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

Rapid reorganization of serotonin projections and antidepressant response to 5-HT1A-biased agonist NLX-101 in fluoxetine-resistant cF1ko mice

Selective serotonin (5-HT) reuptake inhibitors (SSRIs) like fluoxetine remain a first-line treatment for major depression, but are effective in less than half of patients and can take 4-8 weeks to show results. In this study, we examined cF1ko mice with genetically induced upregulation of 5-HT1A autoreceptors that reduces 5-HT neuronal activity. These mice display anxiety- and depression-related behaviors that did not respond to chronic fluoxetine treatment. We examined treatment with NLX-101, a biased agonist that preferentially targets 5-HT1A heteroreceptors. By testing different doses of NLX-101, we found that a dose of 0.2 mg/kg was effective in reducing depression-related behavior in cF1ko mice without causing hypothermia, a 5-HT1A autoreceptor-mediated response. After 1 h, this dose activated dorsal raphe 5-HT neurons and cells in the medial prefrontal cortex (mPFC), increasing nuclear c-fos labelling in cF1ko mice. In cF1ko mice but not wild-type littermates, 0.2 mg/kg NLX-101 administered 1 h prior to each behavioral test for two weeks reduced depressive behavior in the forced swim test, but increased anxiety-related behaviors in the open field, elevated plus maze, and novelty suppressed feeding tests. During this treatment, NLX-101 induced widespread increases in the density of 5-HT axons, varicosities, and especially synaptic and triadic structures, particularly in depression-related brain regions including mPFC, hippocampal CA1 and CA2/3, amygdala and nucleus accumbens of cF1ko mice. Overall, NLX-101 was rapid and effective in reducing depressive behavior in SSRI-resistant mice, but also induced anxiety-related behaviors. The increase in serotonin innervation induced by intermittent NLX-101 may contribute to its behavioral actions.

Deprescribing Antidepressants in Children and Adolescents: A Systematic Review of Discontinuation Approaches, Cross-Titration, and Withdrawal Symptoms

Background: Antidepressant medications, including selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs), are commonly used to treat depressive, anxiety, and obsessive-compulsive disorders in youth. Yet, data on discontinuing these medications, withdrawal symptoms, and strategies to switch between them are limited. Methods: We searched PubMed and ClinicalTrials.gov through June 1, 2024, to identify randomized controlled trials assessing antidepressant discontinuation in youth. We summarized pediatric pharmacokinetic data to inform tapering and cross-titration strategies for antidepressants and synthesized these data with reports of antidepressant withdrawal. Results: Our search identified 528 published articles, of which 28 were included. In addition, 19 records were obtained through other methods, with 14 included. The corpus of records included 13 randomized, double-blind, placebo-controlled trials (3026 patients), including SSRIs (K = 10), SNRIs (K = 4), and TCAs (K = 1), ranging from 4 to 35 weeks. Deprescribing antidepressants requires considering clinical status, treatment response, and, in cross-titration cases, the pharmacokinetics and pharmacodynamics of both medications. Antidepressant withdrawal symptoms are related to the pharmacokinetics of the medication, which vary across antidepressants and may include irritability, palpitations, anxiety, nausea, sweating, headaches, insomnia, paresthesia, and dizziness. These symptoms putatively involve changes in serotonin transporter expression and receptor sensitivity, impacting the serotonin, dopamine, and norepinephrine pathways. Conclusions: Although approaches to deprescribing antidepressants in pediatric patients are frequently empirically guided, accumulating data related to the course of relapse and withdrawal symptoms, as well as the pharmacokinetic and pharmacodynamic properties of medications, should inform these approaches. Recommendations within this review support data-informed discussions of deprescribing-including when and how-that are critically important in the clinician-family-patient relationship.

Proteomics and its application in the research of acupuncture: An updated review

As a complementary and alternative therapy, acupuncture is widely used in the prevention and treatment of various diseases. However, the understanding of the mechanism of acupuncture effects is still limited due to the lack of systematic biological validation. Notably, proteomics technologies in the field of acupuncture are rapidly evolving, and these advances are greatly contributing to the research of acupuncture. In this study, we review the progress of proteomics research in analyzing the molecular mechanisms of acupuncture for neurological disorders, pain, circulatory disorders, digestive disorders, and other diseases, with an in-depth discussion around acupoint prescription and acupuncture manipulation modalities. The study found that proteomics has great potential in understanding the mechanisms of acupuncture. This study will help explore the mechanisms of acupuncture from a proteomic perspective and provide information to support future clinical decisions.

Duloxetine alleviates oxaliplatin-induced peripheral neuropathy by regulating p53-mediated apoptosis

Oxaliplatin (OXA) is a key platinum-based chemotherapeutic agent for treatment of metastatic colorectal cancer, but the side effects of acute and chronic neuropathies limit its clinical application. Duloxetine has been found to have the potential to prevent OXA-induced peripheral neuropathy in several studies, but the underlying mechanisms remain unclear. The purpose of this study was to evaluate the effects of duloxetine on OXA-induced peripheral neuropathy and to find the potential mechanisms. The neuropathic pain mice model was used to explore the role of duloxetine on OXA-induced peripheral neuropathy by measuring the change of thermal withdrawal latency (TWL), paw withdrawal threshold (PWT), and intraepidermal nerve fiber density (IENFD). Moreover, to explore molecular mechanisms, effects of duloxetine on OXA-induced changes in mRNA and protein expression of components of the p53-related pathways in cultured rat dorsal root ganglion (DRG) neurons were measured. In vivo, we found duloxetine treatment could significantly prevent the changes in the TWL, PWT to mechanical stimulation, and the IENFD of mice caused by OXA. In vitro, we found duloxetine notably inhibits the relative mRNA and protein expression levels of p53, Bax/Bcl2, caspase-3, and caspase-9 in DRG neurons, which may indicate duloxetine protected the DRG neuron by inhibiting p53-related pathways. These results suggest that duloxetine could alleviate the OXA-induced peripheral neuropathy. Duloxetine deserves further consideration as a potential protective agent against peripheral neuropathy.

Repeated fluoxetine treatment induces transient and long-term astrocytic plasticity in the medial prefrontal cortex of normal adult rats

Fluoxetine (Flx)-induced neuronal plasticity plays an important role in the effective treatment of depression and mood disorders. It is less understood whether repeated Flx treatment induces astrocytic plasticity that outlasts the presence of the drug in the body. We showed previously that Flx-induced neuronal plasticity in the medial prefrontal cortex (mPFC) persisted up to 20 days after the treatment. In this study, adult rats were subjected to a 15-day repeated Flx treatment at a daily dose of 20 mg/kg body weight. Astrocytic metabolites and markers were assessed in the mPFC at day 1 (d1) and day 20 (d20) after the treatment. Significant transient reductions in the concentrations of astrocytic metabolites taurine and myo-inositol and the expressions of glial fibrillary acidic protein (GFAP) and aquaporin-4 (AQP4) were observed in the mPFC of Flx-treated rats at d1, which recovered to the control levels at d20. Further, Flx treatment resulted in long-lasting changes in Kir4.1 expression in the mPFC, which remained downregulated at d20. The expression of 5-HT_1A receptor in the mPFC of Flx-treated rats was downregulated at d1 but became upregulated at d20. In summary, repeated Flx treatment induces both transient and long-term astrocytic plasticity in the mPFC of adult rats. The changes observed at d1 are consistent with disturbed water homeostasis and astrocytic de-maturation in the mPFC. The persistent changes in the expressions of Kir4.1 and 5-HT_1A at d20, presumably of the astrocytic origin, might have contributed to the long-term neurotrophic effects of repeated Flx treatment in the mPFC.

Fluoxetine-induced recovery of serotonin and norepinephrine projections in a mouse model of post-stroke depression

Chronic treatment with fluoxetine (FLX) is required for its antidepressant effects, but the role of serotonin (5-HT) axonal plasticity in FLX action is unknown. To address this, we examined mice with a stroke in the left medial prefrontal cortex (mPFC) resulting in persistent anxiety-like and depression-like behaviors and memory deficits as a model of post-stroke depression. Chronic treatment with FLX (but not exercise) completely reversed the behavioral phenotype and partially reversed changes in FosB-labeled cells in the mPFC, nucleus accumbens, septum, hippocampus, basolateral amygdala (BLA), and dorsal raphe. In these regions, 5-HT or norepinephrine (NE) innervation was quantified by staining for 5-HT or NE transporters, respectively. 5-HT synapses and synaptic triads were identified as synaptophysin-stained sites on 5-HT axons located proximal to gephyrin-stained or PSD95-stained spines. A week after stroke, 5-HT innervation was greatly reduced at the stroke site (left cingulate gyrus (CG) of the mPFC) and the left BLA. Chronically, 5-HT and NE innervation was reduced at the left CG, nucleus accumbens, and BLA, with no changes in other regions. In these areas, pre-synaptic and post-synaptic 5-HT synapses and triads to inhibitory (gephyrin+) sites were reduced, while 5-HT contacts at excitatory (PSD95+) sites were reduced in the CG and prelimbic mPFC. Chronic FLX, but not exercise, reversed these reductions in 5-HT innervation but incompletely restored NE projections. Changes in 5-HT innervation were verified using YFP staining in mice expressing YFP-tagged channelrhodopsin in 5-HT neurons. Thus, FLX-induced 5-HT axonal neuroplasticity of forebrain projections may help mediate recovery from brain injury.

Neuropsychiatry: Definitions, Concepts, and Patient Types

Neuropsychiatry is an integrative discipline defined by its history, its preferred patients, and its theoretic framework. Dealing with human behavior needs to consider the brain, but such consideration should avoid oversimplification: neurologic understanding is not essential, necessary, or desirable in all conditions encountered in clinical psychiatry. Neuropsychiatric theory is founded on discoveries in the areas of synaptic plasticity and cortical/limbic anatomy (bottom-up), but also evolutionary biology and anthropology (top-down). Going forward, we need to synthesize vital information, distinguish the essential from the trivial or tenuous, and remain open to dialogue with allied disciplines, our patients, and our students.

Norepinephrine and serotonin are required for vagus nerve stimulation directed cortical plasticity

Vagus nerve stimulation (VNS) paired with forelimb training drives robust, specific reorganization of movement representations in the motor cortex. This effect is hypothesized to be mediated by VNS-dependent engagement of neuromodulatory networks. VNS influences activity in the locus coeruleus (LC) and dorsal raphe nucleus (DRN), but the involvement of these neuromodulatory networks in VNS-directed plasticity is unknown. We tested the hypothesis that cortical norepinephrine and serotonin are required for VNS-dependent enhancement of motor cortex plasticity. Rats were trained on a lever pressing task emphasizing proximal forelimb use. Once proficient, all rats received a surgically implanted vagus nerve cuff and cortical injections of either immunotoxins to deplete serotonin or norepinephrine, or vehicle control. Following surgical recovery, rats received half second bursts of 0.8 mA or sham VNS after successful trials. After five days of pairing intracortical microstimulation (ICMS) was performed in the motor cortex contralateral to the trained limb. VNS paired with training more than doubled cortical representations of proximal forelimb movements. Depletion of either cortical norepinephrine or serotonin prevented this effect. The requirement of multiple neuromodulators is consistent with earlier studies showing that these neuromodulators regulate synaptic plasticity in a complimentary fashion.

Serotonergic mechanisms in spinal cord injury

Spinal cord injury (SCI) is a tragic event causing irreversible losses of sensory, motor, and autonomic functions, that may also be associated with chronic neuropathic pain. Serotonin (5-HT) neurotransmission in the spinal cord is critical for modulating sensory, motor, and autonomic functions. Following SCI, 5-HT axons caudal to the lesion site degenerate, and the degree of axonal degeneration positively correlates with lesion severity. Rostral to the lesion, 5-HT axons sprout, irrespective of the severity of the injury. Unlike callosal fibers and cholinergic projections, 5-HT axons are more resistant to an inhibitory milieu and undergo active sprouting and regeneration after central nervous system (CNS) traumatism. Numerous studies suggest that a chronic increase in serotonergic neurotransmission promotes 5-HT axon sprouting in the intact CNS. Moreover, recent studies in invertebrates suggest that 5-HT has a pro-regenerative role in injured axons. Here we present a brief description of 5-HT discovery, 5-HT innervation of the CNS, and physiological functions of 5-HT in the spinal cord, including its role in controlling bladder function. We then present a comprehensive overview of changes in serotonergic axons after CNS damage, and discuss their plasticity upon altered 5-HT neurotransmitter levels. Subsequently, we provide an in-depth review of therapeutic approaches targeting 5-HT neurotransmission, as well as other pre-clinical strategies to promote an increase in re-growth of 5-HT axons, and their functional consequences in SCI animal models. Finally, we highlight recent findings signifying the direct role of 5-HT in axon regeneration and suggest strategies to further promote robust long-distance re-growth of 5-HT axons across the lesion site and eventually achieve functional recovery following SCI.

Pharmacological Modulations of the Serotonergic System in a Cell-Model of Familial Alzheimer's Disease

Serotonin (5-HT) plays a central role in the integrity of different brain functions. The 5-HT homeostasis is regulated by many factors, including serotonin transporter (SERT), monoamine oxidase enzyme (MAO), and several 5-HT receptors, including the 5-HT1B. There is little knowledge how the dynamics of this system is affected by the amyloid-β (Aβ) burden of Alzheimer's disease (AD) pathology. SH-SY5Y neuroblastoma cells transfected with the amyloid precursor protein (APP) gene containing the Swedish mutations causing familial AD (APPswe), were used as a model to explore the effect of Aβ pathology on 5-HT1B and related molecules including the receptor adaptor protein (p11), SERT and MAOA gene expression, and MAOA activity after treatment with selective serotonin reuptake inhibitor (SSRI) (sertraline), and a 5-HT1B receptor antagonist. Sertraline led more than 70 fold increase of 5-HT1B gene expression (p < 0.001), an increased serotonin turnover in both APPswe and control cells and reduced intracellular serotonin levels by 75% in APPswe cells but not in controls (p > 0.05). Treatment with the 5-HT1B receptor antagonist increased SERT gene-expression in control cells but not in the APPswe cells. 5-HT and 5-HT1B antagonist treatment resulted in different p11 expression patterns in APPswe cells compared to controls. Although MAOA gene expression was not changed by APPswe overexpression, adding 5-HT lead to a significant increase in MAOA gene expression in APPswe but not control cells. These findings suggest that the sensitivity of the 5-HT1B receptor and related systems is affected by APPswe overexpression, with potential relevance for pharmacologic intervention in AD. This may at least partly explain the lack of effect of SSRIs in patients with AD and depression.

Do the accelerating actions of tianeptine and l-arginine on cortical spreading depression interact? An electrophysiological analysis in young and adult rats

In the rat, we previously demonstrated that serotonin-enhancing drugs impair cortical spreading depression (CSD) and that l-arginine (arginine) treatment enhances CSD. Here, we investigated the interaction between topical application of the serotonin uptake enhancer tianeptine and systemic arginine administration on CSD. From postnatal day 7-28, female Wistar rats (n=40) received by gavage 300mg/Kg/day arginine (n=20) or water (n=20). Half of the arginine- or water-treated rats underwent CSD recording at 30-40days of age (young), while the other half was recorded at 90-120days (adult). Following baseline recording (four episodes of CSD), we applied tianeptine solution (10mg/ml) to a rectangular portion of the intact dura mater for 10-min and then elicited CSD. This procedure was repeated three times. Compared to baseline values, CSD velocities and amplitudes following tianeptine application increased, and CSD duration decreased significantly (p<0.05) in both young and adult rats, regardless of treatment group. CSD acceleration caused by systemic treatment with arginine is in agreement with previous findings. Topical cortical application of tianeptine replicated the effect of systemic application, suggesting a cortically based mechanism for tianeptine's action. However, the absence of interaction between arginine and tianeptine treatments suggests that they probably act through separate mechanisms.

Mapping the connectivity of serotonin transporter immunoreactive axons to excitatory and inhibitory neurochemical synapses in the mouse limbic brain

Serotonin neurons arise from the brainstem raphe nuclei and send their projections throughout the brain to release 5-HT which acts as a modulator of several neuronal populations. Previous electron microscopy studies in rats have morphologically determined the distribution of 5-HT release sites (boutons) in certain brain regions and have shown that 5-HT containing boutons form synaptic contacts that are either symmetric or asymmetric. In addition, 5-HT boutons can form synaptic triads with the pre- and postsynaptic specializations of either symmetrical or asymmetrical synapses. However, due to the labor intensive processing of serial sections required by electron microscopy, little is known about the neurochemical properties or the quantitative distribution of 5-HT triads within whole brain or discrete subregions. Therefore, we used a semi-automated approach that combines immunohistochemistry and high-resolution confocal microscopy to label serotonin transporter (SERT) immunoreactive axons and reconstruct in 3D their distribution within limbic brain regions. We also used antibodies against key pre- (synaptophysin) and postsynaptic components of excitatory (PSD95) or inhibitory (gephyrin) synapses to (1) identify putative 5-HTergic boutons within SERT immunoreactive axons and, (2) quantify their close apposition to neurochemical excitatory or inhibitory synapses. We provide a 5-HTergic axon density map and have determined the ratio of synaptic triads consisting of a 5-HT bouton in close proximity to either neurochemical excitatory or inhibitory synapses within different limbic brain areas. The ability to model and map changes in 5-HTergic axonal density and the formation of triadic connectivity within whole brain regions using this rapid and quantitative approach offers new possibilities for studying neuroplastic changes in the 5-HTergic pathway.

Imipramine administration induces changes in the phosphorylation of FAK and PYK2 and modulates signaling pathways related to their activity

BACKGROUND

Antidepressants can modify neuronal functioning by affecting many levels of signal transduction pathways that are involved in neuroplasticity. We investigated whether the phosphorylation status of focal adhesion kinase (FAK/PTK2) and its homolog, PYK2/PTK2B, and their complex with the downstream effectors (Src kinase, p130Cas, and paxillin) are affected by administration of the antidepressant drug, imipramine. The treatment influence on the levels of ERK1/2 kinases and their phosphorylated forms (pERK1/2) or the Gαq, Gα11 and Gα12 proteins were also assessed.

METHODS

Rats were injected with imipramine (10 mg/kg, twice daily) for 21 days. The levels of proteins investigated in their prefrontal cortices were measured by Western blotting.

RESULTS

Imipramine induced contrasting changes in the phosphorylation of FAK and PYK2 at Tyr397 and Tyr402, respectively. The decreased FAK phosphorylation and increased PYK2 phosphorylation were reflected by changes in the levels of their complex with Src and p130Cas, which was observed predominantly after chronic imipramine treatment. Similarly only chronic imipramine decreased the Gαq expression while Gα11 and Gα12 proteins were untouched. Acute and chronic treatment with imipramine elevated ERK1 and ERK2 total protein levels, whereas only the pERK1 was significantly affected by the drug.

CONCLUSION

The enhanced activation of PYK2 observed here could function as compensation for FAK inhibition.

GENERAL SIGNIFICANCE

These data demonstrate that treatment with imipramine, which is a routine in counteracting depressive disorders, enhances the phosphorylation of PYK2, a non-receptor kinase instrumental in promoting synaptic plasticity. This effect documents as yet not considered target in the mechanism of imipramine action.

Modulation of early stress-induced neurobiological changes: a review of behavioural and pharmacological interventions in animal models

Childhood adversity alters the predisposition to psychiatric disorders later in life. Those with psychiatric conditions and a history of early adversity exhibit a higher incidence of treatment resistance compared with individuals with no such history. Modulation of the influence early stress exerts over neurobiology may help to prevent the development of psychiatric disorders in some cases, while attenuating the extent of treatment resistance in those with established psychiatric disorders. This review aims to critically evaluate the ability of behavioural, environmental and pharmacologic interventions to modulate neurobiological changes induced by early stress in animal models. Databases were systematically searched to locate literature relevant to this review. Early adversity was defined as stress that resulted from manipulation of the mother-infant relationship. Analysis was restricted to animal models to enable characterisation of how a given intervention altered specific neurobiological changes induced by early stress. A wide variety of changes in neurobiology due to early stress are amenable to intervention. Behavioural interventions in childhood, exercise in adolescence and administration of epigenetic-modifying drugs throughout life appear to best modulate cellar and behavioural alterations induced by childhood adversity. Other pharmacotherapies, such as endocannabinoid system modulators, anti-inflammatories and antidepressants can also influence these neurobiological and behavioural changes that result from early stress, although findings are less consistent at present and require further investigation. Further work is required to examine the influence that behavioural interventions, exercise and epigenetic-modifying drugs exert over alterations that occur following childhood stress in human studies, before possible translational into clinical practice is possible.

The transcription factor SP4 is reduced in postmortem cerebellum of bipolar disorder subjects: control by depolarization and lithium

OBJECTIVES

  Regulation of gene expression is important for the development and function of the nervous system. However, the transcriptional programs altered in psychiatric diseases are not completely characterized. Human gene association studies and analysis of mutant mice suggest that the transcription factor specificity protein 4 (SP4) may be implicated in the pathophysiology of psychiatric diseases. We hypothesized that SP4 levels may be altered in the brain of bipolar disorder (BD) subjects and regulated by neuronal activity and drug treatment.

METHODS

  We analyzed messenger RNA (mRNA) and protein levels of SP4 and SP1 in the postmortem prefrontal cortex and cerebellum of BD subjects (n = 10) and controls (n = 10). We also examined regulation of SP4 mRNA and protein levels by neuronal activity and lithium in rat cerebellar granule neurons.

RESULTS

  We report a reduction of SP4 and SP1 proteins, but not mRNA levels, in the cerebellum of BD subjects. SP4 protein and mRNA levels were also reduced in the prefrontal cortex. Moreover, we found in rat cerebellar granule neurons that under non-depolarizing conditions SP4, but not SP1, was polyubiquitinated and degraded by the proteasome while lithium stabilized SP4 protein.

CONCLUSIONS

  Our study provides the first evidence of altered SP4 protein in the cerebellum and prefrontal cortex in BD subjects supporting a possible role of transcription factor SP4 in the pathogenesis of the disease. In addition, our finding that SP4 stability is regulated by depolarization and lithium provides a pathway through which neuronal activity and lithium could control gene expression suggesting that normalization of SP4 levels could contribute to treatment of affective disorders.

Exposure to 1-bromopropane causes degeneration of noradrenergic axons in the rat brain

1-Bromopropane (1-BP) has been used as an alternative to ozone-depleting solvents. Previous studies showed that 1-BP is neurotoxic in animals and humans. In humans, exposure to 1-BP caused various neurological and neurobehavioral symptoms or signs including depressive or irritated mood. However, the neurobiological changes underlying the depressive symptoms induced by 1-BP remain to be determined. The depressive symptoms are thought to be associated with degeneration of axons containing noradrenaline and serotonin. Based on this hypothesis, the present study examined the effects of repeated exposure to 1-BP on serotonergic and noradrenergic axons. Exposure to 1-BP induced dose-dependent decreases in the density of noradrenergic axons in the rat prefrontal cortex, but no apparent change in the density of serotonergic axons. The results suggest that depressive symptoms in workers exposed to 1-BP are due, at least in part, to the degeneration of noradrenergic axons in the brain.

Promoter specific alterations of brain-derived neurotrophic factor mRNA in schizophrenia

The brain-derived neurotrophic factor (BDNF) gene contains multiple 5' promoters which generate alternate transcripts. Previously, we found that pan-BDNF mRNA and protein are reduced in the dorsolateral prefrontal cortex (DLPFC) from patients with schizophrenia. In this study, we determined which of the four most abundant and best characterized BDNF alternate transcripts, I-IX, II-IX, IV-IX, and VI-IX are altered in schizophrenia. Using a cohort from the NIMH, USA, we found that BDNF II-IX mRNA was significantly reduced in the DLPFC of patients with schizophrenia, and we replicated this finding using a second cohort from Sydney, Australia. Moreover, we show that BDNF protein expression [including prepro ( approximately 32 kDa), pro ( approximately 28 kDa) and mature ( approximately 14 kDa) BDNF] is reduced in the DLPFC of patients with schizophrenia. We next determined the regional specificity of the BDNF mRNA reduction by measuring BDNF transcripts in the parietal cortex and hippocampus and found no significant changes. The effect of antipsychotics on BDNF alternate transcript expression was also examined and we found no relationship between BDNF mRNA expression and antipsychotic use. As schizophrenic patients are often prescribed antidepressants which can up-regulate expression of BDNF, we investigated the relationship between antidepressant treatment and BDNF transcript expression. All four BDNF transcripts were significantly up-regulated in schizophrenic patients treated with antidepressants. Moreover, we found significant reductions in BDNF transcripts II-IX and IV-IX in the parietal cortex and VI-IX in the hippocampus of patients with schizophrenia who did not have a history of treatment with antidepressants. This suggests that down-regulation of at least one out of four major BDNF transcripts occurs in various brain regions of patients with schizophrenia, particularly in the DLPFC which appears to have the most robust BDNF deficit in schizophrenia.

Changes in Cerebral Cortex and Limbic Brain Functions after Short-Term Paroxetine Treatment in Panic Disorder: An [F]FDG-PET Pilot Study

OBJECTIVE

Panic disorder (PD) is a common and often chronic psychiatric illness, and serotonin-specific reuptake inhibitors (SSRIs) are the drugs of choice for the treatment of PD. Previous studies suggested the cerebral cortex and limbic brain structures played a major role in the development of PD, but the therapeutic effect of SSRIs on specific brain structures remains unclear in PD. We examined the changes in PD patients' glucose metabolism using the [(18)F] Fluorodeoxy-glucose-positron emission tomography (FDG-PET) before and after 12 weeks of paroxetine treatment.

METHODS

We assessed the brain glucose metabolism of 5 PD patients, using the [(18)F]FDG-PET, and treated them with paroxetine (12.5-37.5 mg/day) for 12 weeks. Then, we compared before and after treatment PET images of the patients, using voxel-based statistical analysis and a post hoc regions of interest analysis. Furthermore, we measured the patients' clinical variables, including information from the Panic Disorder Severity Scale (PDSS), Clinical Global Impression for Severity (CGI-S), and Hamilton Anxiety Rating Scale (HAMA).

RESULTS

After 12 weeks of paroxetine treatment, the patients showed significant clinical improvement in terms of PDSS, CGI-S and HAMA scores (12.8±1.8 vs. 3.8±2.3, 4.6±0.5 vs. 2.0±1.4, and 15.2±4.0 vs. 5.0±1.2, respectively; all p values<0.05). After treatment, patients' glucose metabolism increased significantly in global brain areas: the right precentral gyrus, right middle frontal gyrus, right amygdala, right caudate body, right putamen, left middle frontal gyrus, left precentral gyrus, left insula, left parahippocampal gyrus, and left inferior frontal gyrus (All areas were significant at uncorrected p<0.001 and cluster level corrected p<0.05).

CONCLUSION

In these PD patients, cerebral cortex and limbic brain functions changed after short-term treatment with paroxetine. The therapeutic action of paroxetine may be related to altered glucose metabolism at both the cerebral cortex and limbic brain areas.

Autoradiographic study of serotonin transporter during memory formation

Serotonin transporter (SERT) has been associated with drugs of abuse like d-methamphetamine (METH). METH is well known to produce effects on the monoamine systems but it is unclear how METH affects SERT and memory. Here the effects of METH and the serotonin reuptake inhibitor fluoxetine (FLX) on autoshaping and novel object recognition (NOR) were investigated. Notably, both memory tasks recruit different behavioral, neural and cognitive demand. In autoshaping task a dose-response curve for METH was determined. METH (1.0mg/kg) impaired short-term memory (STM; lasting less of 90min) in NOR and impaired both STM and long-term memory (LTM; lasting 24 and 48h) in autoshaping, indicating that METH had long-lasting effects in the latter task. A comparative autoradiography study of the relationship between the binding pattern of SERT in autoshaping new untrained vs. trained treated (METH, FLX, or both) animals was made. Considering that hemispheric dominance is important for LTM, hence right vs. left hemisphere of the brain was compared. Results showed that trained animals decreased cortical SERT binding relative to untrained ones. In untrained and trained treated animals with the amnesic dose (1.0mg/kg) of METH SERT binding in several areas including hippocampus and cortex decreased, more remarkably in the trained animals. In contrast, FLX improved memory, increased SERT binding, prevented the METH amnesic effect and re-established the SERT binding. In general, memory and amnesia seemed to make SERT more vulnerable to drugs effects.

Antidepressant-like effects of kappa-opioid receptor antagonists in Wistar Kyoto rats

The Wistar Kyoto (WKY) rat strain is a putative genetic model of comorbid depression and anxiety. Previous research showing increased kappa-opioid receptor (KOR) gene expression in the brains of WKY rats, combined with studies implicating the KOR in animal models of depression and anxiety, suggests that alterations in the KOR system could have a role in the WKY behavioral phenotype. Here, the effects of KOR antagonists in the forced swim test (FST) were compared with the WKY and the Sprague-Dawley (SD) rat strains. As previously reported, WKY rats showed more immobility behavior than SD rats. The KOR antagonists selectively produced antidepressant-like effects in the WKY rats. By contrast, the antidepressant desipramine reduced immobility in both strains. Brain regions potentially underlying the strain-specific effects of KOR antagonists in the FST were identified using c-fos expression as a marker of neuronal activity. The KOR antagonist nor-binaltorphimine produced differential effects on the number of c-fos-positive profiles in the piriform cortex and nucleus accumbens shell between SD and WKY rats. The piriform cortex and nucleus accumbens also contained higher levels of KOR protein and dynorphin A peptide, respectively, in the WKY strain. In addition, local administration of nor-binaltorphimine directly into the piriform cortex produced antidepressant-like effects in WKY rats further implicating this region in the antidepressant-like response to KOR antagonists. These results support the use of the WKY rat as a model of affective disorders potentially involving KOR overactivity and provide more evidence that KOR antagonists could potentially be used as novel antidepressants.

Chronic activation of the 5-HT(2) receptor reduces 5-HT neurite density as studied in organotypic slice cultures

The serotonin system densely innervates the brain and is implicated in psychopathological processes. Here we studied the effect of serotonin and serotonin pharmacological compounds on the outgrowth of serotonergic projections using organotypic slice co-cultures of hippocampus and dorsal raphe nuclei. Immunocytochemical analysis showed that several serotonergic neurites had grown into the target slice within 7 days in culture, after which the neurite density stabilized. These projections expressed the serotonin-synthesizing enzyme Tryptophan hydroxylase and the serotonin transporter and contained several serotonin-positive varicosities that also accumulated presynaptic markers. Chronic application of a 5-HT(2) agonist reduced the serotonergic neurite density, without effects on survival of serotonergic neurons. In contrast, application of a 5-HT(1A) agonist or the serotonin transporter inhibitor fluoxetine did not affect serotonergic neurite density. We conclude that serotonergic connectivity was reproduced in vitro and that the serotonin neurite density is inhibited by chronic activation of the 5-HT(2) receptor.

Effects of postnatal isolation rearing and antidepressant treatment on the density of serotonergic and noradrenergic axons and depressive behavior in rats

The development of monoaminergic axons is affected by pharmacological and environmental manipulations during early periods of brain development. In addition, it has been proposed that changes in the density of monoaminergic axons are involved in the pathophysiology of depression. The present experiments examined the effects of neonatal treatment with antidepressants on the density of monoaminergic axons containing 5-HT or noradrenaline (NA) and depressive behavior in rats. In this study, clomipramine (CL) was used as an antidepressant, because a large amount of data has been accumulated on the effects of neonatal CL treatment on monoaminergic neurons and depressive behavior. It was also examined whether the effects of neonatal CL treatment could be further modified by environmental conditions. In the present experiments, postweaning isolation rearing (Iso) was examined as an environmental condition, because postweaning Iso is reported to change the density of 5-HT axons in the rat brain. Unexpectedly, neonatal CL treatment alone had no effect on the density of 5-HT or NA axons or depressive behavior. Postweaning social Iso rearing reduced the density of 5-HT axons in the central nucleus and basolateral nucleus of the amygdala and CA3 of the hippocampus. In the prelimbic area and infralimbic area of medial prefrontal cortex and the dentate gyrus of the hippocampus, the density of 5-HT axons was not affected by social Iso alone, but was reduced when animals were socially isolated after neonatal CL treatment. Postweaning Iso, but not neonatal CL treatment, increased immobility in the forced swim test in adolescence/early adulthood. These findings suggest that postweaning social Iso alters the density of monoaminergic axons, particularly 5-HT axons, and induces a possible model of depression, while neonatal CL treatment alone has no effect on the density of NA or 5-HT axons or depressive behavior in adolescence/early adulthood.

Acute and chronic effects of citalopram on 5-HT1A receptor-labeling by [18F]MPPF and -coupling to receptors-G proteins

Selective serotonin reuptake inhibitors take several weeks to produce their maximal therapeutic antidepressant effect. This delay has been attributed to the gradual desensitization of somatodendritic serotonin 5-HT(1A) autoreceptors. We evaluated adaptive changes of 5-HT(1A) receptors after acute and chronic citalopram challenges in rat. Small animal positron emission tomography trial and quantitative ex vivo autoradiography studies using [(18)F]MPPF were employed, as well as in vitro 8-OH-DPAT-stimulated [(35)S]-GTPgammaS binding assay. Additionally, 5-HT(1A) receptor knock-out mice were used to assess the specificity of [(18)F]MPPF. Acute treatment with citalopram did not alter [(18)F]MPPF binding in dorsal raphe nucleus (DR), frontal cortex, or hippocampus. The absence of [(18)F]MPPF binding in the brain of 5-HT(1A) knock-out mice demonstrates the specificity of MPPF for 5-HT(1A) receptor brain imaging, but the high affinity of [(18)F]MPPF compared to 5-HT suggests that it would only be displaced by dramatic increases in extracellular 5-HT. Chronic citalopram did not modify 5-HT(1A) receptor density in any of the brain regions studied. In addition, this treatment did not modify 8-OH-DPAT-stimulated [(35)S]-GTPgammaS binding in DR, although a significant increase was observed in frontal cortex and hippocampus. [(18)F]MPPF appears to be an efficient radioligand to quantify specifically 5-HT(1A) receptor density in brain imaging. The delayed therapeutic efficacy of citalopram did not appear to be linked to either a downregulation of 5-HT(1A) receptors or to a 5-HT(1A) receptor-G protein decoupling process in serotonergic neurons, but to increased functional sensitivity of postsynaptic 5-HT(1A) receptors.

Overlapping and distinct brain regions associated with the anxiolytic effects of chlordiazepoxide and chronic fluoxetine

Little is known about the sites of action for the behavioral effects of chronic antidepressants. The novelty-induced hypophagia (NIH) test is one of few animal behavioral tests sensitive to acute benzodiazepines and chronic antidepressants. The goals of these experiments were to examine patterns of brain activation associated with the behavioral response to novelty and identify regions that could regulate the anxiolytic effects of acute benzodiazepine and chronic antidepressant treatments, measured using the NIH test. In the first experiment, rats were treated acutely with the anxiolytic, chlordiazepoxide (2.5 or 5 mg/kg, i.p.). In separate experiments, animals were implanted with osmotic minipumps delivering vehicle or fluoxetine (5 or 20 mg/kg per day s.c.) for 3 or 28 days. NIH was assessed by giving animals access to a familiar palatable food in a novel environment. Associated brain areas were identified using c-fos immunohistochemistry. NIH was mitigated by acute chlordiazepoxide and chronic fluoxetine. Both drugs reversed novelty-induced changes in c-fos expression in the lateral division of the posterolateral part of the bed nucleus of the stria terminalis (STLP), cingulate cortex (Cg), and dorsal field CA2 of the hippocampus (dCA2). Chronic fluoxetine additionally increased c-fos expression in the anterior nucleus accumbens (aAcb) and the piriform cortex (Pir). The effects of the drugs on c-fos expression in many regions correlated with anxiolytic efficacy. These findings identified brain regions where the effects of chronic antidepressants and benzodiazepines may converge to produce anxiolytic activity, as well as distinct sites of action for the two classes of drugs.

Long-term administration of cocaine or serotonin reuptake inhibitors results in anatomical and neurochemical changes in noradrenergic, dopaminergic, and serotonin pathways

The catechol and indole pathways are important components underlying plasticity in the frontal cortex and basal ganglia. This study demonstrates that administering rats either cocaine or a selective serotonin (or 5-hydroxytryptamine; 5-HT) reuptake inhibitor (SSRI) for 16 weeks results in reduced density of dopaminergic and noradrenergic terminals in the striatum and olfactory bulb, respectively, reflecting pruning of the terminal arbor of ventral midbrain dopaminergic and locus coeruleus noradrenergic neurones. In the striatum of cocaine-treated animals, basal dopamine levels, as well as cocaine-induced dopamine release, is diminished compared with controls. In contrast, serotonergic fibers, projecting from the raphe, sprout and have increased terminal density in the lateral septal nucleus and frontal cortex, following long-term cocaine or SSRI treatment. This is associated with elevated basal 5-HT and enhanced cocaine-induced 5-HT release in the frontal cortex. The anatomical and neurochemical changes in serotonergic fibers following cocaine or SSRI treatment may be explained by attenuated 5-HT(1A) autoreceptor function in the raphe. This study demonstrates extensive plasticity in the morphology and neurochemistry of the catechol and indole pathways that contribute to drug-induced plasticity of the corticostriatal (and other) projections. Moreover, our data suggest that drug-induced plastic adaptation is anatomically widespread and consequently, likely to have multiple and complex consequences.

13-cis-retinoic acid alters the cellular morphology of slice-cultured serotonergic neurons in the rat

Retinoids influence cellular processes such as differentiation, proliferation and apoptosis via retinoic acid receptor (RAR) and retinoid X receptor (RXR), and have therapeutic applications in several cancers and dermatologic diseases. Recent reports indicate that depression occasionally occurs in patients using the acne drug Accutane, the active component of which is 13-cis-retinoic acid (13-cis-RA). Although impairment of serotonin (5-HT)-expressing neurons, including morphologic changes, is thought to be associated with depressive symptoms, the effects of 13-cis-RA on 5-HT neurons have not been examined. The present study demonstrated that 13-cis-RA alters the morphology of 5-HT neurons in cultured rat midbrain slices. The 13-cis-RA-induced changes were partially blocked by RXR and RAR antagonists. Furthermore, cotreatment with RAR and RXR agonists altered the morphology of 5-HT neurons to a greater extent than the individual application of each agonist. The morphologic changes were completely blocked by RXR antagonist, whereas RAR antagonist partially blocked the effects. These results suggest that 13-cis-RA exerts its action on slice-cultured 5-HT neurons, at least in part, through specific retinoid receptors. Moreover, RXR has a greater influence on the morphology of 5-HT neurons than RAR. The receptor-mediated actions of 13-cis-RA presented here may provide a clue for further research on depression associated with the use of 13-cis-RA.

Suppressive effect of paroxetine, a selective serotonin uptake inhibitor, on tetrahydrobiopterin levels and dopamine as well as serotonin turnover in the mesoprefrontal system of mice

Tetrahydrobiopterin (BH(4)) is a coenzyme of tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH), which are rate-limiting enzymes of monoamine biosynthesis. According to the monoamine hypothesis of depression, antidepressants will restore the function of the brain monoaminergic system and the BH(4) concentration. In the present study, we investigated the effect of paroxetine, a selective serotonin reuptake inhibitor (SSRI), on the BH(4) levels and dopamine (DA) and serotonin (5-HT) turnover in the mesoprefrontal system, incorporating two risk factors of depression, social isolation and acute environmental change. Male ddY mice (8W) were divided into two housing groups, i.e., group-housing (eight animals per cage; 28 days), and isolation-housing (one per cage; 28 days), being p.o.-administered paroxetine (5 or 10 mg/kg; days 15-28), and exposed to a 20-min novelty stress (day 28). The levels of BH(4), DA, homovanilic acid (HVA), 5-HT, and 5-hydroxyindoleacetic acid (5-HIAA) were measured in the prefrontal cortex and midbrain. In both the regions, novelty stress significantly increased BH(4) levels under the isolation-housing condition, whereas these levels were decreased under the group-housing condition. Thus, social isolation altered the neurochemical response to novelty stress. Paroxetine significantly decreased BH(4) levels under the isolation-housing condition, whereas decreased HVA/DA and 5-HIAA/5-HT ratios were observed under the group-housing condition. Thus, social isolation may have influenced the suppressive effects of paroxetine on BH(4) levels as well as exerted an influence on DA and 5-HT turnover. We replicated our recent findings that SSRI, fluvoxamine, suppressed BH(4) levels, as well as DA and 5-HT turnover in the mouse mesoprefrontal system.

Interferon-α reduces the density of monoaminergic axons in the rat brain

Interferon-alpha commonly induces depressive symptoms in clinical populations; however, the mechanism by which this occurs is unclear. Recent studies suggest that the degeneration of axons containing serotonin and noradrenaline is involved in the pathophysiology of depression. The present immunohistochemical study shows that the density of serotonergic axons decreased in the ventral medial prefrontal cortex and amygdala in the interferon-alpha-treated animals. Additionally, interferon-alpha induced decreases in the density of noradrenergic axons in the dorsal medial prefrontal cortex, ventral medial prefrontal cortex, and dentate gyrus. These results support the hypothesis that long-term administration of interferon-alpha causes the degeneration of monoaminergic axons in specific brain regions, which might be associated with depressive symptoms occurring in interferon-alpha-treated patients.

Chronic antidepressant treatment selectively increases expression of plasticity-related proteins in the hippocampus and medial prefrontal cortex of the rat

Antidepressants protect against hippocampal volume loss in humans and reverse stress-induced atrophic changes in animals thus supporting the hypothesis that the pathophysiology of stress-related disorders such as depression involves reductions in neuronal connectivity and this effect is reversible by antidepressant treatment. However, it is unclear which brain areas demonstrate such alterations in plasticity in response to antidepressant treatment. The aim of the present study was to examine the effect of antidepressant treatment on the expression of three plasticity-associated marker proteins, the polysialylated form of nerve cell adhesion molecule (PSA-NCAM), phosphorylated cyclic-AMP response element binding protein (pCREB) and growth-associated protein 43 (GAP-43), in the rat brain. To this end, rats were treated either acutely (60 min) or chronically (21 days) with imipramine (30 and 15 mg/kg, respectively) and the expression of PSA-NCAM, pCREB, and GAP-43 was assessed using immunohistochemistry. Initial mapping revealed that chronic imipramine treatment increased expression of these plasticity-associated proteins in the hippocampus, medial prefrontal cortex and piriform cortex but not in the other brain regions examined. Since PSA-NCAM and pCREB are expressed in recently-generated neurons in the dentate gyrus, it is likely that chronic imipramine treatment increased their expression in the hippocampus at least partially by increasing neurogenesis. In contrast, since chronic imipramine treatment is not associated with neurogenesis in the medial prefrontal cortex, increased expression of PSA-NCAM and pCREB in the prelimbic cortex implicates changes in synaptic connectivity in this brain region. Acute treatment with imipramine increased the number of pCREB positive nuclei in the hippocampus and the prefrontal cortex but did not alter expression of GAP-43 or PSA-NCAM in any of the brain regions examined. Taken together, the results of the present study suggest that antidepressant treatment increases synaptic plasticity and connectivity in brain regions associated with mood disorders.