Expression of the 5-HT1A serotonin receptor in the hippocampus is required for social stress resilience and the antidepressant-like effects induced by the nicotinic partial agonist cytisine

Cytisine: State of the art in pharmacological activities and pharmacokinetics

Cytisine is a naturally occurring bioactive compound, an alkaloid mainly isolated from legume plants. In recent years, various biological activities of cytisine have been explored, showing certain effects in smoking cessation, reducing drinking behavior, anti-tumor, cardiovascular protection, blood sugar regulation, neuroprotection, osteoporosis prevention and treatment, etc. At the same time, cytisine has the advantages of high efficiency, safety, and low cost, has broad development prospects, and is a drug of great application value. However, a summary of cytisine's biological activities is currently lacking. Therefore, this paper summarizes the pharmacological action, mechanism, and pharmacokinetics of cytisine by referring to numerous databases, and analyzes the new and core targets of cytisine with the help of computer simulation technology, to provide reference for doctors.

Separation and purification of quinolyridine alkaloids from seeds of Thermopsis lanceolata R. Br. by conventional and pH-zone-refining counter-current chromatography

In this work, the preparative separation of quinolyridine alkaloids from seeds of T. lanceolata by conventional and pH-zone-refining counter-current chromatography. Traditional counter-current chromatography separation was performed by a flow-rate changing strategy with a solvent system of ethyl acetate-n-butanol-water (1:9:10, v/v) and 200 mg sample loading. Meanwhile, the pH-zone-refining mode was adopted for separating 2.0 g crude alkaloid extracts with the chloroform-methanol-water (4:3:3, v/v) solvent system using the stationary and mobile phases of 40 mM hydrochloric acid and 10 mM triethylamine. Finally, six compounds, including N-formylcytisine (two conformers) (1), N-acetycytisine (two conformers) (2), (-)-cytisine (3), 13-β-hydroxylthermopsine (4), N-methylcytisine (5), and thermopsine (6) were successfully obtained in the two counter-current chromatography modes with the purities over 96.5%. Moreover, we adopted nuclear magnetic resonance and mass spectrometry for structural characterization. Based on the obtained findings, the pH-zone-refining mode was the efficient method to separate quinolyridine alkaloids relative to the traditional mode.

Oxidation of Membrane Lipids Alters the Activity of the Human Serotonin 1A Receptor

Lipid oxidation has significant effects on lipid bilayer properties; these effects can be expected to extend to interactions between the lipid bilayer and integral membrane proteins. Given that G protein-coupled receptor (GPCR) activity is known to depend on the properties of the surrounding lipid bilayer, these proteins represent an intriguing class of molecules in which the impact of lipid oxidation on protein behavior is studied. Here, we study the effects of lipid oxidation on the human serotonin 1A receptor (5-HT_1AR). Giant unilamellar vesicles (GUVs) containing integral 5-HT_1AR were fabricated by the hydrogel swelling method; these GUVs contained polyunsaturated 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine (PLinPC) and its oxidation product 1-palmitoyl-2-(9'-oxo-nonanoyl)-sn-glycero-3-phosphocholine (PoxnoPC) at various ratios. 5-HT_1AR-integrated GUVs were also fabricated from lipid mixtures that had been oxidized by extended exposure to the atmosphere. Both types of vesicles were used to evaluate 5-HT_1AR activity using an assay to quantify GDP-GTP exchange by the coupled G protein α subunit. Results indicated that 5-HT_1AR activity increases significantly in bilayers containing oxidized lipids. This work is an important step in understanding how hyperbaric oxidation can change plasma membrane properties and lead to physiological dysfunction.

Chronic hM4Di-DREADD-Mediated Chemogenetic Inhibition of Forebrain Excitatory Neurons in Postnatal or Juvenile Life Does Not Alter Adult Mood-Related Behavior

G-protein-coupled receptors (GPCRs) coupled to G_i signaling, in particular downstream of monoaminergic neurotransmission, are posited to play a key role during developmental epochs (postnatal and juvenile) in shaping the emergence of adult anxiodepressive behaviors and sensorimotor gating. To address the role of G_i signaling in these developmental windows, we used a CaMKIIα-tTA::TRE hM4Di bigenic mouse line to express the hM4Di-DREADD (designer receptor exclusively activated by designer drugs) in forebrain excitatory neurons and enhanced G_i signaling via chronic administration of the DREADD agonist, clozapine-N-oxide (CNO) in the postnatal window (postnatal days 2–14) or the juvenile window (postnatal days 28–40). We confirmed that the expression of the HA-tagged hM4Di-DREADD was restricted to CaMKIIα-positive neurons in the forebrain, and that the administration of CNO in postnatal or juvenile windows evoked inhibition in forebrain circuits of the hippocampus and cortex, as indicated by a decline in expression of the neuronal activity marker c-Fos. hM4Di-DREADD-mediated inhibition of CaMKIIα-positive forebrain excitatory neurons in postnatal or juvenile life did not impact the weight profile of mouse pups, and also did not influence the normal ontogeny of sensory reflexes. Further, postnatal or juvenile hM4Di-DREADD-mediated inhibition of CaMKIIα-positive forebrain excitatory neurons did not alter anxiety- or despair-like behaviors in adulthood and did not impact sensorimotor gating. Collectively, these results indicate that chemogenetic induction of G_i signaling in CaMKIIα-positive forebrain excitatory neurons in postnatal and juvenile temporal windows does not appear to impinge on the programming of anxiodepressive behaviors in adulthood.

Knockout of NPFFR2 Prevents LPS-Induced Depressive-Like Responses in Mice

The precise neural mechanisms underlying the pathogenesis of depression are largely unknown, though stress-induced brain inflammation and serotonergic plasticity are thought to be centrally involved. Moreover, we previously demonstrated that neuropeptide FF receptor 2 (NPFFR2) overexpression provokes depressive-like behaviors in mice. Here, we assess whether NPFFR2 is involved in priming of depressive-like behaviors and downregulation of serotonergic 1A receptor (5HT1AR) after lipopolysaccharide (LPS) treatment. The forced swimming test (FST) and sucrose preference test (SPT) were used to quantify depressive-like phenotypes in wild-type (WT) and NPFFR2-knockout (KO) mice. A single dose of LPS (i.p. 1 mg/kg) readily caused increases in toll-like receptor 4 and tumor necrosis factor-α along with decreases in 5-HT1AR mRNA in the ventral hippocampus of WT mice. Furthermore, LPS treatment of WT mice increased immobility time in FST and decreased sucrose preference in SPT. In contrast, none of these effects were observed in NPFFR2-KO mice. While WT mice injected with lentiviral 5-HT1AR shRNA in the ventral hippocampus displayed an unaltered response after LPS challenge, LPS-challenged NPFFR2-KO mice displayed a profound decrease in sucrose preference when pretreated with 5-HT1AR shRNA. Taken together, these results suggest that NPFFR2 modulates LPS-induced depressive-like behavioral phenotypes by downregulating 5HT1AR in the ventral hippocampus.

Cytisine and cytisine derivatives. More than smoking cessation aids

Cytisine, a natural bioactive compound that is mainly isolated from plants of the Leguminosae family (especially the seeds of Laburnum anagyroides), has been marketed in central and eastern Europe as an aid in the clinical management of smoking cessation for more than 50 years. Its main targets are neuronal nicotinic acetylcholine receptors (nAChRs), and pre-clinical studies have shown that its interactions with various nAChR subtypes located in different areas of the central and peripheral nervous systems are neuroprotective, have a wide range of biological effects on nicotine and alcohol addiction, regulate mood, food intake and motor activity, and influence the autonomic and cardiovascular systems. Its relatively rigid conformation makes it an attractive template for research of new derivatives. Recent studies of structurally modified cytisine have led to the development of new compounds and for some of them the biological activities are mediated by still unidentified targets other than nAChRs, whose mechanisms of action are still being investigated. The aim of this review is to describe and discuss: 1) the most recent pre-clinical results obtained with cytisine in the fields of neurological and non-neurological diseases; 2) the effects and possible mechanisms of action of the most recent cytisine derivatives; and 3) the main areas warranting further research.

Mechanisms of Nicotine Addiction

Tobacco smoking results in more than five million deaths each year and accounts for ∼90% of all deaths from lung cancer.³ Nicotine, the major reinforcing component of tobacco smoke, acts in the brain through the neuronal nicotinic acetylcholine receptors (nAChRs). The nAChRs are allosterically regulated, ligand-gated ion channels consisting of five membrane-spanning subunits. Twelve mammalian α subunits (α2-α10) and three β subunits (β2-β4) have been cloned. The predominant nAChR subtypes in mammalian brain are those containing α4 and β2 subunits (denoted as α4β2* nAChRs). The α4β2* nAChRs mediate many behaviors related to nicotine addiction and are the primary targets for currently approved smoking cessation agents. Considering the large number of nAChR subunits in the brain, it is likely that nAChRs containing subunits in addition to α4 and β2 also play a role in tobacco smoking. Indeed, genetic variation in the CHRNA5-CHRNA3-CHRNB4 gene cluster, encoding the α5, α3, and β4 nAChR subunits, respectively, has been shown to increase vulnerability to tobacco dependence and smoking-associated diseases including lung cancer. Moreover, mice, in which expression of α5 or β4 subunits has been genetically modified, have profoundly altered patterns of nicotine consumption. In addition to the reinforcing properties of nicotine, the effects of nicotine on appetite, attention, and mood are also thought to contribute to establishment and maintenance of the tobacco smoking habit. Here, we review recent insights into the behavioral actions of nicotine, and the nAChR subtypes involved, which likely contribute to the development of tobacco dependence in smokers.

Expression of Repressor Element 1 Silencing Transcription Factor (REST) in Serotonin Neurons in the Adult Male Nile Tilapia (Oreochromis niloticus)

Repressor element-1 silencing transcription factor (REST) is highly expressed in the dorsal raphe where serotonin (5-hydroxytryptamine, 5-HT) neurons are located. REST works as a transcription factor for the 5-HT receptor and tryptophan hydroxylase two-gene expression. We hypothesized that REST is co-expressed in 5-HT neurons, which, if demonstrated, would be useful to understand the mechanism of 5-HT dysfunction-related disorders such as negative emotions and depression. Therefore, the present study was designed to examine the expression of the REST gene in the brain (forebrain, midbrain, and hindbrain) of adult male Nile tilapia (Oreochromis niloticus) using rt-PCR. Besides, using immunocytochemistry, co-localization of the REST gene was examined in 5-HT neurons and with neuronal-/glial-cell markers. We found a high expression of the REST gene in the midbrain region of the dorsal raphe, an area of 5-HT neurons. Double-label immunocytochemistry showed neuron-specific expression of REST co-localized in 5-HT neurons in the dorsal and ventral parts of the periventricular pretectal nucleus, paraventricular organ, and dorsal and medial raphe nucleus. Since midbrain 5-HT neurons express REST, we speculate that REST may control 5-HT neuronal activity related to negative emotions, including depression.

Glucocorticoids in the Physiological and Transcriptional Regulation of 5-HT1A Receptor and the Pathogenesis of Depression

There is growing increase in the global prevalence of depression, but treatment outcome of this highly disabling disease is not satisfactory. Many patients are not benefitted by the currently prescribed antidepressants-together with this partial remission is very common. Improving treatment strategies and developing better therapeutic agents for treating depression is therefore highly needed. Stress-related epigenetic changes play a critical role in the pathogenesis as well as treatment of depression. Stressful events activate hypothalamic-pituitary-adrenal axis to increase circulating levels of glucocorticoids (GCs), and a greater sensitivity to this fright and flight response increases risk of depression. A role of serotonin (5-hydroxytryptamine; 5-HT) in responses to stress and in the pathogenesis and treatment of depression is well established. Substantial evidence supports a critical role of 5-HT1A receptors in these effects of 5-HT. The present article targets stress-induced higher and sustained increases of GCs and mediated influences on the physiological as well transcriptional regulation of 5-HT1A receptors to evaluate their causal role in the pathogenesis of depression. It is suggested that synthetic compounds with antagonist activity for GC receptors and agonist activity for 5-HT1A receptors may prove better therapeutic agents for treating depression.

Dipeptide tyrosyl-leucine exhibits antidepressant-like activity in mice

Depression is a worldwide health problem. In the present study, we found that a dipeptide, tyrosyl leucine (Tyr-Leu, YL), administered orally, intracerebroventricularly, or intraperitoneally exhibited a potent antidepressant-like activity in the forced swim and tail suspension tests in naïve mice. YL increased the amount of cells expressing c-Fos, a marker for neuronal activity, in the dentate gyrus of the hippocampus. YL increased bromo-2′-deoxyuridine-positive cells and doublecortin expression in the dentate gyrus of the hippocampus, suggesting that YL enhanced the proliferation of hippocampal progenitor cells in vivo and in vitro. YL did not affect hippocampal mRNA and protein expression of BDNF, which is a regulatory factor of both neurogenesis and depression-like behavior. Intriguingly, YL suppressed activation of the hypothalamo-pituitary-adrenal axis by forced swim stress. Moreover, other aromatic amino acid-leucines, Phe-Leu and Trp-Leu, also exhibited antidepressant-like activities, suggesting that the structure of aromatic amino acid-leucine may be important for antidepressant activity. In addition, bovine milk casein-derived peptide, Tyr-Leu-Gly (YLG), an anxiolytic peptide, exhibited an antidepressant-like activity. Our findings demonstrate that YL exhibits an antidepressant-like effect, moderates the stress response, and induces hippocampal neuronal proliferation through a signal pathway independent of BDNF.

Combined exposure to dinotefuran and chronic mild stress counteracts the change of the emotional and monoaminergic neuronal activity induced by either exposure singly despite corticosterone elevation in mice

Dinotefuran (DIN) belongs to the neonicotinoids (NNs), a class of globally applied pesticides originally developed to exhibit selective toxicity in insects. However, several reports have suggested that NNs also exert neurotoxic effects in mammals. We previously demonstrated neurobehavioral effects of DIN on mice under non-stressful conditions. For further toxicity assessments in the present study, we investigated the effects of DIN on mice exposed to stressful conditions. After subacutely administering a no-observed-effect-level (NOEL) dose of DIN and/or chronic unpredictable mild stress (CUMS) to mice, we conducted three behavioral tests (i.e., open field test [OFT], tail suspension test [TST] and forced swimming test [FST]). In addition, serotonin (5-HT) and tryptophan hydroxylase 2 (TPH2) of the dorsal raphe nuclei (DRN) and median raphe nuclei (MRN) and tyrosine hydroxylase (TH) of the ventral tegmental area and substantia nigra (SN) were evaluated immunohistochemically. A NOEL dose of DIN or CUMS alone increased of the total distance in OFT, decreased or increased the immobility time in TST or FST, respectively, and increased the positive intensity of 5-HT and TPH2 in the DRN/MRN, and TH in the SN. These changes were suppressed under the conditions of combined exposure to DIN and CUMS, though the blood corticosterone level was increased depending on the blood DIN values and the presence of CUMS. The present study suggests the multifaceted toxicity of the neurotoxin DIN.

Resilient Phenotype in Chronic Mild Stress Paradigm Is Associated with Altered Expression Levels of miR-18a-5p and Serotonin 5-HT1a Receptor in Dorsal Part of the Hippocampus

Disturbed serotonergic signaling in the hippocampus observed in many individuals vulnerable to stress has been suggested as one of the primary factors contributing to the development of depression. However, little is known about the physiology of the brain in the resilient phenotype. Resilient subjects maintain a positive mood and psychological balance despite being under the stress influence. In our study, we generated stress-vulnerable and resilient rats by using a chronic mild stress (CMS) paradigm. Using different molecular approaches, we revealed that resilient animals exhibited a significantly decreased expression level of miR-18a-5p and, in the same time, an elevated level of 5-HT1AR in dorsal, but not ventral, part of the hippocampus. Described biochemical changes were not observed in animals behaviorally vulnerable to stress. Further, in vitro analysis showed that miR-18a-5p may be a negative epigenetic regulator of 5-HT1AR since the treatment of adult hippocampal neurons with miR-18a-5p mimic significantly lowered the expression level of mRNA encoding 5-HT1AR. Moreover, bioinformatic analysis of potential target genes expressed in the hippocampus and being regulated by miR-18a-5p showed that this microRNA may regulate biological processes, such as axonogenesis, which are important in the functioning of the hippocampus in both rats and humans. All these molecular features may contribute to serotonergic homeostatic balance at the level of serotonin turnover observed in hippocampi of resilient but not stress-vulnerable rats. Delineation of further molecular and biochemical markers underlying resilience to stress may contribute to the development of new antidepressant strategies which will restore resilient phenotype in depressed patients.

The Effect of Traditional Chinese Medicine Zhike-Houpu Herbal Pair on Depressive Behaviors and Hippocampal Serotonin 1A Receptors in Rats After Chronic Unpredictable Mild Stress

OBJECTIVE

Zhike-Houpu herbal pair (ZKHPHP) is a well-known Chinese medicine to treat gastrointestinal motility dysfunction. Recently, many researchers have found that some of the compounds of ZKHPHP such as meranzin hydrate and magnolol have antidepressant effects. However, little is known about the antidepressant mechanism of ZKHPHP. Therefore, the main aim of the study is to evaluate the antidepressant-like effects of ZKHPHP and its possible mechanism of action on 5-hydroxytryptamine receptor 1A (HTR1A) in the hippocampus CA1 region in rats exposed to chronic unpredictable mild stress.

METHODS

Male Sprague Dawley rats were randomly divided into the following six groups: normal, model, ZKHPHP (3 g/kg), ZKHPHP (10 g/kg), ZKHPHP (20 g/kg), and ZKHPHP (30 g/kg); n = 8 per group. We exposed the rats to chronic unpredictable mild stress and then assessed antidepressant-like effects of ZKHPHP by measuring weight change, observing the open-field test, and measuring sucrose water consumption. The antidepressant mechanism was examined by measuring the effect of ZKHPHP on HTR1A protein expression and HTR1A mRNA expression in the hippocampus CA1 region by using immunohistochemistry analysis, Western blotting, and real-time reverse transcription-polymerase chain reaction.

RESULTS

ZKHPHP (10 or 20 g/kg) reduced the incidence of depressive-like behaviors and increased HTR1A protein and HTR1A mRNA expression in the hippocampus CA1 in rats displaying depressive behavior, whereas ZKHPHP (3 or 30 g/kg) had no obvious effect on the measured depression indicators.

CONCLUSIONS

These data show that ZKHPHP has antidepressant-like effects based on a chronic unpredictable mild stress-induced depression model in rats. ZKHPHP may be attractive as an antidepressant because of its beneficial effects on depression and the absence of gastrointestinal dysregulation, which is a frequently observed unintended effect of many commonly used antidepressive medications.

Biological and Psychological Perspectives of Resilience: Is It Possible to Improve Stress Resistance?

The term “resilience” refers to the ability to adapt successfully to stress, trauma and adversity, enabling individuals to avoid stress-induced mental disorders such as depression, posttraumatic stress disorder (PTSD) and anxiety. Here, we review evidence from both animal models and humans that is increasingly revealing the neurophysiological and neuropsychological mechanisms that underlie stress susceptibility, as well as active mechanisms underlying the resilience phenotype. Ultimately, this growing understanding of the neurobiological mechanisms of resilience should result in the development of novel interventions that specifically target neural circuitry and brain areas that enhance resilience and lead to more effective treatments for stress-induced disorders. Stress resilience can be improved, but the outcomes and effects depend on the type of intervention and the species treated.

Serotonin and brain function: a tale of two receptors

Previous attempts to identify a unified theory of brain serotonin function have largely failed to achieve consensus. In this present synthesis, we integrate previous perspectives with new and older data to create a novel bipartite model centred on the view that serotonin neurotransmission enhances two distinct adaptive responses to adversity, mediated in large part by its two most prevalent and researched brain receptors: the 5-HT1A and 5-HT2A receptors. We propose that passive coping (i.e. tolerating a source of stress) is mediated by postsynaptic 5-HT1AR signalling and characterised by stress moderation. Conversely, we argue that active coping (i.e. actively addressing a source of stress) is mediated by 5-HT2AR signalling and characterised by enhanced plasticity (defined as capacity for change). We propose that 5-HT1AR-mediated stress moderation may be the brain's default response to adversity but that an improved ability to change one's situation and/or relationship to it via 5-HT2AR-mediated plasticity may also be important - and increasingly so as the level of adversity reaches a critical point. We propose that the 5-HT1AR pathway is enhanced by conventional 5-HT reuptake blocking antidepressants such as the selective serotonin reuptake inhibitors (SSRIs), whereas the 5-HT2AR pathway is enhanced by 5-HT2AR-agonist psychedelics. This bipartite model purports to explain how different drugs (SSRIs and psychedelics) that modulate the serotonergic system in different ways, can achieve complementary adaptive and potentially therapeutic outcomes.

Molecular bases of anorexia nervosa, bulimia nervosa and binge eating disorder: shedding light on the darkness

Eating-disorders (EDs) consequences to human health are devastating, involving social, mental, emotional, physical and life-threatening aspects, concluding on impairment and death in cases of extreme anorexia nervosa. It also implies that people suffering an ED need to find psychiatric and psychological help as soon as possible to achieve a fully physical and emotional recovery. Unfortunately, to date, there is a crucial lack of efficient clinical treatment to these disorders. In this review, we present an overview concerning the actual pharmacological and psychological treatments, the knowledge of cells, circuits, neuropeptides, neuromodulators and hormones in the human brain- and other organs- underlying these disorders, the studies in animal models and, finally, the genetic approaches devoted to face this challenge. We will also discuss the need for new perspectives, avenues and strategies to be developed in order to pave the way to novel and more efficient therapeutics.

Cytisine, a Partial Agonist of α4β2 Nicotinic Acetylcholine Receptors, Reduced Unpredictable Chronic Mild Stress-Induced Depression-Like Behaviors

Cytisine (CYT), a partial agonist of α4β2-nicotinic receptors, has been used for antidepressant efficacy in several tests. Nicotinic receptors have been shown to be closely associated with depression. However, little is known about the effects of CYT on the depression. In the present study, a mouse model of depression, the unpredictable chronic mild stress (UCMS), was used to evaluate the activities of CYT. UCMS caused significant depression-like behaviors, as shown by the decrease of total distances in open field test, and the prolonged duration of immobility in tail suspension test and forced swimming test. Treatment with CYT for two weeks notably relieved the depression-like behaviors in the UCMS mice. Next, proteins related to depressive disorder in the brain region of hippocampus and amygdala were analyzed to elucidate the underlying mechanisms of CYT. CYT significantly reversed the decreases of 5-HT1A, BDNF, and mTOR levels in the hippocampus and amygdala. These results imply that CYT may act as a potential anti-depressant in the animals under chronic stress.

Multiple Nicotinic Acetylcholine Receptor Subtypes in the Mouse Amygdala Regulate Affective Behaviors and Response to Social Stress

Electrophysiological and neurochemical studies implicate cholinergic signaling in the basolateral amygdala (BLA) in behaviors related to stress. Both animal studies and human clinical trials suggest that drugs that alter nicotinic acetylcholine receptor (nAChR) activity can affect behaviors related to mood and anxiety. Clinical studies also suggest that abnormalities in cholinergic signaling are associated with major depressive disorder, whereas pre-clinical studies have implicated both β2 subunit-containing (β2*) and α7 nAChRs in the effects of nicotine in models of anxiety- and depression-like behaviors. We therefore investigated whether nAChR signaling in the amygdala contributes to stress-mediated behaviors in mice. Local infusion of the non-competitive non-selective nAChR antagonist mecamylamine or viral-mediated downregulation of the β2 or α7 nAChR subunit in the amygdala all induced robust anxiolytic- and antidepressant-like effects in several mouse behavioral models. Further, whereas α7 nAChR subunit knockdown was somewhat more effective at decreasing anxiety-like behavior, only β2 subunit knockdown decreased resilience to social defeat stress and c-fos immunoreactivity in the BLA. In contrast, α7, but not β2, subunit knockdown effectively reversed the effect of increased ACh signaling in a mouse model of depression. These results suggest that signaling through β2* nAChRs is essential for baseline excitability of the BLA, and a decrease in signaling through β2 nAChRs alters anxiety- and depression-like behaviors even in unstressed animals. In contrast, stimulation of α7 nAChRs by acetylcholine may mediate the increased depression-like behaviors observed during the hypercholinergic state observed in depressed individuals.

Effects of Dopamine and Serotonin Systems on Modulating Neural Oscillations in Hippocampus-Prefrontal Cortex Pathway in Rats

Theta and gamma oscillations are believed to play an important role in cognition and memory, and their phase coupling facilitates the information transmission in hippocampal-cortex network. In a rat model of chronic stress, the phase coupling of both theta and gamma oscillations between ventral hippocampal CA1 (vCA1) and medial prefrontal cortex (mPFC) was found to be disrupted, which was associated with the impaired synaptic plasticity in the pathway. However, little was known about the mechanisms underlying the process. In order to address this issue, both dopamine and serotonin as monoaminergic neurotransmitters were involved in this study, since they were crucial factors in pathological basis of depressive disorder. Local field potentials (LFPs) were recorded simultaneously at both vCA1 and mPFC regions under anesthesia, before and after the injection of dopamine D1 receptor antagonist and 5-HT1A receptor agonist, respectively. The results showed that the blockage of D1 receptor could lead to depression-like decrement on theta phase coupling. In addition, the activation of 5-HT1A receptor enhanced vCA1-mPFC coupling on gamma oscillations, and attenuated CA1 theta-fast gamma cross frequency coupling. These data suggest that the theta phase coupling between vCA1 and mPFC may be modulated by dopamine system that is an underlying mechanism of the cognitive dysfunction in depression. Besides, the serotonergic system is probably involved in the regulation of gamma oscillations coupling in vCA1-mPFC network.

Mood and anxiety regulation by nicotinic acetylcholine receptors: A potential pathway to modulate aggression and related behavioral states

The co-morbidity between smoking and mood disorders is striking. Preclinical and clinical studies of nicotinic effects on mood, anxiety, aggression, and related behaviors, such as irritability and agitation, suggest that smokers may use the nicotine in tobacco products as an attempt to self-medicate symptoms of affective disorders. The role of nicotinic acetylcholine receptors (nAChRs) in circuits regulating mood and anxiety is beginning to be elucidated in animal models, but the mechanisms underlying the effects of nicotine on aggression-related behavioral states (ARBS) are still not understood. Clinical trials of nicotine or nicotinic medications for neurological and psychiatric disorders have often found effects of nicotinic medications on ARBS, but few trials have studied these outcomes systematically. Similarly, the increase in ARBS resulting from smoking cessation can be resolved by nicotinic agents, but the effects of nicotinic medications on these types of mental states and behaviors in non-smokers are less well understood. Here we review the literature on the role of nAChRs in regulating mood and anxiety, and subsequently on the closely related construct of ARBS. We suggest avenues for future study to identify how nAChRs and nicotinic agents may play a role in these clinically important areas. This article is part of the Special Issue entitled 'The Nicotinic Acetylcholine Receptor: From Molecular Biology to Cognition'.