Henrik Jørgensen

Serotonin receptors involved in vasopressin and oxytocin secretion

Serotonin (5‐HT), 5‐HT agonists, the 5‐HT precursor 5‐hydroxytryptophan, 5‐HT‐releasers and ‐reuptake inhibitors stimulate the release of vasopressin and oxytocin. We investigated the involvement of 5‐HT receptors in the serotonergic regulation of vasopressin and oxytocin secretion. Vasopressin and oxytocin secretion was stimulated by 5‐HT, the 5‐HT1A+1B+5A+7 agonist 5‐carboxamidotryptamine (5‐CT), the 5‐HT2A+2C agonist DOI, the 5‐HT2C+2A agonist mCPP, the 5‐HT2C agonist MK‐212, the 5‐HT3 agonist SR 57277 and the 5‐HT4 agonist RS 67506. The 5‐HT1A agonist 8‐OH‐DPAT, which had no effect on vasopressin secretion, stimulated oxytocin secretion. The 5‐HT‐induced release of vasopressin and oxytocin was inhibited by central infusion of the 5‐HT antagonists WAY 100635 (5‐HT1A), LY 53857 (5‐HT2A+2C), ICS 205‐930 (5‐HT3+4) and RS 23597 (5‐HT4). The 5‐HT2+6+7 antagonist metergoline in combination with the 5‐HT1A+2+7 antagonist methysergide inhibited the stimulatory effect of 5‐CT on both hormones, whereas the 5‐HT1A+1B antagonist cyanopindolol only inhibited the oxytocin response. The 5‐HT2A antagonist 4‐(4‐flourobenzoyl)‐1‐(4‐phenylbutyl)‐piperidine oxalate had no effect on DOI‐induced hormone response. The 5‐HT2C antagonist Y 25130 partly inhibited the stimulating effect of MK‐212. ICS 205‐930 and RS 23597 inhibited vasopressin and oxytocin secretion induced by RS 67506. WAY 100635 inhibited 8‐OH‐DPAT‐induced oxytocin secretion. We conclude that 5‐HT‐induced vasopressin secretion primarily is mediated via 5‐HT2C, 5‐HT4 and 5‐HT7 receptors, whereas 5‐HT2A, 5‐HT3 and 5‐HT5A receptors seem to be of minor importance. 5‐HT‐induced oxytocin secretion involves 5‐HT1A, 5‐HT2C and 5‐HT4 receptors; in addition an involvement of 5‐HT1B, 5‐HT5A and 5‐HT7 receptors seems likely, whereas 5‐HT2A and 5‐HT3 receptors seem to be less important.

Involvement of 5-HT1, 5-HT2, and 5-HT3 Receptors in the Mediation of the Prolactin Response to Serotonin and 5-Hydroxytryptophan

Serotonin (5-HT) is involved in the neuroendocrine regulation of prolactin (PRL) secretion as a stimulator. Within the last decade several 5-HT receptor types have been identified, but their individual role in the mediation of the PRL response to 5-HT is only partly understood. We investigated in conscious male rats the effect of different 5-HT1, 5-HT2, and 5-HT3 receptor antagonists on the PRL response to 5-HT or to the 5-HT precursor 5-hydroxytrytophan (5-HTP) which was administered in combination with the 5-HT reuptake inhibitor fluoxetine. 5-HT (0.5-5.0 mg/kg BW i.v.) or 5-HTP (25-100 mg/kg i.p.) in combination with saline or fluoxetine (10 mg/kg i.p.) increased the plasma PRL concentration dose-dependently. Pretreatment with the 5-HT1+2 receptor antagonist methysergide (2.5 mg/kg i.p.) prevented the stimulatory effect of 5-HT or 5-HTP + fluoxetine. Pretreatment with the 5-HT2 receptor antagonists ketanserin or LY 53857 (2.5 mg/kg i.p.) inhibited the PRL response to 5-HT by approximately 80% and to 5-HTP + fluoxetine approximately 100%. A higher dose (10 mg/kg) of the 5-HT2 receptor antagonists possessed only 50% inhibitory effect. Pretreatment with the 5-HT3 receptor antagonists ICS 205-930 or GR 38032F (0.05-2.5 mg/kg i.p.) inhibited the PRL response induced by 5-HT or by 5-HTP + fluoxetine. The maximal inhibitory effect (approximately 80%) was obtained by a dose of 0.1 mg/kg of both compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonergic involvement in stress-induced ACTH release

We investigated the involvement of serotonin (5-HT) and 5-HT receptors in mediation of stress-induced ACTH secretion in adult male rats, which were pretreated by 5-HT antagonists before restraint-, ether-, cold swim-stress or endotoxin. All stressors potently increased plasma ACTH. Lesion of 5-HT neurons with 5, 7-dihydroxytryptamine injected intracerebroventricularly, into the paraventricular nucleus or into the raphe nuclei, inhibited the restraint stress-induced ACTH response by 50%. Restraint increased the content of 5-HT and its metabolite 5-hydroxyindole acetic acid, in the raphe nuclei, whereas the other stressors had no such effect. Pretreatment with the 5-HT1A receptor antagonist WAY 100635 inhibited the restraint stress- and endotoxin-induced ACTH secretion by 50%. The 5-HT1+2 antagonist methysergide or the 5-HT2 antagonist ketanserin inhibited the restraint- or ether stress-induced ACTH response, and eliminated the endotoxin-induced ACTH response. The 5-HT2 receptor antagonist LY 53857 blocked only the endotoxin-induced ACTH response. Pretreatment with the 5-HT3 receptor antagonist ondansetrone had no effect on stress-stimulated ACTH secretion. The 5-HT3+4 receptor antagonist tropisetrone inhibited the restraint- and ether stress-induced response. The ACTH response to swim stress was not affected by any of the antagonists used. It is concluded that the 5-HT1A, the 5-HT2A and the 5-HT2C receptor, but not the 5-HT3 receptor are involved in the stress-induced ACTH secretion. An involvement of the 5-HT4 receptor is possible. Furthermore, that serotonergic neurons in the raphe nuclei are activated during restraint stress, and that these neurons and neurons in PVN of the hypothalamus, are important for the mediation of the restraint stress-induced ACTH response.

Serotonin Stimulates Hypothalamic mRNA Expression and Local Release of Neurohypophysial Peptides

The neurotransmitter serotonin (5‐HT) stimulates the secretion of vasopressin and oxytocin, and 5‐HT is involved in the mediation of the vasopressin and oxytocin response to stress. In male Wistar rats, we investigated the 5‐HT receptors involved in the 5‐HT‐induced increase of mRNA expression of vasopressin and oxytocin in the hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON). The 5‐HT precursor, 5‐hydroxytryptophan, injected in combination with the 5‐HT reuptake inhibitor, fluoxetine, increased oxytocin mRNA expression in the PVN, and the concentration of vasopressin and oxytocin in plasma, whereas mRNA in the SON was not affected. Intracerebroventricular infusion of 5‐HT agonists selective for the 5‐HT1A, 5‐HT1B, 5‐HT2A and 5‐HT2C receptor increased oxytocin mRNA in the SON and PVN. Infusion of agonists selective for the 5‐HT2A + 2C receptor increased vasopressin mRNA in the PVN, whereas none of the 5‐HT agonists affected vasopressin mRNA in the SON. All the 5‐HT agonists infused increased peripheral oxytocin concentration and vasopressin was increased by stimulation of the 5‐HT2A, 5‐HT2C and 5‐HT3 receptor. Intracerebroventricular infusion of 100 nmol 5‐HT increased the extracellular hypothalamic concentration of vasopressin as measured by microdialysis in the PVN. To evaluate the involvement of hypothalamic‐pituitary system in the 5‐hydroxytryptophan and fluoxetine‐induced vasopressin secretion, rats were immunoneutralized with a specific anti‐corticotropin‐releasing hormone antiserum. This treatment reduced plasma vasopressin and oxytocin responses. We conclude that stimulation with 5‐hydroxytryptophan or 5‐HT agonists increases mRNA expression of oxytocin in the PVN and the SON via stimulation of at least 5‐HT1A, 5‐HT1B, 5‐HT2A and 5‐HT2C receptors. Vasopressin mRNA in the PVN was increased only via the 5‐HT2 receptor, whereas vasopressin mRNA in the SON does not seem to be affected by 5‐HT stimulation. Corticotropin‐releasing hormone appears to be partly involved in the mediation of 5‐HT induced vasopressin and oxytocin secretion.

Serotonergic stimulation of corticotropin-releasing hormone and pro-opiomelanocortin gene expression.

The neurotransmitter serotonin (5‐HT) stimulates adrenocorticotropic hormone (ACTH) secretion from the anterior pituitary gland via activation of central 5‐HT1 and 5‐HT2 receptors. The effect of 5‐HT is predominantly indirect and may be mediated via release of hypothalamic corticotropin‐releasing hormone (CRH). We therefore investigated the possible involvement of CRH in the serotonergic stimulation of ACTH secretion in male rats. Increased neuronal 5‐HT content induced by systemic administration of the precursor 5‐hydroxytryptophan (5‐HTP) in combination with the 5‐HT reuptake inhibitor fluoxetine raised CRH mRNA expression in the paraventricular nucleus (PVN) by 64%, increased pro‐opiomelanocortin (POMC) mRNA in the anterior pituitary lobe by 17% and stimulated ACTH secretion five‐fold. Central administration of 5‐HT agonists specific to 5‐HT1A, 5‐HT1B, 5‐HT2A or 5‐HT2C receptors increased CRH mRNA in the PVN by 15–50%, POMC mRNA in the anterior pituitary by 15–27% and ACTH secretion three‐ to five‐fold, whereas a specific 5‐HT3 agonist had no effect. Systemic administration of a specific anti‐CRH antiserum inhibited the ACTH response to 5‐HTP and fluoxetine and prevented the 5‐HTP and fluoxetine‐induced POMC mRNA response in the anterior pituitary lobe. Central or systemic infusion of 5‐HT increased ACTH secretion seven‐ and eight‐fold, respectively. Systemic pretreatment with the anti‐CRH antiserum reduced the ACTH responses to 5‐HT by 80% and 64%, respectively. It is concluded that 5‐HT via activation of 5‐HT1A, 5‐HT2A, 5‐HT2C and possibly also 5‐HT1B receptors increases the synthesis of CRH in the PVN and POMC in the anterior pituitary lobe, which results in increased ACTH secretion. Furthermore, the results indicate that CRH is an important mediator of the ACTH response to 5‐HT.

An area-efficient topology for VLSI implementation of Viterbi decoders and other shuffle-exchange type structures

A topology for single-chip implementation of computing structures based on shuffle-exchange (SE)-type interconnection networks is presented. The topology is suited for structures with a small number of processing elements (i.e. 32-128) whose area cannot be neglected compared to the area required for interconnection. The processing elements are implemented in pairs that are connected to form a ring. In this way three-quarters of the interconnections are between neighbors. The ring structure is laid out in two columns and the interconnection of nonneighbors is routed in the channel between the columns. The topology has been used in a VLSI implementation of the add-compare-select (ACS) module of a fully parallel K=7, R=1/2 Viterbi decoder. Both the floor-planning issues and some of the important algorithm and circuit-level aspects of this design are discussed. The chip has been designed and fabricated in a 2- mu m CMOS process using MOSIS-like simplified design rules. The chip operates at speeds up to 19 MHz under worst-case conditions (V/sub DD/=4.75 V and T/sub A/=70 degrees C). The core of the chip (excluding pad cells) is 7.8*5.1 mm/sup 2/ and contains approximately 50000 transistors. The interconnection network occupies 32% of the area. >

Histaminergic and Catecholaminergic Interactions in the Central Regulation of Vasopressin and Oxytocin Secretion1

Activation of histaminergic and noradrenergic/adrenergic neurons in the brain stimulates the release of the neurohypophysial hormones arginine vasopressin (AVP) and oxytocin (OT) and are involved the mediation of the hormone responses to physiological stimuli such as dehydration and suckling. We therefore investigated whether the two neuronal systems interact in their regulation of AVP and OT secretion in conscious male rats. When administered intracerebroventricularly (i.c.v.), histamine (HA) as well as the H1 receptor agonist 2-thiazolylethylamine or the H2 receptor agonist 4-methylHA stimulated AVP and OT secretion. Prior i.c.v. infusion of antagonists specific to alpha or beta adrenergic receptors or their subtypes did not significantly affect the hormone response to HA or the histaminergic agonists. Infused i.c.v. norepinephrine (NE) or epinephrine (E) increased AVP and OT secretion. Prior i.c.v. infusion of the H1 receptor antagonist mepyramine or the H2 receptor antagonist cimetidine significantly inhibited the AVP and OT responses to NE and the AVP response to E, whereas only cimetidine inhibited the OT response to E significantly. Systemic pretreatment with imetit, which by activation of presynaptic H3 receptors inhibits neuronal synthesis and release of HA, decreased the AVP and OT responses to NE and E significantly. In the doses used, HA and E had no significant effect on mean arterial blood pressure. NE increased mean arterial blood pressure 10% at 1 and 2.5 min, whereafter the blood pressure returned to basal level within 10 min. The results indicate that noradrenergic and adrenergic neurons stimulate AVP and OT secretion via an involvement of histaminergic neurons, which may occur at magnocellular neurons in the supraoptic and paraventricular nuclei of the hypothalamus. The stimulatory effect of the amines on neurohypophysial hormone secretion seems to be independent of a central action on blood pressure. In contrast, a functionally intact noradrenergic and adrenergic neuronal system seems not to be a prerequisite for a HA-induced release of AVP and OT. The present findings further substantiate the role of histaminergic neurons in the central regulation of neurohypophysial hormone secretion.

Adrenocorticotropic Hormone Secretion in Rats Induced by Stimulation with Serotonergic Compounds

The serotonin receptors involved in the secretion of adrenocorticotropin hormone (ACTH) were investigated in conscious adult male rats. Administration of serotonin (5‐HT), 5‐hydroxytryptophan (5‐HTP) in combination with the serotonin reuptake inhibitor fluoxetine (Flx), or of the 5‐HT agonists 8‐OH‐DPAT (5‐HT1A), 5‐carboxamido‐tryptamine (5‐HT1A+1B+5A+7), RU 24969 (5‐HT1B+1A), DOI (5‐HT2A+2C), S‐α‐methyl‐5‐HT (5‐HT2A+2B+2C), MK212 (5‐HT2B+2C), or methyl‐chlorophenyl‐piperazine (5‐HT2A+2C) dose‐dependently stimulated ACTH secretion. The 5‐HT3 agonist 2‐methyl‐5‐HT had no effect. Administration of a 5‐HT1 agonist in combination with any of the 5‐HT2 agonists DOI, S‐α‐methyl‐5‐HT or MK212 had an additive effect on the plasma concentration of ACTH. The ACTH stimulating effect of each of the 5‐HT agonists was inhibited by pretreatment with antagonists with corresponding 5‐HT receptor affinity. The ACTH response to 5‐HT or 5‐HTP/Flx was inhibited by injection with the 5‐HT1A+2A+2C+5A+7 antagonist methysergide, the 5‐HT2A antagonist ketanserine and the 5‐HT2C+2A antagonist LY 53857. The 5‐HT1A antagonist WAY 100635 enhanced 5‐HT‐ and 5‐HTP/Flx‐induced ACTH secretion, suggesting a presynaptic 5‐HT1A autoreceptor effect of the drug. The 5‐HT3 antagonist ondansetrone had no effect on the either of the 5‐HT agonists. The 5‐HT3+4 antagonist tropisetrone attenuated the effect of 5‐HTP/Flx, which may suggest a stimulation of ACTH secretion via 5‐HT4 receptors. It is concluded that 5‐HT1A, 5‐HT2A+2C, and to a lesser extent 5‐HT1B receptors, but not 5‐HT3 receptors are involved in the effects of serotonin agonists on ACTH secretion. Furthermore, an involvement of the 5‐HT5A and the 5‐HT7 receptor is possible.

Effect of Serotonin 5-HT1, 5-HT2, and 5-HT3 Receptor Antagonists on the Prolactin Response to Restraint and Ether Stress

Serotonin (5-HT) appears to be involved in the central control of the prolactin (PRL) response to suckling and estrogen. Furthermore, 5-HT may participate in the mediation of stress-induced PRL release. In order further to elucidate the role of 5-HT and the type of 5-HT receptor(s) involved in the PRL response to stress, we investigated the effect of blockade of 5-HT1, 5-HT2 or 5-HT3 receptors on the restraint or ether stress-induced release of PRL in male rats. Pretreatment with the 5-HT1 + 2 receptor antagonist methysergide (0.5 or 2.5 mg/kg i.p.) inhibited or prevented the PRL response to restraint or ether stress. Pretreatment with the 5-HT2 receptor antagonists ketanserin or LY 53857 (0.5 or 2.5 mg/kg i.p.) inhibited the response to restraint or ether stress approximately 30 or 60%, respectively. Higher doses of both 5-HT2 receptor antagonists (10 mg/kg i.p.) had a minor inhibitory effect (5-30% for ketanserin and 50% for LY 53857). Prior intraperitoneal administration of the 5-HT3 receptor antagonists ICS 205-930 or GR 38032F (0.05-2.5 mg/kg i.p.) inhibited the restraint stress-induced PRL release dose-dependently. Both compounds inhibited the PRL response to ether stress, but only the effect of GR was dose-related. The maximal inhibitory effect (70% inhibition of the PRL response to restraint or ether stress) was obtained for both compounds at a dose of 0.1 mg/kg. We conclude that serotonergic neurons are involved in the mediation of the stress-induced PRL release by activation of 5-HT1, 5-HT2 as well as 5-HT3 receptors.

Role of hypothalamic histaminergic neurons in mediation of ACTH and beta-endorphin responses to LPS endotoxin in vivo

The involvement of hypothalamic histaminergic neurons in the mediation of the ACTH and beta-endorphin (beta-END) response to lipopolysaccharide (LPS) endotoxin was investigated in conscious male rats. LPS stimulated the release of ACTH and beta-END dose-dependently and increased the hypothalamic concentration of the histamine (HA) metabolite tele-methylhistamine significantly and that of HA slightly, indicating an increased turnover of neuronal HA. Pretreatment with the HA synthesis inhibitor alpha-fluoromethyl-histidine administered intracerebroventricularly (i.c.v.) or intraperitoneally (i.p.) inhibited the ACTH and beta-END response to LPS about 60%, whereas i.p. administration of the H3 receptor agonist R(alpha)methylHA, which inhibits HA synthesis and release, decreased the response about 50%. Pretreatment with the H1 receptor antagonist mepyramine (67 micrograms x 2 i.c.v.) inhibited the hormone response to LPS about 50%, while pretreatment with equimolar doses of the H2 receptor antagonists cimetidine (67 micrograms x 2 i.c.v.) or ranitidine (83 micrograms x 2 i.c.v.) had no effect on the LPS-induced release of ACTH and beta-END. When the H1 receptor antagonists mepyramine and cetirizine were administered i.p. in doses (10 mg/kg) which penetrate the blood-brain barrier the hormone response to LPS was inhibited 50% and 30%, respectively. Administered i.p. the H2 receptor antagonists had no effect on the hormone response to LPS. We conclude that hypothalamic histaminergic neurons in rats are involved in the mediation of the ACTH and beta-END response to LPS stimulation via activation of central postsynaptic H1 receptors.