Differential effects of NMDA receptor and dopamine receptor antagonists on cocaine toxicities

Reduction in phencyclidine induced sensorimotor gating deficits in the rat following increased system xc⁻ activity in the medial prefrontal cortex

RATIONALE

Aspects of schizophrenia, including deficits in sensorimotor gating, have been linked to glutamate dysfunction and/or oxidative stress in the prefrontal cortex. System xc(-), a cystine-glutamate antiporter, is a poorly understood mechanism that contributes to both cellular antioxidant capacity and glutamate homeostasis.

OBJECTIVES

Our goal was to determine whether increased system xc(-) activity within the prefrontal cortex would normalize a rodent measure of sensorimotor gating.

METHODS

In situ hybridization was used to map messenger RNA (mRNA) expression of xCT, the active subunit of system xc(-), in the prefrontal cortex. Prepulse inhibition was used to measure sensorimotor gating; deficits in prepulse inhibition were produced using phencyclidine (0.3-3 mg/kg, sc). N-Acetylcysteine (10-100 μM) and the system xc(-) inhibitor (S)-4-carboxyphenylglycine (CPG, 0.5 μM) were used to increase and decrease system xc(-) activity, respectively. The uptake of (14)C-cystine into tissue punches obtained from the prefrontal cortex was used to assay system xc(-) activity.

RESULTS

The expression of xCT mRNA in the prefrontal cortex was most prominent in a lateral band spanning primarily the prelimbic cortex. Although phencyclidine did not alter the uptake of (14)C-cystine in prefrontal cortical tissue punches, intraprefrontal cortical infusion of N-acetylcysteine (10-100 μM) significantly reduced phencyclidine- (1.5 mg/kg, sc) induced deficits in prepulse inhibition. N-Acetylcysteine was without effect when coinfused with CPG (0.5 μM), indicating an involvement of system xc(-).

CONCLUSIONS

These results indicate that phencyclidine disrupts sensorimotor gating through system xc(-) independent mechanisms, but that increasing cystine-glutamate exchange in the prefrontal cortex is sufficient to reduce behavioral deficits produced by phencyclidine.

Pretreatment with group I metabotropic glutamate receptors antagonists attenuates lethality induced by acute cocaine overdose and expression of sensitization to hyperlocomotor effect of cocaine in mice

Cocaine abuse and dependence is a worldwide health problem. However, there are no currently approved medications to reduce cocaine abuse/relapse and toxicity. The aim of the present study was to test, whether group I metabotropic glutamate receptors (mGluRs) antagonists (mGluR1 and mGluR5) differentially regulate toxic versus behavioral effects of cocaine, both phenomena relevant to the psychopathology of cocaine addiction in humans. In the present study, we assessed the impact of mGluR1 antagonist-EMQMCM and mGluR5 antagonist-MTEP on the cocaine-induced lethality and the expression of sensitization to hyperlocomotor effect of cocaine in mice. Our study indicated that EMQMCM and MTEP, both substances at the doses of 5 and 10 mg/kg (but not 2.5 mg/kg), decreased cocaine-induced lethality produced by 75 mg/kg of cocaine, which was given acutely. The effect of EMQMCM was dose-dependent, and this compound at the dose of 10 mg/kg almost completely abolished the lethality induced by cocaine. MTEP reduced this cocaine effect at the doses of 5 and 10 mg/kg, equally. Furthermore, EMQMCM (1.25-5 mg/kg) at the doses of 2.5 and 5.0 mg/kg, and MTEP (2.5-10 mg/kg) only at the highest dose of 10 mg/kg, significantly reduced the expression of cocaine-induced (10 mg/kg) behavioral sensitization. Our results suggest that stimulation of mGluR1 and mGluR5 is involved in lethal effect of cocaine overdose and cocaine seeking behavior evaluated in behavioral sensitization test. However, the participation of mGluR1 in these cocaine effects seems to be dominant. Therefore, antagonists showing preferences towards mGluR1 might be useful in therapy of cocaine toxicity and abuse.

Mechanisms of acute cocaine toxicity

Patients with acute cocaine poisoning present with life-threatening symptoms involving several organ systems. While the effects of cocaine are myriad, they are the result of a limited number of cocaine-protein interactions, including monoamine transporters, neurotransmitter receptors and voltage-gated ion channels. These primary interactions trigger a cascade of events that ultimately produce the clinical effects. The purpose of this article is to review the primary interactions of cocaine and the effects that these interactions trigger. We also describe the progression of symptoms observed in cocaine poisoning as they relate to serum cocaine concentrations.

AMPA and NMDA receptors in P2 fractions of cocaine and cocaine-prazosin-treated rats

Cocaine sensitization results in the development of increased locomotion and stereotypy. It is accompanied by changes in glutamatergic trasmission that appear to be region-specific. The purpose of this article was to determine the effect(s) of cocaine and prazosin plus cocaine treatments on ionotropic glutamate receptors in rat cerebral cortex (CTX) and prefrontal cortex (PFC). Cocaine-sensitized rats (15 mg/kg, i.p. once for 5 days), withdrawn (7 days) and later challenged with a single cocaine dose, showed region-specific in NMDA-2A and Glu-R2 in the CTX and PFC membranes in cocaine- and prazosin-treated rats when compared to the saline controls. Co-administration of prazosin inhibits sensitization and changes in NMDA 2A and Glu-R2. Furthermore, prazosin inhibits the effect of cocaine in CTX and PFC on [(3)H]FW (AMPA agonist) binding when compared to controls. In cortex, cocaine treatment causes a marked increase in total binding, while in PFC there is a significant decrease. In both regions, cocaine-prazosin treatment attenuates the effects of cocaine. These results suggest that cocaine affects ionotropic glutamate receptors (NMDA and AMPA) and that prazosin inhibits such effects in a region-specific form in rat brain.

Chronic inhibition of the norepinephrine transporter in the brain participates in seizure sensitization to cocaine and local anesthetics

The involvement of chronic inhibition of monoamine transporters (MAT) in the brain with respect to sensitization to cocaine- and local anesthetic-induced seizures was studied in mice. Repeated administration of subconvulsive doses of meprylcaine as well as cocaine, both of which inhibit MAT, but not lidocaine, which does not inhibit MAT, increased seizure activity and produced sensitization to other local anesthetics. The effects of five daily treatments of monoamine transporter inhibitors on lidocaine-induced convulsions were examined 2 or 3 days after the last dose of the inhibitors. Daily treatments of GBR 12935, a specific inhibitor of dopamine uptake, significantly increased the incidence and the intensity of lidocaine-induced convulsions at 20 mg/kg and decreased the threshold of the convulsions. Daily treatments of desipramine and maprotiline, selective norepinephrine uptake inhibitors, markedly increased the incidence and intensity of lidocaine-induced convulsions, and decreased the threshold in a dose-dependent manner at between 5 and 20 mg/kg. Daily treatments of citalopram, a selective serotonin uptake inhibitor, at 10 and 20 mg/kg, produced no significant increase in the incidence or intensity of lidocaine-induced convulsions, but decreased the threshold of the convulsions. These results suggest that the chronic intermittent inhibition of monoamine uptake increases susceptibility to cocaine- and local anesthetic-induced seizures, and the norepinephrine transporter is an integral component of this sensitization.

Protective effects of cannabinoid receptor agonists against cocaine and other convulsant-induced toxic behavioural symptoms

Based on the previously reported co-localization and relationship between cannabinoid and dopamine receptors, the effects of cannabinoid receptor agonists against cocaine-induced toxic behavioural symptoms, including convulsive seizures, were examined in mice. The anticonvulsant effect of several cannabimimetics against seizures induced by other convulsants was also compared. The cannabinoid receptor agonists CP 55940 ((-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl)-cyclohexanol) and WIN 55212-2 ((R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone), and the endogenous cannabinoid anandamide were co-administered intraperitoneally with cocaine (75 mg kg(-1)) or other convulsants such as bicuculline, methyl 6,7-dimethoxy-4-ethyl-beta-carboline-carboxylate (DMCM), L-glutamic acid and N-methyl-D-aspartate (NMDA). CP 55940 (2.5 mg kg(-1)) and anandamide (15 mg kg(-1)) significantly antagonized cocaine-induced lethality, and CP 55940 and WIN 55212-2 (2.5 mg kg(-1)) significantly attenuated the severity of cocaine-induced convulsive seizures. Furthermore, ataxic hyperactivity, which was observed only in the cocaine-treated group of mice and could be evaluated by their activity counts, was also depressed in the groups of mice co-treated with each of the three cannabinoid agonists. However, none of these agonists protected against bicuculline- or DMCM-induced lethality or convulsive seizures. In contrast, all of the cannabinoid agonists, most notably anandamide, antagonized both L-glutamic acid (2 g kg(-1))- and NMDA (200 mg kg(-1))-induced convulsive seizures. These data support the previously reported close correlation between dopamine and cannabinoid receptors, and between cannabinoid agonists, especially anandamide, and glutamate (NMDA) receptors. Furthermore, these results suggest a potential therapeutic role for cannabinoid agonists against cocaine- and other-convulsant-induced toxicities.

Spatiotemporal analysis of Fos expression associated with cocaine- and PTZ-induced seizures in prenatally cocaine-treated rats

We previously reported that prenatal cocaine exposure (40 mg/kg s.c., E10-E20) increased susceptibility to convulsant-induced seizures later in life, with female rats becoming more sensitive to seizures induced by cocaine and pentylenetetrazol (PTZ), and males more sensitive to PTZ-induced seizures (Snyder-Keller and Keller, 1995, 2000). In order to determine the locus of enhanced seizure susceptibility in the brains of prenatally cocaine-treated rats, we examined the distribution and density of Fos-immunoreactive cells after cocaine- and PTZ-induced seizures in mature rats. Subconvulsive cocaine doses induced c-fos in cortical areas as well as densely dopamine-innervated regions such as striatum and nucleus accumbens. Following cocaine-induced seizures, intense c-fos induction was observed in piriform cortex, amygdala, and hippocampus. Quantification of the number of Fos-immunoreactive cells in the brains of prenatally cocaine-treated versus prenatally saline-treated rats revealed differences in piriform cortex and amygdala that were indicative of a lower threshold in prenatally cocaine-treated female rats. Following PTZ-induced seizures, the same pattern of limbic structures were recruited with increasing seizure severity. Only females exhibited changes in the number of Fos-immunoreactive cells as a result of prenatal cocaine treatment. Pretreatment with the noncompetitive NMDA antagonist MK-801 blocked both cocaine- and PTZ-induced seizures, and Fos expression in limbic areas was also blocked. The dopamine D1 antagonist SCH 23390 blocked cocaine-induced seizures and associated c-fos induction, but not PTZ-induced seizures or Fos. Examination of the pattern of Fos expression at 15-20 min postseizure revealed that the initial site of c-fos induction associated with PTZ-induced seizures appeared to be the piriform cortex, whereas cocaine-induced seizures induced early expression in both piriform cortex and lateral amygdala. These findings suggest that neural alterations residing in the piriform cortex and amygdala are likely to account for the increased seizure susceptibility of prenatally cocaine-treated rats.

Prevention of cocaine-induced convulsions and lethality in mice: effectiveness of targeting different sites on the NMDA receptor complex

N-methyl-D-aspartate (NMDA) receptors appear to be involved in the behavioral toxic effects of cocaine. Therefore, different classes of NMDA receptor antagonists were compared for their ability to attenuate cocaine-induced convulsions and lethality in male, Swiss Webster mice. The mice were pre-treated (i.p.) with vehicle or an antagonist from one of the following classes: NMDA/glycine site antagonist (7-chlorokynurenic acid, ACEA-1021, ACEA-1031, ACEA-1328, DCQX, R(+)-HA-966), competitive antagonist (CPP, D-AP7), channel blocker (MK-801, memantine), or allosteric modulator (ifenprodil, CP-101,606, Co 101022, haloperidol). After a 15 min pre-treatment period, the mice were administered a convulsive (60 mg/kg, i.p.) or lethal (125 mg/kg, i.p.) dose of cocaine, equivalent to the calculated ED/LD97 values. Pre-treatment with competitive or NMDA/glycine site antagonists dose-dependently attenuated cocaine-induced convulsions and lethality (P<0.05). Pre-treatment with channel blockers or allosteric modulators of the NMDA receptor protected against cocaine-induced convulsions (P<0.05), but were ineffective or less effective than the competitive and glycine site antagonists in preventing death. The glutamate release inhibitor riluzole failed to prevent both the convulsions and lethality induced by cocaine. Significantly, post-treatment with NMDA/glycine site antagonists (ACEA-1021, ACEA-1031, ACEA-1328) after a cocaine overdose prevented death in a significant number of animals. The data suggest that NMDA receptors are involved in the pathophysiology of a cocaine overdose.

Alveolar lesions induced by systemic administration of cocaine to rats

In this work, alveolar lesions induced after systemic administration of cocaine (30 mg/kg per day, i.p.) to rats were evaluated both by light microscope analysis for morphological assessment as well as by measurement of the alveolar area as a quantitative index of the alveolar damage. Rats were examined after different times of exposure: 7, 15, 30, 45, 60 and 75 days. The histopathological evaluation of cocaine-treated rats revealed a remarkable thickening in some interalveolar septa, with interstitial hemorrhages, progressive thrombosis and transformation of reticular and elastic fibers into diffuse fibrosis. A significant decrease of the alveolar area was also observed. These findings are indicative of severe changes in capillaries, alveoli and bronchiole after cocaine exposure, which in turn may progressively disrupt the general function of the lungs. Differential mechanisms of systemic toxicity after cocaine exposure are discussed.

Glutamatergic involvement in psychomotor stimulant action

The sympathomimetic psychomotor stimulants, including cocaine, amphetamines, and the phenylethylamine amphetamine-like derivatives, exert actions in mammalian systems that implicate involvement of the excitatory neurotransmitter, glutamate and its receptors. Despite evidence that psychomotor stimulants do not directly stimulate glutamate receptors, blockade of acute lethal, convulsive, circulatory, thermoregulatory, locomotor and stereotypical responses, as well as interference with slowly developing behavioral sensitization and brain monoaminergic neurotoxicities, can be achieved by receptor antagonists at both N-methyl-D-aspartate and AMPA/kainate glutamate receptor subtypes. Alterations in glutamatergic neurobiology, including elevations in extracellular glutamate levels, changes in glutamate receptor properties and glutamatergic neuronal degeneration, have also been attributed to psychomotor stimulant administration. Blockade of glutamate receptors offers therapeutic options in management of psychomotor stimulant toxicity.

Role of cerebral spermidine in the development of sensitization to convulsant activity of cocaine and lidocaine

We have previously shown that daily treatment with subconvulsant dose of cocaine resulted in the elevation of brain levels of polyamines such as putrescine and spermidine and the development of increased susceptibility to cocaine-induced seizures. The present study examined whether exogenously administered polyamines affect seizure activity caused by various doses of cocaine and lidocaine in mice. Thirty minutes after intracerebroventricular treatments with either saline, putrescine or spermidine (1-4 mumol), animals were injected intraperitoneally with cocaine or lidocaine (60-90 mg/kg); then the occurrence of clonic seizures was observed. Spermidine enhanced cocaine-induced seizure activity, while putrescine had no effect on it. Lidocaine-induced convulsions were also dose-dependently potentiated by spermidine. In addition, spermidine significantly enhanced seizure activity following an injection of N-methyl-DL-aspartate. The results suggest that spermidine plays an important role in the development of sensitization to convulsant activity by cocaine and lidocaine via modulation of N-methyl-D-aspartate receptors.

Brain capillary lesions produced by cocaine in rats

In the last 20 years, acute and chronic cocaine addiction has increased among young and adult people. The effects of cocaine on brain vasculature of young animals have not been histologically studied in depth. In the present study, we report the lesions of brain capillaries, including the choroid plexus, produced by chronic cocaine administration, in adult Wistar rats receiving i.p., 30 mg/kg/day of aqueous cocaine hydrochloride solution. Rats were sacrificed after several days of treatment. Histopathological examination of capillaries from different brain regions and cerebellum was performed using light microscopy. At 7 days, there were initial signs of dilatation, rupture and thrombosis of capillaries. At 15 days of treatment small interstitial oedema and hemorrhages by rupture of the basal membrane of the capillaries was found. At 30 days of treatment, many capillaries from different areas showed fibroid endothelial thickening, and wall fibrosis become evident after 60 days of daily cocaine. In numerous places (cortex, gray nucleus: thalamus, caudate, hippocampus and cerebellum) we observed capillaries with an occluded lumen probably due to fibrosis or thrombi after 90 days of treatment. In the latter treatment, capillaries from the choroid plexuses had their lumen dilated and the epithelial cells vacuolated or necrotic. We hypothesize that the chronic administration of cocaine in rats induced brain lesions in part as a result of capillary disruption and subsequent extravasation of erythrocytes to brain parenchyma.

One-way cross-sensitization and cross-tolerance to seizure activity from cocaine to lidocaine

The present study examined the effects of daily treatment with a subconvulsant dose (50 mg/kg) of cocaine or lidocaine on susceptibility to seizures induced by cross-injections of the same dose of the other local anesthetic, and to seizures induced by pentylenetetrazol (PTZ) or N-methyl-DL-aspartate (NMDLA) in ddY mice. Repeated administration of 50 mg/kg cocaine caused the development of sensitization to cocaine-induced seizures during an initial 3 or 4 days, followed by the development of tolerance on days 4-6. The same dose of lidocaine, however, produced little or no seizure activity following repeated administration. In contrast, when injected 24 hr after 2-4 days of cocaine treatment, 50 mg/kg lidocaine produced severe seizures. Interestingly, this cross-sensitization from cocaine to lidocaine diminished upon further cocaine treatment. In contrast, treatment with lidocaine for 2-6 days had no effect on subsequent changes in seizure susceptibility following repeated cocaine injections. Neither treatment with cocaine nor lidocaine for 2 or 5 days influenced susceptibility to seizures induced by a challenge injection of PTZ (50 mg/kg, i.p.) or NMDLA (300 mg/kg, i.p.) 24 hr after treatment. HPLC analyses revealed that the cocaine treatment paradigm used in these studies increased the levels of the polyamines, putrescine and spermidine, in mouse brain, while lidocaine treatment had no effect on cerebral polyamine levels. These results suggest that there are differences in the neural mechanisms underlying the convulsant properties of cocaine and lidocaine in ddY mice.

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.