Distribution of mRNA encoding three alpha 2-adrenergic receptor subtypes in the developing mouse embryo suggests a role for the alpha 2A subtype in apoptosis

Role of α- and β-adrenergic signaling in phenotypic targeting: significance in benign and malignant urologic disease

The urinary tract is highly innervated by autonomic nerves which are essential in urinary tract development, the production of growth factors, and the control of homeostasis. These neural signals may become dysregulated in several genitourinary (GU) disease states, both benign and malignant. Accordingly, the autonomic nervous system is a therapeutic target for several genitourinary pathologies including cancer, voiding dysfunction, and obstructing nephrolithiasis. Adrenergic receptors (adrenoceptors) are G-Protein coupled-receptors that are distributed throughout the body. The major function of α1-adrenoceptors is signaling smooth muscle contractions through GPCR and intracellular calcium influx. Pharmacologic intervention of α-and β-adrenoceptors is routinely and successfully implemented in the treatment of benign urologic illnesses, through the use of α-adrenoceptor antagonists. Furthermore, cell-based evidence recently established the antitumor effect of α1-adrenoceptor antagonists in prostate, bladder and renal tumors by reducing neovascularity and impairing growth within the tumor microenvironment via regulation of the phenotypic epithelial-mesenchymal transition (EMT). There has been a significant focus on repurposing the routinely used, Food and Drug Administration-approved α1-adrenoceptor antagonists to inhibit GU tumor growth and angiogenesis in patients with advanced prostate, bladder, and renal cancer. In this review we discuss the current evidence on (a) the signaling events of the autonomic nervous system mediated by its cognate α- and β-adrenoceptors in regulating the phenotypic landscape (EMT) of genitourinary organs; and (b) the therapeutic significance of targeting this signaling pathway in benign and malignant urologic disease. Video abstract.

Renal sympathetic nerve activation via α2-adrenergic receptors in chronic kidney disease progression

Chronic kidney disease (CKD) is increasing worldwide without an effective therapeutic strategy. Sympathetic nerve activation is implicated in CKD progression, as well as cardiovascular dysfunction. Renal denervation is beneficial for controlling blood pressure (BP) and improving renal function through reduction of sympathetic nerve activity in patients with resistant hypertension and CKD. Sympathetic neurotransmitter norepinephrine (NE) via adrenergic receptor (AR) signaling has been implicated in tissue homeostasis and various disease progressions, including CKD. Increased plasma NE level is a predictor of survival and the incidence of cardiovascular events in patients with end-stage renal disease, as well as future renal injury in subjects with normal BP and renal function. Our recent data demonstrate that NE derived from renal nerves causes renal inflammation and fibrosis progression through alpha-2 adrenergic receptors (α₂-AR) in renal fibrosis models independent of BP. Sympathetic nerve activation-associated molecular mechanisms and signals seem to be critical for the development and progression of CKD, but the exact role of sympathetic nerve activation in CKD progression remains undefined. This review explores the current knowledge of NE-α₂-AR signaling in renal diseases and offers prospective views on developing therapeutic strategies targeting NE-AR signaling in CKD progression.

Neurotransmitter signaling pathways required for normal development in Xenopus laevis embryos: a pharmacological survey screen

Neurotransmitters are not only involved in brain function but are also important signaling molecules for many diverse cell types. Neurotransmitters are widely conserved, from evolutionarily ancient organisms lacking nervous systems through man. Here, results are reported from a loss- and gain-of-function survey, using pharmacological modulators of several neurotransmitter pathways to examine possible roles for these pathways in normal embryogenesis. Applying reagents targeting the glutamatergic, adrenergic and dopaminergic pathways to embryos of Xenopus laevis from gastrulation to organogenesis stages, we observed and quantified numerous malformations, including craniofacial defects, hyperpigmentation, muscle mispatterning and miscoiling of the gut. These data implicate several key neurotransmitters in new embryonic patterning roles, reveal novel earlier stages for processes involved in eye development, suggest new targets for subsequent molecular-genetic investigation, and highlight the necessity for in-depth toxicology studies of psychoactive compounds to which human embryos might be exposed during pregnancy.

Cannabinoid modulation of alpha2 adrenergic receptor function in rodent medial prefrontal cortex

Endocannabinoids acting at the cannabinoid type 1 receptor (CB1R) are known to regulate attention, cognition and mood. Previous studies have shown that, in the rat medial prefrontal cortex (mPFC), CB1R agonists increase norepinephrine release, an effect that may be attributed, in part, to CB1Rs localised to noradrenergic axon terminals. The present study was aimed at further characterising functional interactions between CB1R and adrenergic receptor (AR) systems in the mPFC using in vitro intracellular electrophysiology and high-resolution neuroanatomical techniques. Whole-cell patch-clamp recordings of layer V/VI cortical pyramidal neurons in rats revealed that both acute and chronic treatment with the synthetic CB1R agonist WIN 55,212-2 blocked elevations in cortical pyramidal cell excitability and increases in input resistance evoked by the α2-adrenergic receptor (α2-AR) agonist clonidine, suggesting a desensitisation of α2-ARs. These CB1R-α2-AR interactions were further shown to be both action potential- and gamma-aminobutyric acid-independent. To better define sites of cannabinoid-AR interactions, we localised α2A-adrenergic receptors (α2A-ARs) in a genetically modified mouse that expressed a hemoagglutinin (HA) tag downstream of the α2A-AR promoter. Light and electron microscopy indicated that HA-α2A-AR was distributed in axon terminals and somatodendritic processes especially in layer V of the mPFC. Triple-labeling immunocytochemistry revealed that α2A-AR and CB1R were localised to processes that contained dopamine-β-hydroxylase, a marker of norepinephrine. Furthermore, HA-α2A-AR was localised to processes that were directly apposed to CB1R. These findings suggest multiple sites of interaction between cortical cannabinoid-adrenergic systems that may contribute to understanding the effect of cannabinoids on executive functions and mood.

Novel cell surface genes expressed in the stomach primordium during gastrointestinal morphogenesis of mouse embryos

The mechanisms of gastrointestinal morphogenesis in mammals are not well understood. This is partly due to the lack of appropriate markers that are expressed with spatiotemporal specificity in the gastrointestinal tract during development. Using mouse embryos, we surveyed markers of the prospective stomach region during gastrointestinal morphogenesis. The initiation of organ bud formation occurs at E10.5 in mice. These primordia for the digestive organs protrude from a tube-like structured endoderm and have their own distinct morphogenesis. We identified 3 cell surface genes -Adra2a, Fzd5, and Trpv6 - that are expressed in the developing stomach region during gastrointestinal morphogenesis using a microarray-based screening. These novel genes will be useful in expanding our understanding of the mechanisms of gastrointestinal development.

Neonatal exposure to fenoterol and betamethasone: effects on the behavioral development in the rat

We investigated longitudinally the behavioral development in the rat following exposure to beta-agonists and glucocorticoids (GC). Neonatal rats received either 1 mg/kg fenoterol (FEN), 0.3 mg/kg betamethasone (BET), or saline (SAL). Weanling and young adult rats were tested in the open field, the elevated-plus maze, and the water maze. FEN-treated as well as BET-treated animals displayed increased anxiety-like behavior. Furthermore, BET-treated adult animals showed a reduced locomotor activity. An enhanced 24-h memory in the water maze in both treatment groups may be facilitated by emotional arousal due to the increased anxiety levels. The possible neurobiological underpinnings are discussed in detail.

Epitope-tagged receptor knock-in mice reveal that differential desensitization of alpha2-adrenergic responses is because of ligand-selective internalization

Although ligand-selective regulation of G protein-coupled receptor-mediated signaling and trafficking are well documented, little is known about whether ligand-selective effects occur on endogenous receptors or whether such effects modify the signaling response in physiologically relevant cells. Using a gene targeting approach, we generated a knock-in mouse line, in which N-terminal hemagglutinin epitope-tagged alpha(2A)-adrenergic receptor (AR) expression was driven by the endogenous mouse alpha(2A)AR gene locus. Exploiting this mouse line, we evaluated alpha(2A)AR trafficking and alpha(2A)AR-mediated inhibition of Ca(2+) currents in native sympathetic neurons in response to clonidine and guanfacine, two drugs used for treatment of hypertension, attention deficit and hyperactivity disorder, and enhancement of analgesia through actions on the alpha(2A)AR subtype. We discovered a more rapid desensitization of Ca(2+) current suppression by clonidine than guanfacine, which paralleled a more marked receptor phosphorylation and endocytosis of alpha(2A)AR evoked by clonidine than by guanfacine. Clonidine-induced alpha(2A)AR desensitization, but not receptor phosphorylation, was attenuated by blockade of endocytosis with concanavalin A, indicating a critical role for internalization of alpha(2A)AR in desensitization to this ligand. Our data on endogenous receptor-mediated signaling and trafficking in native cells reveal not only differential regulation of G protein-coupled receptor endocytosis by different ligands, but also a differential contribution of receptor endocytosis to signaling desensitization. Taken together, our data suggest that these HA-alpha(2A)AR knock-in mice will serve as an important model in developing ligands to favor endocytosis or nonendocytosis of receptors, depending on the target cell and pathophysiology being addressed.

Neonatal programming of rat behavior by downregulation of alpha2A-adrenoreceptor gene expression in the brain

Short-term knockdown of alpha2A-adrenergic receptor gene expression in the rat brain by siRNA or antisense oligodeoxynucleotide during the first days of life induced acute and long-lasting neurochemical and behavioral alterations. The acute effects in the neonatal rats were consistent with the known functions of the alpha2A-adrenergic receptors in the mature animals. The long-lasting alterations suggested involvement of receptor-specific gene expression during the critical period of brain development in early-life programming of anxiety-related behavior.

The influence of catecholamine on the migration of gonadotropin-releasing hormone-producing neurons in the rat foetuses

Catecholamines (CA) play an important role in the regulation of GnRH neurons in adults, and it is probable that they control GnRH-neuron development. Migration of GnRH neurons was evaluated in male and female rats at the 17th embryonic day (E17) and E21, following the daily treatment of their pregnant mothers from the 11th to the 16th and 20th day of gestation with alpha-methyl-para-tyrosine (alphaMPT), an inhibitor of catecholamine synthesis. High-performance liquid chromatography with electrochemical detection (HPLC-ED) was used to specify the alphaMPT-induced CA depletion. There was a 50-70% decrease in dopamine and noradrenaline content in the nose and in the brain of alphaMPT-treated foetuses, proving the efficacy of this pharmacological model. Immunohistochemistry was used to evaluate the percentage (%) of GnRH neurons along their migration pathway from the vomeronasal organ (VNO) in the nose to the septo-preoptic area in the forebrain which is considered as an index of neuron migration. Special attention was paid to the topographic relationships of GnRH neurons with catecholaminergic fibres. These were observed in apposition with GnRH neurons in the entrance to the forebrain. In CA-deficient foetuses, the percentage of GnRH neurons located in the rostral regions extending from the VNO to the septum was greater than in controls. However, no statistically significant difference was found in the forebrain which extended from the septum to the retrochiasmatic area. In conclusion, these data suggest that endogenous catecholamines stimulate the GnRH neuron migration in ontogenesis.

Expression of adrenergic receptors in mouse preimplantation embryos and ovulated oocytes

Epinephrine and norepinephrine can play an important role in basic developmental processes such as embryogenesis and morphogenesis, regulating cell proliferation, differentiation and migration. We showed that beta-adrenergic receptors can mediate the effects of catecholamines on preimplantation embryos in our previous work. In the present study, we designed specific oligonucleotide primers which can distinguish among all members of the alpha-adrenergic receptor family, and showed (using RT-PCR) that the alpha2C-adrenergic receptor is transcribed in ovulated oocytes, 8- to 16-cell morulae and expanded blastocysts. We did not detect the alpha2C-adrenoceptor transcript in 4-cell embryos. Our immunohistochemical study showed the presence of alpha-2C-adrenoceptor protein in ovulated oocytes, 8- to 16- cell embryos and blastocysts, but the signal in 4-cell embryos was weak, and probably represents remaining protein of maternal origin. We did not detect any other alpha-adrenergic receptor in preimplantation embryos and oocytes. Exposure of mouse preimplantation embryos to the alpha2-adrenergic agonist UK 14 304 led to significant reduction of the embryo cell number, and the effect was dose dependent. Our results suggest that epinephrine and norepinephrine could affect the embryo development in the oviduct via adrenergic receptors directly and support the opinion that maternal stress can influence the embryo even in very early pregnancy.

Genomic profiling of cortical neurons following exposure to beta-amyloid

In vitro and in vivo studies have shown that beta-amyloid peptide induces neuronal cell death. To explore the molecular basis underlying beta-amyloid-induced toxicity, we analyzed gene expression profiles of cultured rat cortical neurons treated for 24 and 48 h with synthetic beta-amyloid peptide. From the 8740 genes interrogated by oligonucleotide microarray analysis, 241 genes were found to be differentially expressed and segregated into distinct clusters. Functional clustering based on gene ontologies showed coordinated expression of genes with common biological functions and metabolic pathways. The comparison with genes differentially expressed in cerebellar granule neurons following serum and potassium deprivation indicates the existence of common regulatory mechanisms underlying neuronal cell death. Our results offer a genomic view of the changes that accompany beta-amyloid-induced neurodegeneration.

The alpha2-adrenoceptor antagonist dexefaroxan enhances hippocampal neurogenesis by increasing the survival and differentiation of new granule cells

The generation of new neurons in the hippocampus is a dynamic process regulated by environmental, endocrine, and pharmacological factors. Since enhancement of hippocampal neurogenesis has been associated with learning and memory, and the locus coeruleus-noradrenergic system has been shown to modulate these cognitive functions, we hypothesized that activation of noradrenergic neurotransmission might enhance neurogenesis in the adult hippocampus. To test this hypothesis in vivo, we induced the release of noradrenaline in the hippocampus by blocking presynaptic inhibitory autoreceptors with the selective alpha2-adrenoceptor antagonist dexefaroxan. Confocal microscopy showed that noradrenergic afferents make contact with proliferating and differentiating cells, suggesting a direct noradrenergic influence on neurogenesis. Chronic systemic treatment of rats with dexefaroxan did not affect cell proliferation per se in the dentate gyrus (as monitored by bromodeoxyuridine-labeling), but promoted the long-term survival of newborn neurons by reducing apoptosis. Dexefaroxan treatment also enhanced the number and complexity of the dendritic arborizations of polysialated neural cell adhesion molecule-positive neurons. The trophic effects of dexefaroxan on newborn cells might involve an increase in brain-derived neurotrophic factor, which was upregulated in afferent noradrenergic fiber projection areas and in neurons in the granule cell layer. By promoting the survival of new endogenously formed neurons, dexefaroxan treatment represents a potential therapeutic strategy for maintaining adult neurogenesis in neurodegenerative conditions, such as Alzheimer's disease, that affect the hippocampus.

The zinc finger-only protein Zfp260 is a novel cardiac regulator and a nuclear effector of alpha1-adrenergic signaling

alpha1-Adrenergic receptors mediate several biological effects of catecholamines, including the regulation of myocyte growth and contractility and transcriptional regulation of the atrial natriuretic factor (ANF) gene whose promoter contains an alpha1-adrenergic response element. The nuclear pathways and effectors that link receptor activation to genetic changes remain poorly understood. Here, we describe the isolation by the yeast one-hybrid system of a cardiac cDNA encoding a novel nuclear zinc finger protein, Zfp260, belonging to the Krüppel family of transcriptional regulators. Zfp260 is highly expressed in the embryonic heart but is downregulated during postnatal development. Functional studies indicate that Zfp260 is a transcriptional activator of ANF and a cofactor for GATA-4, a key cardiac regulator. Knockdown of Zfp260 in cardiac cells decreases endogenous ANF gene expression and abrogates its response to alpha1-adrenergic stimulation. Interestingly, Zfp260 transcripts are induced by alpha1-adrenergic agonists and are elevated in genetic models of hypertension and cardiac hypertrophy. The data identify Zfp260 as a novel transcriptional regulator in normal and pathological heart development and a nuclear effector of alpha1-adrenergic signaling.

Expression of beta adrenergic receptors in mouse oocytes and preimplantation embryos

Accumulating evidence indicates the role of endogenous catecholamines in mammalian embryogenesis. We searched public databases containing nucleotide sequences derived from mouse preimplantation cDNA libraries and found a partial sequence homology between a cDNA clone from mouse blastocysts and the mouse beta 2-adrenergic receptor sequence. No significant sequence homology was found for other mouse adrenergic and dopamine receptors. Using RT-PCR, we showed that beta 2-adrenoceptor is transcribed not only at blastocyst stage but also at earlier stages of preimplantation development as well as in oocytes. Moreover, we demonstrated that transcripts encoding both isoforms of the beta 3-adrenoceptor (beta 3a- and beta 3b-) are expressed in mouse oocytes and preimplantation embryos as well. We did not detect the beta 1-adrenoceptor transcript either in oocytes or in preimplantation embryos. Using an antibody against the mouse beta 2-adrenergic receptor, we showed that the receptor protein is expressed in oocytes and preimplantation embryos; in blastocysts, the immufluorescence labeling was stronger in the inner cell mass than in throphectodermal cells. The cell number of the in vitro cultured mouse preimplantation embryos exposed to isoproterenol (a potent beta adrenoceptor agonist) was lower than in control embryos, suggesting that activation of beta adrenergic receptors by appropriate agonist concentration can influence cell proliferation in mouse pre-implantation embryos. Thus, our results indicate that beta adrenergic receptors are expressed in mouse oocytes and preimplantation embryos and that ligands for the receptors can affect the mouse embryo even in the very early stages of development.

Human ganglion cells express the alpha-2 adrenergic receptor: relevance to neuroprotection

BACKGROUND/AIM

Alpha-2alpha adrenergic receptor (alpha(2)-AR) agonists are thought to be neuroprotective, preventing retinal ganglion cell death independent of pressure reduction. Previous studies have identified alpha(2)-ARs in rat retina. The authors aimed to demonstrate the presence and localisation of alpha(2)-ARs in human and rat retina and on the rat retinal ganglion cell line, RGC-5.

METHODS

Seven postmortem human and three postmortem rat eyes were paraformaldehyde fixed and frozen. RGC-5 cells were also paraformaldehyde fixed. The expression of alpha(2A)-ARs was determined by antibody immunofluorescence.

RESULTS

alpha(2A)-AR expression was identified in the human retina, on ganglion cells, and cells in the inner and outer nuclear layers (INL, ONL). Differential alpha(2A)-AR staining patterns in the INL and ONL suggest a further restriction to as yet unidentified neuronal subclasses. The RGC-5 cell line also expressed alpha(2A)-ARs in undifferentiated cells and an increased expression upon fully differentiated cells.

CONCLUSION

alpha(2)-AR agonists in addition to their pressure lowering effects in the eye, may act directly upon retinal neurons, including retinal ganglion cells. The presence of alpha(2)-ARs on the RGC-5 cell line allows future investigation of these possible direct effects using in vitro glaucoma model systems.

Attenuation of alpha2A-adrenergic receptor expression in neonatal rat brain by RNA interference or antisense oligonucleotide reduced anxiety in adulthood

Brain alpha2-adrenergic receptors (alpha2-ARs) have been implicated in the regulation of anxiety, which is associated with stress. Environmental treatments during neonatal development could modulate the level of brain alpha2-AR expression and alter anxiety in adults, suggesting possible involvement of these receptors in early-life programming of anxiety state. The present study was undertaken to determine whether the reduction of the expression of A subtype of these receptors most abundant in the neonatal brain affects anxiety-related behavior in adulthood. We attenuated the expression of alpha2A-ARs during neonatal life by two different sequence specific approaches, antisense technology and RNA interference. Treatment of rats with the antisense oligodeoxynucleotide or short interfering RNA (siRNA) against alpha2A-ARs on the days 2-4 of their life, produced a marked acute decrease in the levels of both alpha2A-AR mRNA and [3H]RX821002 binding sites in the brainstem into which drugs were injected. The decrease of alpha2A-AR expression in the neonatal brainstem influenced the development of this receptor system in the brain regions as evidenced by the increased number of [3H]RX821002 binding sites in the hypothalamus of adult animals with both neonatal alpha2A-AR knockdown treatments; also in the frontal cortex of antisense-treated, and in the hippocampus of siRNA-treated adult rats. These adult animals also demonstrated a decreased anxiety in the elevated plus-maze as evidenced by an increased number of the open arm entries, greater proportion of time spent in the open arms, and more than a two-fold increase in the number of exploratory head dips. The results provide the first evidence that the reduction in the brain expression of a gene encoding for alpha2A-AR during neonatal life led to the long-term neurochemical and behavioral alterations. The data suggests that alterations in the expression of the receptor-specific gene during critical periods of brain development may be involved in early-life programming of anxiety-related behavior.

Transiently overexpressed alpha2-adrenoceptors and their control of DNA synthesis in the developing brain

During brain development, neurotransmitters act as trophic factors controlling the patterns of cell replication and differentiation. Alpha2-adrenoceptors (alpha2ARs) are transiently overexpressed in zones with high mitotic activity and we evaluated whether these receptors are linked to DNA synthesis in the perinatal rat brain. Acute administration of clonidine (2 mg/kg), an alpha2AR agonist, elicited dramatic decreases in DNA synthesis in the forebrain, brainstem, and cerebellum whether given on gestational day (GD) 21, or on postnatal days (PN) 1 or 8. However, alpha2AR blockade elicited by yohimbine (2.5 mg/kg) also resulted in decreased DNA synthesis on GD21 and PN8, albeit to a smaller extent than with clonidine. Yohimbine was able to blunt the effects of clonidine, verifying that both drugs are acting through the same receptor population. Because betaARs are also known to regulate DNA synthesis, we used propranolol (10 mg/kg) blockade of betaARs to evaluate whether the alpha2AR effects were mediated by presynaptic autoreceptors that regulate the release of norepinephrine and consequent betaAR responses; the effects of yohimbine were still discernible in the presence of propranolol. Accordingly, transiently overexpressed alpha2ARs in the developing brain participate in the control of DNA synthesis in a biphasic manner, with promotional actions at low, endogenous levels of stimulation, but inhibitory effects when stimulation is high. Effects on alpha2ARs are likely to contribute to long-term consequences of adrenergic agents used in obstetrics or neurotoxicants that affect adrenergic activity.

Clonidine increases caspase-3 mRNA level and DNA fragmentation in the developing rat brainstem

The densities of alpha2-adrenergic receptors, labeled by 3H-clonidine or 3H-RX821002, reach a peak in the rat brainstem during the first week of its life. This enables the agonist of alpha2-adrenergic receptor clonidine, which is used as a component of anaesthetic solution in infants and children, to have specific effects in this structure of the developing brain. Clonidine was injected into the fetal brain (5 microg in 5 microl of saline) or subcutaneously to the pups (1, 10 microg in 50 microl of saline) 3 days before investigation. Clonidine increased the level of apoptotic enzyme caspase-3 mRNA expression, as measured by RT-PCR and enhanced the DNA fragmentation, as determined by gel electrophoresis, in the brainstem of the 21-day-old fetuses and 8-day-old rats. In the cortex of 8-day-old rat, the alpha2-adrenergic receptors are at a much lower level than the brainstem. Clonidine treatment had no evident effects on caspase-3 mRNA level and DNA fragmentation in the cortex of an 8-day-old rat. The data suggest that clonidine facilitates cell death in the developing brainstem. This drug effect provides a potential mechanism whereby clonidine during early life could induce long-lasting alterations in brain neurochemistry, autonomic functions and behavior.

α2a adrenoceptors regulate phosphorylation of microtubule-associated protein-2 in cultured cortical neurons

Adrenoceptors have been suggested to mediate neuronal development. This study revealed the expression of alpha2A adrenoceptors in the cortical plate of fetal mouse cerebral wall. The effects of alpha2A adrenoceptor on dendrite growth were investigated in primary neuronal cultures. Application of alpha2 adrenoceptor agonists, BHT 933 or UK 14304 for 24 or 72 h resulted in a 1.5-2-fold increase in dendrite lengths. This effect was blocked by alpha2 adrenergic antagonists, RX 821002 or yohimbine, as well as a alpha2A selective antagonist, BRL 44408, but not by alpha2B/alpha2C selective antagonists ARC 239, imiloxan and rauwolscine. Guanfacine, a alpha2A selective agonists, also significantly increased the dendrite lengths in culture. These results suggest that the morphological effect is wholly attributable to alpha2A adrenoceptor activation. We further tested the hypothesis that alpha2A adrenoceptors act through altering the phosphorylation state of microtubule-associated protein 2. The results showed that the phosphorylation of microtubule-associated protein 2 was significantly reduced on both serine and threonine residues by over 40% after 2 h of application of guanfacine and was maintained at this low level for a prolonged time up to 96 h. These findings suggest that alpha2A adrenoceptors regulate the phosphorylation of microtubule-associated protein 2, which in turn mediates dendrite growth of cortical neurons.

Regional distribution of alpha(2C)-adrenoceptors in brain and spinal cord of control mice and transgenic mice overexpressing the alpha(2C)-subtype: an autoradiographic study with [(3)H]RX821002 and [(3)H]rauwolscine

Behavioral studies on gene-manipulated mice have started to elucidate the neurobiological functions of the alpha(2C)-adrenoceptor (AR) subtype. In this study, we applied quantitative receptor autoradiography to investigate the potential anatomical correlates of the observed functional effects of altered alpha(2C)-AR expression. Labeling of brain and spinal cord sections with the subtype non-selective alpha(2)-AR radioligand [(3)H]RX821002 and the alpha(2C)-AR-preferring ligand [(3)H]rauwolscine revealed distinct binding-site distribution patterns. In control mice, [(3)H]rauwolscine binding was most abundant in the olfactory tubercle, accumbens and caudate putamen nuclei, and in the CA1 field of the hippocampus. A mouse strain with overexpression of alpha(2C)-AR regulated by a gene-specific promoter showed approximately two- to four-fold increased levels of [(3)H]rauwolscine binding in these regions. In addition, dramatic increases in [(3)H]rauwolscine binding were seen in the nerve layer of the olfactory bulb, the molecular layer of the cerebellum, and the ventricular system of alpha(2C)-AR-overexpressing mice, representing "ectopic" alpha(2C)-AR expression. Competition-binding experiments with several alpha(2)-AR ligands confirmed the alpha(2C)-AR identity of these sites. Our results provide quantitative evidence of the predominance of the alpha(2A)-AR subtype in most regions of the mouse CNS, but also disclose the wide distribution of alpha(2C)-AR in the normal mouse brain, although at relatively low density, except in the ventral and dorsal striatum and the hippocampal CA1 area. alpha(2C)-AR are thus present in brain regions involved in the processing of sensory information and in the control of motor and emotion-related activities such as the accumbens and caudate putamen nuclei, the olfactory tubercle, the lateral septum, the hippocampus, the amygdala, and the frontal and somatosensory cortices. The current results may help in specifying an anatomical framework for the functional roles of the alpha(2A)- and alpha(2C)-AR subtypes in the mouse CNS.

Effects of the alpha 2-adrenoreceptor antagonist dexefaroxan on neurogenesis in the olfactory bulb of the adult rat in vivo: selective protection against neuronal death

A dysfunction of noradrenergic mechanisms originating in the locus coeruleus has been hypothesised to be the critical factor underlying the evolution of central neurodegenerative diseases [Colpaert FC (1994) Noradrenergic mechanism Parkinson's disease: a theory. In: Noradrenergic mechanisms in Parkinson's disease (Briley M, Marien M, eds) pp 225-254. Boca Raton, FL, USA: CRC Press Inc.]. alpha(2)-Adrenoceptor antagonists, presumably in part by facilitating central noradrenergic transmission, afford neuroprotection in vivo in models of cerebral ischaemia, excitotoxicity and devascularization-induced neurodegeneration. The present study utilised the rat olfactory bulb as a model system for examining the effects of the selective alpha(2)-adrenoceptor antagonist dexefaroxan upon determinants of neurogenesis (proliferation, survival and death) in the adult brain in vivo. Cell proliferation (5-bromo-2'-deoxyuridine labelling) and cell death associated with DNA fragmentation (terminal dideoxynucleotidyl transferase-catalysed 2'-deoxyuridine-5'-triphosphate nick end-labelling assay) were quantified following a 7-day treatment with either vehicle or dexefaroxan (0.63 mg/kg i.p., three times daily), followed by a 3-day washout period. The number of terminal dideoxynucleotidyl transferase-catalysed 2'-deoxyuridine-5'-triphosphate nick end-labelling-positive nuclei in the olfactory bulb was lower in dexefaroxan-treated rats, this difference being greatest and significant in the subependymal layer (-52%). In contrast, 5-bromo-2'-deoxyuridine-immunoreactive nuclei were more numerous (+68%) in the bulbs of dexefaroxan-treated rats whilst no differences were detected in the proliferating region of the subventricular zone. Terminal dideoxynucleotidyl transferase-catalysed 2'-deoxyuridine-5'-triphosphate nick end-labelling combination with glial fibrillary acidic protein or neuronal-specific antigen immunohistochemistry revealed that terminal dideoxynucleotidyl transferase-catalysed 2'-deoxyuridine-5'-triphosphate nick end-labelling-positive nuclei were associated primarily with a neuronal cell phenotype. These findings suggest that dexefaroxan increases neuron survival in the olfactory bulb of the adult rat in vivo, putatively as a result of reducing the apoptotic fate of telencephalic stem cell progenies.

Subtype-specific neuronal differentiation of PC12 cells transfected with alpha2-adrenergic receptors

Cells of the PC12 rat pheochromocytoma cell line acquire characteristics of sympathetic neurons under appropriate treatment. Stably transfected PC12 cells expressing individual alpha2-adrenergic receptor (alpha2-AR) subtypes were used to assess the role of alpha2-ARs in neuronal differentiation and to characterise the signalling pathways activated by the alpha2-AR agonist epinephrine in these cells. The effects of alpha2-AR activation were compared with the differentiating action and the signalling mechanisms of nerve growth factor (NGF). Epinephrine induced neuronal differentiation of PC12alpha2 cells through alpha2-AR activation in a subtype-dependent manner, internalization of all human alpha2-AR subtypes, and activation of mitogen-activated protein kinase (MAPK) and the serine-threonine protein kinase Akt. Epinephrine and NGF showed synergism in their differentiating effects. The MAPK kinase (MEK-1) inhibitor PD 98059 abolished the differentiating effect of epinephrine indicating that the differentiation is dependent on MAPK activation. Activating protein-1 (AP-1) DNA-binding activity was increased after epinephrine treatment in all three PC12alpha2 subtype clones. Evaluation of the potential physiological consequences of these findings requires further studies on endogenously expressed alpha2-ARs in neuronal cells.

High level of alpha2-adrenoceptor in rat foetal liver and placenta is due to alpha2B-subtype expression in haematopoietic cells of the erythrocyte lineage

1. Rat foetal liver contains large amounts of alpha2-adrenoceptors. The present work aimed to identify the receptor subtype and the cell type accounting for high expression and to clarify the mechanisms responsible for the sharp decrease in hepatic receptivity occurring during the late stage of foetal development. 2. Binding experiments indicated that the density of alpha2-adrenoceptors in the foetal liver (embryonic day 18; 615+/-155 fmol mg(-1) of protein) is 18 fold higher than in newborn or adult (35.2+/-4.3 fmol mg(-1)). A high amount of receptor is also found in the placenta (443+/-53 fmol mg(-1)). In both tissues, the rank order of antagonists to inhibit radioligand binding matched the pharmacological profile of the alpha2B-adrenoceptor and exclusively RNG transcripts were detected by RNase protection assays. 3. Isolation of cell fractions from foetal liver showed that alpha2B-adrenoceptor is primarily expressed by haematopoietic cells. Consistent with this view, the receptor is found to be abundant in foetal blood, carried by reticulocytes. The expression in blood gradually declines to zero at 3 weeks of age and it is not recovered following induction of reticulocytosis in adults. 4. In foetal reticulocytes, a low proportion of the receptor population is coupled to G-protein. The alpha2-agonist UK14304 has a marginal effect on cyclic AMP level but significantly increases arachidonic acid release. The function of the receptor remains to be elucidated. However, together with observations on alpha2B-knockout mice, the current finding strongly suggests a role for alpha2B-adrenoceptor during foetal haematopoiesis in rodents.

Expression of the G protein-coupled receptor kinase 2 during early mouse embryogenesis

Whilst several G protein-coupled receptors (GPCRs) have been shown to play important roles during development, little study has been carried out on the G protein-coupled receptor kinases (GRKs) that modulate their activity in embryos. Here, we have analyzed the expression of GRK2, the predominant GRK expressed during embryogenesis. We show that at early stages, the expression of GRK2 is restricted to populations of cells that are undifferentiated, multipotent and in many cases, migratory. As such, GRK2 transcripts were found in the early mesoderm and neural crest as they migrate from the primitive streak and the neural tube, respectively. In the limb bud, GRK2 transcripts were observed in cells of the progress zone and in the interdigital areas. At later stages, the expression in the heart is compatible with the phenotype observed in the GRK2 deficient mice.

Alpha1- and alpha2-adrenoceptor control of sodium transport reverses in developing hypertension

Alpha-Adrenergic receptor (AR) activation enhances sodium retention in certain forms of hypertension. The objective of the present study was to understand the role of alpha-ARs in regulating sodium transport by distal tubules (DT). DT cells were isolated from kidneys of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats at 6 weeks, when hypertension is developing, or at 12 weeks, when hypertension is established. The alpha1-AR agonist phenylephrine increased 22Na uptake by 50% into DT cells of 6-week SHR; no effect was observed with WKY cells. The alpha2-AR agonist B-HT 933 increased uptake by only 10%. At 12 weeks, the pattern of alpha-AR regulation was reversed: alpha1-AR-induced sodium uptake was only 15%, whereas alpha2-AR activation increased sodium uptake by 35% in SHR and WKY cells. alpha1-AR-induced sodium uptake in 6-week SHR cells was abolished by prazosin; alpha2-AR-stimulated sodium uptake was blocked by yohimbine in 12-week SHR and WKY. Competitive binding studies were performed with [3H]prazosin and alpha1A-, alpha1B-, and alpha1D-selective antagonists with DT cell membranes from 6- and 12-week SHR and WKY. alpha2-AR subtypes were determined with [3H]rauwolscine and alpha2A- and alpha2B-selective antagonists. Expression of alpha1B-ARs was increased 4-fold in DT cells during the developing phase of hypertension in SHR. No change was detected in alpha2-AR expression. DT cells transiently increase [Ca2+]i in response to alpha1-AR agonists from 6-week but not 12-week SHR. Conversely, alpha2-AR agonists increase [Ca2+]i at 12 weeks. In summary, during developing hypertension, alpha1-ARs increase sodium uptake and [Ca2+]i in SHR cells. Expression of alpha1B-ARs is selectively upregulated during developing hypertension. In established hypertension (and normotension), alpha2-ARs regulate sodium transport and [Ca2+]i in DT cells. We conclude that a molecular switch of alpha1-AR and alpha2-AR signaling occurs in DT cells during the development of hypertension.