Long-term parental methamphetamine exposure of mice influences behavior and hippocampal DNA methylation of the offspring

The high rate of methamphetamine (METH) abuse among young adults and women of childbearing age makes it imperative to determine the long-term effects of METH exposure on the offspring. We hypothesized that parental METH exposure modulates offspring behavior by disrupting epigenetic programming of gene expression in the brain. To simulate the human pattern of drug use, male and female C57Bl/6J mice were exposed to escalating doses of METH or saline from adolescence through adulthood; following mating, females continue to receive drug or saline through gestational day 17. F1 METH male offspring showed enhanced response to cocaine-conditioned reward and hyperlocomotion. Both F1 METH male and female offspring had reduced response to conditioned fear. Cross-fostering experiments have shown that certain behavioral phenotypes were modulated by maternal care of either METH or saline dams. Analysis of offspring hippocampal DNA methylation showed differentially methylated regions as a result of both METH in utero exposure and maternal care. Our results suggest that behavioral phenotypes and epigenotypes of offspring that were exposed to METH in utero are vulnerable to (a) METH exposure during embryonic development, a period when wide epigenetic reprogramming occurs, and (b) postnatal maternal care.

Long-term memory of visually cued fear conditioning: roles of the neuronal nitric oxide synthase gene and cyclic AMP response element-binding protein

Nitric oxide (NO) produced by neuronal nitric oxide synthase (nNOS) has a role in late-phase long-term potentiation (LTP) and long-term memory (LTM) formation. Our recent studies implicated NO signaling in contextual and auditory cued fear conditioning. The present study investigated the role of NO signaling in visually cued fear conditioning. First, visually cued fear conditioning was investigated in wild-type (WT) and nNOS knockout (KO) mice. Second, the effects of pharmacological modulators of NO signaling on the acquisition of visually cued fear conditioning were investigated. Third, plasma levels of corticosterone were measured to determine a relationship between physiological and behavioral responses to fear conditioning. Fourth, levels of extracellular signal-related kinase (ERK1/2) and cyclic AMP response element binding protein (CREB) phosphorylation, downstream of NO signaling, were determined in the amygdala as potential correlates of fear learning. Mice underwent single or multiple (4) spaced trainings that consisted of a visual cue (blinking light) paired with footshock. WT mice acquired cued and contextual LTM following single and multiple trainings. nNOS KO mice acquired neither cued nor contextual LTM following a single training; however, multiple trainings improved contextual but not cued LTM. The selective nNOS inhibitor S-methyl-thiocitrulline (SMTC) impaired cued and contextual LTM in WT mice. The NO donor molsidomine recovered contextual LTM but had no effect on cued LTM in nNOS KO mice. Re-exposure to the visual cue 24 h posttraining elicited freezing response and a marked increase in plasma corticosterone levels in WT but not nNOS KO mice. The expression of CREB phosphorylation (Ser-133) was significantly higher in naive nNOS KO mice than in WT counterparts, and pharmacological modulators of NO had significant effects on levels of CREB phosphorylation and expression. These findings suggest that visual cue-dependent LTM is impaired in nNOS KO mice, and aberrant modulation of CREB in the absence of the nNOS gene may hinder cued and contextual LTM formation.

Methylphenidate and MDMA adolescent exposure in mice: long-lasting consequences on cocaine-induced reward and psychomotor stimulation in adulthood

Pre-exposure to psychostimulants enhances the rewarding and psychomotor stimulating effects of subsequent drug exposure. Currently, there is a prevalence of adolescent exposure to the psychostimulants methylphenidate (MPD) and 3,4-methylenedioxymethamphetamine (MDMA). However, there is a paucity of investigation concerning the long-term behavioral consequences of exposure to these stimulants during adolescence. The aim of the present study was to investigate the effect of MPD and MDMA exposure in adolescence on cocaine-induced reward and psychomotor stimulation in adulthood. Adolescent Swiss-Webster mice received intraperitoneal injections of saline, MPD (10 mg/kg) or MDMA (10 mg/kg) from PD 26 to PD 32. Animal weights were monitored during and after drug administration. One month later, cocaine-induced conditioned place preference (CPP) and locomotor activity (LMA) were investigated. MPD and MDMA inhibited weight increase from PD 28 to PD 39 compared to the saline group, but weights amongst the three groups equalized by PD 46. MDMA exposure resulted in the same magnitude of cocaine (20 mg/kg)-induced CPP as saline exposure; however, MPD exposure caused significantly less CPP. Two weeks following extinction of CPP and withdrawal from cocaine, a priming injection of cocaine (5 mg/kg) reinstated significantly higher CPP in the MPD and MDMA groups than in the saline group. In the LMA experiments, cocaine (15 mg/kg) was administered for 5 consecutive days. On days 1 and 5, cocaine-induced hyperlocomotion in the MPD group was significantly higher than in the saline and MDMA groups. After a 2-week withdrawal period, cocaine (5 mg/kg) evoked significantly higher LMA responses in the MPD and MDMA groups compared to the saline group. Results suggest that exposure of mice to both MPD and MDMA during adolescence involves long-lasting neural adaptations, manifested as sensitized responses to cocaine-induced reward and psychomotor stimulation following cocaine withdrawal.

Effect of the neuronal nitric oxide synthase inhibitor 7-nitroindazole on methylphenidate-induced hyperlocomotion in mice

The psychostimulant methylphenidate (MPD) is used for the treatment of attention-deficit/hyperactivity disorders (ADHD) in adolescents. In the present study we investigated the effect of repeated administration of a low (10 mg/kg) and a high (40 mg/kg) dose of MPD on the locomotor activity of Swiss Webster mice, and the influence of inhibition of the neuronal nitric oxide synthase (nNOS) on MPD-induced hyperlocomotion. In the first experiment, mice were administered either vehicle or the nNOS inhibitor 7-nitroindazole (7-NI; 25 mg/kg), prior to the administration of MPD (10 or 40 mg/kg), for five consecutive days; injections were paired with the test cage ('novel environment') on days 1 and 5. A challenge injection of MPD (10 or 40 mg/kg), given after a 10-day drug-free period, resulted in sensitization to the motor stimulating effect of the low dose of MPD but tolerance to the high dose of MPD. 7-NI blocked the induction of sensitization but had no effect on the development of tolerance. The place-dependent-hyperlocomotion (e.g. conditioning) that developed after the administration of either the low or high dose of MPD was blocked by pretreatment with the nNOS inhibitor. In the second experiment, mice were administered MPD (10 or 40 mg/kg; 5 days) in their home cage and after a 10-day drug-free period were challenged with either vehicle/MPD or 7-NI/MPD. The low dose of MPD elicited a sensitized response that was blocked by the co-administration of 7-NI. The high dose of MPD produced neither sensitization nor tolerance; 7-NI did not affect the response to the high dose of MPD. These findings suggest: (a) MPD-induced sensitization and tolerance are dependent on the dose of the drug and the environment where the drug is delivered (home cage versus test cage); (b) context-dependent hyperlocomotion developed in the absence of a sensitized response to the drug; (c) nNOS is involved in the induction and expression of sensitization to MPD as well as in the conditioned locomotion produced by the drug; (d) no involvement of nNOS in the effects of a high dose of MPD was detected.

Methamphetamine-induced alteration in striatal p53 and bcl-2 expressions in mice

Methamphetamine (METH)-induced alterations in the expression of p53 and bcl-2 protein were studied in the striatum of wild type, neuronal nitric oxide synthase knockout (nNOS -/-) and copper zinc superoxide dismutase overexpressed (SOD-Tg) mice. METH treatment up-regulated p53 and down-regulated bcl-2 expression in the striatum of wild type mice. No significant alterations were observed in the expression of these proteins in the nNOS -/- or SOD-Tg mice. These data suggest that METH might cause its neurotoxic effects via the production of free radicals and secondary perturbations in the expression of genes known to be involved in apoptosis and cell death machinery.

Methamphetamine-induced dopaminergic neurotoxicity: role of peroxynitrite and neuroprotective role of antioxidants and peroxynitrite decomposition catalysts

Oxidative stress, reactive oxygen (ROS), and nitrogen (RNS) species have been known to be involved in a multitude of neurodegenerative disorders such as Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). Both ROS and RNS have very short half-lives, thereby making their identification very difficult as a specific cause of neurodegeneration. Recently, we have developed a high performance liquid chromatography/electrochemical detection (HPLC/EC) method to identify 3-nitrotyrosine (3-NT), an in vitro and in vivo biomarker of peroxynitrite production, in cell cultures and brain to evaluate if an agent-driven neurotoxicity is produced by the generation of peroxynitrite. We show that a single or multiple injections of methamphetamine (METH) produced a significant increase in the formation of 3-NT in the striatum. This formation of 3-NT correlated with the striatal dopamine depletion caused by METH administration. We also show that PC12 cells treated with METH has significantly increased formation of 3-NT and dopamine depletion. Furthermore, we report that pretreatment with antioxidants such as selenium and melatonin can completely protect against the formation of 3-NT and depletion of striatal dopamine. We also report that pretreatment with peroxynitrite decomposition catalysts such as 5, 10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) and 5, 10, 15, 20-tetrakis (2,4,6-trimethyl-3,5-sulfonatophenyl) porphinato iron III (FETPPS) significantly protect against METH-induced 3-NT formation and striatal dopamine depletion. We used two different approaches, pharmacological manipulation and transgenic animal models, in order to further investigate the role of peroxynitrite. We show that a selective neuronal nitric oxide synthase (nNOS) inhibitor, 7-nitroindazole (7-NI), significantly protect against the formation of 3-NT as well as striatal dopamine depletion. Similar results were observed with nNOS knockout and copper zinc superoxide dismutase (CuZnSOD)-overexpressed transgenic mice models. Finally, using the protein data bank crystal structure of tyrosine hydroxylase, we postulate the possible nitration of specific tyrosine moiety in the enzyme that can be responsible for dopaminergic neurotoxicity. Together, these data clearly support the hypothesis that the reactive nitrogen species, peroxynitrite, plays a major role in METH-induced dopaminergic neurotoxicity and that selective antioxidants and peroxynitrite decomposition catalysts can protect against METH-induced neurotoxicity. These antioxidants and decomposition catalysts may have therapeutic potential in the treatment of psychostimulant addictions.

Peroxynitrite plays a role in methamphetamine-induced dopaminergic neurotoxicity: evidence from mice lacking neuronal nitric oxide synthase gene or overexpressing copper-zinc superoxide dismutase

The use of methamphetamine (METH) leads to neurotoxic effects in mammals. These neurotoxic effects appear to be related to the production of free radicals. To assess the role of peroxynitrite in METH-induced dopaminergic, we investigated the production of 3-nitrotyrosine (3-NT) in the mouse striatum. The levels of 3-NT increased in the striatum of wild-type mice treated with multiple doses of METH (4 x 10 mg/kg, 2 h interval) as compared with the controls. However, no significant production of 3-NT was observed either in the striata of neuronal nitric oxide synthase knockout mice (nNOS -/-) or copper-zinc superoxide dismutase overexpressed transgenic mice (SOD-Tg) treated with similar doses of METH. The dopaminergic damage induced by METH treatment was also attenuated in nNOS-/- or SOD-Tg mice. These data further confirm that METH causes its neurotoxic effects via the production of peroxynitrite.

Scopolamine inhibits cocaine-conditioned but not unconditioned stimulant effects in mice

RATIONALE

In animal models, cocaine cues contribute to the development of conditioned responses to the psychomotor stimulating and rewarding effects of the drug.

OBJECTIVES

In the present study we investigated the effect of scopolamine, known to impair learning and memory, on cocaine-induced conditioned and unconditioned responses in Swiss Webster mice.

METHODS

In the first experiment, mice were treated with saline/saline, saline/cocaine (20 mg/kg), scopolamine (1.0 mg/kg)/cocaine, or scopolamine/saline for 5 days. The treatments were paired with the locomotor activity test cage twice, on days 1 and 5. This allowed to determine: (a) the induction and expression of place-dependent sensitization (PDS) to the psychomotor-stimulating effect of cocaine and (b) place-dependent hyperlocomotion (PDH; i.e., conditioning) as defined by the response to saline injection in the test cage. In the second experiment, all injections were delivered in animals' home cage in order to induce place-independent sensitization (PIS) to cocaine and to avoid the development of PDH. In the third experiment, the effect of scopolamine (1.0 mg/kg) on the acquisition of cocaine-induced conditioned place preference (CPP) was investigated.

RESULTS

Data from the first experiment suggest that pretreatment with scopolamine had no specific effect on the induction and expression of cocaine-induced PIS. However, scopolamine blocked cocaine-induced PDH. Results from the second experiment confirmed that scopolamine had no effect on the induction of PIS to cocaine. Results from the third experiment showed that scopolamine completely blocked cocaine-induced CPP.

CONCLUSIONS

The finding that scopolamine blocked the conditioned behaviors, PDH and CPP, that develop after exposure to cocaine supports the hypothesis that cocaine cue reactivity in the paradigms tested is associated with learning and memory.

nNOS inhibitors attenuate methamphetamine-induced dopaminergic neurotoxicity but not hyperthermia in mice

Methamphetamine (METH)-induced dopaminergic neurotoxicity is associated with hyperthermia. We investigated the effect of several neuronal nitric oxide synthase (nNOS) inhibitors on METH-induced hyperthermia and striatal dopaminergic neurotoxicity. Administration of METH (5 mg/kg; q. 3 h x 3) to Swiss Webster mice produced marked hyperthermia and 50-60% depletion of striatal dopaminergic markers 72 h after METH administration. Pretreatment with the nNOS inhibitors S-methylthiocitrulline (SMTC; 10 mg/kg) or 3-bromo-7-nitroindazole (3-Br-7-NI; 20 mg/kg) before each METH injection did not affect the persistent hyperthermia produced by METH, but afforded protection against the depletion of dopaminergic markers. A low dose (25 mg/kg) of the nNOS inhibitor 7-nitroindazole (7-NI) did not affect METH-induced hyperthermia, but a high dose (50 mg/kg) produced significant hypothermia. These findings indicate that low dose of selective nNOS inhibitors protect against METH-induced neurotoxicity with no effect on body temperature and support the hypothesis that nitric oxide (NO) and peroxynitrite have a major role in METH-induced dopaminergic neurotoxicity.

Comparison between the role of the neuronal and inducible nitric oxide synthase in methamphetamine-induced neurotoxicity and sensitization

The involvement of the neuronal and inducible nitric oxide synthase (nNOS and iNOS, respectively) in methamphetamine (METH)-induced dopaminergic neurotoxicity and behavioral sensitization was investigated. To determine METH-induced neurotoxicity, mice deficient in the nNOS and iNOS genes, nNOS(-/-) and iNOS(-/-) mice, and wild-type controls received either saline or METH (5 mg/kg x 3). After 72 h the level of striatal dopaminergic markers were measured. Administration of METH to nNOS(-/-) mice had no significant effect on the level of striatal dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), or dopamine transporter (DAT) binding sites. However, METH caused 25-40% depletion of dopaminergic markers in iNOS(-/-) mice and 63-69% depletion in the wild-type mice. METH-induced locomotor activity was measured following the administration of a low dose (1 mg/kg) on day 1. Subsequently animals received the high dose of METH (5 mg/kg x 3). On day 4, after a 68-72 h drug free period, animals were challenged with 1 mg/kg METH, and locomotor activity was recorded. The intensity of METH-induced locomotion in nNOS(-/-) mice on day 1 and 4 was similar, suggesting that locomotor sensitization did not develop. However, the intensity of METH-induced locomotion in the iNOS(-/-) and wild-type mice on day 4 was doubled compared to day 1, suggesting the development of sensitization. The present findings indicate that nNOS(-/-) mice are more resistant to METH-induced neurotoxicity and behavioral sensitization than iNOS(-/-) mice. These results suggest a major role for nNOS rather than iNOS in the effects of METH.

Prevention of dopaminergic neurotoxicity by targeting nitric oxide and peroxynitrite: implications for the prevention of methamphetamine-induced neurotoxic damage

Methamphetamine (METH) is a neurotoxic psychostimulant that produces catecholaminergic brain damage by producing oxidative stress and free radical generation. The role of oxygen and nitrogen radicals is well documented as a cause of METH-induced neurotoxic damage. In this study, we have obtained evidence that METH-induced neurotoxicity is the resultant of interaction between oxygen and nitrogen radicals, and it is mediated by the production of peroxynitrite. We have also assessed the effects of inhibitors of neuronal nitric oxide synthase (nNOS) as well as scavenger of nitric oxide and a peroxynitrite decomposition catalyst. Significant protective effects were observed with the inhibitor of nNOS, 7-nitroindazole (7-NI), as well as by the selective peroxynitrite scavenger or decomposition catalyst, 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5-sulfonatophenyl)porphyrinato iron III (FeTPPS). However, the use of a nitric oxide scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), did not provide any significant protection against METH-induced hyperthermia or peroxynitrite generation and the resulting dopaminergic neurotoxicity. In particular, treatment with FeTPPS completely prevented METH-induced hyperthermia, peroxynitrite production, and METH-induced dopaminergic depletion. Together, these data demonstrate that METH-induced dopaminergic neurotoxicity is mediated by the generation of peroxynitrite, which can be selectively protected by nNOS inhibitors or peroxynitrite scavenger or decomposition catalysts.

Effect of riluzole and gabapentin on cocaine- and methamphetamine-induced behavioral sensitization in mice

RATIONALE

Recent studies have suggested the involvement of excitatory amino acid (EAA) and inhibitory gamma amino butyric acid (GABA) transmission in the effects of psychostimulants such as cocaine and amphetamines.

OBJECTIVES

The present study was undertaken to investigate whether drugs that are considered to inhibit glutamate release (e.g., riluzole) or increase GABAergic transmission (e.g., gabapentin) attenuate the induction and expression of sensitization to cocaine and methamphetamine (METH) in Swiss Webster mice.

METHODS

Sensitization to the psychomotor stimulating effect of cocaine and METH was rendered by five daily injections of cocaine (20 mg/kg) or METH (1.0 mg/kg). Locomotor activity was measured by infrared beam interrupts.

RESULTS

Pretreatment with riluzole (2.5-20.0 mg/kg) affected neither the expression nor the induction of sensitization to cocaine. The pretreatment with riluzole (20 mg/kg) blocked the acute response to METH on day 1 and the expression of the sensitized response on day 5 but not the induction of sensitization to METH. Pretreatment with gabapentin (10 mg/kg and 30 mg/kg) affected neither the expression nor the induction of sensitization to cocaine. The pretreatment with gabapentin attenuated the acute response to METH on day 1 and the expression of the sensitized response on day 5, but it failed to block the induction of sensitization to METH. Psychostimulant-induced conditioned locomotion was affected neither by riluzole nor by gabapentin.

CONCLUSIONS

Riluzole and gabapentin had no effect on the induction of sensitization to cocaine and METH; however, they attenuated the expression of sensitization to METH but not to cocaine. These findings suggest that riluzole- and gabapentin-mediated changes in EAA and GABAergic transmission, respectively, had no effect on mechanisms associated with the induction of sensitization, but they may affect the expression of the sensitized response to METH.

Role of peroxynitrite in methamphetamine-induced dopaminergic neurotoxicity and sensitization in mice

Abstract Methamphetamine (METH)-induced dopaminergic neurotoxicity is thought to be associated with the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Recently, we have reported that copper/zinc(CuZn)-superoxide dismutase transgenic mice are resistant to METH-induced neurotoxicity. In the present study, we examined the role of the neuronal nitric oxide synthase (nNOS), susceptibility of nNOS knockout (KO) mice and sensitization to psychostimulants after neurotoxic doses of METH. Male SwissWebster mice were treated with or without 7-nitroindazole (7-NI) along with METH (5 mg/kg,ip,q 3h x 3) and were sacrificed 72 h after the last METH injection. Dopamine (DA) and dopamine transporter (DAT) binding sites were determined in striatum from saline and METH-treated animals. 7-NI completely protected against the depletion of DA, and DAT in striatum. In follow-up experiments nNOS KO mice along with appropriate control (C57BL/6N, SV129 and B6JSV129) mice were treated with METH (5 mg/kg,ip, q 3h x 3) and were sacrificed 72 h after dosing. This schedule of METH administrations resulted in only 10-20% decrease in tissue content of DA and no apparent change in the number of DAT binding sites in nNOS KO mice. However, this regime of METH resulted in a significant decrease in the content of DA as well as DAT binding sites in the wild-type animals. Pre-exposure to single or multiple doses of METH resulted in a marked locomotion sensitization in response to METH. However, the nNOS KO mice show no sensitization in response to METH after single or multiple injections of METH. Therefore, these studies strongly suggest the role of peroxynitrite, nNOS and DA system in METH-induced neurotoxicity and behavioral sensitization.

7-Nitroindazole blocks nicotine-induced conditioned place preference but not LiCl-induced conditioned place aversion

We have shown previously that the neuronal nitric oxide synthase (nNOS) is involved in the rewarding effect of cocaine as determined by the conditioned place preference (CPP) paradigm. In the present study we investigated the effect of the nNOS inhibitor 7-nitroindazole (7-NI) on nicotine-induced CPP and LiCl-induced conditioned place aversion (CPA) in Swiss Webster mice. Mice treated with nicotine (0.5 mg/kg) or saline every other day for 8 days (four drug and four saline sessions) developed CPP that was completely blocked by pretreatment with 7-NI (25 mg/kg). Mice treated with LiCl (150 mg/kg) developed marked aversion to the LiCl-paired compartment. LiCl-induced CPA was not affected by the pretreatment with 7-NI. These findings suggest that nitric oxide (NO) plays a role in the acquisition of reward but not of aversion and that the blockade of nicotine-induced CPP is probably not due to impairment of learning and memory.

Blockade of alcohol-induced locomotor sensitization and conditioned place preference in DBA mice by 7-nitroindazole

Our previous studies indicated that inhibition or ablation of the neuronal nitric oxide synthase (nNOS) prevents the development of sensitization to the locomotor-stimulating effect of cocaine and cocaine-induced conditioned place preference (CPP). The present study was undertaken to investigate the effect of the nNOS inhibitor, 7-nitroindazole (7-NI), on ethanol-induced locomotor sensitization and CPP in DBA/2J mice. Administration of ethanol (1.5 g/kg; i.p.) for 7 days resulted in a progressive increase in the locomotor-stimulating effect of ethanol. Pretreatment with 7-NI (25 mg/kg) blocked the expression of the sensitized response to ethanol. A challenge injection of ethanol given 1 week and then 4 weeks following withdrawal from ethanol indicated that (a) ethanol sensitization was long lasting, and (b) the co-administration of 7-NI and ethanol attenuated the sensitized response to ethanol challenge. The CPP experiments showed that pairing four ethanol (2.5 g/kg) injections with a specific environment resulted in a marked preference for the drug-paired environment. The pretreatment with 7-NI (25 mg/kg) completely blocked ethanol-induced CPP. 7-NI alone produced neither rewarding nor aversive effects. Taken together, results of the present study indicate that blockade of nNOS by 7-NI-attenuated ethanol-induced behavioral sensitization and completely blocked the rewarding effect of ethanol. These findings support the role of NO in ethanol actions and further suggest that the nNOS system is relevant to the rewarding effects of various drugs of abuse.

Cocaine-induced kindling is associated with elevated NMDA receptor binding in discrete mouse brain regions

The present study was undertaken to investigate the involvement of N-methyl-D-aspartate (NMDA) type of glutamate receptors in the induction and maintenance of kindling generated by daily cocaine (35 mg/kg) injections to Swiss Webster mice. In addition, the regulation of NMDA receptor binding following the development of sensitization to horizontal locomotor activity produced by daily injections of a low dose of cocaine (15 mg/kg for 5 days) was investigated. Three days following the administration of the high dose of cocaine (35 mg/kg) a marked augmentation in cocaine-induced horizontal and vertical activities was observed (induction phase). Subsequently, after 10 days of cocaine administration, mice developed stage 5 seizures (Racine scale). Binding of [3H]CGP 39653 to the NMDA receptors revealed a marked increase in receptor densities in the striatum, amygdala and hippocampus associated with the induction phase. The elevation of NMDA receptor binding in the striatum and amygdala was sustained for 10 days following the induction phase. The pattern of altered NMDA receptor binding following the expression of cocaine kindled seizures was different. One day after the expression of kindled seizures NMDA receptor binding was elevated in striatum, amygdala, hippocampus and frontal cortex. However, only the elevation of NMDA receptor binding in the amygdala and hippocampus was sustained for 10 days following the expression of cocaine kindled seizures. In the brains of mice sensitized to the low dose of cocaine (15 mg/kg) no change in NMDA receptor binding was observed compared with control values. The present findings suggest the following: (a) The induction of cocaine kindling is associated with increased NMDA receptor binding activity in the striatum, amygdala and hippocampus; (b) the maintenance of cocaine kindling depends on increased NMDA receptor binding in the amygdala and hippocampus; (c) sensitization to cocaine-induced horizontal locomotor activity may be independent of elevation in NMDA receptor binding.

Methamphetamine- and 1-methyl-4-phenyl- 1,2,3, 6-tetrahydropyridine-induced dopaminergic neurotoxicity in inducible nitric oxide synthase-deficient mice

Previous studies have suggested a role for the retrograde messenger, nitric oxide (NO), in methamphetamine (METH)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)- induced dopaminergic neurotoxicity. Since evidence supported the involvement of the neuronal nitric oxide synthase (nNOS) isoform in the dopaminergic neurotoxicity, the present study was undertaken to investigate whether the inducible nitric oxide synthase (iNOS) isoform is also associated with METH- and MPTP-induced neurotoxicity. The administration of METH (5mg/kg x 3) to iNOS deficient mice [homozygote iNOS(-/-)] and wild type mice (C57BL/6) resulted in significantly smaller depletion of striatal dopaminergic markers in the iNOS(-/-) mice compared with the wild-type mice. METH-induced hyperthermia was also significantly lower in the iNOS(-/-) mice than in wild-type mice. In contrast to the outcome of METH administration, MPTP injections (20 mg/kg x 3) resulted in a similar decrease in striatal dopaminergic markers in iNOS(-/-) and wild-type mice. In the set of behavioral experiments, METH-induced locomotor sensitization was investigated. The acute administration of METH (1.0 mg/kg) resulted in the same intensity of locomotor activity in iNOS(-/-) and wild-type mice. Moreover, 68 to 72 h after the exposure to the high-dose METH regimen (5 mg/kg x 3), a marked sensitized response to a challenge injection of METH (1.0 mg/kg) was observed in both the iNOS(-/-) and wild-type mice. The finding that iNOS(-/-) mice were unprotected from MPTP-induced neurotoxicity suggests that the partial protection against METH-induced neurotoxicity observed was primarily associated with the diminished hyperthermic effect of METH seen in the iNOS(-/-) mice. Moreover, in contrast to nNOS deficiency, iNOS deficiency did not affect METH-induced behavioral sensitization.

Effect of the dopaminergic neurotoxin MPTP on cocaine-induced locomotor sensitization

The blockade of dopamine (DA) uptake via the dopamine transporter (DAT) in the nucleus accumbens (NAC) and striatum by cocaine has a major role in the reinforcing and psychomotor stimulating effects of the drug. Here we investigated the effect of the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on the expression and induction of sensitization to the locomotor stimulating effect of cocaine. MPTP (20 mg/kg x 4) caused 72 and 76% depletion of DAT sites in the NAC and striatum, respectively, in C57BL/6 mice. The magnitude of this depletion 3 and 19 days after MPTP administration was the same. To determine the effect of MPTP on the expression of the sensitized response to cocaine, cocaine-experienced mice (20 mg/kg for 5 days) received MPTP 3 days before a challenge cocaine injection was given on day 15. Cocaine/MPTP mice were significantly more sensitive to the challenge cocaine injection than the cocaine/saline-pretreated mice. To determine whether depletion of NAC and striatal DAT affects the induction of sensitization to cocaine, mice were pretreated with MPTP 3 days before the administration of cocaine (20 mg/kg for 5 days). The magnitude of the sensitized response of MPTP/cocaine-pretreated mice to cocaine challenge was the same as the sensitized response of mice treated with saline/cocaine, while the number of DAT binding sites in the MPTP/cocaine group was significantly lower than the saline/cocaine group. The present study indicates that MPTP exacerbates the expression of locomotor sensitization to cocaine, but it had no effect on the induction of sensitization. We conclude that the expression, but not the induction, of locomotor sensitization to cocaine may be dependent on the level of DAT binding sites.

Effects of cocaine, nicotine, dizocipline and alcohol on mice locomotor activity: cocaine-alcohol cross-sensitization involves upregulation of striatal dopamine transporter binding sites

We investigated if repeated administration of cocaine, nicotine, dizocipline (MK-801) and alcohol yields behavioral cross-sensitization between these agents. Swiss Webster mice received in their home cage one of the following intraperitoneal (i. p.) injections for 5 consecutive days: (a) saline, (b) cocaine (20 mg/kg), (c) nicotine (0.5 mg/kg), (d) MK-801 (0.3 mg/kg) and (e) ethanol (2.0 g/kg). After a 10-day drug free period, each group (n=30) was divided into three subgroups (n=10) and received challenge injections of either cocaine, nicotine or MK-801. The horizontal and vertical movements of the mice were recorded in locomotor activity cages (test cage). Among the various drugs tested, only the cocaine and ethanol experienced mice developed sensitization to a challenge injection of cocaine; MK-801 pretreated mice showed a sensitized response only to a challenge injection of MK-801. In a second experiment, mice in their home cages received (a) saline, (b) cocaine (20 mg/kg) or (c) ethanol (2.0 g/kg) for 5 days, and challenged with an i.p. ethanol injection (2.0 g/kg) after a 10-day drug free period. Both, cocaine and ethanol experienced mice developed marked sensitization to ethanol challenge compared with the saline experienced mice. Assessment of the densities of striatal dopamine transporter (DAT) sites (by [3H]mazindol binding) 11 days after the extinction of repeated treatment with either cocaine or ethanol revealed a significant increase (71-108%) in the number of DAT binding sites. Thus, among the various psychostimulants investigated in the present study cross-sensitization between cocaine and ethanol was only observed. The behavioral sensitization we measured was primarily 'drug-dependent', rather than 'context-dependent', because animals were exposed to the test cage only once. The finding that cocaine- and ethanol-induced behavioral sensitization is associated with upregulation of striatal DAT binding sites supports the hypothesis that similar neural substrates are involved in the psychomotor/rewarding effects of cocaine and alcohol.

Resistance of neuronal nitric oxide synthase-deficient mice to cocaine-induced locomotor sensitization

In brain, nitric oxide (NO) is considered as a retrograde messenger involved in synaptic plasticity. The present study was undertaken to investigate whether mice lacking the neuronal nitric oxide synthase (nNOS) gene are protected from cocaine-induced behavioral sensitization. Mice were administered, IP. either saline or cocaine (15 mg/kg) for 5 days. Sensitization was determined as an increase in cocaine-induced locomotor activity on day 5 compared with day 1 and an amplified response of cocaine-experienced mice to a challenge cocaine injection given after a 10-day drug free period (e.g., on day 15). To investigate the development of a context-dependent locomotion (conditioning), the responses of cocaine- and saline-experienced mice to a saline injection were determined on day 17. Male homozygote nNOS(-/-) mice were sensitive to the acute effect of cocaine (15 mg/kg) on day 1; however, they developed neither a sensitized response to cocaine (on day 5 and 15) nor a conditioned locomotion. Female homozygote nNOS(-/-) mice neither were responsive to 15 mg/kg cocaine on day 1,5 and 15, nor did they develop a conditioned locomotion. In contrast, the same cocaine regimen delivered to male and female heterozygote nNOS(+/-) mice, and wild type mice (B6 J/sv129, C57BL/6 and sv129) resulted in sensitization to cocaine-induced locomotor activity and context-dependent locomotion. Investigation of [3H]cocaine disposition in the striatum and frontal cortex of the mice revealed neither gender nor strain differences in the drug disposition. Also, no major difference in striatal dopaminergic markers between homozygote nNOS(-/-) and wild type mice was observed. The most significant distinction, however, was the finding that nNOS(-/-) mice are completely deficient in striatal nNOS binding sites. Taken together, our results suggest that the resistance of homozygote nNOS(-/-) mice to cocaine-induced behavioral sensitization is primarily due to the deletion of the nNOS gene. Considering the role of NO in synaptic plasticity, it is conceivable that reduced brain NOS activity blunts the processes that underlie the development of sensitization to cocaine.

The role of neuronal nitric oxide synthase in cocaine-induced conditioned place preference

Previous studies suggested the involvement of the neuronal nitric oxide synthase (nNOS) in the development of sensitization to psychostimulants. In the present study we investigated the role of nNOS in the rewarding properties of cocaine. Swiss Webster mice treated with cocaine (20 mg/kg) and saline every other day for 8 days (four drug and four saline sessions) developed conditioned place preference (CPP) for the drug-paired compartment of the cage. Pretreatment with the nNOS inhibitor, 7-nitroindazole (7-NI; 25 mg/kg), completely blocked cocaine-induced CPP. Mice deficient for the nNOS gene (homozygote nNOS(-/-) mice) were resistant to cocaine-induced CPP, while wild-type nNOS(+/+) mice developed a marked CPP following cocaine administration. Both, the pharmacological and genetic manipulations of nNOS suggest that nitric oxide (NO) is involved in the rewarding properties of cocaine.

Effect of melatonin on methamphetamine- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic neurotoxicity and methamphetamine-induced behavioral sensitization

Methamphetamine (METH)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurotoxicity is thought to be associated with the formation of free radicals. Since evidence suggests that melatonin may act as a free radical scavenger and antioxidant, the present study was undertaken to investigate the effect of melatonin on METH- and MPTP-induced neurotoxicity. In addition, the effect of melatonin on METH-induced locomotor sensitization was investigated. The administration of METH (5 mg kg(-1) x 3) or MPTP (20 mg kg(-1) x 3) to Swiss Webster mice resulted in 45-57% depletion in the content of striatal dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, and 57-59% depletion in dopamine transporter binding sites. The administration of melatonin (10 mg kg(-1)) before each of the three injections of the neurotoxic agents (on day 1), and thereafter for two additional days, afforded a full protection against METH-induced depletion of dopamine and its metabolites and dopamine transporter binding sites. In addition, melatonin significantly diminished METH-induced hyperthermia. However, the treatment with melatonin had no significant effect on MPTP-induced depletion of the dopaminergic markers tested. In the set of behavioral experiments, we found that the administration of 1 mg kg(-1) METH to Swiss Webster mice for 5 days resulted in marked locomotor sensitization to a subsequent challenge injection of METH, as well as context-dependent sensitization (conditioning). The pretreatment with melatonin (10 mg kg(-1)) prevented neither the sensitized response to METH nor the development of conditioned locomotion. Results of the present study indicate that melatonin has a differential effect on the dopaminergic neurotoxicity produced by METH and MPTP. Since it is postulated that METH-induced hyperthermia is related to its neurotoxic effect, while regulation of body temperature is unrelated to MPTP-induced neurotoxicity or METH-induced locomotor sensitization, the protective effect of melatonin observed in the present study may be due primarily to diminishing METH-induced hyperthermia.

Effects of 7-nitroindazole, an NOS inhibitor on methamphetamine-induced dopaminergic and serotonergic neurotoxicity in mice

Methamphetamine (METH) is one of the major drugs of abuse that is postulated to cause neurotoxicity by depleting dopamine (DA) and its metabolites, high-affinity DA uptake sites, and the activity of tyrosine hydroxylase. The present study was undertaken to investigate whether the relatively selective, neuronal nitric oxide synthase (NOS) inhibitor, 7-nitroindazole (7-NI), protects against METH-induced neurotoxicity. Male Swiss Webster mice received the following injections intraperitoneally (i.p.) 3 times (every 3 hr): (i) vehicle/saline, (ii) 7-NI (25 mg/kg)/saline, (iii) vehicle/METH (5 mg/kg), and (iv) 7-NI (25 mg/kg)/METH (5 mg/kg). On the second day, groups (i) and (iii) received two vehicle injections and groups (ii) and (iv) received two 7-NI injections (25 mg/kg each). The administration of vehicle/METH resulted in 68, 44 and 55% decreases in the concentration of DA, dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA), respectively, and a 48% decrease in the number of [3H]mazindol binding sites in the striatum compared to control values. The treatment with 7-NI (group iv) provided a full protection against the depletion of DA and its metabolites, and the loss of dopamine transporter binding sites. Multiple injection of METH caused a significant decrease in the concentration of serotonin (5-HT) and its metabolite 5-hydroxyindole acetic acid (5-HIAA). Treatment with 7-NI partially blocked the depletion of 5-HT and completely blocked the reduction in 5-HIAA levels. The administration of 7-NI/saline (group ii) affected neither the tissue concentration of DA, 5-HT and their metabolites (DOPAC, HVA and 5-HIAA) nor the binding parameters of [3H]-mazindol compared to control (vehicle/saline) values. 7-NI had no significant effect on the animals' body temperature, and it did not affect METH-induced hyperthermia. These findings indicate a role for nitric oxide in METH-induced neurotoxicity and also suggest that blockage of NOS may be beneficial for the management of Parkinson's disease.

Effect of ibogaine on the various sites of the NMDA receptor complex and sigma binding sites in rat brain

Although the alkaloid ibogaine is a potent hallucinogenic agent some indications suggest that it may be useful for the treatment of opioid and cocaine addiction. The neurochemical mechanism(s) underlying ibogaine effects remain unclear. In the present study we investigated the interaction of ibogaine with the phencyclidine (PCP) site located in the ionophore of the N-methyl-D-aspartate (NMDA) receptor complex, with the NMDA receptor binding site, and with sigma binding sites. In well-washed membrane preparations of rat cortex and cerebellum, the PCP sites were labeled with [3H]MK-801 or [3H]1-[1(2-theinyl)-cyclohexyl]-piperidine ([3H]TCP), and the NMDA receptor with [3H]-CGP 39653. The sigma-1 and sigma-2 binding site in rat cortex and cerebellum were labeled with [3H]pentazocine and [3H]1,3-di-o-tolyl-guanidine ([3H]DTG), respectively. Results indicated that ibogaine interacts with high- and low-affinity PCP binding sites in the cortex: Ki(H) = 0.01-0.05 microM; Ki(L) = 2-4 microM, and only with low-affinity sites in the cerebellum: Ki = 2-4, microM. In contrast, ibogaine (> 100 microM) had no affinity for [3H]-CGP 39653 binding sites (cortex and cerebellum). The affinity of ibogaine for sigma-1 and -2 binding sites in cortex and cerebellum ranged from 1.5-3 microM. Since NMDA receptor antagonists (e.g., MK-801) are thought to attenuate opioid withdrawal symptoms and cocaine sensitization, it is possible that binding of ibogaine to the PCP sites contributes to its potential 'endabuse' properties. In turn, ibogaine interaction with sigma binding sites may be associated with its adverse effects.

Resistance of neuronal nitric oxide synthase-deficient mice to methamphetamine-induced dopaminergic neurotoxicity

Methamphetamine (METH) is a powerful psychostimulant that produces dopaminergic neurotoxicity manifested by a decrease in the levels of dopamine, tyrosine hydroxylase activity and dopamine transporter (DAT) binding sites in the nigrostriatal system. We have recently reported that blockade of the neuronal nitric oxide synthase (nNOS) isoform by 7-nitroindazole provides protection against METH-induced neurotoxicity in Swiss Webster mice. The present study was undertaken to investigate the effect of a neurotoxic dose of METH on mutant mice lacking the nNOS gene [nNOS(-/-)] and wild-type controls. In addition, we sought to investigate the behavioral outcome of exposure to a neurotoxic dose of METH. Homozygote nNOS(-/-), heterozygote nNOS(+/-) and wild-type animals were administered either saline or METH (5 mg/kg x 3). Dopamine, DOPAC and HVA levels, as well as DAT binding site levels, were determined in striatal tissue derived 72 h after the last METH injection. This regimen of METH given to nNOS(-/-) mice affected neither the tissue content of dopamine and its metabolites nor the number of DAT binding sites. Although a moderate reduction in the levels of dopamine (35%) and DAT binding sites (32%) occurred in striatum of heterozygote nNOS(+/-) mice, a more profound depletion of the dopaminergic markers (up to 68%) was observed in the wild-type animals. METH-induced hyperthermia was observed in all animal strains examined except the nNOS(-/-) mice. Investigation of the animals' spontaneous locomotor activity before and after administration of the neurotoxic dose of METH (5 mg/kg x 3) revealed no differences. A low dose of METH (1.0 mg/kg) administered to naive animals (nNOS(-/-) and wild-type) resulted in a similar intensity of locomotor stimulation. However, 68 to 72 h after exposure to the high-dose METH regimen, a marked sensitized responses to a challenge METH injection was observed in the wild-type mice but not in the nNOS(-/-) mice. Taken together, these results indicate that nNOS(-/-) mice are protected against METH-induced dopaminergic neurotoxicity and locomotor sensitization. It also appears that a partial deficit of dopaminergic transmission in wild-type animals does not prevent the development of sensitization to METH, whereas a deficit in nNOS may attenuate this process.

Depletion of striatal dopamine transporter does not affect psychostimulant-induced locomotor activity

The effect of neurotoxin-induced depletion of striatal dopamine transporter (DAT) binding sites on animals' responses to psychostimulants was investigated. Multiple 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or methamphetamine (METH) injections but not a single METH injection to Swiss Webster mice resulted in > 60% depletion of striatal DAT. MPTP-induced depletion of DAT did not affect METH- and cocaine-stimulated locomotor activity compared with the response of control mice. Pre-exposure to either the neurotoxic or the single non-neurotoxic dose of METH resulted in a marked locomotor sensitization in response to METH or cocaine challenge injections. The present results indicate that > 60% loss in striatal DAT binding sites has no effect on animals' responses to psychostimulants, and suggest that neural systems other than striatal DAT may contribute to the induction of locomotor sensitization to METH and cocaine.

Modulation of cocaine- and methamphetamine-induced behavioral sensitization by inhibition of brain nitric oxide synthase

Evidence suggests the existence of multiple interactions between dopamine, glutamate and nitric oxide (NO) in brain structures associated with psychomotor stimulation. The present study was undertaken to investigate the effect of the relatively selective inhibitor of the neuronal nitric oxide synthase (NOS) isoform, 7-nitroindazole (7-NI), on the development of sensitization to the locomotor stimulating effect of cocaine and methamphetamine (METH). Male Swiss Webster mice that received 15 mg/kg cocaine once a day for 5 days developed a marked locomotor sensitization to a challenge cocaine (15 mg/kg) or cross-sensitization to a challenge METH (0.5 mg/kg) injection given after a 10-day drug-free period. This treatment also produced a context-dependent sensitization as evident by the sensitized response to a challenge saline injection. Pretreatment with 7-NI (25 mg/kg) 30 min before cocaine administration (5 days) completely blocked the induction of sensitization to cocaine, the cross-sensitization to METH and the conditioned locomotion induced by cocaine. 7-NI when given alone, either acutely or for 5 days, had no significant effect on the locomotor activity of animals. Animals treated with METH (1.0 mg/kg) for 5 days developed marked sensitization to challenge METH (0.5 mg/kg), cross-sensitization to challenge cocaine (15 mg/kg) and context-dependent locomotion. Pretreatment with 7-NI (25 mg/kg) attenuated the sensitized response to METH and the cross-sensitization to cocaine as revealed after a 10-day drug-free period. However, the METH-induced conditioned locomotion was unaffected by the pretreatment with 7-NI. The present study supports the role of brain NO in the development of sensitization to both psychostimulants, cocaine and METH. However, it appears that the inability of 7-NI to completely abolish the sensitized responses induced after METH administration is the result of the resistible conditioned locomotion caused by METH, but not by cocaine.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) decreases glutamate uptake in cultured astrocytes

The deleterious effect of the parkinsonian neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on dopaminergic neurons of the substantia nigra is well established. In addition, increased glutamatergic drive to basal ganglia output nuclei is considered a likely contributor to the pathogenesis of Parkinson's disease. One possibility for the increased excitatory tone may be related to an impairment in glutamate uptake. As astrocytes possess efficient transport mechanisms for both MPTP and glutamate, we have examined the effect of this agent on D-aspartate uptake into these cells. Treatment of cultures with 50 microM MPTP for 24 h decreased uptake by 39%. Kinetic analysis revealed that this effect was due to a 35% decrease in Vmax with no change in the Km. Treatment with deprenyl, a monoamine oxidase B inhibitor, produced a complete reversal of MPTP-induced uptake inhibition, but was ineffective following exposure of cells to the MPTP metabolite, 1-methyl-4-phenylpyridinium (MPP+). Removal of MPTP from cultures resulted in a complete restoration of glutamate uptake after 24 h. These results show that MPTP reversibly compromises glutamate uptake in cultured astrocytes, which is dependent on the conversion of MPTP to MPP+. Such findings suggest that the glutamate transporter in astrocytes plays an important role in MPTP-induced neurotoxicity and possibly in parkinsonism.

The neuronal nitric oxide synthase inhibitor, 7-nitroindazole, protects against methamphetamine-induced neurotoxicity in vivo

The present study was undertaken to investigate whether the relatively selective neuronal nitric oxide synthase (NOS) inhibitor, 7-nitroindazole (7-NI), protects against methamphetamine (METH)-induced neurotoxicity. Male Swiss Webster mice received the following treatments (i.p.; q 3 h x 3): (a) vehicle/saline, (b) 7-NI (25 mg/kg)/saline, (c) vehicle/METH (5 mg/kg), and (d) 7-NI (25 mg/kg)/METH (5 mg/kg). On the second day, groups (a) and (b) received two vehicle injections, and groups (c) and (d) received two 7-NI injections (25 mg/kg, each). Administration of vehicle/METH resulted in 68, 44, and 55% decreases in the concentration of dopamine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid, respectively, and a 48% decrease in the number of [3H]mazindol binding sites in the striatum compared with control values. Treatment with 7-NI (group d) provided full protection against the depletion of dopamine and its metabolites and the loss of dopamine transporter binding sites. Administration of 7-NI/saline (group b) affected neither the tissue concentration of dopamine and its metabolites nor the binding parameters of [3H] mazindol compared with control values. 7-NI had no significant effect on animals' body temperature, and it did not affect METH-induced hyperthermia. These findings indicate a role for nitric oxide in methamphetamine-induced neurotoxicity and also suggest that blockade of NOS may be beneficial for the management of Parkinson's disease.

[Findings of periodic thoracic X-ray screening of Israel Defense Forces career personnel]

Findings of routine, periodic, medical examinations of approximately 5000 Israel Defense Forces (IDF) career personnel, included a screening postero-anterior chest radiograph were reviewed. Previous studies have indicated low efficacy of routine chest X-rays in various populations. We evaluated this screening test among 4593 career military personnel. Their chest X-rays were reviewed retrospectively and in 186 (4%) there were abnormal findings. The rate of pathological findings was positively correlated with age. Additional information was found in the X-rays of 25 subjects (0.54%), but the original interpretations of 51 (1.1%) were found to be false-positive. In view of the very low yield of findings in routine chest X-rays of IDF career military personnel, we recommend X-ray screening only in high-risk populations and subjects over the age of 50.

Attenuation of cocaine kindling by 7-nitroindazole, an inhibitor of brain nitric oxide synthase

Recent studies suggest the involvement of the N-methyl-D-aspartate (NMDA) type of glutamate receptors and nitric oxide synthase (NOS) in the process of increased sensitivity to the convulsive effect of cocaine ("cocaine kindling"). The present study was undertaken to analyze the various behavioral stages in the development of cocaine kindling and to investigate the effect of 7-nitroindazole (7-NI), a relatively selective inhibitor of the neuronal NOS isoform, on the induction and expression of sensitization to the convulsive effect of cocaine. Also, the effect of 7-NI on responses produced by acute systemic administration of cocaine or N-methyl-D,L-aspartate (NMDLA) was investigated. Cocaine kindling was assessed on a five-stage scale following the administration of a sub-convulsant dose of the drug (35 mg/kg/day; i.p.) to Swiss Webster mice for 10 days. Stage 5 seizures developed following the 9th day of cocaine administration. Pre-treatment with 7-NI (25 mg/kg/day; i.p.) 15 min before cocaine for 10 days completely prevented the appearance of stage 4 and 5 seizures, and it significantly attenuated stage 3 behavior in response to a challenge cocaine dose (35 mg/kg) given either 24 hr or 10 days after 7-NI/cocaine administration was stopped. A single injection of 7-NI (25 mg/kg; i.p.) completely prevented the expression of cocaine kindled seizures. Whereas 7-NI had no effect on the responses elicited by acute cocaine administration (60 mg/kg; i.p.), this agent partially attenuated the effects induced by systemic administration of the NMDA receptor agonist NMDLA (250 mg/kg; i.p.). The present study indicates that 7-NI attenuates both the induction and expression of sensitization to the convulsive effect of cocaine. The findings that 7-NI attenuated cocaine kindling and partially blocked the effects produced by activation of the NMDA receptor, but not the effects induced by acute cocaine administration, support the role of the NMDA receptor and brain NOS in the development of cocaine kindling rather than in the acute effects of the drug.

Acute liver failure and hyperammonemia increase peripheral-type benzodiazepine receptor binding and pregnenolone synthesis in mouse brain

We investigated the role of brain peripheral-type benzodiazepine receptors (PBRs) and pregnenolone (a product of PBRs activation) in hepatic encephalopathy (HE)/hyperammonemia. Administration of the hepatotoxin, thioacetamide, or ammonium acetate to mice for 3 days significantly increased the number of brain PBRs (138-146% of control) and the affinity of the ligands for these receptors (2-fold). The total content of pregnenolone and its rate of synthesis in brain of the experimental animals were significantly increased. Our results suggest a novel integrated mechanism by which ammonia-induced activation of PBRs leads to elevated levels of pregnenolone-derived neurosteroids which are known to enhance GABA-ergic neurotransmission. This mechanism may play a pivotal role in pathogenesis of HE.

Cocaine kindling in mice. Responses to N-methyl-D,L-aspartate (NMDLA) and L-arginine

Previous studies proposed the involvement of the N-methyl-D-aspartate (NMDA) type of glutamate receptors in the development of sensitization to the convulsive effect of cocaine (cocaine kindling). The present study was undertaken to determine, first, if cocaine kindling is associated with enhanced sensitivity of the NMDA receptor to the convulsive response of N-methyl-D,L-aspartate (NMDLA), and second, whether in vivo modulation of nitric oxide synthase (NOS) function regulates the development of cocaine kindling. The following results were observed: 1. Cocaine-kindled animals were significantly more susceptible to the convulsive effect of the NMDA receptor agonist NMDLA than saline controls; 2. Pretreatment with the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 100 mg/kg; ip) blocked the development of cocaine kindling; 3. The protective effect of L-NAME was partially reversed with the coadministration of the NOS substrate, L-arginine (300 mg/kg; ip), but not D-arginine; and 4. L-Arginine (300 mg/kg; ip), but not D-arginine, amplified the development of cocaine kindling. Taken together, these findings suggest that supersensitivity of the NMDA receptor and activation of NOS may underlie the development of cocaine kindling.

Presence of aromatase inhibitors in cycads

Cycads, the most primitive of the living gymnosperms, have been used and continue to be used for food and medicinal purposes by many cultures, although toxins must be removed before ingestion. In our quest to identify tropical plants that contain inhibitors of the cytochrome P-450 aromatase and thus may be efficacious in treating estrogen-dependent tumors, we have screened extracts from 5 species of cycad folia encompassing 3 genera: Cycas cairnsiana F. Muell., Cycas revoluta Thunb., Cycas rumphii Miq., Dioon spinulosum Dyer and Encephalartos ferox Bertol. All extracts were found to contain inhibitors of the human enzyme.

Ontogeny of peripheral-type benzodiazepine receptors in cultured astrocytes and brain from rat

Peripheral-type benzodiazepine receptors (PBRs) in brain are primarily localized within astroglial cells, and the existence of PBR subtypes have been suggested. In the present study the ontogeny of PBRs labeled with [3H]Ro5-4864 and [3H]PK 11195 in cultured astrocytes was compared to their postnatal in-vivo development. The density of [3H]Ro5-4864 binding sites in cultured astrocytes from rat cortex progressively increased from 1- to 3-week-old cultures and did not change further in 5- and 8-week-old cultures. The density of [3H]PK 11195 binding sites progressively increased from 1- to 5-week-old cultures. The density of [3H]PK 11195 binding sites exceeded the density of [3H]Ro5-4864 binding sites by 40-50% in 2-, 5- and 8-week-old cultures. The affinity of the PBR ligands for the receptor sites was increased by 3- to 4-fold from the first to the second week in cultures, and did not change thereafter. A similar developmental pattern of PBRs was observed in rat cortex, except that: first, the difference between the Bmax of [3H]PK 11195 and [3H]Ro5-4864 was already apparent in postnatal-week-1 and persisted with maturation; second, the high affinity of the ligands for the receptor sites was apparent from postnatal-week-1 and did not change with maturation. Age-related differences in the ratio between the density of PBRs in astrocytes and rat cortex were also observed. These results lead us to suggest that the development of PBRs in vivo during the first postnatal week is more rapid than the development of the receptors in vitro during the first week in culture. Subsequently, the increased ratio between the density of PBRs in cultured astrocytes and brain with maturation indicates the predominantly astrocytic localization of these receptors. The finding that the density of [3H]PK 11195 binding sites in cultured astrocytes and in rat brain cortex is usually 40-50% greater than the density of [3H]Ro5-4864 binding sites further supports the existence of PBR subtypes.

Attenuation of ammonia toxicity in mice by PK 11195 and pregnenolone sulfate

Ammonia and benzodiazepines are thought to be involved in the pathogenesis of hepatic encephalopathy. The present study was undertaken to evaluate the effect of various benzodiazepine-receptor ligands and neurosteroids on ammonia toxicity in mice. Administration of ammonium acetate (8-15 mmole/kg; i.p.) to Swiss Webster mice resulted in a dose-dependent increase in mortality. Pretreatment with the central benzodiazepine receptor agonist clonazepam or the antagonist Ro15-1788 (7 mg/kg each; i.p.) had no significant effect on the lethal response to 10 mmole/kg ammonium acetate. However, pretreatment with the putative antagonist of the peripheral-type benzodiazepine receptor, PK 11195 (10 mg/kg; i.p.), reduced mortality from 50 to 10%. Ro5-4864 (10 mg/kg; i.p.), an agonist of the peripheral-type benzodiazepine receptors, had no effect on ammonia toxicity. The neurosteroid, pregnenolone sulfate (20 mg/kg; i.p.) reduced mortality from 50 to 25%. The non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 (2 mg/kg; i.p.), had no effect on the lethal response to ammonium acetate. The results from the present study suggest a role for peripheral-type benzodiazepine receptors and specific neurosteroids in the alleviation of ammonia toxicity in mice.

Regulation of peripheral-type benzodiazepine receptors in cultured astrocytes by monoamine and amino acid neurotransmitters

Exposure of primary cultured astrocytes for 3 days to 1 microM of either dopamine, serotonin or norepinephrine resulted in upregulation (25-34% increase in Bmax) of the peripheral-type benzodiazepine receptors (PBRs) labeled with [3H]Ro5-4864. A similar treatment with gamma-aminobutyric acid [GABA] caused a 2-fold increase in the affinity (Kd) of [3H]Ro5-4864. The monoamines tested and GABA had no effect on the binding parameters of [3H]PK 11195, another selective PBR ligand. The present study indicates that Ro5-4864 binding sites are susceptible to regulation by specific neurotransmitters and provides further evidence for the distinction between Ro5-4864 and PK 11195 binding sites of the PBRs in cultured astrocytes.

Ammonia-induced upregulation of peripheral-type benzodiazepine receptors in cultured astrocytes labeled with [3H]PK 11195

Evidence suggests that peripheral-type benzodiazepine receptors (PBRs) may play a role in hepatic encephalopathy (HE), a condition associated with increased levels of ammonia in brain. In the present study, the regulation of [3H]PK 11195-binding to PBRs in cultured rat astrocytes that had been previously exposed to NH4Cl was investigated. 24 h treatment of 21-28-day-old cultures with 2, 5 or 10 mM NH4Cl resulted in 25 +/- 3, 48 +/- 3 and 42 +/- 4% increase in the number of [3H]PK 11195-binding sites, respectively. No further change in [3H]PK 11195-binding was observed after exposure of astrocytes to 5 mM NH4Cl for 48 or 72 h. Ammonia treatment did not cause any significant alteration in the affinity of [3H]PK 11195 for PBRs. The present study demonstrates the susceptibility of the PK 11195-binding site of PBRs in cultured astrocytes to ammonia and suggests that increase in brain ammonia concentration causes a supersensitivity of PBRs.

Modulation of the PCP/NMDA receptor complex and sigma binding sites by psychostimulants

The present study was undertaken to determine the role and modulation of the PCP/NMDA receptor complex and sigma binding sites in the central nervous system of animals treated with psychostimulant agents. Repeated exposure of mice to cocaine (45 mg/kg/day; for 7 days) was associated with a progressive increase in convulsive response and lethality rate. The sensitization to the toxic effects of cocaine in mice was completely abolished by pretreatment with either the noncompetitive NMDA receptor antagonist MK-801 (0.35 mg/kg/day), or the nitric oxide synthase inhibitor Ng-nitro-L-arginine methyl ester (100 mg/kg/day). Parallel in vitro receptor binding assays indicated first, upregulation of cortical NMDA receptors labeled with [3H]CGP 39653, and second, glutamate-dependent sensitization of [3H]MK-801 binding to the PCP site in cortical membranes of the mice treated for 7 days with cocaine. Repeated exposure of rats to methamphetamine (4.0 mg/kg/day; for 10 days) resulted in a significant upregulation of the sigma-1 binding site labeled with (+)[3H]pentazocine in the frontal cortex and substantia nigra. The cocaine-related studies suggest that the PCP/NMDA receptor complex is involved in the development of sensitization to the neurotoxic effects of the drug, such as "pharmacological kindling". The methamphetamine-related studies insinuate a potential role of sigma-1 binding sites in psychostimulant-induced behavioral disorders.

Effect of hypoosmotic stress on peripheral-type benzodiazepine receptors in cultured astrocytes

Astrocytes appear to be the primary source of peripheral benzodiazepine (PBZD) receptors in brain. The function of this receptor is not well understood. Since there is evidence that this receptor may be involved in cell volume control, we examined the effect of hypoosmotic stress on the regulation of the PBZD receptors in homogenates of cultured astrocytes derived from neonatal rat cerebral cortex. Exposure of astrocytes that were maintained in the presence of dibutyryl cAMP (dBcAMP) to hypoosmotic medium (200 mOsm) for 24 h resulted in 27 and 57% increased in the number of [3H]PK 11195 and [3H]Ro5-4864-binding sites, respectively, as compared with isoosmotic media (320 mOsm). This receptor upregulation is osmolarity- and time-dependent. However, hypoosmotic stress had no effect on PBZD receptor-binding in astrocytes that were maintained in the absence of dBcAMP. Under isoosmotic conditions, dBcAMP appears to regulate [3H]Ro5-4864 but not [3H]PK 11195-binding sites, a finding which further supports a partial distinction between the binding sites labeled with these ligands. The modulation of PBZD receptors by hypoosmotic stress suggests a possible role for these receptor sites in astrocyte volume control.

Blockade of sensitization to the toxic effects of cocaine in mice by nitric oxide synthase inhibitors

Repeated administration of cocaine to animals results in sensitization to several reactions to the drug, including seizures and mortality. These consequences are thought to be related to the pathology that develops in humans abusing cocaine. Previous studies implied the involvement of the N-methyl-D-aspartate (NMDA) type of glutamate receptors in cocaine-induced toxicity, and recent studies documented a role for nitric oxide in NMDA-receptor mediated neurotoxicity. The present study was undertaken to determine whether nitric oxide synthase inhibitors block the development of sensitization to the toxic effects of cocaine in mice. Repeated administration of cocaine (45 mg/kg/day; intraperitoneally) to Swiss Webster mice, for 7 days, resulted in a progressive increase in the duration of the convulsive response to cocaine, an increase in the number of animals that had seizures, and augmentation in lethality rate. Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME; 100 mg/kg/day; intraperitoneally) or NG-nitro-L-arginine (NO-Arg; 25 mg/kg/day; intraperitoneally) completely abolished the sensitization to the convulsive and lethal responses to cocaine. Receptor binding assays indicated first, that pretreatment with L-NAME apparently diminished cocaine-induced upregulation of cortical NMDA receptors, and second, that the effects of the nitric oxide synthase inhibitors tested are not mediated via a direct interaction of the drugs with the phencyclidine/NMDA receptor complex. Taken together, the present study suggests an important role for nitric oxide in the development of sensitization to the toxic effects of cocaine, and further supports the relationship between NMDA-receptor mediated neurotoxicity and nitric oxide.

Characterization of the peripheral-type benzodiazepine receptors in cultured astrocytes: evidence for multiplicity

In mammalian brain peripheral benzodiazepine (PBZD) receptors are predominantly localized on astroglial cells. Previous studies utilizing whole membrane preparations from brain and peripheral organs of various species have indicated several distinctions between the drug-receptor interactions of the two prototypic PBZD receptor ligands, PK 11195 and Ro5-4864. The present study was undertaken to determine whether putative differences in the binding of PBZD receptor ligands in homogenates of primary astrocyte cultures can be interpreted as the labeling of PBZD receptor subtypes. Equilibrium competition and saturation binding experiments in homogenate preparations of primary astrocytes from cerebral cortex of new born rats revealed that [3H]PK 11195 labels twice the number of [3H]Ro5-4864 binding sites. Unlabeled Ro5-4864 competes for [3H]PK 11195 binding in a manner suggesting the existence of multiple PK 11195 binding sites. The competition binding experiments, using various benzodiazepines, indicate that one binding component of PK 11195 corresponds to Ro5-4864 binding sites, whereas the second is different. The latter binding site does not correspond to the central BZD receptor but displays the pharmacological properties of the PBZD receptor. Further differences between the binding of PK 11195 and Ro5-4864 in astrocytes were detected in the presence of ethanol which was more effective in inhibiting the binding of the latter. Subcellular distribution studies indicated, however, that the binding of both [3H]PK 11195 and [3H]Ro5-4864 is associated primarily with the mitochondrial fraction of astrocytes. Taken together, the present study indicates the existence of non-overlapping PBZD binding sites in astrocytes and thus suggests the existence of PBZD receptor subtypes.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide (NO) synthase inhibitors abolish cocaine-induced toxicity in mice

Repeated administration of cocaine (45 mg/kg/day) for 7 days to Swiss-Webster mice resulted in a progressive increase in the convulsive response to cocaine and augmentation in lethality rate. Pretreatment with the nitric oxide (NO) synthase inhibitors, L-NAME (100 mg/kg/day) or NO-Arg (25 mg/kg/day), prior to cocaine administration completely abolished the sensitization to the convulsive and lethal responses to cocaine. These findings suggest a role for NO in cocaine-induced toxicity.

Differential regulation of brain opioid receptors following repeated cocaine administration to guinea pigs

Recent studies implied a possible involvement of the opioid system in the central nervous system (CNS) effects of cocaine. The present study was undertaken to determine specific alterations in opioid receptor binding following repeated exposure of guinea pigs to cocaine. Animals were treated with either saline or cocaine (40 mg/kg per day; i.p.) for 7 days, sacrificed 24 h after the treatment, and various brain regions were assayed for [3H]DAMGO, [3H]DPDPE and [3H]U-69,593 binding to the three major types of opioid receptors: mu, delta and kappa, respectively. A significant down-regulation of mu-opioid receptors (65-70% of control Bmax) was detected in the frontal cortex, amygdala, thalamus and hippocampus of cocaine-treated animals. Other brain regions examined did not endure changes in mu-opioid receptor binding. In contrast, no significant change in delta-opioid receptor binding was detected at any of the brain regions investigated. Alteration in kappa-opioid receptor binding following exposure to cocaine was found only in the cerebellum: an up-regulation (136% of control Bmax) was observed. These findings indicate that repeated administration of cocaine induces differential regulation of opioid receptors. The down-regulation of mu-opioid receptors in discrete limbic regions may be associated with the addicting properties of cocaine.

Repeated methamphetamine-treatment alters brain sigma receptors

The present study was undertaken to examine whether repeated exposure of rats to the psychostimulant drug, methamphetamine, induces changes in sigma receptor binding. A significant up-regulation (130-145% of control Bmax) of sigma receptors, labeled with [3H](+)pentazocine, was observed in the substantia nigra, frontal cortex and cerebellum of rats treated with methamphetamine (4.0 mg/kg per day; 10 days). These findings suggest that methamphetamine-induced psychosis may be associated with the up-regulation of sigma receptors in critical brain regions.

Sensitization to the toxic effects of cocaine in mice is associated with the regulation of N-methyl-D-aspartate receptors in the cortex

Repeated exposure to cocaine results in sensitization to many of the behavioral effects of the drug. The present study was undertaken to examine the role of the N-methyl-D-aspartate (NMDA) type of glutamate receptors in the development of sensitization to the convulsive and lethal effects of cocaine in Swiss Webster mice. Repeated administration of subconvulsant doses of cocaine (45 mg/kg for 7 days) produced a progressive increase in the convulsive responsiveness to the drug. This phenomenon was accompanied by an increase in lethality rate after the 5th day of the treatment. Pretreatment with the noncompetitive NMDA receptor antagonist, MK-801 (5-methyl-10,11-dihydro-5H-dibenzo[a,d]- cyclohepten-5,10-imine) abolished completely the development of sensitization to cocaine-induced seizures and lethality. In addition, MK-801 attenuated cocaine-induced loss in animals body weight after 7 days of drug treatment. The lethal effects of acute administration of increasing doses of cocaine were also reduced by pretreatment with MK-801. In vitro receptor binding experiments demonstrated an increase (139% of control) in the number of NMDA receptors, labeled with the competitive NMDA receptor antagonist [3H]CGP 39653 ([3H]-2-amino-4-propyl-5-phosphono-3-pentenoic acid), in cortical membranes derived from the mice treated for 7 days with cocaine (45 mk/kg). In agreement with the latter finding, binding of [3H]MK-801 to the phencyclidine/NMDA site in cortical membranes of cocaine-treated mice was more sensitive to the stimulatory effect of glutamate compared to control (saline treatment).(ABSTRACT TRUNCATED AT 250 WORDS)