Ceftriaxone attenuates locomotor activity induced by acute and repeated cocaine exposure in mice

Effects of Hydrocodone Overdose and Ceftriaxone on Astrocytic Glutamate Transporters and Glutamate Receptors, and Associated Signaling in Nucleus Accumbens as well as Locomotor Activity in C57/BL Mice

Chronic opioid treatments dysregulate the glutamatergic system, inducing a hyperglutamatergic state in mesocorticolimbic brain regions. This study investigated the effects of exposure to hydrocodone overdose on locomotor activity, expression of target proteins related to the glutamatergic system, signaling kinases, and neuroinflammatory factors in the nucleus accumbens. The locomotor activity of mice was measured using the Comprehensive Laboratory Animal Monitoring System (CLAMS). CLAMS data showed that exposure to hydrocodone overdose increased locomotion activity in mice. This study tested ceftriaxone, known to upregulate major glutamate transporter 1 (GLT-1), in mice exposed to an overdose of hydrocodone. Thus, ceftriaxone normalized hydrocodone-induced hyperlocomotion activity in mice. Furthermore, exposure to hydrocodone overdose downregulated GLT-1, cystine/glutamate antiporter (xCT), and extracellular signal-regulated kinase activity (p-ERK/ERK) expression in the nucleus accumbens. However, exposure to an overdose of hydrocodone increased metabotropic glutamate receptor 5 (mGluR5), neuronal nitric oxide synthase activity (p-nNOS/nNOS), and receptor for advanced glycation end products (RAGE) expression in the nucleus accumbens. Importantly, ceftriaxone treatment attenuated hydrocodone-induced upregulation of mGluR5, p-nNOS/nNOS, and RAGE, as well as hydrocodone-induced downregulation of GLT-1, xCT, and p-ERK/ERK expression. These data demonstrated that exposure to hydrocodone overdose can cause dysregulation of the glutamatergic system, neuroinflammation, hyperlocomotion activity, and the potential therapeutic role of ceftriaxone in attenuating these effects.

Effects of Beta Lactams on Behavioral Outcomes of Substance Use Disorders: A Meta-Analysis of Preclinical Studies

INTRODUCTION

Preclinical studies demonstrated that beta-lactams have neuroprotective effects in conditions involving glutamate neuroexcitotoxicity, including substance use disorders (SUDs). This meta-analysis aims to analyze the existing evidences on the effects of beta-lactams as glutamate transporter 1 (GLT-1) upregulators in animal models of SUDs, identification of gaps in the literature, and setting the stage for potential translation into clinical phases.

METHODS

Meta-analysis was conducted on preclinical studies retrieved systematically from MEDLINE and ScienceDirect databases. Abused substances were identified by refereeing to the National Institute on Drug Abuse (NIDA). The results were quantitatively described with a focus on the behavioral outcomes. Treatment effect sizes were described using standardized mean difference, and they were pooled using random effect model. I2-statistic was used to assess heterogeneity, and Funnel plot and Egger's test were used for assessment of publication bias.

RESULTS

Literature search yielded a total of 71 studies that were eligible to be included in the analysis. Through these studies, the effects of beta-lactams were evaluated in animal models of nicotine, cannabis, amphetamines, synthetic cathinone, opioids, ethanol, and cocaine use disorders as well as steroids-related aggressive behaviors. Meta-analysis showed that treatments with beta-lactams consistently reduced the pooled undesired effects of the abused substances in several paradigms, including drug-self administration, conditioned place preference, drug seeking behaviors, hyperlocomotion, withdrawal syndromes, tolerance to analgesic effects, hyperalgesia, and hyperthermia.

CONCLUSION

This meta-analysis revealed that enhancing GLT-1 expression in the brain through beta-lactams seemed to be a promising treatment approach in the context of substance use disorders, as indicated by results in animal models.

β_lactam antibiotics against drug addiction: A novel therapeutic option

Drug addiction as a problem for the health of the individual and the society is the result of a complex process in which there is an interaction between brain nuclei and neurotransmitters (such as glutamate). β-lactam antibiotics, due to their enhancing properties on the glutamate transporter glutamate transporter-1, can affect and counteract the addictive mechanisms of drugs through the regulation of extracellular glutamate. Since glutamate is a key neurotransmitter in the development of drug addiction, it seems that β-lactams can be considered as a promising treatment for addiction. However, more research in this field is necessary to identify other mechanisms involved in their effectiveness. This article is a review of the studies conducted on the effect of β-lactam administration in preventing the development of drug addiction, as well as their possible cellular and molecular mechanisms. This review suggests the clinical use of β-lactam antibiotics that have weak antimicrobial properties (such as clavulanic acid) in the treatment of drug dependence.

Glial Glutamate Transporter Modulation Prevents Development of Complete Freund's Adjuvant-Induced Hyperalgesia and Allodynia in Mice

Glial glutamate transporter (GLT-1) modulation in the hippocampus and anterior cingulate cortex (ACC) is critically involved in nociceptive pain. The objective of the study was to investigate the effects of 3-[[(2-methylphenyl) methyl] thio]-6-(2-pyridinyl)-pyridazine (LDN-212320), a GLT-1 activator, against microglial activation induced by complete Freund's adjuvant (CFA) in a mouse model of inflammatory pain. Furthermore, the effects of LDN-212320 on the protein expression of glial markers, such as ionized calcium-binding adaptor molecule 1 (Iba1), cluster of differentiation molecule 11b (CD11b), mitogen-activated protein kinases (p38), astroglial GLT-1, and connexin 43 (CX43), were measured in the hippocampus and ACC following CFA injection using the Western blot analysis and immunofluorescence assay. The effects of LDN-212320 on the pro-inflammatory cytokine interleukin-1β (IL-1β) in the hippocampus and ACC were also assessed using an enzyme-linked immunosorbent assay. Pretreatment with LDN-212320 (20 mg/kg) significantly reduced the CFA-induced tactile allodynia and thermal hyperalgesia. The anti-hyperalgesic and anti-allodynic effects of LDN-212320 were reversed by the GLT-1 antagonist DHK (10 mg/kg). Pretreatment with LDN-212320 significantly reduced CFA-induced microglial Iba1, CD11b, and p38 expression in the hippocampus and ACC. LDN-212320 markedly modulated astroglial GLT-1, CX43, and, IL-1β expression in the hippocampus and ACC. Overall, these results suggest that LDN-212320 prevents CFA-induced allodynia and hyperalgesia by upregulating astroglial GLT-1 and CX43 expression and decreasing microglial activation in the hippocampus and ACC. Therefore, LDN-212320 could be developed as a novel therapeutic drug candidate for chronic inflammatory pain.

Evidence for Modulation of Substance Use Disorders by the Gut Microbiome: Hidden in Plain Sight

The gut microbiome modulates neurochemical function and behavior and has been implicated in numerous central nervous system (CNS) diseases, including developmental, neurodegenerative, and psychiatric disorders. Substance use disorders (SUDs) remain a serious threat to the public well-being, yet gut microbiome involvement in drug abuse has received very little attention. Studies of the mechanisms underlying SUDs have naturally focused on CNS reward circuits. However, a significant body of research has accumulated over the past decade that has unwittingly provided strong support for gut microbiome participation in drug reward. β-Lactam antibiotics have been employed to increase glutamate transporter expression to reverse relapse-induced release of glutamate. Sodium butyrate has been used as a histone deacetylase inhibitor to prevent drug-induced epigenetic alterations. High-fat diets have been used to alter drug reward because of the extensive overlap of the circuitry mediating them. This review article casts these approaches in a different light and makes a compelling case for gut microbiome modulation of SUDs. Few factors alter the structure and composition of the gut microbiome more than antibiotics and a high-fat diet, and butyrate is an endogenous product of bacterial fermentation. Drugs such as cocaine, alcohol, opiates, and psychostimulants also modify the gut microbiome. Therefore, their effects must be viewed on a complex background of cotreatment-induced dysbiosis. Consideration of the gut microbiome in SUDs should have the beneficial effects of expanding the understanding of SUDs and aiding in the design of new therapies based on opposing the effects of abused drugs on the host's commensal bacterial community. SIGNIFICANCE STATEMENT: Proposed mechanisms underlying substance use disorders fail to acknowledge the impact of drugs of abuse on the gut microbiome. β-Lactam antibiotics, sodium butyrate, and high-fat diets are used to modify drug seeking and reward, overlooking the notable capacity of these treatments to alter the gut microbiome. This review aims to stimulate research on substance abuse-gut microbiome interactions by illustrating how drugs of abuse share with antibiotics, sodium butyrate, and fat-laden diets the ability to modify the host microbial community.

Effect of Modulation of the Astrocytic Glutamate Transporters' Expression on Cocaine-Induced Reinstatement in Male P Rats Exposed to Ethanol

AIM

Reinforcing properties of ethanol and cocaine are mediated in part through the glutamatergic system. Extracellular glutamate concentration is strictly maintained through several glutamate transporters, such as glutamate transporter 1 (GLT-1), cystine/glutamate transporter (xCT) and glutamate aspartate transporter (GLAST). Previous findings revealed that cocaine and ethanol exposure downregulated GLT-1 and xCT, and that β-lactam antibiotics restored their expression.

METHODS

In this study, we investigated the effect of ampicillin/sulbactam (AMP/SUL) (200 mg/kg, i.p.), a β-lactam antibiotic, on cocaine-induced reinstatement and locomotor activity in male alcohol preferring (P) rats using free choice ethanol (15 and 30%, v/v) and water. We also investigated the effect of co-exposure to ethanol and cocaine (20 mg/kg, i.p.) on GLT-1, xCT and GLAST expression in the nucleus accumbens (NAc) core, NAc shell and dorsomedial prefrontal cortex (dmPFC).

RESULTS

Cocaine exposure decreased ethanol intake and preference. Cocaine and ethanol co-exposure acquired place preference and increased locomotor activity compared to ethanol-exposed rats. GLT-1 and xCT expression were downregulated after cocaine and ethanol co-exposure in the NAc core and shell, but not in dmPFC. AMP/SUL attenuated reinstatement to cocaine as well attenuated the decrease in locomotor activity and ethanol intake and preference. These effects were associated with upregulation of GLT-1 and xCT expression in the NAc core/shell and dmPFC. GLAST expression was not affected after ethanol and cocaine co-exposure or AMP/SUL treatment.

CONCLUSION

Our findings demonstrate that astrocytic glutamate transporters within the mesocorticolimbic area are critical targets in modulating cocaine-seeking behavior while being consuming ethanol.

Dynamic interactions of ceftriaxone and environmental variables suppress amphetamine seeking

Extrasynaptic glutamate within the nucleus accumbens (NAc) is a driver of relapse. Cocaine, ethanol, and methamphetamine reduce the expression of cystine-glutamate antiporter (xCT) and primary glial glutamate transporter 1 (GLT1) leading to increased extrasynaptic glutamate. Ceftriaxone (CTX) restores xCT and GLT1 expression and effectively suppresses cocaine and ethanol reinstatement, however, the effects of CTX on amphetamine (AMP) reinstatement are not determined. Rodents were reared in an enriched condition (EC), isolated (IC), or standard condition (SC) and trained in AMP self-administration (0.1 mg/kg/infusion). EC, IC, and SC rats received injections of SAL or CTX (200 mg/kg) after daily extinction sessions. Then rats were tested in cue- and AMP-induced reinstatement tests. We hypothesized that EC rearing would reduce reinstatement by altering GLT1 or xCT expression in the NAc and medial prefrontal cortex (mPFC). In Experiment 2, pair-housed rats received once-daily AMP (1.0 mg/kg i.p.) or SAL for eight days followed by once-daily CTX (200 mg/kg i.p.) or SAL injections for 10 days. CTX treatment reduced cue-induced drug seeking in EC rats but not IC or SC rats. In an AMP-induced reinstatement test, CTX reduced AMP-induced drug seeking in EC and SC rats, but not IC rats. Western blot analyses revealed that AMP self-administration and non-contingent repeated AMP exposure did not downregulate GLT1 or xCT in the NAc or mPFC. Therefore, the ability for EC housing to reduce amphetamine seeking may work through other mechanisms.

Effects of glial glutamate transporter activator in formalin-induced pain behaviour in mice

BACKGROUND

Nociceptive pain remains a prevalent clinical problem and often poorly responsive to the currently available analgesics. Previous studies have shown that astroglial glutamate transporter-1 (GLT-1) in the hippocampus and anterior cingulate cortex (ACC) is critically involved in pain processing and modulation. However, the role of astroglial GLT-1 in nociceptive pain involving the hippocampus and ACC remains unknown. We investigated the role of 3-[[(2-Methylphenyl) methyl]thio]-6-(2-pyridinyl)-pyridazine (LDN-212320), a GLT-1 activator, in nociceptive pain model and hippocampal-dependent behavioural tasks in mice.

METHODS

We evaluated the effects of LDN-212320 in formalin-induced nociceptive pain model. In addition, formalin-induced impaired hippocampal-dependent behaviours were measured using Y-maze and object recognition test. Furthermore, GLT-1 expression and extracellular signal-regulated kinase phosphorylation (pERK1/2) were measured in the hippocampus and ACC using Western blot analysis and immunohistochemistry.

RESULTS

The LDN-212320 (10 or 20 mg/kg, i.p) significantly attenuated formalin-evoked nociceptive behaviour. The antinociceptive effects of LDN-212320 were reversed by systemic administration of DHK (10 mg/kg, i.p), a GLT-1 antagonist. Moreover, LDN-212320 (10 or 20 mg/kg, i.p) significantly reversed formalin-induced impaired hippocampal-dependent behaviour. In addition, LDN-212320 (10 or 20 mg/kg, i.p) increased GLT-1 expressions in the hippocampus and ACC. On the other hand, LDN-212320 (20 mg/kg, i.p) significantly reduced formalin induced-ERK phosphorylation, a marker of nociception, in the hippocampus and ACC.

CONCLUSION

These results suggest that the GLT-1 activator LDN-212320 prevents nociceptive pain by upregulating astroglial GLT-1 expression in the hippocampus and ACC. Therefore, GLT-1 activator could be a novel drug candidate for nociceptive pain.

SIGNIFICANCE

The present study provides new insights and evaluates the role of GLT-1 activator in the modulation of nociceptive pain involving hippocampus and ACC. Here, we provide evidence that GLT-1 activator could be a potential therapeutic utility for the treatment of nociceptive pain.

Modulatory effects of Ampicillin/Sulbactam on glial glutamate transporters and metabotropic glutamate receptor 1 as well as reinstatement to cocaine-seeking behavior

Glutamatergic system has an important role in cocaine-seeking behavior. Studies have reported that chronic exposure to cocaine induces downregulation of glutamate transporter-1 (GLT-1) and cystine/glutamate exchanger (xCT) in the central reward brain regions. Ceftriaxone, a β-lactam antibiotic, restored GLT-1 expression and consequently reduced cue-induced reinstatement of cocaine-seeking behavior. In this study, we investigated the reinstatement to cocaine (20mg/kg, i.p.) seeking behavior using a conditioned place preference (CPP) paradigm in male alcohol-preferring (P) rats. In addition, we investigated the effects of Ampicillin/Sulbactam (AMP/SUL) (200mg/kg, i.p.), a β-lactam antibiotic, on cocaine-induced reinstatement. We also investigated the effects of AMP/SUL on the expression of glial glutamate transporters and metabotropic glutamate receptor 1 (mGluR1) in the nucleus accumbens (NAc) core and shell and the dorsomedial prefrontal cortex (dmPFC). We found that AMP/SUL treatment reduced cocaine-triggered reinstatement. This effect was associated with a decrease in locomotor activity. Moreover, GLT-1 and xCT were downregulated in the NAc core and shell, but not in the dmPFC, following cocaine-primed reinstatement. However, cocaine exposure increased the expression of mGluR1 in the NAc core, but not in the NAc shell or dmPFC. Importantly, AMP/SUL treatment normalized GLT-1 and xCT expression in the NAc core and shell; however, the drug normalized mGluR1 expression in the NAc core only. Additionally, AMP/SUL increased the expression of GLT-1 and xCT in the dmPFC as compared to the water naïve group. These findings demonstrated that glial glutamate transporters and mGluR1 in the mesocorticolimbic area could be potential therapeutic targets for the attenuation of reinstatement to cocaine-seeking behavior.

Gut microbiota: Implications in Parkinson's disease

Gut microbiota (GM) can influence various neurological outcomes, like cognition, learning, and memory. Commensal GM modulates brain development and behavior and has been implicated in several neurological disorders like Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, anxiety, stress and much more. A recent study has shown that Parkinson's disease patients suffer from GM dysbiosis, but whether it is a cause or an effect is yet to be understood. In this review, we try to connect the dots between GM and PD pathology using direct and indirect evidence.

Behavioral History of Withdrawal Influences Regulation of Cocaine Seeking by Glutamate Re-Uptake

Withdrawal from cocaine regulates expression of distinct glutamate re-uptake transporters in the nucleus accumbens (NAc). In this study, we examined the cumulative effect of glutamate re-uptake by multiple excitatory amino acid transporters (EAATs) on drug-seeking at two different stages of withdrawal from self-administered cocaine. Rats were trained on fixed ratio 1 (FR1), progressing to FR5 schedule of reinforcement. After one day of withdrawal, microinfusion of a broad non-transportable EAAT antagonist, DL-threo-beta-benzyloxyaspartate (DL-TBOA), into the NAc shell dose-dependently attenuated self-administration of cocaine. Sucrose self-administration was not affected by DL-TBOA, indicating an effect specific to reinforcing properties of cocaine. The attenuating effect on cocaine seeking was not due to suppression of locomotor response, as DL-TBOA was found to transiently increase spontaneous locomotor activity. Previous studies have established a role for EAAT2-mediated re-uptake on reinstatement of cocaine seeking following extended withdrawal and extinction training. We found that blockade of NAc shell EAATs did not affect cocaine-primed reinstatement of cocaine seeking. These results indicate that behavioral history of withdrawal influences the effect of re-uptake mediated glutamate clearance on cocaine seeking. Dynamic regulation of glutamate availability by re-uptake mechanisms may impact other glutamate signaling pathways to account for such differences.

Synthetic cathinone MDPV downregulates glutamate transporter subtype I (GLT-1) and produces rewarding and locomotor-activating effects that are reduced by a GLT-1 activator

Synthetic cathinones produce dysregulation of monoamine systems, but their effects on the glutamate system and the influence of glutamate on behavioral effects related to cathinone abuse are unknown. A principal regulator of glutamate homeostasis is glutamate transporter subtype 1 (GLT-1), an astrocytic protein that clears glutamate from the extracellular space and influences behavioral effects of established psychostimulants. We hypothesized that repeated administration of the synthetic cathinone, MDPV (3,4-methylenedioxypyrovalerone), would affect GLT-1 expression in the corticolimbic circuit, and that a GLT-1 activator (ceftriaxone, CTX) would reduce rewarding and locomotor-stimulant effects of MDPV in rats. GLT-1 protein expression in the nucleus accumbens (NAcc), but not prefrontal cortex (PFC), was decreased following withdrawal (2, 5 and 10 days) from repeated MDPV treatment, but not immediately after the last MDPV injection. CTX (200 mg/kg) pretreatment did not affect acute locomotor activation produced by MDPV (0.5, 1, 3 mg/kg). However, CTX (200 mg/kg) administered during a 7-day MDPV treatment paradigm attenuated the development of MDPV-induced sensitization of repetitive movements in rats challenged with MDPV following 11 days of drug abstinence. Pretreatment with CTX (200 mg/kg) during a 4-day MDPV (2 mg/kg) conditioned place preference (CPP) paradigm reduced the development of place preference produced by MDPV. The present data demonstrate dysregulation of corticolimbic glutamate transport systems during withdrawal from chronic MDPV exposure, and show that a GLT-1 transporter activator disrupts behavioral effects of MDPV that are related to synthetic cathinone abuse.

Clavulanic acid enhances glutamate transporter subtype I (GLT-1) expression and decreases reinforcing efficacy of cocaine in mice

The β-lactam antibiotic ceftriaxone (CTX) reduces cocaine reinforcement and relapse in preclinical assays through a mechanism involving activation of glutamate transporter subtype 1 (GLT-1). However, its poor brain penetrability and intravenous administration route may limit its therapeutic utility for indications related to CNS diseases. An alternative is clavulanic acid (CA), a structural analog of CTX that retains the β-lactam core required for GLT-1 activity but displays enhanced brain penetrability and oral activity relative to CTX. Here, we tested the hypothesis that CA (1, 10 mg/kg ip) would enhance GLT-1 expression and decrease cocaine self-administration (SA) in mice, but at lower doses than CTX. Experiments revealed that GLT-1 transporter expression in the nucleus accumbens of mice treated with repeated CA (1, 10 mg/kg) was enhanced relative to saline-treated mice. Repeated CA treatment (1 mg/kg) reduced the reinforcing efficacy of cocaine (0.56 mg/kg/inf) in mice maintained on a progressive-ratio (PR) schedule of reinforcement but did not affect acquisition of cocaine SA under fixed-ratio responding or acquisition or retention of learning. These findings suggest that the β-lactamase inhibitor CA can activate the cellular glutamate reuptake system in the brain reward circuit and reduce cocaine's reinforcing efficacy at 100-fold lower doses than CTX.

Ceftriaxone attenuates acute cocaine-evoked dopaminergic neurotransmission in the nucleus accumbens of the rat

BACKGROUND AND PURPOSE

Ceftriaxone is a β-lactam antibiotic and glutamate transporter activator that reduces the reinforcing effects of psychostimulants. Ceftriaxone also reduces locomotor activation following acute psychostimulant exposure, suggesting that alterations in dopamine transmission in the nucleus accumbens contribute to its mechanism of action. In the present studies we tested the hypothesis that pretreatment with ceftriaxone disrupts acute cocaine-evoked dopaminergic neurotransmission in the nucleus accumbens.

EXPERIMENTAL APPROACH

Adult male Sprague-Dawley rats were pretreated with saline or ceftriaxone (200 mg kg(-1) , i.p. × 10 days) and then challenged with cocaine (15 mg kg(-1) , i.p.). Motor activity, dopamine efflux (via in vivo microdialysis) and protein levels of tyrosine hydroxylase (TH), the dopamine transporter and organic cation transporter as well as α-synuclein, Akt and GSK3β were analysed in the nucleus accumbens.

KEY RESULTS

Ceftriaxone-pretreated rats challenged with cocaine displayed reduced locomotor activity and accumbal dopamine efflux compared with saline-pretreated controls challenged with cocaine. The reduction in cocaine-evoked dopamine levels was not counteracted by excitatory amino acid transporter 2 blockade in the nucleus accumbens. Pretreatment with ceftriaxone increased Akt/GSK3β signalling in the nucleus accumbens and reduced levels of dopamine transporter, TH and phosphorylated α-synuclein, indicating that ceftriaxone affects numerous proteins involved in dopaminergic transmission.

CONCLUSIONS AND IMPLICATIONS

These results are the first evidence that ceftriaxone affects cocaine-evoked dopaminergic transmission, in addition to its well-described effects on glutamate, and suggest that its ability to attenuate cocaine-induced behaviours, such as psychomotor activity, is due in part to reduced dopaminergic neurotransmission in the nucleus accumbens.

Ceftriaxone attenuates acquisition and facilitates extinction of cocaine-induced suppression of saccharin intake in C57BL/6J mice

Growing evidence implicates glutamate homeostasis in a number of behaviors observed in addiction such as acquisition of drug taking, motivation, and reinstatement. To date, however, the role of glutamate homeostasis in the avoidance of natural rewards due to exposure to drugs of abuse has received little attention. The aim of the current study was to evaluate the beta-lactam antibiotic, ceftriaxone, which has been shown to normalize disrupted glutamate homeostasis associated with exposure to drugs of abuse, in cocaine-induced suppression of saccharin intake in C57BL/6J mice. Briefly, C57BL/6J mice received daily injections of either 200mg/kg ceftriaxone or saline. Mice were then given access to 0.15% saccharin for 1h and immediately injected intraperitoneally with either saline or 30 mg/kg cocaine; taste-drug pairings occurred every 24h for 5 trials followed by a final CS only trial. One week following taste-drug pairings, extinction was evaluated in a series of one- and two-bottle saccharin intake tests. Individual differences in cocaine-induced suppression were observed (i.e., low and high suppressors) with differential effects of ceftriaxone. Ceftriaxone delayed suppression of saccharin intake in high suppressors but prevented suppression in low suppressors. In addition, ceftriaxone history facilitated extinction in the high suppressors. These data suggest that changes in glutamate homeostasis may be involved in the formation and expression of cocaine-induced suppression of saccharin intake in mice.

Levamisole enhances the rewarding and locomotor-activating effects of cocaine in rats

BACKGROUND

The Drug Enforcement Agency estimates that 80% of cocaine seized in the United States contains the veterinary pharmaceutical levamisole (LVM). One problem with LVM is that it is producing life-threatening neutropenia in an alarming number of cocaine abusers. The neuropharmacological profile of LVM is also suggestive of an agent with modest reinforcing and stimulant effects that could enhance cocaine's addictive effects.

METHODS

We tested the hypothesis that LVM (ip) enhances the rewarding and locomotor stimulant effects of cocaine (ip) using rat conditioned place preference (CPP) and locomotor assays. Effects of LVM by itself were also tested.

RESULTS

LVM (0-10 mg/kg) produced CPP at 1mg/kg (P<0.05) and locomotor activation at 5mg/kg (P < 0.05). For CPP combination experiments, a statistically inactive dose of LVM (0.1 mg/kg) was administered with a low dose of cocaine (2.5 mg/kg). Neither agent produced CPP compared to saline (P > 0.05); however, the combination of LVM and cocaine produced enhanced CPP compared to saline or either drug by itself (P < 0.01). For locomotor experiments, the same inactive dose of LVM (0.1mg/kg, ip) was administered with low (10 mg/kg) and high doses (30 mg/kg) of cocaine. LVM (0.1 mg/kg) enhanced locomotor activation produced by 10mg/kg of cocaine (P < 0.05) but not by 30 mg/kg (P>0.05).

CONCLUSIONS

LVM can enhance rewarding and locomotor-activating effects of low doses of cocaine in rats while possessing modest activity of its own.

Attenuation of morphine-induced dependence and tolerance by ceftriaxone and amitriptyline in mice

INTRODUCTION

Tolerance to and dependence on the analgesic effect of opioids is a pharmacological phenomenon that occurs after their prolonged administration.

OBJECTIVE

The aim of this study was to evaluate the protective effects of ceftriaxone and amitriptyline on the development of morphine-induced tolerance and dependence.

METHODS

In this study, 18 groups (9 groups each for tolerance and dependency tests) of mice (n = 8) received saline [10 mL/kg, intraperitoneally (i.p.)], morphine (50 mg/kg, i.p.), ceftriaxone (50 mg/kg, i.p., 100 mg/kg, i.p., and 200 mg/kg, i.p.), amitriptyline (5 mg/kg, i.p., 10 mg/kg, i.p., and 15 mg/kg, i.p.), or a combination of ceftriaxone (50 mg/kg, i.p.) and amitriptyline (5 mg/kg, i.p.) once per day for 4 days for investigation and comparison of the effects of ceftriaxone and amitriptyline on the prevention of dependency and tolerance to morphine. Tolerance was assessed with administration of morphine (9 mg/kg, i.p.) and using the hot plate test on the 5(th) day. In dependency tests, withdrawal symptoms were assessed on the 4(th) day for each animal 30 minutes after the administration of naloxone (4 mg/kg, i.p.; 2 hours after the last dose of morphine).

RESULTS

It was found that treatment with ceftriaxone or amitriptyline attenuated the development of tolerance to the antinociceptive effect of morphine and also reduced naloxone-precipitated withdrawal jumping and standing on feet. Furthermore, coadministration of ceftriaxone and amitriptyline at low doses (50 mg/kg, i.p. and 5 mg/kg, i.p., respectively) prior to morphine injection also decreased both morphine-induced tolerance and dependence.

CONCLUSION

Results indicate that the treatment with ceftriaxone and amitriptyline, alone or in combination, could attenuate the development of morphine-induced tolerance and dependence.

Clavulanic acid reduces rewarding, hyperthermic and locomotor-sensitizing effects of morphine in rats: a new indication for an old drug?

BACKGROUND

Despite the efficacy of ceftriaxone (CTX) in animal models of CNS diseases, including drug addiction, its utility as a CNS-active therapeutic may be limited by poor brain penetrability and cumbersome parenteral administration. An alternative is the β-lactamase inhibitor clavulanic acid (CA), a constituent of Augmentin that prevents antibiotic degradation. CA possesses the β-lactam core necessary for CNS activity but, relative to CTX, possesses: (1) oral activity; (2) 2.5-fold greater brain penetrability; and (3) negligible antibiotic activity.

METHODS

To compare the effectiveness of CA (10mg/kg) and CTX (200mg/kg) against centrally-mediated endpoints, we investigated their effects against morphine's rewarding, hyperthermic, and locomotor-sensitizing actions. Endpoints were based on prior evidence that CTX attenuates morphine-induced physical dependence, tolerance, and hyperthermia.

RESULTS

As expected, rats treated with morphine (4 mg/kg) displayed hyperthermia and conditioned place preference (CPP). Co-treatment with CTX or CA inhibited development of morphine-induced CPP by approximately 70%. Morphine's hyperthermic effect was also suppressed, with CTX and CA producing 57% and 47% inhibition, respectively. Locomotor sensitization induced by repeated morphine exposures was inhibited by CA but not CTX.

CONCLUSIONS

The present findings are the first to suggest that CA disrupts the in vivo actions of morphine and point toward further studying CA as a potential therapy for drug addiction. Further, its ability to disrupt morphine's rewarding effects at 20-fold lower doses than CTX identifies CA as an existing, orally-active alternative to direct CTX therapy for CNS diseases.