Serotonin and anxiety revisited

The Role of Serotonin in Fear Learning and Memory: A Systematic Review of Human Studies

Fear is characterized by distinct behavioral and physiological responses that are essential for the survival of the human species. Fear conditioning (FC) serves as a valuable model for studying the acquisition, extinction, and expression of fear. The serotonin (5-hydroxytryptamine, 5-HT) system is known to play a significant role in emotional and motivational aspects of human behavior, including fear learning and expression. Accumulating evidence from both animal and human studies suggests that brain regions involved in FC, such as the amygdala, hippocampus, and prefrontal cortex, possess a high density of 5-HT receptors, implicating the crucial involvement of serotonin in aversive learning. Additionally, studies exploring serotonin gene polymorphisms have indicated their potential influence on FC. Therefore, the objective of this work was to review the existing evidence linking 5-HT with fear learning and memory in humans. Through a comprehensive screening of the PubMed and Web of Science databases, 29 relevant studies were included in the final review. These studies investigated the relationship between serotonin and fear learning using drug manipulations or by studying 5-HT-related gene polymorphisms. The results suggest that elevated levels of 5-HT enhance aversive learning, indicating that the modulation of serotonin 5-HT2A receptors regulates the expression of fear responses in humans. Understanding the role of this neurochemical messenger in associative aversive learning can provide insights into psychiatric disorders such as anxiety and post-traumatic stress disorder (PTSD), among others.

Active vs passive novelty-related strategies: Sex differences in exploratory behaviour and monoaminergic systems

Sex differences are apparent in numerous behavioural characteristics. In order to compare and characterise male and female variability of exploratory behaviour, 365 male and 401 female rats were assessed in a task where a bimodal response distribution had previously been established in males. Female rats had significantly higher exploratory activity, and presented normal distribution of the behaviour, very differently from the bimodal distribution of males. No major effect of litter or oestrous cycle was detected. Several differences between male and female rats were found in monoamine metabolism measured ex vivo. Male rats had lower levels of dopamine (DA) in frontal cortex, and higher levels of 3,4-dihydroxyphenylacetic acid (DOPAC) in raphe area; higher levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in dorsal striatum but lower levels of 5-HT and 5-HIAA in locus coeruleus area, 5-HIAA levels were also lower in hippocampus as compared to females. Males had higher noradrenaline (NA) levels in hippocampus and lower normetanephrine (NMN) levels in striatum, in both brain regions male animals had lower NMN/NA ratio. No sex difference was found in accumbens. The only brain region with an interaction between sex and the expression of exploratory activity was raphe: Here 5-HT levels were lower, and DOPAC levels and DOPAC/DA and 5-HIAA/5-HT ratios higher in low exploring male but not female rats. Conclusively, female rats not only display higher levels of exploration but the population distribution of this behaviour is distinct; this may be related to differences in the monoaminergic systems between female and male animals.

Protective effect of methylene blue against copper oxide nanoparticle-induced neurobehavioral toxicity

Increasing attention has been paid in the past decade to assessing the toxicological effects of nanoparticles and finding a protectant; thus, the current study aimed to investigate the protective effect of the mitochondria-targeting drug methylene blue (MB) against copper oxide nanoparticle (CuO-NP)-induced neurobehavioral toxicity in rats. For this purpose, twenty rats were allocated to four equal groups (n = 5). The negative control group received distilled water intraperitoneally (IP) and Tween 80 (10 %) orally. The CuO-NP group was given a dose of 100 mg/kg of CuO-NPs, administered orally, and the positive control group was treated with 1 mg/kg MB intraperitoneally (IP). The final group was concurrently exposed to CuO-NPs and MB for 14 consecutive days. At the end of the study, each group was neurobehaviorally blind tested relative to other experimental animals, then brain tissue markers were determined and a histopathological examination was conducted. The results showed that supplementation with CuO-NPs induced neurobehavioral alterations; increased Cu content in the brain; and enhanced lipid peroxidation (malondialdehyde [MDA]), protein peroxidation (protein carbonyl [PC]), and DNA oxidative damage (8-hydroxy-2-deoxyguanosine [8-OH-dG]) compared to other treatments. In addition, a decrease was noted in the mitochondrial dehydrogenases' (aldehyde dehydrogenase 2 [ALDH2], and glutamate dehydrogenase [GDH]) activity in Cu-exposed rats. The histopathological findings revealed shrunken, pyknotic, and hypereosinophic cortical neurons and increased immune positive brown staining of caspase-3 protein, indicating apoptosis. Co-treatment with methylene blue ameliorated the neurotoxic effects of CuO-NPs; therefore, MB evidently had a powerful modulatory effect against the neurotoxicity of nano-Cu oxide via its antioxidant and mitochondrial protection properties.

Effects of chronic exposure to low doses of Δ9- tetrahydrocannabinol in adolescence and adulthood on serotonin/norepinephrine neurotransmission and emotional behaviors

BACKGROUND

Chronic exposure to the Δ9-tetrahydrocannabinol (THC), the main cannabis pharmacological component, during adolescence has been shown to be associated with an increased risk of depression and suicidality in humans.

AIMS

Little is known about the impact of the long-term effects of chronic exposure to low doses of THC in adolescent compared to adult rodents.

METHODS

THC (1mg/kg i.p., once a day) or vehicle was administered for 20 days in both adolescent (post-natal day, PND 30-50) and young adult rats (PND 50-70). After a long washout period (20 days), several behavioral paradigms and electrophysiological recordings of serotonin (5-HT) and norepinephrine (NE) neurons were carried out.

RESULTS

Adolescent THC exposure resulted in depressive lbehaviors: a significant decrease in latency to first immobility in the forced swim test, increased anhedonia in the sucrose preference test. Decrease entries in the open arm were observed in the elevated plus maze after adolescent and adult exposure, indicating anxiousphenotype. A significant reduction in dorsal raphe serotonergic neural activity without changing locus coeruleus noradrenergic neural activity was found in THC adolescent and adult exposure.

CONCLUSIONS

Altogether, these findings suggest that low doses of chronic THC exposure during the developmental period and adulthood could result in increased vulnerability of the 5-HT system and anxiety symptoms; however, depressive phenotypes occur only after adolescent, but not adult exposure, underscoring the higher vulnerability of young ages to the mental effects of cannabis.

Serotonergic mechanisms and suicidal behavior

Disturbances in central serotonin (5-hydroxytryptamine, 5-HT) were first described in depression. They were inferred to exist based on the finding of lowered baseline and post-probenecid concentrations of 5-HIAA in CSF. Initially, depressed patients with and without deimonstrable disturbances in central 5-H1 seemed psychopathologically indistinguishable. Interpreting the available data, at that time, we introduced in 1971 the concept of biochemical heterogeneity of depression. Some forms, we postulated, are linked to disturbances in 5-HT functions, others are not or, to a much lesser extent. Subsequently, we showed the concept of a separate «5-HT depression» to be untenable. It seems more likely now that 5-HT disturbances in depression are not linked to a particular syndromal depression type, but to particular psychopathological dimensions, i.e. heightened anxiety and disturbed aggression regulation. These dimensions might form a prominent aspect of depression or may be virtually absent. They are moreover not specific for depression, but can occur in other psychiatric disorders as well. This might explain the seemingly capricious occurrence of 5-HT disorders in depression as well as their nosological non-specificity.

Based on the dimensional 5-HT hypothesis one might expect drugs that increase 5-HT availability in the brain to be effective in the various anxiety disorders, in depressions marked by increased anxiety and disturbed aggression regulation and in personality disorders with strong aggressive tendencies.

Platelet serotonin binding and plasma cortisol in panic disorder before and after alprazolam plus behavioral guidance treatment

In 32 patients with panic disorder with or without agoraphobia, Bmax measures of 5-HT binding in platelets did not differ from normal controls at baseline. Plasmatic cortisol levels were significantly higher than controls in the morning and in the evening measures as well as in post-dexamethasone assays. Following an 8-week treatment period with alprazolam plus behavioral guidance encouraging exposure, Bmax values did not alter but cortisol measures diminished significantly. Measures of phobic avoidance were negatively correlated with 5-HT Bmax values. Plasmatic cortisol correlated positively with the number of situational panic attacks in the month before treatment. There were no correlations between cortisol and 5-HT Bmax measures. A possible link between serotonin function and phobic avoidance is discussed. Cortisol changes were interpreted as being related to the global severity of the anxious state.

The 5-HT6 receptor interactome: New insight in receptor signaling and its impact on brain physiology and pathologies

The serotonin (5-HT)₆ receptor is a Gs-coupled receptor exclusively expressed in the central nervous system. Highest receptor densities are found in brain regions implicated in mnemonic functions where the receptor is primarily but not exclusively located in the primary cilium of neurons. The 5-HT₆ receptor continues to raise particular interest for neuropharmacologists, given the pro-cognitive effects of antagonists in a wide range of cognitive impairment paradigms in rodents and human. The 5-HT₆ receptor also finely controls key neuro-developmental processes including neuron migration and differentiation. However, its influence upon neurodevelopment and cognition is not solely mediated by its coupling to the Gs-adenylyl cyclase pathway, suggesting alternative signal transduction mechanisms. This prompted studies aimed at characterizing the receptor interactome that identified 125 candidate receptor partners, making the 5-HT₆ receptor one of the G protein-coupled receptors with the most extensively characterized interactome. These studies showed that the receptor localization at the plasma membrane and, consequently, its signal transduction, are finely modulated by several receptor partners. They demonstrated that prefrontal 5-HT₆ receptors engage the mTOR pathway to compromise cognition in neurodevelopmental models of schizophrenia, and a role of the 5-HT₆-mTOR pathway in temporal epilepsy. Finally, they revealed that the receptor activates Cdk5 signaling in an agonist-independent manner through a mechanism involving receptor phosphorylation by the associated Cdk5 and highlighted its key role in the migration of neurons and neurite growth. These new receptor-operated signaling mechanisms should be considered in the future development of drugs acting on 5-HT₆ receptors. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Modulating Effects of Cholecalciferol Treatment on Estrogen Deficiency-Induced Anxiety-Like Behavior of Adult Female Rats

BACKGROUND

Vitamin D can be one of the candidate substances that are used as additional supplementation in the treatment of anxiety-related disorders in women with estrogen imbalance.

MATERIALS AND METHODS

The aim of the present study was to examine the effects of chronic cholecalciferol administration (1.0, 2.5 or 5.0 mg/kg/day, s.c.) on the anxiety-like behavior and monoamines levels in the rat hippocampus following ovariectomy in female rats. Cholecalciferol was given to ovariectomized (OVX) rats and OVX rats treated with 17β-estradiol (17β-E2, 0.5 μg/rat, s.c.). The anxiety-like behavior was assessed in the elevated plus maze (EPM) and the light-dark tests (LDT), locomotor and grooming activities were assessed in the open-field test (OFT).

RESULTS

Cholecalciferol in high doses alone or in combination with 17β-E2-induced anxiolytic-like effects in OVX and OVX rats treated with 17β-E2 as evidenced in the EPM and LDT tests, and increased grooming activity in the OFT test. We found that DA and 5-HT levels increased while 5-HT turnover in the hippocampus decreased in these groups of OVX rats.

CONCLUSION

Our results indicate that cholecalciferol in high doses has a marked anxiolytic-like effect due to an increase in the monoamines levels in the experimental rat model of estrogen deficiency.

Emotional Roles of Mono-Aminergic Neurotransmitters in Major Depressive Disorder and Anxiety Disorders

A growing body of researches support a role for dysfunction of serotoninergic, noradrenergic, and dopaminergic systems in the neurobiological processes involved in major depression disorder (MDD) and anxiety disorders (ADs). The physiological changes underlying abnormal signaling of 5-HT, NE, and DA may be due to either reduced presynaptic release of these neurotransmitters or aberrant signal transductions, and thus contributing to the alterations in regulation or function of receptors and/or impaired intracellular signal processing. Animal models demonstrate crucial responsiveness to disturbance of 5-HT, NE, and DA neurotransmissions. Postmortem and biochemical studies have shown altered concentrations of 5-HT, NE, and DA metabolites in brain regions that contribute importantly to regulation of mood and motivation in patients with MDD or ADs. Neuroimaging studies have found abnormal 5-HT, NE, and DA receptors binding and regulation in regard to receptor numbers. Medications that act on 5-HT, NE, and DA neurons or receptors, such as SSRIs and SNRIs, show efficacy in both MDD and ADs. The overlapping treatment response presumably suggests a common mechanism underlying the interaction of these disorders. In this paper, we reviewed studies from multiple disciplines to interpret the role of altered 5-HT, NE and DA mono-amine neurotransmitter functions in both MDD and ADs.

Relationship between rapheal echogenicity and personality as possible markers of a disposition to develop depressive and anxiety disorders

Early diagnosis of anxiety and depression may be facilitated by the use of neurobiological markers. In depression and panic disorder, transcranial sonography (TCS) has revealed decreased echogenicity of the brainstem raphe (BR). The aim of the present study was to detect whether decreased echogenicity of the BR correlates with personality features described in the five-dimension model, especially neuroticism. We examined 100 healthy volunteers using quantitative and qualitative TCS, the five-dimension revised NEO Personality Inventory, Beck´s scales of anxiety and depression, and the Social Re-adjustment Rating Scale (SRRS). Visual BR anechogenicity was found in 11 subjects, BR hypoechogenicity in 29 subjects, and normal BR echogenicity in 60 subjects. The visual assessment correlated with the digital assessment. Comparing the groups with visual BR anechogenicity and BR normoechogenicity, only increased SRRS score and increased agreeableness z-score were significant. Our hypothesis that BR hypoechogenicity reflects an inclination for depression and anxiety characterized by the personality dimension neuroticism was not supported. However, this disposition may be present in a different state, such as stress.

The neuronal basis of copper induced modulation of anxiety state in rat

Recently, studies have provided strong evidence indicating the involvement of trace elements in the physiopathology of psychiatric disorders, particularly anxiety. We aimed, through the present study, to describe the effect of acute exposure to Cu (10mg/kg BW) on anxiety state together with the serotoninergic and dopaminergic systems in rat by means of neurobehavioral tests (elevated plus maze, dark light box) and immunohistochemistry using anti-serotonin (5HT) and anti-tyrosine hydroxylase (TH). Our data report that Cu enhanced 5HT innervation in the dorsal raphe nucleus (DRN) together with a loss of TH expression within the ventral tegmental area (VTA), Substantia nigra compacta (SNc) and their subsequent outputs including the medial forebrain bundle (MFB) and striatum. In the elevated plus maze Cu significantly increased the time and the number of entries into the open arms, and raised the time spent in the Dark Box indicating a clear reduced anxiety state induced by Cu. The present data show for the first time a powerful neuro-modulatory potential of Cu in rat which involves primarily a dysfunction of 5HT and DA neurotransmissions.

Anxiolytic profile of fluoxetine as monitored following repeated administration in animal rat model of chronic mild stress

Background: Fluoxetine, a selective serotonin re-uptake inhibitor (SSRI), has been proposed to be more effective as an antidepressive drug as compared to other SSRIs. After chronic SSRI administration, the increase in synaptic levels of 5-HT leads to desensitization of somatodentritic 5-HT autoreceptors in the raphe nuclei. Chronic stress may alter behavioral, neurochemical and physiological responses to drug challenges and novel stressors. Methods: Twenty four male rats were used in this study. Animals of CMS group were exposed to CMS. Animals of stressed and unstressed group were administrated with fluoxetine at dose of 1.0 mg/kg s well as 5.0 mg/kg repeatedly for 07 days 1 h before exposed to CMS. The objective of the present study was to evaluate that repeated treatment with fluoxetine could attenuate CMS-induced behavioral deficits. Results: Treatment with fluoxetine attenuated CMS-induced behavioral deficits. Fluoxetine administration induced hypophagia in unstressed as well as CMS rats. Acute and repeated administration of fluoxetine increased motor activity in familiar environment but only repeated administration increased exploratory activity in open field. Anxiolytic effects of fluoxetine were greater in unstressed rats. These anxiolytic effects were produced as result of repeated administration not on acute administration of fluoxetine at 1.0 mg/kg as well as 5.0 mg/kg. Conclusion: The present study demonstrated that CMS exposure resulted into behavioral deficits and produced depressive-like symptoms. Fluoxetine, an SSRI, administration attenuated behavioral deficits induced by CMS. Anxiolytic effects of repeated fluoxetine administration were greater in unstressed than CMS animals.

The Association between Baseline Subjective Anxiety Rating and Changes in Cardiac Autonomic Nervous Activity in Response to Tryptophan Depletion in Healthy Volunteers

The aim of this study was to investigate the influence of serotonin on anxiety and autonomic nervous system (ANS) function; the correlation between subjective anxiety rating and changes of ANS function following tryptophan depletion (TD) in healthy volunteers was examined. Twenty-eight healthy participants, consisting of 15 females and 13 males, with an average age of 33.3 years, were recruited.Baseline Chinese Symptom Checklist-90-Revised and ANS function measurements were taken. TD was carried out on the testing day, and participants provided blood samples right before and 5 hours after TD. ANS function, somatic symptoms, and Visual Analogue Scales (VASs) were determined after TD. Wilcoxon signed rank test and Spearman ρ correlation were adapted for analyses of the results.The TD procedure reduced total and free plasma tryptophan effectively. After TD, the sympathetic nervous activity increased and parasympathetic nervous activity decreased. Baseline anxiety ratings positively correlated with post-TD changes in sympathetic nervous activity, VAS ratings, and physical symptoms. However, a negative correlation with post-TD changes in parasympathetic nervous activity was found.The change in ANS function after TD was associated with the severity of anxiety in healthy volunteers. This supports the fact that the effect of anxiety on heart rate variability is related to serotonin vulnerability. Furthermore, it also shows that the subjective anxiety rating has a biological basis related to serotonin.

Suppression of piriform cortex activity in rat by corticotropin-releasing factor 1 and serotonin 2A/C receptors

The piriform cortex (PC) is richly innervated by corticotropin-releasing factor (CRF) and serotonin (5-HT) containing axons arising from central amygdala and Raphe nucleus. CRFR₁ and 5-HT_2A/2CRs have been shown to interact in manner where CRFR activation subsequently potentiates the activity of 5-HT_2A/2CRs. The purpose of this study was to determine how the activation of CRFR₁ and/or 5-HT₂Rs modulates PC activity at both the circuit and cellular level. Voltage sensitive dye imaging showed that CRF acting through CRFR₁ dampened activation of the Layer II of PC and interneurons of endopiriform nucleus. Application of the selective 5-HT_2A/CR agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) following CRFR₁ activation potentiated this effect. Blocking the interaction between CRFR₁ and 5-HT₂R with a Tat-CRFR₁-CT peptide abolished this potentiation. Application of forskolin did not mimic CRFR₁ activity but instead blocked it, while a protein kinase A antagonist had no effect. However, activation and antagonism of protein kinase C (PKC) either mimicked or blocked CRF modulation, respectively. DOI had no effect when applied alone indicating that the prior activation of CRFR₁ receptors was critical for DOI to show significant effects similar to CRF. Patch clamp recordings showed that both CRF and DOI reduced the synaptic responsiveness of Layer II pyramidal neurons. CRF had highly variable effects on interneurons within Layer III, both increasing and decreasing their excitability, but DOI had no effect on the excitability of this group of neurons. These data show that CRF and 5-HT, acting through both CRFR₁ and 5-HT_2A/CRs, reduce the activation of the PC. This modulation may be an important blunting mechanism of stressor behaviors mediated through the olfactory cortex.

Central nervous system activity of an aqueous acetonic extract of Ficus carica L. in mice

BACKGROUND

Ficus carica Linn. is reported to possess variety of activities, but its potential in CNS disorders is still to be explored.

OBJECTIVE

The present study was carried out to evaluate the CNS depressant activity of aqueous acetonic extract of Ficus carica Linn on different models in mice.

MATERIALS AND METHODS

The aerial parts of the plant Ficus carica L. were extracted with aqueous acetone and the solvent was removed by rotary vacuum evaporator under reduced pressure. A crude extract was given orally and its effects were tested on ketamine-induced sleeping time, muscle-coordination, anxiety (elevated-plus maze and Staircase test), convulsions [maximal electroshock (MES) and pentylenetetrazole (PTZ)-induced seizures], and nociception. In addition, we determined the levels of neurotransmitters, norepinephrine (NE) and 5-hydroxytryptamine (5-HT).

RESULTS

RESULTS FROM THE EXPERIMENTAL MODELS TESTED SHOWED: (1) a delay on onset and prolongation of sleep of ketamine-induced sleeping time; (2) significant muscle relaxant activity; (3) a significant attenuation in the anxiety-response (4) a delay in the onset of seizures and reduction in duration of seizures and mortality induced by MES and PTZ; (5) a reduction in the licking time in nociception test and (6) increased levels of NE and 5-HT.

CONCLUSION

This suggests that Ficus carica L. exerts its CNS depressive effect by modulating the neurotransmitters NE and 5-HT in the brain.

Anxiogenic Effects of Acute Injection of Sesame oil May be Mediated by β-1 Adrenoceptors in the Basolateral Amygdala

PURPOSE

A few studies have indicates that the sesame oil influences anxiety, but many reports show that β-1 adrenoceptors (ARs) of the basolateral amygdala (BLA) plays a pivotal role in this regard. Therefore, in this study the effect of acute injection of sesame oil on anxiety-like behavior in the presence and absence of the BLA β-1 ARs in the male Wistar rats were investigated.

METHODS

Guide cannulas, for seven groups of rats, were implanted bilaterally into the BLA. Two weeks after the stereotaxic surgery, anxiety-like behaviors (the OAT%, OAE % and locomotor activity) were evaluated by Elevated Plus-Maze (EPM) for all groups. 3 groups received different volumes of sesame oil (i.p.) and they were compared with control group (received saline via i.p.), and the anxiogenic volume of sesame oil (1.5ml/kg) was determined. Then, 3 other groups received constant effective volume of sesame oil (1.5ml/kg) along with 3 different doses of betaxolol, selective β-1 ARs antagonist, intra BLA microinjection in order to be compared with sesame oil group (1.5 ml/kg).

RESULTS

The acute injection of sesame oil with the volume dependent manner showed an anxiogenic effect with reduction of the OAT% and OAE% which the maximum effect of sesame oil was observed in the dose of 1.5mg/kg. Also, betaxolol with dose dependent manner attenuated the anxiogenic effects of sesame oil (1.5mg/kg), but this reduction could not remove the anxiety effects completely.

CONCLUSION

It seems that the sesame oil acute (i.p.) injection induces anxiety, and this effect is attenuated by inhibition of β-1ARs in the BLA.

Early life stress is associated with anxiety, increased stress responsivity and preference for "comfort foods" in adult female rats

Chronic stress increases anxiety and encourages intake of palatable foods as "comfort foods". This effect seems to be mediated by altered function of the hypothalamic-pituitary-adrenal axis. In the current study, litters of Wistar rats were subjected to limited access to nesting material (Early-Life Stress group - ELS) or standard care (Control group) from postnatal day 2 to 9. In adult life, anxiety was assessed using the novelty-suppressed feeding test (NSFT), and acute stress responsivity by measurement of plasma corticosterone and ACTH levels. Preference for palatable foods was monitored by a computerized system (BioDAQ, Research Diets(®)) in rats receiving only regular chow or given the choice of regular and palatable diet for 30 days. ELS-augmented adulthood anxiety in the NSFT (increased latency to eat in a new environment; decreased chow intake upon return to the home cage) and increased corticosterone (but not ACTH) secretion in response to stress. Despite being lighter and consuming less rat chow, ELS animals ate more palatable foods during chronic exposure compared with controls. During preference testing, controls receiving long-term access to palatable diet exhibited reduced preference for the diet relative to controls exposed to regular chow only, whereas ELS rats demonstrated no such reduction in preference after prolonged palatable diet exposure. The increased preference for palatable foods showed by ELS animals may result from a habit of using this type of food to ameliorate anxiety.

EMDR and Cognitive Behavioral Therapy in the Treatment of Panic Disorder: A Comparison

A pilot comparison was made between two treatments for panic disorder, eye movement desensitization and reprocessing (EMDR) and cognitive behavioral therapy (CBT). Treatment was provided in the private practice settings of 7 credentialed therapists, whose treatment fidelity was monitored throughout the study. Five outcome measures were administered at pretreatment, posttreatment, and 1-year follow-up. There was significant improvement for participants in both groups (N = 19) after 12 sessions of treatment. No significant differences in outcome were seen between the 2 therapies, except for lower frequency of panic attacks reported by those in the EMDR group. The current study reanalyzed the data previously reported in Faretta (2012). Further research in this area is suggested.

Opposing local effects of endocannabinoids on the activity of noradrenergic neurons and release of noradrenaline: relevance for their role in depression and in the actions of CB(1) receptor antagonists

There is strong evidence that endocannabinoids modulate signaling of serotonin and noradrenaline, which play key roles in the pathophysiology and treatment of anxiety and depression. Most pharmacological and genetic, human and rodent studies suggest that the presence of under-functioning endocannabinoid type-1 (CB(1)) receptors is associated with increased anxiety and elevated extracellular serotonin concentration. In contrast, noradrenaline is presumably implicated in the mediation of depression-type symptoms of CB(1) receptor antagonists. Evidence shows that most CB(1) receptors located on axons and terminals of GABA-ergic, serotonergic or glutamatergic neurons stimulate the activity of noradrenergic neurons. In contrast, those located on noradrenergic axons and terminals inhibit noradrenaline release efficiently. In this latter process, excitatory ionotropic or G protein-coupled receptors, such as the NMDA, alpha1 and beta1 adrenergic receptors, activate local endocannabinoid synthesis at postsynaptic sites and stimulate retrograde endocannabinoid neurotransmission acting on CB(1) receptors of noradrenergic terminals. The underlying mechanisms include calcium signal generation, which activates enzymes that increase the synthesis of both anandamide and 2-arachidonoylglycerol, while G(q/11) protein activation also increases the formation of 2-arachidonoylglycerol from diacylglycerol during the signaling process. In addition, other non-CB(1) receptor endocannabinoid targets such as CB(2), transient receptor potential vanilloid subtype, peroxisome proliferator-activated receptor-alpha and possibly GPR55 can also mediate some of the endocannabinoid effects. In conclusion, both neuronal activation and neurotransmitter release depend on the in situ synthesized endocannabinoids and thus, local endocannabinoid concentrations in different brain areas may be crucial in the net effect, namely in the regulation of neurons located postsynaptically to the noradrenergic synapse.

The efficacy of Hypericum perforatum (St John's wort) for the treatment of premenstrual syndrome: a randomized, double-blind, placebo-controlled trial

BACKGROUND

Premenstrual syndrome (PMS) is a common condition. Some of the most widely prescribed medications are selective serotonin reuptake inhibitors (SSRIs), based on the hypothesized role of serotonin in the production of PMS symptoms. PMS sufferers, especially those experiencing mild to moderate symptoms, are often reluctant to take this form of medication and instead buy over-the-counter preparations to treat their symptoms, for which the evidence base with regard to efficacy is limited. Hypericum perforatum (St John's wort) influences the serotonergic system. As such, this widely available herbal remedy deserves attention as a PMS treatment.

OBJECTIVE

To investigate the effectiveness of Hypericum perforatum on symptoms of PMS.

STUDY DESIGN

This randomized, double-blind, placebo-controlled, crossover study was conducted between November 2005 and June 2007.

SETTING

Institute of Psychological Sciences, University of Leeds, Leeds, UK.

PARTICIPATION

36 women aged 18-45 years with regular menstrual cycles (25-35 days), who were prospectively diagnosed with mild PMS.

INTERVENTION

Women who remained eligible after three screening cycles (n = 36) underwent a two-cycle placebo run-in phase. They were then randomly assigned to receive Hypericum perforatum tablets 900 mg/day (standardized to 0.18% hypericin; 3.38% hyperforin) or identical placebo tablets for two menstrual cycles. After a placebo-treated washout cycle, the women crossed over to receive placebo or Hypericum perforatum for two additional cycles.

MAIN OUTCOME MEASURES

Symptoms were rated daily throughout the trial using the Daily Symptom Report. Secondary outcome measures were the State Anxiety Inventory, Beck Depression Inventory, Aggression Questionnaire and Barratt Impulsiveness Scale. Plasma hormone (follicle-stimulating hormone [FSH], luteinizing hormone [LH], estradiol, progesterone, prolactin and testosterone) and cytokine (interleukin [IL]-1beta, IL-6, IL-8, interferon [IFN]-gamma and tumour necrosis factor [TNF]-alpha) levels were measured in the follicular and luteal phases during Hypericum perforatum and placebo treatment.

RESULTS

Hypericum perforatum was statistically superior to placebo in improving physical and behavioural symptoms of PMS (p < 0.05). There were no significant effects of Hypericum perforatum compared with placebo treatment for mood- and pain-related PMS symptoms (p > 0.05). Plasma hormone (FSH, LH, estradiol, progesterone, prolactin and testosterone) and cytokine (IL-1beta, IL-6, IL-8, IFNgamma and TNFalpha) levels, and weekly reports of anxiety, depression, aggression and impulsivity, also did not differ significantly during the Hypericum perforatum and placebo cycles (p > 0.05).

CONCLUSION

Daily treatment with Hypericum perforatum was more effective than placebo treatment for the most common physical and behavioural symptoms associated with PMS. As proinflammatory cytokine levels did not differ significantly between Hypericum perforatum and placebo treatment, these beneficial effects are unlikely to be produced through this mechanism of action alone. Further work is needed to determine whether pain- and mood-related PMS symptoms benefit from longer treatment duration. Trial registration number (International Standard Randomised Controlled Trial Number Register) ISRCTN31487459.

Pharmacotherapy of alcohol and drug problems

Substantial progress has been made in the pharmacotherapy of withdrawal syndromes and organic complications of alcohol and drug abuse. Diazepam loading (alcohol withdrawal), phenobarbital loading (barbituate withdrawal) and diazepam tapering (benzodiazepine discontinuation) have considerably simplified treatment of withdrawal syndromes and have enhanced efficacy. Propylthiouracil shows considerable promise in the out-patient treatment of alcoholic liver disease. New medications, particularly those modifying serotonergic function, have efficacy in decreasing alcohol consumption and show considerable therapeutic potential. Human pharmacology and pharmacotherapy should be a central part of training programmes in the field in order that further advances can be made.

Effects of acute citalopram on the expression of conditioned freezing in naive versus chronic citalopram-treated rats

An acute challenge with selective serotonin (5-HT) reuptake inhibitors (SSRIs) reduces the conditioned freezing in rats, a model of anxiety. The increase in the 5-HT levels in the nerve terminal induced by SSRIs is closely related to its pharmacological effects. Clinically, SSRIs exert an anxiolytic effect after chronic treatment. The effects of repeated treatment with citalopram on conditioned freezing in rats were examined in the present study. Acute citalopram (10 mg/kg) reduced freezing at a short post-training interval (1 day) significantly. While the effect of citalopram (10 mg/kg) on freezing was diminished by prolonging the interval between conditioning and the exposure to conditioned fear stress, repeated citalopram (10 mg/kg) injection twice daily for 7 days restored the inhibitory effect of acute challenge of citalopram (10 mg/kg) on freezing. By prolonging the period between conditioning and exposure to conditioned fear stress, this model may have a more precise predictive validity of anxiety disorder as an animal model.

Presynaptic receptors for dopamine, histamine, and serotonin

Presynaptic receptors for dopamine, histamine and serotonin that are located on dopaminergic, histaminergic and sertonergic axon terminals, respectively, function as autoreceptors. Presynaptic receptors also occur as heteroreceptors on other axon terminals. Auto- and heteroreceptors mainly affect Ca(2+) -dependent exocytosis from the receptor-bearing nerve ending. Some additionally subserve other presynaptic functions.Presynaptic dopamine, histamine and serotonin receptors are involved in various (patho)physiological conditions. Examples are the following:Dopamine autoreceptors play a role in Parkinson's disease, schizophrenia and drug addiction. Dopamine heteroreceptors affecting the release of acetylcholine and of amino acid neurotransmitters in the basal ganglia are also relevant for Parkinson's disease. Peripheral dopamine heteroreceptors on postganglionic sympathetic terminals influence heart rate and vascular resistance through modulation of noradrenaline release. Blockade of histamine autoreceptors increases histamine synthesis and release and may support higher CNS functions such as arousal, cognition and learning. Peripheral histamine heteroreceptors on C fiber and on postganglionic sympathetic fiber terminals diminish neuropeptide and noradrenaline release, respectively. Both inhibititory effects are beneficial in myocardial ischemia. The inhibition of neuropeptide release also explains the antimigraine effects of some agonists of presynaptic histamine receptors. Upregulation of presynaptic serotonin autoreceptors is probably involved in the pathogenesis of major depression. Correspondingly, antidepressant treatments can be linked with a reduced density of 5-HT autoreceptors. 5-HT Heteroreceptor activation diminishes acetylcholine and GABA release and may therefore increase anxiety. In the periphery, presynaptic 5-HT heteroreceptor agonists shorten migraine attacks by inhibition of the release of neuropeptides from trigeminal afferents, apart from their constrictive action on meningeal vessels.

Behavioral effects of the β3 adrenoceptor agonist SR58611A: Is it the putative prototype of a new class of antidepressant/anxiolytic drugs?

A large body of evidence corroborates the notion that deficiencies of serotonergic system are likely involved in the pathogenesis of both depression and anxiety. Activation of beta(3) adrenoceptors has been shown to increase brain tryptophan content suggesting an elevation of brain serotonin (5HT) synthesis. SR58611A is a selective beta(3) adrenergic agent possessing a profile of antidepressant activity in routine rodents' experimental models of depression. The present study was undertaken to evaluate in rodents the antidepressant properties of SR58611A and to assess its putative anxiolytic value in experimental models of depression and anxiety. Compared to the control group, SR58611A (0.1, 1, 5 or 10 mg/kg) caused a dose-dependent reduction in immobility of Wistar male rats in the forced swim test. The maximum dose appeared to be equivalent to an effective dose of clomipramine (50 mg/kg). In addition, acute injection of SR58611A induced in rats a dose-dependent decrease in grooming response to a novel environment (novelty-induced grooming test). For any dose, the effect was lower than that of diazepam (1 mg/kg). Chronic treatment with SR58611A resulted also in an increased social interaction time in the social interaction test without affecting motor activity of rats. Furthermore, similarly to diazepam a chronic treatment with the highest doses of SR58611A was followed by increased exploratory behavior in Swiss male mice exposed to the elevated plus maze test. These effects are mediated by beta(3) adrenoceptors since i.p. pretreatment with the selective beta(3) adrenoceptor antagonist SR59230A (5 mg/kg) blocked the effects of SR58611A. Finally, also the 5HT antagonist methysergide (2 mg/kg) prevented the antidepressant and anxiolytic-like activity of SR58611A indicating that 5HT transmission is strictly involved in its action.

Effects of rapid eye movement sleep deprivation on hypocretin neurons in the hypothalamus of a rat model of depression

Hypocretin (Hcrt, also known as orexin) is a hypothalamic neuropeptide linked to narcolepsy, a disorder diagnosed by the appearance of rapid eye-movement sleep (REMS)-state characteristics during waking. Major targets of Hcrt-containing fibers include the locus coeruleus and the raphe nucleus, areas with important roles in regulation of mood and sleep. A relationship between REMS and mood is suggested by studies demonstrating that REMS-deprivation (REMSD) ameliorates depressive symptoms in humans. Additional support is found in animal studies where antidepressants and REMSD have similar effects on monoamiergic systems thought to be involved in major depression. Recently, we have reported that Wistar-Kyoto (WKY) rats, an animal model of depression, have reduced number and size of hypothalamic cells expressing Hcrt-immunoractivity compared to the parent, Wistar (WIS) strain, suggesting the possibility that the depressive-like attributes of the WKY rat may be determined by this relative reduction in Hcrt cells [Allard, J.S., Tizabi, Y., Shaffery, J.P., Trouth, C.O., Manaye, K., 2004. Stereological analysis of the hypothalamic hypocretin/orexin neurons in an animal model of depression. Neuropeptides 38, 311-315]. In this study, we sought to test the hypothesis that REMSD would result in a greater increase in the number and/or size of hypothalamic, Hcrt-immunoreactive (Hcrt-ir) neurons in WKY, compared to WIS rats. The effect of REMSD, using the multiple-small-platforms-over-water (SPRD) method, on size and number of Hcrt-ir cells were compared within and across strains of rats that experienced multiple-large-platforms-over-water (LPC) as well as to those in a normal, home-cage-control (CC) setting. In accord with previous findings, the number of Hcrt-ir cells was larger in all three WIS groups compared to the respective WKY groups. REMSD produced a 20% increase (p<0.02) in the number of hypothalamic Hcrt-ir neurons in WKY rats compared to cage control WKY (WKY-CC) animals. However, an unexpected higher increase in number of Hcrt-ir cells was also observed in the WKY-LPC group compared to both WKY-CC (31%, p<0.001) and WKY-SPRD (20%, p<0.002) rats. A similar, smaller, but non-significant, pattern of change was noted in WIS-LPC group. Overall the data indicate a differential response to environmental manipulations where WKY rats appear to be more reactive than WIS rats. Moreover, the findings do not support direct antidepressant-like activity for REMSD on hypothalamic Hcrt neurons in WKY rats.

L’association antidépresseur et anxiolytique aujourd’hui: bilan et prospective

SUMMARY

The potential for drug-drug interactions in psychiatric patients is very high as combination psychopharmacotherapy used to treat comorbid psychiatric disorders, to treat the adverse effects of a medication, to augment a medication effect or to treat concomitant medical illnesses, etc. Interactions can be pharmacodynamic or pharmacokinetic in nature. In clinical practice the benzodiazepines (BZD) are often prescribed together with antidepressant drugs for the treatment of depression. Although there has been no convincing evidence to show that such a combination is more effective than antidepressants alone and no clear indication for the use of this combination. Yet, anxiety frequently coexists with depression, and an anxiolytic is often added. But, it is BZD which are systematically prescribed together with antidepressants. However, BZD themselves have no antidepressive effects and we lack firm evidence for or against this combination therapy. We are focused on the pharmacodynamic interactions between anxiolytic such as BZD, and antidepressant drugs which may resulting in a reduction of the effects of one of the drugs. It is known that BZD decrease the serotoninergic transmission. Also, it may be suggested that combined BZD-specific serotonin reuptake inhibitors, should be avoided. This paper reviews, in vitro and in vivo and particularly in clinical, the evidences for drug interactions between BZD and antidepressant drugs. In clinical, all trials that compared antidepressant-benzodiazepine treatment with antidepressant alone for adult patients with major depression were sought by electronic searches of Medline and several other databases (1970 to 2005), combined with hand searching, reference searching and SciSearch.

CNS activity of Calotropis gigantea roots

Alcoholic extract of peeled roots of Calotropis gigantea R.Br. (Asclepiadaceae) was tested orally in albino rats at the dose level of 250 and 500 mg/kg bodyweight for CNS activity. Prominent analgesic activity was observed in Eddy's hot plate method and acetic acid induced writhings. The paw licking time was delayed and the numbers of writhings were greatly reduced. Significant anticonvulsant activity was seen as there was a delay in the onset of pentylenetetrazole induced convulsions as well as decrease in its severity. The extract treated rats spent more time in the open arm of EPM showing its antianxiety activity. There was a decrease in the locomotor activity. The fall off time (motor coordination) was also decreased. A potentiation in the pentobarbitone-induced sleep due to the sedative effect of the extract was observed. No mortality was seen upto the dose of 1 g/kg. These results show the analgesic, anticonvulsant, anxiolytic and sedative effect of the extract.

Lemon oil vapor causes an anti-stress effect via modulating the 5-HT and DA activities in mice

We examined the anti-stress action of the essential oils of lavender, rose, and lemon using an elevated plus-maze task (EPM), a forced swimming task (FST), and an open field task (OFT) in mice. Lemon oil had the strongest anti-stress effect in all three behavioral tasks. We further investigated a regulatory mechanism of the lemon oil by pre-treatments with agonists or antagonists to benzodiazepine, 5-HT, DA, and adrenaline receptors by the EPM and the FST. The anti-stress effect of lemon oil was significantly blocked by pre-treatment with frumazenil, benzodiazepine receptor antagonist, or apomorphine, a nonselective DA receptor agonist. In contrast, agonists or antagonists to the 5-HT receptor and the alpha-2 adrenaline receptor did not affect the anti-stress effect of lemon oil. Buspirone, DOI, and mianserine blocked the antidepressant-like effect of lemon oil in the FST, but WAY100,635 did not. These findings suggest that the antidepressant-like effect of lemon oil is closely related with the 5-HTnergic pathway, especially via 5-HT(1A) receptor. Moreover, the lemon oil significantly accelerated the metabolic turnover of DA in the hippocampus and of 5-HT in the prefrontal cortex and striatum. These results suggest that lemon oil possesses anxiolytic, antidepressant-like effects via the suppression of DA activity related to enhanced 5-HTnergic neurons.

gamma-Aminobutyric acid-serotonin interactions in healthy men: implications for network models of psychosis and dissociation

BACKGROUND

This study tested the hypothesis that deficits in gamma-aminobutyric acid type A (GABA(A)) receptor function might create a vulnerability to the psychotogenic and perceptual altering effects of serotonergic (5-HT(2A/2C)) receptor stimulation. The interactive effects of iomazenil, an antagonist and partial inverse agonist of the benzodiazepine site of the GABA(A) receptor complex, and m-chlorophenylpiperazine (m-CPP), a partial agonist of 5-HT(2A/2C) receptors, were studied in 23 healthy male subjects.

METHODS

Subjects underwent 4 days of testing, during which they received intravenous infusions of iomazenil/placebo followed by m-CPP/placebo in a double-blind, randomized crossover design. Behavioral, cognitive, and hormonal data were collected before drug infusions and periodically for 200 min after.

RESULTS

Iomazenil and m-CPP interacted in a synergistic manner to produce mild psychotic symptoms and perceptual disturbances without impairing cognition. Iomazenil and m-CPP increased anxiety in an additive fashion. Iomazenil and m-CPP interacted in a synergistic manner to increase serum cortisol.

CONCLUSIONS

Gamma-aminobutyric acid-ergic deficits might increase the vulnerability to the psychotomimetic and perceptual altering effects of serotonergic agents. These data suggest that interactions between GABA(A) and 5-HT systems might contribute to the pathophysiology of psychosis and dissociative-like perceptual states.

The developmental association between eating disorders symptoms and symptoms of depression and anxiety in juvenile twin girls

OBJECTIVE

We investigated the role of genetic and environmental factors in the developmental association among symptoms of eating disorders, depression, and anxiety syndromes in 8-13-year-old and 14-17-year-old twin girls.

METHODS

Multivariate genetic models were fitted to child-reported longitudinal symptom data gathered from clinical interview on 408 MZ and 198 DZ female twin pairs from the Virginia Twin Study of Adolescent Behavioural Development (VTSABD).

RESULTS

Model-fitting revealed distinct etiological patterns underlying the association among symptoms of eating disorders, depression, overanxious disorder (OAD), and separation anxiety disorder (SAD) during the course of development: 1) a common genetic factor influencing liability to all symptoms - of early and later OAD, depression, SAD, and eating symptoms; 2) a distinct genetic factor specifically indexing liability to early eating disorders symptoms; 3) a shared environmental factor specifically influencing early depression and early eating disorders symptoms; and 4) a common environmental factor affecting liability to symptoms of later eating disorders and both early and later separation anxiety.

CONCLUSIONS

These results suggest a pervasive genetic effect that influences liability to symptoms of over-anxiety, separation anxiety, depression, and eating disorder throughout development, a shared environmental influence on later adolescent eating problems and persistent separation anxiety, genetic influences specific to early eating disorders symptoms, and a shared environmental factor influencing symptoms of early eating and depression.

Modulation of anxiety circuits by serotonergic systems

Anxiety is a complex emotional state associated with sustained heightened autonomic and behavioral arousal and an increase in avoidance behavior. Anxiety-related behavior is a form of risk assessment behavior that is associated with a level of uncertainty or unpredictability regarding the outcome of emotionally salient events, often when both rewarding and aversive outcomes are possible. In this review, we highlight recent advances in our understanding of the neural circuits regulating anxiety states and anxiety-related behavior with an emphasis on the role of brainstem serotonergic systems in modulating anxiety-related circuits. In particular, we explore the possibility that the regulation of anxiety states and anxiety-related behavior by serotonergic systems is dependent on a specific, topographically organized mesolimbocortical serotonergic system that originates in the mid-rostrocaudal and caudal parts of the dorsal raphe nucleus.

Anxiogenic effects of Sumatriptan in panic disorder: a double-blind, placebo-controlled study

BACKGROUND

Several lines of evidence point to serotonergic abnormalities in patients with panic disorder (PD). Our goal was to further examine central serotonergic function in panic patients using autonomic and subjective responses to the postsynaptic serotonin 5-HT1D receptor agonist Sumatriptan.

METHOD

Using a double-blind, randomized, placebo-controlled design, we assessed autonomic and subjective responses to oral Sumatriptan (100 mg) and placebo in 15 patients with PD, free of medication. Subjective responses were measured using the Hamilton Anxiety Rating Scale (HAM-A), National Institute of Mental Health Anxiety Scale (NIMHA), a modified version of the Panic Symptom Inventory (PI), Hamilton Depression Rating Scale (HAM-D), and Montgomery-Asberg Depression Rating Scale (MADRS).

RESULTS

PD patients exhibited significantly enhanced autonomic and subjective responses following challenge with Sumatriptan. We observed an increased pulse rate and augmentation of various parameters measured on different anxiety scales. A constant inclination of aggravation of the measured parameters was detected during the hour post challenge.

CONCLUSION

Oral administration of Sumatriptan, a 5-HT1D agonist, has been associated with an anxiogenic effect in PD patients.

"Scared stiff": catatonia as an evolutionary-based fear response

Catatonia, long viewed as a motor disorder, may be better understood as a fear response, akin to the animal defense strategy tonic immobility (after G. G. Gallup & J. D. Maser, 1977). This proposal, consistent with K. L. Kahlbaum's (1874/1973) original conception, is based on similarities between catatonia and tonic immobility ("death feint") as well as evidence that catatonia is associated with anxiety and agitated depression and responds dramatically to benzodiazepines. It is argued that catatonia originally derived from ancestral encounters with carnivores whose predatory instincts were triggered by movement but is now inappropriately expressed in very different modern threat situations. Found in a wide range of psychiatric and serious medical conditions, catatonia may represent a common "end state" response to feelings of imminent doom and can serve as a template to understand other psychiatric disorders.

The cognitive paradox in posttraumatic stress disorder: a hypothesis

Posttraumatic stress disorder (PTSD) is characterized by a peculiar cognitive state. The traumatic event(s) are partly hypermemorized, partly blurred, whereas the ability to store and retrieve new information is impaired. The question is raised as to what the biological systems might be that 'carry' this cognitive paradox. Four possible candidate systems are discussed. It is concluded that understimulation of the corticosteroid receptors, particularly the glucocorticoid receptors (GRs), overactivity of the noradrenaline (NA) and vasopressin (VA) systems, and deficits in the 5-Hydroxytryptamine (5-HT) system, particularly the 5-HT(1A) system, could generate a cognitive syndrome similar to the one observed in PTSD. A dual hypothesis is launched holding that (a) in PTSD, downregulation of the 5-HT(1A) receptor system is the primary lesion, while the other dysfunctions mentioned are subsidiaries and that (b) underdevelopment of or damage to the 5-HT(1A) receptor system will make a person PTSD-prone.

Differential expression of 5HT-1A, alpha 1b adrenergic, CRF-R1, and CRF-R2 receptor mRNA in serotonergic, gamma-aminobutyric acidergic, and catecholaminergic cells of the rat dorsal raphe nucleus

The dorsal raphe nucleus (DR) has a topographic neuroanatomy consistent with the idea that different parts of this nucleus subserve different functions. Here we use dual in situ hybridization to describe the rostral-caudal neurochemical distribution of three major cell groups, serotonin (5-hydroxytryptamine; 5-HT), gamma-aminobutyric acid (GABA), and catecholamine, and their relative colocalization with each other and mRNA encoding four different receptor subtypes that have been described to influence DR responses, namely, 5HT-1A, alpha(1b) adrenergic (alpha(1b) ADR), and corticotropin-releasing factor type 1 (CRF-R1) and 2 (CRF-R2) receptors. Serotonergic and GABAergic neurons were distributed throughout the rostral-caudal extent of the DR, whereas catecholaminergic neurons were generally restricted to the rostral half of the nucleus. These phenotypes essentially represent distinct cell populations, because the neurochemical markers were rarely colocalized. Both 5HT-1A and alpha(1b) ADR mRNA were highly expressed throughout the DR, and the vast majority of serotonergic neurons expressed both receptors. A smaller percentage of GABAergic neurons also expressed 5HT-1A or alpha(1b) ADR mRNA. Very few catecholaminergic cells expressed either 5HT-1A or alpha(1b) ADR mRNA. CRF-R1 mRNA was detected only at very low levels within the DR, and quantitative colocalization studies were not technically feasible. CRF-R2 mRNA was mainly expressed at the middle and caudal levels of the DR. At midlevels, CRF-R2 mRNA was expressed exclusively in serotonin neurons, whereas, at caudal levels, approximately half the CRF-R2 mRNA was expressed in GABAergic neurons. The differential distribution of distinct neurochemical phenotypes lends support to the idea of functional differentiation of the DR.

Use of the elevated T-maze to study anxiety in mice

We have recently suggested that the elevated T-maze (ETM) is not a useful test to study different types of anxiety in mice if a procedure similar to that originally validated for rats is employed. The present study investigated whether procedural (five exposures in the enclosed arm instead of three as originally described for rats) and structural (transparent walls instead of opaque walls) changes to the ETM leads to consistent inhibitory avoidance acquisition (IAA) and low escape latencies in mice. Results showed that five exposures to the ETM provoked consistent IAA, an effect that was independent of the ETM used. However, the ETM with transparent walls (ETMt) seemed to be more suitable for the study of conditioned anxiety (i.e. IAA) and unconditioned fear (escape) in mice, since IAA (low baseline latency with a gradual increase over subsequent exposures) and escape (low latency) profiles rendered it sensitive to the effects of anxiolytic and anxiogenic drugs. In addition to evaluation of drug effects on IAA and escape, the number of line crossings in the apparatus were used to control for locomotor changes. Results showed that whereas diazepam (1.0-2.0 mg/kg) and flumazenil (10-30 mg/kg) impaired IAA, FG 7142 (10-30 mg/kg) did not provoke any behavioral change. Significantly, none of these benzodiazepine (BDZ) receptor ligands modified escape latencies. The 5-HT1A partial receptor agonist buspirone (1.0-2.0 mg/kg) and the 5-HT releaser fenfluramine (0.15-0.30 mg/kg) impaired IAA and facilitated escape, while the full 5-HT1A receptor agonist, 8-OH-DPAT (0.05-0.1 mg/kg) and the 5-HT(2B/2C) receptor antagonist, SER 082 (0.5-2.0 mg/kg) failed to modify either response. mCPP (0.5-2.0 mg/kg), a 5-HT(2B/2C) receptor agonist, facilitated IAA but did not alter escape latency. Neither antidepressant utilized in the current study, imipramine (1.0-5.0 mg/kg) and moclobemide (3.0-10 mg/kg) affected IAA or escape performance in mice. The well-known anxiogenic drugs yohimbine (2.0-8.0 mg/kg) and caffeine (10-30 mg/kg) did not selectively affect IAA, although caffeine did impair escape latencies. Present results suggest the ETMt is useful for the study of conditioned anxiety in mice. However, upon proximal threats (e.g. open arm exposure), mice do not exhibit escape behavior as an immediate defensive strategy, suggesting that latency to leave open arm is not a useful parameter to evaluate unconditioned fear in this species.

Alpha-lactalbumin-enriched diets enhance serotonin release and induce anxiolytic and rewarding effects in the rat

Among food proteins, alpha-lactalbumin (LAC) has the highest ratio of tryptophan (Trp) over its competitor amino acids. Consequently, contrary to casein (CAS), LAC ingestion increases Trp access to the brain leading to enhanced serotonin (5-HT) synthesis. As an index of serotonergic activity, we assessed extracellular 5-HT in response to LAC ingestion, using microdialysis, and performed behavioural tests in rats in order to characterise the suggested improvements of mood observed in humans after ingestion of this protein. Rats were fed with diets enriched either in LAC or CAS as control, acutely (30 min meals) or chronically (3 and 6 days). A 30 min LAC meal significantly increased 5-HT release in the medial hypothalamus. This effect disappeared after 3 and 6 days of diet. The basal premeal 5-HT levels were increasingly enhanced by the LAC diet. Compared to a CAS meal, LAC increased the percentage of time spent on the open arms of the elevated plus maze and the number of visits to the centre of the open field, suggesting an anxiolytic-like effect. A single LAC meal decreased sucrose consumption, while 3 or 6 days diets enhanced it, reflecting an appetitive and/or rewarding action. In conclusion, LAC ingestion induces anxiolytic-like and rewarding effects possibly related to serotonergic activation. Shifting transiently, the commonly consumed CAS-enriched to LAC-enriched diets may induce beneficial effects on mood.

Maternal effects in infant and adult phenotypes of 5HT1A and 5HT1B receptor knockout mice

The influence of the pre- and postweaning maternal environment on the offspring's phenotype was examined in 5-HT1A and 5-HT1B receptor knockout mice (KO1A and KO1B, respectively). We have previously shown that, when born to and raised by homozygous dams of the same genotype, adult KO1A are more anxious than wild-type (WT) mice, and adult KO1B are hyperactive and slightly less anxious than WT mice. We extend our studies here to the behavioral results of the offspring's own genotype, when the dam's genotype is constant, and the effects of the dam's genotype when the offspring's genotype is constant. In Experiments 1 and 2, KO1A-/- pups produced less ultrasonic vocalizations (USV) than controls in an isolation test on postnatal Day 7 when born to and reared by KO1A dams, either -/- or +/-. Heterozygous F1 pups reared by KO1A-/- dams produced more USV and were less anxious in the plus-maze at 2 to 3 months of age than F1 pups born to and reared by WT dams (Experiment 3). F1 pups reared by KO1B-/- dams produced less USV and were more anxious in the plus-maze than F1 pups reared by WT dams (Experiment 4). The results support a role for maternal effects that may comprise direct effects such as the dam's behavior and nutritional care of the pup, and possibly more complex indirect effects through the establishment of idiosyncratic dam-pup dyadic interactions. We recommend that breeding techniques that rely on same genotype (mutant-mutant or WT-WT) breeding pairs not be used to generate offspring when the focus of research is the study of gene function, but rather when familial effects need to be studied.

Panic disorder and depression: relationship between psychological and biochemical aspects

In a group of medication-free out-patients suffering from depression and/or panic disorder we investigated the interdependence between psychological parameters such as aggression and biochemical parameters such as serotonin and tryptophan. We compared the findings in the patient group with a reference group. In the group of patients as a whole negative correlations were observed between the concentration of serotonin in platelets and depression and with hostility and aggression against others. Serotonin in plasma and tryptophan correlated negatively with hostility. The findings support the suggested link between aggression and depression with a low functioning serotonergic system.

Anxiolytic and anticonvulsive activity of Sesbania grandiflora leaves in experimental animals

Various parts of Sesbania grandiflora have been used in the Indian system of medicine, in particular, the leaves of S. grandiflora are used in Ayurveda for the treatment of epileptic fits. In the present study we have evaluated the anticonvulsive activity of S. grandiflora leaves using a variety of animal models of convulsions. Bioassay guided separation was also carried out to identify the fraction possessing anticonvulsant activity. The benzene:ethyl acetate fraction (BE) of the acetone soluble part of a petroleum ether extract significantly delayed the onset of convulsions in pentylenetetrazol (PTZ) and strychnine (STR)- induced seizures in mice and reduced the duration of tonic hindleg extension in the maximum electroconvulsive shock (MES) induced seizures in mice. The BE contained a triterpene as a major component. In addition, the BE also inhibited electrically induced kindled seizures in mice and lithium-pilocarpine-induced status epilepticus in rats. It prolonged the duration of sleep induced by pentobarbital and antagonized the effect of D-amphetamine. Mice treated with BE preferred to remain in the open arm of the elevated plus maze indicating anxiolytic activity. The BE raised the brain contents of gamma-aminobutyric acid and serotonin. Thus the triterpene containing fraction of S. grandiflora exhibits a wide spectrum of anticonvulsant profile and anxiolytic activity.

Brain neurotransmitter receptor binding and nootropic studies on Indian Hypericum perforatum Linn

The high affinity binding sites for serotonin and benzodiazepine in the frontal cortex, for dopamine in the striatum and muscarinic cholinergic receptors in the hippocampus were investigated in the brains of Charles Foster rats treated for 3 days. Transfer latency on elevated plus maze (TL), passive and active avoidance behaviour (PA and AA) and electroconvulsive shock (ECS) induced amnesia were also studied. Pilot studies indicated that single dose administration of Indian Hypericum perforatum (IHp) had little or no acute behavioural effects and hence the extract of IHp was administered orally at two dose levels (100 and 200 mg/kg, p.o.) once daily for 3 consecutive days, while piracetam (500 mg/kg, i.p.), a clinically used nootropic agent, was administered acutely to rats as the standard nootropic agent. Control rats were treated with an equal volume of vehicle (0.3% carboxymethyl cellulose). The results indicate that IHp treatment caused a significant decrease in the binding of [3H] spiroperone (DA-D2 receptor) to the striatum and an increase in the binding of [3H] ketanserin (5-HT2A receptor) and [3H] flunitrazepam (BDZ receptor) to the frontal cortex in rats. Preliminary pharmacological studies with IHp extract indicate the presence of two major behavioural actions, namely, antidepressant and anxiolytic. The present findings tend to elucidate the mechanism of earlier observations, the downregulation of the dopamine D2 receptor being consonant with anxiolytic and the upregulation of 5-HT2A and BDZ receptors being consonant with antidepressant activity. Piracetam when given alone, shortened the TL on days 1, 2 and 9 day and also antagonized the amnesic effects of ECS on the TL significantly, whereas IHp antagonized the amnesia produced by ECS. IHp had no significant effect per se on the retention of the PA in rats but produced a significant reversal of ECS induced PA retention deficit. Piracetam showed a significant facilitatory effect per se on PA retention and also reversed the ECS induced impaired PA retention. In the AA test, piracetam facilitated the acquisition and retention of AA in rats but IHp had no effect per se. Both the doses of IHp and piracetam significantly attenuated the ECS induced impaired retention of AA. These results indicate a possible nootropic action of IHp in amnesic animals, which was comparable qualitatively to piracetam.

Anxiogenic activity of Myristica fragrans seeds

In the present study, the n-hexane extract of Myristica fragrans (MF) seeds, acetone-insoluble part of the n-hexane extract (AIMF) and trimyristin (TM) were assessed for their anxiogenic activity. The MF (10 and 30 mg/kg), AIMF (30, 100, and 300 mg/kg), and TM (10, 30, and 100 mg/kg) administered intraperitoneally exhibited anxiogenic activity in elevated plus-maze (EPM) paradigm. The open-field test and hole-board test were also used to assess anxiogenic activity of AIMF and TM. In the EPM test, MF, AIMF, and TM decreased the time spent by mice in the open arm and the entries in the open arm. Further, the effect of diazepam (1 mg/kg i.p.), serotonin 5-HT3 receptor antagonist, ondansetron (1 mg/kg i.p.), and 5-HT1A receptor agonist, buspirone (1 mg/kg i.p.), on the occupancy in open arm and entries in open arm was significantly reduced by TM. In the open-field test, AIMF as well as TM reduced the number of rearing and locomotion. Both TM and AIMF reduced the number of head pock in the hole-board test. Inhibition of anxiolytic activity of ondansetron (5-HT3 receptor antagonist), buspirone (5-HT1A receptor agonist), and diazepam [acting on gamma-aminobutyric acid (GABAA) receptor] suggests a nonspecific anxiogenic activity of TM and also a link between 5-HT and GABA systems in the anxiogenic activity of TM.

Psychomotor slowing, neuroendocrine responses, and behavioral changes after oral administration of meta-chlorophenylpiperazine in normal volunteers

The mixed 5-HT receptor agonist/antagonist meta-chlorophenylpiperazine (mCPP) is known to suppress locomotor activity in mice and rats. This study aimed: (1) to determine whether mCPP induces cognitive and motor changes in normal human volunteers and how these changes relate to the neuroendocrine effects of mCPP; and (2) to compare these cognitive and motor changes to the known cognitive and motor slowing patterns in depression and schizophrenia. A computerized method (used in previous research) analyzed fine motor behavior during figure-copying tasks. In 14 normal male volunteers behavioral responses, body temperature, plasma levels of prolactin and cortisol, and cognitive and motor performance during figure-copying tasks were measured after a single oral dose of mCPP (0.5 mg/kg). mCPP-induced prolongation of the reaction times in all copying tasks, parallel to increases in cortisol and prolactin and some self-reported behavioral effects. There were no changes in the movement times or the velocities of the writing movements. In conclusion, mCPP induced cognitive, but not motor slowing, in normal male volunteers. This indicates that the human serotonin system is also implicated in psychomotor behavior. This pattern of slowing was different from that in depressed and schizophrenic patients.