Cocaine, pemoline and amphetamine on learning and retention of a discrimination test in mice

Amphetamine and pentylenetetrazole given post-trial 1 enhance one-trial tolerance to the anxiolytic effect of diazepam in the elevated plus-maze in mice

There are several hypotheses to explain the lack of an anxiolytic effect on animals with previous maze experience (one-trial tolerance). Some of these hypotheses are related to learning and memory, so the reduction of trial 1 duration to 1 min or amnesic drug administration before trial 1 prevents the lack of an anxiolytic effect in trial 2. Amphetamine and pentylenetetrazole have been shown to enhance memory consolidation when administered immediately after training. Thus, the aim of the present study was to evaluate the effect of amphetamine (1.0-3.0 mg/kg) or pentylenetetrazole (30.0 mg/kg), at putative memory-enhancing doses, on the effect of diazepam (2.5 mg/kg) in the elevated plus-maze trial 2 on mice exposed to a 1-min long trial 1. Mice were submitted to 1-min trial 1 in the elevated plus-maze immediately followed by drug treatment (saline, amphetamine, or pentylenetetrazole) and to elevated plus-maze trial 2 after 48 h. Animals were treated with vehicle or diazepam 30 min before trial 2. The results showed that post-trial 1 saline and 1.0 mg/kg amphetamine did not induce one-trial tolerance. On the other hand, 2.0 and 3.0 mg/kg amphetamine and 30 mg/kg pentylenetetrazole induced a lack of anxiolytic effect of diazepam on trial 2 even with 1-min trial 1 length. Furthermore, these data were not due to novelty exposure in trial 1 or to amphetamine treatment so that mice exposed to an activity chamber instead of the plus-maze (trial 1) and then immediately submitted to amphetamine treatment (2.0 mg/kg) did not show one-trial tolerance 48 h after trial 1. Taken as a whole, these data support the hypothesis that memory is involved in the lack of an anxiolytic effect in the elevated plus-maze trial 2.

Strain-dependent effects of post-training dopamine receptor agonists and antagonists on memory storage in mice

Post-training administration of the selective D1 or D2 agonists SKF 38393 and LY 171555 dose dependently impairs retention of an inhibitory avoidance response in DBA/2 mice. In agreement, the selective D1 or D2 antagonists SCH 23390 and (-)-sulpiride improve retention. These effects are opposite to those observed in the C57BL/6 strain, as previously reported. Moreover, B6D2F1 hybrids present a response to SKF 38393, LY 171555, SCH 23390, and (-)-sulpiride that parallels that of the C57BL/6 strain, thus suggesting that the neural mechanisms underlying the effects of DA agonists or antagonists on memory processes may be inherited through a dominant mode of inheritance.

Cocaine and amphetamine facilitate retention of jump-up responding in rats

The effects of cocaine and d-amphetamine administration on the acquisition of an automated jump-up active avoidance task were examined in two separate experiments. On days 1 and 2, male Sprague-Dawley rats received one escape-only training trial, followed immediately by the intraperitoneal injection of cocaine, amphetamine, or saline. On day 3, subjects received eight escape/avoidance trials. The posttraining administration of cocaine (2.75 and 5.55 mg/kg) and amphetamine (0.3 and 1.0 mg/kg) on days 1 and 2 facilitated jump-up avoidance performance on day 3. Importantly, both cocaine and amphetamine enhanced learning and memory under experimental conditions that allowed for drug-free training and testing.

Post-training dopamine receptor agonists and antagonists affect memory storage in mice irrespective of their selectivity for D1 or D2 receptors

Post-training administration of the selective D1 and D2 agonists SKF 38393 and LY 171555 dose-dependently facilitated retention of an inhibitory avoidance response in mice, while the selective D1 or D2 antagonists SCH 23390 and (-)sulpiride produced an impairment of retention. These effects are not to be ascribed to a nonspecific action of the drugs on retention performance, as the latencies during the retention test of those mice that had not received a footshock during the training were not increased by the post-training drug administration. The effects on retention performance induced by DA agonists and antagonists seem to be due to an effect on memory consolidation, since they have been observed when drugs were given at short, but not at long, periods of time after training. These results showing a similar role of D1 and D2 receptor types on memory storage appear not to be consistent with a body of neuropharmacological, neurophysiological, and behavioral evidence pointing to a different functional role of these types of DA receptors. This discrepancy is discussed in terms of possible involvement of different brain systems, peripheral systems, or possible second messenger processes activated by the two receptor types and leading to similar effects on memory processes.

Cocaine and vigilance task performance of rats: effects of delay of reinforcement

In two experiments rats were food-reinforced for pressing one of two levers in an operant chamber, with the correct lever being indicated by the position of a briefly illuminated light. In Experiment 1 the levers were always in the chamber, whereas in Experiment 2 the levers were inserted into the chamber immediately after cue light termination and withdrawn immediately after a choice response. The rats were tested under four conditions: after an injection (SC) of saline or 2.5 mg/kg cocaine and with delay of reinforcement (DOR) of either 0 or 8 s. In both experiments, cocaine enhanced accuracy under the 0-s DOR condition. However, in neither experiment was there evidence of facilitation with cocaine under 8-s DOR, which by itself increased choice latencies and decreased accuracy when choice latencies exceeded 0.5 s. These results indicate that cocaine may only enhance performance in vigilance tasks under constrained conditions, e.g., those that require minimal levels of information processing.

Effects of cocaine and d-amphetamine on sustained and selective attention in rats

The effects of cocaine and d-amphetamine were compared in two attention-loading tasks. Cued by the position of a light, rats were food-reinforced for pressing one of two levers in a 2-choice, discrete-trial procedure. In the "sustained attention" task, the cue light was illuminated for a brief period (1.8 sec or less) at the beginning of each trial. In the "selective attention" task, the cue light remained on until a level press, while a blinking light over the incorrect lever served as a distractor. In the sustained attention task, low doses of d-amphetamine (0.25 mg/kg SC) and cocaine (2.5 mg/kg SC) enhanced accuracy; some doses of d-amphetamine (0.75 mg/kg SC) and cocaine (1.25 and 2.5 mg/kg SC) also reduced choice latencies. In the selective attention task, the lower doses of these drugs had no effect on accuracy, the highest dose of d-amphetamine (1.25 mg/kg SC) disrupted accuracy, and all doses of the drugs reduced choice latencies. The time to retrieve food was increased in a dose-dependent fashion by both drugs in both tasks. These results indicate that, other than differences in potency, cocaine and d-amphetamine induce similar behavioral effects in attention-loading tasks, with improvement or interference with performance dependent on the dose and the type of attention demanded of the task.

An hypothesis on the role of glucose in the mechanism of action of cognitive enhancers

This review presents evidence that some cognition enhancing drugs produce their beneficial effects on learning and memory by increasing the availability of glucose for uptake and utilization into the brain. The hypothesis further suggests that many cognition enhancing drugs act through a peripheral mechanism rather than directly on the brain. The general hypothesis is supported by four independent and converging pieces of evidence: 1) Some cognition enhancing drugs may not cross the blood-brain barrier, but can still facilitate memory; 2) Some cognition enhancing drugs are effective only when injected peripherally, but not when injected directly into the brain; 3) Many cognition enhancing drugs are not effective after adrenalectomy; 4) Cognitive function is correlated with glucose regulation in aged animals and humans. These four lines of research have implications for the role of glucose in the action of specific cognitive enhancers.

Cocaine enhances memory storage in mice

Mice were trained on a one-trial inhibitory avoidance task and given immediate post-training intraperitoneal injections of cocaine (0.03-1.00 mg/kg). On a retention test 24 h later, the retention latencies of mice given the 0.10 mg/kg dose were significantly higher than those of the controls. The effect of cocaine on retention was time-dependent: retention latencies were not altered in animals given cocaine 60 min after training. Administration of cocaine (0.1 mg/kg) prior to the retention test did not modify the retention performance of mice that received either saline or cocaine (0.1 mg/kg) immediately post-training. The findings suggest that cocaine affects retention by influencing post-training processes involved in memory storage.

Passive avoidance in rats: disruption by dopamine applied to the nucleus accumbens

The acquisition of a one-trial step-through passive avoidance task was examined in rats following the administration of nialamide IP and dopamine (DA) or saline into the nucleus accumbens. DA-treated rats displayed impaired learning of the task as evidenced by their lower step-through latencies on a retest trial 7 days later. The specificity of this impairment was studied in a 2 x 2 design involving intracerebral injections prior to both training and testing trials. It was found that DA treatment prior to the training trial disrupted learning or memorization of the task but that DA did not affect performance or retrieval and did not induce state-dependent learning. These findings suggest that DA applied to the nucleus accumbens does not facilitate learning per se.

A screening method for substances potentially active on learning and memory

A series of substances from different pharmacological classes was examined by two different tests for their activity on learning and memory. A concomitant evaluation was performed by use of a one-trial passive avoidance immediately followed by electroshock in mice and the pole-climbing test in rats. Only doses not producing changes in gross behavior (Irwin's test) were used. A facilitating action on all the considered parameters was observed for d-amphetamine, caffeine, L-glutamine, Mg pemoline, phosphorylserine, piracetam, strychnine, and tricyanoaminopropene. A worsening action was found for atropine, cycloheximide, diazepam, and morphine. Chlorpheniramine, diphenylhydantoin, GABA, imipramine, meclizine, mescaline, metrazol, and testosterone showed no or doubtful activity. Our results suggest that the parallel use of these relatively simple tests supplies information that is satisfactory for screening purposes and that has a high degree of predictability as substantiated by literature data.

Effects of mescaline and amphetamine on simultaneous visual discrimination in two inbred strains of mice

The effects of mescaline and amphetamine were investigated in BALB/cJ (BALB) and C57BL/6J (C57) mice using the five-choice Yerkes--Thompson Bryant--Bovet-Nitti apparatus for patterns discrimination. Two sets of experiments were carried out. In the first set, pretrial administration of mescaline (5, 10, and 20 mg/kg) was followed by performance improvements in the C57 mice, while performances of the BALB strain were impaired by the treatment, as compared with those of the saline-injected (4 ml/kg) controls. The pretrial administration of amphetamine (0.1, 0.25, and 0.5 mg/kg) improved performances of both strains. In a second set of experiments, the same effects as in the pretrial experiments were observed in both strains following administration of mescaline (20 mg/kg) and amphetamine (0.5 mg/kg) immediately after each experimental session. No effect was evident when the drugs were injected 2 h after training, suggesting that effects of the pretrial treatments were due to influences of mescaline and amphetamine on the consolidation processes of the two strains of mice tested.

Effects of caffeine on discrimination learning, consolidation, and learned behavior in mice

Three sets of experiments were carried out in a Y water maze in which mice had to swim toward the light or the dark, in two different procedures. The first procedure involved, orientation toward a light source (L procedure), corresponding to natural preference, the latter involved orientation toward the dark (D procedure), corresponding to the acquisition of a new pattern of behavior. In pretrial drug treatments caffeine was administered to two groups of naive mice, tested under one of two experimental conditions. Posttrial drug treatments were made in animals learning the D procedure. Pretrained mice in the L or D procedure were finally injected with increasing doses of the drug. The results show that caffeine administration to naive animals was followed, in the D procedure, by a facilitation of learning and consolidation processes, and in the L procedure by improvements of the natural tendencies. Behavioral disruption followed treatment with the drug in mice pretrained in the D procedure, while only very high doses caused disruption in mice pretrained in the L procedure.

Tape test as a simple new method for the study of compounds increasing the problem-solving ability of the rat

A simple new method, the "tape test" has been developed for studying the enhancement of learning by drugs in "learning-dull" rats. A piece of adhesive tape is pressed on the left front pad of the rats. The time of tape removal by the animal, i.e., the problem-solving time is measured. In our experiments the selected learning-dull rats were used which were unable to remove the tape within 60 s observed on 3 consecutive days. The problem-solving ability of the rats was studied on 4 consecutive days, by posttrial administration. The problem-solving ability was found to be increased after treatment with different drugs such as para-chlorphenylalanine (PCPA), pemolin, orotic acid, vitamin B12. The stimulatory effect of vitamin B12 could be inhibited by vincristine.

Effects of nicotine on discrimination learning, consolidation and learned behaviour in two inbred strains of mice

DBA/2J and C57BL/6J mice were injected with nicotine, and tested in a Y water maze in two procedures: the L procedure, coresponding to innate behavior, in which the animals must swim towards the light, and the D procedure, corresponding to the acquisition of a new pattern of behavior, in which they must swim toward the dark. Three sets of experiments were carried out: 1. In the pre-trial experiments, nicotine administration improved the innate tendencies of both strains, while the acquisition of a new behavior was facilitated in the C57 and impaired in the DBA mice. 2. In the post-trial experiments (D procedure), nicotine administration induced clear facilitating effects on the consolidation processes of the C57, while impairing these processes in the DBA strain. 3. The only effect evident, following nicotine administration, before the highest doses were reached, in the trained mice of both strains, was a performance impairment of the DBA mice trained in the L procedure.

Pre-trial cocaine and performance in rat

Cocaine injected pre-trial (10 mg/kg i.p.) improves performance in naive and high-performance (HP) and low-performance (LP) trained rats. When the effect of cocaine is removed, the number of conditioned responses decreases and equals that of drugless sessions. Cocaine favors only performance, not retention.