mGluR5 receptors in the basolateral amygdala and nucleus accumbens regulate cue-induced reinstatement of ethanol-seeking behavior

Pharmacological blockade of the type 5 metabotropic glutamate receptor (mGluR5) attenuates cue-induced reinstatement of ethanol-seeking behavior, yet the brain regions involved in these effects are not yet known. The purpose of the present study was to determine if local blockade of mGluR5 receptors in the basolateral amygdala (BLA) and/or the nucleus accumbens (NAc), two brain regions known to be involved in stimulus-reward associations, attenuate the reinstatement of ethanol-seeking behavior induced by ethanol-paired cues. As a control for possible non-specific effects, the effects of mGluR5 blockade in these regions on cue-induced reinstatement of sucrose-seeking were also assessed. Male Wistar rats were implanted with bilateral microinjection cannulae aimed at the BLA or NAc. Following recovery, animals were trained to self-administer ethanol (10% w/v) or 45 mg sucrose pellets on an FR1 schedule of reinforcement in 30 min daily sessions using a sucrose fading procedure. Following stabilization of responding, animals underwent extinction training. Next, animals received infusions of vehicle or the selective mGluR5 antagonist MTEP (3 μg/μl) into the BLA or NAc prior to cue-induced reinstatement testing sessions. mGluR5 blockade eliminated cue-induced reinstatement of alcohol — but not sucrose-seeking behavior. Results from this study indicate that mGluR5 receptors in the BLA and NAc mediate cue-induced reinstatement of ethanol-seeking behavior, and provide two potential neuroanatomical sites of action where systemically administered mGluR5 antagonists attenuate cue-induced reinstatement. These data are consistent with previous findings that cue-induced reinstatement of ethanol-seeking increases neuronal activity and glutamatergic transmission in these two regions.     

Alcohol relapse induced by discrete cues activates components of AP-1 transcription factor and ERK pathway in the rat basolateral and central amygdala.

Alcohol-related cues may induce relapse to heavy alcohol drinking and promote molecular adaptations in discrete brain regions. An exact nature of these molecular alterations is still unknown. In the present study, rats trained to self-administer ethanol were tested for cue-induced reinstatement of ethanol seeking after 30 days of abstinence. Next, a detailed immunocytochemical analysis of c-Fos activation was performed within seven nuclei of the amygdala. In the second experiment, c-Fos activation after reinstatement of ethanol seeking induced by discrete cues was compared with the activation pattern of its putative partner (c-Jun) and regulators (extracellular signal-regulated kinases and c-Jun N-terminal kinases). Reexposure to ethanol-associated context cues (an extinction session) potentiated c-Fos expression within the basolateral and central amygdala. Repeated presentation of ethanol-associated discrete cues in an extinction/reinstatement session led to even stronger c-Fos activation in the latter nuclei. In the second experiment, reexposure to the ethanol-associated context and discrete cues activated both c-Jun and extracellular signal-regulated kinases (ERK1/2) in the basolateral amygdala. Our observations suggest that the basolateral and central amygdala may be specifically involved in alcohol-seeking behavior induced by discrete cues.     

The effects of lamotrigine on alcohol seeking and relapse

Lamotrigine is a clinically used drug, which inhibits Na⁺ channel activity that in turn reduces glutamate release. Its downstream activity on other neurotransmitter systems such as serotonergic and dopaminergic has also been reported. Since both glutamate and monoamines might be involved in alcohol craving and relapse, our aim was to examine the effects of lamotrigine on alcohol seeking and relapse-like drinking behaviour. Thus, lamotrigine (5 and 15 mg/kg) was tested in two behavioural models for alcohol seeking and relapse – the model of cue-induced reinstatement of alcohol-seeking behaviour and the alcohol deprivation effect (ADE) model in long-term alcohol drinking Wistar rats. Administration of 5 mg/kg of lamotrigine caused a significant decrease of cue-induced reinstatement of alcohol-seeking behaviour. The ADE was significantly reduced with both doses tested. However, the highest dose of lamotrigine produced sedation. The ability of lamotrigine to reduce alcohol seeking as well as relapse-like drinking behaviour provides further support for the proposed involvement of the glutamatergic and dopaminergic/serotonergic systems in alcohol craving and relapse, hence suggesting a good rationale for pharmacological intervention that may reduce craving and relapse in alcohol dependent patients.     

Ionotropic and metabotropic glutamate receptor antagonism attenuates cue-induced cocaine seeking.

Neuroanatomical and pharmacological evidence implicates glutamate transmission in drug-environment conditioning that partly controls drug seeking and relapse. Glutamate receptors could be targets for pharmacological attenuation of the motivational properties of drug-paired cues and for relapse prevention. The purpose of the present study was therefore to investigate the involvement of ionotropic and metabotropic glutamate receptor subtypes in cue-induced reinstatement of cocaine-seeking behavior. Rats were trained to self-administer cocaine using a second-order schedule of reinforcement (FR4(FR5:S)) under which a compound stimulus (light and tone) associated with cocaine infusions was presented contingently. Following extinction, the effects of the competitive NMDA receptor antagonist CGP 39551 (0, 2.5, 5, 10 mg/kg intraperitoneally (i.p.)), two competitive AMPA/kainate antagonists, CNQX (0, 0.75, 1.5, 3 mg/kg i.p.) and NBQX (0, 1.25, 2.5, 5 mg/kg i.p.), the NMDA/glycine site antagonist L-701,324 (0, 0.63, 1.25, 2.5 mg/kg i.p.), and the mGluR5 antagonist MPEP (0, 1.25, 2.5, 5 mg/kg i.p.) on cue-induced reinstatement of cocaine seeking were examined. The AMPA/kainate receptor antagonists CNQX and NBQX, the NMDA/glycine site antagonist L-701,324, and the mGluR5 antagonist MPEP attenuated significantly cue-induced reinstatement. The NMDA antagonist CGP 39551 failed to affect reinstatement. Additional control experiments indicated that attenuation of cue-induced reinstatement by CNQX, NBQX, L-701,324, and MPEP was not accompanied by significant suppression of spontaneous locomotor activity. These results suggest that conditioned influences on cocaine seeking depend on glutamate transmission. Accordingly, drugs with antagonist properties at various glutamate receptor subtypes could be useful in prevention of relapse induced by conditioned stimuli.     

Time-dependent changes in alcohol-seeking behaviour during abstinence.

Exposure of alcohol addicts to alcohol-related environmental cues may elicit alcohol-seeking behaviour even after protracted abstinence. The purpose of the present study was to assess time-dependent changes in alcohol-seeking behaviour in rats trained to respond for alcohol. The rats were re-exposed to alcohol-associated stimuli after 1, 28 or 56 days of withdrawal. During the re-exposure session, the rats were first allowed to respond in extinction. Then, reinstatement of alcohol-seeking behaviour was evoked by a complex of discrete alcohol-associated cues (auditory and light cues combined with taste and smell of alcohol). Extinction behaviour depended on abstinence duration with maximal responding after 28-day abstinence. Reinstatement of alcohol-seeking behaviour evoked by the discrete cues was highest after 56-day abstinence. No correlations were found between individual alcohol intakes, extinction behaviour and cue-induced reinstatement. These results suggest that: (i) alcohol-seeking behaviour may become more intense after long-term imposed abstinence; (ii) alcohol self-administration, extinction behaviour, and reinstatement of alcohol-seeking behaviour may be regulated by separate neural mechanisms.     

Involvement of AMPA/kainate,NMDA, and mGlu5 receptors in the nucleus accumbens core in cue-induced reinstatement of cocaine seeking in rats

Rationale Nucleus accumbens glutamate transmission has been implicated in drug-seeking behavior, but the involvement of glutamate receptor subtypes in drug seeking maintained by drug-associated cues has not been fully investigated. Objective This study examined the effects of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate, N-methyl-d-aspartate (NMDA) and mGlu5 receptor blockade in the nucleus accumbens core on cue-induced reinstatement of cocaine seeking. Method Wistar rats were trained to self-administer cocaine and associate a compound stimulus (light and tone) with the drug under an FR4(FR5:S) second-order schedule of reinforcement. After extinction, during which neither cocaine nor the compound stimulus was available, responding was reinstated by contingent presentations of the compound stimulus. The effects of the intra-accumbal AMPA/kainate receptor antagonist 6-cyano-7-nitro-quinoxaline-2, 3-dione (CNQX; 0, 0.01, and 0.03 μg/side), the NMDA antagonist d-2-amino-5-phosphonopentanoate (D-AP5; 0, 1, and 2 μg/side), and the mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP; 0, 0.5, and 1 μg/side) on reinstatement were examined in a within-subjects design. Results CNQX and D-AP5 attenuated cue-induced reinstatement of cocaine seeking dose-dependently. MPEP, however, decreased cocaine seeking only relative to baseline because also the saline vehicle included in the within-subjects series of injections decreased responding, possibly reflecting conditioned anhedonic effects of MPEP. In additional experiments, none of the antagonists attenuated locomotor activity or responding for sucrose pellets. Conclusions The results suggest that cue-induced reinstatement of cocaine seeking after a period of withdrawal from cocaine is sensitive to AMPA/kainate and NMDA receptor antagonism in the nucleus accumbens core and give further evidence for the role of the accumbal glutamate transmission in modulation of drug-seeking behavior.     

Baclofen attenuates cue-induced reinstatement of alcohol-seeking behavior in Sardinian alcohol-preferring (sP) rats

The GABA_B receptor agonist, baclofen, suppressed alcohol deprivation effect (a proposed experimental model of alcohol relapse) in Sardinian alcohol-preferring rats. The present study was designed to extend the characterization of the “anti-relapse” properties of baclofen to the reinstatement of alcohol-seeking behavior (another proposed model of alcohol relapse). Rats of the sP line were first trained to lever press for alcohol under a fixed ratio 4 schedule of reinforcement. Subsequently, rats were exposed to two within-session 70-min extinction/reinstatement tests with saline or baclofen administered in a counterbalanced, within-subject design. After a 60-min extinction phase, an alcohol-associated stimulus complex was presented (reinstatement phase). Saline or baclofen (3 mg/kg) were administered via a permanent intraperitoneal catheter, 30 min before the reinstatement phase. During the reinstatement phase, baclofen administration: (a) reduced by approximately 60% responses on the previously active lever, (b) increased latency to the first response and (c) decreased the response rate. These results indicate that baclofen reduced cue-induced reinstatement of alcohol-seeking behavior in sP rats.     

The Calpain Inhibitor A-705253 Attenuates Alcohol-Seeking and Relapse with Low Side-Effect Profile

Preclinical studies revealed contribution of N-methyl-D-aspartate receptors (NMDARs) to a variety of neuropsychiatric diseases including alcoholism, but development of NMDAR antagonists for therapeutic use has been a challenge, in part due to severe side effects. One of the key intracellular events resulting from stimulation of NMDAR is activation of calpains—calcium-dependent cysteine proteases. Here we studied whether inhibition of calpains would produce therapeutic-like effects of NMDAR antagonists but without their NMDAR-mediated side-effect profile. The calpain inhibitor A-705253 (3–10 mg/kg) was tested in a model of cue-induced reinstatement of alcohol-seeking behavior in post-dependent Wistar rats and in an alcohol deprivation effect (ADE) model in long-term alcohol drinking Wistar rats, two behavioral models for alcohol-seeking and relapse, respectively. We also tested the effect of A-705253 on the saccharine deprivation effect (SDE) as a selectivity measure. Acute treatment with A-705253 dose-dependently reduced cue-induced reinstatement of alcohol-seeking behavior. Repeated administration of A-705253 caused significant reductions of relapse-like excessive alcohol intake during the post-abstinence drinking days, an effect that persisted during two more successive drug-free drinking weeks, which was selective for the ADE as the SDE was unaffected. However, A-705253 did not produce psychostimulant, cognition impairing (delayed-matching-to-position), or psychotomimetic effects (specifically, phencyclidine discriminative stimulus effects). Taken together, these results demonstrate the involvement of calpains in alcohol-seeking and relapse and present a rationale for a novel pharmacological intervention that may reduce craving and relapse with minimal side effects in alcohol-dependent patients.     

Metabotropic glutamate receptor (mGluR5) antagonist MPEP attenuated cue- and schedule-induced reinstatement of nicotine self-administration behavior in rats

Previous studies suggested that metabotropic glutamate 5 (mGlu5) receptors play an important role in the reinforcing effects of abused drugs. The present experiments evaluated the effects of the mGlu5 receptor antagonist, MPEP (2-methyl-6-(phenylethynyl)-pyridine hydrochloride; 1-10 mg/kg, salt, i.p.), in rat models of nicotine-seeking behavior that may have relevance to relapse to drug-taking. Male Wistar rats (with restricted access to food) were trained to nose-poke to receive intravenous infusions of nicotine (0.03 mg/kg per infusion, base) under a fixed ratio 5 time out 60 s schedule of reinforcement. After stable nicotine self-administration was acquired, nose-poking behavior was extinguished in the absence of nicotine-associated cues. During the reinstatement test phase, independent groups of animals were exposed to: (a) response-contingent nicotine-associated cues (cue-induced reinstatement); or (b) response-noncontingent presentations of 45-mg food pellets under fixed time 2 min schedule (schedule-induced reinstatement). Additional control experiments were conducted to demonstrate that in nicotine-na?ve animals MPEP does not affect cue-induced reinstatement of food-seeking behavior and has no effects on operant behavior maintained by a simple fixed interval 2 min schedule of food reinforcement. Pretreatment with MPEP (10 mg/kg) significantly attenuated the reinstatement of nicotine-seeking in both experiments. Further, MPEP (10 mg/kg) significantly attenuated polydipsia induced by a fixed time 2 min food schedule. In conclusion, the present findings indicate that the blockade of mGlu5 receptors attenuates cue-induced reinstatement of nicotine self-administration behavior (but not food-seeking) and may produce a general inhibition of schedule-induced behaviors, including schedule-induced nicotine-seeking.     

Neuropeptide Y (NPY) suppresses yohimbine-induced reinstatement of alcohol seeking

Introduction  

Reinstatement of responding to a previously alcohol-associated lever following extinction is an established model of relapse-like behavior and can be triggered by stress exposure. Here, we examined whether neuropeptide Y (NPY), an endogenous anti-stress mediator, blocks reinstatement of alcohol-seeking induced by the pharmacological stressor yohimbine.     

mGluR5 antagonist MPEP reduces ethanol-seeking and relapse behavior.

The glutamatergic system plays an important role in mediating neurobehavioral effects of ethanol. Metabotropic glutamate receptors subtype 5 (mGluR5) are modulators of glutamatergic neurotransmission and are abundant in brain regions known to be involved in ethanol self-administration. Here, we studied the effects of 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a highly potent, noncompetitive mGlu5 receptor antagonist, on voluntary ethanol consumption and relapse behavior. For this purpose, we used two models for the measurement of relapse behavior: (i) reinstatement of ethanol-seeking behavior by drug-associated cues and (ii) the alcohol deprivation effect in long-term ethanol-consuming rats. In the first set of experiments, rats were trained to lever press for ethanol in the presence of a distinct set of cues. After extinction, the animals were exposed to the respective cues that initiated reinstatement of responding. A response-contingent ethanol prime further enhanced responding compared to the conditioned cues alone. Under these conditions, MPEP (0, 1, 3, and 10 mg/kg) attenuated ethanol seeking significantly and in a dose-related manner. However, at the highest dose, MPEP also decreased the number of inactive lever responses. In the second set of experiments, rats with 1 year of ethanol experience and repeated deprivation phases were used. A subchronic treatment with MPEP (twice daily; 0, 3, and 10 mg/kg) resulted in a significant and dose-dependent reduction of the alcohol deprivation effect (ADE). Although the same MPEP treatment regimen decreased baseline drinking, this effect was not as pronounced as on the ADE. These results show in two commonly used models of relapse to ethanol that pharmacological targeting of mGlu5 receptors may be a promising approach for the treatment of alcoholism.     

Potentiated reinstatement of cocaine-seeking behavior following D-amphetamine infusion into the basolateral amygdala.

Reinstatement of extinguished drug-seeking behavior following chronic drug self-administration has been demonstrated in rats in the presence of conditioned cues. This experimental model of cue-induced relapse can be used to assess the neural circuitry involved in relapse. We have previously shown that blockade of dopamine D1 receptors in the basolateral amygdala (BLA) abolishes conditioned cue-induced reinstatement of cocaine-seeking behavior. The present study tested the hypothesis that D-amphetamine-induced facilitation of monoamine neurotransmission in the BLA would potentiate conditioned cue-induced reinstatement of extinguished drug-seeking behavior. During daily self-administration sessions over 10 consecutive days, rats pressed a lever to receive cocaine infusions (0.2 mg/0.05 ml) paired with a light+tone compound stimulus. Following self-administration, rats underwent daily extinction sessions, during which no stimuli were presented. On the test days, rats received intra-BLA D-amphetamine (10 or 30 micro g/side) or vehicle infusions followed by extinction or conditioned cue-induced reinstatement testing. D-amphetamine infusions did not alter extinction responding relative to vehicle infusions. During reinstatement testing, conditioned cue presentation significantly increased responding over extinction levels, and intra-BLA D-amphetamine produced a dose-dependent increase in lever responding relative to vehicle infusions. These findings suggest that enhanced monoamine tone in the BLA potentiates the motivational effect and/or salience of cocaine-paired cues during reinstatement.     

Attenuation of reinstatement of methamphetamine-, sucrose-, and food-seeking behavior in rats by fenobam, a metabotropic glutamate receptor 5 negative allosteric modulator

Rationale

Methamphetamine (METH) is a highly potent and addictive psychostimulant with severe detrimental effects to the health of users. Currently, METH addiction is treated with a combination of cognitive and behavioral therapies, but these traditional approaches suffer from high relapse rates. Furthermore, there are currently no pharmacological treatment interventions approved by the FDA specifically for the treatment of METH addiction.

Objectives

Metabotropic glutamate receptor 5 (mGluR5) negative allosteric modulators (NAMs) have shown promise in significantly attenuating drug self-administration and drug-seeking in reinstatement paradigms. However, studies assessing the potential efficacy of mGluR5 NAMs that have been tested in human subjects are lacking. The current study sought to assess the effect of the mGluR5 NAM fenobam on METH-seeking behavior.

Methods

Rats were trained to self-administer METH (0.05 mg/kg i.v.), and following extinction, tested for effects of fenobam (5, 10, or 15 mg/kg intraperitoneal) on cue- and drug-induced reinstatement of METH-seeking. To determine if fenobam also alters reinstatement of seeking of natural reinforcers, separate groups of rats were trained to self-administer sucrose or food pellets and were tested for the effects of fenobam on cue-induced reinstatement of sucrose- and food-seeking.

Results

Fenobam attenuated drug- and cue-induced reinstatement of METH-seeking behavior at doses of 10 and 15 mg/kg. Fenobam also attenuated cue-induced reinstatement of sucrose- and food-seeking at all doses tested.

Conclusions

The mGluR5 NAM fenobam attenuates the reinstatement of METH-seeking behavior, but these effects may be due to nonspecific suppression of general appetitive behaviors.     

Suppression of alcohol self-administration and cue-induced reinstatement of alcohol seeking by the mGlu2/3 receptor agonist LY379268 and the mGlu8 receptor agonist (S)-3,4-DCPG

Glutamatergic neurotransmission has been suggested to modulate cue-induced drug-seeking behavior. Here we examined the effects of metabotropic glutamate receptor agonists on alcohol self-administration and cue-induced reinstatement. Rats were trained to self-administer 10% w/v ethanol under an FR1 schedule of reinforcement during 30-min sessions. In the reinstatement experiments, ethanol and a non-rewarding quinine solution (available on alternating days) were paired with olfactory stimuli (S+/S-) as well as light (CS+) or tone (CS-) stimuli. Following extinction training, reinstatement of responding was induced by the ethanol-associated stimuli (S+/CS+). The mGlu2/3 receptor agonist LY379268 (0, 1, 3 and 5 mg/kg i.p.) and the mGlu8 receptor agonist (S)-3,4-DCPG (0, 5, 10 and 15 mg/kg i.p.) attenuated alcohol self-administration and reinstatement at doses that decreased also spontaneous locomotor activity. The results suggest that metabotropic glutamate receptors may have a role in the modulation of alcohol seeking and self-administration. However, further studies with ligands with fewer motor-suppressant side effects are needed.     

Fenobam sulfate inhibits cocaine-taking and cocaine-seeking behavior in rats: implications for addiction treatment in humans

Rationale

The metabotropic glutamate receptor subtype 5 (mGluR5) has been reported to be critically involved in drug reward and addiction. Because the mGluR5 negative allosteric modulators (NAMs) 2-methyl-6-(phenylethynyl)pyridine (MPEP) and 3-((2-methyl-1,3-thiazol-4-yl)ethynyl)pyridine (MTEP) significantly inhibit addictivelike behaviors of cocaine and other drugs of abuse in experimental animals, it has been suggested that mGluR5 NAMs may have translational potential for treatment of addiction in humans. However, neither MPEP nor MTEP have been evaluated in humans due to their off-target actions and rapid metabolism.

Objectives

Herein, we evaluate a potential candidate for translational addiction research: a new sulfate salt formulation of fenobam, a selective mGluR5 NAM that has been investigated in humans.

Results

In rats, fenobam sulfate had superior pharmacokinetics compared to the free base, with improved maximal plasma concentration (C _max) and longer half life. Oral (p.o.) administration of fenobam sulfate (30 or 60 mg/kg) inhibited intravenous (i.v.) cocaine self-administration, cocaine-induced reinstatement of drug-seeking behavior, and cocaine-associated cue-induced cocaine-seeking behavior in rats. Fenobam sulfate also inhibited p.o. sucrose self-administration and sucrose-induced reinstatement of sucrose-seeking behavior, but had no effect on locomotion.

Conclusions

This study provides additional support for the role of mGluR5 signaling in cocaine addiction and suggests that fenobam sulfate may have translational potential in medication development for the treatment of cocaine addiction in humans.     

Discrete cue-conditioned alcohol-seeking after protracted abstinence: pattern of neural activation and involvement of orexin₁ receptors

BACKGROUND AND PURPOSE

The enduring propensity for alcoholics to relapse even following years of abstinence presents a major hurdle for treatment. Here we report a model of relapse following protracted abstinence and investigate the pattern of neuronal activation following cue-induced reinstatement and administration of the orexin₁ receptor antagonist SB-334867 in inbred alcohol-preferring rats.

EXPERIMENTAL APPROACH

Rats were trained to self-administer alcohol under operant conditions and divided into two groups: immediate (reinstated immediately following extinction) and delayed (extinguished and then housed for 5 months before reinstatement). Prior to reinstatement, animals were treated with vehicle (immediate n= 11, delayed n= 11) or SB-334867 (20 mg·kg⁻¹ i.p.; immediate n= 6, delayed n= 11). Fos expression was compared between each group and to animals that underwent extinction only.

KEY RESULTS

SB-334867 significantly attenuated cue-induced reinstatement in both groups. Immediate reinstatement increased Fos expression in the nucleus accumbens (NAc), infra-limbic (IL), pre-limbic (PrL), orbitofrontal (OFC) and piriform cortices, the lateral and dorsomedial hypothalamus, central amygdala and basolateral amygdala (BLA), and the bed nucleus of the stria terminalis. Following delayed reinstatement, Fos expression was further elevated in cortical structures. Concurrent with preventing reinstatement, SB-334867 decreased Fos in NAc core, PrL and OFC following immediate reinstatement. Following protracted abstinence, SB-334867 treatment decreased reinstatement-induced Fos in the PrL, OFC and piriform cortices.

CONCLUSIONS AND IMPLICATIONS

Cue-induced alcohol seeking can be triggered following protracted abstinence in rats. The effects of SB-334867 on both behaviour and Fos expression suggest that the orexin system is implicated in cue-induced reinstatement, although some loci may shift following protracted abstinence.     

Long-Term Memory Deficits are Associated with Elevated Synaptic ERK1/2 Activation and Reversed by mGluR5 Antagonism in an Animal Model of Autism

A significant proportion of patients with autism exhibit some degree of intellectual disability. The BTBR T⁺ Itpr3^tf/J mouse strain exhibits behaviors that align with the major diagnostic criteria of autism. To further evaluate the BTBR strain''s cognitive impairments, we quantified hippocampus-dependent object location memory (OLM) and found that one-third of the BTBR mice exhibited robust memory, whereas the remainder did not. Fluorescence deconvolution tomography was used to test whether synaptic levels of activated extracellular signal-regulated kinase 1/2 (ERK1/2), a protein that contributes importantly to plasticity, correlate with OLM scores in individual mice. In hippocampal field CA1, the BTBRs had fewer post-synaptic densities associated with high levels of phosphorylated (p-) ERK1/2 as compared with C57BL/6 mice. Although counts of p-ERK1/2 immunoreactive synapses did not correlate with OLM performance, the intensity of synaptic p-ERK1/2 immunolabeling was negatively correlated with OLM scores across BTBRs. Metabotropic glutamate receptor (mGluR) 5 signaling activates ERK1/2. Therefore, we tested whether treatment with the mGluR5 antagonist MPEP normalizes synaptic and learning measures in BTBR mice: MPEP facilitated OLM and decreased synaptic p-ERK1/2 immunolabeling intensity without affecting numbers of p-ERK1/2+ synapses. In contrast, semi-chronic ampakine treatment, which facilitates memory in other models of cognitive impairment, had no effect on OLM in BTBRs. These results suggest that intellectual disabilities associated with different neurodevelopmental disorders on the autism spectrum require distinct therapeutic strategies based on underlying synaptic pathology.     

Dopamine D3 Receptors in the Basolateral Amygdala and the Lateral Habenula Modulate Cue-Induced Reinstatement of Nicotine Seeking

Dopamine D₃ receptors are implicated in cue-induced relapse to drug seeking. We have previously shown that systemic administration of a selective D₃ antagonist reduces cue-induced reinstatement of nicotine seeking in rats. The current study sought to investigate potential neural substrates mediating this effect. The D₃ antagonist SB-277011-A (0.01–1 μg/0.5 μl/side) infused into the basolateral amygdala or the lateral habenula, but not the nucleus accumbens, significantly attenuated cue-induced reinstatement of nicotine seeking. Moreover, infusion of SB-277011-A (1 μg/0.5 μl/side) into the basolateral amygdala or lateral habenula had no effect on food self-administration. Together with the finding that systemic SB-277011-A had no effect on extinction responding, this suggests that the effects observed here were on reinstatement and cue seeking, and not due to nonspecific motor activation or contextual-modified residual responding. The further finding of binding of [¹²⁵I]7-OH-PIPAT to D₃ receptors in the lateral habenula and in the basolateral amygdala is consistent with an important role of D₃ receptors in these areas in nicotine seeking. It was also found that systemic administration of the selective D₂ antagonist L741626 decreased cue-induced reinstatement, consistent with a role of D₂ and D₃ receptors in modulating this behavior. The current study supports an important role for D₃ receptors in the basolateral amygdala and lateral habenula in cue-induced reinstatement.     

The orexin system regulates alcohol-seeking in rats

1. Orexin-containing neurons have been implicated in feeding, sleep-wake cycles and more recently in drug-seeking behaviour. 2. Pretreatment of alcohol-preferring (iP) rats with an orexin1 receptor antagonist (SB-334867, 20 mg kg(-1), intraperitoneally) completely abolished an olfactory cue-induced reinstatement of alcohol-seeking behaviour, and also attenuated alcohol responding under an operant fixed ratio regimen without affecting water responding. 3. The mRNA encoding orexin within the hypothalamus was expressed at a similar density in iP and non-preferring (NP) rats; chronic consumption of ethanol in iP rats did not significantly regulate the density of this expression, but did increase the area of expression within the lateral, but not medial, hypothalamus. 4. These data indicate that while orexin may not be implicated in the development of an alcohol preference, re-exposure of cues previously associated with alcohol availability is sufficient and adequate to activate orexin-containing neurons and drive reinstatement of alcohol-seeking.     

MPEP, mGlu5 receptor antagonist, regulates NPYmRNA expression in hippocampal and amygdalar neurons

Our earlier studies showed that the metabotropic glutamate receptor 5 (mGluR5) antagonist, MPEP, could regulate neuropeptide Y (NPY) neurons in the amygdala, influencing both peptide expression and its antianxiety effects. Two brain structures are particularly engaged in a regulation of anxiety, namely the amygdala and also the hippocampus. They both belong to the limbic system and contain NPY neurons and mGlu5 receptors. Therefore, in the present study, we examined the effect of MPEP on NPY and NPYmRNA expression in the amygdala and the hippocampus of the rat brain. NPY expression was studied by immunohistochemical method, and radioimmunoassay, and the NPY synthesis was examined using NPYmRNA in situ hybridization. Immunohistochemical localization of mGluR5 was also carried out. It was found that MPEP given 3 times every 8 h potently decreased NPYmRNA expression 30 min after the last dose in both those structures (to 8-20% of the control level). After single MPEP treatment, we did not observe any changes in NPYmRNA level in the hippocampus, and its decrease in the amygdala 6 h after MPEP administration. The obtained results suggest a positive regulatory control of NPY synthesis by mGlu5 receptors in hippocampal and amygdalar neurons.