Modulation of second messenger function in rat brain by in vivo alteration of receptor sensitivity: relevance to the mechanism of action of electroconvulsive therapy and antidepressants

Role of central serotonin and noradrenaline interactions in the antidepressants' action: Electrophysiological and neurochemical evidence

The development of antidepressant drugs, in the last 6 decades, has been associated with theories based on a deficiency of serotonin (5-HT) and/or noradrenaline (NA) systems. Although the pathophysiology of major depression (MD) is not fully understood, numerous investigations have suggested that treatments with various classes of antidepressant drugs may lead to an enhanced 5-HT and/or adapted NA neurotransmissions. In this review, particular morpho-physiological aspects of these systems are first considered. Second, principal features of central 5-HT/NA interactions are examined. In this regard, the effects of the acute and sustained antidepressant administrations on these systems are discussed. Finally, future directions including novel therapeutic strategies are proposed.

Repetitive transcranial magnetic stimulation activates specific regions in rat brain

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive technique to induce electric currents in the brain. Although rTMS is being evaluated as a possible alternative to electroconvulsive therapy for the treatment of refractory depression, little is known about the pattern of activation induced in the brain by rTMS. We have compared immediate early gene expression in rat brain after rTMS and electroconvulsive stimulation, a well-established animal model for electroconvulsive therapy. Our result shows that rTMS applied in conditions effective in animal models of depression induces different patterns of immediate-early gene expression than does electroconvulsive stimulation. In particular, rTMS evokes strong neural responses in the paraventricular nucleus of the thalamus (PVT) and in other regions involved in the regulation of circadian rhythms. The response in PVT is independent of the orientation of the stimulation probe relative to the head. Part of this response is likely because of direct activation, as repetitive magnetic stimulation also activates PVT neurons in brain slices.

Forskolin-stimulated platelet adenylyl cyclase activity is lower in persons with major depression

We investigated platelet adenylyl cyclase activity in 17 subjects with a history of major depression ("depressed subjects") and 20 controls. Forskolin was used to directly activate adenylyl cyclase, while guanine nucleotides (Gpp(NH)p) and fluoride ions were used to measure adenylyl cyclase activity modulated through the G proteins. Forskolin-stimulated adenylyl cyclase was significantly lower in the depressed subjects (p < 0.0005). There was a statistically significant difference in basal adenylyl cyclase activity between male depressed subjects and male controls. The basal adenylyl cyclase activity was also lower in female depressed subjects, but this difference did not reach statistical significance (p < 0.2). The adenylyl cyclase activity measured after stimulation with a guanine nucleotide or cesium fluoride did not differ between control and depressed male or female subjects. Severity of current depression and the current use of antidepressant medication were not related to the lower forskolin-stimulated enzyme activity in the depressed subjects. The difference in forskolin-stimulated adenylyl cyclase activity appears to reflect a qualitative difference in the adenylyl cyclase enzyme activity in persons with a history of major depression.

The serotonergic and noradrenergic systems of the hippocampus: their interactions and the effects of antidepressant treatments

Previous reviews have well illustrated how antidepressant treatments can differentially alter several neurotransmitter systems in various brain areas. This review focuses on the effects of distinct classes of antidepressant treatments on the serotonergic and the noradrenergic systems of the hippocampus, which is one of the brain limbic areas thought to be relevant in depression: it illustrates the complexity of action of these treatments in a single brain area. First, the basic elements (receptors, second messengers, ion channels, ...) of the serotonergic and noradrenergic systems of the hippocampus are revisited and compared. Second, the extensive interactions occurring between the serotonergic and the noradrenergic systems of the brain are described. Finally, issues concerning the short- and long-term effects of antidepressant treatments on these systems are broadly discussed. Although there are some contradictions, the bulk of data suggests that antidepressant treatments work in the hippocampus by increasing and decreasing, respectively, serotonergic and noradrenergic neurotransmission. This hypothesis is discussed in the context of the purported function of the hippocampus in the formation of memory traces and emotion-related behaviors.

Long-term decrease in the hippocampal [3H]inositoltriphosphate binding following repeated electroshock in the rat

A quantitative autoradiographic study was made on the binding of the phosphatidylinositol system ligand [3H]inositol(1,4,5)-triphosphate (IP3) to forebrain sections from electroconvulsive shock (ECS)-treated rats. One group of rats was sacrificed 1 day and 1 month, respectively, after 12 ECSs administered three times weekly for 4 weeks. SHAM-stimulated rats served as controls. A single ECS did not change the [3H]IP3 binding in any of the brain regions examined. One day after the last of 12 ECSs, a decrease in [3H]IP3 binding (21%) was found within the CA1 region of the hippocampus and the piriform cortex (39%). In rats sacrificed 1 month after the last of 12 ECSs, the [3H]IP3 binding in piriform cortex had returned to control level. In the CA1 region of the hippocampus, the binding was still decreased (24%). It is possible that changes in the phosphatidylinositol system may play a part in the neurobiological events responsible for the therapeutic effect of electroconvulsive therapy.

Electroconvulsive shocks increase the expression of neuropeptide Y (NPY) mRNA in the piriform cortex and the dentate gyrus

Repeated electroconvulsive stimulations represent one treatment modality for depressive disorders, but the mechanism leading to its effect is largely unknown. Studies of humans and rats have indicated that neuropeptide Y (NPY) is involved in major depression and anxiety. The purpose of the present investigation was to detect changes in the expression of preproNPY mRNA in the limbic cortex of rats exposed to electroconvulsive shocks (ECS) daily for 14 days. Twenty-four hours after the last ECS, the animals were sacrificed, brain sections were hybridized with a synthetic oligonucleotide probe complimentary to rat preproNPY mRNA. Semi-quantitative in situ hybridization histochemistry revealed an about ten-fold increase of preproNPY mRNA levels over the dentate gyrus and the piriform cortex in animals exposed to ECS compared to sham-treated controls. In the dentate gyrus dipped sections showed that the increase of gene expression took place in individual neurons in the polymorph layer. In the piriform cortex a moderate increase in the number of grains was observed over many individual cells in the pyramidal layer. These data show that the expression of preproNPY mRNA is markedly increased in specific brains regions after ECS, but whether this increase is a result of the ECS-induced seizures per se, or rather should be regarded as a protective adaptation to changes in neuronal activity pattern remains to be established.

Electroconvulsive shock alters GABAA receptor subunit mRNAs: use of quantitative PCR methodology

Electroconvulsive shock (ECS) may affect several neurotransmitter systems in brain, including the GABAergic inhibitory system. We used a quantitative PCR-based assay to evaluate mRNAs for five GABAa receptor subunits at 2 to 24 h after ECS. mRNAs for the alpha 1 and beta 2 subunits were significantly increased in cerebellum at 4 and 8 h after ECS, and returned to control levels at 24 h. No changes were observed in alpha 2, beta 3, gamma 1, or gamma 2 subunits, and no changes in any subunit evaluated were observed in cortex or hippocampus. These data corroborate prior results obtained for the alpha 1 subunit using Northern hybridization, and illustrate the utility of the PCR assay in quantitating low-abundance mRNAs.

Effect of clomipramine and lithium on fenfluramine-induced hormone release in major depression

Prolactin (PRL) and cortisol responses to oral administration of d-1 fenfluramine hydrochloride (60 mg) and placebo were examined in patients with endogenous major depressive disorder on three separate occasions: prior to treatment with clomipramine (CMI), after 4 weeks of CMI administration (175-250) mg/day), and 3 weeks after addition of lithium (Li) carbonate (serum level 0.5-0.9 mmol) to the treatment regimen. CMI significantly increased baseline PRL levels which were further elevated following Li supplementation. PRL response to fenfluramine (minus elevated baseline PRL levels) but not to placebo, was significantly increased by CMI administration, reflected over the 6-hr time course examined and in peak minus baseline values. Following addition of Li, the degree of enhancement was diminished although the peak minus baseline value remained significant relative to the pretreatment response. Cortisol levels were not increased by fenfluramine and were not altered by CMI or CMI + Li administration. The effect of CMI extends previous observations regarding the action of antidepressant treatment on serotenergically mediated hormone release. Methodological considerations relevant to the effect of CMI + Li are discussed.

Failure by tricyclic antidepressants to affect the increase of dopamine extracellular concentrations produced by haloperidol in the caudate and accumbens nuclei of rats

The effect of different inhibitors of monoamine uptake on dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) neuronal outflow was studied in the caudate and accumbens nuclei of rats, using the in vivo brain microdialysis method coupled to HPLC electrochemical detection. Under conditions of DA receptor blockade (as produced by the i.p. administration of 0.25 mg/kg of haloperidol), cocaine, GBR-12909 and d-amphetamine increased the concentration of extracellular DA beyond the effect produced by haloperidol alone in both areas studied. GBR-12909 and cocaine also increased DOPAC concentration, while d-amphetamine decreased it. On the contrary, the tricyclic antidepressants (TCA), desipramine and chloripramine, failed to modify the effect of haloperidol on DA and DOPAC neuronal outflow. It was concluded that: (a) nonadrenergic and serotonergic nerve terminals do not take up DA released from dopaminergic neurons, and (b) TCA have no effect on dopaminergic terminals.

Enhanced serotonergic responsivity following electroconvulsive therapy in patients with major depression

Prolactin release in response to fenfluramine hydrochloride (60 mg orally) and placebo was evaluated in 18 medication-free patients with RDC major depressive disorder, endogenous subtype, before and after a series of bilateral treatments with ECT. Before ECT, fenfluramine induced a twofold increase in plasma prolactin levels. This response was significantly enhanced after the ECT series, while baseline prolactin levels and response to the placebo challenge were not altered. There was no significant difference in plasma fenfluramine and norfenfluramine levels during the pre- and post-ECT challenges. These findings suggest that ECT enhances central serotonergic responsivity and extend to depressed patients pre-clinical observations regarding the effect of electroconvulsive shock on serotonergic function.

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.

Peripheral serotonergic markers in patients with suicidal behavior

Peripheral serotonergic parameters were studied in 17 patients with a history of suicidal behavior and in 17 age- and sex-matched healthy controls. Serotonin2 receptor function in platelets, measured as serotonin-induced [32P]phosphatidylinositol 4,5-bisphosphate hydrolysis, was significantly higher in patients than in age- and sex-matched controls. Increased serotonin2 receptor transduction was not correlated to psychiatric diagnosis, drug treatment or a history of violent suicide attempt. Monoamine oxidase activity was lower in platelets from patients with a history of suicidal behavior than in controls. In addition, whole blood serotonin was analyzed but no significant alterations were found in blood from patients.

Further evidence for a glial localization of rat cortical beta-adrenoceptors: studies of in vivo cyclic AMP responses to catecholamines

The present experiments were designed to clarify the cellular localization of postsynaptic beta-receptors in the rat cortex by studying the cellular source and pharmacological characteristics of in vivo cAMP responses to catecholamines. The method used to study in vivo cAMP responses in the brain involved microdialysis both to deliver catecholamines to cerebral tissue and to sample cAMP released in response to local beta-receptor activation. It was found that selective blockade of the metabolism of glial cells by fluorocitrate infusion produced a virtually complete (90%) inhibition of the cortical cAMP response to norepinephrine (NE). Selective damage of neurons by kainic acid infusion had little effect on the response. Pharmacological experiments showed that the response was selectively antagonized by a beta 1-receptor blocker which also selectively antagonized the cAMP response to NE in brain slices known to be localized in glial cells. These results support the hypothesis that beta-adrenoceptors of the rat cortex are predominantly localized on glial cells and therefore strongly suggest that these cells are an important target of the locus coeruleus noradrenergic system.

Electroconvulsive therapy. Current concepts

Recent developments in the practice and theory of ECT are reviewed. Indications, efficacy, and risk/benefit considerations are discussed with emphasis on the clinical utility and cost-effectiveness of increased and earlier usage of ECT in hospitalized patients. Treatment procedures are presented in some detail with listings of medical considerations, management of complications, and other applications to general hospital practice. Research on the mechanism of action, potential future developments, and some training issues are briefly discussed.

Pretreatment with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline accelerates the electroshock-induced decrease in density of beta-adrenoceptors but not functional downregulation

Intrapritoneal injection of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) to rats significantly reduced the density of alpha 1- and alpha 2-adrenoceptors in the cerebral cortex, without affecting beta-adrenoceptors. A single dose of EEDQ markedly accelerated the development of downregulation of beta-adrenoceptors induced by a short series of electroshocks. The accumulation of cAMP, induced by isoproterenol, was unchanged in rats treated with EEDQ, while the effect of noradrenaline was reduced, to the level observed after isoproterenol alone, indicating the attenuation of alpha-adrenoceptor function. The isoproterenol-induced accumulation of cAMP was not changed by EEDQ nor electroshock, not by the combined treatment. The stimulatory action of noradrenaline was reduced after EEDQ alone or in combination with electroshock, but the effect of electroshock alone was insignificant. The results suggest that the acceleration of downregulation of beta-adrenoceptors after combined treatment with an alpha-adrenoceptor blocking agent is related to elimination of the alpha-adrenergic potentiation of accumulation of cAMP mediated by beta-adrenoceptors.

Clinical studies of 5-HT function using i.v. L-tryptophan

1. Preclinical studies reveal that long-term treatment with antidepressant drugs induces significant changes in serotonergic (5-HT) receptor sensitivity. Similarly, clinical studies suggest that brain 5-HT function is abnormal in depression. Of the available methodologies for conducting such clinical studies, the pharmacological challenge strategy has proven particularly useful. 2. I.v. L-TRP has emerged as the most frequently used challenge agent in diagnostic and neuropsychopharmacological studies of 5-HT function. I.v. L-TRP increases serum prolactin (PRL) in humans, probably via 5-HT mechanisms. Under carefully standardized conditions, this PRL response to L-TRP appears to be a reasonably sensitive and valid measure of net 5-HT function. 3. The PRL response to L-TRP is blunted in depressed patients compared with healthy controls. Blunting has not been observed in panic disorder, obsessive compulsive disorder, or schizophrenia, although preliminary findings suggest it may occur in bulimia. 4. The PRL response to L-TRP is enhanced by certain classes of thymoleptic drugs (TCAs, MAOIs, 5-HT reuptake inhibitors, lithium) in a differentially time-dependent fashion. So-called "atypical" antidepressants (trazodone, mianserin) and benzodiazepines have no effect. Such findings are generally consistent with preclinical electrophysiological findings. 5. These clinical studies of the PRL response to L-TRP, in conjunction with emerging evidence that experimentally reduced plasma TRP can reverse the therapeutic effects of some antidepressants, suggest that antidepressant drug action may be more accurately conceptualized as 5-HT dependent rather than 5-HT enhancing. The availability of more selective 5-HT-active drugs promises to further clarify 5-HT mechanisms of neuropsychiatric disease and drug action at the clinical level.