Prenatal Exposure to Methamphetamine: Up-Regulation of Brain Receptor Genes.

Methamphetamine (METH) is a widespread illicit drug. If it is taken by pregnant women, it passes through the placenta and just as it affects the mother, it can impair the development of the offspring. The aim of our study was to identify candidates to investigate for changes in the gene expression in the specific regions of the brain associated with addiction to METH in rats. We examined the various areas of the central nervous system (striatum, hippocampus, prefrontal cortex) for signs of impairment in postnatal day 80 in experimental rats, whose mothers had been administered METH (5 mg/kg/day) during the entire gestation period. Changes in the gene expression at the mRNA level were determined by two techniques, microarray and real-time PCR. Results of two microarray trials were evaluated by LIMMA analysis. The first microarray trial detected either up-regulated or down-regulated expression of 2189 genes in the striatum; the second microarray trial detected either up-regulated or down-regulated expression of 1344 genes in the hippocampus of prenatally METH-exposed rats. We examined the expression of 10 genes using the real-time PCR technique. Differences in the gene expression were counted by the Mann-Whitney U-test. Significant changes were observed in the cocaine- and amphetamine-regulated transcript prepropeptide, tachykinin receptor 3, dopamine receptor D3 gene expression in the striatum regions, in the glucocorticoid nuclear receptor Nr3c1 gene expression in the prefrontal cortex and in the carboxylesterase 2 gene expression in the hippocampus of prenatally METH-exposed rats. The microarray technique also detected up-regulated expression of trace amine-associated receptor 7 h gene in the hippocampus of prenatally METH-exposed rats. We have identified susceptible genes; candidates for the study of an impairment related to methamphetamine addiction in the specific regions of the brain.

Long-term early life adverse experience impairs responsiveness to exteroceptive stimuli in adult rats.

It has been shown that early life traumatic events strongly alter the physiology and behavior in adult rats. In the present study, the effect of postnatal stressor on the spontaneous behavior of adult male rats was evaluated. A method of positive habituation based on a detailed analysis of behavioral patterns and attention of animals to a stimulus object was used. Twenty-four dams and twenty-four of their male progeny were used. Pups were divided into three groups (n = 8): controls (C); maternal social stressor (S); maternal social and physical stressors (SW). Animals (postnatal day 70-80) were individually placed in the open field arena in two habituation sessions with a 24-h delay between them (Test day 1 and Test day 2). Before the start of third session (Test day 3) a solid object was fixed in the center of the arena. Each test lasted 10 min. Our results showed the habituation effect in both stressed-groups. Although there were no significant differences in the number of investigations of the novel object among all tested groups, stress-exposed rats spent less time investigating the object. In conclusion, our findings indicate that long-term neonatal stress may impair an animal's ability to sustain attention to stimuli.

Sex differences in the strategies of spatial learning in prenatally-exposed rats treated with various drugs in adulthood.

In the present study we investigated the sex differences in the effect of adult long-term drug treatment on cognitive functions of Wistar rats, which were prenatally exposed to MA (5mg/kg) or saline. Cognitive functions were tested as an ability of spatial learning in the Morris Water Maze (MWM), which consisted of three types of tests: "Place Navigation Test"; "Probe Test", and "Memory Recall Test". Adult animals were injected daily, after completion of the last trial, either with saline or cocaine (COC; 5mg/kg), MDMA (3,4-methylenedioxy-methamphetamine; 5mg/kg), morphine (MOR; 5mg/kg), or delta-9-tetrahydrocannabinol (THC; 2mg/kg). Results revealed worsened MWM performance in female rats after drug treatment in adulthood. Not only were traditionally investigated parameters affected by drug treatment (latency of platform acquisition, search strategy, distance traveled), but also strategies used by animals (thigmotaxis, scanning). Analyses of search strategies observed in the Place Navigation Test, as well as in the Memory Recall Test, demonstrated variations in the percentage of time spent in thigmotaxis and scanning in females after treatment with COC, MDMA, MOR, and THC. Although we did not see a sensitizing effect of prenatal MA, in some cases the effect of drug treatment in adulthood differed depending on the prenatal drug exposure. The data presented in this study demonstrates that exposure to drugs with various mechanisms of action alters spatial abilities of female rats in the MWM. Alterations in the effect of adult drug treatment with reference to prenatal drug exposure were also found in the present study.

Can Anxiety Tested in the Elevated Plus-maze Be Related to Nociception Sensitivity in Adult Male Rats?

Methamphetamine (MA) is one of the most addictive psychostimulant drugs with a high potential for abuse. Our previous studies demonstrated that MA administered to pregnant rats increases pain sensitivity and anxiety in their adult offspring and makes them more sensitive to acute administration of the same drug in adulthood. Because individuals can differ considerably in terms of behaviour and physiology, such as rats that do not belong in some characteristics (e.g. anxiety) to average, can be described as low-responders or high-responders, are then more or less sensitive to pain. Therefore, prenatally MA-exposed adult male rats treated in adulthood with a single dose of MA (1 mg/ml/kg) or saline (1 ml/kg) were tested in the present study. We examined the effect of acute MA treatment on: (1) the anxiety in the Elevated plus-maze (EPM) test and memory in EPM re-test; (2) nociception sensitivity in the Plantar test; (3) the correlation between the anxiety, memory and the nociception. Our results demonstrate that: (1) MA has an anxiogenic effect on animals prenatally exposed to the same drug in the EPM; (2) all the differences induced by acute MA treatment disappeared within the time of 48 hours; (3) there was no effect of MA on nociception per se, but MA induced higher anxiety in individuals less sensitive to pain than in animals more sensitive to pain. In conclusion, the present study demonstrates unique data showing association between anxiety and nociceptive sensitivity of prenatally MA-exposed rats that is induced by acute drug administration.

Do the effects of prenatal exposure and acute treatment of methamphetamine on anxiety vary depending on the animal model used?

The aim of the present study was an evaluation of prenatal exposure to acute methamphetamine (MA) treatment on manifestations of anxiety. Anxiety was evaluated in adult animals in three different experimental models: the Elevated plus-maze (EPM), Social interaction test (SIT) and Ultrasound vocalization (USV). Female rats were administered saline (S) or MA (5 mg/kg) daily throughout their entire gestation period. The male progeny, in adulthood, were administered with challenge dose of S or MA (1 mg/kg) prior to evaluation of anxiety. The study demonstrated that prenatal MA exposure increased the anxiogenic effect on evaluated behaviour patterns in the USV model and to a lesser degree in the EPM model. In addition, the acute MA challenge in adulthood decreased the time spent during social interaction suggesting an anxiogenic effect in the SIT model as well. On the other hand, some of the evaluated parameters (e.g. the number of head-dipping in the EPM and number of dropped boluses in the SIT) also suggest MA-induced anxiolytic effects. Sensitization to a MA challenge was apparent in several parameters of the EPM (e.g. increased number of entries to the closed arms, increased stretched attend postures and increased approach-avoid conflicts) and SIT (total social interaction and following). The present data demonstrate that prenatal MA exposure and adult challenge of the same drug have diverse effects on animal behaviour that depends on the type of anxiety model used.

Effects of psychostimulants on social interaction in adult male rats.

Psychostimulants are known to have a huge impact on different forms of social behaviour. The aim of the present study was to compare the effects of three different psychostimulants [amphetamine, cocaine and 3,4 methylenedimethoxyamphetamine (MDMA)] on social interaction (SI) in adult male rats. The SI test was performed in a familiar arena and under low-stress environmental conditions. Experimental animals received amphetamine (0.5, 1.0, 1.5 mg/kg), cocaine (0.5, 1.0, 1.5, 2.5, 5.0, 10.0 mg/kg) or MDMA (2.5, 5.0, 10 mg/kg) and control animals received saline (1 ml/kg) 45 min before the SI test. Time spent in SI (individual patterns of social behaviour) and nonsocial activities (locomotion and rearing) were video recorded and then analysed offline, with the following results: (a) all doses of amphetamine decreased SI. Specifically, all doses of amphetamine decreased mutual sniffing, and the higher doses also decreased allo-grooming and following behaviours. (b) The higher doses of cocaine decreased SI, especially mutual sniffing, allo-grooming and climbing over. Cocaine at the dose of 5.0 mg/kg increased genital investigation compared with lower doses. (c) All doses of MDMA decreased mutual sniffing and climbing over; the two higher doses decreased allo-grooming behaviour, and only the highest dose decreased following. The two higher doses of amphetamine and all the doses of MDMA increased locomotion and rearing; cocaine did not affect locomotion, but increased rearing at higher doses. In conclusion, the results confirm the well-known finding that psychostimulants suppress SI, but also show novel differences in the effects of psychostimulants on specific patterns of SI.

Effect of amphetamine on adult male and female rats prenatally exposed to methamphetamine.

The aim of the present study was to examine the cross-sensitization induced by prenatal methamphetamine (MA) exposure to adult amphetamine (AMP) treatment in male and female rats. Rat mothers received a daily injection of MA (5 mg/kg) or saline throughout the gestation period. Adult male and female offspring (prenatally MA- or saline-exposed) were administered with AMP (5 mg/kg) or saline (1 ml/kg) in adulthood. Behaviour in unknown environment was examined in open field test (Laboras), active drug-seeking behaviour in conditioned place preference test (CPP), spatial memory in the Morris water maze (MWM), and levels of corticosterone (CORT) were analyzed by enzyme immunoassay (EIA). Our data demonstrate that in Laboras test, AMP treatment in adulthood increased general locomotion (time and distance travelled) regardless of the prenatal exposure and sex, while AMP increased exploratory activity (rearing) only in prenatally MA-exposed animals. AMP induced sensitization only in male rats, but not in females when tested drug-seeking behaviour in the CPP test. In the spatial memory MWM test, AMP worsened the performance only in females, but not in males. On the other hand, males swam faster after chronic AMP treatment regardless of the prenatal drug exposure. EIA analysis of CORT levels demonstrated higher level in females in all measurement settings. In males, prenatal MA exposure and chronic adult AMP treatment decreased CORT levels. Thus, our data demonstrated that adult AMP treatment affects behaviour of adult rats, their spatial memory and stress response in sex-specific manner. The effect is also influenced by prenatal drug exposure.