Dopaminergic regulation of inhibitory and excitatory transmission in the basolateral amygdala-prefrontal cortical pathway

TRPV1-dependent and -independent alterations in the limbic cortex of neuropathic mice: impact on glial caspases and pain perception

During neuropathic pain, caspases are activated in the limbic cortex. We investigated the role of TRPV1 channels and glial caspases in the mouse prelimbic and infralimbic (PL-IL) cortex after spared nerve injury (SNI). Reverse transcriptase-polymerase chain reaction, western blots, and immunfluorescence showed overexpression of several caspases in the PL-IL cortex 7 days postinjury. Caspase-3 release and upregulation of AMPA receptors in microglia, caspase-1 and IL-1β release in astrocytes, and upregulation of Il-1 receptor-1, TRPV1, and VGluT1 in glutamatergic neurons, were also observed. Of these alterations, only those in astrocytes persisted in SNI Trpv1(-/-) mice. A pan-caspase inhibitor, injected into the PL-IL cortex, reduced mechanical allodynia, this effect being reduced but not abolished in Trpv1(-/-) mice. Single-unit extracellular recordings in vivo following electrical stimulation of basolateral amygdala or application of pressure on the hind paw, showed increased excitatory pyramidal neuron activity in the SNI PL-IL cortex, which also contained higher levels of the endocannabinoid 2-arachidonoylglycerol. Intra-PL-IL cortex injection of mGluR5 and NMDA receptor antagonists and AMPA exacerbated, whereas TRPV1 and AMPA receptor antagonists and a CB(1) agonist inhibited, allodynia. We suggest that SNI triggers both TRPV1-dependent and independent glutamate- and caspase-mediated cross-talk among IL-PL cortex neurons and glia, which either participates or counteracts pain.

Histone H3 phosphoacetylation is critical for heroin-induced place preference

We investigated the role of histone H3 phosphoacetylation in the nucleus accumbens (NAc) in heroin-conditioned place preference paradigm. Heroin could dose-dependently increase histone H3 phosphoacetylation specifically in the NAc and could enhance heroin place preference. Injection of trichostatin A into the NAc significantly augmented heroin-induced histone H3 phosphoacetylation and enhanced heroin place preference. Conversely, injection of MK-801 into the NAc attenuated histone H3 phosphoacetylation and reduced heroin place preference. These data suggest that histone H3 phosphoacetylation in the NAc may play a critical role in heroin addiction.

Differential neuronal changes in medial prefrontal cortex, basolateral amygdala and nucleus accumbens after postweaning social isolation

The mesocorticolimbic system contains dopamine (DA)-producing neurons in the ventral tegmental area (VTA) and their projection targets, including the medial prefrontal cortex (mPFC), amygdala (AMY) and nucleus accumbens (NAc). Disruption of this system might attribute to mental illnesses. In the present study, we adopted the postweaning social isolation paradigm to model neuropsychiatric disorders and studied the functional and structural changes of the mesocorticolimbic system. After 8-9 weeks of isolation, rats exhibited hyperlocomotor activity and impaired sensorimotor gating compared to group-reared controls. However, the number of tyrosine hydroxylase-positive VTA neurons and the volume of VTA were not affected. Comparing with group-reared controls, the DA levels in the isolation-reared were not altered in the VTA, mPFC and NAc but decreased in the AMY. In the structural aspect, dendritic features of layer II/III pyramidal mPFC neurons; pyramidal neurons in the basolateral nucleus of amygdala (BLA) and medium spiny neurons in the core region of the NAc (NAcc) were examined. Interestingly, the neuronal changes were region-specific. The mPFC neurons had reduced dendritic complexity, spine density and elongated terminal branches. The BLA neurons had extensive dendritic arbors with short branches but unchanged spine density. The NAcc neurons had reduced total dendritic length but the segment length and spine density remained the same. Together, the results demonstrated the structural and functional changes in the mesocorticolimbic DA system of socially isolated rats. These changes may account for the behavioral impairments in these rats and attribute to the susceptibility to mental disorders related to schizophrenia and depression.

Repeated amphetamine exposure disrupts dopaminergic modulation of amygdala-prefrontal circuitry and cognitive/emotional functioning

Repeated exposure to psychostimulants such as amphetamine (AMPH) disrupts cognitive and behavioral processes mediated by the medial prefrontal cortical (mPFC) and basolateral amygdala (BLA). The present study investigated the effects of repeated AMPH exposure on the neuromodulatory actions of dopamine (DA) on BLA-mPFC circuitry and cognitive/emotional processing mediated by these circuits. Rats received five AMPH (2 mg/kg) or saline injections (controls) over 10 d, followed by 2-4 week drug washout. In vivo neurophysiological extracellular recordings in urethane-anesthetized rats were used to obtain data from mPFC neurons that were either inhibited or excited by BLA stimulation. In controls, acute AMPH attenuated BLA-evoked inhibitory or excitatory responses; these effects were mimicked by selective D(2) or D(1) agonists, respectively. However, in AMPH-treated rats, the ability of these dopaminergic manipulations to modulate BLA-driven decreases/increases in mPFC activity was abolished. Repeated AMPH also blunted the excitatory effects of ventral tegmental area stimulation on mPFC neural firing. Behavioral studies assessed the effect of repeated AMPH on decision making with conditioned punishment, a process mediated by BLA-mPFC circuitry and mesocortical DA. These treatments impaired the ability of rats to use conditioned aversive stimuli (footshock-associated cue) to guide the direction of instrumental responding. Collectively, these data suggest that repeated AMPH exposure can lead to persistent disruption of dopaminergic modulation of BLA-mPFC circuitry, which may underlie impairments in cognitive/emotional processing observed in stimulant abusers. Furthermore, they suggest that impairments in decision making guided by aversive stimuli observed in stimulant abusers may be the result of repeated drug exposure.

Cannabinoid transmission in the basolateral amygdala modulates fear memory formation via functional inputs to the prelimbic cortex

The cannabinoid CB1 receptor system is critically involved in the control of associative fear memory formation within the amygdala-prefrontal cortical pathway. The CB1 receptor is found in high concentrations in brain structures that are critical for emotional processing, including the basolateral amygdala (BLA) and the prelimbic division (PLC) of the medial prefrontal cortex (mPFC). However, the precise role of CB1 receptor transmission within the BLA during the processing of fear memory is not fully understood. We examined the potential role of BLA CB1 receptor transmission during an olfactory fear-conditioning procedure in rats by pharmacologically modulating CB1 cannabinoid transmission directly within the BLA. We report that blockade of BLA CB1 receptor transmission prevents the acquisition of associative fear memory, while having no effect on the recall or consolidation of these memories. In contrast, intra-BLA activation of CB1 receptor transmission or blockade of endocannabinoid reuptake strongly potentiated the emotional salience of normally subthreshold fear-conditioning stimuli. In addition, pharmacological inactivation of the mPFC before intra-BLA CB1 activation blocked CB1-receptor-mediated potentiation of fear memory formation. In vivo single-unit electrophysiological recordings within the PLC revealed that modulation of BLA CB1 receptor transmission strongly influences neuronal activity within subpopulations of PLC neurons, with blockade of intra-BLA CB1 receptor transmission inhibiting spontaneous PLC neuronal activity and activation of CB1 receptors producing robust activation, in terms of neuronal firing frequency and bursting activity. Thus, cannabinoid transmission within the BLA strongly modulates the processing of associative fear memory via functional interactions with PLC neuronal populations.

Power spectrum scale invariance identifies prefrontal dysregulation in paranoid schizophrenia

Theory and experimental evidence suggest that complex living systems function close to the boundary of chaos, with erroneous organization to an improper dynamical range (too stiff or chaotic) underlying system-wide dysregulation and disease. We hypothesized that erroneous organization might therefore also characterize paranoid schizophrenia, via optimization abnormalities in the prefrontal-limbic circuit regulating emotion. To test this, we acquired fMRI scans from 35 subjects (N = 9 patients with paranoid schizophrenia and N = 26 healthy controls), while they viewed affect-valent stimuli. To quantify dynamic regulation, we analyzed the power spectrum scale invariance (PSSI) of fMRI time-courses and computed the geometry of time-delay (Poincaré) maps, a measure of variability. Patients and controls showed distinct PSSI in two clusters (k(1) : Z = 4.3215, P = 0.00002 and k(2) : Z = 3.9441, P = 0.00008), localized to the orbitofrontal/medial prefrontal cortex (Brodmann Area 10), represented by β close to white noise in patients (β ≈ 0) and in the pink noise range in controls (β ≈ -1). Interpreting the meaning of PSSI differences, the Poincaré maps indicated less variability in patients than controls (Z = -1.9437, P = 0.05 for k(1) ; Z = -2.5099, P = 0.01 for k(2) ). That the dynamics identified Brodmann Area 10 is consistent with previous schizophrenia research, which implicates this area in deficits of working memory, executive functioning, emotional regulation and underlying biological abnormalities in synaptic (glutamatergic) transmission. Our results additionally cohere with a large body of work finding pink noise to be the normal range of central function at the synaptic, cellular, and small network levels, and suggest that patients show less supple responsivity of this region.

Requirement of dopamine signaling in the amygdala and striatum for learning and maintenance of a conditioned avoidance response

Two-way active avoidance (2WAA) involves learning Pavlovian (association of a sound cue with a foot shock) and instrumental (shock avoidance) contingencies. To identify regions where dopamine (DA) is involved in mediating 2WAA, we restored DA signaling in specific brain areas of dopamine-deficient (DD) mice by local reactivation of conditionally inactivated Th genes using viral gene therapy. Among all targeted areas--prefrontal cortex (PFC), amygdala, ventral striatum, dorsal striatum, and whole striatum--only restoration of DA signaling to both the whole striatum together with the amygdala enabled DD mice to acquire 2WAA. However, after prolonged overtraining during which DD mice had DA synthesis systemically reconstituted pharmacologically with L-3,4-dihydroxyphenylalanine (L-Dopa), DA signaling in the striatum alone was sufficient to maintain 2WAA, whereas DA signaling in the PFC together with the amygdala was insufficient to maintain 2WAA. Our results indicate that learning 2WAA requires DA signaling in both the amygdala and the entire striatum; however, after sufficient training, DA signaling in the striatum alone can maintain the learned avoidance behavior.

Transient inflammation-induced ongoing pain is driven by TRPV1 sensitive afferents

Background

Neuropathic pain is a chronic disease resulting from dysfunction within the "pain matrix". The basolateral amygdala (BLA) can modulate cortical functions and interactions between this structure and the medial prefrontal cortex (mPFC) are important for integrating emotionally salient information. In this study, we have investigated the involvement of the transient receptor potential vanilloid type 1 (TRPV1) and the catabolic enzyme fatty acid amide hydrolase (FAAH) in the morphofunctional changes occurring in the pre-limbic/infra-limbic (PL/IL) cortex in neuropathic rats.

Results

The effect of N-arachidonoyl-serotonin (AA-5-HT), a hybrid FAAH inhibitor and TPRV1 channel antagonist, was tested on nociceptive behaviour associated with neuropathic pain as well as on some phenotypic changes occurring on PL/IL cortex pyramidal neurons. Those neurons were identified as belonging to the BLA-mPFC pathway by electrical stimulation of the BLA followed by hind-paw pressoceptive stimulus application. Changes in their spontaneous and evoked activity were studied in sham or spared nerve injury (SNI) rats before or after repeated treatment with AA-5-HT. Consistently with the SNI-induced changes in PL/IL cortex neurons which underwent profound phenotypic reorganization, suggesting a profound imbalance between excitatory and inhibitory responses in the mPFC neurons, we found an increase in extracellular glutamate levels, as well as the up-regulation of FAAH and TRPV1 in the PL/IL cortex of SNI rats. Daily treatment with AA-5-HT restored cortical neuronal activity, normalizing the electrophysiological changes associated with the peripheral injury of the sciatic nerve. Finally, a single acute intra-PL/IL cortex microinjection of AA-5-HT transiently decreased allodynia more effectively than URB597 or I-RTX, a selective FAAH inhibitor or a TRPV1 blocker, respectively.

Conclusion

These data suggest a possible involvement of endovanilloids in the cortical plastic changes associated with peripheral nerve injury and indicate that therapies able to normalize endovanilloid transmission may prove useful in ameliorating the symptoms and central sequelae associated with neuropathic pain.

Opponency revisited: competition and cooperation between dopamine and serotonin

Affective valence lies on a spectrum ranging from punishment to reward. The coding of such spectra in the brain almost always involves opponency between pairs of systems or structures. There is ample evidence for the role of dopamine in the appetitive half of this spectrum, but little agreement about the existence, nature, or role of putative aversive opponents such as serotonin. In this review, we consider the structure of opponency in terms of previous biases about the nature of the decision problems that animals face, the conflicts that may thus arise between Pavlovian and instrumental responses, and an additional spectrum joining invigoration to inhibition. We use this analysis to shed light on aspects of the role of serotonin and its interactions with dopamine.

Biological and psychological interventions: trends in substance use disorders intervention research

Substance use disorders (SUDs) cause serious medical, financial, and social problems for individuals and society. Thus, understanding the large body of research exploring biological and psychological intervention trends is important to researchers and clinicians. Historically, psychological interventions have dominated the literature, in spite of modest outcome data. Recently, a refocus on biological intervention research has led to results suggested as efficacious in treatment of SUDs with promising clinical potential. The current review indicates that there seems to be some incongruence between this growing body of physiological research and psychological clinical research and practice. The current review explores these trends and argues for more solid integration of biological and psychological research and treatment strategies for SUDs, as well as heightened efforts toward translation of research into practice.

Enhanced prefrontal function with pharmacotherapy on a response inhibition task in adolescent bipolar disorder

OBJECTIVE

The aim of the current study is to determine whether pharmacotherapy normalizes cognitive circuitry function supporting voluntary behavioral inhibition in adolescent bipolar disorder.

METHOD

Healthy controls and unmedicated patients with DSM-IV adolescent bipolar disorder in manic, mixed, or hypomanic episodes were matched on demographics and IQ (n = 13 per group; mean age = 14.4 ± 2.4 years). Functional magnetic resonance imaging studies were performed at baseline and after 14 weeks, during which time patients with adolescent bipolar disorder were treated initially with second-generation antipsychotics (SGAs) followed by lamotrigine monotherapy. The primary outcome measure was a Response Inhibition Task, which involved a planned motor response, already "on the way" to execution, that had to be voluntarily inhibited by the subjects in the trials in which a stop signal was presented. There were 6 blocks, each with a predominant rate of either "go" or "stop" trials. The study was conducted from June 2006 through July 2009.

RESULTS

All patients showed significant improvement (P < .001) in both the manic and depressive symptoms from baseline. Behavioral data showed that accuracy improved over 14 weeks in patients and healthy controls. Significant time by group interaction effects for the difference between stop versus go blocks showed greater increases of activation in prefrontal (left inferior and middle frontal gyri and medial frontal gyrus bilaterally) and temporal (left superior temporal gyrus and right middle temporal gyrus) regions and greater decreases in activation in right putamen and bilateral thalamus at follow-up in the adolescent bipolar disorder group than in healthy controls. Increased ventrolateral prefrontal cortex function was related to clinical treatment response.

CONCLUSIONS

Treatment with SGAs followed by lamotrigine monotherapy enhanced prefrontal and temporal lobe activity during a Response Inhibition Task demonstrating the reversal of disorder-relevant neural circuitry dysfunction in patients with adolescent bipolar disorder. Patient performance was not slowed down with this treatment regimen.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00176228.

The basolateral amygdala differentially regulates conditioned neural responses within the nucleus accumbens core and shell

The ability to process information regarding reward-predictive cues involves a diverse network of neural substrates. Given the importance of the nucleus accumbens (NAc) and the basolateral amygdala (BLA) in associative reward processes, recent research has examined the functional importance of BLA-NAc interactions. Here, multi-neuron extracellular recordings of NAc neurons coupled to microinfusion of GABAA and GABAB agonists into the BLA were employed to determine the functional contribution of the BLA to phasic neural activity across the NAc core and shell during a cued-instrumental task. NAc neural response profiles prior to BLA inactivation exhibited largely indistinguishable activity across the core and shell. However, for NAc neurons that displayed cue-related increases in firing rates during the task, BLA inactivation significantly reduced this activity selectively in the core (not shell). Additionally, phasic increases in firing rate in the core (not shell) immediately following the lever press response were also significantly reduced following BLA manipulation. Concurrent with these neural changes, BLA inactivation caused a significant increase in latency to respond for rewards and a decrease in the percentage of trials in which animals made a conditioned approach to the cue. Together, these results suggest that an excitatory projection from the BLA provides a selective contribution to conditioned neural excitations of NAc core neurons during a cued-instrumental task, providing insight into the underlying neural circuitry that mediates responding to reward-predictive cues.

Differences in responsiveness of mediodorsal thalamic and medial prefrontal cortical neurons to social interaction and systemically administered phencyclidine in rats

Phencyclidine (PCP) is a psychotomimetic drug that induces schizophrenia-like symptoms in healthy individuals and behavioral abnormalities with corresponding symptoms of schizophrenia in non-human animals. Our previous studies showed that systemically administered PCP produces tonic activation of neurons in the medial prefrontal cortex (mPFC) of rats and that this activation is mainly via excitatory inputs from regions outside the mPFC. Such long-lasting activation of PFC neurons is now considered to be a pivotal factor in PCP-induced behavioral abnormalities. Although our previous study identified the ventral hippocampus as a possible source of the excitatory inputs, it is not the only source innervating the mPFC. Several regions such as the thalamus also have monosynaptic projections to the mPFC. Recently, increased c-fos expression by systemic PCP administration was reported in the mediodorsal nucleus of the thalamus (MD) and the centromedial nucleus of the thalamus (CM), which have strong reciprocal innervations with the mPFC. However, few studies have reported effects of PCP on the firing activity of MD/CM neurons in unanesthetized animals. In the current study in freely moving rats, we examined effects of systemically administered PCP on the spontaneous firing activity of the MD/CM, after identifying the response properties of recorded neurons in social interaction with an unfamiliar partner. About 30% of MD/CM neurons recorded exhibited tonic excitation following systemic PCP administration, whereas only a few neurons (7%) were inhibited by PCP. The proportion of MD neurons activated by systemic PCP administration was about half of that in the mPFC. Although the proportion of neurons responsive to social interaction did not differ between the two regions (40%), neurons activated during social interaction in the mPFC (90%) were more likely to be affected by systemic PCP administration than those in the MD/CM (45%). These results suggest that neurons responsive to social interaction in the mPFC may be differently affected by PCP than those in the MD/CM.

Altered neurocircuitry in the dopamine transporter knockout mouse brain

The plasma membrane transporters for the monoamine neurotransmitters dopamine, serotonin, and norepinephrine modulate the dynamics of these monoamine neurotransmitters. Thus, activity of these transporters has significant consequences for monoamine activity throughout the brain and for a number of neurological and psychiatric disorders. Gene knockout (KO) mice that reduce or eliminate expression of each of these monoamine transporters have provided a wealth of new information about the function of these proteins at molecular, physiological and behavioral levels. In the present work we use the unique properties of magnetic resonance imaging (MRI) to probe the effects of altered dopaminergic dynamics on meso-scale neuronal circuitry and overall brain morphology, since changes at these levels of organization might help to account for some of the extensive pharmacological and behavioral differences observed in dopamine transporter (DAT) KO mice. Despite the smaller size of these animals, voxel-wise statistical comparison of high resolution structural MR images indicated little morphological change as a consequence of DAT KO. Likewise, proton magnetic resonance spectra recorded in the striatum indicated no significant changes in detectable metabolite concentrations between DAT KO and wild-type (WT) mice. In contrast, alterations in the circuitry from the prefrontal cortex to the mesocortical limbic system, an important brain component intimately tied to function of mesolimbic/mesocortical dopamine reward pathways, were revealed by manganese-enhanced MRI (MEMRI). Analysis of co-registered MEMRI images taken over the 26 hours after introduction of Mn²⁺ into the prefrontal cortex indicated that DAT KO mice have a truncated Mn²⁺ distribution within this circuitry with little accumulation beyond the thalamus or contralateral to the injection site. By contrast, WT littermates exhibit Mn²⁺ transport into more posterior midbrain nuclei and contralateral mesolimbic structures at 26 hr post-injection. Thus, DAT KO mice appear, at this level of anatomic resolution, to have preserved cortico-striatal-thalamic connectivity but diminished robustness of reward-modulating circuitry distal to the thalamus. This is in contradistinction to the state of this circuitry in serotonin transporter KO mice where we observed more robust connectivity in more posterior brain regions using methods identical to those employed here.

Human dopamine receptor D2/D3 availability predicts amygdala reactivity to unpleasant stimuli

Dopamine (DA) modulates the response of the amygdala. However, the relation between dopaminergic neurotransmission in striatal and extrastriatal brain regions and amygdala reactivity to affective stimuli has not yet been established. To address this issue, we measured DA D2/D3 receptor (DRD2/3) availability in twenty-eight healthy men (nicotine-dependent smokers and never-smokers) using positron emission tomography with [18F]fallypride. In the same group of participants, amygdala response to unpleasant visual stimuli was determined using blood oxygen level-dependent (BOLD) functional magnetic resonance imaging. The effects of DRD2/3 availability in emotion-related brain regions and nicotine dependence on amygdala response to unpleasant stimuli were examined by multiple regression analysis. We observed enhanced prefrontal DRD2/3 availability in those individuals with higher amygdala response to unpleasant stimuli. As compared to never-smokers, smokers showed an attenuated amygdala BOLD response to unpleasant stimuli. Thus, individuals with high prefrontal DRD2/3 availability may be more responsive toward aversive and stressful information. Through this mechanism, dopaminergic neurotransmission might influence vulnerability for affective and anxiety disorders. Neuronal reactivity to unpleasant stimuli seems to be reduced by smoking. This observation could explain increased smoking rates in individuals with mental disorders.

Plastic synaptic networks of the amygdala for the acquisition, expression, and extinction of conditioned fear

The last 10 years have witnessed a surge of interest for the mechanisms underlying the acquisition and extinction of classically conditioned fear responses. In part, this results from the realization that abnormalities in fear learning mechanisms likely participate in the development and/or maintenance of human anxiety disorders. The simplicity and robustness of this learning paradigm, coupled with the fact that the underlying circuitry is evolutionarily well conserved, make it an ideal model to study the basic biology of memory and identify genetic factors and neuronal systems that regulate the normal and pathological expressions of learned fear. Critical advances have been made in determining how modified neuronal functions upon fear acquisition become stabilized during fear memory consolidation and how these processes are controlled in the course of fear memory extinction. With these advances came the realization that activity in remote neuronal networks must be coordinated for these events to take place. In this paper, we review these mechanisms of coordinated network activity and the molecular cascades leading to enduring fear memory, and allowing for their extinction. We will focus on Pavlovian fear conditioning as a model and the amygdala as a key component for the acquisition and extinction of fear responses.

Localization of CART-positive neurons in the amygdaloid body and the relationship between their immunoreactivity and the sex steroid level

This is the first study reporting the locations of neurons expressing CART peptide (cocaine-amphetamine-regulated transcript) throughout all the nuclear and paleocortical formations of the amygdaloid body (AB) and demonstrating the effects of sex steroids on immunoreactivity. The immunocytochemical reaction was performed on frontal brain sections from adult rats (seven females in estrus, seven females in metestrus, and seven males). The proportions of immunoreactive neurons to the total number of neurons in adjacent sections stained by the Nissl method were assessed in estrus and metestrus. In the dorsomedial and posterior cortical nuclei and the lateral capsular subnucleus of the central field, the relative numbers of immunoreactive neurons at estrus were significantly greater than at metestrus. These results provide evidence of the involvement of the olfactory and integrative centers of the AB in the pathogenesis of drug dependence and show that new and efficient methods of gene therapy might be developed using the intranasal route for drug administration.

Inhibition of fatty-acid amide hydrolase and CB1 receptor antagonism differentially affect behavioural responses in normal and PCP-treated rats

The 'cannabinoid hypothesis' of schizophrenia tulates that over-activity of the endocannabinoid system might contribute to the aetiology of schizophrenia. In keeping with this hypothesis, increased expression of CB1 receptors, elevation of the endocannabinoid anandamide (AEA) and cannabinoid-induced cognitive changes have been reported in animal models of schizophrenia and psychotic patients. In this study we measured brain endocannabinoid levels and [35S]GTPgammaS binding stimulated by the CB receptor agonist CP55,940 in rats undergoing withdrawal from subchronic administration of phencyclidine (PCP), a well-established pharmacological model of schizophrenia. We also investigated whether systemic application of the fatty-acid amide hydrolase (FAAH) inhibitor URB597 or CB1 receptor blockade by AM251 affected the following PCP-induced behavioural deficits reminiscent of schizophrenia-like symptoms: (1) working-memory impairment (cognitive deficit), (2) social withdrawal (negative symptom), and (3) hyperactivity in response to d-amphetamine challenge (positive symptoms). PCP-treated rats showed increased endocannabinoid levels in the nucleus accumbens and ventral tegmental area, whereas CB1 receptor expression and CP55,940-stimulated [35S]GTPgammaS binding were unaltered. URB597 reversed the PCP-induced social withdrawal but caused social withdrawal and working-memory deficits in saline-treated rats that were comparable to those observed after PCP treatment. Administration of AM251 ameliorated the working-memory deficit in PCP-treated rats, but impaired working memory in saline-injected controls. Taken together, these results suggest that FAAH inhibition may improve negative symptoms in PCP-treated rats but produce deleterious effects in untreated animals, possibly by disturbing endocannabinoid tone. A similar pattern (beneficial for schizophrenia-related cognitive deficits, but detrimental under normal conditions) accompanies CB1 receptor blockade.

Prefrontal control of fear: more than just extinction

Although fear research has largely focused on the amygdala, recent findings highlight cortical control of the amygdala in the service of fear regulation. In rodent models, it is becoming well established that the infralimbic (IL) prefrontal cortex plays a key role in extinction learning, and recent findings are uncovering molecular mechanisms involved in extinction-related plasticity. Furthermore, mounting evidence implicates the prelimbic (PL) prefrontal cortex in the production of fear responses. Both IL and PL integrate inputs from the amygdala, as well as other structures to gate the expression of fear via projections to inhibitory or excitatory circuits within the amygdala. We suggest that dual control of the amygdala by separate prefrontal modules increases the flexibility of an organism's response to danger cues.

The COMT Val108/158Met polymorphism and medial temporal lobe volumetry in patients with schizophrenia and healthy adults

Abnormalities of the medial temporal lobe have been consistently demonstrated in schizophrenia. A common functional polymorphism, Val108/158Met, in the putative schizophrenia susceptibility gene, catechol-O-methyltransferase (COMT), has been shown to influence medial temporal lobe function. However, the effects of this polymorphism on volumes of medial temporal lobe structures, particularly in patients with schizophrenia, are less clear. Here we measured the effects of COMT Val108/158Met genotype on the volume of two regions within the medial temporal lobe, the amygdala and hippocampus, in patients with schizophrenia and healthy control subjects. We obtained MRI and genotype data for 98 schizophrenic patients and 114 matched controls. An automated atlas-based segmentation algorithm was used to generate volumetric measures of the amygdala and hippocampus. Regression analyses included COMT met allele load as an additive effect, and also controlled for age, intracranial volume, gender and acquisition site. Across patients and controls, each copy of the COMT met allele was associated on average with a 2.6% increase in right amygdala volume, a 3.8% increase in left amygdala volume and a 2.2% increase in right hippocampus volume. There were no effects of COMT genotype on volumes of the whole brain and prefrontal regions. Thus, the COMT Val108/158Met polymorphism was shown to influence medial temporal lobe volumes in a linear-additive manner, mirroring its effect on dopamine catabolism. Taken together with previous work, our data support a model in which lower COMT activity, and a resulting elevation in extracellular dopamine levels, stimulates growth of medial temporal lobe structures.

Dopamine D4-receptor modulation of cortical neuronal network activity and emotional processing: Implications for neuropsychiatric disorders

Dopamine (DA) transmission within cortical and subcortical structures is involved critically in the processing of emotionally relevant sensory information. Three interconnected neural regions, the medial prefrontal cortex (mPFC), basolateral nucleus of the amygdala (BLA) and the ventral tegmental area (VTA) have received considerable experimental attention, both in animal and clinical research models, as essential interconnected processors of emotional information. Neuronal network activity within both the mPFC and BLA are strongly modified by DA inputs from the VTA through both DA D(2)-like and D(1)-like receptors. However, emerging evidence from clinical, genetic, behavioral and electrophysiological investigations demonstrates a critical role for the DA D(4)-receptor subtype as a crucial modulator of emotional memory encoding and expression, both at the level of the single neuron, and at the systems level. In this review, we will examine recent evidence at the neuronal, behavioral and genetic levels of analysis that increasingly demonstrates an important role for DA D(4) transmission within cortical and subcortical emotional processing circuits. We will present evidence and some theoretical frameworks suggesting how disturbances in D(4)-receptor related neural circuitry may be involved in the neuropathological manifestations common in many neuropsychiatric disorders including schizophrenia, attention-deficit hyperactivity disorder (ADHD) and addiction.

Corticotropin releasing factor and neuroplasticity in cocaine addiction

Corticotropin releasing factor (CRF), one of the major effectors of stress, plays a major role in the natural course of drug addiction by accelerating the acquisition of psychostimulant self-administration and increasing incentive motivation for the drug itself and for drug-associated stimuli. Stress-induced CRF is also considered a predictor of relapse and is responsible for feelings of anxiety and distress during cocaine withdrawal. Despite this knowledge, the role of CRF has not been explored in the context of recent research on reward-related learning, built on the hypothesis that neuroplastic changes in the mesocorticolimbic circuitry underlie addiction. The present review explores the effects of stress on the pattern of interaction between CRF, dopamine and glutamate in distinct structures of the mesocorticolimbic circuitry, including the ventral tegmental area (VTA), amygdala, bed nucleus of stria terminalis (BNST) and the prefrontal cortex (PFC), after acute and chronic cocaine consumption as well as in early withdrawal and protracted abstinence. A better knowledge of the neurochemical and cellular mechanisms involved in these interactions would be useful to elucidate the role of CRF in cocaine-induced neuronal plasticity, which could be useful in developing new pharmacological strategies for the treatment of cocaine addiction.

Neural correlates of resolving uncertainty in driver's decision making

Neural correlates of driving and of decision making have been investigated separately, but little is known about the underlying neural mechanisms of decision making in driving. Previous research discusses two types of decision making: reward-weighted decision making and cost-weighted decision making. There are many reward-weighted decision making neuroimaging studies but there are few cost-weighted studies. Considering that driving involves serious risk, it is assumed that decision making in driving is cost weighted. Therefore, neural substrates of cost-weighted decision making can be assessed by investigation of driver's decision making. In this study, neural correlates of resolving uncertainty in driver's decision making were investigated. Turning right in left-hand traffic at a signalized intersection was simulated by computer graphic animation based videos. When the driver's view was occluded by a big truck, the uncertainty of the oncoming traffic was resolved by an in-car video assist system that presented the driver's occluded view. Resolving the uncertainty reduced activity in a distributed area including the amygdala and anterior cingulate. These results implicate the amygdala and anterior cingulate as serving a role in cost-weighted decision making.

Heterogeneous dopamine populations project to specific subregions of the primate amygdala

Amygdala dysfunction has been reported among patients with various psychiatric disorders, and dopamine is critical to the amygdala's ability to mediate fear conditioning. Recent work indicates that the midbrain dopaminergic neurons have heterogeneous receptor and membrane channel profiles, as well as differential physiologic responses to discrete stimuli. To begin understanding how dopamine affects amygdala physiology and pathology in higher primates, we mapped the inputs from the midbrain dopaminergic neurons to various amygdala nuclei in the monkey using retrograde and anterograde tracing techniques, and single and double immunofluorescence histochemistry for tracer and tyrosine hydroxylase, a dopamine marker. Our results show that the primate amygdala as a whole receives broad input, mostly from the dorsal tier of the substantia nigra, pars compacta, and the A8-retrorubral field. Input from the A10-ventral tegmental area, while present, was less prominent. These results differ from data in the rat, where the midline A10-ventral tegmental area is a major source of dopamine to the amygdala "mesolimbic" pathway. Both the "amygdala proper" and the "extended amygdala" receive the majority of their input from the dorsal tier of the substantia nigra and A8-retrorubral field, but the extended amygdala receives additional modest input from the ventral tier. In addition, the "extended amygdala" structures have a denser input than the "amygdala proper," with the exception of the lateral core of the central nucleus, which receives no input. Our anterograde studies confirm these findings, and revealed fine, diffuse terminal fibers in the amygdala proper, but a denser network of fibers in the extended amygdala outside the lateral core of the central nucleus. These results indicate that the entire extent of the dorsal tier beyond the A10-ventral tegmental area may regulate the amygdala in primates, and subsequently serve as a source of dysfunction in primate psychopathology.

Reacquisition of heroin and cocaine place preference involves a memory consolidation process sensitive to systemic and intra-ventral tegmental area naloxone

To investigate the effect of naloxone on a putative memory consolidation process underlying reacquisition of heroin and cocaine conditioned place preference, four studies were conducted in male Sprague-Dawley rats using a common procedure involving: place conditioning (0.3 or 1mg/kg heroin or 20mg/kg cocaine; x4 sessions), extinction (vehiclex4 sessions), and reconditioning (0 or 1mg/kg heroin or 20mg/kg cocaine; x1 session). Systemic naloxone injections (0, 1 and 3mg/kg) or bilateral intra-ventral tegmental area (VTA) naloxone methiodide infusions (2 nmol in 0.5 microl x side) were administered at different times following reconditioning. Post-reconditioning administration of naloxone dose-dependently blocked, attenuated and had no effect on reacquisition of heroin CPP when administered immediately, 1h and 6h after reconditioning, respectively. The highest dose of naloxone also blocked reacquisition of cocaine CPP, and did not produce a conditioned place aversion in heroin-naïve and heroin pre-treated animals. Post-reconditioning infusions in the VTA, but not in adjacent structures, blocked reacquisition of heroin CPP when administered immediately, but not 6h, after reconditioning. These data suggest that reacquisition of drug-cues associations involves a memory consolidation process sensitive to manipulations of the endogenous opioid system, and indicate that opioid receptors in the VTA may be critically involved in the re-emergence of drug seeking behavior.

Dopamine is necessary for cue-dependent fear conditioning

Dopamine (DA) is implicated in many behaviors, including motor function, cognition, and reward processing; however, the role of DA in fear processing remains equivocal. To examine the role of DA in fear-related learning, dopamine-deficient (DD) mice were tested in a fear-potentiated startle paradigm. DA synthesis can be restored in DD mice through administration of 3, 4-dihydroxy-l-phenylalanine (l-Dopa), thereby permitting the assessment of fear processing in either a DA-depleted or -replete state. Fear-potentiated startle was absent in DD mice but could be restored by l-Dopa administration immediately after fear conditioning. Selective viral-mediated restoration of DA synthesis within the ventral tegmental area fully restored fear learning in DD mice, and restoration of DA synthesis to DA neurons projecting to the basolateral amygdala restored short-term memory but not long-term memory or shock sensitization. We also demonstrate that the DA D(1) receptor (D(1)R) and D(2)-like receptors are necessary for cue-dependent fear learning. These findings indicate that DA acting on multiple receptor subtypes within multiple target regions facilitates the stabilization of fear memory.

Repeated administration of amphetamine induces a shift of the prefrontal cortex and basolateral amygdala motor function

The role of the medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) in the expression of behavioural locomotor sensitization to amphetamine (Amph) has been poorly studied. In the present study, we investigated how lidocaine infused in the mPFC or BLA modulated motor responses to acute and repeated (sensitization) Amph administration. We showed that reversible blockade of mPFC or BLA by lidocaine increased both locomotor and rearing responses to acute Amph, but blocked the expression of behavioural sensitization to Amph. These findings indicate that under free-lidocaine conditions repeated administration of Amph would produce a shift of mPFC and BLA motor function from an inhibitory to a facilitatory role in response to Amph. We propose that this phenomenon may be of major critical importance in the development of drug dependence.

Sustained conditioned responses in prelimbic prefrontal neurons are correlated with fear expression and extinction failure

During auditory fear conditioning, it is well established that lateral amygdala (LA) neurons potentiate their response to the tone conditioned stimulus, and that this potentiation is required for conditioned fear behavior. Conditioned tone responses in LA, however, last only a few hundred milliseconds and cannot be responsible for sustained fear responses to a tone lasting tens of seconds. Recent evidence from inactivation and stimulation studies suggests that the prelimbic (PL) prefrontal cortex is necessary for expression of learned fears, but the timing of PL tone responses and correlations with fear behavior have not been studied. Using multichannel unit recording techniques in behaving rats, we observed sustained conditioned tone responses in PL that were correlated with freezing behavior on a second-to-second basis during the presentation of a 30 s tone. PL tone responses were also correlated with conditioned freezing across different experimental phases (habituation, conditioning, extinction). Moreover, the persistence of PL responses after extinction training was associated with failure to express extinction memory. Together with previous inactivation findings, the present results suggest that PL transforms transient amygdala inputs to a sustained output that drives conditioned fear responses and gates the expression of extinction. Given the relatively long latency of conditioned responses we observed in PL (approximately 100 ms after tone onset), we propose that PL integrates inputs from the amygdala, hippocampus, and other cortical sources to regulate the expression of fear memories.

Fundamental contribution by the basolateral amygdala to different forms of decision making

Impairments in decision making about risks and rewards have been observed in patients with amygdala damage. Similarly, lesions of the basolateral amygdala (BLA) in rodents disrupts cost/benefit decision making, reducing preference for larger rewards obtainable after a delay or considerable physical effort. We assessed the effects of inactivation of the BLA on risk- and effort-based decision making, using discounting tasks conducted in an operant chamber. Separate groups of rats were trained on either a risk- or effort-discounting task, consisting of four blocks of 10 free-choice trials. Selection of one lever always delivered a smaller reward (one or two pellets), whereas responding on the other delivered a larger, four pellet reward. For risk discounting, the probability of receiving the larger reward decreased across trial blocks (100-12.5%), whereas on the effort task, the larger reward was delivered after a ratio of presses that increased across blocks (2-20). Infusions of GABA agonists baclofen/muscimol into the BLA disrupted risk discounting, inducing a risk-averse pattern of choice, and increased response latencies and trial omissions, most prominently during trial blocks that provided the greatest uncertainty about the most beneficial course of action. Similar inactivations also increased effort discounting, reducing the preference for larger yet more costly rewards, even when the relative delays to reward delivery were equalized across response options. These findings point to a fundamental role for the BLA in different forms of cost/benefit decision making, facilitating an organism's ability to overcome a variety of costs (work, uncertainty, delays) to promote actions that may yield larger rewards.

Dopamine D1 versus D4 receptors differentially modulate the encoding of salient versus nonsalient emotional information in the medial prefrontal cortex

Dopamine (DA) transmission plays a critical role in the processing of emotionally salient information and in associative learning and memory processes. Within the mammalian brain, neurons within the medial prefrontal cortex (mPFC) are involved critically in the encoding, expression, and extinction of emotionally salient learned information. Within the mPFC, dopaminergic transmission is involved importantly in controlling attentional and motivational processes, particularly within the context of emotionally salient sensory information. Considerable evidence suggests differential roles for DA D(1)-like versus D(2)-like receptors, including the D(4) receptor subtype, in the regulation of neuronal activity and emotional processing within the mPFC. Using an olfactory fear-conditioning assay in rats, we compared the roles of DA D(1) versus D(4) receptor activation during the encoding and recall phases of emotional learning and memory. We report that specific activation of DA D(4) receptors within the mPFC strongly potentiates the salience of normally nonsalient emotional associative fear memories and blocks the encoding of suprathreshold conditioned fear associations. However, D(4) receptor activation has no effect on the recall of previously learned emotionally salient conditioned memories. In contrast, intra-mPFC D(1) receptor activation failed to increase the emotional salience of subthreshold fear stimuli but completely blocked the expression of previously learned emotionally relevant information, demonstrating that DA D(4) versus D(1) subtype receptor transmission within the mPFC plays distinct functional roles in the processing of emotionally salient versus nonsalient associative information and differentially modulates the encoding versus recall phases of emotional memory within the mPFC.

Expression pattern of neural synaptic plasticity marker-Arc in different brain regions induced by conditioned drug withdrawal from acute morphine-dependent rats

AIM

The immediate early gene Arc (activity-regulated cytoskeletal-associated protein) mRNA and protein are induced by strong synaptic activation and rapidly transported into dendrites, where they localize at active synaptic sites. Thus, the Arc mRNA and protein are proposed as a marker of neuronal reactivity to map the neural substrates that are recruited by various stimuli. In the present study, we examined the expression of Arc protein induced by conditioned naloxone-precipitated drug withdrawal in different brain regions of acute morphine-dependent rats. The objective of the present study was to address the specific neural circuits involved in conditioned place aversion (CPA) that has not yet been well characterized.

METHODS

Place aversion was elicited by conditioned naloxone-precipitated drug withdrawal following exposure to a single dose of morphine. An immunohistochemical method was employed to detect the expression of Arc, which was used as a plasticity marker to trace the brain areas that contribute to the formation of the place aversion.

RESULTS

Marked increases in Arc protein levels were found in the medial and lateral prefrontal cortex, the sensory cortex, the lateral striatum and the amygdala. This effect was more pronounced in the basolateral amygdala (BLA), the central nucleus of the amygdala (CeA), and the bed nucleus of the striatal terminals (BNST) when compared with the control group.

CONCLUSION

Our results suggest that these brain regions may play key roles in mediating the negative motivational component of opiate withdrawal.

The role of the striatum in aversive learning and aversive prediction errors

Neuroeconomic studies of decision making have emphasized reward learning as critical in the representation of value-driven choice behaviour. However, it is readily apparent that punishment and aversive learning are also significant factors in motivating decisions and actions. In this paper, we review the role of the striatum and amygdala in affective learning and the coding of aversive prediction errors (PEs). We present neuroimaging results showing aversive PE-related signals in the striatum in fear conditioning paradigms with both primary (shock) and secondary (monetary loss) reinforcers. These results and others point to the general role for the striatum in coding PEs across a broad range of learning paradigms and reinforcer types.

Emotion-based dispositions to rash action: positive and negative urgency

Under heightened emotional states, individuals are more inclined to engage in ill-considered or rash actions than at other times. The authors present evidence for the existence of 2 related traits called positive and negative urgency. The traits refer to individual differences in the disposition to engage in rash action when experiencing extreme positive and negative affect, respectively. The authors provide evidence that these traits are distinct from other dispositions toward rash action and that they play distinct roles in predicting problem levels of involvement in behaviors such as alcohol consumption, binge eating, drug use, and risky sexual behavior. The authors identify facilitative conditions for the emergence of the urgency traits from neuroscience. Certain gene polymorphisms are associated with low levels of serotonin and high levels of dopamine; that pattern of neurotransmitter activity in a brain system linking the orbitofrontal cortex and the amygdala appears to facilitate the development of positive and negative urgency. The authors discuss the implications of this theory.

Differential effects of estrogen receptor alpha and beta specific agonists on social learning of food preferences in female mice

There is an evolutionary advantage to learning food preferences from conspecifics, as social learning allows an individual to bypass the risks associated with trial and error individual learning. The social transmission of food preferences (STFP) paradigm examines this advantage. Females in the proestrus and diestrus phases of the estrous cycle show a prolonged preference for the demonstrated food relative to estrus and ovariectomized females. Additionally, both estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta) knockout mice show impaired social recognition, which suggests that both receptors may be involved in other types of socially dependent learning, including the STFP. The present study investigated the effect of the ERalpha selective agonist PPT (1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole) and the ERbeta selective agonist WAY-200070 (7-Bromo-2-(4-hydroxyphenyl)-1,3-benzoxazol-5-ol) on the STFP. Results showed that ovariectomized (ovx) mice treated with PPT failed to learn the socially acquired preference, while WAY-200070-treated ovx mice showed a two-fold prolonged preference for the food eaten by their demonstrator. The effects of PPT on the socially acquired food preference cannot be explained by effects on the total food intake of the groups or on the type of interaction with the demonstrator mouse. The effects of WAY-200070 may be partially due to effects on Submissive Behavior. The higher WAY-200070 doses produced prolonged preferences similar to those seen previously in intact female mice during the proestrus and diestrus phases. This suggests that the estrous cycle's effects on social learning may be due to the action of ERbeta on Submissive Behavior, or to ERbeta countering that of ERalpha.

Entorhinal cortex inhibits medial prefrontal cortex and modulates the activity states of electrophysiologically characterized pyramidal neurons in vivo

The prefrontal cortex receives multiple inputs from the hippocampal complex, which are thought to drive memory-guided behavior. Moreover, dysfunctions of both regions have been repeatedly associated with several psychiatric disorders. Therefore, understanding the interconnections and modulatory interactions between these regions is essential in evaluating their role in behavior and pathology. The effects of entorhinal cortex (EC) stimulation on the activity of identified medial prefrontal cortex (mPFC) pyramidal neurons were examined using single-unit extracellular recordings and sharp-electrode intracellular recordings in anesthetized rats. Single-pulse electrical stimulation of EC induced a powerful inhibition in the majority of mPFC neurons examined during extracellular recording. Intracellular recording showed that EC stimulation evoked a complex synaptic response, in which the greater proportion of neurons exhibited excitatory postsynaptic events and/or a short lasting and a prolonged inhibitory postsynaptic response. Furthermore, stimulation of EC selectively produced an augmentation of the bistable up-down state only in the type 2 regular spiking neurons and in a subclass of nonintrinsic bursting neurons. Taken together, these data suggest that the potent inhibition observed following EC stimulation may mask a direct excitatory response within the mPFC which markedly potentiates the bistable states in a select subpopulation of mPFC pyramidal neurons.

What's in a smile? Maternal brain responses to infant facial cues

OBJECTIVES

Our goal was to determine how a mother's brain responds to her own infant's facial expressions, comparing happy, neutral, and sad face affect.

METHODS

In an event-related functional MRI study, 28 first-time mothers were shown novel face images of their own 5- to 10-month-old infant and a matched unknown infant. Sixty unique stimuli from 6 categories (own-happy, own-neutral, own-sad, unknown-happy, unknown-neutral, and unknown-sad) were presented randomly for 2 seconds each, with a variable 2- to 6-second interstimulus interval.

RESULTS

Key dopamine-associated reward-processing regions of the brain were activated when mothers viewed their own infant's face compared with an unknown infant's face. These included the ventral tegmental area/substantia nigra regions, the striatum, and frontal lobe regions involved in (1) emotion processing (medial prefrontal, anterior cingulate, and insula cortex), (2) cognition (dorsolateral prefrontal cortex), and (3) motor/behavioral outputs (primary motor area). Happy, but not neutral or sad own-infant faces, activated nigrostriatal brain regions interconnected by dopaminergic neurons, including the substantia nigra and dorsal putamen. A region-of-interest analysis revealed that activation in these regions was related to positive infant affect (happy > neutral > sad) for each own-unknown infant-face contrast.

CONCLUSIONS

When first-time mothers see their own infant's face, an extensive brain network seems to be activated, wherein affective and cognitive information may be integrated and directed toward motor/behavioral outputs. Dopaminergic reward-related brain regions are activated specifically in response to happy, but not sad, infant faces. Understanding how a mother responds uniquely to her own infant, when smiling or crying, may be the first step in understanding the neural basis of mother-infant attachment.

The adolescent brain

Adolescence is a developmental period characterized by suboptimal decisions and actions that are associated with an increased incidence of unintentional injuries, violence, substance abuse, unintended pregnancy, and sexually transmitted diseases. Traditional neurobiological and cognitive explanations for adolescent behavior have failed to account for the nonlinear changes in behavior observed during adolescence, relative to both childhood and adulthood. This review provides a biologically plausible model of the neural mechanisms underlying these nonlinear changes in behavior. We provide evidence from recent human brain imaging and animal studies that there is a heightened responsiveness to incentives and socioemotional contexts during this time, when impulse control is still relatively immature. These findings suggest differential development of bottom-up limbic systems, implicated in incentive and emotional processing, to top-down control systems during adolescence as compared to childhood and adulthood. This developmental pattern may be exacerbated in those adolescents prone to emotional reactivity, increasing the likelihood of poor outcomes.

Prefrontal cortex-nucleus accumbens interaction: in vivo modulation by dopamine and glutamate in the prefrontal cortex

Previous experimental studies have shown that the prefrontal cortex (PFC) regulates the activity of the nucleus accumbens (NAc), and in particular the release of dopamine in this area of the brain. In the present report we review recent microinjections/microdialysis studies from our laboratory on the effects of stimulation/blockade of dopamine and glutamate receptors in the PFC that modulate dopamine, and also acetylcholine release in the NAc. Stimulation of prefrontal D2 dopamine receptors, but not group I mGlu glutamate receptors, reduces the release of dopamine and acetylcholine in the NAc and spontaneous motor activity. This inhibitory role of prefrontal D2 receptors is not changed by acute systemic injections of the NMDA antagonist phencyclidine. On the other hand, the blockade of NMDA receptors in the PFC increases the release of dopamine and acetylcholine in the NAc as well as motor activity which suggests that the hypofunction of prefrontal NMDA receptors is able to produce the neurochemical and behavioural changes associated with a dysfunction of the corticolimbic circuit. We suggest here that dopamine and glutamate receptors are, in part, segregated in specific cellular circuits in the PFC. Thus, the stimulation/blockade of these receptors would have a different net impact on PFC output projections to regulate dopamine and acetylcholine release in the NAc and in guided behaviour. Finally, it is speculated that environmental enrichment might produce plastic changes that modify the functional interaction between the PFC and the NAc in both physiological and pathological conditions.