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

Behavioral outputs and overlapping circuits between conditional fear and active avoidance

Aversive learning can produce a wide variety of defensive behavioral responses depending on the circumstances, ranging from reactive responses like freezing to proactive avoidance responses. While most of this initial learning is behaviorally supported by an expectancy of an aversive outcome and neurally supported by activity within the basolateral amygdala, activity in other brain regions become necessary for the execution of defensive strategies that emerge in other aversive learning paradigms such as active avoidance. Here, we review the neural circuits that support both reactive and proactive defensive behaviors that are motivated by aversive learning, and identify commonalities between the neural substrates of these distinct (and often exclusive) behavioral strategies.

Cannabidiol enhances socially transmitted food preference: a role of acetylcholine in the mouse basal forebrain

RATIONALE AND OBJECTIVE

Rodents acquire food information from their conspecifics and display a preference for the conspecifics' consumed food. This social learning of food information from others promotes the survival of a species, and it is introduced as the socially transmitted food preference (STFP) task. The cholinergic system in the basal forebrain plays a role in the acquisition of STFP. Cannabidiol (CBD), one of the most abundant phytocannabinoids, exerts its therapeutic potential for cognitive deficits through versatile mechanisms of action, including its interaction with the cholinergic system. We hypothesize a positive relationship between CBD and STFP because acetylcholine (ACh) is involved in STFP, and CBD increases the ACh levels in the basal forebrain.

MATERIALS AND METHODS

Male C57BL/6J mice were trained to acquire the STFP task. We examined whether CBD affects STFP memory by administering CBD (20 mg/kg, i.p.) before the STFP social training. The involvement of cholinergic system in CBD's effect on STFP was examined by knockdown of brain acetylcholinesterase (AChE), applying a nonselective muscarinic antagonist SCO (3 mg/kg, i.p.) before CBD treatment, and measuring the basal forebrain ACh levels in the CBD-treated mice.

RESULTS

We first showed that CBD enhanced STFP memory. Knockdown of brain AChE also enhanced STFP memory, which mimicked CBD's effect on STFP. SCO blocked CBD's memory-enhancing effect on STFP. Our most significant finding is that the basal forebrain ACh levels in the CBD-treated mice, but not their control counterparts, were positively correlated with mice's STFP memory performance.

CONCLUSION

This study indicates that CBD enhances STFP memory in mice. Specifically, those which respond to CBD by increasing the muscarinic-mediated ACh signaling perform better in their STFP memory.

A common role for psychotropic medications: memory impairment

The psychopathologic profile of mental disorders is very diverse and psychotropic medications used to treat them differ in their chemical structure. Nevertheless, these drugs share these four characteristics: delayed onset of clinical response, not one of them can be said to cure, there is a high number of non-responders, and the mechanism responsible for their therapeutic action is not known. It is hypothesized that the action of psychotropic medications is memory impairment, understanding memory as the trace left in the nervous system not only by individual experiences but also by genetic and epigenetic phenomena. It is suggested that it would be beneficial to translate some research strategies from the neurobiology of learning and memory to the study of the effects of psychotropic medications. The hypothesis is briefly assessed according to the following three criteria: (a). the comparison between the molecular effects of psychotropic medications and the so-called molecular biology of learning and memory, (b). the effects of these drugs, preferentially after chronic use, on memory tests, and (c). the effects of drugs that impair memory on tests used for screening psychotropic medications. Finally, some general suggestions for future research are pointed out.

Cocaine enhances retention of avoidance conditioning in rats

The effects of post-training cocaine administration were tested on retention of a one-way active avoidance task in rats. A 5.0 mg/kg IP dose of cocaine enhanced retention of the avoidance task, in three separate experiments, as indicated by an increase in the number of avoidances made when animals were tested 24 h after training, while both a lower (2.5 mg/kg) and a higher (7.5 mg/kg) cocaine dose had no effect. Lidocaine (4-8 mg/kg) administered post-training did not reliably affect retention in the same task. Cocaine's ability to enhance retention depended on the interval between training and drug injection such that only cocaine administered directly after training enhanced retention the following day. The results show that post-training cocaine administration enhances retention of an active avoidance task in rats, and that this effect is probably independent of the anesthetic properties of the drug.

Dose-dependent impairing effects of morphine on avoidance acquisition and performance in male mice

The effects of morphine (6.3, 12.6, and 25.2 mg/kg) on active avoidance behavior of BALB/C mice are explored in three acquisition sessions and in two subsequent performance sessions. Morphine-treated animals showed an increase in avoidance acquisition with respect to control group without differences in performance. However, a dramatical, concomitant rise in the locomotor activity of the animals (increase in the number of crossings during the intertrial intervals) prompted us to transform the data employing a formula with which a measure of actual learning was obtained. Applying this formula, we have observed that morphine administration impairs, dose-dependently, acquisition and performance of avoidance. Thus, the impairing effects of morphine on avoidance could be masked by their stimulant effects on locomotor activity.

Behavioral effects of N-cyanomethylmethamphetamine, a product derived from smoking methamphetamine with tobacco, in mice and rats

The stimulant effects of N-cyanomethylmethamphetamine (CMMA), a product derived from smoking methamphetamine (MA) mixed in tobacco, were studied by observing stereotyped behavior and measuring spontaneous motor activity in mice and rats over 180 min CMMA. 1.3 and 10 mg/kg IP, elicited strong stimulant-like effects which were almost equivalent to those produced by MA. Drug monitoring for 180 min in mouse and rat plasma revealed that the principal substances responsible for the stimulant effect of CMMA were MA and amphetamine (AP) which were metabolized from CMMA by the animal. There was a species difference in metabolism of CMMA between mice and rats. The major metabolites were MA and AP in mouse plasma, followed by N-formylmethamphetamine (FMA), whereas the major metabolite was FMA in rat plasma, followed by MA and AP. The differences in the stimulant effects of CMMA between mice and rats were discussed in relation to its metabolic fate in mice and rats.

Disturbance of retention of memory after focal cerebral ischemia in rats

BACKGROUND AND PURPOSE

The purpose of this study was to investigate the behavioral changes, in particular retention of memory, after focal cerebral ischemia in rats.

METHODS

Ischemia was produced by permanent occlusion of the left middle cerebral artery (MCA). For quantitative behavioral analysis, one-trial passive avoidance response and active avoidance response with the discrete lever-press avoidance procedure were observed. One group of animals was trained once to learn the passive avoidance task 1 day before surgery. The response latency was examined 4 and 14 days after surgery. The second group was trained to learn the active avoidance task for 2 weeks before surgery. The avoidance rate was examined 3 and 14 days after surgery.

RESULTS

The MCA-occluded group showed significant failure of memory retention in both of these tasks (P < .01). The nonoperated group and sham-operated group showed no definite memory failure.

CONCLUSIONS

Retention of memory in the passive avoidance response and the active avoidance response was disturbed after left MCA occlusion in the rat. These results strongly suggest that this model can be used to assess memory disturbance after focal cerebral ischemia.

Autoradiographic distribution of neurotransmitter and second messenger system receptors in animal brains

We investigated species difference in binding of major neurotransmitters and intracellular second messengers in the gerbil brain and the rat brain using receptor autoradiography. [3H]Phorbol 12,13-dibutyrate (PDBu), [3H]inositol 1,4,5-trisphosphate (IP3), [3H]PN200-110, [3H]muscimol, [3H]MK-801, [3H]cyclohexyladenosine (CHA),and [3H]quinuclidinyl benzilate (QNB) were used to label protein kinase C, IP3 receptor, L-type calcium channel, gamma-aminobutyric acidA (GABAA) receptor, N-methyl-D-aspartate (NMDA) receptor, adenosine A1 receptor, and muscarinic cholinergic receptor, respectively. Autoradiographic distributions of the bindings of most neurotransmitters and second messengers were particularly found in the limbic system and basal ganglia in both gerbil and rat brains. However, marked differences in these bindings between the gerbil brain and the rat brain were also recognized in the above regions. In particular, among 7 ligands used, the gerbil had high [3H]PDBu and [3H]CHA binding sites throughout the brain compared to those in the rat brain except for a few areas. By contrast, the rat exhibited high [3H]MK-801 binding sites in various brain regions, as compared with the gerbil brain. Thus, the gerbil differ from the rat with respect to the binding sites of major second messengers and neurotransmitters in the brain. The results may help better elucidate the relationship or species difference between gerbils and rats for neuronal function and behavioral pharmacology.

Strain-dependent effects of post-training cocaine or nomifensine on memory storage involve both D1 and D2 dopamine receptors

Post-training administration of cocaine (1-10 mg/kg) or nomifensine (1-10 mg/kg) dose-dependently improves retention of an inhibitory avoidance response in C57BL16 mice, while impairign it in the DBA/2 strain. The effects of retention performance induced by the psychostimulant and the dopamine (DA) reuptake blocker in C57BL/6 and DBA/2 mice appear to be due to an effect on memory consolidation. In fact, they were observed when drugs were given at short, but not long, periods of time after training, i.e. when the memory trace is susceptible to modulation. Moreover, these effects are not to be ascribed to an aversive or a rewarding or non-specific 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 affected by the post-training drug administration. The strain-dependent effects of an intermediate dose (5 mg/kg) of both cocaine and nomifensine were reversed by pretreatment with either selective D1 or D2 DA receptor antagonist SCH 23390 and (-)-sulpiride administered at per se non-effective doses (0.025 and 6 mg/kg, respectively), thus suggesting that D1 and D2 receptor types are similarly involved in modulating memory processes. These results show that the effects of cocaine on memory consolidation are related to to its dopaminergic action, since they are similar to those produced by nomifensine and, what is more important, are antagonized by pretreatment with DA receptor antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Post-reactivation cocaine administration facilitates later acquisition of an avoidance response in rats

We previously demonstrated that cocaine administered immediately prior to a reactivation episode comprised of re-exposure to selected features of the original fear-conditioning session alters subsequent memory retrieval or reconsolidation. In the present study we determined that, similar to pre-reactivation administration, post-reactivation administration of cocaine also alters memory retrieval or reorganization, as measured by subsequent conditioned performance. The dose-response function for this effect of cocaine was U-shaped; maximal enhancement of subsequent avoidance performance was produced by a 7.5 mg/kg i.p. dose of cocaine. Because a dose of lidocaine equimolar to the effective cocaine dose was found not to alter subsequent conditioned performance, the effect of cocaine on memory processing most likely is not attributable to its local anesthetic properties.

Aspects of animal experiments for evaluation of cognitive enhancers: in particular, the behavioral characteristics of Mongolian gerbils

1. The step-through passive avoidance response and discrete lever-press avoidance response of Mongolian gerbils were evaluated to point out the basic problems in the learning and memory tests in this species. 2. Mongolian gerbils exhibited extremely poor acquisition and maintenance of the passive avoidance response. 3. In contrast to the result under the passive avoidance situation, Mongolian gerbils demonstrated an excellent performance under the discrete lever-press avoidance situation. 4. A 5-min brain ischemia elicited a severe morphological damage of the pyramidal cells in hippocampal CA1 region. 5. A small part of such ischemic animals showed a deficit of acquisition of the discrete lever-press avoidance. 6. These results suggest that there is merit and demerit of the acquisition dependent on the type of tasks, and that the brain function of Mongolian gerbils may be maintained even after the ischemic operation.

Cocaine enhances one-way avoidance responding in mice

We reported previously that posttraining cocaine injections enhance subsequent performance of an automated jump-up avoidance response and a trough avoidance response in rats. In the present study we examined the species generality of the cocaine enhancement by investigating the effects of posttraining cocaine injection on subsequent performance of a one-way active avoidance response in mice. Cocaine (30 mg/kg, IP) administered to mice immediately following completion of two escape-only trials on day 1 significantly enhanced avoidance response performance on day 2. Neither lidocaine nor cocaine methiodide, when administered in doses equimolar to the effective cocaine dose, altered performance on day 2. These data indicate that cocaine's enhancement of avoidance responding in mice probably is neither peripherally mediated nor attributable to its local anesthetic properties.

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.

Effects of cocaine on conditioning of the rabbit nictitating membrane response

Two experiments were conducted to determine cocaine's (0, 1, 3, and 6 mg/kg) effects on associative, nonassociative, and motor processes in classical conditioning of the rabbit's nictitating membrane response (NMR). In Experiment 1, acquisition training consisted of tone- and light-conditioned stimuli (CSs) each paired on separate trials with a shock unconditioned stimulus (UCS). Cocaine injected prior to each session significantly impaired acquisition of conditioned responses (CRs). In Experiment 2, rabbits received cocaine injections prior to each training session involving explicitly unpaired CS-alone and UCS-alone presentations. Cocaine had no significant effects upon: base rate of NMRs; frequency of NMRs during presentations of the CSs; and frequency, amplitude, and latency of the UCRs. Consequently, cocaine's impairment of CR acquisition could not be attributed to its effects upon the nonassociative processes of base rate, sensitization, and pseudoconditioning, nor upon the sensory processing of the UCS and/or motor functioning of the UCR. Rather, cocaine's effects upon CR acquisition were mediated by the drug's effect upon associative processes. It appears likely that the drug affected the ability of the CS to enter into the associative conditioning process.