Altered dopamine modulation of inhibition in the prefrontal cortex of cocaine-sensitized rats

Enhanced expression of parvalbumin and perineuronal nets in the medial prefrontal cortex after extended-access cocaine self-administration in rats

The medial prefrontal cortex (mPFC) drives cocaine-seeking behaviour in rodent models of cocaine use disorder. Parvalbumin (PV)-containing GABAergic interneurons powerfully control the output of the mPFC, yet few studies have focused on how these neurons modulate cocaine-seeking behaviour. Most PV neurons are surrounded by perineuronal nets (PNNs), which regulate the firing of PV neurons. We examined staining intensity and number of PV and PNNs after long-access (6 h/day) cocaine self-administration in rats followed by either 8-10 days extinction ± cue-induced reinstatement or short-term (1-2 days) or long-term (30-31 days) abstinence ± cue-induced reinstatement. The intensity of PNNs was increased in the prelimbic and infralimbic PFC after long-term abstinence in the absence of cue reinstatement and after cue reinstatement following both daily extinction sessions and after a 30-day abstinence period. PV intensity was increased after 30 days of abstinence in the prelimbic but not infralimbic PFC. Enzymatic removal of PNNs with chondroitinase ABC (ABC) in the prelimbic PFC did not prevent incubation of cue-induced reinstatement but decreased cocaine-seeking behaviour at both 2 and 31 days of abstinence, and this decrease at 31 days was accompanied by reduced c-Fos levels in the prelimbic PFC. Increases in PNN intensity have generally been associated with the loss of plasticity, suggesting that the persistent and chronic nature of cocaine use disorder may in part be attributed to long-lasting increases in PNN intensity that reduce the ability of stimuli to alter synaptic input to underlying PV neurons.

Repeated methamphetamine administration produces cognitive deficits through augmentation of GABAergic synaptic transmission in the prefrontal cortex

Methamphetamine (METH) abuse is associated with the emergence of cognitive deficits and hypofrontality, a pathophysiological marker of many neuropsychiatric disorders that is produced by altered balance of local excitatory and inhibitory synaptic transmission. However, there is a dearth of information regarding the cellular and synaptic mechanisms underlying METH-induced cognitive deficits and associated hypofrontal states. Using PV-Cre transgenic rats that went through a METH sensitization regime or saline (SAL) followed by 7-10 days of home cage abstinence combined with cognitive tests, chemogenetic experiments, and whole-cell patch recordings on the prelimbic prefrontal cortex (PFC), we investigated the cellular and synaptic mechanisms underlying METH-induce hypofrontality. We report here that repeated METH administration in rats produces deficits in working memory and increases in inhibitory synaptic transmission onto pyramidal neurons in the PFC. The increased PFC inhibition is detected by an increase in spontaneous and evoked inhibitory postsynaptic synaptic currents (IPSCs), an increase in GABAergic presynaptic function, and a shift in the excitatory-inhibitory balance onto PFC deep-layer pyramidal neurons. We find that pharmacological blockade of D1 dopamine receptor function reduces the METH-induced augmentation of IPSCs, suggesting a critical role for D1 dopamine signaling in METH-induced hypofrontality. In addition, repeated METH administration increases the intrinsic excitability of parvalbumin-positive fast spiking interneurons (PV + FSIs), a key local interneuron population in PFC that contributes to the control of inhibitory tone. Using a cell type-specific chemogenetic approach, we show that increasing PV + FSIs activity in the PFC is necessary and sufficient to cause deficits in temporal order memory similar to those induced by METH. Conversely, reducing PV + FSIs activity in the PFC of METH-exposed rats rescues METH-induced temporal order memory deficits. Together, our findings reveal that repeated METH exposure increases PFC inhibitory tone through a D1 dopamine signaling-dependent potentiation of inhibitory synaptic transmission, and that reduction of PV + FSIs activity can rescue METH-induced cognitive deficits, suggesting a potential therapeutic approach to treating cognitive symptoms in patients suffering from METH use disorder.

Impact of Perineuronal Net Removal in the Rat Medial Prefrontal Cortex on Parvalbumin Interneurons After Reinstatement of Cocaine Conditioned Place Preference

Parvalbumin (PV)-positive cells are GABAergic fast-spiking interneurons that modulate the activity of pyramidal neurons in the medial prefrontal cortex (mPFC) and their output to brain areas associated with learning and memory. The majority of PV cells within the mPFC are surrounded by a specialized extracellular matrix structure called the perineuronal net (PNN). We have shown that removal of PNNs with the enzyme chondroitinase-ABC (Ch-ABC) in the mPFC prevents the consolidation and reconsolidation of cocaine-associated conditioned place preference (CPP) memories. Here we examined the extent to which retrieval of a CPP memory during cocaine-primed reinstatement altered the levels and function of PV neurons and their surrounding PNNs during the reconsolidation period. We further determined the extent to which PNN removal prior to reinstatement altered PV intensity levels and PV cell function. Male Sprague-Dawley rats were trained for cocaine-induced conditioned place preference (CPP) followed by extinction training, microinjection of Ch-ABC in the prelimbic PFC, and cocaine-induced reinstatement. Rats were sacrificed immediately prior to reinstatement or at 2 h, 6 h, or 48 h after reinstatement for immunohistochemistry or 2 h later for electrophysiology. Our findings indicate that PNN removal only partially diminished reinstatement. Cocaine-primed reinstatement produced only minor changes in PNN or PV intensity in vehicle controls. However, after PNN removal, the intensity of remaining PNN-surrounded PV cells was decreased at all times except at 2 h post-reinstatement, at which time cocaine increased PV intensity. Consistent with this, in vehicle controls, PV neurons naturally devoid of PNNs showed a similar pattern to Ch-ABC-treated rats prior to and after cocaine reinstatement, suggesting a protective effect of PNNs on cocaine-induced changes in PV intensity. Using whole-cell patch-clamp, cocaine-primed reinstatement in Ch-ABC-treated rats decreased the number of elicited action potentials but increased excitatory synaptic transmission, which may have been compensatory. These findings suggest that without PNNs, cocaine-induced reinstatement produces rapid changes in PV intensity and PV cell excitability, which may in turn regulate output of the mPFC post-memory retrieval and diminish the maintenance of cocaine memory during reconsolidation.

Inflammatory Pain Alters Dopaminergic Modulation of Excitatory Synapses in the Anterior Cingulate Cortex of Mice

Pain modulation of dopamine-producing nuclei is known to contribute to the affective component of chronic pain. However, pain modulation of pain-related cortical regions receiving dopaminergic inputs is understudied. The present study demonstrates that mice with chronic inflammatory injury of the hind paws develop persistent mechanical hypersensitivity and transient anxiety. Peripheral inflammation induced by injection of complete Freund's Adjuvant (CFA) induced potentiation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor (AMPAR) currents with a presynaptic component in layer II/III of the ACC. After four days of inflammatory pain, the dopamine-mediated inhibition of AMPAR currents was significantly reduced in the ACC. Furthermore, dopamine enhanced presynaptic modulation of excitatory transmission, but only in mice with inflammatory pain. High-performance liquid chromatography (HPLC) analysis of dopamine tissue concentration revealed that dopamine neurotransmitter concentration in the ACC was reduced three days following CFA. Our results demonstrate that inflammatory pain induces activity-dependent changes in excitatory synaptic transmission and alters dopaminergic homeostasis in the ACC.

Graphene-Based Electrochemical Sensors for Psychoactive Drugs

Sensors developed from nanomaterials are increasingly used in a variety of fields, from simple wearable or medical sensors to be used at home to monitor health, to more complicated sensors being used by border customs or aviation industries. In recent times, nanoparticle-based sensors have begun to revolutionize drug-detection techniques, mainly due to their affordability, ease of use and portability, compared to conventional chromatography techniques. Thin graphene layers provide a significantly high surface to weight ratio compared to other nanomaterials, a characteristic that has led to the design of more sensitive and reliable sensors. The exceptional properties of graphene coupled with its potential to be tuned to target specific molecules have made graphene-based sensors one of the most popular and well-researched sensing materials of the past two decades with applications in environmental monitoring, medical diagnostics, and industries. Here, we present a review of developments in the applications of graphene-based sensors in sensing drugs such as cocaine, morphine, methamphetamine, ketamine, tramadol and so forth in the past decade. We compare graphene sensors with other sensors developed from ultrathin two-dimensional materials, such as transition-metal dichalcogenides, hexagonal boron nitrate, and MXenes, to measure drugs directly and indirectly, in various samples.

Effects of repeated cocaine administration on dopamine D1 receptor modulation of mesocorticolimbic GABA and glutamate transmission

Repeated cocaine exposure alters medial prefrontal cortex (mPFC) function to allow for enhanced excitatory transmission to the nucleus accumbens and ventral tegmental area (VTA). Previous studies have demonstrated changes in receptor function in the mPFC in animals repeatedly exposed to cocaine that produced increased excitatory output. The present report tested the hypothesis that daily injections of cocaine would enhance D1 receptor responsiveness by infusing the D1 receptor agonist SKF 38393 into the mPFC and monitoring glutamate and/or GABA release in the mPFC, nucleus accumbens and VTA of saline- and cocaine-pretreated animals using in vivo microdialysis. The data demonstrated that intra-mPFC SKF 38393 reduced GABA and glutamate levels in the mPFC in control animals. Intra-mPFC SKF 38393 had no effect on glutamate levels in animals 1 day after daily cocaine treatments, increased mPFC glutamate at 7 days of withdrawal and reverted to decreasing glutamate at 30 days of withdrawal. SKF 38393 induced reduction in mPFC GABA is lost at 7 and 30 days of withdrawal. Intra-mPFC SKF 38393 did not alter glutamate levels in the nucleus accumbens or VTA of control animals. Infusion of SKF 38393 into the mPFC of animals previously exposed to cocaine increased and reduced glutamate release in the nucleus accumbens after 7 and 30 days of withdrawal, respectively and increased glutamate levels in the VTA 7 and 30 days after daily cocaine injections. The data suggest that repeated cocaine exposure alters D1 receptor function in the mPFC that could contribute to enhanced behavioral responses that occur following repeated cocaine.

Cocaine Exposure Modulates Perineuronal Nets and Synaptic Excitability of Fast-Spiking Interneurons in the Medial Prefrontal Cortex

We previously reported that perineuronal nets (PNNs) are required for cocaine-associated memories. Perineuronal nets are extracellular matrix that primarily surrounds parvalbumin (PV)-containing, GABAergic fast-spiking interneurons (FSIs) in the medial prefrontal cortex (mPFC). Here we measured the impact of acute (1 d) or repeated (5 d) cocaine exposure on PNNs and PV cells within the prelimbic and infralimbic regions of the mPFC. Adult rats were exposed to 1 or 5 d of cocaine and stained for PNNs (using Wisteria floribunda agglutinin) and PV intensity 2 or 24 h later. In the prelimbic and infralimbic PFC, PNN staining intensity decreased 2 h after 1 d of cocaine exposure but increased after 5 d of cocaine exposure. Cocaine also produced changes in PV intensity, which generally lagged behind that of PNNs. In the prelimbic PFC, both 1 and 5 d of cocaine exposure increased GAD65/67 puncta near PNN-surrounded PV cells, with an increase in the GAD65/67-to-VGluT1 puncta ratio after 5 d of cocaine exposure. In the prelimbic PFC, slice electrophysiology studies in FSIs surrounded by PNNs revealed that both 1 and 5 d of cocaine exposure reduced the number of action potentials 2 h later. Synaptic changes demonstrated that 5 d of cocaine exposure increased the inhibition of FSIs, potentially reducing the inhibition of pyramidal neurons and contributing to their hyperexcitability during relapse behavior. These early and rapid responses to cocaine may alter the network stability of PV FSIs that partially mediate the persistent and chronic nature of drug addiction.

High frequency stimulation-induced plasticity in the prelimbic cortex of rats emerges during adolescent development and is associated with an increase in dopamine receptor function

Recent studies in rats suggest that high frequency stimulation (HFS) in the ventral hippocampus induces long-term depression (LTD) in the deep layer of the medial prefrontal cortex (mPFC), but only after the prefrontal GABA system has sufficiently developed during early-to mid-adolescence. It is not clear whether this LTD is specific to the hippocampus-mPFC circuit or is instead an intrinsitc regulatory mechanism for the developed mPFC neuro-network. The potential mechanisms underlying this HFS-induced LTD are also largely unknown. In the current study, naïve male Sprague Dawley rats were sacrificed during peri-adolescence or young adulthood for in vitro extracellular recording to determine if HFS delivered in the prelimbic cortex (PLC) would induce LTD in an age-dependent manner and if dopamine receptors are involved in the expression of this LTD. We found four trains of stimulation at 50 Hz induced an LTD in the PFC of adult, but not peri-adolescent, rats. This LTD required intact GABA_A receptor functioning and could also be blocked by dopamine D₁ or D₂ receptor antagonists. Bath application of selective D₁ or D₂ receptor agonists produced a significant facilitation or suppression in the field potential, respectively, and these effects were only observed in the adult PLC. Furthermore, neither D₁ nor D₂ stimualtion prior to HFS was able to facilitate LTD in the peri-adolescent PLC. Together, these results suggest dopamine receptor functionality in the PLC increases during adolescent development and it plays an important role in this late-maturating form of plasticity.

Wnt/β-catenin pathway in the prefrontal cortex is required for cocaine-induced neuroadaptations

Behavioral sensitization is a progressive and enduring enhancement of the motor stimulant effects elicited by repeated administration of drugs of abuse. It can be divided into two distinct temporal and anatomical domains, termed initiation and expression, which are characterized by specific molecular and neurochemical changes. This study examines the role of the Wnt canonical pathway mediating the induction of cocaine sensitization. We found that β-catenin levels in the prefrontal cortex (PFC), amygdala (Amyg) and dorsal striatum (CPu) are decreased in animals that show sensitization. Accordingly, GSK3β activity levels are increased in the same areas. Moreover, β-catenin levels in nuclear fraction, mRNA expression of Axin2 and Wnt7b are decreased in the PFC of sensitized animals. Then, in order to demonstrate that changes in the PFC are crucial for initiation of sensitization, we either rescue β-catenin levels with a systemic treatment of a GSK3β inhibitor (Lithium Chloride) or inhibit Wnt/β-catenin pathway with an intracerebral infusion of Sulindac before each cocaine injection. As expected, rescuing β-catenin levels in the PFC as well as CPu and Amyg blocks cocaine-induced sensitization, while decreasing β-catenin levels exclusively in the PFC exacerbates it. Therefore, our results demonstrate a new role for the Wnt/β-catenin pathway as a required neuroadaptation in inducing behavioral sensitization.

Disruption of Akt signaling decreases dopamine sensitivity in modulation of inhibitory synaptic transmission in rat prefrontal cortex

Akt is a serine/threonine kinase, which is dramatically reduced in the prefrontal cortex (PFC) of patients with schizophrenia, and a deficiency in Akt1 results in PFC function abnormalities. Although the importance of Akt in dopamine (DA) transmission is well established, how impaired Akt signaling affects the DA modulation of synaptic transmission in the PFC has not been characterized. Here we show that Akt inhibitors significantly decreased receptor sensitivity to DA by shifting DA modulation of GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs) in prefrontal cortical neurons. Akt inhibition caused a significant decrease in synaptic dopamine D2 receptor (D2R) levels with high-dose DA exposure. In addition, Akt inhibition failed to affect DA modulation of IPSCs after blockade of β-arrestin 2. β-arrestin 2-mediated interaction of clathrin with D2R was enhanced by co-application of a Akt inhibitor and DA. Taken together, the reduced response in DA modulation of inhibitory transmission mainly involved β-arrestin 2-dependent D2R desensitization.

Repeated exposure to amphetamine during adolescence alters inhibitory tone in the medial prefrontal cortex following drug re-exposure in adulthood

Behavioral sensitization following repeated amphetamine (AMPH) exposure is associated with changes in GABA function in the medial prefrontal cortex (mPFC). In rats exposed to AMPH during adolescence compared to adulthood, there are unique patterns of sensitization that may reflect age-dependent differences in drug effects on prefrontal GABAergic function. In the current study, we used a sensitizing regimen of repeated AMPH exposure in adolescent and adult rats to determine if a post-withdrawal AMPH challenge would alter inhibitory transmission in the mPFC in a manner that depends on age of exposure. Male Sprague-Dawley rats were treated with saline or 3mg/kg AMPH (i.p.) during adolescence [postnatal day (P) 27-P45] or adulthood (P85- P103) and were sacrificed either at similar ages in adulthood (∼P133; experiment 1) or after similar withdrawal times (3-4 weeks; experiment 2). Spontaneous inhibitory postsynaptic currents (sIPSCs) were recorded in vitro from deep layer pyramidal cells in the mPFC using the whole-cell configuration. We found no effect of AMPH pre-exposure on baseline sIPSC frequency. Subsequent application of AMPH (25μM) produced a stable increase in sIPSC frequency in controls, suggesting that AMPH increases inhibitory tone in the mPFC. However, AMPH failed to increase sIPSCs in adolescent- or adult-exposed rats. In experiment 2, where withdrawal period was kept similar for both exposure groups, AMPH induced a suppression of sIPSC activity in adolescent-exposed rats. These results suggest that sensitizing treatment with AMPH during adolescence or adulthood dampens inhibitory influences on mPFC pyramidal cells, but potentially through different mechanisms.

When the party is over: depressive-like states in rats following termination of cortical D1 receptor overexpression

RATIONALE

Increased activity of prefrontal D1 dopamine receptors (D1R) is involved in reward-related behavior found in bipolar disorder and drug addiction. While the effects of elevated D1R are known, depressive-like behaviors also occur in these disorders after reward-seeking ends.

OBJECTIVES

The goal is to characterize how termination of D1R overexpression influences depressive-like behaviors.

METHODS

An inducible (Tet.On), lentiviral vector was used to manipulate the expression of the DRD1 gene in glutamate neurons within the prefrontal cortex in male, adult rats. Sexual activity and sucrose preference were studied in both D1R elevated ON and relatively reduced OFF states. Following termination of the D1R ON state, depressive-like behavior was determined in the OFF state. Expression of the transcriptional regulator, cyclic AMP-responsive element-binding protein (CREB), was used as an indication of downstream effects in the nucleus accumbens (NA).

RESULTS

ON D1R expression increased sexual activity that returned to baseline in the OFF state. Sucrose preferences increased ~6 % in ON state but fell 11 % below control levels when OFF. Consistent with a depressive-like phenotype, D1R OFF decreased activity by 40 %, impaired the ability to control (43 %) and motivation to escape shock (27 % more impaired) relative to dsRed OFF. CREB increased 29 % in the NA in the D1R OFF state relative to the ON state.

CONCLUSIONS

This novel approach demonstrates that elevated D1R expression increased hedonic behavior, whereas the termination of D1R overexpression often resulted in depressive-like behavior. These observations support a role for D1R expression cycling in bipolar-associated behaviors and addiction.

D1 receptor-mediated inhibition of medial prefrontal cortex neurons is disrupted in adult rats exposed to amphetamine in adolescence

Amphetamine (AMPH) exposure leads to changes in behavior and dopamine receptor function in the prefrontal cortex (PFC). Since dopamine plays an important role in regulating GABAergic transmission in the PFC, we investigated if AMPH exposure induces long-lasting changes in dopamine's ability to modulate inhibitory transmission in the PFC as well as whether the effects of AMPH differed depending on the age of exposure. Male Sprague-Dawley rats were given saline or 3 mg/kg AMPH (i.p.) repeatedly during adolescence or adulthood and following a withdrawal period of up to 5 weeks (Experiment 1) or up to 14 weeks (Experiment 2), they were sacrificed for in vitro whole-cell recordings in layer V/VI of the medial PFC. We found that in brain slices from either adolescent- or adult-exposed rats, there was an attenuation of dopamine-induced increases in inhibitory synaptic currents in pyramidal cells. These effects did not depend on age of exposure, were mediated at least partially by a reduced sensitivity of D1 receptors in AMPH-treated rats, and were associated with an enhanced behavioral response to the drug in a separate group of rats given an AMPH challenge following the longest withdrawal period. Together, these data reveal a prolonged effect of AMPH exposure on medial PFC function that persisted for up to 14 weeks in adolescent-exposed animals. These long-lasting neurophysiological changes may be a contributing mechanism to the behavioral consequences that have been observed in those with a history of amphetamine abuse.

An investigation into aripiprazole's partial D₂ agonist effects within the dorsolateral prefrontal cortex during working memory in healthy volunteers

RATIONALE

Working memory impairments in schizophrenia have been attributed to dysfunction of the dorsolateral prefrontal cortex (DLPFC) which in turn may be due to low DLPFC dopamine innervation. Conventional antipsychotic drugs block DLPFC D2 receptors, and this may lead to further dysfunction and working memory impairments. Aripiprazole is a D2 receptor partial agonist hypothesised to enhance PFC dopamine functioning, possibly improving working memory.

OBJECTIVES

We probed the implications of the partial D2 receptor agonist actions of aripiprazole within the DLPFC during working memory. Investigations were carried out in healthy volunteers to eliminate confounds of illness or medication status. Aripiprazole's prefrontal actions were compared with the D2/5-HT2A blocker risperidone to separate aripiprazole's unique prefrontal D2 agonist actions from its serotinergic and striatal D2 actions that it shares with risperidone.

METHOD

A double-blind, placebo-controlled, parallel design was implemented. Participants received a single dose of either 5 mg aripiprazole, 1 mg risperidone or placebo before performing the n-back task whilst undergoing fMRI scanning.

RESULTS

Compared with placebo, the aripiprazole group demonstrated enhanced DLPFC activation associated with a trend for improved discriminability (d') and speeded reaction times. In contrast to aripiprazole's neural effects, the risperidone group demonstrated a trend for reduced DLPFC recruitment. Unexpectedly, the risperidone group demonstrated similar effects to aripiprazole on d' and additionally had reduced errors of commission compared with placebo.

CONCLUSION

Aripiprazole has unique DLPFC actions attributed to its prefrontal D2 agonist action. Risperidone's serotinergic action that results in prefrontal dopamine release may have protected against any impairing effects of its prefrontal D2 blockade.

In the blink of an eye: relating positive-feedback sensitivity to striatal dopamine D2-like receptors through blink rate

For >30 years, positron emission tomography (PET) has proven to be a powerful approach for measuring aspects of dopaminergic transmission in the living human brain; this technique has revealed important relationships between dopamine D2-like receptors and dimensions of normal behavior, such as human impulsivity, and psychopathology, particularly behavioral addictions. Nevertheless, PET is an indirect estimate that lacks cellular and functional resolution and, in some cases, is not entirely pharmacologically specific. To identify the relationships between PET estimates of D2-like receptor availability and direct in vitro measures of receptor number, affinity, and function, we conducted neuroimaging and behavioral and molecular pharmacological assessments in a group of adult male vervet monkeys. Data gathered from these studies indicate that variation in D2-like receptor PET measurements is related to reversal-learning performance and sensitivity to positive feedback and is associated with in vitro estimates of the density of functional dopamine D2-like receptors. Furthermore, we report that a simple behavioral measure, eyeblink rate, reveals novel and crucial links between neuroimaging assessments and in vitro measures of dopamine D2 receptors.

Chronic alcohol disrupts dopamine receptor activity and the cognitive function of the medial prefrontal cortex

Dopamine (DA) receptors in the medial prefrontal cortex (mPFC) exert powerful effects on cognition by modulating the balance between excitatory and inhibitory neurotransmission. The present study examined the impact of chronic intermittent ethanol (CIE) exposure on cognitive function and DA receptor-mediated neurotransmission in the rat mPFC. Consistent with alterations in executive function in alcoholics, CIE-exposed rats exhibited deficits in behavioral flexibility in an operant set-shifting task. Since alterations in dopaminergic neurotransmission in the mPFC have been implicated in a number of behavioral disorders including addiction, studies were then performed in the adult acute slice preparation to examine changes in DA receptor function in the mPFC following CIE exposure. In slices obtained from control rats, DA receptor stimulation was observed to exert complex actions on neuronal firing and synaptic neurotransmission that were not only dependent upon the particular receptor subtype but also whether it was a pyramidal cell or a fast-spiking interneuron. In contrast to slices from control rats, there was a near complete loss of the modulatory actions of D2/D4 receptors on cell firing and neurotransmission in slices obtained immediately, 1 and 4 weeks after the last day of CIE exposure. This loss did not appear to be associated with changes in receptor expression. In contrast, CIE exposure did not alter D1 receptor function or mGluR1 modulation of firing. These studies are consistent with the suggestion that chronic alcohol exposure disrupts cognitive function at least in part through disruption of D2 and D4 receptor signaling in mPFC.

Perseveration in the presence of punishment: the effects of chronic cocaine exposure and lesions to the prefrontal cortex

Perseveration is the repetition of a previously appropriate response in a manner, or context, which is detrimental to the individual. Although both cocaine exposure and prefrontal cortex (PFC) dysfunctions have been implicated in perseverative-like behaviours, the underlying nature of the impairments has been debated. The current study tested whether chronic cocaine exposure and PFC lesions induce perseverative-like behaviours by causing insensitivity to punishment. Food-restricted male Sprague-Dawley rats were trained to respond for sucrose on concurrent schedules of reinforcement. After initial training, rats received either a sensitizing regimen of cocaine exposure, or excitotoxic lesions to subregions of the PFC. The test of perseveration involved a choice of responding between two levers associated with fixed ratio and progressive ratio (PR) schedules. Responding on the PR lever was punished by a 1 min timeout period. It was found that, unlike control subjects, those exposed to chronic cocaine, or with lesions to the medial prefrontal cortex, were significantly slower in adapting their responding to avoid punishment. The current study provides evidence that both cocaine exposure and lesions to the prefrontal cortex can increase perseverative-like responding, although the magnitude and permanence of these effects are contingent on the nature of the task.

Father absence in the monogamous california mouse impairs social behavior and modifies dopamine and glutamate synapses in the medial prefrontal cortex

The role of the father in psycho-affective development is indispensable. Yet, the neurobehavioral effects of paternal deprivation (PD) are poorly understood. Here, we examined the behavioral consequences of PD in the California mouse, a species displaying monogamous bonding and biparental care, and assessed its impact on dopamine (DA), serotonin (5-HT), and glutamate (GLU) transmission in the medial prefrontal cortex (mPFC). In adult males, deficits in social interaction were observed, when a father-deprived (PD) mouse was matched with a PD partner. In adult females, deficits were observed when matching a PD animal with a non-PD control, and when matching 2 PD animals. PD also increased aggression in females. Behavioral abnormalities in PD females were associated with a sensitized response to the locomotor-activating effect of amphetamine. Following immunocytochemical demonstration of DA, 5-HT, and GLU innervations in the mPFC, we employed in vivo electrophysiology and microiontophoresis, and found that PD attenuated the basal activity of low-spiking pyramidal neurons in females. PD decreased pyramidal responses to DA in females, while enhancing responses to NMDA in both sexes. We thus demonstrate that, during critical neurodevelopmental periods, PD leads to sex-dependent abnormalities in social and reward-related behaviors that are associated with disturbances in cortical DA and GLU neurotransmission.

Optogenetically evoked gamma oscillations are disturbed by cocaine administration

Drugs of abuse have enormous societal impact by degrading the cognitive abilities, emotional state and social behavior of addicted individuals. Among other events involved in the addiction cycle, the study of a single exposure to cocaine, and the contribution of the effects of that event to the continuous and further use of drugs of abuse are fundamental. Gamma oscillations are thought to be important neural correlates of cognitive processing in the prefrontal cortex (PFC) which include decision making, set shifting and working memory. It follows that cocaine exposure might modulate gamma oscillations, which could result in reduced cognitive ability. Parvalbumin-positive fast-spiking interneurons play an orchestrating role in gamma oscillation induction and it has been shown recently that gamma oscillations can be induced in an anesthetized animal using optogenetic techniques. We use a knock-in mouse model together with optogenetics and in vivo electrophysiology to study the effects of acute cocaine on PFC gamma oscillation as a step toward understanding the cortical changes that may underlie continuous use of stimulants. Our results show that acute cocaine administration increases entrainment of the gamma oscillation to the optogentically induced driving frequency. Our results also suggest that this modulation of gamma oscillations is driven trough activation of D1 receptors. The acute cocaine-mediated changes in mPFC may underlie the enhancement of attention and awareness commonly reported by cocaine users and may contribute to the further use and abuse of psychostimulants.

Enhancement of behavioral sensitization, anxiety-like behavior, and hippocampal and frontal cortical CREB levels following cocaine abstinence in mice exposed to cocaine during adolescence

Adolescence has been linked to greater risk-taking and novelty-seeking behavior and a higher prevalence of drug abuse and risk of relapse. Decreases in cyclic adenosine monophosphate response element binding protein (CREB) and phosphorylated CREB (pCREB) have been reported after repeated cocaine administration in animal models. We compared the behavioral effects of cocaine and abstinence in adolescent and adult mice and investigated possible age-related differences in CREB and pCREB levels. Adolescent and adult male Swiss mice received one daily injection of saline or cocaine (10 mg/kg, i.p.) for 8 days. On day 9, the mice received a saline injection to evaluate possible environmental conditioning. After 9 days of withdrawal, the mice were tested in the elevated plus maze to evaluate anxiety-like behavior. Twelve days after the last saline/cocaine injection, the mice received a challenge injection of either cocaine or saline, and locomotor activity was assessed. One hour after the last injection, the brains were extracted, and CREB and pCREB levels were evaluated using Western blot in the prefrontal cortex (PFC) and hippocampus. The cocaine-pretreated mice during adolescence exhibited a greater magnitude of the expression of behavioral sensitization and greater cocaine withdrawal-induced anxiety-like behavior compared with the control group. Significant increases in CREB levels in the PFC and hippocampus and pCREB in the hippocampus were observed in cocaine-abstinent animals compared with the animals treated with cocaine in adulthood. Interestingly, significant negative correlations were observed between cocaine sensitization and CREB levels in both regions. These results suggest that the behavioral and neurochemical consequences of psychoactive substances in a still-developing nervous system can be more severe than in an already mature nervous system.

Repeated cocaine weakens GABA(B)-Girk signaling in layer 5/6 pyramidal neurons in the prelimbic cortex

Repeated cocaine exposure triggers adaptations in layer 5/6 glutamatergic neurons in the medial prefrontal cortex (mPFC) that promote behavioral sensitization and drug-seeking behavior. While suppression of metabotropic inhibitory signaling has been implicated in these behaviors, underlying mechanisms are unknown. Here, we show that Girk/K(IR)3 channels mediate most of the GABA(B) receptor (GABA(B)R)-dependent inhibition of layer 5/6 pyramidal neurons in the mPFC and that repeated cocaine suppresses this pathway. This adaptation was selective for GABA(B)R-dependent Girk signaling in layer 5/6 pyramidal neurons of the prelimbic cortex (PrLC) and involved a D₁/₅ dopamine receptor- and phosphorylation-dependent internalization of GABA(B)R and Girk channels. Persistent suppression of Girk signaling in layer 5/6 of the dorsal mPFC enhanced cocaine-induced locomotor activity and occluded behavioral sensitization. Thus, the cocaine-induced suppression of GABA(B)R-Girk signaling in layer 5/6 pyramidal neurons of the prelimbic cortex appears to represent an early adaptation critical for promoting addiction-related behavior.

Developmental disruption of gamma-aminobutyric acid function in the medial prefrontal cortex by noncontingent cocaine exposure during early adolescence

BACKGROUND

Drug experimentation during adolescence is associated with increased risk of drug addiction relative to any other age group. To further understand the neurobiology underlying such liability, we investigate how early adolescent cocaine experience impacts medial prefrontal cortex (mPFC) network function in adulthood.

METHODS

A noncontingent administration paradigm was used to assess the impact of early adolescent cocaine treatment (rats; postnatal days [PD] 35-40) on the overall inhibitory regulation of mPFC activity in adulthood (PD 65-75) by means of histochemical and in vivo electrophysiological measures combined with pharmacologic manipulations.

RESULTS

Cocaine exposure during early adolescence yields a distinctive hypermetabolic prefrontal cortex state that was not observed in adult-treated rats (PD 75-80). Local field potential recordings revealed that early adolescent cocaine exposure is associated with an attenuation of mPFC gamma-aminobutyric acid (GABA)ergic inhibition evoked by ventral hippocampal stimulation at beta and gamma frequencies that endures throughout adulthood. Such cocaine-induced mPFC disinhibition was not observed in adult-exposed animals. Furthermore, the normal developmental upregulation of parvalbumin immunoreactivity observed in the mPFC from PD 35 to PD 65 is lacking following early adolescent cocaine treatment.

CONCLUSIONS

Our data indicate that repeated cocaine exposure during early adolescence can elicit a state of mPFC disinhibition resulting from a functional impairment of the local prefrontal GABAergic network that endures through adulthood. A lack of acquisition of prefrontal GABAergic function during adolescence could trigger long-term deficits in the mPFC that may increase the susceptibility for the onset of substance abuse and related psychiatric disorders.

Bidirectional modulation of infralimbic dopamine D1 and D2 receptor activity regulates flexible reward seeking

The development of addictive behavior is marked by a loss of behavioral flexibility. In part, this is due to an increase in the ability of environmental stimuli to elicit responding and decreased importance of the action-outcome relationship in behavioral control. It has previously been demonstrated that both inactivation of and dopamine (DA) infusions in the infralimbic prefrontal cortex (PFC) can restore behavioral flexibility in paradigms measuring habitual reward seeking. Here, we investigated the mechanism by which cortical DA would act to enable goal-directed actions after the transition to habitual behavior has been established. Further, we extended this work to include a novel mouse model of compulsive-like behavior in which we assessed reward seeking despite the possibility of adverse consequences. Our data show that DA receptor D1 inhibition or D2 activation both promote the expression of a flexible responding after the development of habitual or compulsive-like behavior, and we suggest that the ability of DA infusions in the infralimbic PFC to restore sensitivity to changes in outcome value depends on activation of DA D2 receptors.

Repeated cocaine exposure increases fast-spiking interneuron excitability in the rat medial prefrontal cortex

The medial prefrontal cortex plays a key role in cocaine addiction. However, how chronic cocaine exposure affects cortical networks remains unclear. Most studies have focused on layer 5 pyramidal neurons (the circuit output), while the response of local GABAergic interneurons to cocaine remains poorly understood. Here, we recorded from fast-spiking interneurons (FS-IN) after repeated cocaine exposure and found altered membrane excitability. After cocaine withdrawal, FS-IN showed an increase in the number of spikes evoked by positive current injection, increased input resistance, and decreased hyperpolarization-activated current. We also observed a reduction in miniature excitatory postsynaptic currents, whereas miniature inhibitory postsynaptic current activity was unaffected. We show that, in animals with cocaine history, dopamine receptor D(2) activation is less effective in increasing FS-IN intrinsic excitability. Interestingly, these alterations are only observed 1 wk or more after the last cocaine exposure. This suggests that the dampening of D(2)-receptor-mediated response may be a compensatory mechanism to rein down the excitability of FS-IN.

Age-dependent actions of dopamine on inhibitory synaptic transmission in superficial layers of mouse prefrontal cortex

Numerous developmental changes in the nervous system occur during the first several weeks of the rodent lifespan. Therefore, many characteristics of neuronal function described at the cellular level from in vitro slice experiments conducted during this early time period may not generalize to adult ages. We investigated the effect of dopamine (DA) on inhibitory synaptic transmission in superficial layers of the medial prefrontal cortex (PFC) in prepubertal [postnatal age (P; days) 12-20], periadolescent (P30-48), and adult (P70-100) mice. The PFC is associated with higher-level cognitive functions, such as working memory, and is associated with initiation, planning, and execution of actions, as well as motivation and cognition. It is innervated by DA-releasing fibers that arise from the ventral tegmental area. In slices from prepubertal mice, DA produced a biphasic modulation of inhibitory postsynaptic currents (IPSCs) recorded in layer II/III pyramidal neurons. Activation of D2-like receptors leads to an early suppression of the evoked IPSC, which was followed by a longer-lasting facilitation of the IPSC mediated by D1-like DA receptors. In periadolescent mice, the D2 receptor-mediated early suppression was significantly smaller compared with the prepubertal animals and absent in adult animals. Furthermore, we found significant differences in the DA-mediated lasting enhancement of the inhibitory response among the developmental groups. Our findings suggest that behavioral paradigms that elicit dopaminergic release in the PFC differentially modulate inhibition of excitatory pyramidal neuron output in prepuberty compared with periadolescence and adulthood in the superficial layers (II/III) of the cortex.

Cocaine-induced adaptations in metabotropic inhibitory signaling in the mesocorticolimbic system

The addictive properties of psychostimulants such as cocaine are rooted in their ability to activate the mesocorticolimbic dopamine (DA) system. This system consists primarily of dopaminergic projections arising from the ventral tegmental area (VTA) and projecting to the limbic and cortical brain regions, such as the nucleus accumbens (NAc) and prefrontal cortex (PFC). While the basic anatomy and functional relevance of the mesocorticolimbic DA system is relatively well-established, a key challenge remaining in addiction research is to understand where and how molecular adaptations and corresponding changes in function of this system facilitate a pathological desire to seek and take drugs. Several lines of evidence indicate that inhibitory signaling, particularly signaling mediated by the Gi/o class of heterotrimeric GTP-binding proteins (G proteins), plays a key role in the acute and persistent effects of drugs of abuse. Moreover, recent evidence argues that these signaling pathways are targets of drug-induced adaptations. In this review we discuss inhibitory signaling pathways involving DA and the inhibitory neurotransmitter GABA in two brain regions - the VTA and PFC - that are central to the effects of acute and repeated cocaine exposure and represent sites of adaptations linked to addiction-related behaviors including sensitization, craving, and relapse.

Hyperdopaminergic modulation of inhibitory transmission is dependent on GSK-3β signaling-mediated trafficking of GABAA receptors

Cortical dopamine (DA) modulation of the gamma-amino butyric acid (GABA) system is closely associated with cognitive function and psychiatric disorders. We recently reported that the glycogen synthase kinase 3β (GSK-3β) pathway is required for hyperdopamine/D2 receptor-mediated inhibition of NMDA receptors in the prefrontal cortex. Here we explore whether or not GSK-3β is also involved in dopaminergic modulation of GABAA receptor-mediated inhibitory transmission. We confirmed that DA induces a dose-dependent, bidirectional regulatory effect on inhibitory postsynaptic currents (IPSCs) in prefrontal neurons. The modulatory effects of DA were differentially affected by co-application of GSK-3β inhibitors and different doses of DA. GSK-3β inhibitors completely blocked high-dose (20 μM) DA-induced depressive effects on IPSCs but exhibited limited effects on the facilitating regulation of IPSC in low-dose DA (200 nM). We also confirmed that surface expressions of GABAA receptor β2/3 subunits were significantly decreased by DA applied in cultured prefrontal neurons and in vivo administration of DA reuptake inhibitor. These effects were blocked by prior administration of GSK-3β inhibitors. We explored DA-mediated regulation of GABAA receptor trafficking and exhibited the participation of brefeldin A-inhibited GDP/GTP exchange factor 2 (BIG2) or dynamin-dependent trafficking of GABAA receptors. Together, these data suggest that DA may act through different signaling pathways to affect synaptic inhibition, depending on the concentration. The GSK-3β signaling pathway is involved in DA-induced decrease in BIG2-dependent insertion and an increase in the dynamin-dependent internalization of GABAA receptors, which results in suppression of inhibitory synaptic transmission.

Oscillatory power and synchrony in the rat forebrain are altered by a sensitizing regime of D-amphetamine

Repeated injections of psychostimulants, such as D-amphetamine (D-AMPH), provide a well-validated model of progressive cellular and systems-level alterations in brain function and behavior associated with addiction. The present study employed quantitative measures of both power spectral density and synchrony from local field potentials (LFPs) recorded simultaneously from the prefrontal cortex (PFC), parietal cortex (PAR), and hippocampus (HPC) in awake, behaving rats to assess changes in oscillations during different stages of D-AMPH-induced sensitization. The induction and development of sensitization altered the power of multiple frequency bands in a brain region-specific manner, whereas no changes were observed in animals treated with chronic saline. Specifically, the induction of sensitization to D-AMPH was accompanied by alterations in delta (2-5 Hz) and theta (5-11 Hz) oscillations similar to those observed in EEG recordings from addicted individuals describing craving and hedonic experience of the drug. Sensitization was also related to increased theta coherence between the PFC and HPC, along with suppression of cross-frequency correlations between theta and fast-gamma (65-100 Hz) in both the HPC and the PFC. Collectively, the present findings indicated the induction of a state in which the timing and synchronizing effects of oscillations are altered by sensitization to D-AMPH and are especially pronounced in the PFC. Furthermore, numerous LFP-derived measures were characterized that may serve as objective physiological correlates of pathological states observed in addiction.

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.

Cortical disinhibition in the neonatal ventral hippocampal lesion model of schizophrenia: new vistas on possible therapeutic approaches

The neonatal ventral hippocampal lesion (NVHL) model of schizophrenia has been extensively used in many laboratories over the past couple of decades. With more than 120 publications from over 15 research groups, this developmental model yields a number of schizophrenia-relevant behavioral, neurochemical and electrophysiological deficits. An important aspect of this model is the delayed emergence of alterations, typically during adolescence despite the manipulation that causes them having been performed during the first postnatal week. Such delayed timing reflects the periadolescent onset of schizophrenia symptoms and may be related to the protracted maturation of cortical circuits, affected in both the disease and the NVHL model. Here, I will review the work we have done regarding the maturation of prefrontal cortical-accumbens circuits during adolescence, and how this maturation is affected in rats with a NVHL. One of the principal elements affected in NVHL rats is the dopamine modulation of prefrontal cortical interneurons, and this finding is convergent with data from many other developmental, genetic and pharmacological models. An altered maturation of interneuron function would yield a disinhibited cortex, and this opens the way to novel therapeutic approaches for treatment and even prevention of schizophrenia.