The effects of early exposure to MK-801 during environmental enrichment on spatial memory, methamphetamine self-administration and cue-induced renewal in rats

Environmental enrichment and sex, but not n-acetylcysteine, alter extended-access amphetamine self-administration and cue-seeking

There are no approved therapeutics for psychostimulant use and recurrence of psychostimulant use. However, in preclinical rodent models environmental enrichment can decrease psychostimulant self-administration of low unit doses and cue-induced amphetamine seeking. We have previously demonstrated that glutamate-dependent therapeutics are able to alter amphetamine seeking to amphetamine-associated cues only in enriched rats. In the current experiment, we will determine if enrichment can attenuate responding and cue-induced amphetamine seeking during extended access to a high dose of intravenous amphetamine. We will also determine if N-acetylcysteine (NAC), a glutamate dependent therapeutic, can attenuate amphetamine seeking in differentially reared rats. Female and male Sprague-Dawley rats were reared in enriched, isolated, or standard conditions from postnatal day 21-51. Rats were trained to self-administer intravenous amphetamine (0.1 mg/kg/infusion) during twelve 6-hour sessions. During the abstinence period, NAC (100 mg/kg) or saline was administered daily. Following a cue-induced amphetamine-seeking test, astrocyte densities within regions of the medial prefrontal cortex (mPFC) and nucleus accumbens (ACb) were quantified using immunohistochemistry. Environmental enrichment decreased responding for amphetamine and during the cue-induced amphetamine-seeking test. NAC did not attenuate cue-induced amphetamine seeking or alter astrocyte density. Across all groups, female rats self-administered less amphetamine but responded more during cue-induced amphetamine seeking than male rats. While amphetamine increased astrocyte densities within the ACb and mPFC, it did not alter mPFC astrocyte densities in female rats. The results suggest that enrichment can attenuate responding during extended access to a high dose of amphetamine and the associated cues. Sex alters amphetamine-induced changes to astrocyte densities in a regionally specific matter.

Differential rearing alters Fos in the accumbens core and ventral palidum following reinstatement of cocaine seeking in male Sprague-Dawley rats

Rearing rats in environmental enrichment produces a protective effect when exposed to stimulants, as enriched rats display attenuated cocaine seeking during reinstatement. However, less is known about what changes in the brain are responsible for this protective effect. The current study investigated differences in Fos protein expression following reinstatement of cocaine seeking in differentially reared rats. Rats were reared in either enriched (EC) or impoverished (IC) conditions for 30 days, after which rats self-administered cocaine in 2-h sessions. Following self-administration, rats underwent extinction and cue-induced or cocaine-primed reinstatement of cocaine seeking, brains were extracted, and Fos immunohistochemistry was performed. IC rats sought cocaine significantly more than EC rats during cue-induced reinstatement, and cocaine seeking was positively correlated with Fos expression in the nucleus accumbens core and ventral pallidum. IC rats displayed greater Fos expression than EC rats in the accumbens and ventral pallidum, suggesting a role of these areas in the enrichment-induced protective effect.

Neuroprotective effect of histamine H3 receptor blockade on methamphetamine-induced cognitive impairment in mice

OBJECTIVE

Methamphetamine (METH) exposure is commonly believed to result in cognitive impairment. Histamine H3 receptor (H3R) antagonists reportedly have potential applications for treating cognitive impairment accompanied by various neuropsychiatric disorders. The present study aimed to investigate the effect of H3R blockade by Thioperamide (THIO) on METH-induced cognitive impairment and the underlying mechanism.

METHODS

In Experiment 1, C57BL/6 mice received daily injections of saline or 5 mg/kg METH for 5 consecutive days. The Novel Object Recognition (NOR) and Morris water maze (MWM) tasks were used to assess cognitive functions of mice. H3R protein expression and apoptosis were subsequently measured in the hippocampus. In Experiment 2, HT22 cells were first treated with ddH₂O or 3 mM METH. The cell survival rate and H3R protein level were subsequently assessed. In Experiment 3, the animals were first treated with saline or 20 mg/kg THIO for 7 days, followed by co-administration of either saline or 5 mg/kg METH for an additional 5 days. The remaining experiments were carried out in the same manner as Experiment 1. In Experiment 4, HT22 cells were pretreated with either ddH₂O or 5 mM THIO for 2 h, followed by ddH₂O or 3 mM METH treatment for an additional 12 h. The remaining experiments were carried out in the same manner as Experiment 2. In Experiment 5, the changes in MEK1/2, p-MEK1/2, ERK1/2 and p-ERK1/2 protein levels were examined in the hippocampus of all mice from Experiment 3 and HT22 cells from Experiment 4.

RESULTS

METH-treated mice showed significantly worsened NOR and MWM performance, along with markably hippocampal apoptosis. A significantly lower cell survival rate was observed in METH-treated HT22 cells. Increased levels of H3R protein were found in both METH-treated mice and HT22 cells. THIO significantly improved METH-induced cognitive impairment in mice and toxicity in HT22 cells. METH significantly increased the level of p-MEK1/2 and p-ERK1/2 proteins in the hippocampus of mice and HT22 cells, which was reversed by THIO pretreatment.

CONCLUSION

Our findings reveal that H3R blockade by THIO yields a neuroprotective effect against METH-induced cognitive impairment in mice and toxicity in HT22 cells via the raf-MEK-ERK signaling pathway.

Neurobehavioral effects of environmental enrichment and drug abuse vulnerability: An updated review

Environmental enrichment consisting of social peers and novel objects is known to alter neurobiological functioning and have an influence on the behavioral effects of drugs of abuse in preclinical rodent models. An earlier review from our laboratory (Stairs and Bardo, 2009) provided an overview of enrichment-specific changes in addiction-like behaviors and neurobiology. The current review updates the literature in this extensive field. Key findings from this updated review indicate that enrichment produces positive outcomes in drug abuse vulnerability beyond just psychostimulants. Additionally, recent studies indicate that enrichment activates key genes involved in cell proliferation and protein synthesis in nucleus accumbens and enhances growth factors in hippocampus and neurotransmitter signaling pathways in prefrontal cortex, amygdala, and hypothalamus. Remaining gaps in the literature and future directions for environmental enrichment and drug abuse research are identified.

Corallodiscus flabellata B. L. Burtt extract and isonuomioside A ameliorate Aβ25-35-induced brain injury by inhibiting apoptosis, oxidative stress, and autophagy via the NMDAR2B/CamK Ⅱ/PKG pathway

BACKGROUND

Corallodiscus flabellata B. L. Burtt, a traditional Chinese folk medicine used for amnesia, can significantly improve brain injury; however, its active components and underlying mechanism of action remain unclear.

OBJECTIVE

To examine the effects and underlying mechanism of action of Corallodiscus flabellata B. L. Burtt (SDC) extract and isolated isonuomioside A (isA) on Aβ_25-35-induced brain injury.

METHODS

SDC extract (155 mg/kg, i.g.) or IsA (20 mg/kg, i.g.) was administered over a period of 4 weeks, following which brain injury was induced by Aβ_25-35 infusion (200 µM, 3 µl/20 g, i.c.v.). Network pharmacology research gathered existing data on the effects of SDC on Alzheimer's disease. Learning and memory ability, neuronal damage, and the levels of Aβ_1-42/Aβ_1-40, p-Tau, apoptosis, oxidative stress, autophagy, immune cells, NMDAR2B, p-CamK Ⅱ, and PKG were examined. Furthermore, the antagonistic effect of MK-801 (NMDA receptor blocker, 10 µM) in the presence of isA (10 µM) or SDC extract (20 µg/ml) was investigated in Aβ_25-35 (20 µM, 24 h)-induced PC-12 and N9 cells to evaluate whether the observed effects elicited by isA and SDC extract were mediated via the NMDAR2B/CamK Ⅱ/PKG pathway.

RESULTS

IsA and SDC extract improved learning and memory ability, reduced neuronal damage, downregulated Aβ_1-42/Aβ_1-40, p-Tau, apoptosis, oxidative stress, and autophagy, transformed immune cells, and increased the expression levels of NMDAR2B, p-CamK Ⅱ, and PKG following Aβ_25-35 challenge. Moreover, MK-801 blocked the effects of isA and SDC extract on apoptosis, ROS levels, and autophagy in Aβ_25-35-induced N9 and PC-12 cells, indicating that isA and SDC extract likely exert neuroprotective effects via the NMDAR2B/CamK Ⅱ/PKG pathway.

CONCLUSION

IsA and SDC extract ameliorate Aβ_25-35-induced brain injury by inhibiting apoptosis, oxidative stress, and autophagy, which likely occurs via the NMDAR2B/CamK Ⅱ/PKG pathway. These findings may help to elucidate new therapeutic targets and facilitate the development of drugs for the clinical treatment of AD.

Inhibition of PLCβ1 signaling pathway regulates methamphetamine self-administration and neurotoxicity in rats

Studies have shown that the central renin-angiotensin system is involved in neurological disorders. Our previous studies have demonstrated that angiotensin II receptor type 1 (AT1R) in the brain could be a potential target against methamphetamine (METH) use disorder. The present study was designed to investigate the underlying mechanisms of the inhibitory effect of AT1R on various behavioural effects of METH. We first examined the effect of AT1R antagonist, candesartan cilexetil (CAN), on behavioural and neurotoxic effects of METH. Furthermore, we studied the role of phospholipase C beta 1 (PLCβ1) blockade behavioural and neurotoxic effects of METH. The results showed that CAN significantly attenuated METH-induced behavioral disorders and neurotoxicity associated with increased oxidative stress. AT1R and PLCβ1 were significantly upregulated in vivo and in vitro. Inhibition of PLCβ1 effectively alleviated METH-induced neurotoxicity and METH self-administration (SA) by central blockade of the PLCβ1 involved signalling pathway. PLCβ1 blockade significantly decreased the reinforcing and motivation effects of METH. PLCβ1 involved signalling pathway, as well as a more specific role of PLCβ1, involved the inhibitory effects of CAN on METH-induced behavioural dysfunction and neurotoxicity. Collectively, our findings reveal a novel role of PLCβ1 in METH-induced neurotoxicity and METH use disorder.

Exposure to ambient dusty particulate matter impairs spatial memory and hippocampal LTP by increasing brain inflammation and oxidative stress in rats

OBJECTIVES

Exposure of healthy subjects to ambient airborne dusty particulate matter (PM) causes brain dysfunction. This study aimed to investigate the effect of sub-chronic inhalation of ambient PM in a designed special chamber to create factual dust storm (DS) conditions on spatial cognition, hippocampal long-term potentiation (LTP), inflammatory cytokines, and oxidative stress in the brain tissue.

METHODS

Adult male Wistar rats (250-300 g) were randomly divided into four groups: Sham (clean air, the concentration of dusty PM was <150 μg/m³), DS1 (200-500 μg/m³), DS2 (500-2000 μg/m³) and DS3 (2000-8000 μg/m³). Experimental rats were exposed to clean air or different sizes and concentrations of dust PM storm for four consecutive weeks (exposure was during 1-4, 8-11, 15-16 and 20-23 days, 30 min, twice daily) in a real-ambient dust exposure chamber. Subsequently, cognitive performance, hippocampal LTP, blood-brain barrier (BBB) permeability and brain edema of the animals evaluated. As well as, inflammatory cytokines and oxidative stress indexes in the brain tissue measured using ELISA assays.

RESULTS

Exposing to dust PM impaired spatial memory (p < 0.001), hippocampal LTP (p < 0.001). These disturbances were in line with the severe damage to respiratory system followed by disruption of BBB integrity (p < 0.001), increased brain edema (p < 0.001), inflammatory cytokines (p < 0.001) excretion and oxidative stress (p < 0.001) in brain tissue.

CONCLUSIONS

Our study showed that exposure to ambient dust PM increased brain edema and BBB permeability, induced memory impairment and hippocampal LTP deficiency by increasing the inflammatory responses and oxidative stress in the brain of the rats.