Scopolamine augments c-fos and zip/268 messenger RNA expression induced by the full D(1) dopamine receptor agonist SKF-82958 in the intact rat striatum

Effects of intrastriatal injection of the dopamine receptor agonist SKF38393 and quinpirole on locomotor behavior in hemiparkinsonism rats

Dopamine (DA) in the striatum is essential to influence motor behavior and may lead to movement impairment in Parkinson's disease (PD). The present study examined the different functions of the DA D1 receptor (D1R) and DA D2 receptor (D2R) by intrastriatal injection of the D1R agonist SKF38393 and the D2R agonist quinpirole in 6-hydroxydopamine (6-OHDA)-lesioned and control rats. All rats separately underwent dose-response behavior testing for SKF38393 (0, 0.5, 1.0, and 1.5 μg/site) or quinpirole (0, 1.0, 2.0, and 3.0 μg/site) to determine the effects of the optimal modulating threshold dose. Two behavior assessment indices, the time of latency to fall and the number of steps on a rotating treadmill, were used as reliable readouts of motor stimulation variables for quantifying the motor effects of the drugs. The findings indicate that at threshold doses, SKF38393 (1.0 μg/site) and quinpirole (1.0 μg/site) produce a dose-dependent increase in locomotor activity compared to vehicle injection. The ameliorated behavioral responses to either SKF38393 or quinpirole in lesioned rats were greater than those in unlesioned control rats. Moreover, the dose-dependent increase in locomotor capacity for quinpirole was greater than that for SKF38393 in lesioned rats. These results can clarify several key issues related to DA receptors directly and may provide a basis for exploring the potential of future selective dopamine therapies for PD in humans.

The Beneficial Effect of Acute Exercise on Motor Memory Consolidation is Modulated by Dopaminergic Gene Profile

When aerobic exercise is performed following skilled motor practice, it can enhance motor memory consolidation. Previous studies have suggested that dopamine may play a role in motor memory consolidation, but whether it is involved in the exercise effects on consolidation is unknown. Hence, we aimed to investigate the influence of dopaminergic pathways on the exercise-induced modulation of motor memory consolidation. We compared the effect of acute exercise on motor memory consolidation between the genotypes that are known to affect dopaminergic transmission and learning. By combining cluster analyses and fitting linear models with and without included polymorphisms, we provide preliminary evidence that exercise benefits the carriers of alleles that are associated with low synaptic dopamine content. In line with previous reports, our findings implicate dopamine as a modulator of the exercise-induced effects on motor memory consolidation, and suggest exercise as a potential clinical tool to counteract low endogenous dopamine bioavailability. Further experiments are needed to establish causal relations.

Effects of Muscarinic Acetylcholine m1 and m4 Receptor Blockade on Dyskinesia in the Hemi-Parkinsonian Rat

Standard treatment for Parkinson's disease (PD) is L-DOPA, but with chronic administration the majority of patients develop L-DOPA-induced dyskinesia (LID). Emerging evidence implicates the cholinergic system in PD and LID. Muscarinic acetylcholine receptors (mAChR) are known to modulate movement and of late have been implicated as possible targets for LID. Therefore the current study investigated the role of M₁ and M₄ mAChRs in LID, on motor performance following L-DOPA treatment, and sought to identify brain sites through which these receptors were acting. We first administered M₁R-preferring antagonist trihexyphenidyl (0, 0.1, and 1.0 mg/kg, i.p.) or the M₄R-preferring antagonist tropicamide (0, 10, and 30 mg/kg, i.p.) before L-DOPA, after which LID and motor performance were evaluated. Both compounds worsened and extended the time course of LID, while M₁R blockade improved motor performance. We then evaluated the effects of tropicamide and trihexyphenidyl on dyskinesia induced by D₁R agonist SKF81297 or D₂R agonist quinpirole. Surprisingly, both M₁R and M₄R antagonists reduced D₁R agonist-induced dyskinesia but not D₂R agonist-induced dyskinesia, suggesting that mAChR blockade differentially affects MSN firing in the absence of postsynaptic DA. Finally, we evaluated effects of striatum- or PPN-targeted tropicamide microinfusion on LID and motor performance. Despite prior evidence, M₄R blockade in either site alone did not affect the severity of LID via local striatal or PPN infusions. Taken together, these data suggest M₄R as a promising therapeutic target for reducing LID using more selective compounds.

Regulation of Phosphorylation of AMPA Glutamate Receptors by Muscarinic M4 Receptors in the Striatum In vivo

The acetylcholine muscarinic 4 (M4) receptor is a principal muscarinic receptor subtype present in the striatum. Notably, G_αi/o-coupled M4 receptors and G_αs/G_olf-coupled dopamine D1 receptors are coexpressed in striatonigral projection neurons and are thought to interact with each other to regulate neuronal excitability, although underlying molecular mechanisms are poorly understood. In this study, we investigated the role of M4 receptors in the regulation of phosphorylation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in the rat normal and dopamine-stimulated striatum in vivo. We found that a systemic injection of a M4 antagonist tropicamide increased AMPA receptor GluA1 subunit phosphorylation at a protein kinase A-dependent site (S845) in the striatum. The tropicamide-induced S845 phosphorylation was rapid, reversible, and dose-dependent and occurred in the two subdivisions of the striatum, i.e., the caudate putamen and nucleus accumbens. Coadministration of subthreshold doses of tropicamide and a D1 agonist SKF81297 induced a significant increase in S845 phosphorylation. Coadministered tropicamide and a dopamine psychostimulant amphetamine at their subthreshold doses also elevated S845 phosphorylation. Tropicamide alone or coinjected with SKF81297 or amphetamine had no effect on GluA1 phosphorylation at S831. Tropicamide did not affect GluA2 phosphorylation at S880. These results reveal a selective inhibitory linkage from M4 receptors to GluA1 in S845 phosphorylation in striatal neurons. Blockade of the M4-mediated inhibition significantly augments constitutive and dopamine-stimulated GluA1 S845 phosphorylation.

Muscarinic Acetylcholine Receptors Inhibit Fyn Activity in the Rat Striatum In Vivo

The Src family kinase (SFK) is a subfamily of non-receptor tyrosine kinases. SFK members, Src and especially Fyn, are expressed in the striatum. These SFK members are involved in the regulation of neuronal and synaptic activities and are linked to the pathogenesis of a variety of neuropsychiatric and neurodegenerative disorders. Given the fact that muscarinic acetylcholine (mACh) receptors are highly expressed in striatal neurons and are critical for the regulation of striatal function, we investigated the role of mACh receptors in the regulation of SFKs in the adult rat striatum in vivo. We found that pharmacological blockade of mACh receptors by systemic administration of the mACh antagonist scopolamine induced a marked increase in phosphorylation of SFKs in the striatum of male and female rats. This scopolamine-induced increase in SFK phosphorylation occurred in the two subdivisions of the striatum (caudate putamen and nucleus accumbens) and was time-dependent and reversible. Another mACh antagonist atropine was also effective in stimulating SFK phosphorylation. Coadministration of subthreshold doses of scopolamine and a dopamine D1 receptor agonist SKF81297 enhanced striatal SFK phosphorylation. Between Fyn and Src proteins immunoprecipitated from striatal tissue, scopolamine selectively increased phosphorylation of Fyn. The increase in Fyn phosphorylation was accompanied by an increase in Fyn kinase activity in response to scopolamine. These results reveal a significant role of mACh receptors in the regulation of SFKs (mainly Fyn) in striatal neurons. Under normal conditions, endogenous mACh receptors appear to exert an inhibitory effect on Fyn activity.

Dopamine D1 receptor activation maintains motor coordination and balance in rats

Dopamine (DA) modulates motor coordination, and its depletion, as in Parkinson's disease, produces motor impairment. The basal ganglia, cerebellum and cerebral cortex are interconnected, have functional roles in motor coordination, and possess dopamine D₁ receptors (D₁Rs), which are expressed at a particularly high density in the basal ganglia. In this study, we examined whether the activation of D₁Rs modulates motor coordination and balance in the rat using a beam-walking test that has previously been used to detect motor coordination deficits. The systemic administration of the D₁R agonist SKF-38393 at 2, 3, or 4 mg/kg did not alter the beam-walking scores, but the subsequent administration of the D₁R antagonist SCH-23390 at 1 mg/kg did produce deficits in motor coordination, which were reversed by the full agonist SKF-82958. The co-administration of SKF-38393 and SCH-23390 did not alter the beam-walking scores compared with the control group, but significantly prevented the increase in beam-walking scores induced by SCH-23390. The effect of the D₁R agonist to prevent and reverse the effect of the D₁R antagonist in beam-walking scores is an indicator that the function of D₁Rs is necessary to maintain motor coordination and balance in rats. Our results support that D₁Rs mediate the SCH-23390-induced deficit in motor coordination.

Antagonism of Muscarinic Acetylcholine Receptors Alters Synaptic ERK Phosphorylation in the Rat Forebrain

Acetylcholine (ACh) is a key transmitter in the mesocorticolimbic circuit. By interacting with muscarinic ACh receptors (mAChR) enriched in the circuit, ACh actively regulates various neuronal and synaptic activities. The extracellular signal-regulated kinase (ERK) is one of members of the mitogen-activated protein kinase family and is subject to the regulation by dopamine receptors, although the regulation of ERKs by limbic mAChRs is poorly understood. In this study, we investigated the role of mAChRs in the regulation of ERK phosphorylation (activation) in the mesocorticolimbic system of adult rat brains in vivo. We targeted a sub-pool of ERKs at synaptic sites. We found that a systemic injection of the mAChR antagonist scopolamine increased phosphorylation of synaptic ERKs in the striatum (caudate putamen and nucleus accumbens) and medial prefrontal cortex (mPFC). Increases in ERK phosphorylation in both forebrain regions were rapid and transient. Notably, pretreatment with a dopamine D1 receptor (D1R) antagonist SCH23390 blocked the scopolamine-stimulated ERK phosphorylation in these brain regions, while a dopamine D2 receptor antagonist eticlopride did not. Scopolamine and SCH23390 did not change the amount of total ERK proteins. These results demonstrate that mAChRs inhibit synaptic ERK phosphorylation in striatal and mPFC neurons under normal conditions. Blockade of this inhibitory mAChR tone leads to the upregulation of ERK phosphorylation likely through a mechanism involving the level of D1R activity.

Amphetamine elevates phosphorylation of eukaryotic initiation factor 2α (eIF2α) in the rat forebrain via activating dopamine D1 and D2 receptors

Psychostimulants have an impact on protein synthesis, although underlying molecular mechanisms are unclear. Eukaryotic initiation factor 2α-subunit (eIF2α) is a key player in initiation of protein translation and is regulated by phosphorylation. While this factor is sensitive to changing synaptic input and is critical for synaptic plasticity, its sensitivity to stimulants is poorly understood. Here we systematically characterized responses of eIF2α to a systemic administration of the stimulant amphetamine (AMPH) in dopamine responsive regions of adult rat brains. Intraperitoneal injection of AMPH at 5mg/kg increased eIF2α phosphorylation at serine 51 in the striatum. This increase was transient. In the medial prefrontal cortex (mPFC), AMPH induced a relatively delayed phosphorylation of the factor. Pretreatment with a dopamine D1 receptor antagonist SCH23390 blocked the AMPH-stimulated eIF2α phosphorylation in both the striatum and mPFC. Similarly, a dopamine D2 receptor antagonist eticlopride reduced the effect of AMPH in the two regions. Two antagonists alone did not alter basal eIF2α phosphorylation. AMPH and two antagonists did not change the amount of total eIF2α proteins in both regions. These results demonstrate the sensitivity of eIF2α to stimulant exposure. AMPH possesses the ability to stimulate eIF2α phosphorylation in striatal and mPFC neurons in vivo in a D1 and D2 receptor-dependent manner.

Selective activation of D1 dopamine receptors impairs sensorimotor gating in Long-Evans rats

BACKGROUND AND PURPOSE

Sensorimotor gating is a perceptual process aimed at filtering out irrelevant information. In humans and animal models, this function can be operationally measured through the prepulse inhibition (PPI) of the acoustic startle reflex. Notably, PPI deficits are associated with numerous neuropsychiatric conditions characterized by gating disturbances, including schizophrenia and Tourette syndrome. Ample evidence has shown that dopamine plays a key role in PPI regulation and, in particular, rodent studies indicate that this neurotransmitter modulates PPI through D1 and D2 dopamine receptors. In mice, the relative contributions of these two families of receptors are strain-dependent. Conversely, the role of D1 receptors in the regulation of PPI across different rat strains remains unclear.

EXPERIMENTAL APPROACH

We tested the effects of selective D1 and D2 receptor agonists and antagonists on the startle reflex and PPI of Sprague-Dawley, Wistar and Long-Evans rats.

KEY RESULTS

In contrast with Sprague-Dawley and Wistar rats, the full D1 receptor agonist SKF82958 elicited significant PPI deficits in Long-Evans rats, an effect sensitive to the selective D1 antagonist SCH23390.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that, in Long-Evans rats, D1 receptor activation may be sufficient to significantly impair PPI. These data emphasize the role of D1 receptors in the pathophysiology of neuropsychiatric disorders featuring alterations in sensorimotor gating, and uphold the importance of the genetic background in shaping the role of dopamine receptors in the regulation of this key information-processing function.

LINKED ARTICLES

This article is part of a themed section on Updating Neuropathology and Neuropharmacology of Monoaminergic Systems. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.13/issuetoc.

Integrated regulation of AMPA glutamate receptor phosphorylation in the striatum by dopamine and acetylcholine

Dopamine (DA) and acetylcholine (ACh) signals converge onto protein kinase A (PKA) in medium spiny neurons of the striatum to control cellular and synaptic activities of these neurons, although underlying molecular mechanisms are less clear. Here we measured phosphorylation of the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR) at a PKA site (S845) as an indicator of AMPAR responses in adult rat brains in vivo to explore how DA and ACh interact to modulate AMPARs. We found that subtype-selective activation of DA D1 receptors (D1Rs), D2 receptors (D2Rs), or muscarinic M4 receptors (M4Rs) induced specific patterns of GluA1 S845 responses in the striatum. These defined patterns support a local multitransmitter interaction model in which D2Rs inhibited an intrinsic inhibitory element mediated by M4Rs to enhance the D1R efficacy in modulating AMPARs. Consistent with this, selective enhancement of M4R activity by a positive allosteric modulator resumed the cholinergic inhibition of D1Rs. In addition, D1R and D2R coactivation recruited GluA1 and PKA preferentially to extrasynaptic sites. In sum, our in vivo data support an existence of a dynamic DA-ACh balance in the striatum which actively modulates GluA1 AMPAR phosphorylation and trafficking. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'.

Dopaminergic and cholinergic regulation of Fyn tyrosine kinase phosphorylation in the rat striatum in vivo

Src and Fyn are two Src family kinase (SFK) members that are expressed in mammalian brains and play important roles in the regulation of a variety of neuronal and synaptic substrates. Here we investigated the responsiveness of these SFKs to changing dopamine receptor signals in dopamine responsive regions of adult rat brains in vivo. Pharmacological activation of dopamine D1 receptors (D1Rs) by a systemic injection of the selective agonist SKF81297 increased phosphorylation of SFKs at a conserved and activation-associated autophosphorylation site (Y416) in the striatum, indicating activation of SFKs following SKF81297 injection. The dopamine D2 receptor (D2R) agonist quinpirole had no effect. Blockade of D1Rs with an antagonist SCH23390 did not alter striatal Y416 phosphorylation, while the D2R antagonist eticlopride elevated it. Between Src and Fyn, SKF81297 seemed to preferentially facilitate Fyn phosphorylation. Activation of muscarinic acetylcholine M4 receptors (M4Rs) with a positive allosteric modulator VU0152100 suppressed SFK Y416 responses to SKF81297. Additionally, SKF81297 induced a correlated increase in phosphorylation of N-methyl-D-aspartate (NMDA) receptor GluN2B subunits at a Fyn site (Y1472), which was attenuated by VU0152100. SKF81297 also enhanced synaptic recruitments of active Fyn and GluN1/GluN2B-containing NMDA receptors. These data demonstrate that D1Rs regulate Fyn and downstream NMDA receptors in striatal neurons in vivo. Acetylcholine through activating M4Rs inhibits Fyn and NMDA receptors in their sensitivity to D1R signaling.

Regulation of synaptic MAPK/ERK phosphorylation in the rat striatum and medial prefrontal cortex by dopamine and muscarinic acetylcholine receptors

Dopamine and acetylcholine are two principal transmitters in the striatum and are usually balanced to modulate local neural activity and to maintain striatal homeostasis. This study investigates the role of dopamine and muscarinic acetylcholine receptors in the regulation of a central signaling protein, i.e., the mitogen-activated protein kinase (MAPK). We focus on the synaptic pool of MAPKs because of the fact that these kinases reside in peripheral synaptic structures in addition to their somatic locations. We show that a systemic injection of dopamine D1 receptor (D1R) agonist SKF81297 enhances phosphorylation of extracellular signal-regulated kinases (ERKs), a prototypic subclass of MAPKs, in the adult rat striatum. Similar results were observed in another dopamine-responsive region, the medial prefrontal cortex (mPFC). The dopamine D2 receptor agonist quinpirole had no such effects. Pretreatment with a positive allosteric modulator (PAM) of muscarinic acetylcholine M4 receptors (M4Rs), VU0152100, attenuated the D1R agonist-stimulated ERK phosphorylation in the two regions, whereas the PAM itself did not alter basal ERK phosphorylation. All drug treatments had no effect on phosphorylation of c-Jun N-terminal kinases (JNKs), another MAPK subclass, in the striatum and mPFC. These results demonstrate that dopamine and acetylcholine are integrated to control synaptic ERK but not JNK activation in striatal and mPFC neurons in vivo. Activation of M4Rs exerts an inhibitory effect on the D1R-mediated upregulation of synaptic ERK phosphorylation.

Dopamine D(2) Antagonist-Induced Striatal Nur77 Expression Requires Activation of mGlu5 Receptors by Cortical Afferents

Dopamine D₂ receptor antagonists modulate gene transcription in the striatum. However, the molecular mechanism underlying this effect remains elusive. Here we used the expression of Nur77, a transcription factor of the orphan nuclear receptor family, as readout to explore the role of dopamine, glutamate, and adenosine receptors in the effect of a dopamine D₂ antagonist in the striatum. First, we investigated D₂ antagonist-induced Nur77 mRNA in D_2L receptor knockout mice. Surprisingly, deletion of the D_2L receptor isoform did not reduce eticlopride-induced upregulation of Nur77 mRNA levels in the striatum. Next, we tested if an ibotenic acid-induced cortical lesion could block the effect of eticlopride on Nur77 expression. Cortical lesions strongly reduced eticlopride-induced striatal upregulation of Nur77 mRNA. Then, we investigated if glutamatergic neurotransmission could modulate eticlopride-induced Nur77 expression. A combination of a metabotropic glutamate type 5 (mGlu5) and adenosine A_2A receptor antagonists abolished eticlopride-induced upregulation of Nur77 mRNA levels in the striatum. Direct modulation of Nur77 expression by striatal glutamate and adenosine receptors was confirmed using corticostriatal organotypic cultures. Taken together, these results indicate that blockade of postsynaptic D₂ receptors is not sufficient to trigger striatal transcriptional activity and that interaction with corticostriatal presynaptic D₂ receptors and subsequent activation of postsynaptic glutamate and adenosine receptors in the striatum is required. Thus, these results uncover an unappreciated role of presynaptic D₂ heteroreceptors and support a prominent role of glutamate in the effect of D₂ antagonists.

Effects of the adenosine A 2A antagonist KW 6002 (istradefylline) on pimozide-induced oral tremor and striatal c-Fos expression: comparisons with the muscarinic antagonist tropicamide

Typical antipsychotic drugs, including haloperidol and pimozide, have been shown to produce parkinsonian motor effects such as akinesia and tremor. Furthermore, there is an antagonistic interaction between adenosine A(2A) and dopamine D(2) receptors in the basal ganglia, which is important for motor functions related to the production of parkinsonian symptoms. Several experiments were conducted to assess the effects of the selective adenosine A(2A) antagonist KW 6002 on both the motor and cellular effects of subchronic administration of pimozide. The motor test employed was tremulous jaw movements, which is used as a model of parkinsonian tremor. In addition, c-Fos expression in the ventrolateral neostriatum, which is the striatal area most associated with tremulous jaw movements, was used as a marker of striatal cell activity in animals that were tested in the behavioral experiments. Repeated administration of 1.0 mg/kg pimozide induced tremulous jaw movements and increased ventrolateral striatal c-Fos expression, while administration of 20.0 mg/kg of the atypical antipsychotic quetiapine did not. The tremulous jaw movements induced by pimozide were significantly reduced by co-administration of either the adenosine A(2A) antagonist KW 6002 or the muscarinic antagonist tropicamide. Pimozide-induced increases in ventrolateral striatal c-Fos expression were reduced by a behaviorally effective dose of KW 6002, but c-Fos expression in pimozide-treated rats was actually increased by tropicamide. These results indicate that two different drug manipulations that act to reduce tremulous jaw movements can have different effects on DA antagonist-induced c-Fos expression, suggesting that adenosine A(2A) antagonism and muscarinic receptor antagonism exert their motor effects by acting on different striatal circuits.

5-HT6 receptor antagonist reversal of emotional learning and prepulse inhibition deficits induced by apomorphine or scopolamine

5-HT6 receptors have been implicated in consolidation of visuospatial and reward-based learning tasks. Since 5-HT6 receptors may be important in modulation of sensory gating which is often affected in schizophrenic patients, we tested whether Ro 4368554, a 5-HT6 selective antagonist at a dose of 10 mg/kg, could reverse the loss of prepulse inhibition from apomorphine or scopolamine. In addition, we also tested whether Ro 4368554 altered fear conditioning using fear potentiated startle, a model for emotional learning. Prepulse inhibition of startle was disrupted by apomorphine (0.5 mg/kg) when prepulse emissions were 5 dB above background but not above 15 dB, while scopolamine (0.5 mg/kg) caused disruption at both prepulse levels. Scopolamine-mediated disruption was not reversed by Ro 4368854 but apomorphine-mediated disruption was significantly ameliorated by 5-HT6 inhibition. For fear potentiated startle, scopolamine and/or Ro 4368554 were administered before two daily fear conditioning sessions; rats were tested on the following day. Rats that received scopolamine displayed no fear potentiated startle but Ro 4368554 reversed this scopolamine deficit. Additionally, we mapped Fos induction in rats treated with scopolamine and/or Ro 4368554; scopolamine increased Fos expression in the central nucleus of the amygdala and this was attenuated by Ro 4368554. In summary, we have demonstrated the efficacy of 5-HT6 antagonists in modulating sensory gating and fear conditioning, and thus may be of therapeutic use for schizophrenia-related disorders.

Absence of dopamine D2 receptors unmasks an inhibitory control over the brain circuitries activated by cocaine

Cocaine is a psychostimulant and a drug widely abused by humans. Cocaine elicits its effects primarily by blocking the activity of the dopamine (DA) transporter, leading to elevated levels of extracellular DA in areas receiving dopaminergic innervation, with the consequent activation of DA receptors. Cocaine, however, also elevates other neurotransmitter levels, leading to a general activation of interconnected brain circuitries. Studies aimed at unraveling the molecular mechanisms underlying the effects of cocaine have shown a leading role of DA D1 receptors in the cascade of cellular events elicited by this drug. In this study, we have analyzed the acute response to cocaine in animals deleted for the expression of DA D2 receptors (D2R), an inhibitor of DA signaling. Importantly, we show that although D1 receptor-mediated functions are preserved and even enhanced in D2R-/- mutants, the behavioral response to acute cocaine administration is severely altered. In addition, c-fos response to acute cocaine administration, in contrast to wild-type mice, is absent in D2R-/- mutants. Our findings show that the absence of D2R, very likely through a presynaptic mechanism, uncovers an inhibitory signaling pathway normally masked by the activity of this receptor on brain circuitries engaged by abused drugs.

Rotation and immediate-early gene expression in rats treated with the atypical D1 dopamine agonist SKF 83822

Classical agonists of the dopamine D1 receptor activate both adenylyl cyclase and phospholipase C (PLC) signaling pathways. As a result, the extent to which these two pathways are essentially involved in various effects produced by D1 receptor agonists is currently uncertain. In the present report we examined the effects of SKF 83822, a dopamine D1 agonist which has been reported to activate adenylyl cyclase, but not PLC, on behavior and immediate early gene (IEG) expression in rats with unilateral 6-hydroxydopamine lesions. SKF 83822 (25-100 microg/kg) induced dose dependent contralateral rotation in these subjects, and, additionally, stimulated strong expression of the IEG products c-Fos, Fra2, Zif/268 and Arc in the deinnervated striatum. All of these effects could be antagonized by pretreatment with the selective D1 dopamine antagonist SCH 23390 (0.5 mg/kg). Although PLC may be involved in many effects mediated through dopamine D1 receptors, these results suggest that direct activation of PLC is not necessary for the induction of either rotation or IEG expression in dopamine depleted rats.

Co-localization of GABA with other neuroactive substances in the basal ganglia

The dorsal striatum (caudate putamen) contains two types of GABAergic medium spiny neurons (MSNs) that are distinguished by the expression of either the opioid peptide, enkephalin, or the opioid peptide, dynorphin, as well as the tachykinin substance P. Pharmacological studies suggest that these peptides modulate local neurotransmission in the striatum in response to direct and indirect dopamine agonists. In contrast, GABA appears to have minimal impact within the striatum under these conditions. The actions of the peptide cocktail are dependent on the cellular distribution of their receptors in the striatal network. The net result of their actions is a homeostatic response that regulates striatal output and balances dopamine and glutamate receptor stimulation.

Differential effects of a selective dopamine D1-like receptor agonist on motor activity and c-fos expression in the frontal-striatal circuitry of SHR and Wistar-Kyoto rats

BACKGROUND

Molecular genetic studies suggest the dopamine D1 receptor (D1R) may be implicated in attention-deficit/hyperactivity disorder (ADHD). As little is known about the potential motor role of D1R in ADHD, animal models may provide important insights into this issue.

METHODS

We investigated the effects of a full and selective D1R agonist, SKF-81297 (0.3, 3 and 10 mg/kg), on motor behaviour and expression of the plasticity-associated gene, c-fos, in habituated young adult male Spontaneously Hypertensive Rats (SHR), the most commonly used animal model of ADHD, and Wistar-Kyoto (WKY; the strain from which SHR were derived).

RESULTS

SHR rats were more behaviourally active than WKY rats after injection with vehicle. The 0.3 mg/kg dose of SKF-81297 increased motor behaviour (locomotion, sifting, rearing, and sniffing) in both SHR and WKY rats. Total grooming was also stimulated, but only in WKY rats. The same dose increased c-fos mRNA expression in the piriform cortex of both strains. The 3 mg/kg dose increased sifting and sniffing in both strains. Locomotion was also stimulated towards the end of the testing period. The intermediate dose decreased total rearing in both strains, and produced a significant increase in c-fos mRNA in the striatum, nucleus accumbens, olfactory tuberculum, and in the cingulate, agranular insular and piriform cortices. The 10 mg/kg dose of SKF-81297 produced a biphasic effect on locomotion, which was characterized by an initial decrease followed by later stimulation. The latter stimulatory effect was more pronounced in SHR than in WKY rats when compared to their respective vehicle-injected groups. The 10 mg/kg dose also stimulated sifting and sniffing in both strains. Both the 3 and 10 mg/kg doses had no effect on total grooming. The 10 mg/kg dose induced significantly higher levels of c-fos mRNA expression in the nucleus accumbens and adjacent cortical regions (but not striatum) of SHR when compared to WKY rats.

CONCLUSION

The present results suggest a potential alteration in D1R neurotransmission within the frontal-striatal circuitry of SHR involved in motor control. These findings extend our understanding of the molecular alterations in SHR, a heuristically useful model of ADHD.

Extracellular signal-regulated mitogen-activated protein kinase inhibitors decrease amphetamine-induced behavior and neuropeptide gene expression in the striatum

The aim of this study was to determine whether inhibition of the extracellular-regulated kinase signaling pathway decreases acute amphetamine-induced behavioral activity and neuropeptide gene expression in the rat striatum. Western blotting revealed that extracellular-regulated kinase1/2 phosphorylation was highly induced in the rat striatum 15 min after an acute amphetamine (2.5 mg/kg, i.p.) injection without altering the total amount of extracellular-regulated kinase protein. In a separate experiment, the systemic injection of SL327, a selective inhibitor of extracellular regulated kinase kinase that crosses the blood-brain barrier, 1 h prior to amphetamine administration decreased amphetamine-induced vertical and horizontal activity. Quantitative in situ hybridization histochemistry showed that SL327 abolished the high levels of preproenkephalin and preprodynorphin mRNA induced by amphetamine in the striatum with no alteration of their basal levels. In another set of experiments, the hyperlocomotor activity induced by amphetamine was reduced by pretreatment with intra-striatal infusion of U0126. U0126 also blocked the amphetamine-induced increases in phospho-extracellular-regulated kinase and preproenkephalin and preprodynorphin gene expression in the striatum. These data indicate that activation of the extracellular-regulated kinase cascade contributes to the behavioral effects and changes in striatal neuropeptide gene expression induced by acute amphetamine.

Bilateral control of brain activity by dopamine D1 receptors: evidence from induction patterns of regulator of G protein signaling 2 and c-fos mRNA in D1-challenged hemiparkinsonian rats

Recent reports show that striatal dopamine D1-type receptors from one side of the normal rat brain can control brain activity (as measured by c-fos induction) on both sides of the brain. However, this phenomenon has not yet been studied in the presence of sensitized dopamine D1-type receptors. Here we address this issue by investigating the extent to which dopamine D1-type receptors control brain activation in rats with unilaterally sensitized dopamine D1-type receptors. Gene induction assays were used to identify activated regions from midbrain to forebrain in unilaterally 6-hydroxydopamine lesioned (hemiparkinsonian) rats challenged with the full dopamine D1-type agonist SKF82958 (3 mg/kg, 0.5 and 2 h). The genes used are c-fos, the proven neuronal activity marker, and Regulator of G protein Signaling 2, a gene we propose as a marker of signaling homeostasis. SKF82958-mediated induction of both genes is greatly enhanced in hemiparkinsonian rats compared with shams, in both the lesioned and the intact hemisphere. For example, in the denervated caudate-putamen at 2 h postinjection, this enhancement is more than 80-fold for c-fos and up to 20-fold for Regulator of G protein Signaling 2; for the intact side this is 35-fold for c-fos and 27-fold for Regulator of G protein Signaling 2. Cortical induction of c-fos and Regulator of G protein Signaling 2 was generalized to most neocortical regions and was essentially equivalent in both the denervated and intact hemispheres. Interestingly, hippocampal structures also showed strong bilateral induction of both genes. This overall pattern of brain activation can be accounted for by the basal-ganglia thalamocortical and hippocampal circuits which both contain hemisphere-crossing connections and which can be initially activated in the lesioned hemisphere. Some regions, such as the intact striatum or the CA1 region, showed relatively low c-fos induction and relatively high Regulator of G protein Signaling 2 induction, possibly indicating that these regions are engaged in unusually strong signaling regulation activities. Our results show that, besides basal ganglia-thalamocortical circuits, dopamine D1-type-mediated brain activation in hemiparkinsonian rats also involves hippocampal circuits.

Muscarinic receptor blockade attenuates reserpine-mediated Fos induction in the rat striatopallidal pathway

Acute administration of the dopamine-depleting agent reserpine (10 mg/kg) induces Fos expression in striatopallidal neurons of intact rats-an effect that is blocked by pretreatment with the D2 agonist quinpirole (0.5 mg/kg). Systemic administration of the muscarinic antagonist scopolamine (50 mg/kg) partially attenuates reserpine-mediated striatal Fos expression. These data suggest that muscarinic receptors, either within the striatum or in extrastriatal sites, regulate D2 receptor-mediated Fos expression in rat striatopallidal neurons.

Role of dopamine D1 receptors in the striatal and cortical fos expression induced by the muscarinic agonist pilocarpine

Injections of the muscarinic cholinergic receptor agonist pilocarpine (50 mg/kg) induced pronounced expression of the immediate early gene (IEG) product Fos in the striatum and cortex of rats. Pretreatment with the dopamine D1 receptor antagonist 7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-H-3-benzazepine hydrochloride (SCH-23390; 0.2-2.0 mg/kg) drastically attenuated the pilocarpine response in the striatum, but had no effect in the cortex. In contrast, the muscarinic receptor antagonist scopolamine (0.75-3.00 mg/kg) virtually abolished the Fos response at both sites. These results suggest that stimulation of dopamine D1 receptors may mediate the effects of muscarinic agonists on Fos expression in the striatum, but not the cortex.

Ethanol-induced Fos immunoreactivity in the extended amygdala and hypothalamus of the rat brain: focus on cholinergic interneurons of the nucleus accumbens

BACKGROUND

The primary goal of this study was to investigate the effects of varying doses of ethanol on cellular activation, as measured by Fos immunoreactivity, in brain areas that have been implicated in the reinforcing and anxiolytic effects of substance abuse and dependence, namely, the extended amygdala and hypothalamus. Specific regions examined included the central nucleus of the amygdala, bed nucleus of the stria terminalis, substantia innominata, and nucleus accumbens of the extended amygdala, as well as the paraventricular nucleus of the hypothalamus. The cholinergic interneurons of the nucleus accumbens were of particular interest, because these cells have recently been reported to play a pivotal role in substance abuse.

METHODS

Adult Sprague-Dawley rats underwent 10 days of handling and 5 days of habituation. Animals then received an injection of saline or 0.5, 1, or 2 g/kg of ethanol. Rats were perfused 2 hr after the injections, and brain sections were processed for single Fos or dual Fos/choline acetyltransferase immunolabeling procedures. The number of Fos-positive neurons was calculated from a 0.45-mm sample area from each of the brain regions examined.

RESULTS

A dose of 2 g/kg of ethanol significantly increased the number of Fos-immunoreactive neurons in the central nucleus of the amygdala by 149%, in the shell nucleus accumbens by 80%, and in the paraventricular nucleus of the hypothalamus by 321%. Additionally, 1 g/kg of ethanol significantly increased the percentage of Fos-immunoreactive cholinergic neurons in the nucleus accumbens by 59%.

CONCLUSIONS

The findings reported in this study reveal region-specific and dose-dependent changes in Fos immunoreactivity in the extended amygdala and hypothalamus and, more specifically, an increase in neuronal activation of cholinergic cells in the shell nucleus accumbens. These findings contribute to our current knowledge of the brain areas and cellular microcircuits involved in the underlying basis of substance abuse and dependence.

Alteration of dopamine D1 receptor-mediated motor inhibition and stimulation during development in rats is associated with distinct patterns of c-fos mRNA expression in the frontal-striatal circuitry

Dopamine D1 receptors have been implicated in various neurodevelopmental disorders, including attention-deficit/hyperactivity disorder. However, little is known about potential late maturational changes of the motor inhibitory and stimulatory role of these receptors. Here, we investigated the effects of a full and selective D1 receptor agonist, SKF-81297, on motor activity and expression of the plasticity-associated gene, c-fos, in the prefrontal cortex and striatum of juvenile and adolescent male rats. In general, SKF-81297 produced a biphasic effect on motor activity (locomotor and rearing activity), which consisted of an initial short inhibition followed by a long-lasting stimulation. These effects were dose- and age- dependent. The inhibitory phase was more pronounced in adolescent than in juvenile rats whereas the opposite was true for the stimulatory phase. During the initial inhibitory phase of the drug, c-fos mRNA expression was increased in the prefrontal cortex of juvenile rats but reduced in adolescent rats. There was also an increase in c-fos mRNA expression in the medial-dorsal striatum and olfactory tubercle, which was more evident in juvenile rats. In contrast, during the stimulatory phase, c-fos mRNA expression was increased in both the dorsal and ventral striatum, especially in the nucleus accumbens, as well as in the prefrontal cortex, in both age groups. The increase of c-fos mRNA in the dorsal striatum, however, was more pronounced in juvenile rats. These results indicate the presence of two distinct D1 receptor populations within the frontal-striatal circuitry, which have opposite effects on motor activity, and which have different maturational profiles.

Role of dopamine D2 receptors in the striatal immediate early gene response to amphetamine in reserpinized rats

The indirect dopamine agonist amphetamine has been shown to induce a patchy pattern of immediate early gene (IEG) expression in the rostral striatum of both pharmacologically intact and reserpinized rats. The available data suggest that stimulation of D(2) dopamine receptors may play a role in the patterning of amphetamine-induced IEG expression, but direct evidence is lacking. In the current study of reserpinized animals, we found that pretreatment with the selective D(2) dopamine antagonist raclopride did not block the induction of the IEGs Fos and Arc by amphetamine, but greatly reduced the "patchiness" of the induced expression. Raclopride did not induce Fos or Arc expression by itself under the conditions studied here. These findings suggest that although stimulation of D(2) receptors is not necessary for amphetamine to induce IEG expression in reserpinized animals, these receptors do play a critical role in the spatial patterning of the resulting response.

D1 dopamine receptor supersensitivity in the dopamine-depleted striatum results from a switch in the regulation of ERK1/2/MAP kinase

Dopamine effects in the striatum are mediated principally through the D1 and D2 dopamine receptor subtypes, which are segregated to the direct and indirect striatal projection neurons. After degeneration of the nigrostriatal dopamine system, direct pathway neurons display a supersensitive response to D1 dopamine receptor agonists, which is demonstrated by the induction of immediate early genes (IEGs), such as c-fos. Here we show, using analysis of receptor-mediated signal transduction, including protein phosphorylation and induction of IEGs, that D1 dopamine receptor supersensitivity is attributable to a switch to ERK1/2/MAP kinase (extracellular signal-regulated kinase/mitogen-activated protein kinase) in direct pathway neurons. Normally, in the dopamine-intact striatum, activation of ERK1/2/MAP kinase is shown to be restricted to indirect and not direct pathway neurons in response to stimulation of corticostriatal afferents. Moreover, in the dopamine-intact striatum, treatment with full D1 dopamine receptor agonists or stimulation of nigrostriatal dopaminergic afferents, both of which result in the induction of IEGs in direct striatal projection neurons, does not activate ERK1/2/MAP kinase. However, after degeneration of the nigrostriatal dopaminergic pathway, ERK1/2/MAP kinase is activated in direct pathway neurons in response to D1 dopamine receptor agonists either alone or when combined with stimulation of corticostriatal afferents. Inhibitors of MEK (MAP kinase kinase), which is responsible for phosphorylation of ERK1/2/MAP kinase, blocks D1 dopamine receptor agonist activation of ERK1/2/MAP kinase in the dopamine-depleted striatum, as well as the supersensitive induction of IEGs. These results demonstrate that dopamine input to the striatum maintains distinct forms of protein kinase-mediated gene regulation in the direct and indirect striatal projection neurons.

Differential D1 and D2 receptor-mediated effects on immediate early gene induction in a transgenic mouse model of Huntington's disease

The diminished expression of D1 and D2 dopamine receptors is a well-documented hallmark of Huntington's disease (HD), but relatively little is known about how these changes in receptor populations affect the dopaminergic responses of striatal neurons. Using transgenic mice expressing an N-terminal portion of mutant huntingtin (R6/2 mice), we have examined immediate early gene (IEG) expression as an index of dopaminergic signal transduction. c-fos, jun B, zif268, and N10 mRNA levels and expression patterns were analyzed using quantitative in situ hybridization histochemistry following intraperitoneal administration of selective D1 and D2 family pharmacological agents (SKF-82958 and eticlopride). Basal IEG levels were generally lower in the dorsal subregion of R6/2 striata relative to wild-type control striata at 10-11 weeks of age, a finding in accord with previously reported decreases in D1 and adenosine A2A receptors. D2-antagonist-stimulated IEG expression was significantly reduced in the striata of transgenic animals. In contrast, D1-agonist-induced striatal R6/2 IEG mRNA levels were either equivalent or significantly enhanced relative to control levels, an unexpected result given the reduced level of D1 receptors in R6/2 animals. Understanding the functional bases for these effects may further elucidate the complex pathophysiology of Huntington's disease.

Sex differences in the motor inhibitory and stimulatory role of dopamine D1 receptors in rats

We investigated sex differences in the motor responses to the full and selective dopamine D1-like receptor agonist, (+/-)-6-chloro-7,8-dihydroxyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (SKF-81297; 0.3, 3, and 10 mg/kg, s.c.), in non-habituated adult rats. In general, SKF-81297 produced a biphasic effect on motor activity (including locomotion, rearing and exploratory activity) which consisted of an initial short inhibition followed by a long-lasting stimulation. These effects were dose- and sex-dependent. The inhibitory phase was more pronounced in males than females while the opposite was true for the stimulatory phase. Importantly, the motor inhibitory effects of SKF-81297 were not due to an increase in stereotypy (e.g., grooming activity). These biphasic effects on several motor parameters suggest the presence of two distinct dopamine D1 receptor populations which have opposite effects on motor activity and which are, in part, sexually dimorphic.

Contrasting effects of dopamine antagonists and frequency reduction on Fos expression induced by lateral hypothalamic stimulation

To help further identify the reward-relevant regions activated by electrical stimulation of the lateral hypothalamus, Fos expression was quantified in 23 brain regions in naïve, awake rats following non-contingent stimulation with a frequency that supports self-stimulation (100 Hz), a frequency that supports only minimal responding (50 Hz) and a frequency that does not support self-stimulation (25 Hz). Fos expression was also examined in stimulated and unstimulated rats pretreated with SCH 23390 (a dopamine D1 antagonist) or spiperone (a D2-like antagonist), at doses known to greatly inhibit responding for self-stimulation. Lowering the stimulation frequency from 100 to 50 Hz reduced Fos labelling in all areas, except for a few cells immediately surrounding the electrode tip. No differences were observed between unstimulated rats and those receiving 25 Hz stimulation. This suggests that a critical threshold of stimulation is required before other reward-relevant regions in the midbrain and forebrain are recruited with higher frequency stimulation. Pretreatment with SCH 23390 (0.1 mg/kg) inhibited stimulation-induced Fos expression in some key dopamine terminal areas, such as the nucleus accumbens (core and shell) and medial caudate-putamen, but not in directly driven neurons near the stimulation site. In contrast, spiperone (0.1 mg/kg) did not affect the pattern of stimulation-induced Fos expression, but induced immunolabelling in the dorsolateral caudate-putamen, an area associated with the extrapyramidal side-effects of antipsychotic drugs. These results reveal the utility of Fos immunohistochemistry to show how different treatments that alter the rewarding impact of electrical brain stimulation achieve their effects at the neural level.

Molecular dissection of dopamine receptor signaling

The use of genetically engineered mice has provided substantial new insights into the functional organization of the striatum. Increasing evidence suggests that specific genes expressed within the striatum contribute to its functional activity. We studied the dopamine (DA) D1 receptor gene and one of its downstream targets, the transcription factor c-Fos. We have evaluated the functional interaction between the D1 and D2 DA receptor subtypes at the cellular and behavioral levels. Our results show that haloperidol, a DA D2-class receptor antagonist, activates c-Fos predominantly in enkephalin-positive striatal neurons, which project to the globus pallidus and are thought to mediate motor inhibition. Deletion of the DA D1 receptor increased the responsiveness of enkephalin neurons to haloperidol, in that haloperidol-induced increases in c-Fos and catalepsy were enhanced in D1 receptor knockout mice. These results suggest a functionally opposing role of the D1 receptor against the D2 DA-class receptors in the striatum.

An association between the estrogen-dependent hypotensive effect of ethanol and an elevated brainstem c-jun mRNA in female rats

We have recently demonstrated that chronic ethanol administration lowers blood pressure (BP) in female rats and this effect is significantly attenuated by ovariectomy. The present study investigated whether ethanol hypotension is estrogen dependent. Further, since estrogen regulates AP-1 activity, the study was extended to determine whether estrogen/c-jun interaction is involved in the estrogen-dependent hypotensive effect of ethanol. Changes in BP and heart rate (HR) were evaluated in radiotelemetered pair-fed sham-operated (SO), ovariectomized (OVX), and OVX estradiol (E2)-treated rats receiving liquid diet with or without ethanol (5%, w/v) for 12 weeks. The in situ hybridization technique was used to measure the c-jun mRNA expression in two brainstem areas, the nucleus tractus solitarius (NTS) and the rostral ventrolateral medulla (RVLM). Ethanol feeding caused significant (P<0.05) decreases in BP in SO rats that started at week 1 and reached its maximum (approximately 10 mmHg) at week 6 and remained at that level till the end of week 12. In OVX rats, ethanol had no effect on BP during the first 5 weeks after which a decrease of 5 mmHg was demonstrated and remained thereafter. Estrogen replacement (17beta-estradiol subcutaneous pellet, 14.2 microg/day) restored the hypotensive effect of ethanol to a level similar to that of SO rats both in terms of magnitude and duration. Densitometric analysis of the in situ hybridization autoradiograms revealed that OVX and E2 replacement had no effect on c-jun mRNA expression in the NTS or RVLM. Ethanol feeding produced a significant (twofold) increase in c-jun mRNA expression in the RVLM of SO rats versus no effect in the NTS. The increased expression of c-jun mRNA observed following ethanol treatment in the RVLM of SO rats was abolished in OVX rats and restored to SO levels after E2 replacement. These findings suggest a link between the estrogen-dependent hypotensive effect of chronically administered ethanol and the increased expression of c-jun mRNA in the brainstem of female rats.

Anatomy, physiology, and pharmacology of the basal ganglia

The basal ganglia consist of five interconnected nuclei in the basal forebrain that influence cortical control of voluntary movement. Synaptic information travels through the basal ganglia using distinct pathways from the input structure, the striatum, to the output nuclei, the substantia nigra pars reticulata and the globus pallidus internal segment. The activity of the striatal output pathways is influenced by glutamatergic input from the cerebral cortex, dopaminergic input from the substantia nigra pars compacta, and cholinergic interneurons. Since the basal ganglia output nuclei tonically inhibit the motor nuclei of the thalamus, the basal ganglia facilitate motor activity by disinhibiting the thalamus.

Parafascicular thalamic nucleus deafferentation reduces c-fos expression induced by dopamine D-1 receptor stimulation in rat striatum

We investigated the role played by the parafascicular thalamostriatal pathway, one of the major excitatory inputs to the striatum, in the D-1 receptor induction of c-fos messenger RNA expression in the rat striatum. The full D-1 receptor agonist, SKF-82958 (0.05, 0.1, 0.5 and 1 mg/kg, s.c., 30 min), dose-dependently induced c-fos messenger RNA in naive rat striatum as determined by northern blot analysis. One day following electrolytic lesion of the parafascicular thalamostriatal nucleus, striatal c-fos signal by itself was not altered but the stimulated expression of c-fos was strongly decreased. Sections of sham-operated and acute-lesioned dorsal striata of vehicle- or SKF-82958-treated rats were processed for in situ hybridization histochemistry at the single-cell level with an RNA probe for c-fos. The basal expression of striatal c-fos was poorly detectable in sham and lesioned groups. Sections of dorsal striata from sham-operated rats treated with SKF-82958 showed two types of labeled neurons for c-fos: the lightly and the very densely labeled neurons which are few in number. Thalamic lesion strongly reduced SKF-82958 stimulated expression of c-fos RNA in both types of labeled cells. The frequency distribution of c-fos labeling per neuron in dorsal striata of lesioned rats treated with SKF-82958 was shifted to the left, and its median was lower than in the sham-operated striata treated with the D-1 receptor agonist. The results provide evidence that the excitatory projections from the parafascicular nucleus of the thalamus, thought to operate primarily through the N-methyl-D-aspartate receptors, exert a facilitatory control over D-1 receptor-induced c-fos gene expression specifically in the dorsal striatum.

N-tert-butyl-alpha-phenylnitrone, a free radical scavenger with anticholinesterase activity does not improve the cognitive performance of scopolamine-challenged rats

Reversible inhibitors of acetylcholinesterase improve spatial learning and memory in animal models of cognitive impairment. Here we investigate if the beneficial effects of free radical scavenger N-tert-butyl-alpha-phenylnitrone (PBN) on cognitive performance could be explained by its recently discovered anticholinesterase activity. Morris water maze experiment was performed to examine the effect of PBN on the impairment of spatial learning and memory induced by the antagonist of cholinergic muscarinic transmission scopolamine. In situ hybridization histochemistry experiment was performed to study its effects on the induction of immediate early gene expression (c-fos, c-jun) by dopamine D1 receptor agonist SKF-82958 and on the augmentation of the SKF-82958-induced expression of these genes by scopolamine. In both experiments, the effects of PBN were compared to the effects of reversible anticholinesterase physostigmine. We found that physostigmine but not PBN significantly reversed the cognitive impairment in scopolamine-challenged rats, prevented the induction of c-fos and c-jun mRNAs by SKF-82958 and attenuated the augmentation of the SKF-82958-induced expression of these genes by scopolamine. The present experiments did not reveal a significant in vivo anticholinesterase activity of PBN.

Comparative effects of scopolamine and quinpirole on the striatal fos expression induced by stimulation of D(1) dopamine receptors in the rat

Treatment of intact rats with the full D(1) dopamine agonist A-77636 induced Fos-like immunoreactivity in the medial and, to a lesser extent, the lateral portions of the striatum. Pretreatment with the muscarinic antagonist scopolamine hydrobromide (1.5-6 mg/kg) potentiated the response to A-77636 and eliminated the mediolateral staining gradient seen after A-77636 alone. Similar effects were not produced by scopolamine methylbromide, which fails to cross the blood-brain barrier, demonstrating that the actions of scopolamine were centrally mediated. The effects of scopolamine were further compared to those of the D(2)-like dopamine agonist quinpirole using a factorial design in which subjects were pretreated with either scopolamine, quinpirole, or a combination of the two drugs before receiving A-77636. Pretreatment with either scopolamine or quinpirole increased staining in the lateral striatum, but the combination of the two drugs was no more effective than was quinpirole alone. Pretreatment with quinpirole, but not scopolamine, resulted in a markedly "patchy" pattern of staining and actually suppressed staining in the region between patches in the medial striatum. These findings demonstrate that there are both differences and similarities between the effects of scopolamine and quinpirole on D(1) agonist-induced Fos expression and suggest that although inhibition of cholinergic neurons may be one of the mechanisms through which the effects of quinpirole are produced, other factors must also contribute.

Co-stimulation of D(1)/D(5) and D(2) dopamine receptors leads to an increase in c-fos messenger RNA in cholinergic interneurons and a redistribution of c-fos messenger RNA in striatal projection neurons

The anatomical subdivision of striatum in patch and matrix compartments plays an important role for the processing of neurotransmission through the basal ganglia in primates and rodents. Here we report that co-administration of D(1)/D(5) and D(2) receptor agonists, which induces a heterogenous and patchy pattern of c-fos messenger RNA expression in striatum, stimulates c-fos messenger RNA expression in cholinergic interneurons. Moreover, this treatment induces c-fos messenger RNA in projection neurons containing D(1)-, rather than D(2)-receptor messenger RNA. The preferential induction of c-fos messenger RNA in patches does not depend upon a higher degree of co-localization between D(1) and D(2) receptors in this area, since double in situ hybridization experiments showed a large segregation of D(1) and D(2) receptor messenger RNAs in the patch as well as the matrix compartments. By contrast, treatment with a full D(1)/D(5) receptor agonist up-regulates striatal c-fos messenger RNA homogenously and in similar proportions of D(1) and D(2) receptor messenger RNA-containing projection neurons in both medial and lateral striatum, but has only minor effects on c-fos messenger RNA expression in cholinergic interneurons. These results provide a neuroanatomical/neurochemical correlate to the well-known behavioral interaction between dopamine D(1)/D(5) agonists and dopamine D(2) agonists. They also suggest that there may be a relation between a heterogenous, patch-enriched c-fos messenger RNA expression and an increased expression of this immediate early gene in cholinergic interneurons.

Changes in CArG-binding protein A expression levels following injection(s) of the D1-dopamine agonist SKF-82958 in the intact and 6-hydroxydopamine-lesioned rat

We recently characterized the rat brain homolog of mouse muscle CArG-binding protein A initially identified in C2 myogenic cells and showed an inverse temporal correlation between increased expression levels of this messenger RNA, c-fos and zif268 messenger RNA levels following the addition of nerve growth factor to PC12 cells. In addition, we found an inverse correlation between c-Fos protein and CArG-binding protein A messenger RNA levels in the lateral caudate-putamen of rats treated acutely and chronically with the D2 receptor antagonist fluphenazine (phenothiozine typical psychotic). To determine whether D1 receptor stimulation is also capable of inducing CArG-binding protein A up-regulation, drug naive or dopamine-depleted (i.e. 6-hydroxydopamine-lesioned) D1 hypersensitized rats (i.e. rats given repeated daily injections of SKF-82958 for 14days) were acutely injected with the D1 agonist SKF-82958 and examined using a combination of in situ hybridization for CArG binding protein A and immunocytochemistry for c-Fos. Both acutely treated animals and dopamine-depleted hypersensitized animals showed increases in CArG-binding protein A. Moderate increases were found in the medial caudate-putamen and nucleus accumbens core and shell regions following acute treatment whereas large increases in CArG-binding protein A expression levels were found in the medial and lateral caudate-putamen and the shell and core of the nucleus accumbens following hypersensitization. No change in CArG-binding protein A expression level was found in the dopamine-depleted, drug naive animals relative to controls. Regions of the basal ganglia where increases in CArG-binding protein A were detected following each treatment correlated perfectly with c-Fos protein induction. The results demonstrate that CArG-binding protein A responds to SKF-82958 and that the changes in CArG-binding protein A match perfectly with the pattern of c-Fos induction induced by the D1 agonist.

Dopamine D(1) receptor-induced gene transcription is modulated by DARPP-32

The role of the dopamine- and cyclic AMP-regulated phosphoprotein of M(r) 32,000 (DARPP-32) in dopaminergic regulation of gene transcription in striatum and globus pallidus was examined. Mice with targeted disruption of the gene encoding DARPP-32, its homologue, inhibitor-1, or both, were used. Pharmacological characterization showed that mutant mice had normal basal levels of dopamine D(1) and D(2) receptors and adenosine A(2A) receptors. Basal expression levels of the striatonigral-specific neuropeptides substance P and prodynorphin and the immediate early genes c-fos and NGFI-A were also unaltered in mutant mice. A full D(1) receptor agonist, SKF 82958, up-regulated the expression of these neuropeptides and immediate early genes significantly more in wild-type mice than in mice lacking DARPP-32. Moreover, the additive stimulation of SKF 82958 and quinelorane, a D(2) receptor agonist, on c-fos mRNA in globus pallidus was significantly decreased in DARPP-32 and DARPP-32/I-1 knockout mice. No changes in dopamine receptor-induced gene expression were found in I-1 knockout mice. These results demonstrate an important involvement of DARPP-32 in dopamine receptor-mediated regulation of gene expression both in striatal neurons, which are enriched in DARPP-32, and in pallidal neurons, which do not contain DARPP-32.

Sustained behavioral stimulation following selective activation of group I metabotropic glutamate receptors in rat striatum

Group I metabotropic glutamate receptors (mGluRs) are densely expressed in the medium-sized spiny projection neurons of striatum. Activation of this group of the mGluRs modifies neuronal physiology through stimulation of phosphoinositide hydrolysis and intracellular Ca(2)+ release. Unlike the ionotropic glutamate receptors that mediate rapid synaptic transmission, activation of the mGluRs produces long-lasting actions brought about by modulation of activities of intracellular effectors. In this study, the role of the group I mGluRs in the modulation of extrapyramidal motor function was examined using a group I selective agonist, 3, 5-dihydroxyphenylglycine (DHPG), in chronically cannulated rats. Bilateral injections of DHPG at a series of subtoxic doses (20, 40, 80, and 160 nmol) into the central part of the dorsal striatum produced hyperlocomotion and a unique stereotypical behavior (spontaneous and repetitive twitching movement of the head and forepaws) in a dose-dependent manner. The characteristic twitchy behavior usually commenced 30 min to 1 h, and could last as long as 10 to 12 h, after a single injection of the group I agonist. The behavioral responses to DHPG administration were markedly antagonized by intrastriatal injection of the group I antagonist PHCCC (10 nmol), but not the group II/III antagonist MSOPPE (10 nmol). Intrastriatal administration of 20 nmol dantrolene, an inhibitor of intracellular Ca(2)+ mobilization, also prevented DHPG-stimulated motor activities. However, blockade of dopamine D(1) receptors with systemic administration of SCH-23390 (0.1 mg/kg, SC) did not alter the ability of DHPG to provoke behavioral activities. These data indicate that selective activation of the DHPG-sensitive group I mGluRs in the striatum can produce long-lasting stimulation of motor activity. DHPG-induced motor stimulation involves the mobilization of intracellular Ca(2)+ stores, but appears to be independent of D(1) dopaminergic transmission.

In vivo NMDA/dopamine interaction resulting in Fos production in the limbic system and basal ganglia of the mouse brain

Glutamatergic and dopaminergic effects on molecular processes have been extensively investigated in the basal ganglia. It has been demonstrated that NMDA and dopamine D(1) and D(2) receptors interact in the regulation of signal transduction and induction of transcription factors. In the present experiments, NMDA/dopamine interactions were investigated in the normosensitive caudate nucleus, hippocampus and amygdala by monitoring Fos production. We demonstrated that NMDA and the D(1) receptor agonist SKF 38393 triggered Fos levels in a distinct, non-overlapping and region-specific pattern. NMDA injected intraperitoneally (i.p.) elevated Fos levels in all hippocampal subfields and the central amygdala, whereas SKF 38393 triggered Fos production in basomedial, cortical, medial amygdala and caudate nucleus. The NMDA receptor antagonist CGS 19755 prevented NMDA- and SKF 38393-triggered Fos production in all investigated brain areas. Similarly, the D(1) receptor antagonist SCH 23390 inhibited the effects produced by SKF 38393 or NMDA. The D(2) receptor antagonist sulpiride exerted synergistic and antagonistic effects on NMDA- and SKF 38393-triggered Fos production, in a region specific manner. These data suggest that NMDA and dopamine receptors regulate Fos production within the limbic system and basal ganglia through regionally differentiated but interdependent actions.

Clonidine diminishes c-jun gene expression in the cardiovascular sensitive areas of the rat brainstem

The present study investigated the effect of clonidine on the basal and inducible c-jun and c-fos mRNA expression in the nucleus tractus solitarius (middle, mNTS, and rostral, rNTS) and the rostral ventrolateral medulla (caudal, cRVLM, and rostral, rRVLM). Conscious rats received saline, clonidine (30 microg/kg, i.v.), saline plus sodium nitroprusside (NP), or clonidine plus NP. Under basal conditions (saline-infused rats), c-jun mRNA was expressed in the mNTS and rRVLM but not in the rNTS or cRVLM whereas c-fos mRNA was not detectable. Clonidine attenuated the increases in c-fos in the mNTS and cRVLM and c-jun gene expression in the mNTS and rRVLM caused by NP-evoked hypotension and also reduced the basal expression of c-jun mRNA in the mNTS and rRVLM. These findings establish a causal link between clonidine inhibition of c-fos expression in brainstem and its hypotensive action, and provide the first evidence that clonidine attenuates the expression of the closely linked c-jun gene in neurons implicated in centrally mediated hypotension.

L-prolyl-l-leucyl-glycinamide and its peptidomimetic analog 3(R)-[(2(S)-pyrrolidylcarbonyl)amino]-2-oxo-1-pyrrolidineacetamide (PAOPA) attenuate haloperidol-induced c-fos expression in the striatum

Acute treatment of rats with haloperidol results in a rapid and transient increase in striatal c-fos mRNA and Fos immunoreactivity. The induction of immediate early genes by haloperidol may be involved in the development of extrapyramidal side effects. L-Prolyl-L-leucyl-glycinamide (PLG, or MIF-1) has been observed to antagonize the development of haloperidol-induced D(2) receptor supersensitivity in rats. We investigated the modulatory effects of PLG on haloperidol-induced c-fos and Fos protein expression in the rat striatum. We report that coadministration of either PLG or the potent analog of PLG, 3(R)-[(2(S)-pyrrolidylcarbonyl)amino]-2-oxo-1-pyrrolidineacetam ide (PAOPA), attenuated haloperidol-induced c-fos and Fos expression. Haloperidol induced [2 mg/kg, intraperitoneally (i.p.)] c-fos and Fos expression by 500% and 100%, respectively. These responses were attenuated by 170% and 75%, respectively, when coadministered with PLG (20 mg/kg, i.p.) or by 79% by PAOPA (10 microg/kg, i.p.).

Regulation of the subcellular distribution of m4 muscarinic acetylcholine receptors in striatal neurons in vivo by the cholinergic environment: evidence for regulation of cell surface receptors by endogenous and exogenous stimulation

Our aim was to determine how the cholinergic environment influences, in vivo, the membrane abundance and the intracellular trafficking of the muscarinic receptor m4 (m4R). Immunohistochemistry at light and electron microscopic level was used to detect the subcellular localization of m4R in several populations of striatal cholinoceptive neurons, including cholinergic neurons and medium spiny neurons. (1) In control rats, in cholinergic neurons, m4R is mostly restricted to intracytoplasmic sites involved in its synthesis, especially endoplasmic reticulum. In contrast, m4R is preferentially located at the plasma membrane in cell bodies and dendritic shafts and spines of medium spiny neurons. The density of m4R was greater at the membrane of perikarya in patches (striatal areas with low acetylcholine activity) than in matrix (striatal areas with high acetylcholine activity). (2) Stimulation of muscarinic receptor with oxotremorine provokes translocation of m4R from the membrane to endosomes in perikarya and dendrites of medium spiny neurons but has no influence on the localization of m4R in the cytoplasm of cholinergic cell bodies. Our results suggest that the intraneuronal trafficking and the abundance of membrane-bound m4R in vivo is under regulation of the cholinergic environment. The m4R subcellular compartmentalization depends on the phenotype of the cholinoceptive neuron and on its neurochemical environment. Such regulation, by modulating availability of receptor for endogenous and exogenous ligands, may play key roles in the response of target neurons.

Prior D1 dopamine receptor stimulation is required to prime D2-mediated striatal Fos expression in 6-hydroxydopamine-lesioned rats

Repeated dopamine agonist administration to rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway potentiates behavioral and neuronal activation in response to subsequent dopamine agonist treatment. This response sensitization has been termed "priming" or "reverse-tolerance". Our prior work has shown that three pretreatment injections of the mixed D1/D2 agonist apomorphine (0.5 mg/kg) into 6-hydroxydopamine-lesioned rats permits a previously inactive dose of the D2 agonist quinpirole (0.25 mg/kg) to induce robust contralateral rotation and striatal Fos expression in striatoentopeduncular "direct" pathway neurons. These striatal neurons typically express D1 but not D2 receptors. Because apomorphine acts as an agonist at both D1 and D2 receptors, the present study sought to determine whether D1, D2, or concomitant D1/D2 receptor stimulation was required to prime D2-mediated contralateral rotation and striatal Fos expression. Twenty-one days following unilateral stereotaxic injection of 6-hydroxydopamine into the medial forebrain bundle, rats received three pretreatment injections, at three- to six-day intervals, with either: the mixed D1/D2 agonist apomorphine, the D1 agonist SKF38393, the D2 agonist quinpirole, or a combination of SKF38393 + quinpirole. Ten days following the third pretreatment injection, 6-hydroxydopamine-lesioned rats were challenged with the D2 agonist quinpirole (0.25 mg/kg). Pretreatment with SKF38393 (10 mg/kg), quinpirole (1 mg/kg) or SKF38393 (1 mg/kg) + quinpirole (0.25 mg/kg) permitted an otherwise inactive dose of quinpirole (0.25 mg/kg) to induce robust contralateral rotation which was similar in magnitude to that observed following apomorphine priming. However, only pretreatment with SKF38393 (10 mg/kg) or SKF38393 (1 mg/kg) + quinpirole (0.25 mg/kg) permitted the same dose of quinpirole (0.25 mg/kg) to induce striatal Fos expression. These results demonstrate that while prior stimulation of D1, D2 or D1/D2 receptors can effectively prime D2-mediated contralateral rotation, prior stimulation of D1 receptors is required to prime D2-mediated striatal Fos expression. This study demonstrates that priming of 6-hydroxydopamine-lesioned rats with a D1 agonist permits a subsequent challenge with a D2 agonist to produce robust rotational behavior that is accompanied by induction of immediate-early gene expression in neurons that comprise the "direct" striatal output pathway. These responses are equivalent to the changes observed in apomorphine-primed 6-hydroxydopamine-lesioned rats challenged with D2 agonist. In contrast, D2 agonist priming was not associated with D2-mediated induction of striatal immediate-early gene expression even though priming of D2-mediated rotational behavior was not different from that observed following priming with apomorphine or D1 agonist. Therefore, while priming-induced alterations in D2-mediated immediate early gene expression in the "direct" striatal output pathway may contribute to the enhanced motor behavior observed, such changes in striatal gene expression do not appear to be required for this potentiated motor response in dopamine-depleted rats.

Decreased c-fos responses to dopamine D(1) receptor agonist stimulation in mice deficient for D(3) receptors

The acute administration of dopamine D(1) receptor agonists induces the expression of the immediate early gene c-fos. In wild type mice, this induction is completely abolished by pretreatment with the D(1)-selective antagonist SCH23390, and pretreatment with the D(2)-like receptor antagonist eticlopride reduces the levels of c-fos expressed in response to D(1) receptor stimulation. Mice deficient for the dopamine D(3) receptor express levels of D(1) agonist-stimulated c-fos immunoreactivity that are lower than c-fos levels of their wild type littermates. Moreover, the acute blockade of D(2) receptors in D(3) mutant mice further reduces c-fos expression levels. These data indicate that the basal activity of both D(2) and D(3) receptors contributes to D(1) agonist-stimulated c-fos responses. The findings therefore indicate that not only D(2) but also D(3) receptors play a role in dopamine-regulated gene expression.

Regulation of neurotransmitter interactions in the ventral striatum

Transsynaptic activation of neuronal circuits originating in the basal forebrain contributes to psychostimulant-evoked dopamine and glutamate release and consequent changes in medium spiny neuronal gene expression in the ventral striatum. New evidence from microdialysis studies indicates that amphetamine-induced dopamine and glutamate release in vivo is partially calcium dependent. The calcium-dependent component is totally blocked by a kappa opioid receptor agonist, indicating that endogenous opioids may regulate dopamine-glutamate interactions in the ventral striatum. Further, muscarinic receptor blockade increases, and muscarinic receptor stimulation decreases, dialysate glutamate levels in the striatum. Pre- and postsynaptic muscarinic receptors contribute to the ability of the muscarinic antagonist, scopolamine, to augment D1 receptor-stimulated immediate early and neuropeptide gene expression. Moreover, scopolamine prevents a D2 antagonist from blocking D1 agonist-induced gene expression, indicating that activation of cholinergic interneurons contributes to D1/D2 interactions in the striatum. Thus, transsynaptic activity and presynaptic muscarinic and kappa opioid receptors regulate dopamine and glutamate interactions that switch on and off multiple intracellular signaling cascades. Changes in immediate early and neuropeptide gene expression that result from activation of these cascades are mediated by such nuclear transcription factors as phosphorylated cyclase response element-binding protein. In addition, a novel signaling pathway involving the RAR/RXR nuclear hormone receptor complex is implicated in the control of dopamine receptor and neuropeptide gene expression in the striatum.

Compartmental changes in expression of c-Fos and FosB proteins in intact and dopamine-depleted striatum after chronic apomorphine treatment

Chronic administration of dopaminergic agonists to rats with unilateral 6-OH-dopamine (6-OHDA) lesions of nigrostriatal pathway produces behavioral sensitization to subsequent agonist challenges and may serve as a model for DOPA-induced dyskinesias. In order to understand striatal mechanisms behind this long-term behavioral change we examined striatal c-Fos and FosB immunoreactivity induced by apomorphine challenge (5 mg/kg, s.c.) after 3 days of withdrawal following a 2-week administration (5 mg/kg, b.i.d., s.c.) both in intact and 6-OHDA-lesioned animals. In intact rats, c-Fos induction by acute apomorphine exposure showed a striosomal pattern, whereas FosB immunopositivity was diffusely distributed. Following chronic administration, FosB induction turned to a clear striosome dominant pattern similar to c-Fos expression. In denervated striatum, expression of both proteins was profoundly augmented in a homogeneous pattern after a single dose of apomorphine. A distinct striosomal patterning appeared after chronic apomorphine administration in ventromedial part of the denervated striatum with a down-regulation in the matrix and relative enhancement in striosomes. These results suggest that compartmental reorganization of striatal neuronal activity may play a role in long-term behavioral changes induced by chronic dopaminergic treatments both under normal and dopamine-depleted conditions.