Effect of PDE10A inhibitors on MK-801-induced immobility in the forced swim test

Therapeutic-like activity of cannabidiolic acid methyl ester in the MK-801 mouse model of schizophrenia: Role for cannabinoid CB1 and serotonin-1A receptors

Schizophrenia is a psychotic disorder with an increasing prevalence and incidence over the last two decades. The condition presents with a diverse array of positive, negative, and cognitive impairments. Conventional treatments often yield unsatisfactory outcomes, especially with negative symptoms. We investigated the role of prefrontocortical (PFC) N-methyl-D-aspartate receptors (NMDARs) in the pathophysiology and development of schizophrenia. We explored the potential therapeutic effects of cannabidiolic acid (CBDA) methyl ester (HU-580), an analogue of CBDA known to act as an agonist of the serotonin-1A receptor (5-HT1AR) and an antagonist of cannabinoid type 1 receptor (CB1R). C57BL/6 mice were intraperitoneally administered the NMDAR antagonist, dizocilpine (MK-801, .3 mg/kg) once daily for 17 days. After 7 days, they were concurrently given HU-580 (.01 or .05 μg/kg) for 10 days. Behavioural deficits were assessed at two time points. We conducted enzyme-linked immunosorbent assays to measure the concentration of PFC 5-HT1AR and CB1R. We found that MK-801 effectively induced schizophrenia-related behaviours including hyperactivity, social withdrawal, increased forced swim immobility, and cognitive deficits. We discovered that low-dose HU-580 (.01 μg/kg), but not the high dose (.05 μg/kg), attenuated hyperactivity, forced swim immobility and cognitive deficits, particularly in female mice. Our results revealed that MK-801 downregulated both CB1R and 5-HT1AR, an effect that was blocked by both low- and high-dose HU-580. This study sheds light on the potential antipsychotic properties of HU-580, particularly in the context of NMDAR-induced dysfunction. Our findings could contribute significantly to our understanding of schizophrenia pathophysiology and offer a promising avenue for exploring the therapeutic potential of HU-580 and related compounds in alleviating symptoms.

Phosphodiesterase inhibitors in psychiatric disorders

RATIONALE

Challenges in drug development for psychiatric disorders have left much room for the introduction of novel treatments with better therapeutic efficacies and indices. As a result, intense research has focused on identifying new targets for developing such pharmacotherapies. One of these targets may be the phosphodiesterase (PDE) class of enzymes, which play important roles in intracellular signaling. Due to their critical roles in cellular pathways, these enzymes affect diverse neurobiological functions from learning and memory formation to neuroinflammation.

OBJECTIVES

In this paper, we reviewed studies on the use of PDE inhibitors (PDEIs) in preclinical models and clinical trials of psychiatric disorders including depression, anxiety, schizophrenia, post-traumatic stress disorder (PTSD), bipolar disorder (BP), sexual dysfunction, and feeding disorders.

RESULTS

PDEIs are able to improve symptoms of psychiatric disorders in preclinical models through activating the cAMP-PKA-CREB and cGMP-PKG pathways, attenuating neuroinflammation and oxidative stress, and stimulating neural plasticity. The most promising therapeutic candidates to emerge from these preclinical studies are PDE2 and PDE4 inhibitors for depression and anxiety and PDE1 and PDE10 inhibitors for schizophrenia. Furthermore, PDE3 and 4 inhibitors have shown promising results in clinical trials in patients with depression and schizophrenia.

CONCLUSIONS

Larger and better designed clinical studies of PDEIs in schizophrenia, depression, and anxiety are warranted to facilitate their translation into the clinic. Regarding the other conditions discussed in this review (most notably PTSD and BP), better characterization of the effects of PDEIs in preclinical models is required before clinical studies.

Inhibition of PDE10A in a New Rat Model of Severe Dopamine Depletion Suggests New Approach to Non-Dopamine Parkinson's Disease Therapy

Parkinson's disease is the second most common neurodegenerative pathology. Due to the limitations of existing therapeutic approaches, novel anti-parkinsonian medicines with non-dopamine mechanisms of action are clearly needed. One of the promising pharmacological targets for anti-Parkinson drug development is phosphodiesterase (PDE) 10A. The stimulating motor effects of PDE10A inhibition were detected only under the conditions of partial dopamine depletion. The results raise the question of whether PDE10A inhibitors are able to restore locomotor activity when dopamine levels are very low. To address this issue, we (1) developed and validated the rat model of acute severe dopamine deficiency and (2) tested the action of PDE10A inhibitor MP-10 in this model. All experiments were performed in dopamine transporter knockout (DAT-KO) rats. A tyrosine hydroxylase inhibitor, α-Methyl-DL-tyrosine (αMPT), was used as an agent to cause extreme dopamine deficiency. In vivo tests included estimation of locomotor activity and catalepsy levels in the bar test. Additionally, we evaluated the tissue content of dopamine in brain samples by HPLC analysis. The acute administration of αMPT to DAT-KO rats caused severe depletion of dopamine, immobility, and catalepsy (Dopamine-Deficient DAT-KO (DDD) rats). As expected, treatment with the L-DOPA and carbidopa combination restored the motor functions of DDD rats. Strikingly, administration of MP-10 also fully reversed immobility and catalepsy in DDD rats. According to neurochemical studies, the action of MP-10, in contrast to L-DOPA + carbidopa, seems to be dopamine-independent. These observations indicate that targeting PDE10A may represent a new promising approach in the development of non-dopamine therapies for Parkinson's disease.

Behavioral Tasks Evaluating Schizophrenia-like Symptoms in Animal Models: A Recent Update

BACKGROUND

Schizophrenia is a serious mental illness that affects more than 21 million people worldwide. Both genetics and the environment play a role in its etiology and pathogenesis. Symptoms of schizophrenia are mainly categorized into positive, negative, and cognitive. One major approach to identify and understand these diverse symptoms in humans has been to study behavioral phenotypes in a range of animal models of schizophrenia.

OBJECTIVE

We aimed to provide a comprehensive review of the behavioral tasks commonly used for measuring schizophrenia-like behaviors in rodents together with an update of the recent study findings.

METHODS

Articles describing phenotypes of schizophrenia-like behaviors in various animal models were collected through a literature search in Google Scholar, PubMed, Web of Science, and Scopus, with a focus on advances over the last 10 years.

RESULTS

Numerous studies have used a range of animal models and behavioral paradigms of schizophrenia to develop antipsychotic drugs for improved therapeutics. In establishing animal models of schizophrenia, the candidate models were evaluated for schizophrenia-like behaviors using several behavioral tasks for positive, negative, and cognitive symptoms designed to verify human symptoms of schizophrenia. Such validated animal models were provided as rapid preclinical avenues for drug testing and mechanistic studies.

CONCLUSION

Based on the most recent advances in the field, it is apparent that a myriad of behavior tests are needed to confirm and evaluate the congruency of animal models with the numerous behaviors and clinical signs exhibited by patients with schizophrenia.

A Natural Product with High Affinity to Sigma and 5-HT7 Receptors as Novel Therapeutic Drug for Negative and Cognitive Symptoms of Schizophrenia

Dehydrocorybulbine (DHCB), an alkaloid from Corydalis yanhusuo. W.T, has been identified as a dopamine receptor antagonist. We extended our assessment of its pharmacological profile and found that DHCB exhibits high to moderate binding affinities to sigma 1 and 2 receptors, serotonin 5-HT7 receptor, and histamine H2 receptors. This led us to evaluate DHCB properties in pharmacological (apomorphine and MK-801) animal models of schizophrenia in mice. The pharmacological profile of DHCB was screened through radioligand receptor binding assays. Single dose of DHCB reversed the locomotor hyperactivity, stereotypy, and prepulse inhibition deficits induced by the dopaminergic agonist apomorphine. DHCB also reversed the depressive-like behavior and memory deficit induced by the glutamatergic antagonist MK-801 in the forced swim and the novel object recognition assays, respectively. These results indicate that DHCB effectively improves schizophrenia-like behavioral deficits that are induced by the disruption of dopaminergic and glutamatergic systems. The effectiveness of DHCB in reversing responses that mimic negative and cognitive deficits of schizophrenia might suggest that its anti-schizophrenia effects are mediated through modulating the activities of several receptor particularly sigma 1, sigma 2, 5-HT7 and dopamine receptors. Our study casts DHCB as a promising lead for therapeutic treatment of schizophrenia.

Antipsychotic-like effects of a novel phosphodiesterase 10A inhibitor T-251 in rodents

Phosphodiesterase 10A (PDE10A) is a dual-substrate PDE that hydrolyzes both cAMP and cGMP. PDE10A is selectively expressed in medium spiny neurons in the striatum, suggesting the potential of PDE10A inhibitors in the treatment of schizophrenia. This study presents the pharmacological profile of a novel PDE10A inhibitor, 2-[(E)-2-(7-fluoro-3-methylquinoxalin-2-yl)vinyl]-6-pyrrolidin-1-yl-N-(tetrahydro-2H-pyran-4-yl)pyrimidin-4-amine hydrochloride (T-251) in rodent models of schizophrenia. T-251 showed a potent inhibitory activity against human PDE10A (IC₅₀ = 0.050 nmol/L) and showed high selectivity over other PDE families which have over 10,000-fold IC₅₀ values. Oral administration of T-251 (0.1-1.0 mg/kg) increased cAMP and cGMP in the striatum in a dose-dependent manner. Oral administration of T-251 attenuated MK-801 induced hyperactivity (ED₅₀ = 0.68 mg/kg) and suppressed conditioned avoidance response (ID₅₀ = 0.87 mg/kg) in rats in a dose dependent manner. Furthermore, T-251 significantly attenuated MK-801 induced prepulse inhibition deficits and cognitive deficits in rats. Unlike haloperidol and olanzapine, T-251 (1.0-30 mg/kg) did not cause catalepsy in rats. Moreover, T-251 (0.6 and 6.0 mg/kg) did not increase plasma levels of prolactin at 1 h after administration, whereas haloperidol and olanzapine significantly increased them. The antipsychotic-like effects and cognitive enhancement of T-251 without catalepsy or plasma prolactin elevation observed in rats suggests that T-251 would be a novel antipsychotic with an improved side-effect profile.

Galphimia glauca and Natural Galphimines Block Schizophrenia-Like Symptoms Induced with Apomorphine and MK-801 in Mice

BACKGROUND

Galphimia glauca has been used for many years in Mexican Traditional Medicine to calm "insane people." Triterpenes, known as galphimines, were identified in this species. One of them, Galphimine-B (G-B), acts selectively on dopaminergic neurons by antagonizing the effect of glutamate on NMDA receptors. The objective of this study was to evaluate the effect of G. glauca methanolic extract (GgMeOH), a Galphimine-Rich Fraction (GRF), as well as the galphimines G-A, G-B, and G-E, on the acute psychosis induced by Apomorphine (APO) in mice and on schizophrenia-like symptoms induced by subchronic administration of MK-801.

METHOD

On the first day, ICR male mice were given GgMeOH, GRF, or one of the galphimines. On day two, animals were treated with APO, and on day 3, they were subjected to behavioral tests. In a second test, MK-801 was administered daily for 28 days. In this case, animals were treated daily with G. glauca products from day 9 to day 28 and then subjected to behavioral tests (passive avoidance test, open field test, forced swimming test, and social interaction test).

RESULTS

The increased number of stereotyped behaviors and grooming behaviors induced with APO were counteracted by all of the experimental treatments. MK-801 induced an increase in immobility time, which was blocked with G-B; GRF counteracted the decreased social interaction, and GgMeOH and GRF prevented the memory loss induced by MK-801.

CONCLUSION

G. glauca and their derivatives products (GRF and galphimines) were able to interact with the dopaminergic and glutamatergic drugs and to block different behaviors associated with some of the positive, negative, and cognitive symptoms of induced schizophrenia in mice. It is necessary to continue with this research, in order to identify their mechanism of action.

Is Forced Swimming Immobility a Good Endpoint for Modeling Negative Symptoms of Schizophrenia? - Study of Sub-Anesthetic Ketamine Repeated Administration Effects

Immobility time in the forced swimming has been described as analogous to emotional blunting or apathy and has been used for characterizing schizophrenia animal models. Several clinical studies support the use of NMDA receptor antagonists to model schizophrenia in rodents. Some works describe the effects of ketamine on immobility behavior but there is variability in the experimental design used leading to controversial results. In this study, we evaluated the effects of repeated administration of ketamine sub-anesthetic doses in forced swimming, locomotion in response to novelty and novel object recognition, aiming a broader evaluation of the usefulness of this experimental approach for modeling schizophrenia in mice. Ketamine (30 mg/kg/day i.p. for 14 days) induced a not persistent decrease in immobility time, detected 24h but not 72h after treatment. This same administration protocol induced a deficit in novel object recognition. No change was observed in mice locomotion. Our results confirm that repeated administration of sub-anesthetic doses of ketamine is useful in modeling schizophrenia-related behavioral changes in mice. However, the immobility time during forced swimming does not seem to be a good endpoint to evaluate the modeling of negative symptoms in NMDAR antagonist animal models of schizophrenia.

MK-801 (Dizocilpine) Regulates Multiple Steps of Adult Hippocampal Neurogenesis and Alters Psychological Symptoms via Wnt/β-Catenin Signaling in Parkinsonian Rats

Adult hippocampal neurogenesis is directly involved in regulation of stress, anxiety, and depression that are commonly observed nonmotor symptoms in Parkinson's disease (PD). These symptoms do not respond to pharmacological dopamine replacement therapy. Excitotoxic damage to neuronal cells by N-methyl-d-aspartate (NMDA) receptor activation is also a major contributing factor in PD development, but whether it regulates hippocampal neurogenesis and nonmotor symptoms in PD is yet unexplored. Herein, for the first time, we studied the effect of MK-801, an NMDA receptor antagonist, on adult hippocampal neurogenesis and behavioral functions in 6-OHDA (6-hydroxydopamine) induced rat model of PD. MK-801 treatment (0.2 mg/kg, ip) increased neural stem cell (NSC) proliferation, self-renewal capacity, long-term survival, and neuronal differentiation in the hippocampus of rat model of PD. MK-801 potentially enhanced long-term survival, improved dendritic arborization of immature neurons, and reduced 6-OHDA induced neurodegeneration via maintaining the NSC pool in hippocampus, leading to decreased anxiety and depression-like phenotypes in the PD model. MK-801 inhibited glycogen synthase kinase-3β (GSK-3β) through up-regulation of Wnt-3a, which resulted in the activation of Wnt/β-catenin signaling leading to enhanced hippocampal neurogenesis in PD model. Additionally, MK-801 treatment protected the dopaminergic (DAergic) neurons in the nigrostriatal pathway and improved motor functions by increasing the expression of Nurr-1 and Pitx-3 in the PD model. Therefore, MK-801 treatment serves as a valuable tool to enhance hippocampal neurogenesis in PD, but further studies are needed to revisit the role of MK-801 in the neurodegenerative disorder before proposing a potential therapeutic candidate.

Striatal phosphodiesterase 10A and medial prefrontal cortical thickness in patients with schizophrenia: a PET and MRI study

The enzyme phosphodiesterase 10A (PDE10A) is abundant in striatal medium spiny neurons and has been implicated in the pathophysiology of schizophrenia in animal models and is investigated as a possible new pharmacological treatment target. A reduction of prefrontal cortical thickness is common in schizophrenia, but how this relates to PDE10A expression is unknown. Our study aim was to compare, we believe for the first time, the striatal non-displaceable binding potential (BP_ND) of the new validated PDE10A ligand [¹¹C]Lu AE92686 between patients with schizophrenia and healthy controls. Furthermore, we aimed to assess the correlation of PDE10A BP_ND to cortical thickness. Sixteen healthy male controls and 10 male patients with schizophrenia treated with clozapine, olanzapine or quetiapine were investigated with positron emission tomography (PET) and magnetic resonance imaging (MRI). Striatal binding potential (BP_ND) of [¹¹C]Lu AE92686 was acquired through dynamic PET scans and cortical thickness by structural MRI. Clinical assessments of symptoms and cognitive function were performed and the antipsychotic dosage was recorded. Patients with schizophrenia had a significantly lower BP_ND of [¹¹C]Lu AE92686 in striatum (P=0.003) than healthy controls. The striatal BP_ND significantly correlated to cortical thickness in the medial prefrontal cortex and superior frontal gyrus across patients with schizophrenia and healthy controls. No significant correlation was observed between the BP_ND for [¹¹C]Lu AE92686 in striatum and age, schizophrenia symptoms, antipsychotic dosage, coffee consumption, smoking, duration of illness or cognitive function in the patients. In conclusion, PDE10A may be important for functioning in the striato-cortical interaction and in the pathophysiology of schizophrenia.

Involvement of GABAB Receptor Signaling in Antipsychotic-like Action of the Novel Orthosteric Agonist of the mGlu4 Receptor, LSP4-2022

Considering that ligands of metabotropic glutamate and GABA receptors may exert beneficial effects on schizophrenia, we assessed the actions of the first mGlu₄-selective orthosteric agonist, LSP4-2022, in several tests reflecting positive, negative, and cognitive symptoms of schizophrenia. Moreover, we investigated the possible involvement of GABA_B receptors in LSP4-2022-induced actions. Hyperactivity induced by MK-801 or amphetamine and DOI-induced head twitches in mice were used as the models of positive symptoms. The social interaction test, modified forced swim test (FST), and novel object recognition (NOR) test were used as the models of negative and cognitive symptoms of schizophrenia. LSP4-2022 inhibited hyperactivity (in a dose-dependent manner, 0.5-2 mg/kg) induced by MK-801 or amphetamine and DOI-induced head twitches. In mGlu₄ receptor knockout mice, LSP4-2022 was not effective. However, it reversed MK-801-induced impairment in the social interaction test and the MK-801-induced increase of immobility in the modified FST. In the NOR test, LSP4-2022 was active at a dose of 2 mg/kg. GABA_B receptor antagonist, CGP55845 (10 mg/kg), reversed LSP4-2022-induced effects in hyperactivity and head twitch tests. At the same time, the simultaneous administration of subeffective doses of LSP4-2022 (0.1 mg/kg) and a positive allosteric modulator of GABA_B receptor PAM, GS39783 (0.1 mg/kg), induced clear antipsychotic-like effects in those two tests. Such an interaction between mGlu₄ and GABA_B receptors was not observed in the social interaction and NOR tests. Therefore, we suggest that the activation of the mGlu₄ receptor is a promising approach facilitating the discovery of novel antipsychotic drugs, and that the interplay between mGlu₄ and GABA_B receptors may become the basis for a novel therapy for schizophrenic patients with predomination of positive symptoms.

Stimulation of the metabotropic glutamate (mGlu) 2 receptor attenuates the MK-801-induced increase in the immobility time in the forced swimming test in rats

BACKGROUND

Negative symptoms of schizophrenia are poorly managed using the currently available antipsychotics. Previous studies indicate that agonists of the metabotropic glutamate (mGlu) 2/3 receptors may provide a novel approach for the treatment of schizophrenia. However, the effects of mGlu2/3 receptor agonists or mGlu2 receptor positive allosteric modulators have not yet been clearly elucidated in animal models of the negative symptoms of schizophrenia. Recently, we reported that the forced swimming test in rats treated with subchronic MK-801, an NMDA receptor antagonist, may be regarded as a useful test to evaluate the activities of drugs against the negative symptoms of schizophrenia.

METHODS

We evaluated the effects of LY379268, an mGlu2/3 receptor agonist, and BINA, an mGlu2 receptor positive allosteric modulator, on the hyperlocomotion induced by acute administration of MK-801 (0.15mg/kg, sc) and on the increase in the immobility time in the forced swimming test induced by subchronic treatment with MK-801 (0.5mg/kg, sc, twice a day for 7 days) in rats.

RESULTS

Both LY379268 (3mg/kg, sc) and BINA (100mg/kg, ip) attenuated the increase in the immobility time induced by subchronic treatment with MK-801 at the same doses at which they attenuated the MK-801-induced increase in locomotor activity, but had no effect on the immobility time in saline-treated rats.

CONCLUSIONS

The present results suggest that stimulation of the mGlu2 receptor attenuates the increase in the immobility time in the forced swimming test elicited by subchronic administration of MK-801, and may be potentially useful for treatment of the negative symptoms of schizophrenia.

Evaluation of a novel PDE10A PET radioligand, [(11) C]T-773, in nonhuman primates: brain and whole body PET and brain autoradiography

Phosphodiesterase 10A (PDE10A) is considered to be a key target for the treatment of several neuropsychiatric diseases. The characteristics of [(11) C]T-773, a novel positron emission tomography (PET) radioligand with high binding affinity and selectivity for PDE10A, were evaluated in autoradiography and in nonhuman primate (NHP) PET. Brain PET measurements were performed under baseline conditions and after administration of a selective PDE10A inhibitor, MP-10. Total distribution volume (VT ) and binding potential (BPND ) were calculated using various kinetic models. Whole body PET measurements were performed to calculate the effective dose of [(11) C]T-773. Autoradiography studies in postmortem human and monkey brain sections showed high accumulation of [(11) C]T-773 in the striatum and substantia nigra which was blocked by MP-10. Brain PET showed high accumulation of [(11) C]T-773 in the striatum, and the data could be fitted using a two tissue compartment model. BPND was approximately 1.8 in the putamen when the cerebellum was used as the reference region. Approximately 70% of PDE10A binding was occupied by 1.8 mg/kg of MP-10. Whole body PET showed high accumulation of [(11) C]T-773 in the liver, kidney, heart, and brain in the initial phase. The radioligand was partly excreted via bile and the gastrointestinal tract, and partly excreted through the urinary tract. The calculated effective dose was 0.007 mSv/MBq. In conclusion, [(11) C]T-773 was demonstrated to be a promising PET radioligand for PDE10A with favorable brain kinetics. Dosimetry results support multiple PET measurements per person in human studies. Further research is required with [(11) C]T-773 in order to test the radioligand's potential clinical applications.

Pharmacological evaluation of a novel phosphodiesterase 10A inhibitor in models of antipsychotic activity and cognition

In this study, we report the pharmacological effects of a novel PDE10A inhibitor, SEP-39. SEP-39 is a potent (1.0nM) inhibitor of human PDE10A in vitro, with good selectivity (>16000-fold) against other PDEs. In an in vivo occupancy study, the RO50 value was determined to be 0.7mg/kg (p.o.), corresponding to plasma and brain exposures of 28ng/mL and 43ng/g, respectively. Using microdialysis, we show that 3mg/kg (p.o.) SEP-39 significantly increased rat striatal cGMP concentrations. Furthermore, SEP-39 inhibits PCP-induced hyperlocomotion at doses of 1 and 3mg/kg (p.o.) corresponding to 59-86% occupancy. At similar doses in a catalepsy study, the time on the bar was increased but the maximal effect was less than that seen with haloperidol. In an EEG study, 3 and 10mg/kg (p.o.) SEP-39 suppressed REM intensity and increased the latency to REM sleep. We also demonstrate the procognitive effects of SEP-39 in the rat novel object recognition assay. These effects appear to require less PDE10A inhibition than the reversal of PCP-induced hyperlocomotion or EEG effects, as improvements in recognition index were seen at doses of 0.3mg/kg and above. Our data demonstrate that SEP-39 is a potent, orally active PDE10A inhibitor with therapeutic potential in a number of psychiatric indications.

Antipsychotic activity of standardized Bacopa extract against ketamine-induced experimental psychosis in mice: Evidence for the involvement of dopaminergic, serotonergic, and cholinergic systems

CONTEXT

Schizophrenia is a chronic disabling psychiatric disorder affecting 1% of the population worldwide. Due to the adverse effects of available antipsychotic medications, recent investigations have focused on the search for well-tolerated, safe molecules from natural resources to control the severity and progression of schizophrenia.

OBJECTIVE

To screen the standardized extract of Bacopa monniera Linn. (Scrophulariaceae) (BM) for its antipsychotic potential in the ketamine-induced psychosis model with mice.

MATERIALS AND METHODS

Graded dose of BM (40, 80, and 120 mg/kg, p.o.) were given to the mice 1 h prior to ketamine administration and tested for positive symptoms and cognitive deficits. A chronic ketamine treatment regimen was used to study the effect of BM on negative symptoms such as immobility enhancement. Each mouse was used once for the behavioral studies.

RESULTS

BM reduced ketamine-induced hyperactivity with an EC50 value of 76.60 mg/kg. The 80 mg/kg dose was used for all other behavior analysis. Pretreatment with BM at 80 mg/kg showed two-fold increases in transfer latency time (TLT) in passive avoidance task. Chronic BM pretreatment (80 mg/kg p.o. daily × 10 d) ameliorated the ketamine-induced enhanced immobility effect by 21% in the forced swim test. BM treatment reversed ketamine-induced increase in monoamine oxidase activity in both cortex and striatum and normalized the acetylcholinesterase activity and the glutamate levels in the hippocampus.

DISCUSSION AND CONCLUSION

Overall our findings suggest that BM possesses antipsychotic properties which might be due to its modulatory action on dopamine, serotonin, and glutamate neurotransmission.

Immobility behavior during the forced swim test correlates with BNDF levels in the frontal cortex, but not with cognitive impairments

The forced swim test (FST) is widely used to evaluate the antidepressant-like activity of compounds and is sensitive to stimuli that cause depression-like behaviors in rodents. The immobility behavior observed during the test has been considered to represent behavioral despair. In addition, some studies suggest that the FST impairs rats' performance on cognitive tests, but these findings have rarely been explored. Thus, we investigated the effects of the FST on behavioral tests related to neuropsychiatric diseases that involve different cognitive components: novel object recognition (NOR), the object location test (OLT) and prepulse inhibition (PPI). Brain-derived neurotrophic factor (BDNF) levels in the frontal cortex and hippocampus were evaluated. The rats were forced to swim twice (15-min session followed by a 5-min session 24h later) and underwent cognitive tests 24h after the last swimming exposure. The FST impaired the rats' performance on the OLT and reduced the PPI and acoustic startle responses, whereas the NOR was not affected. The cognitive impairments were not correlated with an immobility behavior profile, but a significant negative correlation between the frontal BDNF levels and immobility behavior was identified. These findings suggest a protective role of BDNF against behavioral despair and demonstrate a deleterious effect of the FST on spatial memory and pre-attentive processes, which point to the FST as a tool to induce cognitive impairments analogous to those observed in depression and in other neuropsychiatric disorders.

Donepezil and the alpha-7 agonist PHA 568487, but not risperidone, ameliorate spatial memory deficits in a subchronic MK-801 mouse model of cognitive impairment in schizophrenia

Cognitive impairment associated with schizophrenia (CIAS) is an important etiological feature of this disorder with implications for symptom severity and quality of life. Acute N-methyl-d-aspartate receptor (NMDAR) blockade using MK-801, a non-competitive antagonist to NMDARs, is assumed to produce temporary cognitive impairments in mice similar to those seen in schizophrenia patients. Less is known, however, about the effects of subchronic MK-801 administration on cognition. In the current study, twenty-eight male C57/BL6 mice received a daily dose of MK-801 (0.1mg/kg, i.p.) for seven days. Spatial memory was assessed using an object location task prior to MK-801 administration as well as at multiple time points after the treatment. Subchronic treatment with MK-801 caused lasting memory deficits, which were ameliorated by acute doses of an acetylcholinesterase inhibitor (donepezil) and an alpha-7 nicotinic agonist (PHA 568487), but were unaffected by acute administration of the atypical antipsychotic risperidone. Subchronic administration of MK-801 may lend this pharmaceutical model increased face validity, while its resemblance to prodromal schizophrenia makes it suitable for screening new CIAS treatments.

Phosphodiesterase 10A inhibitor MP-10 effects in primates: comparison with risperidone and mechanistic implications

Phosphodiesterase 10A (PDE10A) is highly expressed in striatal medium spiny neurons of both the direct and indirect output pathways. Similar to dopamine D₂ receptor antagonists acting on indirect pathway neurons, PDE10A inhibitors have shown behavioral effects in rodent models that predict antipsychotic efficacy. These findings have supported the clinical investigation of PDE10A inhibitors as a new treatment for schizophrenia. However, PDE10A inhibitors and D₂ antagonists differ in effects on direct pathway and other neurons of the basal ganglia, indicating that these two drug classes may have divergent antipsychotic efficacy and side effect profile. In the present study, we compare the behavioral effects of the selective PDE10A inhibitor MP-10 to those of the clinical standard D₂ antagonist risperidone in rhesus monkeys using a standardized motor disability scale for parkinsonian primates and a newly designed "Drug Effects on Nervous System" scale to assess non-motor effects. Behavioral effects of MP-10 correlated with its plasma levels and its regulation of metabolic activity in striatal and cortical regions as measured by FDG-PET imaging. While MP-10 and risperidone broadly impacted similar behavioral domains in the primate, their effects had a different underlying basis. MP-10-treated animals retained the ability to respond but did not engage tasks, whereas risperidone-treated animals retained the motivation to respond but were unable to perform the intended actions. These findings are discussed in light of what is currently known about the modulation of striatal circuitry by these two classes of compounds, and provide insight into interpreting emerging clinical data with PDE10A inhibitors for the treatment of psychotic symptoms.

Antidepressants and mood stabilizers effects on histone deacetylase expression in C57BL/6 mice: Brain region specific changes

To determine whether treatment with various antidepressants or mood stabilizers leads to region-specific changes, we investigated the effects of their subchronic (14 days of intraperitoneal injection) administration on the tissue concentration of monoamines, dopamine, serotonin, and norepinephrine, and the protein expression of acetylated histone H3 (AcH3) and histone deacetylases (HDACs) in the mouse striatum (ST), nucleus accumbens (Acb), hippocampus (Hip), cingulate cortex (Cg), and amygdala (Amy). Subchronic administration with the antidepressants (S)-citalopram oxalate (ECM), duloxetine hydrochloride (DLX), and mirtazapine (MIR) commonly induced significant increases in dopamine and serotonin levels in the ST and Cg. By contrast, no common profiles for dopamine, serotonin, or norepinephrine were identified in the Acb, Hip, or Amy. Treatment with sodium valproate (VPA), lithium chloride (Li), lamotrigine (LTG), levetiracetam (LTM), olanzapine (OLZ), clozapine (CLZ), clomipramine (CLM), ECM, and DLX induced significant increases in AcH3 expression in the Acb, while treatment with CLM, ECM, DLX, MIR, carbamazepine (CBZ), LTG, LTM, OLZ, or CLZ induced significant increases in HDAC2 and HDAC3 in the ST. CLM, MIR, VPA, CBZ, LTG, LTM, OLZ, or CLZ induced significant increases in HDAC3 in the Cg, and ECM, DLX, MIR, VPA, CBZ, LTG, LTM, or OLZ resulted in significant increases in HDAC5 in the Amy. Collectively, the changes of monoamine content were restricted for mood stabilizer effects, but increased expression of HDAC2, HDAC3, or HDAC5 in the ST, Cg, or Amy was often found, supporting the possibility that antidepressant-like effects involve epigenetic modifications associated with changes in HDAC expression.

Phosphodiesterase Inhibitors as a New Therapeutic Approach for the Treatment of Parkinson’s Disease

Phosphodiesterases (PDEs) are expressed in different brain areas including the striatum. PDEs have recently emerged as important drug targets for central nervous system disorders, including Parkinson’s disease (PD). Levels of cyclic adenosine monophosphate (cAMP) control many cellular signaling pathways and are crucial for the dopamine signal, which is disturbed in PD due to the progressive loss of dopaminergic neurons. PDEs play a key role in cAMP homeostasis, as they are the enzymes responsible for its degradation. Moreover, beyond dopamine neurotransmission, cAMP is involved in many other cellular processes, such as neuroinflammation and neuronal plasticity. This enhances the value of PDEs as promising pharmacological targets for neurological disorders. Furthermore, cAMP‐PDE inhibitors with drug profiles may be used in the near future as disease‐modifying drugs for the treatment of PD. A concise review of the main roles of cAMP‐PDEs expressed in the striatum and the potential of their inhibitors in different animal models of PD is described in this chapter.

Blonanserin reverses the phencyclidine (PCP)-induced impairment in novel object recognition (NOR) in rats: role of indirect 5-HT(1A) partial agonism

Blonanserin is an atypical antipsychotic drug (APD) which, compared to other atypical APDs, is a relatively selective serotonin (5-HT)2A and dopamine D2 antagonist. Comparing blonanserin with more broadly acting atypical APDs could be useful to test the contributions of actions at other monoamine receptors, e.g. 5-HT1A receptors, to the reversal of PCP-induced novel object recognition (NOR) deficit. In this study, we tested the effect of blonanserin alone, and in combination with 5-HT1A agents, on NOR deficit induced by subchronic treatment with the N-methyl-D-aspartate (NMDA) receptor antagonist, phencyclidine (PCP; 2 mg/kg), b.i.d., for 7 days. Blonanserin, 1mg/kg, but not 0.3mg/kg, improved the PCP-induced NOR deficit. However, at 1mg/kg, object exploration was diminished. Co-administration of sub-effective doses of blonanserin (0.3 mg/kg) and the 5-HT1A partial agonist, tandospirone (0.2 mg/kg), significantly reversed the NOR deficit without diminishing activity during the acquisition or retention periods. The combination of WAY100635 (0.6 mg/kg), a 5-HT1A antagonist, and blonanserin (1 mg/kg), also diminished object exploration which prevented assessment of the effect of this combination on NOR. WAY100635 (0.6 mg/kg) blocked the ameliorating effect of risperidone (0.1 mg/kg), another atypical APD with low affinity for 5-HT1A receptors, but did not impair exploration. These results suggest that blonansein and risperidone, atypical APDs which lack a direct action on 5-HT1A receptors require 5-HT1A receptor stimulation to reverse the subchronic PCP-induced NOR deficit and provide a support for clinical trial of blonanserin in combination with tandospirone to ameliorate cognitive impairment in schizophrenia and to have fewer side effects.