in females.     

Acamprosate attenuates cue-induced reinstatement of nicotine-seeking behavior in rats

Acamprosate is used in the treatment of alcoholism; however, there is little information on its effects on nicotine addiction. The objective of this study was to determine whether acamprosate inhibits cue-induced relapse to nicotine self-administration in the rat. Rats were trained to press a lever to obtain intravenous infusions of nicotine (0.03 mg/kg/infusion) that were associated with the illumination of a cue light. After 29 days of nicotine self-administration sessions, extinction sessions were run during which responses on the active lever did not result in the infusion of nicotine or the illumination of the cue light. After 14 days of extinction sessions the rats received twice-daily injections of saline or acamprosate (50, 100, or 200 mg/kg/intraperitoneally). Seven days later the response to the previously conditioned cue was tested, but only saline infusions were delivered. Pretreatment with all doses of acamprosate reduced responding to a cue previously associated with nicotine. The lowest dose of acamprosate (50 mg/kg) reduced responding for the cue previously associated with nicotine infusions, but had no effect on food-rewarded behavior. These results show that acamprosate reduced cue-induced nicotine-seeking behavior and suggest that acamprosate might be efficacious in treating nicotine addiction in humans.     

Propranolol transiently inhibits reinstatement of nicotine-seeking behaviour in rats

Noradrenergic transmission has been implicated in the affective component of relapse to tobacco smoking. Evidence in human and laboratory animals showed that smoking or nicotine administration may cause changes of the noradrenergic system resulting in hyperactivity in this system after cessation. It has been hypothesised that the anti-adrenergic beta-blocker propranolol may decrease affective activation and arousal observed during drug withdrawal or cue-induced relapse. The aim of the present work was to test the effects of propranolol pre-treatment in a rat model of nicotine cue-induced relapse to nicotine seeking. We also tested the effects of propranolol on food cue-induced reinstatement of food seeking in rats trained on food self-administration. Propranolol transiently inhibited nicotine cue-induced reinstatement. The inhibitory effect of propranolol reached a peak after 30 min from the beginning of the reinstatement session and then it declined until it was completely absent at the end of the 3-h session. This inhibitory effect of propranolol was not observed when the drug was tested versus reinstatement with food cues. The present study suggests a weak effect of propranolol to counteract nicotine cue-induced reinstatement of nicotine seeking. Therefore, these findings do not support a potential use of propranolol for prevention of smoking relapse.     

Effect of acetyl-L-carnitine on ethanol consumption and alcohol abstinence syndrome in rats

The effect of acetyl-L-carnitine on alcohol consumption and its possible ability to alleviate all symptomatology of ethanol withdrawal syndrome has been investigated in rats. Alcohol-dependence was induced in animals (9-15 g/kg ethanol solution at 20% for a period of 4 days) in order to measure the effects of acetyl-L-carnitine on ethanol abstinence syndrome. The ethanol dependence phase was characterized by the onset of signs and responses of progressive severity: hyperactivity, tremors, spastic rigidity and spontaneous convulsive seizures. After 4 days, 8 h after the last ethanol administration, two groups of animals received acetyl-L-carnitine (125 mg/kg and 250 mg/kg intraperitoneally, respectively) and the intensity of the withdrawal syndrome was assessed on the basis of the appearance of tremors. The effect of acetyl-L-carnitine on voluntary alcohol consumption was investigated in a rat line selected for innate ethanol preference. For 15 days the animals could freely choose both water and/or a hydroalcoholic solution (10% p:v). Acetyl-L-carnitine was given intraperitoneally at a dose of 200 mg/kg twice daily. The water and the hydroalcoholic solution levels were checked at the same time daily. Acetyl-L-carnitine treatment significantly reduced the onset of tremors in ethanol withdrawal syndrome as well as the level of ethanol intake in alcohol-preferring rats. These results suggest a possible pharmacological role of acetyl-L-carnitine in the treatment of alcohol dependence.     

Effect of social stress during acute nicotine abstinence

Rationale  

Relapse to smoking is often precipitated by stress, yet little is known about the effects of nicotine withdrawal on responses to acute stress, or whether nicotine replacement reverses withdrawal-induced changes in stress response.     

Effects of trifluoperazine upon wheel-running activity of rats

Rats in group A were injected with 0.9 % NaCl solution while those in group B received trifluoperazine. Six hours later, these injected animals from both groups were placed in individual activity wheels and a measure was taken of their activity over a 2-hr period. After each test trial the rats were returned to their home cage and fed. Following 8 test trials the animals were given 5 additional test trials in which the conditions were reversed. Rats in group A received trifluoperazine while those in group B were injected with saline. The results clearly showed that trifluoperazine depressed the motor activity of rats in a running wheel. This effect was demonstrated between independent groups receiving either the drug or the saline injections and was also evident in the immediate decline in running activity when the rats were switched from saline to trifluoperazine injections.     

Nicotine self-administration and reinstatement of nicotine-seeking in male and female rats

Background

Tobacco addiction is a relapsing disorder that constitutes a substantial worldwide health problem, with evidence suggesting that nicotine and nicotine-associated stimuli play divergent roles in maintaining smoking behavior in men and women. While animal models of tobacco addiction that utilize nicotine self-administration have become more widely established, systematic examination of the multiple factors that instigate relapse to nicotine-seeking have been limited. Here, we examined nicotine self-administration and subsequent nicotine-seeking in male and female Sprague-Dawley rats using an animal model of self-administration and relapse.

Methods

Rats lever pressed for nicotine (0.03 and 0.05 mg/kg/infusion, IV) during 15 daily 2-h sessions, followed by extinction of lever responding. Once responding was extinguished, we examined the ability of previously nicotine-paired cues (tone + light), the anxiogenic drug yohimbine (2.5 mg/kg, IP), a priming injection of nicotine (0.3 mg/kg, SC), or combinations of drug + cues to reinstate nicotine-seeking.

Results

Both males and females readily acquired nicotine self-administration and displayed comparable levels of responding and intake at both nicotine doses. Following extinction, exposure to the previously nicotine-paired cues or yohimbine, but not the nicotine-prime alone, reinstated nicotine-seeking in males and females. Moreover, when combined with nicotine-paired cues, both yohimbine and nicotine enhanced reinstatement. No significant sex differences or estrous cycle dependent changes were noted across reinstatement tests.

Conclusions

These results demonstrate the ability to reinstate nicotine-seeking with multiple modalities and that exposure to nicotine-associated cues during periods of a stressful state or nicotine can increase nicotine-seeking.     

Reinstatement of nicotine-seeking behavior by drug-associated stimuli after extinction in rats

Rationale Smoking-related environmental stimuli have been implicated as an important factor in triggering relapse in abstinent tobacco smokers, and recent evidence indicates that drug-associated stimuli can reinstate nicotine-seeking in rats. However, there is little investigation on the factors that contribute to the latter effect. Objective This study examined whether a nicotine-associated visual stimulus (VS) can reinstate nicotine-seeking after extinction in a response-reinstatement model of relapse, and whether the behavioral effects of the VS are sensitive to pharmacological blockade of nicotinic neurotransmission. It also determined whether active lever reassignment after food training influences nicotine self-administration and the VS-induced reinstatement. Methods Male Sprague–Dawley rats were trained to self-administer nicotine (0.03 mg/kg/infusion, IV) and associate a VS with each nicotine infusion in 30 daily 1-h sessions. Half of the animals received nicotine infusions for responding at the same lever that previously delivered food; for the other half, infusions resulted from pressing the previously inactive lever during food training. Then, the nicotine-maintained response was extinguished by saline substitution and withholding the VS. One day after rats reached extinction criterion, the reinstatement tests were conducted where the VS was response-contingent represented without further delivery of nicotine. In pharmacological tests, a nicotinic antagonist, mecamylamine, was subcutaneously administered 30 min before reinstatement sessions. Results Presentation of the nicotine-associated VS significantly reinstated responding at the previously drug-reinforced lever and pretreatment with mecamylamine effectively attenuated the response-reinstating effect of the VS. Additionally, animals showed similar profiles of nicotine-taking and nicotine-seeking behavior regardless of reassignment of the active lever after food training. Conclusions Nicotine self-administration and the VS-induced reinstatement of nicotine-seeking do not result from a lever bias due to prior experience for food reinforcement. Significantly, these results suggest that environmental stimuli associated with nicotine self-administration can effectively elicit nicotine-seeking behavior in abstinent subjects, that this effect is blocked by nicotine antagonism, and that the present procedures may be useful for studying neurobiological mechanisms of nicotine-seeking behavior and relapse.     

Mecamylamine attenuates cue-induced reinstatement of nicotine-seeking behavior in rats.

Mecamylamine, a noncompetitive nicotinic cholinergic antagonist, inhibits nicotine self-administration in animals and may attenuate tobacco smoking in humans trying to quit. Our preliminary data suggested that this agent, at a dose of 2 mg/kg (subcutaneous (s.c.)), also attenuates cue-induced relapse to nicotine-seeking behavior in rats. This study determined whether mecamylamine-induced attenuation can be obtained at doses lower than the high 2 mg/kg dose used in the first study, and whether it is specific to nicotine-associated cues. Male Sprague-Dawley rats were trained to intravenously self-administer nicotine (0.03 mg/kg/infusion) on a fixed-ratio 5 schedule. Each infusion was accompanied by a visual cue (1 s onset of a lever light followed by offset of a house light for 20 s during which time no infusions could be obtained). After the nicotine-maintained responding was extinguished by withholding the delivery of nicotine (saline substitution) and its associated cue, reinstatement tests were conducted. Response-contingent re-presentation of the cue without further availability of nicotine significantly reinstated extinguished responding at the previously nicotine-reinforced lever. Pretreatment with mecamylamine (0.5, 1, and 2 mg/kg, s.c.) dose-dependently attenuated the cue-induced reinstatement of lever responding. Mecamylamine did not change food-taking and -seeking responses, whereas the highest dose (2 mg/kg) decreased nicotine self-administration behavior. The results confirm previous findings that stimuli conditioned to nicotine self-administration effectively elicit reinstatement of nicotine-seeking behavior after extinction and demonstrate that mecamylamine, besides suppressing self-administration of nicotine, effectively attenuates cue-induced nicotine-seeking behavior. These findings suggest that the response-reinstatement procedures used in this study may be useful for studying neurobiological mechanisms of nicotine-seeking behavior and that mecamylamine-like drugs may be potential candidates for pharmacological treatment and prevention of relapse to tobacco smoking in abstinent smokers.     

Amplified reacquisition of nicotine self-administration in rats by repeated stress during abstinence

Rationale

Quitting smoking is often very challenging, leading to frequent relapse. Exposure to acute and chronic stress during abstinence increases the likelihood of relapse to smoking. In rodents, stress acutely reinstates nicotine seeking after extinction of nicotine self-administration (SA). However, whether reacquisition of nicotine taking is amplified by chronic stress during abstinence from nicotine SA has not been determined in animals.

Objectives

We sought to determine effects of repeated restraint stress during abstinence on reacquisition of nicotine SA.

Methods

Rats acquired nicotine SA (23 h/day) under a fixed-ratio (FR) 5 schedule of reinforcement, which was followed by an abstinence phase. Restraint (0, 2, and 4 times) was administered during abstinence. Animals reacquired nicotine SA, first under a progressive ratio (PR) schedule, beginning immediately after the final stress, followed by an FR5 schedule. In another experiment, reacquisition (FR5) began 24 h after the final stress. No PR testing was conducted.

Results

Four restraint stress exposures during abstinence, but not only two, enhanced reacquisition of nicotine SA by increasing nicotine injections under a PR schedule beginning immediately after the final stress (p?<?0.05) followed by increasing nicotine intake under an FR5 schedule (p?<?0.05). This was observed even when the final stress and reacquisition trial were separated by 24 h. Moreover, repeated stress-induced nicotine taking during the behaviorally inactive phase (i.e., lights on) of the 24-h diurnal cycle.

Conclusions

Chronic (i.e., repeated) stress during abstinence promotes reacquisition of nicotine SA and affects diurnal pattern of nicotine intake.     

The effects of amphetamine and scopolamine on adjunctive drinking and wheel-running in rats

Two groups of rats were exposed to a fixed-interval 90 s schedule of food reinforcement. One group had access to a drinking tube containing water and the second had access to a running wheel. Amphetamine (0.3–10.0 mg/kg) and scopolamine (0.1–3.0 mg/kg) were assessed for their effects on lever-pressing, adjunctive drinking and adjunctive wheel-running. Low to moderate doses of amphetamine increased overall rates of lever-pressing, whereas the highest dose decreased them. Scopolamine decreased overall lever-pressing rates in a dose-dependent manner. Both drugs changed the within-interval pattern of lever-pressing from one of increasing probability through the interval to almost constant probability throughout. Overall rates of adjunctive drinking and adjunctive wheel-running were decreased by amphetamine and scopolamine. Amphetamine failed to alter the within-interval patterns of either drinking or wheel-running in any substantial manner. The effect of scopolamine was to make the probabilities of each adjunctive behaviour more even through the interval. Although the two drugs had different actions, there was little difference in the way drinking and wheel-running were affected by each.     

Effects of alcohol consumption during pregnancy on subsequent maternal behaviour in rats

Nine Holtzman rats were maintained from days 5-18 of pregnancy on a liquid diet of which ethanol constituted 35% of the calories while nine rats were pair-fed an isocaloric diet that had maltose-dextrin substituted for the ethanol. Beginning on day 19 of gestation and continuing for five days the dams in both groups were given a choice among lab chow, water, and their respective liquid diets. During the five days of choice, alcohol consumption dropped to approximately 20% of pre-choice levels. The dams and pups showed no behavioural withdrawal symptoms. While the alcohol-treated litters showed greater variability in litter size and more pup deaths during nursing, the maternal behaviour of the alcohol dams was essentially normal, with only their pup protectiveness being rated lower than that of the control dams.     

Effect of peripheral administration of cinnarizine and verapamil on the abstinence syndrome in diazepam-dependent rats

The effects of two calcium channel blockers (verapamil and cinnarizine) were evaluated on diazepam withdrawal symptoms. Rats were made diazepam dependent by chronic treatment with daily injections of the drug, 20 mg/kg IP for 3 weeks. On abrupt termination of the drug, animals showed withdrawal hyperactivity that was assessed by autonomic, behavioural and motor signs. The peak effect was seen 3 days after the withdrawal of diazepam. On IP administration, verapamil and cinnarizine (10, 20 and 40 mg/kg) given on eight occasions at an interval of 12 h reversed the withdrawal-induced increase in spontaneous motor activity. Cinnarizine in higher doses (20 and 40 mg/kg) was found to be effective in suppressing the behavioural signs but verapamil did not show any protective effect against startle response and irritability. These results suggest that modulation of the calcium influx in the CNS might influence withdrawal.This study was presented in XIth International Congress of Pharmacology (IUPHAR) at Amsterdam (July 1–6, 1990)     

Changes in fixed-interval behavior during chronic morphine treatment and morphine abstinence in rats

Rats previously trained to a fixed-interval schedule (FI 2 min) were treated twice daily with saline or morphine hydrochloride (final dose 40 mg/kg i.p.) for 44 days.On day 45 an abstinence state was induced by withdrawing morphine or by giving nalorphine (1 mg/kg i.p.). Operant behavior was recorded on alternate days during the period of chronic treatment and during the withdrawal phase (21 days). It was found that the number of lever presses decreased significantly during the first days of morphine administration but increased later over the control values. The quarter-life was not changed during this period. Morphine withdrawal and nalorphine treatment both caused a further increase in lever presses that lasted about 11 days. Again quarter-life was not changed. These results indicate that the effects of morphine on FI behavior in rats not only undergo tolerance but are actually reversed during the chronic treatment.The data obtained during the withdrawal phase are discussed in relation to the secondary abstinence syndrome described by Martin et al. (1963).     

Cortico-limbic circuitry for conditioned nicotine-seeking behavior in rats involves endocannabinoid signaling

Rationale The endocannabinoid system plays an important role in conditioned drug seeking, but the neuronal mechanisms involved in this behavior are unclear. Objectives Here, we evaluate the role of endogenous cannabinoids in the cortico-limbic circuitry in cue-induced nicotine-seeking behavior in rats. Methods Animals were first trained to self-administer nicotine (0.03 mg/kg/injection, IV) under conditions in which responding was reinforced jointly by response-contingent nicotine injections and audiovisual stimuli. During subsequent sessions, nicotine was withdrawn and responding was reinforced by contingent presentation of the stimuli only. One month after nicotine removal, the cannabinoid CB1 receptor antagonist, rimonabant, was injected bilaterally into the shell of the nucleus accumbens (ShNAcc, 0.3, 3, or 30 ng/0.5 μl), the basolateral amygdala (BLA, 30 ng/0.5 μl), or the prelimbic cortex (PLCx, 30 ng/0.5 μl). Results Rimonabant injected into the ShNAcc dose-dependently reduced nicotine-seeking behavior without modifying spontaneous locomotor activity. Similar results were obtained when the drug (30 ng) was injected into the BLA or the PLCx. The anatomical specificity was confirmed in a control experiment using [³H]rimonabant. Fifteen minutes after drug injection, when the behavioral effects of rimonabant were already achieved, radioactivity was detected at the site of injection and had not diffused to adjacent regions. Conclusions These findings demonstrate that increased endocannabinoid transmission critically triggers conditioned nicotine-seeking behavior in key cortico-limbic regions.     

Factors that determine a propensity for cocaine-seeking behavior during abstinence in rats.

Individual differences in locomotor responses to novelty and psychostimulants, and sensitization following repeated drug exposure, predict increased sensitivity to the reinforcing effects of psychostimulants and are thought to underlie vulnerability to drug addiction. This study tested whether these factors determine another core feature of drug addiction, the propensity for drug-seeking behavior during abstinence in rats with prior cocaine-self-administration experience. Low and high response groups for each of these factors were determined in outbred rats by the median locomotor response to novelty and amphetamine prior to cocaine self-administration (pre-test), and to amphetamine during abstinence (post-test). Cocaine-seeking behavior during abstinence was measured by the level of drug-paired lever responding during extinction, and also during reinstatement induced by cocaine-associated cues, an amphetamine priming injection, and footshock stress. Animals with low and high locomotor responses to novelty and the amphetamine pre-test showed similar levels of cocaine-seeking behavior during extinction and reinstatement testing. Locomotor responses to amphetamine following cocaine self-administration (post-test) also failed to determine amphetamine's ability to reinstate cocaine-seeking behavior. Conversely, high levels of amphetamine-induced reinstatement were associated specifically with escalating cocaine intake during prior self-administration. These animals also developed locomotor sensitization to amphetamine following cocaine self-administration (post-test vs. pre-test), but the capacity to develop locomotor sensitization was not sufficient to determine a propensity for cocaine-seeking behavior. The findings suggest that the relationship between locomotor responses to novelty, amphetamine and behavioral sensitization a,nd the propensity for cocaine-seeking behavior during abstinence is complex, while the level of drug intake during prior self-administration is a primary determinant of this behavior.     

The cannabinoid antagonist AM251 attenuates nicotine self-administration and nicotine-seeking behaviour in rats

The cannabinoid receptor subtype (CB1) antagonist rimonabant (SR141716) has been shown to decrease nicotine self-administration and attenuate nicotine-evoked dopamine release in the nucleus accumbens; effects that support recent findings on its clinical efficacy as a smoking cessation aid. The present experiments aim to advance our understanding on the role of CB1 receptors in rodent models of nicotine dependence. AM251, a selective antagonist at CB1 receptors dose-dependently (1, 3 and 10mg/kg IP) suppressed intravenous nicotine (0.03mg/kg per infusion) self-administration in rats during three successive days of pre-treatment. This reduction was short lasting since behaviour was reinstated by suspending AM251 pre-treatment. This was relatively specific to nicotine self-administration since the profile of these reductions produced by AM251 was significantly different from the responses maintained by food pellets. In a model of nicotine-seeking behaviour, rats that had been extinguished by removal of nicotine and associated cues, and presented with a priming dose of nicotine (0.2mg/kg SC) with the cues, showed robustly reinstated responses to nicotine-seeking behaviour. Acute pre-treatment with AM251 (1-10mg/kg IP) dose-dependently attenuated the reinstatement effects produced by nicotine and the contingently presented cues. These preclinical findings support the use of rimonabant as a smoking cessation aid and highlight the CB1 receptor as a viable target to control intake of nicotine and prevent relapse.     

Effect of duration of pilocarpine-induced status epilepticus on subsequent cognitive function in rats

The aim of this study was to determine the effect of the duration of pilocarpine-induced status epilepticus (SE) on subsequent cognitive function in rats. SE was induced by pilocarpine (320 mg/kg i.p.) and was terminated by injection of 1 mg/kg diazepam at 30, 60 and 90 min in 3 groups of 10 rats each. Cognitive function was tested by a passive avoidance task and was assessed at the baseline and on days 1, 7, 14 and 21 (post SE). It was found that cognitive function was disrupted on days 7, 14 and 21 post SE in rats who had SE for 60 and 90 min, whereas it was not affected in rats that had 30 min of SE. Hence, the duration of SE may affect future cognitive performance and mandates emergency treatment.     

Naloxone suppression and morphine enhancement of voluntary wheel-running activity in rats.

This study examines the effects of the opioid receptor antagonist, naloxone, and the agonist, morphine, on voluntary wheel-running activity (WR) in rats. Male Sprague-Dawley rats were given 1-h access to a running wheel under non-deprived conditions. Naloxone injections (1.0, 0.5, or 0.25 mg/kg, ip), administered immediately before access to running wheels, dose-dependently suppressed WR. In another experiment, subjects were given 6-h access to running wheels under nondeprived conditions for 5 consecutive days. Morphine injections (2.0 mg/kg, sc) were found to increase WR after an initial suppression. These data demonstrate that naloxone inhibits WR, while morphine both suppresses and enhances WR depending on time and dose. These are in agreement with data on other behaviors that indicate that endogenous opioid systems play a major role in the mediation of motivational behaviors.     

Effects of caffeine on persistence and reinstatement of nicotine-seeking behavior in rats: interaction with nicotine-associated cues

Rationale  

Caffeine and nicotine are the most commonly co-used psychostimulants. However, it is still unclear whether caffeine exposure enhances nicotine-seeking behavior.