Dopamine D2-receptor messenger RNA is differentially regulated by dopaminergic agents in rat anterior and neurointermediate pituitary

Is it time to consider the expression of specific-pituitary hormone genes when typifying pituitary tumours?

The aim of the present study is to check whether we can replicate, in an independent series, previous results showing that the molecular study of pituitary-specific gene expression complements the inmunohistochemical identification of pituitary neuroendocrine tumours. We selected 112 patients (51 (46.4%) women; mean age 51.4±16 years; 102 macroadenomas (91.9%), 9 microadenomas (8.1%)) with complete clinical, radiological, immunohistochemical and molecular data from our data set of pituitary neuroendocrine tumours. Patients were different from those previously studied. We measured the expression of the pituitary-specific hormone genes and type 1 corticotrophin-releasing hormone and arginine vasopressin 1b receptors, by quantitative real-time polymerase chain reaction using TaqMan probes. Afterwards, we identified the different pituitary neuroendocrine tumour subtypes following the 2017 World Health Organization classification of pituitary tumours, calculating the concordance between their molecular and immuhistochemical identification. The concordance between molecular and immunohistochemical identification of functioning pituitary neuroendocrine tumours with the clinical diagnosis was globally similar to the previous series, where the SYBR Green technique was used instead of TaqMan probes. Our results also corroborated the poor correlation between molecular and immunohistochemical detection of the silent pituitary neuroendocrine tumour variants. This discrepancy was more remarkable in lactotroph, null-cell and plurihormonal pituitary neuroendocrine tumours. In conclusion, this study validates the results previously published by our group, highlighting a complementary role for the molecular study of the pituitary-specific hormone genes in the typification of pituitary neuroendocrine tumours subtypes.

Immunohistochemical demonstration of dopamine receptor D2R in the primary cilia of the mouse pituitary gland

Dopamine regulates the synthesis and secretion of prolactin and α-MSH/β-endorphin in lactotrophs and melanotrophs, respectively. While a predominant dopamine receptor, D2R, is known to be expressed in both the anterior and intermediate lobes of the pituitary gland, no previous immunohistochemical studies have shown the existence of D2R in the plasma membrane of pituitary endocrine cells. The present study clearly demonstrated a selective localization of the D2R immunoreactivity in primary cilia of lactotrophs and melanotrophs in the mouse adenohypophysis. Another immunoreactivity of D2R was found along the plasma membrane of melanotrophs. The intensity of immunoreactivity for D2R in the primary cilia of lactrotrophs changed during the estrous cycle and with genital conditions in contrast to a consistent immunolabeling in the melanotrophs. Since there is accumulating evidence that the primary cilium functions as a sensory device at a cellular level, the D2R-expressing primary cilia in the pituitary gland may be involved in the sensation of dopamine and dopaminergic compounds-though their involvement differs between the anterior and intermediate lobes.

Dopamine-regulated adrenocorticotropic hormone secretion in lactating rats: functional plasticity of melanotropes

Pro-opiomelanocortin (POMC) is processed to adrenocorticotropic hormone (ACTH) and beta-lipotropin in corticotropes of the anterior lobe, and to alpha-melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin in melanotropes of the intermediate lobe (IL) of the pituitary gland. While ACTH secretion is predominantly under the stimulatory influence of the hypothalamic factors, hormone secretion of the IL is tonically inhibited by neuroendocrine dopamine (NEDA) neurons. Lobe-specific POMC processing is not absolute. For example, D(2) type DA receptor (D2R)-deficient mice have elevated plasma ACTH levels, although it is known that corticotropes do not express D2R(s). Moreover, observations that suckling does not influence alpha-MSH release, while it induces an increase in plasma ACTH is unexplained. The aim of the present study was to investigate the involvement of the NEDA system in the regulation of ACTH secretion and the participation of the IL in ACTH production in lactating rats. Untreated and estradiol (E(2))-substituted ovariectomized (OVX) females were also studied. The concentration of ACTH in the IL was higher in lactating rats than in OVX rats, while the opposite change in alpha-MSH level of the IL was observed. DA levels in the IL and the neural lobe were lower in lactating rats than in OVX rats. Suckling-induced ACTH response was eliminated by pretreatment with the DA receptor agonist, bromocriptine (BRC). Inhibition of DA biosynthesis by alpha-methyl-p-tyrosine (alphaMpT) and blockade of D2R by domperidone (DOM) elevated plasma ACTH levels, but did not influence plasma alpha-MSH levels in lactating rats. The same drugs had opposite effects in OVX and OVX + E(2) animals. In lactating mothers, BRC was able to block ACTH responses induced by both alphaMpT and DOM. Surgical denervation of the IL elevated basal plasma levels of ACTH. Taken together, these data indicate that melanotropes synthesize ACTH during lactation and its release from these cells is regulated by NEDA neurons.

Cloning of sole proopiomelanocortin (POMC) cDNA and the effects of stocking density on POMC mRNA and growth rate in sole, Solea solea

Proopiomelanocortin (POMC) is an important gene implicated in different functions, such as the stress response of the hypothalamus-pituitary-adrenal axis. The aim of the present study was to determine whether farming conditions, such as stocking density, can be considered a powerful stressor influencing in turn the growth rate in juvenile fish. Thus, POMC cDNA expression was investigated during adaptation to farming conditions in sole (Solea solea), as a model for studying the effects of rearing densities on stress response; different stocking densities (50, 100, and 250 animals/m(2)) were applied and, after 7 and 21 days, the fishes were examined for body weight and plasma cortisol levels as indicators of stress. In addition, proopiomelanocortin was cloned and sequenced from the brain of sole, allowing semi-quantitative RT-PCR to be performed to evaluate POMC mRNA expression in brain tissue. There was a significant increase in cortisol levels in fish reared at high stocking densities of 250/m(2) compared to fish reared at control densities of 100 and 50/m(2), in both experimental times, i.e., 7 and 21 days. The high stocking densities were also found to decrease the specific growth rate of fish. Moreover, it was demonstrated that the highest stocking density induced a significant decrease in sole POMC mRNA expression. It is concluded that POMC and cortisol are both involved in the stress response due to high rearing densities, during which cortisol may serve as a negative regulator of POMC.

Strain-specific steroidal control of pituitary function

We have previously shown that 7B2 null mice on the 129/SvEvTac (129) genetic background die at 5 weeks of age with hypercorticosteronemia due to a Cushing's-like disease unless they are rescued by adrenalectomy; however, 7B2 nulls on the C57BL/6NTac (B6) background remain healthy, with normal steroid levels. Since background exerts such a profound influence on the phenotype of this mutation, we have evaluated whether these two different mouse strains respond differently to high circulating steroids by chronically treating wild-type 129 and B6 mice with the synthetic steroid dexamethasone (Dex). Dex treatment decreased the dopamine content of the neurointermediate lobes (NIL) of 129 mice, leading to NIL enlargement and increased total D(2)R mRNA in the 129, but not the B6, NIL. Despite the decrease in this inhibitory transmitter, Dex-treated 129 mice exhibited reduced circulating alpha-melanocyte-stimulating hormone (alpha-MSH) along with reduced POMC-derived peptides compared with controls, possibly due to reduced POMC content in the NIL. In contrast, Dex-treated B6 mice showed lowered cellular ACTH, unchanged alpha-MSH and beta-endorphin, and increased circulating alpha-MSH, most likely due to increased cleavage of NIL ACTH by increased PC2. Dex-treated 129 mice exhibited hyperinsulinemia and lowered blood glucose, whereas Dex-treated B6 mice showed slightly increased glucose levels despite their considerably increased insulin levels. Taken together, our results suggest that the endocrinological response of 129 mice to chronic Dex treatment is very different from that of B6 mice. These strain-dependent differences in steroid sensitivity must be taken into account when comparing different lines of transgenic or knockout mice.

Treatment of pituitary tumors: dopamine agonists

The neurotransmitter/neuromodulator dopamine plays an important role in both the central nervous system and the periphery. In the hypothalamopituitary system its function is a dominant and tonic inhibitory regulation of pituitary hormone secretion including prolactin- and proopiomelanocortin-derived hormones. It is well known that dopamine agonists, such as bromocriptine, pergolide, quinagolide, cabergoline, and lisuride, can inhibit PRL secretion by binding to the D(2) dopamine receptors located on normal as well as tumorous pituitary cells. Moreover, they can effectively decrease excessive PRL secretion as well as the size of the tumor in patients having prolactinoma. Furthermore, dopamine agonists can also be used in other pituitary tumors. The major requirement for its use is that the tumor cells should express D(2) receptors. Therefore, in addition to prolactinomas, targets of dopamine agonist therapy are somatotroph tumors, nonfunctioning pituitary tumors, corticotroph pituitary tumors, Nelson's syndrome, gonadotropinomas, and thyrotropin-secreting pituitary tumors. It is also an option for the treatment of pituitary disease during pregnancy. Differences between the effectiveness and the resistance of different dopaminergic agents as well as the future perspectives of them in the therapy of pituitary tumors are discussed.

Dopamine as a prolactin (PRL) inhibitor

Dopamine is a small and relatively simple molecule that fulfills diverse functions. Within the brain, it acts as a classical neurotransmitter whose attenuation or overactivity can result in disorders such as Parkinson's disease and schizophrenia. Major advances in the cloning and characterization of biosynthetic enzymes, transporters, and receptors have increased our knowledge regarding the metabolism, release, reuptake, and mechanism of action of dopamine. Dopamine reaches the pituitary via hypophysial portal blood from several hypothalamic nerve tracts that are regulated by PRL itself, estrogens, and several neuropeptides and neurotransmitters. Dopamine binds to type-2 dopamine receptors that are functionally linked to membrane channels and G proteins and suppresses the high intrinsic secretory activity of the pituitary lactotrophs. In addition to inhibiting PRL release by controlling calcium fluxes, dopamine activates several interacting intracellular signaling pathways and suppresses PRL gene expression and lactotroph proliferation. Thus, PRL homeostasis should be viewed in the context of a fine balance between the action of dopamine as an inhibitor and the many hypothalamic, systemic, and local factors acting as stimulators, none of which has yet emerged as a primary PRL releasing factor. The generation of transgenic animals with overexpressed or mutated genes expanded our understanding of dopamine-PRL interactions and the physiological consequences of their perturbations. PRL release in humans, which differs in many respects from that in laboratory animals, is affected by several drugs used in clinical practice. Hyperprolactinemia is a major neuroendocrine-related cause of reproductive disturbances in both men and women. The treatment of hyperprolactinemia has greatly benefited from the generation of progressively more effective and selective dopaminergic drugs.

Differential effects on D2 dopamine receptor and prolactin gene expression by haloperidol and aripiprazole in the rat pituitary

[3H]Spiperone-binding assay to D2 receptors and quantitative ribonuclease protection assay for both isoforms (D2L and D2S receptor) of the D2 receptor mRNA and the prolactin mRNA were performed on pituitaries from the control rat and from the rat injected orally daily with either haloperidol (2 mg/kg) or aripiprazole (24 mg/kg) for 21 days. Haloperidol treatment increased the [3H]spiperone-binding by 28%, the levels of D2L and D2S receptor mRNA by 41% and 38%, respectively, and the level of prolactin mRNA by 26%. In contrast, the treatment with aripiprazole, a newly developed atypical antipsychotic with reduced side effects, decreased the [3H]spiperone-binding by 24% and the levels of D2L and D2S receptor mRNA by 23% and 23%, respectively, and did not have any effect on the level of prolactin mRNA. The same treatment with sulpiride (100 mg/kg) increased the levels of D2L and D2S receptor mRNA by 59% and 62%, respectively, but treatment with clozapine (25 mg/kg) did not cause any effect. Neither treatment changed the ratio of the level of D2S receptor mRNA to the level of D2L receptor mRNA in the pituitary. These findings indicate that D2 receptor densities in the pituitary are influenced differentially by the treatment with these antipsychotics, which could be induced at least partly by the changes in the levels of mRNA without any effects on the splicing mechanisms and thus affect the plasticity of the prolactin mRNA expression. The inhibitory effects of chronic aripiprazole treatment on D2 receptors in the pituitary might underlie this drug's clinical property of reduced hyperprolactinemia side effect.

Antiproliferative role of dopamine: loss of D2 receptors causes hormonal dysfunction and pituitary hyperplasia

The function of dopamine (DA) in the nervous system is paralleled by its neuroendocrine control of pituitary gland functions. Here, we document the neuroendocrine function of dopamine by studying the pituitary gland of mice lacking DA D2 receptors (D2R). These mice present a striking, progressive increase in lactotroph number, which ultimately leads to tumors in aged animals. Females develop tumors much earlier than males. An estrogen-mediated lactotroph proliferation cannot account for this sexual dimorphism, since D2R-null females are hypoestrogenic and, thus, have estrogen levels similar to males. In contrast, prolactin levels are six times higher in females than in males. We show that active prolactin receptors are present in the pituitary and their expression increases in concomitance with tumor expansion. These results point to prolactin as an autocrine proliferative factor in the pituitary gland. Additionally, they demonstrate an antiproliferative function for DA regulated through D2 receptor activation.

Dopamine D2 receptor stimulation alters G-protein expression in rat pituitary intermediate lobe melanotropes

Stimulation of dopamine D2 receptors inhibits melanotrope pro-opiomelanocortin (POMC) biosynthesis and alpha-melanocyte-stimulating hormone (MSH) secretion. These effects are mediated by G-protein alpha i- and alpha o-subunits and are reversed by stimulating receptors linked to activation of G alpha s protein. Melanotrope activity is increased by haloperidol, a D2 receptor antagonist, and decreased by bromocriptine, a D2 receptor agonist. Both the short and long isoforms of the D2 receptor mRNA and protein increase following chronic haloperidol treatment. After chronic bromocriptine treatment the short isoform is downregulated, whereas the long isoform is upregulated. Our hypothesis is that specific G protein alpha- subunits alter in pattern of expression similarly to the receptor isoforms. Using immunohistochemistry and in situ hybridization, this study examined changes in G alpha i, G alpha o, and G alpha s protein and mRNA expression following chronic treatments with bromocriptine or haloperidol. G alpha i3 and G alpha o immunoreactivities increased following bromocriptine treatment, whereas G alpha s and G alpha i1/2 did not change. Gs immunoreactivity increased after haloperidol treatment, whereas G alpha i1/2, G alpha i3, and G alpha o did not change. G alpha i and G alpha o mRNA increased following bromocriptine and decreased following haloperidol treatments, whereas the inverse results were observed with G alpha s mRNA. These results suggest D2 receptor activation can specifically increase G alpha i3 and G alpha o expression, and D2 receptor blockade increases G alpha s expression.

Effects of endophyte-infected tall fescue, environmental temperature and prazosin injection on the rat

Effects of an alpha 1 antagonist, prazosin, injection on the rat (Rattus rattus) exposed to warm vs normal environments and fed endophyte-infected (E+) or -free (E-) tall fescue seed were studied. Rats were injected IP daily with placebo or prazosin (1 mg/kg BW). Daily skin and rectal temperatures and food intake measurements were recorded. Selected brain tissues were dissected to determine treatment effects on monoamine receptor density. Rats fed E+ and injected with placebo had reduced (P < 0.01) food intake compared with all other treatments. By day 5 of injection, an endophyte x temperature interaction for increased (P < 0.03) skin and rectal temperatures was measured when rats were fed E+ and housed at 32 degrees C. Also by day 5, injection of rats consuming E+ with prazosin reduced (P < 0.01) skin and rectal temperatures 0.4 degree C compared with those consuming E+ and injected with placebo. Monoamine receptor (alpha 1, alpha 2, and D2) densities were similar (P > 0.10) among treatments. Prazosin injection reduced E+ induced body temperature increases chronically and increased food intake acutely to E- levels. Monoamine receptor densities were unchanged; therefore, E+ effects via monoamine receptors may be due to acute modulation of receptor-associated activity.

Melanotrope dopamine D2 receptor isoform expression in the developing rat pituitary

This study measured melanotrope mRNA and protein expression for the dopamine D2 receptor, and its long isoform, in relation to the appearance of dopamine in axons of the postnatal rat pituitary intermediate lobe. At postnatal day 2, prior to the onset of dopaminergic innervation, D2 receptor (D2T) mRNA was expressed heterogeneously in a subpopulation of melanotropes which also expressed the long isoform (DL). The D2L mRNA appeared to be predominant during early postnatal development, since the D2T probe, which did not discriminate between the isoforms, and the D2L probe hybridized generally to the same cells, as demonstrated in serial sections. Immunohistochemical methods, using two different antisera for the D2T receptor, however, indicated a low level of protein in most melanotropes. Localization of D2L protein corresponded well to D2T receptor mRNA distribution. At day 10, representing a time when dopamine is present in axons throughout the lobe, both D2T receptor mRNA and protein were detected in a significantly larger population of melanotropes than those expressing D2L mRNA and protein. This suggests the appearance of detectable short isoform (D2S) mRNA in virtually all melanotropes and implicates dopamine as a possible signal for increasing D2S isoform mRNA expression.

Altered expression of dopamine D2 receptor mRNA 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.

Developmental and age-related changes in the D2 dopamine receptor mRNA subtypes in rat brain

The influence of ontogeny and aging on the D2 dopamine receptor mRNA in rat brain were examined using in situ hybridization histochemistry and Northern analysis utilizing oligonucleotide probes complementary to the different D2 mRNA subtypes. At birth, there was a high level of D2 dopamine receptor mRNA in corpus striatum relative to that found in the cerebral cortex and other brain areas. The hybridization signal of striatum (using a probe that hybridizes to both the D2A and D2B mRNA) increased during the first two postnatal weeks, reached a peak at day 16, then declined slightly. The D2A mRNA showed a similar distribution and developmental pattern. Intracisternal injection of 6-hydroxydopamine into neonates did not significantly alter the increase of the D2 dopamine receptor mRNAs, suggesting that neuronal input does not influence the ontogenetic development of this mRNA. In striatum, olfactory tubercule and inferior colliculus, the D2A mRNA declined between 3 and 24 months of age. By contrast, there was an age-related increase in the D2A mRNA in the anterior and intermediate lobes of the pituitary. The mRNA for the D2B dopamine receptor showed very low but nevertheless detectable levels in striatum, olfactory tubercule and pituitary. Like with the D2A mRNA, in 24-month-old rats the D2B mRNA declined in striatum and olfactory tubercule and increased in pituitary. These results show that there are differential tissue-related changes in the mRNAs for the D2 dopamine receptor during both development and aging.

Differential influence of haloperidol and sulpiride on dopamine receptors and peptide mRNA levels in the rat striatum and pituitary

We examined the effect of chronic administration (14 days) of haloperidol (2 mg/kg/day) or sulpiride (100 mg/kg/day), on the mRNA levels of various genes in the rat striatum and pituitary by quantitative in situ and Northern blot hybridizations. In the pituitary, haloperidol and sulpiride induced similar increases of mRNAs of pro-opiomelanocortin (POMC) (+65% and +73%), prolactin (PRL) (+821% and +840%) and growth hormone (GH) (+32% and +47%), but sulpiride induced a greater increase of D2R mRNA (+125%) than haloperidol (+92%). In the striatum, sulpiride and haloperidol had different effects: sulpiride induced a higher increase than haloperidol of both preproenkephalin A (PPA) mRNA (+67% versus +47%) and D2 dopamine receptor (D2R) mRNAs (+72% versus +40%). Moreover, haloperidol and sulpiride had opposite effects on substance P (SP) mRNA. Haloperidol decreased the amount of SP mRNA by 20% while sulpiride increased it by 20%. The D1 dopamine receptor (D1R) mRNA level was not significantly modified after either treatment. Our results demonstrate that the effect of a chronic haloperidol treatment on striatal dopamine receptors and neuropeptide mRNA levels is different to that of sulpiride, whereas it is similar on pituitary hormones mRNA levels.

The effect of haloperidol on D2 dopamine receptor subtype mRNA levels in the brain

Chronic neuroleptic treatment induces an increase in the density of D2 dopamine receptors in the striatum. The effect of prolonged administration of haloperidol on mRNA levels of the short (D2S) and long (D2L) isoforms of the D2 dopamine receptor and the D3 dopamine receptor in different brain regions was examined. Haloperidol caused a significant rise in both D2L and D2S mRNA levels in the striatum, but had no effect on D3 mRNA levels. This rise was restricted to the striatum, showing that the effect of haloperidol on dopamine receptor mRNA is both subtype- and tissue-specific.

Expression of the Xenopus D2 dopamine receptor. Tissue-specific regulation and two transcriptionally active genes but no evidence for alternative splicing

In the amphibian Xenopus laevis the D2 dopamine receptor is involved in the regulation of the melanotrope cells of the intermediate pituitary during background adaptation of the animal. The Xenopus D2 receptor has been found to be pharmacologically different from the mammalian D2 receptor. In a number of mammalian species alternative splicing generates two molecular forms of the D2 receptor. These isoforms differ by the presence or absence of 29 amino acids in the third cytoplasmic loop which is thought to be involved in guanine-nucleotide-binding-regulatory-protein (G-protein) binding of the receptor. We previously described a cDNA encoding the large isoform of the Xenopus D2 receptor. Here we report on the isolation of a brain cDNA encoding a second, structurally different Xenopus D2 dopamine receptor. Both Xenopus receptors correspond to the large isoform of the D2 receptor and they display a high degree of sequence identity with their mammalian counterparts. Their occurrence reflects the expression of two Xenopus D2 receptor genes and they are expressed to approximately the same level. In contrast to mammals, PCR analysis gave no evidence for alternative splicing during D2 receptor expression in Xenopus brain and pituitary. Tissue-specific expression of the Xenopus D2 receptor was observed in the pituitary during background adaptation. The low level of receptor mRNA in melanotrope cells of white animals compared to that of black animals may be caused by chronic dopamine stimulation of melanotrope cells in white animals with consequent cellular desensitization and down regulation of the D2 receptor gene.

Dopamine regulates D2 receptor gene expression in normal but not in tumorous rat pituitary cells

Abnormalities of dopamine D2 receptors may be implicated in the development of some pituitary tumours. Previously we have identified dopamine D2 receptor gene expression both in normal rat pituitaries and in dopamine resistant GH3 rat pituitary tumour cells. In this study we have examined the effect of dopamine on D2 receptor gene expression in these cells using a probe specific for both D2 receptor isoforms. Normal rat pituitary cells were maximally stimulated by 100 nM dopamine at which concentration D2 receptor mRNA concentrations were 400% greater than that measured in controls. No increase in D2 receptor gene expression was observed in GH3 pituitary tumour cells.

Lack of effect of haloperidol or methamphetamine treatment on the mRNA levels of two dopamine D2 receptor isoforms in rat brain

In order to investigate whether changes of the two mRNAs encoding the D2 receptor isoforms were induced by chronic haloperidol or methamphetamine treatment in rats, we measured the brain mRNA levels using in situ hybridization histochemistry (ISHH). We used two oligonucleotide probes, an "insert" probe to hybridize with the longer D2 receptor, D2(444), mRNA, and a "spanning" probe to hybridize with the shorter D2 receptor, D2(415), mRNA. Both D2 mRNAs were detected by ISHH in the caudate putamen, nucleus accumbens, substantia nigra, pars compacta and ventral tegmental area. The distributions and the amounts of the mRNAs for the two D2 isoforms did not change after chronic administration of haloperidol (1 mg/kg/day for 14 days, ip) or methamphetamine (4 mg/kg/day for 14 days, ip). These results suggest that the changes of D2 receptor density induced by chronic neuroleptic and psychostimulant treatment are not due primarily to receptor expression.

Localization of multiple dopamine receptor subtype mRNAs in human and monkey motor cortex and striatum

Dopamine plays a critical role in motor and cognitive function through actions mediated by specific receptors, multiple subtypes of which have recently been identified. The distribution of mRNAs encoding D1, D2 and D5 receptors in the motor cortex of humans and in the motor cortex and striatum of macaque monkeys was examined using in situ hybridization. In motor cortices from both primate species, hybridization to each receptor probe resulted in numerous labeled cells throughout layers II-VI. In contrast to neocortex, in monkey striatum only the D1 and D2 receptor probes showed significant hybridization. Thus, not only does primate neocortex possess a broader representation of the dopamine receptor subtype mRNAs examined in comparison with striatum, but the unexpected presence and widespread distribution of D2 and D5 receptor mRNAs in cortex suggests that, along with D1 receptors, D2 and D5 receptors play a crucial role in the dopaminergic modulation of cognition and motor behavior, and in dopamine dysfunction associated with neuropsychiatric disorders.

Chronic estradiol treatment increases anterior pituitary but not striatal D2 dopamine receptor mRNA levels in rats

The effect of chronic 17 beta-estradiol treatment (10 micrograms, twice each day, for 2 weeks) of ovariectomized rats on D2 dopamine (DA) receptor mRNA levels was investigated in striatum and anterior pituitary gland tissues. We used 32P-labeled probes specific for D2 receptor and beta-actin mRNAs in Northern blot analysis. The ratio of D2 DA receptor mRNA/beta-actin mRNA level was significantly increased in the anterior pituitary of estradiol-treated rats compared to vehicle-treated animals. The D2 DA receptor mRNA/beta-actin mRNA ratio in the striatum was not affected by estradiol treatment. However, the medial portion of the striatum showed a significantly lower ratio compared to the lateral portion of the striatum in both vehicle- and estradiol-treated rats. Thus, the estradiol effect on anterior pituitary D2 receptors may implicate transcriptional regulation, whereas our results do not support this hypothesis for the estradiol action on striatal D2 receptors.

Quantitation of isotypes of D2 receptors using solution hybridization

Solution hybridization was used to quantitate the expression of the long and short splice variants of mRNA coding for the dopamine D2 receptor. Sequences corresponding to 450 bases of the coding region of the long form of the third intracellular loop and the full-length coding sequences of the long and short isoforms of the D2 receptor were amplified using PCR and cloned into a Bluescribe (pBS+) vector. Phage polymerases were used to synthesize riboprobes complementary to the third intracellular loop. Hybridization was carried out using sense strand RNA or total RNA isolated from tissue or cells. After hybridization and digestion with nucleases, the hybridization products were size-fractionated on a urea acrylamide gel. The RNA coding for the D2 receptor appeared as two distinct bands. One band (438 base pairs) represents the long form of the receptor and a second band (285 base pairs) represents the short form of the RNA coding for the receptor. Quantitation of the amount of RNA present suggests that in the striatum the long form of RNA coding for the receptor is expressed at higher levels than is the short form. In a cell line containing dopamine receptors derived from the pituitary (SUPI), the long form predominates to an even greater extent than in the striatum.

Expression of rat striatal D1 and D2 dopamine receptor mRNAs: Ontogenetic and pharmacological studies

The developmental characteristics of D1 and D2 dopamine receptor mRNA levels were determined by Northern blot analyses. Striatal D1 and D2 receptor mRNAs of male Fischer 344 rats were about 60% of adults levels at postnatal day 1 and reached their highest measured levels at day 30 (126-139% adults levels) and then decreased by day 120 (100%). D1 and D2 receptor densities at day 30 were about 8-fold higher than at day 1, while mRNA levels showed only a 2-fold increase. The highest level of D2 receptor mRNA in midbrain as reached at day 14 (195% adult level) while levels at day 1 were 31% higher than dose at day 120. Treatment with selective D2 receptor antagonist, haloperidol (0.5 mg/kg/day, s.c., for 2 h, 7, 14, 21 days or 21 days + 3 days withdrawal) had no effect on Sprague-Dawley rat striatal D2 receptor mRNA levels in spite of significant increases in receptor density at the later time points. However, the selective D1 receptor antagonist, SCH 23390 (0.5 mg/kg/day, s.c.) produced increases in striatal D1 receptors and mRNA levels after treatments of 7, 14 and 21 days + 3 days withdrawal.

Effects of dopaminergic transmission interruption on the D2 receptor isoforms in various cerebral tissues

We examined the effects of an interruption of dopamine neurotransmission, by either dopamine receptor blockade or degeneration of dopamine neurons by 6-hydroxydopamine, on the levels of D2 receptor mRNAs. In addition, we evaluated by the polymerase chain reaction (PCR) the relative abundance of the two D2 receptor isoform mRNAs generated by alternative splicing. Daily injections of 4 mg/kg of haloperidol to rats elicited in striatum a rapid and progressive increase in D2 receptor mRNA levels, which reached 70% after a 15-day treatment. By contrast, there was no apparent change in D2 receptor mRNA levels in cerebral cortex and pons-medulla, in spite of an increased density of D2 receptor in the former tissue. Using the PCR with primers flanking the alternative exon, we observed that the relative proportion of the shorter receptor isoform (D2S) mRNA was slightly but significantly enhanced in cerebral cortex (17%) and pons-medulla (18%) after a 15-day haloperidol treatment. Unilateral degeneration of dopamine neurons induced by local injection of 6-hydroxydopamine resulted in a marked decrease in levels of total D2 receptor mRNAs in substantia nigra (-79%) and ventral tegmental (-63%) area, two cell body areas. In the substantia nigra, the longer isoform (D2L) mRNA was significantly more decreased in content than the D2S isoform mRNA, so that there was a large enhancement in the relative abundance of the latter (81%).(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of D1A and D2 dopamine receptor mRNA during ontogenesis, lesion and chronic antagonist treatment

The developmental characteristics of D1A and D2 dopamine receptor mRNA levels were determined by Northern blot analyses. Striatal D1A and D2 dopamine receptor mRNAs of male Fischer 344 rats were about 60% of adult (day 120) levels at postnatal day 1 and reached their highest levels at day 30 (126 and 139% adult levels) and then decreased by day 120 (100%). D1 and D2 dopamine receptors showed much greater quantitative changes with densities at day 30 about 6- and 14-fold higher than at day 1, respectively, while mRNA levels showed only a 2-fold increase. The highest level of D2 dopamine receptor mRNA in the midbrain was reached at day 14 (195% of adult levels) while the level at day 1 was 31% higher than that at day 120. Striatal beta-actin mRNA levels decreased gradually as the rats developed with the level at postnatal day 1 almost twice that at day 120 postpartum. Treatment of adult rats with the selective D2 dopamine receptor antagonist, haloperidol (0.5 mg/kg/day, s.c., for 2 h, 7, 14, 21 days or 21 days + 3 days withdrawal) had no effect on striatal D2 dopamine receptor mRNA levels in spite of significant increases in dopamine receptor density at the later time points. However, 21 days following a 6-hydroxydopamine lesion of the nigrostriatal pathway, striatal D2 dopamine receptor mRNA levels were increased by 53%.

Dopamine D2-receptor mRNA level in rat striatum after chronic haloperidol treatment

Chronic treatment with haloperidol, a D2-receptor antagonist and a neuroleptic, increases the number of D2-receptors in rat striatum. However, there have been inconsistent reports on the D2-receptor mRNA level, one showing the increase in the mRNA level and another detecting no changes. Furthermore, they did not distinguish the two isoforms of D2-receptor, D2A and D2B. In the present work, both D2- and DeA-receptor mRNA levels in rat striatum were estimated after chronic administration of haloperidol. There was, within the sensitivity of the assay, no significant increase in either of them between 3 and 24 h after the last administration. This suggests that chronic haloperidol treatment does not affect the transcriptional regulation of the D2-receptor gene or the alternative splicing process of its transcripts.

Alternative transcripts of the rat and human dopamine D3 receptor

A cDNA for the rat dopamine D3 receptor containing a 113 bp deletion has been isolated. The segment deleted, encompassing the first extracellular loop and third transmembrane domain, alters the reading frame, introducing 19 amino acids not found in the full length receptor followed by a premature stop codon. This novel mRNA encodes a 109 amino acid protein containing two putative transmembrane domains. A similar variant cDNA for the human D3 receptor has also been identified.

From neurotransmitter to gene: identifying the missing links

Survival demands adaptation to changes in the environment, and some of the most important adaptations are accomplished by the nervous system. Adaptive processes such as learning and memory are mediated by complex intracellular adjustments that result, at least in part, from changes in the levels of certain proteins. The involvement of neurotransmitters in the regulation of protein biosynthesis has recently become the focus of much investigation. Questions that are beginning to be explored include: how do neurotransmitters regulate the expression of specific genes in various cell populations? How can a gene product be regulated in opposing or coordinated fashion by different stimuli? How does a neurotransmitter exert differential regulatory influences in the same cell type under different growth conditions? Teresa Esterle and Elaine Sanders-Bush examine these questions with an emphasis on the studies that explore the ability of neurotransmitters to have diverse actions on the same target gene in different tissues or on different genes in the same cell.

Either isoform of the dopamine D2 receptor can mediate dopaminergic repression of the rat prolactin promoter

Hypophyseal portal dopamine is a major negative regulator of pituitary prolactin (PRL) production. Dopamine has been reported to repress PRL gene transcription in pituitary cells. To facilitate further study of the effect of dopamine on PRL gene activation, we introduced PRL promoter and D2 receptor (D2R) constructs into GH3 cells. Since two D2R isoforms (termed D2S and D2L) have been cloned previously, we first determined which isoform(s) is present in the lactotroph by measuring the level of each mRNA species in rat prolactinoma. mRNA for each D2R isoform was found to be present, with the D2L mRNA in great (c. 6-fold) excess. Because the lactotroph contains both isoforms, the effect of each on the PRL promoter was investigated. The cDNA for each receptor isoform was synthesized by polymerase chain reaction, and cloned into an RSV-based expression vector. GH3 cells were then transiently co-transfected with either of the resulting RSV-D2R constructs plus a PRL-chloramphenicol acetyltransferase (CAT) construct containing the first 1957 base-pairs of PRL gene 5'-flanking DNA. The cells were then incubated 48 h plus or minus the dopamine agonist ergocryptine (ECR). In the presence of either RSV-D2R isoform, ECR yielded a 4-5-fold decrease in CAT activity, an effect not seen in the absence of the RSV-D2R. The promoter specificity of this effect was demonstrated by the inability of ECR to regulate expression of a control RSV-CAT construct. The PRL promoter repression mediated by each receptor isoform had appropriate pharmacology: the specific D2R agonist, quinpirole, yielded results similar to ECR, and the ECR repression was reversed by the dopamine antagonist spiperone.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased abundance of alternatively spliced forms of D2 dopamine receptor mRNA after denervation

The existence of two molecular forms of D2 dopamine receptors suggests that differences in the distribution or regulation of the two forms could be exploited for the pharmacological treatment of disease. Using probes selective for each alternatively spliced variant of D2 receptor mRNA, we determined that both variants were widely distributed in rat brain and pituitary but that the ratio of the forms varied among regions. mRNA for the 444-amino acid-long variant, D2(444), was the most abundant form in pituitary and neostriatum. Intermediate levels of both D2(444) mRNA and the short form, D2(415), were detected in midbrain, and low levels of D2(444) and D2(415) mRNAs were detected in all other regions examined, including hippocampus, cerebellum, and cortex. The D2(444)/D2(415) ratio was generally lower in the regions of low expression than in pituitary and neostriatum. Dopamine-depleting lesions increased the density of D2 receptors in the denervated neostriatum by 29% without altering the affinity of the receptors for [3H]spiperone. The proliferation of receptors appeared to be due to a lesion-induced increase of up to 120% in the abundance of both variants of mRNA in the neostriatum.

Distribution of dopamine D2 receptor mRNA splice variants in the rat by solution hybridization/protection assay

We investigated the distribution of the two dopamine D2 receptor mRNA splice variants in the rat using a sensitive and quantitative solution hybridization/nuclease protection assay. In all brain and endocrine regions studied, both splice variants were detected and the mRNA of the longer form (D2L) was more abundant than that of the shorter form (D2S). The lowest percentages of D2S were found in the pituitary and adrenal glands.

Haloperidol treatment increases D2 dopamine receptor protein independently of RNA levels in mice

Haloperidol, administered to mice in their drinking water, produced a 21% increase in striatal D2 dopamine receptor density after seven days of continuous exposure. The steady-state D2 receptor RNA prevalence was unaffected by this treatment, yet the RNA coding for preproenkephalin was elevated, as expected. These data indicate that the homologous up-regulation of dopamine receptor density by antipsychotic drugs proceeds by mechanisms other than changes in RNA abundance.

Striatal neurons express increased level of dopamine D2 receptor mRNA in response to haloperidol treatment: a quantitative in situ hybridization study

In the present study, quantitative in situ hybridization was used to analyse the effect of haloperidol treatment on D2 dopamine receptor gene expression in the rat caudate-putamen nucleus. Variations of D2 receptor mRNA level were studied and measured at the macroscopic level of densitometric analysis of X-ray film and at the microscopic level by counting of autoradiographic silver grains in striatal cells. Macroscopic analysis demonstrated that haloperidol treatment two times 1 mg/kg per day during seven, 14 and 21 days increased D2 receptor mRNA level in the caudate-putamen. Detailed microscopic analysis demonstrated a significant increase in D2 receptor mRNA in the two neuronal populations known to express the D2 receptor gene: medium-sized neurons previously identified as enkephalinergic neurons, and large-sized neurons previously identified as cholinergic neurons. The increase was more important in cholinergic neurons (+119%) than in enkephalinergic neurons (+54%). Haloperidol treatment did not modify the number of medium-sized enkephalinergic neurons expressing the D2 receptor mRNA. In contrast, it significantly increased the percentage of large-sized neurons containing D2 receptor mRNA (from 80 to 94%). These results demonstrate that haloperidol treatment acts at the gene level to modulate D2 receptor content in striatal dopaminoceptive neurons, and that the D2 receptor mRNA increase in postsynaptic neurons contributes to dopamine supersensitivity induced by neuroleptics in the rat. This suggests that dopamine acts trans-synaptically to control D2 receptor gene expression in target striatal neurons. These results suggest that modifications of D2 receptor gene expression may be part of the biological events that lead to the movement disorders induced by neuroleptic drugs or Parkinson's disease.

Effect of haloperidol on expression of dopamine D2 receptor mRNAs in rat brain

Chronic administration of the neuroleptic drug haloperidol previously has been shown to increase the density of striatal dopamine D2 receptor, which is believed to be the underlying factor in neuroleptic-induced tardive dyskinesia. To search for the mechanism of receptor upregulation, the expression of the isoforms of dopamine D2 receptor mRNA in rat striatum was analyzed by Northern, solution, and in situ hybridizations in haloperidol-treated rats (1-35 days). Northern blot analysis of poly(A)+ RNA hybridized with a probe common for both isoforms as well as an insert-specific probe for the long isoform of the receptor revealed no significant difference in hybridization signal between the control and any of the haloperidol-treated groups of rats. The receptor density, however, was increased by 30-40% in animals receiving haloperidol for 7-35 days. Solution hybridization with an antisense riboprobe specific for a consensus sequence as well as in situ hybridization with a consensus oligonucleotide probe similarly failed to detect any increase in the expression of receptor mRNA following haloperidol treatment. The results suggest that post-transcriptional mechanisms may be responsible for regulating the haloperidol-induced increase in dopamine D2 receptors.