Design and functional evaluation of an optically active µ-opioid receptor.

The use of opioids, which achieve therapeutic analgesia through activation of µ-opioid receptors, are limited in the management of chronic pain by adverse effects including tolerance and addiction. Optogenetics is an emerging approach of designing molecular targets that can produce cell-specific receptor-mediated analgesia with minimal side effects. Here we report the design and functional characterization of a chimeric µ-opioid receptor that could be photoactivated to trigger intracellular signaling. A prototype optoactive µ-opioid receptor (optoMOR) was designed by replacing the intracellular domains from rhodopsin with those of the native µ-opioid receptor and was transiently expressed in human embryonic kidney (HEK293) cells. Expression and distribution of the protein were confirmed by immunocytochemistry. The signal-transduction mechanisms induced by photoactivation of the optoMOR were evaluated and compared with the native µ-opioid receptor stimulation by an agonist, D-Ala(2), N-MePhe(4), Gly-ol-enkephalin (DAMGO). Cells were depolarized by extracellular potassium and the depolarization-induced calcium (Ca(2+)) influx was quantified by using Fura-2 imaging. The forskolin-stimulated adenylate cyclase/cAMP cascade was evaluated by ELISA or western blotting of brain-derived neurotrophic factor (BDNF) and the phosphorylation of cAMP response element binding protein (CREB). The optoMOR protein distribution was observed intracellularly and on the plasma membrane similar to the native µ-opioid receptor in HEK293 cells. Photoactivation of optoMOR decreased the Ca(2+) influx and inhibited the forskolin-induced cAMP generation, activation of CREB, and BDNF levels in optoMOR-expressing cells similar to the activation of native µ-opioid receptor by DAMGO. Thus the current study has accomplished the design of a prototype optoMOR and characterized the cellular signaling mechanisms activated by light stimulation of this receptor.

Animal models of depression and neuroplasticity: assessing drug action in relation to behavior and neurogenesis.

Depression is among the most prevalent forms of mental illness and a major cause of morbidity worldwide. Diagnosis of depression is mainly based on symptomatic criteria, and the heterogeneity of the disease suggests that multiple different biological mechanisms may underlie its etiology. Animal models have been important for recent advances in experimental neuroscience, including modeling of human mood disorders, such as depression and anxiety. Over the past few decades, a number of stress and neurobiochemical models have been developed as primary efficacy measures in depression trials, which are paving the way for the discovery of novel therapeutic targets. Recent data indicates that stress-related mood disorders have influence on neuroplasticity and adult neurogenesis. In this chapter, several currently available animal models are presented as powerful tools for both mechanistic studies into the neurobiology of the antidepressant response and for drug discovery.

Curcumin prevents corticosterone-induced neurotoxicity and abnormalities of neuroplasticity via 5-HT receptor pathway.

Curcumin, a major active component of Curcuma longa, possesses antioxidant and neuroprotective activities. The present study explores the mechanisms underlying the neuroprotective effect of curcumin against corticosterone and its relation to 5-hydroxy tryptamine (5-HT) receptors. Exposure of cortical neurons to corticosterone results in decreased mRNA levels for three 5-HT receptor subtypes, 5-HT(1A), 5-HT(2A) and 5-HT(4), but 5-HT(1B,) 5-HT(2B), 5-HT(2C), 5-HT(6) and 5-HT(7) receptors remain unchanged. Pre-treatment with curcumin reversed this effect on mRNA for the 5-HT(1A) and 5-HT(4) receptors, but not for the 5-HT(2A) receptor. Moreover, curcumin exerted a neuroprotective effect against corticosterone-induced neuronal death. This observed effect of curcumin was partially blocked by either 5-HT(1A) receptor antagonist p-MPPI or 5-HT(4) receptor antagonist RS 39604 alone; whereas, the simultaneous application of both antagonists completely reversed the effect. Curcumin was also found to regulate corticosterone-induced morphological changes such as increases in soma size, dendritic branching and dendritic spine density, as well as elevate synaptophysin expression in cortical neurons. p-MPPI and RS 39604 reversed the effect of curcumin-induced change in neuronal morphology and synaptophysin expression of corticosterone-treated neurons. In addition, an increase in cyclic adenosine monophosphate (cAMP) level was observed after curcumin treatment, which was further prevented by RS 39604, but not by p-MPPI. However, curcumin-induced elevation in protein kinase A activity and phosphorylation of cAMP response element-binding protein levels were inhibited by both p-MPPI and RS 39604. These findings suggest that the neuroprotection and modulation of neuroplasticity exhibited by curcumin might be mediated, at least in part, via the 5-HT receptor-cAMP-PKA-CREB signal pathway.

Antidepressant-like effect of trans-resveratrol: Involvement of serotonin and noradrenaline system.

The antidepressant-like effect of trans-resveratrol, a phenolic compound present in polygonum cuspidatum, was evaluated through behavioral and neurochemical methods. trans-Resveratrol (20, 40 and 80 mg/kg, via gavage) significantly decreased the immobility time in mouse models of despair tests, but did not influence locomotor activity. Two behavioral models and neurochemical assays suggested that trans-resveratrol produced a significant increase in serotonin and noradrenaline levels at 40 or 80 mg/kg in brain regions. In addition, trans-resveratrol dose dependently inhibited MAO-A activity. These findings indicate that the antidepressant-like effect of trans-resveratrol might be related to serotonergic and noradrenergic activation.

Antidepressant-like effect of low molecular proanthocyanidin in mice: involvement of monoaminergic system.

Proanthocyanidin is a phenolic product present in plants which has antioxidant, antinociceptive and neuroprotective properties, without inducing significant toxicological effects. The present study tested the hypothesis that low molecular proanthocyanidin from grapes that has optimized bioavailability, would exert antidepressant-like activities in behavioral despair tests. The results suggested that oral administration proanthocyanidin at doses of 25 and 50mg/kg for 7days significantly reduced the duration of immobility in both the tail suspension and forced swimming tests. The doses that affected the immobile response did not affect locomotor activity. In addition, the neurochemical and neuropharmacological assays showed that proanthocyanidin produced a marked increase of 5-HT levels at 25 and 50mg/kg in three brain regions, the frontal cortex, hippocampus and hypothalamus. Noradrenaline and dopamine levels were also increased when higher dose of proanthocyanidin (50mg/kg) administration both in the frontal cortex and hippocampus. These effects were similar to those observed for the classical antidepressant imipramine (10mg/kg, i.p.). Moreover, Our study suggested that proanthocyanidin (12.5, 25 and 50mg/kg) dose dependently inhibited monoamine oxidase-A (MAO-A) activity, while MAO-B inhibitory activity was also found at higher doses (25 and 50mg/kg) after 7days administration. MAO-A selective inhibitor, moclobemide (20mg/kg, i.g.) produced MAO-A inhibition of 70.5% in the mouse brain. These findings suggest that the antidepressant-like effects of proanthocyanidin may involve the central monoaminergic neurotransmitter systems.

Curcumin reverses impaired cognition and neuronal plasticity induced by chronic stress.

Chronic stress occurs in everyday life and induces impaired spatial cognition, neuroendocrine and plasticity abnormalities. A potential therapeutic for these stress related disturbances is curcumin, derived from the curry spice turmeric. Previously we demonstrated that curcumin reversed the chronic stress-induced behavioral deficits in escape from an aversive stimulus, however the mechanism behind its beneficial effects on stress-induced learning defects and associated pathologies are unknown. This study investigated the effects of curcumin on restraint stress-induced spatial learning and memory dysfunction in a water maze task and on measures related neuroendocrine and plasticity changes. The results showed that memory deficits were reversed with curcumin in a dose dependent manner, as were stress-induced increases in serum corticosterone levels. These effects were similar to positive antidepressant imipramine. Additionally, curcumin prevented adverse changes in the dendritic morphology of CA3 pyramidal neurons in the hippocampus, as assessed by the changes in branch points and dendritic length. In primary hippocampal neurons it was shown that curcumin or imipramine protected hippocampal neurons against corticosterone-induced toxicity. Furthermore, the portion of calcium/calmodulin kinase II (CaMKII) that is activated (phosphorylated CaMKII, pCaMKII), and the glutamate receptor sub-type (NMDA(2B)) expressions were increased in the presence of corticosterone. These effects were also blocked by curcumin or imipramine treatment. Thus, curcumin may be an effective therapeutic for learning and memory disturbances as was seen within these stress models, and its neuroprotective effect was mediated in part by normalizing the corticosterone response, resulting in down-regulating of the pCaMKII and glutamate receptor levels.

Curcumin reverses impaired hippocampal neurogenesis and increases serotonin receptor 1A mRNA and brain-derived neurotrophic factor expression in chronically stressed rats.

Curcuma longa is a major constituent of Xiaoyao-san, the traditional Chinese medicine, which has been used to effectively manage stress and depression-related disorders in China. As the active component of curcuma longa, curcumin possesses many therapeutic properties; we have previously described its antidepressant activity in our earlier studies using the chronic unpredictable stress model of depression in rats. Recent studies show that stress-induced damage to hippocampal neurons may contribute to the phathophysiology of depression. The aim of this study was to investigate the effects of curcumin on hippocampal neurogenesis in chronically stressed rats. We used an unpredictable chronic stress paradigm (20 days) to determine whether chronic curcumin treatment with the effective doses for behavioral responses (5, 10 and 20 mg/kg, p.o.), could alleviate or reverse the effects of stress on adult hippocampal neurogenesis. Our results suggested that curcumin administration (10 and 20 mg/kg, p.o.) increased hippocampal neurogenesis in chronically stressed rats, similar to classic antidepressant imipramine treatment (10 mg/kg, i.p.). Our results further demonstrated that these new cells mature and become neurons, as determined by triple labeling for BrdU and neuronal- or glial-specific markers. In addition, curcumin significantly prevented the stress-induced decrease in 5-HT(1A) mRNA and BDNF protein levels in the hippocampal subfields, two molecules involved in hippocampal neurogenesis. These results raise the possibility that increased cell proliferation and neuronal populations may be a mechanism by which curcumin treatment overcomes the stress-induced behavioral abnormalities and hippocampal neuronal damage. Moreover, curcumin treatment, via up-regulation of 5-HT(1A) receptors and BDNF, may reverse or protect hippocampal neurons from further damage in response to chronic stress, which may underlie the therapeutic actions of curcumin.