Maternal adrenalectomy abrogates the effect of fetal alcohol exposure on the interleukin-1beta-induced febrile response: gender differences

Avian prolactin (PRL) secretion is regulated by vasoactive intestinal peptide (VIP) neurons residing in the infundibular nuclear complex (INF) of the hypothalamus. This VIPergic activity is modulated by stimulatory dopaminergic inputs. Dynorphin, serotonin (5-HT), dopamine (DA) and VIP all appear to stimulate PRL secretion along a hypothalamic pathway, expressing kappa opioid, serotonergic, dopaminergic and VIPergic receptors in succession, with the VIPergic system as the final mediator. Electrical stimulation (ES) within the turkey hypothalamus at the level of the medial preoptic area (POA), the ventromedial hypothalamic nucleus (VMN), the INF or the median eminence (ME) results in the release of PRL. When the selective D(1) DA receptor antagonist SCH-23390 HCl was infused intraventricularly at the rate of 10 nmol/min, ES in the POA or VMN was unable to increase PRL levels, while ES in the INF and ME did increase PRL to the same level as that of controls. These results were interpreted to suggest that the D(1) DA receptors involved in PRL release lie caudally to the VMN and dorsally to the INF. Bilateral microinjections (50 ng) of the D(1) DA receptor agonist SKF-38393 HCl into the POA or VMN failed to produce any increase in PRL, while similar microinjections in the INF increased PRL significantly within 15 min. Bilateral microinjections of the D(1) DA antagonist (50 ng) into the INF blocked the rise in PRL associated with ES in the POA. Bilateral microinjections of a D(2) DA antagonist (50 ng) into the INF failed to block PRL secretion induced by ES in the POA. Tract tracing, using double-label immunocytochemistry, revealed the presence of a monosynaptic dopaminergic pathway projecting from the POA to the INF. These data imply that the only hypothalamic D(1) DA receptors involved in the regulation of avian PRL secretion are those residing within the INF in the same region as the VIP neurons known to be involved in PRL secretion.     

Genetic deletion of MAO-A promotes serotonin-dependent ventricular hypertrophy by pressure overload

The potential role of serotonin (5-HT) in cardiac function has generated much interest in recent years. In particular, the need for a tight regulation of 5-HT to maintain normal cardiovascular activity has been demonstrated in different experimental models. However, it remains unclear how increased levels of 5-HT could contribute to the development of cardiac hypertrophy. Availability of 5-HT depends on the mitochondrial enzyme monoamine oxidase A (MAO-A). Therefore, we investigated the consequences of MAO-A deletion on ventricular remodeling in the model of aortic banding in mice. At baseline, MAO-A deletion was associated with an increase in whole blood 5-HT (39.4 ± 1.9 μM vs. 24.0 ± 0.9 μM in KO and WT mice, respectively). Cardiac 5-HT_2A, but not 5-HT_2B receptors were overexpressed in MAO-A KO mice, as demonstrated by real-time PCR and Western-blot experiments. After aortic banding, MAO-A KO mice demonstrated greater increase in heart wall thickness, heart to body weight ratios, cardiomyocyte cross-section areas, and myocardial fibrosis compared to WT. Exacerbation of hypertrophy in KO mice was associated with increased amounts of 5-HT in the heart. In order to determine the role of 5-HT and 5-HT_2A receptors in ventricular remodeling in MAO-A KO mice, we administered the 5-HT_2A receptor antagonists ketanserin (1 mg/kg/day) or M100907 (0.1 mg/kg/day) during 4 weeks of aortic banding. Chronic administration of these antagonists strongly prevented exacerbation of ventricular hypertrophy in MAO-A KO mice. These results show for the first time that regulation of peripheral 5-HT by MAO-A plays a role in ventricular remodeling via activation of 5-HT_2A receptors.     

Serotonin and Its Role in Colonic Function and in Gastrointestinal Disorders

Serotonin (5-HT) is most commonly thought of as a neurotransmitter in the central nervous system. However, the predominant site of serotonin synthesis, storage, and release is the enterochromaffin cells of the intestinal mucosa. Within the intestinal mucosa, serotonin released from EC cells activates neural reflexes associated with intestinal secretion, motility, and sensation. Two important receptors for serotonin that are located in the neural circuitry of the intestines are the 5-HT₃ and 5-HT₄ receptors; these are the targets of drugs designed to treat gastrointestinal disorders. 5-HT₃ receptor antagonists are used to treat nausea and emesis associated with chemotherapy and for functional disorders associated with diarrhea. 5-HT₄ receptor agonists are used as promotility agents to promote gastric emptying and to alleviate constipation. Because of the importance of serotonin in normal gut function and sensation, a number of studies have investigated potential changes in mucosal serotonin signaling in pathologic conditions. Despite the inconsistencies in the current literature, changes in serotonin signaling have now been demonstrated in inflammatory bowel disease, irritable bowel syndrome, postinfectious irritable bowel syndrome, and idiopathic constipation. Emerging evidence has led to many contradictory theories regarding serotonin signaling and its roles in the pathology of gut disorders. This review summarizes the current medications affecting serotonin signaling and provides an overview of our current knowledge of the changes in serotonin that occur in pathologic conditions. Supported by NIH grant DK62267, Novartis Pharmaceuticals, and NIH P20 COBRE grant RR16435. Reprints are not available.     

Presynaptic serotonin 2A receptors modulate thalamocortical plasticity and associative learning

Higher-level cognitive processes strongly depend on a complex interplay between mediodorsal thalamus nuclei and the prefrontal cortex (PFC). Alteration of thalamofrontal connectivity has been involved in cognitive deficits of schizophrenia. Prefrontal serotonin (5-HT)_2A receptors play an essential role in cortical network activity, but the mechanism underlying their modulation of glutamatergic transmission and plasticity at thalamocortical synapses remains largely unexplored. Here, we show that 5-HT_2A receptor activation enhances NMDA transmission and gates the induction of temporal-dependent plasticity mediated by NMDA receptors at thalamocortical synapses in acute PFC slices. Expressing 5-HT_2A receptors in the mediodorsal thalamus (presynaptic site) of 5-HT_2A receptor-deficient mice, but not in the PFC (postsynaptic site), using a viral gene-delivery approach, rescued the otherwise absent potentiation of NMDA transmission, induction of temporal plasticity, and deficit in associative memory. These results provide, to our knowledge, the first physiological evidence of a role of presynaptic 5-HT_2A receptors located at thalamocortical synapses in the control of thalamofrontal connectivity and the associated cognitive functions.The prefrontal cortex (PFC) is a brain region critical for many high-level cognitive processes, such as executive functions, attention, and working and contextual memories (1). Pyramidal neurons located in layer V of the PFC integrate excitatory glutamatergic inputs originating from both cortical and subcortical areas. The latter include the mediodorsal thalamus (MD) nuclei, which project densely to the medial PFC (mPFC) and are part of the neuronal network underlying executive control and working memory (2–4). Disruption of this network has been involved in cognitive symptoms of psychiatric disorders, such as schizophrenia (3, 5). These symptoms severely compromise the quality of life of patients and remain poorly controlled by currently available antipsychotics (3, 6).The PFC is densely innervated by serotonin (5-hydroxytryptamine, 5-HT) neurons originating from the dorsal and median raphe nuclei and numerous lines of evidence indicate a critical role of 5-HT in the control of emotional and cognitive functions depending on PFC activity (7, 8). The modulatory action of 5-HT reflects its complex pattern of effects on cortical network activity, depending on the 5-HT receptor subtypes involved, and on receptor localization in pyramidal neurons, GABAergic interneurons or nerve terminals of afferent neurons.Among the 14 5-HT receptor subtypes, the 5-HT_2A receptor is a Gq protein-coupled receptor (9, 10) particularly enriched in the mPFC, with a predominant expression in apical dendrites of layer V pyramidal neurons (11–14). Moreover, a low proportion of 5-HT_2A receptors was detected presynaptically on thalamocortical fibers (12, 15–17).Activation of 5-HT_2A receptors exerts complex effects upon the activity of the PFC network (18). The most prominent one is an increase in pyramidal neuron excitability, which likely results from the inhibition of slow calcium-activated after hyperpolarization current (19). 5-HT_2A receptor stimulation also increases the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs) in pyramidal neurons (19–22). The prevailing view is that postsynaptic 5-HT_2A receptors expressed on pyramidal neurons located in layer V are key modulators of glutamatergic PFC network activity (14, 21–24). However, the role of presynaptic 5-HT_2A receptors located on thalamic afferents in the modulation of glutamatergic transmission at thalamocortical synapses remains unexplored.Here, we addressed this issue by combining electrophysiological recordings in acute PFC slices with viral infections to specifically rescue the expression of 5-HT_2A receptors at the presynaptic site (MD) or postsynaptic site (PFC) in 5-HT_2A receptor-deficient (5-HT_2A^−/−) mice (25). We focused our study on NMDA transmission in line with previous findings indicating that many symptoms of schizophrenia might arise from modifications in PFC connectivity involving glutamatergic transmission at NMDA receptors (26, 27). To our knowledge, we provide the first direct evidence that stimulation of presynaptic 5-HT_2A receptors at thalamocortical synapses gates the induction of spike timing-dependent long-term depression (t-LTD) by facilitating the activation of presynaptic NMDA receptors at these synapses. In line with the role of t-LTD in associative learning (28), these studies were extended by behavioral experiments to explore the role of presynaptic 5-HT_2A receptors at thalamocortical synapses in several paradigms of episodic-like memory.     

Effects of Maternal Ethanol Consumption and Buspirone Treatment on 5-HT1A and 5-HT2A Receptors in Offspring

In utero ethanol exposure results in a decreased concentration of serotonin (5-HT) in brain regions containing the cell bodies of 5-HT neurons and their cortical projections. The concentration of 5-HT reuptake sites is also reduced in several brain areas. The present study extended prior work by evaluating the effects of chronic maternal ethanol consumption and maternal buspirone treatment on 5-HT_1A and 5-HT_2A receptors in multiple brain areas of offspring. Receptors were quantitated early in postnatal development and at an age when the 5-HT networks are normally well-established. Because fetal 5-HT functions as an essential neurotrophic factor, these studies also determined whether treatment of pregnant rats with buspirone, a 5-HT_1A agonist, could overcome the effects of the fetal 5-HT deficit and prevent ethanol-associated receptor abnormalities. The results demonstrated that in utero ethanol exposure significantly alters the binding of 0.1 nM [³H]-8-hydroxy-dipropylaminotetralin to 5-HT_1A receptors in developing animals. Ethanol impaired the development of 5-HT_1A receptors in the frontal cortex, parietal cortex, and lateral septum; these receptors did not undergo the normal developmental increase between postnatal days 19 and 35. The dentate gyms was also sensitive to the effects of in utero ethanol exposure. 5-HT_1A receptors were increased in this region at 19 days. Maternal buspirone treatment prevented the ethanol-associated abnormalities in 5-HT_1A receptors in the dentate gyms, frontal cortex, and lateral septum. Neither maternal ethanol consumption nor buspirone treatment altered the binding of 2 nM [³H]ketanserin to 5-HT_2A receptors in the ventral dentate gyrus, dorsal raphe, parietal and frontal cortexes, striatum, substantia nigra, or nucleus accumbens.     

Dynamics and Patterning of 5-Hydroxytryptamine 2 Subtype Receptors in JC Polyomavirus Entry

The organization and dynamics of plasma membrane receptors are a critical link in virus-receptor interactions, which finetune signaling efficiency and determine cellular responses during infection. Characterizing the mechanisms responsible for the active rearrangement and clustering of receptors may aid in developing novel strategies for the therapeutic treatment of viruses. Virus-receptor interactions are poorly understood at the nanoscale, yet they present an attractive target for the design of drugs and for the illumination of viral infection and pathogenesis. This study utilizes super-resolution microscopy and related techniques, which surpass traditional microscopy resolution limitations, to provide both a spatial and temporal assessment of the interactions of human JC polyomavirus (JCPyV) with 5-hydroxytrypamine 2 receptors (5-HT₂Rs) subtypes during viral entry. JCPyV causes asymptomatic kidney infection in the majority of the population and can cause fatal brain disease, and progressive multifocal leukoencephalopathy (PML), in immunocompromised individuals. Using Fluorescence Photoactivation Localization Microscopy (FPALM), the colocalization of JCPyV with 5-HT₂ receptor subtypes (5-HT_2A, 5-HT_2B, and 5-HT_2C) during viral attachment and viral entry was analyzed. JCPyV was found to significantly enhance the clustering of 5-HT₂ receptors during entry. Cluster analysis of infected cells reveals changes in 5-HT₂ receptor cluster attributes, and radial distribution function (RDF) analyses suggest a significant increase in the aggregation of JCPyV particles colocalized with 5-HT₂ receptor clusters in JCPyV-infected samples. These findings provide novel insights into receptor patterning during viral entry and highlight improved technologies for the future development of therapies for JCPyV infection as well as therapies for diseases involving 5-HT₂ receptors.     

Expression of D1 and D2 dopamine receptors in the hypothalamus and pituitary during the turkey reproductive cycle: colocalization with vasoactive intestinal peptide

The regulation of avian prolactin (PRL) secretion and PRL gene expression is influenced by hypothalamic vasoactive intestinal peptide (VIP), the PRL-releasing factor in avian species. Recent evidence indicates that D(1) and D(2) dopamine (DA) receptors play a pivotal role in VIP and PRL secretion. The differential expression of DA receptors located on hypothalamic VIP neurons and anterior pituitary cells may affect the degree of prolactinemia observed during the turkey reproductive cycle. The relative expression of D(1D) and D(2) DA receptor subtype mRNA was quantitated using in situ hybridization histochemistry (ISH). D(1D) and D(2) DA receptor mRNA was found expressed throughout the hypothalamus and pituitary. The expression of D(1D) DA receptor mRNA in the hypothalamus was found to be 6.8-fold greater than that of D(2) DA receptor mRNA. Higher D(1D) DA receptor mRNA content was found in the anterior hypothalamus (3.6-fold), the ventromedial nucleus (2.0-fold), the infundibular nuclear complex (INF; 1.9-fold), and the medial preoptic nucleus (1.5-fold) of laying hens as compared to that of reproductively quiescent non-photostimulated hens. The levels seen in incubating hyperprolactinemic hens were essentially the same as in laying hens, except for the INF where levels were 52% higher. During the photorefractory stage (hypoprolactinemia), the D(1D) DA receptor mRNA was at its lowest level in all areas tested. No differences were observed in hypothalamic D(2) DA receptor mRNA abundance throughout the reproductive cycle, except for an increase in D(2) DA receptor mRNA within the INF of photorefractory hens. Also, a marked reduction in D(2) DA receptor mRNA was observed in the pituitary of incubating hens. Pituitary D(1D) DA receptor levels did not change when birds entered the incubating phase. Double ISH revealed that D(1D) and D(2) DA receptor mRNAs were co-expressed within neurons expressing VIP mRNA, predominantly within the lateral hypothalamus and INF. D(1D) DA receptor mRNA was more highly expressed than D(2) DA receptor mRNA. The present findings clearly demonstrate that the expression of stimulatory D(1) DA receptor mRNA in the hypothalamus increases in hyperprolactinemic incubating hens, whereas inhibitory D(2) DA receptor mRNA increases in the pituitary of hypoprolactinemic photorefractory hens.     

The dopaminergic system in the brain of the native Thai chicken, Gallus domesticus: localization and differential expression across the reproductive cycle

Dopamine (DA) has a pivotal role in avian prolactin (PRL) secretion, acting centrally through D₁ DA receptors to stimulate PRL secretion by operating through vasoactive intestinal peptide (VIP). DA also inhibits PRL secretion by activating D₂ DA receptors at the pituitary level. This study was designed to investigate the distribution of DA neurons in the native Thai chicken, utilizing tyrosine hydroxylase (TH) as a marker for dopaminergic neurons. The differential expression of hypothalamic TH immunoreactive (TH-ir) neurons was also compared across the reproductive cycle. The results revealed that TH-ir neurons and fibers were found throughout the brain of the laying hen and were predominantly located within the diencephalon and mesencephalon. The observed distribution pattern of TH immunoreactivity was consistent with that reported previously in several avian species. However, changes in the number of TH-ir neurons in the nucleus intramedialis (nI) were observed across the reproductive cycle and correlated directly with variations in PRL levels. The population of TH-ir neurons in the nI increased significantly during the egg incubation period, where circulating PRL levels were the greatest. This study indicates, for the first time, that an association exists between DA neurons and the regulation of the reproductive system in the native Thai chicken. There is a paucity of information about the reproductive neuroendocrine regulation of tropical non-seasonally breeding avian species and it is suggested that the differential expression of DA neurons in the nI might play a role in the control of VIP secretion and subsequent PRL release in such birds.     

Serotoninergic control of gonadotrophin and prolactin secretion in women

OBJECTIVE Due to conflicting observations from previous investigations, the role of serotonin (5-HT) in the regulation of the human menstrual cycle has not been clearly established. We have therefore investigated the possible participation of 5-HR in the control of gonadotrophin and PRL secretion in women, using the potent 5-HT₃ receptor antagonist ondansetron as a pharmacological probe. DESIGN Serum profiles of LH, FSH and PRL were obtained in 9 normally cycling women during a control and a treatment cycle, during which ondansetron (8 mg orally) was administered daily. On day 10 of both cycles, the serum pulsatility of LH, FSH and PRL was assessed by frequent blood sampling (at 10-minute intervals for 10 hours). Pituitary responsiveness was tested by administration of a GnRH bolus (25 μg I.v. after 8 hours). MEASUREMENTS LH, FSH and PRL were serially determined in all blood samples by immunofluorescence assays. The resulting hormone data arrays were searched for significant fluctuations by the Cluster pulse algorithm. RESULTS Compared with control cycles, the temporal organization and the endocrine characteristics of the treatment cycles remained virtually unaltered. Serotonin antagonism did not noticeably affect the LH pulse attributes (frequencies, interpulse intervals, amplitudes). Although FSH amplitudes declined markedly (P < 0·05), the remaining pulse attributes were unchanged. A clear increase (P < 0·05) in the PRL pulse frequency was noted, while PRL pulse amplitudes tended to increase (P= 0·1). Gonadotrophin and PRL release in response to GnRH administration was unaltered by ondansetron treatment. CONCLUSIONS Serotoninergic blockade by a selective 5-HT₃ receptor antagonist failed to modify pulsatile LH secretion, but induced distinct changes in episodic FSH and PRL secretion. Since the pituitary gonadotrophin and PRL responsiveness remained unaltered during 5-HT₃ receptor blockade, the observed alterations in the FSH and PRL secretion presumably relate to altered hypo-thalamic regulation of these pituitary hormones. Thus, the central regulation of pulsatile FSH and PRL release in women appears to involve 5-HT₃ receptor-mediated processes.     

5-HT 2A Receptor and 5-HT Degradation Play a Crucial Role in Atherosclerosis by Modulating Macrophage Foam Cell Formation,Vascular Endothelial Cell Inflammation,and Hepatic Steatosis

Aim: Previously, we found that diabetes-related liver dysfunction is due to activation of the 5-HT _2A receptor (5-HT _2A R) and increased synthesis and degradation of 5-HT. Here, we investigated the role of 5-HT in the development of atherosclerosis. Methods: The study was conducted using high-fat diet-fed male ApoE ^−/− mice, THP-1 cell-derived macrophages, and HUVECs. Protein expression and biochemical indexes were determined by Western blotting and quantitative analysis kit, respectively. The following staining methods were used: oil red O staining (showing atherosclerotic plaques and intracellular lipid droplets), immunohistochemistry (showing the expression of 5-HT _2A R, 5-HT synthase, and CD68 in the aortic wall), and fluorescent probe staining (showing intracellular ROS). Results: In addition to improving hepatic steatosis, insulin resistance, and dyslipidemia, co-treatment with a 5-HT synthesis inhibitor and a 5-HT _2A R antagonist significantly suppressed the formation of atherosclerotic plaques and macrophage infiltration in the aorta of ApoE ^−/− mice in a synergistic manner. Macrophages and HUVECs exposed to oxLDL or palmitic acid in vitro showed that activated 5-HT _2A R regulated TG synthesis and oxLDL uptake by activating PKCε, resulting in formation of lipid droplets and even foam cells; ROS production was due to the increase of both intracellular 5-HT synthesis and mitochondrial MAO-A-catalyzed 5-HT degradation, which leads to the activation of NF-κB and the release of the inflammatory cytokines TNF-α and IL-1β from macrophages and HUVECs as well as MCP-1 release from HUVECs. Conclusion: Similar to hepatic steatosis, the pathogenesis of lipid-induced atherosclerosis is associated with activation of intracellular 5-HT _2A R, 5-HT synthesis, and 5-HT degradation.     

Dopamine infusion into the third ventricle increases gene expression of hypothalamic vasoactive intestinal peptide and pituitary prolactin and luteinizing hormone beta subunit in the turkey

Turkey prolactin (PRL) secretion is controlled by vasoactive intestinal peptide (VIP) neurons residing in the infundibular nuclear complex (INF) of the hypothalamus. The VIPergic activity is modulated by dopamine (DA) via stimulatory D(1) DA receptors. DA (10 nmol/min for 40 min) was infused into the third ventricle of laying turkey hens to study its effect on circulating PRL, hypothalamic VIP and pituitary PRL and LHbeta subunit mRNA levels. Plasma PRL was significantly elevated after 20 min of DA infusion and remained elevated 30 min after cessation of infusion. Hypothalamic VIP mRNA content was significantly greater in the INF of DA-infused birds than it was in the INF of vehicle-infused control birds. No increase in VIP mRNA due to DA infusion was noted in the preoptic area. Pituitary PRL and LHbeta subunit mRNAs were increased in DA-infused hens as compared to vehicle-infused controls but the rate of increase was more in PRL than LHbeta subunit. This study demonstrates that exogenous DA activates hypothalamic VIP gene expression and this increased expression is limited exclusively to the avian INF. The increased VIP mRNA in the INF is correlated with increased levels of circulating PRL and PRL and LHbeta mRNAs in the anterior pituitary.     

Role of the 5-HT2AReceptor and α1-adrenoceptor in the Contractile Response of Rat Pulmonary Artery to 5-HT in the Presence and Absence of Nitric Oxide

This study investigated the role of 5-HT_2Areceptors andα₁ -adrenoceptors in the contractile response to 5-HT in the first branch pulmonary artery of the rat and their interaction with endogenous nitric oxide. 5-HT and phenylephrine induced concentration-dependent contractions. Theα₁ -adrenoceptor antagonists prazosin, HV723 and phentolamine produced concentration-dependent rightward shifts of the 5-HT concentration-response curves (CRC) consistent with an action at α₁-adrenoceptors. The 5-HT₂receptor antagonists ritanserin, ketanserin and methysergide produced rightward shifts that were less than would have been predicted for an action solely at 5-HT_2Areceptors. 5-HT and phenylephrine CRCs were shifted to the left by -NAME. Endothelium denudation also increased the tissue sensitivity to 5-HT. In the presence of -NAME, ketanserin produced greater antagonism of the 5-HT CRC but not the phenylephrine CRC. Ketanserin also produced greater antagonism of the 5-HT CRC in endothelium denuded rings compared with endothelium intact rings. These findings indicate (a) that both theα₁ -adrenoceptor class and the 5-HT_2Areceptor is involved in the contractile response to 5-HT; (b) in the presence of endogenous nitric oxide the contractile response to 5-HT is mediated predominently byα₁ -adrenoceptors; (c) inhibition of endogenous nitric oxide potentiates the 5-HT_2Areceptor-mediated component of the contraction.     

Evidence for prolactin feedback actions on hypothalamic oxytocin, vasoactive intestinal peptide and dopamine secretion

Ovariectomized rats, when transplanted with 4 anterior pituitaries (APs) to the kidney capsule for 2-3 weeks, had elevated plasma prolactin (PRL) levels (3.8-fold) and showed decreased in situ AP weights (0.62-fold) and PRL concentrations (0.63-fold). The concentrations of dopamine (DA) and oxytocin (OT) in pituitary portal plasma of hyperprolactinemic rats were increased 1.7- and 1.9-fold, respectively. However, the levels of vasoactive intestinal peptide (VIP) in pituitary portal plasma of these rats were decreased 0.31-fold. The secretion of DA, dihydroxyphenylalanine (DOPA) and OT from fetal hypothalamic cells in primary culture was increased, whereas VIP secretion from these cells was reduced in a dose-dependent fashion following PRL treatment. These data are the first in vivo and in vitro demonstration of a stimulatory action of PRL on OT release and an inhibitory action of PRL on VIP release. Furthermore, these data suggest that a subtle imbalance between the secretion of the PRL-inhibiting factor (DA) and the PRL-releasing factors (VIP and OT) during elevated systemic levels of PRL is responsible for decreased lactotrophic function.     

Antisera to vasoactive intestinal polypeptide inhibit basal prolactin release from dispersed anterior pituitary cells

Vasoactive intestinal polypeptide (VIP) has been identified in hypothalamic tissue, is secreted into hypophysial portal blood, and stimulates prolactin (PRL) release in vivo and in vitro. It has been proposed, therefore, that VIP is a physiologic PRL-releasing factor. In this study, we confirm that VIP stimulates PRL release from rat pituitary cells in vitro, and demonstrate that an anti-VIP antiserum blocks VIP-induced PRL secretion. Surprisingly, the anti-VIP antiserum inhibited basal PRL secretion from rat pituitary cells in 3 separate experiments. Data from these experiments were pooled, as the responses were similar, revealing basal PRL release of 10.7 +/- 1.3 ng rPRL/10(5) cells (X +/- SE), while anti-VIP antisera significantly inhibited release to 4.4 +/- 0.6 ng rPRL/10(5) cells (p less than 0.001). PRL release in incubates containing control non-immune sera did not differ from basal release, 8.1 ng rPRL/10(5) cells. A further control experiment was conducted wherein cells were incubated with an anti-ACTH antiserum, representing another hyperimmune serum, which had no effect on PRL secretion. These data suggest that VIP, in addition to its possible role as a hypothalamic-derived PRL-releasing factor, may play a role within the pituitary as a regulator of basal PRL secretion.     

The serotonin type 3A receptor facilitates luteinizing hormone release and LHbeta promoter activity in immortalized pituitary gonadotropes

The 5-hydroxytryptamine type 3_A receptor (5-HT3_AR) is a ligand-gated cation channel activated by serotonin. This receptor is expressed throughout the nervous system as well as in the pituitary gland. Although it has been documented that the 5-HT3_AR modulates exocytosis in neurons, its role in the pituitary gland has not been determined. Previous research has shown that the 5-HT3_AR modulates circulating gonadotropin levels in vivo. It is unclear, however, if its activation in the pituitary gland mediates these effects or if receptors elsewhere in the hypothalamus-pituitary-gonadal axis are responsible. To investigate the potential for the 5-HT3_AR to modulate gonadotropin release from pituitary gonadotropes, the gonadotrope-derived LβT2 cell line was used as a model system and radioimmunoassays were employed to investigate how 5-HT3_AR activation influences luteinizing hormone (LH) release. Our studies demonstrate that gonadotropin releasing hormone (GnRH)-stimulated LH release was decreased by the 5-HT3_AR-specific antagonist MDL 72222 in a concentration-dependent manner. In addition, it was found that overexpressing the 5-HT3_AR in LβT2 cells enhanced both basal and GnRH-stimulated LH release and also increased LHβ gene promoter activity. These results suggest that the 5-HT3_AR may participate in the hypothalamus-pituitary-gonadal axis at the level of the pituitary gonadotrope to mediate pituitary hormone release.     

The N-terminal region of reelin regulates postnatal dendritic maturation of cortical pyramidal neurons

Cajal-Retzius cells, located in layer I of the cortex, synthesize and secrete the glycoprotein reelin, which plays a pivotal role in neuronal migration during embryonic development. Cajal-Retzius cells persist after birth, but their postnatal role is unknown. Here we show that Cajal-Retzius cells receive a major excitatory synaptic input via serotonin 5-HT₃ receptors. Blocking this input using pharmacological tools or neutralization of reelin signaling results in hypercomplexity of apical, but not basal, dendrites of cortical layer II/III pyramidal neurons. A similar hypercomplexity is observed in the cortex of the 5-HT_3A receptor knockout mouse. The increased dendritic complexity can be rescued by application of recombinant full-length reelin or its N-terminal fragment, but not by the central fragment of reelin, and involves a signal transduction pathway independent of the activation of the canonical reelin receptors. Taken together, our results reveal a novel role of serotonin, Cajal-Retzius cells, and reelin in the postnatal maturation of the cortex.     

Adrenergic,dopaminergic and serotonergic gene expression in low dose,long time insulin and somatotropin treatment to ageing rats: rejuvenation of brain function

Somatotropin (GH) and insulin (INS) low dose, long-term brain rejuvenation effect was studied in the cerebral cortex using NE, EPI, DA and 5-HT receptor subtypes of young (group I—treatment started 4 weeks continued to 16 weeks) and old rats (group II—treatment started 60 weeks continued to 90 weeks). GH and INS treatment showed significant decrease in NE and EPI content in cerebral cortex of both young and old rats. α_2A-adrenergic receptors showed decreased expression whereas β₂-adrenergic receptors showed enhanced expression with age. GH and INS treatment significantly increased α_2A-adrenergic receptor protein in group I rats whereas INS treatment could increase β₂-adrenergic receptor protein expression in group II rats. DA and 5-HT content decrease with age. GH and INS administration showed increase in DA and 5-HT content in the brain regions-corpus striatum and brainstem of both young and old rats. Also, DA D₂ and 5-HT_2C receptor gene expression were increased significantly by GH and INS treatment in both young and old rats. In conclusion, low dose, long-term treatment of INS and GH to ageing rats improved the adrenergic, dopaminergic and serotonergic receptor subtypes activity and rejuvenation of brain function.