Chronic alterations in dopaminergic neurotransmission produce a persistent elevation of deltaFosB-like protein(s) in both the rodent and primate striatum

Identification of rat brainstem neuronal structures activated during cancer-induced anorexia

In cancer-related anorexia, body weight loss is paradoxically associated with reduced appetite, which is contrary to the situation during starvation, implying that the normal coupling of food intake to energy expenditure is disarranged. Here we examined brainstem mechanisms that may underlie suppression of food intake in a rat model of cancer anorexia. Cultured Morris 7777 hepatoma cells were injected subcutaneously in Buffalo rats, resulting in slowly growing tumor and reduced food intake and body weight loss after about 10 days. The brainstem was examined for induced expression of the transcription factors Fos and FosB as signs of neuronal activation. The results showed that anorexia and retarded body weight growth were associated with Fos protein expression in the area postrema, the general visceral region of the nucleus of the solitary tract, and the external lateral parabrachial nucleus, structures that also display Fos after peripheral administration of satiating or anorexigenic stimuli. The magnitude of the Fos expression was specifically related to the size of induced tumor, and not associated with weight loss per se, because it was not present in pair-fed or food-deprived rats. It also appeared to be independent of proinflammatory cytokines, as determined by the absence of increased cytokine levels in plasma and induced cytokine and cyclooxygenase expression in the brain. The findings thus provide evidence that cancer-associated anorexia and weight loss in this model is associated with activation of brainstem circuits involved in the suppression of food intake, and suggest that this occurs by inflammatory-independent mechanisms.

L-type calcium channel blockade on haloperidol-induced c-Fos expression in the striatum

Haloperidol-induced c-Fos expression in the lateral part of the neostriatum has been correlated with motor side effects while c-Fos induction in the medial part of the neostriatum and the nucleus accumbens is thought to be associated with the therapeutic effects of the drug. Induction of c-Fos in the striatum by haloperidol involves dopamine D(2) (DA D(2)) receptor antagonism and is dependent on activation of N-methyl-d-aspartate (NMDA) receptors and L-type Ca(2+) channels. In the current study, pretreatment with L-type Ca(2+) channel blockers suppressed haloperidol-induced c-Fos throughout the neostriatum and the nucleus accumbens at 2 h postinjection. However, elevated c-Fos protein expression was observed only in the lateral part of the neostriatum at 5 h postinjection of haloperidol following pretreatment of L-type Ca(2+) channel blocker compared with rats pretreated with vehicle alone. In addition, pretreatment prolonged the duration of haloperidol-induced catalepsy in rats. Infusions of L-type Ca(2+) channel blockers directly into the neostriatum mimicked similar patterns of changes in haloperidol-induced c-Fos expression. Prolonged expression of c-Fos was not observed following coadministration of nifedipine and a dopamine D(1) (DA D(1)) receptor agonist, SKF 81297, but could be mimicked by the DA D(2/3) receptor antagonist raclopride, suggesting that the phenomenon is likely related to DA D(2) receptor antagonism. Moreover, the expression levels of haloperidol-induced zif 268 and haloperidol-induced phosphorylated CREB and phosphorylated Elk-1 were also substantially elevated for a prolonged period of time in the lateral, but not the medial part of the neostriatum, following blockade of L-type Ca(2+) channels. Collectively, the results suggest that coadministration of L-type Ca(2+) channel blockers affects haloperidol signaling in the lateral part of the neostriatum and may exacerbate the development of acute motor side effects.

Spatiotemporal pattern of striatal ERK1/2 phosphorylation in a rat model of L-DOPA-induced dyskinesia and the role of dopamine D1 receptors

BACKGROUND

We examined the activation pattern of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and its dependence on D1 versus D2 dopamine receptors in hemiparkinsonian rats treated with 3,4-dihydroxyphenyl-L-alanine (L-DOPA).

METHODS

6-Hydroxydopamine-lesioned rats were treated acutely or chronically with L-DOPA in combination with antagonists for D1 or D2 receptors. Development of dyskinesia was monitored in animals receiving chronic drug treatment. Phosphorylation of ERK1/2, mitogen- and stress-activated protein kinase-1 (MSK-1), and the levels of FosB/DeltaFosB expression were examined immunohistochemically.

RESULTS

L-DOPA treatment caused phosphorylation of ERK1/2 in the dopamine-denervated striatum after acute and chronic administration. Similar levels were observed in matrix and striosomes, and in enkephalin-positive and dynorphin-positive neurons. The severity of dyskinesia was positively correlated with phospho-ERK1/2 levels. Phosphorylation of ERK1/2 and MSK-1 was dose-dependently blocked by SCH23390, but not by raclopride. SCH23390 also inhibited the development of dyskinesia and the induction of FosB/DeltaFosB.

CONCLUSIONS

L-DOPA produces pronounced activation of ERK1/2 signaling in the dopamine-denervated striatum through a D1-receptor-dependent mechanism. This effect is associated with the development of dyskinesia. Phosphorylated ERK1/2 is localized to both dynorphinergic and enkephalinergic striatal neurons, suggesting a general role of ERK1/2 as a plasticity molecule during L-DOPA treatment.

MPTP administration in mice changes the ratio of splice isoforms of fosB and rgs9

Most cases of Parkinson's disease (PD) are sporadic, suggesting an environmental influence on individuals affected by this neurodegenerative disorder. Environmental stresses often lead to changes in the regulation of splicing of pre-mRNA transcripts and this may lead to the pathogenesis of the disease. A 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)/probenecid mouse model was used to examine the changes in the splicing of the fosB and rgs9 transcripts. The ratio of DeltafosB/fosB transcript was decreased in the substantia nigra and unchanged in the striatum after acute MPTP treatment. The DeltafosB/fosB transcript ratio decreased initially and then increased in the striatum of chronically MPTP-treated animals due to different degrees of reduction for the splice variants over time, whereas the ratio was unchanged in the substantia nigra. The ratio of rgs9-2/rgs9-1 transcript decreased in the substantia nigra of mice after acute MPTP treatment and increased temporarily in the striatum after chronic MPTP treatment. There was an increase in the DeltaFosB/FosB and RGS9-2/RGS9-1 protein ratios 3 weeks and 3 days post-treatment, respectively, in chronically treated mice. The data indicate that the pattern of splice isoforms of fosB and rgs9 reflects the brain's immediate and long-term responses to the physiological stress associated with Parkinsonism.

Chronic 3,4-dihydroxyphenylalanine treatment induces dyskinesia in aphakia mice, a novel genetic model of Parkinson's disease

L-DOPA-induced dyskinesia (LID) is one of the main limitations of long term L-DOPA use in Parkinson's disease (PD) patients. We show that chronic L-DOPA treatment induces novel dyskinetic behaviors in aphakia mouse with selective nigrostriatal deficit mimicking PD. The stereotypical abnormal involuntary movements were induced by dopamine receptor agonists and attenuated by antidyskinetic agents. The development of LID was accompanied by preprodynorphin and preproenkephalin expression changes in the denervated dorsal striatum. Increased FosB-expression was also noted in the dorsal striatum. In addition, FosB expression was noted in the pedunculopontine nucleus and the zona incerta, structures previously not examined in the setting of LID. The aphakia mouse is a novel genetic model with behavioral and biochemical characteristics consistent with those of PD dyskinesia and provides a more consistent, convenient, and physiologic model than toxic lesion models to study the mechanism of LID and to test therapeutic approaches for LID.

Expression of amino acid receptors and neural peptides in the weaver mouse brain

In the present study, we conducted: (i) in situ hybridization in order to investigate the expression of kainate and GABA(A) receptor subunits and the pre-proenkephalin and prodynorphin peptides in the brain of weaver mouse (a genetic model of dopamine deficiency) and (ii) immunocytochemistry in order to study the somatostatin-positive cells in weaver striatum. Our results indicated: (i) increases in mRNA levels of KA2 and GluR6 kainate receptor subunits, of alpha(4) and beta(3) GABA(A) receptor subunits and of pre-proenkephalin and prodynorphin in 6-month-old weaver striatum; (ii) a decrease in alpha(1) and beta(2) GABA(A) subunit mRNAs in 6-month-old weaver globus pallidus; (iii) increases in KA2, alpha(4) and beta(3) and decreases in alpha(2) and beta(2) mRNAs in the 6-month-old weaver somatosensory cortex; and (iv) an increase in somatostatin-immunopositive cells in 3-month-old weaver striatum. We suggest that: (i) in striatum, the alterations are induced by the induction of the transcription factor DeltafosB (for GluR6, pre-proenkephalin and prodynorphin mRNAs) and the suppression of transcription factors like NGF-IB (nerve growth factor inducible B; for the KA2 mRNA), in response to dopamine depletion; (ii) in striatum and cortex, the alterations in the expression of the GABA(A) subunits indicate an increase of extrasynaptic versus a decrease of synaptic GABA(A) receptors; and (iii) in globus pallidus, the increased striatopallidal GABAergic transmission leads to a decrease in the number of GABA(A) receptors. Our results further clarify the regulatory role of dopamine in the expression of amino acid receptors and striatal neuropeptides.

Expression pattern of JunD after acute or chronic l-DOPA treatment: Comparison with ΔFosB

In this study, we have used 6-hydroxydopamine-lesioned rats to examine changes in striatal junD and fosB/deltafosB expression induced by acute and chronic treatment with L-DOPA (5 and 15 days). Changes at the protein levels were studied using Western immunoblotting while mRNA changes were compared using in situ hybridization histochemistry. We observed a significant increase in the level of deltaFosB proteins after chronic treatment with L-DOPA, an effect that was not observed for JunD proteins. In addition, the upregulation of deltaFosB was already present after an acute treatment but increased upon chronic treatment. By contrast, junD and deltafosB mRNA were both upregulated significantly above control levels after an acute injection of L-DOPA. In conclusion, this study suggests a differential expression pattern of junD and deltafosB in a rat model of L-DOPA-induced dyskinesia. The upregulation of deltaFosB protein, but not JunD, is likely to reflect an increased stability of the deltaFosB proteins without ongoing enhanced transcription of the encoding genes.

Impaired behavioural and molecular adaptations to dopamine denervation and repeated L‐DOPA treatment in Nur77‐knockout mice

We have previously shown that dopamine (DA) denervation and repeated L-DOPA treatment modulate the pattern of Nur77 mRNA expression in the striatum. However, the exact role of this nuclear receptor in L-DOPA-induced molecular and behavioural adaptations observed in animal models of Parkinson's disease is still unknown. In the present study, we investigated the effects of Nur77 gene deletion on the development of behavioural sensitization and on changes in the regulation of neuropeptides and DA D(3) receptor expression following DA denervation and repeated L-DOPA treatment in Nur77+/+ and Nur77-/- hemiparkinsonian mice. One week postsurgery, hemiparkinsonian mice were treated with L-DOPA (10 mg/kg) plus benserazide (3 mg/kg) once a day for 7 days. Despite similar extents of nigrostriatal denervation, L-DOPA-induced rotational response was exacerbated in Nur77-/- mice compared to Nur77+/+ ones. However, the rate of increase of the rotational behaviour after repeated L-DOPA injections was similar in the two mouse strains. Lesioning the nigrostriatal pathway increased enkephalin (ENK) and neurotensin (NT) mRNA levels in both mouse strains. However, the up-regulation of these neuropeptides was significantly reduced in Nur77-/- mice. There was no difference in the modulation of D3 receptor density and dynorphin (DYN) mRNA expression between the two mouse strains. The present results suggest that Nur77 is involved in setting the threshold level for L-DOPA-induced rotational behaviour, rather than controlling the development of behavioural sensitization. This specific behavioural change is associated with a selective regulation of neuropeptide expression specifically in the indirect striatal output pathway.

MTH1, an oxidized purine nucleoside triphosphatase, prevents the cytotoxicity and neurotoxicity of oxidized purine nucleotides

In human and rodent cells, MTH1, an oxidized purine nucleoside triphosphatase, efficiently hydrolyzes oxidized dGTP, GTP, dATP and ATP such as 2'-deoxy-8-oxoguanosine triphosphate (8-oxo-dGTP) and 2'-deoxy-2-hydroxyadenosine triphosphate (2-OH-dATP) in nucleotide pools, thus avoiding their incorporation into DNA or RNA. MTH1 is expressed in postmitotic neurons as well as in proliferative tissues, and it is localized both in the mitochondria and nucleus, thus suggesting that MTH1 plays an important role in the prevention of the mutagenicity and cytotoxicity of such oxidized purines as 8-oxoG which are known to accumulate in the cellular genome. Our recent studies with MTH1-deficient mice or cells revealed that MTH1 efficiently minimizes accumulation of 8-oxoG in both nuclear and mitochondrial DNA in the mouse brain as well as in cultured cells, thus contributing to the protection of the brain from oxidative stress.

Neonatal ventral hippocampal lesions produce an elevation of DeltaFosB-like protein(s) in the rodent neocortex

Rats that have sustained bilateral excitotoxic lesions of the ventral hippocampus (VH) as neonates develop behavioral abnormalities as adults (hyper-responsiveness to stress, diminished prepulse inhibition, and increased sensitivity to dopamine agonists), which resemble certain aspects of schizophrenia. Although this behavioral profile is thought to reflect dysregulation of the mesolimbic dopamine system, the precise neuroanatomical and neurochemical substrates that mediate the emergence of these abnormalities during brain maturation are unclear. In order to identify putative sites responsible for the development of behavioral abnormalities following neonatal lesions of the VH, we utilized the chronic neuronal activity marker DeltaFosB. By comparison to sham lesioned animals, bilateral destruction of the VH elevated DeltaFosB expression throughout the caudate putamen and neocortex of animals lesioned as neonates. These increases were not observed in rats lesioned as young-adults, suggesting that DeltaFosB induction in the cortex of neonatally lesioned rats may be related to altered cortical neurodevelopment. Accumulating evidence implicates DeltaFosB in mediation of the long-lasting effects of altered dopaminergic neurotransmission on behavior. The present findings are consistent with this proposal and suggest that elevated expression of DeltaFosB identifies overactive neurons that may contribute to the enhanced sensitivity to stress and dopaminergic agonists of rats that have sustained bilateral ventral hippocampal lesions as neonates.

Docosahexaenoic acid reduces levodopa‐induced dyskinesias in 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine monkeys

OBJECTIVE

The objective of the present study was to investigate the effect of docosahexaenoic acid (DHA), a polyunsaturated fatty acid (omega-3), on levodopa-induced dyskinesias (LIDs) in parkinsonian 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys.

METHODS

We explored the effect of DHA in two paradigms. First, a group of MPTP monkeys was primed with levodopa for several months before introducing DHA. A second group of MPTP monkeys (de novo) was exposed to DHA before levodopa therapy.

RESULTS

DHA administration reduced LIDs in both paradigms without alteration of the anti-parkinsonian effect of levodopa indicating that DHA can reduce the severity or delay the development of LIDs in a nonhuman primate model of Parkinson's disease.

INTERPRETATION

These results suggest that DHA can reduce the severity or delay the development of LIDs in a nonhuman primate model of Parkinson's disease. DHA may represent a new approach to improve the quality of life of Parkinson's disease patients.

Focal not widespread grafts induce novel dyskinetic behavior in parkinsonian rats

Dyskinesias are a common consequence of dopaminergic therapy in patients with Parkinson's disease. Little is known about the influence of cellular replacement strategies upon drug-induced dyskinesias. In the current study, we employed parkinsonian rats to test whether the distribution of dopamine neuron grafts could differentially alter striatal circuitry and levodopa-induced dyskinesias. Specifically, we compared behavioral and neurochemical consequences of dopamine reinnervation restricted to a focal region of the striatum to innervation encompassing the majority of the striatum by distributing the same number of cells into single locus or multiple locations. Both the single-site and widespread grafts reduced pregraft dyskinesias and normalized FosB/DeltaFosB in the dorsal two-thirds of the lateral striatum. However, single-site DA graft recipients developed a robust, novel forelimb-facial stereotypy and upregulated FosB/DeltaFosB expression in the ventrolateral striatum, an area associated with movements of tongue and forelimbs. The onset of forelimb-facial stereotypy correlated with measures of increased graft function.

Rhes, the Ras homolog enriched in striatum, is reduced under conditions of dopamine supersensitivity

Striatal dopamine receptors become supersensitive when dopaminergic input is removed through either surgical denervation or pharmacological depletion. Although alterations such as increased D2 receptor binding and increased receptor-G protein coupling have been described in supersensitive striatal tissue, their roles in the mechanism of supersensitivity remain uncertain. The Ras Homolog Enriched in Striatum (Rhes) is expressed in brain areas that receive dopaminergic input, and here we test whether alterations in its expression accompany treatments that promote dopamine receptor supersensitivity in rats. Removal of dopamine input to the striatum by surgical denervation with 6-hydroxydopamine resulted in a decrease in rhes mRNA expression throughout striatum, as measured with quantitative in situ hybridization. The decrease was detected as early as two weeks and as late as seven months after surgery. Furthermore, a decrease in rhes mRNA was evident after repeated or acute reserpine treatment. Chronic daily injection of rats with the D2 antagonist eticlopride, which is known to up-regulate D2 receptors without inducing profound receptor supersensitivity, did not alter the expression of rhes mRNA in striatum. Thus, changes in rhes mRNA expression are strictly correlated with receptor supersensitivity, perhaps as a result of continuous removal of dopaminergic input. These findings suggest that rhes mRNA expression is maintained by dopamine and may play a role in determining normal dopamine receptor sensitivity.

Denervation and repeated l-DOPA induce complex regulatory changes in neurochemical phenotypes of striatal neurons: Implication of a dopamine D1-dependent mechanism

Motor complications induced through repeated L-DOPA treatment in patients with Parkinson's disease are thought to be the consequence of molecular adaptations that occur in response to repeated dopamine receptors stimulation. Here, we studied the molecular changes taking place in the denervated striatum of unilaterally 6-OHDA-lesioned rats repeatedly treated with L-DOPA alone or combined to the D1 receptor antagonist SCH23390. We looked at the territorial patterns of expression of neurotensin (NT), dynorphin (DYN), enkephalin (ENK) and Nur77 (also known as NGFI-B) mRNA expression in the striatum and contrasted these with markers of glutamatergic transport and dopaminergic receptor functions. The denervation process induced NT and Nur77 mRNA expression in ENK-positive cells. Subsequent repeated L-DOPA treatment led to a sensitization of L-DOPA-induced rotational response and produced a second surge of NT induction, this time limited to DYN-positive cells and preferentially restricted to the lateral striatum. In this specific territory, the number of Nur77-positive cells was decreased, in response to L-DOPA, when compared to the medial part of the lesioned striatum. L-DOPA treatment increased dopamine D3 receptor and glutamate transporter 1 (GLT1) mRNA expression in the lesioned striatum and that, specifically in an area overlapping one of Nur77 decrease and of NT/DYN induction. The concomitant administration of SCH23390 with repeated L-DOPA treatment blocked the development of behavioral sensitization and the appearance of all L-DOPA-induced molecular reorganizations reported above. Our results showed that repeated L-DOPA treatment produces, in a denervated striatum, a complex pattern of genes regulation in both the direct and the indirect striatal output pathways. This phenomenon is located preferentially in a striatal area receiving converging inputs from the thalamus and sensorimotor cortex and is dependent upon D1 receptor stimulation.

Nondopaminergic mechanisms in levodopa-induced dyskinesia

It has become increasingly apparent that Parkinson's disease involves many transmitter systems other than dopamine. This nondopaminergic involvement impacts on the generation of symptoms, on the neurodegenerative process, but, most tellingly, in the generation of side effects of current treatments, in particular, levodopa-induced dyskinesia (LID). Such mechanisms contribute not only to the expression of LID once it has been established but also to the mechanisms responsible for the development, or priming, of the dyskinetic state and the subsequent maintenance of the brain in that primed state. Within the basal ganglia, abnormalities in different nondopaminergic components of the circuitry have been defined in LID. In particular, a role for enhanced inhibition of basal ganglia outputs by the GABAergic direct pathway has been suggested as a basic mechanism generating LID. We speculate that the external globus pallidus and subthalamic nucleus may play distinct roles in different forms of dyskinesia, e.g., chorea/dystonia; peak/diphasic/off. At the cellular level, an appreciation of abnormal signaling by, among others, glutamatergic (NMDA and AMPA receptors in particular), alpha2 adrenergic, serotonergic (5HT), cannabinoid and opioid mechanisms in both priming and expression of LID has begun to emerge over the last decade. This is being consolidated, though in many cases questions remain regarding the specific sites of such abnormality within the circuitry. Very recently, at the molecular level, mechanisms controlling neurotransmitter release and impacting on the ability of neurons to maintain particular forms of firing patterning and synchronization, e.g., SV2A, have been identified. This increased understanding has already delivered and will continue to define novel approaches to treatment that target both pre- and postsynaptic signaling molecules throughout the basal ganglia circuitry.

Pathophysiology of motor fluctuations in Parkinson's disease

Loss of dopamine neurons in Parkinson's disease (PD) initiates a complex stream of effects that results in the development of tremor, bradykinesia, and rigidity. While levodopa remains the most effective drug for the symptomatic treatment of PD, its chronic administration is associated with the development of motor fluctuations and dyskinesias. The risk of developing motor fluctuations has been linked to disease severity, dosage of levodopa, and the age of the patient. A recent body of preclinical data has demonstrated that alterations in dopaminergic tone as well as in treatment patterns results in cellular adaptations, including alterations in gene expression. This body of preclinical data suggests that nonphysiological, pulsatile stimulation of dopamine receptors induces the development of motor fluctuations and dyskinesias and raises the possibility that nonpulsatile stimulation of dopamine receptors (continuous dopaminergic stimulation) might induce fewer fluctuations. We discuss the theory of continuous dopaminergic stimulation and its implications for the management of motor fluctuations in patients with advanced and early PD.

DeltaFosB accumulates in a GABAergic cell population in the posterior tail of the ventral tegmental area after psychostimulant treatment

The transcription factor deltaFosB is induced in the nucleus accumbens and dorsal striatum by chronic exposure to several drugs of abuse, and increasing evidence supports the possibility that this induction is involved in the addiction process. However, to date there has been no report of deltaFosB induction by drugs of abuse in the ventral tegmental area (VTA), which is also a critical brain reward region. In the present study, we used immunohistochemistry to demonstrate that chronic forced administration of cocaine induces deltaFosB in the rat VTA. This induction occurs selectively in a gamma-aminobutyric acid (GABA) cell population within the posterior tail of the VTA. A similar effect is seen after chronic cocaine self-administration. Induction of deltaFosB in the VTA occurs after psychostimulant treatment only: it is seen with both chronic cocaine and amphetamine, but not with chronic opiates or stress. The expression of deltaFosB appears to be mediated by dopamine systems, as repeated administration of a dopamine uptake inhibitor induced deltaFosB in the VTA, while administration of serotonin or norepinephrine uptake inhibitors failed to produce this effect. Time course analysis showed that, following 14 days of cocaine administration, deltaFosB persists in the VTA for almost 2 weeks after cocaine withdrawal. This accumulation and persistence may account for some of the long-lasting changes in the brain associated with chronic drug use. These results provide the first evidence of deltaFosB induction in a discrete population of GABA cells in the VTA, which may regulate the functioning of the brain's reward mechanisms.

Pharmacological validation of a mouse model of l-DOPA-induced dyskinesia

Dyskinesia (abnormal involuntary movements) is a common complication of l-DOPA pharmacotherapy in Parkinson's disease, and is thought to depend on abnormal cell signaling in the basal ganglia. Dopamine (DA) denervated mice can exhibit behavioral and cellular signs of dyskinesia when they are treated with l-DOPA, but the clinical relevance of this animal model remains to be established. In this study, we have examined the pharmacological profile of l-DOPA-induced abnormal involuntary movements (AIMs) in the mouse. C57BL/6 mice sustained unilateral injections of 6-hydroxydopamine (6-OHDA) in the striatum. The animals were treated chronically with daily doses of l-DOPA that were sufficient to ameliorate akinetic features without inducing overt signs of dyskinesia upon their first administration. In parallel, other groups of mice were treated with antiparkinsonian agents that do not induce dyskinesia when administered de novo, that is, the D2/D3 agonist ropinirole, and the adenosine A2a antagonist KW-6002. During 3 weeks of treatment, l-DOPA-treated mice developed AIMs affecting the head, trunk and forelimb on the side contralateral to the lesion. These movements were not expressed by animals treated with ropinirole or KW-6002 at doses that improved forelimb akinesia. The severity of l-DOPA-induced rodent AIMs was significantly reduced by the acute administration of compounds that have been shown to alleviate l-DOPA-induced dyskinesia both in parkinsonian patients and in rat and monkey models of Parkinson's disease (amantadine, -47%; buspirone, -46%; riluzole, -33%). The present data indicate that the mouse AIMs are indeed a functional equivalent of l-DOPA-induced dyskinesia.

Induction of deltaFosB in reward-related brain structures after chronic stress

Acute and chronic stress differentially regulate immediate-early gene (IEG) expression in the brain. Although acute stress induces c-Fos and FosB, repeated exposure to stress desensitizes the c-Fos response, but FosB-like immunoreactivity remains high. Several other treatments differentially regulate IEG expression in a similar manner after acute versus chronic exposure. The form of FosB that persists after these chronic treatments has been identified as DeltaFosB, a splice variant of the fosB gene. This study was designed to determine whether the FosB form induced after chronic stress is also DeltaFosB and to map the brain regions and identify the cell populations that exhibit this effect. Western blotting, using an antibody that recognizes all Fos family members, revealed that acute restraint stress caused robust induction of c-Fos and full-length FosB, as well as a small induction of DeltaFosB, in the frontal cortex (fCTX) and nucleus accumbens (NAc). The induction of c-Fos (and to some extent full-length FosB) was desensitized after 10 d of restraint stress, at which point levels of DeltaFosB were high. A similar pattern was observed after chronic unpredictable stress. By use of immunohistochemistry, we found that chronic restraint stress induced DeltaFosB expression predominantly in the fCTX, NAc, and basolateral amygdala, with lower levels of induction seen elsewhere. These findings establish that chronic stress induces DeltaFosB in several discrete regions of the brain. Such induction could contribute to the long-term effects of stress on the brain.

The effects of a selective dopamine D2 receptor agonist on behavioral and pathological outcome in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated squirrel monkeys

In this study, we investigated antiparkinsonian activity of the novel, highly selective dopamine D(2) receptor agonist sumanirole compared with two clinically effective dopaminergic therapies in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) primate model of Parkinson's disease. Squirrel monkeys were rendered parkinsonian by chronic administration of MPTP and subsequently dosed with vehicle, L-DOPA plus carbidopa (L-DOPA), ropinirole, or sumanirole over a duration of 8 weeks. Antiparkinsonian effects measured with a parkinsonian primate rating scale (PPRS) showed that sumanirole elicited improved functional outcome compared with vehicle. The dopamine D2/D3 agonist ropinirole improved behavioral outcome similar to sumanirole, whereas L-DOPA treatment yielded the most significant symptomatic improvement. The relative rank of therapies that elicited normalization of PPRS was L-DOPA > sumanirole; ropinirole did not normalize PPRS in any of the treated monkeys. Dyskinesias were present with L-DOPA treatment but were not observed in sumanirole-, ropinirole-, or placebo-treated primates. Pathologically, all MPTP-treated animals displayed neurodegeneration of dopaminergic neurons in the substantia nigra pars compacta and reactive astrocytosis. Neurons immunoreactive with antibodies to the nuclear transcription factor DeltaFosB were most significantly increased in the striatum of L-DOPA-treated monkeys. These results suggest that sumanirole can exert antiparkinsonian effects similar to L-DOPA without the behavioral and morphological consequences of the latter.

Repeated administration of the monoamine reuptake inhibitor BTS 74 398 induces ipsilateral circling in the 6-hydroxydopamine lesioned rat without sensitizing motor behaviours

BTS 74 398 (1-[1-(3,4-dichlorophenyl)cyclobutyl]-2-(3-diaminethylaminopropylthio)ethanone monocitrate) is a monoamine reuptake inhibitor that reverses motor deficits in MPTP-treated (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) common marmosets without provoking established dyskinesia. However, it is not known whether BTS 74 398 primes the basal ganglia for dyskinesia induction. In this study, the ability of BTS 74 398 to sensitize 6-hydroxydopamine (6-OHDA)-lesioned rats for the production of abnormal motor behaviours and the induction of striatal DeltaFosB were determined in comparison with l-3,4-dihydroxyphenylalanine methyl ester (L-dopa). Acute administration of BTS 74 398 induced a dose-dependent ipsilateral circling response in unilaterally 6-OHDA-lesioned rats whereas L-dopa produced dose-dependent contraversive rotation. The ipsilateral circling response to BTS 74 398 did not alter during 21 days of administration. In contrast, L-dopa treatment for 21 days caused a marked increase in rotational response. Repeated administration of both L-dopa and BTS 74 398 increased general motor activity and stereotypic behaviour. In L-dopa-treated rats, orolingual, locomotive, forelimb and axial abnormal movements developed whereas BTS 74 398 produced only locomotion with a side bias but no other abnormal movements. Sensitization of circling responses and the development of abnormal movements in 6-OHDA-lesioned rats have been associated with the potential of dopaminergic drugs to induce dyskinesia. Furthermore, striatal DeltaFosB immunoreactivity, shown to correlate with dyskinesia induction, was increased by L-dopa but was unaffected by repeated BTS 74 398 administration. The lack of such changes following repeated BTS 74 398 treatment suggests that it may be an effective antiparkinsonian therapy that is unlikely to produce involuntary movements.

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

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

Induction patterns of transcription factors of the nur family (nurr1, nur77, and nor-1) by typical and atypical antipsychotics in the mouse brain: implication for their mechanism of action

Monitoring gene expression has been intensively used to identify neurobiological and neuroanatomical substrates associated with administration of antipsychotic drugs. Transcription factors of the Nur family (Nurr1, Nur77, and Nor-1) are orphan nuclear receptors that have been recently associated with dopamine neurotransmission. Nurr1 is involved in midbrain dopamine neuron development. Nur77 and Nor-1 are expressed in dopaminoceptive areas such as the striatum, nucleus accumbens, and prefrontal cortex. To better understand the relationship between Nur and antipsychotic drug effects, we conducted a comprehensive evaluation of the effect of various typical and atypical antipsychotic drugs on the modulation of Nur mRNA levels. We show that differential patterns of Nur expression can be obtained with typical and atypical antipsychotic drugs. Modulation of Nur77 and Nor-1 mRNA expression by antipsychotics can be used to calculate an index that is predictive of the typical or atypical profile of antipsychotic drugs. Inductions of Nur by anti-psychotic drugs are correlated with dopamine D2 receptor in the striatum and D2 and D3 receptor subtypes in the nucleus accumbens. The 5-hydroxytryptamine 2A/D2 affinity ratio of antipsychotics can also predict these patterns of inductions. In addition to classical gene patterns induced in the striatal complex (striatum, accumbens) and cortex, most antipsychotic drugs tested strongly induced Nur77, Nor-1, and increased Nurr1 mRNA levels in the substantia nigra and ventral tegmental area. These data suggest that typical and atypical antipsychotic drugs might induce in multiple brain regions distinct Nur-dependent transcriptional activities, which may contribute to their pharmacological effects.

Clozapine-, but not haloperidol-, induced increases in ΔFosB-like immunoreactivity are completely blocked in the striatum of mice lacking D3 dopamine receptors

On the basis of anatomical and pharmacological evidence, we have proposed that D3 receptor antagonism plays a role in the mediation of clozapine-, but not haloperidol-, induced immediate-early gene expression in the striatum. To test this hypothesis directly, we compared the effects of repeated administration of vehicle (8 mL/kg/day), clozapine (20 mg/kg/day) and haloperidol (2 mg/kg/day) for 17 days on expression of deltaFosB-like immunoreactivity (deltaFosB-Ir) in the island of Calleja major, nucleus accumbens and caudate-putamen of wild-type C57Bl6 (WT) and D3 receptor knockout (D3KO) mice. In vehicle-treated mice, the number of deltaFosB-Ir neurons in the nucleus accumbens was greater in D3KO than in WT mice. This finding is consistent with results implicating D3 receptor activation in the tonic inhibition of this limbic structure. Unlike rats, clozapine significantly increased the number of deltaFosB-Ir neurons in both the nucleus accumbens and the caudate-putamen of WT mice albeit to a lesser extent in the caudate-putamen than nucleus accumbens. Similar to rats, however, deltaFosB-Ir in the island of Calleja major of WT mice was elevated by clozapine but not by haloperidol. In the nucleus accumbens and caudate-putamen, haloperidol produced similar increases in deltaFosB-Ir in WT and D3KO mice. By contrast, clozapine-induced increases in deltaFosB-Ir in the island of Calleja major, nucleus accumbens and caudate-putamen of WT mice were absent in D3KO mice. These findings, which indicate that D3 receptor blockade is essential for clozapine-induced increases in striatal deltaFosB-Ir, suggest that D3 receptor antagonism may contribute to the unique therapeutic profile of this atypical antipsychotic.

ΔFosB: a molecular switch for long-term adaptation in the brain

DeltaFosB is a unique transcription factor that plays an essential role in long-term adaptive changes in the brain associated with diverse conditions, such as drug addiction, Parkinson's disease, depression, and antidepressant treatment. It is induced in brain, in a region- and cell-type-specific manner by many types of chronic perturbations. Once induced, it persists for long periods of time due to its unusual stability. The transcriptional effects of DeltaFosB are complex, because the protein can function as both a transcriptional activator and repressor. Progress has been made in identifying specific target genes for DeltaFosB and in relating some of these genes to DeltaFosB's cellular and behavioral actions. Future studies will help us to better understand the biochemical basis of DeltaFosB's unique stability, as well as the precise molecular pathways through which this transcription factor produces its complex effects on neuronal plasticity and complex behavior.

Dopamine D2-like antagonists induce chromatin remodeling in striatal neurons through cyclic AMP-protein kinase A and NMDA receptor signaling

Antipsychotic drugs regulate gene transcription in striatal neurons by blocking dopamine D2-like receptors. Little is known about the underlying changes in chromatin structure, including covalent modifications at histone N-terminal tails that are epigenetic regulators of gene expression. We show that treatment with D2-like antagonists rapidly induces the phosphorylation of histone H3 at serine 10 and the acetylation of H3-lysine 14 in bulk chromatin from striatum and in nuclei of striatal neurons. We find that, in vivo, D2-like antagonist-induced H3 phospho-acetylation is inhibited by the NMDA receptor antagonist MK-801 and by the protein kinase A (PKA) inhibitor Rp-adenosine 3c',5c'-cyclic monophosphorothioate triethylammonium salt but increased by the PKA activator Sp-adenosine 3c',5c'-cyclic monophosphorothioate triethylammonium salt. Furthermore, in dissociated striatal cultures which lack midbrain and cortical pre-synaptic inputs, H3 phospho-acetylation was induced by glutamate, L-type Ca2+ channel agonists and activators of cAMP-dependent PKA but inhibited by NMDA receptor antagonists or PKA antagonists. The dual modification, H3pS10-acK14, was enriched at genomic sites with active transcription and showed the kinetics of the early response. Together, these results suggest that histone modifications and chromatin structure in striatal neurons are dynamically regulated by dopaminergic and glutamatergic inputs converging on the cellular level. Blockade of D2-like receptors induces H3 phospho-acetylation, H3pS10-acK14, through cAMP-dependent PKA, and post-synaptic NMDA receptor signaling.

A model of L-DOPA-induced dyskinesia in 6-hydroxydopamine lesioned mice: relation to motor and cellular parameters of nigrostriatal function

L-DOPA-induced dyskinesia is a major complication of L-DOPA pharmacotherapy in Parkinson's disease, and is thought to depend on abnormal cell signaling in the basal ganglia. In this study, we have addressed the possibility to model L-DOPA-induced dyskinesia in the mouse at both the behavioral and the molecular level. C57BL/6 mice sustained unilateral injections of 6-hydroxydopamine (6-OHDA) either in the medial forebrain bundle (MFB) or in the sensorimotor part of the striatum. Both types of lesion produced a similar degree of forelimb akinesia on the contralateral side of the body. The lowest dose of L-DOPA that could significantly relieve this akinetic deficit (i.e., 6 mg/kg) did not differ between MFB and intrastriatal lesions. The L-DOPA threshold dose for the induction of dyskinesia did however differ between the two lesion types. A daily dose of 6 mg/kg L-DOPA caused MFB lesioned mice to develop abnormal movements affecting orofacial, trunk, and forelimb muscles on the side contralateral to the lesion, whereas a daily dose of 18 mg/kg was required to produce comparable dyskinetic effects in the intrastriatally lesioned animals. The development of abnormal movements was accompanied by a striatal induction of DeltaFosB-like proteins and prodynorphin mRNA, that is, molecular markers that are associated with L-DOPA-induced dyskinesia in both rats and nonhuman primates. We conclude that 6-OHDA lesioned mice exhibit behavioral and cellular features of akinesia and L-DOPA-induced dyskinesia that are similar to those previously characterized in rats. The mouse model of L-DOPA-induced dyskinesia will provide a useful tool to study the molecular determinants of this movement disorder in transgenic mice strains.

Persistent increase in olfactory type G-protein alpha subunit levels may underlie D1 receptor functional hypersensitivity in Parkinson disease

Although L-dopa remains the most effective treatment of Parkinson disease, its long-term administration is hampered by the appearance of dyskinesia. Hypersensitivity of dopamine D1 receptors in the striatum has been suggested to contribute to the genesis of these delayed adverse effects. However, D1 receptor amounts are unchanged in Parkinson disease, suggesting alterations of downstream effectors. In rodents, striatal D1 receptors activate adenylyl cyclase through olfactory type G-protein alpha subunit (Galphaolf) and G-protein gamma 7 subunit (Ggamma7). We found that Galphaolf was enriched in human basal ganglia and was markedly diminished in the putamen of patients with Huntington disease, in relation with the degeneration of medium spiny neurons. In contrast, in the putamen of patients with Parkinson disease, Galphaolf and Ggamma7 levels were both significantly increased. In the rat, the degeneration of dopamine neurons augmented Galphaolf levels in the striatal neurons, specifically at the plasma membrane, an effect accounting for the increase of D1 response on cAMP production in dopamine-depleted striatum. In lesioned rats, Galphaolf levels were normalized by a 3 week treatment with l-dopa or a D1 agonist but not with aD2-D3 agonist, supporting a Galphaolf regulation by D1 receptor usage. In contrast, the increases of Galphaolf levels in patients were not affected by the duration of l-dopa treatment but correlated with duration of disease. In conclusion, our results revealed in the parkinsonian putamen a prolonged elevation of Galphaolf levels that may lead to a persistent D1 receptor hypersensitivity and contribute to the genesis of long-term complications of L-dopa.

Chronic treatment with atypical neuroleptics induces striosomal FosB/DeltaFosB expression in rats

BACKGROUND

Studies have shown that neuroleptics regulate expression of the transcription factor FosB/DeltaFosB in the striatum, including the accumbens and caudate-putamen; however, the striatum is also divided into another structural dimension, the striosome and matrix compartments. The precise distribution of FosB/DeltaFosB induced by chronic neuroleptics in these striatal compartments is poorly understood.

METHODS

Rats received either single acute injections or chronic injections of clozapine (0 or 20 mg/kg, intraperitoneally [IP]), olanzapine (0 or 5 mg/kg, IP), or haloperidol (0 or 1.5 mg/kg, IP) for 25 days. The levels and compartmental distribution of FosB/DeltaFosB were examined.

RESULTS

Chronic clozapine induced clustered FosB/DeltaFosB expression within striosomes of the caudate-putamen. This pattern was due to increased levels of FosB/DeltaFosB in striosomes within the ventrolateral caudate-putamen and reduced levels of basal FosB/DeltaFosB in the matrix in the entire caudate-putamen. In contrast, chronic haloperidol increased FosB/DeltaFosB equally within the matrix and striosomes throughout the entire caudate-putamen. Chronic olanzapine induced an intermediate pattern.

CONCLUSIONS

The relative absence of FosB/DeltaFosB expression in the matrix correlates with the lack of parkinsonism of atypical neuroleptics. Expression of FosB/DeltaFosB in the matrix may contribute to parkinsonism of typical neuroleptics.

Cyclin-dependent kinase 5 is a mediator of dopaminergic neuron loss in a mouse model of Parkinson's disease

Recent evidence indicates that cyclin-dependent kinases (CDKs, cdks) may be inappropriately activated in several neurodegenerative conditions. Here, we report that cdk5 expression and activity are elevated after administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a toxin that damages the nigrostriatal dopaminergic pathway. Supporting the pathogenic significance of the cdk5 alterations are the findings that the general cdk inhibitor, flavopiridol, or expression of dominant-negative cdk5, and to a lesser extent dominant-negative cdk2, attenuates the loss of dopaminergic neurons caused by MPTP. In addition, CDK inhibition strategies attenuate MPTP-induced hypolocomotion and markers of striatal function independent of striatal dopamine. We propose that cdk5 is a key regulator in the degeneration of dopaminergic neurons in Parkinson's disease.

Inhibition of calpains prevents neuronal and behavioral deficits in an MPTP mouse model of Parkinson's disease

The molecular mechanisms mediating degeneration of midbrain dopamine neurons in Parkinson's disease (PD) are poorly understood. Here, we provide evidence to support a role for the involvement of the calcium-dependent proteases, calpains, in the loss of dopamine neurons in a mouse model of PD. We show that administration of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) evokes an increase in calpain-mediated proteolysis in nigral dopamine neurons in vivo. Inhibition of calpain proteolysis using either a calpain inhibitor (MDL-28170) or adenovirus-mediated overexpression of the endogenous calpain inhibitor protein, calpastatin, significantly attenuated MPTP-induced loss of nigral dopamine neurons. Commensurate with this neuroprotection, MPTP-induced locomotor deficits were abolished, and markers of striatal postsynaptic activity were normalized in calpain inhibitor-treated mice. However, behavioral improvements in MPTP-treated, calpain inhibited mice did not correlate with restored levels of striatal dopamine. These results suggest that protection against nigral neuron degeneration in PD may be sufficient to facilitate normalized locomotor activity without necessitating striatal reinnervation. Immunohistochemical analyses of postmortem midbrain tissues from human PD cases also displayed evidence of increased calpain-related proteolytic activity that was not evident in age-matched control subjects. Taken together, our findings provide a potentially novel correlation between calpain proteolytic activity in an MPTP model of PD and the etiology of neuronal loss in PD in humans.

Differential effect of dopamine deficiency on the expression of NMDA receptor subunits in the weaver mouse brain

The weaver mutant mouse is characterized by degeneration of the dopaminergic mesencephalic neurons. The role of the dopaminergic system in the regulation of N-methyl-d-aspartate (NMDA) receptor subunit expression was addressed in the present study. In situ hybridization experiments were conducted to determine the expression levels of the NMDA receptor subunit mRNAs, z1, epsilon1 and epsilon2, in striatum, nucleus accumbens, olfactory tubercle and cerebral cortical regions of 26-day-, 3- and 6-month-old weaver mice. Data indicated statistically significant increases in z1 and epsilon2 mRNA levels in 6-month-old weaver striatum, whereas at the same age epsilon1 mRNA expression was decreased in all striatal regions, as well as in the cortex. In the 26-day-old weaver striatum and nucleus accumbens, statistically significant increases were observed in epsilon1 mRNA levels, whereas no changes were observed in the other two subunits. In the somatosensory cortex of 26-day-old weaver brain an increased expression of all three subunits was observed. The upregulation of NMDA receptor subunit expression observed in the somatosensory cortex can be attributed to a decreased activity of the glutamatergic thalamocortical pathway, following the degeneration of the nigrostriatal dopaminergic fibres. In the striatum, the present results demonstrate a differential control on the expression of z1 and epsilon2 subunits on the one hand, and epsilon1 subunit on the other. It is suggested that dopamine exerts a negative control on the expression of z1 and epsilon2 subunits, through a downregulation of transcription factors associated with the AP1 regulatory site, which is mediated by the activation of striatal dopamine D2 receptors.

DeltaFosB, but not FosB, induces delayed apoptosis independent of cell proliferation in the Rat1a embryo cell line

The fates of Rat1a cells expressing FosB and DeltaFosB as fusion proteins (ER-FosB, ER-DeltaFosB) with the ligand binding domain of human estrogen receptor were examined. The binding of estrogen to the fusion proteins resulted in their nuclear translocation and triggered cell proliferation, and thereafter delayed cell death was observed only in cells expressing ER-DeltaFosB. The proliferation of Rat1a cells, but not cell death triggered by ER-DeltaFosB, was completely abolished by butyrolactone I, an inhibitor of cycline-dependent kinases, and was partly suppressed by antisense oligonucleotides against galectin-1, whose expression is induced after estrogen administration. The cell death was accompanied by the activation of caspase-3 and -9, the fragmentation of the nuclear genome and cytochrome c release from the mitochondria, and was suppressed by zDEVD-fmk and zLEHD-fmk but not zIETD-fmk. The cell death was not suppressed by exogenous His-PTD-Bcl-x(L) at all, suggesting involvement of a Bcl-x(L)-resistant pathway for cytochrome c release.

The fluctuating Parkinsonian patient--clinical and pathophysiological aspects

Although levodopa-related motor response complications remain challenging from a pathophysiological and therapeutic standpoint, major advances have been made in the last decade, supporting the development of several promising drugs. Eventually, these drugs may help us to prevent, alleviate, or even "deprime" these frequent and disabling complications. Knowledge of the basic mechanisms and hypotheses underlying this fascinating conversion in the parkinsonian brain allows neurologists to understand the rationale behind emerging treatment strategies.

Cellular and behavioural effects of the adenosine A2a receptor antagonist KW-6002 in a rat model of l-DOPA-induced dyskinesia

We have examined the ability of KW-6002, an adenosine A2a antagonist, to modulate the dyskinetic effects of L-DOPA in 6-hydroxydopamine-lesioned rats. In animals rendered dyskinetic by a previous course of L-DOPA treatment, KW-6002 did not elicit any abnormal involuntary movements on its own, but failed to reduce the severity of dyskinesia when coadministered with L-DOPA. A second experiment was undertaken in order to study the effects of KW-6002 in L-DOPA-naive rats. Thirty-five animals were allotted to four groups to receive a 21-day treatment with: (i) KW-6002 (10 mg/kg/day); (ii) L-DOPA (6 mg/kg/day) i.p.; (iii) KW-6002 plus L-DOPA (same doses as above) or (iv) vehicle. Chronic treatment with KW-6002-only produced a significant relief of motor disability in the rotarod test in the absence of any abnormal involuntary movements. Combined treatment with L-DOPA and KW-6002 improved rotarod performance to a significantly higher degree than did each of the two drugs alone. However, this combined treatment induced dyskinesia to about the same degree as did L-DOPA alone. In situ hybridization histochemistry showed that KW-6002 treatment alone caused an approximately 20% reduction in the striatal levels of preproenkephalin mRNA, whereas neither the coadministration of KW-6002 and L-DOPA nor L-DOPA alone significantly altered the expression of this transcript in the dopamine-denervated striatum. Either alone or in combination with L-DOPA, KW-6002 did not have any modulatory effect on prodynorphin mRNA expression or FosB/DeltaFosB-like immunoreactivity in the dopamine-denervated striatum. These results show that monotreatment with an adenosine A2a receptor antagonist can relieve motor disability without inducing behavioural and cellular signs of dyskinesia in rats with 6-hydroxydopamine lesions. Cotreatment with KW-6002 and L-DOPA potentiates the therapeutic effect but not the dyskinesiogenic potential of the latter drug.

Time course of striatal DeltaFosB-like immunoreactivity and prodynorphin mRNA levels after discontinuation of chronic dopaminomimetic treatment

DeltaFosB-like proteins are particularly stable transcription factors that accumulate in the brain in response to chronic perturbations. In this study we have compared the time-course of striatal FosB/DeltaFosB-like immunoreactivity and prodynorphin mRNA expression after discontinuation of chronic cocaine treatment to intact rats and chronic L-DOPA treatment to unilaterally 6-hydroxydopamine (6-OHDA) lesioned rats. The animals were killed between 3 h and 16 days after the last drug injection. In both treatment paradigms, the drug-induced FosB/DeltaFosB immunoreactivity remained significantly elevated in the caudate putamen even at the longest withdrawal period examined. The concomitant upregulation of prodynorphin mRNA, a target of DeltaFosB, paralleled the time-course of DeltaFosB-like immunoreactivity in the 6-OHDA-lesion/L-DOPA model, but was more transient in animals treated with cocaine. These results suggest that DeltaFosB-like proteins have exceptional in vivo stability. In the dopamine-denervated striatum, these proteins may exert sustained effects on the expression of their target genes long after discontinuation of L-DOPA pharmacotherapy.

Both short- and long-acting D-1/D-2 dopamine agonists induce less dyskinesia than L-DOPA in the MPTP-lesioned common marmoset (Callithrix jacchus)

The current concept of dyskinesia is that pulsatile stimulation of D-1 or D-2 receptors by L-DOPA or short-acting dopamine agonists is more likely to induce dyskinesia compared to long-acting drugs producing more continuous receptor stimulation. We now investigate the ability of two mixed D-1/D-2 agonists, namely pergolide (long-acting) and apomorphine (short-acting), to induce dyskinesia in drug-nai;ve MPTP-lesioned primates, compared to L-DOPA. Adult common marmosets (Callithrix jacchus) were lesioned with MPTP (2 mg/kg/day sc for 5 days) and subsequently treated with equieffective antiparkinsonian doses of L-DOPA, apomorphine, or pergolide for 28 days. L-DOPA, apomorphine, and pergolide reversed the MPTP-induced motor deficits to the same degree with no difference in peak response. L-DOPA and apomorphine had a rapid onset of action and short duration of effect producing a pulsatile motor response, while pergolide had a slow onset and long-lasting activity producing a continuous profile of motor stimulation. L-DOPA rapidly induced dyskinesia that increased markedly in severity and frequency over the course of the study, impairing normal motor activity by day 20. Dyskinesia in animals treated with pergolide or apomorphine increased steadily, reaching mild to moderate severity but remaining significantly less marked than that produced by L-DOPA. There was no difference in the intensity of dyskinesia produced by apomorphine and pergolide. These data suggest that factors other than duration of drug action may be important in the induction of dyskinesia but support the use of dopamine agonists in early Parkinson's disease, as a means of delaying L-DOPA therapy and reducing the risk of developing dyskinesia.

Acute and repeated treatment with L-DOPA increase c-jun expression in the 6-hydroxydopamine-lesioned forebrain of rats and common marmosets

L-DOPA was acutely or repeatedly administered to rats and common marmosets (Callithrix jacchus) with unilateral 6-hydroxydopamine (6-OHDA) denervation of the dopamine inputs to the forebrain. Using in situ hybridization it was found that L-DOPA-treated animals exhibited a pronounced induction in the gene expression of both c-jun and c-fos in striatum and cerebral cortex restricted to the dopamine-depleted hemisphere. In contrast, acute treatment with cocaine induced c-fos mRNA, but not c-jun mRNA, in the striatum of normal animals. These data suggest that dopamine denervation leads to neurochemical adaptations which enables L-DOPA to induce a sustained gene expression of c-jun. Such aberrant gene regulation may underlie the development of L-DOPA-induced movement disorders which are commonly found in patients with Parkinson's disease.

Increases in striatal preproenkephalin gene expression are associated with nigrostriatal damage but not L-DOPA-induced dyskinesias in the squirrel monkey

Changes in preproenkephalin expression in the caudate and putamen have been linked to the development of L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias in primate models of Parkinson's disease, although not all investigators have been able to confirm this association. Because nigrostriatal damage per se is associated with increases in striatal preproenkephalin mRNA levels, it is difficult to know if changes in transcript levels are a result of lesioning or concurrent L-DOPA treatment and resulting dyskinesias. To circumvent these difficulties, we measured striatal preproenkephalin mRNA levels in monkeys with L-DOPA-induced dyskinesias both with and without lesions of the nigrostriatal system. The latter model is not confounded by morphological and biochemical changes resulting from nigrostriatal damage. Monkeys were gavaged with L-DOPA (15 mg/kg) twice daily for a 2-week period and killed 3 days after treatment. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment alone resulted in an increase in preproenkephalin mRNA levels as previously shown. However, striatal transcript levels were similarly elevated in dyskinetic MPTP-lesioned animals treated with L-DOPA. In unlesioned animals, preproenkephalin mRNA levels were also similar in control and L-DOPA-treated dyskinetic monkeys. Because drug-induced changes in mRNA may not be sustained for a prolonged period after treatment, a second series of experiments were done in which animals were killed 3-4 h after the last dose of L-DOPA, but the results were similar to those obtained after 3 days. These data show that, while elevations in striatal preproenkephalin mRNA levels are associated with nigrostriatal damage, they are not linked to the development of L-DOPA-induced dyskinesias. These results thus question the importance of preproenkephalin mRNA in the pathogenesis of this disabling complication of L-DOPA therapy in Parkinson's disease.

Use of the dopamine agonist cabergoline in the treatment of movement disorders

Cabergoline is an ergot-derived dopamine agonist used in the treatment of Parkinson's disease (PD). Both ergot and non-ergot-derived dopamine agonists directly stimulate dopamine receptors, unlike levodopa, which must undergo presynaptic breakdown to dopamine beforehand. Cabergoline has the longest half-life of the dopamine agonists currently available and is effective when given once-daily. It has been proposed that therapy with cabergoline may mimic physiological dopaminergic stimulation in PD by providing striatal intrasynaptic dopamine replacement. Its long half-life is likely to result in sustained rather than pulsatile dopaminergic stimulation, the preferred manner of treating PD. Placebo-controlled trials using cabergoline as an adjunctive therapy in PD have shown that it significantly reduces 'off' time, improves motor function and reduces levodopa requirements. Cabergoline has been shown to be as effective as other dopamine agonists in improving motor function as monotherapy in early PD, and a 5-year levodopa-controlled study indicates the superiority of cabergoline over levodopa in reducing dyskinesias. The efficacy of cabergoline in PD patients with nocturnal disabilities, restless leg syndrome and augmentation has also been demonstrated. Audits of the clinical efficacy of cabergoline indicate that it is well-tolerated and has an acceptable side effect profile.

Spatial and temporal profile of haloperidol-induced immediate-early gene expression and phosphoCREB binding in the dorsal and ventral striatum of amphetamine-sensitized rats

To determine if D(2) dopamine receptor-mediated nuclear signaling is altered during the development of amphetamine sensitization, we examined the expression of immediate-early gene (IEG) products, Fos, Jun, and Fos-related antigen (FRA), in both controls and amphetamine-sensitized rats after a challenge with the D(2) antagonist haloperidol. When chronic saline- or amphetamine (5 mg/kg, i.p. for 14 days)-treated rats were challenged with 2 mg/kg haloperidol at withdrawal day 3 (w3), more 35-kDa FRA was induced in the ventral striatum of the control group than in the amphetamine-treated rats. In contrast, more Jun and 35-kDa FRA were expressed in the ventral striatum of the amphetamine-treated group than in the controls when haloperidol was given at w10. Topographical analyses indicate that the decrease in FRA immunoreactive neuronal density in amphetamine-treated rats at w3 were located in the dorsolateral caudate/putamen and the nucleus accumbens shell and core subregions. Conversely, the increase in Jun-immunoreactive neurons in amphetamine-treated rats at w10 was observed in the dorsolateral caudate/putamen; in the case of the FRAs, the increase was observed in the nucleus accumbens shell. In addition, the time-dependent profile of IEG expression paralleled the activation of an upstream regulator, cAMP-response element binding protein, in the ventral striatum after haloperidol treatment. These neurochemical changes may be associated with behavioral plasticity, since amphetamine-treated rats displayed a lower amount of locomotor activity when exposed to a novel environment at w3, but had recovered at w10. Overall, the current study reveals that there is a distinct temporal and spatial profile of haloperidol-induced IEG expression and/or CREB phosphorylation in amphetamine-treated rats, suggesting that there is a critical transition between the early and late withdrawal periods.

Levodopa response motor complications--GABA receptors and preproenkephalin expression in human brain

Post-mortem studies in human brain of patients with Parkinson's disease have greatly contributed to our understanding of the disease. However, few human brain studies have focused on levodopa-induced dyskinesias, which considerably limit the beneficial effect of levodopa (LD) in the treatment of Parkinson's disease. We have taken advantage of the fact that some patients develop dyskinesias and other do not to compare biochemical markers between them. In post-mortem samples from LD-treated parkinsonian patients, increased preproenkephalin expression in the putamen and increased GABA(A) receptors content in the internal globus pallidus (GPi) are found in dyskinetic parkinsonian patients compared to non-dyskinetic patients. These data are consistent with previous observations in MPTP monkeys developing dyskinesias following LD or dopamine agonist treatment. This combination of data in an animal model and in humans strongly suggests that increased enkephalinergic activity in the putamen and increased sensitivity of GABA(A) receptors in the GPi are implicated in the pathogenesis of LD-induced dyskinesias in Parkinson's disease.

Repeated ventral tegmental area amphetamine administration alters dopamine D1 receptor signaling in the nucleus accumbens

Neuroadaptations of the mesoaccumbens dopamine (DA) system likely underlie the emergence of locomotor sensitization following the repeated intermittent systemic administration of amphetamine (AMPH). In the nucleus accumbens (NAc), such neuroadaptations include enhanced DA overflow in response to a subsequent AMPH challenge as well as increased sensitivity to the inhibitory effects of D1 DA receptor (D1R) activation and an altered profile of D1R-dependent induction of immediate early genes (IEGs). Previous results indicate that AMPH acts in the ventral tegmental area (VTA) to initiate those changes leading to sensitization of the locomotor activity and NAc DA overflow produced by systemic administration of this drug. These observations are intriguing, given that acute infusion of AMPH into the VTA does not stimulate locomotor activity or, as we report presently, increase extracellular NAc DA concentrations. Two experiments, therefore, assessed the ability of repeated VTA AMPH to produce adaptations in D1R signaling in the NAc. Rats were administered three bilateral VTA infusions of saline or AMPH (2.5 microg/0.5 microl/side, one every third day). In the first experiment, in vivo extracellular electrophysiological recordings revealed that previous exposure to VTA AMPH enhanced the sensitivity of NAc neurons to the inhibitory effects of iontophoretic application of the D1R agonist SKF 38393. This effect was observed early (2-3 days) and at 1 month of withdrawal, but not after 2 months. Similarly, in the second experiment it was found that the D1R-dependent induction by AMPH of Fos, FosB, and JunB, but not NGFI-A, in the NAc was enhanced in rats exposed 1 week earlier to repeated VTA AMPH. These findings indicate that repeated VTA AMPH administration initiates relatively long-lasting adaptations in D1R signaling in the NAc that may, together with presynaptic adaptations affecting DA overflow, contribute to the expression of locomotor sensitization by this drug.

Animal models of neurological deficits: how relevant is the rat?

Animal models of neurological deficits are essential for the assessment of new therapeutic options. It has been suggested that rats are not as appropriate as primates for the symptomatic modelling of disease, but a large body of data argues against this view. Comparative analyses of movements in rats and primates show homology of many motor patterns across species. Advances have been made in identifying rat equivalents of akinesia, tremor, postural deficits and dyskinesia, which are relevant to Parkinson's disease. Rat models of hemiplegia, neglect and tactile extinction are useful in assessing the outcome of ischaemic or traumatic brain injury, and in monitoring the effects of therapeutic interventions. Studies in rodents that emphasize careful behavioural analysis should continue to be developed as effective and inexpensive models that complement studies in primates.

Increase of preproenkephalin mRNA levels in the putamen of Parkinson disease patients with levodopa-induced dyskinesias

The expression of preproenkephalin messenger RNA was studied in the brain of Parkinson disease (PD) patients using in situ hybridization. All these patients were treated with levodopa (LD) and the development of motor complications was recorded. Eleven normal controls and 14 PD patients were used, of which 4 developed dyskinesias, 3 developed wearing-off, 3 developed both dyskinesias and wearing-off, and 4 developed no adverse effect following dopaminomimetic therapy. Nigrostriatal denervation was similar between the subgroups of PD patients as assessed using 125I-RTI-specific binding to the dopamine transporter and measures of catecholamine concentrations by HPLC. A significant increase of preproenkephalin messenger RNA levels was observed in the lateral putamen of dyskinetic patients in comparison to controls (+210%; p < 0.01) and in comparison to nondyskinetic patients (+112%; p < 0.05). No change was observed in medial parts of the putamen or in the caudate nucleus. No relationship between preproenkephalin messenger RNA levels and other clinical variables such as development of wearing-off, age of death, duration of disease, or duration of LD therapy was found. These findings suggest that increase synthesis of preproenkephalin in the medium spiny output neurons of the striatopallidal pathway play a role in the development of dyskinesias following long-term LD therapy in Parkinson disease.

cAMP response element-binding protein is required for dopamine-dependent gene expression in the intact but not the dopamine-denervated striatum

The cAMP response element-binding protein (CREB) is believed to play a pivotal role in dopamine (DA) receptor-mediated nuclear signaling and neuroplasticity. Here we demonstrate that the significance of CREB for gene expression depends on the experimental paradigm. We compared the role of CREB in two different but related models: l-DOPA administration to unilaterally 6-hydroxydopamine lesioned rats, and cocaine administration to neurologically intact animals. Antisense technology was used to produce a local knockdown of CREB in the lateral caudate-putamen, a region that mediates the dyskinetic or stereotypic manifestations associated with l-DOPA or cocaine treatment, respectively. In intact rats, CREB antisense reduced both basal and cocaine-induced expression of c-Fos, FosB/DeltaFosB, and prodynorphin mRNA. In the DA-denervated striatum, CREB was not required for l-DOPA to induce these gene products, nor did CREB contribute considerably to DNA binding activity at cAMP responsive elements (CREs) and CRE-like enhancers. DeltaFosB-related proteins and JunD were the main contributors to both CRE and AP-1 DNA-protein complexes in l-DOPA-treated animals. In behavioral studies, intrastriatal CREB knockdown caused enhanced activity scores in intact control animals and exacerbated the dyskinetic effects of acute l-DOPA treatment in 6-OHDA-lesioned animals. These data demonstrate that CREB is not required for the development of l-DOPA-induced dyskinesia in hemiparkinsonian rats. Moreover, our results reveal an unexpected alteration of nuclear signaling mechanisms in the parkinsonian striatum treated with l-DOPA, where AP-1 transcription factors appear to supersede CREB in the activation of CRE-containing genes.

Pharmacological validation of behavioural measures of akinesia and dyskinesia in a rat model of Parkinson's disease

In an attempt to define clinically relevant models of akinesia and dyskinesia in 6-hydroxydopamine (6-OHDA)-lesioned rats, we have examined the effects of drugs with high (L-DOPA) vs. low (bromocriptine) dyskinesiogenic potential in Parkinson's disease on three types of motor performance, namely: (i) abnormal involuntary movements (AIMs) (ii) rotational behaviour, and (iii) spontaneous forelimb use (cylinder test). Rats with unilateral 6-OHDA lesions received single daily i.p. injections of L-DOPA or bromocriptine at therapeutic doses. During 3 weeks of treatment, L-DOPA but not bromocriptine induced increasingly severe AIMs affecting the limb, trunk and orofacial region. Rotational behaviour was induced to a much higher extent by bromocriptine than L-DOPA. In the cylinder test, the two drugs initially improved the performance of the parkinsonian limb to a similar extent. However, L-DOPA-treated animals showed declining levels of performance in this test because the drug-induced AIMs interfered with physiological limb use, and gradually replaced all normal motor activities. L-DOPA-induced axial, limb and orolingual AIM scores were significantly reduced by the acute administration of compounds that have antidyskinetic efficacy in parkinsonian patients and/or nonhuman primates (-91%, yohimbine 10 mg/kg; -19%, naloxone 4-8 mg/kg; -37%, 5-methoxy 5-N,N-dimethyl-tryptamine 2 mg/kg; -30%, clozapine 8 mg/kg; -50%, amantadine 40 mg/kg). L-DOPA-induced rotation was, however, not affected. The present results demonstrate that 6-OHDA-lesioned rats do exhibit motor deficits that share essential functional similarities with parkinsonian akinesia or dyskinesia. Such deficits can be quantified using novel and relatively simple testing procedures, whereas rotometry cannot discriminate between dyskinetic and antiakinetic effects of antiparkinsonian treatments.