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E Sanders-Bush

Publications and source records attributed to E Sanders-Bush.

At least 73 records · Page 4Linked to original sources
PubMed1990

Adaptation of brain 5HT2 receptors after mianserin treatment: receptor sensitivity, not receptor binding, more accurately correlates with behavior.

This study investigates the possibility that mianserin, a serotonin-2 (5HT2) receptor antagonist, produces a prolonged antagonism of quipazine discrimination, consistent with its prolonged biochemical effects. Rats were trained on a saline-quipazine (1.5 mg/kg) discrimination; following acquisition, the animals were assigned to groups and given injections of 2.0 mg/kg mianserin. Individual groups were tested at 45 min and successive 12-hr intervals for their ability to discriminate 0.75 mg/kg of quipazine, a dose that elicited 75% responding on the quipazine lever. Blockade of the quipazine cue persisted for 48 hr following mianserin administration. The above procedure was replicated using lower doses of mianserin (0.25, 0.10 and 0.05 mg/kg) and two other 5HT2 antagonists, pizotifen and metergoline (2.0 mg/kg), both of which showed similar profiles of extended antagonism. Changes in both receptor density and receptor sensitivity were investigated as possible mechanisms of mianserin's prolonged activity. Analysis of [3H]ketanserin binding revealed that a single 2.0-mg/kg dose of mianserin produced a significant decrease in the number of receptor sites (44%) 24 hr after treatment; however, this loss of sites recovered by 36 hr post-injection and could therefore not account for mianserin's continued antagonism at this and later times. 5HT-mediated phosphoinositide hydrolysis in cerebral cortex slices was used as a measure of 5HT2 receptor sensitivity. Treatment of rats with 2 mg/kg of mianserin caused a marked reduction in the maximum phosphoinositide response to 5HT that persisted for up to 36 hr. Hence, the time course for recovery of 5HT2 receptor sensitivity corresponded more closely to behavioral recovery than did 5HT2 receptor binding.

Animals↗
PubMed1990

Serotonin1c receptor reserve in choroid plexus masks receptor subsensitivity.

This paper tests the hypothesis that spare serotonin 5-HT1c receptors are present in the rat choroid plexus and explores the possible influence of such sites on the adaptive regulation of the 5-HT1c receptor. The consequences of partial receptor inactivation were compared for the natural agonist 5-HT and the putative partial agonists trifluoromethylphenylpiperazine (TFMPP) and (+)-lysergic acid diethylamide (LSD). These studies showed approximately 50% reserve of 5-HT1c receptors in the rat choroid plexus. The calculated KA for 5-HT obtained by partial irreversible inactivation was 36 nM. Phenoxybenzamine reduced the maximum response elicited by TFMPP and LSD, without shifting the EC50 values, consistent with the interpretation that TFMPP and LSD are partial agonist at the 5-HT1c receptor in rat choroid plexus. The KA of TFMPP and LSD was 0.16 microM and 9 nM, respectively. Quantitative analysis of percentage of receptor occupancy vs. percentage of maximum response showed that 5-HT occupied only 70% of the receptors to give a maximum response, whereas a linear relationship between percentage of occupancy and response was found for TFMPP. These differences had functional consequences as demonstrated in studies of regulation of the 5-HT1c receptor. Chronic administration of the 5-HT agonist quipazine produced a 32% loss of 5-HT1c binding sites in the choroid plexus, with no change in the 5-HT-induced phosphoinositide hydrolysis response. This dissociation between binding and function is likely explained by the receptor reserve that exists for the 5-HT1c receptors. Consistent with this interpretation, the TFMPP-induced phosphoinositide hydrolysis signal was reduced to the same extent as the loss of binding sites. These results show that the 5-HT1c receptor in the choroid plexus adapts predictably to chronic receptor activation and suggest the possibility that the paradoxical regulation that has been described for other 5-HT receptors might be explained partially by the unrecognized existence of receptor reserve.

Animals↗
PubMed1989

Transferrin gene expression and synthesis by cultured choroid plexus epithelial cells. Regulation by serotonin and cyclic adenosine 3',5'-monophosphate.

Primary cultures of rat choroid plexus epithelial cells were established and used to investigate the role of the choroid plexus in the synthesis and secretion of transferrin. Transferrin gene expression was determined by a Northern blot analysis with a transferrin cRNA probe. A single transferrin mRNA species was detected and found to be the same size as the transcripts in the liver and Sertoli cells. Immunoprecipitation of radiolabeled secreted proteins with an antiserum transferrin antibody demonstrated that cultured choroid plexus epithelial cells synthesize and secrete a 70-kDa species of transferrin. Levels of transferrin secretion by rat choroid plexus epithelial cells in culture were measured by radioimmunoassay. Treatment of the choroid plexus epithelial cells in culture with cell-permeable cAMP analogs or serotonin led to time- and concentration-dependent changes in the levels of transferrin in the medium. Dibutyryl-cAMP and 8-bromo-cAMP decreased the levels of transferrin synthesized and secreted by choroid plexus epithelial cells with an EC50 value of 30 nM. Serotonin, however, increased the levels of transferrin with an EC50 value of 100 nM. A concomitant change in transferrin mRNA concentrations was observed in response to serotonin. These data suggest that the synthesis of transferrin by the choroid plexus is reciprocally regulated by the neurotransmitter serotonin and by regulatory agents coupled to adenylate cyclase. Regulatory agents such as serotonin may have a critical role in modulating the proteins synthesized by the choroid plexus, thereby influencing the composition of the cerebrospinal fluid.

Animals↗
PubMed1989

Sertraline-induced desensitization of the serotonin 5HT-2 receptor transmembrane signaling system.

Sertraline is a new, selective serotonin (5HT) uptake inhibitor with antidepressant activity. The effect of chronic administration of sertraline on 5HT-2 receptors in rat cortex was compared with that of the tricyclic antidepressant, amitriptyline. 5HT-2 receptors were evaluated in binding assays using [3H]-ketanserin and in functional assays of transmembrane signaling, hydrolysis of phosphoinositides. The daily injection of 17 mg/kg sertraline induced a desensitization of 5HT-2-mediated phosphoinositide hydrolysis after 28, but not 21, days. The administration of 1.2 mg/kg/day via continuous release pumps caused a more rapid desensitization. Amitriptyline administered chronically also produced a desensitization of the 5HT-2-mediated phosphoinositide hydrolysis response. A decrease in the density of 5HT-2 binding sites accompanies the functional desensitization after amitriptyline, but changes in 5HT-2 binding sites were not detected after chronic sertraline administration. Studies of the mechanism of action of sertraline show that the desensitization of the phosphoinositide hydrolysis response is homologous in nature, and that it is not secondary to changes in the synthesis of precursor lipids. Other possibilities such as alterations in coupling efficiency or in the activity of effector enzymes are currently being considered. The present results suggest a new postsynaptic action of antidepressant drugs at central 5HT-2 receptors (i.e., changes in 5HT-2 signal transduction at a site distal to the cell surface binding site) and illustrate the importance of studies of receptor signaling pathways to complement radioligand binding.

1-Naphthylamine↗
PubMed1988

The serotonin/norepinephrine-link in brain. II. Role of serotonin in the regulation of beta adrenoceptors in the low agonist affinity conformation.

The present studies were undertaken to characterize further the role of serotonin (5-HT) in the regulation of the norepinephrine (NE) beta adrenoceptor coupled adenylate cyclase system in the rat cortex. Although 5-HT in vitro did not influence maximum binding and Kd values of [3H]dihydroalprenolol binding or the IC50 value for isoproterenol as estimated from competition binding curves in cortical tissue from control animals, 5-HT abolished the increase in beta adrenoceptor number and the marked elevation of the IC50 value for isoproterenol in cortical membrane preparations after selective lesions with 5,7-dihydroxytryptamine (5,7-DHT). Nonlinear regression analysis of competition binding curves revealed that the increase in the maximum binding of beta adrenoceptors after 5,7-DHT is due exclusively to an increase in beta adrenoceptors in the agonist low affinity conformation and that it is this receptor population that is reduced by nanomolar concentrations of 5-HT. The increase in the density of beta adrenoceptors in the low affinity conformation occurred approximately 11 days after the lesions and remained elevated throughout the experimental period of 28 days. Ritanserin in a dose that virtually abolished 5-HT2 receptor binding in cortex did not mimic the effect of 5,7-DHT.(ABSTRACT TRUNCATED AT 250 WORDS)

5,7-Dihydroxytryptamine↗
PubMed1988

Lysergic acid diethylamide and 2,5-dimethoxy-4-methylamphetamine are partial agonists at serotonin receptors linked to phosphoinositide hydrolysis.

Based on electrophysiological, radioligand binding, and behavioral studies in laboratory animals, it is generally believed that the psychotomimetic effects of the phenethylamine and indolealkylamine hallucinogens are mediated by central serotonin (5-HT) receptors, in particular the 5-HT-2 subtype. Agonist-stimulated phosphoinositide hydrolysis was utilized to determine the potency and efficacy of racemic 1-(2,5)-dimethoxy-4-methyl-phenyl)-2-aminopropane (DOM), and d-lysergic acid diethylamide (LSD) at the 5-HT-2 receptor in rat cerebral cortex and the 5-HT-1c receptor in rat choroid plexus. Both DOM and LSD stimulated phosphoinositide hydrolysis in cerebral cortex. These effects were blocked by the 5-HT-2 antagonists, ketanserin and spiperone, but not by antagonists of muscarinic, alpha-1 adrenergic or histaminergic receptors. The maximum responses of DOM and LSD, respectively, were 76% and 25% of the maximum response to 5-HT. However, LSD was 500 times more potent than was racemic DOM. Consistent with a partial agonist effect, LSD partially blocked the effect of 5-HT, with a maximal inhibition equivalent to the intrinsic activity of LSD alone. In choroid plexus, DOM and LSD stimulated phosphoinositide hydrolysis and both responses were blocked by mianserin and less effectively by spiperone. The maximum effect of DOM was 67% of that of 5-HT, whereas the maximum effect of LSD was only 34% of the maximum response of 5-HT. LSD was 50 times more potent than was racemic DOM. LSD partially antagonized the effect of 5-HT in the choroid plexus, consistent with a partial agonist effect at the 5-HT-1c receptor in this tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

DOM 2,5-Dimethoxy-4-Methylamphetamine↗
PubMed1988

Putative selective 5-HT-2 antagonists block serotonin 5-HT-1c receptors in the choroid plexus.

The binding of [3H]mianserin to rat choroid plexus was characterized and compared with two other radioligands that label the 5-HT (serotonin)-1c receptor ([3H]mesulergine and [125I] lysergic acid diethylamide). [3H]Mianserin binding to a crude membrane preparation of choroid plexus from rat brain was rapid, saturable and of high affinity (Kd = 1 nM). The density of sites labeled by [3H]mianserin and [3H]mesulergine was equal. Furthermore, an excellent correlation was found between the potencies of drugs in competing for [3H]mianserin binding and for [125]lysergic acid diethylamide binding. Based on these data, it was concluded that [3H]mianserin labels the 5-HT-1c binding site. Using this ligand, the binding of the putative selective 5-HT-2 antagonist ritanserin to the 5-HT-1c site was evaluated. Ritanserin was a potent inhibitor of [3H]mianserin binding with a Ki value of 0.2 nM. Functional studies of 5-HT-stimulated phosphoinositide hydrolysis, the transmembrane signaling pathway for the 5-HT-1c receptor, showed that ritanserin blocks the effect of 5-HT and that it functions as a competitive antagonist of the 5-HT-1c receptor in intact choroid plexus. The potencies of ritanserin and several other drugs, including other 5-HT-2 antagonists, at the 5-HT-1c binding site correlated with their potencies at blocking 5-HT-stimulated phosphoinositide hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

5HT2 binding sites after mianserin: comparison of loss of sites and brain levels of drug.

The purpose of this study was to evaluate the role of residual drug in mediating the loss of 5HT2 binding sites after in vivo treatment with mianserin. Brain levels of mianserin were measured using a radioreceptor assay and compared with the extent of receptor loss. Peak brain levels were found within 0.5 to 1 h after dosing and the drug disappeared from brain with a half-life of 1-3 h. A dissociation was found between the levels of mianserin and the loss of binding sites. At the time of peak drug levels, the density of 5HT2 sites was not changed, while 24 h later, a significant loss of sites was evident. Although some drug-related material remained in the brain at 24 h after treatment, there was no apparent relationship between the regional distribution of residual drug and the distribution of 5HT2 binding sites. Studies with [3H]mianserin confirmed these results. Furthermore, incubation of brain slices with mianserin did not lead to a decrease in 5HT2 binding site density, consistent with the conclusion that the in vivo effects of the drug do not reflect a direct action.

Animals↗
PubMed1987

Denervation supersensitivity of 5-HT-1c receptors in rat choroid plexus.

Serotonin (5-HT)-stimulated phosphoinositide hydrolysis in the choroid plexus is mediated by the 5-HT-1c receptor. The current study demonstrates that treatment of rats with the serotonergic neurotoxin, 5,7-dihydroxytryptamine, caused a marked depletion of 5-HT and a supersensitive 5-HT-1c mediated phosphoinositide hydrolysis response. These data suggest that the 5-HT-1c site in choroid plexus receives tonic serotonergic input.

5,7-Dihydroxytryptamine↗
PubMed1987

The serotonin/noradrenaline-link in brain. I. The role of noradrenaline and serotonin in the regulation of density and function of beta adrenoceptors and its alteration by desipramine.

The present studies were undertaken to assess the role of noradrenaline (NA) and serotonin (5HT) in the regulation of the NA receptor coupled adenylate cyclase system and its alteration by desipramine (DMI) in brain structures with or without noradrenergic neuronal projections. In contrast to cortex and limbic forebrain, where chronic DMI administration caused subsensitivity of the NA sensitive adenylate cyclase linked to a down-regulation of beta adrenoceptors, the drug failed to alter the NA receptor coupled adenylate cyclase system in the striatum. Selective lesions of serotonergic axons with 5,7-dihydroxytryptamine caused a significant increase in the density of beta adrenoceptors in cortex, limbic forebrain and striatum and prevented the down-regulation by DMI of beta adrenoceptors in cortex and limbic forebrain while the responsiveness of the NA sensitive adenylate cyclase was reduced to the same extent as in sham-lesioned control animals. The discrepancy between beta adrenoceptor number and NA responsiveness following lesions of 5HT axons was particularly profound in the striatum. The analysis of high- and low-affinity components of agonist binding demonstrated that the increase in striatal beta adrenoceptors is due to a marked increase in receptors with low affinity while the number of receptors with high affinity is unchanged. The results lend further support to the view that the synaptic availability of NA is a prerequisite for the induction of subsensitivity of the NA sensitive adenylate cyclase and for the down-regulation of its beta adrenoceptor population by DMI and that 5HT plays a pivotal role in both the regulation of the number and the function of central beta adrenoceptors.

5,7-Dihydroxytryptamine↗
PubMed1987

Central serotonin receptors: effector systems, physiological roles and regulation.

Radioligand binding studies have revealed four distinct serotonin (5HT) binding sites in rat brain that are thought to function as 5HT receptors. These include the 5HT-1a, 5HT-1b, 5HT-1c, and 5HT-2 binding sites. Studies have shown that the 5HT-2 binding site mediates a number of effects of 5HT agonists and serves as a 5HT receptor in neuronal and non-neuronal tissues. The 5HT-2 site employs phosphoinositide hydrolysis for signal transduction. The 5HT-1c binding site is also a functional receptor that is linked to phosphoinositide hydrolysis. However, the physiological role of the 5HT-1c receptor is not yet known. Lack of appropriate pharmacological tools for probing the 5HT-1a and 5HT-1b binding sites has made it difficult to definitively determine whether these binding sites are coupled to biochemical effector systems or mediate any of the physiological responses to 5HT agonists. However, there is some evidence that the 5HT-1a site is coupled to adenylate cyclase, and a number of functional roles for the 5HT-1a and 5HT-1b sites have been proposed.

Adenylyl Cyclases↗
PubMed1987

Relative efficacies of piperazines at the phosphoinositide hydrolysis-linked serotonergic (5-HT-2 and 5-HT-1c) receptors.

Serotonin (5-HT)-stimulated phosphoinositide hydrolysis is mediated by the 5-HT-2 receptor in rat cerebral cortex and by the 5-HT-1c receptor in rat choroid plexus. These systems were used to determine relative efficacies of piperazine derivatives at the 5-HT-2 and 5-HT-1c receptors. Both quipazine and 6-chloro-2-[1-piperazinyl]-pyrazine (MK-212) stimulated phosphoinositide hydrolysis in cerebral cortex, and these effects were blocked by ketanserin. The maximum responses to these agonists were 80% of the maximum response to 5-HT. m-Trifluoromethylphenylpiperazine (TFMPP), m-chlorophenylpiperazine (MCPP) and 1-(1-naphthyl)-piperazine (1-NP) did not stimulate phosphoinositide hydrolysis in cerebral cortex at concentrations that blocked the effect of 5-HT. In the choroid plexus, TFMPP and MCPP, as well as MK-212 and quipazine, increased phosphoinositide hydrolysis and mianserin blocked these effects. MK-212 had an efficacy which was equal to that of 5-HT, whereas quipazine, MCPP and TFMPP were partial agonists in the choroid plexus. 1-NP did not stimulate phosphoinositide hydrolysis in choroid plexus but completely blocked the effect 5-HT. On the basis of these data, we conclude that quipazine and MK-212 are partial agonists at 5-HT-2 receptors in cerebral cortex, whereas 1-NP, TFMPP and MCPP are pure antagonists of the cortical 5-HT-2 receptor. However, TFMPP and MCPP as well as quipazine and MK-212 are agonists at the 5-HT-1c receptor, while 1-NP is a pure antagonist of the 5-HT-1c receptor in choroid plexus.

Animals↗
PubMed1986

Biochemical characterization of serotonin stimulated phosphoinositide turnover.

Serotonin (5HT) stimulates phosphoinositide turnover in a number of tissues, but it is not known whether this effect is due to activation of a 5HT receptor which is coupled to phosphoinositide hydrolysis or if the effect is secondary to 5HT stimulated arachidonate metabolism or to the release of another neurotransmitter. In the present study we show that neither indomethacin nor BW 755C inhibits 5HT stimulated phosphoinositide hydrolysis in rat cerebral cortex, suggesting that neither cyclooxygenase nor lipoxygenase activity is required for the response to 5HT. Proteinase inhibitors do not potentiate the response to 5HT, suggesting that 5HT's effect is not due to stimulation of release of a peptide neurotransmitter. Tetrodotoxin does not inhibit the effect of 5HT and 5HT's effect is additive with that of KCl and veratrine. These data suggest that 5HT stimulated phosphoinositide hydrolysis is not dependent upon release of another neurotransmitter.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1986

Adaptive changes in the 5-HT2 binding site after chronic administration of agonists and antagonists.

This study confirms and extends an earlier report that acute administration of the serotonin (5-HT) antagonist, mianserin, caused a marked decrease in the density of 5-HT2 binding sites in brain of the rat (Blackshear and Sanders-Bush, 1982). Using [3H]ketanserin, a selective ligand for the 5-HT2 site, the present study further investigated the mechanism of this effect. The effects of mianserin in vivo and in vitro were compared with those of trifluoromethylphenylpiperazine (TFPP), a directly acting 5-HT agonist. While TFPP, unlike mianserin, was not active in single doses, it caused a 58% decrease in the density of 5-HT2 sites after repeated doses. The adaptive change induced by chronic treatment with TFPP was qualitatively and quantitatively similar to that caused by chronic administration of mianserin. Furthermore, mianserin and TFPP had similar effects in vitro; preincubation of membranes from brain induced a concentration-dependent increase in the Kd value with no change in the Bmax value. Similar adaptive changes in 5-HT2 sites after administration of mianserin, a presumed 5-HT antagonist, and after TFPP, a presumed 5-HT agonist, suggests that adaptive mechanisms in the serotonergic system are different from those in other aminergic systems or that the drugs used to characterize 5-HT receptor systems need to be re-evaluated.

Animals↗
PubMed1986

A unique serotonin receptor in choroid plexus is linked to phosphatidylinositol turnover.

A novel serotonergic binding site, the 5-HT1C site, has been characterized recently in choroid plexus and several brain regions. The biochemical and physiological roles of this site have not been previously described. In this report we show that serotonin (5-hydroxytryptamine, 5-HT) stimulates phosphatidylinositol turnover in rat choroid plexus. The pharmacology of serotonin-stimulated phosphatidylinositol hydrolysis in choroid plexus was compared to the pharmacology in cerebral cortex, where this response is mediated by the serotonin 5-HT2 receptor. Serotonin increased phosphatidylinositol turnover in choroid plexus by 6-fold and in cerebral cortex by 2.5-fold. Serotonin was greater than 10-fold more potent in choroid plexus (EC50 = 46 nM) than in cerebral cortex (EC50 = 540 nM). The serotonin antagonists ketanserin, mianserin, and spiperone inhibited the response in the two tissues with different potencies. In cerebral cortex all three exhibited nanomolar affinities consistent with their potencies at the 5-HT2 site. In choroid plexus, however, the rank order (mianserin greater than ketanserin much greater than spiperone) and absolute potencies were consistent with binding to the 5-HT1C site. These data suggest that the 5-HT1C site in choroid plexus is a functional receptor that utilizes phosphatidylinositol turnover as its biochemical effector system.

Animals↗
PubMed1986

Agonist-induced phosphoinositide hydrolysis in choroid plexus.

5-Hydroxytryptamine (5-HT, serotonin) stimulates phosphoinositide hydrolysis in choroid plexus by interacting with the 5-HTlc site. In the present study, the effects of 5-HT were compared with those of other agonists. 5-HT stimulates a rapid release of all three inositol sugars in a mianserin-sensitive manner. Inositol bisphosphate and inositol trisphosphate levels increase about twofold within 2.5 min, whereas inositol monophosphate levels are not appreciably elevated until 5 min. In contrast, glutamate, carbachol, histamine, substance P, and vasopressin, agents that increase phosphoinositide hydrolysis in other tissues, do not stimulate this response in choroid plexus. High concentrations of norepinephrine increase inositol phosphate release in choroid plexus, but this effect is apparently mediated by activation of the 5-HTlc site. The depolarizing agents KCl and veratrine also fail to stimulate phosphoinositide hydrolysis in choroid plexus. These results, combined with the finding that the phosphoinositide response to 5-HT is insensitive to tetrodotoxin, suggest that the effects of 5-HT are not secondary to neurotransmitter release. Furthermore, an indirect effect mediated via arachidonic acid metabolism is unlikely, since inhibitors of cyclooxygenase and lipoxygenase do not reduce the 5-HT response. We conclude, therefore, that phosphoinositide hydrolysis is the transducing mechanism of the 5-HT 5-HTlc receptor and that the choroid plexus will serve as a useful model system for studies of this receptor.

Animals↗
PubMed1986

Regulation of serotonin-stimulated phosphoinositide hydrolysis: relation to the serotonin 5-HT-2 binding site.

The hypothesis that serotonin (5-HT)-stimulated phosphoinositide hydrolysis is mediated by the 5-HT-2 binding site in cerebral cortex was tested by comparing antagonist Kd values determined by Schild analyses with Ki values at the 5-HT-2 binding site. A significant correlation was found between Kd values and Ki values at competing for 3H-ketanserin binding (R = 0.98), suggesting that the phosphoinositide-linked receptor and the 5-HT-2 site are identical. The 5-HT-2-mediated phosphoinositide response was then used as a measure of 5-HT-2 receptor sensitivity after in vivo treatments that alter the availability of 5-HT. Chronic treatment with the 5-HT-2 antagonist mianserin resulted in a significant decrease (52%) in the density of 5-HT-2 binding sites and a significant decrease (49%) in the maximal phosphoinositide hydrolysis response to 5-HT. Depletion of 5-HT levels with para-chlorophenylalanine or chemical denervation of serotonergic neurons with 5,7-dihydroxytryptamine had no significant effect upon 5-HT-2 receptor density or upon the phosphoinositide response to 5-HT. These data suggest that changes or lack of changes in 5-HT-2 receptor density following in vivo manipulations reflect the functional state of the receptor.

5,7-Dihydroxytryptamine↗