Reuptake Sites Research Articles

First dual NK 1 antagonists–serotonin reuptake inhibitors: synthesis and SAR of a new class of potential antidepressants

Compounds combining NK 1 antagonism and serotonin reuptake inhibition are described, and potentially represent a new generation of antidepressants. Compound 24 displays good affinities for both the NK 1 receptor and the serotonin reuptake site (32 and 25 nM, respectively).

Loss of the circadian variation of platelet [ 3H]imipramine binding in delusional compared with non-delusional endogenously depressed patients

Background: The circadian variations of the serotonin reuptake sites were studied in 16 patients meeting DSM-IV criteria for major depression with melancholia, either with ( n=8) or without ( n=8) psychotic symptomatology. Method: The [ 3H]imipramine binding sites were measured in platelet samples. Results: While no statistically significant difference was found between the morning (09:00 h) and evening (21:00 h) [ 3H]imipramine B max values in the control group, both the non-delusional and delusional melancholic patients showed higher evening than morning B max values, which were only statistically significant in the former. When both diagnostic groups were compared, the delusional patients showed significantly lower [ 3H]imipramine binding values than the non-delusional patients both in the morning and evening samples. Within the non-delusional depressed patients, those individuals with mood circadian variation, assessed by the 18th item of the HDRS, showed significantly lower B max values than those without mood variation. Lowest morning and evening B max values were noted in the delusional depressed group without mood variations. Conclusions: These results suggest that delusional depressions might have a different neurobiological substrate with loss of chronobiological rhythms.

Dose optimisation in antidepressant drug development

There are four main obstacles in achieving optimal drug doses in the development of antidepressant drugs. The first is the large placebo response. This is known to be proportional to the initial severity of the illness such that subjects with less severe depressive illnesses show the greatest placebo response. Up to 40% of depressed patients with mild illnesses will spontaneously remit over 4 weeks of placebo therapy. Treatment with an effective antidepressant produces rates of 60–70% in this population. Thus, improvement directly attributable to a pharmacological action of the drug occurs in only 20–30% of treated patients. The second difficulty is that depression is probably heterogeneous in its response to antidepressant drugs. There is reasonable evidence that depression with psychosis is poorly responsible at least to existing antidepressant drug therapies but specifically responsive to electroconvulsive therapy. Patients with bipolar affective disorder may switch into mania when treated with antidepressant drugs and some bipolar patients develop chronic depression which is very resistant to drug therapy. The third difficulty, which is not unique to antidepressant drugs, is that 4 weeks of therapy is probably insufficient to observe maximal response and improvement in depression may continue for 6–8 weeks. Improvement in other disorders such as obsessional compulsive disorder may continue well beyond 8 weeks. The fourth difficulty is that the pharmacological mechanism of action of antidepressants has some uncertainty and so it is difficult to develop in vivo surrogate markers. Modern imaging techniques offer a way forward. For example, new drugs can be investigated for their ability to displace radioligand binding to the receptor identified with antidepressant response. Positron emission tomography radioligands are being developed for monoamine reuptake sites and this could be used to optimise drug dosage with new monoamine uptake blocking antidepressants. There is a strong thrust of evidence which implicates post-synaptic 5HT1A receptor in mediating the antidepressant effects of drugs and these can already be visualised in using the radioligand WAY100635. The ability of antidepressant drugs to increase 5HT release could be detected by a displacement of WAY100635 by increased endogenous release of 5HT. Pharmaco magnetic resonance imaging is an emerging technology for dose optimisation of CNS drugs. The direct effect on neuronal metabolism in different regions of the brain can be monitored by following the local changes in blood flow. However, the technique is not yet quantitative. Another approach is to evoke regional neuronal activation using psychological tasks which engage different brain circuits or by the experimental induction of low mood itself.

The noradrenaline–dopamine interaction in the rat medial prefrontal cortex studied by multi-probe microdialysis

Multi-probe microdialysis was used to investigate the interaction between the release of noradrenaline and dopamine in the medial prefrontal cortex. Retrograde microdialysis was used to stimulate or inhibit the activity of the locus coeruleus for a restricted period of time, and the response of extracellular noradrenaline and dopamine in the ipsilateral and contralateral medial prefrontal cortex was recorded with microdialysis probes. Infusion of clonidine into the locus coeruleus (100 μM for 45 min) suppressed noradrenaline release and slightly inhibited dopamine release in the ipsilateral medial prefrontal cortex. Application of carbachol to the locus coeruleus (100 μM for 45 min) stimulated both the noradrenaline and dopamine release in the ipsilateral medial prefrontal cortex. No changes were seen in the contralateral medial prefrontal cortex. In the ipsilateral nucleus accumbens, extracellular noradrenaline levels increased, but dopamine levels remained unchanged. Application to the locus coeruleus (during 10 min) of the glutamate receptor agonists N-methyl- d-aspartate (NMDA) (300 μM) or kainate (100 μM) strongly increased extracellular noradrenaline and dopamine levels in the ipsilateral medial prefrontal cortex. However, in the contralateral probe the release of dopamine (but not of noradrenaline) was also stimulated. Application of carbachol to the locus coeruleus was used as a model to further investigate the presumed noradrenaline–dopamine interaction. In a series of dual-probe experiments, α 1-, α 2-, and β-adrenoceptor antagonists (prazosin, idazoxan, propranolol) or a reuptake-inhibitor (nomifensine) was administered during carbachol stimulation of the locus coeruleus. Prazosin and propranolol were administered systemically in a dose of 3 mg/kg, whereas idazoxan (10 μM) and nomifensine (100 μM) were infused into the medial prefrontal cortex. However, none of these pretreatments modified the effects of the control carbachol-infusions. The results did not identify a receptor-interaction or a common reuptake site that explained the presumed interaction between dopamine and noradrenaline in the medial prefrontal cortex. Therefore, the noradrenaline–dopamine interaction hypothesis could not be confirmed or refuted.

No change in striatal dopamine re-uptake site density in psychotropic drug naive and in currently treated Tourette’s disorder patients: a [ 123I]-β-CIT SPECT-study

Background: There is evidence that Tourette’s disorder (TD) is associated with abnormalities in the dopaminergic system involving the dopamine transporter (DAT). Data from [ 123I]-β-CIT single photon emission computed tomography (SPECT) studies and postmortem findings concerning DAT densities in TD patients are not conclusive. The objective of our study was to measure DAT densities with [ 123I]-β-CIT binding in TD patients who were either psychotropic drug naive or currently treated with antipsychotics (AP) and healthy controls. Method: Altogether 20 TD patients were investigated. A total of 15 patients were psychotropic drug naive and five were currently treated with AP. Ten psychotropic drug naive patients were compared with ten age and sex matched healthy subjects. Five currently treated patients were compared with five age and sex matched psychotropic drug naive TD patients. The investigation was carried out using [ 123I]-β-CIT (2-β-carbomethoxy-3-β(4-iodophenyl)-tropane and SPECT. Regions of interest (ROI) were drawn over the striatum and the cerebellum. Results: The DAT densities measured by the striatal/cerebellar (S/C) binding ratio did not differ between drug naive TD patients and the controls. The difference between currently AP treated and psychotropic drug naive TD patients did not reach the level of significance. There was no correlation between the ratio and severity of tics and illness. Conclusion: Our study with psychotropic drug naive TD patients contributed to clarify the inconsistent results concerning the DAT.

Venlafaxine occupation at the noradrenaline reuptake site: in-vivo determination in healthy volunteers.

Venlafaxine, a serotonin and noradrenaline reuptake inhibitor, is an effective antidepressant at doses of 75 mg p.o. daily and above. Preclinical and healthy volunteer studies have demonstrated that venlafaxine is more potent at the serotonin than at the noradrenaline reuptake site, with noradrenergic blocking effects being observed at doses >75 mg p.o. in man. We used the Multiple Organs Coincidences Counter and [11C] meta hydroxy ephedrine (MHED) to test whether significant occupation of cardiac sympathetic neurones was achieved in man in vivo after the acute administration of venlafaxine 75 mg p.o. in nine healthy volunteers. MHED is a tracer which binds at the noradrenaline reuptake site. This study demonstrates that the [11C]MHED signal is significantly reduced after the administration of venlafaxine 75 mg p.o. thus showing that noradrenaline reuptake blockade is observable at this dose. This effect is predominantly seen in volunteers who received > 1 mg/kg venlafaxine.

Project title: IPT—Imaging DA reuptake sites during cocaine withdrawal

Project title: IPT—Imaging DA reuptake sites during cocaine withdrawal

Functional Brain Receptor Imaging with Positron Emission Tomography

A new cocaine derivative for imaging the dopamine transporter has been developed. Measurements of radioligand binding of 11C-(+)-McN-5652 in vivo with PET suggests that ecstasy interacts directly with the serotonin reuptake sites and that a single oral dose of ecstasy (1.5 mg/kg) does not cause any changes in the serotonin transporter density in the human brain. Finally, a number of epibatidine derivatives have been developed as ligands to study the central nAChRs in vivo, however, toxicity studies prevented further clinical use.

Effects of Fluvoxamine Treatment on the in Vivo Binding of [F-18]FESP in Drug Naive Depressed Patients: A Pet Study

Thisstudy investigates the effect of chronic treatment with Fluvoxamine, a potent and specific serotonin reuptake sites inhibitor (SSRI), on 5HT2 serotonin and D2 dopamine receptors in the brain of drug naive unipolar depressed patients. Drug effect was evaluated in different cortical areas and in the basal ganglia by positron emission tomography (PET) and fluoro-ethyl-spiperone ([18F]FESP), an high affinity 5HT2 serotonin and D2 dopamine receptors antagonist. Patients underwent a PET study at recruitment and after clinical response to Fluvoxamine treatment. Nine of the 15 patients recruited completed the study. Fluvoxamine treatment significantly improved clinical symptoms and modified [18F]FESP binding in the frontal and occipital cortex of all of the nine patients who completed the study; in these regions a mean 31% increase in the in vivo [18F]FESP binding was found (P < 0.01). On the contrary, no significant changes in the in vivo [18F]FESP binding were found in the basal ganglia where [18F]FESP binds mainly to D2 dopamine receptors. Chronic treatment with Fluvoxamine significantly increases the in vivo binding of [18F]FESP in the frontal and occipital cortex of drug naive unipolar depressed patients. The increase of the in vivo binding of [18F]FESP may reflect a modification in 5HT2 binding capacity secondary to changes in cortical serotonin activity.

Imaging the serotonin transporter with positron emission tomography: initial human studies with [11C]DAPP and [11C]DASB.

Two novel radioligands, N,N-dimethyl-2-(2-amino-4-methoxyphenylthio) b enzylamine (DAPP) and (N,N-dimethyl-2-(2-amino-4-cyanophenylthio) benzylamine (D ASB), were radiolabeled with carbon-11 and evaluated as in vivo probes of the serotonin transporter (SERT) using positron emission tomography (PET). Both compounds are highly selective, with nanomolar affinity for the serotonin transporter and micromolar affinity for the dopamine and norepinephrine transporters. Six volunteers were imaged twice, once with each of the two radioligands. Both ligands displayed very good brain penetration and selective retention in regions rich in serotonin reuptake sites. Both had similar brain uptake and kinetics, but the cyano analogue, [11C]DASB, had a slightly higher brain penetration in all subjects. Plasma analysis revealed that both radiotracers were rapidly metabolized to give mainly hydrophilic species as determined by reverse-phase high-performance liquid chromatography. Inhibition of specific binding to the SERT was demonstrated in three additional subjects imaged with [11C]DASB following an oral dose of the selective serotonin reuptake blocker citalopram. These preliminary studies indicate that both these substituted phenylthiobenzylamines have highly suitable characteristics for probing the serotonin reuptake system with PET in humans.

Sibutramine does not decrease the number of 5-HT re-uptake sites in rat brain and, like fluoxetine, protects against the deficits produced by dexfenfluramine

The effect of sibutramine and dexfenfluramine on 5-HT re-uptake sites, labelled with [ 3H]paroxetine, have been determined in various rat brain regions. In addition, the ability of fluoxetine and sibutramine to protect against the changes in [ 3H]paroxetine binding produced by dexfenfluramine was examined. Sibutramine (9 mg/kg, p.o.) and dexfenfluramine (1, 3 and 10 mg/kg, p.o.) were administered twice daily (before 09.00 h and after 16.00 h) for four days, followed by a 14 day drug-free period. In the protection studies, fluoxetine (10 mg/kg, i.p.) and sibutramine (9 mg/kg, p.o.) were given 1 h prior to dexfenfluramine (10 mg/kg, p.o.) using the same dosing regimen as described above. Sibutramine (9 mg/kg, p.o.; three times its ED 50 to inhibit food intake at 2 h) had no significant effect on the number or affinity of 5-HT re-uptake sites the brain regions studied. In contrast, dexfenfluramine at an equivalent dose (3 mg/kg, p.o.) significantly decreased the number of 5-HT re-uptake sites in frontal cortex (by 35%), hippocampus (by 47%) and hypothalamus (by 27%). This effect was dose-dependent with marked decreases (by 58–84%) in the number of sites following 10 mg/kg, p.o. These effects were not associated with changes in binding affinity. Fluoxetine (10 mg/kg, i.p.) completely blocked the effect of dexfenfluramine (10 mg/kg, p.o.) without having any significant effect alone. Sibutramine (9 mg/kg, p.o.) also blocked the effects of dexfenfluramine, although the reversal was only partial in frontal cortex, hippocampus and hypothalamus. Thus sibutramine, unlike dexfenfluramine, does not alter brain 5-HT re-uptake sites. Furthermore, sibutramine and fluoxetine protect against the deficits in 5-HT re-uptake sites produced by dexfenfluramine. These data provide further evidence that sibutramine is a 5-HT re-uptake inhibitor and it does not have neurotoxic potential.

Dopamine transporter binding in Gilles de la Tourette syndrome.

Preliminary studies in patients with Gilles de la Tourette syndrome (TS) provided evidence of presynaptic dopaminergic dysfunction, demonstrating increased reuptake sites. Therefore we investigated striatal dopamine transporter binding in 12 TS patients and 9 control subjects using single photon emission computed tomography and 123I-labeled 2beta-carbomethoxy-3beta-(4-iodophenyl)tropane. In TS patients we found significantly higher relative striatal activity ratios (mean +/- SD 12.33 +/- 3.58) than in controls (9.36 +/- 1.35, P< 0.05). Only five patients, however, showed striatum/occipital cortex ratios more than 2 SD above the normal means. Seven patients had activity ratios within the average ratio of the control group plus 2 SD. Regarding the relationship between clinical parameters and striatum/occipital cortex ratios, we found an association between binding ratios and "self-injurious behavior" and "lack of impulse control." This study corroborates previous data suggesting an involvement of the dopaminergic system in TS pathology. Our results demonstrate that an increase in dopamine transporter capacity is a possible but not a necessary alteration, and which appears more likely when self-injurious behavior and lack of impulse control are associated.

Reboxetine: a pharmacologically potent, selective, and specific norepinephrine reuptake inhibitor

Background: Reboxetine is a potent antidepressant, with efficacy comparable to that of imipramine, desipramine, and fluoxetine, and has improved side-effect profile. The basis of its efficacy and improved tolerability is sought through studies of reboxetine in a number of pharmacological models of depression. Methods: Pharmacological selectivity for uptake systems was defined by uptake and binding assays for the three monoamine uptake sites. Specificity was determined in 39 different receptor and 6 enzyme assays. In vivo selectivity was defined by measurement of neuronal firing rates in the locus coeruleus, dorsal raphe, and substantia nigra. Reserpine-induced blepharospasm and hypothermia, clonidine-induced hypothermia, defined reboxetine’s in vivo pharmacology. Reboxetine’s antidepressant potential was evaluated behaviorally by the tail-suspension test, forced swimming, and the DRL 72 operant responding test. Results: Reboxetine is a potent, selective, and specific norepinephrine reuptake inhibitor (selective NRI) as determined by both in vitro and in vivo measurements. Unlike desipramine or imipramine, reboxetine has weak affinity (Ki > 1000 nmol/L) for muscarinic, histaminergic H1, adrenergic α 1, and dopaminergic D 2 receptors. In vivo action of reboxetine is entirely consistent with the pharmacological action of an antidepressant with preferential action at the norepinephrine reuptake site. Reboxetine showed an antidepressant profile in all tests of antidepressant activity used. Significant decreases in immobility were observed in the tail suspension test and behavioral despair test. Increased efficiency in responding was observed in the DRL 72 test. Conclusions: Reboxetine is a potent, selective, and specific noradrenergic reuptake inhibitor. It has a superior pharmacological selectivity to existing tricyclic antidepressants and selective serotonin reuptake inhibitors when tested in a large number of in vitro and in vivo systems. Given the pharmacological profile, reboxetine is expected to be a selective and potent tool for psychopharmacological research. The use of reboxetine in the clinic will also help clarify the role norepinephrine plays in depression.

Desipramine binding to noradrenaline reuptake sites in cardiac sympathetic neurons in man in vivo

Noradrenergic reuptake blockade is a recognised mechanism of antidepressant action, but the extent of the blockade necessary for therapeutic effect is not known and plasma levels do not provide a guide to therapy. We report a method to assess noradrenaline reuptake blockade in vivo in man using [ 11C] meta-hydroxyephedrine and the multiple organs' coincidences counter. Eight healthy volunteers had two scans, one with tracer alone and one after preloading with desipramine 50–75 mg p.o. In all subjects, there was an increased washout rate of the radioligand from the heart following preloading ( t=4.38; P<0.003) as well as a decrease of the area under the [ 11C] meta-hydroxyephedrine time activity curve ( t=7.4; P=0.001). In one subject who had three doses of desipramine, the increase in washout rate was dose-dependent. In conclusion, [ 11C] meta-hydroxyephedrine in the multiple organs' coincidences counter gives a valid, low radiation method to assess noradrenergic reuptake blockade in the clinic.

Evaluation of [O-methyl- 11C]fluvoxamine as a tracer for serotonin re-uptake sites

We evaluated [ 11C]fluvoxamine as a tracer for the serotonin re-uptake site. Studies of the distribution of the tracer in rat and primate brain showed adequate uptake of [ 11C]fluvoxamine, but failed to reveal regions with known high density of serotoninergic re-uptake sites. Pretreatment with unlabeled fluvoxamine did not substantially change the distribution. In rat brain tissue, nearly all radioactivity represented intact [ 11C]fluvoxamine. [ 11C]Fluvoxamine does not function as a tracer for serotonin re-uptake sites, owing to high nonspecific binding in the brain.

Aging regulates 5-HT 1B receptors and serotonin reuptake sites in the SCN

Middle age is associated with changes in circadian rhythms (e.g., alterations in the timing of the circadian wheel running rhythm) which resemble changes induced by selective destruction of the serotonergic input to the suprachiasmatic nucleus (SCN), the principal mammalian circadian pacemaker. We hypothesized that serotonergic neurotransmission in the SCN is decreased in middle-aged hamsters, as compared to young adults. This hypothesis was tested indirectly by investigating the effect of aging on two markers of serotonin neurotransmission, 5-HT 1B receptors and serotonin reuptake sites, which are regulated by serotonin. Previous studies have shown that experimentally induced decreases in serotonergic neurotransmission increase 5-HT 1B receptors but decrease serotonin reuptake sites. Quantitative autoradiography was conducted using [ 125 I ]iodocyanopindolol ([ 125 I ]ICYP) and [ 3 H ]paroxetine, selective radioligands for the 5-HT 1B receptors and the serotonin reuptake sites, respectively. Consistent with the hypothesis, specific ([ 125 I ]ICYP binding was significantly elevated in the SCN of middle-aged hamsters, as compared to young hamsters. The results also showed that serotonin reuptake sites in the SCN were significantly increased in both middle-aged and old hamsters, as compared to young controls. This result could not have been caused by decreased serotonin release. Alternatively, increased serotonin reuptake, which would reduce serotonin levels in the synaptic cleft, may cause or contribute to the increase in 5-HT 1B receptor binding in the SCN in middle aged animals. These results show that the SCN exhibits changes in serotonergic function during middle age, which has been characterized by changes in the expression of circadian rhythms. Because these changes occur during middle age, they probably reflect the aging process, rather than senescence or disease.

Introduction

Introduction

Autoradiographic study of striatal dopamine re-uptake sites and dopamine D 1 and D 2 receptors in a 6-hydroxydopamine and quinolinic acid double-lesion rat model of striatonigral degeneration (multiple system atrophy) and effects of embryonic ventral mesencephalic, striatal or co-grafts

The influence of embryonic mesencephalic, striatal and mesencephalic/striatal co-grafts on amphetamine- and apomorphine-induced rotation behaviour was assessed in a rat model of multiple system atrophy/striatonigral degeneration type using dopamine D 1 ([ 3H]SCH23390) and D 2 ([ 3H]spiperone) receptor and dopamine re-uptake ([ 3H]mazindol) autoradiography. Male Wistar rats subjected to a sequential unilateral 6-hydroxydopamine lesion of the medial forebrain bundle followed by a quinolinic acid lesion of the ipsilateral striatum were divided into four treatment groups, receiving either mesencephalic, striatal, mesencephalic/striatal co-grafts or sham grafts. Amphetamine- and apomorphine-induced rotation behaviour was recorded prior to and up to 10 weeks following transplantation. 6-Hydroxydopamine-lesioned animals showed ipsiversive amphetamine-induced and contraversive apomorphine-induced rotation behaviour. Amphetamine-induced rotation rates persisted after the subsequent quinolinic acid lesion, whereas rotation induced by apomorphine was decreased. In 11 of 14 animals receiving mesencephalic or mesencephalic/striatal co-grafts, amphetamine-induced rotation scores were decreased by >50% at the 10-week post-grafting time-point. In contrast, only one of 12 animals receiving non-mesencephalic (striatal or sham) grafts exhibited diminished rotation rates at this time-point. Apomorphine-induced rotation rates were significantly increased following transplantation of mesencephalic, striatal or sham grafts. The largest increase of apomorphine-induced rotation rates approaching post-6-hydroxydopamine levels were observed in animals with striatal grafts. In contrast, in the co-graft group, there was no significant increase of apomorphine-induced rotation compared to the post-quinolinic acid time-point. Morphometric analysis revealed a 63–74% reduction of striatal surface areas across the treatment groups. Striatal [ 3H]mazindol binding on the lesioned side (excluding the demarcated graft area) revealed a marked loss of dopamine re-uptake sites across all treatment groups, indicating missing graft-induced dopaminergic re-innervation of the host. In eight (73%) of the 11 animals with mesencephalic grafts and reduced amphetamine-induced circling, discrete areas of [ 3H]mazindol binding (“hot spots”) were observed, indicating graft survival. Dopamine D 1 and D 2 receptor binding was preserved in the remaining lesioned striatum irrespective of treatment assignment, except for a significant reduction of D 2 receptor binding in animals receiving mesencephalic grafts. “Hot spots” of dopamine D 1 and D 2 receptor binding were observed in 10 (83%) and nine (75%) of 12 animals receiving striatal grafts or co-grafts, consistent with survival of embryonic primordial striatum grafted into a severely denervated and lesioned striatum. Our study confirms that functional improvement may be obtained from embryonic neuronal grafts in a double-lesion rat model of multiple system atrophy/striatonigral degeneration type. Co-grafts appear to be required for reversal of both amphetamine- and apomorphine-induced rotation behaviour in this model. We propose that the partial reversal of amphetamine-induced rotation asymmetry in double-lesioned rats receiving mesencephalic or mesencephalic/striatal co-grafts reflects non-synaptic graft-derived dopamine release. The changes of apomorphine-induced rotation following transplantation are likely to reflect a complex interaction of graft- and host-derived striatal projection pathways and basal ganglia output nuclei. Further studies in a larger number of animals are required to determine whether morphological parameters and behavioural improvement in the neurotransplantation multiple system atrophy rat model correlate.

5-HT1A and 5-HT1B receptors control the firing of serotoninergic neurons in the dorsal raphe nucleus of the mouse: studies in 5-HT1B knock-out mice.

The characteristics of the spontaneous firing of serotoninergic neurons in the dorsal raphe nucleus and its control by serotonin (5-hydroxytryptamine, 5-HT) receptors were investigated in wild-type and 5-HT1B knock-out (5-HT1B-/-) mice of the 129/Sv strain, anaesthetized with chloral hydrate. In both groups of mice, 5-HT neurons exhibited a regular activity with an identical firing rate of 0.5-4.5 spikes/s. Intravenous administration of the 5-HT reuptake inhibitor citalopram or the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) induced a dose-dependent inhibition of 5-HT neuronal firing which could be reversed by the selective 5-HT1A antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohe xane carboxamide (WAY 100635). Both strains were equally sensitive to 8-OH-DPAT (ED50 approximately 6.3 microgram/kg i.v.), but the mutants were less sensitive than wild-type animals to citalopram (ED50 = 0.49 +/- 0.02 and 0.28 +/- 0.01 mg/kg i.v., respectively, P < 0.05). This difference could be reduced by pre-treatment of wild-type mice with the 5-HT1B/1D antagonist 2'-methyl-4'-(5-methyl-[1,2,4]oxadiazol-3-yl)-biphenyl-4-carbox yli c acid [4-methoxy-3-(4-methyl-piperazine-1-yl)-phenyl]amide (GR 127935), and might be accounted for by the lack of 5-HT1B receptors and a higher density of 5-HT reuptake sites (specifically labelled by [3H]citalopram) in 5-HT1B-/- mice. In wild-type but not 5-HT1B-/- mice, the 5-HT1B agonists 3-(1,2,5, 6-tetrahydro-4-pyridyl)-5-propoxypyrrolo[3,2-b]pyridine (CP 94253, 3 mg/kg i.v.) and 5-methoxy-3-(1,2,3, 6-tetrahydropyridin-4-yl)-1H-indole (RU 24969, 0.6 mg/kg i.v.) increased the firing rate of 5-HT neurons (+22.4 +/- 2.8% and +13.7 +/- 6.0%, respectively, P < 0.05), and this effect could be prevented by the 5-HT1B antagonist GR 127935 (1 mg/kg i.v.). Altogether, these data indicate that in the mouse, the firing of 5-HT neurons in the dorsal raphe nucleus is under both an inhibitory control through 5-HT1A receptors and an excitatory influence through 5-HT1B receptors.

In utero ethanol exposure decreased the density of serotonin neurons. Maternal ipsapirone treatment exerted a protective effect

Prior studies from this laboratory showed that in utero ethanol exposure severely retards the development of the serotonin (5-HT) system; we demonstrated a reduced concentration of 5-HT and 5-HT reuptake sites and alterations in the concentration of 5-HT 1A receptors in ethanol-exposed offspring. These investigations also found that maternal treatment with a 5-HT 1A agonist, buspirone, prevented most of the ethanol-associated damage to the developing 5-HT system. In the present investigation, we investigated whether the ethanol-associated changes in the 5-HT system are due to a reduction of 5-HT neurons and whether any changes in the density of 5-HT neurons can be prevented by maternal treatment with another 5-HT 1A agonist, ipsapirone. Using immunocytochemistry, we found that in utero ethanol exposure reduced the density of 5-HT immunopositive neurons in the dorsal raphe, median raphe and B9 neurons of postnatal day 5 (PN5) rats. In all three brain areas, the offspring of ethanol-fed, saline-treated dams exhibited a 28%–40% reduction in 5-HT neurons. Ipsapirone prevented the ethanol-induced reduction in 5-HT immunopositive neurons in the dorsal raphe, median raphe and B9 neurons. In the dorsal and median raphe of control offspring, ipsapirone did not alter the concentration of 5-HT neurons. However, this drug did reduce 5-HT neurons in the B9 region of the offspring of control-fed rats.