Cortical stimulation induces Fos expression in striatal neurons via NMDA glutamate and dopamine receptors

Regulation of Dendrite and Dendritic Spine Formation by TCF20

Mutations in the Transcription Factor 20 (TCF20) have been identified in patients with autism spectrum disorders (ASDs), intellectual disabilities (IDs), and other neurological issues. Recently, a new syndrome called TCF20-associated neurodevelopmental disorders (TAND) has been described, with specific clinical features. While TCF20's role in the neurogenesis of mouse embryos has been reported, little is known about its molecular function in neurons. In this study, we demonstrate that TCF20 is expressed in all analyzed brain regions in mice, and its expression increases during brain development but decreases in muscle tissue. Our findings suggest that TCF20 plays a central role in dendritic arborization and dendritic spine formation processes. RNA sequencing analysis revealed a downregulation of pre- and postsynaptic pathways in TCF20 knockdown neurons. We also found decreased levels of GABRA1, BDNF, PSD-95, and c-Fos in total homogenates and in synaptosomal preparations of knockdown TCF20 rat cortical cultures. Furthermore, synaptosomal preparations of knockdown TCF20 rat cortical cultures showed significant downregulation of GluN2B and GABRA5, while GluA2 was significantly upregulated. Overall, our data suggest that TCF20 plays an essential role in neuronal development and function by modulating the expression of proteins involved in dendrite and synapse formation and function.

Whole-brain analysis of CO2 chemosensitive regions and identification of the retrotrapezoid and medullary raphé nuclei in the common marmoset (Callithrix jacchus)

Respiratory chemosensitivity is an important mechanism by which the brain senses changes in blood partial pressure of CO2 (PCO2). It is proposed that special neurons (and astrocytes) in various brainstem regions play key roles as CO2 central respiratory chemosensors in rodents. Although common marmosets (Callithrix jacchus), New-World non-human primates, show similar respiratory responses to elevated inspired CO2 as rodents, the chemosensitive regions in marmoset brain have not been defined yet. Here, we used c-fos immunostainings to identify brain-wide CO2-activated brain regions in common marmosets. In addition, we mapped the location of the retrotrapezoid nucleus (RTN) and raphé nuclei in the marmoset brainstem based on colocalization of CO2-induced c-fos immunoreactivity with Phox2b, and TPH immunostaining, respectively. Our data also indicated that, similar to rodents, marmoset RTN astrocytes express Phox2b and have complex processes that create a meshwork structure at the ventral surface of medulla. Our data highlight some cellular and structural regional similarities in brainstem of the common marmosets and rodents.

Cannabis use is associated with sexually dimorphic changes in executive control of visuospatial decision-making

When the outcome of a choice is less favorable than expected, humans and animals typically shift to an alternate choice option on subsequent trials. Several lines of evidence indicate that this “lose-shift” responding is an innate sensorimotor response strategy that is normally suppressed by executive function. Therefore, the lose-shift response provides a covert gauge of cognitive control over choice mechanisms. We report here that the spatial position, rather than visual features, of choice targets drives the lose-shift effect. Furthermore, the ability to inhibit lose-shift responding to gain reward is different among male and female habitual cannabis users. Increased self-reported cannabis use was concordant with suppressed response flexibility and an increased tendency to lose-shift in women, which reduced performance in a choice task in which random responding is the optimal strategy. On the other hand, increased cannabis use in men was concordant with reduced reliance on spatial cues during decision-making, and had no impact on the number of correct responses. These data (63,600 trials from 106 participants) provide strong evidence that spatial-motor processing is an important component of economic decision-making, and that its governance by executive systems is different in men and women who use cannabis frequently.

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.

Segregation and crosstalk of D1 receptor-mediated activation of ERK in striatal medium spiny neurons upon acute administration of psychostimulants

The convergence of corticostriatal glutamate and dopamine from the midbrain in the striatal medium spiny neurons (MSN) triggers synaptic plasticity that underlies reinforcement learning and pathological conditions such as psychostimulant addiction. The increase in striatal dopamine produced by the acute administration of psychostimulants has been found to activate not only effectors of the AC5/cAMP/PKA signaling cascade such as GluR1, but also effectors of the NMDAR/Ca(2+)/RAS cascade such as ERK. The dopamine-triggered effects on both these cascades are mediated by D1R coupled to Golf but while the phosphorylation of GluR1 is affected by reductions in the available amount of Golf but not of D1R, the activation of ERK follows the opposite pattern. This segregation is puzzling considering that D1R-induced Golf activation monotonically increases with DA and that there is crosstalk from the AC5/cAMP/PKA cascade to the NMDAR/Ca(2+)/RAS cascade via a STEP (a tyrosine phosphatase). In this work, we developed a signaling model which accounts for this segregation based on the assumption that a common pool of D1R and Golf is distributed in two D1R/Golf signaling compartments. This model integrates a relatively large amount of experimental data for neurons in vivo and in vitro. We used it to explore the crosstalk topologies under which the sensitivities of the AC5/cAMP/PKA signaling cascade to reductions in D1R or Golf are transferred or not to the activation of ERK. We found that the sequestration of STEP by its substrate ERK together with the insensitivity of STEP activity on targets upstream of ERK (i.e. Fyn and NR2B) to PKA phosphorylation are able to explain the experimentally observed segregation. This model provides a quantitative framework for simulation based experiments to study signaling required for long term potentiation in MSNs.

Phasic-like stimulation of the medial forebrain bundle augments striatal gene expression despite methamphetamine-induced partial dopamine denervation

Methamphetamine-induced partial dopamine depletions are associated with impaired basal ganglia function, including decreased preprotachykinin mRNA expression and impaired transcriptional activation of activity-regulated, cytoskeleton-associated (Arc) gene in striatum. Recent work implicates deficits in phasic dopamine signaling as a potential mechanism linking methamphetamine-induced dopamine loss to impaired basal ganglia function. This study thus sought to establish a causal link between phasic dopamine transmission and altered basal ganglia function by determining whether the deficits in striatal neuron gene expression could be restored by increasing phasic dopamine release. Three weeks after pretreatment with saline or a neurotoxic regimen of methamphetamine, rats underwent phasic- or tonic-like stimulation of ascending dopamine neurons. Striatal gene expression was examined using in situ hybridization histochemistry. Phasic-like, but not tonic-like, stimulation induced immediate-early genes Arc and zif268 in both groups, despite the partial striatal dopamine denervation in methamphetamine-pretreated rats, with the Arc expression occurring in presumed striatonigral efferent neurons. Phasic-like stimulation also restored preprotachykinin mRNA expression. These results suggest that disruption of phasic dopamine signaling likely underlies methamphetamine-induced impairments in basal ganglia function, and that restoring phasic dopamine signaling may be a viable approach to manage long-term consequences of methamphetamine-induced dopamine loss on basal ganglia functions.

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.

Context modulates the expression of conditioned motor sensitization, cellular activation and synaptophysin immunoreactivity

We tested the hypothesis that amphetamine (AMPH)-induced conditioned motor sensitization is accompanied by cellular activation (measured by Fos immunoreactivity) and synaptophysin immunoreactivity in reward-related brain areas. Forty-eight rats were tested for conditioned motor sensitization using a conditioning paradigm that was performed in a three-chambered apparatus. Rats underwent two drug pairings with 1.0 mg/kg AMPH in one outer chamber and, on alternate days, were paired with saline in the other. On the fifth day, relative to the first AMPH treatment, AMPH administration increased motor activity in the AMPH-paired context but not in the saline-paired context. Relative to the first saline treatment, saline on the fifth day produced a conditioned increase in motor activity when given in the chamber previously paired with AMPH, and saline given in the saline-paired context produced a conditioned decrease in motor activity. AMPH administered in the AMPH-paired context increased the density of both Fos and synaptophysin immunoreactivity in the dentate gyrus, cornu ammonis (CA)1, CA3, basolateral amygdala and dorsolateral striatum. This pairing between context and drug increased Fos but not synaptophysin immunoreactivity in the nucleus accumbens core and shell. Saline administered in the AMPH-paired context increased the density of Fos immunoreactivity in the basolateral amygdala and nucleus accumbens core. These data indicate that the basolateral amygdala-nucleus accumbens core pathway is necessary for the context-elicited conditioned motor responses, while the hippocampus encodes the spatial context.

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.

Differential induction of c-Jun and Fos-like proteins in rat hippocampus and dorsal striatum after training in two water maze tasks

Research examining the neuroanatomical bases of memory in mammals suggests that the hippocampus and dorsal striatum are parts of independent memory systems that mediate "cognitive" and stimulus-response "habit" memory, respectively. At the molecular level, increasing evidence indicates a role for immediate early gene (IEG) expression in memory formation. The present experiment examined whether acquisition of cognitive and habit memory result in differential patterns of IEG protein product expression in these two brain structures. Adult male Long-Evans rats were trained in either a hippocampal-dependent spatial water maze task, or a dorsal striatal-dependent cued water maze task. Ninety minutes after task acquisition, brains were removed and processed for immunocytochemical procedures, and the number of cells expressing Fos-like immunoreactivity (Fos-like-IR) and c-Jun-IR in sections from the dorsal hippocampus and the dorsal striatum were counted. In the dorsal hippocampus of rats trained in the spatial task, there were significantly more c-Jun-IR pyramidal cells in the CA1 and CA3 regions, relative to rats that had acquired the cued task, yoked controls (free-swim), or naïve (home cage) rats. Relative to rats receiving cued task training and control conditions, increases in Fos-like IR were also observed in the CA1 region of rats trained in the spatial task. In rats that had acquired the cued task, patches of c-Jun-IR were observed in the posteroventral striatum; no such patches were evident in rats trained in the spatial task, yoked-control rats, or naïve rats. The results demonstrate that IEG protein product expression is up-regulated in a task-dependent and brain structure-specific manner shortly after acquisition of cognitive and habit memory tasks.

Dopamine manipulation alters immediate-early gene response of striatal parvalbumin interneurons to cortical stimulation

Cortical projections provide the major excitatory inputs to the striatum. In addition to innervating medium spiny cells, these axons contact striatal interneurons that are parvalbumin-immunoreactive (PV-ir). PV-ir interneurons make synaptic connections with many medium spiny cells, and thus can modulate striatal output. The striatum also receives dopaminergic projections from the substantia nigra, but it has been challenging to study the impact of dopamine (DA) cell injury on corticostriatal activity in vivo due to limitations in the methods used to induce cortical activity. Using epidural application of the GABA(A) antagonist picrotoxin, which produces a topographically restricted region of striatal immediate-early gene expression, we have investigated the effect of DA cell injury or DA receptor antagonism on immediate-early gene (IEG) expression in striatal medium spiny cells and PV-ir interneurons. Epidural application of picrotoxin to the rat's M1 motor cortex induced Fos in ipsilateral dorsolateral striatum. Animals previously given 6-hydroxydopamine (6-OHDA) injections into the ascending DA pathways had greater total numbers of cortical stimulation-induced striatal Fos-ir cells but fewer Fos-ir/PV-ir cells, compared to sham-operates. In a separate experiment, rats given cortical stimulation and treated with the DA D2-class antagonist eticlopride (0.10 mg/kg) exhibited fewer Fos-ir/PV-ir cells than did vehicle-treated rats. Taken together, these results indicate that DA may importantly control striatal output via influences on PV-ir interneurons. Possible mechanisms for these influences are discussed.

Coincident stimulation of convergent cortical inputs enhances immediate early gene induction in the striatum

The effect of coincident stimulation of convergent corticostriatal inputs was analyzed by the induction of immediate early genes in striatal neurons. Cortical motor areas were stimulated through implanted electrodes in awake, behaving rats, and the induction of the mRNAs encoding the immediate early genes (IEGs) c-fos and arc was analyzed in the striatum with in situ hybridization histochemistry. In the first experiment, unilateral stimulation of the medial agranular cortex, orofacial region of the lateral agranular cortex or the forelimb region of the lateral agranular cortex resulted in IEG induction in the striatum, which was restricted to the topographically related area receiving input from the stimulated cortical area. In a second experiment, stimulation parameters were altered, including frequency, number of pulses/train, and number of trains/s. These parameters did not have a significant effect on IEG induction. Notably, in some cases, in which there was IEG induction not only in the stimulated cortical region, but also in the homologous area in the contralateral hemisphere, very robust IEG induction was observed in the striatum. In a third experiment, the orofacial regions of the lateral agranular cortex of both hemispheres were stimulated coincidently. All of these animals showed robust striatal IEG induction. This IEG induction was attenuated by pretreatment with an NMDA antagonist MK-801. In a fourth experiment, we tested whether the coincidence of bilateral cortical stimulation contributed to the efficacy of striatal IEG induction. Either alternating stimulation or coincident stimulation of non-homologous cortical regions produced significantly lower striatal IEG induction than obtained with coincident stimulation of homologous cortical areas. Enhanced striatal IEG induction occurred in indirect striatal neurons, labeled with enkephalin, but was also present in a large number of enkephalin-negative neurons, most of which are likely direct pathway neurons. These results suggest that regional and temporal convergence of cortical inputs enhances striatal IEG induction.

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.

Role of NMDA receptor subtypes in the induction of catalepsy and increase in Fos protein expression after administration of haloperidol

The increase of Fos expression in the striatum induced by haloperidol, an antagonist of the dopamine D2 receptor, might be related to the activation of glutamatergic neurotransmission, especially that of N-methyl-D-aspartate (NMDA) receptors. In this study, using behavioral and immunohistochemical techniques, we examined the effects of a noncompetitive NMDA antagonist, (+)-MK-801, and an NMDA receptor NR2B subunit antagonist, ifenprodil, on catalepsy, an extrapyramidal symptom; in this context, we also considered the expression of Fos protein in the forebrain after the administration of haloperidol. Catalepsy in mice, induced by the administration of haloperidol (1 mg/kg), was inhibited by pretreatment with (+)-MK-801 (0.2 mg/kg) or ifenprodil (10 mg/kg). Furthermore, pretreatment with (+)-MK-801 (0.2 mg/kg) significantly attenuated the induction of Fos-immunoreactive (IR) cells in the dorsomedial, dorsolateral, and ventrolateral striatum, but not in the shell region of the nucleus accumbens after the administration of haloperidol, whereas pretreatment with ifenprodil (10 mg/kg) significantly attenuated the induction of Fos-IR cells in all of these areas. It is known that ifenprodil binds sigma receptors and alpha-1 adrenergic receptors with high affinity. Pretreatment with the sigma receptor antagonist BD-1407 (3 mg/kg) or the alpha-1 adrenergic receptor antagonist prazosin (3 mg/kg) affected neither catalepsy nor the expression of Fos-IR cells after the administration of haloperidol. However, pretreatment with CP-101,606 (1 mg/kg), a selective antagonist for the NR2B subunit of the NMDA receptor, significantly attenuated catalepsy and the expression of Fos-IR cells in the forebrain after the administration of haloperidol. These results suggest that the NMDA receptor antagonists attenuated the induction of catalepsy and Fos-IR cells in forebrain after the administration of haloperidol. It was also suggested that haloperidol-induced expression of Fos-IR cells in the shell region of the nucleus accumbens might be differentially regulated by NMDA receptor subunits. Therefore, it appears that selective antagonists for the NR2B subunit of the NMDA receptor (e.g., CP-101,606) might be useful drugs for the treatment of extrapyramidal side effects (EPS) associated with the chronic use of typical antipsychotics such as haloperidol.

Interaction between the noradrenergic and serotonergic systems in locomotor hyperactivity and striatal expression of Fos induced by amphetamine in rats

It is classically considered that Amphetamine acts by increasing extracellular dopamine levels. However, some data suggest a relevant role of other neurochemical systems. The striatum is of particular interest to the study of this question. We have investigated the involvement of the noradrenergic and serotonergic systems and their possible interaction in the striatal responses to Amphetamine using a double behavioral and immunohistochemical approach (i.e., changes in locomotor activity and striatal expression of Fos). In normal rats, Amphetamine induced locomotor hyperactivity and striatal expression of Fos. Pretreatment with the alpha1-adrenergic-receptor antagonist Prazosin or lesion of the serotonergic system significantly reduced the locomotor hyperactivity and striatal Fos expression induced by Amphetamine. Administration of Prazosin to rats with serotonergic denervation did not produce any further reduction in the Amphetamine-induced locomotor hyperactivity or striatal Fos expression compared with that observed in rats with serotonergic denervation only. Amphetamine did not induce a detectable increase in Fos expression in dopamine-denervated striata, and elicited intense rotation towards the dopamine-denervated side. This suggests that striatal dopamine release is essential in the Amphetamine-induced effects on striatal neurons. However, the noradrenergic system plays an important role, and the serotonergic system is necessary for mediating the effects of the Amphetamine-induced noradrenergic stimulation. Concurrent stimulation of dopaminergic and serotonergic receptors appears necessary to regulate Amphetamine-induced responses in the striatal neurons.

Amphetamine-evoked c-fos mRNA expression in the caudate-putamen: the effects of DA and NMDA receptor antagonists vary as a function of neuronal phenotype and environmental context

Dopamine (DA) and glutamate neurotransmission is thought to be critical for psychostimulant drugs to induce immediate early genes (IEGs) in the caudate-putamen (CPu). We report here, however, that the ability of DA and glutamate NMDA receptor antagonists to attenuate amphetamine-evoked c-fos mRNA expression in the CPu depends on environmental context. When given in the home cage, amphetamine induced c-fos mRNA expression predominately in preprodynorphin and preprotachykinin mRNA-containing neurons (Dyn-SP+ cells) in the CPu. In this condition, all of the D1R, D2R and NMDAR antagonists tested dose-dependently decreased c-fos expression in Dyn-SP+ cells. When given in a novel environment, amphetamine induced c-fos mRNA in both Dyn-SP+ and preproenkephalin mRNA-containing neurons (Enk+ cells). In this condition, D1R and non-selective NMDAR antagonists dose-dependently decreased c-fos expression in Dyn-SP+ cells, but neither D2R nor NR2B-selective NMDAR antagonists had no effect. Furthermore, amphetamine-evoked c-fos expression in Enk+ cells was most sensitive to DAR and NMDAR antagonism; the lowest dose of every antagonist tested significantly decreased c-fos expression only in these cells. Finally, novelty-stress also induced c-fos expression in both Dyn-SP+ and Enk+ cells, and this was relatively resistant to all but D1R antagonists. We suggest that the mechanism(s) by which amphetamine evokes c-fos expression in the CPu varies depending on the stimulus (amphetamine vs. stress), the striatal cell population engaged (Dyn-SP+ vs. Enk+ cells), and environmental context (home vs. novel cage).

Impairment of context-adapted movement selection in a primate model of presymptomatic Parkinson's disease

The MPTP model allows the presymptomatic stage of parkinsonism to be studied in primates and hence specific behavioural manifestations of moderate nigrostriatal denervation to be identified. On the basis of the physiological literature, we hypothesized that depletion of striatal dopamine could impair the selection of context-relevant habits. To examine this hypothesis, we trained three African green monkeys to perform a simple reach-and-grasp task, including three contexts differing only in terms of the presence and position of transparent obstacles. At the end of training, the analysis of reaching trajectories showed that intact monkeys had built a repertoire of movements, from which they could select the appropriate one depending on the context. In the course of MPTP intoxication (0.3-0.4 mg/kg every 4-5 days) and before parkinsonian motor symptoms appeared, the reaction time (RT), movement time (MT) and variability of reaching trajectories increased in all monkeys. Frequently, the initial direction was not adapted to the context, and consequently the movement was either corrected online or restarted under visual assistance. These non-adapted trajectories appeared to be the main reason for the increase in both RT (because of difficulty in selecting) and MT (because of the need to make corrections). These observations indicate that moderate MPTP-induced dopamine depletion results in a deficit in the selection of context-adapted movement, which is compensated by corrections using either proprioceptive or visual feedback. Similar behavioural disorders might therefore occur in the presymptomatic stage of human Parkinson's disease.

Host brain regulation of dopaminergic grafts function: role of the serotonergic and noradrenergic systems in amphetamine-induced responses

The indirect dopaminergic (DA) agonist amphetamine has frequently been used to study functional responses of DA grafted neurons. However, it is not known if striatal responses, primarily related to DA release by the grafted neurons, are modulated by the host striatal afferents. We investigated the changes in amphetamine-induced rotational behavior and striatal expression of Fos in DA-denervated and grafted rats subjected to serotonergic denervation and/or treatment with the alpha(1)-adrenergic receptor antagonist Prazosin. Acute serotonergic lesions with p-chlorophenylalanine suppressed the expression of Fos induced by 1 mg/kg of amphetamine in both the grafted and the contralateral striatum. Chronic serotonergic denervation with 5,7-dihydroxytryptamine induced a significant reduction in Fos expression in both the grafted and nongrafted striata and a nonsignificant reduction in the contraversive rotation. In DA-innervated striata, Prazosin significantly reduced the expression of Fos but only in the presence of serotonergic innervation. However, Prazosin did not decrease the expression of Fos induced by grafts located in striata not subjected to serotonergic denervation. The present results suggest functional integration of transplanted DA neurons and major host striatal afferent systems, particularly the serotonergic system, in modulating responses of the host striatal neurons. However, indirect effects exerted by the noradrenergic system on the normal striatum were not observed in the DA-denervated and grafted striata.

Basal EGR-1 (zif268, NGFI-A, Krox-24) expression in developing striatal patches: role of dopamine and glutamate

Egr-1 (also known as zif268, NGFI-A, or Krox 24) is an immediate-early gene of the zinc finger family that exhibits relatively high constitutive expression in the brain, as well as inducibility by seizure activity, stimulants, and salient physiological stimuli. Immunocytochemical detection of the Egr-1 protein in the developing striatum revealed that in the late prenatal and early postnatal period, Egr-1 protein was expressed selectively in patches of striatal neurons under basal conditions. Egr-1 immunoreactivity was co-expressed with known markers of striatal patch neurons, indicating that expression was greatest in the striatal patch compartment. This patchy expression of Egr-1 transitioned to a nearly homogeneous pattern of Egr-1-immunoreactive cells by postnatal day 10, at which time most striatal neurons appeared to be Egr-1-immunoreactive. The dopamine D1 antagonist SCH23390 (0.5-1.0 mg/kg) reduced Egr-1 expression during the first week postnatal, but it was no longer effective at postnatal day 10. On the other hand, the noncompetitive NMDA antagonist MK-801 (0.5-1.0 mg/kg) became more effective at reducing Egr-1 expression with age. Neonatal destruction of nigrostriatal dopamine afferents reduced the basal pattern of Egr-1 expression for 2-3 days after the lesion, but then Egr-1 expression returned. Thus, Egr-1 expression in the developing striatum appears to be driven first by dopaminergic afferents, and then later in development by excitatory glutamatergic afferents.

Immediate-early gene expression in concurrent prenatal ethanol- and/or cocaine-exposed rat pups: intrauterine differences in cocaine levels and Fos expression

Concurrent use of cocaine and ethanol is a common mode of abuse. Cocaine and ethanol have distinctive pharmacologies but both have been shown to cause uterine vasoconstriction and fetal hypoxia. We developed a paradigm of chronic ethanol exposure via liquid diet coupled with binge cocaine exposure on the last day of gestation. Lipton et al. demonstrated unequal segregation of cocaine in rat fetuses as a function of proximal-distal location in the uterus, indicating a differential vasoconstriction of the two main arteries supplying the uterus in rats receiving cocaine. By performing C-sections after exposure to cocaine, we were able to measure the cocaine content and immediate-early gene (IEG) induction in the brains of fetuses according to their intrauterine position and assess the potentially vasoconstrictive effect of ethanol. HPLC analysis of fetal brains exposed to cocaine supported the study of Lipton et al.: fetuses from the proximal (lower) end of the uterus had more cocaine than fetuses from the distal (upper) end. Concurrent ethanol decreased the amount of cocaine reaching the fetuses and diminished the proximal-distal gradient. There were increased numbers of Fos-immunoreactive cells in fetuses exposed to both ethanol and cocaine compared to cocaine binge only. Additionally, the gradient of c-fos induction observed as a function of intrauterine position in cocaine-treated rats was in the opposite direction: most distal fetuses generally had the most Fos-immunoreactive cells. These results indicate that IEG induction in fetal brains exposed to cocaine and ethanol may be more related to hypoxic consequences of prenatal drug exposure.

Mechanisms of the effects of exogenous levodopa on the dopamine-denervated striatum

The efficacy of exogenous levodopa (L-DOPA) is attributed to its conversion to dopamine by the enzyme aromatic L-amino-acid decarboxylase in striatal dopaminergic terminals. However, there is controversy about the mechanisms underlying the therapeutic and adverse effects of L-DOPA after almost all striatal dopaminergic afferents have disappeared (i.e. in the later stages of Parkinson's disease). After administration of 30mg/kg or 100mg/kg of L-DOPA, rats subjected to unilateral dopaminergic denervation showed intense contraversive rotation and a high density of Fos-immunoreactive nuclei throughout the denervated striatum, with no significant induction of Fos in the intact striatum. Injection of the central aromatic L-amino-acid decarboxylase inhibitor NSD-1015 30min before and 15min after the injection of L-DOPA suppressed the rotational behavior and the striatal induction of Fos. Comparison of results obtained in rats subjected to unilateral and bilateral dopaminergic denervation indicated that the presence of contralateral dopaminergic innervation does not significantly modulate the effects of L-DOPA on the denervated striatum. Serotonergic denervation led to slight and statistically non-significant decrease in the rotational behavior and Fos expression induced by high doses of L-DOPA (100mg/kg) in the dopamine-denervated striatum, but totally suppressed the rotational behavior and Fos expression induced by low doses of L-DOPA (30mg/kg). The present data indicate that the major effects observed after administration of exogenous L-DOPA are not due to a direct action of L-DOPA on dopamine receptors, or to extrastriatal release of dopamine, but to conversion of L-DOPA to dopamine by serotonergic terminals and probably some intrastriatal cells. Given that serotonergic neurons appear to play an important role in the action of L-DOPA in the later stages of Parkinson's disease, strategies targeting the serotonergic system should be considered for the treatment of Parkinson's disease and for combating undesirable side effects of L-DOPA therapy.

Amphetamine and cocaine induce different patterns of c-fos mRNA expression in the striatum and subthalamic nucleus depending on environmental context

In the dorsal striatum, there are two major populations of medium spiny projection neurons. One population is positive for dynorphin mRNA (DYN+), and these cells project preferentially to the substantia nigra, forming the so-called 'direct pathway'. A second population is positive for enkephalin mRNA (ENK+), and these cells influence the substantia nigra indirectly, via the globus pallidus and subthalamic nucleus. Psychostimulant drugs, such as amphetamine and cocaine, are reported to induce immediate early genes (IEGs) in only one subpopulation of dorsal striatal projection neurons, DYN+ cells. However, this apparent selectivity appears to be a function of environmental context. We found that when given in the animal's home cage, amphetamine and cocaine increased expression of the IEG, c-fos, almost exclusively in DYN+ cells. However, when given in a novel environment, amphetamine and cocaine increased c-fos mRNA in both DYN+ and ENK+ cells. Furthermore, amphetamine and cocaine increased c-fos mRNA expression in the subthalamic nucleus when administered in the novel environment, but not when given at home. We conclude that the neural circuitry engaged by psychostimulant drugs, and their ability to induce specific patterns of gene expression, are determined by the environmental context in which they are experienced. This may be related to the ability of environmental novelty to facilitate psychostimulant drug-induced neuroplasticity.

The neurotensin antagonist SR 48692 attenuates haloperidol-induced striatal Fos expression in the rat

Neurotensin interacts with central dopamine systems and has been suggested to exert antipsychotic drug-like actions. Antipsychotic drugs such as haloperidol induce striatal immediate-early gene expression. In order to study neurotensin's role in antipsychotic drug actions, rats were pretreated with the neurotensin antagonist SR 48692 and then injected with haloperidol. SR 48692 dose-dependently decreased haloperidol-elicited immediate-early gene expression in the dorsolateral and central striatum but not other striatal areas. SR 48692 reduced Fos expression in the striatal patch (striosome) and matrix compartments, with a significantly greater effect in the patch. These data suggest that neurotensin may play a role in the actions of haloperidol. In view of proposed functional roles of the striatal patch and matrix, we suggest that neurotensin may be important in the therapeutic rather than side effects of antipsychotic drugs.

The genomic action potential

Neurons compute in part by integrating, on a time scale of milliseconds, many synaptic inputs and generating a digital output-the "action potential" of classic electrophysiology. Recent discoveries indicate that neurons also perform a second, much slower, integration operating on a time scale of minutes or even hours. The output of this slower integration involves a pulse of gene expression which may be likened to the electrophysiological action potential. Its function, however, is not directed toward immediate transmission of a synaptic signal but rather toward the experience-dependent modification of the underlying synaptic circuitry. Commonly termed the "immediate early gene" (IEG) response, this phenomenon is often assumed to be a necessary component of a linear, deterministic cascade of memory consolidation. Critical review of the large literature describing the phenomenon, however, leads to an alternative model of IEG function in the brain. In this alternative, IEG activation is not directed at the consolidation of memories of a specific inducing event; instead, it sets the overall gain or efficiency of memory formation and directs it to circuits engaged by behaviorally significant contexts. The net result is a sharpening of the selectivity of memory formation, a recruitment of temporally correlated associations, and an ultimate enhancement of long-term memory retrieval.

Fenfluramine-induced increase in preproenkephalin mRNA levels in the striatum: interaction between the serotonergic, glutamatergic, and dopaminergic systems

Fenfluramine (FE) is a halogenated amphetamine derivative that has been used in the treatment of obesity. It has been suggested that the effects of FE on the striatum are mediated by serotonergic mechanisms. However, several major afferent systems may be involved, and administration of FE may be useful to study interactions between these systems. In this work, the effects of FE on striatopallidal neurons and the possible involvement of the major striatal afferent systems were studied in rats by determination of FE-induced changes in striatal levels of preproenkephalin (PPE) mRNA using in situ hybridization. Injection of FE induced a significant increase (60%) in striatal levels of PPE mRNA. This increase was blocked by pretreatment with the D(1) dopamine receptor antagonist SCH-23390 or with the NMDA glutamate receptor antagonist MK-801, or by lesion of the serotonergic system with 5,7-dihydroxytryptamine or p-chlorophenylalanine. In 6-hydroxydopamine lesioned rats, the lesion-induced increase in PPE mRNA levels was not affected by injection of FE, but was reduced by simultaneous serotonergic deafferentation. The results suggest that the serotonergic, glutamatergic, and dopaminergic system interact to increase striatal PPE mRNA levels after FE administration.

Towards a protocol for the preparation and delivery of striatal tissue for clinical trials of transplantation in Huntington's disease

There is a growing body of scientific evidence contributing to the development of clinical transplantation programs in patients with Huntington's disease. Phase I clinical trials have already commenced in France and North America and are starting in the near future in Sweden and the UK. Protocols for patient selection, surgical implantation, and pre- and postoperative follow-up are well defined. However, considerable variability exists with respect to the harvesting, preparation, and timing of implantation of the donor material. In this article we review the scientific evidence on which a rational protocol for donor tissue preparation and delivery may be based. Strategies aimed at minimizing the variability of tissue preparation should reduce the variability of functional outcome of striatal transplantation observed in animal models of Huntington's disease.

Locomotor activity and accumbens Fos expression driven by ventral hippocampal stimulation require D1 and D2 receptors

Numerous studies have suggested that excitatory projections from the ventral hippocampus to the nucleus accumbens modulate locomotor activity in rats. Furthermore, the ability of ventral hippocampal neurons to alter locomotor activity may involve the dense dopaminergic innervation found in the nucleus accumbens. The purpose of this study was to: (i) more fully characterize the locomotor effects of acute alterations in ventral hippocampal activity; (ii) ascertain the influence of dopamine agonists and antagonists on locomotor changes produced by altered ventral hippocampal activity; and (iii) use immediate early gene induction to determine whether dopamine antagonists alter the response of nucleus accumbens neurons to ventral hippocampal stimulation. By comparing a variety of excitatory amino acid agonists, it was found that ventral hippocampal infusion of N-methyl-D-aspartate elevated locomotor activity in a subconvulsive manner, while other excitatory amino acid receptor agonists did not. Inactivation of the ventral hippocampus achieved by lidocaine infusion did not suppress ongoing locomotor activity, nor did it affect amphetamine-induced increases in locomotor activity. Increases in locomotor activity induced by ventral hippocampal N-methyl-D-aspartate infusion were blocked by systemic administration of haloperidol (a D2 receptor antagonist), SCH-23390 (a D1 receptor antagonist) or reserpine. Cellular expression of the protein product of the immediate early gene, c-fos, was dramatically increased in the nucleus accumbens shell after ventral hippocampal N-methyl-D-aspartate infusion, and haloperidol, SCH-23390 and reserpine attenuated this effect. These results suggest that the increases, but not decreases, in ventral hippocampal activity have a measurable effect on ongoing rates of locomotion, and that this effect requires both D1 and D2 receptors. Moreover, the studies of Fos expression suggest that dopamine receptor antagonists attenuate neuronal responses to ventral hippocampal stimulation within the nucleus accumbens, a brain region important in the generation and maintenance of locomotor activity.

Cortically driven Fos induction in the striatum is amplified by local dopamine D2-class receptor blockade

Dopamine D2-class receptors have been shown to control the excitability of striatal neurons in response to cortical activation. It has been unclear, however, whether such receptors could regulate the number of striatal neurons activated by cortical stimulation, and thus affect the population response of the striatum to its cortical inputs. We used Fos induction as a readout to measure the ensemble response of striatal neurons to localized stimulation of the frontal cortex and tested for the effects of D2-class dopamine receptor blockade on this response. In freely moving rats, we stimulated the frontal cortex by local epidural application of a dose of a GABAA receptor antagonist (picrotoxin) just threshold for inducing Fos in the striatum. We combined this treatment with D2-class dopamine receptor antagonist treatments at dose levels also just threshold for inducing Fos, using either (i) systemic haloperidol or (ii) intrastriatal (-)sulpiride. Both systemic and intrastriatal blockade of D2-class receptors sharply increased the numbers of striatal neurons exhibiting cortically evoked Fos induction. These findings suggest that local activation of intrastriatal D2-class dopamine receptors can regulate the number of striatal neurons responsive to cortical inputs, thus dynamically shaping the flow of information through the striatum.

Effect of a functional impairment of corticostriatal transmission on cortically evoked expression of c-Fos and zif 268 in the rat basal ganglia

The activity-dependent induction of immediate-early genes is commonly used to map activated neuronal networks. In a previous analysis of the cortico-basal ganglia circuits, we have shown that a cortical stimulation produces Fos protein expression in the striatum and the subthalamic nucleus, with a pattern which conforms to the anatomical organization of cortical projections [Sgambato V. et al. (1996) Neuroscience 81, 93-112]. In the present study, we examined the effects of a unilateral blockade of the corticostriatal transmission on c-fos and zif 268 messenger RNA expression evoked in the substantia nigra pars reticulata and the subthalamic nucleus following stimulation of the ipsilateral motor cortex. The blockade of the corticostriatal pathway was performed either by an excitotoxic striatal lesion or by an application of the AMPA/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione within the striatum. After application of the glutamate receptor antagonist, which prevented the cortical stimulation activating the GABAergic striatonigral pathway, the induction of both c-fos and zif 268 messenger RNAs was facilitated in the ipsilateral substantia nigra pars reticulata. In the subthalamic nucleus ipsilateral to the application of 6-cyano7-nitroquinoxaline-2,3-dione, the cellular discharges evoked by stimulation of the cortex were considerably shortened as a result of the blockade of the disinhibitory striato-pallido-subthalamic circuit. However, a strong expression of immediate-early genes was still induced by the cortical stimulation. By contrast, after unilateral kainate lesion of the striatum, the cortical stimulation was no longer able to induce c-fos and zif 268 messenger RNA expression in the ipsilateral subthalamic nucleus and in the substantia nigra pars reticulata bilaterally. The lack of immediate-early gene induction strongly contrasted with the neuronal discharges evoked in these nuclei by the cortical stimulation. Comparison between the cortically evoked neuronal activities and the pattern of immediate-early gene expression suggests that the induction of immediate-early genes in the basal ganglia mainly reflects the level of synaptic activity rather than the frequency of discharge of the postsynaptic neurons. Moreover, the results stress that modifications of immediate-early gene expression observed in the basal ganglia after an acute or a chronic interruption of the corticostriatal transmission are not superimposable.

Locomotor-activity-induced changes in striatal levels of preprotachykinin and preproenkephalin mRNA. Regulation by the dopaminergic and glutamatergic systems

The mechanisms by which dopaminergic and glutamatergic inputs interact to regulate striatal neuropeptide expression during physiological motor activity are poorly understood. In this work, striatal expression of preprotachykinin (PPT) and preproenkephalin (PPE) mRNA was studied by in situ hybridization in rats killed 2 h after treadmill running (36 m/min for 20 min). Treadmill running induced a significant increase in the levels of both PPT (60% increase) and PPE (90% increase) mRNA in the striatum of normal rats. The increase in the level of PPT mRNA was blocked in rats previously subjected to nigrostriatal deafferentation (i.e., 6-hydroxydopamine lesion) or pretreated with D1-receptor antagonist SCH-23390 (0.1 mg/kg), the D2-receptor antagonist eticlopride (0.5 mg/kg), or the N-methyl-D-aspartate (NMDA) glutamate receptor antagonist MK-801 (0.1 mg/kg). The running-induced increase in the level of PPE mRNA was blocked in rats pretreated with SCH-23390 or MK-801. Rats subjected to nigrostriatal deafferentation or pretreated with eticlopride showed an increase in PPE mRNA levels (around 150% and 40% increase, respectively), that was enhanced by running (around 230% and 160% increase, respectively). These results suggest that locomotor activity increases, in a NMDA receptor dependent fashion, the excitatory influence of the corticostriatal glutamatergic system on the two populations of striatal projection neurons, as reflected by increases in the levels of PPT and PPE mRNA. The results obtained after dopamine depletion or injection of dopamine receptor antagonists suggest that a concomitant increase in dopamine release may enhance PPT mRNA level in striatonigral neurons via D1 receptors, and reduce PPE mRNA level in striatopallidal neurons via D2 receptors. Additionally, levels of dopamine and glutamate may be regulated by other complex indirect mechanisms.

Cortically driven immediate-early gene expression reflects modular influence of sensorimotor cortex on identified striatal neurons in the squirrel monkey

Current understanding of basal ganglia function emphasizes their involvement in the focal, context-dependent release of motor and cognitive circuits in the brainstem and frontal lobes. How such selective action can arise despite the existence of massively convergent inputs from the cerebral cortex is unknown. However, anatomical work has suggested that specificity could be achieved in corticostriatal circuits by modular patterns of convergent and divergent cortical inputs to striatal projection neurons. To test for such modular activation of striatal neurons, we electrically microstimulated physiologically identified sites in the primary somatosensory (SI) and primary motor (MI) cortex of the squirrel monkey. We compared the efferent fiber distributions anterogradely traced from these sites to the distributions of striatal neurons activated by microstimulation to express Fos- and Jun B-like immediate-early gene proteins. We show that the microstimulation of sensorimotor cortex induces Fos and Jun B expression in localized cell clusters in the putamen and that these clusters match the anatomical input fiber clusters (matrisomes). The modular activation of striatal neurons by sensorimotor cortex seems likely. Unexpectedly, >75% of the Fos-positive nuclei in densely labeled cell clusters were in enkephalin-immunoreactive neurons. This expression pattern suggests that the primate sensorimotor cortex exerts a differential influence on the enkephalinergic (indirect pathway) as opposed to the substance P/dynorphin (direct pathway) projection neurons of the putamen. The densely labeled clusters of Fos-labeled enkephalinergic neurons occurred within larger zones containing sparsely distributed Fos-labeled parvalbumin neurons. Moreover, when the cortical stimulation induced expression of Fos-like protein only in sparsely distributed neurons, almost every putamenal neuron expressing Fos was a parvalbumin-containing (GABAergic) interneuron. These patterns suggest a model in which the primate sensorimotor cortex can target parvalbumin-containing inhibitory interneurons, which in turn depress the remaining neuronal activity within and around matrisomes in a feed-forward manner until sufficient coherent cortical input can overcome the inhibition to influence selectively enkephalinergic projection neurons in the activated matrisomes. Tuning of cortical input by striatal interneurons thus may be an important mechanism by which broader anatomical connections are dynamically adjusted to achieve selective flow of information through the basal ganglia.

Subcellular and subsynaptic distribution of the NR1 subunit of the NMDA receptor in the neostriatum and globus pallidus of the rat: co-localization at synapses with the GluR2/3 subunit of the AMPA receptor

Glutamatergic neurotransmission in the neostriatum and the globus pallidus is mediated through NMDA-type as well as other glutamate receptors and is critical in the expression of basal ganglia function. In order to characterize the cellular, subcellular and subsynaptic localization of NMDA receptors in the neostriatum and globus pallidus, multiple immunocytochemical techniques were applied using antibodies that recognize the NR1 subunit of the NMDA receptor. In order to determine the spatial relationship between NMDA receptors and AMPA receptors, double labelling was performed with the NR1 antibodies and an antibody that recognizes the GluR2 and 3 subunits of the AMPA receptor. In the neostriatum all neurons with characteristics of spiny projection neurons, some interneurons and many dendrites and spines were immunoreactive for NR1. In the globus pallidus most perikarya and many dendritic processes were immunopositive. Immunogold methods revealed that most NR1 labelling is associated with asymmetrical synapses and, like the labelling for GluR2/3, is evenly spread across the synapse. Double immunolabelling revealed that in neostriatum, over 80% of NR1-positive axospinous synapses are also positive for GluR2/3. In the globus pallidus most NR1-positive synapses are positive for GluR2/3. In both regions many synapses labelled only for GluR2/3 were also detected. These results, together with previous data, suggest that NMDA and AMPA receptor subunits are expressed by the same neurons in the neostriatum and globus pallidus and that NMDA and AMPA receptors are, at least in part, colocalized at individual asymmetrical synapses. The synaptic responses to glutamate in these regions are thus likely be mediated by both AMPA and NMDA receptors at the level of individual synapses.

Extracellular signal-regulated kinase (ERK) controls immediate early gene induction on corticostriatal stimulation

Activity-dependent changes in neuronal structure and synaptic remodeling depend critically on gene regulation. In an attempt to understand how glutamate receptor stimulation at the membrane leads to gene regulation in the nucleus, we traced intracellular signaling pathways targeting DNA regulatory elements of immediate early genes (IEGs). For this purpose we used an in vivo electrical stimulation of the glutamatergic corticostriatal pathway. We show that a transient activation of extracellular signal-regulated kinase (ERK) proteins (detected by immunocytochemistry with an anti-active antibody) is spatially coincident with the onset of IEG induction [c-fos, zif 268, and map kinase phosphatase-1 (MKP-1) detected by in situ hybridization] in the striatum, bilaterally. Both Elk-1 and CREB transcription factors (targeting SRE and CRE DNA regulatory elements, respectively) were hyperphosphorylated in register with ERK activation and IEG mRNA induction. However, their hyperphosphorylation occurred in different subcellular compartments: the cytoplasm and the nucleus for Elk-1 and the nucleus for CREB. The role of the ERK signaling cascade in gene regulation was confirmed after intrastriatal and unilateral injection of the specific ERK inhibitor PD 98059, which completely abolished c-fos, zif 268, and MKP-1 mRNA induction in the injected side. Of interest, both Elk-1 and CREB hyperphosphorylation also was impaired after PD 98059 injection. Thus two different ERK modules, one depending on the cytoplasmic activation of Elk-1 and the other one depending on the nuclear activation of CREB, control IEG transcriptional regulation in our model. Our findings provide significant insights into intracellular mechanisms underlying synaptic plasticity in the striatum.

The basal ganglia and chunking of action repertoires

The basal ganglia have been shown to contribute to habit and stimulus-response (S-R) learning. These forms of learning have the property of slow acquisition and, in humans, can occur without conscious awareness. This paper proposes that one aspect of basal ganglia-based learning is the recoding of cortically derived information within the striatum. Modular corticostriatal projection patterns, demonstrated experimentally, are viewed as producing recoded templates suitable for the gradual selection of new input-output relations in cortico-basal ganglia loops. Recordings from striatal projection neurons and interneurons show that activity patterns in the striatum are modified gradually during the course of S-R learning. It is proposed that this recoding within the striatum can chunk the representations of motor and cognitive action sequences so that they can be implemented as performance units. This scheme generalizes Miller's notion of information chunking to action control. The formation and the efficient implementation of action chunks are viewed as being based on predictive signals. It is suggested that information chunking provides a mechanism for the acquisition and the expression of action repertoires that, without such information compression would be biologically unwieldy or difficult to implement. The learning and memory functions of the basal ganglia are thus seen as core features of the basal ganglia's influence on motor and cognitive pattern generators.

Expression of messenger RNAs encoding ionotropic glutamate receptors in rat brain: regulation by haloperidol

In situ hybridization was used to study the regional distribution of messenger RNAs encoding ionotropic glutamate receptor subtypes in the rat brain's dopaminergic cell body regions and their forebrain projection areas. Short oligonucleotide probes specific for the messenger RNAs encoding the flip or flop splice forms of the GluR1 and GluR2 AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) receptor subunits, or for the messenger RNAs encoding the N-methyl-D-aspartate R1 subunit, were used. Significant differences were seen in the relative messenger RNA levels, and the distribution of the flip and flop splice forms, of GluR1 and GluR2. In the dopaminergic cell groups of the substantia nigra pars compacta and the ventral tegmental area, the flip form of both GluR1 and GluR2 dominated over the flop form. Similarly, in the core division of the nucleus accumbens, GluR1 and GluR2 flip forms dominated over the flop forms. In contrast, in the accumbens shell, the GluR1 and GluR2 flop forms dominated over the flip forms. As a comparison to the AMPA receptor subunits, N-methyl-D-aspartate R1 messenger RNA was relatively evenly distributed in all the regions analysed. The results demonstrate a heterogeneous distribution of the flip and flop splice forms of GluR1 and GluR2 in the brain's dopaminergic pathways, which could contribute to physiological differences in regulation of the pathways by glutamatergic neurotransmission. We also studied regulation of glutamate receptor subunit expression in these regions by antipsychotic drugs, based on previous reports of altered levels of subunit immunoreactivity after drug treatment. Chronic administration of the typical antipsychotic drug, haloperidol, caused a small but significant induction of GluR2 flip messenger RNA in the dorsolateral caudate putamen. This effect was not seen after chronic administration of the atypical antipsychotic drug, clozapine. Significant drug regulation of the other glutamate receptor subunits studied was not observed.

Interaction between the serotonergic, dopaminergic, and glutamatergic systems in fenfluramine-induced Fos expression in striatal neurons

Fenfluramine (FE) is a halogenated amphetamine derivative used in the treatment of obesity and thought to induce serotonin (5-HT) release from nerve terminals and to reduce re-uptake. However, other pathways may also be involved. In this work, the effects of FE on the major striatal afferent systems, and the possible interactions of these systems in FE-induced striatal expression of Fos, were studied by lesion of the serotonergic and/or dopaminergic system and administration of NMDA glutamate (MK-801) or D1 dopamine (SCH-23390) receptor antagonists. Both the D1 and NMDA receptor antagonists suppressed Fos expression in response to FE almost entirely. FE-induced Fos expression was also dramatically reduced 24 h after 6-hydroxydopamine (6-OHDA) lesion of the dopaminergic system. However, the reduction was not so marked after chronic 6-OHDA lesion, probably due to compensatory changes. Chronic (5,7-dihydroxytryptamine injection, 4 weeks before) or acute (p-chlorophenylalanine injection) lesion of the serotonergic system led to a marked reduction in Fos expression in response to FE (decrease of about 50%). After simultaneous chronic lesion of both serotonergic and dopaminergic systems, a considerable number of Fos-positive nuclei were still observed (decrease of about 70% in the dorsal and dorsomedial regions). The FE-induced expression of Fos was almost totally suppressed (decrease of about 95% in the dorsal and dorsomedial regions) after simultaneous acute lesion. Our results indicate that FE-induced striatal expression of Fos is due in large measure to DA release and dopaminergic stimulation of D1 receptors. However, concurrent stimulation of NMDA glutamate receptors also appears to be essential, and 5-HT release (although not indispensable) doubles striatal Fos expression.

Effect of electrical stimulation of the cerebral cortex on the expression of the Fos protein in the basal ganglia

The protein Fos is a transcription factor which is quickly induced in response to a variety of extracellular signals. Since this protein is expressed in a variety of neuronal systems in response to activation of synaptic afferents, it has been suggested that it might contribute to activity-dependent plasticity in neural networks. The present study investigated the effect of cortical electrical stimulation on the expression of Fos in the basal ganglia in the rat, a group of structures that participate in sensorimotor learning. Results show that the repetitive application of electrical shocks in restricted areas of the cerebral cortex induces an expression of Fos mostly confined to the striatum and the subthalamic nucleus. The induction which can be elicited from different cortical areas (sensorimotor, auditory and limbic areas) does not require particular temporal patterns of stimulation but rather depends on the total number of shocks delivered during a given period of time. Moreover, it appears to be rather independent of the number of spikes discharged by the activated cells. In the striatum, the distribution of immunoreactive neurons is precisely delineated and conforms to the known topographical organization of stimulated corticostriatal projections. As demonstrated using a variety of double labelling techniques (combination of the immunocytochemical detection of Fos with the autoradiography of mu opioid receptors, calbindin immunocytochemistry, in situ hybridization of preproenkephalin and preprotachykinin A messenger RNAs), striatal neurons which express Fos are mostly localized in the matrix compartment and concern equally enkephaline and substance P containing efferent neurons. In the subthalamic nucleus, Fos expression evoked by cortical stimulation is also confined to discrete regions of the nucleus, the localizations corresponding to the primary projection site of the stimulated cortical cells. These results indicate that in addition to its phasic synaptic influence on the basal ganglia, the cerebral cortex could exert a long-term effect on the functional state of this system via a genomic control. Since the basal ganglia are involved in sensorimotor learning and motor habit formation, it is tempting to speculate that the activity-dependent Fos induction at corticostriatal and subthalamic synapses may contribute to consolidate the functionality of the neuronal networks activated during the completion of given motor tasks.

Modulation of c-fos expression in the rat striatum by diazepam

The benzodiazepine agonist, diazepam, inhibits cAMP production in the rat brain. Since cAMP influences c-fos activity, we examined the effects of diazepam on expression of this immediate early gene, as indicated by Western blot analysis. Intraperitoneal administration of diazepam increased Fos protein levels in the striatum, but not in the hippocampus. In contrast, pretreatment with diazepam blocked the potent inducing effect of amphetamine, in both brain regions. Similar induction and blockade effects were also observed for a 90 kDa Fos related antigen (Fra), in the striatum and hippocampus. The possible mechanisms underlying the modulatory effects of diazepam on c-fos expression in the brain are discussed.

Time course of striatal, pallidal and thalamic alpha 1, alpha 2 and beta 2/3 GABAA receptor subunit changes induced by unilateral 6-OHDA lesion of the nigrostriatal pathway

Immunocytochemical techniques were used to investigate the distribution and abundance of GABAA receptor subunits (alpha 1, alpha 2 and beta 2/3) in the brains of unilaterally 6-OHDA-lesioned rats. Three and 7 days after lesion, the alpha 2-subunit was significantly more abundant in the lesion-ipsilateral striatum than in the lesion-contralateral striatum; by 4 weeks after lesion, however, no significant between-side differences were observed. Three and 7 days after lesion, the alpha 1-subunit was significantly less abundant in the lesion-ipsilateral globus pallidus than in the lesion-contralateral side; again, this difference disappeared within 4 weeks of lesion. Similarly, alpha 1 was initially less abundant in several relay thalamic nuclei on the lesioned side while alpha 2 was initially more abundant in intralaminar thalamic nuclei on the lesioned side. There were no significant between-side changes for the beta 2/3-subunits. Comparison of non-lesioned and 6-OHDA-lesioned rats revealed significant differences in brain areas which also showed differences on comparison of the lesioned and non-lesioned sides of 6-OHDA-lesioned rats. These results suggest that there is an early adaptation to the lesion, achieved through changes in GABAA receptor abundance. That some of these changes are no longer apparent after 4 weeks is due not only to partial reversion of the changes in the lesioned side but also to compensatory changes in the non-lesioned side.