Changes in Dendritic Spine Density and Inhibitory Perisomatic Connectivity onto Medium Spiny Neurons in L-Dopa-Induced Dyskinesia

Using bacterial artificial chromosome-double transgenic mice expressing tdTomato in D1 receptor-medium spiny neurons (MSNs) and enhanced green fluorescent protein in D2 receptor-MSNs, we have studied changes in spine density and perisomatic GABAergic boutons density in MSNs of both the D1R and D2R pathways, in an experimental model of parkinsonism (mouse injected with 6-hydroxydopamine in the medial forebrain bundle), both in the parkinsonian and dyskinetic condition induced by L-DOPA treatment. To assess changes in perisomatic GABAergic connectivity onto MSNs, we measured the number of contacts originated from parvalbumin (PV)-containing striatal "fast-spiking" interneurons (FSIs), the major component of a feed-forward inhibition mechanism that regulates spike timing in MSNs, in both cell types as well as the number of vesicular GABA transporter (VGAT) contacts. Furthermore, we determined changes in PV-immunoreactive cell density by PV immunolabeling combined with Wisteria floribunda agglutinin (WFA) labeling to detect FSI in a PV-independent manner. We also explored the differential expression of striatal activity-regulated cytoskeleton-associated protein (Arc) and c-Fos in both types of MSNs as a measure of neuronal activation. Our results confirm previous findings of major structural changes in dendritic spine density after nigrostriatal denervation, which are further modified in the dyskinetic condition. Moreover, the finding of differential modifications in perisomatic GABAergic connectivity and neuronal activation in MSNs suggests an attempt by the system to regain homeostasis after denervation and an imbalance between excitation and inhibition leading to the development of dyskinesia after exposure to L-DOPA.

Circuit-specific signaling in astrocyte-neuron networks in basal ganglia pathways

Astrocytes are important regulatory elements in brain function. They respond to neurotransmitters and release gliotransmitters that modulate synaptic transmission. However, the cell- and synapse-specificity of the functional relationship between astrocytes and neurons in certain brain circuits remains unknown. In the dorsal striatum, which mainly comprises two intermingled subtypes (striatonigral and striatopallidal) of medium spiny neurons (MSNs) and synapses belonging to two neural circuits (the direct and indirect pathways of the basal ganglia), subpopulations of astrocytes selectively responded to specific MSN subtype activity. These subpopulations of astrocytes released glutamate that selectively activated N-methyl-d-aspartate receptors in homotypic, but not heterotypic, MSNs. Likewise, astrocyte subpopulations selectively regulated homotypic synapses through metabotropic glutamate receptor activation. Therefore, bidirectional astrocyte-neuron signaling selectively occurs between specific subpopulations of astrocytes, neurons, and synapses.

The role of dopamine receptors in the neurotoxicity of methamphetamine

Methamphetamine is a synthetic drug consumed by millions of users despite its neurotoxic effects in the brain, leading to loss of dopaminergic fibres and cell bodies. Moreover, clinical reports suggest that methamphetamine abusers are predisposed to Parkinson's disease. Therefore, it is important to elucidate the mechanisms involved in methamphetamine-induced neurotoxicity. Dopamine receptors may be a plausible target to prevent this neurotoxicity. Genetic inactivation of dopamine D1 or D2 receptors protects against the loss of dopaminergic fibres in the striatum and loss of dopaminergic neurons in the substantia nigra. Protection by D1 receptor inactivation is due to blockade of hypothermia, reduced dopamine content and turnover and increased stored vesicular dopamine in D1R(-/-) mice. However, the neuroprotective impact of D2 receptor inactivation is partially dependent on an effect on body temperature, as well as on the blockade of dopamine reuptake by decreased dopamine transporter activity, which results in reduced intracytosolic dopamine levels in D2R(-/-) mice.

Distribution of diacylglycerol lipase alpha, an endocannabinoid synthesizing enzyme, in the rat forebrain

1,2-diacylglycerol lipase alpha (DAGLα) is responsible for the biosynthesis and release of 2-arachidonoyl-glycerol (2-AG), the most abundant endocannabinoid in the brain. Although its expression has been detected in discrete regions, we showed here an integrated description of the distribution of DAGLα mRNA and protein in the rat forebrain using in situ hybridization histochemistry and immunohistochemistry. As novelty, we described the distribution of DAGLα protein expression in the olfactory system, the rostral migratory stream, neocortex, septum, thalamus, and hypothalamus. Similar DAGLα immunostaining pattern was also found in the brain of wild-type, but not of DAGLα knockout mice. Immunohistochemical data were correlated by the identification of DAGLα mRNA expression, for instance, in the somata of specific cells in olfactory structures, rostral migratory stream and neocortex, cells in some septal-basal-amygdaloid areas and the medial habenula, and magnocellular cells of the paraventricular hypothalamic nucleus. This widespread neuronal distribution of DAGLα is consistent with multiple roles for endocannabinoids in synaptic plasticity, including presynaptic inhibition of neurotransmitter release. We discuss our comparative analysis of the forebrain expression patterns of DAGLα and other components of the endocannabinoid signaling system, including the CB(1) receptor, monoacylglyceride lipase (MAGL), and fatty acid amide hydrolase (FAAH), providing some insight into the potential physiological and behavioral roles of this system.

Genetic inactivation of pleiotrophin triggers amphetamine-induced cell loss in the substantia nigra and enhances amphetamine neurotoxicity in the striatum

Pleiotrophin (PTN) is a neurotrophic factor with important effects in survival and differentiation of dopaminergic neurons that has been suggested to play important roles in drug of abuse-induced neurotoxicity. To test this hypothesis, we have studied the effects of amphetamine (10 mg/kg, four times, every 2 h) on the nigrostriatal pathway of PTN genetically deficient (PTN-/-) mice. We found that amphetamine causes a significantly enhanced loss of dopaminergic terminals in the striatum of PTN-/- mice compared to wild type (WT+/+) mice. In addition, we found a significant decrease ( approximately 20%) of tyrosine hydroxylase (TH)-positive neurons only in the substantia nigra of amphetamine-treated PTN-/- mice, whereas this area of WT+/+ animals remained unaffected after amphetamine treatment. This effect was accompanied by enhanced amphetamine-induced astrocytosis in the substantia nigra of PTN-/- mice. Interestingly, we found a significant decrease in the phosphorylation levels of p42 extracellular-signal regulated kinase (ERK2) in both saline- and amphetamine-treated PTN-/- mice, whereas phosphorylation of p44 ERK (ERK1) was almost abolished in the striatum of PTN-/- mice compared to WT+/+ mice, suggesting that basal deficiencies in the phosphorylation levels of ERK1/2 could underlie the higher vulnerability of PTN-/- mice to amphetamine-induced neurotoxic effects. The data suggest an important role of PTN in the protection of nigrostriatal pathways against amphetamine insult.

Hypoxia transduction by carotid body chemoreceptors in mice lacking dopamine D(2) receptors

Hypoxia-induced dopamine (DA) release from carotid body (CB) glomus cells and activation of postsynaptic D(2) receptors have been proposed to play an important role in the neurotransmission process between the glomus cells and afferent nerve endings. To better resolve the role of D(2) receptors, we examined afferent nerve activity, catecholamine content and release, and ventilation of genetically engineered mice lacking D(2) receptors (D(2)(-/-) mice). Single-unit afferent nerve activities of D(2)(-/-) mice in vitro were significantly reduced by 45% and 25% compared with wild-type (WT) mice during superfusion with saline equilibrated with mild hypoxia (Po(2) approximately 50 Torr) or severe hypoxia (Po(2) approximately 20 Torr), respectively. Catecholamine release in D(2)(-/-) mice was enhanced by 125% in mild hypoxia and 75% in severe hypoxia compared with WT mice, and the rate of rise was increased in D(2)(-/-) mice. We conclude that CB transduction of hypoxia is still present in D(2)(-/-) mice, but the response magnitude is reduced. However, the ventilatory response to acute hypoxia is maintained, perhaps because of an enhanced processing of chemoreceptor input by brain stem respiratory nuclei.

Absence of quasi-morphine withdrawal syndrome in adenosine A2A receptor knockout mice

RATIONALE

Caffeine and other methylxanthines induce behavioral activation and anxiety responses in mice via antagonist action at A2A adenosine receptors. When combined with the opioid antagonist naloxone, methylxanthines produce a characteristic quasi-morphine withdrawal syndrome (QMWS) in opiate-naive animals.

OBJECTIVES

The aim of this study was to establish the role of A2A receptors in the quasi-morphine withdrawal syndrome induced by co-administration of caffeine and naloxone and in the behavioral effects of caffeine.

METHODS

We have used A2A receptor knockout (A(2A)R(-/-)) mice in comparison with their wild-type and heterozygous littermates to measure locomotor activity in the open field and withdrawal symptoms induced by caffeine and naloxone. Naïve wild-type and knockout mice were also examined for enkephalin and dynorphin mRNA expression by in situ hybridization and for mu-opiate receptor by ligand binding autoradiography to check for possible opiate receptor changes induced by A2A receptor inactivation.

RESULTS

Caffeine increases locomotion and anxiety in wild-type animals, but it has no psychomotor effects in A(2A)R(-/-) mice. Co-administration of caffeine (20 mg/kg) and naloxone (2 mg/kg) resulted in a severe quasi-morphine withdrawal syndrome in wild-type mice that was almost completely abolished in A(2A)R(-/-) mice. Heterozygous animals exhibited a 40% reduction in withdrawal symptoms, suggesting that there is no genetic/developmental compensation for the inactivation of one of the A(2A)R alleles. A(2A)R(-/-) and wild-type mice have similar levels of striatal mu-opioid receptors, thus the effect is not due to altered opioid receptor expression.

CONCLUSIONS

Our results demonstrate that A2A receptors are required for the induction of quasi-morphine withdrawal syndrome by co-administration of caffeine and naloxone and implicate striatal A2A receptors and mu-opiate receptors in tonic inhibition of motor activity in the striatum.

Neuroanatomical relationship between type 1 cannabinoid receptors and dopaminergic systems in the rat basal ganglia

Dopamine and endocannabinoids are neurotransmitters known to play a role in the activity of the basal ganglia motor circuit. While a number of studies have demonstrated functional interactions between type 1 cannabinoid (CB1) receptors and dopaminergic systems, we still lack detailed neuroanatomical evidence to explain their relationship. Single- and double-labeling methods (in situ hybridization and immunohistochemistry) were employed to determine both the expression and localization of CB1 receptors and tyrosine hydroxylase (TH) in the basal ganglia. In the striatum, we found an intense signal for CB1 receptor transcripts but low signal for CB1 receptor protein, whereas in the globus pallidus and substantia nigra we found the opposite; no hybridization signal but intense immunoreactivity. Consequently, CB1 receptors are synthesized in the striatum and mostly transported to its target areas. No co-expression or co-localization of CB1 receptors and TH was found. In the caudate-putamen, globus pallidus and substantia nigra, TH-immunoreactive fibers were interwoven with the CB1 receptor-immunoreactive neuropil and fibers. Our data suggest that the majority of the striatal CB1 receptors are located presynaptically on inhibitory GABAergic terminals, in a position to modulate neurotransmitter release and influence the activity of substantia nigra dopaminergic neurons. In turn, afferent dopaminergic fibers from the substantia nigra innervate CB1 receptor-expressing striatal neurons that are known to also express dopamine receptors. In conclusion, these data provide a neuroanatomical basis to explain functional interactions between endocannabinoid and dopaminergic systems in the basal ganglia.

5-hydroxytryptamine (5-HT)1A autoreceptor adaptive changes in substance P (neurokinin 1) receptor knock-out mice mimic antidepressant-induced desensitization

Antagonists at substance P receptors of the neurokinin 1 (NK1) type have been shown to represent a novel class of antidepressant drugs, with comparable clinical efficacy to the selective serotonin (5-HT) reuptake inhibitors (SSRIs). Because 5-HT(1A) receptors may be critically involved in the mechanisms of action of SSRIs, we examined whether these receptors could also be affected in a model of whole-life blockade of NK1 receptors, i.e. knock-out mice lacking the latter receptors (NK1-/-). 5-HT(1A) receptor labeling by the selective antagonist radioligand [(3)H]N-[2-[4-(2-methoxyphenyl)1-piperazinyl]-ethyl]-N-(2-pyridinyl)-cyclohexanecarboxamide (WAY 100635) and 5-HT(1A)-dependent [(35)S]GTP-gamma-S binding at the level of the dorsal raphe nucleus (DRN) in brain sections, as well as the concentration of 5-HT(1A) mRNA in the anterior raphe area were significantly reduced (-19 to -46%) in NK1-/- compared with NK1+/+ mice. Furthermore, a approximately 10-fold decrease in the potency of the 5-HT(1A) receptor agonist ipsapirone to inhibit the discharge of serotoninergic neurons in the dorsal raphe nucleus within brainstem slices, and reduced hypothermic response to 8-OH-DPAT, were noted in NK1-/- versus NK1+/+ mice. On the other hand, cortical 5-HT overflow caused by systemic injection of the SSRI paroxetine was four- to sixfold higher in freely moving NK1-/- mutants than in wild-type NK1+/+ mice. Accordingly, the constitutive lack of NK1 receptors appears to be associated with a downregulation/functional desensitization of 5-HT(1A) autoreceptors resembling that induced by chronic treatment with SSRI antidepressants. Double immunocytochemical labeling experiments suggest that such a heteroregulation of 5-HT(1A) autoreceptors in NK1-/- mutants does not reflect the existence of direct NK1-5-HT(1A) receptor interactions in normal mice.

Serotonin 5-HT(1A) receptor expression is selectively enhanced in the striosomal compartment of chronic parkinsonian monkeys

Cynomolgus monkeys (Macaca fascicularis) were chronically treated with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) until stable parkinsonism was reached. Two months later, monkeys were sacrificed and monoamine content was measured in different brain regions of the lesioned monkeys and of age-matched controls. 5-HT(1A) serotonin receptor density was measured in coronal sections labeled with [(3)H]8-OH-DPAT. As expected, dopamine was virtually nonexistent in the caudate nucleus and putamen of MPTP-treated monkeys. Serotonin levels were significantly reduced in different brain regions, particularly in the raphe nuclei. 5-HT(1A) receptor density of control animals was high in the hippocampus, notably in the CA1 field and also in the raphe nuclei, and much lower in the striatum, where 5-HT(1A) receptors showed a patchy distribution which corresponded to striosomes with poor calbindin immunostaining. 5-HT(1A) receptor density was reduced in hippocampal fields and in the raphe nuclei of parkinsonian monkeys. Conversely, in the severely lesioned striatal nuclei 5-HT(1A) receptor density was increased at caudal levels of the striatum, particularly in the putamen. The results tend to support the possibility of an increased synthesis of 5-HT(1A) receptors in brain regions with higher neuronal cell death. Upregulation of this 5-HT receptor subtype in the limbic compartment of the striatum may represent a compensatory event for the serotonergic dysfunction and associated mental disorders in neurodegenerative diseases such as Parkinson disease.

The role of the D(2) dopamine receptor (D(2)R) in A(2A) adenosine receptor (A(2A)R)-mediated behavioral and cellular responses as revealed by A(2A) and D(2) receptor knockout mice

The A(2A)R is largely coexpressed with D(2)Rs and enkephalin mRNA in the striatum where it modulates dopaminergic activity. Activation of the A(2A)R antagonizes D(2)R-mediated behavioral and neurochemical effects in the basal ganglia through a mechanism that may involve direct A(2A)R-D(2)R interaction. However, whether the D(2)R is required for the A(2A)R to exert its neural function is an open question. In this study, we examined the role of D(2)Rs in A(2A)R-induced behavioral and cellular responses, by using genetic knockout (KO) models (mice deficient in A(2A)Rs or D(2)Rs or both). Behavioral analysis shows that the A(2A)R agonist 2-4-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine reduced spontaneous as well as amphetamine-induced locomotion in both D(2) KO and wild-type mice. Conversely, the nonselective adenosine antagonist caffeine and the A(2A)R antagonist 8-(3-chlorostyryl)caffeine produced motor stimulation in mice lacking the D(2)R, although the stimulation was significantly attenuated. At the cellular level, A(2A)R inactivation counteracted the increase in enkephalin expression in striatopallidal neurons caused by D(2)R deficiency. Consistent with the D(2) KO phenotype, A(2A)R inactivation partially reversed both acute D(2)R antagonist (haloperidol)-induced catalepsy and chronic haloperidol-induced enkephalin mRNA expression. Together, these results demonstrate that A(2A)Rs elicit behavioral and cellular responses despite either the genetic deficiency or pharmacological blockade of D(2)Rs. Thus, A(2A)R-mediated neural functions are partially independent of D(2)Rs. Moreover, endogenous adenosine acting at striatal A(2A)Rs may be most accurately viewed as a facilitative modulator of striatal neuronal activity rather than simply as an inhibitory modulator of D(2)R neurotransmission.

Selective attenuation of psychostimulant-induced behavioral responses in mice lacking A(2A) adenosine receptors

A(2A) adenosine receptors are highly expressed in the striatum where they modulate dopaminergic activity. The role of A(2A) receptors in psychostimulant action is less well understood because of the lack of A(2A)-selective compounds with access to the central nervous system. To investigate the A(2A) adenosinergic regulation of psychostimulant responses, we examined the consequences of genetic deletion of A(2A) receptors on psychostimulant-induced behavioral responses. The extent of dopaminergic innervation and expression of dopamine receptors in the striatum were indistinguishable between A(2A) receptor knockout and wild-type mice. However, locomotor responses to amphetamine and cocaine were attenuated in A(2A) knockout mice. In contrast, D(1)-like receptor agonists SKF81297 and SKF38393 produced identical locomotor stimulation and grooming, respectively, in wild-type and A(2A) knockout mice. Similarly, the D(2)-like agonist quinpirole produced motor-depression and stereotypy that were indistinguishable between A(2A) knockout and wild-type mice. Furthermore, attenuated amphetamine- (but not SKF81297-) induced locomotion was observed in pure 129-Steel as well as hybrid 129-SteelxC57BL/6 mice, confirming A(2A) receptor deficiency (and not genetic background) as the cause of the blunted psychostimulant responses in A(2A) knockout mice. These results demonstrate that A(2A) receptor deficiency selectively attenuates psychostimulant-induced behavioral responses and support an important role for the A(2A) receptor in modulating psychostimulant effects.

Pancreatic homeodomain transcription factor IDX1/IPF1 expressed in developing brain regulates somatostatin gene transcription in embryonic neural cells

Hox-like homeodomain proteins play a critical role during embryonic development by regulating the transcription of genes that are important for the generation of specific organs or cell types. The homeodomain transcription factor IDX1/IPF1, the expression of which was thought until recently to be restricted to the pancreas and foregut, is required for pancreas development and for the expression of genes controlling glucose homeostasis. We report that IDX1/IPF1 is also expressed in embryonic rat brain at a time coincident with active neurogenesis. Electrophoretic mobility shift assays with nuclear extracts of embryonic brains indicated that IDX1/IPF1 binds to two somatostatin promoter elements, SMS-UE-B and the recently discovered SMS-TAAT3. The requirement of these elements for IDX1/IPF1 transactivation of the somatostatin gene in neural cells was confirmed in transfection studies using embryonic cerebral cortex-derived RC2.E10 cells. Immunohistochemical staining of rat embryos showed IDX1/IPF1-positive cells located near the ventricular surface in germinative areas of the developing central nervous system. Cellular colocalization of IDX1/IPF1 and somatostatin was found in several areas of the developing brain, including cortex, ganglionic eminence, hypothalamus, and inferior colliculus. These results support the notion that IDX1/IPF1 regulates gene expression during development of the central nervous system independent of its role on pancreas development and function.

The activity-regulated cytoskeletal-associated protein arc is expressed in different striosome-matrix patterns following exposure to amphetamine and cocaine

The activity-regulated, cytoskeletal-associated gene, arc, is a brain-enriched immediate-early gene whose expression is rapidly induced in the striatum by dopamine receptor agonists. This rapid induction of arc in the striatum is similar to that of other early response genes such as c-fos, junB, deltafosB, fra, and NGFI-A, which code for transcription factors. Unlike these proteins, however, Arc is a cytoskeletal protein expressed not only in the nucleus of neurons but also in their dendrites. We investigated the patterns of Arc expression evoked in the rat striatum by acute exposures to two psychomotor stimulants, cocaine and amphetamine. Cocaine induced arc in striatal neurons that were broadly distributed within both striosome and matrix compartments of the caudoputamen. Amphetamine also evoked Arc expression in striatal projection neurons, but these were heavily concentrated in the striosomal compartment and only sparsely in the matrix compartment in the rostral striatum. The contrasting patterns of Arc expression evoked by cocaine and amphetamine parallel those of c-Fos, JunB, FRA, and NGFI-A expression induced by these two psychomotor stimulants. This difference in the action of cocaine and amphetamine at the level of protein expression may be linked to the different effects of these psychomotor stimulants on behavior.

Interaction between the serotoninergic and dopaminergic systems in d-fenfluramine-induced activation of c-fos and jun B genes in rat striatal neurons

To test for the relative contributions of the dopaminergic and serotoninergic systems in the striatum to the effects of d-fenfluramine, an indirect serotonin receptor agonist, we assessed the expression of Fos/Jun proteins induced by d-fenfluramine given alone or in the presence of dopaminergic or serotoninergic agents. To determine the neuronal targets of d-fenfluramine in the striatum, we identified the phenotypes of striatal neurons in which d-fenfluramine induced Fos expression. Our results demonstrated that d-fenfluramine evokes nuclear expression of Fos/Jun B proteins in the striatum, and that the Fos expression was dose-dependent and accompanied by transient induction of c-fos mRNA. Fos expression was blocked by p-chloroamphetamine, a serotoninergic neurotoxin. Pretreatment with SCH 23390, a D1-dopamine receptor antagonist, led to a marked decrease in Fos/Jun B expression in the caudoputamen, but not in the cortex, whereas pretreatment with methiothepin, a nonselective serotonin 5-HT1 receptor antagonist, blocked Fos expression completely in the cortex and only partially in the caudoputamen. The expression of Fos/Jun B in the striatum occurred mainly in dynorphin-containing neurons and in a subpopulation of striatal interneurons that exhibited NADPH-diaphorase activity. Most of the enkephalin-containing neurons of the striatum did not show Fos/Jun B staining. These results suggest that the mechanism by which d-fenfluramine induces c-fos and jun B expression in the rat caudoputamen depends at least in part on activation of the dopaminergic system by serotonin.

A(2A) adenosine receptor deficiency attenuates brain injury induced by transient focal ischemia in mice

Extracellular adenosine critically modulates ischemic brain injury, at least in part through activation of the A(1) adenosine receptor. However, the role played by the A(2A) receptor has been obscured by intrinsic limitations of A(2A) adenosinergic agents. To overcome these pharmacological limitations, we explored the consequences of deleting the A(2A) adenosine receptor on brain damage after transient focal ischemia. Cerebral morphology, as well as vascular and physiological measures (before, during, and after ischemia) did not differ between A(2A) receptor knock-out and wild-type littermates. The volume of cerebral infarction, as well as the associated neurological deficit induced by transient filament occlusion of the middle cerebral artery, were significantly attenuated in A(2A) receptor knock-out mice. This neuroprotective phenotype of A(2A) receptor-deficient mice was observed in different genetic backgrounds, confirming A(2A) receptor disruption as its cause. Together with complimentary pharmacological studies, these data suggest that A(2A) receptors play a prominent role in the development of ischemic injury within brain and demonstrate the potential for anatomical and functional neuroprotection against stroke by A(2A) receptor antagonists.

Dopamine D3 receptor mutant mice exhibit increased behavioral sensitivity to concurrent stimulation of D1 and D2 receptors

The dopamine D3 receptor is expressed primarily in regions of the brain that are thought to influence motivation and motor functions. To specify in vivo D3 receptor function, we generated mutant mice lacking this receptor. Our analysis indicates that in a novel environment, D3 mutant mice are transiently more active than wild-type mice, an effect not associated with anxiety state. Moreover, D3 mutant mice exhibit enhanced behavioral sensitivity to combined injections of D1 and D2 class receptor agonists, cocaine and amphetamine. However, the combined electrophysiological effects of the same D1 and D2 agonists on single neurons within the nucleus accumbens were not altered by the D3 receptor mutation. We conclude that one function of the D3 receptor is to modulate behaviors by inhibiting the cooperative effects of postsynaptic D1 and other D2 class receptors at systems level.

D1-class dopamine receptors influence cocaine-induced persistent expression of Fos-related proteins in striatum

Chronic intermittent exposure to psychomotor stimulants induces in the striatum the expression of Fos-related proteins (Fras) that persist after the end of drug treatment. We carried out experiments to determine whether such Fras ("chronic Fras') require dopamine D1-class receptor function for their persistent expression in the striatum. We chronically administered cocaine to rats in a behavioral sensitization protocol and blocked D1-class receptors with SCH23390 before a final cocaine challenge. Western blotting and immunohistochemical analyses indicate that Fras persistently expressed in response to chronic treatment include proteins of two types: those that have become independent of D1-class dopamine receptor activation and those that remain dependent on D1-class receptors for their expression following drug challenge.

Cellular responses to psychomotor stimulant and neuroleptic drugs are abnormal in mice lacking the D1 dopamine receptor

Stimulation of dopamine D1 receptors has profound effects on addictive behavior, movement control, and working memory. Many of these functions depend on dopaminergic systems in the striatum and D1-D2 dopamine receptor synergies have been implicated as well. We show here that deletion of the D1 dopamine receptor produces a neural phenotype in which amphetamine and cocaine, two addictive psychomotor stimulants, can no longer stimulate neurons in the striatum to express cFos or JunB or to regulate dynorphin. By contrast, haloperidol, a typical neuroleptic that acts preferentially at D2-class receptors, remains effective in inducing catalepsy and striatal Fos/Jun expression in the D1 mutants, and these behavioral and neural effects can be blocked by D2 dopamine receptor agonists. These findings demonstrate that D2 dopamine receptors can function without the enabling role of D1 receptors but that D1 dopamine receptors are essential for the control of gene expression and motor behavior by psychomotor stimulants.

Network-level changes in expression of inducible Fos-Jun proteins in the striatum during chronic cocaine treatment and withdrawal

Repeated exposure to psychomotor stimulants produce long-term changes in behavior ranging from addiction to behavioral sensitization. Many of these behaviors depend on the nigrostriatal system of the basal ganglia. We show here that chronic cocaine exposure not only leads to time-varying alterations in the inducibility of bZIP transcription factors in individual striatal neurons, but also to long-lasting network changes in which ensembles of striatal neurons express these proteins. These network-level adaptations suggest that the behavioral sensitization induced by repeated psychomotor stimulant exposure may reflect an enduring functional reorganization of basal ganglia circuits.

Elimination of cocaine-induced hyperactivity and dopamine-mediated neurophysiological effects in dopamine D1 receptor mutant mice

The brain mesoaccumbens dopamine system is intricately involved in the psychomotor stimulant activities of cocaine. However, the extent to which different dopamine receptors mediate these effects has not yet been firmly established. The present study used dopamine D1 receptor mutant mice produced by gene targeting to investigate the role of this receptor in the effects induced by cocaine. In contrast with wild-type mice, which showed a dose-dependent increase in locomotion, D1 mutant mice exhibited a dose-dependent decrease. Electrophysiological studies of dopamine-sensitive nucleus accumbens neurons demonstrated a marked reduction in the inhibitory effects of cocaine on the generation of action potentials. In addition, the inhibitory effects of dopamine as well as D1 and D2 agonists were almost completely abolished, whereas those of serotonin were unaffected. D2-like dopamine receptor binding was also normal. These results demonstrate the essential role of the D1 receptor in the locomotor stimulant effects of cocaine and in dopamine-mediated neurophysiological effects within the nucleus accumbens.

Dopamine D1 receptor mutant mice are deficient in striatal expression of dynorphin and in dopamine-mediated behavioral responses

The brain dopaminergic system is a critical modulator of basal ganglia function and plasticity. To investigate the contribution of the dopamine D1 receptor to this modulation, we have used gene targeting technology to generate D1 receptor mutant mice. Histological analyses suggested that there are no major changes in general anatomy of the mutant mouse brains, but indicated that the expression of dynorphin is greatly reduced in the striatum and related regions of the basal ganglia. The mutant mice do not respond to the stimulant and suppressive effects of D1 receptor agonists and antagonists, respectively, and they exhibit locomotor hyperactivity. These results suggest that the D1 receptor regulates the neurochemical architecture of the striatum and is critical for the normal expression of motor activity.

Coordinate expression of c-fos and jun B is induced in the rat striatum by cocaine

In cells in culture, specific stimuli induce selective patterns of immediate-early gene induction. In the present study, we tested for such selectivity of stimulated gene expression by monitoring the expression of fos/jun gene mRNAs in the striatum in rats treated in vivo with the indirect dopamine agonist cocaine. We found by Northern blot and in situ hybridization analysis that cocaine induces the coordinate expression of c-fos and jun B mRNAs in neurons of the rat's striatum. By contrast, another immediate-early gene of the leucine-zipper family, c-jun, was not induced in striatal neurons by cocaine at any time tested from 1 to 24 hr after treatment. With the same probe, we could detect the induction of c-jun mRNA (as well as that of c-fos and jun B mRNAs) in the hippocampus following administration of pentylenetetrazol. The induction of expression of c-fos and jun B was rapid and transient, with peak expression occurring at approximately 1 hr after cocaine administration, and the induction of the two genes was in similar striatal sites. These results establish that differential patterns of expression of fos/jun genes occur in striatal neurons following exposure to cocaine, a potent psychomotor stimulant. We suggest that these tissue-specific patterns of gene expression may contribute to the response specificity of striatal neurons to stimulation by monoamines including dopamine.

Regional effects of pertussis toxin in vivo and in vitro on GABAB receptor binding in rat brain

Agonist binding to GABAB receptors modulates the activity of the guanine nucleotide binding proteins, Go and Gi. These G proteins are ADP-ribosylated by pertussis toxin and this prevents them from coupling to the GABAB receptor resulting in a reduction in high-affinity GABAB binding. GTP, which binds to a different site on the G protein alpha subunit, also reduces the affinity of the receptor for the G protein, and this can be used as a "marker" for G protein-GABAB receptor linkage. We have examined GABAB binding site distribution in rat brain after unilateral intrahippocampal pertussis toxin injection in vivo, and after incubating brain slices in pertussis toxin in vitro, using the technique of receptor autoradiography. The effect of pertussis toxin was compared with that of GTP gamma S on GABAB binding. Intrahippocampal pertussis toxin administration reduced GABAB but not GABAA receptor binding and the effects appeared to be limited by pertussis toxin diffusion. More widespread reductions in GABAB binding were seen after incubation of brain slices in vitro but the extent varied in different brain regions. No reduction was detected in the corpus striatum. GABAB binding was also reduced in membranes prepared from cerebral cortex, hippocampus and cerebellum but there was no significant reduction in the corpus striatum after pertussis toxin treatment. GTP gamma S reduced GABAB binding to a similar extent in all areas studied irrespective of their sensitivity to pertussis toxin suggesting that while GABAB binding sites are linked to G proteins throughout the rat brain, those in the corpus striatum may be predominantly pertussis toxin insensitive.

Dynamic regulation of NGFI-A (zif268, egr1) gene expression in the striatum

The expression of immediate-early genes of the fos/jun leucine zipper family can be regulated in striatal neurons by stimuli affecting the dopaminergic nigrostriatal system. The regulatory effects are gene specific, region specific, and striatal compartment specific. In the experiments reported here, we have explored the possibility that dopaminergic stimulation might also affect striatal expression of NGFI-A, a member of the zinc finger family of immediate-early genes. We treated healthy adult rats with amphetamine or cocaine and monitored the acute response of striatal neurons by in situ hybridization with oligonucleotide probes for NGFI-A mRNA. Both drugs evoked rapid, anatomically patterned increases in NGFI-A mRNA expression in the dorsal striatum (caudoputamen) and in the ventral striatum (nucleus accumbens, olfactory tubercle). The main response to each drug was in medium-sized neurons, known to be the projection neurons of the striatum. At every dose of amphetamine eliciting a response, the increased NGFI-A mRNA expression was preferentially concentrated in striosomes of the rostral caudoputamen, whereas cocaine at each dose given induced expression of NGFI-A mRNA in both striosomes and matrix at these striatal levels. The two indirect agonists evoked NGFI-A expression in both striatal compartments farther caudally, especially in the central and medial caudoputamen. Activation by both drugs was blocked by pretreatment with the D1-selective dopamine receptor antagonist SCH23390. These patterns of NGFI-A activation are remarkably similar to those found for Fos-like immunoreactivity following acute amphetamine and cocaine treatments, suggesting that coordinate activation of members of at least two immediate-early gene families occurs in the striatum following catecholaminergic stimulation. Such patterns of induction strongly support the view that the genomic responsiveness of the striosome and of the matrix compartments of the rostral striatum are distinct at the level of early-response gene expression. These findings raise the interesting possibility that some of the well-known effects of dopaminergic stimulation on neuropeptide and neurotransmitter expression in the striatum may reflect particular combinatorial patterns of immediate-early gene activation.

Differential vulnerability of primate caudate-putamen and striosome-matrix dopamine systems to the neurotoxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

The meperidine analogue derivative 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces nigrostriatal fiber damage and severe parkinsonism in humans and animals. MPTP-induced parkinsonism has been proposed as a model of Parkinson disease, but doubts have been raised about whether the patterns of nigrostriatal fiber loss in the two conditions are similar. We report here observations on [3H]mazindol monoamine (principally dopamine) uptake-site binding in the striatum of monkeys (Saimiri sciureus) exposed to low doses of MPTP. We show that this treatment can produce a pattern of nigrostriatal degeneration characteristic of that seen in Parkinson disease, in which there is greater depletion of dopaminergic markers in the putamen than in the caudate nucleus, especially posteriorly. Moreover, within the regions of diminished uptake-site binding in the MPTP-treated monkeys, there is differential preservation of binding in striosomes relative to the surrounding matrix. We suggest that both regional and striosome/matrix patterns of nigrostriatal depletion are key features of MPTP-induced neurodegeneration and that both patterns may provide clues to the mechanisms underlying neurodegeneration in Parkinson disease as well.

Expression of the immediate early gene c-fos in basal ganglia: induction by dopaminergic drugs

Expression of the immediate early gene c-fos is increased in mammalian neurons by a number of stimuli and the usefulness of this gene as a marker of neuronal activation has been demonstrated in several systems. Directly-acting dopamine agonists of the D1-type (SKF 38393, CY 208-243) and indirectly-acting dopamine agonists (amphetamine, cocaine) all produce a rapid and transient increase in Fos protein levels in varying patterns in striatum and cerebral cortex. Directly-acting dopamine agonists only produce c-fos activation in denervated (supersensitive) striatum whereas cocaine and amphetamine activate c-fos in striatum in naive animals. Remarkably, D2 selective antagonists such as haloperidol, albeit in high doses, also activate c-fos expression. Activation of c-fos and other immediate early genes may play a part in the development of such long-term dopamine-related effects as dyskinetic movements and addiction.

Amphetamine and cocaine induce drug-specific activation of the c-fos gene in striosome-matrix compartments and limbic subdivisions of the striatum

Amphetamine and cocaine are stimulant drugs that act on central monoaminergic neurons to produce both acute psychomotor activation and long-lasting behavioral effects including addiction and psychosis. Here we report that single doses of these drugs induce rapid expression of the nuclear proto-oncogene c-fos in the forebrain and particularly in the striatum, an extrapyramidal structure implicated in addiction and in long-term drug-induced changes in motor function. The two drugs induce strikingly different patterns of c-fos expression in the striosome-matrix compartments and limbic subdivisions of the striatum, and their effects are pharmacologically distinct, although both are sensitive to dopamine receptor blockade. We propose that differential activation of immediate-early genes by psychostimulants may be an early step in drug-specific molecular cascades contributing to acute and long-lasting psychostimulant-induced changes in behavior.

Dopamine uptake sites in the striatum are distributed differentially in striosome and matrix compartments

A major mechanism of neurotransmitter inactivation at catecholaminergic synapses is reuptake of released transmitter at high-affinity uptake sites on presynaptic terminals. We have analyzed the anatomical distribution of site-selective ligand binding for dopamine uptake sites in the striatum of rat, cat, and monkey. We report here that desipramine-sensitive [3H]mazindol binding sites have highly heterogeneous distributions in the dorsal and the ventral striatum. In the caudate nucleus of cat and monkey, [3H]mazindol binding observes striosomal ordering, being reduced in striosomes and heightened in the extrastriosomal matrix. Some local heterogeneity appears in the ventral caudoputamen of the rat. Different subdivisions of the nucleus accumbens also have different binding levels. These findings suggest that some functional effects of psychoactive drugs, such as cocaine, that bind to the dopamine-uptake complex could be related to the distribution of these specific uptake sites. The findings also raise the possibility that these distributions could result in selective neuronal vulnerability to neurotoxins, such as 1-methyl-4-phenylpyridine (MPP+), that depend on the dopamine-uptake complex for entry into neurons.

Benzodiazepine receptor autoradiography in corpus striatum of rat after large frontal cortex lesions and chronic treatment with diazepam

It has previously been shown that diazepam impairs behavioural recovery from partial unilateral ablation of the cerebral cortex in rats. The present study confirmed this in rats with large unilateral lesions of the frontal cortex and showed that diazepam (5 mg/kg i.p. daily for 14 days immediately after surgery) prevented recovery from sensory asymmetry even after 120 days. In saline-treated rats greater than 80% recovery had occurred by this time. A study of binding to benzodiazepine receptors, using an in vitro autoradiographic technique, was performed to determine whether the lack of recovery after administration of diazepam was associated with any long-term receptor changes on the damaged side of the brain. Binding of [3H]Ro15-1788 was increased by up to 40% in the caudate putamen on the decorticated side at 14-120 days. This was not significantly altered by treatment with diazepam. Binding of [3H]Ro15-1788 in the nucleus accumbens was not altered by lesion of the frontal cortex alone or after treatment with diazepam. It is concluded that the lack of recovery from sensory asymmetry, produced by diazepam after lesion of the frontal cortex cannot be correlated with any change in binding to benzodiazepine receptors within the corpus striatum.

In vivo stimulation of phosphoinositide metabolism in the brainstem of rats following osmotic stress

We have investigated the effects of osmotic stress on the activity of inositol phospholipid turnover in the central nervous system of rats. Intracerebroventricular injection of [3H]myo-inositol was used for metabolic labelling of brain phosphoinositides in vivo. The levels of radiolabelled inositol lipids increased in a time-dependent manner in several areas of the brain, reaching a maximum 24 h after the injection. Treatment with LiCl 20 h after the administration of tritiated myo-inositol did not modify the levels of inositol lipids, but resulted in a dose-dependent accumulation of inositol phosphates. In rats treated with 10 mEq/kg LiCl, intraperitoneal injections of hypertonic saline (1.50 M NaCl) resulted in the stimulation of phosphoinositide turnover in the brainstem, but not in any of the other regions of the brain studied. This response was not prevented by unilateral cervical vagotomy, but was significantly lower in vasopressin-deficient Brattleboro rats. Brain phosphoinositide metabolism was not stimulated by acute blood volume depletion. We conclude that osmotic stress, but not acute hypovolemia, results in vasopressin-dependent activation of brainstem neurons by stimulating inositol phospholipid metabolism. In addition, metabolic labelling in vivo followed by treatment with LiCl provides a useful approach for assessing the physiological significance of the activation of polyphosphoinositide metabolism in the central nervous system in vivo. Our study provides evidence for a functional role of this second messenger system in the brainstem.

Neonatal administration of vasopressin antiserum induces long-term deficits on active and passive avoidance behaviour in rats

Two-day-old male rats received a subcutaneous injection of arginine-vasopressin (AVP) antiserum and avoidance behaviour was studied 3 months later. Rats treated with the antiserum showed a clear retention deficit in a one-trial learning, step-through passive avoidance situation. Anti-AVP treatment also induced an impairment on the acquisition of a two-way active avoidance task. Systolic blood pressure was lower than normal in these animals. The results obtained appear to be indicative of the high vulnerability of the developing nervous system, and are discussed in the context of the different hypothesis on the role of central or peripheral mechanisms in the behavioural effects of AVP. Although no definite conclusions may be drawn in this regard, the present data strongly suggest that neonatal administration of AVP antiserum exerts long-lasting effects upon the functionality of several physiological mechanisms related to the behavioural adaptation of the organism.

Pharmacological study of the new mucolytic drug N-guanyl-cysteine

The pharmacological evaluation of N-guanyl-cysteine (IQB-782) is reported. This new cysteine derivative shows a potent mucolytic-expectorant activity in different test systems. Thus, IQB-782 protects rats against tobacco-smoke-induced respiratory airway obstruction, increases the tracheo-bronchial mucus secretion in rabbits and increases the pulmonary excretion of fluorescein in mice, an index of broncho-secretagogue activity. Like other mucolytics, IQB-782 is also effective in vitro in reducing the viscosity of a suspension of gastric mucin. This new drug is apparently devoid of any cardiovascular or autonomic activity and shows a moderate CNS depressant effect. IQB-782 is consequently a new thiol derivative which may offer some advantages in the treatment of different types of obstructive pulmonary disease.

Long-term hyperalgesia in rats induced by neonatal administration of vasopressin antiserum

Vasopressin antiserum was given to two day old rats and the nociceptive thresholds were evaluated three months later. The rats were hypersensitive to pain when electrical current, but not heat, was used as the noxious stimulus. These animals were also insensitive to cold-water swim, a non-opioid form of stress analgesia. The vasopressin content in the pituitary or in the hypothalamus was not however modified by the neonatal treatment. The present results suggest a physiological role for vasopressin in non-opioid pain inhibitory systems.