Behavioral deficits and exaggerated feedback control over raphe-hippocampal serotonin neurotransmission in restrained rats

Deciphering the role of siRNA in anxiety and depression

Anxiety and depression are central nervous system illnesses that are among the most prevalent medical concerns of the twenty-first century. Patients with this condition and their families bear psychological, financial, and societal hardship. There are currently restrictions when utilizing the conventional course of treatment. RNA interference is expected to become an essential approach in anxiety and depression due to its potent and targeted gene silencing. Silencing of genes by post-transcriptional modification is the mechanism of action of small interfering RNA (siRNA). The suppression of genes linked to disease is typically accomplished by siRNA molecules in an efficient and targeted manner. Unfavourable immune responses, off-target effects, naked siRNA instability, nuclease vulnerability, and the requirement to create an appropriate delivery method are some of the challenges facing the clinical application of siRNA. This review focuses on the use of siRNA in the treatment of anxiety and depression.

Omeprazole affects the expression of serotonin-1A in the brain regions and alleviates anxiety in rat model of immobilization-induced stress

Omeprazole, a drug of choice for the management of gastric hyperacidity, influences serotonergic neurotransmission in brain regions and its long-term use is known to cause stress-related behavioral deficits including anxiety. Aim of the current study was to explore the effects of omeprazole treatment on immobilization-induced anxiety in rats, specifically on the role of serotonin (5-HT). In view of the role of serotonin-1A (5-HT1A) autoreceptor in the availability of 5-HT in brain regions, mRNA expression of this autoreceptor was performed in raphe nuclei. Similarly, because of the role of hippocampal 5-HT neurotransmission in anxiety-like disorders, expression of the 5-HT1A heteroreceptors was determined in this region. We found that the treatment with omeprazole reduces anxiety-like behavior in rats, increases the expression of 5-HT1A autoreceptor in the raphe and decreases the hippocampal expression of 5-HT1A heteroreceptor. This suggests a role of 5-HT1A receptor types in omeprazole-induced behavioral changes. It also indicates a potential role of omeprazole in the management of serotonergic disorders.

Behavioral, Hormonal, and Serotonergic Responses to Different Restricted Feeding Schedules in Rats

To determine the effect of long-term restricted feeding schedules on behavior, serotonergic responses, and neuro-endocrine functions, metabolism of serotonin (5-HT) in the striatum, expression of serotonin-1A (5-HT1A) auto-receptor in the raphe nuclei and circulating levels of leptin and corticosterone were determined in female Wistar rats kept on excessive food restriction schedule. Due to a role of dietary deficiency of tryptophan (Trp) in influencing serotonergic neurotransmission, circulating levels of Trp were also determined. Estimations were done in 2 different restricted feeding models: time-restricted feeding (TRF) and diet restricted (DR). TRF animals were given access to food ad libitum only for 2 hours/day. The DR animals were given a small calculated amount of food each day. We found that chronic food restriction for 5 weeks cause a significant decrease in the body weight and produced hyperactivity in both, TRF and DR animals. Levels of Trp were declined in circulation and in the striatum. Similarly, the levels of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were decreased in the striatum. Also, the expression of 5-HT1A auto-receptor was declined in the raphe nuclei. These changes in 5-HT metabolism and 5-HT1A auto-receptor expression were more profound in DR animals as compare to TRF animals. Similarly, hypoleptinemia and increased corticosterone found in both models was higher in DR animals. Effect of dietary deficiency of Trp in the modulation of striatal 5-HT metabolism and its consequences on circulating leptin and corticosterone are discussed.

Elevated anxiety, hypoactivity, memory deficits, decreases of brain serotonin and 5-HT-1A receptors expression in rats treated with omeprazole

Omeprazole (OM) is one of the most prescribed drugs worldwide for the treatment of hyperacidity and gastric reflux. However, concerns regarding its safety have emerged recently, and the drug is reported to enhance the risk for anxiety and cognitive deficits, particularly in elderly patients. The present study investigated these adverse effects, if any, in adult male rats. Associated changes in brain serotonin (5-hydroxytryptamine; 5-HT) and dopamine metabolism and the expression of 5-HT-1A receptors in the raphe and hippocampus were also determined. The drug was injected i.p. in doses of 10 and 20 mg/kg for 15 days. Both doses of OM decreased motor activity in an open field and impaired learning and memory in the Morris water maze test. Anxiety monitored in an elevated plus maze test was enhanced in rats treated with 20 mg/kg OM only. The levels of 5-HT and its metabolite 5-hydroxyindoleacetic acid and of homovanillic acid, a metabolite of dopamine, determined by HPLC-EC, were decreased in the brain of OM treated rats. The expression of 5-HT-1A receptor, determined by qRT-PCR, was reduced markedly in the hippocampus and moderately in the raphe. Our results provide evidence that OM use can reduce raphe hippocampal serotonin neurotransmission to lead to anxiety/depression and cognitive impairment. There is a need for increased awareness and prescription guidelines for therapeutic use of OM and possibly also other proton pump inhibitors.

Environmental pollution and mental health: a narrative review of literature

Pollutant agents are exponentially increasing in modern society since industrialization processes and technology are being developed worldwide. Impact of pollution on public health is well known but little has been described on the association between environmental pollutants and mental health. A literature search on PubMed and EMBASE has been conducted and 134 articles published on the issue of pollution and mental health have been included, cited, reviewed, and summarized. Emerging evidences have been collected on association between major environmental pollutants (air pollutants, heavy metals, ionizing radiation [IR], organophosphate pesticides, light pollution, noise pollution, environmental catastrophes) and various mental health disorders including anxiety, mood, and psychotic syndromes. Underlying pathogenesis includes direct and indirect effects of these agents on brain, respectively, due to their biological effect on human Central Nervous System or related to some levels of stress generated by the exposure to the pollutant agents over the time. Most of emerging evidences are still nonconclusive. Further studies should clarify how industrial production, the exploitation of certain resources, the proximity to waste and energy residues, noise, and the change in lifestyles are connected with psychological distress and mental health problems for the affected populations.

Behavioral and Biochemical Effects of Mukia madrespatana Following Single Immobilization Stress on Rats

BACKGROUND AND OBJECTIVES

Elevated oxidative stress has been shown to play an important role in the diagnosis and prognosis of stress and memory-related complications. Mukia madrespatana (M. madrespatana) has been reported to have various biological and antioxidant properties. We intended to evaluate the effect of M. madrespatana peel on single immobilization stress-induced behavioral deficits and memory changes in rats. Materials and Methods: M. madrespatana peel (2000 mg/kg/day, orally) was administered to control and immobilize stressed animals for 4 weeks. Anxiolytic, antidepressant, and memory-enhancing effects of M. madrespatana were observed in both unstressed and stressed animals. Results: Lipid peroxidation was decreased while antioxidant enzymes were increased in both unstressed and stressed animals. Acetylcholine level was increased while acetylcholinesterase activity was decreased in both M. madrespatana treated unstressed and stressed rats. There was also an improvement in memory function. Serotonin neurotransmission was also regulated in M. madrespatana treated rats following immobilization stress with anxiolytic and anti-depressive effects. Conclusion: Based on the current study, it is suggested that M. madrespatana has strong antioxidant properties and may be beneficial as dietary supplementation in stress and memory-related conditions.

Impact of [d-Lys(3)]-GHRP-6 and feeding status on hypothalamic ghrelin-induced stress activation

Ghrelin administration directly into hypothalamic nuclei, including the arcuate nucleus (ArcN) and the paraventricular nucleus (PVN), alters the expression of stress-related behaviors. In the present study we investigated the effect of feeding status on the ability of ghrelin to induce stress and anxiogenesis. Adult male Sprague Dawley rats were implanted with guide cannula targeting either the ArcN or PVN. In the first experiment we confirmed that ArcN and PVN ghrelin treatment produced anxiety-like behavior as measured using the elevated plus maze (EPM) paradigm. Ghrelin was administered during the early dark cycle. Immediately after microinjections rats were placed in the EPM for 5min. Both ArcN and PVN treatment reduced open arm exploration. The effect was attenuated by pretreatment with the ghrelin 1a receptor antagonist [d-Lys(3)]-GHRP-6. In a separate group of animals ghrelin was injected into either nucleus and rats were returned to their home cages for 60min with free access to food. An additional group of rats was returned to home cages with no food access. After 60min with or without food access all rats were tested in the EPM. Results indicated that food consumption just prior to EPM testing reversed the avoidance of the open arms of the EPM. In contrast, rats injected with ghrelin, placed in their home cage for 60min without food, and subsequently tested in the EPM, exhibited an increased avoidance of the open arms, consistent with stress activation. Overall, our findings demonstrate that ghrelin 1a receptor blockade and feeding status appear to impact the ability of ArcN and PVN ghrelin to elicit stress and anxiety-like behaviors.

Behavioral, hormonal and central serotonin modulating effects of injected leptin

Leptin is viewed as an important target for developing novel therapeutics for obesity, depression/anxiety and cognitive dysfunctions. The present study therefore concerns behavioral, hormonal and central serotonin modulating effects of systemically injected leptin. Pharmacological doses (100 and 500 μg/kg) of leptin injected systemically decreased 24h cumulative food intake and body weight in freely feeding rats and improved acquisition and retention of memory in Morris water maze test. Potential anxiety reducing, hormonal and serotonin modulating effects of the peptide hormone were determined in a separate experiment. Animals injected with 100 or 500 μg/kg leptin were tested for anxiety in an elevated plus maze test 1h later. A significant increase in the number of entries and time passed in open arm of the elevated plus maze in leptin injected animals suggested pronounced anxiety reducing effect. Moreover, circulating levels of leptin correlated significantly with anxiety reducing effects of the peptide hormone. Serum serotonin increased and ghrelin decreased in leptin injected animals and correlated, positively and negatively respectively, with circulating leptin. Corticosterone increased at low dose and levels were normal at higher dose. Serotonin metabolism in the hypothalamus and hippocampus decreased only at higher dose of leptin. The results support a role of leptin in the treatment of obesity, anxiety and cognitive dysfunctions. It is suggested that hormonal and serotonin modulating effects of leptin can alter treatment efficacy in particularly comorbid conditions.

Inhibition of apomorphine-induced behavioral sensitization in rats pretreated with fluoxetine

Despite a number of clinically useful effects, there is growing evidence that psychosis and impulse control disorders develop in patients on apomorphine therapy. Evidence suggests a critical role of serotonin-1A receptors in psychosis, drug abuse, and in the mechanism of action of the prototypical selective serotonin reuptake inhibitor fluoxetine. We investigated whether fluoxetine can prevent apomorphine-induced behavioral sensitization in a rat model of psychosis. Animals treated with fluoxetine (5 and 10 mg/kg) for 2 weeks were subsequently cotreated with apomorphine (1.0 mg/kg) for 7 days. A single injection of apomorphine increased motor activity, whereas repeated daily injections produced a progressive sensitization of motor behavior. The sensitization effects of apomorphine did not occur in fluoxetine-pretreated and subsequently cotreated animals. To further elucidate the mechanism involved in the inhibition of apomorphine sensitization in fluoxetine-treated animals, we found that apomorphine-induced motor behavior was much greater in repeated apomorphine-treated than repeated saline-treated animals. It was also greater in apomorphine and fluoxetine-cotreated animals, but not in animals pretreated and cotreated with fluoxetine. The mechanism involved in the inhibition of apomorphine sensitization in fluoxetine-pretreated animals is discussed. The findings introduce an innovative approach for extending the therapeutic use of apomorphine and classical psychostimulant drugs.

Midbrain raphe 5-HT1A receptor activation alters the effects of ghrelin on appetite and performance in the elevated plus maze

Prior research suggests that midbrain serotonergic signaling and hypothalamic ghrelinergic signaling both play critical roles in appetitive and emotional behaviors. In the present study, we investigated the effects of median raphe nucleus (MRN) somatodentritic 5-HT1A receptor activation on the feeding-stimulant and anxiogenic action of paraventricular nucleus (PVN) ghrelin. In an initial experiment, adult male Sprague-Dawley rats were injected with either ghrelin (200-800 pmol) into the PVN or 8-OH-DPAT (2.5-10 nmol), a 5-HT1A receptor agonist, into the MRN. Performance on the elevated plus maze (EPM) was then assessed. In separate rats, MRN 8-OH-DPAT (2.5-5 nmol) was administered 5 min prior to PVN injection of ghrelin (400 pmol) followed by EPM testing. The orexigenic effects of MRN 8-OH-DPAT (0.1-1.6 nmol) paired with PVN ghrelin (50 pmol) were also examined. When administered alone into the PVN, ghrelin significantly decreased the number of entries and time spent in the open arms of the EPM. This anxiogenic effect was blocked if rats were allowed to eat immediately after ghrelin administration and then tested in the plus maze. MRN injections of 8-OH-DPAT were anxiolytic, and when rats were pretreated with 8-OH-DPAT prior to ghrelin, the anxiogenic action of the peptide was attenuated. In contrast, MRN administration of 8-OH-DPAT potentiated the eating-stimulant effect of PVN ghrelin. Overall, our findings demonstrate that ghrelinergic and serotonergic circuits interact in the neural control of eating and anxiety-like behaviors, with 5-HT1A receptor mechanisms potentiating the orexigenic action of ghrelin while inhibiting ghrelin-induced anxiogenesis as measured via the EPM.

Investigations into the involvement of leptin in responses to stress

Stress is defined as a state that can threaten homeostasis in an organism to initiate the adaptive process. Stress mediators, which include the classic neuroendocrine hormones and a number of neurotransmitters, cytokines, and growth factors, regulate both basal and threatened homeostasis to help control the stress. Severity of stress, as well as malfunctioning of stress pathways, may impair its controllability, leading to the pathogenesis of psychiatric illnesses including depression. Leptin was initially identified as an antiobesity hormone, acting as a negative feedback adiposity signal to control energy homeostasis by binding to its receptors in the hypothalamus. Accumulating evidence has expanded the function of leptin from the control of energy balance to the regulation of other physiological and psychological processes. The aim of this paper is to evaluate the potential role of leptin in stress controllability. To this end, studies on the role of leptin in stress-induced activation of the hypothalamus-pituitary-adrenocortical axis, feeding behavior, learned helplessness, and other depression models have been accumulated. The knowledge accumulated in this article may facilitate the development of alternative treatment strategies, beyond serotonin and noradrenaline reuptake inhibition, for psychiatric care and stress-related disorders.

Activation of postsynaptic 5-HT1A receptors improve stress adaptation

RATIONALE

Serotonin-1A (5-HT1A) receptors modulate the stress response and have been implicated in the etiology and treatment of depression and anxiety disorders. A reduction in postsynaptic 5-HT1A receptor function in limbic areas has consistently been observed following exposure to chronic stress.

OBJECTIVES

To investigate the hypothesis that increased activation of 5-HT1A receptors in rats having reduced 5-HT function may improve stress adaptation and the behavioral sequelae commonly associated with chronic stress.

METHODS

One hundred forty-four Sprague-Dawley rats received injections of para-chlorophenylalanine to partially deplete 5-HT then were given daily systemic pretreatment with the 5-HT1A receptor agonist, 8-hydroxy-2- (di-n-propylamino) tetralin (8-OH-DPAT), the antagonist, WAY 100635, or vehicle prior to either restraint stress (6 h/day for 10 daily sessions) or control conditions. Anxiety- and depressive-like behaviors were then assessed using the open field and sucrose preference tests. Protein level of hippocampal glucocorticoid receptors (GR) and mineralocorticoid receptors was detected by immunohistochemistry and brain-derived neurotrophic factor (BDNF) was determined by in situ hybridization.

RESULTS

8-OH-DPAT pretreatment prior to stress exposure attenuated later stress-induced anxiety- and depression-like behaviors and increased GR and BDNF mRNA expression in the hippocampus relative to vehicle- and WAY 100635-pretreated, stressed animals.

CONCLUSION

The stress-related impairments associated with 5-HT deficiency can be improved by 8-OH-DPAT pretreatment prior to stress exposure and are associated with an augmentation of GR-like immunoreactivity and BDNF mRNA expression in the hippocampus. It suggested that selective activation of 5-HT1A receptors may be a potential treatment strategy for stress-related disorders such as anxiety and depression.

Inhibition of immobilization stress-induced anorexia, behavioral deficits, and plasma corticosterone secretion by injected leptin in rats

Leptin, originally identified as an anti-obesity hormone, also has an important role in the regulation of mood and emotion. The present study was designed to monitor effects of injected leptin on immobilization stress-induced anorexia, behavioral deficits, and plasma corticosterone secretion in rats. Exposure to 2 h immobilization stress decreased food intake and body weight in saline-injected animals. Animals exposed to open field, elevated plus maze, and light-dark transition tests the day following immobilization exhibited anxiety-like behavior. Leptin injected at doses of 0.1 and 0.5 mg/kg also decreased food intake and body weight in unstressed animals and elicited anxiolytic effects at dose of 0.5 mg/kg, monitored on the following day. Immobilization-induced decreases in food intake, body weight, as well as stress-induced behavioral deficits in the open field, elevated plus maze, and light-dark transition test were reversed by exogenous leptin in a dose-dependent (0.1-0.5 mg/kg) manner. Acute exposure to 2 h immobilization produced a fourfold rise in plasma levels of corticosterone. Animals injected with leptin at a dose of 0.1 mg/kg, but not at dose of 0.5 mg/kg, exhibited a marginal increase in plasma corticosterone. Immobilization-induced increases of plasma corticosterone were reversed by leptin injected at doses of 0.1 or 0.5 mg/kg. The data suggest that exogenous leptin can reduce stress perception, resulting in an inhibition of stress effects on the activity of hypothalamic-pituitary-adrenal axis and behavior. The reported pharmacological effects of leptin represent an innovative approach for the treatment of stress-related disorders.

Citalopram decreases tryptophan 2,3-dioxygenase activity and brain 5-HT turnover in swim stressed rats

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) are the most widely prescribed antidepressant class today and exert their effects by increasing synaptic concentrations of serotonin (5-HT). The forced swim test (FST) is the most widely used animal test predictive of antidepressant action. Rationale of the present study was to investigate the acute effects of citalopram on hepatic tryptophan metabolism and disposition in rats exposed to FST.

METHODS

We investigated the effects of acute citalopram (20 mg/kg, ip) administration on rat's behavioral responses in FST paradigm, hepatic tryptophan 2,3-dioxygenase (TDO) activity, serum corticosterone levels and brain regional 5-HT metabolism.

RESULTS

Citalopram administered to swim-stressed rats showed a decrease in FST-induced increases in plasma corticosterone concentration and 5-HT turnover in hypothalamus, amygdala and hippocampus. The drug also decreases immobility and increases swimming during the FST. Citalopram administration to unstressed rats increases plasma corticosterone concentration but decreases 5-HT turnover in all three brain areas examined.

CONCLUSIONS

Our findings support the hypothesis that acute citalopram administration increases tryptophan (by inhibiting TDO activity) availability for 5-HT synthesis and activates serotonergic neurotransmission in limbic brain areas in rats exposed to FST paradigm. The mechanism of action of citalopram in ameliorating social stress related depressive disorder in humans is discussed.

Serotonin 2A receptor gene (HTR2A) polymorphism in alcohol-dependent patients

BACKGROUND

The serotonergic (5-HT) dysfunction has been frequently described in subjects with alcohol dependence (AD). In the present study, a potential relationship between T102C polymorphism in the 5-HT receptor subtype 2Agene (HTR2A) and alcohol dependence was examined.

METHODS

Genotypes were analyzed in 150 AD patients diagnosed with DSM-IV criteria and in 80 healthy controls.

RESULTS

The genetic analysis showed that the frequency of 102C allele and C102C genotype in AD subjects was significantly higher than in controls. Moreover, AD patients homozygous for C allele had significantly lower age at onset of alcohol problems than subjects having at least one T allele.

CONCLUSION

The results suggest a potential role of the T102C HTR2A polymorphism in development of alcohol dependence.