Prenatal methamphetamine exposure induces long-lasting alterations in memory and development of NMDA receptors in the hippocampus.

Since close relationship was shown between drug addiction and memory formation, the aim of the present study was to investigate the effects of interaction between prenatal methamphetamine (MA) exposure and MA treatment in adulthood on spatial and non-spatial memory and on the structure of the N-methyl-D-aspartate (NMDA) receptors in the hippocampus. Adult male rats prenatally exposed to MA (5 mg/kg) or saline were tested in adulthood. Non-spatial memory was examined in the Object Recognition Test (ORT) and spatial memory in the Object Location Test (OLT) and in the Memory Retention Test (MRT) conducted in the Morris Water Maze (MWM), respectively. Based on the type of the memory test animals were injected either acutely (ORT, OLT) or long-term (MWM) with MA (1 mg/kg). After each testing, animals were sacrificed and brains were removed. The hippocampus was then examined in Western Blot analysis for occurrence of different NMDA receptors' subtypes. Our results demonstrated that prenatal MA exposure affects the development of the NMDA receptors in the hippocampus that might correspond with improvement of spatial memory tested in adulthood in the MWM. On the other hand, the effect of prenatal MA exposure on non-spatial memory examined in the ORT was the opposite. In addition, we showed that the effect of MA administration in adulthood on NMDA receptors is influenced by prenatal MA exposure, which seems to correlate with the spatial memory examined in the OLT.

Gender differences in the effect of prenatal methamphetamine exposure and challenge dose of other drugs on behavior of adult rats.

The aim of the present study was to compare the response to acute application of several drugs in adult male and female rats prenatally exposed to methamphetamine (MA). Spontaneous locomotor activity and exploratory behavior of adult male and female rats prenatally exposed to MA (5 mg/kg) or saline were tested in a Laboras apparatus (Metris B.V., Netherlands) for 1 h. Challenge dose of the examined drug [amphetamine - 5 mg/kg; cocaine - 5 mg/kg; MDMA (3,4-methylenedioxymethamphetamine) - 5 mg/kg; morphine - 5 mg/kg; THC (delta9-tetrahydrocannabinol) - 2 mg/kg] or saline was injected prior to testing. Our data demonstrate that prenatal MA exposure did not affect behavior in male rats with cocaine or morphine treatment, but increased locomotion and exploration in females. Application of amphetamine and MDMA in adulthood increased activity in both sexes, while cocaine and THC only in female rats. Morphine, on the other hand, decreased the activity in the Laboras test in both sexes. As far as sex and estrous cycle is concerned, the present study shows that males were generally less active than females and also females in proestrus-estrus phase of the estrous cycle were more active than females in diestrus. In conclusion, the present study shows that the prenatal MA exposure does not induce general sensitization but affects the sensitivity to drugs dependently to mechanism of drug action and with respect to gonadal hormones.

Do prenatally methamphetamine-exposed adult male rats display general predisposition to drug abuse in the conditioned place preference test?

Drug abuse of pregnant women is a growing problem. The effect of prenatal drug exposure may have devastating effect on development of the offsprings that may be long-term or even permanent. One of the most common drug abused by pregnant women is methamphetamine (MA), which is also the most frequently abused illicit drug in the Czech Republic. Our previous studies demonstrated that prenatal MA exposure alters behavior, cognition, pain and seizures in adult rats in sex-specific manner. Our most recent studies demonstrate that prenatal MA exposure makes adult rats more sensitive to acute injection of the same or related drugs than their controls. The aim of the present study was to examine the effect of prenatal MA exposure on drug-seeking behavior of adult male rats tested in the Conditioned place preference (CPP). Adult male rats were divided to: prenatally MA-exposed (5 mg/kg daily for the entire prenatal period), prenatally saline-exposed (1 ml/kg of physiological saline) and controls (without maternal injections). The following drugs were used in the CPP test in adulthood: MA (5 mg/kg), amphetamine (5 mg/kg), cocaine (5 and 10 mg/kg), morphine (5 mg/kg), MDMA (5 mg/kg) and THC (2 mg/kg). Our data demonstrated that prenatally MA-exposed rats displayed higher amphetamine-seeking behavior than both controls. MA as well as morphine induced drug-seeking behavior of adult male rats, however this effect did not differ based on the prenatal MA exposure. In contrast, prenatal MA exposure induced rather tolerance to cocaine than sensitization after the conditioning in the CPP. MDMA and THC did not induce significant effects. Even though the present data did not fully confirmed our hypotheses, future studies are planned to test the drug-seeking behavior also in self-administration test.

Does prenatal methamphetamine exposure induce cross-sensitization to cocaine and morphine in adult male rats?

The aim of the present study was to examine the cross-sensitization induced by prenatal methamphetamine (MA) exposure to challenge dose of cocaine or morphine. Rat mothers received a daily injection of MA (5 mg/kg) or saline throughout the gestation period. Adult male offspring (prenatally MA- or saline-exposed) were divided to groups with challenge doses of saline (1 ml/kg), cocaine (5 mg/kg) or morphine (5 mg/kg). Behavior in unknown environment was examined in Laboras, nociception in Plantar test, and active drug-seeking behavior in conditioned place preference (CPP). Our data demonstrate that cocaine increased the exploratory activity in Laboras test in prenatally saline-exposed, but decreased it in prenatally MA-exposed rats. An analgesic effect of cocaine was demonstrated only by the tail withdrawal and it was independent of the prenatal drug exposure. CPP test showed that prenatal MA exposure induced rather tolerance than sensitization to cocaine. In contrast to cocaine effects, morphine decreased rearing activity in both, prenatally MA-exposed and saline-exposed rats, and locomotion only in prenatally MA-exposed rats in the Laboras. In the Plantar test, the results demonstrated that morphine had an analgesic effect in prenatally saline-exposed rats but this effect was suppressed in prenatally MA-exposed rats. In the CPP test morphine induced drug-seeking behavior, which however was not affected by prenatal drug exposure. Thus, our data demonstrate that there is a cross-effect between prenatal MA exposure and the challenge dose of other drug in adulthood, however drug-seeking behavior is not increased by prenatal MA exposure as we expected.

Sex differences in anxiety-like behavior and locomotor activity following prenatal and postnatal methamphetamine exposure in adult rats.

The aim of the present study was to investigate the impact of prenatal and postnatal methamphetamine (MA) exposure on behavior and anxiety in adult male and female rats. Mothers were daily exposed to injection of MA (5 mg/kg) or saline (S): prior to impregnation and throughout gestation and lactation periods. On postnatal day 1, pups were cross-fostered so that each mother raised 6 saline-exposed pups and 6 MA-exposed pups. Based on the prenatal and postnatal exposure 4 experimental groups (S/S, S/MA, MA/S, MA/MA) were tested in the Open field (OF) and in the Elevated plus maze (EPM) in adulthood. Locomotion, exploration, immobility and comforting behavior were evaluated in the OF, while anxiety was assessed in the EPM. While prenatal MA exposure did not affect behavior and anxiety in adulthood, postnatal MA exposure (i.e. MA administration to lactating mothers) induced long-term changes. Specifically, adult female rats in diestrus and adult males postnatally exposed to MA via breast milk (S/MA and MA/MA) had decreased locomotion and exploratory behavior in the OF and showed increased anxiety-like behavior in the EPM when compared to female rats in diestrus or males postnatally exposed to saline (S/S and MA/S). In adult females in proestrus, postnatal exposure to MA affected only exploratory behavior in the OF when compared to rats in proestrus postnatally exposed to saline. Thus, the present study shows that postnatal exposure to MA via breast milk impairs behavior in unfamiliar environment and anxiety-like behavior of adult male and female rats more than prenatal MA exposure.

Impact of prenatal methamphetamine exposure on the sensitivity to the same drug in adult male rats.

There are only few studies that examine the effect of prenatal methamphetamine (MA) exposure on the sensitivity to the same drug and the drug-seeking behavior in adulthood. The aim of the present study was to examine the effect of prenatal MA exposure on exploratory behavior and nociception with respect to challenge dose of the same drug. Mothers of the tested offspring received a daily injection of MA (5 mg/kg) or saline throughout the gestation period. Adult male offspring (prenatally MA- or saline-exposed) were divided to groups with challenge dose of MA (1 mg/kg) or saline. A modified Open field test (Laboras) was used to examine behavior in unknown environment. Plantar test was used to measure nociception on forelimbs, hind limbs, and the tail. Conditioned place preference (CPP) test was used to examine drug-seeking behavior. Our results in Laboras demonstrated that prenatal MA exposure sensitized the animals to the challenge dose of MA. Specifically prenatally MA-exposed animals that received the challenge MA in adulthood displayed higher locomotion and rearing activity relative to all the other groups. The Plantar test data suggest analgesic effect of MA (1 mg/kg), which however, did not differ based on the prenatal drug exposure. The results of CPP test showed that MA (5 mg/kg) conditioning resulted in increased drug-seeking behavior, but this effect was not affected by prenatal drug exposure. Thus, our data demonstrate that the effects of prenatal MA exposure and the challenge dose of the same drug in adulthood depend on behavioral model used.

Perinatal effect of methamphetamine on nociception in adult Wistar rats.

Methamphetamine is a psychostimulant drug which causes the release of monoamine neurotransmitters. Although drugs of abuse are known to have analgesic effects, there is a lack of evidence regarding the effect of prenatal exposure to methamphetamine on nociception in adulthood. Adult Wistar rats whose mothers had received daily exposure to methamphetamine (5 mg/kg; s.c.) or saline, during gestation or gestation and lactation periods, were examined for: (1) gender differences in nociception; (2) an association between nociception and gross-motor behavior in the plantar test; (3) effects of cross-fostering on nociception; and (4) analgesic effects of an acute injection of methamphetamine (1 mg/kg s.c.). Nociception was tested using the plantar test on postnatal days 85-90. Prenatal methamphetamine increased sensitivity to pain on forelimbs (p<0.0001) and hind limbs (p<0.05) in females only. Prenatal methamphetamine treated male rats fostered by adoptive injection stressed mothers had higher sensitivity to pain than prenatally injection stressed rats fostered by methamphetamine treated mothers (p<0.05). Acute methamphetamine induced analgesia faster in prenatally methamphetamine exposed rats than in controls. In all groups, analgesia increased in the cranio-caudal direction (p<0.0001). From our behavioral data it can be concluded that exposure to methamphetamine during the prenatal period completely dissociates the relationship between nociception and intensity of overall behavior observed in intact animals in adulthood. Thus, our results indicate that perinatal exposure to psychostimulants may have long-term impact on several functions related to dopaminergic system.

Responsiveness to methamphetamine in adulthood is altered by prenatal exposure in rats.

Methamphetamine (MA) is a drug causing potent psychomotor activation. The aim of the present study was: (1) to assess the effect of prenatal and acute MA administration on behavior in adult male rats and (2) to find out if the prenatal exposure to MA increases sensitivity to acute MA application in adulthood. Behavior of adult male rats prenatally exposed to MA (5mg/kg) or saline was tested in Open field (OF) and Elevated plus maze (EPM). Subcutaneously administered MA (1mg/kg) or saline were used as challenge in adulthood, 30 min prior to testing. Our results showed that prenatal MA did not have an effect on baseline behavior in either of the tests. By contrast, acute MA increased overall psychomotor activity by increasing locomotion and exploratory behavior and decreasing comforting behavior. Moreover, adult rats prenatally exposed to MA exhibited increased sniffing and decreased rearing after acute MA dose in adulthood relative to prenatally saline-exposed rats. In addition, while acute MA application decreased anxiety in rats prenatally exposed to MA, rats prenatally exposed to saline were less sensitive to the anxiolytic effects of MA. Our results indicate that changes caused by prenatal exposure to psychostimulants may become apparent as different reactivity to drugs of abuse when an individual encounters them later in life. In addition, we found that the anxiolytic effect of acute MA (1mg/kg) probably depends also on the reactivity to stress and the activity of hypothalamo-pituitary-adrenal axis.

Does cross-fostering modify the prenatal effect of methamphetamine on learning of adult male rats?

Our previous studies demonstrated that methamphetamine administered during gestation and lactation periods impairs maternal behavior, alters the functional development of rat pups and affects behavior in adulthood. The aim of our study was to investigate the effect of prenatal methamphetamine exposure and cross-fostering on learning tested in Morris water maze (MWM) in adult male rats. Mothers were daily exposed to injection of methamphetamine (MA) (5 mg/kg) or saline (S): prior to impregnation and throughout gestation and lactation periods. On postnatal day 1, pups were cross-fostered so that each mother received some of her own and some of the pups of mother with the opposite treatment. Based on the prenatal and postnatal treatments 4 experimental groups (S/S, S/MA, MA/S, MA/MA) were tested in MWM. Two types of tests were used: (1) "Place navigation test" (Learning) and (2) "Probe test" (Probe). In the test of learning, all animals fostered by methamphetamine-treated dams had longer latencies and trajectories, and bigger search error than the animals fostered by saline-treated control mother, regardless of prenatal exposure. Further, the animals prenatally exposed to methamphetamine swam slower than the animals prenatally exposed to saline, regardless of postnatal exposure in the test of learning and in the Probe test. Our results showed that neither prenatal nor postnatal methamphetamine exposure affected the Probe test. Our results showed that prenatal exposure to methamphetamine at dose of 5 mg/kg does not impair learning in the MWM, while postnatal exposure to methamphetamine from mothers' breastmilk and maternal care of mother exposed to methamphetamine impairs learning of adult male rats. On the other hand, the maternal care of control mothers does not impair learning of rat pups prenatally exposed to methamphetamine. The present study demonstrates that cross-fostering may affect learning in adulthood.

Impact of prenatal and acute methamphetamine exposure on behaviour of adult male rats.

Psychostimulants have been shown to alter behaviour in both rats and humans. The aim of the present study was: (1) to assess the effect of prenatal and acute methamphetamine (MA) administration on behaviour in adult male rats and (2) to find out if the prenatal exposure to MA increases sensitivity to acute MA application in adulthood. Behaviour of adult male rats prenatally exposed to MA (5 mg/kg) or no drug was tested in Open field (OF) and Elevated plus maze (EPM). Half of the animals were injected with MA (1 mg/kg) subcutaneously 30 minutes prior to testing. Locomotion, exploration, comforting behaviour and anxiety were evaluated in the OF, while anxiety and exploratory behaviour were assessed in the EPM. Our results showed that prenatal MA did not have an effect on baseline behaviour in either of the tests. By contrast, acute MA increased overall psychomotor activity by increasing locomotion and exploratory behaviour and decreasing comforting behaviour. Moreover, adult rats prenatally exposed to MA were more sensitive to the effects of acute MA on exploration. In addition, acute MA application decreased anxiety in the OF as well as in the EPM. Our present study, thus, demonstrates that acute MA increases overall psychomotor activity and decreases anxiety to novel environment. To further support our hypothesis that prenatal MA exposure increases sensitivity to drugs in adulthood, studies investigating the levels of dopamine in the rat brain after prenatal MA exposure are planned.

Cognitive functions and drug sensitivity in adult male rats prenatally exposed to methamphetamine.

The aim of the present study was to investigate the impact of prenatal methamphetamine (MA) exposure and application of the same drug in adulthood on cognitive functions of adult male rats tested in Morris water maze (MWM). Adult male rats prenatally exposed to MA (5 mg/kg), saline or no injection were examined. Half of the animals were injected daily with MA (1 mg/kg) after finishing the testing. Three types of tests were used: (1) "Place navigation test" (Learning), (2) "Probe test" and (3) "Retention memory test" (Memory). Our results showed that prenatal MA exposure did not affect the test of learning and the Probe test. In the test of memory prenatally MA-exposed rats showed smaller search errors and used spatial strategies more than both control groups. Further, MA application in adulthood prolonged trajectories, increased the incidence of random search and decreased the incidence of direct swim in the Place navigation test. In addition, MA administration in adulthood increased the speed of swimming regardless of prenatal exposure. The present study thus demonstrates that 1) Prenatal MA exposure does not affect learning in the MWM, 2) Prenatal MA exposure improves performance in the Retention memory test in the MWM, and 3) MA application in adulthood impairs learning in the Morris water maze.

Does cross-fostering modify the impairing effect of methamphetamine on postnatal development of rat pups?

Our previous studies demonstrated that methamphetamine (MA) administered during gestation and lactation periods impairs maternal behavior as well as the postnatal development of rat pups. The present study tested the hypothesis that the cross-fostering influences the development of rat pups. Mothers were daily exposed to injection of MA (5 mg/kg) and saline for 9 weeks: three weeks prior to impregnation, throughout the entire gestation period and during lactation. As a control (C) females with no injections were used. On postnatal day (PD 1), pups were cross-fostered so that each mother received some of her own and some of the pups of mother with the other treatments. Pup's development and sensorimotor coordination was examined between PD 1 and PD 23. Following tests were used: tail pull (PD 10), righting reflex on surface (PD 12), righting reflex on mid-air (PD 17) and rotarod (PD 23). Our results showed that the birth weight in prenatally MA-exposed pups was lower than controls or saline-exposed pups regardless of sex. Prenatally MA-exposed pups gained less weight than controls or saline-exposed pups regardless of postnatal treatment and sex. Further, our data demonstrated that prenatal and postnatal MA exposure impairs sensorimotor functions. On the other hand, postnatal care of control mothers at least partially suppressed the negative effect of prenatal MA exposure. Our hypothesis, that the cross-fostering may affect postnatal development of pups, was confirmed. Our results support the hypothesis that variation in rat maternal care could serve as a mechanism for a non-genomic behavioral mode of transmission of traits.

Impact of methamphetamine administered prenatally and in adulthood on cognitive functions of male rats tested in Morris water maze.

Studies showed that stimulant drugs that affect the monoaminergic system alter both behavioral and cognitive processes. The aim of the present study was to investigate the impact of prenatal and acute methamphetamine (MA) exposure on cognitive functions of adult male rats tested in Morris water maze (MWM). We tested adult male rats prenatally exposed to MA (5 mg/kg), saline or no injection. Half of the animals were injected daily with MA (1 mg/kg) after finishing the testing. All injections were administered subcutaneously. Three types of tests were used: (1) "Place navigation test" (Learning), (2) "Probe test" (Probe) and (3) "Retention memory test" (Memory). Our results showed that prenatal MA exposure did not affect the test of learning and the Probe test. In the test of memory prenatally MA-exposed rats had lower latencies than animals prenatally exposed to saline. Further, acute MA administration increased the speed of swimming in all rats regardless of prenatal drug exposure and the type of test and, however, the increase in the speed was significantly greater in rats prenatally exposed to MA than in rats without any prenatal exposure. In addition, acute MA application significantly prolonged trajectories in the Place navigation test. The present study thus demonstrates that: (1) Prenatal MA exposure does not affect learning in the MWM. (2) Prenatal MA exposure increases the sensitivity to acute drug injection. (3) Acute MA application impairs learning in the MWM.

Prenatal and perinatal factors influencing nociception, addiction and behavior during ontogenetic development.

This review, which summarizes our findings concerning the long-term effects of pre-, peri- and postnatal factors affecting development, nociception and sensorimotor functions, focuses on three areas: 1) perinatal factors influencing nociception in adult rats were examined in rats with hippocampal lesions, after the administration of stress influencing and psychostimulant drugs (dexamethasone, indomethacine and methamphetamine); 2) the effect of pre- and early postnatal methamphetamine administration was shown to impair the development of sensorimotor functions tested in rat pups throughout the preweaning period; 3) the effect of extensive dorsal rhizotomy of the brachial plexus during the early postnatal period was studied with respect to neuropathic pain development and sensorimotor functions. The present study indicates that prenatal or neonatal stress, as well as various drugs, may disturb the development of the nociceptive system and cause long-term behavioral changes persisting to adulthood and that some types of neuropathic pain cannot be induced during the first two postnatal weeks at all. A mature nervous system is required for the development of the described pathological behaviors.