Magdalena Kusek

The antipsychotic‐like effects of positive allosteric modulators of metabotropic glutamate mGlu4 receptors in rodents

Because agonists at metabotropic glutamate receptors exert beneficial effects in schizophrenia, we have assessed the actions of Lu AF21934 and Lu AF32615, two chemically distinct, selective and brain‐penetrant positive allosteric modulators (PAMs) of the mGlu4 receptor, in several tests reflecting positive, negative and cognitive symptoms of schizophrenia in rodents.

The GABAB receptor agonist CGP44532 and the positive modulator GS39783 reverse some behavioural changes related to positive syndromes of psychosis in mice

BACKGROUND AND PURPOSE An important role of GABAergic neurotransmission in schizophrenia was proposed a long time ago, but there is limited data to support this hypothesis. In the present study we decided to investigate GABAB receptor ligands in animal models predictive for the antipsychotic activity of drugs. The GABAB receptor antagonists CGP51176 and CGP36742, agonist CGP44532 and positive allosteric modulator GS39783 were studied.

Acute and repeated treatment with the 5-HT7 receptor antagonist SB 269970 induces functional desensitization of 5-HT7 receptors in rat hippocampus

BACKGROUND SB 269970, a 5-HT(7) receptor antagonist may produce a faster antidepressant-like effect in animal models, than do antidepressant drugs, e.g., imipramine. The present work was aimed at examining the effect of single and repeated (14 days) administration of SB 269970 on the 5-HT(7) receptor in the hippocampus. METHODS The reactivity of 5-HT(7) receptors was determined using 5-carboxamidotryptamine (5-CT), which increased the bursting frequency of spontaneous epileptiform activity in hippocampal slices. Additionally, the effects of SB 269970 administration on the affinity and density of 5-HT(7) receptors were investigated using [(3)H]-SB 269970 and the influence of SB 269970 and imipramine on mRNA expression levels of Gα(s) and Gα(12) mRNA were studied using RT-qPCR. RESULTS Acute and repeated treatment with SB 269970 led to attenuation of the excitatory effects of activation of 5-HT(7) receptors. Neither single nor repeated administration of SB 269970 changed the mean affinity of 5-HT(7) receptors for [(3)H]-SB 269970. Repeated, but not single, administration of SB 269970 decreased the maximum density of [(3)H]-SB 269970 binding sites. While administration of imipramine did not change the expression of mRNAs for Gα(s) and Gα(12) proteins after both single and repeated administration of SB 269970, a reduction in Gα(s) and Gα(12) mRNA expression levels was evident. CONCLUSIONS These findings indicate that even single administration of SB269970 induces functional desensitization of the 5-HT(7) receptor system, which precedes changes in the receptor density. This mechanism may be responsible for the rapid antidepressant-like effect of the 5-HT(7) antagonist in animal models.

5-HT7 receptor modulates GABAergic transmission in the rat dorsal raphe nucleus and controls cortical release of serotonin.

The 5-HT7 receptor is one of the several serotonin (5-HT) receptor subtypes that are expressed in the dorsal raphe nucleus (DRN). Some earlier findings suggested that 5-HT7 receptors in the DRN were localized on GABAergic interneurons modulating the activity of 5-HT projection neurons. The aim of the present study was to find out how the 5-HT7 receptor modulates the GABAergic synaptic input to putative 5-HT DRN neurons, and whether blockade of the 5-HT7 receptor would affect the release of 5-HT in the target structure. Male Wistar rats with microdialysis probes implanted in the prefrontal cortex (PFC) received injections of the 5-HT7 receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine hydrochloride (SB 269970), which induced an increase in the levels of 5-HT and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) in the PFC. In another set of experiments whole-cell recordings from presumed projection neurons were carried out using DRN slices. SB 269970 application resulted in depolarization and in an increase in the firing frequency of the cells. In order to activate 5-HT7 receptors, 5-carboxamidotryptamine (5-CT) was applied in the presence of N-[2-[4-(2-methoxyphenyl)-1piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY100635). Hyperpolarization of cells and a decrease in the firing frequency were observed after activation of the 5-HT7 receptor. Blockade of 5-HT7 receptors caused a decrease in the mean frequency of spontaneous inhibitory postsynaptic currents (sIPSCs), while its activation induced an increase. The mechanism of these effects appears to involve tonically-active 5-HT7 receptors modulating firing and/or GABA release from inhibitory interneurons which regulate the activity of DRN serotonergic projection neurons.

Stress- and antidepressant treatment-induced modifications of 5-HT7 receptor functions in the rat brain

This paper summarizes a series of electrophysiological studies aimed at finding the effects of the activation of 5-HT(7) receptors on neuronal excitability as well as on excitatory and inhibitory synaptic transmission in the hippocampus and in the frontal cortex of the rat. These studies demonstrated that 5-HT(7) receptors play an important role in the modulation of the activity of the hippocampal network by regulating the excitability of pyramidal cells of the CA1 area, as well as via their effect on GABA and glutamatergic transmission. The reactivity of 5-HT(7) receptors in the hippocampus is decreased by repeated administration of antidepressant drugs and increased by a prolonged high level of corticosterone. More importantly, administration of antidepressant drug, imipramine, prevents the occurrence of corticosterone-induced changes in the function of hippocampal 5-HT(7) receptors. It has also been found that the blockade of 5-HT(7) receptors by the selective antagonist SB 269970, lasting for a few days, causes similar changes to those observed after long-term administration of antidepressants. Thus, it seems that the pharmacological blockade of 5-HT(7) receptors produces faster effects compared to classic antidepressant drugs. A similarity between the changes in the glutamatergic transmission induced by the blockade of 5 HT7 receptors and those caused by repeated administration of the antidepressant drug, imipramine, has also been found in the frontal cortex. It has also been shown that the changes in glutamatergic transmission and the impairment of long-term synaptic plasticity in the frontal cortex of animals subjected to repeated restraint stress are reversed by the blockade of 5-HT(7) receptors. Overall, these studies, together with the data provided by other investigators, support the hypothesis that 5-HT(7) receptor antagonists may become a prototype of a new class of antidepressant drugs. Such compounds will not function by blocking 5-HT reuptake, as many of the currently used drugs, but through a direct interaction with the 5-HT(7) receptor. This type of action is highly selective and usually does not require the occurrence of adaptive changes in neuronal functions, thus allowing for a much quicker therapeutic effect.

Neurochemical and behavioral studies on the 5-HT1A-dependent antipsychotic action of the mGlu4 receptor agonist LSP4-2022.

&NA; LSP4‐2022 is a novel, orthosteric agonist of mGlu4 receptor that induces antipsychotic‐like activity in animal studies. In the present study, the involvement of 5‐HT1A receptors in LSP4‐2022‐induced antipsychotic actions and the neurochemical background of that interaction were investigated. In several behavioral tests the actions of effective doses of the compound (0.5–2 mg/kg) were antagonized via the administration of the 5‐HT1A antagonist WAY100635 (0.1 mg/kg). The co‐administration of sub‐effective dose of the 5‐HT1A agonist (R)‐(S)‐8‐OH‐DPAT (0.01 mg/kg) intensified the activity of ineffective doses of LSP4‐2022, having no influence on the efficacy of the active doses. The co‐administration of effective doses of both compounds did not intensify each others action. In the microdialysis in vivo tests, MK‐801 (0.6 mg/kg) induced an enhancement of the release of dopamine, serotonin, glutamate and GABA in the prefrontal cortex. Administration of LSP4‐2022 (2 mg/kg) abolished this MK‐801‐induced effect on neurotransmitter release. Co‐administration with WAY100635 (0.1 mg/kg), a 5‐HT1A antagonist, completely (dopamine, serotonin) or partially (glutamate, GABA) counteracted this LSP4‐2022‐induced effect. Subsequently, the patch‐clamp recordings of spontaneous EPSCs were performed. sEPSCs were evoked in slices from the mouse prefrontal cortex by DOI (10 &mgr;M). LSP4‐2022 (2.5; 5 and 10 &mgr;m) reversed DOI‐induced changes in both the frequency and amplitude of the sEPSCs, but the more robust effect on the frequency was observed. The administration of WAY100635 had no effect on the LSP4‐2022‐induced effects on sEPSCs, indicating that the mGlu4‐5‐HT1A interaction does not occur via single‐neuron signaling but involves neuronal circuits that regulate neurotransmitter release. This article is part of the Special Issue entitled ‘Metabotropic Glutamate Receptors, 5 years on’. HighlightsLSP4‐2022 antagonizes MK‐801‐induced release of dopamine, serotonin, glutamate and GABAThe action of LSP4‐2022 is 5‐HT1A dependentmGlu4‐5‐HT1A interaction does not occur within a single neuron

[Possible involvement of 5-HT₇ receptor in pathophysiology of affective disorders and action of antidepressant drugs].

The 5-HT7 receptor has recently received considerable attention since its involvement has been implicated in cognitive disturbances, sleep and circadian rhythmicity disorders, anxiety and depression. At the cellular level, 5-HT7 receptors increase the excitability of excitatory cells and appear to modulate both glutamatergic and GABAergic transmission in the hippocampus. It has been proposed that 5-HT7 receptors also modulate glutamatergic and GABAergic transmission in the raphe nuclei and these effects may play a role in the regulation of circadian rhythms. Repeated administration of the selective 5-HT7 receptor antagonist induced functional desensitization of the 5-HT7 receptor system at the level of its reactivity and effector proteins. These effects resemble the outcome of treatment of rats with antidepressant drugs. Chronic stress and elevated level of corticosterone increase the reactivity of 5-HT7 receptors in the hippocampus. Treatment of rats with a selective 5-HT7 receptor antagonist also results in attenuation of glutamatergic transmission in the frontal cortex and it prevents the occurrence of stress-induced modifications of glutamatergic transmission and long-term synaptic plasticity. These results are consistent with the hypothesis that 5-HT7 receptor antagonism might, potentially, be used for the treatment of cognitive deficits and mood disorders.

Nitric oxide synthase inhibitor attenuates the effects of repeated restraint stress on synaptic transmission in the paraventricular nucleus of the rat hypothalamus

Corticotropin-releasing hormone (CRH)-synthesizing parvocellular neuroendocrine cells (PNCs) of the hypothalamic paraventricular nucleus (PVN) play a key role in the activation of the hypothalamic-pituitary-adrenocortical (HPA) axis. Several studies have demonstrated that synaptic inputs to these cells may undergo stress-related enhancement but, on the other hand, it has been reported that exposition to the same stressor for prolonged time periods may induce a progressive reduction in the response of the HPA axis to homotypic stressors. In the present study rats were subjected to 10 min restraint sessions, repeated twice daily for 3 or 7 days. Miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs) were then recorded from PNCs in ex vivo hypothalamic slice preparations obtained 24 h after the last restraint. Restraint stress repeated over 3 days resulted in increased mean frequency and decreased rise time and decay time constant of mEPSCs, accompanied by a decrease in the excitability of PNCs, however, no such changes were evident in slices obtained from rats subjected to restraint over 7 days. There were no changes in mIPSCs after repeated restraint. Administration of the unspecific nitric oxide synthase (NOS) blocker Nω-Nitro-L-arginine (L-NNA) before each restraint, repeated over 3 days, prevented the occurrence of an increase in mEPSC frequency. However, animals receiving L-NNA and subjected to repeated restraint had similar changes in PNCs membrane excitability and mEPSC kinetics as stressed rats not receiving L-NNA. Comparison of the effects of a single 10 min restraint session followed by either an immediate or delayed (24 h) decapitation revealed an increase in the mean mEPSC frequency and a decrease in the mean mIPSC frequency in slices prepared immediately after restraint, with no apparent effects when slice preparation was delayed by 24 h. These results demonstrate that restraint, lasting 10 min and repeated twice daily for 3 days, induces a selective and long-lasting enhancement of excitatory synaptic input onto PNCs, partially by a NOS-dependent mechanism, and reduces PNC excitability, whereas prolongation of repeated stress for up to 7 days results in an adaptation.

Mutual activation of glutamatergic mGlu4 and muscarinic M4 receptors reverses schizophrenia-related changes in rodents

RationaleMetabotropic glutamate receptors and muscarinic M4 receptors have been proposed as novel targets for various brain disorders, including schizophrenia. Both receptors are coupled to Go/i proteins and are expressed in brain circuits that are important in schizophrenia. Therefore, their mutual activation may be an effective treatment and allow minimizing the doses of ligands required for optimal activity.ObjectivesIn the present studies, subactive doses of mGlu4 and M4 activators (LSP4-2022 and VU152100, respectively) were administered to investigate the mutual interaction between mGlu4 and M4 receptors in animal models of schizophrenia.MethodsThe behavioral tests used were MK-801-induced hyperactivity, (±)-2.5-dimethoxy-4-iodoamphetamine hydrochloride (DOI)-induced head twitches, the modified forced swim test, and MK-801-induced disruptions of social interactions and novel object recognition. DOI-induced spontaneous excitatory postsynaptic currents (sEPSCs) in brain slices and positron emission tomography (PET) in were used to establish the ability of these compounds to modulate the glutamatergic and dopaminergic systems. Rotarod was used to assess putative adverse effects.ResultsThe mutual administration of subactive doses of LSP4-2022 and VU152100 exerted similar antipsychotic-like efficacy in animals as observed for active doses of both compounds, indicating their additive actions. VU152100 inhibited the DOI-induced frequency (but not amplitude) of sEPSCs in the frontal cortex, confirming presynaptic regulation of glutamate release. Both compounds reversed amphetamine-induced decrease in D2 receptor levels in the striatum, as measured with [18F]fallypride. The compounds did not induce any motor impartments when measured in rotarod test.ConclusionsBased on our results, the simultaneous activation of M4 and mGlu4 receptors is beneficial in reversing MK-801- and amphetamine-induced schizophrenia-related changes in animals.

Simultaneous activation of muscarinic and GABAB receptors as a bidirectional target for novel antipsychotics

Abstract Recent preclinical studies point to muscarinic and GABAB receptors as novel therapeutic targets for the treatment of schizophrenia. This study was aimed to assess the role of muscarinic and GABAB receptor interactions in animal models of schizophrenia, using positive allosteric modulators (PAMs) of GABAB receptor (GS39783), muscarinic M4 (VU0152100) and M5 (VU0238429) receptor, and partial allosteric agonist of M1 receptor (VU0357017). DOI‐induced head twitches, social interaction and novel object recognition tests were used as the models of schizophrenia. Analyses of DOI‐induced increases in sEPSCs (spontaneous excitatory postsynaptic currents) were performed as complementary experiments to the DOI‐induced head twitch studies. Haloperidol‐induced catalepsy and the rotarod test were used to examine the adverse effects of the drugs. All three activators of muscarinic receptors were active in DOI‐induced head twitches. When administered together with GS39783 in subeffective doses, only the co‐administration of VU0152100 and GS39783 was effective. The combination also reduced the frequency but not the amplitude of DOI‐induced sEPSCs. Neither VU0357017 nor VU0238429 were active in social interaction test when given alone, and also the combination of VU0152100 and GS39783 failed to reverse MK‐801‐induced deficits observed in this test. All muscarinic activators when administered alone or in combination with GS39783 reversed the MK‐801‐induced disruption of memory in the novel object recognition test, and their actions were blocked by specific antagonists. None of the tested compounds or their combinations influenced the motor coordination of the animals. The compounds had no effect on haloperidol‐induced catalepsy and did not induce catalepsy when administered alone. Pharmacokinetic analysis confirmed lack of possible drug‐drug interactions after combined administration of GS39783 with VU0357017 or VU0152100; however, when the drug was co‐administered with VU0238429 its ability to pass the blood‐brain barrier slightly decreased, suggesting potential drug‐drug interactions. Our data show that modulation of cholinergic and GABAergic systems can potentially be beneficial in the treatment of the positive and cognitive symptoms of schizophrenia without inducing the adverse effects typical for presently used antipsychotics.