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

Drug dependence as a disorder of neural plasticity: focus on dopamine and glutamate

Drug addiction, as a disease, has grown to reach the level of a social illness. Psychostimulants, opiates, alcohol, nicotine and cannabis abuse affects millions worldwide and virtually all classes of modern society. In spite of the enormous proportions of its spread, intimate neurobiological mechanisms leading to distintictive features of this pathological status, such as craving for the abused substance and loss of control over intake, remain largely obscure and pharmacotherapies sadly unsatisfactory. In the last decade, preclinical and clinical research in this field has made great progress to improve our understanding of the brain mechanisms which form the basis of this illness. The review of recent literature, which represents the focus of the present paper, leads to the emerging consensus that an alteration of physiological mechanisms of neural plasticity within the brain dopamine and glutamate systems may underlie some of the behavioral abnormalities occurring during the dependence cycle. In particular, a reduction of dopamine neuronal activity and glutamate neurotransmission at the level of the ventrotegmental area, after withdrawal from chronic administration of drugs of abuse, may work in concert with alterations in other forebrain areas, such as the nucleus accumbens and the amygdaloid complex. In addition, following prolonged periods of abstinence, even after somatic withdrawal signs have vanished, responsiveness of these systems to drugs of abuse remains abnormal. This suggests that these two neurotransmitters may play a substantial role in the long-lasting, enduring changes typical of the addictive process and may represent ideal targets for pharmacological intervention aimed at normalizing forms of neural plasticity impaired after chronic drug intake.

Persistent changes in striatal gene expression induced by long-term L-DOPA treatment in a rat model of Parkinson's disease

Current knowledge of the molecular changes induced by dopamine denervation and subsequent treatment with L-DOPA is based on studies performed on relatively acute and young animal models of parkinsonism. It is highly warranted to ask how well these models simulate the state of chronic denervation and sustained L-DOPA pharmacotherapy which are typical of advanced Parkinson's disease. This study investigates the effects of time postdenervation and L-dopa treatment duration on the striatal expression of opioid precursor mRNAs and FosB/DeltaFosB-related proteins. Unilaterally 6-hydroxydopamine-lesioned rats were treated with therapeutical doses of L-DOPA for one year (long-term group) or a few weeks (short-term group). Age-matched lesioned rats received injections of vehicle or bromocriptine, an antiparkinsonian compound which does not produce dyskinesia when administered de novo. The lesion-induced up-regulation of preproenkephalin mRNA expression persisted at more than one year postlesion, and was unaffected by the pharmacological treatments applied. L-DOPA, but not bromocriptine, induced high striatal levels of FosB/DeltaFosB immunoreactivity and prodynorphin mRNA, and these did not differ between short-term and long-term L-DOPA-treated rats. The present data provide the first demonstration that L-DOPA maintains high striatal levels of fosB and prodynorphin gene expression during a prolonged course of treatment, which simulates the clinical practice in Parkinson's disease more closely than the short-treatment paradigms studied thus far.

Enhancement of laminar FosB expression in frontal cortex of rats receiving long chronic clozapine administration

The frontal cortex (FrC) and cingulate cortex (CgC) are critical sites for normal cognitive function, as well as cognitive dysfunction in schizophrenia. Thus, modulation of synaptic transmission within these cortical areas may, in part, account for the therapeutic actions of antipsychotic drugs such as haloperidol and clozapine. FosB and DeltaFosB are immediate-early gene (IEG) products sensitive to changes in response to chronic neuroleptic drug administration. We quantitatively examine whether there are light microscopic regional and/or laminar variations in FosB or DeltaFosB in the FrC or CgC of normal adult rats, or animals receiving 6 months administration of either drinking water clozapine, or depot haloperidol. Only animals receiving chronic haloperidol developed vacuous chewing movements, the equivalent of tardive dyskinesia in humans. In control animals, the deep and superficial layers of the FrC showed a higher area density of FosB, but not DeltaFosB immunoreactive cells than the medial layers of FrC or any of the CgC layers. In animals receiving clozapine, but not haloperidol there was increase in the area density of FosB immunoreactive neurons in all FrC layers, but the major increase occurs in medial layers. These findings suggest that FosB expression identifies those FrC neurons that are most active during normal waking behaviors and are further activated following chronic administration of atypical neuroleptics without motor side effects. The results also indicate that the actions of clozapine are attributed in large part to modulation of the output of frontal cortical pyramidal neurons residing in the medial layers.

L-DOPA produces strong induction of c-fos messenger RNA in dopamine-denervated cortical and striatal areas of the common marmoset

Common marmosets (Callithrix jacchus) with near-complete unilateral 6-hydroxydopamine denervation of the dopaminergic input received a single injection of saline or L-DOPA (15mg/kg plus 6.25mg/kg benserazide). Using in situ hybridization, the effects of these treatments on c-fos messenger RNA expression in the cerebral cortex, the striatal complex and the external layer of the pallidum were studied. Moreover, receptor autoradiography was used to determine the levels of dopamine D(1) and D(2) receptors in these areas. In the cerebral cortex, animals treated with L-DOPA displayed a high expression of c-fos messenger RNA restricted to the dopamine-denervated hemisphere. No changes in the levels of cortical D(1) and D(2) receptors were found in the dopamine-denervated hemisphere. L-DOPA treatment also induced a strong expression of c-fos messenger RNA in the striatal complex in the dopamine-denervated hemisphere. The levels of striatal D(2), but not D(1), receptors were increased in the dopamine-denervated hemisphere. In the external pallidum, the major terminal region for D(2) dopamine receptor-containing striatal projection neurons, L-DOPA treatment induced c-fos messenger RNA expression in both the intact and the dopamine-denervated hemispheres.Thus, using c-fos messenger RNA as a biochemical marker of postsynaptic neuronal activation, these results provide evidence that near-complete dopamine depletion causes a profound supersensitization to L-DOPA treatment in the cerebral cortex and in the striatal complex, but not in the external layer of the pallidum, of the primate brain. The cortical response may be unique to the primate brain, but c-fos messenger RNA activation within the striatum has also been reported in the rodent. The effects of L-DOPA probably depend both on a direct activation of supersensitized dopamine receptors by dopamine produced in the few remaining, but hyperactive, dopaminergic nerve terminals and in serotonergic nerve terminals, as well as on indirect actions of L-DOPA related to activation of circuitries connecting cerebral cortex and basal ganglia structures. These results provide novel information on the mechanisms underlying L-DOPA's action in the cerebral cortex, striatum and external pallidum in a primate model of Parkinson's disease.

FosB in rat striatum: normal regional distribution and enhanced expression after 6-month haloperidol administration

Subcortical motor nuclei show differential expression of FosB immediate early gene products and specifically deltaFosB after short (8, 19, or 21 days) chronic exposure to typical and atypical neuroleptics represented by haloperidol and clozapine, respectively. We quantitatively examined whether there are light microscopic regional variations in area density of FosB or the truncated deltaFosB in several motor-related nuclei of adult rats receiving vehicle or long chronic (6 months) administration of either depot haloperidol or clozapine in their drinking water. In control animals the dorsomedial and ventromedial caudate-putamen nucleus (CPN) had a significantly higher density of FosB-immunoreactive cells than the dorsolateral and ventrolateral regions. The nucleus accumbens (NAc) core also serving motor functions had a higher basal expression than the limbic shell region in control animals. The mediolateral gradient in area density of FosB-labeled cells was maintained in animals receiving either haloperidol or clozapine. In animals receiving haloperidol, but not clozapine, however, there was a regionally selective increase in the area density of only FosB-immunoreactive neurons in the dorsolateral and ventrolateral CPN and in both the core and shell of the NAc. Only the animals receiving chronic haloperidol showed vacuous chewing movements, the animal equivalent of tardive dyskinesia in humans. Our results suggest that, whereas the medial striatal neurons are activated under basal conditions, long chronic haloperidol induced FosB expression more exclusively in the lateral CPN and NAc core, implicating these regions specifically in the motor side effects of this drug.

deltaFosB: a molecular switch underlying long-term neural plasticity

Numerous chronic perturbations have been shown to induce highly stable isoforms of the transcription factor deltaFosB in the brain in a region-specific manner. This review examines the functional consequences of the induction of deltaFosB in particular neuronal populations as well as its possible role in behavioral abnormalities such as drug addiction and movement disorders.

Possible role for the FosB/JunD AP-1 transcription factor complex in glutamate-mediated excitotoxicity in cultured cerebellar granule cells

The potent excitatory and neurotoxic actions of glutamate are known to influence the expression of a variety of genes, including those encoding the AP-1 transcription factor, which comprises proteins belonging to the Fos and Jun families. However, the precise role of Fos- and Jun-like transcription factors in these events remains elusive. Here we demonstrate, using primary cultures of mouse brain cerebellar granule cells as an in vitro model system, a possible involvement of the FosB/JunD heterodimer in excitotoxicity. Granule cells were grown for either 2 or 7 days in vitro (DIV) before exposure to varying concentrations (1-3000 microM) of the excitotoxin glutamate. In 7-DIV cells, glutamate induced a concentration-dependent neuronal death, whereas, in 2-DIV cells, no glutamate-induced neuronal damage was seen. We were particularly interested in comparing the protein composition of the AP-1 transcription factor complex in cells exposed to excitotoxic and to nontoxic conditions. AP-1 DNA binding activity was demonstrated by gel shift analysis in nuclear extracts derived from 7-DIV cells following exposure to either a nontoxic (10 microM) or an excitotoxic (250 microM) dose of glutamate and was similarly observed in extracts of 2-DIV cells exposed to the same levels of glutamate. Gel supershift analysis using antibodies against the different Fos and Jun family members allowed differentiation between AP-1 DNA binding in nuclear extracts as a function of both 1) viability status and 2) the stage of development. Of major significance was the finding that FosB could be detected as a component of AP-1 in 7-DIV cells only under excitotoxic conditions, whereas c-Fos, Fra-2, and JunD proteins were detectable under both excitotoxic and nontoxic conditions in cells of this age. In 2-DIV cells (in which glutamate is nontoxic), AP-1 comprised combinations of only Fra-1, Fra-2, c-Jun, and JunD. Because Fos family members are unable to form homodimers, this finding raises the possibility that the FosB/JunD heterodimer may have special significance in the mechanism of excitotoxic neuronal death.

Contrasting patterns and cellular specificity of transcriptional regulation of the nuclear receptor nerve growth factor-inducible B by haloperidol and clozapine in the rat forebrain

This study was designed to investigate the possible involvement of members of the nuclear receptor family of transcription factors in the effects of antipsychotic drugs used in the treatment of schizophrenia. We have identified, using RT-PCR screening, an important modulation of nerve growth factor-inducible B (NGFI-B) mRNA levels by typical and atypical neuroleptics in the rat forebrain. NGFI-B, a member of the nuclear receptor family, can be observed in target structures of dopaminergic pathways. Using in situ hybridization, we also demonstrate that typical and atypical antipsychotics induced contrasting patterns of expression of NGFI-B after both acute and chronic administration. An acute treatment with clozapine or haloperidol induces high NGFI-B mRNA levels in the prefrontal and cingulate cortices and in the nucleus accumbens shell. However, haloperidol, but not clozapine, dramatically increases NGFI-B expression in the dorsolateral striatum. In contrast, chronic treatment with clozapine reduces NGFI-B expression below basal levels in the rat forebrain, whereas haloperidol still induces high NGFI-B mRNA levels in the dorsolateral striatum. Finally, using a double in situ hybridization technique, we show that acute administration of both neuroleptics increases NGFI-B expression in neurotensin-containing neurons in the nucleus accumbens shell, whereas the effects of haloperidol in the dorsolateral striatum are mainly observed in enkephalin-containing neurons. These results are the first demonstration that members of the nuclear receptor family of transcription factors could play an important role in the effects of antipsychotic drugs.

Dopamine-receptor stimulation: biobehavioral and biochemical consequences

The MPTP monkey is a well-characterized animal model of parkinsonism and provides an exceptional tool for the study of dyskinesias induced by dopamine-like agents. Several such agents have been tested during the past 15 years, and it has been found that the duration of action of these compounds is the most reliable variable with which to predict their dyskinesiogenic profile. It is proposed that L-dopa-induced dyskinesias represent a form of pathological learning caused by chronic pulsatile (nonphysiological) stimulation of dopamine receptors, which activates a cascade of molecular and biochemical events. These events include defective regulation of Fos proteins that belong to the deltaFosB family, increased expression of neuropeptides, and defective GABA- and glutamate-mediated neurotransmission in the output structures of the basal ganglia.

Continuous dopamine-receptor stimulation in early Parkinson's disease

Chronic L-dopa therapy is associated with the development of motor complications in the majority of Parkinson's disease (PD) patients. Although the precise mechanism responsible for these events is not known, increasing laboratory and clinical evidence points to a sequence of events that is initiated by abnormal pulsatile stimulation of dopamine receptors by the intermittent administration of agents with short half-lives such as L-dopa. Initiating therapy with a long-acting dopamine agonist has been shown to delay the onset and reduce the severity of motor complications in MPTP monkeys and PD patients. Administering L-dopa with a catechol-O-methyltransferase (COMT) inhibitor to block its peripheral metabolism increases its plasma half-life and might have a similar effect. Thus, a rational strategy for treating PD would be to initiate therapy with a long-acting dopamine-receptor agonist and supplement at the appropriate time with L-dopa combined with a COMT inhibitor.

Effects of oligonucleotide antisense to dopamine D(1A) receptor messenger RNA in a rodent model of levodopa-induced dyskinesia

Dyskinesias are abnormal involuntary movements which develop as a side-effect of long-term treatment with levodopa in patients with Parkinson's disease. The pathophysiology underlying these dyskinesias remains unclear, although, it has been suggested that heightened activity of dopamine D(1) receptor-bearing striatonigral neurons may play a key role. Chronic pulsatile levodopa administration to hemiparkinsonian rats results in sensitization of rotational responses to apomorphine. This sensitization is thought to be analogous to levodopa-induced dyskinesias in humans. In these studies, we further clarify the role of the dopamine D(1A) receptor in this rodent model of levodopa-induced dyskinesias using an in vivo oligonucleotide antisense approach. Hemiparkinsonian rats received twice daily injections of levodopa for three weeks followed by intrastriatal infusion of dopamine D(1A) receptor antisense (7nmol/day, three days), a scrambled missense control sequence, or saline. Those animals treated with antisense displayed significantly fewer apomorphine-induced rotations than saline- or missense-treated controls.By reducing dopamine D(1A) receptor expression, we were able to attenuate sensitization of the response to apomorphine resulting from chronic pulsatile levodopa treatment. Thus, the dopamine D(1A) receptor appears to play a significant role in levodopa-induced dyskinesias and warrants further examination. These findings may have important implications for the development of selective treatment strategies designed to alleviate parkinsonian symptoms, while minimizing motor complications.

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.

Fos-related antigen 2: potential mediator of the transcriptional activation in rat adrenal medulla evoked by repeated immobilization stress

The precise mechanisms by which beneficial responses to acute stress are transformed into long-term pathological effects of chronic stress are largely unknown. Western blot analyses revealed that members of the AP1 transcription factor family are differentially regulated by single and repeated stress in the rat adrenal medulla, suggesting distinct roles in establishing stress-induced patterns of gene expression in this tissue. The induction of c-fos was transient, whereas marked elevation of long-lasting Fos-related antigens, including Fra2, was observed after repeated immobilization. We investigated DNA protein interactions at the AP1-like promoter elements of two stress-responsive genes, tyrosine hydroxylase and dopamine beta-hydroxylase. Increased DNA-binding activity was displayed in adrenomedullary extract from repeatedly stressed rats, which was predominantly composed of c-Jun- and Fra2-containing dimers. The induction of Fra2 and increased AP1-like binding activity was reflected in sustained transcriptional activation of tyrosine hydroxylase and dopamine beta-hydroxylase genes after repeated episodes of stress. The functional link between Fra2 and regulation of tyrosine hydroxylase and dopamine beta-hydroxylase transcription was confirmed in PC12 cells coexpressing this factor and the corresponding promoter-reporter gene constructs. These studies emphasize the potential importance of stress-evoked increases in the expression of the Fra2 gene for in vivo adaptations of the adrenal catecholamine producing system.

Chronic dopaminergic signaling in the basal ganglia: a damage perspective on kinases and fos-related antigens

Abstract Specific protein phosphorylation pathways have been shown to play a role in cellular adaptation responses underlying addiction to psychostimulants such as methamphetamine and cocaine. Transcriptional regulation through fos-related antigens constitutes one element through which these dopaminergic agonists exert their persistent actions. In addition to their addictive properties, amphetamines are known to damage dopaminergic nerve terminals. Although not widely appreciated, protein phosphorylation cascades and fos-related antigens also may play a role in the neurotoxic actions of substituted amphetamines such as methamphetamine. Here we document the involvement of the dopaminoceptive phosphoprotein, DARPP-32, the fos-related antigen, FRA-2, and the growth associated protein kinase, MAP kinase, in the neurotoxic action of known dopaminergic neurotoxicants, including methamphetamine. The addictive and neurotoxic properties of psychostimulants may share some molecular signaling mechanisms.

Induction of c-fos-like and fosB-like immunoreactivity reveals forebrain neuronal populations involved differentially in pup-mediated maternal behavior in juvenile and adult rats

Juvenile rats can exhibit maternal behavior after being exposed continuously to rat pups, a process called sensitization. Maternal behavior in juveniles is robust and is similar to adult maternal behavior (Mayer and Rosenblatt [1979] Dev. Psychobiol. 12:407-424; Gray and Chesley [684] J. Comp. Psychol. 98:91-99). In this study, immunocytochemical detection of the protein products of two immediate-early genes, c-fos and fosB, was used as a tool to identify forebrain neuronal populations involved in the maternal behavior of 27-day-old juvenile rats compared with 60-day-old adults. To sensitize them, rats were exposed continuously to foster pups. Once they were maternal, they were isolated from pups overnight, reexposed to pups for 2 hours, and then killed. Nonmaternal control animals also were isolated overnight and were either reexposed to pups for 2 hours or kept isolated from pups before killing. The lateral habenula (LH) was the only area in which both maternal juveniles and maternal adults had more c-Fos-immunoreactive (-Ir) neurons compared with controls. In maternal adults, the number of neurons that expressed c-Fos and FosB immunoreactivity increased in the medial preoptic area (MPO) and the ventral bed nucleus of the stria terminalis (BSTv), whereas the dorsal bed nucleus of the stria terminalis (BSTd) and the medial and cortical nuclei of the amygdala (MEA and COA, respectively) had increases only in the number of neurons that expressed c-Fos immunoreactivity. In contrast, juveniles, whether or not they were maternal, had the same number of c-Fos-IR and FosB-Ir neurons in all these areas. The adult-like increase in the number of c-Fos-Ir neurons found in maternal juveniles suggests that the juvenile LH participates in the neural circuit that supports maternal behavior in an adult-like manner. The lack of c-fos or fosB induction in the MPO, BSTv, BSTd, COA, or MEA of maternal juveniles compared with maternal adults may reflect the immaturity of these brain regions in juvenile rats. Exactly what this immaturity consists of and when the responses of these regions become adult-like remain to be determined.

Changes in the regional and compartmental distribution of FosB- and JunB-like immunoreactivity induced in the dopamine-denervated rat striatum by acute or chronic L-dopa treatment

This study was carried out in order to examine the effects of acute or chronic L-DOPA treatment on striatally expressed FosB- and JunB-like proteins in a rat model of Parkinson's disease. Rats with a unilateral, near-total 6-hydroxydopamine lesion of the ascending mesostriatal projection received either an acute challenge or a one-week treatment with 10 mg/kg/day methyl L-DOPA (combined with 15 mg/mg benserazide), and were killed at either 3 h or two days post-injection. Both acute and chronic L-DOPA treatment caused a pronounced, persistent increase in the number of FosB-like immunoreactive cells in the dopamine-denervated striata (five- and seven-fold increase, respectively, above the levels found in lesioned but non-drug-treated controls), but the two treatment groups differed markedly with respect to both the average amount of staining per cell, which was two-fold larger in the chronic L-DOPA cases, and the anatomical distribution of the labeled cells. After an acute injection of L-DOPA, FosB-positive cells were distributed rather uniformly across all striatal subregions, whereas chronic L-DOPA treatment induced discrete clusters of strongly FosB-like immunoreactive cells within medial and central striatal subregions, as well as in a large, yet sharply defined portion of the lateral caudate-putamen. Strongly labeled cell clusters that appeared in the medial and central caudate-putamen were preferentially located within calbindin-poor, mu-opioid receptor-rich striosomes, whereas the lateral area displaying FosB activation encompassed both striosomal and matrix domains. In both the medial and the lateral striatum a near-total overlap was found between strongly FosB-like immunoreactive cell groups and areas showing pronounced dynorphin expression. NADPH-diaphorase-positive striatal interneurons did not express FosB-like immunoreactivity after a 6-hydroxydopamine lesion alone, a negligible proportion of them did after an acute L-DOPA challenge, but about 8% of these interneurons were FosB positive following chronic L-DOPA treatment. Like FosB, JunB was induced in the DA-denervated striatum by both acute and chronic L-DOPA treatment, and exhibited similar distribution patterns. However, JunB did not exhibit prolonged expression kinetics, and was somewhat down-regulated in the chronically compared with the acutely L-DOPA-treated rats. The present results show that L-DOPA administration produces a long-lasting increase in the levels of FosB-, but not JunB-like immunoreactivity in the dopamine-denervated striatum. More importantly, these data show that striatal induction of FosB- and JunB-like proteins by chronic L-DOPA treatment exhibits both regional and compartmental specificity.

Striatal fosB expression is causally linked with l-DOPA-induced abnormal involuntary movements and the associated upregulation of striatal prodynorphin mRNA in a rat model of Parkinson's disease

Rats with unilateral dopamine-denervating lesions sustained a 3-week treatment with a daily l-DOPA dose that is in the therapeutic range for Parkinson's disease. In most of the treated animals, chronic l-DOPA administration gradually induced abnormal involuntary movements affecting cranial, trunk, and limb muscles on the side of the body contralateral to the lesion. This effect was paralleled by an induction of FosB-like immunoreactive proteins in striatal subregions somatotopically related to the types of movements that had been elicited by l-DOPA. The induced proteins showed both regional and cellular colocalization with prodynorphin mRNA. Intrastriatal infusion of fosB antisense inhibited the development of dyskinetic movements that were related to the striatal subregion targeted and produced a local specific downregulation of prodynorphin mRNA. These data provide compelling evidence of a causal role for striatal fosB induction in the development of l-DOPA-induced dyskinesia in the rat and of a positive regulation of prodynorphin gene expression by FosB-related transcription factors.

Region-specific induction of deltaFosB by repeated administration of typical versus atypical antipsychotic drugs

Whereas acute administration of many types of stimuli induces c-Fos and related proteins in brain, recent work has shown that chronic perturbations cause the region-specific accumulation of novel Fos-like proteins of 35-37 kD. These proteins, termed chronic FRAs (Fos-related antigens), have recently been shown to be isoforms of DeltaFosB, which accumulate in brain due to their enhanced stability. In the present study, we sought to extend earlier findings that documented the effects of acute administration of antipsychotic drugs (APDs) on induction of Fos-like proteins by investigating the ability of typical and aytpical APDs, after chronic administration, to induce these DeltaFosB isoforms in several brain regions implicated in the clinical actions of these agents. By Western blotting we found that chronic administration of the typical APD, haloperidol, dramatically induces DeltaFosB in caudate-putamen (CP), a brain region associated with the extrapyramidal side effects of this drug. A smaller induction was seen in the nucleus accumbens (NAc) and prefrontal cortex (PFC), brain regions associated with the antipsychotic effects of the drug. In contrast, chronic administration of the prototype atypical APD clozapine failed to significantly increase levels of DeltaFosB in any of the three brain regions, and even tended to reduce DeltaFosB levels in the NAc. Two putative atypical APDs, risperidone and olanzapine, produced small but still significant increases in the levels of DeltaFosB in CP, but not NAc or PFC. Studies with selective receptor antagonists suggested that induction of DeltaFosB in CP and NAc is most dependent on antagonism of D2-D3 dopamine receptors, with antagonism of D1-like receptors most involved in the PFC. Immunohistochemical analysis confirmed the greater induction of DeltaFosB in CP by typical versus atypical APDs, with no significant induction seen in PFC with either class of APD. Together, these findings demonstrate that repeated administration of APDs results in the induction of long-lasting Fos-like transcription factors that could mediate some of the persistent and region-specific changes in brain function associated with chronic drug exposure. Synapse 33:118-128, 1999.

Rationale for use of dopamine agonists in Parkinson's disease: review of ergot derivatives

While dopamine agonists are still traditionally used as adjunct medications to improve performance and smooth out motor response complications in advanced levodopa-treated Parkinson's disease, they are increasingly used in monotherapy or early in combination with levodopa particularly in patients under 65 years of age. Long-term studies using bromocriptine showed efficacy in lowering the cumulative levodopa dose and reducing the early incidence of levodopa-related motor response complications. New dopamine agonists have recently shown efficacy as adjunct medications in short-term trials. While we now have more options to fit our individual patients' needs and tolerance, it is important to view the new agonists in the light of the results obtained with ergot derivatives. In this article, the rationale for use and efficacy profile of the ergolines are briefly reviewed.

DeltaFosB: a molecular mediator of long-term neural and behavioral plasticity

DeltaFosB, a member of the Fos family of transcription factors, is derived from the fosB gene via alternative splicing. Just as c-Fos and many other Fos family members are induced rapidly and transiently in specific brain regions in response to many types of acute perturbations, novel isoforms of DeltaFosB accumulate in a region-specific manner in brain uniquely in response to many types of chronic perturbations, including repeated administration of drugs of abuse or of antidepressant or antipsychotic treatments. Importantly, once induced, these DeltaFosB isoforms persist in brain for relatively long periods due to their extraordinary stability. Mice lacking the fosB gene show abnormal biochemical and behavioral responses to chronic administration of drugs of abuse or antidepressant treatments, consistent with an important role for DeltaFosB in mediating long-term adaptations in the brain. More definitive evidence to support this hypothesis has recently been provided by inducible transgenic mice, wherein biochemical and behavioral changes, which mimic the chronic drug-treated state, are seen upon overexpression of DeltaFosB in specific brain regions. This evolving work supports the view that DeltaFosB functions as a type of 'molecular switch' that gradually converts acute responses into relatively stable adaptations that underlie long-term neural and behavioral plasticity to repeated stimuli.

Dopamine agonist-mediated rotation in rats with unilateral nigrostriatal lesions is not dependent on net inhibitions of rate in basal ganglia output nuclei

Current models of basal ganglia function predict that dopamine agonist-induced motor activation is mediated by decreases in basal ganglia output. This study examines the relationship between dopamine agonist effects on firing rate in basal ganglia output nuclei and rotational behavior in rats with nigrostriatal lesions. Extracellular single-unit activity ipsilateral to the lesion was recorded in awake, locally-anesthetized rats. Separate rats were used for behavioral experiments. Low i.v. doses of D1 agonists (SKF 38393, SKF 81297, SKF 82958) were effective in producing rotation, yet did not change average firing rate in the substantia nigra pars reticulata or entopeduncular nucleus. At these doses, firing rate effects differed from neuron to neuron, and included increases, decreases, and no change. Higher i.v. doses of D1 agonists were effective in causing both rotation and a net decrease in rate of substantia nigra pars reticulata neurons. A low s.c. dose of the D1/D2 agonist apomorphine (0.05 mg/kg) produced both rotation and a robust average decrease in firing rate in the substantia nigra pars reticulata, yet the onset of the net firing rate decrease (at 13-16 min) was greatly delayed compared to the onset of rotation (at 3 min). Immunostaining for the immediate-early gene Fos indicated that a low i.v. dose of SKF 38393 (that produced rotation but not a net decrease in firing rate in basal ganglia output nuclei) induced Fos-like immunoreactivity in the striatum and subthalamic nucleus, suggesting an activation of both inhibitory and excitatory afferents to the substantia nigra and entopeduncular nucleus. In addition, D1 agonist-induced Fos expression in the striatum and subthalamic nucleus was equivalent in freely-moving and awake, locally-anesthetized rats. The results show that decreases in firing rate in basal ganglia output nuclei are not necessary for dopamine agonist-induced motor activation. Motor-activating actions of dopamine agonists may be mediated by firing rate decreases in a small subpopulation of output nucleus neurons, or may be mediated by other features of firing activity besides rate in these nuclei such as oscillatory firing pattern or interneuronal firing synchrony. Also, the results suggest that dopamine receptors in both the striatum and at extrastriatal sites (especially the subthalamic nucleus) are likely to be involved in dopamine agonist influences on firing rates in the substantia nigra pars reticulata and entopeduncular nucleus.

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.

Opposite tonic modulation of dopamine and adenosine on c-fos gene expression in striatopallidal neurons

The impulse flow-dependent dopamine release in the striatum was acutely blocked by unilateral lesion of the medial forebrain bundle with 6-hydroxydopamine. Within 45 min this disruption reduced the striatal extracellular dopamine levels by 80% as determined by in vivo voltammetry. A strong induction of c-fos messenger RNA was detected in the ipsilateral dorsolateral striatum 75 min after 6-hydroxydopamine injection by in situ hybridization. Double labelling demonstrates that this induction was confined to neurons expressing the dopamine D2 receptor messenger RNA. At this time-point, there were no changes in the striatal levels of either tyrosine hydroxylase immunoreactivity or dopamine D2 receptor messenger RNA. The c-fos messenger RNA expression induced by acute 6-hydroxydopamine injection was abolished by intraperitoneal pretreatment with the dopamine D2 receptor agonist, quinelorane (2 mg/kg) and strongly reduced by administration of the selective adenosine A2A receptor antagonist SCH-58261 (5 mg/kg). The results reported here show, by using a novel methodological approach, that an acute decrease of dopamine release causes an induction of c-fos messenger RNA in dopamine D2 receptor-containing striatopallidal neurons. This, together with previous findings, demonstrates that the c-fos gene expression is tonically inhibited by the impulse flow-dependent dopamine release via D2 receptors. In addition, this study provides evidence that endogenous adenosine, acting via adenosine A2A receptors, induces striatal c-fos messenger RNA when extracellular dopamine levels are strongly reduced. Thus endogenous dopamine and adenosine exert opposite effects on the activity of the D2-containing striatopallidal neurons.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Pattern of neuronal activation in rats with CHF after myocardial infarction

To identify neuronal populations possibly contributing to the sympathetic hyperactivity in rats with congestive heart failure (CHF) after myocardial infarction (MI), immunohistochemical detection of Fra-like immunoreactivity (Fra-LI) was used as a marker of long-term neuronal activation. In adult Wistar rats, 2 and 4 wk after left coronary artery ligation, left ventricular (LV) peak systolic pressure and LV end-diastolic pressure were measured, immediately followed by transcardial perfusion and removal of the heart and brain. The brains were processed using an antibody that recognizes Fos, FosB, Fra-1, and Fra-2 for the detection of Fra-LI and using an antibody that only recognizes Fos-like immunoreactivity (Fos-LI). At both 2 and 4 wk after large MI, LV peak systolic pressure was significantly decreased and LV end-diastolic pressure increased. At 2 wk post-MI or sham surgery, Fra-LI was observed in several areas of either group but was significantly higher in the MI versus the sham group in the magnocellular division of the paraventricular nucleus (PVN), supraoptic nucleus (SON), subfornical organ, and caudal part of the nucleus of the solitary tract. At 4 wk after large MI, Fra-LI was clearly detected in the parvocellular and magnocellular divisions of the PVN, SON, and locus ceruleus. Modest expression was noted in these nuclei in rats with small MI, whereas Fra-like positive immunoreactive neurons were barely detectable in the sham group 4 wk postsurgery. In these nuclei, the extent of expression of Fra-LI correlated significantly with the LV end-diastolic pressure. Fos-LI was only noted in the cerebral cortex. These results indicate clear activation of neurons as identified by Fra-LI in specific cardiovascular control centers in rats with CHF 2 and 4 wk post-MI.

Essential role of the fosB gene in molecular, cellular, and behavioral actions of chronic electroconvulsive seizures

The role of Fos-like transcription factors in neuronal and behavioral plasticity has remained elusive. Here we demonstrate that a Fos family member protein plays physiological roles in the neuronal, electrophysiological, and behavioral plasticity associated with repeated seizures. Repeated electroconvulsive seizures (ECS) induced isoforms of DeltaFosB in frontal cortex, an effect that was associated with increased levels of the NMDA receptor 1 (NMDAR1) glutamate receptor subunit. Induction of DeltaFosB and the upregulation of NMDAR1 occurred within the same neurons in superficial layers of neocortex. Activator protein-1 (AP-1) complexes composed of DeltaFosB were bound to a consensus AP-1 site in the 5'-promoter region of the NMDAR1 gene. The upregulation of NMDAR1 was absent in mice with a targeted disruption of the fosB gene. In addition, repeated ECS treatment caused progressively shorter motor seizures (tolerance) in both rats and wild-type mice, as well as reduced NMDA-induced inward currents in pyramidal neurons from superficial layers of the neocortex of wild-type mice. These behavioral and electrophysiological effects were also significantly attenuated in fosB mutant mice. These findings identify fosB gene products as transcription factors critical for molecular, electrophysiological, and behavioral adaptations to motor seizures.

Chronic activation of brain areas by high-sodium diet in Dahl salt-sensitive rats

To map changes in neuronal activity in the brains of Dahl salt-sensitive (Dahl S) vs. salt-resistant (Dahl R) rats by high-sodium diet, we used immunohistochemical detection of Fra-like proteins as a marker for long-term neuronal activation. Compared with Dahl R rats during regular sodium intake, Dahl S rats showed modestly higher expression of Fra-like immunoreactivity (Fra-LI) in the supraoptic nucleus, anterior hypothalamic area (AHA), central gray, and nucleus of solitary tract (NTS) at 5,6, and 9 wk of age but clearly elevated Fra-LI in the magnocellular part of the paraventricular nucleus (PVN) at 6 wk of age (but not at 5 and 9 wk). In the median preoptic nucleus (MnPO) Fra-LI was lower at 9 wk of age and no differences were observed in the parvocellular PVN and subfornical organ in Dahl S vs. Dahl R rats on regular sodium intake. Compared with Dahl S rats on a regular-sodium diet, Dahl S rats on a high-sodium diet from 4 to 9 wk of age had significantly increased blood pressure and experienced transient activation of magnocellular PVN and MnPO and virtually no changes in the activity of the parvocellular PVN, AHA, and NTS. In contrast, Dahl R rats showed marked activation in the magnocellular PVN after 1 and 2 wk on a high-sodium diet compared with Dahl R rats on a regular-sodium diet. The present study demonstrates that Dahl S rats show differential activation of brain areas participating in regulation of osmotic and cardiovascular homeostasis during development of sodium-sensitive hypertension.

Expression of c-fos, fos B, and egr-1 in the medial preoptic area and bed nucleus of the stria terminalis during maternal behavior in rats

The spatial and temporal pattern of expression of the protein products of immediate early genes (IEGs) c-fos, fos B, and egr-1 were mapped in medial preoptic area (MPOA) and ventral bed nucleus of stria terminalis (VBST) during maternal behavior in rats. Immunocytochemical analysis indicated significant increases in the number of cells expressing c-Fos after 2 h of pup exposure, while Fos B levels showed a delayed response, reaching maximal levels after 6 h.

Expression of Fos protein in the limbic regions of the rat following haloperidol decanoate

To identify sites of antipsychotic drug action, the effects of acute and chronic haloperidol treatment on Fos protein expression in rat brain regions were examined by immunohistochemical methods. Male Wistar rats were injected with haloperidol decanoate (40 mg/kg, i.m. ) or vehicle. Fourteen days after injection, each rat was given an acute subcutaneous injection of haloperidol (0.25 mg/kg) or vehicle, and was transcardially perfused 2 h after the second injection. A single dose of haloperidol to chronic vehicle-treated rats produced significant increases in Fos-positive neurons in 18 of 21 brain regions examined including the several cortical areas, caudate-putamen, nucleus accumbens, lateral septum, thalamic nuclei, amygdala, hippocampus CA1, mesencephalic dopaminergic nuclei, and periaqueductal grey. The rats treated with acute vehicle after chronic haloperidol showed persistent Fos increases in confined brain regions comprising the lateral and central amygdala, lateral septum, and entorhinal cortex. Additional haloperidol injection to the chronic haloperidol-treated rats induced significant increases in Fos immunoreactivity in more widespread limbic-thalamo-cortical areas, whereas no significant increase was seen in the dorsolateral caudate-putamen. The persisting effects of haloperidol in the limbic and related structures, especially the amygdala, lateral septum, and entorhinal area may be of significance to the efficacy of long-term haloperidol treatment.

D1-Receptor-related priming is attenuated by antisense-meditated 'knockdown' of fosB expression

Administration of dopamine receptor agonists to rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway produce changes in the denervated striatum that enable a subsequent injection to elicit more vigorous circling. The molecular basis for this behavioural phenomenon, termed priming, is unknown. D1-receptor-related priming has been associated with a profound elevation of immediate-early gene (IEG) expression in the denervated striatum. Since immediate-early genes encode known transcriptional regulating factors, this observation has led to the suggestion that IEG induction may play a role in the gene signaling pathways which mediate priming. In the present study, we addressed the role of induction of the IEG fosB in dopamine agonist-induced priming by examining whether inhibition of the synthesis of FosB proteins (FosB and DeltaFosB) by intrastriatal delivery of an antisense oligonucleotide to fosB reduced apomorphine-induced priming. Intrastriatal delivery of an antisense, but not a random, oligonucleotide to fosB 18 and 6 h before apomorphine reduced the ability of this mixed D1¿D2-like receptor agonist to prime circling induced by the specific D1-like receptor agonist SKF 38393. Immunohistochemical analysis revealed that only the antisense oligonucleotide blocked apomorphine-induced increases in FosB-like immunoreactivity in the denervated striatum. In contrast, apomorphine-induced increases in JunB-, NGFI-A- and Fos2-16-like immunoreactivities were unaffected by either the antisense or random oligonucleotides, indicating that the antisense oligonucleotide attenuated apomorphine-induced priming by selectively blocking the synthesis of FosB proteins. Taken together, these findings suggest that fosB induction in the denervated striatum plays a role in mediating D1-receptor-related priming. Dopamine replacement therapy for Parkinson's disease is often complicated by the development of dyskinetic side effects. Results from the present study suggest that D1-receptor-mediated increases in fosB expression may be involved in those intracellular events responsible for the generation of these debilitating side effects.

MPTP-Parkinsonism is accompanied by persistent expression of a delta-FosB-like protein in dopaminergic pathways

Parkinson's disease (PD) is characterized by the relatively selective and progressive loss of dopaminergic neurons in the substantia nigra. During the early stages of PD, there are marked compensatory changes in the dopaminergic system, although little is known of how these responses are orchestrated. Since the induction of cellular immediate-early genes (cIEG) has been linked to adaptive responses in the nervous system, we examined their expression in the N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) murine model of PD. MPTP elicited an induction of c-fos, fosB, Delta-fosB and c-jun mRNAs in the striatum that persisted for 24 h. There was a parallel increase in AP-1-like DNA binding activity for up to 7 days post-treatment. At 7 days, AP-1 complexes were specifically supershifted with antisera to FosB and JunD. Immunoblotting of MPTP-treated striata with a FosB-specific antiserum revealed elevated levels of approximately 35 and approximately 46 kDa cross-reactive proteins. Only the 35 kDa protein was increased at 7 days. Thus, the persistent AP-1 complex seen in the MPTP-treated striatum is composed of JunD and a 35 kDa FosB-related protein, possibly Delta-FosB. In situ hybridization revealed elevated expression of fosB and Delta-fosB in the MPTP-treated brain. Expression of both transcripts was highest in ventral striatum, nucleus accumbens and other terminal fields of the mesolimbic system, such as the olfactory tubercle and Islands of Calleja. Thus, the increased fosB expression accompanying MPTP treatment was predominantly associated with dopaminergic pathways. Since FosB was expressed in both vulnerable and spared neuronal populations, we suggest that Delta-FosB-JunD heterodimers play a role in the adaptive response to MPTP neurotoxicity.

Behavioural sensitization in 6-hydroxydopamine-lesioned rats is related to compositional changes of the AP-1 transcription factor: evidence for induction of FosB- and JunD-related proteins

Rats with unilateral dopamine denervation exhibit turning behaviour in response to the selective D1 agonist SKF 38393 only after a previous exposure to dopamine agonists. We demonstrate here that this 'priming' phenomenon is related to both an increased expression of the pre-existing AP-1 complex and the occurrence of novel AP-1 complexes which are formed by FosB- and JunD-related proteins. While the former protein is expressed as a consequence of the dopamine denervation, the latter is related to the first exposure to a dopamine agonist. Pre-treatment with MK-801, an antagonist for glutamatergic receptors, prevents both the priming development and the AP-1 compositional changes. Rotational behaviour induced by SKF 38393 closely correlates with the presence of the priming AP-1 complexes, regardless of the capability of the D1 agonist to induce the immediate-early gene cFos.

FosB mutant mice: loss of chronic cocaine induction of Fos-related proteins and heightened sensitivity to cocaine's psychomotor and rewarding effects

Chronic exposure to cocaine leads to prominent, long-lasting changes in behavior that characterize a state of addiction. The striatum, including the nucleus accumbens and caudoputamen, is an important substrate for these actions. We previously have shown that long-lasting Fos-related proteins of 35-37 kDa are induced in the striatum by chronic cocaine administration. In the present study, the identity and functional role of these Fos-related proteins were examined using fosB mutant mice. The striatum of these mice completely lacked basal levels of the 35- to 37-kDa Fos-related proteins as well as their induction by chronic cocaine administration. This deficiency was associated with enhanced behavioral responses to cocaine: fosB mutant mice showed exaggerated locomotor activation in response to initial cocaine exposures as well as robust conditioned place preference to a lower dose of cocaine, compared with wild-type littermates. These results establish the long-lasting Fos-related proteins as products of the fosB gene (specifically DeltaFosB isoforms) and suggest that transcriptional regulation by fosB gene products plays a critical role in cocaine-induced behavioral responses. This finding demonstrates that a Fos family member protein plays a functional role in behavioral responses to drugs of abuse and implicates fosB gene products as important determinants of cocaine abuse.

Chronic Fos-related antigens: stable variants of deltaFosB induced in brain by chronic treatments

Fos family transcription factors are believed to play an important role in the transcriptional responses of the brain to a variety of stimuli. Previous studies have described 35 and 37 kDa Fos-like proteins, termed chronic Fos-related antigens (FRAs), that are induced in brain in a region-specific manner in response to several chronic perturbations, including chronic electroconvulsive seizures, psychotropic drug treatments, and lesions. We show in this study that the chronic FRAs are isoforms of deltaFosB, a truncated splice variant of FosB that accumulate in brain after chronic treatments because of their stability. doffaFosB cDNA encodes the expression of 33, 35, and 37 kDa proteins that arise from a single AUG translation start site. The 35 and 37 kDa proteins correspond to the chronic FRAs that are induced in brain by chronic treatments, whereas the 33 kDa protein corresponds to a Fos-like protein that is induced in brain by acute treatments, findings based on migration on one- and two-dimensional Western blots with anti-FRA and anti-FosB antibodies. Using cells in which deltaFosB or FosB expression is under the control of a tetracycline-regulated gene expression system, we show that the 37 kDa deltaFosB protein exhibits a remarkably long half-life, the 35 kDa DeltaFosB protein exhibits an intermediate half-life, and the 33 kDa deltaFosB protein and all FosB-derived proteins exhibit relatively short half-lives. Moreover, we show that the 33 kDa deltaFosB protein is the first to appear after activation of deltaFosB expression. Finally, deltaFosB proteins are shown to possess DNA-binding activity and to exert potent transactivating effects in reporter gene assays. Together, these findings support a scheme wherein deltaFosB, expressed as a 33 kDa protein, is modified to form highly stable isoforms of 35 and 37 kDa. As a result, these stable isoforms gradually accumulate in the brain with repeated treatments to mediate forms of long-lasting neural and behavioral plasticity.

Changes in expression of delta FosB and the Fos family proteins following NMDA receptor activation in the rat striatum

Receptor-induced expression of transcription factors of the activator protein-1 (AP-1) family in neurons occurs in a unique temporal pattern which regulates subsequent downstream gene expression. We investigated the expression of the Fos family proteins following injection of the NMDA receptor agonist quinolinic acid (QA) into the rat striatum. The c-Fos protein is rapidly and transiently expressed, followed by the sequential and overlapping expression in the same striatal neurons of FosB, from 4 to 8 h post-lesion and delta FosB from 6 h to beyond 30 h post-lesion. Analysis confirms that mRNA transcripts of both fosB and alternatively spliced delta fosB are expressed in the striatum after QA lesion. The Fos-related antigens Fra-1 and Fra-2 and three previously uncharacterized c-Fos-related proteins were additionally found in the striatum which do not increase following lesion. These proteins are related to the highly conserved DNA-binding domain of c-Fos but are not immunologically related to the FosB protein as has been previously reported for proteins induced following chronic stimulation of the striatum. We additionally demonstrate that the c-Fos and delta FosB proteins expressed following QA lesion bind to the functional AP-1 site in the promoter of the nerve growth factor (NGF) gene, the regulation of which temporally and spatially coincides with the AP-1 protein increases in the QA-lesioned striatum. However, the levels of binding to the NGF AP-1 site do not increase throughout time following lesion despite the induced expression of Fos family proteins, suggesting that the regulation of the NGF gene in this paradigm does not simply involve increased binding to the AP-1 site in the NGF gene promoter.

The neurotensin antagonist SR 48692 fails to modify the behavioural responses to a dopamine D1 receptor agonist in the rat

The effects of the neurotensin antagonist SR 48692 on the behavioural responses to the dopamine D1 receptor agonist SKF 38393 were investigated in the rat. SKF 38393 (5 mg/kg s.c.) elicited vacuous chewing movements (VCMs) and grooming, which were unaffected by SR 48692 (50 micrograms/kg i.p.). The dopamine D2 receptor antagonist raclopride (0.5 mg/kg s.c.) elicited a small increase in VCMs in animals treated with SR 48692 and attenuated grooming induced by SKF 38393. These effects were not otherwise modified by SR 48692. We conclude that VCMs induced by acute administration of a dopamine D1 receptor agonist are unlikely to be dependent upon enhanced release of neurotensin in the striatum or its projections. This is contrast to the vacuous chewing response which emerges following chronic administration of neuroleptics, which is attenuated by neurotensin receptor antagonist. Thus, inasmuch as chronic neuroleptic-induced VCMs in the rat may be analogous to tardive dyskinesia in humans, the responses induced by acute administration of a D1 agonist to the rat cannot be used as a model of this disorder. Furthermore, the behavioural effects of chronic neuroleptic administration reflect more than a simple shift in the balance of D1 versus D2 receptor stimulation.

Cabergoline, a long-acting dopamine D2-like receptor agonist, produces a sustained antiparkinsonian effect with transient dyskinesias in parkinsonian drug-naive primates

Continuous dopaminergic receptor stimulation is now considered as an interesting approach for the control of motor complications often seen in parkinsonian patients treated chronically with levodopa. Cabergoline, which is a long-acting dopamine D2-like receptor agonist, has been tried recently with good results as an adjunct in patients already on levodopa-therapy. Thus, the present study was designed to test the effects of repeated s.c. administration of cabergoline as sole therapeutic agent during a month in 3 drug-naive MPTP parkinsonian monkeys to see whether or not cabergoline, given every other day at 0.25 mg/kg, would have a sustained antiparkinsonian effect and would induce dyskinesias. The animals were rated to quantify the antiparkinsonian as well as the dyskinetic response and gross locomotor activity was monitored by photocells. The averaged locomotor response, initially greatly increased (approximately 9 times higher than after saline treatment in the same animals), decreased by approximately 50% after 2 weeks but was thereafter maintained at this level until the end of the study. The parkinsonian features were improved in a sustained manner in all monkeys and transient dyskinesias (week 1 and 2) were present in 2 of 3 monkeys. After sacrifice receptor binding assays were performed on striatal and pallidal tissues homogenates with tritiated selective ligands and compared with those of 3 normal and 3 MPTP-exposed monkeys otherwise untreated. A significant decrease in dopamine D2-like receptor density in the putamen (-36% on average vs. untreated MPTP-exposed monkeys) may be involved in the behavioral partial tolerance to antiparkinsonian effect of cabergoline and the disappearance of dyskinesias. A reversal of the supersensitivity of GABAA receptor in the internal segment of the globus pallidus (-15% on average vs. untreated MPTP-exposed monkeys) may also be implicated in this latter behavioral effect.

Contrasting effects of chronic clozapine, Seroquel(TM) (ICI 204,636) and haloperidol administration of deltaFosB-like immunoreactivity in the rodent forebrain

We have recently demonstrated that specific neuroanatomical patterns of Fos-like immunoreactivity are predictive of atypical antipsychotic activity. However, the fact that neuroleptics must be administered chronically in order to generate both extrapyramidal side effects and an optimal therapeutic response calls into question the relevance of acute changes in Fos-like immunoreactivity for these slowly developing events. Fos-like immunoreactivity cannot be used to identify neurons activated by chronic neuroleptic administration because the increase in Fos-like immunoreactivity produced by an acute antipsychotic injection is dramatically reduced following repeated neuroleptic administration. In contrast, expression of the immediate-early gene product deltaFosB is persistently elevated in the striatum by chronic haloperidol administration. This suggests that deltaFosB-like immunoreactivity may be used to identify neurons activated by chronic antipsychotic administration. Since typical and atypical neuroleptics elevate Fos-like immunoreactivity in different regions of the forebrain acutely, the purpose of the present study was to determine whether typical (haloperidol) and atypical (clozapine, ICI 204,636) antipsychotics produce distinct patterns of elevated deltaFosB-like immunoreactivity in the forebrain after chronic administration. Administration of haloperidol (2 mg/kg/day) to rats for 19 days induced a homogeneous elevation of neurons which displayed deltaFosB-like immunoreactivity in the ventral, medial and dorsolateral aspects of the striatum. Chronic haloperidol administration did not enhance the deltaFos-like immunoreactivity in the prefrontal cortex and lateral septal nucleus. Repeated administration of clozapine (20 mg/kg/day) and ICI 204,636 (20 mg/kg/day) for 19 days elevated deltaFosB-like immunoreactivity not only in the ventral striatum but also in the prefrontal cortex and lateral septal nucleus. However, these compounds had weak effects on deltaFosB-like immunoreactivity in the dorsolateral striatum. These results suggest that a preferential action on limbic structures such as the prefrontal cortex, ventral striatum and lateral septal nucleus may account for the ability of chronic clozapine and ICI 204, 636 administration to reduce the symptoms of schizophrenia without generating extrapyramidal side effects.