Expression of noradrenergic alpha1, serotoninergic 5HT2a and dopaminergic D2 receptors on neurons activated by typical and atypical antipsychotic drugs

The α1-adrenergic receptors in the amygdala regulate the induction of learned despair through protein kinase C-beta signaling

Hyperactivity of amygdala is observed in patients with major depressive disorder. Although the role of α1-adrenoceptor in amygdala on fear memory has been well studied, the role of α1-adrenoceptor in amygdala on depression-like behaviors remains unclear. Therefore, we investigated the effect of α1A-adrenoreceptor in amygdala on despair behavior, evaluated by the immobility time during tail suspension test (TST), pharmacological intervention, and immunohistological methods. C57BL6/J mice given a bilateral intra-amygdala injection of artificial cerebrospinal fluid exhibited an increased duration of immobility in the latter half of both trials of TST with a 24-h interval, a phenomenon known as learned despair. Intra-amygdala injection of WB4101 (1.7 nmol/0.1 µl), an α1 adrenoreceptor antagonist, but not propranolol (250 pmol/0.1 µl), a β-adrenoreceptor antagonist, blocked the induction of learned despair during TST. Immunostaining experiments revealed that ~61-75% of α1A-adrenoreceptor-positive neurons were colocalized with GAD65/67 in amygdala, implying that the α1-adrenoceptors in amygdala may enormously regulate the GABA release. Protein kinase C-beta (PKCβ) was predominantly expressed in the α1A-adrenoreceptor-positive neurons in the BLA, whereas protein kinase C-epsilon (PKCε) was highly expressed with the α1A-adrenoreceptor in the Central nucleus of amygdala. Intra-amygdala injection of ruboxistaurin (10 pmol/0.1 µl), a PKCβ inhibitor, blocked the induction of learned despair during TST, whereas neither TAT-εV1-2 (500 ng/0.1 μl), a cell-permeant PKCε inhibitory peptide, nor HBDDE (50 pmol/0.1 µl), an inhibitor of PKCα and -γ, affected the duration of immobility during TST. These data suggest that the α1-adrenoreceptor in amygdala regulates the induction of learned despair via PKCβ.

A systematic review of genetic variants associated with metabolic syndrome in patients with schizophrenia

Metabolic syndrome (MetS) is a cluster of factors that increases the risk of cardiovascular disease (CVD), one of the leading causes of mortality in patients with schizophrenia. Incidence rates of MetS are significantly higher in patients with schizophrenia compared to the general population. Several factors contribute to this high comorbidity. This systematic review focuses on genetic factors and interrogates data from association studies of genes implicated in the development of MetS in patients with schizophrenia. We aimed to identify variants that potentially contribute to the high comorbidity between these disorders. PubMed, Web of Science and Scopus databases were accessed and a systematic review of published studies was conducted. Several genes showed strong evidence for an association with MetS in patients with schizophrenia, including the fat mass and obesity associated gene (FTO), leptin and leptin receptor genes (LEP, LEPR), methylenetetrahydrofolate reductase (MTHFR) gene and the serotonin receptor 2C gene (HTR2C). Genetic association studies in complex disorders are convoluted by the multifactorial nature of these disorders, further complicating investigations of comorbidity. Recommendations for future studies include assessment of larger samples, inclusion of healthy controls, longitudinal rather than cross-sectional study designs, detailed capturing of data on confounding variables for both disorders and verification of significant findings in other populations. In future, big genomic datasets may allow for the calculation of polygenic risk scores in risk prediction of MetS in patients with schizophrenia. This could ultimately facilitate early, precise, and patient-specific pharmacological and non-pharmacological interventions to minimise CVD associated morbidity and mortality.

Simultaneous activation of the α1A-, α1B- and α1D-adrenoceptor subtypes in the nucleus accumbens reduces accumbal dopamine efflux in freely moving rats

Intra-accumbal infusion of the α1-adrenergic agonist methoxamine, which has comparable affinity for α1A-, α1B- and α1D-adrenoceptor subtypes, fails to alter noradrenaline efflux but reduces dopamine efflux in the nucleus accumbens of rats. In-vivo microdialysis experiments were carried out to analyse the putative contribution of α1A-, α1B- and α1D-adrenoceptor subtypes to the methoxamine-induced decrease in accumbal dopamine efflux in freely moving rats. The drugs used were dissolved in the infusion medium and administered locally through a dialysis membrane. Intra-accumbal infusions of the α1A-adrenoceptor antagonist 5-methylurapidil (6 pmol), the α1B-adrenoceptor antagonist cyclazosin (0.6 and 6 pmol) and the α1D-adrenoceptor antagonist BMY 7378 (0.6 pmol) did not alter accumbal efflux of noradrenaline or dopamine: pretreatment with each of these α1-adrenoceptor subtype-selective antagonists counteracted the methoxamine (24 pmol)-induced decrease in accumbal dopamine efflux. Doses indicated are the total amount of drug administered over a 60-min infusion period. These results clearly suggest that the α1A-, α1B- and α1D-adrenoceptor subtypes in the nucleus accumbens mediate the α1-adrenergic agonist methoxamine-induced decrease in accumbal dopamine efflux. The present study also provides in-vivo neurochemical evidence indicating that concomitant, but not separate, activation of the α1A-, α1B- and α1D-adrenoceptors in the nucleus accumbens is required for α1-adrenergic inhibition of accumbal dopaminergic activity.

Drug elucidation: invertebrate genetics sheds new light on the molecular targets of CNS drugs

Many important drugs approved to treat common human diseases were discovered by serendipity, without a firm understanding of their modes of action. As a result, the side effects and interactions of these medications are often unpredictable, and there is limited guidance for improving the design of next-generation drugs. Here, we review the innovative use of simple model organisms, especially Caenorhabditis elegans, to gain fresh insights into the complex biological effects of approved CNS medications. Whereas drug discovery involves the identification of new drug targets and lead compounds/biologics, and drug development spans preclinical testing to FDA approval, drug elucidation refers to the process of understanding the mechanisms of action of marketed drugs by studying their novel effects in model organisms. Drug elucidation studies have revealed new pathways affected by antipsychotic drugs, e.g., the insulin signaling pathway, a trace amine receptor and a nicotinic acetylcholine receptor. Similarly, novel targets of antidepressant drugs and lithium have been identified in C. elegans, including lipid-binding/transport proteins and the SGK-1 signaling pathway, respectively. Elucidation of the mode of action of anesthetic agents has shown that anesthesia can involve mitochondrial targets, leak currents, and gap junctions. The general approach reviewed in this article has advanced our knowledge about important drugs for CNS disorders and can guide future drug discovery efforts.

Mutual independence of 5-HT(2) and α1 noradrenergic receptors in mediating deficits in sensorimotor gating

RATIONALE

Prepulse inhibition (PPI), a preattentional information-filtering mechanism, is disrupted by serotonin (5-HT) or norepinephrine (NE) agonists to model deficits seen in schizophrenia, but whether this effect occurs through interactions between these systems is not known.

OBJECTIVES

These studies investigated whether PPI/activity changes induced by agonists of one system were dependent on neurotransmission within the other.

METHODS

Male Sprague-Dawley rats received the 5-HT(2) receptor agonist DOI (1-[2,5-dimethoxy-4-iodophenyl]-2-aminopropane) (0, 0.3 mg/kg), with or without antagonists for α1 (prazosin:0, 0.3, or 1 mg/kg) or β (timolol:0, 3, or 10 mg/kg) receptors or their combination (0 or 0.3 mg/kg prazosin + 3 mg/kg timolol), or the 5-HT(2) antagonist ritanserin (0, 2 mg/kg). Separately, the α1-adrenergic receptor agonist cirazoline (0, 0.68 mg/kg) was given with and without ritanserin (0, 0.5, or 2 mg/kg) or the NE antagonists (0 or 0.3 mg/kg prazosin + 3 mg/kg timolol). Finally, combinations of subthreshold doses of DOI (0, 0.01, 0.025 mg/kg) and cirazoline (0, 0.1, 0.25 mg/kg) were tested for their ability to disrupt PPI, and concomitant administration of all three antagonists (0 vs. 0.3 mg/kg prazosin + 3 mg/kg timolol + 2 mg/kg ritanserin) was assessed for its ability to modify PPI. Locomotion was assessed in an additional set of experiments.

RESULTS

Doses/combinations of prazosin and timolol that reversed cirazoline-induced effects did not alter DOI-induced effects, and ritanserin did not affect cirazoline at doses that blocked DOI-mediated effects. Concomitant antagonism of α1 + β + 5-HT(2) receptors did not modify PPI, nor did combinations of subthreshold doses of cirazoline and DOI.

CONCLUSIONS

5-HT(2) receptors and α1 and β NE receptors may act through independent mechanisms to modulate sensorimotor gating and locomotor activity.

Cardiac and neuroprotection regulated by α(1)-adrenergic receptor subtypes

Sympathetic nervous system regulation by the α(1)-adrenergic receptor (AR) subtypes (α(1A), α(1B), α(1D)) is complex, whereby chronic activity can be either detrimental or protective for both heart and brain function. This review will summarize the evidence that this dual regulation can be mediated through the different α(1)-AR subtypes in the context of cardiac hypertrophy, heart failure, apoptosis, ischemic preconditioning, neurogenesis, locomotion, neurodegeneration, cognition, neuroplasticity, depression, anxiety, epilepsy, and mental illness.

Ventral striatal noradrenergic mechanisms contribute to sensorimotor gating deficits induced by amphetamine

The psychotomimetic drug D-amphetamine (AMPH), disrupts prepulse inhibition (PPI) of the startle response, an operational measure of sensorimotor gating that is deficient in schizophrenia patients. Historically, this effect has been attributed to dopaminergic substrates; however, AMPH also increases norepinephrine (NE) levels, and enhancement of central NE transmission has been shown recently to disrupt PPI. This study examined the extent to which NE might participate in AMPH-induced disruptions of PPI and increases in locomotor activity, another classic behavioral effect of AMPH, by determining whether antagonism of postsynaptic NE receptors blocked these effects. Separate groups of male Sprague-Dawley rats received either the α1 receptor antagonist, prazosin (0, 0.3, 1 mg/kg), or the β receptor antagonist timolol (0, 3, 10 mg/kg) before administration of AMPH (0 or 1 mg/kg) before testing for PPI or locomotor activity. As an initial exploration of the anatomical substrates underlying possible α1 receptor-mediated effects on AMPH-induced PPI deficits, the α1 receptor antagonist terazosin (0 or 40 μg/0.5 μl) was microinfused into the nucleus accumbens shell (NAccSh) in conjunction with systemic AMPH administration before startle testing in a separate experiment. Prazosin, but not timolol, blocked AMPH-induced hyperactivity; both drugs reversed AMPH-induced PPI deficits without altering baseline startle responses. Interestingly, AMPH-induced PPI deficits also were partially blocked by terazosin in NAccSh. Thus, behavioral sequelae of AMPH (PPI disruption and hyperactivity) may be mediated in part by NE receptors, with α1 receptors in NAccSh possibly having an important role in the sensorimotor gating deficits induced by this psychotomimetic drug.

Kappa-opioid ligands in the study and treatment of mood disorders

The biological basis of mood is not understood. Most research on mood and affective states has focused on the roles of brain systems containing monoamines (e.g., dopamine, norepinephrine, serotonin). However, it is becoming clear that endogenous opioid systems in the brain may also be involved in the regulation of mood. In this review, we focus on the potential utility of kappa-opioid receptor (KOR) ligands in the study and treatment of psychiatric disorders. Research from our group and others suggests that KOR antagonists might be useful for depression, KOR agonists might be useful for mania, and KOR partial agonists might be useful for mood stabilization. Currently available KOR agents have some unfavorable properties that might be addressed through medicinal chemistry. The development of KOR-selective agents with improved drug-like characteristics would facilitate preclinical and clinical studies designed to evaluate the possibility that KORs are a feasible target for new medications.

An antagonistic interaction between A2B adenosine and D2 dopamine receptors modulates the function of rat carotid body chemoreceptor cells

We have previously demonstrated that adenosine controls the release of catecholamines (CA) from carotid body (CB) acting on A2B receptors. Here, we have tested the hypothesis that the control is exerted via an interaction between adenosine A2B and dopamine D2 receptors present in chemoreceptor cells. Experiments were performed in vitro in CB from 3 months rats. The effect of A2B adenosine and D2 dopamine agonists and antagonists applied alone or in combination were studied on basal (20%O2) and hypoxia (10%O2)-evoked release of CA and cAMP content of CB. We have found that adenosine A2 agonists and D2 antagonists dose-dependently increased basal and evoked release CA from the CB while A2 antagonists and D2 agonists had an inhibitory action. The existence of A2B-D2 receptor interaction was established because the inhibitory action of A2 antagonists was abolished by D2 antagonists, and the stimulatory action of A2 agonists was abolished by D2 agonists. Further, A2 agonists increased and D2 agonist decreased cAMP content in the CB; their co-application eliminated the response. The present results provide direct pharmacological evidence that an antagonistic interaction between A2B adenosine and D2 dopamine receptors exist in rat CB and would explain the dopamine-adenosine interactions on ventilation previously observed.

An investigation of the alpha1A-adrenergic receptor gene and antipsychotic-induced side-effects

Antipsychotic treatment is hampered by the induction of side-effects such as tardive dyskinesia (TD), weight gain, sedation and extrapyramidal side-effects (EPS). Identification of the factors related to their development would facilitate their avoidance and the improvement of antipsychotic treatment. It has been hypothesised that genetic variants in drug targeted receptors may contribute to the development of side-effects. In this study, we have investigated the possible influence of genetic variants (-563-C/T, -4155-G/C and -4884-A/G) of the alpha(1A)-adrenergic receptor, an important target of atypical antipsychotic drugs, and development of side-effects after antipsychotic medication in a sample of N = 427 US Caucasian patients. We found several marginal associations (p < 0.05) between alpha(1A)-adrenergic genetic variants and antipsychotic-induced side-effects which did not reach statistical significance after corrections for multiple analyses. These results do not support a major role of alpha(1A)-adrenergic genetic variants in obesity and other side-effects observed after prolonged treatment with antipsychotic medications.

An animal model of emotional blunting in schizophrenia

Schizophrenia is often associated with emotional blunting—the diminished ability to respond to emotionally salient stimuli—particularly those stimuli representative of negative emotional states, such as fear. This disturbance may stem from dysfunction of the amygdala, a brain region involved in fear processing. The present article describes a novel animal model of emotional blunting in schizophrenia. This model involves interfering with normal fear processing (classical conditioning) in rats by means of acute ketamine administration. We confirm, in a series of experiments comprised of cFos staining, behavioral analysis and neurochemical determinations, that ketamine interferes with the behavioral expression of fear and with normal fear processing in the amygdala and related brain regions. We further show that the atypical antipsychotic drug clozapine, but not the typical antipsychotic haloperidol nor an experimental glutamate receptor 2/3 agonist, inhibits ketamine's effects and retains normal fear processing in the amygdala at a neurochemical level, despite the observation that fear-related behavior is still inhibited due to ketamine administration. Our results suggest that the relative resistance of emotional blunting to drug treatment may be partially due to an inability of conventional therapies to target the multiple anatomical and functional brain systems involved in emotional processing. A conceptual model reconciling our findings in terms of neurochemistry and behavior is postulated and discussed.

Association between 5-HT2A, TPH1 and GNB3 genotypes and response to typical neuroleptics: a serotonergic approach

BACKGROUND

Schizophrenia is a common psychiatric disease affecting about 1% of population. One major problem in the treatment is finding the right the drug for the right patients. However, pharmacogenetic results in psychiatry can seldom be replicated.

METHODS

We selected three candidate genes associated with serotonergic neurotransmission for the study: serotonin 2A (5-HT2A) receptor gene, tryptophan hydroxylase 1 (TPH1) gene, and G-protein beta-3 subunit (GNB3) gene. We recruited 94 schizophrenia patients representing extremes in treatment response to typical neuroleptics: 43 were good responders and 51 were poor responders. The control group consisted of 392 healthy blood donors.

RESULTS

We do, in part, replicate the association between 5-HT2A T102C polymorphism and response to typical neuroleptics. In female patients, C/C genotype was significantly more common in non-responders than in responders [OR = 6.04 (95% Cl 1.67-21.93), p = 0.005] or in the control population [OR = 4.16 (95% CI 1.46-11.84), p = 0.005]. TPH1 A779C C/A genotype was inversely associated with good treatment response when compared with non-responders [OR = 0.59 (95% Cl 0.36-0.98), p = 0.030] or with the controls [OR = 0.44 (95% CI 0.23-0.86, p = 0.016], and GNB3 C825T C/T genotype showed a trend-like positive association among the male patients with a good response compared with non-responders [OR = 3.48 (95% Cl 0.92-13.25), p = 0.061], and a clearer association when compared with the controls [OR = 4.95 (95% CI 1.56-15.70), p = 0.004].

CONCLUSION

More findings on the consequences of functional polymorphisms for the role of serotonin in the development of brain and serotonergic neurotransmission are needed before more detailed hypotheses regarding susceptibility and outcome in schizophrenia can be formulated. The present results may highlight some of the biological mechanisms in different courses of schizophrenia between men and women.

CART peptides increase 5-hydroxytryptamine in the dorsal raphe and nucleus accumbens of freely behaving rats

Cocaine and amphetamine-regulated transcript peptides (CART) are implicated in the antidepressant effect. This may involve in 5-hydroxytryptamine (5-HT) in the CNS. The aim of the present studies was to investigate the effect of CART peptides on extracellular 5-HT in the dorsal raphe nucleus (DRN) and nucleus accumbens (NAcc) using a microdialysis approach in freely behaving rats. Reverse infusion of CART61-102 in the DRN produced a concentration (10-100 microM) -dependent increase in 5-HT in the DRN. Similarly, CART62-76 (10-100 microM) infused into the DRN and NAcc elevated 5-HT in the DRN and NAcc, respectively. Thus, CART increases extracellular 5-HT in both the DRN and NAcc. In addition, infusion of CART62-76 (100 microM) in the DRN produced a significant increase in 5-HT in the NAcc, implying an existence of CART receptors responsible for the depolarization-dependent release. In summary, the results of the present studies suggest that CART peptides may have an antidepressant effect through increases in extracellular 5-HT.

Typical and atypical antipsychotic drugs target dopamine and cyclic AMP-regulated phosphoprotein, 32 kDa and neurotensin-containing neurons, but not GABAergic interneurons in the shell of nucleus accumbens of ventral striatum

Specific neurons in the brain are the primary targets of the action of antipsychotic drugs. Identification and characterization of the nature of these neurons are important for understanding how antipsychotic drugs produce their effects. In previous studies GABAergic/dynorphinergic neurons were identified as a principal cell target of antipsychotic drugs in the shell of nucleus accumbens. In the present study, we further characterized which subpopulations of GABAergic neurons in this area respond after acute administration of antipsychotic drugs. Rats were treated with the typical antipsychotic haloperidol, or the prototype atypical antipsychotic clozapine and killed two hours after treatment. In appropriate sections of brain, double immunofluorescence labeling was performed with antibodies directed against markers specific to candidate cell types and Fos-like proteins (a marker to identify drug-induced cell activation). We reported here that haloperidol- and clozapine-activated neurons showed the following features: 1) approximately 54-57% of them express dopamine and cyclic AMP-regulated phosphoprotein, 32 kDa (a marker for GABAergic medium spiny projection neurons), 2) they appear rarely to be GABAergic interneurons, marked by the calcium binding proteins, parvalbumin, calretinin or calbindin-D28K, 3) about 84-86% of them express the neuropeptide neurotensin (a neurotransmitter most often associated with projection neurons in the site tested). The results suggest that most of the antipsychotic drug-activated neurons in the shell of nucleus accumbens are likely to be neurotensin containing projection neurons.