Differential expression of dopaminergic D2 receptor messenger RNAs during development

Hypofunctional Dopamine Uptake and Antipsychotic Treatment-Resistant Schizophrenia

Antipsychotic treatment resistance in schizophrenia remains a major issue in psychiatry. Nearly 30% of patients with schizophrenia do not respond to antipsychotic treatment, yet the underlying neurobiological causes are unknown. All effective antipsychotic medications are thought to achieve their efficacy by targeting the dopaminergic system. Here we review early literature describing the fundamental mechanisms of antipsychotic drug efficacy, highlighting mechanistic concepts that have persisted over time. We then reconsider the original framework for understanding antipsychotic efficacy in light of recent advances in our scientific understanding of the dopaminergic effects of antipsychotics. Based on these new insights, we describe a role for the dopamine transporter in the genesis of both antipsychotic therapeutic response and primary resistance. We believe that this discussion will help delineate the dopaminergic nature of antipsychotic treatment-resistant schizophrenia.

Maternal immune activation alters sensitivity to action-outcome contingency in adult rat offspring

Epidemiological studies have provided convincing evidence for a role of maternal immune activation in the pathogenesis of neurodevelopmental disorders such as autism and schizophrenia. In recent years, several research groups have capitalised on this discovery and developed animal models such as the maternal immune activation (MIA) model that emulates many phenotypes characteristic of disorders such as schizophrenia. In the present series of experiments we used the MIA model to examine motivation, a core component of the negative symptomatology in schizophrenia. Contrary to what we expected, in the progressive ratio task, which assesses an animals' willingness to work for a reward under increasing effort requirements, we found that MIA rats appeared more motivated than controls. Subsequent tests showed that this seemingly enhanced motivation was not due to an overall increase in responding, nor due to enhanced attribution of incentive salience to reward associated responses. Instead, we found that the increased willingness to work exhibited by MIA animals was due to an inability to detect changes in the contingency between their behaviour and the resulting rewarding outcome. With regard to motivation, the experiments reported here are the first to subject the MIA model to a rigorous experimental analysis of behaviour by parsing underlying processes that give rise to the overt symptoms in psychiatric disease.

CK2-An Emerging Target for Neurological and Psychiatric Disorders

Protein kinase CK2 has received a surge of attention in recent years due to the evidence of its overexpression in a variety of solid tumors and multiple myelomas as well as its participation in cell survival pathways. CK2 is also upregulated in the most prevalent and aggressive cancer of brain tissue, glioblastoma multiforme, and in preclinical models, pharmacological inhibition of the kinase has proven successful in reducing tumor size and animal mortality. CK2 is highly expressed in the mammalian brain and has many bona fide substrates that are crucial in neuronal or glial homeostasis and signaling processes across synapses. Full and conditional CK2 knockout mice have further elucidated the importance of CK2 in brain development, neuronal activity, and behavior. This review will discuss recent advances in the field that point to CK2 as a regulator of neuronal functions and as a potential novel target to treat neurological and psychiatric disorders.

The non-human primate striatum undergoes marked prolonged remodeling during postnatal development

We examined the postnatal ontogeny of the striatum in rhesus monkeys (Macaca mulatta) to identify temporal and spatial patterns of histological and chemical maturation. Our goal was to determine whether this forebrain structure is developmentally static or dynamic in postnatal life. Brains from monkeys at 1 day, 1, 4, 6, 9, and 12 months of age (N = 12) and adult monkeys (N = 4) were analyzed. Nissl staining was used to assess striatal volume, cytoarchitecture, and apoptosis. Immunohistochemistry was used to localize and measure substance P (SP), leucine-enkephalin (LENK), tyrosine hydroxylase (TH), and calbindin D28 (CAL) immunoreactivities. Mature brain to body weight ratio was achieved at 4 months of age, and striatal volume increased from ∼1.2 to ∼1.4 cm(3) during the first postnatal year. Nissl staining identified, prominently in the caudate nucleus, developmentally persistent discrete cell islands with neuronal densities greater than the surrounding striatal parenchyma (matrix). Losses in neuronal density were observed in island and matrix regions during maturation, and differential developmental programmed cell death was observed in islands and matrix regions. Immunohistochemistry revealed striking changes occurring postnatally in striatal chemical neuroanatomy. At birth, the immature dopaminergic nigrostriatal innervation was characterized by islands enriched in TH-immunoreactive puncta (putative terminals) in the neuropil; TH-enriched islands aligned completely with areas enriched in SP immunoreactivity but low in LENK immunoreactivity. These areas enriched in SP immunoreactivity but low in LENK immunoreactivity were identified as striosome and matrix areas, respectively, because CAL immunoreactivity clearly delineated these territories. SP, LENK, and CAL immunoreactivities appeared as positive neuronal cell bodies, processes, and puncta. The matrix compartment at birth contained relatively low TH-immunoreactive processes and few SP-positive neurons but was densely populated with LENK-immunoreactive neurons. The nucleus accumbens part of the ventral striatum also showed prominent differences in SP, LENK, and CAL immunoreactivities in shell and core territories. During 12 months of postnatal maturation salient changes occurred in neurotransmitter marker localization: TH-positive afferents densely innervated the matrix to exceed levels of immunoreactivity in the striosomes; SP immunoreactivity levels increased in the matrix; and LENK-immunoreactivity levels decreased in the matrix and increased in the striosomes. At 12 months of age, striatal chemoarchitecture was similar qualitatively to adult patterns, but quantitatively different in LENK and SP in caudate, putamen, and nucleus accumbens. This study shows for the first time that the rhesus monkey striatum requires more than 12 months after birth to develop an adult-like pattern of chemical neuroanatomy and that principal neurons within striosomes and matrix have different developmental programs for neuropeptide expression. We conclude that postnatal maturation of the striatal mosaic in primates is not static but, rather, is a protracted and dynamic process that requires many synchronous and compartment-selective changes in afferent innervation and in the expression of genes that regulate neuronal phenotypes.

Identification of two functionally distinct endosomal recycling pathways for dopamine D₂ receptor

Dopamine D₂ receptor (DRD2) is important for normal function of the brain reward circuit. Lower DRD2 function in the brain increases the risk for substance abuse, obesity, attention deficit/hyperactivity disorder, and depression. Moreover, DRD2 is the target of most antipsychotics currently in use. It is well known that dopamine-induced DRD2 endocytosis is important for its desensitization. However, it remains controversial whether DRD2 is recycled back to the plasma membrane or targeted for degradation following dopamine stimulation. Here, we used total internal reflection fluorescent microscopy (TIRFM) to image DRD2 with a superecliptic pHluorin tagged to its N terminus. With these technical advances, we were able to directly visualize vesicular insertion events of DRD2 in cultured mouse striatal medium spiny neurons. We showed that insertion of DRD2 occurs on neuronal somatic and dendritic surfaces. Lateral diffusion of DRD2 was observed following its insertion. Most importantly, using our new approach, we uncovered two functionally distinct recycling pathways for DRD2: a constitutive recycling pathway and a dopamine activity-dependent recycling pathway. We further demonstrated that Rab4 plays an important role in constitutive DRD2 recycling, while Rab11 is required for dopamine activity-dependent DRD2 recycling. Finally, we demonstrated that the two DRD2 recycling pathways play distinct roles in determining DRD2 function: the Rab4-sensitive constitutive DRD2 recycling pathway determines steady-state surface expression levels of DRD2, whereas the Rab11-sensitive dopamine activity-dependent DRD2 recycling pathway is important for functional resensitization of DRD2. Our findings underscore the significance of endosomal recycling in regulation of DRD2 function.

Developmental changes in human dopamine neurotransmission: cortical receptors and terminators

Background

Dopamine is integral to cognition, learning and memory, and dysfunctions of the frontal cortical dopamine system have been implicated in several developmental neuropsychiatric disorders. The dorsolateral prefrontal cortex (DLPFC) is critical for working memory which does not fully mature until the third decade of life. Few studies have reported on the normal development of the dopamine system in human DLPFC during postnatal life. We assessed pre- and postsynaptic components of the dopamine system including tyrosine hydroxylase, the dopamine receptors (D1, D2 short and D2 long isoforms, D4, D5), catechol-O-methyltransferase, and monoamine oxidase (A and B) in the developing human DLPFC (6 weeks -50 years).

Results

Gene expression was first analysed by microarray and then by quantitative real-time PCR. Protein expression was analysed by western blot. Protein levels for tyrosine hydroxylase peaked during the first year of life (p < 0.001) then gradually declined to adulthood. Similarly, mRNA levels of dopamine receptors D2S (p < 0.001) and D2L (p = 0.003) isoforms, monoamine oxidase A (p < 0.001) and catechol-O-methyltransferase (p = 0.024) were significantly higher in neonates and infants as was catechol-O-methyltransferase protein (32 kDa, p = 0.027). In contrast, dopamine D1 receptor mRNA correlated positively with age (p = 0.002) and dopamine D1 receptor protein expression increased throughout development (p < 0.001) with adults having the highest D1 protein levels (p ≤ 0.01). Monoamine oxidase B mRNA and protein (p < 0.001) levels also increased significantly throughout development. Interestingly, dopamine D5 receptor mRNA levels negatively correlated with age (r = -0.31, p = 0.018) in an expression profile opposite to that of the dopamine D1 receptor.

Conclusions

We find distinct developmental changes in key components of the dopamine system in DLPFC over postnatal life. Those genes that are highly expressed during the first year of postnatal life may influence and orchestrate the early development of cortical neural circuitry while genes portraying a pattern of increasing expression with age may indicate a role in DLPFC maturation and attainment of adult levels of cognitive function.

The dopamine D2 receptor regulates the development of dopaminergic neurons via extracellular signal-regulated kinase and Nurr1 activation

Because the dopaminergic pathways in the midbrain have been closely associated with serious neuropsychiatric disorders, the elucidation of the mechanisms underlying dopaminergic neuronal development should provide some important clues for related disorders. In mice lacking the dopamine D2 receptor (D2R-/-), stereological cell counting analysis showed that the number of mesencephalic tyrosine hydroxylase (TH) cells was significantly low during ontogeny, compared with that observed in wild-type (WT) mice, thereby indicating an alteration in dopaminergic neuronal development in the absence of D2R. The results of immunohistochemical and reverse transcription-PCR analyses revealed that the expression of Nurr1, an orphan nuclear receptor, as well as Ptx3 expression, was selectively reduced in D2R-/- mice during the embryonic stage. A reporter gene assay using the Nur response element linked to the luciferase reporter gene indicated that the stimulation of D2R results in the activation of the Nurr1-mediated reporter gene. This D2R-mediated Nur response element-dependent transcriptional activity was regulated via the activation of extracellular signal-regulated kinase (ERK). Furthermore, quinpirole treatment was shown to elicit an increase in the number of TH-positive neurons, as well as the neuritic extension of TH neurons, coupled with ERK activation and Nurr1 activation in the TH-positive neurons in primary mesencephalic cultures from WT mice. However, this regulation was not detected in the D2R-/- mice. These results suggest that signaling through D2R in association with Nurr1 using ERK, plays a critical role in mesencephalic dopaminergic neuronal development.

Phenotypic analysis of dopamine receptor knockout mice; recent insights into the functional specificity of dopamine receptor subtypes

The functional specificity of dopamine receptor subtypes remains incompletely understood, in part due to the absence of highly selective agonists and antagonists. Phenotypic analysis of dopamine receptor knockout mice has been instrumental in identifying the role of dopamine receptor subtypes in mediating dopamine's effects on motor function, cognition, reward, and emotional behaviors. In this article, we provide an update of recent studies in dopamine receptor knockout mice and discuss the limitations and future promise of this approach.

Dopamine D2L receptor knockout mice display deficits in positive and negative reinforcing properties of morphine and in avoidance learning

The dopamine D2 receptor (D2) is implicated in drug addiction, learning and memory. Two isoforms of the D2 receptor, termed D2L (long form) and D2S (short form), have been identified. We previously generated mice lacking D2L (D2L-/-), but expressing functional D2S. In this study, we investigated the role of D2L in the positive and negative reinforcing properties of abused drugs and electrical stimuli, using D2L-/- mice as a model system. Mice were trained in three associative learning tasks: conditioned place preference to morphine and cocaine, conditioned place aversion to naloxone-precipitated morphine withdrawal, and active avoidance. D2L-/- mice, like wild type mice, developed a place preference to cocaine. In contrast to wild type mice, D2L-/- mice did not develop a place preference to morphine, nor did they attain a place aversion to morphine withdrawal. D2L-/- mice also failed to acquire avoidance behavior in response to electrical stimuli. There were no significant differences between D2L-/- and wild type mice in mu-opioid receptor density, morphine-induced locomotor stimulation and morphine withdrawal symptoms. These results suggest that D2L may have a greater impact than D2S on the rewarding aspects of morphine, and the aversive properties of morphine withdrawal and electrical stimulus. These findings also suggest that the presence of D2L is critical in the acquisition (learning) and/or retention (memory) of context-stimulus associations in certain situations. On the other hand, D2L is not essential for the rewarding aspects of cocaine and for the development of morphine dependence. Thus, these studies reveal distinct functional roles of D2L and/or D2S in drug addiction and avoidance learning, which may lead to a better understanding of the neurobiological basis underlying these behaviors.

Effects of dopamine and estrogen upon cortical neurons that express parvalbumin in vitro

The purpose of these experiments was to study the effects of dopamine (DA) and 17 beta-estradiol (EST) upon parvalbumin expression in rodent frontal cortex during development. Organotypic slice cultures of the frontal cortex were prepared from neonatal rats (postnatal day 2/3) and maintained for 14 days in vitro in serum-enriched medium and medium treated with either DA, EST or DA+EST. Cultured slices were then fixed and immunostained for parvalbumin immunoreactivity. Under control conditions, parvalbumin immunoreactive somata and fibers were primarily found in the deep laminae. In comparison, slices in all treatment groups exhibited a pattern of parvalbumin expression that was significantly different than controls. Specifically, DA treatment increased the percentage of parvalbumin immunoreactive somata, dendritic length and density in the deep cortical layers, but not in the superficial cortical layers. Both EST and DA+EST treatments induced similar changes in both the deep and the superficial cortical layers. These treatment induced changes represent more mature patterns of parvalbumin expression when compared to controls, indicating that both DA and EST enhance cortical expression of the protein.

Catecholamine systems in the brain of vertebrates: new perspectives through a comparative approach

A comparative analysis of catecholaminergic systems in the brain and spinal cord of vertebrates forces to reconsider several aspects of the organization of catecholamine systems. Evidence has been provided for the existence of extensive, putatively catecholaminergic cell groups in the spinal cord, the pretectum, the habenular region, and cortical and subcortical telencephalic areas. Moreover, putatively dopamine- and noradrenaline-accumulating cells have been demonstrated in the hypothalamic periventricular organ of almost every non-mammalian vertebrate studied. In contrast with the classical idea that the evolution of catecholamine systems is marked by an increase in complexity going from anamniotes to amniotes, it is now evident that the brains of anamniotes contain catecholaminergic cell groups, of which the counterparts in amniotes have lost the capacity to produce catecholamines. Moreover, a segmental approach in studying the organization of catecholaminergic systems is advocated. Such an approach has recently led to the conclusion that the chemoarchitecture and connections of the basal ganglia of anamniote and amniote tetrapods are largely comparable. This review has also brought together data about the distribution of receptors and catecholaminergic fibers as well as data about developmental aspects. From these data it has become clear that there is a good match between catecholaminergic fibers and receptors, but, at many places, volume transmission seems to play an important role. Finally, although the available data are still limited, striking differences are observed in the spatiotemporal sequence of appearance of catecholaminergic cell groups, in particular those in the retina and olfactory bulb.

Dopamine affects parvalbumin expression during cortical development in vitro

This study was undertaken to determine how dopamine influences cortical development. It focused on morphogenesis of GABAergic neurons that contained the calcium-binding protein parvalbumin (PV). Organotypic slices of frontoparietal cortex were taken from neonatal rats, cultured with or without dopamine, harvested daily (4-30 d), and immunostained for parvalbumin. Expression of parvalbumin occurred in the same regional and laminar sequence as in vivo. Expression in cingulate and entorhinal preceded that in lateral frontoparietal cortices. Laminar expression progressed from layer V to VI and finally II-IV. Somal labeling preceded fiber labeling by 2 d. Dopamine accelerated PV expression. In treated slices, a dense band of PV-immunoreactive neurons appeared in layer V at 7 d in vitro (DIV), and in all layers of frontoparietal cortex at 14 DIV, whereas in control slices such labeling did not appear until 14 and 21 DIV, respectively. The laminar distribution and dendritic branching of PV-immunoreactive neurons were quantified. More labeled neurons were in the superficial layers, and their dendritic arborizations were significantly increased by dopamine. Treatment with a D1 receptor agonist had little effect, whereas a D2 agonist mimicked dopamine's effects. Likewise, the D2 but not the D1 antagonist blocked dopamine-induced changes, indicating that they were mediated primarily by D2 receptors. Parvalbumin expression was accelerated by dopaminergic reinnervation of cortical slices that were cocultured with mesencephalic slices. Coapplication of the glutamate NMDA receptor antagonist MK801 or AP5 blocked dopamine-induced increases in dendritic branching, suggesting that changes were mediated partly by interaction with glutamate to alter cortical excitability.

Quantitation of dopamine D2 receptor mRNA in a mesencephalic cell culture using a nonradioactive competitive reverse transcription polymerase chain reaction method

Studies on gene expression during differentiation and maturation processes have to cope with determinations of extremely low steady state levels of specific mRNA. Using the experimental model of dopamine D2 receptor (D2R) expression in a primary mesencephalic cell culture we worked out a quantitative reverse transcription polymerase chain reaction method which allows to analyze and quantify mRNA levels of cells present in a few wells of the culture. The method uses an internal cRNA standard which shares both primer binding sites and PCR product length with the target sequence. The amplicons are quantitated in microplates by hybridization with immobilized capture probes that allow for the distinction of internal standard and target sequences followed by the chemiluminescent detection of hybridized DNA. Applying this method the levels of D2 receptor mRNA of the mesencephalic cell culture on day in vitro 1 amounted to about 250 fg/microgram RNA and increased to about 1200 fg/microgram RNA on day in vitro 13-15.

A developmental study of the dopamine D2R receptors in the human basal ganglia and thalamus

The development of the dopamine D2R receptors (D2R) in the human basal ganglia (BG) and thalamus was investigated in 25 normal brains by means of an immunohistochemical method and Western blotting. Immunoreactivity to D2R was detected in the cytoplasm and dendrites of small and large neurons in the BG and thalamus. D2R-positive neurons were clearly observed at 19 weeks of gestation (GW) in the globus pallidus and thalamus, and at 21 GW in the striatum. The number of D2R-positive neurons gradually increased and reached a peak at 27 GW in the globus pallidus, at 39 GW in the thalamus, and at 1 month of age in the striatum. The number of D2R-positive large neurons in the globus pallidus and small neurons in the striatum decreased after 1 year and about 10 years of age, respectively. Western blotting confirmed the specificity of the immunohistochemistry. Our results suggest that the D2R protein begins to be synthesized at an early fetal stage in the BG and thalamus, and the development of D2R is mostly consistent with neuronal maturation in the BG. D2R may play an important role in regulating the neuronal development of the BG. The decrease in D2R-positive neurons may be related to D2R post-transcriptional regulation.

Expression of human placental D2-dopamine receptor during normal and abnormal pregnancies

Previous studies have demonstrated the presence of D2-dopamine binding sites in the human placenta, and that dopamine (DA), via these D2-like receptors, inhibits both basal- and hormone-stimulated secretion of human placental lactogen (hPL) from trophoblastic cells. However, nothing is known about the ontogenesis of this placental D2-dopamine receptor (D2R) during pregnancy. Therefore, the aim of this study was to analyse the expression of these receptors throughout gestation in placentae from normal as well as abnormal pregnancies. Western and Northern blot analysis were performed on membrane protein and messenger RNA (mRNA) preparations of human placentae from various weeks of gestation as well as from pregnancies complicated by pre-eclampsia of hydatidiform mole. The autoradiographs of both proteins and mRNA showed differential expression of placental D2R during normal pregnancy. When the relative levels of D2R proteins were analysed throughout pregnancy, there was a significant but transient decrease of approximately 23 per cent of D2R content at 9-16 weeks of gestation with a return to baseline levels at 17-18 weeks. An increase in mRNA levels began at week 19 of gestation and reached a maximum value at term. During the first half of gestation, the relative levels of D2R mRNA (2.5 kb) showed an inverse pattern of expression when compared to D2R protein content. Specifically, the levels of D2R mRNA increased by approximately 26 per cent between weeks 9 and 16 of pregnancy in comparison with the values observed at 7-8 weeks, and returned to baseline levels at 17-18 weeks of gestation. The D2R relative protein levels subsequently increased from 19 to 30 weeks of gestation, and then remained stable. The autoradiographs of both proteins and mRNA showed significantly decreased expressions in placentae from both pre-eclamptic (approximately 45 per cent inhibition) and molar (approximately 0-70 per cent inhibition) pregnancies. Moreover, there was important variability in the expression of placental D2R from hydatidiform moles. Using immunological and molecular biology techniques, the present study confirms the presence of D2R in human placenta. The variations of placental D2R expression during normal and abnormal pregnancies argue for an important role of DA in human placental function, although this remains to be investigated further.

Nerve growth factors and the control of neurotransmitter phenotype selection in the mammalian central nervous system

Determination of neurotransmitter phenotype in the peripheral nervous system (PNS) has been intensively characterized. However, relatively little is known about the underlying molecular and biochemical events involved in determination of transmitter phenotype in the central nervous system (CNS). It has been well established that nerve growth factors regulate cell growth and differentiation. They are increasingly recognized as playing an important role in many decision-making steps during development. Published data suggest that neurotransmitter phenotype is determined largely by exogenous stimuli, such as nerve growth factors--acidic/basic fibroblast growth factor, epidermal growth factor, neurotrophins, etc., working in concert with the genetic programmes. They exert potent effects independently or synergistically with other molecules by acting either on neural precursor cells or differentiated neuronal cells. However, the process of transmitter phenotype determination in the CNS is only beginning to be understood, with more uncharacterized substances, with considerable potency in this respect being reported and in need of isolation and further study. These studies will bring great advances in our existing knowledge of brain development and have potential value for the development of new treatments for neurodegenerative diseases.

Expression of dopamine D2 receptor mRNA isoforms in the carotid body of rat, cat and rabbit

Using the Reverse transcription-Polymerase chain reaction, we detected dopamine D2 receptor mRNA short and long isoforms in the adult carotid body of rats, cats, and rabbits. For these animals, the relative short/long ratios were 0.60, 0.65 and 0.57, respectively. Our results suggest that the variety of dopamine effects on carotid chemoreceptor activity, that has been related to species differences, may not be dependent on the expression levels of the dopamine D2 receptor mRNA isoforms in the studied species.

Induction of dopaminergic neurotransmitter phenotype in rat embryonic cerebrocortex by the synergistic action of neurotrophins and dopamine

Neurotrophins, including nerve growth factor, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4/5 (NT-4/5), have been shown to enhance survival and differentiation of a variety of central neuronal populations, such as those with the dopaminergic, cholinergic, GABAergic phenotype during development. In this paper we present evidence that BDNF, NT-3 and NT-4/5 acting synergistically with dopamine (DA) can artificially induce the full dopaminergic phenotype in rat fetal cerebral cortex which normally has very few dopaminergic neurons in adulthood. Thus, BDNF/DA, NT-3/DA, NT-4/DA elicited a great increase in the number of tyrosine hydroxylase (TH)-immunoreactive cells, which was up to 5-7% of total neuronal population in cultures of fetal rat cortical cells. This stimulatory effect was not dependent on glial proliferation, or on addition of serum to the culture. Pharmacological studies showed that dopamine receptors D1 and D2 were involved in this effect. The TH+ cortical cells possessed other biochemical phenotypic features of dopaminergic neurons. Thus, high-affinity DA uptake was elevated in cortical cultures treated with neurotrophin/DA. Also DA and 3,4-dihydroxyphenlacetic acid production was detected (5.42 +/- 1.24 and 13.72 +/- 2.84 pmol/dish respectively, zero in controls). This show the presence of functionally active TH, aromatic acid decarboxylase and monoamine oxidase. Neurotrophins/DA had no effect on noradrenergic phenotype expression by cortical fetal cells. Taken together, these results support the long-standing view that development of the central nervous system is determined not only by intrinsic genetic programmes, but also involves environmental influences such as the action of growth factors and extracellular neurotransmitter. In this case we report the effect of specific DA phenotype-inducing agents.

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.

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.

Early expression of D3 dopamine receptors in murine embryonic development

In order to determine whether the D2 and D3 dopamine receptors may have a role in prenatal development, we have studied the mRNA expression and distribution of these receptors during murine embryonic development. Using RT-PCR on RNA from embryos taken at progressive stages of development, we have shown that the D3 receptor is expressed significantly earlier than the D2 receptor, being detectable at day 9.5 post-conception (p.c.) compared with day 13.5 p.c. for the D2 subtype. We have also examined the mRNA distribution of the two receptors by whole mount in situ hybridisation. In agreement with the PCR assays, the D3 receptor was expressed earlier than the D2 subtype. D3 receptor transcripts were first detected at day 9.5 p.c. in the ventral aspect of the anterior neural tube, whereas D2 receptor transcripts first appeared a day later. By day 10.5-11.5 p.c. both D3 and D2 receptor transcripts were present in the developing forebrain, and later also in the branchial arches and along the prospective vertebral column. The early appearance of the D3 subtype in murine development and its predominance over the D2 subtype suggest that the D3 receptor may have a functional role in prenatal development.

Dopamine receptors mediate differential morphological effects on cerebral cortical neurons in vitro

A morphogenic role of neurotransmitters during cellular differentiation in vitro has been demonstrated in recent years. Using in situ hybridization, we confirm the presence of the D1 receptor at E16 and show additionally that the transcript is relatively widespread and present in both proliferative and differentiating areas of the cerebral wall. Because DA receptor expression precedes the arrival of presynaptic terminals during forebrain development, we examined the role of DA in cerebral cortical neuron differentiation in vitro, using immunohistochemical markers of dendrites, microtubule-associated-membrane protein 2 (MAP2) and axons, neurofilament protein (NF-H). Neurite length, cell size, and cell viability in response to D1 and D2 receptor agonists SKF38393 and quinpirole, respectively, and to DA were analyzed in neurons obtained from embryonic (E) day 16 rats. We have shown that 1) paradoxically, DA at different concentrations can either stimulate or inhibit neurite outgrowth; 2) there is a bimodal pattern of DA-induced axonal outgrowth, i.e., at low and high doses; 3) D2 receptor activation induces neurite outgrowth while D1 receptor activation is inhibitory; 4) D2-mediated neurite elongation is preferentially axonal while D1 receptor activation reduces both axonal and dendritic outgrowth; 5) low doses of DA promote the expression of cytoskeletal components of axonal maturation; and 6) D1 receptor activation decreases neuronal size. We suggest that DA may influence cellular differentiation and circuitry formation early in development of the cerebral cortex through receptor-mediated effects on process outgrowth, which could lead to effects on circuit formation.

Ontogenic development of dopamine D4 receptor in rat brain

The postnatal development of rat brain dopamine D4 receptor gene expression was studied in animals 1 day to 1 year old, using the polymerase chain reaction technique. The level of expression of the D4 mRNA was appreciable at birth (day 1), increased to maximum at day 3, and showed declines at day 28. D4 mRNA expression remained unchanged at the ages of 6 months to 1 year. The mRNA expression at day 1 is about 50% of that observed on day 3, and declines approximately 50% by day 28. In contrast, the dopamine D2 mRNA expression was maximum at day 28, which is consistent with the reported studies.

Dopamine D2, D3, and D4 receptor mRNA levels in rat brain and pituitary during aging

Reverse Transcriptase-Polymerase Chain Reaction technique was used to determine the levels of the mRNAs encoding different receptors belonging to the D2 family in various brain areas of 6-, 12-, 18-, and 24-month-old rats. We found a progressive, age-dependent reduction in the mRNA levels of D2 short and D2 long receptors in corpus striatum, substantia nigra, and frontal cortex. D2 short and D2 long receptor mRNA levels were unchanged in hippocampus and olfactory tubercle, while they increased in pituitary. D3 receptor mRNA levels were reduced in olfactory tubercle and unchanged in striatum. D4 receptor mRNA levels were unmodified in pituitary gland. These data suggest that the molecular mechanisms responsible for regulating the pattern of expression of the various dopamine receptors are differentially regulated by aging.

Ontogeny of D1A and D2 dopamine receptor subtypes in rat brain using in situ hybridization and receptor binding

The prenatal and postnatal ontogeny of D1A and D2 dopamine receptors was assessed by in situ hybridization of messenger RNAs encoding the receptors and by radioligand binding autoradiography. On gestational day 14, signals for D1A and D2 dopamine receptor messages were observed in selected regions in ventricular and subventricular zones which contain dividing neuroblasts, and in intermediate zones that contain maturing and migrating neurons. Specifically, D1A and D2 dopamine receptor message was observed in the developing caudate-putamen, olfactory tubercle, and frontal, cingulate, parietal and insular cortices. Additionally, D1A dopamine receptor messenger RNA was found in the developing epithalamus, thalamus, hypothalamus, pons, spinal cord and neural retina; D2 dopamine receptor messenger RNA was also observed in the mesencephalic dopaminergic nuclear complex. Gene expression of D1A and D2 dopamine receptor subtypes in specific cells as they differentiate precedes dopamine innervation and implies that receptor expression is an intrinsic property of these neurons. The early expression of dopamine receptor messenger RNA suggests a regulatory role for these receptors in brain development. While the signal for both messages increased in the intermediate zones on gestational day 16, it decreased in the ventricular and subventricular zones, and was no longer apparent in these zones by gestational day 18. By gestational day 18, abundant D1A or D2 dopamine receptor messenger RNA was observed in cell groups similar in location to those observed in the adult brain. On gestational day 18, D1A dopamine receptor message was noted in the neural retina, anterior olfactory nucleus, the insular, prefrontal, frontal, cingulate, parietal and retrosplenial cortices, the olfactory tubercle, caudate-putamen, lateral habenula, dorsolateral geniculate nucleus, ventrolateral and mediolateral thalamic nuclei, and the suprachiasmatic and ventromedial nuclei of the hypothalamus. D2 dopamine receptor message was observed on gestational day 18 in the insular, prefrontal, frontal and cingulate cortices, the olfactory tubercle, caudate-putamen, ventral tegmental area, substantia nigra, and the intermediate lobe of the pituitary. At birth, expression of messenger RNA for both dopamine receptor subtypes in the striatum approximated that seen in mature rats. In contrast, D1A and D2 receptor binding, measured with [3H]SCH-23390 and [3H]raclopride, respectively, was low at birth and progressively increased to reach adult levels between days 14 and 21. The in situ hybridization data showing early prenatal expression of messenger RNA for the D1A and D2 dopamine receptors are consistent with the hypothesis that these receptors have a regulatory role in neuronal development.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential regulation of glutamate decarboxylase and preproenkephalin mRNA levels in the rat striatum

The mRNA levels encoding for the enzyme glutamate decarboxylase (GAD67) and the peptide enkephalin were measured in the striatum of adult and 15 day-old rats by in situ hybridization histochemistry and radioautography after neonatal injections of 6-hydroxydopamine or after acute pharmacological blockade of dopamine receptors with haloperidol or sulpiride. In adult rats injected as neonates with 6-hydroxydopamine or treated with the D1/D2 dopamine receptors antagonist, haloperidol, an increase in preproenkephalin and GAD67 mRNA levels was measured in the striatum. The D2 dopamine receptor antagonist, sulpiride, did not change the mRNA levels of either GAD67 or PPE in the striatum. In 15-day-old rats, neonatal 6-hydroxydopamine or haloperidol treatment resulted in increased preproenkephalin but unchanged GAD67 mRNA levels compared to controls. In these 15-day-old rats, however, sulpiride produced an increase in GAD67 but not preproenkephalin mRNA levels. Intrastriatal injections to adult rats of pertussis toxin which uncouples Gi/Go proteins from their receptors resulted in a dramatic increase in preproenkephalin without concomitant change in GAD67 mRNA levels. Altogether, these results show that GAD67 and preproenkephalin mRNA levels are modulated in parallel in adult but not in 15 day-old rats after 6-hydroxydopamine injections or dopaminergic blockade. In keeping with evidence of a co-localization of GAD67 and preproenkephalin mRNAs in some striatal neurons, the results indicate that these two mRNAs can be differentially regulated in the same neurons. In addition, the differential effect of haloperidol, sulpiride or pertussis toxin on GAD67 and preproenkephalin mRNA levels suggests that these two mRNAs are regulated through different dopamine receptor subtypes.

Transcription of the rat dopamine-D2-receptor gene from two promoters

Modulation of the expression of the D2-dopamine receptor gene is involved in several pathological and developmental circumstances. The gene and the corresponding promoter regions of the rat D2 receptor were isolated and partly characterized to study its regulation. The rat D2-receptor gene spans at least 50 kb, and possesses eight exons; its organization was compared to those of the other dopamine-receptor genes in a phylogenetic perspective. The gene contains two transcription-start sites: the major one is located about 320 bp upstream from the 3' end of the first exon, and a minor site is 70 bp further upstream. Transient-expression assays with fusion constructs comprising fragments of the D2-promoter region and the luciferase reporter gene confirmed the existence of two independent, TATA-lacking promoters. Both promoters separately induced transcription of the luciferase gene in C6 glioma, primary fibroblasts, GH3 and MMQ pituitary cell lines, among which only the MMQ cells normally express the D2 receptor. Transcription is enhanced by the reunion of the two promoters, and modified by the addition of upstream sequences. Thus the 1-kb promoter region analysed does not contain all the elements necessary to confer tissue-specific expression of the gene, but does carry some positive and negative regulatory elements, which remain to be characterized.

Morphogenic potentials of D2, D3, and D4 dopamine receptors revealed in transfected neuronal cell lines

Molecular cloning studies have defined a family of dopamine D2-like receptors (D2, D3, and D4), which are the products of separate genes. Our previous work has shown that stimulation of dopamine D2-like receptors in cultures of fetal cortical neurons increases the extension and branching of neurites. To determine which D2-like receptors possess morphogenic potentials, a clonal mesencephalic cell line (MN9D) was transfected with D2, D3, or D4 receptor subtypes and treated with quinpirole, an agonist of D2-like receptors, and changes in morphological characteristics were quantitated. Stimulation of D2 receptors increased the number and branching of neurites with little effect on neurite extension; stimulation of D3 and D4 receptors increased the branching and extension of neurites. Similar results were found for primary mesencephalic cultures stimulated with quinpirole. These results suggest that the known D2-like receptors have specific developmental roles in regulating neuronal morphogenesis of dopaminergic pathways.

Effects of dopamine on the carotid chemosensory response to hypoxia in newborn kittens

In a previous study, it has been shown that bolus injections of dopamine could either stimulate or inhibit the carotid chemosensory discharge in the kitten (Marchal et al., 1992a). To further characterize dopaminergic mechanisms in the carotid body during development, the effects of a continuous infusion of dopamine on carotid chemosensory activity in air, hypoxia (8% O2 in N2) and hyperoxia (100% O2) were studied in ten anesthetized, paralyzed and artificially ventilated kittens, aged 1 to 21 days and in three adult cats. One carotid sinus nerve was prepared for recording the activity of a single or a few chemosensory afferents. In the kittens, the immediate effect of dopamine at the onset of infusion (10 micrograms/kg/min) was an inhibition of the discharge in five kittens, a progressive excitation in four and no change in one. Four minutes after the onset of dopamine infusion, there was a significant increase in chemosensory activity both in room air (from 4.5 +/- 0.8 impulse/sec to 8.8 +/- 1.4 impulse/sec, mean +/- SEM, P < 0.05) and in hypoxia (from 24.6 +/- 3.7 impulse/sec to 33.4 +/- 5.3 impulse/sec, P < 0.05) but not in hyperoxia (0.5 +/- 0.2 impulse/sec vs 0.7 +/- 0.3 impulse/sec). The adult cats received four successive dopamine infusions at the rate of 2.5, 5, 7.5 and 10 micrograms/kg/min, in an attempt to establish a dose-response relationship. The effects of dopamine infusions were consistent within, but variable between, cats. The onset of dopamine infusion was associated with an inhibition of the discharge in two cats, at all infusion rates. In one of them, chemosensory activity returned quickly to control and the response to hypoxia was enhanced. In the other cat, the inhibition of the discharge persisted for the duration of the infusion, and the response to hypoxia was inhibited. In the third cat, dopamine had no effect on the chemosensory discharge. The patterns of chemosensory responses evoked by dopamine are qualitatively similar in kittens and cats, but the excitatory type of response appear to be more readily elicited in the kitten.

Antisense oligodeoxynucleotide inhibits D2 dopamine receptor-mediated behavior and D2 messenger RNA

There are several subtypes of dopamine receptors in the central nervous system which mediate the actions of dopamine in producing its diverse motor and behavioral effects. In this study we determined whether an antisense oligodeoxynucleotide directed to the mRNA encoding one of the subtypes of the dopamine receptor can inhibit a specific dopamine-mediated behavior. Accordingly, the effects of a phosphorothioate-modified antisense oligodeoxynucleotide targeted toward the D2 dopamine receptor mRNA (D2 antisense) was studied in mice with unilateral 6-hydroxydopamine-induced lesions of the corpus striatum. Rotational behavior in response to different agents, and the levels of D2 and D1 dopamine receptors and D2 and D1 dopamine receptor mRNAs in corpus striatum were then measured. In control mice, lesioning resulted in a contralateral rotational behavior in response to the D1 dopamine receptor agonist SKF 38393, the D2 dopamine agonist quinpirole, and the muscarinic cholinergic agonist oxotremorine. Lesioning also caused an increase in D2 dopamine receptor mRNA levels in the dorsolateral striatum. Intraventricular injections of the D2 antisense inhibited rotational behavior induced by quinpirole but not that induced by SKF 38393 or that induced by oxotremorine. Repeated administration of the D2 antisense significantly reduced the levels of the D2 dopamine receptor and D2 dopamine receptor mRNA in the dorsolateral but not the dorsomedial striatum. Similar treatment failed to significantly alter the levels of the D1 dopamine receptor or D1 receptor mRNA in dorsolateral or dorsomedial striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Prenatal D1, D1b and D3 dopamine receptor gene expression in the rat forebrain: detection by reverse polymerase chain reaction

Three dopamine receptor mRNAs were detected by reverse polymerase chain reaction in the rat forebrain during ontogeny. The D1 receptor mRNA gave a faint signal from gestational day 11 (G11) on, while the D1b receptor was not detectable before G12. The D3 receptor mRNA was slightly expressed at G11 and clearly present at G14. Our results show that these mRNAs are present at early stages of fetal life, each one with its specific time of appearance.

D2-dopaminergic agonist quinpirole and 8-bromo-cAMP have opposite effects on Go alpha GTP-binding protein mRNA without changing D2 dopamine receptor mRNA levels in striatal neurones in primary culture

Long-term coordinated regulations (during development or by agonists and second messenger molecules) of the expression of mRNAs encoding D2-dopamine (DA) receptors and D2 receptor-linked Go alpha proteins have been studied by Northern blot analysis in mouse embryonic striatal neurones in primary culture. During the course of the cell culture, the levels of both mRNAs increased, in conjunction with the maturation of the neurones. When the preparation was treated with the D2-DA agonist quinpirole (5-15 hrs, 10(-4) M), which decreases cAMP in these neurones, the levels of Go alpha mRNAs were enhanced whereas that of the D2 mRNA remained unchanged. Conversely, the Go alpha mRNAs, but not the D2 mRNA, decreased when the neurones were exposed to 8-bromo-cAMP (16 hrs, 10(-6) M). It is concluded that, in these experimental conditions where neurones have not yet established their connexions, the longterm regulation of the membrane transmission of D2-DA signal might implicate mainly the Go alpha encoding gene.

Neural development is regulated by classical neurotransmitters: dopamine D2 receptor stimulation enhances neurite outgrowth

The classical neurotransmitters serotonin and dopamine are thought to be involved in the etiology or treatment of a variety of psychiatric disorders. Recent studies suggest that these neurotransmitters may also have roles as neural morphogens during brain development. Previously, we have demonstrated that stimulation of serotonin 5-HT1A receptors selectively inhibited neurite branching in an in vitro system (Sikich et al 1990). In the present study, the developmental role of dopamine D2 receptors in the control of neurite outgrowth has been investigated by quantitating the morphological response of cortical neurons to agonist stimulation in vitro. Cultures of fetal rat frontal, cortical neurons were shown to express both alternatively spliced forms of D2 receptor messenger RNA (mRNA). The larger mRNA form predominated (D2A444:D2A415 ratio of about 6:1). In a small but significant percentage of these neurons, culture in the presence of the D2 receptor selective agonist, quinpirole, resulted in a three-to ten-fold increase in the length of neurites and in the number of branch points per neurite. These effects were blocked by the D2 receptor antagonists eticlopride and spiperone. Early abnormalities in the stimulation of dopamine or serotonin receptor subtypes could lead to the types of neuroanatomical changes observed in studies of schizophrenia, bipolar affective disorder, and autism. These morphogenic effects of classical transmitters could unite neurodevelopmental and neurotransmitter theories of the etiology of severe psychiatric disorders.

Ontogeny of dopamine D2 receptor mRNA in rat brain

The postnatal development of rat brain dopamine D2 receptor gene expression was investigated in animals 1 day to 1 year old. The level of expression of the striatal D2 mRNA was appreciable at birth (day 1), steadily increased to a maximum at day 28, and showed declines at ages 6 months and one year. The mRNA development profile was similar to that of [3H]spiroperidol binding in striatal membranes except that there was a lack of correlation between mRNA levels and [3H]spiroperidol binding during the early developmental periods. For example, although the mRNA expression at day 1 is about 75% of the 28-day value, the corresponding level of [3H]spiroperidol binding is only 15% of the value observed at day 28. Polymerase chain reaction (PCR) analysis of alternatively spliced forms of D2 receptor mRNA showed that the developmental expression of the two isoforms proceeded in parallel as the ratio of D2L and D2S mRNAs remained more or less constant in different age group of rats. In situ hybridization revealed a differential developmental profile of D2 mRNA for major dopaminergic regions of rat brain such as caudate putamen, nucleus accumbens, olfactory tubercle and substantia nigra.

Age-related variations in relative abundance of alternative spliced D2 receptor mRNAs in brain areas of two rat strains

Age-related reduction in the steady-state levels of messenger RNA for D2(415) and D2(444), the alternatively spliced form of dopamine D2 receptors, was observed in different rat brain areas using the sensitive reverse transcription (RT)-polymerase chain reaction (PCR) technique. In both Sprague-Dawley and Wistar aged rats, the decrease was more pronounced in the D2(444) isoform mRNA thus leading to a changed ratio in striatum as well as in the hippocampus.