Dopamine D2 Receptor Messenger RNA Research Articles

Ethanol and Estradiol Modulate Alternative Splicing of Dopamine D2 Receptor Messenger RNA and Abolish the Inhibitory Action of Bromocriptine on Prolactin Release From the Pituitary Gland

Background: Several reports show evidence for the existence of high levels of prolactin (PRL) in alcoholic men and women. Previously we have shown that ethanol increases PRL release both in vivo and in vitro. How ethanol increases PRL release is not well understood.Methods: In this study, we determined the effects of ethanol in the presence and absence of estradiol‐17β on PRL messenger RNA (mRNA) levels, dopamine D2 receptor mRNA splicing, and the PRL‐inhibitory response of a dopaminergic agent, bromocriptine, in the pituitary of Fischer‐344 rats and in primary cultures of anterior pituitary cells. Real‐time reverse transcriptase‐polymerase chain reaction was used for mRNA detection, and radioimmunoassay was used for hormone detection.Results: Estradiol and ethanol alone increased PRL mRNA expression in the pituitary gland. Ethanol also potentiated estradiol action on PRL mRNA expression in the pituitary. Determination of the D2 receptor splicing, by determining the changes in the percentage of D2 receptor mRNA expressed as its long form (D2L) and as its short form (D2S), revealed that both ethanol and estradiol altered D2 receptor splicing. Ethanol and estradiol, alone and together, increased the percentage of the D2L receptor but decreased the D2S receptor percentage. Similarly, ethanol and estradiol alone and in combination increased D2L, but decreased the D2S receptor percentage in primary cultures of pituitary cells. Evaluation of bromocriptine's inhibition of PRL release in primary cultures of pituitary cells indicated that ethanol reduced the ability of this D2 receptor agonist to inhibit PRL release.Conclusions: These results confirm estradiol's inhibition of D2 function and provide novel evidence that ethanol, like estradiol, reduces dopamine's ability to inhibit PRL release by modifying alternative splicing of the dopamine D2 receptor in the pituitary.

Late direct and transneuronal effects in mice with targeted expression of a toxin gene to D1 dopamine receptor neurons

Detailed analysis of a novel transgenic model of basal ganglia disease has been undertaken. In this model the expression of an attenuated form of the diphtheria toxin gene was tightly controlled by D1 dopamine receptor regulatory domains. The behavioral and both direct toxin-mediated and transneuronal effects observed in pups in the first postnatal week have been described. Although younger pups are bradykinetic, older pups have a hyperkinetic syndrome with gait abnormality, postural instability and myoclonic jerks typical of human basal ganglia diseases such as Huntington's disease. As expected, striatal D1 dopamine receptor, dynorphin and substance P transcripts were not detected by in situ hybridization but there was a 27% increase in striatal D2 dopamine receptor messenger RNA and a 65% increase in enkephalin messenger RNA expression. Receptor autoradiographic studies confirmed the lack of D1-class binding in the mutant striatum and in contrast to young pups, a substantial increase in striatal D2-class binding. Autoradiographic quantitation also showed a 30% increase in striatal dopamine transporter binding. In addition to the changes described in the striatopallidal and nigrostriatal pathways, up-regulated dynorphin and substance P messenger RNA expression was also seen in the cortex. The capacity of the developing brain for neurochemical adaptation following injury is dramatic. The results show that primary loss of D1 dopamine receptor-positive striatonigral pathway neurons is sufficient to generate a hyperkinetic phenotype.

Prolactinomas in Male and Female Patients: A Comparative Clinicopathologic Study

To explore the basis of the gender-based differences in endocrine and surgical findings in patients with prolactinoma (prolactin cell adenoma) as well as in their clinical outcome. In young or reproductive-age female patients, older women (beyond 40 years of age), and male patients, we systematically studied the following factors: operative and endocrine features (tumor size, invasiveness, preoperative serum prolactin level, and biochemical outcome), specific biologic variables (mitotic index, MIB-1 labeling index, and p27 immunoreactivity), and hormone receptor status (estrogen and progesterone receptor proteins as well as dopamine D2 receptor messenger RNA). Of the various factors assessed, the preoperative prolactin level and MIB-1 labeling index were lower in young female patients in comparison with older female and particularly male patients. Hormone levels were also positively associated with mitotic activity as well as the MIB-1 labeling index. Although invasion was infrequent in microadenomas of young female patients, no statistically significant differences in tumor size or invasiveness were noted among the three patient groups. Absence of differences in invasiveness may, in part, be explained by artifacts of case selection. The basis for the observed differences in proliferative activities in tumors of the three study groups is not readily apparent but may reflect differences in the endocrine milieu or the effect of sex steroid hormone receptors, tumoral vascularity, or specific growth factors.

Developmental expression of tyrosine hydroxylase, D2-dopamine receptor and substance P genes in the carotid body of the rat.

Alterations in the level of putative neurotransmitters/neuromodulators and corresponding receptors may be a possible mechanism involved in changes in chemosensitivity of peripheral chemoreceptors in the carotid body during development. Using quantitative in situ hybridization histochemistry, levels of messenger RNAs encoding tyrosine hydroxylase, the rate-limiting enzyme for dopamine synthesis, the D2-dopamine receptor and substance P of newborn rats at postnatal days 0, 2, 14 and 21 were determined. For comparison, during the same time points during development, we also determined the level of expression of these messenger RNAs in the cells of the superior cervical ganglion which are not chemosensitive. Tyrosine hydroxylase and D2-dopamine receptor messenger RNAs were co-localized in many of the cells in both the carotid body and the superior cervical ganglion. In the carotid body, the level of tyrosine hydroxylase messenger RNA expression was greatest at birth, significantly decreased by 48 h postnatal age and remained decreased at 14 and 21 postnatal days. In contrast, D2-dopamine receptor messenger RNA levels significantly increased with postnatal age in the carotid body. This profile of an D2-dopamine receptor was not observed in the superior cervical ganglion where tyrosine hydroxylase and D2-dopamine receptor messenger RNAs levels did not significantly change from postnatal days 0 to 21. Lastly, in the rat carotid body, substance P messenger RNA was not detected. However, substance P messenger RNA was abundant in the nodose and petrosal ganglion. The increasing contribution of carotid body on ventilation with increasing postnatal age is associated with changes in levels of gene expression for tyrosine hydroxylase and D2-dopamine receptor in the carotid body.

Subchronic administration of clozapine, but not haloperidol or metoclopramide, decreases dopamine D2 receptor messenger RNA levels in the nucleus accumbens and caudate-putamen in rats.

The effects of unique profile antipsychotic drugs on dopamine D2 receptors and D2 receptor messenger RNA were assessed following subchronic administration in rats. Male, Sprague-Dawley rats were administered oral haloperidol, clozapine, metoclopramide or no drug for three weeks via their drinking water. Tissue from the medial nucleus accumbens and dorsolateral caudate-putamen was dissected and analyzed by Northern blot analysis for levels of dopamine D2 receptor messenger RNA and binding assays conducted with [3H]spiperone for dopamine D2 receptors. Haloperidol and metoclopramide, but not clozapine, significantly increased [3H]spiperone in the caudate-putamen, but not the nucleus accumbens. Clozapine significantly decreased D2 messenger RNA levels in the caudate-putamen and the nucleus accumbens, while metoclopramide and haloperidol had no significant effect in either brain region. The finding of decreased D2 receptor messenger RNA levels produced by subchronic clozapine may account for the lack of striatal D2 receptor up-regulation, which was robustly observed after subchronic haloperidol and metoclopramide. Furthermore, since haloperidol and metoclopramide have a high liability for motor side effects, the current results relate favorably to the low motor side effect profile of clozapine.

Cellular Localization of Dopamine D2 Receptor Messenger RNA in the Rat Trigeminal Ganglion

Cellular Localization of Dopamine D2 Receptor Messenger RNA in the Rat Trigeminal Ganglion

Cellular localization of dopamine D2 receptor messenger RNA in the rat trigeminal ganglion.

The actions of dopamine are mediated by specific, high-affinity, G protein-coupled receptors. Multiple subtypes of dopamine receptors have been characterized, including the D2 subtype (D2R). Cells within the dorsal root and petrosal ganglia of the rat express D2R messenger RNA (mRNA) consistent with D2R expression by primary sensory neurons. We hypothesized that neurons of the trigeminal ganglion express D2R mRNA. Total cellular RNA from rat trigeminal ganglia was analyzed on Northern blots under high stringency conditions. Hybridization of trigeminal ganglion RNA resulted in a signal which comigrated with striatal, pituitary, and hypothalamic D2R mRNA. To determine the distribution of D2R expressing cells in the trigeminal ganglion, cryostat sections were analyzed by in situ hybridization followed by emulsion autoradiography. We identified a population of clustered cells labeled with dense grain concentrations over their cytoplasms. These findings demonstrate the expression of D2 dopamine receptor mRNA in discrete subpopulations of neurons in the rat trigeminal ganglion. Our observations suggest that drugs active at dopamine receptors of the D2 subtype are potential modulators of sensory activity of neurons whose cell bodies reside in the trigeminal ganglion. D2 dopamine receptors may thus have a role in clinical pain syndromes involving the head and neck.

Sex steroid hormones change the differential distribution of the isoforms of the D2 dopamine receptor messenger RNA in the rat brain.

The two isoforms of the rat dopamine D2 receptor are generated by alternative splicing of the pre-messenger RNA and differ in the length of their third cytoplasmic loop involved in coupling to G-proteins. As quantified by polymerase chain reaction, the long isoform D2L is predominant in the pituitary gland, the striatum and to a lesser extend in the olfactory tubercle, whereas the short isoform D2S is relatively more abundant in the hypothalamus and the substantia nigra. Changes in circulating sex hormone levels modulated the splicing without affecting the total amount of D2 receptor messenger RNA. Castration of male rats increased the ratio D2L/D2S in the pituitary, hypothalamus and substantia nigra, and decreased it in the olfactory tubercle. Testosterone substitution reversed the effect of castration in the pituitary and olfactory tubercle but not in the substantia nigra. In castrated rats, 17beta-estradiol had a similar effect to that of testosterone in the olfactory tubercle, indicating that testosterone may act after aromatization of estradiol. In the hypothalamus, 17beta-estradiol alone reversed the effect of castration. In the striatum, neither castration nor hormonal treatments modified the splicing of the D2 receptor mRNA. Treatment of animals with specific androgen and estrogen receptor blockers confirmed that steroids were acting through their specific intracellular receptors. These observations suggest a molecular mechanism, physiologically relevant, by which circulating sex hormones could modulate dopamine transmission in areas implicated in reproductive and parental behaviours.

Acute and chronic amphetamine treatments differently regulate neuropeptide messenger RNA levels and Fos immunoreactivity in rat striatal neurons.

Repeated administration of amphetamine results in the well known phenomenon of reverse tolerance or sensitization. However, little is known about cellular and molecular mechanisms underlying acute versus chronic response to amphetamine. In this paper, we investigated the effects of acute (1.5 or 5 mg/kg) and chronic (5 mg/kg/day for 14 days) amphetamine treatment on locomotor activity, stereotypy, Fos immunoreactivity and messenger RNA levels of molecules implicated in dopamine transmission in the rat striatum and substantia nigra. In agreement with other studies, acute amphetamine induced a dose dependent increase in locomotor activity and stereotypy. Also, a comparison between the behavior observed after the first injection and the last injection of amphetamine in chronically treated rats showed sensitization as demonstrated by a higher rating of stereotypy. We have found that acute and chronic amphetamine treatments differently modulate the activity of several output neurons. A double labeling procedure with Fos immunohistochemistry coupled with in situ hybridization demonstrated that acute amphetamine treatment induces Fos immunoreactivity predominantly in striatal neurons expressing substance P messenger RNA (77.07 +/- 1.42%). Only 32.6 +/- 2.07% of Fos immunoreactive neurons expressed preproenkephalin A messenger RNA. In chronic amphetamine treated rats, 56.21 +/- 1.32% of the Fos immunoreactive neurons expressed substance P messenger RNA while 52.12 +/- 1.84% expressed preproenkephalin A messenger RNA. Statistical analysis revealed that this difference is mainly due to a decrease in the density of substance P immunoreactive neurons in chronically treated rats in comparison to acute. Amphetamine treatments induced Fos immunoreactivity in the substantia nigra in non-dopamine neurons. As measured by quantitative in situ hybridization, acute amphetamine induced an increase in substance P, preproenkephalin A and dynorphin messenger RNA levels (+23 +/- 0.05%, +45 +/- 0.07% and +24 +/- 0.05%, respectively). No difference in these increases was observed in relation with the dose injected (1.5 or 5 mg/kg). Chronic amphetamine treatment enhanced only substance P and dynorphin messenger RNA levels (+23 +/- 0.04% and +42 +/- 0.04%, respectively). Neither acute nor chronic amphetamine treatment had any effects on D1 or D2 dopamine receptor messenger RNA levels. Our main conclusions are: (1) in acutely treated rats Fos is essentially expressed by substance P neurons; (2) in chronically treated rats, Fos immunoreactivity is expressed by the two efferent striatal populations (i.e. preproenkephalin A and substance P neurons) and the number of Fos immunoreactive neurons is reduced as compared with acute; (3) neuropeptide messenger RNA levels, but not dopamine receptor messenger RNAs, are affected in the response to acute or chronic treatment with amphetamine.