Decreased beta-adrenergic receptors in rat brain after chronic administration of the selective serotonin uptake inhibitor fluoxetine

Metabotropic glutamate receptors and neuroadaptation to antidepressants: imipramine-induced down-regulation of beta-adrenergic receptors in mice treated with metabotropic glutamate 2/3 receptor ligands

Antidepressant drugs have a clinical latency that correlates with the development of neuroadaptive changes, including down-regulation of beta-adrenergic receptors in different brain regions. The identification of drugs that shorten this latency will have a great impact on the treatment of major depressive disorders. We report that the time required for the antidepressant imipramine to reduce the expression of beta-adrenergic receptors in the hippocampus is reduced by a co-administration with centrally active ligands of type 2/3 metabotropic glutamate (mGlu2/3) receptors. Daily treatment of mice with imipramine alone (10 mg/kg, i.p.) reduced the expression of beta-adrenergic receptors in the hippocampus after 21 days, but not at shorter times, as assessed by western blot analysis of beta1-adrenergic receptors and by the amount of specifically bound [3H]CGP-12177, a selective beta-adrenergic receptor ligand. Down-regulation of beta-adrenergic receptors occurred at shorter times (i.e. after 14 days) when imipramine was combined with low doses (0.5 mg/kg, i.p.) of the selective mGlu2/3 receptor agonist LY379268, or with the preferential mGlu2/3 receptor antagonist LY341495 (1 mg/kg, i.p.). Higher doses of LY379268 (2 mg/kg, i.p.) were inactive. This intriguing finding suggests that neuroadaptation to imipramine--at least as assessed by changes in the expression of beta1-adrenergic receptors--is influenced by drugs that interact with mGlu2/3 receptors and stimulates further research aimed at establishing whether any of these drugs can shorten the clinical latency of classical antidepressants.

Paroxetine: a review of its pharmacology, pharmacokinetics and utility in the treatment of a variety of psychiatric disorders

Paroxetine is a selective serotonin re-uptake inhibitor (SSRI). In vitro studies show that it is able to produce a concentration-dependent competitive inhibition of serotonin uptake into brain synaptosomes. This effect can also be demonstrated following in vivo administration of the compound to animals. Paroxetine is almost completely absorbed following oral administration. However, the drug undergoes extensive first pass metabolism. As a result, less than 50% of a single dose of paroxetine reaches the general circulation. Paroxetine is primarily metabolised by the cytochrome P4502D6 isoenzyme. The compound has also been shown to inhibit the activity of this enzyme. As a result, plasma levels of compounds metabolised by the cytochrome P4502D6 isoenzyme can be increased in patients given paroxetine. Paroxetine has been extensively evaluated in clinical studies in depressed patients. The compound shows efficacy superior to placebo, and similar to that obtained with standard tricyclic or tetracyclic agents. Paroxetine also appears to be as efficacious as other SSRIs. The efficacy seen in short-term studies with paroxetine in the treatment of depression is maintained when the drug is given chronically. More recently, paroxetine has been shown to be efficacious in the treatment of panic disorder, obsessive-compulsive disorder, and social anxiety disorder. Nausea, headache and somnolence are the most common adverse events reported by patients given paroxetine. As with other selective serotonin re-uptake inhibitors, a significant percentage of men under therapy with paroxetine report abnormal ejaculation. Paroxetine is well-tolerated by elderly patients, and appears to be associated with few serious adverse events.

[Potentializing of tricyclics and serotoninergics by thyroid hormones in resistant depressive disorders]

In response to the increase of resistant depressive disorders and in spite of improved treatments, numerous studies were conducted in the last thirty Years aiming at assessing the pre-morbid thyroid state of depressed patients resistant to well conducted tricyclic treatments. "Minimal" thyroid abnormalities were evidenced as well as central thyroid disorders which may not be detected by peripheral-i.e plasmatic- dosages. Regarding the premorbid thyroid status, the hypothesis of subclinical hypothyroidism was considered by many Authors. It is marked by four grades including T3 and T4 decreased levels, basal TSH concentration abnormalities as well as increased TSH response to TRH stimulation, and the presence of antimicrosomal and antithyroglobulin antibodies. Although, there are different views on the existence or not of these abnormalities, we'll focus our attention on a metaanalysis including six studies. It shows in a population with a resistant depression, 52% of patients with subclinical hypothyroidism, against 8 to 17% in patients with simple depression and 5% in the overall population.Similarly, antithyroid antibody levels (group IV hypothyroidism) were significantly higher in depressed patients (9% to 20% against 7,5% in the overall population). For many Years, a central hypothyroidism was hypothesized on the basis of an exhausted T3-T4 transference mechanism and a lowered TRH hypothalamic biodisponibility.In the last Years, new data emerged on the role of transthyretin, a cerebral carrier T4 protein, whose concentration in the CSF was found significantly lower in depressed patients than in a control group, the lowest levels being observed in the most severely depressed. This decreased level of transthyretin would result in a lower central T4 biodisponibility-hence, in view of a T4-T3 desiodation insufficiency, a T3 deficit is observed. A low transthyretin level associated or not to subclinical hypothyroidism could be a factor of depressive vulnerability on one hand, of resistance to tricyclic treatment on the other one. Conversely, subclinical hypothyroidism could be a predictive factor of a good response to a potentializing strategy. The pharmacological mechanisms involved in this potentializing phenomenon are now well known: they consist in an interaction between depression, adrenergic receptors and thyroid hormones biodisponibility. The decreased norepinephrine level observed in depressive patients is associated, in case of increased thyroid hormones biodisponibility, with a higher sensitivity of adre-nergic receptors, mostly betaadrenergic. This seems to underly the recovery process. According to some Authors, the serotoninergic system might be involved in the potentialization of tricyclics by thyroid hormones. We know that in animals with hypothyroidism, the serotonin synthesis is decreased and that the administration of T3 increases the brain levels of serotonin and its 5HIA catabolite. In addition, T3 could correct the down-regulation induced by serotoninergics on beta-adrenergic receptors. On the basis of numerous studies carried out on the potentializing of tricyclics, we suggest practical modalities of treatment - which until today did not materialize in every day practice in the absence of a clear consensus based on statistically reliable data: after four to six weeks of inefficient tricyclic or serotoninergic treatment on a correct dosage testified by plasmatic dosages, it is recommended to initiate a T3 treatment on a effective posology (25 to 50 micrograms per day), which must be reached in 2 or 3 days, except in case of rare and transitory side effects (sweating, shaking, tachycardia, nervousness, anxiety). If the treatment is not rapidly efficient, it must be discontinued in case there is no improvement after 3 weeks. Until today, there is no consensus about the duration of a T3 treatment. It is important to take into account the predictive criteria of good or bad response to a T3 potentialization, since they have direct consequences on the management of depressed patients. For example, a high degree of chronic evolution with resistance to numerous treatments, associated disorders according to the DSM IV axis I and a comorbidity of addiction, point to a bad prognosis of a potentialization treatment. In addition, we'll examine the few recent studies on the potentializing of serotoninergic antidepressant drugs by thyroid hormones.

Extracts of St. John's wort and various constituents affect beta-adrenergic binding in rat frontal cortex

The present study was designed to get further insight into the mode of antidepressant action of extracts prepared from St. John's wort (SJW) and relevant active constituents. Down-regulation of central beta-adrenergic receptors (beta-AR's) has been widely considered a common biochemical marker of antidepressant efficacy. Although previous studies have reported a beta-AR down-regulation for SJW extracts, in vivo studies that compare the effects of SJW extracts with those of relevant active constituents on beta-AR density have not been done yet. We used quantitative radioligand receptor-binding-studies to examine in rats the effects of short-term (2 wks) and long-term (8 wks) administration of different SJW extracts and constituents on beta-AR binding in rat frontal cortex. The effects were compared to those of the standard antidepressants imipramine and fluoxetine. [125I]CYP binding to beta-AR was found to be decreased after short as well as after long-term treatment with imipramine (36%, 40%). Short-term treatment with fluoxetine decreased the number of beta-adrenergic receptors (17%) while long-term treatment with fluoxetine elicited an increase (14%) in beta-AR-binding. This effect was comparable to that of the lipophilic CO2 extract which decreased beta-AR-binding (13%) after two weeks and slightly increased the number of beta-AR's after 8 weeks (9%). Short-term treatment with the methanolic SJW extract decreased beta-AR-binding (14%), no effects for this extract were observed after 8 weeks. Treatment with hypericin led to a significant down-regulation (13%) of beta-AR's in the frontal cortex after 8-weeks, but not after 2 weeks, while hyperforin (used as trimethoxybenzoate, TMB), and hyperoside were ineffective in both treatment paradigms. Compared to the SJW extracts and single compounds the effect of imipramine on beta-AR-binding was more pronounced in both treatment paradigms.

Acute dystonic reaction in an elderly patient with mood disorder after titration of paroxetine: possible mechanisms and implications for clinical care

The administration of a serotonin reuptake inhibitor may lead to extra pyramidal signs, as reported in the literature. The risk seems to be increased in elderly people. We describe a case of acute dystonic reaction to paroxetine treatment in an elderly patient, who presented with a bipolar affective disorder. The underlying mechanism, possibly generated in the subcortical motor areas, is linked to changes that occur in the pharmacokinetic variables, the decreased neuroplasticity of ageing neurones and to previous exposure to neuroleptic medications.

Pindolol and mianserin augment the antidepressant activity of fluoxetine in hospitalized major depressed patients, including those with treatment resistance

The aims of this study were to examine whether pindolol, a serotonin (5-hydroxytryptamine [5-HT])-1A receptor antagonist, and mianserin, a 5-HT2A/C and alpha2-adrenoceptor (alpha2-AR) antagonist, may augment the clinical efficacy of fluoxetine, a selective serotonin reuptake inhibitor, and shorten the latency of onset of antidepressive activity in the treatment of major and treatment-resistant depression (TRD). Ten days after admission to the hospital, 31 major depressed patients were randomly assigned using a double-blind, controlled design to receive fluoxetine 20 mg daily, fluoxetine 20 mg daily plus pindolol 7.5 mg daily, or fluoxetine 20 mg plus mianserin 30 mg daily for 5 weeks. The 17-item Hamilton Rating Scale for Depression (HAM-D) score was the primary outcome measure. Analysis of efficacy was conducted according to the intent-to-treat analysis principle considering the change from baseline to endpoint. It was found that fluoxetine plus pindolol and fluoxetine plus mianserin were significantly more effective than fluoxetine alone. Using an outcome measure of 50% reduction in the HAM-D, a 60% response rate was found in patients treated with either fluoxetine plus pindolol or fluoxetine plus mianserin compared with a 9% response rate in patients treated with fluoxetine alone. The HAM-D score 1 week after starting fluoxetine plus mianserin decreased more than 4 points and was significantly greater than that obtained by fluoxetine alone. The results suggest that pindolol and mianserin augment the efficacy of fluoxetine in the treatment of TRD and that mianserin, but not pindolol, may significantly shorten the latency of onset of antidepressive action when combined with fluoxetine.

Mechanism of action of serotonin selective reuptake inhibitors. Serotonin receptors and pathways mediate therapeutic effects and side effects

Serotonin selective reuptake inhibitors (SSRIs) are currently among the most frequently prescribed therapeutic agents in all of medicine. Their therapeutic actions are diverse, ranging from efficacy in depression to obsessive-compulsive disorder, panic disorder, bulimia and other conditions as well. The plethora of biological substrates, receptors and pathways for serotonin are candidates to mediate not only the therapeutic actions of SSRIs, but also their side effects. Specifically, the immediate actions of SSRIs are mostly side effects, and may be mediated by the initiating actions of SSRIs, namely negative allosteric modulation of the serotonin transporter. A leading hypothesis to explain these immediate side effects is that serotonin is increased at specific serotonin receptor subtypes in discrete regions of the body where the relevant physiologic processes are regulated. Desensitization of post-synaptic receptors in these same discrete brain regions may explain the development of tolerance to these same side effects. The explanation for therapeutic effects characteristic of SSRIs may be found in delayed neurochemical adaptations. A leading hypothesis for this action is desensitization of somatodendritic serotonin 1A autoreceptors in the midbrain raphe. The hypothesis to explain why SSRIs have such diverse therapeutic actions is that somatodendritic 5HT1A autoreceptor desensitization increases serotonin in those critical brain regions and at those key serotonin receptor subtype(s) which may mediate the pathophysiologies of the various disorders. Understanding the topography of serotonin receptor subtypes in discrete anatomical pathways may enhance our understanding of both the therapeutic actions and side effects of these important pharmaceutical agents.

Validation of S-1'-[18F]fluorocarazolol for in vivo imaging and quantification of cerebral beta-adrenoceptors

S-1'-[18F]fluorocarazolol (S-(-)-4-(2-hydroxy-3-(1'-[18F]fluoroisopropyl)-aminopropoxy)carba zole, a non-subtype-selective beta-adrenoceptor antagonist) has been investigated for in vivo studies of beta-adrenoceptors. Previous results indicated that uptake of this radioligand in heart and lung can be inhibited by beta-adrenoceptor agonists and antagonists. In the present study, blocking, displacement and saturation experiments were performed in rats, in combination with metabolite analysis to investigate the suitability of this radioligand for in vivo positron emission tomography (PET) imaging and quantification of beta-adrenoceptors in the brain. The results demonstrate that, (i) the uptake of S-1'-[18F]fluorocarazolol reflects specific binding to beta-adrenoceptors, (ii) binding of S-1'-[18F]fluorocarazolol to atypical or non-beta-adrenergic sites is negligible, (iii) uptake of radioactive metabolites in the brain is less than 25% of total radioactivity, 60 min after injection, (iv) in vivo measurements of receptor densities (Bmax) in cortex, cerebellum, heart, lung and erythrocytes are within range of densities determined from in vitro assays, (v) binding of S-1'-[18F]fluorocarazolol can be displaced. In conclusion, S-1'-[18F]fluorocarazolol seems to possess the appropriate characteristics to visualize and quantify beta-adrenoceptors in vivo in the central nervous system using PET.

Behavioural effects of selective serotonin reuptake inhibitors following direct micro injection into the left red nucleus of the rat

The behavioural effects of selective serotonin reuptake inhibitors (paroxetine, sertraline, citalopram, fluvoxamine, fluoxetine) and reference compounds (N,N'-di(o-tolyl)guanidine, haloperidol, 3-(3-hydroxyphenyl)-N-(l-propyl)piperidine and chlorpromazine) were studied for their ability to produce dystonia and torticollis following direct micro injection into the left red nucleus of the rat, an area of the brain containing a high density of sigma2 receptors but relatively devoid of biogenic amine receptors. Each animal was monitored for abnormalities in posture and movement for a period of 30 min and then sacrificed 40 min following drug administation. Only fluvoxamine (100 nmol) and fluoxetine (100 nmol) elicited acute dystonic behaviour (1-5 min). The onset of dystonia was accompanied by facial spasticity, vacuous chewing movements and grooming behaviour which reflected the extent of dystonia. The dystonic behaviour following the direct intrarubal injection of fluvoxamine and fluoxetine suggest the possible activation of sigma2 receptors while citalopram, sertraline and paroxetine were without effect. The results of this study support the role of sigma2 receptors in the regulation and control of movement and coordination and provides preliminary evidence to suggest the in vivo activity of sigma receptors by fluoxetine and fluvoxamine.

Chronic treatment with citalopram induces noradrenaline receptor hypoactivity. A microdialysis study

To investigate whether chronic citalopram administration influences the cyclic AMP (cAMP) synthesis in vivo, microdialysis was used to assess citalopram-induced alterations in extracellular concentrations of cAMP in the dorsal hippocampus of freely moving rats. Citalopram administration for 4 weeks (40 mg/kg p.o. daily) did not affect the baseline levels of cAMP but decreased the noradrenaline-induced enhancement of cAMP levels. No change in forskolin-induced enhancement of cAMP levels was observed. Citalopram in situ did not exert any effect on the cAMP levels. These data support the hypothesis that chronic administration of antidepressants alters the function of noradrenergic receptors.

SSRI differentiation: Pharmacology and pharmacokinetics

Although the acute pharmacology properties of antidepressants is predominantly due to their presynaptic action, their therapeutic activity is believed to derive from adaptive post-synaptic changes in monoaminergic neurones. The selective serotonin reuptake inhibitors (SSRIs) exhibit differences in potency at inhibiting serotonin reuptake, although the differences do not correlate with clinical posology. There are also differences in their effects on neurotransmitter receptors; paroxetine has a slight affinity for muscarinic cholinergic receptors whilst citalopram has a slight affinity for histamine-H1 receptors. These properties may be related to clinical adverse effects. The pharmacokinetic profiles of the SSRIs show many differences. Whilst fluvoxamine, paroxetine and citalopram are metabolized to inactive products, fluoxetine is metabolized to norfluoxetine which is pharmacologically active and, like its parent compound, has a long half-life. Fluvoxamine is less protein-bound than the other SSRIs and sertraline is only well absorbed when taken with food. Differences are also apparent in the suitability of individual SSRIs in special patient groups. There has been considerable speculation over the inhibition of cytochrome P450 isoenzymes which are responsible for the metabolism of SSRIs and other drugs. In clinical practice, the differences between the SSRIs in this respect are probably of limited importance. However, it is worthwhile that clinicians be made aware of possible interactions between drugs that act as inhibitors or substrates of the hepatic cytochrome P450 system.

Prozac (fluoxetine, Lilly 110140), the first selective serotonin uptake inhibitor and an antidepressant drug: twenty years since its first publication

In this review, we describe the evolutionary process involved in the discovery of the selective 5-HT uptake inhibitor, fluoxetine, and summarize some of the large body of scientific research performed on fluoxetine in the 20 years since the first publication. The historical background of the proposed involvement of 5-HT in psychiatric disorders and the activity of tricyclic antidepressants in depression is reviewed. The effects of fluoxetine in various in vitro assays and in animal studies including receptor down-regulation, neurochemical and behavioral models are summarized. In addition, the clinical effectiveness of fluoxetine in depression and obsessive compulsive disorders and its potential use in other disorders are examined.

Effect of fluoxetine on melatonin in patients with seasonal affective disorder and matched controls

BACKGROUND

The aim was to investigate the secretion profile of melatonin and seasonal affective disorder before and after treatment with fluoxetine.

METHOD

A six-week case-controlled study with repeated overnight blood sampling was conducted. Ten patients fulfilling the criteria for major depressive disorder, seasonal type, with a 29-item Hamilton Depression Rating Scale (HDRS) score of at least 20 were compared with ten age- and sex-matched healthy controls in a clinical laboratory. The effects of fluoxetine (20 mg/day) on the HDRS and melatonin concentration were measured.

RESULTS

Fluoxetine significantly reduced melatonin levels in both groups. There was no significant difference in melatonin secretion between the groups.

CONCLUSIONS

The effect of fluoxetine differs from tricyclics and fluvoxamine, both of which increase melatonin.

Recent pharmacologic advances in antidepressant therapy

The serotonergic properties of newer generation antidepressants underscore the role of 5-hydroxytryptamine (5-HT, serotonin) in both the pathophysiology and the pharmacotherapy of major depression. Clinical differences between selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs) are attributed to the greater potency and selectivity for 5-HT transporter inhibition by the SSRIs and the comparatively weak interaction of the SSRIs with nonserotonin neurotransmitter receptors. The SSRIs, monoamine oxidase inhibitors (MAOIs), and TCAs share a common adaptive regulation of noradrenergic, 5-HT, and glutamate neurotransmission, suggesting possible unifying mechanisms of action underlying their antidepressant effects. In vivo neuroimaging techniques, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT) have yielded a functional neuroanatomy of compromised neurocircuitry in major depression and promise to be invaluable in mapping the in vivo effects of future novel antidepressant drugs.

Selective serotonin reuptake inhibitors: pharmacologic profiles and potential therapeutic distinctions

OBJECTIVE

To review the respective pharmacologic profiles of the selective serotonin reuptake inhibitors (SSRIs), with particular emphasis placed on clinically relevant distinctions.

DATA SOURCES

A MEDLINE search was conducted to identify English language literature published within the last five years on the four SSRIs (fluoxetine, sertraline, paroxetine, fluvoxamine). Previous review articles were scrutinized for additional citations, and manufacturers provided a contemporary bibliography of more recent material.

STUDY SELECTION/DATA EXTRACTION

Studies were selected for specific citation on the basis of comparative research merit and the contribution of this original literature to the pharmacologic profile(s) described.

DATA SYNTHESIS

All SSRIs appear to be more efficacious than placebo for the acute treatment of major depressive disorder (MDD). Short-term (six-week) efficacy was comparable with that of tricyclic antidepressants for the amelioration of MDD regarded as moderate in severity. Further comparative trials are clearly indicated to demonstrate the therapeutic benefits of SSRIs in specific populations (e.g., geriatric, severely ill) and to demonstrate sustained benefit with long-term prophylaxis. Other potential indications for SSRIs include obsessive-compulsive disorder, panic disorder, bulimia, and chronic pain syndromes. Pharmacokinetic profiles of the four SSRIs reveal similar parametric values, and most quantitative differences are of limited clinical significance. Adverse effects are common but ordinarily mild and transient, primarily restricted to the gastrointestinal tract and central nervous system. Important differences in the prevalence or severity of these adverse effects await the accumulation of further clinical experience and the completion of additional comparative trials. Similarly, the relative propensity of SSRIs to inhibit the metabolism of other medications is currently under investigation.

CONCLUSIONS

The four SSRIs studied appear to be more similar than they are different. Slowly, important distinctions are beginning to emerge with regard to adverse effect profiles and potential drug interactions. Given that the costs of these respective medications are comparable, such differences may ultimately serve to establish the preferential selection of individual agents in specific clinical situations.

Up-regulation of beta 1-adrenergic receptors in rat brain after chronic citalopram and fluoxetine treatments

Quantitative receptor autoradiography was used to study the effects of the selective serotonin reuptake inhibitors citalopram and fluoxetine and the tricyclic antidepressant imipramine on the regulation of beta 1-adrenergic receptors in the rat brain. Rats were treated with saline, citalopram (10 mg kg-1), fluoxetine (10 mg kg-1), or imipramine (15 mg kg-1) SC once daily for 14 days. [125I]Iodocyanopindolol binding to beta 1-adrenergic receptors was found to increase significantly in the caudate-putamen and the somatosensory areas of the frontal cortex after both citalopram and fluoxetine treatments. Imipramine treatment elicited a marked decrease in beta 1 binding in the outer laminae of the cingulate cortex, as well as in the motor and somatosensory areas of the frontal cortex. In a separate experiment, rats were treated with saline, citalopram (2.5, 10 and 20 mg kg-1) or fluoxetine (2.5, 10 and 20 mg kg-1) SC once daily for 14 days. The effects of citalopram and fluoxetine on beta 1 receptors in the somatosensory cortex and caudate-putamen were replicated. These results demonstrate that chronic administration of selective serotonin reuptake inhibitors, in contrast to imipramine, can cause a regional up-regulation of beta 1-adrenergic receptors in the rat brain.

Short-term fluoxetine treatment alters monoamine levels and turnover in discrete brain nuclei

The effects of short-term fluoxetine administration on monoamine levels and turnover were assessed in discrete brain nuclei. Adult male rats received fluoxetine HCl (10 mg/kg) or saline injections intraperitoneally for 4 days and monoamine levels determined by high performance liquid chromatography. The major metabolite of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), was decreased by fluoxetine treatment in the ventromedial hypothalamic nucleus (VMN), the lateral hypothalamic area and the CA1 region of the hippocampus. Fluoxetine treatment significantly increased serotonin (5-HT) levels in the VMN but did not change 5-HT levels in any other area examined. Norepinephrine (NE) levels were higher in fluoxetine-treated rats in the dorsomedial hypothalamic nucleus, dorsal raphe nucleus and parietal motor cortex (MCTX). 5-HT and NE turnover were also determined by the pargyline method. Fluoxetine treatment decreased 5-HT turnover in the VMN and increased 5-HT turnover in the median raphe. NE turnover was decreased in the preoptic area, the MCTX and parietal sensory cortex by fluoxetine administration. These results demonstrate that brain areas with similar 5-HT innervation respond differently to fluoxetine administration and fluoxetine, which selectively alters 5-HT uptake, also affects NE levels and turnover in several brain nuclei.

5-Hydroxytryptamine2 and beta-adrenergic receptor regulation in rat brain following chronic treatment with desipramine and fluoxetine alone and in combination

A chronic (14-day) study was initiated to investigate the effects of combined fluoxetine (FLU) and desipramine (DMI) treatment on the densities and affinities of beta-adrenergic and 5-hydroxytryptamine2 (5-HT2) receptors. Male Sprague-Dawley rats were administered the following doses using osmotic minipumps: FLU, 10 mg/kg/day; DMI, 5, 10, or 15 mg/kg/day; FLU, 10 mg/kg/day, plus DMI, 5 mg/kg/day; or vehicle (distilled water). After 14 days the cortex was dissected out and used for [3H]-ketanserin (5-HT2) binding, [3H]CGP-12177 (beta-adrenergic) binding, and drug level analysis. All animals receiving DMI showed significant down-regulation of 5-HT2 receptors except those receiving FLU in combination. DMI down-regulated beta-adrenergic receptors in a dose-dependent manner, with significantly greater down-regulation seen with the combination than with DMI (5 mg/kg/day) alone. This latter effect was apparently the result of greater levels of DMI in cortex with the combination than with DMI (5 mg/kg/day) alone. FLU had no effect on 5-HT2 or beta-adrenergic receptors on its own. Coadministration of FLU and DMI resulted in a doubling of levels of FLU and its demethylated metabolite, norfluoxetine (NFLU), and a tripling of DMI levels compared with values observed when FLU (10 mg/kg/day) or DMI (5 mg/kg/day) was administered alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical pharmacokinetics of fluoxetine

Fluoxetine is well absorbed after oral intake, is highly protein bound, and has a large volume of distribution. The elimination half-life of fluoxetine is about 1 to 4 days, while that of its metabolite norfluoxetine ranges from 7 to 15 days. Fluoxetine has a nonlinear pharmacokinetic profile. Therefore, the drug should be used with caution in patients with a reduced metabolic capability (i.e. hepatic dysfunction). In contrast with its effect on the pharmacokinetics of other antidepressants, age does not affect fluoxetine pharmacokinetics. This finding together with the better tolerability profile of fluoxetine (compared with tricyclic antidepressants) makes this drug particularly suitable for use in elderly patients with depression. Furthermore, the pharmacokinetics of fluoxetine are not affected by either obesity or renal impairment. On the basis of results of plasma concentration-clinical response relationship studies, there appears to be a therapeutic window for fluoxetine. Concentrations of fluoxetine plus norfluoxetine above 500 micrograms/L appear to be associated with a poorer clinical response than lower concentrations. Fluoxetine interacts with some other drugs. Concomitant administration of fluoxetine increased the blood concentrations of antipsychotics or antidepressants. The interactions between fluoxetine and lithium, tryptophan and monoamine oxidase inhibitors, in particular, are potentially serious, and can lead to the 'serotonergic syndrome'. This is because of synergistic pharmacodynamic effects and the influence of fluoxetine on the bioavailability of these compounds.

Beta-adrenergic receptor binding in frontal cortex from suicide victims

Beta-adrenergic binding in frontal cortex samples from suicide victims has been reported to be increased, unaltered, and decreased compared to matched controls. Subject's diagnoses and drug exposures in these studies were not equivalently documented and were possibly different. In the present study, diagnostic and symptomatic information was systematically collected from family members of 15 subjects committing suicide and 15 matched controls using standardized interview techniques. The goal was to test the hypothesis that alterations in beta-adrenergic binding were more likely to be found in subjects with evidence of depressive disorders. [125I]pindolol binding in frontal cortex was found to be significantly lower in the group committing suicide compared to the matched controls (21.1 +/- 1.1 fmol/mg protein vs. 24.8 +/- 0.8 fmol/mg protein, p < .02). However, no diagnostic subgroup among the suicide victims appeared distinct.

Actions of lithium on the cyclic AMP signalling system in various regions of the brain--possible relations to its psychotropic actions. A study on the adenylate cyclase in rat cerebral cortex, corpus striatum and hippocampus

It has been estimated that in most industrialized countries 1 person out of every 1000 in the population is undergoing lithium treatment to stabilize their episodic mood disturbances due to manic-depressive illness. Lithium may stabilize mood swings by altering the action of certain neurotransmitters at the synaptic level in the brain. Recent research suggests that lithium alters neurotransmission by affecting neurotransmitter-coupled second messenger systems. A major second messenger system is the adenylate cyclase, which generates intracellular cAMP from ATP. The adenylate cyclases (type I-IV) are regulated by stimulatory and inhibitory receptors, which either stimulate or inhibit the adenylate cyclase activity. The stimulatory and inhibitory neurotransmitter-receptor signals are transferred to the catalytic unit of the adenylate cyclase by Gs and Gi, respectively. The activated receptor induces GTP stimulation of the heterotrimeric G protein, leading to a dissociation of the protein into the active alpha*GTP and the beta gamma complex. The former stimulates the catalytic unit of adenylate cyclase. The stimulation is terminated by a GTPase located on the alpha subunit that converts GTP to inactive GDP. At present, G proteins are known to play a central role in coupling receptors to effector proteins. In addition to extracellular regulation due to neurotransmitters, some adenylate cyclases (type I, III) are regulated by CaM as a consequence of enhanced intracellular concentrations of free Ca2+. The Ca(2+)-dependent stimulation of adenylate cyclase by CaM is assumed to occur by a direct effect on the catalytic unit. The catalytic units sensitive to Ca(2+)-CaM are also subjected to regulation by stimulatory and inhibitory neurotransmitter stimuli. Magnesium is essential for adenylate cyclase activity, since MgATP2- is the enzyme substrate. Furthermore, one Mg2+ site located on the G protein regulates both the receptor agonist affinity and the dissociation of the G protein during the activation cycle. A second Mg2+ site on the catalytic unit is responsible for Mg2+ regulation of the catalytic activity. The present work aimed at investigating the mechanisms by which lithium in vitro and after chronic treatment (ex vivo) affects adenylate cyclase activities in various regions of the rat brain. Lithium in vitro and ex vivo inhibited the selective stimulation of adenylate cyclase by Ca(2+)-CaM in the cerebral cortex. Furthermore, lithium in vitro interacted directly with the catalytic unit of adenylate cyclase.(ABSTRACT TRUNCATED AT 400 WORDS)

Repeated administration of desipramine and a GABAB receptor antagonist, CGP 36742, discretely up-regulates GABAB receptor binding sites in rat frontal cortex

1. GABAB receptor binding site densities within laminar regions of the rat frontal cortex were examined autoradiographically following repeated administration (21 days) of the antidepressants desipramine, paroxetine and amitriptyline in addition to the GABAB receptor antagonists, CGP 35348 and CGP 36742. beta 1-Adrenoceptor autoradiography was studied in parallel with that for GABAB receptor sites. 2. The effects of these compounds were examined concomitantly on the GABAB receptor-mediated inhibition of forskolin- and enhancement of noradrenaline-stimulated cyclic AMP production. 3. GABAB receptor binding was increased by both desipramine (20 mg kg-1, p.o. and 10 mg kg-1, i.p.) and CGP 36742 (100 mg kg-1, i.p.) in the outer laminar region of the frontal cortex by around 50% above control levels. Conversely, no significant changes were mediated by paroxetine, amitriptyline, CGP 35348 or the GABAB receptor agonist, baclofen. 4. With the exception of paroxetine, all compounds down-regulated the total beta-adrenoceptor population throughout frontal cortical laminae which was attributable to the beta 1-adrenoceptor subtype. In contrast, the reduction in beta-adrenoceptors mediated by CGP 35348 and CGP 36742 did not occur as a consequence of reduced beta 1-adrenoceptor numbers. 5. Protracted treatment with CGP 35348, failed to influence forskolin-stimulated cyclic AMP production; however, a significant increase in the accumulation of cyclic AMP produced in response to forskolin was seen after treatment with CGP 36742. 6. Such discretely localized changes in GABAB receptor densities induced by desipramine and CGP 36742 may provide an explanation for the discrepancies reported in membrane binding studies and possibly implicate a role for GABAB receptor antagonists in antidepressant therapy.

Differential effects of fluoxetine on isoprenaline-stimulated water intake in ethanol-treated rats: a role for beta-adrenoceptors

We examined the effects of subchronic (4 days) administration of the 5-hydroxytryptamine (5-HT) re-uptake inhibitors, fluoxetine, fluvoxamine and zimelidine and the noradrenaline-uptake inhibitor, desipramine, on isoprenaline-induced water drinking in rats treated with ethanol. These rats demonstrated significant increases in water drinking as compared to control rats that had received only i.p. injections of distilled water (P < 0.01). Administration of fluoxetine (5-20 mg/kg daily i.p., for 4 days) dose-dependently decreased water intake as compared to that of rats treated with ethanol only. In contrast, fluvoxamine, zimelidine (10 mg/kg i.p.) and desipramine (5 mg/kg i.p.) produced no significant effects on water intake. Pretreatment of animals with spiperone, methysergide, ritanserin, zacopride and BRL 43694A, together with fluoxetine, failed to reverse the inhibitory effect of the latter on isoprenaline-stimulated water intake. The results of the present study indicate that the action of fluoxetine on isoprenaline-stimulated water drinking in ethanol-treated rats may be mediated by an action on beta-adrenoceptors.

p-chlorophenylalanine-reversible reduction of sigma binding sites by chronic imipramine treatment in rat brain

Repeated treatment with imipramine (10 mg/kg intraperitoneally (i.p.), once daily for 14 days) caused a decrease in the Bmax, without affecting the Kd, of [3H]DTG (1,3-di-o-tolylguanidine) binding to the haloperidol-sensitive sigma sites in the striatum, hippocampus and cerebral cortex of the rat. A similar reduction was observed after chronic administration of a selective serotonin uptake inhibitor, fluoxetine (10 mg/kg i.p., twice daily for 14 days), but not of a selective norepinephrine uptake inhibitor, desipramine (10 mg/kg i.p., once daily for 14 days). Neither a single injection of imipramine (10 mg/kg i.p.) nor addition of imipramine or fluoxetine into the binding assay medium mimicked the changes in the maximal binding of brain sigma sites induced by chronic treatment with these drugs. Finally, depletion of brain serotonin by means of repeated administration of p-chlorophenylalanine, which produces inhibition of the amine synthesis, blocked the ability of repeated imipramine treatment to reduce the maximal number of [3H]DTG binding sites in the striatum and hippocampus. The present results suggest that cerebral serotonergic transmission may play a role in the regulation of cerebral sigma binding sites in the rat.

A comparison of trazodone and fluoxetine: implications for a serotonergic mechanism of antidepressant action

Trazodone is an atypical antidepressant drug that is commonly referred to as a serotonin (5-hydroxytryptamine; 5-HT) uptake inhibitor. However, the most potent pharmacological effect of trazodone appears to be antagonist action at 5-HT2/1C receptors. This is in contrast to fluoxetine, for which inhibition of 5-HT uptake is the most potent pharmacological action. The effects of trazodone and fluoxetine on several antidepressant drug screens are mediated by antagonist action at 5-HT2 receptors and inhibition of 5-HT uptake, respectively. While fluoxetine is an effective agent for the treatment of major depression, obsessive-compulsive disorder (OCD) and panic disorder, trazodone does not appear to be effective in the treatment of OCD and panic disorder. In addition, trazodone and fluoxetine differ in humans with respect to their effects on sleep and weight. Taken together, the preclinical and clinical data suggest that trazodone acts as an antidepressant via antagonist action at 5-HT2/1C receptors, while fluoxetine likely acts as an antidepressant via inhibition of 5-HT uptake.

Fluoxetine: a review of receptor and functional effects and their clinical implications

Downregulation of serotonin 5-HT1 receptors is the most frequently reported central nervous system neural effect of subchronic exposure to fluoxetine in rodents. However, downregulation of these receptors has not been universally demonstrated. Effects of subchronic exposure on 5-HT2 receptors are mixed. Fluoxetine exposure appears to have no effect on cholinergic muscarinic receptors. Effects on beta-adrenergic receptors are controversial, as only one laboratory has reported downregulation. The majority of studies have failed to show an effect on beta-adrenergic-receptor-stimulated cAMP generation. Electrophysiologic studies support the concept that fluoxetine facilitates net serotonergic transmission through downregulation of presynaptic inhibitory autoreceptors. Data suggest that its subchronic specificity and selectivity distinguish fluoxetine from members of other classes of available antidepressants, making it a distinct therapeutic option.

Thyroid hormone supplementation of fluoxetine in the treatment of major depression

A patient with major depression who did not respond to treatment with fluoxetine alone responded to thyroid hormone augmentation of fluoxetine.

Refractory depression: the addition of lithium to fluoxetine or desipramine

We carried out an open clinical study with 60 consecutive patients suffering from major depression with melancholia who were resistant to anti-depressants. After at least 6 weeks of desipramine (DMI) or fluoxetine (FX) without improvement, lithium carbonate was added to the anti-depressant. Semistructured clinical interviews using the 7-point Clinical Global Impression Scale and 90-item Symptom Checklist were done at baseline and weeks 1, 6 and 14. Following the addition of lithium, more patients on FX improved within the first week than those on DMI. However, with FX, 6 relapses occurred during the 2 months of follow-up and none with DMI. The unified serotonergic and noradrenergic hypothesis for the antidepressant action could be relevant in drug-refractory depression and should be studied further.

Citalopram. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in depressive illness

Citalopram is an antidepressant belonging to a new class of drugs which enhance serotoninergic neurotransmission through potent and selective inhibition of serotonin reuptake. Preliminary trials suggest that its short term therapeutic efficacy is significantly greater than that of placebo and mianserin, and comparable to that of amitriptyline, maprotiline and imipramine. It appears to be a weaker antidepressant agent than clomipramine, but better tolerated. Its elimination half-life of 33 hours permits once daily oral administration. Symptomatic improvement obtained with short term treatment has been maintained when therapy has been extended for up to 1 year; in the few patients studied for this extended period, the relapse rate was lower than with fluvoxamine, fluoxetine or imipramine. Compared to standard antidepressant agents, citalopram is well tolerated. It does not appear to be cardiotoxic, has not been associated with seizures in humans, and is relatively nonsedating. Unlike the tricyclic antidepressants, citalopram has minimal anticholinergic effects. Mild and transient nausea, with or without vomiting, is the most frequent adverse effect--occurring in 20% of patients--and increased perspiration, headache, dry mouth, tremor and insomnia are experienced by 15 to 18% of patients. Citalopram thus offers similar therapeutic efficacy and a more favourable tolerability profile than the tricyclic antidepressants. Preliminary data suggest that it may be particularly useful in patients who cannot tolerate the anticholinergic or cardiovascular side effects of tricyclic antidepressants and in those for whom sedation is not indicated.

Paroxetine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in depressive illness

Paroxetine is a potent and selective inhibitor of the neuronal reuptake of serotonin, thereby facilitating serotoninergic transmission; this action appears to account for the antidepressant activity observed with this drug. A mean terminal elimination half-life of approximately 24 hours permits once daily administration. Results of short term clinical trials have shown paroxetine to be significantly superior to placebo, and comparable to amitriptyline, clomipramine, imipramine, dothiepin and mianserin in relieving symptoms associated with major depressive disorders. Paroxetine has shown some preliminary promise in the treatment of depressive illness resistant to tricyclic antidepressant therapy but further studies are required before any conclusions can be drawn. Paroxetine in therapeutic doses has been very well tolerated, and the favourable tolerability profile of this agent appears to be its primary advantage over traditional antidepressant agents. Paroxetine causes minimal anticholinergic-type adverse effects, and unlike tricyclic antidepressants, it does not precipitate cardiovascular effects or provoke cardiac conduction disturbances. Nausea has been the most frequently reported adverse event during short term use of paroxetine, but it is generally mild and transient and subsides with continued use. With longer term use headache, sweating and constipation were the most frequently reported side effects but the incidence rate was not significantly different from that noted for comparator antidepressants. Furthermore, the frequency of withdrawal due to adverse effects is less with paroxetine than with tricyclic antidepressant agents. Overall, available data appear to indicate that while the efficacy of paroxetine is similar to that of traditional antidepressant drugs, the newer agent possesses much improved tolerability. In addition, the wide therapeutic index of paroxetine may be beneficial when treating patients with an increased risk of suicide. Thus, paroxetine clearly looks to become a valuable addition to the range of drugs currently available to treat depressive illness. Future research may help to further define the relative place of this newer agent in antidepressant therapy and determine how its overall therapeutic efficacy compares with that of other related antidepressant agents such as fluoxetine.

Effect of chronic administration of antidepressant drugs on 5-HT2-mediated behavior in the rat following noradrenergic or serotonergic denervation

Chronic (14 day) administration of several pharmacologically-distinct antidepressant drugs resulted in marked reductions in the serotonin2 (5-HT2)-mediated quipazine-induced head shake response which were accompanied by significant reductions in the density of cortical beta-adrenergic and 5-HT2 binding sites. Noradrenergic (DSP4[N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine]-induced) and serotonergic (5,7-DHT[5,7-dihydroxytryptamine]-induced) lesions either attenuated or blocked antidepressant-induced reductions in 5-HT2-mediated behavior. DSP4- and 5,7-DHT lesions did not alter the down-regulation of 5-HT2 binding sites produced by imipramine, desipramine, phenelzine or iprindole. To a large extent, the antagonism of antidepressant-induced reductions in 5-HT2-mediated behavior was coincident with the blockade of down-regulation of beta-adrenergic binding sites by both noradrenergic and serotonergic denervation. The functional interrelationship of 5-HT2 and beta-adrenergic receptors suggested by the present findings may provide insight into a common mechanism underlying the action of pharmacologically-distinct antidepressant drugs.

Effects of chronic fluoxetine treatment on behavioral and neuroendocrine responses to meta-chlorophenylpiperazine in obsessive-compulsive disorder

To investigate the effect of fluoxetine on serotonergic sensitivity in obsessive-compulsive disorder (OCD), the partial serotonin agonist metachlorophenylpiperazine (mCPP) was compared to placebo under double-blind conditions in six patients with OCD before and during treatment with fluoxetine. Readministration of oral mCPP (0.5 mg/kg) after at least 12 weeks of fluoxetine treatment did not increase obsessive-compulsive (OC) symptoms, in contrast to exacerbation of OC symptoms produced by mCPP before treatment. Chronic fluoxetine treatment resulted in a significant increase in prolactin and cortisol response to mCPP. This may be accounted for, however, by substantially increased plasma mCPP levels during fluoxetine treatment. Chronic fluoxetine treatment diminished the behavioral sensitivity to mCPP and did not diminish, but may have partially normalized, the neuroendocrine response to mCPP in patients with OCD. These adaptive homeostatic effects may reflect fluoxetine's antiobsessional mechanism.

Fluoxetine, a selective inhibitor of serotonin uptake

In summary, fluoxetine is a highly selective serotonin uptake inhibitor in vitro and in vivo. The conformation of fluoxetine, which resembles that of sertraline and other serotonin uptake inhibitors, appears to be a key feature that enables its high affinity and selective interaction with the serotonin transporter. The para-trifluoromethyl substituent, however, is also a pivotal structural element. The molecular pharmacology of fluoxetine has been well-defined, and its in vivo pharmacological effects appear to be mediated almost exclusively by serotonin uptake inhibition. Its selectivity for the serotonin transporter, lack of affinity for neurotransmitter receptors, and retention of selectivity following metabolism to norfluoxetine make fluoxetine a useful tool to explore pharmacologically induced increases in serotonin neurotransmission. Fluoxetine has found a variety of therapeutic application. Its use in treating depression has been most extensively studied, but controlled clinical studies also suggest the drug may have a role in treating obesity and bulimia. Moreover, a variety of other psychiatric disorders may be treatable with this drug. Regardless of the outcome of these clinical trials, it is apparent that fluoxetine has found a useful niche in therapy, and can be used as a probe to determine the role of serotonin in modulating human pathophysiologies.

Effects of treatment with a lithium-imipramine combination on components of adenylate cyclase in the cerebral cortex of the rat

This study was aimed at investigating the effects of treatment with a lithium-imipramine combination on the activity of adenylate cyclase in membranes from the cerebral cortex of the rat. Treatment with (1) lithium for 2 weeks, yielding a level of lithium in serum of 0.54 +/- 0.12 mmol/l, (2) imipramine for 4 weeks (10 mg/kg i.p. twice per day) and (3) a combination of the two drugs reduced isoprenaline-induced stimulation of adenylate cyclase by GTP, with a greater decrement with the combined treatment. None of the treatments exerted any effect on the activity of the enzyme stimulated by GTP alone. Lithium ex vivo inhibited the calcium (Ca2+)- and Gpp(NH)p-stimulated activity of adenylate cyclase, but imipramine ex vivo did not affect the activity of adenylate cyclase, stimulated by these activators. The lithium-imipramine treatment reduced Ca2(+)- and Gpp(NH)p-stimulated activity of adenylate cyclase, but this was not different from that observed in the lithium-treated group. In conclusion, the beta-adrenoceptor-stimulated adenylate cyclase was affected markedly by administration of lithium and imipramine together. In contrast to lithium ex vivo, imipramine ex vivo did not impair the activity of either the guanine nucleotide regulatory protein or the catalytic subunit, since no change in activity was observed in the presence of beta,gamma-imidoguanosine-5' triphosphate (Gpp(NH)p) or Ca2+. Furthermore, lithium ex vivo exerted its post-receptor effects on the adenylate cyclase, independent of imipramine. The decrement in activity of beta-adrenergic adenylate cyclase, induced by administration of the two drugs together may partly be involved in the therapeutic action of the augmentation of antidepressants by lithium in refractory depression.

[3H] sertraline binding to rat brain membranes

Tritiated sertraline, a radiolabeled form of a potent and selective inhibitor of serotonin uptake, was found to bind with high affinity to rat whole brain membranes. Characterization studies showed that [3H] sertraline binding occurred at a single site with the following parameters: KD 0.57 nM, Bmax 821 fmol/mg protein, nH 1.06. This binding was reversible; the dissociation constant calculated from kinetic measurements (KD 0.81 nM) agreed with that determined by saturation binding experiments. [3H] Sertraline binding in the presence of serotonin, paroxetine, fluoxetine or imipramine suggested competitive inhibition of binding (large increase in KD with little change in Bmax). The rank order of potency of inhibition of [3H] sertraline binding was similar to that of inhibition of serotonin uptake for known uptake inhibitors and the 1-amino-4-phenyltetralin uptake blockers. A marked decrease in ex vivo [3H] sertraline binding in the brain of rats 7 days after treatment with p-chloroamphetamine was consistent with the loss of serotonin uptake sites induced by this agent. The results of our study indicated that [3H] sertraline labels serotonin uptake sites in rat brain.

Effect of prolonged 5-hydroxytryptamine uptake inhibition by paroxetine on cortical beta 1 and beta 2-adrenoceptors in rat brain

The effects of prolonged (21 day) oral administration of the antidepressants paroxetine (0.9 to 8.9 mg/kg/day) and amitriptyline (2.7 to 27 mg/kg/day), on rat brain cortical beta 1- and beta 2-adrenoceptor numbers and affinities were investigated using [3H]-CGP 12177. Although amitriptyline, 27 mg/kg, caused a significant (p less than 0.05) 20% reduction in the number of beta 1-adrenoceptors, paroxetine, at doses up to 8.9 mg/kg p.o., did not influence binding of [3H]-CGP 12177 to cortical beta 1- or beta 2-adrenoceptors. This study with paroxetine provides further evidence that the down-regulation of central beta 1-adrenoceptors in rat brain after repeated administration is not a property of all antidepressant drugs.

Autism: review of neurochemical investigation

The neurochemistry of autism, the most well-validated childhood neuropsychiatric disorder, has been studied extensively over the past three decades. Autism is of interest neurochemically because it represents a relatively homogeneous disorder with a triad of social, communicative, and intellectual developmental disturbance. Because a sufficient animal model has been lacking and relatively few diagnosed people with autism have died, most investigation has been of peripheral fluids and tissues. The most consistent finding has been that over 25% of autistic children and adolescents are hyperserotonemic. However, after 29 years of investigation, the mechanism of hyperserotonemia has not been determined. Hyperserotonemia has been found to be familial. Elevated plasma norepinephrine has also been a replicated finding. Cerebrospinal fluid (CSF) opiate activity has been found to be elevated in two studies. Plasma cyclic adenosine monophosphate (cAMP) has been found to be elevated in autistic children. A high rate of nonsuppression after dexamethasone and blunted or delayed growth hormone response to L-dopa have been found. Abnormal cell-mediated immunity has been replicated consistently in autism. Although several pharmacological trials have been conducted and shown promise in initial open trials, only "typical" antipsychotic drugs have shown replicable chronic ameliorating effects in double-blind trials. However, chronic neurotoxicity (tardive dyskinesia) has also been revealed. Findings of morphological changes in the cerebellum have been replicated. Findings in need of replication include diminished platelet function, increased baseline CSF homovanillic acid, decreased nerve cell adhesion molecule serum fragment, blunted prolactin response to fenfluramine, amelioration of symptoms by naltrexone and bromocriptine, reduced electroretinographic (ERG) b-wave amplitude, and morphological changes in the hippocampus, amygdala, and septal nuclei. In addition to refining and replicating past findings, future directions that may be fruitful include investigation of neurochemical aspects of platelet function, of interactions between monoaminergic systems, of phosphatidylinositides, and of pharmacological response to "atypical" antipsychotic agents and relatively selective serotonin receptor subtype agonists or antagonists.

Effects of the novel antidepressant S-adenosyl-methionine on alpha 1- and beta-adrenoceptors in rat brain

alpha 1- and beta-adrenoceptors were studied ex vivo in the brains of rats receiving repeated daily treatment with the standard antidepressant imipramine or the atypical antidepressant S-adenosyl-L-methionine (SAM), which has minimal effects on monoamine reuptake or turnover. Consistent with past studies, a decrease in the density of beta receptors at three weeks and an increase in the affinity of alpha 1 receptors for the agonist phenylephrine at one week of treatment was observed with imipramine. By comparison, an increase in the density of beta receptors and a decrease in the affinity of alpha 1 receptors for phenylephrine was observed at one week of treatment with SAM. These changes were no longer apparent at three weeks of treatment. The results suggest that treatment with SAM does lead to changes in adrenergic neurotransmission, but that down regulation of beta receptors or increased agonist affinity of alpha 1 receptors may not be necessary for the production of antidepressant effects.

New perspectives on the molecular pharmacology of affective disorders

Research with antidepressants has emphasized the importance of a delayed deamplification of the linked serotonin (5HT)/norepinephrine (NE) receptor coupled adenylate cyclase system in brain. The basic phenomena of regulation of receptor number and function of the beta adrenoceptor linked adenylate cyclase system in brain are well established, with NE regulating beta adrenoceptors in the high agonist affinity conformation (linked to adenylate cyclase and down-regulated by antidepressants), and with 5HT regulating those receptors in the low agonist affinity conformation. The biochemical effector systems of NE and 5HT are discussed and it is concluded that the final common pathway of signal transduction is protein kinase mediated phosphorylation of cellular proteins. Glucocorticoid receptors are located in the perikarya of aminergic cell bodies and may exert their effects by modifying the genomic expression of the diffusely projecting stress-responsive monoamine systems. The molecular neurobiology of beta adrenoceptors, with its implication for genetic and immunologic investigations, is briefly discussed and further research on stimulus-transcription coupling and regulation of gene expression in brain is suggested as an exciting new direction in central receptor research relevant to the psychopharmacology of affective and other disorders.

Effects of long-term administration of antidepressants and neuroleptics on receptors in the central nervous system

1. A review of the effects of long-term administration of antidepressants and neuroleptics on receptors in the central nervous system is presented. 2. The effects of antidepressants on adenylate cyclase activity and on receptor binding in brain tissue are discussed. Effects on a variety of receptor types are considered. 3. The utilization of electrophysiological, behavioral, and neurochemical studies to assess receptor function after chronic antidepressant administration is discussed, as is the use of peripheral receptor estimations in clinical studies. 4. Animal studies on the actions of chronic administration of neuroleptics on pre- and postsynaptic dopamine receptors are reviewed. Effects of these drugs on dopamine receptors in humans are considered from the following perspectives: postmortem and in vivo binding studies in schizophrenia, tardive dyskinesia, and central versus peripheral receptor estimation.

Rapid down regulation of beta-adrenoceptors by co-administration of desipramine and fluoxetine

Co-administration of desipramine and fluoxetine resulted in a 27% decline in cerebral cortical beta-adrenoceptor density after four days - a time point at which neither agent alone was effective. After 14 days, desipramine- and desipramine + fluoxetine-treated rats showed decreased receptor levels, with a greater decrement seen with the combined treatment. Fluoxetine, alone, had no affect on beta-adrenoceptor density at any time point examined. These effects are attributable to central serotonergic action since they were prevented by prior treatment with p-chlorophenylalanine. Cyproheptadine, a 5-HT2 antagonist, did not block these effects. Independent administration of fluoxetine and desipramine produced approximately 20% decrement in isoproterenol-stimulated cyclic AMP accumulation after four days of treatment. Co-administration of desipramine and fluoxetine resulted in a 35% decrement in cyclic AMP accumulation which was nearly additive with that produced by either drug alone. Consequently, the combination of a norepinephrine and serotonin uptake inhibitor may be an advantageous and rapid treatment for the alleviation of certain forms of depression.

Chronic administration of sertraline, a selective serotonin uptake inhibitor, decreased the density of beta-adrenergic receptors in rat frontoparietal cortex

Sertraline, a potent and selective inhibitor of serotonin uptake, was chronically administered to laboratory rats. Using in vitro receptor autoradiographic techniques, we found that the binding of [3H]dihydroalprenolol ([3H]DHA) was reduced in cortex layers IV-VI. Results of a saturation experiment indicated that the reduction in cortex layer IV was due to a change in number but not affinity of beta-adrenergic receptors.