Involvement of serotonin receptor subtypes in the antidepressant-like effect of trim in the rat forced swimming test

The role of nitric oxide and hormone signaling in chronic stress, anxiety, depression and post-traumatic stress disorder

This paper provides a summary of the role of nitric oxide (NO) and hormones in the development of chronic stress, anxiety, depression, and post-traumatic stress disorder (PTSD). These mental health conditions are prevalent globally and involve complex molecular interactions. Although there is a significant amount of research and therapeutic options available, the underlying mechanisms of these disorders are still not fully understood. The primary pathophysiologic processes involved in chronic stress, anxiety, depression, and PTSD include dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, the intracellular influence of neuronal nitric oxide synthase (nNOS) on transcription factors, an inflammatory response with the formation of nitrergic oxidative species, and reduced serotonergic transmission in the dorsal raphe nucleus. Despite the extensive literature on this topic, there is a great need for further research to clarify the complexities inherent in these pathways, with the primary aim of improving psychiatric care.

Effects of mirabegron on depression, anxiety, learning and memory in mice

Mirabegron is the first b3-adrenoceptor agonist to enter clinical practice and has been approved for the treatment of symptoms of OAB. The aim of this study is to investigate whether the mirabegron has an effect on depression, anxiety, learning, and memory. We investigated the effects of mirabegron on depression, anxiety, learning and memory by using forced swimming test, elevated plus maze test, passive avoidance and Morris water maze in mice. Imipramine and mirabegron (3, 6 and 9 mg/kg) significantly reduced immobility time in forced swimming test. Diazepam and mirabegron (3, 6 and 9 mg/kg) significantly increased the time spent in open arms and the number of entries to the open arms in elevated plus maze test. Furthermore, cognitive performance impaired with scopolamine has been significantly improved with 9 mg/kg mirabegron. Mirabegron (6 and 9 mg/kg) significantly increased the time spent in the target quadrant in naive mice. While scopolamine significantly increased the swimming speed, mirabegron (9 mg/kg) significantly decreased the swimming speed in scopolamine-treated mice. Mirabegron might be clinically useful for the treatment of OAB in elderly patients that should use drugs against depression and anxiety, without disrupt learning and memory.

Neuronal Nitric Oxide Synthase in Nucleus Accumbens Specifically Mediates Susceptibility to Social Defeat Stress through Cyclin-Dependent Kinase 5

Stress-induced depression is common worldwide. NAc, a "reward" center, is recently reported to be critical to confer the susceptibility to chronic social defeat stress (CSDS) and the depression-related outcome. However, the underlying molecular mechanisms have not been well characterized. In this study, we induced depression-like behaviors with CSDS and chronic mild stress in male mice to mimic social and environmental factors, respectively, and observed animal behaviors with social interaction test, tail suspension test, and sucrose preference test. To determine the role of neuronal nitric oxide synthase (nNOS) and its product nitric oxide (NO), we used brain region-specifically nNOS overexpression and stereotaxic injection of NO inhibitor or donor. Moreover, the downstream molecular cyclin-dependent kinase 5 (CDK5) was explored by conditional KO and gene mutation. We demonstrate that nNOS-implicated mechanisms in NAc shell (NAcSh), including increased cell number, increased protein expression levels, and increased specific enzyme activity, contribute the susceptibility to social defeat and the following depression-like behaviors. NAcSh nNOS does not directly respond to chronic mild stress but facilitates the depression-like behaviors. The increased NAcSh nNOS expression after CSDS leads to the social avoidance and depression-like behaviors in defeated mice, which is dependent on the nNOS enzyme activity and NO production. Moreover, we identify the downstream signal in NAcSh. S-nitrosylation of CDK5 by NO contributes to enhanced CDK5 activity, leading to depression-related behaviors in susceptible mice. Therefore, NAcSh nNOS mediates susceptibility to social defeat stress and the depression-like behaviors through CDK5.SIGNIFICANCE STATEMENT Stress-induced depression is common worldwide, and chronic exposure to social and psychological stressors is important cause of human depression. Our study conducted with chronic social defeat stress mice models demonstrates that nNOS in NAcSh is crucial to regulate the susceptibility to social defeat stress and the following depression-like behaviors, indicating NAcSh nNOS as the responding molecule to social factors of depression. Moreover, we discover the downstream mechanism of NAcSh nNOS in mediating the susceptibility is NO and S-nitrosylation of CDK5. Thus, NAcSh nNOS mediates susceptibility to social defeat stress through CDK5 is a potential mechanism for depression, which may interpret how the brain transduces social stress exposure into depression.

Neuronal nitric oxide synthase and affective disorders

Affective disorders including major depressive disorder (MDD), bipolar disorder (BPD), and general anxiety affect more than 10% of population in the world. Notably, neuronal nitric oxide synthase (nNOS), a downstream signal molecule of N-methyl-D-aspartate receptors (NMDARs) activation, is abundant in many regions of the brain such as the prefrontal cortex (PFC), hippocampus, amygdala, dorsal raphe nucleus (DRN), locus coeruleus (LC), and hypothalamus, which are closely associated with the pathophysiology of affective disorders. Decreased levels of the neurotransmitters including 5-hydroxytryptamine or serotonin (5-HT), noradrenalin (NA), and dopamine (DA) as well as hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis are common pathological changes of MDD, BPD, and anxiety. Increasing data suggests that nNOS in the hippocampus play a crucial role in the etiology of MDD whereas nNOS-related dysregulation of the nitrergic system in the LC is closely associated with the pathogenesis of BPD. Moreover, hippocampal nNOS is implicated in the role of serotonin receptor 1 A (5-HTR1 A) in modulating anxiety behaviors. Augment of nNOS and its carboxy-terminal PDZ ligand (CAPON) complex mediate stress-induced anxiety and disrupting the nNOS-CAPON interaction by small molecular drug generates anxiolytic effect. To date, however, the function of nNOS in affective disorders is not well reviewed. Here, we summarize works about nNOS and its signal mechanisms implicated in the pathophysiology of affective disorders. On the basis of this review, it is suggested that future research should more fully focus on the role of nNOS in the pathomechanism and treatment of affective disorders.

Repeated treatment with nitric oxide synthase inhibitor attenuates learned helplessness development in rats and increases hippocampal BDNF expression

BACKGROUND

Nitric oxide synthase (NOS) inhibitors induce antidepressant-like effects in animal models sensitive to acute drug treatment such as the forced swimming test. However, it is not yet clear if repeated treatment with these drugs is required to induce antidepressant-like effects in preclinical models.

OBJECTIVE

The aim of this study was to test the effect induced by acute or repeated (7 days) treatment with 7-nitroindazole (7-NI), a preferential inhibitor of neuronal NOS, in rats submitted to the learned helplessness (LH) model. In addition, we aimed at investigating if 7-NI treatment would increase brain-derived neurotrophic factor (BDNF) protein levels in the hippocampus, similarly to the effect of prototype antidepressants.

METHODS

Animals were submitted to a pre-test (PT) session with inescapable footshocks or habituation (no shocks) to the experimental shuttle box. Six days later they were exposed to a test with escapable footshocks. Independent groups received acute (a single injection after PT or before test) or repeated (once a day for 7 days) treatment with vehicle or 7-NI (30 mg/kg).

RESULTS

Repeated, but not acute, treatment with 7-NI attenuated LH development. The effect was similar to repeated imipramine treatment. Moreover, in an independent experimental group, only repeated treatment with 7-NI and imipramine increased BDNF protein levels in the hippocampus.

CONCLUSION

The results suggest the nitrergic system could be a target for the treatment of depressive-like conditions. They also indicate that, similar to the positive control imipramine, the antidepressant-like effects of NOS inhibition could involve an increase in hippocampal BDNF levels.

ZL006, a small molecule inhibitor of PSD-95/nNOS interaction, does not induce antidepressant-like effects in two genetically predisposed rat models of depression and control animals

N-methyl-D-aspartate receptor (NMDA-R) antagonists and nitric oxide inhibitors have shown promising efficacy in depression but commonly induce adverse events. To circumvent these, a more indirect disruption of the nitric oxide synthase/postsynaptic density protein 95 kDa complex at the NMDA-R has been proposed. This disruption can be achieved using small molecule inhibitors such as ZL006, which has attracted attention as ischemic stroke therapy in rodents and has been proposed as a potential novel treatment for depression. Based on this, our aim was to translate these findings to animal models of depression to elucidate antidepressant-like properties in more detail. In the present study, we administered ZL006 to two established animal models of depression and control rodents. Following treatment, we measured locomotion in the Open Field and depressive-like behavior in the Forced Swim Test and Tail Suspension Test. Our experimental designs included the use of different species (rats, mice), strains (Flinders Sensitive Line rats, Flinders Resistant Line rats, Wistar Kyoto rats, Wistar Hanover rats, Sprague Dawley rats, B6NTac mice), routes of administration (intraperitoneal, intracerebroventricular), times of administration (single injection, repeated injections), treatment regimens (acute, sustained), and doses (5, 10, 15, 50 mg/kg). ZL006 did not affect behavior in any of the described settings. On a molecular level, ZL006 significantly reduced total nitrate/nitrite concentrations in the cerebellum, supporting that it is capable of reducing nitric oxide metabolites in the brain. Future studies using different experimental parameters are needed to further investigate the behavioral profile of ZL006.

Effects of 1-(2-trifluoromethylphenyl)-imidazole (TRIM) on receptor-independent and -dependent contractile responses in rat aorta

BACKGROUND/AIM

This study investigates whether 1-(2-trifluoromethylphenyl)-imidazole (TRIM), originally proposed as a nitric oxide synthase inhibitor and also suggested to be an inhibitor of store-operated calcium entry in mouse anococcygeal muscle, inhibits receptor-independent and -dependent responses in rat thoracic aorta.

MATERIALS AND METHODS

Cyclopiazonic acid- and serotonin-induced vascular responses were investigated in aortic segments isolated from male Sprague Dawley rats using isolated tissue experiments. Changes in intracellular calcium levels were also monitored via front surface fluorescence measurements in fura-2-loaded embryonic rat vascular smooth muscle cell line A7r5.

RESULTS

TRIM inhibited serotonin-mediated vascular contractions without affecting cyclopiazonic acid-induced responses. In addition, TRIM caused a nonlinear rightward shift in the serotonin concentration-response curve, possibly via serotonin receptor modulation.

CONCLUSION

TRIM may have an impact on investigation of tissue-specific receptor-independent and -dependent vascular responses. It may also be used as a lead compound in the development of selective serotonin receptor modulators.

Functional Selectivity and Antidepressant Activity of Serotonin 1A Receptor Ligands

Serotonin (5-HT) is a monoamine neurotransmitter that plays an important role in physiological functions. 5-HT has been implicated in sleep, feeding, sexual behavior, temperature regulation, pain, and cognition as well as in pathological states including disorders connected to mood, anxiety, psychosis and pain. 5-HT1A receptors have for a long time been considered as an interesting target for the action of antidepressant drugs. It was postulated that postsynaptic 5-HT1A agonists could form a new class of antidepressant drugs, and mixed 5-HT1A receptor ligands/serotonin transporter (SERT) inhibitors seem to possess an interesting pharmacological profile. It should, however, be noted that 5-HT1A receptors can activate several different biochemical pathways and signal through both G protein-dependent and G protein-independent pathways. The variables that affect the multiplicity of 5-HT1A receptor signaling pathways would thus result from the summation of effects specific to the host cell milieu. Moreover, receptor trafficking appears different at pre- and postsynaptic sites. It should also be noted that the 5-HT1A receptor cooperates with other signal transduction systems (like the 5-HT1B or 5-HT2A/2B/2C receptors, the GABAergic and the glutaminergic systems), which also contribute to its antidepressant and/or anxiolytic activity. Thus identifying brain specific molecular targets for 5-HT1A receptor ligands may result in a better targeting, raising a hope for more effective medicines for various pathologies.

Serotonergic mechanisms are involved in antidepressant-like effects of bisbenzylisoquinolines liensinine and its analogs isolated from the embryo of Nelumbo nucifera Gaertner seeds in mice

Objectives

We attempted to ascertain if bisbenzylisoquinoline alkaloids, liensinine and isoliensinine from Nelumbo nucifera Gaertner have antidepressant-like effects and compare the effects with those previously obtained by their analogue neferine.

Methods

Using mice, the forced swimming test (FST) was carried out after treatment with liensinine, isoliensinine and neferine.

Key findings

Liensinine and isoliensinine elicited antidepressant-like effects in mice after the FST. Anti-immobility effects of liensinine and isoliensinine were antagonized by the 5-hydroxytryptamine1A (5-HT1A) receptor antagonist WAY 100635, but not by the α1-adrenoceptor antagonist prazosin. The anti-immobility effects of liensinine, isoliensinine and neferine were blocked by pretreatment with p-chlorophenylalanine (PCPA), which depletes serotonin (5-HT).

Conclusions

These data suggest that liensinine and isoliensinine from Nelumbo nucifera Gaertner have antidepressant-like effects and that antidepressant-like effects of liensinine and its analogues are closely related to serotonergic mechanisms.

Response of the nitrergic system to activation of the neuroendocrine stress axis

Exposure to stressful stimuli causes activation of the hypothalamic-pituitary-adrenal axis which rapidly releases high concentrations of glucocorticoid stress hormones, resulting in increased cellular metabolism and spontaneous oxygen and nitrogen radical formation. High concentrations of nitrogen radicals, including nitric oxide, cause damage to cellular proteins in addition to inhibiting components of the mitochondrial transport chain, leading to cellular energy deficiency. During stress exposure, pharmacological inhibition of nitric oxide production reduces indicators of anxiety- and depressive-like behavior in animal models. Therefore, the purpose of this review is to present an overview of the current literature on stress-evoked changes in the nitrergic system, particularly within neural tissue.

Small-molecule inhibitors at the PSD-95/nNOS interface have antidepressant-like properties in mice

Previous studies have demonstrated that nitric oxide (NO) synthase inhibitors are as efficacious as tricyclic antidepressants in preclinical antidepressant screening procedures and in attenuating behavioural deficits associated with animal models of depression. The N-methyl-D-aspartate receptor (NMDA-R) complex gates Ca(2+), which interacts with calmodulin to subsequently activate NO synthase. We hypothesised that uncoupling neuronal nitric oxide synthase (nNOS) from the NMDA-R through the scaffolding protein postsynaptic density protein 95 (PSD-95) would produce behavioural antidepressant effects similar to NO synthase inhibitors. Small-molecule inhibitors of the PSD-95/nNOS interaction, IC87201 (0.01-2 mg/kg) and ZL006 (10 mg/kg) were tested for antidepressant properties in tests of antidepressant activity namely the tail suspension and forced swim tests in mice. We now report that IC87201 and ZL006 produce antidepressant-like responses in the forced swimming test (FST) and tail suspension test (TST) following a single administration in mice. By contrast to the tricyclic antidepressant imipramine (25 mg/kg), the effects are not observed 1 h following drug administration but are apparent 24 and 72 h later. Furthermore prior exposure to the TST or FST is required in order to observe the antidepressant-related activity. Similar delayed and sustained antidepressant-like effects were observed following TRIM (50 mg/kg) and ketamine (30 mg/kg) in the TST. The antidepressant-like effects of ZL006 also generalise to IC87201 in the TST. IC87201 was devoid of effects on locomotor activity and step-through latency in the passive avoidance cognition test. These data support the hypothesis that targeting the PSD-95/nNOS interaction downstream of NMDA-R produces antidepressant effects and may represent a novel class of therapeutics for major depressive disorders.

Evidence that the anxiolytic-like effects of the beta3 receptor agonist amibegron involve serotoninergic receptor activity

Anxiety disorders are the most common behavioral disorders, and they exhibit high comorbidity rates. The aim of the present study was to confirm the effects of Amibegron, the first selective beta 3 adrenergic agent, on anxiety and to demonstrate that different serotoninergic receptor subtypes are involved in this effect. We administered the serotonin 5-HT1A receptor antagonist WAY-100635, the serotonin 5-HT2A receptor antagonist Ketanserin and the serotonin 5-HT3 receptor antagonist Ondansetron in mice and evaluated their performance in the elevated plus-maze test. Mice administered with Amibegron (5 and 10 mg/kg) showed a dose-dependent prolonged time spent in the open arms and an increase in the number of entries into the open arms during the elevated plus-maze (EPM) test. However, in the control mice, administration of WAY, Ketanserin and Ondansetron demonstrated no effect on the time spent in the open arms and the number of entries into the open arms. In addition, these treatments all significantly reversed the effect of the Amibegron-induced (10 mg/kg) increase in the time spent in the open arms. However, only WAY and Ketanserin treatments reversed the Amibegron-induced increase in the number of entries into the open arms. In conclusion, Amibegron exerted a significant anxiolytic effect, which was as effective as Diazepam, in mice during the EPM test. This effect of Amibegron may be mediated by interactions with the serotonin 5-HT1A, 5-HT2A and 5-HT3 receptors.

Involvement of serotonin receptor subtypes in the antidepressant-like effect of beta receptor agonist Amibegron (SR 58611A): an experimental study

New therapeutic strategies against depression, with less side effects and thus greater efficacy in larger proportion of depressed patients, are needed. Amibegron (SR58611A) is the first selective β3 adrenergic agent that has been shown to possess a profile of antidepressant activity in rodents. To investigate the involvement of serotonin receptors in the effects of amibegron, we used the serotonin 5HT1A receptor antagonist WAY-100635 (WAY) or serotonin 5HT2A-2C receptor antagonist ketanserin or serotonin 5HT3 receptor antagonist ondansetron in mice forced swimming test (FST). The locomotor activity was evaluated by measuring the total distance moved in the apparatus and the speed of the animals in the open field test. Imipramine (30mg/kg) significantly reduced immobility time compared to vehicle-treated group while amibegron (5 and 10mg/kg) dose dependently reduced immobility time in the FST. WAY(0.1mg/kg), ondansetron (1mg/kg), ketanserin(5mg/kg) had no effect on immobility time in naive mice while all of the drugs partially and significantly reversed amibegron (10mg/kg) induced decreasement in the immobility time in FST. None of the drugs alter locomotor activity in the open field test. The antidepressant-like effect of amibegron in the FST seems to be mediated by an interaction with serotonin 5-HT1A, serotonin 5-HT2A-2C and serotonin 5-HT3 receptors.

Effects of diphenyl diselenide on depressive-like behavior in ovariectomized mice submitted to subchronic stress: involvement of the serotonergic system

RATIONALE

The transition to menopause is associated with an increased risk of depressed mood.

OBJECTIVES

This study was conducted to investigate whether diphenyl diselenide [(PhSe)₂] treatment could reduce the effects of postmenopausal depression-like behavior in ovariectomized female mice submitted to subchronic stress exposure.

METHODS

Mice were divided into four groups: sham, (PhSe)₂, ovariectomy (OVX), and OVX + (PhSe)₂. Animals were ovariectomized/sham-operated and subjected to stress session once a day for 7 days from the fifth to the 11th day after OVX. The behavioral tests (open field, tail suspension (TST), and forced swimming (FST)) were performed on the 14th day after OVX. Mice were treated orally once a day with vehicle (canola oil, 10 ml/kg) or (PhSe)₂ (10 mg/kg; 10 ml/kg) 30 min before being exposed to subchronic stress, or from the 11th to the 14th day. Paroxetine (8 mg/kg i.p.) and pargyline (30 mg/kg i.p.) were used as positive controls. The involvement of serotonergic receptor subtypes in the antidepressant-like effect of (PhSe)₂ was assessed in the FST using WAY 100635 (0.1 mg/kg s.c.), ritanserin (1 mg/kg i.p.), and ondansetron (1 mg/kg i.p.) as serotonergic antagonists. Monoamine oxidase (MAO) A and B activities were also determined.

RESULTS

The prolongation of immobility time in TST and FST in OVX mice submitted to subchronic stress was prevented by (PhSe)₂ treatment. Ritanserin and ondansetron blocked the antidepressive-like effect of (PhSe)₂, suggesting the involvement of 5-HT(2A/2C) and 5-HT₃ receptor subtypes. Both paroxetine and pargyline were effective in reducing the immobility time of stressed OVX mice in the FST. No alterations in locomotor activity were observed. Although (PhSe)₂ had inhibited in vitro MAO-A and MAO-B activities, none of the groups presented alterations neither in ex vivo MAO-A nor in MAO-B activity.

CONCLUSIONS

(PhSe)₂ treatment could influence mood and behavior, indicating a promising role of this organoselenium compound in the management of postmenopausal depressive symptoms.

Subchronic treatment with fluoxetine and ketanserin increases hippocampal brain-derived neurotrophic factor, β-catenin and antidepressant-like effects

BACKGROUND AND PURPOSE

5-HT(2A) receptor antagonists improve antidepressant responses when added to 5-HT-selective reuptake inhibitors (SSRIs) or tricyclic antidepressants. Here, we have studied the involvement of neuroplasticity pathways and/or the 5-hydroxytryptaminergic system in the antidepressant-like effect of this combined treatment, given subchronically.

EXPERIMENTAL APPROACH

Expression of brain-derived neurotrophic factor (BDNF) and its receptor (TrkB), 5-bromo-2'-deoxyuridine (BrdU) incorporation, and β-catenin protein expression in different cellular fractions, as well as 5-HT(1A) receptor function were measured in the hippocampus of rats treated with fluoxetine, ketanserin and fluoxetine + ketanserin for 7 days, followed by a forced swimming test (FST) to analyse antidepressant efficacy.

KEY RESULTS

mRNA for BDNF was increased in the CA3 field and dentate gyrus of the hippocampus by combined treatment with fluoxetine + ketanserin. Expression of β-catenin was increased in total hippocampal homogenate and in the membrane fraction, but unchanged in the nuclear fraction after combined treatment with fluoxetine + ketanserin. These effects were paralleled by a decreased immobility time in the FST. There were no changes in BrdU incorporation, TrkB expression and 5-HT(1A) receptor function in any of the groups studied.

CONCLUSIONS AND IMPLICATIONS

The antidepressant-like effect induced by subchronic co-treatment with a SSRI and a 5-HT(2A) receptor antagonist may mainly be because of modifications in hippocampal neuroplasticity (BDNF and membrane-associated β-catenin), without a significant role for other mechanisms involved in chronic antidepressant response, such as hippocampal neuroproliferation or 5-HT(1A) receptor desensitization in the dorsal raphe nucleus.

The antidepressant-like effect of Hedyosmum brasiliense and its sesquiterpene lactone, podoandin in mice: evidence for the involvement of adrenergic, dopaminergic and serotonergic systems

We have recently shown that the ethanol extract of the leaves of Hedyosmum brasiliense exhibits an antidepressant-like effect in the tail suspension and forced swimming tests in mice. The present study investigates the mechanisms involved in the antidepressant-like effect of H. brasiliense extract, together with the antidepressant potential of podoandin, an isolated sesquiterpenoid. H. brasiliense (50mg/kg, i.p.) and podoandin (10mg/kg, i.p.) decreased the immobility time in the forced swimming test, without any accompanying changes in ambulation in the open-field test. The anti-immobility effect of the H. brasiliense extract was prevented by pre-treating the mice with ondansetron, NAN 190, pindolol, prazosin, yohimbine, haloperidol, SCH23390, and sulpiride. On the other hand, pre-treating the mice with: p-chlorophenylalanine (4 consecutive days), ketanserin, naloxone, naltrindole, bicuculline, phaclofen, or l-arginine did not block the antidepressant-like effect of H. brasiliense. In addition, pre-treatment of the animals with methylene blue, NG-nitro-l-arginine or 7-nitroindazole, at subeffective doses, did not cause a synergistic effect with H. brasiliense extract at an effective dose in the forced swimming test. The anti-immobility effect of podoandin was also prevented by pre-treating the mice with NAN-190, ondansetron, prazosin, yohimbine, sulpiride and haloperidol. The results indicate that the antidepressant-like effect of H. brasiliense (and podoandin) is dependent on the serotonergic, noradrenergic and dopaminergic systems, but not on the GABAergic, opioid and oxidonitrergic systems.

The role of 5-HT₁A receptors in fish oil-mediated increased BDNF expression in the rat hippocampus and cortex: a possible antidepressant mechanism

Epidemiological and dietary studies show that nutritional deficit of omega-3 polyunsaturated fatty acids (ω-3 PUFA) is directly related to the prevalence and severity of depression. Supplementation with docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) during critical periods of development (pregnancy and lactation) is essential for cortical maturation, synaptogenesis and myelination, and may also mitigate the risk for cognitive deficits and psychopathologies in young adults. The present study was performed to evaluate the involvement of serotonin (5-HT) receptors, particularly of 5-HT(1A), and hippocampal brain-derived neurotrophic factor (BDNF) expression in the antidepressant effect of ω-3 PUFA supplementation. In Experiment 1, the antidepressant effects of fish oil were assessed by the modified forced swim test in adult rats. The data indicated a robust antidepressant effect produced by this supplementation and that treatment of the rats with WAY 100135 reversed this effect. In Experiment 2, cortical and hippocampal contents of BDNF, 5-HT, dopamine (DA) and its metabolites, 5-hydroxyindoleacetic acid (5-HIAA), and 3,4-dihydroxyphenylacetic acid (DOPAC), were determined in animals subjected to the same protocol. Increased BDNF expression in the cortex and hippocampus of both age groups was detected. In 90 day-old rats, 5-HT content in the hippocampus was increased, whereas 5-HIAA formation was diminished in the fish oil group. We suggest the occurrence of a reciprocal involvement of 5-HT(1A) receptors activation and the hippocampal BDNF-increased expression mediated by fish oil supplementation. These data corroborate and expand the notion that supplementation with ω-3 PUFA produces antidepressant effects mediated by an increase in serotonergic neurotransmission, particularly in the hippocampus. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Nitric oxide and major depression

Nitric oxide has been known to play a significant role in the pathophysiology of various disorders of the body. Despite its very short half-life, nitric oxide is known to modulate various neurotransmitter system(s) in the body and thus is speculated to play an imperative role in the pathogenesis of neurological disorders. This "wonder" molecule has been often found to possess a "dual role" in many neurological disorders of the body. Evidences have shown its prominent role in the pathogenesis of major depression. Nitric oxide modulates norepinephrine, serotonin, dopamine, glutamate, the major neurotransmitters involved in the neurobiology of major depression. The nitric oxide modulatory activity of various new generations of antidepressants has been demonstrated. Clinical studies have also confirmed the nitric oxide modulatory activity of various antidepressants particularly belonging to the class of selective serotonin reuptake inhibitors. The present review attempts to discuss the role of nitric oxide in the pathophysiology of major depression. Further, the involvement of nitric oxide system in the mechanism of various antidepressants has been discussed in detail. Nitric oxide based antidepressants can be the future drugs of choice for major depression, particularly in the treatment of pharmacoresistant depression.

The role of serotonin receptor subtypes in treating depression: a review of animal studies

RATIONALE

Serotonin reuptake inhibitors (SSRIs) are effective in treating depression. Given the existence of different families and subtypes of 5-HT receptors, multiple 5-HT receptors may be involved in the antidepressant-like behavioral effects of SSRIs.

OBJECTIVE

Behavioral pharmacology studies investigating the role of 5-HT receptor subtypes in producing or blocking the effects of SSRIs were reviewed.

RESULTS

Few animal behavior tests were available to support the original development of SSRIs. Since their development, a number of behavioral tests and models of depression have been developed that are sensitive to the effects of SSRIs, as well as to other types of antidepressant treatments. The rationale for the development and use of these tests is reviewed. Behavioral effects similar to those of SSRIs (antidepressant-like) have been produced by agonists at 5-HT(1A), 5-HT(1B), 5-HT(2C), 5-HT(4), and 5-HT(6) receptors. Also, antagonists at 5-HT(2A), 5-HT(2C), 5-HT(3), 5-HT(6), and 5-HT(7) receptors have been reported to produce antidepressant-like responses. Although it seems paradoxical that both agonists and antagonists at particular 5-HT receptors can produce antidepressant-like effects, they probably involve diverse neurochemical mechanisms. The behavioral effects of SSRIs and other antidepressants may also be augmented when 5-HT receptor agonists or antagonists are given in combination.

CONCLUSIONS

The involvement of 5-HT receptors in the antidepressant-like effects of SSRIs is complex and involves the orchestration of stimulation and blockade at different 5-HT receptor subtypes. Individual 5-HT receptors provide opportunities for the development of a newer generation of antidepressants that may be more beneficial and effective than SSRIs.

Localization of 5-HT1A and 5-HT2A positive cells in the brainstems of control age-matched and Alzheimer individuals

Serotonin receptor 1A and 2A positive cells in postmortem brainstems were demonstrated via immunohistochemistry in eight control age-matched elderly individuals and eight Alzheimer patients. The 5-HT1A positive cells were found in substantia nigra, pontile nucleus, and vagal as well as dorsal raphe nucleus, while 5-HT2A receptor positive cells were found in motor, sensory and spinal trigeminal nuclei, pontile nucleus, substantia nigra, and nucleus solitarius. A comparison in density of positive cells per unit area was made between control age-matched and Alzheimer individuals. Statistically significant differences (p ≤ 0.01) in density were observed in 5-HT1A cells in pontile, dorsal raphe, and vagal nuclei between control age-matched and Alzheimer, and in 5-HT2A positive cells in the sensory trigeminal nucleus, between control and Alzheimer. This de novo study indicated the presence of 5-HT1A and 5-HT2A receptor positive cells in the above nuclei of human brainstem and revealed differences in density between control age-matched and Alzheimer, indicating possible functional derangements in Alzheimer patients in these areas. In addition, colocalization studies indicated that 5-HT1A receptors were in cholinergic cells and gamma-aminobutyric acid positive fibers were linked to 5-HT2A receptor positive cells. It is hoped that understanding these two important 5-HT receptors and their localization might lead to advances in future therapeutic development.