Dopamine and glutamate agonists stimulate neuron-specific expression of Fos-like protein in the striatum

Prenatal exposition to haloperidol: A preclinical narrative review

Pre-existing maternal mental disorders may affect the early interactions between mother and baby, impacting the child's psychoemotional development. The typical antipsychotic haloperidol can be used during pregnancy, even with some restrictions. Its prescription is not limited to psychotic disorders, but also to other psychiatric conditions of high incidence and prevalence in the woman's fertile period. The present review focused on the preclinical available data regarding the biological and behavioral implications of embryonic exposure to haloperidol. The understanding of the effects of psychotropic drugs during neurodevelopment is important for its clinical aspect since there is limited evidence regarding the risks of antipsychotic drug treatment in pregnant women and their children. Moreover, a better comprehension of the mechanistic events that can be affected by antipsychotic treatment during the critical period of neurodevelopment may offer insights into the pathophysiology of neurodevelopmental disorders. The findings presented in this review converge to the existence of several risks associated with prenatal exposure to such medication and emphasize the need for further studies regarding its dimensions.

Dopamine-mediated striatal activity and function is enhanced in GlyRα2 knockout animals

The glycine receptor alpha 2 (GlyRα2) is a ligand-gated ion channel which upon activation induces a chloride conductance. Here, we investigated the role of GlyRα2 in dopamine-stimulated striatal cell activity and behavior. We show that depletion of GlyRα2 enhances dopamine-induced increases in the activity of putative dopamine D1 receptor-expressing striatal projection neurons, but does not alter midbrain dopamine neuron activity. We next show that the locomotor response to d-amphetamine is enhanced in GlyRα2 knockout animals, and that this increase correlates with c-fos expression in the dorsal striatum. 3-D modeling revealed an increase in the neuronal ensemble size in the striatum in response to D-amphetamine in GlyRα2 KO mice. Finally, we show enhanced appetitive conditioning in GlyRα2 KO animals that is likely due to increased motivation, but not changes in associative learning or hedonic response. Taken together, we show that GlyRα2 is an important regulator of dopamine-stimulated striatal activity and function.

Beyond Neuronal Activity Markers: Select Immediate Early Genes in Striatal Neuron Subtypes Functionally Mediate Psychostimulant Addiction

Immediate early genes (IEGs) were traditionally used as markers of neuronal activity in striatum in response to stimuli including drugs of abuse such as psychostimulants. Early studies using these neuronal activity markers led to important insights in striatal neuron subtype responsiveness to psychostimulants. Such studies have helped identify striatum as a critical brain center for motivational, reinforcement and habitual behaviors in psychostimulant addiction. While the use of IEGs as neuronal activity markers in response to psychostimulants and other stimuli persists today, the functional role and implications of these IEGs has often been neglected. Nonetheless, there is a subset of research that investigates the functional role of IEGs in molecular, cellular and behavioral alterations by psychostimulants through striatal medium spiny neuron (MSN) subtypes, the two projection neuron subtypes in striatum. This review article will address and highlight the studies that provide a functional mechanism by which IEGs mediate psychostimulant molecular, cellular and behavioral plasticity through MSN subtypes. Insight into the functional role of IEGs in striatal MSN subtypes could provide improved understanding into addiction and neuropsychiatric diseases affecting striatum, such as affective disorders and compulsive disorders characterized by dysfunctional motivation and habitual behavior.

Attenuated hypothalamic responses to α-melanocyte stimulating hormone during pregnancy in the rat

KEY POINTS

Increased appetite and weight gain occurs during pregnancy, associated with development of leptin resistance, and satiety responses to the anorectic peptide α-melanocyte stimulating hormone (α-MSH) are suppressed. This study investigated hypothalamic responses to α-MSH during pregnancy, using c-fos expression in specific hypothalamic nuclei as a marker of neuronal signalling, and in vivo electrophysiology in supraoptic nucleus (SON) oxytocin neurons, as a representative α-MSH-responsive neuronal population that shows a well-characterised α-MSH-induced inhibition of firing. While icv injection of α-MSH significantly increased the number of c-fos-positive cells in the paraventricular, supraoptic, arcuate and ventromedial hypothalamic nuclei in non-pregnant rats, this response was suppressed in pregnant rats. Similarly, SON oxytocin neurons in pregnant rats did not demonstrate characteristic α-MSH-induced inhibition of firing that was observed in non-pregnant animals. Given the known functions of α-MSH in the hypothalamus, the attenuated responses are likely to facilitate adaptive changes in appetite regulation and oxytocin secretion during pregnancy.

ABSTRACT

During pregnancy, a state of positive energy balance develops to support the growing fetus and to deposit fat in preparation for the subsequent metabolic demands of lactation. As part of this maternal adaptation, the satiety response to the anorectic peptide α-melanocyte stimulating hormone (α-MSH) is suppressed. To investigate whether pregnancy is associated with changes in the response of hypothalamic α-MSH target neurons, non-pregnant and pregnant rats were treated with α-MSH or vehicle and c-fos expression in hypothalamic nuclei was then examined. Furthermore, the firing rate of supraoptic nucleus (SON) oxytocin neurons, a known α-MSH responsive neuronal population, was examined in non-pregnant and pregnant rats following α-MSH treatment. Intracerebroventricular injection of α-MSH significantly increased the number of c-fos-positive cells in the paraventricular, arcuate and ventromedial hypothalamic nuclei in non-pregnant rats, but no significant increase was observed in any of these regions in pregnant rats. In the SON, α-MSH did induce expression of c-fos during pregnancy, but this was significantly reduced compared to that observed in the non-pregnant group. Furthermore, during pregnancy, SON oxytocin neurons did not demonstrate the characteristic α-MSH-induced inhibition of firing rate that was observed in non-pregnant animals. Melanocortin receptor mRNA levels during pregnancy were similar to non-pregnant animals, suggesting that receptor down-regulation is unlikely to be a mechanism underlying the attenuated responses to α-MSH during pregnancy. Given the known functions of α-MSH in the hypothalamus, the attenuated responses will facilitate adaptive changes in appetite regulation and oxytocin secretion during pregnancy.

A Brief Introduction to the Transduction of Neural Activity into Fos Signal

The immediate early gene c-fos has long been known as a molecular marker of neural activity. The neuron's activity is transformed into intracellular calcium influx through NMDA receptors and L-type voltage sensitive calcium channels. For the transcription of c-fos, neural activity should be strong enough to activate mitogen-activated protein kinase (MAPK) signaling pathway which shows low calcium sensitivity. Upon translation, the auto-inhibition by Fos protein regulates basal Fos expression. The pattern of external stimuli and the valence of the stimulus to the animal change Fos signal, thus the signal reflects learning and memory aspects. Understanding the features of multiple components regulating Fos signaling is necessary for the optimal generation and interpretation of Fos signal.

Using c-fos to study neuronal ensembles in corticostriatal circuitry of addiction

Learned associations between drugs and environment play an important role in addiction and are thought to be encoded within specific patterns of sparsely distributed neurons called neuronal ensembles. This hypothesis is supported by correlational data from in vivo electrophysiology and cellular imaging studies in relapse models in rodents. In particular, cellular imaging with the immediate early gene c-fos and its protein product Fos has been used to identify sparsely distributed neurons that were strongly activated during conditioned drug behaviors such as drug self-administration and context- and cue-induced reinstatement of drug seeking. Here we review how Fos and the c-fos promoter have been employed to demonstrate causal roles for Fos-expressing neuronal ensembles in prefrontal cortex and nucleus accumbens in conditioned drug behaviors. This work has allowed identification of unique molecular and electrophysiological alterations within Fos-expressing neuronal ensembles that may contribute to the development and expression of learned associations in addiction.

Cocaine-induced changes in NMDA receptor signaling

Addictive states are often thought to rely on lasting modification of signaling at relevant synapses. A long-standing theory posits that activity at N-methyl-D-aspartate receptors (NMDARs) is a critical component of long-term synaptic plasticity in many brain areas. Indeed, NMDAR signaling has been found to play a role in the etiology of addictive states, in particular, following cocaine exposure. However, no consensus is apparent with respect to the specific effects of cocaine exposure on NMDARs. Part of the difficulty lies in the fact that NMDARs interact extensively with multiple membrane proteins and intracellular signaling cascades. This allows for highly heterogeneous patterns of NMDAR regulation by cocaine in distinct brain regions and at distinct synapses. The picture is further complicated by findings that cocaine effects on NMDARs are sensitive to the behavioral history of cocaine exposure such as the mode of cocaine administration. This review provides a summary of evidence for cocaine-induced changes in NMDAR expression, cocaine-induced alterations in NMDAR function, and cocaine effects on NMDAR control of intracellular signaling cascades.

Optogenetic insights into striatal function and behavior

Recent breakthroughs in optogenetic technologies to alter neuronal firing and function with light, combined with cell type-specific transgenic animal lines, has led to important insights into the function of distinct neuronal cell subtypes and afferent connections in the heterogeneously complex striatum. A vital part of the basal ganglia, the striatum is heavily implicated in both motor control and motivation-based behavior; as well as in neurological disorders and psychiatric diseases including Parkinson's Disease, Huntington's Disease, drug addiction, depression, and schizophrenia. Researchers are able to manipulate firing and cell signaling with temporal precision using optogenetics in the two striatal medium spiny neuron (MSN) subpopulations, the striatal interneurons, and striatal afferents. These studies confirmed the classical hypothesis of movement control and reward seeking behavior through direct versus indirect pathway MSNs; illuminated a selective role for TANs in cocaine reward; dissected the roles of glutamatergic and dopaminergic inputs to striatum in reward; and highlighted a role for striatal signaling molecules including an adrenergic G-protein coupled receptor in reward and the rho-GTPase Rac1 in cocaine reward and cocaine induced structural plasticity. This review focuses on how the evolving optogenetic toolbox provides insight into the distinct behavioral roles of striatal cell subpopulations and striatal afferents, which has clinically relevant implications into neurological disorders and psychiatric disease.

Addiction-related gene regulation: risks of exposure to cognitive enhancers vs. other psychostimulants

The psychostimulants methylphenidate (Ritalin, Concerta), amphetamine (Adderall), and modafinil (Provigil) are widely used in the treatment of medical conditions such as attention-deficit hyperactivity disorder and narcolepsy and, increasingly, as "cognitive enhancers" by healthy people. The long-term neuronal effects of these drugs, however, are poorly understood. A substantial amount of research over the past two decades has investigated the effects of psychostimulants such as cocaine and amphetamines on gene regulation in the brain because these molecular changes are considered critical for psychostimulant addiction. This work has determined in some detail the neurochemical and cellular mechanisms that mediate psychostimulant-induced gene regulation and has also identified the neuronal systems altered by these drugs. Among the most affected brain systems are corticostriatal circuits, which are part of cortico-basal ganglia-cortical loops that mediate motivated behavior. The neurotransmitters critical for such gene regulation are dopamine in interaction with glutamate, while other neurotransmitters (e.g., serotonin) play modulatory roles. This review presents (1) an overview of the main findings on cocaine- and amphetamine-induced gene regulation in corticostriatal circuits in an effort to provide a cellular framework for (2) an assessment of the molecular changes produced by methylphenidate, medical amphetamine (Adderall), and modafinil. The findings lead to the conclusion that protracted exposure to these cognitive enhancers can induce gene regulation effects in corticostriatal circuits that are qualitatively similar to those of cocaine and other amphetamines. These neuronal changes may contribute to the addiction liability of the psychostimulant cognitive enhancers.

Nucleus accumbens D2- and D1-receptor expressing medium spiny neurons are selectively activated by morphine withdrawal and acute morphine, respectively

Opioids are effective analgesic agents but serious adverse effects such as tolerance and withdrawal contribute to opioid dependence and limit their use. Opioid withdrawal involves numerous brain regions and includes suppression of dopamine release and activation of neurons in the ventral striatum. By contrast, acute opioids increase dopamine release. Like withdrawal, acute opioids also activate neurons in the ventral striatum, suggesting that different populations of ventral striatal neurons may be activated by withdrawal and acute opioid actions. Here, immunofluorescence for the activity-related immediate-early gene, c-Fos, was examined in transgenic reporter mouse lines by confocal microscopy to study the specific populations of ventral striatal neurons activated by morphine withdrawal and acute morphine. After chronic morphine, naloxone-precipitated withdrawal strongly increased expression of c-Fos immunoreactivity, predominantly in D2-receptor (D2R) medium-sized spiny neurons (MSNs) of the nucleus accumbens (NAc) core and shell regions. By contrast, a single injection of morphine exclusively activated c-Fos immunoreactivity in D1-receptor expressing (D1R) MSNs of the core and shell of the NAc. These results reveal a striking segregation of neuronal responses occurring in the two populations of MSNs of the NAc in response to morphine withdrawal and acute morphine.

Suppression of c-Fos protein and mRNA expression in pentylenetetrazole-induced kindled mouse brain by isoxylitones

An early immediate gene c-fos has been proposed as the gene responsible for turning on molecular events that might underlie the long-term neural changes occurring during kindling. We have evaluated the effects of novel anticonvulsant isomeric compounds isoxylitones [(E/Z)-2-propanone-1,3,5,5-trimethyl-2-cyclohexen-1-ylidine] on the c-Fos protein and mRNA expression in the brain samples of kindled mice and compared it with the normal and untreated kindled groups. Kindling was induced in male NMRI mice by repeated administration of sub-convulsive dose (50 mg/kg) of pentylenetetrazole (PTZ) until a seizure score of 4-5 was achieved. The c-Fos expression was quantified by combination of immunohistochemistry and RT-PCR protocols. Both the immunohistochemical and RT-PCR analysis revealed a marked increase in the expression of c-fos mRNA and protein in the brain regions tested in case of PTZ-kindled control group compared to normal control. In contrast, the isoxylitone (30 mg/kg)-treated group demonstrated significant reduction of c-Fos expression compared to PTZ-kindled control animals. However, low expression of c-fos mRNA was only detected in the thalamus of the isoxylitone-treated brain samples. Based on these observations, we suggest that isoxylitones may have the capacity to control the seizure pattern by mechanism such as the suppression of c-Fos protein and mRNA levels in different regions of the brain. Further investigations to explore the mechanism of action of these compounds are under process.

Basal Ganglia disorders associated with imbalances in the striatal striosome and matrix compartments

The striatum is composed principally of GABAergic, medium spiny striatal projection neurons (MSNs) that can be categorized based on their gene expression, electrophysiological profiles, and input–output circuits. Major subdivisions of MSN populations include (1) those in ventromedial and dorsolateral striatal regions, (2) those giving rise to the direct and indirect pathways, and (3) those that lie in the striosome and matrix compartments. The first two classificatory schemes have enabled advances in understanding of how basal ganglia circuits contribute to disease. However, despite the large number of molecules that are differentially expressed in the striosomes or the extra-striosomal matrix, and the evidence that these compartments have different input–output connections, our understanding of how this compartmentalization contributes to striatal function is still not clear. A broad view is that the matrix contains the direct and indirect pathway MSNs that form parts of sensorimotor and associative circuits, whereas striosomes contain MSNs that receive input from parts of limbic cortex and project directly or indirectly to the dopamine-containing neurons of the substantia nigra, pars compacta. Striosomes are widely distributed within the striatum and are thought to exert global, as well as local, influences on striatal processing by exchanging information with the surrounding matrix, including through interneurons that send processes into both compartments. It has been suggested that striosomes exert and maintain limbic control over behaviors driven by surrounding sensorimotor and associative parts of the striatal matrix. Consistent with this possibility, imbalances between striosome and matrix functions have been reported in relation to neurological disorders, including Huntington’s disease, L-DOPA-induced dyskinesias, dystonia, and drug addiction. Here, we consider how signaling imbalances between the striosomes and matrix might relate to symptomatology in these disorders.

Identification of a specific assembly of the g protein golf as a critical and regulated module of dopamine and adenosine-activated cAMP pathways in the striatum

In the principal neurons of striatum (medium spiny neurons, MSNs), cAMP pathway is primarily activated through the stimulation of dopamine D1 and adenosine A_2A receptors, these receptors being mainly expressed in striatonigral and striatopallidal MSNs, respectively. Since cAMP signaling pathway could be altered in various physiological and pathological circumstances, including drug addiction and Parkinson’s disease, it is of crucial importance to identify the molecular components involved in the activation of this pathway. In MSNs, cAMP pathway activation is not dependent on the classical Gs GTP-binding protein but requires a specific G protein subunit heterotrimer containing Gαolf/β2/γ7 in particular association with adenylyl cyclase type 5. This assembly forms an authentic functional signaling unit since loss of one of its members leads to defects of cAMP pathway activation in response to D1 or A_2A receptor stimulation, inducing dramatic impairments of behavioral responses dependent on these receptors. Interestingly, D1 receptor (D1R)-dependent cAMP signaling is modulated by the neuronal levels of Gαolf, indicating that Gαolf represents the rate-limiting step in this signaling cascade and could constitute a critical element for regulation of D1R responses. In both Parkinsonian patients and several animal models of Parkinson’s disease, the lesion of dopamine neurons produces a prolonged elevation of Gαolf levels. This observation gives an explanation for the cAMP pathway hypersensitivity to D1R stimulation, occurring despite an unaltered D1R density. In conclusion, alterations in the highly specialized assembly of Gαolf/β2/γ7 subunits can happen in pathological conditions, such as Parkinson’s disease, and it could have important functional consequences in relation to changes in D1R signaling in the striatum.

The striatal balancing act in drug addiction: distinct roles of direct and indirect pathway medium spiny neurons

The striatum plays a key role in mediating the acute and chronic effects of addictive drugs, with drugs of abuse causing long-lasting molecular and cellular alterations in both dorsal striatum and nucleus accumbens (ventral striatum). Despite the wealth of research on the biological actions of abused drugs in striatum, until recently, the distinct roles of the striatum’s two major subtypes of medium spiny neurons (MSNs) in drug addiction remained elusive. Recent advances in cell-type-specific technologies, including fluorescent reporter mice, transgenic, or knockout mice, and viral-mediated gene transfer, have advanced the field toward a more comprehensive understanding of the two MSN subtypes in the long-term actions of drugs of abuse. Here we review progress in defining the distinct molecular and functional contributions of the two MSN subtypes in mediating addiction.

FACS identifies unique cocaine-induced gene regulation in selectively activated adult striatal neurons

Numerous studies with the neural activity marker Fos indicate that cocaine activates only a small proportion of sparsely distributed striatal neurons. Until now, efficient methods were not available to assess neuroadaptations induced specifically within these activated neurons. We used fluorescence-activated cell sorting (FACS) to purify striatal neurons activated during cocaine-induced locomotion in naive and cocaine-sensitized cfos-lacZ transgenic rats. Activated neurons were labeled with an antibody against β-galactosidase, the protein product of the lacZ gene. Cocaine induced a unique gene expression profile selectively in the small proportion of activated neurons that was not observed in the nonactivated majority of neurons. These genes included altered levels of the immediate early genes arc, fosB, and nr4a3, as well as genes involved in p38 MAPK signaling and cell-type specificity. We propose that this FACS method can be used to study molecular neuroadaptations in specific neurons encoding the behavioral effects of abused drugs and other learned behaviors.

Continuous, but not intermittent, antipsychotic drug delivery intensifies the pursuit of reward cues

Chronic exposure to antipsychotic medications can persistently change brain dopamine systems. Most studies on the functional significance of these neural changes have focused on motor behavior and few have addressed how long-term antipsychotic treatment might influence dopamine-mediated reward function. We asked, therefore, whether a clinically relevant antipsychotic treatment regimen would alter the incentive motivational properties of a reward cue. We assessed the ability of a Pavlovian-conditioned stimulus to function as a conditioned reward, as well as to elicit approach behavior in rats treated with haloperidol, either continuously (achieved via subcutaneous osmotic minipump) or intermittently (achieved via daily subcutaneous injections). Continuous, but not intermittent, treatment enhanced the ability of amphetamine to potentiate the conditioned reinforcing effects of a cue associated with water. This effect was not related to differences in the ability to attribute predictive value to a conditioned stimulus (as measured by conditioned approach behavior), but was potentially linked to the development of behavioral supersensitivity to amphetamine and to augmented amphetamine-induced immediate early-gene expression (c-fos and Nur77) in dorsal striatopallidal and striatonigral cells. By enhancing the ability of reward cues to control behavior and by intensifying dopamine-mediated striatopallidal and striatonigral cell activity, standard (ie, continuous) antipsychotic treatment regimens might exacerbate drug-seeking and drug-taking behavior in schizophrenia. Achieving regular but transiently high antipsychotic levels in the brain (as modeled in the intermittent condition) might be a viable option to prevent these changes. This possibility should be explored in the clinic.

Regulation of the immediate-early genes arc and zif268 in a mouse operant model of cocaine seeking reinstatement

Reinstatement of extinguished operant responding for drug is an appropriate model of relapse to drug abuse. Due to the difficulty of implementing in mice the procedure of instrumental intravenous self-administration, mechanisms of reinstatement have so far been studied almost exclusively in rats. A mouse model of reinstatement of cocaine seeking has recently been characterized (Soria et al. 2008). The aim of the present study was to assess regional brain activation, as measured by induction of the immediate early genes (IEG) arc and zif268, during priming- or cue-elicited reinstatement of cocaine seeking using this new mouse model and the in situ hybridization technique. We have demonstrated that cue-elicited reinstatement of cocaine seeking was associated with induction of the IEG in the medial prefrontal cortex (prelimbic and infralimbic) and basolateral amygdala. Priming-induced reinstatement produced a more widespread up-regulation of those genes in forebrain regions including medial prefrontal, orbitofrontal and motor cortex, dorsal striatum and basolateral amygdala. These patterns of IEG expression are in agreement with previous results obtained in rats and thus indicate that the new mouse model of reinstatement is functionally equivalent to rat models. That comparability adds to the usefulness of the mouse model as a tool for addressing neurobiological mechanisms of addiction.

Role of dopamine D1 receptors in the activation of nucleus accumbens extracellular signal-regulated kinase (ERK) by cocaine-paired contextual cues

Exposure to drug-paired cues can trigger addicts to relapse into drug seeking. Although the molecular mechanisms underlying cue-elicited cocaine seeking are incompletely understood, the protein kinase extracellular signal-regulated kinase (ERK) is known to have an important role. Psychostimulants and their associated cues can activate ERK in medium spiny neurons of the nucleus accumbens core (AcbC). These medium spiny neurons can be classified according to their projections (to ventral pallidum and/or substantia nigra) and by their mRNA expression. The present experiments were designed to determine which distinct set of AcbC projection neurons expresses phosphorylated ERK (pERK) in response to cocaine-paired contextual cues. Combined use of the retrograde label Flurogold with immunohistochemical staining of pERK was used to show that the AcbC pERK accompanying preference for cocaine-paired contexts occurs in both the accumbens (Acb)-nigral and Acb-pallidal projections. The gene expression characteristics of the neurons expressing pERK in response to cocaine-paired cues was further investigated using combined in situ hybridization and immunocytochemistry to show that AcbC pERK+ cells correspond to D1, but not preproenkephalin, mRNA+ cells. Furthermore, intra-AcbC infusion of the D1-antagonist SCH23390 attenuated cue-induced AcbC pERK expression. In aggregate, these results indicate that (i) the D1-expressing AcbC neurons evidence long-term plasticity related to drug-cue memories and (ii) local dopamine D1 receptors are necessary for the expression of cocaine-paired cue-induced pERK in these AcbC neurons.

Strain-specific proportion of the two isoforms of the dopamine D2 receptor in the mouse striatum: associated neural and behavioral phenotypes

Genetic variability in the proportion of the two alternative dopamine D2 receptor (D2R) mRNA splice variants, D2R-long (D2L) and D2R-short (D2S), influence corticostriatal functioning and could be implicated in liability to psychopathology. This study compared mesostriatal D2L/D2S ratios and associated neural and behavioral phenotypes in mice of the DBA/2J and C57BL/6J-inbred strains, which differ for schizophrenia- and addiction-like phenotypes. Results showed that DBA/2J mice lack the striatal predominance of D2L that has been reported in the rat and in C57BL/6J mice and confirmed in the latter strain by this study. Only C57BL/6J mice showed enhanced striatal c-Fos expression under D1R and D2/3R co-stimulation, indicating synergistic interaction between the subtypes of DA receptors. Instead, DBA/2J mice were characterized by opposing effects of D2/3R and D1R stimulation on striatal c-Fos expression, in line with a more pronounced influence of D2S isoform, and did not express stereotyped climbing under D1R and D2/3R co-stimulation, as reported for D2L-/- mice. Finally, strain-specific modulation of c-Fos expression by D1R and D2/3R co-stimulation was selectively observed in striatal compartments receiving inputs from the prefrontal cortex and involved in the control of motivated behaviors. These results show differences in tissue-specific D2R splicing in mice with intact genotypes and support a role for this phenotype in individual variability of corticostriatal functioning and in liability to psychopathology.

Cocaine addiction and personality: a mathematical model

The existence of a close relation between personality and drug consumption is recognized, but the corresponding causal connection is not well known. Neither is it well known whether personality exercises an influence predominantly at the beginning and development of addiction, nor whether drug consumption produces changes in personality. This paper presents a dynamic mathematical model of personality and addiction based on the unique personality trait theory (UPTT) and the general modelling methodology. This model attempts to integrate personality, the acute effect of drugs, and addiction. The UPTT states the existence of a unique trait of personality called extraversion, understood as a dimension that ranges from impulsive behaviour and sensation-seeking (extravert pole) to fearful and anxious behaviour (introvert pole). As a consequence of drug consumption, the model provides the main patterns of extraversion dynamics through a system of five coupled differential equations. It combines genetic extraversion, as a steady state, and dynamic extraversion in a unique variable measured on the hedonic scale. The dynamics of this variable describes the effects of stimulant drugs on a short-term time scale (typical of the acute effect); while its mean time value describes the effects of stimulant drugs on a long-term time scale (typical of the addiction effect). This understanding may help to develop programmes of prevention and intervention in drug misuse.

Differential effects of methamphetamine and SCH23390 on the expression of members of IEG families of transcription factors in the rat striatum

Methamphetamine (METH) is a psychostimulant that can cause long-lasting neurodegenerative effects in humans and animals. These toxic effects appear to occur, in part, via activation of dopamine (DA) D1 receptors. This paper assessed the possibility that the DA D1 receptor antagonist, SCH23390, might inhibit METH-induced changes in the expression of several members of immediate early genes (IEGs) which are known to control more delayed expression of other genes. We found that injections of METH (4x10 mg/kg, given at 2 h intervals) caused significant increases in c-fos and fra-2 expression which lasted from 30 min to 4 h. Pre-treatment with SCH23390, given 30 min before each METH injection, completely blocked METH-induced expression of c-fos, but only partially inhibited fra-2 mRNA expression. These results were confirmed by Western blot analysis which showed METH-induced changes in c-Fos protein expression that were blocked by pretreatment with SCH23390. There were also delayed METH-induced DA D1 receptor-dependent effects on fosB mRNA expression. Even though fra-1 expression was not affected by pretreatment with METH alone, the repeated injections of SCH23390 caused substantial decreases in fra-1 mRNA expression in both the presence and absence of METH. The repeated injections of METH caused no changes in the mRNAs for c-jun, junB or junD. However, there were significant increases in the phosphorylation of c-Jun protein (ser63). Phosphorylation of c-Jun occurred in a delayed fashion (16 and 24 h after the last METH injections) and was attenuated by SCH23390 pretreatment. Interestingly, SCH23390 given alone caused significant decreases in phospho-c-Jun at all time-points. The METH injections also caused delayed induction in the expression of members of the Egr family of transcription factors in a DA D1 receptor-dependent fashion. Repeated injections of SCH23390 caused substantial suppression of basal striatal egr-1 and egr-2 mRNA expression but not of that of egr-3. Both crem and arc mRNA levels were induced by METH in a SCH23390-sensitive fashion. Moreover, multiple injections of SCH23390 given alone caused marked inhibition of basal arc expression. These results show that multiple injections of METH can differentially affect the expression of several IEGs, some of which occurred in a DA D1 receptor dependent fashion. The SCH23390-mediated suppression of basal fra-1, egr-1, and egr-2 mRNA levels suggests that their basal expression in the striatum might be dependent on tonic stimulation of the DA D1 receptor.

Cocaine activates Homer1 immediate early gene transcription in the mesocorticolimbic circuit: differential regulation by dopamine and glutamate signaling

Homer proteins are intracellular scaffolding proteins that, among glutamate receptors, selectively bind to group1 metabotropic glutamate receptors and regulate their trafficking and intracellular signaling. Homer proteins have been implicated in synaptic and behavioral plasticity, including drug-seeking behavior after cocaine treatment. Homer1 gene activation leads to transcription of a variant mRNA (Homer1a), which functions as an immediate early gene. Homer1a competes with the constitutive Homer proteins (Homer1b/c/d, Homer2a/b, Homer3) for binding to group1 metabotropic glutamate and IP3 receptors. Binding of Homer1a to these proteins disrupts their association with the intracellular signaling scaffold and modulates receptor function. In this study, using RT-PCR, activation of Homer1a mRNA transcription in response to acute and repeated administration of cocaine was characterized in prefrontal cortex, nucleus accumbens, and ventral tegmental area, three mesocorticolimbic nuclei of the rat brain. Moreover, the dopaminergic and glutamatergic regulation of Homer1 gene activation by cocaine was investigated. Acute cocaine rapidly and transiently activated transcription of Homer1a mRNA in all three nuclei. However, repeated administration of cocaine was not effective in inducing the Homer1a mRNA transcription after various withdrawal times ranging from 2 h to 3 weeks. The acute cocaine-mediated activation of Homer1 gene was regulated by D1 but not D2 dopamine receptors. The blockade of AMPA or NMDA glutamate receptors did not prevent cocaine-mediated activation of Homer1 gene in the three mesocorticolimbic nuclei. These data indicate that acute administration of cocaine transiently activates Homer1 gene producing the immediate early gene Homer1a mRNA in the three mesocorticolimbic nuclei of the rat brain. Activation of Homer1 gene may contribute to the cocaine-mediated synaptic and behavioral plasticity.

Maturation of coordinated immediate early gene expression by cocaine during adolescence

Adolescence may be a critical period for drug addiction. Young adolescent male rats have greater locomotor responses than adults after acute low dose cocaine administration. Further, repeated cocaine administration produces as much or more conditioned place preference but reduced locomotor sensitization in adolescents compared to adults. Acute activation of neurons by cocaine induces long-term changes in behavior by activating transcriptional complexes. The purpose of the present study was to correlate cocaine-induced locomotor activity with neuronal activation in subregions of the striatum and cortex by acute cocaine in young adolescent (postnatal (PN) 28) and adult (PN 65) male rats by measuring the induction of the plasticity-associated immediate early genes (IEGs) c-fos and zif268 using in situ hybridization. Animals were treated with saline, low (10 mg/kg), or high (40 mg/kg) dose cocaine in locomotor activity chambers and killed 30 min later. Low dose cocaine induced more locomotor activity and striatal c-fos expression in adolescents than adults whereas high dose cocaine induced more locomotor activity, striatal c-fos, and striatal zif268 expression in adults. Locomotor activity correlated with the expression of both genes in adults but correlated with striatal c-fos only in adolescents. Finally, there was a significant correlation between the expression of c-fos and zif268 in the adult striatum but not in adolescents. Our results suggest that the coordinated expression of transcription factors by cocaine continues to develop during adolescence. The immature regulation of transcription factors by cocaine could explain why adolescents show unique sensitivity to specific long-term behavioral alterations following cocaine treatment.

Striatal dopamine and glutamate receptors modulate methamphetamine-induced cortical Fos expression

Methamphetamine (mAMPH) is a psychostimulant drug that increases extracellular levels of monoamines throughout the brain. It has previously been observed that a single injection of mAMPH increases immediate early gene (IEG) expression in both the striatum and cerebral cortex. Moreover, this effect is modulated by dopamine and glutamate receptors since systemic administration of dopamine or glutamate antagonists has been found to alter mAMPH-induced striatal and cortical IEG expression. However, because dopamine and glutamate receptors are found in extra-striatal as well as striatal brain regions, studies employing systemic injection of dopamine or glutamate antagonists fail to localize the effects of mAMPH-induced activation. In the present experiments, the roles of striatal dopamine and glutamate receptors in mAMPH-induced gene expression in the striatum and cerebral cortex were examined. The nuclear expression of Fos, the protein product of the IEG c-fos, was quantified in both the striatum and the cortex of animals receiving intrastriatal dopamine or glutamate antagonist administration. Intrastriatal infusion of dopamine (D1 or D2) or glutamate [N-methyl-D-aspartic acid (NMDA) or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)] antagonists affected not only mAMPH-induced striatal, but also cortical, Fos expression. Overall, the effects of the antagonists occurred dose-dependently, in both the infused and non-infused hemispheres, with greater influences occurring in the infused hemisphere. Finally, unilateral intrastriatal infusion of dopamine or glutamate antagonists changed the behavior of the rats from characteristic mAMPH-induced stereotypy to rotation ipsilateral to the infusion. These results demonstrate that mAMPH's actions on striatal dopamine and glutamate receptors modulate the widespread cortical activation induced by mAMPH. It is hypothesized that dopamine release from nigrostriatal terminals modulates activity within striatal efferent pathways, thereby disinhibiting thalamo-cortical circuits. By extension, these results suggest processes through which repeated exposure to mAMPH might influence cortical function in mAMPH abusers.

Masculinization induced by neonatal exposure to PGE(2) or estradiol alters c-fos induction by estrous odors in adult rats

Processing of relevant olfactory and pheromonal cues has long been known as an important process necessary for social and sexual behavior in rodents. Several nuclei that receive input from the vomeronasal projection pathway are involved in sexual behavior and show changes in immediate early gene expression after stimulation with a variety of sex-related stimuli. The nuclei in this pathway are sexually dimorphic due to the early patterning events induced by estradiol derived from testicular androgens, which developmentally defeminize and masculinize the brain and adult sexual behavior. Masculinization can be induced independently of estradiol via prostaglandin-E(2) (PGE(2)), and therefore assessed separately from defeminization. Here we examined the effects of brain defeminization and masculinization on neuronal response to sex-related odors using Fos, the protein product of the immediate early gene c-fos, as an indicator of activity. Female rat pups treated with a cyclooxygenase-2 inhibitor, to reduce PGE(2), plus estradiol, estradiol alone, and PGE(2) alone were exposed to estrous female odor as adults and the resulting Fos expression was examined in the medial amygdala, preoptic area, and ventromedial nucleus of the hypothalamus. Defeminized and/or masculinized females all showed patterns of Fos activity similar to control males and significantly different from control females. These results suggest that early exposure to estradiol and PGE(2) do not affect olfaction in females, but switch the activity pattern of sex-related nuclei in females to resemble that of males following exposure to sexually-relevant cues.

Effects of dopamine and NMDA receptors on cocaine-induced Fos expression in the striatum of Fischer rats

Cocaine is an addictive psychostimulant that induces immediate early gene (IEG) expression by activating dopamine (DA) D1 and glutamate NMDA receptors in the striatum. In this study, we show that a single cocaine administration (30 mg/kg) time-dependently increases ERK phosphorylation, c-Fos and FosB protein expression, and MKP-1 phosphorylation (p-MKP-1), in the caudate-putamen (CPu) and nucleus accumbens (NAc) of Fischer rats. In the CPu, 1 h after cocaine injection, the increase in c-Fos and FosB protein expressions is totally abolished by pre-administration of DA-D1 receptor antagonist, SCH23390. In the NAc, SCH23390 also inhibits cocaine-induced c-Fos protein expression. The pre-treatment of NMDA receptor antagonist, MK801, partially reduces cocaine-activated c-Fos protein expression in the CPu. Furthermore, the escalation of p-MKP-1 after acute cocaine administration is dependent on both DA-D1 and NMDA receptor activation in both brain regions examined. Our data suggest that cocaine may modulate ERK pathway signaling through the activation of DA-D1 and NMDA receptors, subsequently influencing the IEG protein expression.

Expression of amphetamine sensitization is associated with recruitment of a reactive neuronal population in the nucleus accumbens core

RATIONALE

Repeated exposure to psychostimulant drugs causes a long-lasting increase in the psychomotor and reinforcing effects of these drugs and an array of neuroadaptations. One such alteration is a hypersensitivity of striatal activity such that a low dose of amphetamine in sensitized animals produces dorsal striatal activation patterns similar to acute treatment with a high dose of amphetamine.

OBJECTIVES

To extend previous findings of striatal hypersensitivity with behavioral observations and with cellular activity in the nucleus accumbens and prefrontal cortex in sensitized animals.

MATERIALS AND METHODS

Rats treated acutely with 0, 1, 2.5, or 5 mg/kg i.p. amphetamine and sensitized rats challenged with 1 mg/kg i.p. amphetamine were scored for stereotypy, rearing, and grooming, and locomotor activity recorded. c-fos positive nuclei were quantified in the nucleus accumbens and prefrontal cortex after expression of sensitization with 1 mg/kg i.p. amphetamine.

RESULTS

Intense stereotypy was seen in animals treated acutely with 5 mg/kg amphetamine, but not in the sensitized group treated with 1 mg/kg amphetamine. The c-fos response to amphetamine in the accumbens core was augmented in amphetamine-pretreated animals with a shift in the distribution of optical density, while no effect of sensitization was seen in the nucleus accumbens shell or prefrontal cortex.

CONCLUSIONS

A lack of stereotypy in the sensitized group indicates a dissociation of behavioral responses to amphetamine and striatal immediate-early gene activation patterns. The increase in c-fos positive nuclei and shift in the distribution of optical density observed in the nucleus accumbens core suggests recruitment of a new population of neurons during expression of sensitization.

The rate of intravenous cocaine administration alters c-fos mRNA expression and the temporal dynamics of dopamine, but not glutamate, overflow in the striatum

The rapid entry of drugs into the brain is thought to increase the propensity for addiction. The mechanisms that underlie this effect are not known, but variation in the rate of intravenous cocaine delivery does influence its ability to induce immediate early gene expression (IEG) in the striatum, and to produce psychomotor sensitization. Both IEG induction and psychomotor sensitization are dependent upon dopamine and glutamate neurotransmission within the striatum. We hypothesized, therefore, that varying the rate of intravenous cocaine delivery might influence dopamine and/or glutamate overflow in the striatum. To test this we used microdialysis coupled to on-line capillary electrophoresis and laser-induced fluorescence, which allows for very rapid sampling, to compare the effects of a rapid (5 s) versus a slow (100 s) intravenous cocaine infusion on extracellular dopamine and glutamate levels in the striatum of freely moving rats. An acute injection of cocaine had no effect on extracellular glutamate, at either rate tested. In contrast, although peak levels of dopamine were unaffected by infusion rate, dopamine levels increased more rapidly when cocaine was administered over 5 versus 100 s. Moreover, c-fos mRNA expression in the region of the striatum sampled was greater when cocaine was administered rapidly than when given slowly. These data suggest that small differences in the temporal dynamics of dopamine neurotransmission may have a large effect on the subsequent induction of intracellular signalling cascades that lead to immediate early gene expression, and in this way influence the ability of cocaine to produce long-lasting changes in brain and behavior.

Repeated amphetamine administration outside the home cage enhances drug-induced Fos expression in rat nucleus accumbens

Induction of the immediate early gene protein product Fos has been used extensively to assess neural activation in the striatum after repeated amphetamine administration to rats in their home cages. However, this technique has not been used to examine striatal activation after repeated administration outside the home cage, an environment where repeated drug administration produces more robust psychomotor sensitization. We determined the dose-response relationship for amphetamine-induced psychomotor activity and Fos expression in nucleus accumbens and caudate-putamen 1 week after repeated administration of amphetamine or saline in locomotor activity chambers. Repeated administration of amphetamine enhanced amphetamine-induced locomotor activity and stereotypy and Fos expression in nucleus accumbens, but not in caudate-putamen. In comparison, levels of Fos expression induced by 1mg/kg amphetamine were not altered in nucleus accumbens or caudate-putamen by repeated amphetamine administration in the home cage. Double-labeling of Fos protein and enkephalin mRNA indicates that Fos is expressed in approximately equal numbers of enkephalin-negative and enkephalin-positive neurons in nucleus accumbens and caudate-putamen following injections outside the home cage. Furthermore, repeated amphetamine administration increased drug-induced Fos expression in enkephalin-positive, but not enkephalin-negative, neurons in nucleus accumbens. We conclude that repeated amphetamine administration outside the home cage recruits the activation of enkephalin-containing nucleus accumbens neurons during sensitized amphetamine-induced psychomotor activity.

Dopamine D(1) and D(3) receptors oppositely regulate NMDA- and cocaine-induced MAPK signaling via NMDA receptor phosphorylation

Development of drug addiction involves complex molecular changes in the CNS. The mitogen-activated protein kinase (MAPK) signaling pathway plays a key role in mediating neuronal activation induced by dopamine, glutamate, and drugs of abuse. We previously showed that dopamine D(1) and D(3) receptors play different roles in regulating cocaine-induced MAPK activation. Although there are functional and physical interactions between dopamine and glutamate receptors, little is known regarding the involvement of D(1) and D(3) receptors in modulating glutamate-induced MAPK activation and underlying mechanisms. In this study, we show that D(1) and D(3) receptors play opposite roles in regulating N-methyl-d-aspartate (NMDA) -induced activation of extracellular signal-regulated kinase (ERK) in the caudate putamen (CPu). D(3) receptors also inhibit NMDA-induced activation of the c-Jun N-terminal kinase and p38 kinase in the CPu. NMDA-induced activation of the NMDA-receptor R1 subunit (NR1), Ca(2+)/calmodulin-dependent protein kinase II and the cAMP-response element binding protein (CREB), and cocaine-induced CREB activation in the CPu are also oppositely regulated by dopamine D(1) and D(3) receptors. Finally, the blockade of NMDA-receptor reduces cocaine-induced ERK activation, and inhibits phosphorylation of NR1, Ca(2+)/calmodulin-dependent protein kinase II, and CREB, while inhibiting ERK activation attenuates cocaine-induced CREB phosphorylation in the CPu. These results suggest that dopamine D(1) and D(3) receptors oppositely regulate NMDA- and cocaine-induced MAPK signaling via phosphorylation of NR1.

Dysregulation of gene induction in corticostriatal circuits after repeated methylphenidate treatment in adolescent rats: differential effects on zif 268 and homer 1a

Psychostimulants and other dopamine agonists produce molecular changes in neurons of cortico-basal ganglia-cortical circuits, and such neuronal changes are implicated in behavioural disorders. Methylphenidate, a psychostimulant that causes dopamine overflow (among other effects), alters gene regulation in neurons of the striatum. The present study compared the effects of acute and repeated methylphenidate treatment on cortical and striatal gene regulation in adolescent rats. Changes in the expression of the immediate-early genes zif 268 and homer 1a were mapped in 23 striatal sectors and 22 cortical areas that provide input to these striatal sectors, in order to determine whether specific corticostriatal circuits were affected by these treatments. Acute administration of methylphenidate (5 mg/kg, i.p.) produced modest zif 268 induction in cortical areas. These cortical zif 268 responses were correlated in magnitude with zif 268 induction in functionally related striatal sectors. In contrast, after repeated methylphenidate treatment (10 mg/kg, 7 days), cortical and striatal gene induction were dissociated. In these animals, the methylphenidate challenge (5 mg/kg) produced significantly greater gene induction (zif 268 and homer 1a) in the cortex. This enhanced response was widespread but regionally selective, as it occurred predominantly in premotor, motor and somatosensory cortical areas. At the same time, striatal gene induction was partly suppressed (zif 268) or unchanged (homer 1a). Thus, repeated methylphenidate treatment disrupted the normally coordinated gene activation patterns in cortical and striatal nodes of corticostriatal circuits. This drug-induced dissociation in cortical and striatal functioning was associated with enhanced levels of behavioural stereotypies, suggesting disrupted motor switching function.

Fos and glutamate AMPA receptor subunit coexpression associated with cue-elicited cocaine-seeking behavior in abstinent rats

Cocaine-associated cues acquire incentive motivational effects that manifest as craving in humans and cocaine-seeking behavior in rats. We have reported an increase in neuronal activation in rats, measured by Fos protein expression, in various limbic and cortical regions following exposure to cocaine-associated cues. This study examined whether the conditioned neuronal activation involves glutamate AMPA receptors by measuring coexpression of Fos and AMPA glutamate receptor subunits (GluR1, GluR2/3, or GluR4). Rats trained to self-administer cocaine subsequently underwent 22 days of abstinence, during which they were exposed daily to either the self-administration environment with presentations of the light/tone cues previously paired with cocaine infusions (Extinction group) or an alternate environment (No Extinction group). All rats were then tested for cocaine-seeking behavior (i.e. responses without cocaine reinforcement) and Fos and AMPA glutamate receptor subunits were measured postmortem using immunocytochemistry. The No Extinction group exhibited increases in cocaine-seeking behavior and Fos expression in limbic and cortical regions relative to the Extinction group. A large number of Fos immunoreactive cells coexpressed GluR1, GluR2/3, and GluR4, suggesting that an action of glutamate at AMPA receptors may in part drive cue-elicited Fos expression. Importantly, there was an increase in the percentage of cells colabeled with Fos and GluR1 in the anterior cingulate and nucleus accumbens shell and cells colabeled with Fos and GluR4 in the infralimbic cortex, suggesting that within these regions, a greater, and perhaps even different, population of AMPA receptor subunit-expressing neurons is activated in rats engaged in cocaine-seeking behavior.

Motor-skill learning-associated gene regulation in the striatum: effects of cocaine

Psychostimulant-induced molecular changes in cortico-basal ganglia-cortical circuits play a critical role in addiction and dependence. These changes include alterations in gene regulation particularly in projection neurons of the sensorimotor striatum. We previously showed that cocaine-induced gene regulation in such neurons is dependent on the behavior performed during drug action. Rats trained on a running wheel under the influence of cocaine for 4 days subsequently displayed greater c-fos induction by cocaine than untrained controls. This effect was selective for the sensorimotor striatum, which is known to mediate forms of motor learning. In the present study, we investigated whether this enhanced cellular responsiveness was associated with learning of wheel running or with prolonged running (exercising), by assessing c-fos inducibility after 1, 2, or 8 days of training. Wheel training was performed after injection of cocaine (25 mg/kg) or vehicle, and c-fos induction by a cocaine challenge was measured 24 h later. Rats that trained under cocaine (but not vehicle) showed a greater c-fos response in the striatum compared to locked-wheel controls. This effect was present after the 1-day training, peaked after 2 days, and dissipated by 8 days of training. Similar effects were found for substance P, but not enkephalin, expression. These changes in striatal gene regulation paralleled improvement in wheel running, which was facilitated by cocaine. Thus, these training-induced molecular changes do not appear to represent exercising effects, but may reflect motor learning-associated neuronal changes altered by cocaine. Such cocaine effects may contribute to aberrant motor learning implicated in psychostimulant addiction.

Does neuronal expression of GDNF effectively protect dopaminergic neurons in a rat model of Parkinson's disease?

The transfer of the Glial cell line-derived neurotrophic factor (GDNF) gene to the central nervous system by a recombinant adenoviral vector (Ad) was studied. We constructed the adenovirus vector Ad-NSE-GDNF from which the E1, E3/E4 regions of Ad5 have been deleted and in which the GDNF gene was under the control of a neuron-specific enolase (NSE) promoter. The vector was injected into the striatum of a rat model of Parkinson's disease. We found that (i) the NSE promoter can restrict transgene expression in neurons; (ii) Ad-NSE-GDNF significantly protected dopaminergic (DA) neurons in the substantia nigra (SN) but did not reverse the impairments of amphetamine-induced rotational behavior in lesioned rats.

Effects of pelvic, pudendal, or hypogastric nerve cuts on Fos induction in the rat brain following vaginocervical stimulation

In the female rat, genitosensory input is conveyed to the central nervous system predominantly through the pelvic, pudendal, and hypogastric nerves. The present study examined the relative contribution of those three nerves in the expression of Fos immunoreactivity within brain regions previously shown to be activated by vaginocervical stimulation (VCS). Bilateral transection of those nerves, or sham neurectomy, was conducted in separate groups of ovariectomized, sexually-experienced females. After recovery, females were primed with estrogen and progesterone and given either 50 manual VCSs with a lubricated glass rod over the course of 1 h. VCS increased the number of neurons expressing Fos immunoreactivity in the medial preoptic area, lateral septum, bed nucleus of the stria terminalis, ventromedial hypothalamus, and medial amygdala of sham neurectomized females. Transection of the pelvic nerve reduced Fos immunoreactivity in the medial preoptic area, bed nucleus of the stria terminalis, ventromedial hypothalamus, and medial amygdala, whereas transection of the pudendal nerve had no effect. In contrast, transection of the hypogastric nerve increased Fos immunoreactivity in the medial preoptic area and lateral septum, whereas transaction of the pelvic nerve increased Fos immunoreactivity in the lateral septum, following VCS. All females given VCS, except those with pelvic neurectomy, displayed a characteristic immobility during each application. These data confirm that the pelvic nerve is largely responsible for the neural and behavioral effects of VCS, and support a separate function for the hypogastric nerve.

Cocaine‐induced locomotor activity and Fos expression in nucleus accumbens are sensitized for 6 months after repeated cocaine administration outside the home cage

Induction of the immediate early gene protein product Fos has been used extensively to assess neural activation in the striatum after repeated cocaine administration to rats in their home cages but rarely after repeated administration outside the home cage, which produces more robust locomotor sensitization. In the present study, we found cocaine-induced Fos expression in nucleus accumbens, but not caudate-putamen, was enhanced 1 and 6 months after repeated drug administration in locomotor activity chambers. Double-labelling of Fos protein and enkephalin mRNA indicated that Fos expression in nucleus accumbens was enhanced in enkephalin-positive, but not enkephalin-negative, medium spiny neurons. In contrast, cocaine-induced Fos expression was absent altogether in nucleus accumbens and unaltered in caudate-putamen 1 month after repeated cocaine administration in the home cage. As cocaine-induced locomotor activity was also enhanced 1 and 6 months after repeated cocaine administration in locomotor activity chambers, we wanted to confirm that neuronal activity in nucleus accumbens mediates cocaine-induced locomotor activity using our particular treatment regimen. Bilateral infusions of the GABA agonists baclofen and muscimol (1 microg/side) into nucleus accumbens of sensitized rats blocked cocaine-induced Fos expression and locomotor activity. Thus, while neuronal activity in both D1- and D2-type neurons in nucleus accumbens can mediate acute cocaine-induced locomotor activity, the enhanced activation of enkephalinergic D2-type neurons suggests that these latter neurons mediate the enhancement of cocaine-induced locomotor activity for up to 6 months after repeated drug administration outside the home cage.

Amphetamine-elicited striatal Fos expression is attenuated in neurotensin null mutant mice

Neurotensin (NT) has been suggested to interact with dopamine systems in different forebrain sites to exert both antipsychotic- and psychostimulant-like effects. We previously found that genetic or pharmacological manipulations that disrupt endogenous NT signaling attenuate antipsychotic drug-induced Fos expression in the dorsolateral and central striatum but not other striatal regions. To assess the role of NT in psychostimulant responses, we examined the ability of d-amphetamine (AMP) to induce Fos in wild-type and NT null mutant mice. AMP-elicited Fos expression was significantly attenuated in the medial striatum of NT null mutant mice, but was unaffected in other striatal territories. Similar results were obtained in rats and mice pretreated with the high affinity neurotensin receptor (NTR1) antagonist SR 48692. The effect of the NTR1 antagonist was particularly apparent in the striatal patch (striosome) compartment, as defined by mu-opioid receptor immunoreactivity. These data suggest that NT is required for the full activation by AMP of medial striatal neurons.

Inhibition of methylphenidate-induced gene expression in the striatum by local blockade of D1 dopamine receptors: interhemispheric effects

Psychostimulants change the function of cortico-basal ganglia circuits. Some of these effects are mediated by altered gene regulation in projection neurons of the striatum which participate in these circuits. Psychostimulant-induced changes in gene expression in these neurons are a consequence of excessive stimulation of G-protein-coupled receptors, particularly the D1 dopamine receptor subtype. Recent findings show that the psychostimulant methylphenidate, which causes dopamine overflow in the striatum, produces changes in striatal gene regulation similar, but not identical, to those induced by psychostimulants such as cocaine and amphetamine. We investigated, in rats, the role of striatal D1 receptors in methylphenidate-induced gene expression, by intrastriatal administration of the D1 receptor antagonist SCH-23390. Effects on the expression of two plasticity-related molecules, the transcription factor zif 268 and the synaptic plasticity factor Homer 1a, in the striatum and cortex were assessed. Intrastriatal infusion of SCH-23390 (2-10 microg) attenuated zif 268 and Homer 1a mRNA expression induced by methylphenidate (10 mg/kg, i.p.) in a dose-dependent manner. Moreover, this unilateral SCH-23390 infusion not only inhibited gene induction at the infusion site in the central striatum, but also in distant striatal regions including the nucleus accumbens, as well as throughout the entire contralateral striatum. These results indicate that striatal D1 receptors are critical for gene induction by methylphenidate. Moreover, the ipsilateral and contralateral effects of local SCH-23390 administration suggest that D1 receptor-stimulated striatal output exerts robust control over widespread striatal activities/gene expression via regulation of input to the striatum.

Induction of immediate early gene expression by high-frequency stimulation of the subthalamic nucleus in rats

Deep brain stimulation is associated with delayed improvement of parkinsonian symptoms, such as hypokinesia with subthalamic nucleus stimulation, or dystonia with globus pallidus internus stimulation. The latency observed is better explained by molecular alterations than immediate electrophysiological processes, and clinical improvement may involve adaptive gene expression. Here, we have studied immediate early gene expression as fast molecular response to subthalamic nucleus stimulation. Bipolar electrodes were implanted bilaterally into the subthalamic nucleus of anesthetized male Wistar rats. High-frequency stimulation (130 Hz or 80 Hz, 60 micros, 300 microA) or low-frequency stimulation (5 Hz, 60 micros, 300 microA) was performed with the right electrode for 15, 60, 120, and 240 min whereas the silent left electrode served as negative control. Brains were fixed by transcardial perfusion and frozen sections were stained with polyclonal antibodies directed against three immediate early gene-encoded proteins, c-Fos, c-Jun, and Krox-24 (NGFI-A, Egr-1, Zif268, Tis8, Zenk). After 120 and 240 h, c-Fos immunoreactivity was strongly upregulated in subthalamic nucleus neurons on the stimulated site. In contrast, no c-Fos immunoreactivity was detected on the non-stimulated site except for single positive cells located in close proximity to the electrode tracks. Furthermore, c-Fos immunoreactivity was induced in subthalamic nucleus projection areas, such as primary and secondary motor cortex, primary somatosensory and insular cortex, lateral and medial globus pallidus, suprageniculate thalamic nucleus, pontine nuclei, medial geniculate nucleus, and substantia nigra. Similarly, c-Jun and Krox-24 were induced at the site of stimulation and in projection areas following high-frequency subthalamic nucleus stimulation. Whereas high frequency stimulation with 80 Hz was similarly effective none of the three immediate early gene-encoded proteins was induced with low-frequency stimulation (5 Hz) for 4 h. This is in accordance with the therapeutic effects of deep brain stimulation which are only elicited with high frequency stimulation. Our data provide evidence that immediate early gene expression in the subthalamic nucleus is rapidly and substantially induced by high-frequency stimulation. The induction of immediate early genes in projection sites suggests ipsilateral transsynaptic modulation of neuronal activity.

Psychostimulants, madness, memory... and RGS proteins?

The ingestion of psychostimulant drugs by humans imparts a profound sense of alertness and well-being. However, repeated use of these drugs in some individuals will induce a physiological state of dependence, characterized by compulsive behavior directed toward the acquisition and ingestion of the drug, at the expense of customary social obligations. Drugs of abuse and many other types of experiences share the ability to alter the morphology and density of neuronal dendrites and spines. Dopaminergic modulation of corticostriatal synaptic plasticity is necessary for these morphological changes. Changes in the density of dendritic spines on striatal neurons may underlie the development of this pathological pattern of drug-seeking behavior. Identifying proteins that regulate dopaminergic signaling are of value. A family of proteins, the regulators of G protein signaling (RGS) proteins, which regulate signaling from G protein-coupled receptors, such as dopamine and glutamate, may be important in this regard. By regulating corticostriatal synaptic plasticity, RGS proteins can influence presynaptic activity, neurotransmitter release, and postsynaptic depolarization and thereby play a key role in the development of this plasticity. Pharmacological agents that modify RGS activity in humans could be efficacious in ameliorating the dependence on psychostimulant drugs.

Failure of MK-801 to suppress D1 receptor-mediated induction of locomotor activity and striatal preprotachykinin mRNA expression in the dopamine-depleted rat

N-methyl-D-aspartate receptor antagonism exerts suppressive influences over dopamine D1 receptor-mediated striatal gene expression and locomotor behavior in the intact rat. The present study examined the effects of the N-methyl-D-aspartate receptor antagonist MK-801 on locomotor activity and striatal preprotachykinin mRNA expression stimulated by the D1 agonist (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide in rats with bilateral dopamine lesions. Two months after neonatal dopamine lesions with 6-hydroxydopamine, rats were challenged with (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (1.0 mg/kg) 15 min after administration of the N-methyl-D-aspartate receptor antagonist MK-801 (0.1 mg/kg). In the intact rat, MK-801 prevented the induction of striatal preprotachykinin mRNA by D1 agonism. Similarly, direct infusion of (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (3.0 microg) into the intact striatum produced an increase in locomotor activity that was suppressed by MK-801 (1.0 microg) co-infusion. In the dopamine-depleted rat, MK-801 (0.1 mg/kg) administered prior to (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (1.0 mg/kg) increased, rather than suppressed, striatal preprotachykinin mRNA levels. Intrastriatal infusion of MK-801 (1.0 microg) failed to inhibit D1-mediated induction of motor activity in dopamine-depleted animals. Together, these data provide further support that N-methyl-D-aspartate receptor antagonists lose their ability to block D1-mediated behavioral activation following dopamine depletion. The activation, rather than suppression, of tachykinin neurons of the direct striatonigral pathway may play a facilitatory role in this mechanism.

Cocaine induction of ERK proteins in dorsal striatum of Fischer rats

Cocaine is an addictive psychostimulant that induces fos and opioid gene expression by activating the dopamine receptors and the PKA pathways in dopamine D1 and a glutamate NMDA-dependent mechanisms in the striatum. In this study, we show that a single cocaine administration induces ERK phosphorylation in the caudate/putamen of Fischer rats. This increase in Phospho-ERK is diminished by pre-administration of SCH23390, or MK801 but not with pre-administration of eticlopride. Furthermore, this single cocaine administration does not alter the levels of phospho-CREB protein or CREB-DNA bindings in the caudate/putamen protein extracts but does increase phospho-Elk-1 protein levels in the same extracts.

Importance of D(1) receptors for associative components of amphetamine-induced behavioral sensitization and conditioned activity: a study using D(1) receptor knockout mice

RATIONALE

Repeated exposure to psychostimulant drugs results in conditioned activity and behavioral sensitization. Nonassociative cellular changes are necessary for behavioral sensitization, while associative processes appear to modify the sensitized response.

OBJECTIVE

The purpose of the present study was to determine whether the absence of the D(1) receptor would disrupt associative processes modulating sensitization and conditioned activity.

METHODS

Wild-type and D(1) receptor knockout mice (i.e., D(1)-deficient mice) were injected with amphetamine (AMPH; 8 mg/kg, IP) before being placed in a previously novel test chamber (AMPH-Test group) or before being returned to the home cage (AMPH-Home group). Separate groups of mice were injected with saline (SAL) at the same time points. Distance traveled was measured 60 min each day, with the preexposure phase lasting 1 or 7 days. Sensitization was subsequently assessed after an injection of AMPH (1 mg/kg, IP), while conditioned activity was assessed after an injection of SAL.

RESULTS

After a 1-day preexposure phase, wild-type and D(1)-deficient mice exhibited similar patterns of sensitization and conditioned activity. After a 7-day preexposure phase, (1) D(1)-deficient mice exhibited more robust context-specific sensitization than wild-type mice, (2) only D(1)-deficient mice showed context-independent sensitization, and (3) only D(1)-deficient mice showed conditioned activity.

CONCLUSIONS

Repeatedly treating D(1)-deficient mice with AMPH appears to cause a general increase in responsivity. The reason for this hyper-responsivity is uncertain, but it is possible that cues from the testing environment were unable to inhibit responding (i.e., associative processes were disrupted). Alternatively, compensatory mechanisms (e.g., increases in D(2)-like receptors) may affect processes underlying sensitization and conditioned activity.

Different responsiveness of striatonigral and striatopallidal neurons to L-DOPA after a subchronic intermittent L-DOPA treatment

Early gene induction by L-DOPA in the striatum of dopamine denervated rats represents a useful way to study long-term modifications produced by this drug. The effects of acute and subchronic L-DOPA administration on zif-268 mRNA expression were compared in 6-hydroxydopamine-lesioned rats. Rats received a subchronic intermittent L-DOPA (6 mg/kg) treatment, which produces behavioural sensitization, a correlate of dyskinetic movements. Three days after interruption of subchronic treatment, zif-268 mRNA was evaluated after an L-DOPA challenge. Zif-268 mRNA levels increased in the lesioned dorsolateral striatum after either acute or subchronic L-DOPA administration. Double labelling of striatal cells with zif-268 and enkephalin or dynorphin mRNA probes was performed to assess neuronal activation in the indirect and direct output pathway. Single acute L-DOPA significantly increased zif-268 in all striatal neurons reflecting a hyperresponsiveness of dopamine-depleted striatum. After subchronic L-DOPA, zif-268 mRNA labelling was still increased in the striatonigral pathway, limited to dynorphin(+) neurons, whereas in all other neurons it was similar to the control value. Results suggest that striatal neurons responding to acute L-DOPA differ from those responding to subchronic L-DOPA. L-DOPA-induced behavioural sensitization was associated to a down-regulation in the responsiveness of striatopallidal and striatonigral dynorphin(-) neurons, whereas in striatonigral neurons containing dynorphin a hyperresponsiveness to L-DOPA was observed. High levels of zif-268, together with a persistent hyperresponsiveness of striatonigral dymorphinergic neurons and hyporesponsiveness of striatopallidal neurons, by creating an unbalanced state of striatal efferent neurons, may be implicated in dyskinetic movements observed in Parkinson's disease (PD).

Neural Substrates of Coping Behavior in the Rat: Possible Importance of Mesocorticolimbic Dopamine System

This study measured expression of Fos protein, an indicator of neural activation, in 116 brain regions of rats that were able to control a stressor (i.e., avoid and/or escape an electric shock), and compared the changes with those observed in yoked rats that received the same shocks but without having control over them. The authors' interest was to find brain regions where elevated activity occurs in conjunction with control. Activity in these brain regions might be responsible for the consequences of having control, such as reduction of stress responses. Eleven brain regions were found in which rats with control showed significantly more Fos expression than was seen in yoked rats that did not have control. Six of these brain regions were part of the mesocorticolimbic dopamine system. These results point to the mesocorticolimbic dopamine system as being importantly involved in the mediation and/or the consequences of coping behavior.

The rate of cocaine administration alters gene regulation and behavioral plasticity: implications for addiction

The rapid delivery of drugs of abuse to the brain is thought to promote addiction, but why this occurs is unknown. In the present study, we characterized the influence of rate of intravenous cocaine infusion (5-100 sec) on three effects thought to contribute to its addiction liability: its ability to block dopamine (DA) uptake, to activate immediate early gene expression, and to produce psychomotor sensitization. Rapid infusions potentiated the ability of cocaine to block DA reuptake, to induce c-fos and arc mRNA expression, especially in mesocorticolimbic regions, and to produce psychomotor sensitization. Thus, the rate at which cocaine is delivered influences both its neurobiological impact and its ability to induce a form of drug experience-dependent plasticity implicated in addiction. We propose that rapidly delivered cocaine may be more addictive, in part, because this more readily induces forms of neurobehavioral plasticity that lead to the compulsive pursuit of drugs.

Cocaine-induced Fos expression in rat striatum is blocked by chloral hydrate or urethane

Anesthetics used in electrophysiological studies alter the effects of cocaine and amphetamine on neural activity in the striatum. However, the mechanism underlying this alteration has not been established. In the present study, we examined the effects of anesthetics on cocaine-induced neural activity in the striatum. We first assayed the ability of 20 mg/kg cocaine to induce Fos expression in the striatum following pretreatment with 400 mg/kg chloral hydrate or 1.3 g/kg urethane, two of the most commonly used anesthetics for in vivo electrophysiology. Chloral hydrate blocked, while urethane strongly attenuated cocaine-induced Fos expression without affecting basal levels of expression. We then examined dopaminergic and glutamatergic mechanisms for anesthetic effects on cocaine-induced Fos expression. Chloral hydrate and urethane did not attenuate basal or cocaine-induced increases of dopamine levels as assessed by microdialysis in dorsal striatum. In contrast, chloral hydrate attenuated glutamatergic neurotransmission as assessed by microdialysis in the presence of the glutamate transport blocker L-trans-pyrrolidone-2,4-dicarboxylic acid. Chloral hydrate attenuated basal levels of glutamate by 70%, while cocaine had no effect on glutamate levels. Since glutamate levels were tetrodotoxin-sensitive, the majority of glutamate measured in our assay was by synaptic release. To assess a causal role for a reduction of glutamatergic neurotransmission in anesthetic effects on cocaine-induced Fos expression, we injected the glutamate receptor agonists AMPA and NMDA into the dorsal striatum of chloral hydrate-anesthetized rats. The glutamate receptor agonists partially reinstated cocaine-induced Fos expression in anesthetized rats. We conclude anesthetics attenuate cocaine-induced neuronal activity by reducing glutamatergic neurotransmission.

Increased extracellular dopamine concentrations and FosB/ΔFosB expression in striatal brain areas of heterozygous GDNF knockout mice

Glial cell line-derived neurotrophic factor (GDNF) has been shown to be involved in the maintenance of striatal dopaminergic neurons. To study whether reduced levels of endogenous GDNF affect the striatal dopaminergic transmission we estimated the basal extracellular levels of dopamine in vivo, the basal expression of FosB-related proteins in striatal brain areas as well as the effects of acute and repeated cocaine on locomotor activity and dopamine output in mice lacking one GDNF allele (heterozygous GDNF+/- mice). As expected the striatal GDNF protein content was found to be smaller in the GDNF+/- mice than in their wild-type littermates. Unexpectedly the extracellular dopamine concentration in the GDNF+/- mice in the dorsal striatum (CPu) was 2.0-fold, and in the nucleus accumbens (NAc) 1.6-fold the concentration found in the wild-type littermates. Also FosB/DeltaFosB-like immunoreactivity was found to be elevated in the CPu as well as in the core and in the shell of NAc of the GDNF+/- mice as compared with the wild-type mice. This suggests chronic postsynaptic activation of these brain areas and is in line with elevated extracellular dopamine concentrations. Cocaine's effects acutely and after repeated treatment on locomotor activity were similar in the GDNF+/- and the wild-type mice. Neither did cocaine's acute effects on dopamine output differ between the mice of the two strains. Our findings demonstrate that reduced levels of endogenous GDNF induce alterations in dorsal striatal and accumbal dopaminergic transmission, and stress the importance of endogenous GDNF in the regulation of the dopaminergic neurons.

Morphine-induced c-fos mRNA expression in striatofugal circuits: modulation by dose, environmental context, and drug history

Opiates and psychostimulants produce many shared behavioral and neurobiological adaptations, such as behavioral sensitization and the induction of immediate early genes in the caudate-putamen (CPu). Previous studies indicate that factors such as dose, the environmental context surrounding drug administration and drug history can influence both morphine- and psychostimulant-induced behavioral sensitization. In addition, these factors can modulate the ability of psychostimulants to engage striatofugal circuits in the CPu. The present study, therefore, sought to examine whether these factors have similar influences over the ability of morphine to engage cortico-striatofugal circuits. We report that, when given in the home cage, morphine produced a small, but significant increase in the number of c-fos+ striatonigral cells and c-fos+ cells in cingulate cortex, but had no effect on the number of c-fos+ striatopallidal cells. When given in a novel test environment, however, morphine dramatically increased the number of c-fos+ striatonigral cells in a dose-dependent fashion, and this effect was maintained following repeated treatment. Unexpectedly, morphine treatment in a novel environment produced a dose-dependent reduction in the number of c-fos+ striatopallidal cells and c-fos+ cells in cingulate cortex, relative to exposure to novelty alone-effects that were reversed by repeated morphine treatment. We suggest that alterations in c-fos expression patterns in striatofugal circuits following morphine administration may be involved in drug-experience-dependent plasticity.