Effect of raclopride on dopamine D2 receptor mRNA expression in rat brain

Frontal dopaminergic abnormality in Tourette syndrome: a postmortem analysis

Frontal-subcortical abnormalities have been implicated in the pathophysiology of Tourette syndrome (TS). The goal of this study was to more extensively evaluate a possible underlying neurochemical abnormality in frontal cortex. Postmortem brain tissue from frontal and occipital regions (Brodmann's areas 4, 6, 9, 10, 11, 12, and 17) from three TS patients and three age-and sex-matched controls were analyzed by semiquantitative immunoblotting. Relative densities were measured for a variety of neurochemical markers including dopamine (D1, D2), serotonin (5HT-1A), and alpha-adrenergic (alpha-2A) receptors, the dopamine transporter (DAT), a monoamine terminal marker (vesicular monoamine transporter type 2, VMAT-2), and vesicular docking and release proteins (VAMP-2, synaptotagmin, SNAP-25, syntaxin, synaptophysin). Data from each TS sample, corrected for actin content, was expressed as a percentage value of its control. Results identified consistent increases of DAT and D2 receptor density in five of six frontal regions in all three TS subjects. D1 and alpha-2A receptor density were increased in a few frontal regions. These results support the hypothesis of a dopaminergic dysfunction in the frontal lobe and a likely role in the pathophysiology of TS.

Chronic administration with nandrolone decanoate induces alterations in the gene-transcript content of dopamine D(1)- and D(2)-receptors in the rat brain

Some adolescent and young males are engaged in misuse of anabolic-androgenic steroids (AASs) in connection with multiple drug use, in order to become intoxicated and brave, apart from currently known motives connected to sports performance and physical appearance. Recent studies suggest that alterations in neurobiological circuits implicated in the regulation of reward-related learning, aggression and motoric behavior underlie the behavioral changes associated with AAS misuse. We have previously shown that AASs induce alterations in dopamine receptor densities. The aim of the present study was to investigate if these effects could be attributed to altered mRNA content for tyrosine hydroxylase, L-amino acid decarboxylase, dopamine D(1)- and dopamine D(2)-receptor as measured by in situ hybridisation. Male Sprague-Dawley rats were subjected to 2 weeks of treatment with daily intramuscular injections of the AAS nandrolone decanoate at three different doses (1, 5 and 15 mg/kg/day). Results of the in situ hybridization showed that the mRNA content of the dopamine D(1)-receptor subtype was significantly reduced at all doses in the caudate putamen and at the highest doses in the nucleus accumbens shell. The mRNA expression of the dopamine D(2)-receptor was significantly increased at the two lowest doses in the caudate putamen and the nucleus accumbens shell. In conclusion, nandrolone has been shown to affect the expression of gene transcripts of dopaminergic receptors possibly implicated in underlying mechanisms of reward-related behavioral changes among AAS misusers.

Chronic infusion of a melanocortin receptor agonist modulates dopamine receptor binding in the rat brain

Previous studies have shown that melanocortin peptides have facilitatory effects on dopaminergic neurotransmission. In the present study we tested the hypothesis that chronic exposure to melanocortin receptor agonists causes a prolonged release of dopamine resulting in changes in the expression of dopamine receptor subtypes. Using an autoradiographic approach we found that a 2 week intracerebroventricular infusion of the melanocortin receptor agonist melanotan-II induced changes in dopamine D(1)-like and D(2)-like receptor binding in several regions of the rat brain. D(1)-like receptor binding was increased in the nucleus accumbens and the caudate putamen, but reduced in the substantia nigra (reticular part), whereas D(2)-like receptor binding was reduced in the caudate putamen, but increased in the periaqueductal grey, substantia nigra (compact part) and the ventral tegmental area. These data suggest that chronic infusion of a melanocortin receptor agonist alters the activity of dopaminergic neurons in the ventral tegmental area and substantia nigra, and support the hypothesis that melanocortin peptides may regulate the activity of central dopamine neurons.

Differential actions of dopamine receptor antagonism in rats upon food intake elicited by either mercaptoacetate or exposure to a palatable high-fat diet

Selective dopamine receptor antagonists have been shown to reduce food intake of rats under such regulatory challenge conditions as food deprivation and 2-deoxy-D-glucose-induced glucoprivation, and under such palatable conditions as acute exposure to sucrose solutions. Food intake is increased following either pretreatment with the free fatty acid oxidation inhibitor, mercaptoacetate (MA), or acute exposure to a palatable high-fat source. The present study examined whether equimolar doses (50-800 nmol/kg, s.c.) of either the selective D(1) receptor antagonist, SCH23390, or the selective D(2) receptor antagonist, raclopride, would alter food intake elicited by either MA (70 mg/kg, i.p.) or acute exposure to a high-fat diet (67% ground rat chow, 33% vegetable shortening). SCH23390 significantly and dose-dependently reduced MA-induced feeding with the two higher (400 and 800 nmol/kg) doses eliminating this response after the first 2 h and the two lower (50 and 200 nmol/kg) doses preventing the occurrence of significant MA-induced feeding. Raclopride eliminated MA-induced feeding at the highest dose, and produced dose-dependent reductions at lower doses. A different pattern of dopamine antagonist effects emerged for high-fat intake. The identical dose range of SCH23390 failed to alter high-fat intake. In contrast, whereas the highest (800 nmol/kg) dose of raclopride significantly reduced high-fat intake after 1 h, the middle (200 and 400 nmol/kg) doses of raclopride significantly increased high-fat intake after 2 h. These data are discussed in terms of the modulatory actions of dopamine upon food intake, of the differential actions of dopamine receptor subtypes upon intake under challenge and palatable conditions, and of the potential participation of presynaptic and postsynaptic receptor populations in these responses.

Role of D(1) and D(2) dopamine receptors in the acquisition and expression of flavor-preference conditioning in sham-feeding rats

The present study examined the effects of D(1) and D(2) antagonists on flavor-preference conditioning by the sweet taste of sucrose. All sessions were conducted under sham-feeding conditions to minimize post-ingestive influences. The rats were trained in alternating, one-bottle sessions to sham-feed a 16% sucrose solution containing one novel flavor (CS+) and a less-preferred 0.2% saccharin solution containing a different flavor (CS-). Three groups of food-restricted rats were treated with either vehicle (control group), the D(1) antagonist, SCH23390 (200 nmol/kg), or the D(2) antagonist, raclopride (200 nmol/kg) during one-bottle training. A fourth group (yoked group) was vehicle-treated and its training intakes were matched to that of the D(1) and D(2) drug groups. Preferences were assessed in two-bottle tests with the CS+ and CS- flavors presented in mixed 8% sucrose+0.1% saccharin solutions following systemic doses of 0, 200, or 800 nmol/kg of either the D(1) or D(2) antagonists. All groups significantly preferred the CS+ flavor in vehicle tests, although the preferences were weaker in the D(1), D(2), and yoked groups compared to the control group. All groups selectively reduced their CS+ intakes when treated with either D(1) or D(2) antagonists during two-bottle testing, and the CS+ preference was blocked at the higher doses. These data show that D(1) and D(2) receptor antagonists block the expression of a sucrose-conditioned preference, but produces substantially lesser effects upon the acquisition of this form of flavor conditioning.

Analysis of dopamine receptor antagonism upon feeding elicited by mu and delta opioid agonists in the shell region of the nucleus accumbens

The nucleus accumbens (NAcc) has been implicated as an important reward site for the mediation of unconditioned reinforcers such as food. Although both mu-selective and delta-selective opioid agonists in the NAcc induce spontaneous and palatable feeding, these effects are mediated by multiple opioid receptor subtypes within the nucleus. A role for dopaminergic mediation of feeding in the NAcc is based upon selective antagonist-induced suppression of feeding induced by systemic amphetamine. The present study investigated whether feeding elicited by infusion of either mu ([D-Ala(2), NMe-Phe(4), Gly-ol(5)]-enkephalin) or delta(2) ([D-Ala(2), Glu(4)]-deltorphin) opioid receptor subtype agonists in the shell region of the NAcc would be modified by intra-accumbens pretreatment with equimolar (12-100 nmol) doses of either D(1)-selective (SCH23390) or D(2)-selective (raclopride) antagonists. Both opioid agonists displayed comparable magnitudes and durations of feeding responses in the NAcc. SCH23390 significantly and dose-dependently reduced mu agonist-induced feeding in the NAcc with significant reductions noted following the two higher, but not two lower doses. In contrast, raclopride pretreatment produced inconsistent effects upon mu agonist-induced feeding with limited actions across doses and test times. Further, neither SCH23390 nor raclopride pretreatment in the NAcc affected feeding elicited by the delta(2) opioid agonist. These data indicate that the role of dopamine receptors in mediating opioid-induced feeding within the shell region of the NAcc is both dependent upon the dopamine receptor subtype that was blocked (D(1) vs. D(2)) as well as the opioid receptor subtype which was being stimulated mu vs. delta(2)).

Pharmacology of flavor preference conditioning in sham-feeding rats: effects of dopamine receptor antagonists

Opioid and dopamine systems are both implicated in the response to sweet solutions. Our laboratory previously reported that the opioid antagonist, naltrexone, reduced the intake of sweet solutions, yet had little or no effect on sucrose-conditioned flavor preferences in sham-feeding rats. The present study examined the role of dopamine D(1) and D(2) receptors in the expression of flavor preferences conditioned by the sweet taste of sucrose. All sessions were conducted under sham-feeding conditions to minimize postingestive influences. Training was accomplished by adding a novel flavor (CS+) to a 16% sucrose solution, a different flavor (CS-) to a less-preferred 0.2% saccharin solution in alternating, one-bottle sessions. Preferences were assessed in two-bottle tests with the CS+ and CS- flavors presented in mixed sucrose (8%)-saccharin (0.1%) solutions following systemic doses of 0, 50, 200, 400, or 800 nmol/kg of the D(2) antagonist, raclopride (Experiment 1) or the D(1) antagonist, SCH23390 (Experiment 2) under either food-restricted or unrestricted conditions. Rats significantly preferred the CS+ solutions in vehicle tests, and displayed equipotent and dose-dependent reductions in total intake and CS+ preference following either D(1) or D(2) receptor antagonism. Similar results were obtained with SCH23390 and raclopride in Experiment 3 conducted with water-restricted rats. These data indicate that dopaminergic D(1) and D(2) receptors play pivotal and functionally equivalent roles in the expression of flavor preferences conditioned by the sweet taste of sucrose.

The problem of antipsychotic treatment for functional imaging in Huntington's disease: receptor binding, gene expression and locomotor activity after sub-chronic administration and wash-out of haloperidol in the rat

It has been demonstrated that withdrawal from chronic treatment with haloperidol is associated with a long-lasting increase in the number of striatal dopamine D(2) receptors and variable changes in D(1) receptors. We have investigated the effect of withdrawal from sub-chronic administration of haloperidol on the density of dopamine receptors, dopamine receptor gene expression, and spontaneous locomotor activity. Following a 3-week treatment period with haloperidol (1.5 mg/kg, i.p.), spontaneous locomotor activity measurements, autoradiography of D(1) and D(2) receptors and in situ hybridisation histochemistry of D(1) and D(2) mRNA were performed. Using [3H]raclopride as the ligand, sub-chronic haloperidol administration produced a robust upregulation in D(2) binding in the striatum of rats which correlated with parallel increases in spontaneous locomotor activity from 24 h to 4 weeks. Using, [3H]SCH23390 as the ligand, D(1) binding was largely unaffected by the drug treatment. Non-significant changes were measured in the striatal expression of D(1) receptor mRNA or the nigral or striatal expression of D(2) receptor mRNA. Our findings have implications for the use of dopaminergic ligands in positron emission tomography (PET) imaging of patients under regimens of chronic neuroleptics in particular in the context of forthcoming trials of neural grafts in Huntington's disease (HD) striatum.

Antipsychotic regulation of dopamine D1, D2 and D3 receptor mRNA

A range of antipsychotic drugs, both "typical" and "atypical", was administered to rats over a time course and at several different dosages. The mRNA levels of dopamine D1, D2 and D3 receptor were measured in either whole brain or dissected brain regions. D3 receptor mRNA was up-regulated in whole brain by clozapine (10 and 30 but not 3 mg/kg/day), sulpiride (50 and 100 but not 20 mg/kg/day). haloperidol (3 but not 1 or 0.3 mg/kg/day), flupenthixol (3 but not 1 or 0.3 mg/kg/day), pimozide (4.5 but not 1.5 or 0.5 mg/kg/day) and loxapine (1.2 and 4 mg/kg/day but not 0.4 mg/kg/day). Sulpiride (100 mg/kg/day), clozapine (30 mg/kg/ day) and haloperidol (3 mg/kg/day) all up-regulated the D3 receptor mRNA in nucleus accumbens and olfactory tubercles but not striatum. D1 and D2 receptor mRNA was up-regulated in whole brain by haloperidol and loxapine only, and in the case of haloperidol this was localized to striatum and prefrontal cortex. Haloperidol, clozapine and sulpiride all down-regulated D1 mRNA in hippocampus and additionally haloperidol and sulpiride down-regulated it in the cerebellum. This work shows that all the drugs tested up-regulated D3 receptor, but effects on D1 and D2 receptors were less general.

Antisense strategies in dopamine receptor pharmacology

Recent advances in molecular biology have provided pharmacologists the opportunity of developing an entirely new type of agent for studying and treating a variety of biological disorders. These agents, termed antisense oligodeoxynucleotides, have as their target the messenger RNAs encoding specific proteins. They act by binding to selected portions of these mRNAs through complimentary interactions and thereby prevent the synthesis of these proteins. These novel pharmacological tools have the promise of being easier to design and being more selective and predictable in their actions. In addition, insofar as agents targeted to receptors for neurotransmitters are concerned, unlike the classical pharmacological agents, these new compounds may not lead to the upregulation of the very receptors the drugs are designed to inhibit. The present review summarizes briefly studies on the effect of oligodeoxynucleotides antisense to the mRNAs encoding the various subtypes of the dopamine receptor. The studies show that oligodeoxynucleotides antisense to the D2 dopamine receptor when intracerebroventricularly into brains of rodents are rapidly taken up into the brain tissue, distributed to brain cells, and produce effects characteristic of highly selective D2 dopamine antagonists. The compounds also produced specific reductions in the levels of D2 dopamine receptor mRNA and D2 dopamine receptors. Similarly, injecting an antisense oligodeoxynucleotide targeted to the D1 dopamine receptor mRNA produces effects characteristic of D1 dopamine receptor antagonists. Other studies using these agents has produced evidence that there is a small pool of receptors that turn over very rapidly and which constitute the functional pool of these receptors. The evidence suggests further that antisense oligodeoxynucleotides inhibit the synthesis of this small functional pool of dopamine receptors, thereby providing an explanation of why there is often a discordance between changes in dopaminergic function and changes in the levels of dopamine receptors. Studies of antisense oligodeoxynucleotides targeted to the other subtypes of dopamine receptor may help reveal the biological roles that these and other newly discovered subtypes of neurotransmitter receptors have. They may also provide an entirely new and potentially more selective therapeutic regimen for altering the functions of these receptors.

Effects of intermittent and continuous subchronic administration of raclopride on motor activity, dopamine turnover and receptor occupancy in the rat

With the purpose of finding means to circumvent the marked pharmacokinetic differences of raclopride between rats and man, the effects of intermittent and continuous administration of raclopride were compared in rats. Intermittent administration of raclopride via subcutaneous injections resulted in a prompt increase of dopamine (DA) turnover and decrease of motor activity but these effects were of short duration, probably due to rapidly decreasing raclopride DA D2 receptor occupancy. In contrast, but similar to schizophrenic patients on raclopride treatment, stable plasma raclopride levels and a steady DA D2 receptor occupancy above 70% were produced in the caudate-putamen and nucleus accumbens/olfactory tubercle, when raclopride was administered continuously via minipumps at daily doses above 2 mg/kg. Tolerance to the acute effects of raclopride on DA turnover and locomotion was found with both routes of administration but it was more marked with continuous administration. At continuous raclopride administration, tolerance to the effects of raclopride on DA turnover and spontaneous motor activity as well as supersensitivity to amphetamine-induced motor activity occurred when 70% or more of DA D2 receptor sites were occupied, i.e. the same degree of receptor occupancy as found in patients given therapeutic doses of raclopride.

Regional variability in changes in 5-HT2A receptor mRNA levels in rat brain following irreversible inactivation with EEDQ

In this study, the relationship between the expression of 5-HT2A receptors and level of 5-HT2A receptor mRNA in discrete regions of rat brain was examined by inactivating 5-HT2A receptors with the alkylating agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ; 10 mg/kg, i.p.) and measuring the time course of receptor recovery and changes in mRNA levels. In untreated controls, the distribution and levels of 5-HT2A receptors labeled with [3H]ketanserin and receptor mRNA labeled with a 230-base 33P-labeled riboprobe were found to be highly correlated in most sub-regions of the cortex, the caudate-putamen and the claustrum but not in the piriform cortex or the hippocampus. Administration of EEDQ produced 90-99% inactivation of 5-HT2A receptors and the rate of receptor recovery was uniform in most regions studied. 5-HT2A receptors in most regions reached control levels by day 14, the lone exception being the caudate-putamen where receptors reached only 56% of control by day 14. Following inactivation of receptors with EEDQ there was a transient increase in levels of 5-HT2A receptor mRNA in several regions. Although rates of receptor recovery were uniform, four distinct patterns of mRNA response were observed: (1) early elevation followed by late elevation, (2) early elevation only, (3) late elevation only, and (4) no detectable change. The absence of a direct relationship between changes in 5-HT2A receptor mRNA and 5-HT2A receptor recovery in this model system suggests that transcriptional regulation is not the mechanism controlling the recovery of these receptors after irreversible inactivation. This study also lends support to the idea that alternative mechanisms may play a role in 5-HT2A receptor regulation after other pharmacological and physiological manipulations. The regional variability in 5-HT2A mRNA regulation reported here highlights the importance of using techniques with a high level of anatomical resolution to study changes in 5-HT2A receptor mRNA levels.

Time-course of recovery of 5-HT1A receptors and changes in 5-HT1A receptor mRNA after irreversible inactivation with EEDQ

In this study, the relationship between the expression of 5-HT1A receptors and level of receptor mRNA in discrete regions of rat brain was examined by inactivation of 5-HT1A receptors with the alkylating agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ; i.p., 10 mg/kg) and measurement of the time-course of receptor recovery and changes in receptor mRNA levels. Inactivation of 5-HT1A receptors ranged from 84% in the dorsal raphe to 97% in the cortex 12 h after administration of EEDQ. Receptor levels returned to 62-100% of control levels by day 7 and the rate of recovery was uniform across all regions examined. The rate of recovery of 5-HT1A receptors labeled by the agonist [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([3H]8-OH-DPAT) and by the putative antagonist [125I]4-(2'-methoxy)phenyl-1-[2'-(N-2"-pyridinyl)-p-iodobenzamido] ethylpiperazine ([125I]p-MPPI) did not differ across regions, suggesting that the ratio of high versus low affinity states of the 5-HT1A receptor remains relatively constant during receptor recovery. However, there did appear to be a short lag in the recovery of sites labeled with the agonist. Significant increases in 5-HT1A receptor mRNA levels were observed as early as 12 h after treatment in all regions but the magnitude of these increases varied. The time-courses of recovery of 5-HT1A receptors and changes in mRNA levels were not parallel in individual regions. Moreover, inactivation of low (8-26%) to moderate (29-57%) levels of 5-HT1A receptors produced no change in mRNA levels, whereas inactivation of greater than 90% elicited a robust increase in mRNA levels. Thus, changes in 5-HT1A receptor expression are not mediated exclusively by changes in mRNA levels and extensive receptor inactivation is required to trigger transcriptional regulation.

Dopamine D1 receptor, D2 receptor, proenkephalin A and substance P gene expression in the caudate nucleus of control and schizophrenic tissue: a quantitative cellular in situ hybridisation study

The cellular expression of the mRNAs encoding the dopamine D1 receptor, dopamine D2 receptor and the neuropeptides enkephalin and substance P was determined in fresh frozen sections of human post-mortem caudate nucleus from control and schizophrenic brains using the technique of radioactive in situ hybridisation coupled with computer-assisted image analysis. Measurements of silver grain densities and mean cross-sectional somatic areas revealed no significant differences in the expression of any of these four gene transcripts. Further, cell count estimates revealed that each of these four mRNAs was expressed by approximately 20% of caudate cells (neurones and glia) in both control and schizophrenic tissue. These data demonstrate that the cellular expression of the dopamine D1 and D2 receptors and the neuropeptides enkephalin and substance P mRNAs are stable post mortem and that the relative cellular abundance of these mRNAs is not altered in the caudate nucleus of schizophrenic brains when compared to controls. These findings draw into focus the possible sites of action of clinically prescribed neuroleptics and suggest that chronic neuroleptic treatment of patients displaying negative schizophrenic symptoms may 're-set' an underlying neurochemical imbalance within the caudate nucleus.

A paradoxical regulation of the dopamine D3 receptor expression suggests the involvement of an anterograde factor from dopamine neurons

The effects of interruption of dopaminergic transmission or sustained blockade of dopamine receptors by neuroleptics on the dopamine D3 receptor in the shell of the nucleus accumbens were investigated in rats. In this brain area the D3 receptor is abundant and may mediate antipsychotic drug effects. The D3 receptor density and mRNA abundance were evaluated with 7-[3H]hydroxy-N,N-di-n-propyl-2-aminotetralin and by quantitative PCR or image analysis of in situ hybridization signals, respectively. Unilateral dopamine neuron degeneration by 6-hydroxydopamine or sections triggered, after a few days, a marked decrease (up to 50%) in D3 receptor binding and mRNA in the nucleus accumbens. In contrast, a 2-week treatment with the neuroleptic haloperidol (20 mg/kg) had no effect on D3 receptor density and mRNA but enhanced D2 receptor density and mRNA level by > 50%. In addition, tolerance to the haloperidol-induced change of neurotensin mRNA mediated by the D2 receptor developed, but there was no tolerance to the opposite change mediated by the D3 receptor. Reserpine, a monoamine-depleting drug with antipsychotic activity, did not modify D3 receptor mRNA. These observations reinforce the idea that the D3 receptor may be an important target for neuroleptics whose antipsychotic actions, but not extrapyramidal motor actions, do not display tolerance. The D3 receptor mRNA level was also decreased by a unilateral injection in dopamine cell body areas of colchicine, a drug blocking the anterograde axonal transport, or by baclofen, a type A gamma-aminobutyric acid receptor agonist reducing dopamine neuron activity, but not by sustained blockade of D1-like and D2-like, neurotensin, or cholecystokinin receptors. We therefore propose that an anterograde factor present in mesolimbic dopaminergic neurons, but distinct from dopamine and known peptide cotransmitters, plays a positive role on transcription of the D3 receptor gene.

Dopamine receptor blockade increases dopamine D2 receptor and glutamic acid decarboxylase mRNAs in mouse substantia nigra

To study the influence of dopaminergic activity on the expression of dopamine D2 receptors and glutamic acid decarboxylase in substantia nigra, mice were treated daily for several days with an irreversibly acting dopamine D1 and dopamine D2 receptor antagonist N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) or with a selective irreversible D2 dopamine receptor antagonist fluphenazine-N-mustard. Mice were killed 24 h after the last injection. Dopamine D1 and dopamine D2 receptors were determined by receptor autoradiography, and dopamine D1 and dopamine D2 receptor mRNA and glutamic acid decarboxylase mRNA were determined by in situ hybridization histochemistry. The results showed that treatment with EEDQ, which blocked 80% to 85% of the dopamine D2 and dopamine D1 receptors in substantia nigra, increased the levels of dopamine D2 receptor mRNA in substantia nigra by about 27%. Treatment with fluphenazine-N-mustard, which blocked about 85% of the dopamine D2 receptors in substantia nigra but had no significant effect on dopamine D1 receptors, increased the levels of dopamine D2 receptor mRNA by about 34%. There were no detectable levels of dopamine D1 receptors, increased the levels of dopamine D2 receptor mRNA by about 34%. There were no detectable levels of dopamine D1 receptor mRNA in substantia nigra either in control animals or in animals treated with the dopamine receptor antagonists. Glutamic acid decarboxylase mRNA was expressed in several regions of the mid-brain but only that expressed in substantia nigra was altered by treatment with dopamine receptor antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

D2 dopamine receptor messenger RNA is altered to a greater extent by blockade of glutamate receptors than by blockade of dopamine receptors

To study further the molecular mechanisms by which glutamate and dopamine interact to regulate the functions of the basal ganglia, the effects of persistently inhibiting dopamine receptors and glutamate N-methyl-D-aspartate receptors on the density of D1 and D2 dopamine receptors and on the level of their transcripts were examined in mouse brain. To block dopamine receptors, mice were treated with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline once daily for two and six days, or were treated with fluphenazine-N-mustard once daily for five days. To block N-methyl-D-aspartate receptors, mice were treated with dizocilpine by continuous infusion with osmotic mini-pumps for two and six days. The density of D1 and D2 dopamine receptors was measured by receptor autoradiography, and the level of D1 and D2 dopamine receptor messenger RNA was measured by in situ hybridization histochemistry. The results showed that N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline blocked about 90% of both D1 and D2 dopamine receptors, but had no significant effect on the level of either D1 or D2 dopamine receptor messenger RNA. Fluphenazine-N-mustard, which was as effective as N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline in blocking D2 dopamine receptors but had little effect on D1 dopamine receptors, also had no significant effect on the level of D1 and D2 dopamine receptor messenger RNAs. By contrast, continuously infusing dizocilpine significantly decreased the levels of D2 dopamine receptor messenger RNA in striatum, nucleus accumbens and olfactory tubercle. Dizocilpine also caused small decreases in the density of D2 dopamine receptors, but only in posterior striatum was this decrease statistically significant. Dizocilpine slightly and transiently decreased the levels of D1 dopamine receptor messenger RNA in striatum but had no significant effect on the density of D1 dopamine receptors in any region examined. This study demonstrates that persistent blockade of D1 and D2 dopamine receptors has relatively little effect on the levels of D1 and D2 dopamine receptor messenger RNA, but that blockade of N-methyl-D-aspartate receptors produces a rapid and profound decrease in the levels of D2 dopamine receptor messenger RNA and a smaller decrease in the density of D2 dopamine receptors. These results suggest that N-methyl-D-aspartate receptors play an important role in the expression of D2 dopamine receptors in basal ganglia.

Dopaminergic regulation of cannabinoid receptor mRNA levels in the rat caudate-putamen: an in situ hybridization study

By quantitative in situ hybridization, we examined in vivo in the rat caudate-putamen the effects on levels of cannabinoid receptor mRNA of an interruption of dopamine neurotransmission for up to 1 month, by either 6-hydroxydopamine lesioning of the medial forebrain bundle or dopamine receptor blockade. We found, in a first set of experiments, that unilateral 6-hydroxydopamine dopaminergic deafferentation of the striatum (characterized by a contralateral turning behavior in response to apomorphine, the almost complete disappearance of the tyrosine hydroxylase hybridization signal in the substantia nigra, and an increase of preproenkephalin A mRNA level in the striatum) was associated with significantly increased (45%) cannabinoid receptor mRNA levels in the homolateral caudate-putamen. In a second set of experiments, treatments with the dopamine D1 receptor antagonist SCH-23390, haloperidol, and the D2 receptor antagonist sulpiride induced significantly higher cannabinoid receptor mRNA levels (respectively, 67, 34, and 27%) in the caudate-putamen. These observations suggest for the first time that, in vivo, cannabinoid receptor gene expression in the caudate-putamen is under the negative control of dopamine receptor-mediated events.

Effects of neonatal 6-hydroxydopamine injections on glutamate decarboxylase, preproenkephalin and dopamine D2 receptor mRNAs in the adult rat striatum

The effects of neonatal 6-hydroxydopamine injections on the levels and cellular distribution of glutamate decarboxylase (GAD67), preproenkephalin and dopamine D2 receptor messenger RNAs were studied in the striatum of adult rats. Cerebroventricular injections of 150 micrograms or 100 micrograms of 6-hydroxydopamine to 3-day-old neonate rats resulted in the total disappearance of neurons labeled with a tyrosine hydroxylase probe in sections of the substantia nigra and ventral tegmental area. In the striatum of adults, both doses of 6-hydroxydopamine induced an increase in GAD67 and preproenkephalin mRNA levels compared to controls. A smaller but consistent increase in dopamine D2 receptor mRNA levels was also found on adjacent sections of the striatum only in animals injected with 150 micrograms of 6-hydroxydopamine. Regional analysis of labeling showed that the increased GAD67, preproenkephalin or dopamine D2 receptor mRNA levels occurred in all striatal sectors examined. Emulsion radioautographs confirmed the increased GAD67, preproenkephalin and dopamine D2 receptor mRNA labeling at cellular level. The present study demonstrates that bilateral 6-hydroxydopamine lesions of dopamine neurons in neonate rats are able to induce a long-term and widespread alteration in the expression of genes encoding for GAD67, preproenkephalin and dopamine D2 receptor in the striatum. In view of previous results after 6-hydroxydopamine lesions in adults, it appears that the behavioral differences observed after adult or neonatal 6-hydroxydopamine lesions are accompanied by a similar alteration of GAD67, preproenkephalin and dopamine D2 receptor gene expression in presumed striatal projection neurons.

Differential regulation of preprotachykinin-A mRNA expression in striatum by excitation of hippocampal neurons

In this report we have studied the influence of hippocampal neurons on neuropeptide mRNA expression in both dorsal and ventral striatum in the rat. Intrahippocampal unilateral kainic acid injections were performed in control animals and in animals with a unilateral 6-hydroxydopamine-induced dopamine deafferentation of the striatum. In situ hybridization combined with quantitative image analysis was used to study the expression of preprotachykinin A mRNA encoding the neuropeptides substance P and neurokinin A. The 6-hydroxydopamine-induced lesion caused a decrease of preprotachykinin A mRNA levels in the ipsilateral dorsal striatum and in both sides of the ventral striatum. In normal rats, the intrahippocampal kainic acid injection caused a twofold increase in preprotachykinin A mRNA in the limbic parts of the striatum, which are innervated by the hippocampus. No effect of the kainic acid injection was seen in the lateral parts of the dorsal striatum, a region which does not appear to be innervated by the hippocampus. Animals with a 6-hydroxydopamine lesion showed a similar kainic acid-mediated increase in preprotachykinin A mRNA in parts of the ventral striatum. In the dopamine-lesioned dorsal striatum and ventral striatum the decreased preprotachykinin A mRNA levels were normalized by the intrahippocampal kainic acid injection. These results show that kainic acid-mediated excitation of hippocampal neurons causes a dopamine-independent induction of preprotachykinin A mRNA expression in parts of the ventral striatum, and reverses the dopamine deafferentation-induced decrease of preprotachykinin A mRNA in both dorsal and ventral striatum. Combined, our results suggest that hippocampal neurons can regulate preprotachykinin A mRNA expression in both the ventral and the dorsal striatum.

Effect of long term caffeine treatment on A1 and A2 adenosine receptor binding and on mRNA levels in rat brain

The effect of long-term oral treatment with caffeine on A1 and A2 receptors in the rat brain was studied. Caffeine was added to the drinking water and the animals were sacrificed after a 12 day treatment period. The plasma caffeine concentration was close to 100 microM. A1 receptors were studied using quantitative autoradiography with [3H]cyclohexyladenosine (CHA). Caffeine treatment increased the number of A1 receptors in the CA3 subfield of the hippocampus from 337 to 393 fmol/mg with no change in KD (0.692 vs. 0.675 nM). A1 mRNA was measured using Northern blots and quantitative in situ hybridization. There was no increase in A1 mRNA. A2a receptors, located in dopamine rich regions of the rat brain, were studied with quantitative autoradiography using [3H]CGS 21680 as the ligand, and the A2a mRNA was determined using quantitative in situ hybridization. Caffeine treatment produced no significant change in either receptor number or mRNA, even though the apparent Bmax tended to increase from 322 +/- 8 to 352 +/- 8 fmol/mg. The results show that treatment with caffeine in a dose that causes tolerance to several effects of caffeine and increases some effects of adenosine analogues increases the number of A1 receptors without any change in A1 mRNA, suggesting that the adaptive changes are at a post-translational level. There were no significant changes in A2 receptors indicating that the two types are regulated differently and/or that the amount of endogenous agonist is sufficient to regulate A1, but not A2 receptors.