Localization of GABA(B) receptors in midbrain monoamine containing neurons in the rat.

The localization of gamma-aminobutyric acid (GABA)(B) receptors in the midbrain of the rat was examined in multiple labeling studies using antibodies directed against the GABA(B) receptor and either tryptophan hydroxylase or tyrosine hydroxylase. Almost all of the serotonergic and dopaminergic cell bodies in the midbrain displayed GABA(B) receptor-like immunoreactivity. Conversely, most neurons in the raphe nuclei and ventral tegmentum which exhibited intense immunoreactivity for GABA(B) receptors were also immunopositive for serotonergic or dopaminergic markers. These results demonstrate directly that GABA(B) receptors are present in monoaminergic neurons in certain regions of the midbrain.

Nicotine-induced behavioral sensitization is associated with extracellular dopamine release and expression of c-Fos in the striatum and nucleus accumbens of the rat.

It is well known that repeated injections of nicotine produce progressively larger increases in locomotor activity, an effect referred to as behavioral sensitization. This study was carried out to investigate the neural mechanisms underlying nicotine-induced behavioral sensitization using in vivo microdialysis and Fos-like immunohistochemistry (FLI). Rats were given repeated injections of saline or nicotine (0.4 mg/kg s.c., twice daily for 7 days) followed by one challenge injection on the 4th day after the last daily injection. Systemic challenge with nicotine produced a much larger increase in locomotor activity in nicotine-pretreated rats (659.1+/-94.9 counts/2 h) than in saline-pretreated rats (218.1+/-61 counts/2 h). A direct local challenge of nicotine (1 or 5 mM) via a microdialysis probe in the nucleus accumbens or striatum induced a much greater dose-dependent increase of dopamine (DA) output in nicotine-pretreated rats than in saline-pretreated rats. Furthermore, in parallel with the behavioral and biochemical data, systemic challenge with nicotine produced marked Fos-like immunohistochemistry in the nucleus accumbens and the striatum in the nicotine-pretreated rats. Taken together, this study demonstrates that behavioral sensitization is clearly associated with an increase in DA release and activation of Fos-like immunoreactive cells in the striatum and the nucleus accumbens produced by repeated nicotine treatment. Our results strongly suggest that the striatum and the nucleus accumbens may play a major role in nicotine-induced behavioral sensitization. The present results are discussed in terms of the development and expression of nicotine-induced behavioral sensitization.

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.

Forebrain lesions differentially affect drinking elicited by dipsogenic challenges and injections of muscimol into the median raphe nucleus.

Injections of muscimol into the median raphe nucleus (MR) elicit intense drinking in normally hydrated rats. To determine whether this response is dependent on forebrain systems mediating other aspects of water intake, the authors examined the effects of lesions of the subfornical organ (SFO), median preoptic nucleus (MnPO), lateral preoptic area (LPO), or lateral hypothalamus (LH) on the drinking. Lesions of the SFO or LH attenuated muscimol-elicited drinking, whereas lesions of the MnPO or LPO increased water intake after the treatment. All of the lesion groups showed a deficit in drinking to injections of polyethylene glycol and at least one of the doses of hypertonic saline. Only the SFO- and LH-lesioned groups showed a suppression of drinking to systemic injections of angiotensin II, suggesting that the drinking elicited by intra-MR injections of muscimol may involve changes in the central circuits mediating angiotensin-induced drinking.

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.

Quinpirole attenuates the striatal immediate early gene expression, but not the hyperactivity, induced by the serotonin agonist RU-24969.

Systemic administration of the mixed 5-HT(1A/1B) agonist RU-24969 has been shown to produce a dramatic increase in locomotor activity and to induce robust c-Fos expression in the rat striatum. Previous studies have also shown that pretreatment with the D2-like dopamine agonist quinpirole virtually abolishes RU-24969-induced striatal c-Fos expression. The present study was undertaken to determine whether the effects of RU-24969 on immediate early gene expression extend to the additional Fos family transcription factors FosB and Fra-2. Additionally, this study quantitatively examined the effect of quinpirole pretreatment on the ability of RU-24969 to induce both locomotor hyperactivity and striatal immediate early gene expression. RU-24969 alone produced elevations in locomotor activity and induced clear expression of c-Fos, FosB and Fra-2 throughout the entire striatal complex. Quinpirole pretreatment virtually abolished RU-24969-induced expression of all three transcription factors, but did not alter the elevated locomotor activity produced by RU-24969. These results demonstrate that the effects of RU-24969 on locomotor activity can be dissociated from its effects on immediate early gene expression within the striatum.

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.

Clozapine antagonizes the induction of striatal Fos expression by typical neuroleptics.

Previous studies have shown that the atypical neuroleptic clozapine is less potent at inducing Fos expression in the dorsolateral striatum than are typical neuroleptics. We report here that pretreatment with clozapine (5-20 mg/kg) actually attenuates the striatal Fos expression induced by the typical neuroleptics haloperidol and raclopride. These results suggest clozapine has pharmacological properties which actively antagonize the effects of dopamine D2 receptor blockade on striatal immediate-early gene expression.

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.

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.

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.

D1 dopamine receptors mediate neuroleptic-induced Fos expression in the islands of Calleja.

Systemic injections of the selective, full, D1 agonists A-77636 and SKF-82958 induced pronounced Fos-like immunoreactivity in the islands of Calleja in the olfactory tubercle of intact rats. Fos expression in this region could also be induced by injections of the D2-like dopamine antagonist raclopride (0.5 mg/kg). Pretreatment with the selective D1 dopamine antagonist SCH-23390 (0.2 mg/kg) completely abolished this response, but was without significant effect on raclopride-induced Fos expression in the dorsolateral region of the striatum. SCH-23390 was also able to prevent the atypical neuroleptic clozapine (30 mg/kg) from inducing Fos expression in the islands of Calleja. These findings demonstrate that stimulation of D1 dopamine receptors plays an essential role in neuroleptic induction of Fos-like immunoreactivity in the islands of Calleja, but not in the dorsal striatum, and thus suggest that different mechanisms underlie neuroleptic stimulation of immediate early gene expression in these two structures.

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.

Interactive effects of stimulation of D1 and D2 dopamine receptors on Fos expression in the lateral habenula.

We have previously shown that systemic administration of non-selective dopamine agonists results in a pronounced expression of the proto-oncoprotein Fos within the lateral habenula. In the current study we examined the effects of selective D1 and D2 dopamine receptor agonists on habenular Fos expression. Rats were injected with various doses of the selective D2 agonist quinpirole (0, 0.62 or 2.5 mg/kg) either alone or in combination with various doses of the selective full D1 agonist A-77636 (0, 0.75 or 3.0 mg/kg). The selective agonists, by themselves, induced only small increases in Fos-like immunoreactivity within the lateral habenula, but combinations of the two drugs resulted in a very robust response. These findings indicate that D1 and D2 receptor agonists interact to induce Fos expression within the habenula and that the nature of this interaction differs from that reported in the striatum and the globus pallidus.

The distribution of reduced nicotinamide adenine dinucleotide phosphate-diaphorase in the leopard frog telencephalon and related projections.

The distribution of reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-D) was mapped histochemically in the forebrain of Rana pipiens, the leopard frog. Intense staining was observed which was strikingly restricted to certain nuclear groups and fiber tracts. The densest concentrations of NADPH-D stained cell bodies and fibers were observed in the granule layer of the accessory olfactory bulb and in the ventral aspect of the lateral pallium. Intense staining has also been reported in the presumed mammalian homologues of these regions. Less densely packed clusters of intensely stained neurons were found in the striatum, the anterior entopeduncular nucleus, the olfactory tubercle and the pars lateralis of the amygdala, whereas the preoptic region and the medial septum exhibited dense accumulations of lightly stained cells. Several fiber systems or terminal fields could be detected, including a ring of heavy staining which enclosed the striatum and an apparent terminal field in the lateral part of the medial pallium. A prominent compact tract, which may be homologous to a component of the stria terminalis of mammals, could be also followed from the ventral portion of the lateral pallium to the infundibular hypothalamus.

Dissociation of hippocampal serotonin release and locomotor activity following pharmacological manipulations of the median raphe nucleus.

In vivo microdialysis was used to investigate the role of serotonin in the locomotor hyperactivity produced by injections of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OHDPAT), muscimol and baclofen into the median raphe nucleus (MR) of unanesthetized rats. Intra-MR injections of the GABA(A) agonist muscimol (25 ng) resulted in a pronounced increase in locomotor activity which was accompanied by a 42% decrease in hippocampal serotonin release during the first hour following injection. Intra-MR injections of the GABA(B) agonist baclofen (125 ng) induced hyperactivity of a similar magnitude, but failed to affect hippocampal serotonin release. In contrast, the serotonin (5-HT1A) agonist 8-OHDPAT (5 microg) produced only a small effect on locomotor activity but reduced hippocampal serotonin output by 51%. These findings demonstrate that it is possible to dissociate the effects of intra-MR drug injections on locomotor activity and hippocampal 5-HT release and strongly support the view that nonserotonergic neurons in the paramedian tegmentum are importantly involved in the control of behavioral arousal.

Amphetamine induces Fos-like immunoreactivity in the striatum of primates.

Injections of D-amphetamine (5 mg/kg) three hours before sacrifice were found to elicit robust Fos-like immunoreactivity in the striatum of cynomolgus monkeys and of the common marmoset. Labeled cells were most frequently observed in the medial portion of the caudate nucleus and were distributed in a patchy fashion. Comparison with adjacent sections stained for the calcium binding protein calbindin indicated that the patches of amphetamine induced labeling corresponded to the calbindin-poor striosomes. These results are consistent with those reported in rats and thus suggest similarities in the basic organization of striatal mechanisms underlying the response to amphetamine in rodents and primates.