Distribution of dopamine D-2 receptors in the rat striatal complex and its comparison with acetylcholinesterase

Mechanisms of action of antipsychotic drugs of different classes, refractoriness to therapeutic effects of classical neuroleptics, and individual variation in sensitivity to their actions: Part I

Many issues remain unresolved about antipsychotic drugs. Their therapeutic potency scales with affinity for dopamine D2 receptors, but there are indications that they act indirectly, with dopamine D1 receptors (and others) as possible ultimate targets. Classical neuroleptic drugs disinhibit striatal cholinergic interneurones and increase acetyl choline release. Their effects may then depend on stimulation of muscarinic receptors on principle striatal neurones (M4 receptors, with reduction of cAMP formation, for therapeutic effects; M1 receptors for motor side effects). Many psychotic patients do not benefit from neuroleptic drugs, or develop resistance to them during prolonged treatment, but respond well to clozapine. For patients who do respond, there is a wide (>ten-fold) range in optimal doses. Refractoriness or low sensitivity to antipsychotic effects (and other pathologies) could then arise from low density of cholinergic interneurones. Clozapine probably owes its special actions to direct stimulation of M4 receptors, a mechanism available when indirect action is lost.

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.

Immunocytochemical evidence for the striatal nature of the rat lateral part of interstitial nucleus of the posterior limb of the anterior commissure (IPAC)

The present study focuses on the basal forebrain region originally designated as fundus striati, but currently known as 'interstitial nucleus of the posterior limb of the anterior commissure' (IPAC). Using multiple immunofluorescence of the calcium-binding proteins parvalbumin and calbindin, the GABA(A) receptor alpha1-subunit, vasoactive intestinal polypeptide (VIP), met(5)-enkephalin (MENK) and glutamic acid decarboxylase (GAD), it was shown that VIP-immunostained axons, which are typical for major parts of the extended amygdala, densely innervate only the medial part of IPAC, while they are absent in the lateral part. On the other hand, large-sized GABAergic, parvalbumin- and GABA(A) receptor alpha1-subunit-immunoreactive neurons, which are densely covered by separate GAD- and MENK-immuno reactive terminals and a type of medium-sized alpha1-subunit-monolabelled cells, occur in the dorsal striatum and in the adjacent lateral part of IPAC as well. Large-sized neurons double labelled for parvalbumin and the GABA(A) receptor alpha1-subunit are also widely distributed in the neighbouring ventral pallidum. Neurons of this type are absent, however, in the medial part of IPAC and other extended amygdala subunits. Our findings confirm the recent suggestion of a morphofunctional dichotomy of IPAC (Comp. Neurol. 439 (2001) 104), as only the medial part reveals characteristics as typical for extended amygdala, while its lateral part exhibits cytochemical peculiarities of striatal tissue. Therefore, the term 'lateral part of IPAC' should be replaced by the term 'putaminal fundus (fundus putaminis)' according to recently published designations of corresponding striatal constituents (Atlas of the Human Brain, 2002, Academic Press, San Diego, CA; J. Chem. Neuroanat. 23 (2002) 75).

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.

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

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

Differences in D2 dopamine receptor binding in the neostriatum between cats hemidecorticated neonatally or in adulthood

In order to study differences in response to neocortical injury sustained at different ages at the neurotransmitter level, we examined the density in D2 dopamine receptors in the neostriatum of cats hemidecorticated neonatally (N = 4) or in adulthood (N = 4), as well as in intact brains (N = 6). Receptor densities were measured using quantitative autoradiography and [3H]-spiperone binding in 12 regions of the neostriatum and nucleus accumbens septi. We found that the anterior lateral caudate nucleus on both sides of the brain contained a higher D2 receptor density in neonatal-lesioned as compared to adult-lesioned brains. Ipsilateral to the lesion, the increase was 101% (P < 0.05) and contralaterally it amounted to 77% (P < 0.05). Moreover, this region of the ipsilateral caudate nucleus of neonatal-lesioned cats tended to be more densely labeled than that of intact brain by 58% (P < 0.1). D2 receptor densities in adult-lesioned cats did not differ from that of intact controls. Comparison of these data with those of a former morphological study using the same animals suggested that this bilateral elevation of D2 receptor density in neonatally lesioned brains represents a higher mean density of binding sites per neuron. The elevation in the neonatal-lesioned cats might be a response of the striatum to neuroplastic changes in the striatal neuropil, including the corticostriatal afferents, since such changes are different in neonatal- as compared to adult-lesioned cats.

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.

Distribution and postnatal ontogeny of adenosine A2A receptors in rat brain: comparison with dopamine receptors

In adult rat brain, adenosine A2A receptors and dopamine D2 receptors are known to be located on the same cells where they interact in an antagonistic manner. In the present study we wanted to examine when this situation develops and compared the postnatal ontogeny of the binding of the adenosine A2A receptor agonist [3H]CGS 21680, the binding of the dopamine D1 receptor antagonist [3H]SCH 23390 and the dopamine D2 receptor antagonist [3H]raclopride. All three radioligands bound to the striatum at birth and this binding increased several-fold during the postnatal period. [3H]SCH 23390 binding developed first (mostly during the first week), followed by [3H]raclopride binding (first to third week) and [3H]CGS 21680 binding (only during second and third week). For all three radioligands the binding tended to decrease between 21 days and adulthood. This occurred earlier and was more pronounced in the globus pallidus than in the other examined structures. The increase in [3H]CGS 21680 binding from newborn to adult was mainly due to four-fold increase in the number of binding sites. The pharmacology of [3H]CGS 21680 binding to caudate-putamen was similar in newborn, one-week-old and adult animals, and was indicative of A2A receptors. The binding was inhibited by guanylyl imidodiphosphate at all ages, indicating that A2A receptors are G-protein-coupled already at birth. In contrast to the large increase in [3H]CGS 21680 binding, there was a decrease in the levels of A2A messenger RNA during the postnatal period in the caudate-putamen. In cerebral cortex [3H]CGS 21680 bound to a different site than the A2A receptor. From birth to adulthood cortical binding of [3H]CGS 21680 increased four-fold and that of the adenosine A1 agonist [3H]cyclohexyladenosine 19-fold. During early postnatal development [3H]SCH 23390 binding was higher in deep than in superficial cortical layers, but this difference disappeared in adult animals. There was binding of both [3H]CGS 21680 and [3H]cyclohexyladenosine to the olfactory bulb, suggesting a role of the two adenosine receptors in processing of olfactory information. [3H]CGS 21680 binding was present in the external plexiform layer and glomerular layer, and increased during development, but the density of binding sites was about one tenth of that seen in caudate putamen. [3H]cyclohexyladenosine showed a very different labelling pattern, resembling that observed with [3H]SCH 23390. Postnatal changes in adenosine receptors may explain age-dependent differences in stimulatory caffeine effects and endogenous protection against seizures. Since A2A receptors show a co-distribution with D2 receptors throughout development, caffeine may partly exert such actions by regulating the activity of D2 receptor-containing striatopallidal neurons.

Regulation of dopamine D1 and D2 receptors on striatal acetylcholine release in rats

The effects of dopamine (DA) D1 and D2 receptors on striatal acetylcholine (ACh) releases were investigated by in vivo microdialysis. All drugs were applied via dialysis membrane directly to the striatum. The levels of ACh release were increased by 10(-4) M SKF38393, a D1 receptor agonist. Although 10(-4) M SCH23390, a D1 receptor antagonist, exhibited an increase in the levels of ACh release, the agonist (10(-4) M) induced-increase in the levels of ACh release was suppressed by coperfusion of the antagonist (10(-4) M). In contrast, the levels of ACh release were decreased by the D2 receptor agonist, N-434, in a dose-dependent manner (10(-4) M to 10(-7) M) and increased by the D2 receptor antagonist, sulpiride, in a dose-dependent manner (10(-5) M to 10(-7) M). The agonist (10(-5) M) induced-decrease in the levels of ACh release was suppressed by coperfusion of the antagonist (10(-4) M). Coperfusion of D1 (10(-4) M) and D2 (10(-5) M) agonists blocked both effects of respective drug alone. In order to clarify the effect of endogenous DA, two drugs with different mechanisms for enhancing DA concentration in the synaptic cleft, the DA release-inducer methamphetamine, and the DA uptake inhibitor nomifensine were perfused separately. Both (10(-4) M to 10(-5) M) produced a dose- and a time-dependent decrease in the levels of ACh release. Significant higher levels of ACh release were observed in the striatum of the 6-hydroxydopamine (8 micrograms/10 microliters)-treated rats with significant depletion of striatal DA content. These results suggest that in striatal DA-ACh interaction ACh release, as cholinergic interneuron's activity, is tonically inhibited via the D2 receptor, mainly by dopaminergic input, and the D1 receptor probably modifies the effect of the D2 receptor indirectly.

Lack of cross-tolerance between haloperidol and clozapine towards Fos-protein induction in rat forebrain regions

We investigated whether the acute effects of haloperidol and clozapine on Fos expression in the rat forebrain are mediated by the same receptors through evaluation of cross-tolerance, particularly in the commonly affected areas. Acutely administered haloperidol (1 mg/kg. i.p.) and clozapine (20 mg/kg, i.p.) induce regionally different (e.g., the striatum, the hypothalamic paraventricular and supraoptic nuclei, and the central amygdala) and overlapping (e.g., the nucleus accumbens and the lateral septum) patterns of Fos-protein distribution in the rat forebrain. After long-term treatment, part of the acute effects of these drugs disappears in most brain areas, except in the lateral septum, the hypothalamic paraventricular and supraoptic nuclei and the amygdala following haloperidol administration. Cross-tolerance between haloperidol and clozapine was determined by administering a challenge dose of the one antipsychotic, following a 21-day pretreatment with the same or the other drug or saline. In none of the investigated brain regions was cross-tolerance towards Fos-protein induction found after haloperidol challenge in the clozapine-treated rats. Conversely, a competitive dose of clozapine in long-term haloperidol-treated rats showed cross-tolerance in the lateral septum, while the common effect of the drugs in both the dorsomedial and the dorsolateral parts of the striatum was very small. These findings indicate that, for the major part, the responses to haloperidol and clozapine are mediated by different receptors, even in brain areas that are affected by both drugs.

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.

Functional and molecular differentiation of the dopamine system induced by neonatal denervation

The administration of the neurotoxin 6-hydroxydopamine (6-OHDA) to damage the mesostriatal dopamine (DA) system in the neonate results in different neurochemical and behavioral consequences as compared to lesions made in adulthood. There have been few direct data to support the conclusion that the behavioral changes following neonatal 6-OHDA lesions reflect plasticity of the DA system. It is our hypothesis that the plasticity of the developing DA system is fundamentally different from that of the adult. Responses to 6-OHDA lesions can only be understood within the context of the status of the mesostriatal DA system at the time of the lesion. There are stages of development in the early postnatal period when certain components of the mesostriatal DA system are differentially sensitive to 6-OHDA lesions. These "windows" of vulnerability can be predicted from an analysis of the developmental expression of DA receptors and the maturation of the subpopulation of the mesostriatal DA system that innervates them. We review the differences in the behavioral plasticity of the adult and neonate sustaining 6-OHDA lesions to the mesostriatal DA system, the mechanisms responsible for the behavioral plasticity in the adult, and our conceptualization of which mechanisms are affected in the neonate.

Differential Fos-protein induction in rat forebrain regions after acute and long-term haloperidol and clozapine treatment

Both acute and long-term effects of haloperidol and clozapine on Fos-like immunoreactive nuclei in several rat forebrain areas were quantified. Rats were treated with saline (1 ml/kg.day, control), haloperidol (1 mg/kg.day) and clozapine (20 mg/kg.day) i.p. for 21 days. Two hours before perfusion fixation a single (acute treatment) or last (long-term treatment) dose of the drug was given. Drug-induced catalepsy and gain in body weight were also measured. A single dose of haloperidol produced large increases in Fos-like immunoreactive nuclei in the striatum, the nucleus accumbens and central amygdala. Following long-term treatment these increases were reduced in all nuclei studied, except the lateral septum. Acute clozapine treatment had slight (if any) effects on the number of Fos-like immunoreactivity-expressing nuclei in the striatum, but the increases in the nucleus accumbens, the lateral septum, the paraventricular and supraoptic nuclei of the hypothalamus and the central amygdala were substantial. Long-term clozapine treatment reduced the acute response significantly in all the areas except the nucleus accumbens. Both haloperidol and clozapine treatment reduced the weight gain of the rats. Haloperidol, but not clozapine, induced catalepsy that remained maximal during the long-term haloperidol treatment. These results indicate that in most brain areas high Fos-protein levels are not necessary to maintain antipsychotic activity or side-effects. The persisting effect of clozapine in the nucleus accumbens may be of significance to the efficacy of this drug in treatment-refractory schizophrenia.

Dopamine receptors: molecular biology, biochemistry and behavioural aspects

The description of new dopamine (DA) receptor subtypes, D1-(D1 and D5) and D2-like (D2A, D2B, D3, D4), has given an impetus to DA research. While selective agonists and antagonists are not generally available yet, the receptor distribution in the brain suggests that they could be new targets for drug development. Binding characteristics and second messenger coupling has been explored in cell lines expressing the new cloned receptors. The absence of selective ligands has meant that in vivo studies have lagged behind. However, progress has been made in understanding the function of DA-containing discrete brain nuclei and the functional consequence of the DA's interaction with other neurotransmitters. This review explores some of the latest advances in these various areas.

Interactive effects of stimulation of D1 and D2 dopamine receptors on fos-like immunoreactivity in the normosensitive rat striatum

Systemic administration of the selective, full, D1 dopamine agonist A-77636 [(1R,3S)3-(1'-adamantyl)-1-aminomethyl-3,4- dihydro-5,6-dihydroxy-1H-2-benzopyran hydrochloride] (0.36-2.9 mg/kg) led to a dose-dependent induction of Fos-like immunoreactivity (FLI) in the striatum. Quantitative analysis of the sections indicated that immunoreactive cells were more numerous in the medial than the lateral striatum and, within these regions, appeared to be randomly distributed. The staining produced by A-77636 could be abolished by pretreatment with the selective D1 antagonist SCH-23390. The selective D2 dopamine agonist quinpirole (3 mg/kg) had no effect on striatal FLI when given by itself, but markedly potentiated the weak striatal staining produced by low doses of A-77636. When combined with the highest dose of A-77636, which produced substantial staining by itself, quinpirole produced an increase in the number of immunoreactive cells seen in the lateral striatum but actually decreased the number present in the medial striatum. Statistical analysis of the distribution of immunoreactive cells demonstrated that, in both regions, quinpirole converted the relatively homogeneous staining seen after A-77636 alone into a markedly patchy pattern. These findings indicate that stimulation of D2 receptors produces both stimulatory and inhibitory effects on the D1-mediated expression of Fos in the striatum and that the interaction between D1 and D2 receptor stimulation must, therefore, be more complex than the simple synergism suggested by previous studies.

Islands and striosomes in the neostriatum of the rhesus monkey: non-equivalent compartments

Cytoarchitectonically defined cell-dense islands and regions of low acetylcholinesterase reactivity referred to as striosomes have been regarded as equivalent markers of the non-matrix compartment in the neostriatum. We examined islands and striosomes in adjacent sections to determine the degree of correspondence between the two neostriatal compartmental markers. Islands are aggregated centrally within the caudate, whereas striosomes are located throughout the entire nucleus, including the dorsolateral and ventromedial sectors. Moreover, even within the central sector, striosomes are more prevalent than islands. The present quantitative analysis suggests that islands may be further characterized as acetylcholinesterase-poor since the vast majority of islands co-localize with striosomes. However, due to the fact that striosomes are more numerous and more widely distributed throughout the neostriatum, less than a third of all striosomes are coincident with islands in adjacent sections. Comparison of each of these compartmental markers with the patterned terminal field of the prefrontal cortical projection revealed a near one-to-one correspondence between islands and terminal-free zones in the prefrontal projection. The percentage of striosomes which are aligned with fenestrations in the prefrontal projection is also quite high; however, because more striosomes than islands are found within the prefrontal terminal domain, some striosomes that fit within terminal-free zones do not have corresponding islands. These results indicate that islands and striosomes are not entirely equivalent compartmental markers and further suggest that contemporary, two-compartment models may not adequately represent the heterogeneity of the neostriatum.

Striatal single-unit responses to amphetamine and neuroleptics in freely moving rats

Single-unit recordings from 50 striatal neurons in freely moving rats revealed generally low activity (< 3 spikes/sec) during resting behavior and movement-related excitations in most (n = 36) neurons. While activating behavior, d-amphetamine (1.0 mg/kg, sc) usually excited and inhibited motor- and nonmotor-related neurons, respectively, relative to resting baseline firing rates. A behavioral clamping analysis, which controlled for neuronal effects secondary to behavior, yielded results suggesting a primary, amphetamine-induced excitation of striatal motor-related neurons. Haloperidol (0.1-1.0 mg/kg) strongly inhibited behavior and neuronal activity when injected 30 min after amphetamine. Clozapine (5.0-30.0 mg/kg) inhibited only selected behaviors, but reliably produced haloperidol-like reversals of amphetamine-induced neuronal excitations. A literature review revealed that the neuronal results in behaving animals differ markedly from the inhibitory striatal responses to amphetamine and the excitatory responses to dopamine antagonists often found in immobilized or anesthetized rat preparations. These contrasting, preparation-dependent results support a model based on drug interactions with a proposed neuromodulatory function of striatal dopamine, which is to facilitate or attenuate the activity of neurons receiving, respectively, substantial, or little excitatory afferent input.

Heterogeneous distribution of dopamine D1 and D2 receptors in the human ventral striatum

The distribution of dopamine D1 and D2 receptors was examined in the human ventral striatum using in vitro quantitative autoradiography. Both D1 and D2 receptors have a markedly heterogeneous distribution, that includes regional differences in binding for the D1 receptor and a pattern of smaller heterogeneities for both receptors. The latter heterogeneities in D1 and D2 binding are interrelated and, in addition, appear to be related to inhomogeneities in the acetylcholinesterase histochemistry and cellular density of the ventral striatum. The present data indicate that in the human ventral striatum the ratio between D1 and D2 receptors varies widely from one area to another.

Regional effects of neurotensin on the electrically stimulated release of [3H]dopamine and [14C]acetylcholine in the rat nucleus accumbens

This study has shown that neurotensin (NT) increases the electrically stimulated release of [3H]DA to a similar extent in all but the extreme caudolateral area of the rat nucleus accumbens and appears to modulate DA release equally in the medial and lateral zones of this brain area. The simultaneous release of ACh was not significantly affected by NT.

5'-nucleotidase: a new marker for striosomal organization in the rat caudoputamen

The distribution of the adenosine-producing ectoenzyme 5'-nucleotidase was studied by means of a histochemical lead technique in the caudoputamen of normal adult rats and of rats in which injections either of 6-hydroxydopamine in the medial forebrain bundle or of ibotenic acid in the caudoputamen had been made 1-3 weeks previously. The patterns of striatal 5'-nucleotidase activity in these animals were compared in serial sections to the patterns of calbindin-D28k immunoreactivity and of 3H-naloxone ligand binding, which respectively mark the known matrix and striosome (patch) compartments of the caudoputamen. In the normal rats, 5'-nucleotidase activity was differentially concentrated in striosomes, where it produced a dense staining of the neuropil. The enzymatic staining followed a striosomal distribution in all but the caudal caudoputamen. Within the striatal matrix, 5'-nucleotidase staining also observed a lateromedial density gradient. Depletion of the dopamine-containing nigrostriatal innervation of the caudoputamen with 6-hydroxydopamine did not alter the striosomal selectivity of 5'-nucleotidase activity. Destruction of intrastriatal neurons by ibotenic acid led to a strongly 5'-nucleotidase-positive gliosis within the resulting necrotic region. Elsewhere in the caudoputamen, the enzyme's striosomal distribution was not detectably altered. We conclude that 5'-nucleotidase histochemistry provides an advantageous tool for detecting the striosomal architecture of the rat's caudoputamen. Moreover, 5'-nucleotidase is prominently associated with glial membranes in the central nervous system, so that the concentration of this enzyme in striosomes could mark these as sites of selective glial populations within striatum. These properties and actions of 5'-nucleotidase in purinergic neurotransmission and in neuroadhesion may contribute to the specialized functions of striosomes and matrix.

Compartmentalization of excitatory amino acid receptors in human striatum

Division of the mammalian neostriatum into two intermingled compartments called striosomes and matrix has been established by analysis of enzyme activity, neuropeptide distribution, nucleic acid hybridization, and neurotransmitter receptor binding. Striosomes and matrix are distinct with respect to afferent and efferent connections, and these regions provide the potential for modulation and integration of information flow within basal ganglia circuitry. The primary neurotransmitters of corticostriatal afferents are excitatory amino acids, but to date no correlation of excitatory amino acid receptors and striatal compartments has been described. We examined binding to the three pharmacologically distinct ionotropic excitatory amino acid receptors, N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid, and kainate, in human striatum using in vitro receptor autoradiography and compared the binding to striosomes and matrix histochemically defined by acetylcholinesterase activity. Our findings reveal increased binding to N-methyl-D-aspartate receptors and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors in matrix relative to striosomes and increased kainate receptor binding in striosomes relative to matrix. These results suggest that afferent input to the two striatal compartments may be mediated by pharmacologically distinct excitatory amino acid receptor subtypes.

Regulation of aromatic L-amino acid decarboxylase by dopamine receptors in the rat brain

Decarboxylation of phenylalanine by aromatic L-amino acid decarboxylase (AADC) is the rate-limiting step in the synthesis of 2-phenylethylamine (PE), a putative modulator of dopamine transmission. Because neuroleptics increase the rate of accumulation of striatal PE, these studies were performed to determine whether this effect may be mediated by a change in AADC activity. Administration of the D1 antagonist SCH 23390 at doses of 0.01-1 mg/kg significantly increased rat striatal AADC activity in an in vitro assay (by 16-33%). Pimozide, a D2-receptor antagonist, when given at doses of 0.01-3 mg/kg, also increased AADC activity in the rat striatum (by 25-41%). In addition, pimozide at doses of 0.3 and 1 mg/kg increased AADC activity in the nucleus accumbens (by 33% and 45%) and at doses of 0.1, 0.3, and 1 mg/kg increased AADC activity in the olfactory tubercles (by 23%, 30%, and 28%, respectively). Analysis of the enzyme kinetics indicated that the Vmax increased with little change in the Km with L-3,4-dihydroxyphenylalanine as substrate. The AADC activity in the striatum showed a time-dependent response after the administration of SCH 23390 and pimozide: the activity was increased within 30 min and the increases lasted 2-4 h. Inhibition of protein synthesis by cycloheximide (10 mg/kg, 0.5 h) had no effect on the striatal AADC activity or on the increases in striatal AADC activity produced by pimozide or SCH 23390. The results indicate that the increases in AADC activity induced by dopamine-receptor blockers are not due to de novo synthesis of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional differences in the regulation of acetylcholine release upon D2 dopamine and N-methyl-D-aspartate receptor activation in rat nucleus accumbens and neostriatum

The effect of D2 dopamine receptor activation on either the electrically, or N-methyl-D-aspartate induced release of radiolabeled acetylcholine (ACh) was investigated in different areas of the nucleus accumbens and the neostriatum of rats, by using a superfusion technique. Sequential slices of 100 microns were chopped along either a rostrocaudal, mediolateral or dorsoventral axis. In every slice the effect of a supramaximal concentration of the selective D2 receptor agonist quinpirole on the release of ACh was measured. In the entire neostriatum the release of ACh was reduced by approximately 70% in the presence of quinpirole. By contrast, in the nucleus accumbens, a gradual decrease in the inhibitory effect of quinpirole on the release of ACh was observed along both the rostral-to-caudal and the lateral-to-medial axes. Whereas in the rostrolateral part a 50% inhibition could be observed, in the caudomedial part no significant inhibition could be detected. Also the N-methyl-D-aspartate induced release of ACh was smaller in the caudomedial part as compared to the rostrolateral part of the nucleus accumbens. It is concluded that the nucleus accumbens is a very heterogeneous structure with respect to the regulation of the release of ACh by D2 dopamine and N-methyl-D-aspartate receptor activation.

Heterogeneous distribution of dopamine D2 receptor mRNA in the rat striatum: a quantitative analysis with in situ hybridization histochemistry

Dopamine D2 receptor mRNAs have recently been cloned and their gross distribution in the central nervous system described. Quantitative in situ hybridization histochemistry with a cRNA probe complementary to the mRNAs encoding approximately 70% of the third intracellular loop of the rat D2 receptor was performed on sections of rat brain to determine whether differences previously observed in the density of ligand binding sites in subregions of the striatum were related to differences in mRNA levels. Film autoradiographic analysis demonstrated 30% more hybridization signal in the lateral compared to the medial caudate-putamen, a distribution parallel to that of binding of ligands specific for the D2 receptor. Inspection at the cellular level using emulsion autoradiography also indicated a differential distribution of the D2 receptor mRNA. Fewer positively labelled cells, as well as fewer silver grains per cell, were seen in the medial compared to the lateral half of the striatum. This suggests that the gradient seen in autoradiographic studies of the distribution of D2 receptors is related both to regional differences in D2 mRNA levels and to the density of cells expressing the receptor. In addition, the distribution of cells expressing D2 receptor mRNA in the extrastriosomal matrix was compared to that in striosomes identified by the presence of a high density of 3H-naloxone binding sites. Labelled cells were mainly found in the matrix (3H-naloxone binding-poor) but were also seen in striosomes (3H-naloxone binding-rich). The results suggest that differences in levels of D2 binding sites in subregions of the striatum are related to differences in the level of expression of this receptor in intrinsic striatal neurons, suggesting differential regulation of dopamine D2 receptor gene expression in topographically distinct striatal neurons.

Differential response of striatal dopamine and muscarinic cholinergic receptor subtypes to the loss of dopamine. I. Effects of intranigral or intracerebroventricular 6-hydroxydopamine lesions of the mesostriatal dopamine system

Quantitative autoradiography was utilized to examine the response of the dopamine (DA) and muscarinic cholinergic system within the striatum to lesions of the mesostriatal DA system following intranigral 6-hydroxydopamine (6-OHDA) injections. In addition, the response of DA system was examined in the striatum of animals treated with low, medium, or high doses of 6-OHDA made intracerebroventricularly (icv). Three weeks following removal of the mesostriatal DA fibers with intranigral 6-OHDA, there was an almost complete depletion of DA and [3H]mazindol binding throughout the striatum. The resulting increase in D2 receptors labeled with [3H]spiroperidol (27%) was most evident in the lateral striatum and topographically correlated with an increase in choline uptake sites labeled with [3H]hemicholinium-3 (20%). There was a smaller but significant decrease in D1 receptors labeled with [3H]SCH 23390 (15-18%) that was not topographically related to changes in [3H]spiroperidol or [3H]hemicholinium-3 binding. All doses of icv 6-OHDA produced a significant loss of DA and of [3H]mazindol binding as compared to vehicle injections that was more pronounced in the medial than in the lateral striatum. No increase in D1 receptors was observed with any dose of 6-OHDA and greater than 90% loss of DA and [3H]mazindol resulted in an increase in D2 receptors in the lateral striatum and a reduction in D1 receptors in the dorsal striatum. These data are consistent with the evidence that there is independent regulation of the two subtypes of the DA receptor. Moreover, the distribution and regulation of the subtypes of the muscarinic receptor were independent. Muscarinic M2 receptors ([3H]N-methylscopolamine in presence of excess pirenzepine) showed a lateral to medial gradient (highest laterally) that was related to the pattern of choline uptake sites and D2 receptors. Loss of DA resulted in a reduction in M2 receptors (24-30%) that was correlated with the increase in choline uptake sites. In contrast, M1 ([3H]pirenzepine) receptors showed a reverse gradient from the M2 receptor and a smaller reduction following loss of DA.

Differential response of striatal dopamine and muscarinic cholinergic receptor subtypes to the loss of dopamine. II. Effects of 6-hydroxydopamine or colchicine microinjections into the VTA or reserpine treatment

In the previous paper it was demonstrated that striatal dopamine (DA) D1 and D2 receptor subtypes and muscarinic M1 and M2 receptor subtypes show differing responses to lesions of the mesostriatal DA system. To examine this differential regulation further rats were given unilateral injections of 6-hydroxydopamine (6-OHDA) or colchicine into the ventral tegmental area (VTA), or treated chronically with reserpine or saline. Two weeks later the animals were tested for their behavioral response to a subthreshold dose of apomorphine and 24 h later their brains were removed and processed for quantitative autoradiography or for analysis of DA levels by high-performance liquid chromatography. The 6-OHDA-lesioned animals showed a supersensitive rotational response to apomorphine. The loss of DA, loss of DA uptake sites, regulation of DA D1 and D2 receptors and regulation of the muscarinic cholinergic system was similar to the previous paper. Injection of colchicine in the VTA resulted in incomplete loss of striatal DA (50%), [3H]mazindol binding (50%), and no behavioral supersensitivity to apomorphine. There was a small loss of presynaptically located D2 receptors (13%). Similar to the 6-OHDA lesions there was a loss of D1 (12%) and M1 receptors. Reserpine treatment produced an 86% decrease in DA levels, an enhanced stereotyped responsiveness to apomorphine, and an increase of both D2 (28%) and D1 receptors (26%). There was a loss of muscarinic M1 but not M2 receptors. Thus removal of DA terminals or blockade of transport of proteins in the mesostriatal axons can lead to a reduction in D1 receptor density in the striatum. In contrast, loss of DA without removal of DA terminals leads to a significant up-regulation of the D1 receptor. D2 receptors show increases following removal of DA or of DA terminals. Alteration in the muscarinic cholinergic system following damage to the mesostriatal DA system is a complex response not mimicked by either reserpine or colchicine treatment.

Ontogeny of dopamine D1 and D2 receptor subtypes in rat basal ganglia: a quantitative autoradiographic study

The ontogeny of D1 and D2 dopamine (DA) receptors in rat basal ganglia was examined by quantitative autoradiography using the iodinated ligands [125I]SCH 23982 and [125I]iodobenzamide [( 125I]IBZM), respectively. Temporal and spatial differences in the development of the receptor subtypes were observed. Scatchard transformation of saturation isotherms conducted at postnatal day 10 (P10) and P60, showed that there was no age-related change in the affinity of [125I]SCH 23982 binding to D1 receptors (Kd = 2.6 nM) but there was a significant increase in the Bmax (771 compared to 2032 fmol/mg protein, P = 0.002). A statistically significant difference in Kd was noted between ages P10 and P60 for [125I]IBZM labelling of D2 receptors (0.62 vs 1.00 nM, respectively, P less than 0.01). A significant increase in the Bmax (211 and 721 fmol/mg protein, P less than 0.01) was also observed. D1 receptors were visible as distinct patches at P1. The highest density was found in the ventrolateral caudate-putamen (CPu). By P5 the patches were found in all subregions of the CPu and nucleus accumbens. Between P7 and P10 the binding became distinctly less patchy due to a marked increase in the density of D1 receptors in non-patch (matrix) regions. Adult levels of receptor were seen by P30. The concentration of DA (measured by HPLC) and binding of [3H]mazindol to DA uptake sites in whole striatum showed similar and nonlinear increases with age. The age-related change in the topography of binding sites for [3H]mazindol was similar to that of D1 receptors at the same ages. Both D2 receptors and [3H]hemicholinium-3 (HC-3) binding to high affinity transport sites for choline developed initially in the dorso-lateral CPu. Their topography was largely overlapping but distinct from that of the D1 receptor. D2 receptors were not consistently observed until P3 in the CPu, and zones of enriched binding were aligned with zones of low density for D1 receptors. The density of D2 receptors reached adult levels by P30. The differential development of the DA receptors was also evident in the substantia nigra (SN) and globus pallidus (GP). D1 receptors were found in SN prior to the appearance of D2 receptors and throughout development the density was greater in pars reticulata than in pars compacta, whereas the density of D2 receptors was higher in the pars compacta. At all ages the density of D1 receptors was greater than the density of D2 receptors in the GP and reached adult levels before reaching it in the CPu or SN.(ABSTRACT TRUNCATED AT 400 WORDS)

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.