Serotonin type-1A receptor imaging in depression

Reduced hippocampal volume in unmedicated, remitted patients with major depression versus control subjects

BACKGROUND

Hippocampal volumes obtained from a group of medication-free, remitted subjects with recurrent major depressive disorder (MDD) were compared against corresponding measures from healthy controls.

METHODS

Thirty-one subjects with recurrent MDD in full remission, and 57 healthy controls underwent high resolution magnetic resonance imaging (MRI) on a GE 3T scanner. Eight patients with MDD were medication-naive, and twenty-three MDD patients were off antidepressant medications for a mean of 30 months at the time of the MRI study.

RESULTS

Patients showed smaller total and posterior hippocampal volume relative to controls. Anterior hippocampal volume did not differ between patients and controls.

CONCLUSIONS

Recurrent depression is associated with smaller hippocampal volume which is most prominent in the posterior hippocampus. Smaller hippocampal volume appears to be a trait characteristic for MDD.

Cellular mechanisms underlying the effects of an early experience on cognitive abilities and affective states

In the present study we investigated the effects of neonatal handling, an animal model of early experience, on spatial learning and memory, on hippocampal glucocorticoid (GR), mineralocorticoid (MR) and type 1A serotonin (5-HT1A) receptors, as well as brain derived neurotrophic factor (BDNF), and on circulating leptin levels, of male rats.

METHOD

Spatial learning and memory following an acute restraint stress (30 min) were assessed in the Morris water maze. Hippocampal GR, MR and BDNF levels were determined immunocytochemically. 5-HT1A receptors were quantified by in vitro binding autoradiography. Circulating leptin levels, following a chronic forced swimming stress, were measured by radioimmunoassay (RIA). Data were statistically analyzed by analysis of variance (ANOVA).

RESULTS

Neonatal handling increased the ability of male rats for spatial learning and memory. It also resulted in increased GR/MR ratio, BDNF and 5-HT1A receptor levels in the hippocampus. Furthermore, leptin levels, body weight and food consumption during chronic forced swimming stress were reduced as a result of handling.

CONCLUSION

Neonatal handling is shown to have a beneficial effect in the males, improving their cognitive abilities. This effect on behavior could be mediated by the handling-induced increase in hippocampal GR/MR ratio and BDNF levels. The handling-induced changes in BDNF and 5-HT1A receptors could underlie the previously documented effect of handling in preventing "depression". Furthermore, handling is shown to prevent other maladaptive states such as stress-induced hyperphagia, obesity and resistance to leptin.

Alterations in cell adhesion molecule L1 and functionally related genes in major depression: a postmortem study

BACKGROUND

Current research in depression aims to delineate genes involved in neuronal plasticity that are altered in the disease or its treatment. We have shown antidepressant induced increases in three interrelated genes, cell adhesion molecule L1 (CAM-L1), laminin, and cAMP response element binding protein (CREB), and a reciprocal decrease in these genes consequent to stress. Presently we hypothesized that CAM-L1, CREB, and laminin may be altered in post mortem brains of depressed subjects.

METHODS

Studies were performed in the prefrontal and in the ventral parieto-occipital cortices, of 59 brains from depressed, bipolar, and schizophrenic subjects, and normal controls, obtained from the Stanley Foundation Brain Collection. mRNA and protein levels were determined by RT-PCR and Western blot analysis, respectively.

RESULTS

Levels of CAM-L1 and of phosphorylated CREB (pCREB) were increased in the prefrontal cortex of the depressed group, while CAM-L1, laminin and pCREB were decreased in the parieto-occipital cortex. Depressed subjects receiving antidepressants differed from subjects not receiving antidepressants in the expression of CAM-L1 and laminin in the parieto-occipital cortex, and in the expression of pCREB in the prefrontal cortex.

CONCLUSIONS

The present findings of specific alterations in depression and antidepressant treatment particularly in CAM-L1 suggest that this gene may play an important role in the pathophysiology and treatment of depression.

5-HT1A receptors, gene repression, and depression: guilt by association

The serotonin system is implicated in major depression and suicide and is negatively regulated by somatodendritic 5-HT1A autoreceptors. Desensitization of 5-HT1A autoreceptors is implicated in the 2- to 3-week latency for antidepressant treatments. Alterations in 5-HT1A receptor levels are reported in depression and suicide, and gene knockout of the 5-HT1A receptor results in an anxiety phenotype, suggesting that abnormal transcriptional regulation of this receptor gene may underlie these disorders. The 5-HT1A receptor gene is negatively regulated in neurons by repressors including REST/NRSF, Freud-1, NUDR/Deaf-1, and Hes5. The association with major depression, suicide, and panic disorder of a new functional 5-HT1A polymorphism at C(-1019)G that selectively blocks repression of the 5-HT1A autoreceptor by NUDR further suggests a causative role for altered regulation of this receptor in predisposition to mental illness. The authors review evidence that altered transcription of the 5-HT1A receptor can affect the serotonin system and limbic and cortical areas, leading to predisposition to depression.

Wheel running alters serotonin (5-HT) transporter, 5-HT1A, 5-HT1B, and alpha 1b-adrenergic receptor mRNA in the rat raphe nuclei

BACKGROUND

Altered serotonergic (5-HT) neurotransmission is implicated in the antidepressant and anxiolytic properties of physical activity. In the current study, we investigated whether physical activity alters factors involved in the regulation of central 5-HT neural activity.

METHODS

In situ hybridization was used to quantify levels of 5-HT transporter (5-HTT), 5-HT(1A), 5-HT(1B), and alpha(1b)-adrenergic receptor (alpha(1b) ADR) messenger ribonucleic acids (mRNAs) in the dorsal (DRN) and median raphe (MR) nuclei of male Fischer rats after either sedentary housing or 3 days, 3 weeks, or 6 weeks of wheel running.

RESULTS

Wheel running produced a rapid and lasting reduction of 5-HT(1B) mRNA in the ventral DRN. Three weeks of wheel running decreased 5-HTT mRNA in the DRN and MR and increased alpha(1b) ADR mRNA in the DRN. After 6 weeks of wheel running, 5-HTT mRNA remained reduced, but alpha(1b) ADR mRNA returned to sedentary levels. Serotonin(1A) mRNA was increased in the MR and certain DRN subregions after 6 weeks only.

CONCLUSIONS

Data suggest that the central 5-HT system is sensitive to wheel running in a time-dependent manner. The observed changes in mRNA regulation in a subset of raphe nuclei might contribute to the stress resistance produced by wheel running and the antidepressant and anxiolytic effects of physical activity.

Brain 5-HT1A receptor binding in chronic fatigue syndrome measured using positron emission tomography and [11C]WAY-100635

BACKGROUND

Research from neuroendocrine challenge and other indirect studies has suggested increased central 5-HT function in chronic fatigue syndrome (CFS) and increased 5-HT1A receptor sensitivity. We assessed brain 5-HT1A receptor binding potential directly using the specific radioligand [11C]WAY-100635 and positron emission tomography (PET).

METHODS

We selected 10 patients from a tertiary referral clinic who fulfilled the CDC consensus criteria for CFS. To assemble a homogenous group and avoid confounding effects, we enrolled only subjects who were completely medication-free and did not have current comorbid psychiatric illness. We also scanned 10 healthy control subjects.

RESULTS

There was a widespread reduction in 5-HT1A receptor binding potential in CFS relative to control subjects. This was particularly marked in the hippocampus bilaterally, where a 23% reduction was observed.

CONCLUSIONS

There is evidence of decreased 5-HT1A receptor number or affinity in CFS. This may be a primary feature of CFS, related to the underlying pathophysiology, or a finding secondary to other processes, such as previous depression, other biological changes or the behavioral consequences of CFS.

The Darwinian concept of stress: benefits of allostasis and costs of allostatic load and the trade-offs in health and disease

Why do we get the stress-related diseases we do? Why do some people have flare ups of autoimmune disease, whereas others suffer from melancholic depression during a stressful period in their life? In the present review possible explanations will be given by using different levels of analysis. First, we explain in evolutionary terms why different organisms adopt different behavioral strategies to cope with stress. It has become clear that natural selection maintains a balance of different traits preserving genes for high aggression (Hawks) and low aggression (Doves) within a population. The existence of these personality types (Hawks-Doves) is widespread in the animal kingdom, not only between males and females but also within the same gender across species. Second, proximate (causal) explanations are given for the different stress responses and how they work. Hawks and Doves differ in underlying physiology and these differences are associated with their respective behavioral strategies; for example, bold Hawks preferentially adopt the fight-flight response when establishing a new territory or defending an existing territory, while cautious Doves show the freeze-hide response to adapt to threats in their environment. Thus, adaptive processes that actively maintain stability through change (allostasis) depend on the personality type and the associated stress responses. Third, we describe how the expression of the various stress responses can result in specific benefits to the organism. Fourth, we discuss how the benefits of allostasis and the costs of adaptation (allostatic load) lead to different trade-offs in health and disease, thereby reinforcing a Darwinian concept of stress. Collectively, this provides some explanation of why individuals may differ in their vulnerability to different stress-related diseases and how this relates to the range of personality types, especially aggressive Hawks and non-aggressive Doves in a population. A conceptual framework is presented showing that Hawks, due to inefficient management of mediators of allostasis, are more likely to be violent, to develop impulse control disorders, hypertension, cardiac arrhythmias, sudden death, atypical depression, chronic fatigue states and inflammation. In contrast, Doves, due to the greater release of mediators of allostasis (surplus), are more susceptible to anxiety disorders, metabolic syndromes, melancholic depression, psychotic states and infection.

Serotonin 1A receptor binding and treatment response in late-life depression

Depression in late life carries an increased risk of dementia and brittle response to treatment. There is growing evidence to support a key role of the serotonin type 1A (5-HT(1A)) receptor as a regulator of treatment response, particularly the 5-HT(1A) autoreceptor in the dorsal raphe nucleus (DRN). We used [11C]WAY 100635 and positron emission tomography (PET) to test our hypothesis that 5-HT(1A) receptor binding in the DRN and prefrontal cortex is altered in elderly depressives and that these measures relate to treatment responsivity. We studied 17 elderly subjects with untreated (nonpsychotic, nonbipolar) major depression (four men, 13 women; mean age: 71.4+/-5.9) and 17 healthy control subjects (eight men, nine women; mean age: 70.0+/-6.7). Patients were subsequently treated with paroxetine as part of a clinical trial of maintenance therapies in geriatric depression. [11C]WAY 100635 PET imaging was acquired and binding potential (BP) values derived using compartmental modeling. We observed significantly diminished [11C]WAY 100635 binding in the DRN in depressed (BP = 2.31+/-0.90) relative to control (BP = 3.69+/-1.56) subjects (p = 0.0016). Further, the DRN BP was correlated with pretreatment Hamilton Depression Rating Scores (r = 0.60, p = 0.014) in the depressed cohort. A trend level correlation between DRN binding and time to remission (r = 0.52, p = 0.067) was observed in the 14 depressed patients for whom these data were available. Our finding of decreased [11C]WAY 100635 binding in the brainstem region of the DRN in elderly depressed patients supports evidence of altered 5-HT(1A) autoreceptor function in depression. Further, this work indicates that dysfunction in autoreceptor activity may play a central role in the mechanisms underlying treatment response to selective serotonin reuptake inhibitors in late-life depression.

Effect of chronic lithium treatment on glucocorticoid and 5-HT1A receptor messenger RNA in hippocampal and dorsal raphe nucleus regions of the rat brain

The therapeutic mechanism of action of lithium in the treatment of bipolar disorder is not well understood. Dysfunction of both 5-HT(1A) receptor mediated neurotransmission and the glucocorticoid receptor is associated with mood disorders, and preclinical studies suggest that lithium treatment can modulate these receptor subtypes. In this study, we investigated the effect of chronic lithium treatment on 5-HT(1A) receptors and glucocorticoid receptors in the rat brain. Male Sprague-Dawley rats were treated with lithium (3 mmol/kg/day) or saline for 28 days via subcutaneous implanted mini-osmotic pumps. After 28 days of treatment, the expression of mRNA for 5-HT(1A) receptors and glucocorticoid receptors in the rat hippocampus and dorsal raphe nucleus was determined by in situ hybridization histochemistry. Chronic administration of lithium decreased mRNA coding for post-synaptic 5-HT(1A) receptors in hippocampal subregions but not for somatodentritic 5-HT(1A) receptors in the dorsal raphe nucleus. Chronic administration of lithium did not affect mRNA coding for glucocorticoid receptors in hippocampal subregions or in the dorsal raphe nucleus. Mean plasma lithium levels in the lithium-treated group were 0.50 +/- 0.03 mmol/l; all animals appeared healthy and maintained a normal increase in body weight. Given recent reports implicating hypersensitive post-synaptic 5-HT(1A) receptors in bipolar manic patients, the present study suggests that down-regulation of this receptor population may be important in the therapeutic mechanism of action of lithium.

Discovering endophenotypes for major depression

The limited success of genetic studies of major depression has raised questions concerning the definition of genetically relevant phenotypes. This paper presents strategies to improve the phenotypic definition of major depression by proposing endophenotypes at two levels: First, dissecting the depressive phenotype into key components results in narrow definitions of putative psychopathological endophenotypes: mood bias toward negative emotions, impaired reward function, impaired learning and memory, neurovegetative signs, impaired diurnal variation, impaired executive cognitive function, psychomotor change, and increased stress sensitivity. A review of the recent literature on neurobiological and genetic findings associated with these components is given. Second, the most consistent heritable biological markers of major depression are proposed as biological endophenotypes for genetic studies: REM sleep abnormalities, functional and structural brain abnormalities, dysfunctions in serotonergic, catecholaminergic, hypothalamic-pituitary-adrenocortical axis, and CRH systems, and intracellular signal transduction endophenotypes. The associations among the psychopathological and biological endophenotypes are discussed with respect to specificity, temporal stability, heritability, familiality, and clinical and biological plausibility. Finally, the case is made for the development of a new classification system in order to reduce the heterogeneity of depression representing a major impediment to elucidating the genetic and neurobiological basis of this common, severe, and often life-threatening illness.

A positron emission tomography study of the 5-HT1A receptor in schizophrenia and during clozapine treatment

Several post-mortem studies have identified increases of 5-HT1A receptor density in frontal cortical areas in schizophrenic patients, and one has found increases in the cerebellar vermis. Clozapine has moderate affinity at the 5-HT1A receptor, and this may be of therapeutic importance. This positron emission tomography (PET) study attempted to replicate the post-mortem findings in vivo and sought an occupancy effect of clozapine at the 5-HT1A receptor. We recruited healthy controls, and patients with schizophrenia who were divided into those receiving clozapine and those receiving neuroleptics lacking 5-HT1A receptor affinity. Each volunteer received a PET scan, using the 5-HT1A receptor radioligand [carbonyl-11C]WAY-100635, and a magnetic resonance imaging scan. The cerebellar vermis was examined by comparing time-activity data between groups. For other brain regions (the raphe and subdivisions of the cerebral cortex), binding potential images were generated to reflect receptor density, then analysed using 'region of interest' and voxel-by-voxel methods. No significant changes of 5-HT1A receptor density were found in schizophrenic patients compared to controls. Two other PET studies, containing drug naïve rather than medicated schizophrenic patients, have also reported no increase in 5-HT1A receptor density in the frontal cortex. The results obtained in vivo bring into question the importance of the receptor in the pathophysiology of the illness. Clozapine did not occupy the 5-HT1A receptor at clinical doses. This is consistent with recent related PET results: 5-HT1A agonists do not appear to measurably block the binding of antagonist radiotracers in man at doses that are pharmacologically active but which are limited by tolerability.

Platelet serotonin and plasma prolactin and cortisol in healthy, depressed and schizophrenic women

Serotonin (5-hydroxytryptamine, 5-HT) is involved in the regulation of hypothalamic-pituitary-adrenal axis (HPA) activity and prolactin (PRL) secretion. The present study examined the relationship between platelet 5-HT and plasma cortisol and PRL concentrations in 20 schizophrenic, 25 depressed, and 25 healthy women. At the time of blood sampling, the schizophrenic and depressed patients had been drug-free for at least 7 days. Platelet 5-HT, plasma cortisol and PRL concentrations were determined by spectrofluorimetric, radioimmunoassay and immunoradiometric methods, respectively. Platelet 5-HT concentration was significantly higher in schizophrenic patients than in depressed patients or in healthy controls, while it was significantly lower in depressed patients than in healthy controls or in schizophrenic patients. Plasma cortisol levels were significantly increased both in schizophrenic and in depressed patients compared with values in healthy controls. Values of plasma PRL were similar across groups. A significant correlation was found between platelet 5-HT and plasma cortisol, and platelet 5-HT and plasma PRL concentrations in healthy controls, but not in schizophrenic or depressed patients. There was no significant relationship between plasma PRL and cortisol levels in any of the groups. Our data, although obtained on peripheral biochemical markers, indicate that depression and schizophrenia are characterized by disturbed 5-HT transmission and dysregulated HPA axis activity.

Occupancy of agonist drugs at the 5-HT1A receptor

Drugs acting on the 5-HT1A receptor are used in the treatment of depression, generalized anxiety disorder, and schizophrenia. This study investigated 5-HT1A receptor occupancy by the 5-HT1A agonist drugs flesinoxan (a highly selective probe for the 5-HT1A receptor) and ziprasidone (a novel atypical antipsychotic drug). Using a within-subject design, 14 healthy volunteers each received two positron emission tomography scans using the selective 5-HT1A antagonist radiotracer [11C]WAY-100635. One scan constituted a baseline, while the other followed either 1 mg flesinoxan or 40 mg ziprasidone orally. In addition, rats were pretreated with intravenous flesinoxan at doses ranging from 0.001 to 5 mg/kg then [11C]WAY-100635 binding measured ex vivo. Cerebral cortical and hippocampal regions of interest, and cerebellar reference regions were sampled to estimate 5-HT1A receptor occupancy (inferred from reductions in specific radioligand binding). In man, occupancy was not significant despite volunteers experiencing side effects consistent with central serotonergic activity. The mean cerebral cortex occupancy (+/- 1 SD) for flesinoxan was 8.7% (+/- 13%), and for ziprasidone 4.6% (+/- 17%). However, in rats, flesinoxan achieved significant and dose-related occupancy (17-57%) at 0.25 mg/kg and above. We conclude that 5-HT1A receptor agonists produce detectable occupancy only at higher doses that would produce unacceptable levels of side effects in man, although lower doses are sufficient to produce pharmacological effects. The development of agonist radiotracers may increase the sensitivity of detecting agonist binding, as 5-HT1A antagonists bind equally to low- and high-affinity receptor states, while agonists bind preferentially to the high-affinity state.

ATF2, a member of the CREB/ATF family of transcription factors, in chronic stress and consequent to antidepressant treatment: animal models and human post-mortem brains

The regulation of gene expression has been implicated in the etiology and treatment of depression. Transcription factors serve as the intermediates between intracellular cascades and gene expression, and may therefore be involved in the pathophysiology and pharmacotherapy of depression. We and others have previously reported an increase in the phosphorylation of the transcription factor cAMP response element binding protein (CREB) by antidepressants, alongside brain region-specific alterations in pCREB by stress. In the present study, we examined the expression of another member of the CREB/ATF family of transcription factors, ATF2, in the brains of rats chronically treated with two different antidepressants, and in rats 4 months after their exposure to prolonged stress. ATF2 phosphorylation was decreased by antidepressants and increased at the aftermath of prolonged stress, specifically in the frontal cortex. We also examined ATF2 expression in the ventral parieto-occipital region of post-mortem human brains of normal controls, depressed, bipolar, and schizophrenic patients, obtained from the Stanley Foundation Brain Consortium. No alterations were observed in the levels of ATF2. However, in the depressed group, the pATF2 levels were higher in unmedicated compared to medicated patients, suggesting an antidepressant-induced reduction in pATF2. We discuss the possible role of ATF2 in depression, and propose that an interplay between ATF2 and CREB, and possibly other transcription factors, determines the final gene expression pattern in the etiology and treatment of depression.

Gene expression profiling of depression and suicide in human prefrontal cortex

Mood disorders are a major cause of disability. Etiology includes genetic and environmental factors, but the responsible genes have yet to be identified. Using DNA microarrays, we have conducted a large-scale gene expression analysis, in two regions of the human prefrontal cortex from post-mortem matched groups of subjects with major depression who had died by suicide, and control subjects who died from other causes and were free from psychiatric disorders. Bioinformatic analysis was used to investigate molecular and cellular pathways potentially involved in depression and suicidal behavior. We tested several hypotheses of disease pathology and of their putative molecular impact, including changes in single genes, the existence of subgroups of patients or disease subtypes, or the possibility of common biological pathways being affected in the disease process. Within the analytical limits of this relatively large genomic study, we found no evidence for molecular differences that correlated with depression and suicide, suggesting a pathology that is below the detection level of current genomic approaches, or that is either localized to other brain areas, or more associated with post-transcriptional effects and/or changes in protein levels or functions, rather than altered transcriptome in the prefrontal cortex.

Abnormal behavioral phenotypes of serotonin transporter knockout mice: parallels with human anxiety and depression

Evidence of a link between genetic variation of the serotonin transporter and depression and anxiety prompted the generation of serotonin transporter knockout mice. Loss of serotonin reuptake function in knock-outs causes reduced clearance of extracellular serotonin and associated alterations in serotonin neuronal firing and receptor function. Behavioral phenotyping function in knock-outs revealed genetic background-related abnormalities, including increased anxiety-like behaviors, reduced aggression, and exaggerated stress responses. Ongoing studies focus on identifying environmental, genetic, and developmental factors interacting with the htt mutation to produce these abnormalities. Serotonin transporter null mutant mice provide a model system to study how genetic variation in serotonin transporter function affects risk for neuropsychiatric disease.

Impaired repression at a 5-hydroxytryptamine 1A receptor gene polymorphism associated with major depression and suicide

Inhibition of serotonergic raphe neurons is mediated by somatodendritic 5-HT1A autoreceptors, which may be increased in depressed patients. We report an association of the C(-1019)G 5-HT1A promoter polymorphism with major depression and suicide in separate cohorts. In depressed patients, the homozygous G(-1019) allele was enriched twofold versus controls (p = 0.0017 and 0.0006 for G/G genotype and G allele distribution, respectively), and in completed suicide cases the G(-1019) allele was enriched fourfold (p = 0.002 and 0.00008 for G/G genotype and G allele distribution, respectively). The C(-1019) allele was part of a 26 bp imperfect palindrome that bound transcription factors nuclear NUDR [nuclear deformed epidermal autoregulatory factor (DEAF-1)]/suppressin and Hairy/Enhancer-of-split-5 (Drosophila) (Hes5) to repress 5-HT1A or heterologous promoters, whereas the G(-1019) allele abolished repression by NUDR, but only partially impaired Hes5-mediated repression. Recombinant NUDR bound specifically to the 26 bp palindrome, and endogenous NUDR was present in the major protein-DNA complex from raphe nuclear extracts. Stable expression of NUDR in raphe cells reduced levels of endogenous 5-HT1A protein and binding. NUDR protein was colocalized with 5-HT1A receptors in serotonergic raphe cells, hippocampal and cortical neurons, and adult brain regions including raphe nuclei, indicating a role in regulating 5-HT1A autoreceptor expression. Our data indicate that NUDR is a repressor of the 5-HT1A receptor in raphe cells the function of which is abrogated by a promoter polymorphism. We suggest a novel transcriptional model in which the G(-1019) allele derepresses 5-HT1A autoreceptor expression to reduce serotonergic neurotransmission, predisposing to depression and suicide.

Chronic stress attenuates glucocorticoid negative feedback: involvement of the prefrontal cortex and hippocampus

Disruption of the glucocorticoid negative feedback system is observed in approximate one half of human depressives, and a similar condition is induced in animals by chronic stress. This disruption is thought to involve down-regulation of glucocorticoid receptors (GRs) in the feedback sites of the brain. However, the responsible site of the brain has not been well elucidated. Here we examined the effects of chronic stress induced by water immersion and restraint (2 h/day) for 4 weeks followed by recovery for 10 days on the GR levels in the prefrontal cortex (PFC), hippocampus, and hypothalamus of rats using a Western immunoblot technique. In the PFC, the cytosolic GR levels were decreased, but the nuclear GR levels were not changed. In the hippocampus, the levels of cytosolic and nuclear GRs were increased. However, there were no marked changes in the GR levels in the hypothalamus. The changes in the cytosolic GR levels were confirmed at the mRNA level by an in situ hybridization technique. We next examined the suppressive effects of dexamethasone (DEX) infusions into these regions on the circulating corticosterone levels. When DEX was infused into the PFC or hippocampus of the chronically stressed rats, the suppressive response to DEX was abolished, but the response was normal in the hypothalamus. In addition, when DEX was injected systemically to the chronically stressed rats, the suppressive response to DEX was significantly attenuated. These results suggest that the abnormal changes in GRs in the higher centers of the hypothalamo-pituitary-adrenal axis are involved in the chronic stress-induced attenuation of the feedback. Since dysfunction of the PFC or hippocampus is implicated in the pathogenesis of depression, the present findings would help to understand the mechanisms underlying the disrupted feedback system and its relation to brain dysfunction in depression.

Altered glucocorticoid rhythm attenuates the ability of a chronic SSRI to elevate forebrain 5-HT: implications for the treatment of depression

Both glucocorticoids and selective serotonin reuptake inhibitors (SSRIs) alter aspects of 5-HT function including somatodendritic 5-HT1A autoreceptor sensitivity. Many depressed patients prescribed SSRIs have pre-existing flattened diurnal gluococorticoid rhythm. In these patients, interactions between flattened glucocorticoid rhythm and chronic SSRIs, which impact on the SSRI's ability to elevate forebrain 5-HT, may alter clinical efficacy. To address this issue rats underwent implantation of slow-release corticosterone (75 mg pellet s.c.) (to flatten the glucocorticoid rhythm) or sham surgery, and injection of fluoxetine (10 mg/kg/day i.p., 12 days) or vehicle. Using microdialysis in the frontal cortex we found that (21 h after the last injection) extracellular 5-HT was elevated in fluoxetine- or corticosterone-treated animals, but not in those treated with corticosterone plus fluoxetine. In fluoxetine-treated animals, blockade of terminal reuptake by local perfusion of fluoxetine increased 5-HT to the same level as it did in controls, suggesting normal terminal 5-HT release after chronic fluoxetine. However, 5-HT levels following local reuptake blockade in both the corticosterone and corticosterone plus fluoxetine groups were lower than controls, suggesting a corticosterone-induced decrease in terminal release. Finally in fluoxetine, corticosterone, and corticosterone plus fluoxetine groups, there was marked 5-HT1A receptor desensitization, evidenced by attenuation of the decrease in 5-HT release following systemic fluoxetine injection. The data indicate that, despite desensitization of 5-HT1A autoreceptors, concurrent flattened glucocorticoid rhythm compromises the ability of SSRIs to elevate forebrain 5-HT. These findings suggest a potential mechanism for the reduced antidepressant efficacy of SSRIs in those patients with pre-existing glucocorticoid abnormalities.

Early life adversity programs changes in central 5-HT neuronal function in adulthood

Early life adversity is associated with an increased incidence of psychiatric illness in adulthood. Although the mechanisms underlying this association are unclear, one possible substrate is brain 5-hydroxytryptamine neurotransmission, which is reportedly abnormal in several psychiatric disorders. This study examined the effect of a rat model of early life adversity, early maternal separation, on 5-hydroxytryptamine neurotransmission in adulthood. In vitro electrophysiological experiments revealed that, in early maternal separation rats compared with controls, the sensitivity of alpha1-adrenoceptors on 5-hydroxytryptamine neurons in the dorsal raphe nucleus was significantly reduced, whilst the sensitivity of 5-hydroxytryptamine1A receptors showed a nonsignificant trend to reduction. In in vivo microdialysis experiments, the 5-hydroxytryptamine1A receptor agonist-induced suppression of 5-hydroxytryptamine release in the frontal cortex was reduced in early maternal separation animals, suggesting desensitization of 5-hydroxytryptamine1A autoreceptors. There was no increase in basal 5-hydroxytryptamine in the frontal cortex as measured by microdialysis and a nonsignificant trend towards increased basal firing activity of classical (non-bursting) 5-hydroxytryptamine neurons in the dorsal raphe nucleus measured by in vivo electrophysiology. Finally, early maternal separation failed to alter expression of messenger ribonucleic acids coding for 5-hydroxytryptamine1A or alpha1B receptors in the dorsal raphe nucleus as measured by in situ hybridization histochemistry, suggesting that functional changes in receptor sensitivity observed are not due to changes in receptor gene transcription. The findings demonstrate that early life adversity programs changes in sensitivity of the two principal regulators of 5-hydroxytryptamine neuronal activity. Similar effects in humans may contribute to the increased incidence of psychiatric illness in individuals exposed to early life adversity.

Implantation of a slow release corticosterone pellet induces long-term alterations in serotonergic neurochemistry in the rat brain

Many studies point to an involvement of deficits in the serotonergic nervous system and hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis function with depression. Indeed early life stress, involving HPA axis activation, may predispose susceptible individuals to develop depression in later life. This study investigates the effects of elevating the neuroendocrine stress hormone, corticosterone, for 1 week in adolescent rats on markers of serotonergic neurone function at adulthood. Slow release corticosterone pellets were implanted for 7 days and various serotonergic parameters, as well as plasma corticosterone levels, were measured on day 7 or on day 28 (21 days following removal of the pellet). The corticosterone implant attenuated weight gain and reduced adrenal weights compared to that in control rats implanted with a cholesterol pellet. After 7 days, with the implant still in place, the diurnal variation in plasma corticosterone was reduced so that the level was approximately at that of the evening peak throughout the day. Twenty-one days after removal of the implant, the diurnal variation in plasma corticosterone returned. Corticosterone treatment decreased [3H] 8-hydroxy-2-(di-n-propylamino)tetralin binding to the 5-hydroxytryptamine1A receptor in the cortex but not in the hippocampus. Corticosterone treatment also enhanced the circadian rhythm observed in 5-hydroxyindoleacetic acid level and the ratio of 5-hydroxyindoleacetic acid to the 5-hydroxytryptamine in the frontal cortex. Despite corticosterone pellet removal 21 days earlier, there was a persistent decrease in whole body and adrenal weight, cortical 5-hydroxytryptamine1A receptor binding and an alteration in the diurnal variation in the 5-hydroxytryptamine "turnover" in the frontal cortex.

Saiko-ka-ryukotsu-borei-to, a herbal medicine, ameliorates chronic stress-induced depressive state in rotarod performance

Exposure to chronic stress is thought to play an important role in the etiology of depression. This disorder has been shown to involve disruption of the hypothalamo-pituitary-adrenal (HPA) system and dysfunction of the prefrontal cortex (PFC). We have demonstrated that chronic stress in rats induces similar HPA disruption or a depressive state caused by a reduction of dopaminergic and serotonergic transmission in the PFC. We have also shown that saiko-ka-ryukotsu-borei-to, a herbal medicine, prevents such chronic stress-induced HPA disruption. However, the behavioral and neurochemical bases of this drug remain unclear. Here we examined the effects of saiko-ka-ryukotsu-borei-to on the depressive behavioral state and the reduction of transmission resulting from chronic stress. The chronic stress was induced by water immersion and restraint (2 h/day) for 4 weeks followed by recovery for 10 days. The treatment with saiko-ka-ryukotsu-borei-to (100, 300, or 1000 mg/kg p.o.) ameliorated the stress-induced depressive state in a dose-dependent manner, evaluated by a rotarod test. A microdialysis study indicated that the drug treatment significantly prevented the chronic stress-induced decreases in extracellular concentrations of dopamine and serotonin in the PFC. These results suggest that saiko-ka-ryukotsu-borei-to ameliorates the chronic stress-induced depressive state based on the prevention of PFC dysfunction. These findings provide important information for treatment of depression.

EEG effects of buspirone and pindolol: a method of examining 5-HT1A receptor function in humans

RATIONALE

An involvement of 5-HT(1A) receptors is postulated in the pathophysiology of affective disorders and mechanism of action of antidepressants. Methods for studying their functional integrity in humans are, however, limited. Preliminary data suggests that activation of somatodendritic 5-HT(1A) receptors cause a negative shift in the EEG frequency spectrum. Animal research suggests that pindolol is an agonist at these receptors but an antagonist at postsynaptic 5-HT(1A) receptors.

OBJECTIVE

We postulated that while pindolol would antagonise known postsynaptic mediated neuroendocrine responses to the 5-HT(1A) agonist buspirone, both drugs would have a similar effect on the EEG frequency spectrum.

METHODS

Fourteen healthy men were administered placebo or pindolol (20 mg orally) 90 min before placebo or buspirone (30 mg orally) in a double blind cross-over study. Plasma prolactin and growth hormone were assayed and EEGs recorded before and after drug administration.

RESULTS

A significant negative shift in the EEG frequency spectrum was found for both buspirone and pindolol, with the combination producing a similar effect to each drug alone. In contrast, the neuroendocrine response to buspirone was significantly attenuated by pindolol.

CONCLUSIONS

The data obtained are consistent with the EEG effects of buspirone and pindolol being mediated by somatodendritic 5-HT(1A) receptors, in contrast to the neuroendocrine response, which is known to be mediated by postsynaptic receptors. The development of this novel method of assessing somatodendritic 5-HT(1A) receptors in humans is a potentially important advance which may allow the testing of hypotheses of its involvement in depression and response to antidepressants.

Flattening the corticosterone rhythm attenuates 5-HT1A autoreceptor function in the rat: relevance for depression

Depression is associated with glucocorticoid abnormalities, in particular a flattening of the diurnal cortisol rhythm. Recent data suggest that an important factor in the aetiology of depression may be a deficit in the function and expression of 5-HT(1A) receptors, which has been reported in depressed patients. The present study assessed the possibility that this cortisol abnormality is causal in the 5-HT(1A) receptor deficits. First, a rat model of flattened glucocorticoid rhythm was developed. Controlled release corticosterone pellets implanted for 14 days flattened the corticosterone rhythm and maintained levels constant midway between the nadir and zenith levels observed in sham-operated rats. Secondly, using microdialysis to assess 5-HT release in the hippocampus, the inhibitory response to 8-OHDPAT was measured to determine the sensitivity of somatodendritic 5-HT(1A) autoreceptors. Corticosterone treatment was found to induce a significant attenuation in the response to 8-OHDPAT, indicating functional desensitization of somatodendritic 5-HT(1A) autoreceptors. There was no effect of corticosterone treatment on basal extracellular 5-HT levels. The data suggest that the glucocorticoid abnormalities associated with depression may impact on the functioning of 5-HT(1A) receptors in the brain. These findings suggest that resolution of cortisol abnormalities may be a valuable target for pharmacotherapy in the treatment of depression.

Neural and behavioral substrates of mood and mood regulation

A review of behavioral and neurobiological data on mood and mood regulation as they pertain to an understanding of mood disorders is presented. Four approaches are considered: 1) behavioral and cognitive; 2) neurobiological; 3) computational; and 4) developmental. Within each of these four sections, we summarize the current status of the field and present our vision for the future, including particular challenges and opportunities. We conclude with a series of specific recommendations for National Institute of Mental Health priorities. Recommendations are presented for the behavioral domain, the neural domain, the domain of behavioral-neural interaction, for training, and for dissemination. It is in the domain of behavioral-neural interaction, in particular, that new research is required that brings together traditions that have developed relatively independently. Training interdisciplinary clinical scientists who meaningfully draw upon both behavioral and neuroscientific literatures and methods is critically required for the realization of these goals.

Involvement of 5-HT1A receptors in homeostatic and stress-induced adaptive regulations of paradoxical sleep: studies in 5-HT1A knock-out mice

For the last two decades, the involvement of 5-HT(1A) receptors in the regulation of vigilance states has been studied extensively thanks to pharmacological tools, but clear-cut conclusion has not been reached yet. By studying mutant mice that do not express this receptor type (5-HT(1A)-/-) and their wild-type 129/Sv counterparts, we herein demonstrate that 5-HT(1A) receptors play key roles in the control of spontaneous sleep-wakefulness cycles, as well as in homeostatic regulation and stress-induced adaptive changes of paradoxical sleep. Both strains of mice exhibited a diurnal sleep-wakefulness rhythm, but 5-HT(1A)-/- animals expressed higher amounts of paradoxical sleep than wild-type mice during both the light and the dark phases. In wild-type mice, pharmacological blockade of 5-HT(1A) receptors by WAY 100635 (0.5 mg/kg, i.p.) promoted paradoxical sleep, whereas the 5-HT(1A) agonist 8-OH-DPAT (0.25-1 mg/kg, s.c.) had an opposite effect. In contrast, none of the 5-HT(1A) receptor ligands affected sleep significantly in 5-HT(1A)-/- mice. However, 5-HT(1B) receptor stimulation by CP 94253 (1-3 mg/kg, i.p.) induced a reduction in paradoxical sleep in both strains, this effect being more pronounced in 5-HT(1A)-/- mutants. Finally, in contrast to wild-type mice, 5-HT(1A)-/- mutants did not exhibit any rebound of paradoxical sleep after either a 9 hr instrumental paradoxical sleep deprivation or a 90 min immobilization stress. Altogether, these data indicate that, in the mouse, 5-HT(1A) receptors participate in the spontaneous and homeostatic regulation, as well as in stress-induced adaptive changes of paradoxical sleep.

A chronic treatment with fluoxetine decreases 5-HT(1A) receptors labeling in mice selected as a genetic model of helplessness

Two lines of mice were bred for their opposite helpless behavior in the tail suspension test, i.e., helpless (HL) mice and non helpless (NHL) mice. The 5-HT(1A) receptor labeling was quantified by means of autoradiography with (3)H-8-OH-DPAT on brain sections from mice of these two lines. We observed a significantly higher level of (3)H-8-OH-DPAT binding sites density in HL mice comparatively to NHL mice, in the medial prefrontal, cingulate, motor and sensorial cortices, in several regions of the limbic system, such as CA3 field of hippocampus, dentate gyrus, medial and baso-medial amygdala, and in dorsal and median raphe nuclei. A chronic 21-day treatment with the antidepressant fluoxetine (10 mg/kg, i.p. daily) attenuated significantly the spontaneous helplessness in HL mice but did not alter the behavior of NHL mice. In the brain of HL mice chronically injected with fluoxetine, the elevated (3)H-8-OH-DPAT binding sites density was no longer observed after treatment in several regions, among which the raphe nuclei. Conversely, the antidepressant treatment did not modify the (3)H-8-OH-DPAT binding sites density in NHL mice. The variation of 5-HT(1A) receptors binding density in the HL mice in response to a chronic fluoxetine treatment parallels the attenuation of the spontaneous helplessness observed in the tail suspension test, and may underlie this behavior.

Effects of medications on cerebral blood flow in late-life depression

Both normal aging and late-life depression (LLD) are associated with reductions in regional cerebral blood flow (rCBF). The impact of medication treatment in baseline rCBF abnormalities in LLD is being investigated via functional imaging research. Some of this work can be informed by pharmacologic challenge studies, which exploit the role of serotonin in regulating rCBF. Preliminary evidence suggests that there may be both state- and trait-level disturbances in rCBF in LLD, and that a common pathway towards clinical response to somatic antidepressant treatments involves reduction in rCBF in critical prefrontal cortical brain regions. Studies of the effects of medications on rCBF in LLD have implications for understanding the neurobiology of treatment resistance in the elderly as well as the mechanisms of action of antidepressant treatments.

Chronic stress impairs rotarod performance in rats: implications for depressive state

Exposure to chronic stress is thought to precipitate or exacerbate several neuropsychiatric disorders such as depression. Here, we examined the effects of chronic stress administered by water immersion and restraint (2 h/day) for 4 weeks followed by a 10-day recovery period on rotarod performance. The time course study revealed that the riding time on a rotating rod was not affected at Day 1 or Week 1 of the stress period, but was significantly decreased at Week 4 and after the 10-day recovery period. However, traction performance and locomotor activity were not changed by chronic stress. We next examined the involvement of a serotonergic mechanism in the impairment of rotarod performance. The post-stress administration of a serotonergic antidepressant, trazodone (10 mg/kg, daily for 10 days) significantly ameliorated the impairment of rotarod performance. A microdialysis study also revealed a decrease in the extracellular concentration of serotonin in the prefrontal cortex. These results indicate that chronic stress impairs the rotarod performance in a manner that is not due to muscle relaxation or motor dysfunction, and this impairment may imply a behaviorally depressive state mediated by a serotonergic mechanism. These findings provide insight into the underlying mechanisms of stress-induced neuropsychiatric disorders.

Serotonin(1A) receptors in mood disorders: a combined genetic and genomic approach

The serotonin1A (5-HT1A) receptor has been under intense investigation, mostly due to its putative role in both the etiology and therapeutic treatments of depression and anxiety-related behaviors. However, the exact contribution of this receptor to normal brain physiology and disease processes remains poorly understood, due to a complex expression pattern and multiple functions. Recent development in genetic and genomic approaches allows not only for more refined functional dissection, but also for probing large gene databases for unknown gene product interactions. Here, we describe an experimental approach that is based on a combination of regional and temporal genetic manipulations of the 5-HT1A receptor with large-scale gene expression profiling to attempt to untangle the distinct roles for this receptor in particular brain regions, as well as to identify molecular partners that mediate its function. In turn, new leads for understanding mechanisms of anxiety, depression and their pharmacological treatments may be generated.

Effect of 5-HT on binding of [(11)C] WAY 100635 to 5-HT(IA) receptors in rat brain, assessed using in vivo microdialysis nd PET after fenfluramine

By using a combination of positron emission tomography (PET) and postmortem tissue dissection, the effect of increased endogenous serotonin on specific binding of [(11)C]WAY 100635 to the 5-HT(1A) receptor was investigated in rat brain in vivo. The binding studies were complemented by in vivo microdialysis to monitor 5-HT levels in similarly treated isoflurane-anaesthetised rats, with the dialysis probe locations corresponding to two of the tissues sampled for specific binding of the radioligand. Fenfluramine treatment (10 mg/kg i.p.) resulted in a approximately 5-fold increase in extracellular 5-HT in medial prefrontal cortex and a approximately 15-fold increase in lateral hippocampus, maximal at approximately 40 min after injection. PET scan duration was either 60 or 90 min, beginning 30 min after fenfluramine injection. The specific binding of [(11)C]WAY 100635 was reduced by 10-20% in hippocampus, which showed highest binding in control animals. Specific binding, however, was unaffected in both prefrontal cortex and midbrain raphe, each additional high binding regions. The minimal effects are consistent with a low baseline occupancy of the 5-HT(1A) receptor by 5-HT in vivo, so that only a large change in endogenous agonist concentration will affect radioligand binding. This implies that utilisation of [(11)C]WAY 100635 in human PET to quantify 5-HT(1A) receptor expression can be extended to pathology where synaptic 5-HT levels are altered as a consequence of the disease state.

Pharmacology of antidepressants

Presently in the United States, 21 compounds have been approved by the Food and Drug Administration as antidepressants. Two additional drugs marketed outside the United States as antidepressants have been approved for obsessive-compulsive disorder. Nearly one half of all these compounds became available within the past 12 years, whereas the first antidepressant was available more than 40 years ago. After the clinical aspects of depression are introduced in this article, the pharmacology of the newer generation drugs is reviewed in relationship to the older compounds. The information in this review will help clinicians treat acute depression with pharmacological agents.

Corticosteroids in relation to fear, anxiety and psychopathology

Corticosteroids play extremely important roles in fear and anxiety. The mechanisms by which corticosteroids exert their effects on behavior are often indirect, because, although corticosteroids do not regulate behavior, they induce chemical changes in particular sets of neurons making certain behavioral outcomes more likely in certain contexts as a result of the strengthening or weakening of particular neural pathways. The timing of corticosteroid increase (before, during or after exposure to a stressor) determines whether and how behavior is affected. The present review shows that different aspects of fear and anxiety are affected differentially by the occupation of the mineralocorticoid receptor (MR) or glucocorticoid receptor (GR) at different phases of the stress response. Corticosteroids, at low circulating levels, exert a permissive action via brain MRs on the mediation of acute freezing behavior and acute fear-related plus-maze behavior. Corticosteroids, at high circulating levels, enhance acquisition, conditioning and consolidation of an inescapable stressful experience via GR-mechanisms. Brain GR-occupation also promotes processes underlying fear potentiation. Fear potentiation can be seen as an adjustment in anticipation of changing demands. However, such feed-forward regulation may be particularly vulnerable to dysfunction. MR and/or GR mechanisms are involved in fear extinction. Brain MRs may be involved in the extinction of passive avoidance, and GRs may be involved in mediating the extinction of active avoidance. In the developing brain, corticosteroids play a facilitatory role in the ontogeny of freezing behavior, probably via GRs in the dorsal hippocampus, and their influence on the development of the septo-hippocampal cholinergic system. Corticosteroids can exert maladaptive rather than adaptive effects when their actions via MRs and GRs are chronically unbalanced due to chronic stress. Both mental health of humans and animal welfare is likely to be seriously threatened after psychosocial stress, prolonged stress, prenatal stress or postnatal stress, especially when maternal care or social support is absent, because these can chronically dysregulate the central MR/GR balance. In such circumstances the normally adaptive corticosteroid responses can become maladaptive.