Chronic antidepressant therapy and associated changes in central monoaminergic receptor functioning

The effects of selective serotonin reuptake inhibitors on memory functioning in older adults: A systematic literature review

INTRODUCTION

Selective serotonin reuptake inhibitors (SSRIs) are commonly prescribed to older adults. In contrast to young subjects, it is unclear whether older adults may be vulnerable to cognitive side effects. Serotonin is involved in cognitive functions (e.g. memory). It is of great importance to examine the effects of SSRIs on memory functioning in older adults.

OBJECTIVES

The objective of this systematic literature review is to summarize studies in which the effects of SSRI treatment on all aspects of memory functioning in older adults are investigated.

METHODS

PubMed, PsycINFO, CINAHL, and Embase were searched for all studies published until 18th of October 2021. Articles were included if they fulfilled the inclusion criteria as follows: (1) study design is (randomized) controlled trial, cross-sectional, or prospective cohort study; (2) study population consists of older adults (mean age ⩾65 years), or results for this age-group are reported separately; (3) intervention is use of an SSRI; and (4) effects on performance of any memory domain are measured and clearly described.

RESULTS

The search yielded 1888 articles, of which 136 were included for the full-text review. Eventually, 40 articles were included. Most studies reported no association between SSRI use and memory functioning. The studies that found a positive association mainly investigated older adults with mental or neurological disorders (e.g. depression or stroke). A few studies found a negative association in the following subgroups: non-responders (depression), patients with frontal brain disease, and women.

CONCLUSION

Overall, no consistent negative effects of SSRIs on memory functioning in older adults were found after SSRI treatment. Most studies reported no change in memory functioning after SSRI use. Some studies even showed an improvement in memory performance. Positive effects of SSRIs on memory functioning were especially found in older adults with mental or neurological disorders, such as subjects with depression or stroke.

Time of Administration of Acute or Chronic Doses of Imipramine Affects its Antidepressant Action in Rats

The pathogenesis and therapeutics of depression are linked to the operation of the circadian system. Here, we studied the chronopharmacological action of a tricyclic antidepressant, imipramine. Male adult Wistar–Hannover rats were administered imipramine acutely or chronically in the morning or in the evening. The antidepressant action of imipramine was analyzed using the forced swim test (FST). A single dose of imipramine (30 mg/kg) in the morning, but not in the evening, reduced immobility and increased climbing in the FST. The plasma concentrations of imipramine and its metabolite, desipramine, were slightly higher in the morning than in the evening, which might explain the dosing time-dependent action of imipramine. Next, we analyzed the effect of chronic imipramine treatment. Rats received imipramine in the morning or in the evening for 2 weeks. The morning treatment resulted in larger effects in the FST than the evening treatment, and was effective at a dose that was ineffective when administered acutely. The levels of brain α-adrenergic receptors tended to decrease after chronic imipramine treatment. Imipramine might interact with noradrenergic neurons, and this interaction might chronically alter receptor expression. This alteration seemed greater in the morning than in the evening, which might explain the dosing time-dependent action of imipramine.

How do antidepressants work? New perspectives for refining future treatment approaches

Most currently available antidepressants target monoamine neurotransmitter function. However, a purely neurotransmitter-based explanation for antidepressant drug action is challenged by the delayed clinical onset of most agents and the need to explain how neurochemical changes reverse the many different symptoms of depression. Novel approaches to understanding of antidepressant drug action include a focus on early changes in emotional and social processing and the role of neural plasticity. In this Review, we discuss the ways in which these two different theories reflect different or complementary approaches, and how they might be integrated to offer novel solutions for people with depression. We consider the predictions made by these mechanistic approaches for the stratification and development of new therapeutics for depression, and the next steps that need to be made to facilitate this translation of science to the clinic.

Circuits Regulating Pleasure and Happiness-Mechanisms of Depression

According to our model of the regulation of appetitive-searching vs. distress-avoiding behaviors, the motivation to display these essential conducts is regulated by two parallel cortico-striato-thalamo-cortical, re-entry circuits, including the core and the shell parts of the nucleus accumbens, respectively. An entire series of basal ganglia, running from the caudate nucleus on one side, to the centromedial amygdala on the other side, controls the intensity of these reward-seeking and misery-fleeing behaviors by stimulating the activity of the (pre)frontal and limbic cortices. Hyperactive motivation to display behavior that potentially results in reward induces feelings of hankering (relief leads to pleasure). Hyperactive motivation to exhibit behavior related to avoidance of misery results in dysphoria (relief leads to happiness). These two systems collaborate in a reciprocal fashion. In clinical depression, a mismatch exists between the activities of these two circuits: the balance is shifted to the misery-avoiding side. Five theories have been developed to explain the mechanism of depressive mood disorders, including the monoamine, biorhythm, neuro-endocrine, neuro-immune, and kindling/neuroplasticity theories. This paper describes these theories in relationship to the model (described above) of the regulation of reward-seeking vs. misery-avoiding behaviors. Chronic stress that leads to structural changes may induce the mismatch between the two systems. This mismatch leads to lack of pleasure, low energy, and indecisiveness, on one hand, and dysphoria, continuous worrying, and negative expectations on the other hand. The neuroplastic effects of monoamines, cortisol, and cytokines may mediate the induction of these structural alterations. Long-term exposure to stressful situations (particularly experienced during childhood) may lead to increased susceptibility for developing this condition. This hypothesis opens up the possibility of treating depression with psychotherapy. Genetic and other biological factors (toxic, infectious, or traumatic) may increase sensitivity to the induction of relevant neuroplastic changes. Reversal or compensation of these neuroplastic adjustments may explain the effects of biological therapies in treating depression.

Behavioral effects induced by subchronic exposure to Pb and their reversion are concentration and gender dependent

Lead (Pb) seems to be involved in the etiology of psychological pathologies. This study investigated the effects of subchronic Pb exposure from weaning to adulthood on anxiety, depression and aggressiveness in male and female Swiss mice. Moreover, the reversibility of the effects was evaluated retesting the animals 30 days after the end of exposure. Swiss male and female mice (21 days) were exposed to 0, 50, 100 or 500 ppm of Pb, as Pb acetate, in drinking water for 70 days and were submitted to the forced swimming, tail suspension, elevated plus-maze or intruder—resident tests. Pb exposure to 50 and 500 ppm induced anti-depressant-like effect in both males and females, whereas exposure to 500 ppm induced anxiogenic effect only in males. Interruption of exposure was able to reverse the behavioral alterations in females, but not in males exposed to the highest concentration (500 ppm). Our results suggest that behavioral effects induced by subchronic exposure to Pb from weaning to adulthood and their reversion are concentration and gender dependent. [Human & Experimental Toxicology] (2007) 26, 733—739

Simultaneous alterations of brain and plasma serotonin concentrations and liver cytochrome P450 in rats fed on a tryptophan-free diet

Our previous study suggested involvement of the brain serotonergic system in the regulation of liver cytochrome P450 (CYP). The aim of the present study was to demonstrate simultaneous responsiveness of liver CYP and the peripheral and brain serotonergic systems to a tryptophan deficient diet during three days and one or three weeks of ingestion. The concentrations of serotonin, noradrenaline, dopamine and their metabolites were measured in blood plasma, the hypothalamus and brain stem of male rats. The enzyme activity and protein levels in the liver were determined for isoforms CYP1A, CYP2A, CYP2B, CYP2C6, CYP2C11, CYP2D and CYP3A. A three-day tryptophan-free diet increased serotonin content in the hypothalamus (but not in the brain stem or plasma). After one week, the level of serotonin was not changed in the brain, but was markedly increased in the plasma. A three week tryptophan restriction significantly reduced the concentration of serotonin in the brain and plasma. Changes in CYP2C6 and CYP2C11 (an increase and a decrease, respectively) were maintained throughout the experiment, while those found in other CYP isoforms varied, which usually resulted in a gradual increase in the enzyme activity within three weeks. The observed alterations in liver CYPs suggest involvement of both central and peripheral serotonin in the regulation of liver CYP expression whose mechanism is discussed. In conclusion, a deficit in tryptophan in the diet may be responsible for very serious food-cytochrome P450 and food-drug metabolism interactions. Interactions of this type may also refer to drugs acting via serotonergic system.

Effects of prazosin, clonidine, and propranolol on the elevations in brain reward thresholds and somatic signs associated with nicotine withdrawal in rats

RATIONALE

Tobacco withdrawal is characterized by a negative mood state and relatively mild somatic symptoms. Increased noradrenergic transmission has been reported to play an important role in opioid withdrawal, but little is known about the role of noradrenergic transmission in nicotine withdrawal.

OBJECTIVES

The aim of these experiments was to investigate the effects of prazosin, clonidine, and propranolol on the negative mood state and somatic signs associated with nicotine withdrawal in rats.

METHODS

A discrete-trial intracranial self-stimulation procedure was used to assess the negative affective state of nicotine withdrawal. Elevations in brain reward thresholds are indicative of a deficit in brain reward function.

RESULTS

In all the experiments, the nicotinic acetylcholine receptor antagonist mecamylamine (3 mg/kg) elevated the brain reward thresholds of the nicotine-treated rats and did not affect those of the control rats. The α1-adrenergic receptor antagonist prazosin (0.0625 and 0.125 mg/kg) dose-dependently attenuated the elevations in brain reward thresholds associated with precipitated nicotine withdrawal. The α2-adrenergic receptor agonist clonidine (10-40 μg/kg) and the nonselective β-adrenergic receptor antagonist propranolol (2.5-10 mg/kg) did not attenuate the elevations in brain reward thresholds associated with nicotine withdrawal. Furthermore, mecamylamine (2 mg/kg) induced more somatic signs in the nicotine-treated rats than in the control rats. Clonidine and propranolol, but not prazosin, decreased the total number of somatic signs associated with nicotine withdrawal.

CONCLUSION

Blockade of α1-adrenergic receptors attenuates the deficit in brain reward function associated with nicotine withdrawal. Antagonism of β-adrenergic receptors or stimulation of α2-adrenergic receptors attenuates the somatic symptoms of nicotine withdrawal.

The effect of increased serotonergic neurotransmission on aggression: a critical meta-analytical review of preclinical studies

RATIONALE

The role of serotonin (5-HT) on aggression has been extensively studied; nonetheless, the role of this neurotransmitter in aggression is still inconclusive.

OBJECTIVES

The current meta-analytical review investigated the role of increased 5-HT neurotransmission in aggression.

METHODS

Preclinical studies using serotonin reuptake inhibitors, 5-hydroxytryptophan, L-tryptophan, or serotonin (5-HT) to increase 5-HT levels were included in this meta-analysis. An overall effect of serotonin on aggression was calculated, and the role of several moderator variables was analyzed.

RESULTS

A total of 218 effect sizes revealed that increased 5-HT had an overall significant inhibitory effect on aggression (r = 0.3). The results showed that increased 5-HT had the strongest inhibitory effect on aggression when (1) a specific strain or species (e.g., Long Evans) was used; (2) aggression was offensive or predatory and/or induced by administration of 5,7-dihydroxytryptamine or p-chlorophenylalanine; (3) zimelidine, sertraline, L-tryptophan, citalopram, or 5-HT were used to increase 5-HT; (4) treatment was acute; (5) long chronic treatment durations were used; and (6) time between last injection and behavior testing was within 8 h before or after peak plasma concentration of drug. In contrast, the results revealed that increased-5-HT-facilitated aggression could be predicted when (1) Wistar rats, (2) social isolation or stress to induce aggression, and/or (3) animals treated for less than 3 weeks were used.

CONCLUSIONS

Although 5-HT has an overall inhibitory effect on aggression, the animal's genetic background, drug, treatment time, aggression inducing paradigm, and aggression type are critical variables that influence and modify this effect.

A possible role for the endocannabinoid system in the neurobiology of depression

The present review synthetically describes the currently advanced hypotheses for a neurobiological basis of depression, ranging from the classical monoaminergic to the more recent neurotrophic hypothesis. Moreover, the Authors review the available preclinical and clinical evidence suggesting a possible role for the endocannabinoid system in the physiopathology of depression. Indeed, in spite of the reporting of conflicting results, the pharmacological enhancement of endocannabinoid activity at the CB1 cannabinoid receptor level appears to exert an antidepressant-like effect in some animal models of depression. On the contrary, a reduced activity of the endogenous cannabinoid system seems to be associated with the animal model of depression, namely the chronic mild stress model. Moreover, a few studies have reported an interaction of antidepressants with the endocannabinoid system. With regard to clinical studies, several authors have reported an alteration of endocannabinoid serum levels in depression, while post mortem studies have demonstrated increased levels of endocannabinoids associated to a concomitant hyperactivity of CB1 receptor in the prefrontal cortex of suicide victims. No clinical trials carried out using cannabinoids in the treatment of affective disorders have been published to date, although anecdotal reports have described both antidepressant and antimanic properties of cannabis as well as the ability of cannabis to induce mania that has also been documented. These findings are discussed, leading us to conclude that, although data available are sufficient to suggest a possible involvement of the endogenous cannabinoid system in the neurobiology of depression, additional studies should be performed in order to better elucidate the role of this system in the physiopathology of depression.

Platelet radioligand binding and neuroendocrine challenge tests in depression

The purpose of this work was to examine the number and function of alpha 2-adrenoceptors and the number of serotonin uptake sites in depressed patients and controls. Platelet alpha 2-adrenoceptors and platelet serotonin uptake sites were labelled with [3H]yohimbine and [3H]imipramine respectively. Central alpha 2-adrenoceptor function was assessed by growth hormone and other responses to challenge with the alpha 2-agonist clonidine. No overall difference in the binding parameters was observed between the control and depressed groups, but the results highlight the importance of drug-free interval, menopausal status and membrane protein concentration within the binding assays in the interpretation of such studies. The growth hormone response to clonidine tended to be blunted in depressed females and was significantly blunted in the subgroup of depressives who failed to suppress plasma cortisol concentrations in response to dexamethasone. Depressed subjects also showed a smaller decrease in diastolic blood pressure and a smaller increase in sedation than control subjects.

Functional interaction between α2-adrenoceptors, μ- and κ-opioid receptors in the guinea pig myenteric plexus: Effect of chronic desipramine treatment

The existence of a functional interplay between alpha(2)-adrenoceptor and opioid receptor inhibitory pathways modulating neurotransmitter release has been demonstrated in the enteric nervous system by development of sensitivity changes to alpha(2)-adrenoceptor, mu- and kappa-opioid receptor agents on enteric cholinergic neurons after chronic sympathetic denervation. In the present study, to further examine this hypothesis we evaluated whether manipulation of alpha(2)-adrenoceptor pathways by chronic treatment with the antidepressant drug, desipramine (10 mg/kg i.p. daily, for 21 days), could entail changes in enteric mu- and kappa-opioid receptor pathways in the myenteric plexus of the guinea pig distal colon. In this region, subsensitivity to the inhibitory effect of both UK14,304 and U69,593, respectively alpha(2A)-adrenoceptor and kappa-opioid receptor agonist, on the peristaltic reflex developed after chronic desipramine treatment. On opposite, in these experimental conditions, supersensitivity developed to the inhibitory effect of [D-Ala, N-Me-Phe4-Gly-ol5]-enkephalin (DAMGO), mu-opioid receptor agonist, on propulsion velocity. Immunoreactive expression levels of alpha(2A)-adrenoceptors, mu- and kappa-opioid receptors significantly decreased in the myenteric plexus of the guinea pig colon after chronic desipramine treatment. In these experimental conditions, mRNA levels of alpha(2A)-adrenoceptors, mu- and kappa-opioid receptors significantly increased, excluding a direct involvement of transcription mechanisms in the regulation of receptor expression. Levels of G protein-coupled receptor kinase 2/3 and of inhibitory G(i/o) proteins were significantly reduced in the myenteric plexus after chronic treatment with desipramine. Such changes might represent possible molecular mechanisms involved in the development of subsensitivity to UK14,304 and U69,593 on the efficiency of peristalsis. Alternative molecular mechanisms, including a higher efficiency in the coupling between receptor activation and downstream intracellular effector systems, possibly independent from inhibitory G(i/o) proteins, may be accounted for the development of supersensitivity to DAMGO. Increased sensitivity to the mu-opioid agonist might compensate for the development of alpha(2A)-adrenoceptor and kappa-opioid receptor subsensitivity. On the whole, the present data further strengthen the concept that, manipulation of alpha(2)-adrenergic inhibitory receptor pathways in the enteric nervous system entails changes in opioid inhibitory receptor pathways, which might be involved in maintaining homeostasis as suggested for mu-opioid, but not for kappa-opioid receptors.

Is there a role for the endocannabinoid system in the etiology and treatment of melancholic depression?

With advances in basic and clinical neuroscience, many gaps have appeared in the traditional monoamine theory of depression that have led to reformulation of the hypotheses concerning the neurobiology of depression. The more recent hypotheses suggest that melancholic depression is characterized by central glucocorticoid resistance that results in hypercortisolemia, which in turn leads to down-regulation of neurotrophins and subsequent neurodegeneration. Examining the neurobiology of depression from this perspective suggests that the endocannabinoid system may play a role in the etiology of melancholic depression. Specifically, pharmacological and genetic blockade of the cannabinoid CB1 receptor induces a phenotypic state that is analogous to melancholic depression, including symptoms such as reduced food intake, heightened anxiety, increased arousal and wakefulness, deficits in extinction of aversive memories and supersensitivity to stress. These similarities between melancholic depression and an endocannabinoid deficiency become more interesting in light of recent findings that endocannabinoid activity is down-regulated by chronic stress and possibly increased by some antidepressant regimens. We propose that an endocannabinoid deficiency may underlie some of the symptoms of melancholic depression, and that enhancement of this system may ultimately be a novel form of pharmacotherapy for treatment-resistant depression.

Evidence that serotonin reuptake modulators increase the density of serotonin innervation in the forebrain

The mechanism of action of commonly used antidepressants remains an issue of debate. In the experiments reported here we studied the effects of three representative compounds, the selective serotonin reuptake inhibitor fluoxetine, the selective serotonin reuptake enhancer tianeptine and the selective norepinephrine reuptake inhibitor desipramine on the structure of central serotonin pathways after a 4-week administration. We found that the serotonin modulators fluoxetine and tianeptine, but not desipramine, increase the density of 5-HT and serotonin transporter (SERT)-immunoreactive axons in the neocortical layer IV and certain forebrain limbic areas, such as piriform cortex and the shell region of nucleus accumbens. These changes were noted in the absence of a significant effect of serotonin antidepressants on the expression of tryptophan hydroxylase (TPH-2), i.e. the rate-limiting enzyme for 5-HT biosynthesis and of SERT at the mRNA level. In addition, we found that anterogradely filled terminal axons from injections of biotinylated dextran amine into the dorsal raphe showed significantly more branching in animals treated with fluoxetine compared with animals treated with liposyn vehicle. Our findings suggest that antidepressants may exert very selective structural effects on their cognate monoamine systems in normal animals and raise the possibility that neurotrophic mechanisms may play a role in their clinical efficacy.

Pindolol augmentation of selective serotonin reuptake inhibitors: accounting for the variability of results of placebo-controlled double-blind studies in patients with major depression

Co-administration of pindolol with SSRIs in patients with depression has been suggested as a way to both hasten and augment antidepressant response. Clinical trials have examined the efficacy of this treatment regime and conflicting results have been reported. The present review briefly presents the results of placebo-controlled double-blind trials of pindolol augmentation of SSRIs in patients with major depression, and focuses on factors that may account for the variability of findings. Additionally, a profile of the subset of patients who may most benefit from pindolol augmentation is outlined. Methodological factors such as qualitative differences in definitions of antidepressant response, the timing of pindolol administration and heterogeneous clinical characteristics of patient samples may contribute to the variability in the results of clinical trials to date. Similarly, individual differences in neuropathology, neurophysiology and genotype may also account for some of the inconsistencies in the findings. Finally, the results of recent neuroimaging studies suggest that the 2.5 mg t.i.d. dose of pindolol that has been used in all but one of these investigations may be suboptimal for achieving reliable and significant occupancy of 5-HT1A autoreceptors and may explain the contradictory nature of the results of investigations of pindolol augmentation.

Beta-adrenergic receptor density and adenylate cyclase activity in lead-exposed rat brain after cessation of lead exposure

To understanding the reversible or irreversible harm to the beta-adrenergic system in the brain of lead-exposed rats, this study sets up an animal model to estimate the change in the sympathetic nervous system of brain after lead exposure was withdrawn. We address the following topics in this study: (a) the relationship between withdrawal time of lead exposure and brain beta-adrenergic receptor, blood lead level, and brain lead level in lead-exposed rats after lead exposure was stopped; and (b) the relationship between lead level and beta-adrenergic receptor and cyclic AMP (c-AMP) in brain. Wistar rats were chronically fed with 2% lead acetate and water for 2 months. Radioligand binding was assayed by a method that fulfilled strict criteria of beta-adrenergic receptor using the ligand [125I]iodocyanopindolol. The levels of lead were determined by electrothermal atomic absorption spectrometry. The c-AMP level was determined by radioimmunoassay. The results showed a close relationship between decreasing lead levels and increasing numbers of brain beta-adrenergic receptors and brain adenylate cyclase activity after lead exposure was withdrawn. The effect of lead exposure on the beta-adrenergic system of the brain is a partly reversible condition.

Effectiveness of pindolol plus serotonin uptake inhibitors in depression: a meta-analysis of early and late outcomes from randomised controlled trials

BACKGROUND

Contradictory results on the efficacy of pindolol associated with selective serotonin reuptake inhibitors (SSRIs) in depressive illness have been published and no former review has produced an overall figure of its efficacy. This study aims to review the efficacy and tolerability of pindolol plus SSRIs in depressive illness.

METHODS

A meta-analysis of randomised controlled trials (RCTs) comparing pindolol plus SSRIs with placebo plus SSRIs.

RESULTS

Nine RCTs met inclusion criteria. Outcome favoured pindolol at 2 weeks time (N=5; OR=2.8; 95% CI 1.4-5.7), but not at four to 6 weeks (N=7; OR=1.4; 95% CI 0.8-2.7). Results for early outcome studies were robust to sensitivity analysis. Nineteen more studies, averaging null results, would be needed to change the overall probability (P=0.0001) to a non-significant figure.

CONCLUSIONS

Pindolol seems to hasten the response to SSRIs in depression with a timing window circumscribed to the first weeks of treatment.

In the rat forced swimming test, chronic but not subacute administration of dual 5-HT/NA antidepressant treatments may produce greater effects than selective drugs

The rat forced swimming test (FST) distinguishes selective serotonin (5-HT) and selective noradrenaline (NA) reuptake-inhibitors, which respectively increase swimming and climbing behaviours. However, NA-system-mediated inhibition of 5-HT-induced swimming prevents dual 5-HT/NA reuptake-inhibition to produce concurrently climbing with swimming. Since adaptative neurochemical processes occur in the treatment of depression, we examined the influence of long-term antidepressant treatment on these interactions.

METHODS

(1) Selective [fluoxetine: 10 mg/kg; desipramine: 10 mg/kg] and non-selective [milnacipran: 40 mg/kg; mirtazapine: 20 mg/kg] antidepressants were administered subacutely (3inj) and chronically (17inj) over 16 days. (2) A subacute fluoxetine-desipramine combination (10-10 mg/kg) was administered in rats that were pre-treated with chronic-desipramine (10 mg/kg per day, 14 days). (3) NA-system-mediated interactions were further examined by combining the alpha(2)-receptor agonist clonidine (5, 10, 20, 200 microg/kg) with 10 mg/kg fluoxetine.

RESULTS

(1) Long-term treatment with either fluoxetine or desipramine does not modify the behavioural response produced by their subacute administration. (2) In contrast, whereas subacute-milnacipran increases climbing solely, chronic-milnacipran produces greater anti-immobility effects and increases both climbing and swimming behaviours. Similarly, the fluoxetine-desipramine combination produces climbing solely, but increases both climbing and swimming behaviours in animals pre-treated with chronic-desipramine. Chronic but not subacute-mirtazapine increases swimming behaviour. (3) clonidine dose-dependently antagonizes fluoxetine-induced anti-immobility effects and swimming behaviour.

CONCLUSIONS

Chronic enhancement of NA-transmission alters NA-system-mediated inhibition of 5-HT-induced behaviour in the FST, which may involve alpha(2)-receptors.

Comparison of pramipexole, fluoxetine, and placebo in patients with major depression

Pramipexole, a dopamine D2 receptor agonist, was tested in 174 patients with major depression, with or without melancholia and without psychotic features. Three daily dose levels (0.375 mg, 1.0 mg, and 5.0 mg) were compared to fluoxetine (Prozac) at 20 mg and placebo in a randomized, double-blind, parallel-group study. After a 1 week placebo run-in period, patients were treated for 8 weeks, had a post-study follow-up (week 9), and were evaluated primarily with the Hamilton Psychiatric Rating Scale for Depression (HAM-D), the Montgomery-Asberg Depression Rating Scale (MADRS), and the Clinician's Global Impressions-Severity of Illness scale (CGI-SI). All patients who received one dose of study medication were included in the observed-case analysis (no missing data were replaced). Results indicated that by endpoint (week 8), patients receiving pramipexole at the 1.0 mg per day dose had significant improvement over baseline compared to the placebo group by measure of the HAM-D, MADRS, and CGI-SI. Significant improvement in this dose group was seen at other timepoints as well. The most obvious improvement was seen in the pramipexole 5.0 mg group, although a substantial dropout rate for this group precluded statistical tests vs. placebo late in the study. Patients taking fluoxetine also showed significant improvements at endpoint on the MADRS and earlier in the study on the HAM-D. No new or unusual safety concerns were generated during this study. Pramipexole helped safely alleviate the symptoms of depression at 1.0 mg per day and especially in those patients who could tolerate the escalation to 5 mg per day.

Alterations in beta-adrenergic receptor density and adenylate cyclase activity in the rat brain treated chronically with lead

Behavioral and memory impairment resulting from lead exposure is well known but the mechanism is not. We utilized the brain of lead exposed rats to investigate this problem. In an effort to elucidate the mechanism responsible for this alteration we examined blood and brain lead levels, brain beta-adrenoceptor density and cyclic AMP production in lead exposed rats. Wistar rats used in these trials were divided into six groups of ten animals each. Five groups were given drinking water containing 0.05, 0.1, 0.5, 1 and 2% lead acetate for a period of 60 days. One group (control group, 0% lead acetate) was given pure water. Application of a trend test indicated that both blood and brain lead levels increased significantly from group 0% to group 2% (group 0% <group 0.05% <group 0.1% <group 0. 5%<group 1%<group 2%), but that brain beta-adrenoceptor density and cyclic AMP levels stimulated by isoproterenol decreased (group 2%<group 1%<group 0.5%<group 0.1%<group 0.05%<group 0%). Kd did not vary among the six groups and this indicated that the affinity of the remaining beta-adrenoceptors for [125I]iodocyanopindolol was not changed. Linear regression analysis showed that beta-adrenoceptor density and stimulated cyclic AMP level in brain was found to be negatively correlated with brain lead level (P<0.001). The results show lead exposure that may be the result of an alteration of beta-adrenergic receptor and adenylate cyclase activity in brain.

Effect of acute treatment with YM992 on extracellular norepinephrine levels in the rat frontal cortex

The effects of acute treatment with (S)-2-[[(7-fluoroindan-4-yl)oxy]methyl]morpholine monohydrochloride (YM992), venlafaxine, fluoxetine and citalopram on extracellular norepinephrine levels were examined in the rat frontal cortex by in vivo microdialysis. YM992 (3, 10, 30 mg/kg, i.p.) dose-dependently increased extracellular norepinephrine levels (3-fold at 10 mg/kg, 5. 5-fold at 30 mg/kg). While venlafaxine and 30 mg/kg fluoxetine also produced significant increases in norepinephrine levels, 30 mg/kg citalopram had no effect. The combined administration of MDL100,907 (a selective 5-HT(2A) receptor antagonist) and citalopram did significantly increase norepinephrine levels compared with either saline or citalopram treatment. Therefore, a synergistic effect due to 5-HT reuptake inhibition and 5-HT(2A) receptor antagonism of YM992 may partly contribute to the increase of extracellular norepinephrine levels. YM992 enhances the neurotransmission of not only 5-HT system but also norepinephrine, and as such may have a preclinical profile different from that of a selective serotonin reuptake inhibitor.

Regulation of signal transduction pathways and gene expression by mood stabilizers and antidepressants

OBJECTIVE

To determine whether the currently available evidence supports the hypothesis that antidepressants and mood stabilizers may bring about some of their long-term therapeutic effects by regulating signal transduction pathways and gene expression in the central nervous system.

METHODS

To address this question, we reviewed the evidence showing that chronic administration of antidepressants and mood stabilizers involves alterations in signaling pathways and gene expression in the central nervous system.

RESULTS

A large body of data has shown that lithium and valproate exert effects on the protein kinase C signaling pathway and the activator protein 1 family of transcription factors; in contrast, antidepressants affect the cyclic adenosine monophosphate pathway and may bring about their therapeutic effects by modulating cyclic adenosine monophosphate-regulated gene expression in the central nervous system.

CONCLUSIONS

Given the key roles of these signaling cascades in the amplification and integration of signals in the central nervous system, the findings have clear implications not only for research into the etiology and pathophysiology of the severe mood disorders but also for the development of novel and innovative treatment strategies.

Changes in platelet alpha-2-adrenoceptors in fibromyalgia: effects of treatment with antidepressants

The aim of this study was to determine platelet alpha(2)-adrenergic receptor (alpha(2)-AR) binding sites in fibromyalgia both before and after treatment with sertraline or placebo. The maximum number of binding sites (B(max)) and their affinity (K(d)) for [(3)H]rauwolscine, a selective alpha(2)-AR antagonist, were measured in 13 normal volunteers and 22 fibromyalgia patients. Severity of illness was evaluated by means of the Hamilton Depression Rating Scale (HDRS) and dolorimetric assessments of tenderness at tender points. Fibromyalgia patients had repeated measurements of [(3)H]rauwolscine binding characteristics both before and after subchronic treatment with sertraline or placebo for 12 weeks. [(3)H]rauwolscine binding K(d) values were significantly higher in fibromyalgia patients than in normal volunteers. There were significant inverse correlations between [(3)H]rauwolscine binding K(d) values and duration of illness, age and lower energy. Significantly higher [(3)H]rauwolscine binding K(d) values were found in fibromyalgia patients in an early phase of illness (<3 years) than in fibromyalgia patients with a protracted illness (>3 years). Repeated administration of sertraline had no significant effects on [(3)H]rauwolscine binding B(max) or K(d) values. The results suggest that fibromyalgia and, in particular, fibromyalgia in an early phase of illness, is accompanied by lowered affinity of platelet alpha(2)-ARs.

Decreased platelet alpha-2 adrenoceptor density in major depression: effects of tricyclic antidepressants and fluoxetine

BACKGROUND

It has been suggested that major depression is accompanied by a subsensitivity of central alpha 2-adrenoceptors (alpha 2-ARs) and, consequently, by an impaired negative feedback on the presynaptic catecholaminergic neuron, which, in turn, may induce a disinhibition of noradrenergic output and norepinephrine release in response to any activation.

METHODS

The maximum number of platelet binding sites (Bmax) and their affinity for [3H]-rauwolscine, a selective alpha 2-AR antagonist, were measured in unmedicated and medicated major depressed patients and in normal volunteers. Specific binding was defined as that inhibited by idazoxan, another alpha 2-AR antagonist.

RESULTS

Unmedicated major depressed patients had significantly decreased platelet [3H]-rauwolscine binding Bmax values compared to normal volunteers. [3H]-rauwolscine binding Kd values did not differ significantly between unmedicated major depressed patients and normal controls. [3H]-rauwolscine binding Kd values were significantly higher in depressed patients treated with tricyclic antidepressants than in unmedicated patients. Subchronic treatment with fluoxetine did not significantly alter either [3H]-rauwolscine binding Bmax or Kd values. [3H]-rauwolscine binding Bmax values were significantly greater in men than in women.

CONCLUSIONS

The results suggest that i) major depression is accompanied by decreased platelet alpha 2-AR density; and that ii) subchronic treatment with tricyclic antidepressants, but not fluoxetine, results in a decreased affinity of rauwolscine for platelet alpha 2-ARs.

Pathophysiology of the locus coeruleus in suicide

Clinical and basic research findings implicate a role for brain norepinephrine in the pathophysiology of psychiatric disorders that can lead to suicide. However, the precise biological abnormality of neurons that produce norepinephrine in the brain in these disorders has not been elucidated. We have studied the biochemistry of the locus coeruleus (LC), the principal source of brain norepinephrine, from suicide victims and from age-matched, natural or accidental death control subjects. Levels of tyrosine hydroxylase (rate-limiting enzyme in norepinephrine biosynthesis) and amounts of binding to a2 adrenoceptors (norepinephrine receptors) are elevated in the LC of suicide victims as compared to control subjects. These biological abnormalities in the LC from suicide victims are very similar to biochemical changes observed in the rat LC following repeated exposure to environmental stimuli that activate the LC or to treatment with pharmacological agents that deplete brain norepinephrine. It is hypothesized that persons who commit suicide have experienced chronic activation of the LC, resulting in depletion of synaptic norepinephrine and compensatory changes in concentrations of noradrenergic proteins.

Influence of imipramine on the hypothalamic/pituitary/thyroid axis of the rat

The effects of the tricyclic antidepressant drug imipramine at different levels of the hypothalamic/pituitary/thyroid axis were investigated in the rat. Intraperitoneal (IP) treatment for 14 days with imipramine at 10 mg/kg, but not 2 mg/kg, reduced serum total thyroxine (T4) and triiodothyronine (T3). A similar decrease in serum total T4 was observed in thyroidectomized T4-treated rats, suggesting that imipramine treatment enhances T4 clearance instead of reducing T4 secretion. There were no parallel decreases in serum free T4 and T3 concentrations, due to the simultaneous increase in the free fractions of both T4 and T3 following imipramine treatment. In vitro experiments using equilibrium dialysis indicated that neither imipramine nor its metabolite desipramine directly influenced the binding of T4 or T3 to their transport proteins following addition to normal serum, suggesting an indirect effect of imipramine or desipramine on free hormone concentrations in vivo. Concentrations of T4 and T3 in the brain, liver, and heart were unaffected by imipramine treatment, suggesting that the drug did not affect cellular uptake and metabolism of T4 and T3. Serum concentrations of thyrotropin (TSH) were unaffected by imipramine pretreatment at either dose level, compatible with the fact that serum free T4 and T3 concentrations were not reduced. Moreover, there was no difference in thyrotrope responsiveness to stimulation by TSH-releasing hormone (TRH) and to inhibition by T4 and T3 in rat anterior pituitary cells cultured ex vivo for 18 hours from control and imipramine-treated rats. Furthermore, in vitro exposure of cultured rat anterior pituitary cells to imipramine and desipramine indicated that both agents decreased TSH secretion only at concentrations greater than 10(-6) mol/L. These concentrations of imipramine and desipramine in the culture medium would exceed the free concentrations of these drugs seen in vivo therapeutically. In addition, no direct effects of 10(-6) mol/L imipramine or desipramine on the TSH response to TRH or to T3 were observed in vitro in cultured pituitary cells. A potential indirect effect of imipramine or desipramine on TSH secretion via altered hypothalamic control of thyrotropes does not seem likely, due to the lack of effect of imipramine treatment on serum TSH concentrations in imipramine-treated rats. In conclusion, imipramine treatment reduces serum total T4 and T3 in the rat, with enhanced clearance being the most likely explanation for the effect on T4. There was no evidence for altered tissue T4 or T3 concentrations or for altered thyrotrope function. The enhanced T4 clearance may explain the reduction in total T4 reported for imipramine-treated depressed patients. However, the effects of imipramine treatment on the transport of thyroid hormones in plasma need to be examined in more detail in patients, since interspecies differences in the nature of the transport proteins preclude extrapolation of the present results from the rat.

Brain alpha-adrenoceptors in depressed suicides

alpha1-Adrenoceptors and alpha2-adrenoceptors were measured by radioligand binding to homogenates of brain samples obtained at post-mortem from suicides with a retrospective diagnosis of depression, and age and gender-matched controls. Suicides were subdivided into those who had been free of antidepressant drugs for at least three months, and those in whom prescription of antidepressant drugs was clearly documented. The number of alpha1-adrenoceptors (or alpha1A + alpha1D-adrenoceptors) did not differ significantly between antidepressant-free or antidepressant-treated suicides and controls. In antidepressant-free suicides, the number of alpha2-adrenoceptors was significantly higher in temporal cortex (Ba 21/22). alpha2A-Adrenoceptors did not differ significantly from controls in this brain region, suggesting the involvement of other alpha2-adrenoceptor subtypes. In antidepressant-treated suicides, significantly lower numbers of alpha2-adrenoceptors were found in occipital cortex and hippocampus (and for alpha2A-adrenoceptors in caudate and amygdala) compared to controls.

Structure-activity studies for a novel series of N-(arylethyl)-N-(1,2,3,4-tetrahydronaphthalen-1-ylmethyl)-N-methylamine s possessing dual 5-HT uptake inhibiting and alpha2-antagonistic activities

In search of an alpha2-antagonist/5-HT uptake inhibitor as a potential new class of antidepressant with a more rapid onset of action, compound 3 was prepared and observed to possess high affinity for the alpha2-receptor (K(i) = 6.71 nM) and the 5-HT uptake site (20.6 nM). A series of tertiary amine analogs of 3 were synthesized and assayed for their affinity at both the alpha2-receptor and the 5-HT uptake site. The structure-activity relationship reveals that a variety of structural modifications to the arylethyl fragment are possible with retention of this dual activity. On the tetralin portion, 5-OMe substitution and the (R) stereochemistry at C-1 are optimal with alternate substitutions producing compounds retaining high affinity for the alpha2-receptor but lacking affinity for the 5-HT uptake site. Data for several rigidified 5-O-alkyl analogs suggests that the favored orientation of the oxygen lone pairs may be away from the 6-position of the tetralin.

Desipramine administration in the olfactory bulbectomized rat: changes in brain beta-adrenoceptor and 5-HT2A binding sites and their relationship to behaviour

1. The effects of repeated administration of the tricyclic antidepressant drug, desipramine (DMI), on behaviour (locomotor activity and rearing) and the number and affinity of brain beta-adrenoceptor and 5-HT2A receptor binding sites were examined in olfactory bulbectomized (OB) and sham-operated control rats. 2. Locomotor activity and rearing were increased in OB rats compared to sham-operated controls. The effect of various doses of DMI (administered orally twice daily for 21 days) on these behavioural measures was examined. A dose of 7.5 mg kg-1 provided optimal reversal of hyperlocomotion and increased rearing in OB rats, without changing these measures in sham-operated controls. 3. The time course of DMI (7.5 mg kg-1) on behavioural and neurochemical measures was examined. locomotion and rearing in OB rats were not significantly altered after 7 days, were significantly attenuated after 14 days and were normalized after 21 days. 4. After 7 days of DMI administration the number of beta-adrenoceptors was lower in frontal and occipital cortex and hippocampus. This reduction was largely restricted to the beta 1-adrenoceptor subtype. Administration of DMI for 14 or 21 days did not further reduce the number of beta-adrenoceptors. The DMI induced reduction in beta-adrenoceptors did not differ in OB and sham-operated control rats. 5. DMI administration for up to 21 days produced a progressive reduction in the number of 5-HT2A receptors in frontal cortex, without significant alterations in occipital cortex. 6. The time course of the reduction in the number of 5-HT2A receptors was similar to that of the DMI-induced behavioural changes whereas that for the reduction in beta-adrenoceptors was clearly different. 7. The present results suggest that the action of DMI in this animal model is unlikely to be directly related to a reduction in beta-adrenoceptors but may be related to a reduction in frontal cortical 5-HT2A receptors.

Biochemical profile of YM992, a novel selective serotonin reuptake inhibitor with 5-HT2A receptor antagonistic activity

YM992, (S)-2-[[(7-fluoro-4-indanyl)oxy]methyl]morpholine monohydrochloride, exhibited the biochemical profile of a selective serotonin (5-HT) reuptake inhibitor (SSRI) with 5-HT2A receptor antagonistic activity. YM922 showed the same high affinity as fluoxetine against the 5-HT reuptake site (Ki = 21 nM) and a similar affinity to that of crazodone against the 5-HT2A receptor (Ki = 86 nM). In other receptor binding studies, an affinity for the adrenergic alpha 1 receptor (Ki = 200 nM) and 5-HT2C receptor (Ki = 680 nM) was observed. In a monoamine uptake study, YM992 showed a selective 5-HT uptake inhibition (IC50 = 0.15 microM), but only very weakly inhibited both noradrenaline (NA) and dopamine (DA) uptake (IC50 = 3.1 microM (NA), > 10 microM (DA)). YM992 was also found to potently inhibit the aggregation of human platelets (IC50 = 1.9 microM), revealing antagonistic activity for the 5-HT2A receptor in vitro. Enhanced serotonergic neurotransmission, in particular that mediated by the 5-HT1A receptor, has recently been reported to be important in the long-term treatment of depressive disorders with antidepressants. In addition, some 5-HT1A receptor-mediated responses are known to be potentiated by co-administration of 5-HT2A receptor antagonists. Thus, YM992, having both selective 5-HT reuptake inhibition and 5-HT2A antagonistic activity, might show potent therapeutic activity as a novel antidepressant in comparison with conventional SSRIs.

Transcriptional regulation of the 5-HT2A receptor

Complex transcriptional control mechanisms are responsible for the cell-type and antidepressant-induced regulation of the 5-HT2A receptor. Repressor domains in the 5' flanking region of the 5-HT2A receptor gene are the primary determinants to generate neuronal cell-specific transcription. Glial cell expression of the 5-HT2A receptor is achieved through a cell-type specific promoter activation. The downregulation of the 5-HT2A receptor by the atypical antidepressant mianserin is mediated by a drug response sequence in the 5' flanking region of the receptor gene.

Regulation of central 5-HT2A receptors: a review of in vivo studies

Numerous investigations have studied in vivo regulation of central 5-HT2A receptors. The majority of pharmacological studies point to non-classical regulation of this site. Serotonergic denervation does not modify 5-HT2A receptor density or second messenger responses (phosphoinositide hydrolysis). 5-HT2A receptor downregulation is produced by the chronic administration of 5-HT2A receptor agonists and uniquely among monoamine receptors by antagonists. Several classes of psychotherapeutic agents also downregulate 5-HT2A receptors with chronic administration including classical antidepressants and antipsychotics. 5-HT2A receptor downregulation produced by 5-HT2A antagonists and antidepressants occurs after presynaptic 5-HT denervation, suggesting that 5-HT2A receptors are postsynaptically localized and emphasizing that they are regulated differently than traditional monoaminergic receptors. Interestingly, the behavioral and biochemical effects of 5-HT2A receptor activation are modulated by activity at other 5-HT receptor subtypes (5-HT1A), as well as by stimulation of receptors for other neurotransmitters and hormones such as norepinephrine (beta-adrenergic) and melatonin. It is suggested that these diverse modulatory influences on 5-HT2A receptor regulation and function may meaningfully impact the therapeutic actions of drugs, including pharmacologically distinct antidepressants.

Stress and antidepressant effects on hippocampal and cortical 5-HT1A and 5-HT2 receptors and transport sites for serotonin

The interactions between 14 days of repeated restraint stress and daily administration of imipramine or tianeptine (2 h before the beginning of stress) were investigated in rats to assess responses of 5-HT2 and 5-HT1A receptors and serotonin transporter sites labelled by [3H]paroxetine in the cerebral cortex and hippocampus, two brain regions in which adrenal steroid effects on serotonin receptor-binding have been reported. 5-HT2 sites, labelled by [125I]7-amino-8-iodo ketanserin, were decreased in parietal cerebral cortex layers 3 and 5 by imipramine treatment, but not by tianeptine treatment and not by daily restraint stress. Stress, but not antidepressant, depressed 5-HT1A sites labelled with [3H]8-hydroxy-DPAT in hippocampal fields CA3, CA4 and dentate gyrus. [3H]paroxetine-binding to serotonin transporter sites was decreased by tianeptine treatment as well as by imipramine in both hippocampus and cerebral cortex, with some overlap of the fields that were significantly affected, whereas there were no effects of stress per se and no evidence of a stress x drug interaction. These results are discussed in relation to similarities and differences in the effects of different antidepressant drugs on the serotonergic system of the rat brain. Whereas the actions of imipramine and tianeptine on 5-HT2 and 5-HT1A receptors are specific to each drug, the surprising finding of a similar effect of both drugs to reduce serotonin transporter sites labelled by [3H]paroxetine suggest the possibility of a common action for these two drugs in spite of their opposite effects on serotonin re-uptake.

beta-adrenoceptors in brain and pineal from depressed suicide victims

beta-Adrenoceptors were measured by saturation binding of [3H]CGP 12177 in nine brain regions and pineal from suicides, with a firm retrospective diagnosis of depression, and age and sex matched controls. Twenty one suicides had not recently received antidepressant drugs, 17 had been receiving drugs prior to death. In antidepressant drug-free suicides, the number of total beta-adrenoceptors was significant lower in temporal cortex (Brodmann area 38) and beta 1-adrenoceptors (Brodmann areas 21/22) was significant lower than matched controls. Suicides who died by violent means had significantly lower numbers of total beta- and beta 1-adrenoceptors in the frontal cortex and lower numbers of beta 1-adrenoceptors in temporal cortex (Brodmann areas 21/22) than matched controls. Suicides who died by non-violent means had lower numbers of total beta-adrenoceptors in occipital cortex controls and lower numbers of total beta- and beta 1-adrenoceptors in temporal cortex (Brodmann area 38) than matched controls. In antidepressant drug-treated suicides, significantly lower number of beta-adrenoceptor binding sites were found in temporal cortex (Brodmann area 38) and thalamus compared to matched controls. The lower number of beta-adrenoceptors binding sites in the thalamus appeared to be related to drug treatment. There were no differences in beta-adrenoceptor binding in the pineal gland between antidepressant-free and antidepressant-treated suicides and controls, although there were apparent differences between suicides and controls related to the time of death and season of death.

Effects of chronic desipramine administration on the locus coeruleus neuronal activity in the learned helplessness paradigm

One week after inescapable shock (IS) exposure, animals showed an increased number of escape failures in the shuttlebox and a decreased noradrenergic (NA) transmission. The latter was assessed by electric activity of locus coeruleus (LC) neurons. Seven daily injections of desipramine (DMI) were effective in reducing the number of escapes failures in the shuttlebox, but such treatment did not modify the decreased electric activity of LC NA neurons observed 7 days after IS. These results are discussed in terms of the action of DMI on NA terminals in reversing the behavioral deficit induced by IS.

Biogenic amines in seasonal affective disorder: effects of light therapy

Wintertime measures of central and peripheral monoamine neurotransmitter system activity in 17 medication-free depressed patients with seasonal affective disorder (SAD) were compared with those in eight healthy volunteers. Mean cerebrospinal fluid (CSF) concentrations of the principal metabolites of norepinephrine (NE), serotonin, and dopamine did not differ between the two groups, nor did mean basal or orthostatically stimulated plasma NE levels. Patients' pretreatment depression ratings were inversely correlated with resting plasma NE concentrations. Fourteen SAD patients were clear responders to 2 weeks of full-spectrum bright light treatment. Neither the transmitter measures nor their interrelatedness was affected significantly by phototherapy.

Idazoxan down-regulates β-adrenoceptors on C6 glioma cells in vitro

Incubation of the C6 cells with 10 microM idazoxan (an alpha 2-adrenoceptor antagonist and putative antidepressant) for 5 days in vitro resulted in a 23% reduction of beta-adrenoceptor number and a 37% decrease in isoproterenol-induced cyclic AMP accumulation. In contrast, post-receptor stimulated cyclic AMP accumulation (by the use of forskolin or cholera toxin) was unaffected. The desensitization of the beta-adrenoceptor was accompanied by an increase in the KL/KH ratio for this receptor. Chronic in vitro treatment of C6 glioma cells with idazoxan did not significantly affect cholera or pertussis toxin catalyzed ribosylation of Gs and Gi/Go in these cells. Similarly, idazoxan did not alter either the basal levels of protein kinase C (PKC) alpha, or its cytoplasm to membrane translocation. These results suggest that idazoxan may have direct postsynaptic effects, the site of which may be at the level of receptor/G protein interaction.

Signal-transducing G proteins and antidepressant drugs: evidence for modulation of alpha subunit gene expression in rat brain

Signal-transducing G proteins, heterotrimers formed of alpha, beta, and gamma subunits, are central to the coordination of receptor-effector communication. They are derived from a large gene family, and recent cloning and sequencing of cDNAs encoding the alpha subunits, which confer receptor and effector specificity on the heterotrimer, have defined four major classes, Gs, Gi, Gq, and G12, with at least 16 isotypes. The G proteins that coordinate receptor-effector activity are especially important in the central nervous system (CNS), where they serve widespread, critical roles in the regulation of neuronal function, maintain the functional balance between neurotransmitter systems, and, as such, represent attractive potential targets for antidepressant drugs. We describe an integrated series of animal and cell culture studies aimed at testing the hypothesis that alterations in G protein function may contribute the complex neuroadaptive mechanisms involved in the clinical actions of antidepressants, and demonstrate that long-term administration of a wide spectrum of antidepressant drugs regulate G alpha s, G alpha i1, G alpha i2, G alpha o, G alpha q, and G alpha 12 mRNA and protein expression in various areas of the rat brain. Additionally, we present the polymerase chain reaction-(PCR) mediated cross-species partial cDNA cloning and sequencing of rat and human G alpha o and rat G alpha 12, illustrate the regional distribution of G alpha mRNA and protein in rat brain, and provide evidence that different classes of antidepressants alter expression and/or stability of the recently identified G alpha 12 mRNA. We conclude that long-term treatment with antidepressant drugs exerts differential effects on G alpha mRNA and protein expression in rat brain, thus modifying signal transduction as an integral part of complex neuroadaptive mechanisms that may underlie their therapeutic efficacy. The development of novel drugs with G proteins as primary targets remains an attractive prospect for the future.

Actions of oxaprotiline in the rat hippocampal slice

1. Recordings were obtained from transverse slices of rat hippocampus, which were placed in a perfusion chamber and superfused with oxygenated artificial cerebrospinal fluid. 2. The effects of 10 microM (+)- or (-)-oxaprotiline applied by the bath were examined on the population spike, postsynaptic excitability in low Ca2+-high Mg2+ medium, the epileptiform discharge in Mg2+-free medium and long-term potentiation (LTP). Only the last paradigm (LTP) was significantly enhanced by (+)-oxaprotiline. 3. In rats chronically injected with (+)-oxaprotiline, neither LTP nor the actions of a variety of neurotransmitters in low Ca2+-high Mg2+ medium were significantly altered. 4. Intracellular recordings showed a small depolarization (3.5 +/- 1.6 mV) in response to 10 microM (+)- or (-)-oxaprotiline. Neither input resistance nor inward rectification, long-lasting afterhyperpolarization or accommodation were significantly altered. 5. Acute application, but not chronic treatment with (+)-oxaprotiline affects long-term potentiation in the hippocampal slice, presumably due to an effect on gabaergic inhibition.

Clinical and biochemical aspects of depressive disorders: II. Transmitter/receptor theories

The present document is the second of three parts in a review that focuses on recent data from clinical and animal research concerning the biochemical bases of depressive disorders, diagnosis, and treatment. Various receptor/transmitter theories of depressive disorders are discussed in this section. Specifically, data supporting noradrenergic, serotonergic, cholinergic, dopaminergic, GABAergic, and peptidergic theories, as well as interactions between noradrenergic and serotonergic, or cholinergic and catecholaminergic systems are presented. Problems with the data and future directions for research are also discussed. A previous publication, Part I of this review, dealt with the classification of depressive disorders and research techniques for studying the biochemical mechanisms of these disorders. A future publication, Part III of this review, discusses treatments for depression and some of the controversies in this field.

Effect of imipramine on the membrane anisotropy and on the phospholipid methylation in the central nervous system of the rat

An ex-vivo and in-vitro study of the effects of imipramine on the membrane anisotropy and phospholipid methylation in the rat cortical membranes was carried out. A comparative study of the membrane fluidity in various brain regions indicated different basal anisotropy of the areas and different reaction of these membranes to imipramine. It was found that imipramine when given to rats chronically (14 x 10 mg kg-1, i.p.) or added externally to the cortical membranes of naive rats or rats treated with a single dose of imipramine (10 mg kg-1, i.p.) decreased the anisotropy of cortical membranes. Chronic imipramine produced some changes of the membrane architecture in the cortex, whereas imipramine in different concentrations did not fluidize these membranes in-vitro. Imipramine in concentrations corresponding to its mean concentration in the rat brain after administration at a dose of 10 mg kg-1 i.p., potentiated phospholipid methylation in the cortical membranes of naive rats and rats receiving imipramine in a single dose of 10 mg kg-1 i.p. in an in-vitro study, whereas the prolonged administration of imipramine decreased the sensitivity of phospholipid methyltransferases to the stimulating effect of the drug in-vitro.

Central administration of 1-isoproterenol in vivo induces a preferential regulation of beta 2-adrenoceptors in the central nervous system of the rat

1-Isoproterenol has equal affinity for beta 1- and beta 2-adrenoceptors and is a full agonist at both subtypes. However, when infused in vivo into the rat brain, it has been shown to induce a preferential reduction of central beta 2-adrenoceptors. To investigate this phenomenon further, in the present study rats were infused centrally with higher doses of 1-isoproterenol (15 or 45 micrograms/h). Furthermore, isoproterenol was infused into rats lesioned neonatally with 6-hydroxydopamine (6-OHDA). Subtypes of beta-adrenoceptors were measured by quantitative autoradiography of the binding of [125I]iodopindolol ([125I]IPIN). In sham lesioned rats, infusions of isoproterenol at both doses caused comparable reductions in the density of [125I]IPIN binding sites in many brain regions. The binding to beta 2-adrenoceptors was decreased in a larger number of brain areas than the binding to beta 1-adrenoceptors and the magnitude of the reduction was greater for beta 2- than for beta 1-adrenoceptors. However, isoproterenol at these doses did produce greater effects on the beta 1-subtype than those found previously with a lower dose. Treatment with 6-OHDA induced significant increases in the binding of [125I]IPIN to both beta 1- and beta 2-adrenoceptors in cerebral cortical and hippocampal areas, indicating that endogenous norepinephrine may regulate both subtypes in these regions. Even in the 6-OHDA-lesioned rats, the binding of [125I]IPIN to beta 2-adrenoceptors was reduced to a greater extent that the binding to beta 1-adrenoceptors. Thus, these studies demonstrate that the non-selective beta-adrenergic agonist isoproterenol induces a preferential regulation of beta 2-adrenoceptors, even at relatively high doses and in norepinephrine-depleted animals.

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.

Brain beta-adrenoceptor binding sites in depressed suicide victims: effects of antidepressant treatment

beta-Adrenoceptor binding sites were measured by saturation binding of [3H]CGP 12177 in nine brain regions from 13 suicides, with a firm retrospective diagnosis of depression, who had been receiving antidepressant drugs, and 11 matched controls. Significantly lower numbers of beta-adrenoceptor binding sites were found in thalamus and temporal cortex (Brodmann area 38), but not in other brain regions, of antidepressant-treated suicides compared to controls. The lower number of beta-adrenoceptor binding sites in thalamus appeared to be related to drug treatment, whereas lower numbers of beta-adrenoceptors in temporal cortex were also found in antidepressant-free suicides.

Corticosterone and prolactin response to TFMPP in rats during repeated antidepressant administration

The corticosterone and prolactin response to acute administration of the 5-HT agonist 1-(m-trifluoromethylphenyl) piperazine (TFMPP) (10 mg kg-1) was assessed in rats treated for 10 days with either saline, amitriptyline (20 mg kg-1 day-1) or nialamide (40 mg kg-1 day-1). For all groups, TFMPP significantly increased both serum corticosterone and prolactin concentrations compared with control animals challenged with saline. However, the corticosterone response to TFMPP was attenuated significantly by nialamide pretreatment, while the prolactin response to TFMPP was enhanced significantly by amitriptyline pretreatment. These results support previous reports that antidepressants differentially affect 5-HT-ergic systems involved in the regulation of corticosterone and prolactin secretion.

Acute and chronic desipramine treatment effects on rewarding electrical stimulation of the lateral hypothalamus

Two weeks of chronic desipramine HCl (DMI) (10 mg/kg, IP) treatment did not alter reward or motor/performance components of intracranial self-stimulation (ICSS) as assessed with the rate-frequency method. Acute DMI treatment produced an ICSS reward decrement relative to saline control treatment, which was similar in size on Day 1 and Day 15 of chronic testing. The failure to find a chronic DMI effect on ICSS reward suggests that ICSS in normal rats may not be a valid animal model of depression. A better paradigm may be to test the ability of antidepressants to reverse a chronic reduction in ICSS reward function that is first produced by some other method.