Latent inhibition in rats neonatally treated chronically with MK-801: Differential effects on conditioned taste aversion and conditioned emotional response

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.

Network pharmacology, experimental validation and pharmacokinetics integrated strategy to reveal pharmacological mechanism of goutengsan on methamphetamine dependence

Background

Goutengsan (GTS) is a traditional Chinese medicine formula that can improve multiple nervous system diseases, such as methamphetamine (MA) dependence. However, the mechanism how GTS treats MA dependence remains unclear. This study was aimed to investigate the action mechanism of GTS on MA dependence using network pharmacology, in vivo/in vitro experimental validation, pharmacokinetics, and tissue distribution in the brain.

Materials and Methods

The bioactive ingredients from GTS and possible targeted genes for treating MA dependence were predicted using network pharmacology. The binding of key components of GTS to the predicted proteins was studied using molecular docking, and the key components were verified by HPLC. The effects of GTS on an MA-induced model in rats and SH-SY5Y cells were studied. The regulatory effects of GTS on the expressions of predicted MAPK pathway-related proteins in rat brain tissues and SH-SY5Y cells were validated. Furthermore, the plasma exposure and brain tissue distribution of GTS ingredients for MA dependence treatment and MAPK pathway regulation were studied in mice.

Results

Network pharmacology screened 53 active ingredients, and 287 potential targets of GTS, and showed the MAPK pathway was among the most relevant pathways. Molecular docking showed that key active ingredients (e.g., 6-gingerol, liquiritin and rhynchophylline) bound strongly with MAPK core targets, such as MAPK3, and MAPK8. Five compounds of GTS were detected by HPLC, including 6-gingerol, chlorogenic acid, liquiritin, 5-o-methylviscumaboloside and hesperidin. GTS had a therapeutic effect on MA-dependent rats, and reduced hippocampal CA1 damage and relative expressions of p-MAPK3/MAPK3, p-MAPK8/MAPK8 in brain tissues induced by MA. GTS counteracted aberrant alterations in cAMP, 5-TH and cellular morphology induced by MA induction and exerts therapeutic effects on MA-induced SH-SY5Y cell models. GTS also can antagonize the high expressions of MAPK-related proteins in MA-induced SH-SY5Y cells. Pharmacokinetic experiment revealed the four ingredients of GTS (e.g., chlorogenic acid, 5-o-methylviscumaboloside, hesperidin and rhynchophylline) were exposed in the plasma and brain, which demonstrates its pharmacological effect on MA dependence.

Conclusion

GTS treats MA dependence by regulating the MAPK pathway via multiple bioactive ingredients. The network pharmacology, experimental validation and pharmacokinetics integrated strategy is efficient in discovering the key pharmacological mechanism of herbal formulae.

Rhynchophylline inhibits methamphetamine dependence via modulating the miR-181a-5p/GABRA1 axis

ETHNOPHARMACOLOGICAL RELEVANCE

Uncaria rhynchophylla (Miq.) Miq. ex Havil. is a plant species that is routinely devoted in traditional Chinese medicine to treat central nervous system disorders. Rhynchophylline (Rhy), a predominant alkaloid isolated from Uncaria rhynchophylla (Miq.) Miq. ex Havil., has been demonstrated to reverse methamphetamine-induced (METH-induced) conditioned place preference (CPP) effects in mice, rats and zebrafish. The precise mechanism is still poorly understood, thus further research is necessary.

AIM OF STUDY

This study aimed to investigate the role of miRNAs in the inhibitory effect of Rhy on METH dependence.

MATERIALS AND METHODS

A rat CPP paradigm and a PC12 cell addiction model were established. Microarray assays were used to screen and identify the candidate miRNA. Behavioral assessment, real-time PCR, dual-luciferase reporter assay, western blotting, stereotaxic injection of antagomir/agomir and cell transfection experiments were performed to elucidate the effect of the candidate miRNA and intervention mechanism of Rhy on METH dependence.

RESULTS

Rhy successfully reversed METH-induced CPP effect and the upregulated miR-181a-5p expression in METH-dependent rat hippocampus and PC12 cells. Moreover, suppression of miR-181a-5p by antagomir 181a reversed METH-induced CPP effect. Meanwhile, overexpression of miR-181a-5p by agomir 181a in combination with low-dose METH (0.5 mg/kg) elicited a significant CPP effect, which was blocked by Rhy through inhibiting miR-181a-5p. Finally, the result demonstrated that miR-181a-5p exerted its regulatory role by targeting γ-aminobutyric acid A receptor α1 (GABRA1) both in vivo and in vitro.

CONCLUSION

This finding reveals that Rhy inhibits METH dependence via modulating the miR-181a-5p/GABRA1 axis, which may be a promising target for treatment of METH dependence.

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.

Effects of chronic forced-swim stress on behavioral properties in rats with neonatal repeated MK-801 treatment

The two-hit hypothesis has been used to explain the onset mechanism of schizophrenia. It assumes that predisposition to schizophrenia is originally attributed to vulnerability in the brain which stems from genetic or early developmental factors, and that onset is triggered by exposure to later detrimental factors such as stress in adolescence or adulthood. Based on this hypothesis, the present study examined whether rats that had received neonatal repeated treatment with an N-methyl-d-aspartate (NMDA) receptor antagonist (MK-801), an animal model of schizophrenia, were vulnerable to chronic stress. Rats were treated with MK-801 (0.2mg/kg) or saline twice daily on postnatal days 7-20, and animals in the stress subgroups were subjected to 20days (5days/week×4weeks) of forced-swim stress in adulthood. Following this, behavioral tests (prepulse inhibition, spontaneous alternation, open-field, and forced-swim tests) were carried out. The results indicate that neonatal repeated MK-801 treatment in rats inhibits an increase in immobility in the forced-swim test after they have experienced chronic forced-swim stress. This suggests that rats that have undergone chronic neonatal repeated NMDA receptor blockade could have a reduced ability to habituate or adapt to a stressful situation, and supports the hypothesis that these rats are sensitive or vulnerable to stress.

Activation of the hypothalamic-pituitary-adrenal axis in lithium-induced conditioned taste aversion learning

Intraperitoneal injections (ip) of lithium chloride at large doses induce c-Fos expression in the brain regions implicated in conditioned taste aversion (CTA) learning, and also activate the hypothalamic-pituitary-adrenal (HPA) axis and increase the plasma corticosterone levels in rats. A pharmacologic treatment blunting the lithium-induced c-Fos expression in the brain regions, but not the HPA axis activation, induced CTA formation. Synthetic glucocorticoids at conditioning, but not glucocorticoid antagonist, attenuated the lithium-induced CTA acquisition. The CTA acquisition by ip lithium was not affected by adrenalectomy regardless of basal corticosterone supplement, but the extinction was delayed in the absence of basal corticosterone. Glucocorticoids overloading delayed the extinction memory formation of lithium-induced CTA. ip lithium consistently induced the brain c-Fos expression, the HPA activation and CTA formation regardless of the circadian activation of the HPA axis. Intracerebroventricular (icv) injections of lithium at day time also increased the brain c-Fos expression, activated the HPA axis and induced CTA acquisition. However, icv lithium at night, when the HPA axis shows its circadian activation, did not induce CTA acquisition nor activate the HPA axis, although it increased the brain c-Fos expression. These results suggest that the circadian activation of the HPA axis may affect central, but not peripheral, effect of lithium in CTA learning in rats, and the HPA axis activation may be necessary for the central effect of lithium in CTA formation. Also, glucocorticoids may be required for a better extinction; however, increased glucocorticoids hinder both the acquisition and the extinction of lithium-induced CTA.