Ritanserin antagonism of m-chlorophenylpiperazine effects in neuroleptic-free schizophrenics patients: support for serotonin-2 receptor modulation of schizophrenia symptoms

Delivering Glioblastoma a Kick-DGKα Inhibition as a Promising Therapeutic Strategy for GBM

Diacylglycerol kinase α (DGKα) inhibition may be particularly relevant for the treatment of glioblastoma (GBM), a relatively common brain malignancy incurable with current therapies. Prior reports have shown that DGKα inhibition has multiple direct activities against GBM cells, including suppressing the oncogenic pathways mTOR and HIF-1α. It also inhibits pathways associated with the normally treatment-resistant mesenchymal phenotype, yielding preferential activity against mesenchymal GBM; this suggests possible utility in combining DGKα inhibition with radiation and other therapies for which the mesenchymal phenotype promotes resistance. The potential for DGKα inhibition to block or reverse T cell anergy also suggests the potential of DGKα inhibition to boost immunotherapy against GBM, which is generally considered an immunologically "cold" tumor. A recent report indicates that DGKα deficiency increases responsiveness of macrophages, indicating that DGKα inhibition could also have the potential to boost macrophage and microglia activity against GBM-which could be a particularly promising approach given the heavy infiltration of these cells in GBM. DGKα inhibition may therefore offer a promising multi-pronged attack on GBM, with multiple direct anti-GBM activities and also the ability to boost both adaptive and innate immune responses against GBM. However, both the direct and indirect benefits of DGKα inhibition for GBM will likely require combinations with other therapies to achieve meaningful efficacy. Furthermore, GBM offers other challenges for the application of DGKα inhibitors, including decreased accessibility from the blood-brain barrier (BBB). The ideal DGKα inhibitor for GBM will combine potency, specificity, and BBB penetrability. No existing inhibitor is known to meet all these criteria, but the strong potential of DGKα inhibition against this lethal brain cancer should help drive development and testing of agents to bring this promising strategy to the clinic for patients with GBM.

DGKA Mediates Resistance to PD-1 Blockade

Immunologic checkpoint blockade has been proven effective in a variety of malignancies. However, high rates of resistance have substantially hindered its clinical use. Understanding the underlying mechanisms may lead to new strategies for improving therapeutic efficacy. Although a number of signaling pathways have been shown to be associated with tumor cell-mediated resistance to immunotherapy, T cell-intrinsic resistant mechanisms remain elusive. Here, we demonstrated that diacylglycerol kinase alpha (Dgka) mediated T-cell dysfunction during anti-PD-1 therapy by exacerbating the exhaustion of reinvigorated tumor-specific T cells. Pharmacologic ablation of Dgka postponed T-cell exhaustion and delayed development of resistance to PD-1 blockade. Dgka inhibition also enhanced the efficacy of anti-PD-1 therapy. We further found that the expression of DGKA in cancer cells promoted tumor growth via the AKT signaling pathway, suggesting that DGKA might be a target in tumor cells as well. Together, these findings unveiled a molecular pathway mediating resistance to PD-1 blockade and provide a potential therapeutic strategy with combination immunotherapy.

The past and future of novel, non-dopamine-2 receptor therapeutics for schizophrenia: A critical and comprehensive review

Since the discovery of chlorpromazine in the 1950's, antipsychotic drugs have been the cornerstone of treatment of schizophrenia, and all attenuate dopamine transmission at the dopamine-2 receptor. Drug development for schizophrenia since that time has led to improvements in side effects and tolerability, and limited improvements in efficacy, with the exception of clozapine. However, the reasons for clozapine's greater efficacy remain unclear, despite the great efforts and resources invested therewith. We performed a comprehensive review of the literature to determine the fate of previously tested, non-dopamine-2 receptor experimental treatments. Overall we included 250 studies in the review from the period 1970 to 2017 including treatments with glutamatergic, serotonergic, cholinergic, neuropeptidergic, hormone-based, dopaminergic, metabolic, vitamin/naturopathic, histaminergic, infection/inflammation-based, and miscellaneous mechanisms. Despite there being several promising targets, such as allosteric modulation of the NMDA and α7 nicotinic receptors, we cannot confidently state that any of the mechanistically novel experimental treatments covered in this review are definitely effective for the treatment of schizophrenia and ready for clinical use. We discuss potential reasons for the relative lack of progress in developing non-dopamine-2 receptor treatments for schizophrenia and provide recommendations for future efforts pursuing novel drug development for schizophrenia.

Schizophrenia and depression, two poles of endocannabinoid system deregulation

The activity of certain G protein-coupled receptors (GPCRs) and of glutamate N-Methyl-D-aspartate receptors (NMDARs) is altered in both schizophrenia and depression. Using postmortem prefrontal cortex samples from subjects with schizophrenia or depression, we observed a series of opposite changes in the expression of signaling proteins that have been implicated in the cross-talk between GPCRs and NMDARs. Thus, the levels of HINT1 proteins and NMDAR NR1 subunits carrying the C1 cytosolic segment were increased in depressives and decreased in schizophrenics, respect to matched controls. The differences in NR1 C1 subunits were compensated for via altered expression of NR1 subunits lacking the C1 segment; thus, the total number of NR1 subunits was comparable among the three groups. GPCRs influence the function of NR1 C1-containing NMDARs via PKC/Src, and thus, the association of mu-opioid and dopamine 2 receptors with NR1 C1 subunits was augmented in depressives and decreased in schizophrenics. However, the association of cannabinoid 1 receptors (CB1Rs) with NR1 C1 remained nearly constant. Endocannabinoids, via CB1Rs, control the presence of NR1 C1 subunits in the neural membrane. Thus, an altered endocannabinoid system may contribute to the pathophysiology of schizophrenia and depression by modifying the HINT1-NR1 C1/GPCR ratio, thereby altering GPCR-NMDAR cross-regulation.

Role of GABA Deficit in Sensitivity to the Psychotomimetic Effects of Amphetamine

Some schizophrenia patients are more sensitive to amphetamine (AMPH)-induced exacerbations in psychosis-an effect that correlates with higher striatal dopamine release. This enhanced vulnerability may be related to gamma-aminobutyric acid (GABA) deficits observed in schizophrenia. We hypothesized that a pharmacologically induced GABA deficit would create vulnerability to the psychotomimetic effects to the 'subthreshold' dose of AMPH in healthy subjects, which by itself would not induce clinically significant increase in positive symptoms. To test this hypothesis, a GABA deficit was induced by intravenous infusion of iomazenil (IOM; 3.7 μg/kg), an antagonist and partial inverse agonist of benzodiazepine receptor. A subthreshold dose of AMPH (0.1 mg/kg) was administered by intravenous infusion. Healthy subjects received placebo IOM followed by placebo AMPH, active IOM followed by placebo AMPH, placebo IOM followed by active AMPH, and active IOM followed by active AMPH in a randomized, double-blind crossover design over 4 test days. Twelve healthy subjects who had a subclinical response to active AMPH alone were included in the analysis. Psychotomimetic effects (Positive and Negative Syndrome Scale (PANSS)), perceptual alterations (Clinician Administered Dissociative Symptoms Scale (CADSS)), and subjective effects (visual analog scale) were captured before and after the administration of drugs. IOM significantly augmented AMPH-induced peak changes in PANSS positive symptom subscale and both subjective and objective CADSS scores. There were no pharmacokinetic interactions. In conclusion, GABA deficits increased vulnerability to amphetamine-induced psychosis-relevant effects in healthy subjects, suggesting that pre-existing GABA deficits may explain why a subgroup of schizophrenia patients are vulnerable to AMPH.

Alterations in the serotonin system in schizophrenia: a systematic review and meta-analysis of postmortem and molecular imaging studies

Serotonergic dysfunction is thought to contribute to the pathophysiology of schizophrenia but the evidence has not been systematically synthesised before. We therefore systematically reviewed postmortem and in vivo molecular imaging studies of serotonin function in schizophrenia. We identified fifty relevant studies investigating eight different serotonin receptor systems in a total of 684 patients and 675 controls. Meta-analysis of postmortem studies found an elevation in prefrontal 5-HT1A receptors with a moderate to large effect size (N=8, 85 patients and 94 controls, SMD=0.60; CI: 0.17-1.03; p=0.007) and a reduction with a large effect size in prefrontal 5-HT2A receptors (N=8, 168 patients and 163 controls, SMD=-0.73; CI: -1.33, -0.12; p=0.019) in schizophrenia vs healthy controls. The evidence for alterations in serotonin transporter availability or other serotonin receptors (5-HT1B; 5-HT1D; 5-HT3; 5-HT4; 5-HT7) is limited. There are fewer studies investigating 5-HT receptors in schizophrenia with neuroimaging. Findings indicated possible 5-HT alterations at psychosis onset, although due to the limited number it was not possible to combine studies in a meta-analysis. Further in vivo studies, particularly in drug naive patients using radiotracers that can index high affinity states, will help determine if the postmortem findings are primary or secondary to other factors.

Atypical antipsychotics cause an acute increase in cutaneous hand blood flow in patients with schizophrenia and schizoaffective disorder

OBJECTIVE

Clinical studies suggest resting thermoregulatory cutaneous vasomotor tone could be increased in schizophrenia, resulting in reduced hand blood flow. In animal models, atypical antipsychotics including clozapine potently inhibit sympathetic neural outflow to the thermoregulatory cutaneous vascular beds. We have now determined whether antipsychotic medication administration is associated with an acute increase in hand blood flow in patients with schizophrenia and schizoaffective disorder, and whether this increase correlates with clinical status.

METHOD

Hand temperature was measured with an infrared camera in 12 patients with chronic schizophrenia or schizoaffective disorder 30 min prior to, then 30 and 60 min following medication. Clinical status was assessed via the Brief Psychiatric Rating Scale (BPRS). Results were compared using regression and repeated measures analysis of variance.

RESULTS

A robust and significant increase in hand temperature (p < 0.001) was observed following antipsychotic administration. The mean increase after 60 min was 4.1 ± 2.4°C. This increase was significantly associated with colder hand temperature prior to medication (p < 0.05; suggestive of increased resting vasoconstriction) and with more severe psychiatric symptoms (p < 0.05).

CONCLUSIONS

Atypical antipsychotics were associated with increased hand blood flow, consistent with inhibition of thermoregulatory sympathetic outflow to the cutaneous vascular bed in patients with schizophrenia and schizoaffective disorder. This increase correlated with symptom severity. Hand temperature increase following antipsychotic medication may therefore be a simple and informative physiological marker of disease activity and potential response in patients with schizophreniform disorders. Given that antipsychotics also inhibit sympathetic outflow to brown adipose tissue, which normally converts energy to heat, future studies should examine whether antipsychotic-induced hand temperature increase is associated with antipsychotic-induced weight gain.

Overexpression of serotonin receptor and transporter mRNA in blood leukocytes of antipsychotic-free and antipsychotic-naïve schizophrenic patients: gender differences

BACKGROUND

Abnormal serotonin (5-HT) activity has been implicated in schizophrenia. However, the role of 5-HT receptors and transporter (5-HTT) in male and female schizophrenia remains largely unknown. Recent studies suggest that 5-HT system expressed in the peripheral leukocyte could be a marker of the illness.

METHODS

46 acute schizophrenic patients (male=35, female=11) that were antipsychotic-naïve or antipsychotic-free for at least three months (average=27.3 months) and 44 age- and sex-matched healthy subjects (male=24, female=20) were included for blood leukocytes expression of 5-HT(1A), 5-HT(2A) and 5-HT(7) receptor and 5-HTT mRNA, using real-time PCR technique.

RESULTS

ANOVA analysis showed a significant increase of 5HT(2A) mRNA and 5-HTT mRNA (each >2-fold, P<0.01) and a trend increase of 5HT(1A) mRNA (P<0.15) and 5-HT(7) mRNA (P<0.09) level in blood leukocytes of pooled schizophrenic patients than in the healthy subjects. The elevation was mainly found in the male patients. Within-sex analysis showed that the male antipsychotic-free schizophrenic patients exhibited greater 5-HT(1A) and 5-HT(7) mRNA expression (P<0.05, each ) whereas female antipsychotic-free patients showed decreased 5-HT(1A) mRNA expression (P<0.05) when compared with the male and female healthy subjects, respectively. The correlations between 5-HT mRNA and clinical symptoms (PANSS scales) were calculated.

CONCLUSIONS

The present findings showed an abnormal expression of leukocyte 5-HT system in antipsychotic-free and antipsychotic-naïve schizophrenia especially in the male patients. Because of the greater accumulative dose of antipsychotics in the relatively smaller number of the female patients of the study, further study is needed to confirm the present findings. If replicated, blood serotonergic markers could add to the diagnosis and individualized pharmacotherapy of schizophrenic patients, especially the male patients.

Hypersensitivity of 5-HT2 receptors in OCD patients. An increased prolactin response after a challenge with meta-chlorophenylpiperazine and pre-treatment with ritanserin and placebo

INTRODUCTION

Several studies in obsessive compulsive disorder (OCD) have provided circumstantial evidence that the 5-HT-system is involved in the pathophysiology of OCD. To further examine the role of 5-HT receptors we studied the behavioural and neuroendocrine effects of different doses of meta-chlorophenylpiperazine (mCPP) in OCD patients and healthy controls, after pre-treatment with ritanserin, a 5-HT2 receptor antagonist, and placebo.

DESIGN

Twenty patients and 20 healthy controls received 0.1, 0.3 or 0.5 mg/kg mCPP or placebo orally. Each subject was tested two times, receiving both times the same dosage of mCPP or placebo with ritanserin or placebo pre-treatment. All was done under double-blind conditions. OC-symptoms and hormone levels were measured.

RESULTS

The increase in prolactin level after mCPP administration was more robust in patients than in controls. The prolactin response following 0.5 mg/kg of mCPP was partially blocked by ritanserin in patients, but totally blocked in healthy controls. The cortisol responses in both groups did not differ statistically significant from each other and were entirely blocked by ritanserin. None of the subjects experienced an exacerbation of obsessive compulsive symptoms.

CONCLUSION

The neuroendocrine results show an enhanced susceptibility of OCD patients for the mCPP-induced prolactin response, which effect seems to be due to an increased sensitivity of 5-HT2 receptors.

CP-809,101, a selective 5-HT2C agonist, shows activity in animal models of antipsychotic activity

CP-809,101 is a potent, functionally selective 5-HT(2C) agonist that displays approximately 100% efficacy in vitro. The aim of the present studies was to assess the efficacy of a selective 5-HT(2C) agonist in animal models predictive of antipsychotic-like efficacy and side-effect liability. Similar to currently available antipsychotic drugs, CP-809,101 dose-dependently inhibited conditioned avoidance responding (CAR, ED(50)=4.8 mg/kg, sc). The efficacy of CP-809,101 in CAR was completely antagonized by the concurrent administration of the 5-HT(2C) receptor antagonist, SB-224,282. CP-809,101 antagonized both PCP- and d-amphetamine-induced hyperactivity with ED(50) values of 2.4 and 2.9 mg/kg (sc), respectively and also reversed an apomorphine induced-deficit in prepulse inhibition. At doses up to 56 mg/kg, CP-809,101 did not produce catalepsy. Thus, the present results demonstrate that the 5-HT(2C) agonist, CP-809,101, has a pharmacological profile similar to that of the atypical antipsychotics with low extrapyramidal symptom liability. CP-809,101 was inactive in two animal models of antidepressant-like activity, the forced swim test and learned helplessness. However, CP-809,101 was active in novel object recognition, an animal model of cognitive function. These data suggest that 5-HT(2C) agonists may be a novel approach in the treatment of psychosis as well as for the improvement of cognitive dysfunction associated with schizophrenia.

Mechanism of action of atypical antipsychotic drugs and the neurobiology of schizophrenia

Atypical antipsychotics have greatly enhanced the treatment of schizophrenia. The mechanisms underlying the effectiveness and adverse effects of these drugs are, to date, not sufficiently explained. This article summarises the hypothetical mechanisms of action of atypical antipsychotics with respect to the neurobiology of schizophrenia.When considering treatment models for schizophrenia, the role of dopamine receptor blockade and modulation remains dominant. The optimal occupancy of dopamine D(2) receptors seems to be crucial to balancing efficacy and adverse effects - transient D(2) receptor antagonism (such as that attained with, for example, quetiapine and clozapine) is sufficient to obtain an antipsychotic effect, while permanent D(2) receptor antagonism (as is caused by conventional antipsychotics) increases the risk of adverse effects such as extrapyramidal symptoms. Partial D(2) receptor agonism (induced by aripiprazole) offers the possibility of maintaining optimal blockade and function of D(2) receptors. Balancing presynaptic and postsynaptic D(2) receptor antagonism (e.g. induced by amisulpride) is another mechanism that can, through increased release of endogenous dopamine in the striatum, protect against excessive blockade of D(2) receptors. Serotonergic modulation is associated with a beneficial increase in striatal dopamine release. Effects on the negative and cognitive symptoms of schizophrenia relate to dopamine release in the prefrontal cortex; this can be modulated by combined D(2) and serotonin 5-HT(2A) receptor antagonism (e.g. by olanzapine and risperidone), partial D(2) receptor antagonism or the preferential blockade of inhibitory dopamine autoreceptors. In the context of the neurodevelopmental disconnection hypothesis of schizophrenia, atypical antipsychotics (in contrast to conventional antipsychotics) induce neuronal plasticity and synaptic remodelling, not only in the striatum but also in other brain areas such as the prefrontal cortex and hippocampus. This mechanism may normalise glutamatergic dysfunction and structural abnormalities and affect the core pathophysiological substrates for schizophrenia.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

The atypical antipsychotics olanzapine and quetiapine, but not haloperidol, reduce ACTH and cortisol secretion in healthy subjects

RATIONALE

Increased activity of the hypothalamic-pituitary-adrenal (HPA) axis is an important aspect of the pathophysiology of major depression and schizophrenia. Despite the usefulness of atypical antipsychotics in the treatment of depression and their positive influence on cognitive functioning possibly related to their impact on cortisol, little is known about their effect on HPA axis function.

OBJECTIVE

Therefore, this double-blind, placebo-controlled, randomized cross-over study investigated the influence of the atypical antipsychotics quetiapine and olanzapine in comparison with haloperidol and placebo on plasma adrenocorticotropic hormone (ACTH), cortisol, and prolactin levels. Eleven healthy male volunteers were studied during four sessions one week apart, orally receiving placebo, quetiapine (50 mg), olanzapine (5 mg), or haloperidol (3 mg). Blood samples were taken at hourly intervals from 0900 until 1700 hours. For ACTH, cortisol, and prolactin a significant effect of treatment condition (p < or = 0.005; p < or = 0.035; p < or = 0.0001, respectively) for area under the curve (AUC) was found. In comparison to placebo, quetiapine and olanzapine significantly reduced ACTH (p < or = 0.002; p < or = 0.05, respectively) and cortisol (p < or = 0.005; p < or = 0.03, respectively). No effect of haloperidol on AUC of ACTH or cortisol levels was observed. In comparison with placebo, haloperidol (p < or = 0.0001) and olanzapine (p < or = 0.0001) elevated AUC of prolactin plasma levels, whereas no significant effect was observed for quetiapine as a main effect of treatment condition. The atypical antipsychotics' strong influence on HPA-function with pronounced ACTH and cortisol lowering is possibly related to the atypicals' blockade of serotonergic receptors, but blockade of adrenergic or histaminergic receptors may play a role as well. The observed HPA-axis down-regulation may be clinically important for the atypicals' effects on depressive symptomatology and cognitive functioning.

gamma-Aminobutyric acid-serotonin interactions in healthy men: implications for network models of psychosis and dissociation

BACKGROUND

This study tested the hypothesis that deficits in gamma-aminobutyric acid type A (GABA(A)) receptor function might create a vulnerability to the psychotogenic and perceptual altering effects of serotonergic (5-HT(2A/2C)) receptor stimulation. The interactive effects of iomazenil, an antagonist and partial inverse agonist of the benzodiazepine site of the GABA(A) receptor complex, and m-chlorophenylpiperazine (m-CPP), a partial agonist of 5-HT(2A/2C) receptors, were studied in 23 healthy male subjects.

METHODS

Subjects underwent 4 days of testing, during which they received intravenous infusions of iomazenil/placebo followed by m-CPP/placebo in a double-blind, randomized crossover design. Behavioral, cognitive, and hormonal data were collected before drug infusions and periodically for 200 min after.

RESULTS

Iomazenil and m-CPP interacted in a synergistic manner to produce mild psychotic symptoms and perceptual disturbances without impairing cognition. Iomazenil and m-CPP increased anxiety in an additive fashion. Iomazenil and m-CPP interacted in a synergistic manner to increase serum cortisol.

CONCLUSIONS

Gamma-aminobutyric acid-ergic deficits might increase the vulnerability to the psychotomimetic and perceptual altering effects of serotonergic agents. These data suggest that interactions between GABA(A) and 5-HT systems might contribute to the pathophysiology of psychosis and dissociative-like perceptual states.

Quetiapine reduces nocturnal urinary cortisol excretion in healthy subjects

RATIONALE

Hypothalamic-pituitary-adrenal (HPA) axis dysfunction is a frequent finding in psychiatric disorders, including psychotic depression and schizophrenia. Conflicting results exist concerning the influence of antipsychotics on the HPA-axis.

OBJECTIVE

Therefore, this double-blind, placebo-controlled, randomized cross-over study investigated the effect of quetiapine on nocturnal urinary cortisol and melatonin excretion in 13 healthy male subjects under conditions of undisturbed and experimentally disturbed sleep.

METHODS

Volunteers were studied 3 times for 3 consecutive nights (N0, adaptation; N1, standard sleep conditions; N2, acoustic stress) 4 days apart. Placebo, quetiapine 25 mg or quetiapine 100 mg was administered orally 1 h before bedtime on nights 1 and 2. Urine produced during the 8-h bedtime period was collected for later determination of cortisol and melatonin concentrations by standard radioimmunoassays.

RESULTS

MANOVA showed a significant effect for N1 vs. N2 with elevated total amount of cortisol ( p<0.005) and melatonin ( p<0.05) excretion after acoustic stress. Both quetiapine 25 mg and 100 mg significantly ( p<0.0005) reduced the total amount of cortisol excretion in comparison to placebo. No interaction effect of stress condition was observed. There was no effect of quetiapine on melatonin levels.

CONCLUSION

The significant reduction of nocturnal cortisol excretion following quetiapine reflects a decreased activity of the HPA-axis in healthy subjects. This finding may be an important aspect in quetiapine's mode of action in different patient populations.

Discriminative stimulus effects of m-chlorophenylpiperazine as a model of the role of serotonin receptors in anxiety

Serotonin is known to play a role in anxiety. The roles of serotonin reuptake and 5-HT1A receptors have been well characterized, but the contribution of other serotonin receptor subtypes is not as clear. 1-(3-Chlorophenyl)-piperazine (mCPP), which binds non-selectively to a wide range of serotonin receptors, has often been used to produce anxiety in humans and in animal models. Because functional assays indicate that mCPP is significantly more potent at 5-HT2C receptors, it may serve as a tool to investigate the contribution of 5-HT2C receptors to anxiety. This paper reviews the results of behavioral tests using mCPP, including the drug discrimination assay, to model anxiety. Although the discriminative stimulus effects of mCPP do not seem to be a useful screen for general anxiolytics, they do seem to be useful for characterization of the contribution of 5-HT1B and 5-HT2C receptors to the mediation of anxiety-like behaviors.

Effects of m-CPP in altering neuronal function: blocking depolarization in invertebrate motor and sensory neurons but exciting rat dorsal horn neurons

The compound m-chlorophenylpiperazine (m-CPP) is used clinically to manipulate serotonergic function, though its precise mechanisms of actions are not well understood. m-CPP alters synaptic transmission and neuronal function in vertebrates by non-selective agonistic actions on 5-HT(1) and 5-HT(2) receptors. In this study, we demonstrated that m-CPP did not appear to act through a 5-HT receptor in depressing neuronal function in the invertebrates (crayfish and Drosophila). Instead, m-CPP likely decreased sodium influx through voltage-gated sodium channels present in motor and primary sensory neurons. Intracellular axonal recordings showed that m-CPP reduced the amplitude of the action potentials in crayfish motor neurons. Quantal analysis of excitatory postsynaptic currents, recorded at neuromuscular junctions (NMJ) of crayfish and Drosophila, indicated a reduction in the number of presynaptic vesicular events, which produced a decrease in mean quantal content. m-CPP also decreased activity in primary sensory neurons in the crayfish. In contrast, serotonin produces an increase in synaptic strength at the crayfish NMJ and an increase in activity of sensory neurons; it produces no effect at the Drosophila NMJ. In the rat spinal cord, m-CPP enhances the occurrence of spontaneous excitatory postsynaptic potentials with no alteration in evoked currents.