Cholinergic dysfunction in depression

Natural products for the treatment of stress-induced depression: Pharmacology, mechanism and traditional use

ETHNOPHARMACOLOGICAL RELEVANCE

Depression, one of the most common psychiatric disorders, is the fourth leading cause of long-term disability worldwide. A series of causes triggered depression, including psychological stress and conflict, as well as biological derangement, among which stress has a pivotal role in the development of depression. Traditional herbal medicine has been used for the treatment of various disorders including depression for a long history with multi-targets, multi-levels and multi-ways, attracting great attention from scholars. Recently, natural products have been commercialized as antidepressants which have become increasingly popular in the world health drug markets. Major research contributions in ethnopharmacology have generated and updated vast amount of data associated with natural products in antidepressant-like activity.

AIMS OF THE REVIEW

This review aims to briefly discuss the pathological mechanism, animal models of stress-induced depression, traditional use of herbal medicines and especially recapitulate the natural products with antidepressant activity and their pharmacological functions and mechanism of action, which may contribute to a better understanding of potential therapeutic effects of natural products and the development of promising drugs with high efficacy and low toxicity for the treatment of stress-induced depression.

MATERIALS AND METHODS

The contents of this review were sourced from electronic databases including PubMed, Sci Finder, Web of Science, Science Direct, Elsevier, Google Scholar, Chinese Knowledge On frastructure (CNKI), Wan Fang, Chinese Scientific and Technological Periodical Database (VIP) and Chinese Biomedical Database (CBM). Additional information was collected from Yao Zhi website (https://db.yaozh.com/). Data were obtained from April 1992 to June 2021. Only English language was applied to the search. The search terms were 'stress-induced depression', 'pathological mechanism' in the title and 'stress', 'depression', 'animal model' and 'natural products' in the whole text.

RESULTS

Stress-induced depression is related to the monoaminergic system, hypothalamic-pituitary-adrenal (HPA) axis, neuronal plasticity and a series of inflammatory factors. Four main types of animal models of stress-induced depression were represented. Fifty-eight bioactive phytochemical compounds, fifty-six herb medicines and five formulas from traditional Chinese medicine were highlighted, which exert antidepressant effects by inhibiting monoamine oxidase (MAO) reaction, alleviating dysfunction of the HPA axis and nerve injury, and possessing anti-inflammatory activities.

CONCLUSIONS

Natural products provide a large number of compounds with antidepressant-like effects, and their therapeutic impacts has been highlighted for a long time. This review summarized the pathological mechanism and animal models of stress-induced depression, and the natural products with antidepressant activity in particular, which will shed light on the action mechanism and clinical potential of these compounds. Natural products also have been a vital and promising source for future antidepressant drug discovery.

DARK Classics in Chemical Neuroscience: Atropine, Scopolamine, and Other Anticholinergic Deliriant Hallucinogens

Anticholinergic drugs based on tropane alkaloids, including atropine, scopolamine, and hyoscyamine, have been used for various medicinal and toxic purposes for millennia. These drugs are competitive antagonists of acetylcholine muscarinic (M-) receptors that potently modulate the central nervous system (CNS). Currently used clinically to treat vomiting, nausea, and bradycardia, as well as alongside other anesthetics to avoid vagal inhibition, these drugs also evoke potent psychotropic effects, including characteristic delirium-like states with hallucinations, altered mood, and cognitive deficits. Given the growing clinical importance of anti-M deliriant hallucinogens, here we discuss their use and abuse, clinical importance, and the growing value in preclinical (experimental) animal models relevant to modeling CNS functions and dysfunctions.

Interaction between noradrenergic and cholinergic signaling in amygdala regulates anxiety- and depression-related behaviors in mice

Medications that target the noradrenergic system are important therapeutics for depression and anxiety disorders. More recently, clinical studies have shown that the α2-noradrenergic receptor (α2AR) agonist guanfacine can decrease stress-induced smoking relapse during acute abstinence, suggesting that targeting the noradrenergic system may aid in smoking cessation through effects on stress pathways in the brain. Acetylcholine (ACh), like the nicotine in tobacco, acts at nicotinic acetylcholine receptors (nAChRs) to regulate behaviors related to anxiety and depression. We therefore investigated interactions between guanfacine and ACh signaling in tests of anxiolytic and antidepressant efficacy in female and male C57BL/6J mice, focusing on the amygdala as a potential site of noradrenergic/cholinergic interaction. The antidepressant-like effects of guanfacine were blocked by shRNA-mediated knockdown of α2AR in amygdala. Knockdown of the high-affinity β2 nAChR subunit in amygdala also prevented antidepressant-like effects of guanfacine, suggesting that these behavioral effects require ACh signaling through β2-containing nAChRs in this brain area. Ablation of NE terminals prevented the anxiolytic- and antidepressant-like effects of the nicotinic partial agonist cytisine, whereas administration of the cholinesterase antagonist physostigmine induced a depression-like phenotype that was not altered by knocking down α2AR in the amygdala. These studies suggest that ACh and NE have opposing actions on behaviors related to anxiety and depression and that cholinergic signaling through β2-containing nAChRs and noradrenergic signaling through α2a receptors in neurons of the amygdala are critical for regulation of these behaviors.

Antidepressant-like effects of guanfacine and sex-specific differences in effects on c-fos immunoreactivity and paired-pulse ratio in male and female mice

RATIONALE

The a2A-noradrenergic agonist guanfacine can decreases stress-induced smoking in female, but not male, human smokers. It is not known whether these effects are due to effects on mood regulation and/or result from nicotinic-cholinergic interactions.

OBJECTIVES

The objective of the study was to determine whether there are sex differences in the effect of guanfacine in tests of anxiolytic and antidepressant efficacy in mice at baseline and in a hypercholinergic model of depression induced by the acetylcholinesterase inhibitor physostigmine.

METHODS

The effects of guanfacine were measured in the light/dark box, tail suspension, and the forced swim test in female and male C57BL/6J mice. In parallel, electrophysiological properties were evaluated in the prefrontal cortex, a critical brain region involved in stress responses. c-fos immunoreactivity was measured in other brain regions known to regulate mood.

RESULTS

Despite a baseline sex difference in behavior in the forced swim test (female mice were more immobile), guanfacine had similar, dose-dependent, antidepressant-like effects in mice of both sexes (optimal dose, 0.15 mg/kg). An antidepressant-like effect of guanfacine was also observed following pre-treatment with physostigmine. A sex difference in the paired-pulse ratio in the prefrontal cortex (PFC) (male, 1.4; female, 2.1) was observed at baseline that was normalized by guanfacine. Other brain areas involved in cholinergic control of depression-like behaviors, including the basolateral amygdala and lateral septum, showed sex-specific changes in c-fos expression.

CONCLUSIONS

Guanfacine has a robust antidepressant-like effect and can reverse a depression-like state induced by increased acetylcholine (ACh) signaling. These data suggest that different brain areas are recruited in female and male mice, despite similar behavioral responses to guanfacine.

Targeting the noradrenergic system for gender-sensitive medication development for tobacco dependence

INTRODUCTION

Tobacco use remains the leading cause of morbidity and mortality for both women and men in the United States, and women often experience poorer smoking cessation outcomes than men. Preliminary evidence suggests there are sex differences in medication effectiveness for smoking cessation. However, current medications do not take into account gender-sensitive treatment development and efficacy, underscoring the importance of this underdeveloped area of research.

METHODS

We reviewed preclinical and clinical evidence for gender differences in the inability to quit smoking by examining (a) the effect of increased negative affect and stress reactivity on smoking outcomes in women and (b) smoking for nicotine reinforcement in men. We also reviewed the current literature targeting the noradrenergic system as a novel gender-sensitive treatment strategy for tobacco dependence.

RESULTS

We hypothesize that noradrenergic agents that normalize noradrenergic activity may differentially attenuate stress reactivity in women and nicotine-related reinforcement in men, indicating that targeting the noradrenergic system for smoking cessation may be effective for both genders, with benefits operating through sex-specific mechanisms.

CONCLUSIONS

Converging lines of preclinical and clinical evidence suggest that gender-sensitive approaches to medication development for smoking cessation are a critical next step for addressing low quit rates and exacerbated health risks among women. Evidence reviewed indicates that smoking activates different brain systems modulated by noradrenergic activity in women versus men, and noradrenergic compounds may preferentially target these gender-sensitive systems.

Sex differences in animal models of psychiatric disorders

Psychiatric disorders are characterized by sex differences in their prevalence, symptomatology and treatment response. Animal models have been widely employed for the investigation of the neurobiology of such disorders and the discovery of new treatments. However, mostly male animals have been used in preclinical pharmacological studies. In this review, we highlight the need for the inclusion of both male and female animals in experimental studies aiming at gender-oriented prevention, diagnosis and treatment of psychiatric disorders. We present behavioural findings on sex differences from animal models of depression, anxiety, post-traumatic stress disorder, substance-related disorders, obsessive-compulsive disorder, schizophrenia, bipolar disorder and autism. Moreover, when available, we include studies conducted across different stages of the oestrous cycle. By inspection of the relevant literature, it is obvious that robust sex differences exist in models of all psychiatric disorders. However, many times results are conflicting, and no clear conclusion regarding the direction of sex differences and the effect of the oestrous cycle is drawn. Moreover, there is a lack of considerable amount of studies using psychiatric drugs in both male and female animals, in order to evaluate the differential response between the two sexes. Notably, while in most cases animal models successfully mimic drug response in both sexes, test parameters and treatment-sensitive behavioural indices are not always the same for male and female rodents. Thus, there is an increasing need to validate animal models for both sexes and use standard procedures across different laboratories.

Antidepressant treatment history as a predictor of response to scopolamine: clinical implications

BACKGROUND

The intravenous administration of scopolamine produces rapid antidepressant effects. Generally, failing multiple previous antidepressant trials is associated with a poor prognosis for response to future medications. This study evaluated whether treatment history predicts antidepressant response to scopolamine.

METHODS

Treatment resistant patients (2 failed medication trials) (n=31) and treatment naïve patients (no exposure to psychotropic medication) (n=31) with recurrent major depressive or bipolar disorder participated in a double-blind, placebo-controlled, crossover clinical trial. Following a placebo lead-in, participants randomly received P/S or S/P (P=3 placebo; S=3 scopolamine (4ug/kg) sessions 3 to 5 days apart). The Montgomery-Asberg Depression Rating Scale (MADRS) was the primary outcome measure. A linear mixed model was used to examine the interaction between clinical response and treatment history, adjusting for baseline MADRS.

RESULTS

Treatment resistant and treatment naïve subjects combined responded significantly to scopolamine compared to placebo (F=15.06, p<0.001). Reduction in depressive symptoms was significant by the first post-scopolamine session (F=42.75, p<0.001). A treatment history by scopolamine session interaction (F=3.37, p=0.04) indicated treatment naïve subjects had lower MADRS scores than treatment resistant patients; this was significant after the second scopolamine infusion (t=2.15, p=0.03).

LIMITATIONS

Post-hoc analysis: Also, we used a single regimen to administer scopolamine, and smokers were excluded from the sample, limiting generalizability.

CONCLUSIONS

Treatment naïve and treatment resistant patients showed improved clinical symptoms following scopolamine, while those who were treatment naïve showed greater improvement. Scopolamine rapidly reduces symptoms in both treatment history groups, and demonstrates sustained improvement even in treatment resistant patients.

Pupillometry in Chinese female patients with depression: a pilot study

The pupillary responses to light in patients with depression and normal controls were evaluated among Chinese females. Four parameters related to the pupil were assessed using a video-based pupillometer. The results showed that there were significant differences in the pupil area in the darkness and the pupil area at the peak of constriction between depressed patients and normal controls.

IgM-mediated autoimmune responses directed against anchorage epitopes are greater in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) than in major depression

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and depression are considered to be neuro-immune disorders (Maes and Twisk, BMC Medicine 8:35, 2010). There is also evidence that depression and ME/CFS are accompanied by oxidative and nitrosative stress (O&NS) and by increased autoantibodies to a number of self-epitopes some of which have become immunogenic due to damage by O&NS. The aim of this study is to examine IgM-mediated autoimmune responses to different self-epitopes in ME/CFS versus depression. We examined serum IgM antibodies to three anchorage molecules (palmitic and myristic acid and S-farnesyl-L-cysteine); acetylcholine; and conjugated NO-modified adducts in 26 patients with major depression; 16 patients with ME/CFS, 15 with chronic fatigue; and 17 normal controls. Severity of fatigue and physio-somatic (F&S) symptoms was measured with the Fibromyalgia and Chronic Fatigue Syndrome Rating Scale. Serum IgM antibodies to the three anchorage molecules and NO-phenylalanine were significantly higher in ME/CFS than in depression. The autoimmune responses to oxidatively, but not nitrosatively, modified self-epitopes were significantly higher in ME/CFS than in depression and were associated with F&S symptoms. The autoimmune activity directed against conjugated acetylcholine did not differ significantly between ME/CFS and depression, but was greater in the patients than controls. Partially overlapping pathways, i.e. increased IgM antibodies to a multitude of neo-epitopes, underpin both ME/CFS and depression, while greater autoimmune responses directed against anchorage molecules and oxidatively modified neo-epitopes discriminate patients with ME/CFS from those with depression. These autoimmune responses directed against neoantigenic determinants may play a role in the dysregulation of key cellular functions in both disorders, e.g. intracellular signal transduction, cellular differentiation and apoptosis, but their impact may be more important in ME/CFS than in depression.

Persistent β2*-nicotinic acetylcholinergic receptor dysfunction in major depressive disorder

BACKGROUND

Modulation of nicotinic acetylcholine receptors (nAChRs), specifically those containing the β2 subunit, may be effective in treating patients with major depressive disorder. Using [123I]5-I-A-85380 single photon emission computed tomography (SPECT), the authors studied the availability of β2-subunit-containing nAChRs (β2*-nAChRs) in depressed patients. To understand its molecular basis, the authors also studied β2*-nAChR binding in postmortem brain samples from depressed subjects.

METHOD

The participants were 23 medication-free, nonsmoking subjects with familial, early-onset depression (eight acutely ill and 15 recovered) and 23 age- and gender-matched nonsmoking comparison subjects. Each received one [123I]5-I-A-85380 SPECT scan and an MRI scan. The availability of β2*-nAChRs was quantified as VT/fP. Postmortem analysis of β2*-nAChR binding was conducted with [123I]5-I-A-85380 on prefrontal cortex samples from 14 depressed subjects and 14 age-matched comparison subjects.

RESULTS

The β2*-nAChR availability in both the acutely ill and recovered depressed subjects was significantly lower across all brain regions than in the respective comparison subjects, and it was lower in the acutely ill subjects than in those who were recovered. In the depressed patients, β2*-nAChR availability was significantly correlated with lifetime number of depressive episodes, trauma score, and anxiety score. There were no differences in β2*-nAChR number between groups in the postmortem study.

CONCLUSIONS

Depressed patients have lower β2*-nAChR availability than do healthy subjects. The difference between β2*-nAChR availability in vivo and in post-mortem samples may be analogous to data with dopaminergic PET ligands and dopamine receptor availability; lower receptor availability for the SPECT ligand could be caused by greater endogenous acetylcholine.

IgM-mediated autoimmune responses directed against multiple neoepitopes in depression: new pathways that underpin the inflammatory and neuroprogressive pathophysiology

BACKGROUND

There is evidence that depression is accompanied by oxidative and nitrosative stress (O&NS), as indicated by increased free radical levels, lipid peroxidation, and lowered antioxidant levels. The aims of the present study are to examine whether depression is accompanied by autoimmune responses directed against a) neoepitopes that are formed following O&NS damage; and b) the major anchorage molecules, i.e. palmitic and myristic acids and S-farnesyl-L-cysteine.

METHODS

We examined serum IgM antibodies to the conjugated fatty acids, palmitic and myristic acids; acetylcholine; S-farnesyl-L-cysteine; and NO-modified adducts in 26 depressed patients and 17 normal controls. Severity of depression was measured with the Hamilton Depression Rating Scale and severity of fatigue and somatic (F&S) symptoms with the Fibromyalgia and Chronic Fatigue Syndrome (FF) Rating Scale.

RESULTS

The prevalences and mean values for the serum IgM levels directed against conjugated palmitic and myristic acids, acetylcholine, S-farnesyl-L-cysteine; and the conjugated NO adducts, NO-tyrosine, NO-phenylalanine, NO-aspartate, NO-histidine, and NO-creatine were significantly higher in depressed patients than in normal controls. The autoimmune responses were significantly related to FF symptoms, such as fatigue and a flu-like malaise, whereas the indicants of nitrosative stress were related to gastro-intestinal and autonomic symptoms.

DISCUSSION

Depression is characterized by IgM-related autoimmune responses directed against a) neoepitopes that are normally not detected by the immune system but that due to damage by O&NS have become immunogenic; and b) anchorage epitopes, i.e. palmitic and myristic acids, and S-farnesyl-L-cysteine. These autoimmune responses play a role in the inflammatory and O&NS pathophysiology of depression and may mediate the cellular dysfunctions that contribute to neuroprogression, e.g. aberrations in signal transduction, cellular differentiation and apoptosis.

Scopolamine produces larger antidepressant and antianxiety effects in women than in men

Some antidepressant agents generate differential benefit based on gender. Blocking cholinergic muscarinic receptors using scopolamine produces robust and rapid antidepressant effects in males and females combined. This study evaluated if males and females differ in the antidepressant response magnitude following scopolamine administration. A total of 52 male and female outpatients meeting criteria for recurrent major depressive or bipolar disorder participated in a double-blind, randomized, placebo-controlled, crossover clinical trial involving seven i.v. infusions of placebo or scopolamine (4 μg/kg). Following a single-blind placebo lead-in, participants entered either a placebo-block/scopolamine-block or a scopolamine-block/placebo-block sequence. Each block included three sessions. Clinical ratings were acquired before each infusion and included the Montgomery-Asberg Depression Rating Scale (MADRS) and the Hamilton Anxiety Rating Scale (HAM-A). A treatment group × block interaction (F=21.0, p<0.001) was observed in MADRS scores across gender, and the reduction was significant by the evaluation following the first scopolamine administration (F=8.4, p=0.006). The treatment group × block interaction was also significant in males (F=3.8, p=0.043) and females (F=35.6, p<0.001) separately. A block × gender interaction (F=7.4, p=0.009) indicated that the response magnitude was larger in women. The treatment × block interaction was significant for the HAM-A across gender (F=12.0, p<0.001), and was significant for females (F=24.9, p<0.001) but not for males (F=1.3, p=0.30). When comparing the baseline block to study end, the block × gender interaction (F=12.6, p=0.001) showed that the antianxiety response was greater in women. Men and women show a rapid antidepressant response following scopolamine, but the magnitude of response is larger in women than in men.

A genetic survey of fluoxetine action on synaptic transmission in Caenorhabditis elegans

Fluoxetine is one of the most commonly prescribed medications for many behavioral and neurological disorders. Fluoxetine acts primarily as an inhibitor of the serotonin reuptake transporter (SERT) to block the removal of serotonin from the synaptic cleft, thereby enhancing serotonin signals. While the effects of fluoxetine on behavior are firmly established, debate is ongoing whether inhibition of serotonin reuptake is a sufficient explanation for its therapeutic action. Here, we provide evidence of two additional aspects of fluoxetine action through genetic analyses in Caenorhabditis elegans. We show that fluoxetine treatment and null mutation in the sole SERT gene mod-5 eliminate serotonin in specific neurons. These neurons do not synthesize serotonin but import extracellular serotonin via MOD-5/SERT. Furthermore, we show that fluoxetine acts independently of MOD-5/SERT to regulate discrete properties of acetylcholine (Ach), gamma-aminobutyric acid (GABA), and glutamate neurotransmission in the locomotory circuit. We identified that two G-protein-coupled 5-HT receptors, SER-7 and SER-5, antagonistically regulate the effects of fluoxetine and that fluoxetine binds to SER-7. Epistatic analyses suggest that SER-7 and SER-5 act upstream of AMPA receptor GLR-1 signaling. Our work provides genetic evidence that fluoxetine may influence neuronal functions and behavior by directly targeting serotonin receptors.

Effects of galanin on monoaminergic systems and HPA axis: Potential mechanisms underlying the effects of galanin on addiction- and stress-related behaviors

Like a number of neuropeptides, galanin can alter neural activity in brain areas that are important for both stress-related behaviors and responses to drugs of abuse. Accordingly, drugs that target galanin receptors can alter behavioral responses to drugs of abuse and can modulate stress-related behaviors. Stress and drug-related behaviors are interrelated: stress can promote drug-seeking, and drug exposure and withdrawal can increase activity in brain circuits involved in the stress response. We review here what is known about the ability of galanin and galanin receptors to alter neuronal activity, and we discuss potential mechanisms that may underlie the effects of galanin on behaviors involved in responses to stress and addictive drugs. Understanding the mechanisms underlying galanin's effects on neuronal function in brain regions related to stress and addiction may be useful in developing novel therapeutics for the treatment of stress- and addiction-related disorders.

No evidence for association between 19 cholinergic genes and bipolar disorder

Cholinergic dysfunction has been proposed for the pathogenesis of bipolar disorder (BD), and we have therefore performed a systematic association study of cholinergic system genes in BD (including schizoaffective disorder bipolar type). We genotyped 93 single nucleotide polymorphisms (SNPs) in 19 genes (CHAT, CHRM1-5, CHRNA1-7, CHRNA9, CHRNA10, and CHRNB1-4) in two series of samples: the National Institute of Mental Health (NIMH) Genetics Initiative pedigrees with 474 samples from 152 families, and the Clinical Neurogenetics (CNG) pedigrees with 83 samples from 22 multiplex families. Sib-transmission/disequilibrium test (sib_TDT) analysis showed nominally significant transmission bias for four SNPs (CHRNA2: rs7017417, P = 0.024; CHRNA5: rs514743, P = 0.031; CHRNB1: rs2302762, P = 0.049; CHRNB4: rs1948, P = 0.031). Haploview analyses showed nominally significant transmission bias of several haplotypes in CHRNA2, CHRNA7, CHRNB1, and CHRNB4, respectively. However, none of these associations reached gene-wide significance after correction by permutation. Alcohol dependence (including alcohol abuse) was not a significant covariate in the present genetic association analysis. Thus, it is unlikely that these 19 cholinergic genes play a major role in the pre-disposition to BD in these pedigrees.

Future antidepressants: what is in the pipeline and what is missing?

Monoamine reuptake inhibitors still reign in the treatment of major depression, but possibly not for long. While medicinal chemists have been able to reduce the side effects of these drugs, their delayed onset of action and considerable non-response rate remain problematic. Of late, serious questions have been raised regarding the efficacy of monoamine reuptake inhibitors. The present review presents an inventory of what is (and until recently was) in the antidepressant pipeline of pharmaceutical companies. Novel antidepressant compounds can be categorised into four groups depending on their target(s): (i) monoamine receptors; (ii) non-monoamine receptors; (iii) neuropeptide receptors; and (iv) hormone receptors. Other possible targets include components of post-receptor intracellular processes and elements of the immune system; to date, however, compounds specifically aimed at these targets have not been the subject of clinical trials. Development of several compounds targeted at monoamine receptors has recently been discontinued. At least five neurokinin-1 (NK(1)) receptor antagonists were until recently in phase II of clinical testing. However, the apparent interest in the NK(1) receptor should not be interpreted as representing a departure from the monoamine hypothesis since neurokinins also modulate monoaminergic systems. In the authors' view, development of future antidepressants will continue to rely on the serendipity-based monoamine hypothesis. However, an alternative approach, based on the hypothesis that chronic stress precipitates depressive symptoms, might be more productive. Unfortunately, clinical results using drugs targeted at components of the HPA axis have not been very encouraging to date. In the short run, the authors believe that augmentation strategies offer the best hope for improving the efficacy of antidepressant treatment. Several approaches to improve the efficacy of SSRIs are conceivable, such as concurrent blockade of monoamine autoreceptors and the addition of antipsychotics, neuromodulators or hormones (HPA axis and gender related). In the long-term, however, construction of a scientifically verified conceptual framework will be needed before more effective antidepressants can be developed. It can be argued that it is not depression itself that should be treated, but rather that its duration should be reduced by pharmacological means. Animal models that take this concept into consideration and identify mechanisms for acceleration of recovery from the effects of stress need to be developed.

Effect of nicotine and nicotinic receptors on anxiety and depression

Nicotine has been shown to have effects on anxiety and depression in both human and animal studies. These studies suggest that nicotinic acetylcholine receptors (nAChRs) can modulate the function of pathways involved in stress response, anxiety and depression in the normal brain, and that smoking can result in alterations of anxiety level and mood. The effects of nicotine are complex however, and nicotine treatment can be either anxiolytic or anxiogenic depending on the anxiety model tested, the route of nicotine administration and the time course of administration. The paradoxical effects of nicotine on emotionality are likely due to the broad expression of nAChRs throughout the brain, the large number of nAChR subtypes that have been identified and the ability of nicotine treatment to both activate and desensitize nAChRs. Activation of nAChRs has been shown to modulate many systems associated with stress response including stress hormone pathways, monoaminergic transmission and release of classical neurotransmitters throughout the brain. Local administration studies in animals have identified brain areas that may be involved in the anxiogenic and anxiolytic actions of nicotine including the lateral septum, the dorsal raphe nuclei, the mesolimbic dopamine system and the hippocampus. The ensemble of studies to date suggest that under certain conditions nicotine can act as an anxiolytic and an antidepressant, but that following chronic use, adaptations to nicotine can occur resulting in increased anxiety and depression following withdrawal.

Seaweed accelerates the excretion of dioxin stored in rats

To prevent health problems of humans exposed to dioxin, it is important to enhance the fecal excretion of dioxin stored in the body. The effects of seaweed such as wakame, hiziki, and kombu on the gastrointestinal absorption and reabsorption of 17 types of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) congeners was investigated in Wistar rats. Rats were fed 4 g of the basal diet or a seaweed diet containing PCDD and PCDF standard solution [233 ng of toxic equivalents (TEQ)/kg of body weight] once during the experiment period. In the group fed the 10% wakame diet, the levels of fecal excretion of PCDD and PCDF congeners were higher (p < 0.01) from days 1 to 5 by 2.8-fold for 2,3,7,8-TCDD, by 4.0-fold for 1,2,3,7,8-pentaCDD, by 3.4-fold for 1,2,3,4,7,8-hexaCDD, by 3.2-fold for 1,2,3,6,7,8-hexaCDD, by 2.5-fold for 1,2,3,7,8,9-hexaCDD, by 1.7-fold for 1,2,3,4,6,7,8-heptaCDD, by 1.1-fold for 1,2,3,4,6,7,8,9-octaCDD, by 3.0-fold for 2,3,7,8-tetraCDF, by 3.7-fold for 1,2,3,7,8-pentaCDF, by 3.7-fold for 2,3,4,7,8-pentaCDF, by 3.2-fold for 1,2,3,4,7,8-hexaCDF, by 3.0-fold for 1,2,3,6,7,8-hexaCDF, by 3.2-fold for 1,2,3,7,8,9-hexaCDF, by 2.9-fold for 2,3,4,6,7,8-hexaCDF, by 1.6-fold for 1,2,3,4,6,7,8-heptaCDF, by 2.2-fold for 1,2,3,4,7,8,9-heptaCDF, and by 1.2-fold for 1,2,3,4,6,7,8,9-octaCDF than those of the basal group, respectively. Rats were fed 4 g of the basal diet containing PCDD and PCDF standard solution (2991 ng of TEQ/kg of body weight) once on day 1 and then place on the basal diet for 7 days. After 1 week, the rats were fed either the basal diet or seaweed diet from days 8 to 35. In the group fed the 10% wakame diet, the levels of fecal excretion of PCDD and PCDF congeners were higher (p < 0.01 or p < 0.05) during the period from days 8 to 35 by 1.7-fold for 2,3,7,8-TCDD, by 1.8-fold for 1,2,3,7,8-pentaCDD, by 2.0-fold for 1,2,3,4,7,8-hexaCDD, by 1.9-fold for 1,2,3,6,7,8-hexaCDD, by 1.6-fold for 1,2,3,7,8,9-hexaCDD, by 1.5-fold for 1,2,3,4,6,7,8-heptaCDD, by 2.0-fold for 2,3,4,7,8-pentaCDF, by 2.1-fold for 1,2,3,4,7,8-hexaCDF, by 1.9-fold for 1,2,3,6,7,8-hexaCDF, by 1.7-fold for 2,3,4,6,7,8-hexaCDF, by 1.5-fold for 1,2,3,4,6,7,8-heptaCDF, and by 1.9-fold for 1,2,3,4,7,8,9-heptaCDF than those of the basal group, respectively. These findings suggest that the administration of seaweed such as wakame is efficient in preventing the absorption and reabsorption of dioxin from the gastrointestinal tract and might be useful in treatment of humans exposed to dioxin.

Cholinergic sensitivity predicts severity of mania

Our laboratory and others have reported that pupillary constrictions following application of the cholinergic agonist pilocarpine are increased in depressed patients. Moreover, mood improvements in manic patients, given lithium or Depakote, are also correlated with increases in pupil sensitivity. The present report describes the relationship between symptom severity and cholinergic sensitivity in a larger group (N=20) of manic patients (bipolar I; 296.4x). Pupil responses to pilocarpine eye drops (0-2%) were recorded using infrared pupillometry. The results were compared with pupil sizes measured under conditions of cholinergic blockade (0.5% tropicamide). Pupil responses were computed as percentages of the maximal range of areas measured under saturating agonist and antagonist conditions. Dose response curves were subjected to a log-logit transformation and ED(50) values were determined by weighted least squares regression. Bech-Rafaelsen mania ratings were found to be linearly related to ED(50) values (r=0.48). Patients with more severe mania required higher concentrations of pilocarpine in order to elicit a 50% reduction in pupil size. The present findings support a putative cholinergic role in the regulation of mood state. Moreover, the results suggest that pupillary responses may provide a simple and non-invasive means to evaluate cholinergic sensitivity in patients with affective disorders.

Activation of the Ah receptor by tryptophan and tryptophan metabolites

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates many of the biological and toxicological actions of a variety of hydrophobic natural and synthetic chemicals, including the environmental contaminant 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin). A variety of indole-containing chemicals, such as indole-3-carbinol, indolo[3, 2-b]carbazole, and UV photoproducts of tryptophan (TRP), have previously been identified as ligands for AhR. Here we have examined the ability of endogenous metabolites of tryptophan (TRP) to bind to and activate AhR in vitro and in cells in culture. Although hydroxylated TRP metabolites were inactive, two metabolites, namely tryptamine (TA) and indole acetic acid (IAA), were shown to be AhR agonists. Not only do TA and IAA bind competitively to AhR, but they also can stimulate AhR transformation and DNA binding and induce expression of an AhR-dependent reporter gene in cells. In addition to being an AhR ligand, TA is also a competitive substrate for cytochrome P4501A1, a well-characterized AhR- and TCDD-inducible gene product. Although these compounds are relatively weak ligands, compared to TCDD, they represent some of the first endogenous hydrophilic AhR agonists identified to date.

Increased pupillary sensitivity to pilocarpine in depression

1. The present study was undertaken to examine the hypothesis that muscarinic receptor sensitivity is increased in depression. 2. Pupillary responses to increasing concentrations of pilocarpine (O.08%-O.23%) given in a 2 ml solution were compared between ten male patients with major depression and a matched group of normal controls. 3. Individual differences in pupil size due to anatomic variability or adrenergic tone were evaluated under conditions of maximum pupil dilation following cholinergic blockade (tropicamide, 0.5 percent). 4. In contrast to controls, depressed patients exhibited significantly greater reductions in pupillary diameter following pilocarpine in doses between 0.095%-0.185%. This was true regardless of whether or not the results were adjusted for differences in dilated pupil size. 5. These results are consistent with the idea that muscarinic sensitivity is increased in depression and indicate that depressed patients may be discriminated from controls on the basis of pupillary sensitivity to pilocarpine.

Pharmacological validation of the chronic mild stress model of depression

Chronic exposure to mild unpredictable stress has previously been found to depress the consumption of palatable sweet solutions, and this effect was reversed by chronic treatment with a variety of antidepressant drugs. The present study reports three experiments examining the effects in this model of further antidepressant agents, a number of non-antidepressants, and some compounds of indeterminate clinical status. Male Wistar rats were exposed sequentially to a variety of mild stressors, which continued throught the experiments. Drug treatments commenced after 3 weeks of stress, by which time intake of a 1% sucrose solution (measured in a 1-h weekly test) was significantly depressed. No drug effects were seen after 1 week of treatment. Normal levels of sucrose drinking were seen following chronic (3-5 weeks) of treatment with the antidepressants imipramine (10 mg/kg per day), brofaromine (20 mg/kg per day), and buspirone (5 mg/kg per day). Positive effects were also seen following chronic treatment with atropine (1 mg/kg per day) and mepyramine (5 mg/kg per day). d-Amphetamine (1 and 3 mg/kg per day), the neuroleptics haloperidol and chlorprothixene (1 mg/kg per day), and morphine (administered at doses rising to 110 mg/kg per day) were ineffective; amphetamine (3 mg/kg) and morphine decreased sucrose intake in control animals. No inferences can be drawn from the effects of atropine and mepyramine, which are of indeterminate clinical status; data from the other seven agents tested support the hypothesis that the chronic mild stress model responds appropriately to antidepressant and non-antidepressant agents.