Chronic treatment with imipramine or mirtazapine antagonizes stress- and FG7142-induced increase in cortical norepinephrine output in freely moving rats

Mangosteen Pericarp and Its Bioactive Xanthones: Potential Therapeutic Value in Alzheimer's Disease, Parkinson's Disease, and Depression with Pharmacokinetic and Safety Profiles

Alzheimer’s disease (AD), Parkinson’s disease (PD), and depression are growing burdens for society globally, partly due to a lack of effective treatments. Mangosteen (Garcinia mangostana L.,) pericarp (MP) and its xanthones may provide therapeutic advantages for these disorders. In this review, we discuss potential therapeutic value of MP-derived agents in AD, PD, and depression with their pharmacokinetic and safety profiles. MP-derived agents have shown multifunctional effects including neuroprotective, antioxidant, and anti-neuroinflammatory actions. In addition, they target specific disease pathologies, such as amyloid beta production and deposition as well as cholinergic dysfunction in AD; α-synuclein aggregation in PD; and modulation of monoamine disturbance in depression. Particularly, the xanthone derivatives, including α-mangostin and γ-mangostin, exhibit potent pharmacological actions. However, low oral bioavailability and poor brain penetration may limit their therapeutic applications. These challenges can be overcome in part by administering as a form of MP extract (MPE) or using specific carrier systems. MPE and α-mangostin are generally safe and well-tolerated in animals. Furthermore, mangosteen-based products are safe for humans. Therefore, MPE and its bioactive xanthones are promising candidates for the treatment of AD, PD, and depression. Further studies including clinical trials are essential to decipher their efficacy, and pharmacokinetic and safety profiles in these disorders.

Mirtazapine Reduces Adipocyte Hypertrophy and Increases Glucose Transporter Expression in Obese Mice

Simple Summary

Mirtazapine, a tetracyclic antidepressant, acts through noradrenergic and specific serotonergic systems. Consequently, it was recently applied in major depressive disorder treatment. Moreover, because mirtazapine may have effective glucose control function, its mechanism of action warrants further investigation. In our study, we examined how mirtazapine affects metabolic parameters, insulin profiles, glucose metabolism, and obesity changes in high-fat diet-fed C57BL6/J mice. Our results indicated that compared with untreated mice, mirtazapine-treated obese mice had lower insulin levels, daily food efficiency, body weight, serum triglyceride levels, aspartate aminotransferase levels, liver and epididymal fat pad weight, and fatty acid regulation marker expression. Moreover, the blood glucose levels and area under the curve for glucose levels observed over a 120 min assessment period were lower in the treated mice, but the insulin sensitivity and glucose transporter 4 expression levels were higher in these mice. They also demonstrated a considerable decrease in fatty liver scores and mean fat cell size in the epididymal white adipose tissue, paralleling adenosine monophosphate (AMP)-activated protein kinase expression activation. In conclusion, mirtazapine administration may alleviate type 2 diabetes mellitus with hyperglycemia.

Abstract

Metabolic syndrome is known to engender type 2 diabetes as well as some cardiac, cerebrovascular, and kidney diseases. Mirtazapine—an atypical second-generation antipsychotic drug with less severe side effects than atypical first-generation antipsychotics—may have positive effects on blood glucose levels and obesity. In our executed study, we treated male high-fat diet (HFD)-fed C57BL/6J mice with mirtazapine (10 mg/kg/day mirtazapine) for 4 weeks to understand its antiobesity effects. We noted these mice to exhibit lower insulin levels, daily food efficiency, body weight, serum triglyceride levels, aspartate aminotransferase levels, liver and epididymal fat pad weight, and fatty acid regulation marker expression when compared with their counterparts (i.e., HFD-fed control mice). Furthermore, we determined a considerable drop in fatty liver scores and mean fat cell size in the epididymal white adipose tissue in the treated mice, corresponding to AMP-activated protein kinase expression activation. Notably, the treated mice showed lower glucose tolerance and blood glucose levels, but higher glucose transporter 4 expression. Overall, the aforementioned findings signify that mirtazapine could reduce lipid accumulation and thus prevent HFD-induced increase in body weight. In conclusion, mirtazapine may be useful in body weight control and antihyperglycemia therapy.

Garcinia mangostana Linn displays antidepressant-like and pro-cognitive effects in a genetic animal model of depression: a bio-behavioral study in the Flinders Sensitive Line rat

There is abundant evidence for both disorganized redox balance and cognitive deficits in major depressive disorder (MDD). Garcinia mangostana Linn (GM) has anti-oxidant activity. We studied the antidepressant-like and pro-cognitive effects of raw GM rind in Flinders Sensitive Line (FSL) rats, a genetic model of depression, following acute and chronic treatment compared to a reference antidepressant, imipramine (IMI). The chemical composition of the GM extract was analysed for levels of α- and γ-mangostin. The acute dose-dependent effects of GM (50, 150 and 200 mg/kg po), IMI (20 mg/kg po) and vehicle were determined in the forced swim test (FST) in FSL rats, versus Flinders Resistant Line (FRL) control rats. Locomotor testing was conducted using the open field test (OFT). Using the most effective dose above coupled with behavioral testing in the FST and cognitive assessment in the novel object recognition test (nORT), a fixed dose 14-day treatment study of GM was performed and compared to IMI- (20 mg/kg/day) and vehicle-treated animals. Chronic treated animals were also assessed with respect to frontal cortex and hippocampal monoamine levels and accumulation of malondialdehyde. FSL rats showed significant cognitive deficits and depressive-like behavior, with disordered cortico-hippocampal 5-hydroxyindole acetic acid (5-HIAA) and noradrenaline (NA), as well as elevated hippocampal lipid peroxidation. Acute and chronic IMI treatment evoked pronounced antidepressant-like effects. Raw GM extract contained 117 mg/g and 11 mg/g α- and γ-mangostin, respectively, with acute GM demonstrating antidepressant-like effects at 50 mg/kg/day. Chronic GM (50 mg/kg/d) displayed significant antidepressant- and pro-cognitive effects, while demonstrating parity with IMI. Both behavioral and monoamine assessments suggest a more prominent serotonergic action for GM as opposed to a noradrenergic action for IMI, while both IMI and GM reversed hippocampal lipid peroxidation in FSL animals. Concluding, FSL rats present with cognitive deficits and depressive-like behaviors that are reversed by acute and chronic GM treatment, similar to that of IMI.

Impact of anxiety on prefrontal cortex encoding of cognitive flexibility

Anxiety often is studied as a stand-alone construct in laboratory models. But in the context of coping with real-life anxiety, its negative impacts extend beyond aversive feelings and involve disruptions in ongoing goal-directed behaviors and cognitive functioning. Critical examples of cognitive constructs affected by anxiety are cognitive flexibility and decision making. In particular, anxiety impedes the ability to shift flexibly between strategies in response to changes in task demands, as well as the ability to maintain a strategy in the presence of distractors. The brain region most critically involved in behavioral flexibility is the prefrontal cortex (PFC), but little is known about how anxiety impacts PFC encoding of internal and external events that are critical for flexible behavior. Here we review animal and human neurophysiological and neuroimaging studies implicating PFC neural processing in anxiety-induced deficits in cognitive flexibility. We then suggest experimental and analytical approaches for future studies to gain a better mechanistic understanding of impaired cognitive inflexibility in anxiety and related disorders.

Long-Term Citalopram Treatment Alters the Stress Responses of the Cortical Dopamine and Noradrenaline Systems: the Role of Cortical 5-HT1A Receptors

BACKGROUND

Cortical dopamine and noradrenaline are involved in the stress response. Citalopram, a selective serotonin reuptake inhibitor, has direct and indirect effects on the serotonergic system. Furthermore, long-term treatment with citalopram affects the dopamine and noradrenaline systems, which could contribute to the therapeutic action of antidepressants.

METHODS

The effects of long-term treatment with citalopram on the responses of the dopamine and noradrenaline systems in the rat prefrontal cortex to acute handling stress were evaluated using in vivo microdialysis.

RESULTS

Acute handling stress increased dopamine and noradrenaline levels in the prefrontal cortex. The dopamine and noradrenaline responses were suppressed by local infusion of a 5-HT1A receptor agonist, 7-(Dipropylamino)-5,6,7,8-tetrahydronaphthalen-1-ol;hydrobromide, into the prefrontal cortex. The dopamine response was abolished by long-term treatment with citalopram, and the abolished dopamine response was reversed by local infusion of a 5-HT1A receptor antagonist, (Z)-but-2-enedioic acid;N-[2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl]-N-pyridin-2-ylcyclohexanecarboxamide into the prefrontal cortex. On the other hand, long-term treatment with citalopram reduced the basal noradrenaline levels (approximately 40% of the controls), but not the basal dopamine levels. The noradrenaline response was maintained despite the low basal noradrenaline levels. Signaling from the 5-HT1A receptors and α2-adrenoceptors was not involved in the decrease in the basal noradrenaline levels but partially affected the noradrenaline response.

CONCLUSIONS

Chronic citalopram treatment differentially suppresses the dopamine and noradrenaline systems in the prefrontal cortex, and the dopamine stress response was preferentially controlled by upregulating 5-HT1A receptor signaling. Our findings provide insight into how antidepressants modulate the dopamine and noradrenaline systems to overcome acute stress.

Behavioural, neurochemical and neuroendocrine effects of the endogenous β-carboline harmane in fear-conditioned rats

The putative endogenous imidazoline binding site ligand harmane enhances neuronal activation in response to psychological stress and alters behaviour in animal models of anxiety and antidepressant efficacy. However, the neurobiological mechanisms underlying harmane's psychotropic effects are poorly understood. We investigated the effects of intraperitoneal injection of harmane (2.5 and 10 mg/kg) on fear-conditioned behaviour, hypothalamo-pituitary-adrenal axis activity, and monoaminergic activity within specific fear-associated areas of the rat brain. Harmane had no significant effect on the duration of contextually induced freezing or 22 kHz ultrasonic vocalisations and did not alter the contextually induced suppression of motor activity, including rearing. Harmane reduced the duration of rearing and tended to increase freezing in non-fear-conditioned controls, suggesting potential sedative effects. Harmane increased plasma ACTH and corticosterone concentrations, and serotonin (in hypothalamus, amygdaloid cortex, prefrontal cortex and hippocampus) and noradrenaline (prefrontal cortex) content, irrespective of fear-conditioning. Furthermore, harmane reduced dopamine and serotonin turnover in the PFC and hypothalamus, and serotonin turnover in the amygdaloid cortex in both fear-conditioned and non-fear-conditioned rats. In contrast, harmane increased dopamine and noradrenaline content and reduced dopamine turnover in the amygdala of fear-conditioned rats only, suggesting differential effects on catecholaminergic transmission in the presence and absence of fear. The precise mechanism(s) mediating these effects of harmane remain to be determined but may involve its inhibitory action on monoamine oxidases. These findings support a role for harmane as a neuromodulator, altering behaviour, brain neurochemistry and neuroendocrine function.

Mirtazapine inhibits tumor growth via immune response and serotonergic system

To study the tumor inhibition effect of mirtazapine, a drug for patients with depression, CT26/luc colon carcinoma-bearing animal model was used. BALB/c mice were randomly divided into six groups: two groups without tumors, i.e. wild-type (no drug) and drug (mirtazapine), and four groups with tumors, i.e. never (no drug), always (pre-drug, i.e. drug treatment before tumor inoculation and throughout the experiment), concurrent (simultaneously tumor inoculation and drug treatment throughout the experiment), and after (post-drug, i.e. drug treatment after tumor inoculation and throughout the experiment). The “psychiatric” conditions of mice were observed from the immobility time with tail suspension and spontaneous motor activity post tumor inoculation. Significant increase of serum interlukin-12 (sIL-12) and the inhibition of tumor growth were found in mirtazapine-treated mice (always, concurrent, and after) as compared with that of never. In addition, interferon-γ level and immunocompetent infiltrating CD4+/CD8+ T cells in the tumors of mirtazapine-treated, tumor-bearing mice were significantly higher as compared with that of never. Tumor necrosis factor-α (TNF-α) expressions, on the contrary, are decreased in the mirtazapine-treated, tumor-bearing mice as compared with that of never. Ex vivo autoradiography with [¹²³I]ADAM, a radiopharmaceutical for serotonin transporter, also confirms the similar results. Notably, better survival rates and intervals were also found in mirtazapine-treated mice. These findings, however, were not observed in the immunodeficient mice. Our results suggest that tumor growth inhibition by mirtazapine in CT26/luc colon carcinoma-bearing mice may be due to the alteration of the tumor microenvironment, which involves the activation of the immune response and the recovery of serotonin level.

Chronic cocaine self-administration attenuates the anxiogenic-like and stress potentiating effects of the benzodiazepine inverse agonist, FG 7142

Stress is a well-known risk factor in relapse to drug abuse. Several forms of stress in animals have been used with varied degrees of success to elicit reinstatement of drug-seeking after chronic drug self-administration. Here, we tested the ability of the benzodiazepine (BZ) inverse agonist, FG 7142, to elicit anxiety-like behavior and potentiate stress responses in rats as measured by standard behavioral and hormonal indices and for its ability to affect reinstatement of cocaine-seeking in rats with a prior history of cocaine self-administration. FG 7142 elicited anxiety-like behavior on the elevated plus maze (EPM) in cocaine-naïve rats, and cocaine-naïve rats injected with FG 7142 exhibited increased plasma corticosterone levels following EPM exposure. However, in animals with a history of cocaine self-administration, FG 7142 failed to affect elevated plus maze performance and did not affect plasma corticosterone response to the EPM. Furthermore, FG 7142 failed to reinstate cocaine-seeking, nor did it alter conditioned cue-induced reinstatement. These data indicate that the anxiety-related and stress potentiating qualities of BZ inverse agonism are attenuated in cocaine-experienced animals and do not lead to reinstatement of cocaine-seeking.

Chronic vagus nerve stimulation induces neuronal plasticity in the rat hippocampus

Vagus nerve stimulation (VNS) is used to treat pharmacotherapy-resistant epilepsy and depression. However, the mechanisms underlying the therapeutic efficacy of VNS remain unclear. We examined the effects of VNS on hippocampal neuronal plasticity and behaviour in rats. Cell proliferation in the hippocampus of rats subjected to acute (3 h) or chronic (1 month) VNS was examined by injection of bromodeoxyuridine (BrdU) and immunohistochemistry. Expression of doublecortin (DCX) and brain-derived neurotrophic factor (BDNF) was evaluated by immunofluorescence staining. The dendritic morphology of DCX+ neurons was measured by Sholl analysis. Our results show that acute VNS induced an increase in the number of BrdU+ cells in the dentate gyrus that was apparent 24 h and 3 wk after treatment. It also induced long-lasting increases in the amount of DCX immunoreactivity and in the number of DCX+ neurons. Neither the number of BrdU+ cells nor the amount of DCX immunoreactivity was increased 3 wk after the cessation of chronic VNS. Chronic VNS induced long-lasting increases in the amount of BDNF immunoreactivity and the number of BDNF+ cells as well as in the dendritic complexity of DCX+ neurons in the hippocampus. In contrast to chronic imipramine treatment, chronic VNS had no effect on the behaviour of rats in the forced swim or elevated plus-maze tests. Both chronic and acute VNS induced persistent changes in hippocampal neurons that may play a key role in the therapeutic efficacy of VNS. However, these changes were not associated with evident behavioural alterations characteristic of an antidepressant or anxiolytic action.

Mechanisms of the blunting of the sympatho-adrenal response: a theory

Development of therapeutic measures to reduce the risk of potentially fatal episodes of hypoglycaemia and thus to achieve the full benefits of intensive insulin therapy in diabetic patients requires a complete understanding of the multi-factorial mechanisms for repeated hypoglycaemia-induced blunting of the sympatho-adrenal response (BSAR). After critical analysis of the hypotheses, this review paper suggests a heuristic theory. This theory suggests two mechanisms for the BSAR, each involving a critical role for the central brain noradrenergic system. Furthermore, this theory also suggests that the lateral hypothalamus (LH) plays an important role in this phenomenon. Within the framework of this theory, explanations for 1) sexual dimorphism in the adrenomedullary response (AR), 2) dissociation in the blunting of the AR and the sympathetic response (SR) and 3) antecedent exercise-induced blunting of the AR are provided. In addition, habituation of orexin-A neurons is suggested to cause defective awakening. Moreover, potential therapeutics measures have been also suggested that will reduce or prevent severe episodes of hypoglycaemia.

Stressors can affect immobility time and response to imipramine in the rat forced swim test

We subjected Wistar rats to the forced swim test (FST) to compare the effects of two doses of imipramine in physically stressed rats (P: unavoidable electric footshocks), emotionally stressed rats (E: odors), or non-stressed rats (C). Stress or control sessions lasted 35 days. Drug treatments began on day 21 and continued for the next 14 days. E rats were placed for 10 min, once per day for 35 days, in a small non-movement-restricting cage impregnated with urine collected from a P rat. E and P rats exhibited opposite changes in locomotion. After 21 days of stress sessions, P rats displayed the longest immobility times in the FST, followed by E rats. In the P group, on day 7 of treatment (day 28 of the study), imipramine (2.5 mg/kg) reduced immobility time to baseline values. In the E group, immobility time decreased only after 14 days of treatment with the low imipramine dose. The high dose of imipramine (5.0 mg/kg) reduced immobility time at day 7 of treatment in all groups. In conclusion, physical and emotional stress similarly increased immobility time in the FST, but emotional stress appears to be more resistant to imipramine treatment.

Pharmacology of the beta-carboline FG-7,142, a partial inverse agonist at the benzodiazepine allosteric site of the GABA A receptor: neurochemical, neurophysiological, and behavioral effects

Given the well-established role of benzodiazepines in treating anxiety disorders, beta-carbolines, spanning a spectrum from full agonists to full inverse agonists at the benzodiazepine allosteric site for the GABA(A) receptor, can provide valuable insight into the neural mechanisms underlying anxiety-related physiology and behavior. FG-7,142 is a partial inverse agonist at the benzodiazepine allosteric site with its highest affinity for the alpha1 subunit-containing GABA(A) receptor, although it is not selective. FG-7,142 also has its highest efficacy for modulation of GABA-induced chloride flux mediated at the alpha1 subunit-containing GABA(A) receptor. FG-7,142 activates a recognized anxiety-related neural network and interacts with serotonergic, dopaminergic, cholinergic, and noradrenergic modulatory systems within that network. FG-7,142 has been shown to induce anxiety-related behavioral and physiological responses in a variety of experimental paradigms across numerous mammalian and non-mammalian species, including humans. FG-7,142 has proconflict actions across anxiety-related behavioral paradigms, modulates attentional processes, and increases cardioacceleratory sympathetic reactivity and neuroendocrine reactivity. Both acute and chronic FG-7,142 treatment are proconvulsive, upregulate cortical adrenoreceptors, decrease subsequent actions of GABA and beta-carboline agonists, and increase the effectiveness of subsequent GABA(A) receptor antagonists and beta-carboline inverse agonists. FG-7,142, as a partial inverse agonist, can help to elucidate individual components of full agonism of benzodiazepine binding sites and may serve to identify the specific GABA(A) receptor subtypes involved in specific behavioral and physiological responses.

Presynaptic metabotropic glutamate and GABAB receptors

Glutamate and GABA, the two most abundant neurotransmitters in the mammalian central nervous system, can act on metabotropic receptors that are structurally quite dissimilar from those targeted by most other neurotransmitters/modulators. Accordingly, metabotropic glutamate receptors (mGluRs) and GABA(B) receptors (GABA(B)Rs) are classified as members of family 3 (or family C) of G protein-coupled receptors. On the other hand, mGluRs and GABA(B)Rs exhibit pronounced and partly unresolved differences between each other. The most intriguing difference is that mGluRs exist as multiple pharmacologically as well as structurally distinct subtypes, whereas, in the case of GABA(B)Rs, molecular biologists have so far identified only one structurally distinct heterodimeric complex whose few variants seem unable to explain the pharmacological heterogeneity of GABA(B)Rs observed in many functional studies. Both mGluRs and GABA(B)Rs can be localized on axon terminals of different neuronal systems as presynaptic autoreceptors and heteroreceptors modulating the exocytosis of various transmitters.

Early life stress causes FG-7142-induced corticolimbic dysfunction in adulthood

Maternal separation (MS) during the neonatal period enhances stress responsivity in adulthood. The medial prefrontal cortex (mPFC) and the basolateral amygdala (BLA) are involved in coordinating various stress responses. Evidence indicates that MS reduces benzodiazepine and GABA(A) receptor expression in these regions, although their effects on neuronal function in the mPFC and the BLA remain unknown. The present study was conducted to assess the effects of MS on neuronal activity in the mPFC and BLA in response to the benzodiazepine receptor partial inverse agonist N-methyl-beta-carboline-3-carboxamide (FG-7142). Rat pups were subjected to MS (360 min), brief handling (H; 15 min) or standard animal facility rearing (AFR) on postnatal days 2-14. In adult males, in vivo electrophysiology under isoflurane anesthesia was used to conduct acute recordings of extracellular unit activity in response to systemic FG-7142 administration. Animals subjected to H showed significantly increased basal mPFC activity compared to MS and AFR animals. There were no differences in basal BLA activity between the early rearing groups. In response to FG-7142, MS animals showed significantly attenuated mPFC activity compared to H animals and a nonsignificant trend towards attenuated mPFC activity compared to AFR animals. In contrast to mPFC, MS animals showed significantly potentiated FG-7142-induced activity in the BLA, compared to both H and AFR animals. These findings indicate that MS induces functionally relevant alterations in corticolimbic GABA(A) receptor signaling. Given that FG-7142 mimics several behavioral and physiological effects of stress, these results may also model stress-induced corticolimbic dysfunction caused by early life stress.

Influence of caffeine ingestion on perceived mood states, concentration, and arousal levels during a 75-min university lecture

This investigation aimed to assess the effect of a caffeine supplement on perceived mood state, concentration, and arousal during a 75-min university lecture. Methods. This randomized, blind, cross-over design investigation ran over a course of 2 consecutive weeks. During week 1, 10 third-year Human Movement and Exercise Science students were assigned to either a caffeine- or placebo-supplemented group and were subsequently required to attend a 75-min exercise rehabilitation lecture. Seven days later, students were assigned to the opposite supplementation group before attending a second follow-on lecture, equal in duration to that of week 1. At the conclusion of each lecture, students were required to complete a mood perception questionnaire to assess the perceived level of mood state, concentration, and arousal during the lecture. The results showed that after caffeine consumption, students perceived themselves to be significantly more awake, clear minded, energetic, alert, and anxious (P < 0.05). Additionally, students also felt they were better able to concentrate and had a greater level of arousal than when the placebo was consumed (P < 0.05). In conclusion, the results of this investigation show that university students report enhanced perceptual feelings of behavior and mood state when a low dose of caffeine is consumed 60 min prior to a 75-min academic lecture.

Vagus nerve stimulation increases norepinephrine concentration and the gene expression of BDNF and bFGF in the rat brain

Vagus nerve stimulation therapy, effective for treatment-resistant epilepsy, has recently been approved also for treatment-resistant depression; nevertheless, the molecular mechanism(s) underlying its therapeutic action remains unclear. Given that neurotrophic factors and monoamines could play a crucial role in the pathophysiology of depression, we tested whether vagus nerve stimulation increases the expression of brain-derived neurotrophic factor, fibroblast growth factor, and nerve growth factor as well as the concentration of norepinephrine in the rat brain. Rats were implanted with a vagus nerve stimulator device and the effects of acute stimulation were evaluated on the growth factors mRNA levels and norepinephrine concentration by ribonuclease protection assay and microdialysis, respectively. We found that acute vagus nerve stimulation increased the expression of brain-derived neurotrophic factor and fibroblast growth factor in the hippocampus and cerebral cortex, decreased the abundance of nerve growth factor mRNA in the hippocampus, and, similar to the antidepressant drug venlafaxine, increased the norepinephrine concentration in the prefrontal cortex. This study demonstrates that acute vagus nerve stimulation triggers neurochemical and molecular changes in the rat brain involving neurotransmitters and growth factors known to play a crucial role in neuronal trophism. These new findings contribute to the elucidation of the molecular mechanisms underlying the therapeutic actions of vagus nerve stimulation in both treatment-resistant depression and epilepsy.

Systemic administration of the benzodiazepine receptor partial inverse agonist FG-7142 disrupts corticolimbic network interactions

The medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) coordinate various stress responses. Although the effects of stressors on mPFC and BLA activity have been previously examined, it remains unclear to what extent stressors affect functional interactions between these regions. In vivo electrophysiology in the anesthetized rat was used to examine mPFC and BLA activity simultaneously in response to FG-7142, a benzodiazepine receptor partial inverse agonist that mimics various stress responses, in an attempt to model the effects of stressors on corticolimbic functional connectivity. Extracellular unit and local field potential (LFP) recordings, using multielectrode arrays positioned in mPFC and BLA, were conducted under basal conditions and in response to systemic FG-7142 administration. This drug increased mPFC and BLA unit firing at the lowest dose tested, whereas higher doses of FG-7142 decreased various burst firing parameters in both regions. Moreover, LFP power was attenuated at lower (<1 Hz) and potentiated at higher frequencies in mPFC (1-12 Hz) and BLA (4-8 Hz). Interestingly, FG-7142 diminished synchronized unit firing, both within and between mPFC and BLA. Finally, FG-7142 decreased LFP synchronization between these regions. In a separate group of animals, pretreatment with the selective benzodiazepine receptor antagonist flumazenil blocked the changes in burst firing, LFP power and synchronized activity induced by FG-7142, confirming direct benzodiazepine receptor-mediated effects. These results indicate that FG-7142 disrupts corticolimbic network interactions via benzodiazepine receptor partial inverse agonism. Perturbation of mPFC-BLA functional connectivity induced by FG-7142 may provide a useful model of corticolimbic dysfunction induced by stressors.

Effects of the vasopressin (V1b) receptor antagonist, SSR149415, and the corticotropin-releasing factor 1 receptor antagonist, SSR125543, on FG 7142-induced increase in acetylcholine and norepinephrine release in the rat

Arginine vasopressin and corticotropin-releasing factor are two neuroactive peptides that regulate hypothalamic-pituitary-axis and associated stress response. While the potential antidepressant and anxiolytic profiles of corticotropin-releasing factor 1 antagonists have been well studied, the concept of blockade of vasopressin system as another approach for the treatment of emotional processes has only been made available recently by the synthesis of the first non-peptide antagonist at the V1b receptor, SSR149415. In the present study SSR149415 has been compared with the corticotropin-releasing factor 1 antagonist SSR125543 and with anxiolytic and antidepressant drugs on the response of hippocampal cholinergic and cortical noradrenergic systems to the anxiogenic benzodiazepine receptor inverse agonist FG 7142. Acute (0.3-10 mg/kg, i.p.) and long-term administration (10 mg/kg, i.p., 21 days) of SSR149415 and SSR125543 reduced the FG 7142-induced increase in extracellular concentrations of acetylcholine in the hippocampus of anesthetized rats measured by microdialysis. By contrast acute and long-term administration of SSR149415 failed to reduce the FG 7142-induced increase in the release of norepinephrine in the cortex of freely moving rats. The present results demonstrate that the two compounds have similar profiles in a model of activation by an anxiogenic drug of the hippocampal cholinergic system and they suggest that SSR149415 and SSR125543 may have anti-stress anxiolytic and antidepressant effects via a mechanism of action different from classical benzodiazepine ligands and noradrenergic antidepressants.

Stress-induced sensitization of the limbic system in ovariectomized rats is partly restored by cyclic 17beta-estradiol administration

Chronic stress induces neurobiological alterations which have consequences for subsequent stress handling. In the current experiment, ovariectomized rats were subjected daily to a stressor for 21 days. Thereafter, the rats were treated for 21 days with 17beta-estradiol benzoate (10 microg/250 g, once every 4 days) or mirtazapine (10 mg/kg, daily). In this way, we were able to evaluate the ability of these compounds to reverse chronic stress-induced changes in the activity of the limbic system. After 21 days of recovery and treatment, the rats were re-exposed to the adverse environment of the initial stressor and perfused 2 h later. Ovariectomized rats displayed increased numbers of c-Fos-positive nuclei, after re-exposure to the stressor, in the paraventricular nucleus of the hypothalamus, dentate gyrus, medial prefrontal cortex and central and medial amygdala. Cyclic estradiol treatment attenuated the sensitization of the paraventricular nucleus and central amygdala. Mirtazapine increased the number of c-Fos-positive nuclei in the central amygdala and dentate gyrus. Long-term transcriptional changes induced by chronic stress were determined with DeltaFosB immunoreactivity. The medial prefrontal cortex showed an increased number of DeltaFosB-positive nuclei after chronic stress and this was not affected by estradiol or mirtazapine administration during recovery. In conclusion, cyclic estradiol administration reversed chronic stress-induced sensitization in the limbic system, the paraventricular nucleus and central amygdala of female rats, output regions of the limbic system involved in fear responses. Mirtazapine did not achieve this reversal of stress-induced aberrations in the limbic system after 21 days of treatment.

Nicotine has a permissive role on the activation of metabotropic glutamate 5 receptors coexisting with nicotinic receptors on rat hippocampal noradrenergic nerve terminals

The existence of metabotropic glutamate receptors (mGluRs) on hippocampal noradrenergic nerve terminals and their interaction with coexisting nicotinic acetylcholine receptors (nAChRs) were investigated in superfused rat synaptosomes using [(3)H]-noradrenaline ([(3)H]-NA) release as a readout. The selective agonist of group I mGluRs, (S)-3,5-dihydroxyphenylglycine (DHPG), inactive on its own, acquired ability to release [(3)H]-NA when added together with (-)-nicotine. The effect of DHPG was prevented by 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a selective antagonist of mGluR5, but not by 7-(hydroxyimino)cyclopropane[b]chromen-1-carboxylate ethyl ester (CPCCOEt), selective antagonist of mGluR1. The [(3)H]-NA release evoked by (-)-nicotine plus DHPG was totally abrogated by the nAChR antagonist mecamylamine. Veratrine mimicked the permissive role of (-)-nicotine on the activation of mGluR5 mediating [(3)H]-NA release. The mGluR5-mediated component of the [(3)H]-NA release provoked by DHPG plus (-)-nicotine was blocked by xestospongin C, a selective antagonist of inositoltrisphosphate (IP(3)) receptors. It can be concluded that (i) release-enhancing mGluRs of subtype 5 exist on hippocampal noradrenergic axon terminals; (ii) activation of mGluR5 to mediate IP(3)-dependent NA release requires activation of depolarizing nAChRs coexisting on the same terminals.

Splenic norepinephrine depletion following acute stress suppresses in vivo antibody response

Exposure to an intense acute stressor immediately following immunization leads to a reduction in anti-KLH IgM, IgG, and IgG2a, but not IgG1. Stress also depletes splenic norepinephrine (NE) content. Immunization during pharmacological (alpha-methyl-p-tyrosine) or stress-induced splenic NE depletion results in antibody suppression similar to that found in rats immunized prior to stressor exposure. Prevention of splenic NE depletion during stress by tyrosine, but not pharmacological elevation (mirtazapine) of NE, resulted in normal antibody responses. These data support the hypothesis that splenic NE depletion is necessary and sufficient for stress-induced suppression of antibody to a T-cell dependent antigen.

Chronic administration of the SSRI fluvoxamine markedly and selectively reduces the sensitivity of cortical serotonergic neurons to footshock stress

We have evaluated, with the use of vertical microdialysis, the effects of fluvoxamine, a selective serotonin reuptake inhibitor (SSRI) on the increase in serotonin and norepinephrine output elicited in rats prefrontal cortex by exposure to footshock stress. Exposure to footshock stress induced a marked increase in the cortical extracellular concentration of both serotonin and norepinephrine (+70% and +100%, respectively) in control rats. Long term, but not acute administration of fluvoxamine (10 mg/kg, i.p. once a days for 21 days) completely antagonized the stress induced increase in cortical serotonin extracellular concentration, while failed to modify the sensitivity of cortical noradrenergic neurons to the same stressful stimulus. Our results have shown that it is possible to independently modulate the sensitivity of cortical serotonergic neurons to stressful stimuli without altering the responsiveness of noradrenergic neurons to the same stress. Given the different role played by serotonin and norepinephrine in the modulation of the stress response, the availability of drugs able to selectively modulate the plastic response of serotonergic neurons to stress in specific brain areas might be important for the pharmacotherapy of anxiety disorders.

Blockade of the mGlu5 receptor decreases basal and stress-induced cortical norepinephrine in rodents

RATIONALE

Glutamate, the major excitatory neurotransmitter in the brain mediates its effects by both ionotropic and metabotropic receptor subtypes. Recently, the search for selective ligands for glutamate receptor subtypes has led to the discovery of 2-methyl-6-(phenylethynyl)pyridine (MPEP), an antagonist specific for metabotropic glutamate receptor 5 (mGlu5). This receptor is highly expressed in limbic forebrain regions and is thought to modulate anxiety-related processes. The noradrenergic nucleus locus coeruleus (LC) is an important mediator of stress responses and dysfunction of this system is implicated in affective disorders such as anxiety and depression.

OBJECTIVES

We sought to assess the effects of mGlu5 receptor antagonists, MPEP and 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) on cortical norepinephrine (NE) levels.

METHODS

In vivo microdialysis and high-pressure liquid chromatography with electrochemical detection (HPLC-ED) were used to assess the effects of mGlu5 antagonism on extracellular NE in the frontal cortex, a major terminal field of the LC.

RESULTS

Blockade of the mGlu5 receptor elicited significant reductions in extracellular NE in the frontal cortex. The benzodiazepine diazepam also reduced cortical NE. Furthermore, MPEP administration attenuated stress-induced increases in extracellular NE.

CONCLUSIONS

Taken together, these data show that MPEP and MTEP, through their blockade of the mGlu5, reduce extracellular norepinephrine, the impact of which may contribute to their anxiolytic actions.

Neurosteroids and neuroactive drugs in mental disorders

Clinical and preclinical studies have suggested that fluctuations in the peripheral and brain concentrations of progesterone and deoxycorticosterone and its metabolites 3alpha,5alpha-tetrahydroprogesterone and 3alpha,5alpha-tetrahydrodeoxycorticosterone, respectively, might play an important role in certain pathological conditions characterized by emotional or affective disturbances, including major depression, anxiety disorders, and schizophrenia. Moreover, it has been shown that administration of drugs having clinical relevance in the treatment of these pathologies influence the secretion of these steroids. It remains to be determined, however, whether such changes in the concentrations of neuroactive steroids are a cause of, a risk factor for, or a consequence of mental disorders. The observation that effective pharmacological treatment of some of these pathologies influences the concentrations of neuroactive steroids suggests that these endogenous compounds might themselves prove to be efficacious in the treatment of mental illness.

Attenuation of cue-induced cigarette craving and anterior cingulate cortex activation in bupropion-treated smokers: a preliminary study

In untreated smokers, exposure to cigarette-related cues increases both the intensity of cigarette craving and relative glucose metabolism of the perigenual/ventral anterior cingulate cortex (ACC). Given that treatment with bupropion HCl reduces overall cigarette craving levels in nicotine dependent subjects, we performed a preliminary study of smokers to determine if bupropion HCl treatment attenuates cue-induced cigarette craving and associated brain metabolic activation. Thirty-seven, otherwise healthy smokers (20 untreated and 17 who had received open-label treatment with bupropion HCl) underwent two (18)F-fluorodeoxyglucose positron emission tomography scanning sessions in randomized order--one when presented with neutral cues and the other when presented with cigarette-related cues. Bupropion-treated smokers had smaller cigarette cue-induced increases in craving scores on the Urge to Smoke (UTS) Scale and less activation of perigenual/ventral ACC metabolism from the neutral to the cigarette cue scan than untreated smokers. Thus, in addition to its known effects on spontaneous cigarette craving and withdrawal symptoms, bupropion HCl diminishes cue-induced cigarette craving and appears to attenuate cigarette cue-induced ACC activation. These results are consistent with the known effects of bupropion HCl, including its enhancement of catecholaminergic neurotransmission.

Antagonism of the stress-induced increase in cortical norepinephrine output by the selective norepinephrine reuptake inhibitor reboxetine

We have previously shown that long-term treatment of rats with antidepressant drugs that affect the activity of noradrenergic and serotonergic neurons by different mechanisms, inhibits the increase in cortical norepinephrine output induced by stress. With the use of microdialysis, we have now evaluated the effects of reboxetine, an antidepressant drug that selectively inhibits norepinephrine reuptake, on the increase in cortical norepinephrine output elicited in rats by exposure to foot-shock stress or by the acute administration of N-methyl-beta-carboline-3-carboxamide (FG 7142) (20 mg/kg, i.p.). Foot-shock stress and FG 7142 each induced a marked increase in the cortical extracellular concentration of norepinephrine (+200 and +90%, respectively) in control rats. Long-term treatment with reboxetine (10 mg/kg, i.p., once a day for 21 days) reduced the effect of foot-shock stress and completely antagonized the effect of FG 7142 on cortical norepinephrine output. Our results suggest that changes in the activity of noradrenergic neurons in the cortex might be relevant to the anxiolytic and antidepressant effects of reboxetine.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Prevention of the stress-induced increase in the concentration of neuroactive steroids in rat brain by long-term administration of mirtazapine but not of fluoxetine

The effects of acute and chronic administration of fluoxetine on the basal and stress-induced increases in cerebrocortical and plasma concentrations of allopregnanolone (3alpha,5alpha-tetrahydroprogesterone; 3alpha,5alpha-TH PROG) and tetrahydrodeoxycorticosterone (3alpha,5alpha-TH DOC) were compared with those of mirtazapine, an antidepressant that (unlike fluoxetine) is not a selective serotonin reuptake inhibitor. A single injection (20 mg/kg i.p.) of fluoxetine or mirtazapine resulted in significant increases in the cerebrocortical and plasma concentrations of 3alpha,5alpha-TH PROG and 3alpha,5alpha-TH DOC. In contrast, long-term administration (10 mg/kg i.p., once daily for 2 weeks) of fluoxetine, but not that of mirtazapine, induced marked decreases in the cortical and plasma concentrations of these neuroactive steroids. Chronic treatment with fluoxetine, however, did not inhibit the increases in the cortical and plasma concentrations of 3alpha,5alpha-TH PROG and 3alpha,5alpha-TH DOC induced by acute foot-shock stress. In contrast, chronic treatment with mirtazapine prevented or significantly reduced the stress-induced increases in neurosteroid concentrations in the cerebral cortex and plasma, respectively. These results show that mirtazapine, similar to fluoxetine, initially increases the cortical concentration of neuroactive steroids; however, chronic administration of this drug modulates the plasma and brain availability of these hormones in a manner distinct from that of fluoxetine.

Inhibition by venlafaxine of the increase in norepinephrine output in rat prefrontal cortex elicited by acute stress or by the anxiogenic drug FG 7142

Venlafaxine is an antidepressant drug that inhibits the reuptake of serotonin and norepinephrine with different efficacies. The effects of repeated administration of this drug on the increase in the extracellular concentration of norepinephrine in the prefrontal cortex, induced by stress or by the anxiogenic drug FG 7142, were studied in freely moving rats. Exposure to foot-shock stress induced a marked increase (+120%) in the extracellular norepinephrine concentration in the prefrontal cortex of control rats. Long-term administration of venlafaxine (10 mg/kg i.p., once a day for 21 days) reduced the effect of stress on norepinephrine output by 75%. This effect of venlafaxine persisted for at least 5 days after discontinuation of drug treatment. Acute administration of FG 7142 (20 mg/kg i.p.), a benzodiazepine receptor inverse agonist, increased norepinephrine output (+90%) in control rats. Chronic treatment with venlafaxine prevented the effect of FG 7142. In contrast, the acute administration of this antidepressant had no effect on the stress- or FG 7142-induced increase in norepinephrine output. These plastic changes in the sensitivity of norepinephrine neurones to foot-shock stress and to an anxiogenic drug may reveal an important neuronal mechanism for the physiological regulation of emotional state. Furthermore, this mechanism might be relevant to the anxiolytic and antidepressant effects of venlafaxine.