Reciprocal effects of combined administration of serotonin, noradrenaline and dopamine reuptake inhibitors on serotonin and dopamine levels in the rat prefrontal cortex: the role of 5-HT1A receptors

The Atypical Dopamine Transporter Inhibitor CE-158 Enhances Dopamine Neurotransmission in the Prefrontal Cortex of Male Rats: A Behavioral, Electrophysiological, and Microdialysis Study

BACKGROUND

Dopamine plays a key role in several physiological functions such as motor control, learning and memory, and motivation and reward. The atypical dopamine transporter inhibitor S,S stereoisomer of 5-(((S)-((S)-(3-bromophenyl)(phenyl)methyl)sulfinyl)methyl)thiazole (CE-158) has been recently reported to promote behavioral flexibility and restore learning and memory in aged rats.

METHODS

Adult male rats were i.p. administered for 1 or 10 days with CE-158 at the dose of 1 or 10 mg/kg and tested for extracellular dopamine in the medial prefrontal cortex by means of intracerebral microdialysis and single unit cell recording in the same brain area. Moreover, the effects of acute and chronic CE-158 on exploratory behavior, locomotor activity, prepulse inhibition, working memory, and behavioral flexibility were also investigated.

RESULTS

CE-158 dose-dependently potentiated dopamine neurotransmission in the medial prefrontal cortex as assessed by intracerebral microdialysis. Moreover, repeated exposure to CE-158 at 1 mg/kg was sufficient to increase the number of active pyramidal neurons and their firing frequency in the same brain area. In addition, CE-158 at the dose of 10 mg/kg stimulates exploratory behavior to the same extent after acute or chronic treatment. Noteworthy, the chronic treatment at both doses did not induce any behavioral alterations suggestive of abuse potential (e.g., motor behavioral sensitization) or pro-psychotic-like effects such as disruption of sensorimotor gating or impairments in working memory and behavioral flexibility as measured by prepulse inhibition and Y maze.

CONCLUSIONS

Altogether, these findings confirm CE-158 as a promising pro-cognitive agent and contribute to assessing its preclinical safety profile in a chronic administration regimen for further translational testing.

Potentiating glymphatic drainage minimizes post-traumatic cerebral oedema

Cerebral oedema is associated with morbidity and mortality after traumatic brain injury (TBI)1. Noradrenaline levels are increased after TBI2-4, and the amplitude of the increase in noradrenaline predicts both the extent of injury5 and the likelihood of mortality6. Glymphatic impairment is both a feature of and a contributor to brain injury7,8, but its relationship with the injury-associated surge in noradrenaline is unclear. Here we report that acute post-traumatic oedema results from a suppression of glymphatic and lymphatic fluid flow that occurs in response to excessive systemic release of noradrenaline. This post-TBI adrenergic storm was associated with reduced contractility of cervical lymphatic vessels, consistent with diminished return of glymphatic and lymphatic fluid to the systemic circulation. Accordingly, pan-adrenergic receptor inhibition normalized central venous pressure and partly restored glymphatic and cervical lymphatic flow in a mouse model of TBI, and these actions led to substantially reduced brain oedema and improved functional outcomes. Furthermore, post-traumatic inhibition of adrenergic signalling boosted lymphatic export of cellular debris from the traumatic lesion, substantially reducing secondary inflammation and accumulation of phosphorylated tau. These observations suggest that targeting the noradrenergic control of central glymphatic flow may offer a therapeutic approach for treating acute TBI.

The role of central serotonergic markers and estradiol changes in perinatal mental health

OBJECTIVE

Women have an increased risk for mental distress and depressive symptoms in relation to pregnancy and birth. The serotonin transporter (SERT) may be involved in the emergence of depressive symptoms postpartum and during other sex-hormone transitions. It may be associated with cerebrospinal fluid (CSF) levels of the main serotonin metabolite 5-hydroxyindolacetic acid (5-HIAA). In 100 healthy pregnant women, who were scheduled to deliver by cesarean section (C-section), we evaluated 5-HIAA and estradiol contributions to mental distress 5 weeks postpartum.

METHODS

Eighty-two women completed the study. CSF collected at C-section was analyzed for 5-HIAA, with high performance liquid chromatography. Serum estradiol concentrations were quantified by liquid chromatography tandem mass spectrometry before C-section and postpartum. Postpartum mental distress was evaluated with the Edinburgh Postnatal Depression Scale (EPDS). Associations between EPDS, 5-HIAA, and Δestradiol were evaluated in linear regression models adjusted for age, parity and SERT genotype.

RESULTS

Higher levels of postpartum mental distress symptoms were negatively associated with a large decrease in estradiol concentrations (β_ΔE2  = 0.73, p = 0.007) and, on a trend level, positively associated with high antepartum 5-HIAA levels (β_5-HIAA  = 0.002, p = 0.06).

CONCLUSION

In a cohort of healthy pregnant women, postpartum mental distress was higher in women with high antepartum 5-HIAA (trend) and lower in women with a large perinatal estradiol decrease. We speculate that high antepartum 5-HIAA is a proxy of SERT levels, that carry over to the postpartum period and convey susceptibility to mental distress. In healthy women, the postpartum return to lower estradiol concentrations may promote mental well-being.

Disruption of the PDZ domain-binding motif of the dopamine transporter uniquely alters nanoscale distribution, dopamine homeostasis, and reward motivation

The dopamine (DA) transporter (DAT) is part of a presynaptic multiprotein network involving interactions with scaffold proteins via its C-terminal PDZ domain-binding sequence. Using a mouse model expressing DAT with mutated PDZ-binding sequence (DAT-AAA), we previously demonstrated the importance of this binding sequence for striatal expression of DAT. Here, we show by application of direct stochastic reconstruction microscopy not only that the striatal level of transporter is reduced in DAT-AAA mice but also that the nanoscale distribution of this transporter is altered with a higher propensity of DAT-AAA to localize to irregular nanodomains in dopaminergic terminals. In parallel, we observe mesostriatal DA adaptations and changes in DA-related behaviors distinct from those seen in other genetic DAT mouse models. DA levels in the striatum are reduced to ∼45% of that of WT, accompanied by elevated DA turnover. Nonetheless, fast-scan cyclic voltammetry recordings on striatal slices reveal a larger amplitude and prolonged clearance rate of evoked DA release in DAT-AAA mice compared with WT mice. Autoradiography and radioligand binding show reduced DA D2 receptor levels, whereas immunohistochemistry and autoradiography show unchanged DA D1 receptor levels. In behavioral experiments, we observe enhanced self-administration of liquid food under both a fixed ratio of one and progressive ratio schedule of reinforcement but a reduction compared with WT when using cocaine as reinforcer. In summary, our data demonstrate how disruption of PDZ domain interactions causes changes in DAT expression and its nanoscopic distribution that in turn alter DA clearance dynamics and related behaviors.

Detection of six novel de novo mutations in individuals with low resilience to psychological stress

Genetic bases of psychological stress resilience have been studied previously, but mechanisms and genetic variants which are involved in stress resilience are still unclear. The present study aimed to evaluate the associations between variants in dopaminergic pathway genes with stress resilience. Subjects of the present study were divided into four groups. Group A included persons with normal reactions to major life events stressors; group B included persons with an acute stress reaction to major life events stressor; group C included persons with normal reactions to Crises/catastrophes stressors, and group D included persons with an acute stress reaction to Crises/catastrophes stressors. DNA was extracted from the subject's blood, and the entire length of 14 genes DRD1, DRD2, DRD3, DRD4, DRD5, COMT, DBH, TH, MAOA, DDC, DAT, 5-HTT, BDNF, and GDNF were sequenced by automated sequencers ABI 3700. Results showed 24 point mutations in 12 genes, including 16 SNPs and six novel mutations, which were significantly correlated to low-stress resilience. Most of the SNPs were known as risk alleles in psychiatric disorders. Several associations were found between genetic variants and psychological characteristics. Findings suggest dopaminergic as an important pathway in stress and stress resilience also indicated shared genetic bases between low-stress resilience and several psychiatric disorders.

Biomarkers for moral cognition: Current status and future prospects for neurotransmitters and neuropeptides

The translational neuroscience of moral cognitions draws together developments throughout the fields of neuroscience pertaining to moral cognitions in order to better the human condition. That condition, seen through this lens, is one in which much of the violence and suffering we endure and inflict upon one another is based on moral cognitions-attitudes, beliefs, judgments-that are thought to result from correct or incorrect perceptions of moral properties. The biology tells a different story; namely, that moral cognitions, like other cognitions and mental states, are predicted and determined by biological mechanisms modulated by genotype, neurotransmitter availability and receptor density, neurophysiology, and individual differences among these as well as biology-environment interactions including nutrition, experience, and microbiome. A wealth of research has demonstrated that moral reasoning and judgments are easily alterable with the application of pharmaceuticals including SSRIs, and simpler treatments and conditions like the amount of time since one's last meal. Public health experts have pushed for analysis of violence and development of interventions treating violence as a public health pandemic. We see this research as a response to that call. Work in this field demonstrates that we are unaware of both the sources and nature of the cognitions on which we base much of our violent behaviors, societally and individually. Animal studies bolster the human subjects research, demonstrating the evolutionary roots of the causal mechanisms beneath our social structures and group formations.

Liraglutide as adjunct to insulin treatment in type 1 diabetes does not interfere with glycaemic recovery or gastric emptying rate during hypoglycaemia: A randomized, placebo-controlled, double-blind, parallel-group study

AIM

Glucagon-like peptide-1 receptor agonist (GLP-1RA) therapy is a potential treatment as adjunct to insulin in type 1 diabetes (T1D). However, GLP-1RAs inhibit glucagon secretion and delay the gastric emptying (GE) rate and may impair recovery from hypoglycaemia. We evaluated the effect of the GLP-1RA liraglutide on counterregulatory responses and GE rate during hypoglycaemia in persons with T1D.

MATERIALS AND METHODS

In a 12-week, randomized, double-blind, placebo-controlled study, 20 patients aged >18 years with T1D and HbA1c ≥8% (64 mmol/mol) were randomly assigned (1:1) to liraglutide 1.2 mg once daily or placebo as add-on to insulin treatment. Before and at end of treatment a hypoglycaemic clamp (plasma glucose target 2.5 mmol/L) was carried out, followed by a liquid meal. Primary endpoint was change in GE rate (evaluated by area under the paracetamol curve and time to peak). Secondary endpoints included changes in glycaemic recovery, counter-regulatory hormones, pancreatic polypeptide (PP), GLP-1, blood pressure and heart rate.

RESULTS

During the period June 2013 to October 2014, 20 patients were enrolled. After 12 weeks of treatment, changes in GE rates did not differ significantly between groups ( P  = .96), with no significant changes from baseline, whether evaluated from AUCs or time to peak. The secondary endpoints, glycaemic recovery, counter-regulatory hormone responses, systolic blood pressure and GLP-1 and PP responses, were also similar. Heart rate increased with liraglutide from 69 ± 4 to 80 ± 5 beats/min ( P  = .02).

CONCLUSIONS

Liraglutide does not compromise glycaemic recovery, GE rate or counter-regulatory hormone responses in T1D patients during hypoglycaemia. No treatment-related safety issues were identified.

The effects of reduced dopamine transporter function and chronic lithium on motivation, probabilistic learning, and neurochemistry in mice: Modeling bipolar mania

BACKGROUND

Bipolar disorder (BD) mania patients exhibit poor cognition and reward-seeking/hypermotivation, negatively impacting a patient's quality of life. Current treatments (e.g., lithium), do not treat such deficits. Treatment development has been limited due to a poor understanding of the neural mechanisms underlying these behaviors. Here, we investigated putative mechanisms underlying cognition and reward-seeking/motivational changes relevant to BD mania patients using two validated mouse models and neurochemical analyses.

METHODS

The effects of reducing dopamine transporter (DAT) functioning via genetic (knockdown vs. wild-type littermates), or pharmacological (GBR12909- vs. vehicle-treated C57BL/6J mice) means were assessed in the probabilistic reversal learning task (PRLT), and progressive ratio breakpoint (PRB) test, during either water or chronic lithium treatment. These tasks quantify reward learning and effortful motivation, respectively. Neurochemistry was performed on brain samples of DAT mutants ± chronic lithium using high performance liquid chromatography.

RESULTS

Reduced DAT functioning increased reversals in the PRLT, an effect partially attenuated by chronic lithium. Chronic lithium alone slowed PRLT acquisition. Reduced DAT functioning increased motivation (PRB), an effect attenuated by lithium in GBR12909-treated mice. Neurochemical analyses revealed that DAT knockdown mice exhibited elevated homovanillic acid levels, but that lithium had no effect on these elevated levels.

CONCLUSIONS

Reducing DAT functioning recreates many aspects of BD mania including hypermotivation and improved reversal learning (switching), as well as elevated homovanillic acid levels. Chronic lithium only exerted main effects, impairing learning and elevating norepinephrine and serotonin levels of mice, not specifically treating the underlying mechanisms identified in these models.

Hyperactivity and lack of social discrimination in the adolescent Fmr1 knockout mouse

The aims of this study were to investigate behaviour relevant to human autism spectrum disorder (ASD) and the fragile X syndrome in adolescent Fmr1 knockout (KO) mice and to evaluate the tissue levels of striatal monoamines. Fmr1 KO mice were evaluated in the open field, marble burying and three-chamber test for the presence of hyperactivity, anxiety, repetitive behaviour, sociability and observation of social novelty compared with wild-type (WT) mice. The Fmr1 KO mice expressed anxiety and hyperactivity in the open field compared with WT mice. This increased level of hyperactivity was confirmed in the three-chamber test. Fmr1 KO mice spent more time with stranger mice compared with the WT. However, after a correction for hyperactivity, their apparent increase in sociability became identical to that of the WT. Furthermore, the Fmr1 KO mice could not differentiate between a familiar or a novel mouse. Monoamines were measured by HPLC: Fmr1 KO mice showed an increase in the striatal dopamine level. We conclude that the fragile X syndrome model seems to be useful for understanding certain aspects of ASD and may have translational interest for studies of social behaviour when hyperactivity coexists in ASD patients.

The Rapidly Acting Antidepressant Ketamine and the mGlu2/3 Receptor Antagonist LY341495 Rapidly Engage Dopaminergic Mood Circuits

Ketamine is a rapidly acting antidepressant in patients with treatment-resistant depression (TRD). Although the mechanisms underlying these effects are not fully established, inquiry to date has focused on the triggering of synaptogenesis transduction pathways via glutamatergic mechanisms. Preclinical data suggest that blockade of metabotropic glutamate (mGlu2/3) receptors shares many overlapping features and mechanisms with ketamine and may also provide rapid efficacy for TRD patients. Central dopamine circuitry is recognized as an end target for mood regulation and hedonic valuation and yet has been largely neglected in mechanistic studies of antidepressant-relevant effects of ketamine. Herein, we evaluated the changes in dopaminergic neurotransmission after acute administration of ketamine and the mGlu2/3 receptor antagonist LY341495 [(2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid ] in preclinical models using electrophysiologic, neurochemical, and behavioral endpoints. When given acutely, both ketamine and LY341495, but not the selective serotonin reuptake inhibitor (SSRI) citalopram, increased the number of spontaneously active dopamine neurons in the ventral tegmental area (VTA), increased extracellular levels of dopamine in the nucleus accumbens and prefrontal cortex, and enhanced the locomotor stimulatory effects of the dopamine D2/3 receptor agonist quinpirole. Further, both ketamine and LY341495 reduced immobility time in the tail-suspension assay in CD1 mice, which are relatively resistant to SSRI antidepressants. Both the VTA neuronal activation and the antidepressant phenotype induced by ketamine and LY341495 were attenuated by the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo- (9CI)-benzo[f]quinoxaline-7-sulfonamide, indicating AMPA-dependent effects. These findings provide another overlapping mechanism of action of ketamine and mGlu2/3 receptor antagonism that differentiates them from conventional antidepressants and thus support the potential rapidly acting antidepressant actions of mGlu2/3 receptor antagonism in patients.

Comparison of the Efficiency of Adeprophen and Antidepressants of Various Groups on the Model of Reserpine-Induced Depression in Rats

A new (aryloxyalkyl)adenine derivative Adeprophen (9-[2-(4-isopropylphenoxy)ethyl]adenine, VMA-99-82) has a strong antidepressant effect on the model of reserpine-induced depression in rats (single dose 4 mg/kg, intraperitoneally). This effect manifested in suppression of depression-like behavior in the Porsolt forced swimming test (shortening of immobility time and increase in immobility latency, number of jumping episodes, and time of active swimming) and sucrose consumption/preference test (increase in the consumption of 20% sucrose solution in g/100 g body weight and percentage of sucrose preference in relation to the total fluid preference). Adeprophen had a greater antidepressant effect than sertraline and fluoxetine, but was less potent than amitriptyline, imipramine, venlafaxine, and to a lesser extent to paroxetine.

Resistance to antidepressant drugs: the case for a more predisposition-based and less hippocampocentric research paradigm

The first half of this paper briefly reviews the evidence that (i) stress precipitates depression by damaging the hippocampus, leading to changes in the activity of a distributed neural system involving, inter alia, the amygdala, the ventromedial and dorsolateral prefrontal cortex, the lateral habenula and ascending monoamine pathways, and (ii) antidepressants work by repairing the damaged hippocampus, thus restoring the normal balance of activity within that circuitry. In the second half of the paper we review the evidence that heightened vulnerability to depression, either because of a clinical history of depression or because of the presence of genetic, personality or developmental risk factors, also confers resistance to antidepressant drug treatment. Thus, although antidepressants provide an efficient means of reversing the neurotoxic effects of stress, they are much less effective in conditions where vulnerability to depression is elevated and the role of stress in precipitating depression is correspondingly lower. Consequently, the issue of vulnerability should feature much more prominently in antidepressant research. Most of the current animal models of depression are based on the induction of a depressive-like phenotype by stress, and pay scant attention to vulnerability. As antidepressants are relatively ineffective in vulnerable individuals, this in turn implies a need for the development of different clinical and preclinical methodologies, and a shift of focus away from the current preoccupation with the hippocampus as a target for antidepressant action in vulnerable patients.

The effects of LPM570065, a novel triple reuptake inhibitor, on extracellular serotonin, dopamine and norepinephrine levels in rats

Triple reuptake inhibitors (TRIs) are currently being developed as a new class of promising antidepressants that block serotonin (5-HT), dopamine (DA) and norepinephrine (NE) transporters, thereby increasing extracellular monoamine concentrations. The purpose of this study was to investigate the effects of LPM570065, a novel TRI and a desvenlafaxine prodrug, on extracellular 5-HT, DA and NE levels in the rat striatum after acute and chronic administration relative to desvenlafaxine, using High Performance Liquid Chromatography (HPLC) and microdialysis. Acute administration was performed by providing rodents with oral solutions (0.06 mmol·kg(-1) p.o.), oral suspensions (0.06 mmol·kg(-1) p.o.) and intravenous solutions (0.04 mmol·kg(-1) i.v.) of LPM570065 and desvenlafaxine. Oral suspensions (0.06 mmol·kg(-1)·day(-1)) of the two drugs were also administered for a 14-day chronic period. HPLC analysis revealed that LPM570065 rapidly penetrated the rat striatum, converted into desvenlafaxine and exhibited larger total exposure compared with the administration of desvenlafaxine. Microdialysis revealed that acute and chronic administration of oral suspension of LPM570065 increased the 5-HT, DA and NE levels more than the relative administration of desvenlafaxine. Unlike desvenlafaxine, acute administration of an intravenous LPM570065 solution did not induce the undesirable 90% decrease in extracellular 5-HT levels. In contrast to the fully dose-dependent elevation of 5-HT induced by desvenlafaxine, the acute administration of LPM570065 showed a capped increase in extracellular 5-HT levels when combined with WAY-100635. Additionally, forced swim test demonstrated that acute and chronic administration of LPM570065 reduced the immobility time more than the relative administration of desvenlafaxine. These data suggest that LPM570065 may have greater efficacy and/or a more rapid onset of antidepressant action than desvenlafaxine and also counterbalance the harmful effects of desvenlafaxine on 5-HT neurotransmission related to 5-HT1A autoreceptors. Thus, this new class of drugs, TRIs has the potential to provide a new therapeutic mechanism for treating depression.

Serotonin 1A receptor inhibits the status epilepticus induced by lithium-pilocarpine in rats

Status epilepticus (SE) is a life-threatening neurological emergency associated with a high mortality rate. The serotonin 1A (5-HT1A) receptor is a possible target for the treatment of SE, but its role in animal models and the precise area of brain involved remain controversial. The hippocampus is a candidate site due to its key role in the development of SE and the existence of a high density of 5-HT1A receptors. Therefore, we investigated the effects of subcutaneous and intrahippocampal activation of 5-HT1A receptors in lithium-pilocarpine-induced SE, and tested whether the hippocampus is a true effector site. We developed SE in male Sprague-Dawley rats by giving lithium chloride (LiCl; 3 meq/kg, i.p.) 22-24 h prior to pilocarpine (25 mg/kg, i.p.), and found that 8-OH-DPAT, a 5-HT1A receptor agonist administered subcutaneously (s.c.) at 0.5 or 1.0 mg/kg 1 h before pilocarpine injection increased the latency to the first epileptiform spikes, the electrographic SE, and the behavioral generalized seizures (GS), while reducing the total EEG seizure time (P <0.01). The duration of GS was shortened only by 1.0 mg/kg 8-OH-DPAT s.c. (P <0.05). All these effects were inhibited by combined administration of WAY-100635 (1.0 mg/kg, s.c.) (P <0.05), an antagonist of the 5-HT1A receptor, but WAY-100635 alone and low doses of 8-OHDPAT (0.01 and 0.1 mg/kg) did not alter seizure activity. Furthermore, intrahippocampal 8-OH-DPAT only shortened the GS duration (P <0.05). These findings imply that the 5-HT1A receptor is a promising therapeutic target against the generation and propagation of SE, and hippocampal receptors are involved in reducing the seizure severity.

Potential usefulness of the kampo medicine yokukansan, containing uncaria hook, for paediatric emotional and behavioural disorders: a case series

Background. Paediatric emotional and behavioural disorders (EBD) are relatively common diseases. Although nonpharmacologic and pharmacologic treatments are utilized in these cases, it is sometimes difficult to manage the symptoms of EBD. Historically, Uncaria hook has been used for treating nighttime crying and convulsions in children. Recent clinical studies have demonstrated that the Kampo medicine Yokukansan (YKS), which contains Uncaria hook, is efficacious for behaviour disorders in Alzheimer's disease patients. Herein, we investigated the clinical efficacy and safety of YKS in a series of cases with paediatric EBD. Patients and Methods. We retrospectively reviewed all paediatric patients who sought Japanese Kampo therapy at our outpatient clinics between April 1, 2012, and April 30, 2013; we selected patients who were diagnosed with paediatric EBD and were treated with YKS. Results. After screening all candidates, 3 patients were eligible for this analysis. Their average age was 11.6 years (range 10–13 years). All 3 patients responded very well to YKS within 1 month. No drug-related adverse events were observed during the course of YKS treatment. Conclusion. Yokukansan may be efficacious for paediatric EBD. We believe these results warrant further evaluation of the clinical efficacy and safety of Yokukansan for paediatric EBD in a carefully designed, double-blind, randomized clinical study.

The neurobiology of depression and antidepressant action

We present a comprehensive overview of the neurobiology of unipolar major depression and antidepressant drug action, integrating data from affective neuroscience, neuro- and psychopharmacology, neuroendocrinology, neuroanatomy, and molecular biology. We suggest that the problem of depression comprises three sub-problems: first episodes in people with low vulnerability ('simple' depressions), which are strongly stress-dependent; an increase in vulnerability and autonomy from stress that develops over episodes of depression (kindling); and factors that confer vulnerability to a first episode (a depressive diathesis). We describe key processes in the onset of a 'simple' depression and show that kindling and depressive diatheses reproduce many of the neurobiological features of depression. We also review the neurobiological mechanisms of antidepressant drug action, and show that resistance to antidepressant treatment is associated with genetic and other factors that are largely similar to those implicated in vulnerability to depression. We discuss the implications of these conclusions for the understanding and treatment of depression, and make some strategic recommendations for future research.

Effect of prenatal administration of venlafaxine on postnatal development of rat offspring

About 3% of pregnant women are treated with antidepressant drugs during gestation. After delivery the number of treated women increases to 5 to 7%. Most prescribed antidepressants in pregnancy are selective serotonin re-uptake inhibitors and/or serotonin and noradrenaline re-uptake inhibitors, such as fluoxetine, paroxetine, sertraline, citalopram and venlafaxine (VENF). Despite the fact that VENF has been assigned to pregnancy category C by the FDA, experimental studies with this drug are rare. The aim of this pilot study was to investigate the effect of prenatal administration of VENF on early postnatal development of rat offspring and selected biochemical variables at weaning of pups. Pregnant female Wistar rats were treated with VENF from day 15 to 20 of gestation at the doses of 7.5, 37.5 and 70 mg/kg. Females were allowed to spontaneously deliver their pups. After delivery the pups were inspected for viability, gross malformation and they were weighed on day 0, 4 and 21 post partum. On day 21 post partum, the pups were killed, brains were removed from the skulls and blood samples were collected for biochemical assay (proteins, glucose-GOD, glucose-HEX, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase and total antioxidant status). The study showed that prenatal VENF administration resulted in a mild maternal intoxication manifested by decreased body weight gain of pregnant females. There was no effect of the drug tested on the body and brain weights of offspring. No obvious morphological alterations were observed in the delivered pups. Similarly, there were no changes in the selected biochemical variables determined.

On the Role of Cannabinoid CB1- and μ-Opioid Receptors in Motor Impulsivity

Previous studies using a rat 5-choice serial reaction time task have established a critical role for dopamine D2 receptors in regulating increments in motor impulsivity induced by acute administration of the psychostimulant drugs amphetamine and nicotine. Here we investigated whether cannabinoid CB1 and/or μ-opioid receptors are involved in nicotine-induced impulsivity, given recent findings indicating that both receptor systems mediate amphetamine-induced motor impulsivity. Results showed that the cannabinoid CB1 receptor antagonist SR141716A, but not the opioid receptor antagonist naloxone, reduced nicotine-induced premature responding, indicating that nicotine-induced motor impulsivity is cannabinoid, but not opioid receptor-dependent. In contrast, SR141716A did not affect impulsivity following a challenge with the dopamine transporter inhibitor GBR 12909, a form of drug-induced impulsivity that was previously found to be dependent on μ-opioid receptor activation. Together, these data are consistent with the idea that the endogenous cannabinoid, dopamine, and opioid systems each play important, but distinct roles in regulating (drug-induced) motor impulsivity. The rather complex interplay between these neurotransmitter systems modulating impulsivity will be discussed in terms of the differential involvement of mesocortical and mesolimbic neurocircuitry.

Unusual effects of nicotine as a psychostimulant on ambulatory activity in mice

The present study examined the effect of nicotine, alone and in combination with various drugs that act on the CNS, on ambulatory activity, a behavioral index for locomotion, in ICR (CD-1) strain mice. Nicotine at 0.25–2 mg/kg acutely reduced ambulatory activity of ICR mice. The effect of nicotine was similar to that of haloperidol and fluphenazine but distinct from that of bupropion and methylphenidate. ICR mice developed tolerance against the inhibitory effect of nicotine on ambulatory activity when nicotine was repeatedly administered. This effect was also distinct from bupropion and methylphenidate as they produced augmentation of their ambulation-stimulating effects in ICR mice. Nicotine reduced the ambulation-stimulating effects of bupropion and methylphenidate as well as haloperidol and fluphenazine. Taken together, nicotine exhibited unusual effects as a psychostimulant on ambulatory activity in ICR mice.

Blue again: perturbational effects of antidepressants suggest monoaminergic homeostasis in major depression

Some evolutionary researchers have argued that current diagnostic criteria for major depressive disorder (MDD) may not accurately distinguish true instances of disorder from a normal, adaptive stress response. According to disorder advocates, neurochemicals like the monoamine neurotransmitters (serotonin, norepinephrine, and dopamine) are dysregulated in major depression. Monoamines are normally under homeostatic control, so the monoamine disorder hypothesis implies a breakdown in homeostatic mechanisms. In contrast, adaptationist hypotheses propose that homeostatic mechanisms are properly functioning in most patients meeting current criteria for MDD. If the homeostatic mechanisms regulating monoamines are functioning properly in these patients, then oppositional tolerance should develop with prolonged antidepressant medication (ADM) therapy. Oppositional tolerance refers to the forces that develop when a homeostatic mechanism has been subject to prolonged pharmacological perturbation that attempt to bring the system back to equilibrium. When pharmacological intervention is discontinued, the oppositional forces cause monoamine levels to overshoot their equilibrium levels. Since depressive symptoms are under monoaminergic control, this overshoot should cause a resurgence of depressive symptoms that is proportional to the perturbational effect of the ADM. We test this prediction by conducting a meta-analysis of ADM discontinuation studies. We find that the risk of relapse after ADM discontinuation is positively associated with the degree to which ADMs enhance serotonin and norepinephrine in prefrontal cortex, after controlling for covariates. The results are consistent with oppositional tolerance, and provide no evidence of malfunction in the monoaminergic regulatory mechanisms in patients meeting current diagnostic criteria for MDD. We discuss the evolutionary and clinical implications of our findings.

Characterization of the electrophysiological properties of triple reuptake inhibitors on monoaminergic neurons

Triple reuptake inhibitors represent a potential new class of antidepressant drugs that block norepinephrine (NE), dopamine (DA) and serotonin [5-hydroxytryptamine (5-HT)] transporters. The present in-vivo electrophysiological study was undertaken to determine the effects of the triple reuptake inhibitors SEP-225289 and DOV216303 on the neuronal activities of locus coeruleus (LC) NE, ventral tegmental area (VTA) DA and dorsal raphe (DR) 5-HT neurons. Administered acutely, SEP-225289 and DOV216303 dose-dependently decreased the spontaneous firing rate of LC NE, VTA DA and DR 5-HT neurons through the activation of α₂, D₂ and 5-HT(₁A) autoreceptors, respectively. Both compounds predominantly inhibited the firing rate of LC NE neurons while producing only a partial decrease in VTA DA and DR 5-HT neuronal discharge. SEP-225289 was equipotent at inhibiting 5-HT and NE transporters since it prolonged to the same extent the time required for a 50% recovery (RT₅₀) of the firing activity of dorsal hippocampus CA3 pyramidal neurons from the inhibition induced by microiontophoretic application of 5-HT and NE. Finally, in the presence of WAY100635, a 5-HT(₁A) receptor antagonist, SEP-225289 activated 5-HT neurons at doses that normally did not inhibit them. Taken together, the present results indicate that reciprocal interactions among NE, DA and 5-HT inputs need to be considered to anticipate the net effect of triple reuptake inhibitors on the enhancement of brain monoamine transmission. The results also suggest that the therapeutic action of triple reuptake inhibitors may be potentiated by antagonizing the cell body 5-HT(₁A) autoreceptors.

Neuroadaptive responses to citalopram in rats using pharmacological magnetic resonance imaging

RATIONALE

The majority of psychoactive compounds, including antidepressants in clinical practice, were discovered largely by serendipity. The underlying neuropharmacological mechanisms of action of these compounds leading to resolution of depressive symptomatology are targets of the current research. Pharmacological magnetic resonance imaging (phMRI), a rapidly developing advancement of blood oxygenation level dependent (BOLD) contrast offers the potential to localize the regional sites of action in the CNS.

OBJECTIVE

Acute and chronic effects of the clinically effective selective serotonin reuptake inhibitor (SSRI) citalopram were examined for changes in BOLD contrast using phMRI in rats. To pharmacologically characterize the specific involvement of the 5-HT(1A) receptors, citalopram was co-administered with a highly selective 5-HT(1A) receptor antagonist WAY100635.

RESULTS

Acute citalopram treatment (10 and 20 mg/kg i.p.) produced a widespread and dose-dependent activation throughout the whole brain. Following 14 days of chronic daily administration of citalopram (20 mg/kg i.p.), localized effects were observed; regions integral in the therapeutic antidepressant effects included the hypothalamus, hippocampus, and cortical regions, suggesting desensitization of serotonergic receptors in the midbrain contributing to elevated levels of 5-HT. Co-administration with WAY100635 (0.3 mg/kg s.c.) increased BOLD activation in the frontal cortex and decreased BOLD contrast in the hypothalamus, hippocampus, and hindbrain structures.

CONCLUSION

The present findings highlight the adaptive nature of responses to citalopram which exhibits regional and pharmacological specificity. These findings translate well to the clinical findings and suggest that this approach may offer the opportunity to develop more efficacious antidepressants with a faster clinical response.

The selective 5-HT(1A) receptor antagonist NAD-299 increases acetylcholine release but not extracellular glutamate levels in the frontal cortex and hippocampus of awake rat

The effects of the HT(1A) receptor antagonist NAD-299 on extracellular acetylcholine (ACh) and glutamate (Glu) levels in the frontal cortex (FC) and ventral hippocampus (HPC) of the awake rats were investigated by the use of in vivo microdialysis. Systemic administration of NAD-299 (0.3; 1 and 3micromol/kg s.c.) caused a dose-dependent increase in ACh levels in FC and HPC (peak value of 209% and 221%, respectively) and this effect was comparable to that induced by donepezil (2.63micromol/kg s.c.). Moreover, the ACh levels in the FC increased even after repeated (14days) treatment with NAD-299 and when NAD-299 was injected locally into the nucleus basalis magnocellularis or perfused through the microdialysis probe implanted in the cortex. In contrast, NAD-299 failed to alter the extracellular levels of glutamate after systemic (3micromol/kg s.c.) or local (100microM) administration. The present data support the hypothesis that cholinergic transmission in cortico-limbic regions can be enhanced via blockade of postsynaptic 5-HT(1A) receptors, which may underlie the proposed cognitive enhancing properties of NAD-299 in models characterized by cholinergic deficit.

Design, synthesis, and pharmacological evaluation of phenoxy pyridyl derivatives as dual norepinephrine reuptake inhibitors and 5-HT1A partial agonists

Preclinical studies suggest that compounds with dual norepinephrine reuptake inhibitor (NRI) and 5-HT(1A) partial agonist properties may provide an important new therapeutic approach to ADHD, depression, and anxiety. Reported herein is the discovery of a novel chemical series with a favorable NRI and 5-HT(1A) partial agonist pharmacological profile as well as excellent selectivity for the norepinephrine transporter over the dopamine transporter.

Cooperative opioid and serotonergic mechanisms generate superior antidepressant-like effects in a mice model of depression

Although complete remission of symptoms is the goal of any depression treatment, many patients fail to attain or maintain a long-term, symptom-free status. The opioid system has been implicated in the aetiology of depression, and some preclinical and clinical data suggest that opioids possess a genuine antidepressant-like effect. This study aimed to investigate a potential antidepressant strategy combining different classes of monoaminergic compounds with the weak mu-opioid agonist codeine in the tail suspension test in mice, a paradigm aimed at screening potential antidepressants. The results showed that codeine produced an antidepressant-like effect when administered alone, that was effectively antagonized by the opioid antagonist naloxone. The combination of subeffective doses of codeine with the selective serotonin reuptake inhibitors (fluoxetine or citalopram) lead to an accentuated reduction in immobility time. In contrast, immobility time remained unchanged when codeine was combined with a noradrenaline reuptake inhibitor (desipramine) or with a noradrenaline/serotonin reuptake inhibitor (duloxetine). The immobility time also remained unchanged with the combination of subeffective doses of codeine plus (+/-)-tramadol (weak mu-opioid agonist with serotonin/noradrenaline reuptake inhibitor properties) or (-)-tramadol (noradrenaline reuptake inhibitor). Conversely, the combination with (+)-tramadol (mu-opioid agonist with serotonin reuptake inhibitor properties) produced a large decrease in the immobility time. All these combinations were without effects on motor behaviour in mice. These data support the hypothesis that a combination of classical serotonergic antidepressants and weak opioid receptor agonists may be a helpful new strategy in the treatment of refractory depression.

In vivo evidence that constitutive activity of serotonin2C receptors in the medial prefrontal cortex participates in the control of dopamine release in the rat nucleus accumbens: differential effects of inverse agonist versus antagonist

Control of the mesoaccumbens dopamine (DA) pathway by central serotonin(2C) receptors (5-HT(2C)Rs) involves different 5-HT(2C)R populations located within multiple brain areas. Here, using in vivo microdialysis in halothane-anesthetized rats, we assessed the role of medial prefrontal cortex (mPFC) 5-HT(2C)Rs in the control of basal and activated accumbal DA outflow, to identify the modalities of their recruitment and the role of 5-HT(2C)R constitutive activity. Intra-mPFC injection of the 5-HT(2C)R inverse agonist SB 206553 (0.5 microg/0.2 microL), without effect by itself, decreased accumbal DA outflow induced by morphine (2.5-10 mg/kg, s.c.), haloperidol (0.01 mg/kg, s.c.) or GBR 12909 (2.5 mg/kg, i.p.). Conversely, intra-mPFC injection of the 5-HT(2C)R antagonist SB 242084 (0.5 microg/0.2 microL), without effect by itself, decreased the effect of 10 mg/kg morphine, the only drug enhancing basal 5-HT outflow in the mPFC. The inhibitory effect of SB 206553 on 2.5 mg/kg morphine-stimulated DA outflow was suppressed by the concomitant intra-mPFC injection of SB 242084. Finally, changes of basal DA outflow induced by the 5-HT(2C)R agonist Ro 60-0175 (3 mg/kg, i.p.) or SB 206553 (5 mg/kg, i.p.) were unaffected by intra-mPFC injection of SB 242084. These results, showing that 5-HT(2C)R antagonist and inverse agonist behave differently in vivo, demonstrate that mPFC 5-HT(2C)Rs facilitate activated accumbal DA outflow and that 5-HT(2C)R constitutive activity participates in this interaction.

Dual- and triple-acting agents for treating core and co-morbid symptoms of major depression: novel concepts, new drugs

The past decade of efforts to find improved treatment for major depression has been dominated by genome-driven programs of rational drug discovery directed toward highly selective ligands for nonmonoaminergic agents. Selective drugs may prove beneficial for specific symptoms, for certain patient subpopulations, or both. However, network analyses of the brain and its dysfunction suggest that agents with multiple and complementary modes of action are more likely to show broad-based efficacy against core and comorbid symptoms of depression. Strategies for improved multitarget exploitation of monoaminergic mechanisms include triple inhibitors of dopamine, serotonin (5-HT) and noradrenaline reuptake, and drugs interfering with feedback actions of monoamines at inhibitory 5-HT(1A), 5-HT(1B) and possibly 5-HT(5A) and 5-HT(7) receptors. Specific subsets of postsynaptic 5-HT receptors mediating antidepressant actions are under study (e.g., 5-HT(4) and 5-HT(6)). Association of a clinically characterized antidepressant mechanism with a nonmonoaminergic component of activity is an attractive strategy. For example, agomelatine (a melatonin agonist/5-HT(2C) antagonist) has clinically proven activity in major depression. Dual neurokinin(1) antagonists/5-HT reuptake inhibitors (SRIs) and melanocortin(4) antagonists/SRIs should display advantages over their selective counterparts, and histamine H(3) antagonists/SRIs, GABA(B) antagonists/SRIs, glutamatergic/SRIs, and cholinergic agents/SRIs may counter the compromised cognitive function of depression. Finally, drugs that suppress 5-HT reuptake and blunt hypothalamo-pituitary-adrenocorticotrophic axis overdrive, or that act at intracellular proteins such as GSK-3beta, may abrogate the negative effects of chronic stress on mood and neuronal integrity. This review discusses the discovery and development of dual- and triple-acting antidepressants, focusing on novel concepts and new drugs disclosed over the last 2 to 3 years.

Dopamine inhibits mitochondrial motility in hippocampal neurons

Background

The trafficking of mitochondria within neurons is a highly regulated process. In an earlier study, we found that serotonin (5-HT), acting through the 5-HT1A receptor subtype, promotes axonal transport of mitochondria in cultured hippocampal neurons by increasing Akt activity, and consequently decreasing glycogen synthase kinase (GSK3β) activity. This finding suggests a critical role for neuromodulators in the regulation of mitochondrial trafficking in neurons. In the present study, we investigate the effects of a second important neuromodulator, dopamine, on mitochondrial transport in hippocampal neurons.

Methodology/Principal Findings

Here, we show that dopamine, like 5-HT, regulates mitochondrial motility in cultured hippocampal neurons through the Akt-GSK3β signaling cascade. But, in contrast to the stimulatory effect of 5-HT, administration of exogenous dopamine or bromocriptine, a dopamine 2 receptor (D2R) agonist, caused an inhibition of mitochondrial movement. Moreover, pretreatment with bromocriptine blocked the stimulatory effect of 5-HT on mitochondrial movement. Conversely, in cells pretreated with 5-HT, no further increases in movement were observed after administration of haloperidol, a D2R antagonist. In contrast to the effect of the D2R agonist, addition of SKF38393, a dopamine 1 receptor (D1R) agonist, promoted mitochondrial transport, indicating that the inhibitory effect of dopamine was actually the net summation of opposing influences of the two receptor subtypes. The most pronounced effect of dopamine signals was on mitochondria that were already moving directionally. Western blot analysis revealed that treatment with either a D2R agonist or a D1R antagonist decreased Akt activity, and conversely, treatment with either a D2R antagonist or a D1R agonist increased Akt activity.

Conclusions/Significance

Our observations strongly suggest a role for both dopamine and 5-HT in regulating mitochondrial movement, and indicate that the integrated effects of these two neuromodulators may be important in determining the distribution of energy sources in neurons.