Amphetamine induces Fos-like immunoreactivity in the striatum of primates

The role of endogenous neurotensin in psychostimulant-induced disruption of prepulse inhibition and locomotion

The neuropeptide neurotensin (NT) is closely associated with dopaminergic and glutamatergic systems in the rat brain. Central injection of NT into the nucleus accumbens (NAcc) or peripheral administration of NT receptor agonists, reduces many of the behavioral effects of psychostimulants. However, the role of endogenous NT in the behavioral effects of psychostimulants (e.g. DA agonists and NMDA receptor antagonists) remains unclear. Using a NTR antagonist, SR142948A, the current studies were designed to examine the role of endogenous NT in DA receptor agonist- and NMDA receptor antagonist-induced disruption of prepulse inhibition of the acoustic startle response (PPI), locomotor hyperactivity and brain-region specific c-fos mRNA expression. Adult male rats received a single i.p. injection of SR142948A or vehicle followed by D-amphetamine, apomorphine or dizocilpine challenge. SR142948A had no effect on baseline PPI, but dose-dependently attenuated d-amphetamine- and dizocilpine-induced PPI disruption and enhanced apomorphine-induced PPI disruption. SR142948A did not significantly affect either baseline locomotor activity or stimulant-induced hyperlocomotion. Systemic SR142948A administration prevented c-fos mRNA induction in mesolimbic terminal fields (prefrontal cortex, lateral septum, NAcc, ventral subiculum) induced by all three psychostimulants implicating the VTA as the site for NT modulation of stimulant-induced PPI disruption. Further characterization of the NT system may be valuable to find clinical useful compounds for schizophrenia and drug addiction.

Repetitive behaviors in monkeys are linked to specific striatal activation patterns

The spontaneous behavior of humans can be altered dramatically by repeated exposure to psychomotor stimulants. We have developed a primate model for analyzing the neurobiology underlying such drug-induced behavioral changes. We performed ethogram-based behavioral assays on squirrel monkeys given single or multiple cocaine treatments, and in the same monkeys made anatomical plots of striatal neurons that were activated to express early-gene proteins. A final cocaine challenge after chronic intermittent exposure to cocaine induced highly patterned behavioral changes in the monkeys, affecting individual behavioral motifs in distinct ways. In the striatum, the challenge dose induced striosome-predominant expression combined with intense dorsal early-gene expression, especially in the putamen. These patterns of gene expression were highly predictive of the levels of stereotypy exhibited by the monkeys in response to cocaine challenge. The total levels of expression, on the other hand, appeared to reflect increased spontaneous behavioral activation during the drug-free period after the cocaine exposure. We suggest that in the primate, compartmentally and regionally specific striatal activation patterns contribute to the striatal modulation of psychostimulant-induced behaviors. These observations in nonhuman primates raise the possibility that monitoring such basal ganglia activity patterns could help to delineate the neural mechanisms underlying drug-induced repetitive behaviors and related syndromes in which stereotypies are manifest.

The distribution of m4 muscarinic acetylcholine receptors in the islands of Calleja and striatum of rats and cynomolgus monkeys

The distribution of m4 muscarinic acetylcholine receptors, and their relation to a number other markers, was examined using immunocytochemical techniques. Staining in the dorsal striatum tended to be more pronounced in the striosomal than the matrix compartment of both rats and cynomolgus monkeys. Within the ventral striatum, immunoreactivity was more pronounced within the olfactory tubercle and the shell region of the nucleus accumbens than in the nucleus accumbens core and was especially marked within the lateral striatal stripe. Modest staining was also seen in the external plexiform layer of the olfactory bulb. By far, the most intense staining in the forebrain of both rats and cynomolgus monkeys was found in islands of Calleja, where it appeared to be a selective marker for the core or hilus regions of the islands, or an analogous region found adjacent to them. The core regions of different islands appear to be continuous with each other so as to form a complex three-dimensional structure, which is largely encased by layers of granule cells. The neuronal elements in the islands of Calleja, which express m4 receptors, remain to be identified, but it is unlikely that cholinergic neurons are a major locus of these receptors. Although there are certain similarities between the islands of Calleja and other components of the striatal complex, the current studies emphasize the extent to which the islands are unique in terms of their architecture and chemical anatomy.

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

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

Effects of haloperidol and clozapine on Fos expression in the primate striatum

In cynomolgus monkeys, the typical neuroleptic haloperidol induced strong expression of the immediate early gene product Fos in both the nucleus accumbens shell and the dorsal striatum. In the caudate nucleus, haloperidol induced staining was more marked in the striosomes than the matrix. The atypical neuroleptic clozapine also induced Fos expression in the nucleus accumbens, but, in contrast to haloperidol, had only a small effect in the dorsal striatum. Additionally, clozapine was more potent than haloperidol at inducing Fos-like immunoreactivity in the islands of Calleja. These results are similar to those typically obtained in rodents, and suggest that the basic mechanisms underlying the regional specificity of the effects of atypical neuroleptics are likely be conserved between these two mammalian orders.

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.

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

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

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.

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

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

A comparison of the patterns of striatal Fos-like immunoreactivity induced by various dopamine agonists in rats

In contrast to the highly patchy patterns of Fos-like immunoreactivity seen in the rostral striatum after administration of a number of dopamine agonists, the monoamine uptake blocker cocaine has been reported to produce a relatively homogeneous pattern of gene expression. In the current study we extended these observations by using a quantitative technique to demonstrate that while amphetamine and apomorphine produce patchy striatal Fos expression, the selective dopamine uptake inhibitors amfonelic acid, nomifensine and GBR-12909 all, like cocaine, produce near random patterns of gene expression. These findings suggest that the production of relatively 'non-patchy' patterns of immediate early gene expression may be a general property of dopamine transport inhibitors unrelated to any unique pharmacological properties of cocaine.

Haloperidol induces Fos expression in the globus pallidus and substantia nigra of cynomolgus monkeys

Systemic injections of the dopamine antagonist haloperidol (0.1-2.5 mg/kg) induced a dose dependent increase in Fos-like immunoreactivity (FLI) in the internal segment of the globus pallidus (GPi) and in the substantia nigra (SN) of cynomolgus monkeys. These findings are consistent with models of basal ganglia organization which predict that blockade of dopamine receptors should result in a disinhibition of cells in these structures. In the GPi, labeling was most pronounced along the ventral, lateral and medial borders of the nucleus and none of the pallidal cells expressing FLI were immunopositive for choline acetyltransferase. In the SN, immunoreactive nuclei were concentrated in the pars reticulata and the majority of labeled nigral neurons did not display tyrosine hydroxylase-like immunoreactivity. A small number of cells displaying FLI were also observed in the external pallidal segment, but no labeling was seen in the subthalamic nucleus. These findings indicate that blockade of dopamine receptors induces a characteristic pattern of Fos expression in the primate brain which strongly resembles that previously reported in rodents.

Unilateral dopamine depletion paradoxically enhances amphetamine-induced Fos expression in basal ganglia output structures

The ability of amphetamine to induce expression of the immediate early gene protein, Fos, was examined by immunocytochemistry in animals with unilateral 6-hydroxydopamine lesions of the nigrostriatal bundle. Amphetamine induced Fos expression in the globus pallidus (GP) on the intact side of the brain, but this response was greatly attenuated on the dopamine-depleted side. In contrast, amphetamine induced little Fos expression in the entopeduncular nucleus (EPN) and the substantia nigra pars reticulata (SNpr) on the intact side of the brain, but resulted in pronounced expression in these structures on the lesioned side. These findings demonstrate that unilateral dopamine depletion results in a pathophysiological state in which some responses to amphetamine are attenuated while others are paradoxically potentiated. One explanation of these effects is that amphetamine may indirectly activate excitatory inputs to the SNpr and the EPN on both sides of the brain. On the intact side, these effects would be opposed by the simultaneous activation of inhibitory pathways arising in the striatum and the GP, with the result that little Fos expression would be seen. On the dopamine-depleted side, however, engagement of these inhibitory pathways would be attenuated and the unopposed effects of the excitatory inputs mobilized by amphetamine would result in exaggerated Fos synthesis.

Drugs of abuse and immediate-early genes in the forebrain

A diverse array of chemical agents have been self administered by humans to alter the psychological state. Such drugs of abuse include both stimulants and depressants of the central nervous system. However, some commonalties must underlie the neurobiological actions of these drugs, since the desire to take the drugs often crosses from one drug to another. Studies have emphasized a role of the ventral striatum, especially the nucleus accumbens, in the actions of all drugs of abuse, although more recent studies have implicated larger regions of the forebrain. Induction of immediate-early genes has been studied extensively as a marker for activation of neurons in the central nervous system. In this review, we survey the literature reporting activation of immediate-early gene expression in the forebrain, in response to administration of drugs of abuse. All drugs of abuse activate immediate-early gene expression in the striatum, although each drug induces a particular neuroanatomical signature of activation. Most drugs of abuse activate immediate-early gene expression in several additional forebrain regions, including portions of the extended amygdala, cerebral cortex, lateral septum, and midline/intralaminar thalamic nuclei, although regional variations are found depending on the particular drug administered. Common neuropharmacological mechanisms responsible for activation of immediate-early gene expression in the forebrain involve dopaminergic and glutamatergic systems. Speculations on the biological significance and clinical relevance of immediate-early gene expression in response to drugs of abuse are presented.

Quinpirole attenuates striatal c-fos induction by 5-HT, opioid and muscarinic receptor agonists

Pretreatment with the dopamine D2 receptor agonist quinpirole (0.025-2.5 mg/kg) produced a marked, dose-dependent, attenuation of the striatal Fos expression induced by the serotonin (5-Hydroxytryptamine, 5-HT) releasing agent fenfluramine (25 mg/kg). Quinpirole (2.5 mg/kg) was also able to drastically attenuate the striatal Fos response produced by injections of the direct 5-HT1/2 receptor agonist N-(3-trifluoromethylphenyl)piperazine hydrochloride (TFMPP) (5 mg/kg), the selective 5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI) (6.64 mg/kg), the 5-HT1A/1B receptor agonist RU-24969 (5-methoxy-3-(1,2,3,6-tetrahydropyridin-4-yl)1H-indole) (5 mg/kg), the mu-opioid receptor agonist morphine (5 mg/kg) and the muscarinic cholinergic receptor agonist pilocarpine (50 mg/kg). These results are in marked contrast to the previously reported ability of quinpirole to potentiate the response to D1 dopamine receptor agonists and demonstrate that stimulation of D2-like receptors can have differential effects on the Fos responses induced by various drugs.

Serotonin-1B agonists induce compartmentally organized striatal Fos expression in rats

The 5HT1B agonist RU24969 (2.5-5.0 mg/kg) and anpirtoline (2.0 mg/kg) induced a striking increase in striatal Fos-like immunoreactivity in rats. In the rostral and dorsal regions of the striatum staining was dense and relatively homogeneous. In the ventral region of the striatum at more caudal levels, however, both drugs induced staining in patches which were in register with the opiate receptor rich striosomes. The effects of RU24969 could not be antagonized by the selective 5HT1A antagonist p-MPPI and little or no striatal Fos expression could be observed after injections of the selective 5HT1A agonist 8-OHDPAT or the selective 5HT3 antagonist MDL-72222.

Placement in a novel environment induces fos-like immunoreactivity in supramammillary cells projecting to the hippocampus and midbrain

Injections of fluorescent retrograde tracers into either the hippocampal formation or the midbrain raphe nuclei resulted in retrograde labeling of many cells in the supramammillary region of the hypothalamus. Double labeling studies indicated that these two projections originate from different populations of supramammillary cells. Expression of the proto-oncoprotein Fos could be induced in some retrogradely labeled cells by placing rats in a novel open field before sacrifice. Although seen in both cell types, Fos-like immunoreactivity was significantly more common in supramammillary cells projecting to the hippocampus than in those projecting to the midbrain. These findings suggest that the supramammillary region may contain several populations of neurons which are differentially responsive to certain behavioral manipulations.

Quinpirole attenuates the striatal fos expression induced by escape behavior

Several studies have shown that the D2-like dopamine receptor agonist quinpirole is able to markedly potentiate the striatal Fos expression induced by D1 agonists. The present study examined the effects of quinpirole on the striatal Fos-like immunoreactivity (FLI) induced by escape behavior. Male rats were pretreated with either saline or quinpirole (0.156, 0.625, 1.25 or 2.5 mg/kg) and 30 min later, placed in a shuttle box and required to crossover every 30 s in order to escape mild footshock. Animals were sacrificed 30 min following the completion of a 1-h block of escape trials and sections through the striatum were processed for FLI. Pretreatment with quinpirole produced a marked, dose-dependent, attenuation of escape-induced FLI in the striatum. These findings demonstrate that quinpirole affects the striatal Fos expression induced by shuttling in a very different fashion than it does that induced by D1 agonists, and further support the view that dopaminergic mechanisms play an important role in behaviorally induced striatal Fos expression.

Compartmentally specific effects of quinpirole on the striatal Fos expression induced by stimulation of D1-dopamine receptors in intact rats

Injections of the full D1-agonist A-77636 (1.45 mg/kg) were found to induce clear Fos-like immunoreactivity (FLI) in the striatum of neurologically intact rats. Pretreatment with the D2-like agonist quinpirole (3 mg/kg) potentiated staining in the lateral striatum, but actually decreased the number of immunoreactive cells observed in the medial portion of the rostral striatum. Comparison with adjacent sections processed for the calcium binding protein calbindin, indicated that quinpirole pretreatment specifically suppressed staining in the matrix compartment of the striatum while tending to potentiate it in the striosomes, resulting in an extremely patchy pattern of labeling. These results suggest that exogenous stimulation of D2-receptors, although not essential for the induction of FLI, may play an important role in the compartmental patterning of neuronal activity within the striatum.