Conditioned lever-press avoidance response in mice: acquisition processes and effects of diazepam

Effects of environmental and pharmacological manipulations on cocaine-vs-negative reinforcer choice in male and female rats

RATIONALE

The adverse consequences of human addictive drug use could be the result of either addictive drug consumption resulting in punishment (e.g., incarceration) or failure to engage in negative-reinforced behaviors that might compete with drug-maintained behaviors (e.g., contingency management strategies that reset payment amounts for drug free urines).

OBJECTIVE

The goal of the present study was to establish a discrete-trial cocaine-vs-negative reinforcer (SNR) choice procedure where rats were presented with a simplified model of this conflict: choose negative reinforcement (i.e., escape or avoid foot shock) or choose an intravenous (IV) cocaine infusion followed by an inescapable shock.

METHODS

Responding was maintained in male and female rats by IV cocaine infusions (0.32-1.8 mg/kg/inf) and a SNR (0.1-0.7 mA shock) under a discrete-trial concurrent "choice" schedule during daily sessions. Following parametric reinforcer magnitude and response requirement experiments, the effects of 12 h extended access cocaine self-administration and acute diazepam (0.32-10 mg/kg, IP) pretreatment were determined on cocaine-vs-SNR choice.

RESULTS

Negative reinforcement was chosen over all cocaine doses. Lowering shock magnitude or increasing SNR response requirement failed to promote behavioral reallocation towards cocaine. Extended access cocaine self-administration sessions resulted in high daily cocaine intakes but failed to significantly increase cocaine choice in all (19) but one rat. Acute diazepam pretreatment also did not alter choice behavior up to doses that produced behavioral depression.

CONCLUSIONS

These results suggest that SNRs may be a source of reinforcement that effectively compete with and mitigate maladaptive addictive drug-maintained behaviors in the general population.

Variable-interval schedules of timeout from avoidance: effects of chlordiazepoxide, CGS 8216, morphine, and naltrexone

Rats were trained on concurrent schedules in which pressing one lever postponed shock and pressing the other occasionally (variable-interval schedule) produced a 2-min timeout during which the shock-postponement schedule was suspended and its correlated stimuli were removed. These procedures provided a baseline for studying the effects of drugs on behavior maintained by different sources of negative reinforcement (shock avoidance and timeout from avoidance). Experiment 1 studied a benzodiazepine agonist, chlordiazepoxide, and antagonist, CGS 8216. Chlordiazepoxide (2.5-30 mg/kg) had little effect on avoidance responding except at higher doses, when it reduced responding. By comparison, responding on the timeout lever was increased in 5 of 6 rats. These effects were reversed by CGS 8216 (2.5-5 mg/kg) in the 2 rats tested, but CGS 8216 had no effect by itself. Experiment 2 studied an opiate agonist, morphine, and antagonist, naltrexone, with 3 rats. Morphine's (2.5-20 mg/kg) effects were opposite those of chlordiazepoxide: At doses that either increased or had no effect on avoidance responding, morphine depressed timeout responding. Naltrexone (5 mg/kg) reversed these actions but had no effect by itself.

Differences in acquisition of discrete lever-press and shuttle avoidance responses in 6 strains of mice

Characteristics of the acquisition processes of discrete lever-press and shuttle avoidance responses (intertrial interval = 25 sec, warning duration = 5 sec with an escape contingency, and 1 session = 1 hr training/day) as well as those of the ambulatory activity were investigated in 6 strains of mice (dd, ICR, BALB/c, C57BL/6, C3H/He and DBA/2). In the lever-press avoidance situation, the dd, BALB/c and DBA/2 strains demonstrated a good avoidance response, showing average avoidance rates of higher than 80% within 10-15 sessions of the training. The C3H/He also demonstrated a good avoidance response, though 20 sessions or more of the training were required to attain to the level. The ICR and C57BL/6 strains demonstrated a poorer avoidance response than the other 4 strains, and achieved average avoidance rates of 30-40%. The dd, BALB/c, C3H/He and DBA/2 strains also demonstrated a good shuttle avoidance response when they were trained in an experimental box of 50 cm in width. In contrast, the ICR and C57BL/6 strains demonstrated an extremely poor avoidance response in this situation, showing an average avoidance rate of less than 10%. However, when the dd, ICR and C57BL/6 strains were trained in a shuttle box of 30 cm in width, they rapidly acquired the avoidance response, and the average avoidance rates finally achieved were much higher than those of the mice trained in the shuttle box of 50 cm in width. In particular, the C57BL/6 strain exhibited the best avoidance response among the 3 strains. The ambulatory activity of the C57BL/6 strain was less than those of the other 5 strains.

Effects of psychoactive drugs on conditioned avoidance response in Mongolian gerbils (Meriones unguiculatus): comparison with Wistar rats and dd mice

In order to examine applicability of Mongolian gerbils as experimental animals in the field of behavioral pharmacology, the acquisition process of a discrete lever-press avoidance response and effects of psychoactive drugs thereon were studied. The results were compared with those in Wistar rats and dd mice. The gerbils learned the avoidance response much better than the rats and mice. The response rates established were higher in an order of the mice, the gerbils and the rats. Methamphetamine (0.13-1 mg/kg SC), cocaine (2.5-20 mg/kg SC) and morphine (1.3-10 mg/kg SC) facilitated the gerbils' avoidance response, i.e., eliciting a dose-dependent increase in the response rate and a slight increase in the avoidance rate. In contrast, chlorpromazine (0.5-4 mg/kg SC), haloperidol (0.025-0.2 mg/kg SC), pilocarpine (1-8 mg/kg SC), physostigmine (0.05-0.4 mg/kg SC), pentobarbital (5-20 mg/kg SC) and diazepam (0.5-2 mg/kg SC) suppressed the gerbils' avoidance response, i.e., eliciting a dose-dependent decrease in both the response and avoidance rates. Atropine (1.3-10 mg/kg SC) decreased only the response rate without a marked change in the avoidance rate. Scopolamine (0.031-0.5 mg/kg SC) did not produce a marked change in the avoidance response. The qualitative changes in the avoidance response in the gerbils were similar with those in the rats and mice after administration of central stimulants, antipsychotics, cholinergic agonists, central depressant and antianxiety drug, though the sensitivities were different. In particular, the gerbils showed a high sensitivity to the avoidance-suppressing effect of diazepam.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparisons between discrete lever-press and shuttle avoidance responses in mice: acquisition processes and effects of psychoactive drugs

Acquisition processes of discrete lever-press (L-type) and shuttle (S-type) avoidance responses as well as effects of psychoactive drugs thereon were investigated in dd strain mice. The mice showed a more rapid acquisition of S-type avoidance than L-type. However, the mean avoidance rates and occurrences of good-performing mice (showing an avoidance rate of higher than 75%) were almost the same in both types when the training was carried out for more than 15 sessions of 1 hr each. The response rate of L-type avoidance was 2.5-3 times as high as that of S-type avoidance. Methamphetamine and cocaine increased the response rate in almost the same grade in both types of avoidance. Chlorpromazine, haloperidol, pilocarpine and physostigmine suppressed both L-type and S-type avoidance responses. However, the L-type showed a higher sensitivity than the S-type to the avoidance-suppressing effect of these drugs. Atropine, scopolamine and morphine suppressed L-type avoidance response, while they facilitated S-type avoidance. The drug-induced changes in the response rate of the S-type were well correlated with those in the ambulatory activity. The changes in the response rate of the L-type were also consistent with those in the ambulatory activity after administration of methamphetamine, cocaine, chlorpromazine, haloperidol, pilocarpine and physostigmine, but inconsistent after atropine, scopolamine and morphine. The present results suggest that L-type and S-type avoidance responses in mice sometimes show a different change after administration of psychoactive drugs.

Animal models for the study of anti-anxiety agents: a review

Animal models for the study of anxiolytic agents are reviewed and evaluated according to pharmacological and behavioral criteria. Although there are important exceptions, in general, most early animal models have not provided a reliable basis for identifying compounds with potential anxiolytic action, or for delineating the mechanisms of anxiolytic drug action. The possibility that phylogenetically 'prepared' forms of defensive learning might serve as a basis for the study of anxiolytic agents is introduced.