MK-801-induced and scopolamine-induced hyperactivity in rats neonatally treated chronically with MK-801

Two distinct enriched housings differentially ameliorate object and place recognition deficits in a rat model of schizophrenia

Schizophrenia is a psychiatric disorder characterized by cognitive dysfunctions. These dysfunctions significantly impact the daily lives of schizophrenic patients, yet effective interventions remain scarce. In this study, we explored the effects of two enriched housing types-cognitive and physical-on cognitive dysfunctions in a rat model of schizophrenia. Male neonatal Wistar-Imamichi rats were administered MK-801, a noncompetitive NMDAR antagonist, twice daily from postnatal day (PND) 7 to PND 20. Physical enrichment ameliorated memory deficits in both object and place recognition tests, while cognitive enrichment primarily improved object recognition performance. Our findings suggest that exercise therapy could be a potential approach to address cognitive dysfunctions in schizophrenia patients.

Tacrine-Based Hybrids: Past, Present, and Future

Alzheimer's disease (AD) is a neurodegenerative disorder which is characterized by β-amyloid (Aβ) aggregation, τ-hyperphosphorylation, and loss of cholinergic neurons. The other important hallmarks of AD are oxidative stress, metal dyshomeostasis, inflammation, and cell cycle dysregulation. Multiple therapeutic targets may be proposed for the development of anti-AD drugs, and the "one drug-multiple targets" strategy is of current interest. Tacrine (THA) was the first clinically approved cholinesterase (ChE) inhibitor, which was withdrawn due to high hepatotoxicity. However, its high potency in ChE inhibition, low molecular weight, and simple structure make THA a promising scaffold for developing multi-target agents. In this review, we summarized THA-based hybrids published from 2006 to 2022, thus providing an overview of strategies that have been used in drug design and approaches that have resulted in significant cognitive improvements and reduced hepatotoxicity.

Neonatal blockade of NR2A-containing but not NR2B-containing NMDA receptor induces spatial working memory deficits in adult rats

The immature brain is highly sensitive to disturbances in the functioning of N-methyl-d-aspartate (NMDA) receptor in rodents, and blockade of the receptor during postnatal brain development period causes schizophrenia-like behavior in adulthood. During the postnatal period, NR2A- and NR2B-containing NMDA receptors are highly expressed, and these two subunits show different expression patterns in the brain. However, the functions of these two NMDA receptors are unknown. In this study, we treated rats with an NR2A-preferring NMDA receptor antagonist (PEAQX, 10 mg/kg), an NR2B-selective NMDA receptor antagonist (ifenprodil, 7.5 mg/kg), or a nonselective blocker of the NMDA receptor (MK-801, 0.4 mg/kg) during the neonatal period. Rats neonatally treated with MK-801 or PEAQX showed spatial working memory deficits in the Y-maze test. PEAQX-treated rats also showed greater reactivity to acoustic stimuli and hypersensitivity to acute MK-801 challenge. However, ifenprodil treatment did not cause any detectable behavioral changes. These results suggest that the NR2A-containing NMDA receptor is indispensable for proper brain development in rats, and functional disturbances in this subunit impair hippocampus-dependent spatial working memory in adulthood.

Antipsychotic-like profile of CIQ isomers in animal models of schizophrenia

Earlier, we have shown the efficacy of racemic (±) CIQ, a positive allosteric modulator of GluN2C/2D receptor against MK-801 induced impairment of prepulse inhibition as well as working memory. The present study investigated the antipsychotic-like profile of different CIQ (±, +, -) isomers against schizophrenia-like symptoms in series of behavioural animal models like apomorphine climbing, social isolation behaviour and NMDA receptor antagonist MK-801 induced cognitive deficits. Further, we also tested CIQ (±, +, -) isomers in neurodevelopmental model against MK-801induced deficits using open field test, Y-maze test and novel object recognition test. CIQ (±, +, -) isomers decreased climbing behaviour, increased social interaction and improved the MK-801 induced deficits in working memory in Y-maze. Further, CIQ (±, +) but not CIQ (-) improved the recognition memory in novel object recognition test as well as reduced hyperlocomotion and stereotyped behaviour. We conclude that CIQ (±, +) but not CIQ (-) exhibit the significant antipsychotic-like profile.

Effect of Neuroprotective Magnesium Sulfate Treatment on Brain Transcription Response to Hypoxia Ischemia in Neonate Mice

MgSO₄ is widely used in the prevention of preterm neurological disabilities but its modes of action remain poorly established. We used a co-hybridization approach using the transcriptome in 5-day old mice treated with a single dose of MgSO₄ (600 mg/kg), and/or exposed to hypoxia-ischemia (HI). The transcription of hundreds of genes was altered in all the groups. MgSO₄ mainly produced repressions culminating 6 h after injection. Bio-statistical analysis revealed the repression of synaptogenesis and axonal development. The putative targets of MgSO₄ were Mnk1 and Frm1. A behavioral study of adults did not detect lasting effects of neonatal MgSO₄ and precluded NMDA-receptor-mediated side effects. The effects of MgSO₄ plus HI exceeded the sum of the effects of separate treatments. MgSO₄ prior to HI reduced inflammation and the innate immune response probably as a result of cytokine inhibition (Ccl2, Ifng, interleukins). Conversely, MgSO₄ had little effect on HI-induced transcription by RNA-polymerase II. De novo MgSO₄-HI affected mitochondrial function through the repression of genes of oxidative phosphorylation and many NAD-dehydrogenases. It also likely reduced protein translation by the repression of many ribosomal proteins, essentially located in synapses. All these effects appeared under the putative regulatory MgSO₄ induction of the mTORC2 Rictor coding gene. Lasting effects through Sirt1 and Frm1 could account for this epigenetic footprint.

Positive allosteric modulation of M1 and M4 muscarinic receptors as potential therapeutic treatments for schizophrenia

Current antipsychotic drugs provide symptomatic relief for positive symptoms of schizophrenia, but do not offer symptom management for negative and cognitive symptoms. In addition, many patients discontinue treatment due to adverse side effects. Therefore, there is a critical need to develop more effective and safe treatment options. Although the etiology of schizophrenia is unclear, considerable data from post-mortem, neuroimaging and neuropharmacology studies support a role of the muscarinic acetylcholine (mAChRs) in the pathophysiology of schizophrenia. Substantial evidence suggests that activation of mAChRs has the potential to treat all symptom domains of schizophrenia. Despite encouraging results in demonstrating efficacy, clinical trials of nonselective mAChR agonists were limited in their clinical utility due to dose-limiting peripheral side effects. Accordingly, efforts have been made to specifically target centrally located M1 and M4 mAChR subtypes devoid of adverse-effect liability. To circumvent this limitation, there have been tremendous advances in the discovery of ligands that bind at allosteric sites, binding sites distinct from the orthosteric site, which are structurally less conserved and thereby afford high levels of receptor subtype selectivity. The discovery of subtype-specific allosteric modulators has greatly advanced our understanding of the physiological role of various muscarinic receptor subtypes in schizophrenia and the potential utility of M1 and M4 mAChR subtypes as targets for the development of novel treatments for schizophrenia and related disorders. This article is part of the Special Issue entitled 'Neuropharmacology on Muscarinic Receptors'.

MK-801-induced deficits in social recognition in rats: reversal by aripiprazole, but not olanzapine, risperidone, or cannabidiol

Deficiencies in social activities are hallmarks of numerous brain disorders. With respect to schizophrenia, social withdrawal belongs to the category of negative symptoms and is associated with deficits in the cognitive domain. Here, we used the N-methyl-D-aspartate receptor antagonist dizocilpine (MK-801) for induction of social withdrawal in rats and assessed the efficacy of several atypical antipsychotics with different pharmacological profiles as putative treatment. In addition, we reasoned that the marijuana constituent cannabidiol (CBD) may provide benefit or could be proposed as an adjunct treatment in combination with antipsychotics. Hooded Lister rats were tested in the three-chamber version for social interaction, with an initial novelty phase, followed after 3 min by a short-term recognition memory phase. No drug treatment affected sociability. However, distinct effects on social recognition were revealed. MK-801 reduced social recognition memory at all doses (>0.03 mg/kg). Predosing with aripiprazole dose-dependently (2 or 10 mg/kg) prevented the memory decline, but doses of 0.1 mg/kg risperidone or 1 mg/kg olanzapine did not. Intriguingly, CBD impaired social recognition memory (12 and 30 mg/kg) but did not rescue the MK-801-induced deficits. When CBD was combined with protective doses of aripiprazole (CBD-aripiprazole at 12 :  or 5 : 2 mg/kg) the benefit of the antipsychotic was lost. At the same time, activity-related changes in behaviour were excluded as underlying reasons for these pharmacological effects. Collectively, the combined activity of aripiprazole on dopamine D2 and serotonin 5HT1A receptors appears to provide a significant advantage over risperidone and olanzapine with respect to the rescue of cognitive deficits reminiscent of schizophrenia. The differential pharmacological properties of CBD, which are seemingly beneficial in human patients, did not back-translate and rescue the MK-801-induced social memory deficit.

Enriched environment improves synaptic plasticity and cognitive deficiency in chronic cerebral hypoperfused rats

Recent studies have indicated that environmental enrichment (EE) increases the sensorial and social stimulations and leads to strengthened plastic changes in the brain. In models of chronic cerebral hypoperfusion, the ability of an EE to restore the cognition depends on hippocampal synaptic plasticity. The mechanisms for this effect have not, however, been adequately studied. Thus, the aim of the present study was to evaluate the neuroprotective effects and underlying mechanism of environmental enrichment by assessment of spatial memory tasks as well as parameters of synaptic plasticity in rats subjected to occlusion of the bilateral common carotid arteries (2-VO) model. Male Sprague-Dawley rats were used in this study. The model group was established by occlusion of the bilateral common carotid arteries. The animals were tested for learning, memory performance and synaptic plasticity using Morris water maze (MWM), 8-arm Radial Maze (RM), and field potential recording, respectively. The rats subjected to 2-VO in EE exhibited a significantly lower number of working errors and reference errors in RM. Moreover, the enriched environment recovered the memory performance of hypoperfused rats and decreased the swimming time to reach the platform in MWM. In addition, conditions of the environment did not have any effect on baseline synaptic transmission and presynaptic plasticity, but housing the animals in EE rescued the impairment of LTP induction induced by 2-VO. These results suggest that EE ameliorates the LTP and spatial memory impairment induced by 2-VO. Our data indicated that the LTP recovery by EE in the rat models of 2-VO is probably mediated by post-synaptic mechanisms.

Enriched environment prevents cognitive and motor deficits associated with postnatal MK-801 treatment

RATIONALE

Previous studies have shown the beneficial effects of enriched environment (EE) in rescuing behavioral deficits such as pre-pulse inhibition and locomotor hyperactivity associated with N-methyl-D-aspartate (NMDA) receptor blockade; however, cognitive deficits remain unresponsive.

OBJECTIVES

We designed experiments to determine the consequences of raising rat pups in an EE on several behavioral aberrations, mainly cognitive deficits, observed in rats postnatally exposed to MK-801 (NMDA receptor antagonist).

METHODS

Male Wistar rats were injected with MK-801 (1 mg/kg) from postnatal day (P) 6-10. Rat pups were housed in an EE from birth up to the time of behavioral experiments at P28-34. The effects of EE in correcting MK-801-associated behaviors were assessed by rotarod, wire grip, open filed, and Morris water maze tests.

RESULTS

We found that EE not only has beneficial effects on cognitive performance of normal rats but also prevents spatial learning and memory deficits in Morris water maze induced by MK-801. Postnatal MK-801 treatment also led to motor deficits both in wire grip and accelerating rotarod tests. These deficits were not observed in MK-801-treated rats raised in EE. In the open field test, EE prevented increase in "frequency of grooming" and decrease in "time spent in the center" associated with MK-801.

CONCLUSIONS

Our results suggest that exposure to an EE would be strongly beneficial in correcting deficits, notably cognitive, associated with MK-801. Given that the postnatal MK-801 treatment represents an animal model of schizophrenia, we propose timely environmental interventions might be an effective strategy in the protection against schizophrenia.