Neonatal methamphetamine administration induces region-specific long-term neuronal morphological changes in the rat hippocampus, nucleus accumbens and parietal cortex

The multi-faceted impact of methamphetamine on Alzheimer's disease: From a triggering role to a possible therapeutic use

Although it has been initially synthesized for therapeutic purposes and currently FDA-approved and prescribed for obesity, attention-deficit/hyperactivity disorder, narcolepsy and depression, methamphetamine became a recreational drug that is nowadays massively manufactured illegally. Because it is a powerful and extremely addictive psychotropic agent, its abuse has turned out to become a major health problem worldwide. Importantly, the numerous effects triggered by this drug induce neurotoxicity in the brain ultimately leading to serious neurological impairments, tissue damage and neuropsychological disturbances that are reminiscent to most of the symptoms observed in Alzheimer's disease and other pathological manifestations in aging brain. In this context, there is a growing number of compelling evidence linking methamphetamine abuse with a higher probability of developing premature Alzheimer's disease and consequent neurodegeneration. This review proposes to establish a broad assessment of the effects that this drug can generate at the cellular and molecular levels in connection with the development of the age-related Alzheimer's disease. Altogether, the objective is to warn against the long-term effects that methamphetamine abuse may convey on young consumers and the increased risk of developing this devastating brain disorder at later stages of their lives, but also to discuss a more recently emerging concept suggesting a possible use of methamphetamine for treating this pathology under proper and strictly controlled conditions.

Effect of α-lipoic acid on spatial memory and structural integrity of developing hippocampal neurons in rats subjected to sodium arsenite exposure

BACKGROUND

Exposure to arsenic has been reported to affect the nervous system in a number of ways. Various epidemiological studies suggest cognitive impairment in subjects following exposure to environmental arsenic. The goal of the present study was to determine if supplementation of exogenous α-lipoic acid (ALA) could ameliorate sodium arsenite (NaAsO₂) induced adverse effects on learning and memory and synaptic connectivity in rat hippocampus.

METHODS

Accordingly, NaAsO₂ alone (1.5/2.0 mg/kg bw) or NaAsO₂ along with ALA (70 mg/kg bw) was administered by intraperitoneal (i.p.) route from postnatal day (PND) 4-17 to Wistar rat pups (experimental groups) and the Control groups received either distilled water or no treatment at all. After carrying out Elevated Plus Maze (EPM) and Morris Water Maze (MWM) test, the fresh brain tissues were collected on PND 18 and processed for Golgi Cox staining.

RESULTS

Observations of MWM test revealed impaired learning and memory in iAs alone treated animals as against those co-exposed to iAs and ALA. In Golgi stained hippocampal sections of iAs alone treated animals, decreased dendritic arborization and reduced number of spines in pyramidal neurons (CA1) and granule cells (DG) was observed whereas neuronal morphology was preserved in the controls and ALA supplemented groups CONCLUSIONS: These observations are suggestive of beneficial effects of ALA on iAs induced effects on learning and memory as well as on hippocampal neuronal morphology.

Prolonged methamphetamine exposure during a critical period in neonatal Sprague Dawley rats does not exacerbate egocentric and allocentric learning deficits but increases reference memory impairments

Children exposed to methamphetamine (MA) in utero have cognitive deficits. MA administration in rats for 5-10 days between postnatal days (P)6 and 20 produces cognitive deficits. The purpose of this study was to determine if extending MA administration by 5 days within P6-20 would exacerbate allocentric (Morris water maze) and egocentric (Cincinnati water maze) learning deficits. Sprague Dawley female and male offspring (split-litter design) were administered saline (SAL) or MA (10 mg/kg) four times daily from P6 to 20 to create four groups: (a) SAL from P6 to 20, (b) MA from P6 to 20 (MA6-20), (c) MA from P6 to 15 (MA6-15), or (d) MA from P11 to 20 (MA11-20); the latter groups received saline on days they did not receive MA. Egocentric, allocentric, and conditioned freezing tests began on P60. The MA6-15 and MA6-20 groups showed egocentric deficits, all MA groups had allocentric deficits but no differences in conditioned freezing compared with SAL controls. The MA6-15 and MA6-20 groups had similar deficits in learning and memory that were larger than in the MA11-20 group. Learning in both mazes was sex dependent, but no interactions with MA were found. The data demonstrate that extending the exposure period of MA beyond the sensitive periods (P6-15 and P11-20) did not exacerbate the cognitive deficits.

Dopamine D1 and D2 Receptors Differentially Regulate Rac1 and Cdc42 Signaling in the Nucleus Accumbens to Modulate Behavioral and Structural Plasticity After Repeated Methamphetamine Treatment

BACKGROUND

Methamphetamine (METH) is a highly addictive psychostimulant that strongly activates dopamine receptor signaling in the nucleus accumbens (NAc). However, how dopamine D₁ and D₂ receptors (D₁Rs and D₂Rs, respectively) as well as downstream signaling pathways, such as those involving Rac1 and Cdc42, modulate METH-induced behavioral and structural plasticity is largely unknown.

METHODS

Using NAc conditional D₁R and D₂R deletion mice, Rac1 and Cdc42 mutant viruses, and a series of behavioral and morphological methods, we assessed the effects of D₁Rs and D₂Rs on Rac1 and Cdc42 in modulating METH-induced behavioral and structural plasticity in the NAc.

RESULTS

D₁Rs and D₂Rs in the NAc consistently regulated METH-induced conditioned place preference, locomotor activation, and dendritic and spine remodeling of medium spiny neurons but differentially regulated METH withdrawal-induced spatial learning and memory impairment and anxiety. Interestingly, Rac1 and Cdc42 signaling were oppositely modulated by METH, and suppression of Rac1 signaling and activation of Cdc42 signaling were crucial to METH-induced conditioned place preference and structural plasticity but not to locomotor activation. D₁Rs activated Rac1 and Cdc42 signaling, while D₂Rs inhibited Rac1 signaling but activated Cdc42 signaling to mediate METH-induced conditioned place preference and structural plasticity but not locomotor activation. In addition, NAc D₁R deletion aggravated METH withdrawal-induced spatial learning and memory impairment by suppressing Rac1 signaling but not Cdc42 signaling, while NAc D₂R deletion aggravated METH withdrawal-induced anxiety without affecting Rac1 or Cdc42 signaling.

CONCLUSIONS

D₁Rs and D₂Rs differentially regulate Rac1 and Cdc42 signaling to modulate METH-induced behavioral plasticity and the structural remodeling of medium spiny neurons in the NAc.

Learning and memory effects of neonatal methamphetamine exposure in rats: Role of reactive oxygen species and age at assessment

In utero methamphetamine (MA) exposure leads to a range of adverse effects, such as decreased attention, reduced working-memory capability, behavioral dysregulation, and spatial memory impairments in exposed children. In the current experiment, preweaning Sprague-Dawley rats-as a model of third trimester human exposure-were administered the spin trapping agent, N-tert-butyl-α-phenylnitrone (PBN), daily prior to MA. Rats were given 0 (SAL) or 40 mg/kg PBN prior to each MA dose (10 mg/kg, 4× per day) from postnatal day (P) 6-15. Littermates underwent Cincinnati water maze, Morris water maze, and radial water maze assessment beginning on P30 (males) or P60 (females). Males were also tested for conditioned contextual and cued freezing, while females were trained in passive avoidance. Findings show that, regardless of age/sex, neonatal MA induced deficits in all tests, except passive avoidance. PBN did not ameliorate these effects, but had a few minor effects. Taken together, MA induced learning deficits emerge early and persist, but the mechanism remains unknown.

Estrogen and Progesterone Replacement Therapy Prevent Methamphetamine-Induced Synaptic Plasticity Impairment in Ovariectomized Rats

BACKGROUND

Methamphetamine (METH) is one of the most popular psychostimulants which produce long lasting learning and memory impairment. Previous studies have indicated that estrogen and progesterone replacement therapy attenuate cognitive impairment against a wide array of neurodegenerative diseases. Present study was designed to figure out the effects of estrogen, progesterone alone or in combination, on early long-term potentiation (E-LTP) at the cornu ammonis (CA1) area of the hippocampus in METH-exposed ovariectomized (OVX) rat.

METHODS

Twenty-one days after ovariectomy, the OVX rats received vehicle, estrogen [1 mg/kg, intraperitoneal (IP)] or progesterone (8 mg/kg, IP) and co-administration of estrogen plus progesterone during 14 consecutive days. On the 28th day, animals were exposed to neurotoxic METH regimens [four injections 6 mg/kg, subcutaneous (SC), 2 h intervals] 30 min after the hormones replacement. Finally, we investigated the effect of those ovarian hormones on synaptic plasticity using in vivo extracellular recording in the CA1 area of the hippocampus 2 days after last treatment.

FINDINGS

The findings showed that the induction and maintenance phase of E-LTP was impaired in the METH exposed animals compared to the saline group. Data from this study demonstrated that treatment with estrogen and progesterone showed a significant facilitation for induction and enhancement of the maintenance of LTP in animals that received METH. In addition, co-administration of estrogen plus progesterone did not significantly affect the hippocampal synaptic plasticity in METH-exposed OVX rats in comparison with METH-exposed animals that received vehicle injections.

CONCLUSION

The present findings provide new insight about treatment with ovarian hormones on synaptic plasticity deficits induced by METH.

Neonatal exposure to amphetamine alters social affiliation and central dopamine activity in adult male prairie voles

The prairie vole (Microtus ochrogaster) is a socially monogamous rodent species that forms pair bonds after mating. Recent data have shown that amphetamine (AMPH) is rewarding to prairie voles as it induces conditioned place preferences. Further, repeated treatment with AMPH impairs social bonding in adult prairie voles through a central dopamine (DA)-dependent mechanism. The present study examined the effects of neonatal exposure to AMPH on behavior and central DA activity in adult male prairie voles. Our data show that neonatal exposure to AMPH makes voles less social in an affiliation test during adulthood, but does not affect animals' locomotor activity and anxiety-like behavior. Neonatal exposure to AMPH also increases the levels of tyrosine hydroxylase (TH) and DA transporter (DAT) mRNA expression in the ventral tegmental area (VTA) in the brain, indicating an increase in central DA activity. As DA has been implicated in AMPH effects on behavioral and cognitive functions, altered DA activity in the vole brain may contribute to the observed changes in social behavior.

Neurobehavioral Effects from Developmental Methamphetamine Exposure

Intrauterine methamphetamine exposure adversely affects the neurofunctional profile of exposed children, leading to a variety of higher order cognitive deficits, such as decreased attention, reduced working-memory capability, behavioral dysregulation, and spatial memory impairments (Kiblawi et al. in J Dev Behav Pediatr 34:31-37, 2013; Piper et al. in Pharmacol Biochem Behav 98:432-439 2011; Roussotte et al. in Neuroimage 54:3067-3075, 2011; Twomey et al. in Am J Orthopsychiatry 83:64-72, 2013). In animal models of developmental methamphetamine, both neuroanatomical and behavioral outcomes critically depend on the timing of methamphetamine administration. Methamphetamine exposure during the third trimester human equivalent period of brain development results in well-defined and persistent wayfinding and spatial navigation deficits in rodents (Vorhees et al. in Neurotoxicol Teratol 27:117-134, 2005, Vorhees et al. in Int J Dev Neurosci 26:599-610, 2008; Vorhees et al. in Int J Dev Neurosci 27:289-298, 2009; Williams et al. in Psychopharmacology (Berl) 168:329-338, 2003b), whereas drug delivery during the first and second trimester equivalents produces no such effect (Acuff-Smith et al. in Neurotoxicol Teratol 18:199-215, 1996; Schutova et al. in Physiol Res 58:741-750, 2009a; Slamberova et al. in Naunyn Schmiedebergs Arch Pharmacol 380:109-114, 2009, Slamberova et al. in Physiol Res 63:S547-S558, 2014b). In this review, we examine the impact of developmental methamphetamine on emerging neural circuitry, neurotransmission, receptor changes, and behavioral outcomes in animal models. The review is organized by type of effects and timing of drug exposure (prenatal only, pre- and neonatal, and neonatal only). The findings elucidate functional patterns of interconnected brain structures (e.g., frontal cortex and striatum) and neurotransmitters (e.g., dopamine and serotonin) involved in methamphetamine-induced developmental neurotoxicity.

Neuronal reorganization in adult rats neonatally exposed to (±)-3,4-methylenedioxymethamphetamine

The abuse of methylenedioxymethamphetamine (MDMA) during pregnancy is of concern. MDMA treatment of rats during a period of brain growth analogous to late human gestation leads to neurochemical and behavioral changes. MDMA from postnatal day (P)11–20 in rats produces reductions in serotonin and deficits in spatial and route-based navigation. In this experiment we examined the impact of MDMA from P11 to P20 (20 mg/kg twice daily, 8 h apart) on neuronal architecture. Golgi impregnated sections showed significant changes. In the nucleus accumbens, the dendrites were shorter with fewer spines, whereas in the dentate gyrus the dendritic length was decreased but with more spines, and for the entorhinal cortex, reductions in basilar and apical dendritic lengths in MDMA animals compared with saline animals were seen. The data show that neuronal cytoarchitectural changes are long-lasting following developmental MDMA exposure and are in regions consistent with the learning and memory deficits observed in such animals.

Reduced amygdala and hippocampal volumes in patients with methamphetamine psychosis

The similarity between psychotic symptoms in patients with schizophrenia such as hallucinations and delusions and those caused by administration of methamphetamine has been accepted. While the etiology of schizophrenia remains unclear, methamphetamine induced psychosis, which is obviously occurred by methamphetamine administration, had been widely considered as a human pharmaceutical model of exogenous psychosis. Although volume reductions in medial temporal lobe structure in patients with schizophrenia have repeatedly been reported, those in patients with methamphetamine psychosis have not yet been clarified. Magnetic resonance images (MRI) were obtained from 20 patients with methamphetamine psychosis and 20 age, sex, parental socio-economic background, and IQ matched healthy controls. A reliable manual tracing methodology was employed to measure the gray matter volume of the amygdala and the hippocampus from MRIs. Significant gray matter volume reductions of both the amygdala and hippocampus were found bilaterally in the subjects with methamphetamine psychosis compared with the controls. The degree of volume reduction was significantly greater in the amygdala than in hippocampus. While the total gray, white matter and intracranial volumes were also significantly smaller-than-normal in the patients; the regional gray matter volume reductions in these medial temporal structures remained statistically significant even after these global brain volumes being controlled. The prominent volume reduction in amygdala rather than that in hippocampus could be relatively specific characteristics of methamphetamine psychosis, since previous studies have shown significant volume reductions less frequently in amygdala than in hippocampus of the other psychosis such as schizophrenia.

Methamphetamine exposure during brain development alters the brain acetylcholine system in adolescent mice

Children exposed to methamphetamine during brain development as a result of maternal drug use have long-term hippocampus-dependent cognitive impairments, but the mechanisms underlying these impairments are not understood. The acetylcholine system plays an important role in cognitive function and potential methamphetamine-induced acetylcholine alterations may be related to methamphetamine-induced cognitive impairments. In this study, we investigated the potential long-term effects of methamphetamine exposure during hippocampal development on the acetylcholine system in adolescence mice on postnatal day 30 and in adult mice on postnatal day 90. Methamphetamine exposure increased the density of acetylcholine neurons in regions of the basal forebrain and the area occupied by acetylcholine axons in the hippocampus in adolescent female mice. In contrast, methamphetamine exposure did not affect the density of GABA cells or total neurons in the basal forebrain. Methamphetamine exposure also increased the number of muscarinic acetylcholine receptors in the hippocampus of adolescent male and female mice. Our results demonstrate for the first time that methamphetamine exposure during hippocampal development affects the acetylcholine system in adolescent mice and that these changes are more profound in females than males.

Effects of neonatal methamphetamine treatment on adult stress-induced corticosterone release in rats

In rats, neonatal (+)-methamphetamine (MA) exposure and maternal separation stress increase corticosterone during treatment and result in learning and memory impairments later in life. Early-life stress also changes later responses to acute stress. We tested the hypothesis that neonatal MA exposure would alter adult corticosterone after acute stress or MA challenge. Rats were treated with MA (10 mg/kg × 4/day), saline, or handling on postnatal (P) days 11-15 or 11-20 (days that lead to learning and memory impairments at this dose). As adults, corticosterone was measured before and after 15 min forced swim (FS) or 15 min forced confinement (FC), counterbalanced, and after an acute MA challenge (10 mg/kg) given last. FS increased corticosterone more than FC; order and stress type interacted but did not interact with treatment; treatment interacted with FS but not with FC. In the P11-15 regimen, MA-treated rats showed more rapid increases in corticosterone after FS than controls. In the P11-20 regimen, MA-treated rats showed a trend toward more rapid decrease in corticosterone after FS. No differences were found after MA challenge. The data do not support the hypothesis that neonatal MA causes changes in adult stress responsiveness to FS, FC, or an acute MA challenge.

Abnormalities in parentally rated executive function in methamphetamine/polysubstance exposed children

Methamphetamine/polysubstance abuse in women of childbearing age is a major concern because of the potential long-term detrimental effects on the brain function of the fetus following in utero exposure. A battery of established tests, including the Wechsler Abbreviated Scale of Intelligence, Conners' Continuous Performance Test II, Behavioral Rating Inventory of Executive Function, the CMS Family Pictures and Dot Location tests, the Spatial Span test from the WISC-IV-Integrated, and a recently developed spatial learning and memory measure (Memory Island), was used to assess the effects of prenatal drug exposure on neurobehavioral performance. Participants were 7 to 9 year old children from similar socioeconomic backgrounds who either had (N=31) or had not (N=35) been exposed to methamphetamine/polysubstance during pregnancy. Compared to unexposed children, exposed children showed pronounced elevations (i.e. more problems) in parental ratings of executive function, including behavioral regulation and metacognition. Exposed children also exhibited subtle reductions in spatial performance in the Memory Island test. In contrast, IQ, Spatial Span, Family Pictures, Dot Location, and vigilance performance were unaffected by prenatal drug exposure history. Thus, children of women who reported using methamphetamine and other recreational drugs during pregnancy showed a selective profile of abnormalities in parentally rated executive function.

Long-term effects of neonatal methamphetamine exposure on cognitive function in adolescent mice

Exposure to methamphetamine during brain development impairs cognition in children and adult rodents. In mice, these impairments are greater in females than males. Adult female, but not male, mice show impairments in novel location recognition following methamphetamine exposure during brain development. In contrast to adulthood, little is known about the potential effects of methamphetamine exposure on cognition in adolescent mice. As adolescence is an important time of development and is relatively understudied, the aim of the current study was to examine potential long-term effects of neonatal methamphetamine exposure on behavior and cognition during adolescence. Male and female mice were exposed to methamphetamine (5 mg/kg) or saline once a day from postnatal days 11 to 20, the period of rodent hippocampal development. Behavioral and cognitive function was assessed during adolescence beginning on postnatal day 30. During the injection period, methamphetamine-exposed mice gained less weight on average compared to saline-exposed mice. In both male and female mice, methamphetamine exposure significantly impaired novel object recognition and there was a trend toward impaired novel location recognition. Anxiety-like behavior, sensorimotor gating, and contextual and cued fear conditioning were not affected by methamphetamine exposure. Thus, neonatal methamphetamine exposure affects cognition in adolescence and unlike in adulthood equally affects male and female mice.

Effects on plasma corticosterone levels and brain serotonin from interference with methamphetamine-induced corticosterone release in neonatal rats

Methamphetamine (MA) induces multiple effects in rats including alterations to corticosterone (CORT) and adrenocorticotropic hormone (ACTH). This effect is age dependent showing a U-shaped function similar to that of other stressors during the stress hyporesponsive period. Neonatal MA treatment leads to adult learning and memory impairments, but whether these are related to MA-induced CORT release is unknown. Here in, four methods were tested in neonatal rats previously established in adult rats for inhibiting stress-induced CORT release: inhibiting synthesis (metyrapone (MET) or ketoconazole (KTZ)) or surgically by adrenalectomy or adrenal autotransplantation (ADXA). Pretreatment on postnatal day 11 with MET or KTZ prior to four doses of 10 mg/kg of MA initially suppressed MA-induced increases in plasma CORT, but 24 h later, even with additional inhibitor treatment, a large CORT increase was seen which exceeded that of MA alone. Adrenalectomy blocked MA-induced increases in CORT but caused a secondary effect on brain serotonin (5-HT) and dopamine (DA), causing greater reductions than those caused by MA alone. ADXA inhibited MA-induced CORT release without causing a 24-h CORT increase and did not produce additional effects on brain 5-HT or DA. Neonatal ADXA is a new model for developmental drug or stress experiments designed to test the role of CORT in mediating early effects on later outcomes.

Long-term effects of methamphetamine exposure on cognitive function and muscarinic acetylcholine receptor levels in mice

Exposure to methamphetamine during brain development impairs cognition in humans and rodents. In mice, these impairments are more severe in females than males. Genetic factors, such as apolipoprotein E genotype, may modulate the cognitive effects of methamphetamine. Methamphetamine-induced alterations in the brain acetylcholine system may contribute to the cognitive effects of methamphetamine and may also be modulated by apolipoprotein E isoform. We assessed the long-term effects of methamphetamine exposure during brain development on cognitive function and muscarinic acetylcholine receptors in mice, and whether apolipoprotein E isoform modulates these effects. Mice expressing human apolipoprotein E3 or E4 were exposed to methamphetamine (5 mg/kg) or saline once a day from postnatal days 11-20 and behaviorally tested in adulthood. Muscarinic acetylcholine receptor binding was measured in the hippocampus and cortex. Methamphetamine exposure impaired novel location recognition in female, but not male, mice. Methamphetamine-exposed male and female mice showed impaired novel object recognition and increased number of muscarinic acetylcholine receptors in the hippocampus. The cognitive and cholinergic effects of methamphetamine were similar in apolipoprotein E3 and E4 mice. Thus, the cholinergic system, but not apolipoprotein E isoform, might play an important role in the long-term methamphetamine-induced cognitive deficits in adulthood.

Neurotoxic effects of methamphetamine on rat hippocampus pyramidal neurons

Methamphetamine (MAP) is known to alter behavior and cause deficits in learning and memory. While the major site of action of MAP is on mesolimbic dopaminergic pathways, the effects on learning and memory raise the possibility of important actions in the hippocampus. We have studied electrophysiologic and morphologic effects of MAP in the CA1 region of hippocampus from young male rats chronically exposed to MAP, male rats exposed during gestation only and the effects of bath perfusion of MAP onto brain slices from control rats. Pyramidal neurons in brain slices from chronically exposed rats had reduced membrane potential and membrane resistance. Long-term potentiation (LTP) was reduced as compared to control, but when MAP was acutely perfused over control slices the amplitude of LTP was increased. LTP in young adult animals that had been gestationally exposed to MAP showed reduced LTP as compared to controls. Morphologically CA1 pyramidal neurons in chronically exposed animals showed a high prevalence of extensive blebbing of dendrites. We conclude that the NMDA receptor and the process of LTP are also targets of MAP dysfunction, at least in the hippocampus.

Early exposure to haloperidol or olanzapine induces long-term alterations of dendritic form

Exposure of the developing brain to a wide variety of drugs of abuse (e.g., stimulants, opioids, ethanol, etc.) can induce life-long changes in behavior and neural circuitry. However, the long-term effects of exposure to therapeutic, psychotropic drugs have only recently begun to be appreciated. Antipsychotic drugs are little studied in this regard. Here, we quantitatively analyzed dendritic architecture in adult mice treated with paradigmatic typical- (haloperidol) or atypical (olanzapine) antipsychotic drugs at developmental stages corresponding to fetal or fetal plus early childhood stages in humans. In layer 3 pyramidal cells of the medial and orbital prefrontal cortices and the parietal cortex and in spiny neurons of the core of the nucleus accumbens, both drugs induced significant changes (predominantly reductions) in the amount and complexity of dendritic arbor and the density of dendritic spines. The drug-induced plasticity of dendritic architecture suggests changes in patterns of neuronal connectivity in multiple brain regions that are likely to be functionally significant.

Neonatal methamphetamine-induced corticosterone release in rats is inhibited by adrenal autotransplantation without altering the effect of the drug on hippocampal serotonin

Rat neonatal methamphetamine exposure results in corticosterone release and learning and memory impairments in later life; effects also observed after neonatal stress. Previous attempts to test the role of corticosterone release after methamphetamine using corticosterone inhibitors were unsuccessful and adrenalectomy caused reductions in hippocampal serotonin greater than those caused by methamphetamine alone. Here we tested whether adrenal autotransplantation could be used to attenuate methamphetamine-induced corticosterone release without also altering the effects of the drug on serotonin. Adrenal autotransplantation surgery occurred on postnatal day 9 followed by methamphetamine or saline treatment from postnatal day 11-20 (10mg/kg/dosex4/day). Plasma corticosterone and hippocampal serotonin and 5-hydroxyindoleacetic acid were determined 30min following the first treatment on each day between postnatal days 11-20. Adrenal autotransplantation attenuated neonatal methamphetamine-induced corticosterone release by approximately 70% initially, approximately 55% midway through treatment, and approximately 25% by the end of treatment. Methamphetamine reduced serotonin and 5-hydroxyindoleacetic acid in the hippocampus in the ADXA rats to the same degree as in SHAM rats. The data show that neonatal adrenal autotransplantation is an effective method for partially reducing treatment-induced corticosterone release while providing sufficient corticosterone to sustain normal growth and development. The method should be applicable to other models of developmental stress/corticosterone release.

(+)-Methamphetamine increases corticosterone in plasma and BDNF in brain more than forced swim or isolation in neonatal rats

(+)-Methamphetamine (MA) administered on postnatal days (P) 11-15 (four times/day) results in increased corticosterone that overlaps the stress hyporesponsive period (SHRP; P2-14) and leads to later learning and memory deficits. Elevated corticosterone during the SHRP results in neurotrophin changes and long-term effects on learning. We determined whether two known stressors could mimic the effects of MA [10 (mg/kg)/dose] administration in neonatal rats. Stressors were four 15-min sessions of forced swim or isolation (confinement in forced swim tubes without water). Saline and weighed-only controls were included and all five treatments were represented within each litter. Corticosterone in plasma and brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in neostriatum and hippocampus were examined after one or four treatments on P11 or P15 (0.5, 1.75, 6.5, or 24 h after first dose). MA increased corticosterone and BDNF; forced swim and isolation also increased corticosterone, but to a lesser extent than MA, and neither stressor increased BDNF. NGF was unaffected by saline treatment, but there was a minor reduction in NGF in the forced swim group compared with the weighed-only group. The data show that MA is more potent at releasing corticosterone and increasing BDNF than short-term, repeated episodes of forced swim or isolation. The possible relationship between these changes and the long-term cognitive effects of developmental MA administration are discussed.

Short- and long-term effects of (+)-methamphetamine and (+/-)-3,4-methylenedioxymethamphetamine on monoamine and corticosterone levels in the neonatal rat following multiple days of treatment

Rats treated with (+/-)-3,4-methylenedioxymethamphetamine (MDMA) or (+)-methamphetamine (MA) neonatally exhibit long-lasting learning impairments (i.e., after treatment on postnatal days (P)11-15 or P11-20). Although both drugs are substituted amphetamines, they each produce a unique profile of cognitive deficits (i.e., spatial vs. path integration learning and severity of deficits) which may be the result of differential early neurochemical changes. We previously showed that MA and MDMA increase corticosterone (CORT) and MDMA reduces levels of serotonin (5-HT) 24 h after treatment on P11, however, learning deficits are seen after 5 or 10 days of drug treatment, not just 1 day. Accordingly, in the present experiment, rats were treated with MA or MDMA starting on P11 for 5 or 10 days (P11-15 or P11-20) and tissues collected on P16, P21, or P30. Five-day MA administration dramatically increased CORT on P16, whereas MDMA did not. Both drugs decreased hippocampal 5-HT on P16 and P21, although MDMA produced larger reductions. Ten-day treatment with either drug increased dopamine utilization in the neostriatum on P21, whereas 5-day treatment had no effect. No CORT or brain 5-HT or dopamine changes were found with either drug on P30. Although the monoamine changes are transient, they may alter developing neural circuits sufficiently to permanently disrupt later learning and memory abilities.

Age-dependent effects of neonatal methamphetamine exposure on spatial learning

Neonatal rats exposed to (+)-methamphetamine (MA) display spatial learning and reference memory deficits in the Morris water maze. In separate experiments the emergence and permanence of these effects were determined. Twenty litters were used in each experiment, and two male/female pairs/litter received saline or MA (5 mg/kg four times a day) on postnatal days (P) 11-20. In experiment 1, one MA and one saline pair from each litter began testing on either P30 or P40, whereas in experiment 2, testing began on P180 or P360. Animals received trials in a straight swimming channel and then in the Morris maze (acquisition, reversal, and reduced platform phases). In both experiments, MA-treated groups showed impaired learning in the platform trials and impaired reference memory in the probe trials, which were largely independent of age. The P30 and P40 MA impairments were seen on acquisition and reduced platform trials but not on reversal. In the probe trials, MA effects were seen during all phases. The P180 and P360 MA-induced deficits were seen in all phases of the platform trials. In probe trials, deficits were only seen during the reversal and reduced platform phases. The results demonstrate that neonatal MA treatment induces spatial learning and reference memory deficits that emerge early and persist until at least 1 year of age, suggesting permanence.

The Roles of Glial Cell Line-Derived Neurotrophic Factor, Tumor Necrosis Factor-α, and an Inducer of These Factors in Drug Dependence

There are few efficacious medications for drug dependence at present. Recent evidence has suggested that various cytokines are involved in the effects of abused drugs, suggesting that these factors play a role in drug dependence. In this article, the roles of glial cell line-derived neurotrophic factor (GDNF) and tumor necrosis factor-alpha (TNF-alpha) in drug dependence are discussed. GDNF inhibits the cocaine-induced upregulation of tyrosine hydroxylase activity in the ventral tegmental area and blocks behavioral responses to cocaine. TNF-alpha attenuates rewarding effects and locomotor sensitization induced by methamphetamine (METH) and morphine (MOR). Moreover, we mentioned the potential of Leu-Ile, which induces the expression of GDNF and TNF-alpha, as a novel therapeutic agent for drug dependence. Leu-Ile inhibits not only the development but also the maintenance of METH- or MOR-induced place preference and locomotor sensitization in mice. The inhibitory effect of Leu-Ile on METH- or MOR-induced place preference is not observed in GDNF heterozygous and TNF-alpha knockout mice. Leu-Ile inhibits METH- or MOR-induced place preference and sensitization by attenuating the METH- or MOR-induced increase in extracellular dopamine levels in the nucleus accumbens via the induction of GDNF and TNF-alpha expression. These findings suggest that Leu-Ile could be a novel therapeutic agent for drug dependence.

Comparison of monoamine and corticosterone levels 24 h following (+)methamphetamine, (+/-)3,4-methylenedioxymethamphetamine, cocaine, (+)fenfluramine or (+/-)methylphenidate administration in the neonatal rat

We have previously shown that neonatal administration of (+/-)3,4-methylenedioxymethamphetamine and (+)fenfluramine produce deficits in spatial and path integration learning, whereas (+)methamphetamine causes deficits in spatial learning. Conversely, cocaine and (+/-)methylphenidate have no effect on either form of learning following neonatal administration. The purpose of the present study was to determine whether corticosterone and/or monoamine levels were changed following subcutaneous administration of 10 mg/kg (+)methamphetamine, (+/-)3,4-methylenedioxymethamphetamine, (+)fenfluramine, (+/-)methylphenidate or cocaine every 2 h (total of four injections) on postnatal day 11. Twenty-four hours after the first dose, plasma, striatum and hippocampus were collected. Corticosterone levels were increased in methamphetamine-, fenfluramine-, methylenedioxymethamphetamine- and methylphenidate-treated rats relative to levels in saline-treated rats, whereas cocaine-treated rats were unaffected. In the striatum and hippocampus, serotonin and 5-hydroxyindolacetic acid were reduced in animals treated with methylenedioxymethamphetamine or fenfluramine, compared with levels in saline controls. Dopamine levels were not changed by any of the drugs, although 3,4-dihydroxyphenylacetic acid was decreased following methylenedioxymethamphetamine or methamphetamine. Minimal effects were seen in neurotransmitter levels following injection of cocaine or methylphenidate. These data suggest that drugs that affect corticosterone and hippocampal serotonin are associated with both spatial learning and path integration deficits, and those that affect corticosterone and 3,4-dihydroxyphenylacetic acid are associated with spatial learning deficits only.

Ontogeny of the adrenal response to (+)-methamphetamine in neonatal rats: the effect of prior drug exposure

We examined the ontogeny of the corticosterone response to (+)-methamphetamine in neonatal rats. In experiment-1, animals were injected with 10 mg/kg of (+)-methamphetamine or saline and plasma corticosterone levels were examined in separate groups 30 or 105 min later on postnatal day (P) 1, 3, 5, 7, 9, 11, 13, 15, 17, or 19. The adrenal response to methamphetamine was best described by a U-shaped function with the nadir of corticosterone release occurring between P7 and P13. Experiment-2 was similar except that the effect of four consecutive days of exposure to (+)-methamphetamine (four times daily at 2 h intervals with 10 mg/kg) was assessed with a single final dose early on the fifth day (i.e. P1-5, 3-7, 5-9, 7-11, 9-13, 11-15, 13-17, 15-19). The 30 min corticosterone response after multiple methamphetamine doses was augmented compared to single exposures, with the exception of the two earliest dosing intervals ending on P5 and P7, where the responses were lower. In addition, at 105 min, the levels of corticosterone were attenuated relative to a single drug administration. With the exception of animals receiving methamphetamine from P15 to P19, thymus weights were unaffected. The data demonstrate that (+)-methamphetamine is a robust activator of corticosterone release in developing animals and this release is extensively modified by age and previous drug exposure.