Dopamine D2 Receptor mRNA Levels Research Articles

Time-course of changes in key catecholaminergic receptors and trophic systems in rat brain after antidepressant administration

Several biochemical parameters within the brain are altered by antidepressants. However, it is still uncertain which parameters are important for the evaluation of the effectiveness of these drugs. What seems certain is that the response of the nervous system is dynamic. The dynamic nature of the nervous system is still poorly understood, although it has implications in clinical management. Criteria for evaluating treatment resistant depression are based on this temporal variability. The present study was designed to evaluate dynamic alterations in catecholaminergic receptors and calcyon (associated with monoaminergic theory of depression) in the rat brain as well as brain-derived neurotrophic factor (BDNF) and tyrosine kinase beta (TRKB; related to neurotrophin theory) induced by three antidepressant drugs (ADs) with various pharmacological profiles (imipramine, desipramine, and citalopram) administered for 21 days or acutely, followed by various drug-free periods. Receptor autoradiography and in situ hybridization studies allowed us to identify changes in various brain regions simultaneously in each rat. Repeated treatment with ADs induced biochemical alterations, which were in agreement with the results of previous studies. These alterations include the downregulation of β1, β2, and α1 adrenergic receptors, upregulation of α2-adrenergic receptors and dopamine D2 receptors, and increased expression of BDNF in the hippocampus. Additionally, we observed dynamic alterations in the measured parameters after acute drug administration, particularly at the level of dopamine receptors, which were extremely sensitive to a single dose of ADs followed by various drug-free periods. All three ADs induced the upregulation of dopamine D2 receptor mRNA levels in the nucleus accumbens. The same effect was induced by single doses of ADs followed by various drug-free periods. The obtained results indicate that alterations in the availability of neurotransmitters at synapses induced by ADs are strong enough to induce immediate and long-lasting adaptive changes in the neuronal network.

Implication of the ERK/MAPK Pathway in Antipsychotics-induced Dopamine D2 Receptor Upregulation and in the Preventive Effects of (±)-α-lipoic acid in SH-SY5Y Neuroblastoma Cells

Chronic administration of antipsychotics (APs) has been associated with dopamine D2 receptor (D2R) upregulation and tardive dyskinesia. We previously showed that haloperidol, a first-generation AP, exerted a more robust increase in D2R expression than amisulpride, a second-generation AP and that (±)-α-lipoic acid pre-treatment reversed the AP-induced D2R upregulation. We also demonstrated that the Akt/GSK-3β/β-catenin pathway is involved in the control of D2R expression levels, but is unlikely implicated in the preventive effects of (±)-α-lipoic acid since co-treatment with haloperidol and (±)-α-lipoic acid exerts synergistic effects on Akt/GSK-3β activation. These findings led us to examine whether the ERK/MAPK signaling pathway may be involved in D2R upregulation elicited by APs, and in its reversal by (±)-α-lipoic acid, in SH-SY5Y human neuroblastoma cells. Our results revealed that haloperidol, in parallel with an elevation in D2R mRNA levels, induced a larger increase of ERK (p42/p44) phosphorylation than amisulpride. Pre-treatment with the selective ERK inhibitor U0126 attenuated haloperidol-induced increase in D2R upregulation. Furthermore, (±)-α-lipoic acid prevented AP-induced ERK activation. These results show that (1) the ERK/MAPK pathway is involved in haloperidol-induced D2R upregulation; (2) the preventive effect of (±)-α-lipoic acid on haloperidol-induced D2R upregulation is in part mediated by an ERK/MAPK-dependent signaling cascade. Taken together, our data suggest that (±)-α-lipoic acid exerts synergistic effects with haloperidol on the Akt/GSK-3β pathway, potentially involved in the therapeutic effects of APs, and antagonism of ERK activation and D2R upregulation, potentially involved in tardive dyskinesia and treatment resistance.

Preadolescent drd1-EGFP mice exhibit cocaine-induced behavioral sensitization

In adult mice, repeated cocaine administration induces behavioral sensitization measured as increased horizontal locomotor activity. Cocaine-induced locomotor sensitization has been well characterized in adult mice. In adult animals, the D1 dopamine receptor is important for mediating effects of cocaine. The effect of cocaine on D1 receptor expression and function in preadolescent animals is less understood. The recently described drd1-enhanced green fluorescent protein (drd1-EGFP) reporter mouse is a useful model for performing such mechanistic studies; however, preadolescent drd1-EGFP mice have not been characterized previously. Here we studied cocaine-induced locomotor sensitization in preadolescent drd1-EGFP reporter mice. We administered 15mg/kg cocaine three times daily at 1h intervals for seven consecutive days beginning on postnatal day 23 to drd1-EGFP reporter mice and the commonly used C57BL/6 mice. Under this regimen, preadolescent mice of both strains exhibited cocaine-induced locomotor sensitization; however, by day 7 the cocaine-induced locomotor activity in the drd1-EGFP mice was maintained for a longer duration compared to the C57BL/6 mice. The preadolescent drd1-EGFP mice also exhibited elevated basal locomotor activity in a novel environment and had higher D1 and D2 dopamine receptor mRNA levels in the caudate nucleus compared to the C57BL/6 mice. The cocaine-induced locomotor sensitization was not retained when the drd1-EGFP mice were maintained cocaine-free for two weeks suggesting that in preadolescent drd1-EGFP mice the cocaine-induced changes do not persist.

α-Lipoic Acid Interaction with Dopamine D2 Receptor-Dependent Activation of the Akt/GSK-3β Signaling Pathway Induced by Antipsychotics: Potential Relevance for the Treatment of Schizophrenia

Chronic administration of antipsychotics has been associated with dopamine D2 receptor (D2R) upregulation and tardive dyskinesia. We have previously shown that haloperidol, a first-generation antipsychotic (FGA), exerted an increase in D2R expression and oxidative stress and that (±)-α-lipoic acid reversed its effect. Previous studies have implicated the Akt/glycogen synthase kinase-3β (GSK-3β) signaling pathway in antipsychotic action. These findings led us to examine whether the Akt/GSK-3β pathway was involved in D2R upregulation and oxidative stress elicited by antipsychotics and, in (±)-α-lipoic acid-induced reversal of these phenomena, in SH-SY5Y cells. Antipsychotics increased phosphorylation of Akt and GSK-3β, and additive effects were observed with (±)-α-lipoic acid. GSK-3β inhibitors reversed haloperidol-induced overexpression of D2R mRNA levels but did not affect haloperidol-induced oxidative stress. Sustained antipsychotic treatment increased β-arrestin-2 and D2R receptor interaction. Regarding Akt/GSK-3β downstream targets, antipsychotics increased β-catenin levels, whereas (±)-α-lipoic acid induced an elevation of mTOR activation. These results suggest (1) that the effect of antipsychotics on the Akt/GSK-3β pathway in SH-SY5Y cells is reminiscent of their in vivo action, (2) that (±)-α-lipoic acid partially synergizes with antipsychotic drugs (APDs) on the same pathway, and (3) that the Akt/GSK-3β signaling cascade is not involved in the preventive effect of (±)-α-lipoic acid on antipsychotics-induced D2R upregulation.

Dopamine D2 Receptor Overexpression Alters Behavior and Physiology inDrd2-EGFPMice

Bacteria artificial chromosome (BAC) transgenic mice expressing the reporter protein enhanced green fluorescent protein (EGFP) under the control of the D1 and D2 dopamine receptor promoters (Drd1-EGFP and Drd2-EGFP) have been widely used to study striatal function and have contributed to our understanding of the physiological and pathological functions of the basal ganglia. These tools were produced and promptly made available to address questions in a cell-specific manner that has transformed the way we frame hypotheses in neuroscience. However, these mice have not been fully characterized until now. We found that Drd2-EGFP mice display an ∼40% increase in membrane expression of the dopamine D2 receptor (D2R) and a twofold increase in D2R mRNA levels in the striatum when compared with wild-type and Drd1-EGFP mice. D2R overexpression was accompanied by behavioral hypersensitivity to D2R-like agonists, as well as enhanced electrophysiological responses to D2R activation in midbrain dopaminergic neurons. Dopamine (DA) transients evoked by stimulation in the nucleus accumbens showed slower clearance in Drd2-EGFP mice, and cocaine actions on DA clearance were impaired in these mice. Thus, it was not surprising to find that Drd2-EGFP mice were hyperactive when exposed to a novel environment and locomotion was suppressed by acute cocaine administration. All together, this study demonstrates that Drd2-EGFP mice overexpress D2R and have altered dopaminergic signaling that fundamentally differentiates them from wild-type and Drd1-EGFP mice.

Dopamine D2 receptor mRNA expression is increased in the jugular-nodose ganglia of rats with nitrogen dioxide-induced chronic bronchitis

The bronchodilatatory effect of inhaled dopamine or dopamine D2 receptor agonists in cases of bronchial constriction may involve the suppression of pathologically increased airway sensory nerve activity. The aim of this study is to investigate the regulation of the dopamine D2 receptor mRNA expression in the ganglia of rats with nitrogen dioxide-induced chronic bronchitis compared with that in ganglia of healthy control animals. Rats were exposed to nitrogen dioxide (10ppm, 20d) and dopamine D2 receptor mRNA levels in sensory ganglia (jugular-nodose, trigeminal, cervical dorsal root and thoracic dorsal root ganglia) were examined by quantitative real-time polymerase chain reaction and compared to control tissues. Whereas for trigeminal and dorsal root ganglia the dopamine D2 receptor expression levels showed no difference between both animal groups, there was a significant (p<0.05) increase in the jugular-nodose ganglia with a 2.1-fold factor. The increase of dopamine D2 receptor mRNA in jugular-nodose sensory neurons which innervate the airways may represent a neurochemical basis for the effects seen in man and animal models following topical administration of dopamine or dopamine agonists onto the respiratory epithelium.

Isolated Flinders Sensitive Line rats have decreased dopamine D2 receptor mRNA

Social isolation has profound effects on animal behavior and dopamine systems. We investigated the effect of social isolation on the dopamine receptor and neuropeptide mRNAs in the brain reward system in an animal model of depression, the Flinders Sensitive Line rats and Sprague-Dawley controls. We demonstrate that socially isolated but not group housed Flinders sensitive line rats had lower dopamine D2 receptor mRNA levels compared with Sprague-Dawley rats. Isolated and group housed Flinders Sensitive Line rats had higher levels of dopamine D1 receptor and substance P and enkephalin but not dynorphin mRNAs when compared with Sprague-Dawley rats. Our findings of decreased dopamine D2 receptor levels in socially isolated Flinders Sensitive Line rats suggest that low D2 receptor expression may play a role in pathophysiology of depression.

Down-Regulation of D2 Dopamine Receptor and Increased Protein Kinase Cμ Phosphorylation in Aldosterone-Producing Adenoma Play Roles in Aldosterone Overproduction

The mechanism associated with the overproduction of aldosterone by aldosterone-producing adenomas (APA) is unknown. The objective of the study was to explore the role of the D2 dopamine receptor (D2R) on aldosterone synthesis and secretion and clarify the clinical importance of this role on aldosterone overproduction in APA. D2R expression in APA was examined in 24 patients and was much less than that in the nontumorous adrenal cortex. D2R mRNA levels in APA were inversely correlated with CYP11B2 mRNA levels and the patient's plasma aldosterone concentration. Angiotensin II (AII)-stimulated aldosterone secretion and CYP11B2 mRNA expression in human adenocarcinoma cells (H295R) was attenuated by the D2 agonist, bromocriptine (BMC). BMC selectively attenuated AII-induced protein kinase C (PKC)-mu phosphorylation and its translocation to the cell membrane. PKCmu-specific short-hairpin RNA significantly decreased AII-induced CYP11B2 mRNA expression and aldosterone secretion. BMC also attenuated the AII-induced increase in cytoplasmic calcium, partially through an inhibition of cytoplasmic inositol 1,4,5 triphosphate production. Despite similar total PKCmu levels in APA and the nontumorous adrenal cortex, expression of phosphorylated PKCmu in APA was much higher. This is the first study to demonstrate that the D2R modulated aldosterone secretion and synthesis through a specific attenuation of PKCmu activity, as well as the intracellular calcium level. Down-regulation of the D2R in APA, in turn, increased PKCmu activity and led to overproduction of aldosterone in affected patients. The D2R may thus serve as a potential treatment target for primary aldosteronism.

Differential regulation of short and long dopamine D2 receptor mRNA levels by hypoxia in the adrenals of 1-day-old and adult rabbits

We tested the hypothesis that hypoxic exposure exerts distinct modulation on the mRNA level of the short and long isoform of the D2 dopamine (DA) receptor (D 2r) and on tyrosine hydroxylase (TH) in the adrenals and superior cervical ganglion (SCG) of 1-day-old and adult rabbits. One-day-old and adult rabbits have been exposed to moderate (FiO 2: 0.15) or severe (FiO 2: 0.08) hypoxia for 0 (control), 6 or 24 h. At the end of the hypoxic exposure, the adrenals and SCG were rapidly dissected and kept frozen. Standard procedure for Northern blot and RT-PCR for evaluation of the short (D 2S) or long (D 2L) isoform of D 2r and TH have been used. In the adrenals of adult rabbits, moderate and severe hypoxia decreased the D 2S and D 2L mRNA with a more prominent effect on the short isoform and increased TH mRNA. In 1-day-old rabbits, changes of D 2r and TH mRNA levels were observed only after 24 h of severe or moderate hypoxic exposure and only the D 2S receptor mRNA was significantly reduced. In the SCG, the expression level of both TH and D 2r mRNA were not affected by hypoxic exposure in adult and newborn rabbits. Hence, sustained hypoxic exposure exerts distinct changes on mRNA level of D 2r isoform and TH in an age- and tissue-dependent pattern.

Neuroendocrine alterations in a high-dose, extended-access rat self-administration model of escalating cocaine use

One approach for studying cocaine addiction has been to permit escalating patterns of self-administration (SA) by rats by prolonging daily drug availability. Rats provided long access (LgA) to high cocaine doses, but not rats provided shorter cocaine access (ShA), progressively escalate their cocaine intake and display characteristics of human addiction. The purpose of the present study was to investigate the effects of 14 days of ShA or LgA, high-dose cocaine SA on plasma corticosterone (CORT), prolactin (PRL), and related mRNAs. Acutely, cocaine SA increased plasma CORT and reduced plasma PRL levels. SA training produced circadian increases in CORT that appeared to occur in anticipation of cocaine availability. With repeated LgA, high-dose SA, the daily CORT area under the curve (AUC) progressively decreased, apparently due to tolerance to cocaine’s effects on CORT and a reduction in basal CORT levels. In contrast, the daily CORT AUC in ShA rats increased across testing despite constant rates of SA. When measured 12 days after SA testing, pro-opioimelanocortin and glucocorticoid receptor mRNA levels in the anterior pituitary were lower in LgA rats than in ShA rats. The effects of SA on PRL remained constant across SA testing in LgA rats, but increased in duration in ShA rats. Anterior pituitary dopamine D2 receptor mRNA levels were lower in LgA rats than in ShA rats. These findings indicate that the transition to escalating patterns of SA may be associated with altered levels of hormones and gene expression within neuroendocrine systems. Such changes may underlie the onset of human addictive disease.

Antenatal Treatment with Corticosteroids Affects mRNA Expression of Dopamine D1 and D2 Receptors in the Striatum of Developing Rabbit

The expression levels of dopamine D1 and D2 receptor mRNA have been investigated using Northern blot analysis in developing rabbit striatum after antenatal exposure to betamethasone. Pregnant rabbits were given either 0.1 mg/kg betamethasone or 0.1 mg/kg saline doses twice within 24 h. Dopamine D1 receptor mRNA levels were found significantly higher in the fetuses exposed to antenatal betamethasone than in the saline-treated controls. After birth, dopamine D1 and D2 receptor mRNA levels were both significantly lower in 1- and 25-day-old treated pups but recovered to normal levels in adulthood. These data suggest that antenatal exposure to betamethasone can lead to lasting abnormalities.

Prenatal nicotine affects catecholamine gene expression in newborn rat carotid body and petrosal ganglion.

Nicotine exposure modifies the expression of catecholamine and opioid neurotransmitter systems involved in attenuation of hypoxic chemosensitivity. We used in situ hybridization histochemistry to determine the effect of prenatal and early postnatal nicotine exposure on tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DbetaH), preproenkephalin (PPE), and D2-dopamine receptor mRNA levels in the rat carotid body and petrosal ganglion during postnatal development. In the carotid body, nicotine increased TH mRNA expression in animals at 0 and 3 postnatal days (both, P < 0.05 vs. control) without affecting TH mRNA levels at 6 and 15 days. At 15 postnatal days, DbetaH mRNA levels were increased in the carotid body of nicotine-exposed animals. Dopamine D2-receptor mRNA levels in the carotid body increased with postnatal age but were unaffected by nicotine exposure. PPE was not expressed in the carotid body at any of the ages studied in control or treated animals. In the petrosal ganglion, nicotine increased the number of ganglion cells expressing TH mRNA in animals at 3 days (P < 0.01 vs. control). DbetaH mRNA expression was not induced nor was PPE mRNA expression increased in the petrosal ganglion in treated animals. Prenatal nicotine exposure upregulates mRNAs involved in the synthesis of two inhibitory neuromodulators, dopamine and norepinephrine, in peripheral arterial chemoreceptors, which may contribute to abnormalities in cardiorespiratory control observed in nicotine exposed animals.

Effects of immobilization stress on estrogen-induced surges of luteinizing hormone and prolactin in ovariectomized rats.

Reproductive function has been known to be impaired by various kinds of physical and emotional stress, but the mechanism by which stress impairs the reproductive axis has not been clearly understood. In the present study, the effects of immobilization stress were studied on the surges of luteinizing hormone (LH) and prolactin (PRL) induced by 17beta-estradiol (E2) in ovariectomized rats. Two weeks after bilateral ovariectomy, animals were implanted with the capsule containing E2 or vehicle at 1000 h (designated as d 0). Immobilization was started at 1000 h and continued to 2100 h on d 2. Blood samples were collected according to the time schedule by a jugular vein catheter procedure. Immobilization stress inhibited basal release of LH and abolished E2-induced LH and PRL surges in ovariectomized (OVX) rats. Daily repeated immobilization (from 1200 h to 1800 h, 6 h/d) for 3 d also abolished LH and PRL surges when examined at 1800 h on d 2. Although daily repeated immobilization stress reduced E2-induced PRL mRNA levels, this stress failed to change LHbeta mRNA levels in the anterior pituitary as determined by Northern blot analysis. Gonadotropin-releasing hormone (GnRH) receptor mRNA levels in the anterior pituitary were lowered by immobilization stress in the OVX, E2-treated group. Dopamine D2 receptor mRNA levels in the anterior pituitary of OVX, E2-treated rats were significantly decreased at 1800 h, compared with those at 1000 h. However, immobilization prevented a decrease in dopamine D2 receptor mRNA levels at 1800 h. GnRH content was increased in the mediobasal hypothalamus by immobilization in the OVX, E2-treated group, suggesting that GnRH release was inhibited. Interestingly, GnRH mRNA levels in the preoptic area-anterior hypothalamic area were suppressed by immobilization stress in OVX, E2-treated rats when determined at 1800 h. Therefore, we concluded that immobilization stress blocks E2-induced LH surge possibly by inhibiting synthesis and release of GnRH at the hypothalamic level, and an increase of dopaminergic activity via D2 receptor at the pituitary level might be involved in the stress blockage of E2-induced PRL surge.

Brain dopamine D2 receptor mRNA levels are elevated in young spontaneously hypertensive rats.

Levels of brain dopamine D2 receptor expression were compared between spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) controls by quantitative in situ hybridisation, using a complementary RNA probe for D2 receptor mRNA. In SHR which were 6 weeks of age, significantly higher levels of D2 receptor mRNA were found in the caudate-putamen (42%), nucleus accumbens (23%), olfactory tubercle (17%) and substantia nigra (38%) compared to age-matched WKY controls. D2 receptor mRNA levels were also higher in the substantia nigra (27%) of 12-14-week old SHR compared to WKY. The increased levels of dopamine D2 receptor gene expression displayed in young prehypertensive SHR could implicate altered central dopaminergic activity in the pathogenesis of hypertension.

Chronic morphine exposure and spontaneous withdrawal are associated with modifications of dopamine receptor and neuropeptide gene expression in the rat striatum.

The influence of chronic morphine and spontaneous withdrawal on the expression of dopamine receptors and neuropeptide genes in the rat striatum was investigated. Morphine dependence was induced by subcutaneous implantation of two morphine pellets for 6 days. Rats were made abstinent by removal of the pellets 1, 2 or 3 days before they were killed. The mRNA levels coding for D1- and D2-dopamine receptors, dynorphin, preproenkephalin A and substance P were determined by quantitative in situ hybridization. The caudate putamen and the nucleus accumbens showed equivalent modifications in dopamine receptor and neuropeptide gene expression. After 6 days of morphine, a decrease in D2-dopamine receptor and neuropeptide mRNA levels was observed (-30%), but there was no change in D1-dopamine receptor mRNA. In abstinent rats, both D1- and D2-dopamine receptor mRNA levels were decreased 1 day after withdrawal (-30% compared with chronic morphine). In contrast, neuropeptide mRNA levels were unaffected when compared with those observed after 6 days of morphine. During the second and third day of withdrawal, there was a gradual return to the levels seen in the placebo-treated group, for both dopamine receptor and neuropeptide mRNAs. Phenotypical characterization of striatal neurons expressing mu and kappa opioid receptor mRNAs showed that, in striatonigral neurons, both mRNAs were colocalized with D1-receptor and Dyn mRNAs. Our results suggest that during morphine dependence, dopamine and morphine exert opposite effects on striatonigral neurons, and that effects occurring on striatopallidal neurons are under dopaminergic control. We also show that withdrawal is associated with a down regulation of the postsynaptic D1 and D2 receptors.

Modulation of Dopamine D&lt;sub&gt;2&lt;/sub&gt; Receptor Expression by an NMDA Receptor Antagonist in Rat Brain

The expression of dopamine D2 receptor mRNA was studied in rat brain following micro-injection of a competitive N-methyl D-aspartate (NMDA) receptor antagonist at the prefrontal cortex. Male Sprague-Dawley rats cannulated bilaterally into the medial prefrontal cortex were injected with a competitive NMDA receptor antagonist (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP). The levels of mRNA for NMDA-R1 and dopamine D2 receptors were measured by reverse transcriptase-polymerase chain reaction (RT-PCR), and D2 receptor density was quantified by [3H]spiperone binding in the cortex and striatum of these animals. In the prefrontal cortex, the levels of NMDA-R1 receptor mRNA showed significant decrease in CPP-treated animals compared to control animals. However, NMDA-R1 mRNA levels in striatum remained unchanged in any of the experimental groups. The D2 receptor mRNA levels and [3H]spiroperidol binding in prefrontal cortical membranes showed no significant difference between the CPP-treated and control groups of animals. In the striatum, a significant increase in striatal dopamine D2 receptor mRNA levels was shown in animals treated with CPP. The increase in D2 mRNA level was correlated with an increase in the D2 receptor binding sites in the striatal membranes. These results suggest a possible interaction between prefrontal cortical NMDA receptors and striatal dopamine receptors.

Effects of repeated methamphetamine administration on dopamine D1 receptor, D2 receptor and adenylate cyclase type V mRNA levels in the rat striatum

Dopamine D1 receptor (D1R), D2 receptor (D2R) and adenylate cyclase type V (AC5) mRNAs in the rat dorsal striatum(CPu) and ventral striatum (Acb) were measured by in situ hybridization histochemistry (ISHH) after repeated methamphetamine (MAP) administration. MAP (4 mg/kg) or an equivalent volume of saline was administered intraperitoneally once daily for 10 days to male Wistar rats. After 7 days of abstinence, behavioral experiment with MAP-challenge revealed that a significant behavioral sensitization was achieved in MAP-treated animals. The animals were sacrificed 7 days after the last injection and brain sections were analyzed by ISHH using 35S-labeled antisense oligonucleotide probes. We found that D1R mRNA levels in the CPu were significantly increased (124% of control, P<0.01). In contrast, repeated MAP-treatment did not significantly affect the expression of D1R mRNA in Acb or mRNA for D2R or AC5. It was concluded that MAP-induced behavioral sensitization is accompanied by increased D1R mRNA levels in CPu.

Effects of in utero cocaine exposure on the expression of mRNAS encoding the dopamine transporter and the D1, D2 and D5 dopamine receptor subtypes in fetal rhesus monkey

The effects of in utero cocaine exposure on the development of the mRNAs encoding the dopamine transporter (DAT) and the D1, D2 and D5 dopamine receptor subtypes were determined in fetal monkey brains at day 45 and day 60 of gestation. Pregnant monkeys were treated with cocaine 3 mg/kg or saline i.m., four times a day from day 18 of gestation until the pregnancy was terminated at day 45 or day 60. The fetal brains were dissected, and tissue RNA extracted and quantified using ribonuclease protection assay analysis. In day 45 fetal monkeys, dopamine D1 and D2 receptor subtype mRNAs and DAT mRNA were found in low quantities both in control and cocaine-treated subjects. In day 60 fetal monkeys, D1 receptor mRNA levels were highest in the frontal cortex/striatal area, and low to moderate quantities were found in diencephalic and mesencephalic fetal brain regions. Dopamine D2 receptor mRNA levels were highest in the frontal cortex/striatal area, diencephalon and the midbrain, moderate in the brainstem and low in the caudal temporal lobe and surrounding cortical areas. Dopamine D5 receptor mRNA was expressed in low quantities throughout the day 60 fetal monkey brain, whereas DAT mRNA was found in the midbrain only. In utero cocaine exposure caused a significant increase in dopamine D1, D2 and D5 receptor subtype mRNAs in the frontal cortex/striatal area of day 60 fetal monkeys. These results support the hypothesis that dopamine synthesis and release may be reduced in cocaine-treated fetuses, which results in dopamine receptor up-regulation.

Effects of in utero cocaine exposure on the expression of mRNAS encoding the dopamine transporter and the D1, D2 and D5 dopamine receptor subtypes in fetal rhesus monkey

The effects of in utero cocaine exposure on the development of the mRNAs encoding the dopamine transporter (DAT) and the D1, D2 and D5 dopamine receptor subtypes were determined in fetal monkey brains at day 45 and day 60 of gestation. Pregnant monkeys were treated with cocaine 3 mg/kg or saline i.m., four times a day from day 18 of gestation until the pregnancy was terminated at day 45 or day 60. The fetal brains were dissected, and tissue RNA extracted and quantified using ribonuclease protection assay analysis. In day 45 fetal monkeys, dopamine D1 and D2 receptor subtype mRNAs and DAT mRNA were found in low quantities both in control and cocaine-treated subjects. In day 60 fetal monkeys, D1 receptor mRNA levels were highest in the frontal cortex/striatal area, and low to moderate quantities were found in diencephalic and mesencephalic fetal brain regions. Dopamine D2 receptor mRNA levels were highest in the frontal cortex/striatal area, diencephalon and the midbrain, moderate in the brainstem and low in the caudal temporal lobe and surrounding cortical areas. Dopamine D5 receptor mRNA was expressed in low quantities throughout the day 60 fetal monkey brain, whereas DAT mRNA was found in the midbrain only. In utero cocaine exposure caused a significant increase in dopamine D1, D2 and D5 receptor subtype mRNAs in the frontal cortex/striatal area of day 60 fetal monkeys. These results support the hypothesis that dopamine synthesis and release may be reduced in cocaine-treated fetuses, which results in dopamine receptor up-regulation.

Altered expression of dopamine D2 receptor rnRNA splice variants in brain and pituitary of spontaneously hypertensive rats

Both central and peripheral dopamine (DA) has been shown to play a role in the regulation of blood pressure. Using sensitive nuclease protection analysis, we have compared the expression of DA D-2 receptor (D2-R) mRNA splice variants in brain and pituitary of spontaneously hypertensive rats (SHR) with normotensive Wistar-Kyoto (WKY) controls. Levels of D2-R mRNA were significantly altered in pituitary anterior lobe (AL) and neurointermediate lobe (NIL), and in striatum of SHR, but not in any other brain regions examined. SHR pituitary expressed 50–80% higher levels of D2-R mRNA, coupled with an increase in the relative proportion of the long (D2-L) mRNA variant. In contrast, overall D2-R mRNA expression in SHR striatum was only 75% that of WKY controls, however, the relative proportion of the D2-L splice variant was increased. The present data demonstrate that tissue specific alterations in D2-R mRNA levels and primary transcript splicing exist in the SHR and suggest that these changes may in part mediate differential responsiveness to DA that may be related to the development of hypertension.