Impact of 1-day and 4-day MWM training techniques on oxidative and neurochemical profile in rat brain: A comparative study on learning and memory functions

Cognitive comorbidities in the rat pilocarpine model of epilepsy

Patients with epilepsy are prone to cognitive decline, depression, anxiety and other behavioral disorders. Cognitive comorbidities are particularly common and well-characterized in people with temporal lobe epilepsy, while inconsistently addressed in epileptic animals. Therefore, the aim of this study was to ascertain whether there is good evidence of cognitive comorbidities in animal models of epilepsy, in particular in the rat pilocarpine model of temporal lobe epilepsy. We searched the literature published between 1990 and 2023. The association of spontaneous recurrent seizures induced by pilocarpine with cognitive alterations has been evaluated by using various tests: contextual fear conditioning (CFC), novel object recognition (NOR), radial and T-maze, Morris water maze (MWM) and their variants. Combination of results was difficult because of differences in methodological standards, in number of animals employed, and in outcome measures. Taken together, however, the analysis confirmed that pilocarpine-induced epilepsy has an effect on cognition in rats, and supports the notion that this is a valid model for assessment of cognitive temporal lobe epilepsy comorbidities in preclinical research.

Maresin1 ameliorates postoperative cognitive dysfunction in aged rats by potentially regulating the NF-κB pathway to inhibit astrocyte activation

Postoperative cognitive dysfunction (POCD) is one of the most serious postoperative complications in the elderly population. Perioperative central neuroinflammation is considered to be an important pathological mechanism of POCD, with the activation of astrocytes playing a key role in central neuroinflammation. Maresin1 (MaR1) is a specific pro-resolving mediator synthesized by macrophages in the resolution stage of inflammation, and provides unique anti-inflammatory and pro-resolution effects by limiting excessive neuroinflammation and promoting postoperative recovery. However, the question remains whether MaR1 can have a positive effect on POCD. The objective of this study was to investigate the protective effect of MaR1 on POCD cognitive function in aged rats after splenectomy. Morris water maze test and IntelliCage test showed that splenectomy could cause transient cognitive dysfunction in aged rats; however, the cognitive impairment of rats was significantly mitigated when MaR1 pretreatment was administered. MaR1 significantly alleviated the fluorescence intensity and protein expression of glial fibrillary acidic protein and central nervous system specific protein in the cornu ammonis 1 region of the hippocampus. Simultaneously, the morphology of astrocytes was also severely altered. Further experiments showed that MaR1 inhibited the mRNA and protein expression of several key proinflammatory cytokines-interleukin-1β, interleukin-6, and tumor necrosis factor-α in the hippocampus of aged rats following splenectomy. The molecular mechanism underlying this process was explored by evaluating expression of components of the nuclear factor κB (NF-κB) signaling pathway. MaR1 substantially inhibited the mRNA and protein expression of NF-κB p65 and κB inhibitor kinase β. Collectively, these results suggest that MaR1 ameliorated splenectomy-induced transient cognitive impairment in elderly rats, and this neuroprotective mechanism may occur through regulating the NF-κB pathway to inhibit astrocyte activation.

Evaluation of the Activity of Choline Acetyltransferase From Different Synaptosomal Fractions at the Distinct Stages of Spatial Learning in the Morris Water Maze

Accumulated data have evidenced that brain cholinergic circuits play a crucial role in learning and memory; however, our knowledge about the participation of neocortical and hippocampal cholinergic systems in spatial learning needs to be refined. The aim of this study was to evaluate the association of the activity of membrane-bound and soluble choline acetyltransferase (ChAT) in the synaptosomal sub-fractions of the neocortex and hippocampus with performance of the spatial navigation task in the Morris water maze at different temporal stages of memory trace formation. To identify distinct stages of memory formation, rats were trained using a 5-day protocol with four trials per day. The mean escape latency for each trial was collected, and the entire dataset was subjected to principal component analysis. Based on the Morris water maze protocol, there were three relatively distinct stages of memory formation: days 1-2, day 3, and days 4-5. The remotely stored memory trace tested in repeated and reversal learning beginning on day 19 (14 days after the end of initial learning) was associated at the individual level mainly with performance during the second trial on day 21 (the third day or repeated or reversal learning). The ChAT activity data suggest the participation of cortical cholinergic projections mainly in the first stage of spatial learning (automatic sensory processing) and the involvement of hippocampal interneurons in the second stage (error-corrected learning). Cholinergic cortical interneurons participated mainly in the stage of asymptotic performance (days 4-5). It is advisable to evaluate other signalling pathways at the identified stages of memory formation.

Amelioration of oxidative stress and neuroinflammation in lipopolysaccharide-induced memory impairment using Rosmarinic acid in mice

Oxidative stress plays a pivotal part in the manifestation of neuroinflammation, which further leads to neurodegenerative diseases like Alzheimer's disease (AD). Systemic administration of lipopolysaccharide (LPS) induces neuroinflammation resulting in memory impairment (MI) and cognitive decline. In this study, we evaluated whether prophylactic administration of Rosmarinic acid (RA), a naturally occurring compound, exerts a neuroprotective effect in LPS-induced MI and cognitive decline. Herein, Swiss albino mice were pre-treated with RA (0.5 mg/kg and 1 mg/kg i.p.) for 28 days and were intermittently exposed to LPS (0.25 mg/kg i.p.) for 7 days. LPS caused poor memory retention and increased cognitive decline in Morris water maze (MWM) and Y maze paradigms respectively. Additionally, LPS increased oxidative stress which was denoted by a decrease in superoxide dismutase (SOD) activity, decrease in reduced glutathione (GSH) levels, and increased lipid peroxidation in the brain. Imbalance in the cholinergic system was analyzed by measuring the acetylcholinesterase (AChE) activity. Pre-treatment with RA improved memory and behavioral disturbances by alleviating oxidative stress and AChE activity. LPS augmented levels of tumor necrosis factor (TNF-α), interleukin (IL)-6, caspase-3, and c-Jun. Pre-treatment with RA revitalized the elevated levels of proinflammatory cytokines and apoptotic proteins. In conclusion, this study showcases the amelioration of MI by RA in LPS-challenged memory and cognitive decline, which could be credited to its anti-oxidant effect, inhibitory effect on both proinflammatory cytokines and apoptotic regulators, and reduction in AChE activity.

Astaxanthin alleviates pathological brain aging through the upregulation of hippocampal synaptic proteins

Oxidative stress is currently considered to be the main cause of brain aging. Astaxanthin can improve oxidative stress under multiple pathological conditions. It is therefore hypothesized that astaxanthin might have therapeutic effects on brain aging. To validate this hypothesis and investigate the underlying mechanisms, a mouse model of brain aging was established by injecting amyloid beta (Aβ)25–35 (5 μM, 3 μL/injection, six injections given every other day) into the right lateral ventricle. After 3 days of Aβ_25–35 injections, the mouse models were intragastrically administered astaxanthin (0.1 mL/d, 10 mg/kg) for 30 successive days. Astaxanthin greatly reduced the latency to find the platform in the Morris water maze, increased the number of crossings of the target platform, and increased the expression of brain-derived neurotrophic factor, synaptophysin, sirtuin 1, and peroxisome proliferator-activated receptor-γ coactivator 1α. Intraperitoneal injection of the sirtuin 1 inhibitor nicotinamide (500 μM/d) for 7 successive days after astaxanthin intervention inhibited these phenomena. These findings suggest that astaxanthin can regulate the expression of synaptic proteins in mouse hippocampus through the sirtuin 1/peroxisome proliferator-activated receptor-γ coactivator 1α signaling pathway, which leads to improvements in the learning, cognitive, and memory abilities of mice. The study was approved by the Animal Ethics Committee, China Medical University, China (approval No. CMU2019294) on January 15, 2019.

Free L-glutamate-induced modulation in oxidative and neurochemical profile contributes to enhancement in locomotor and memory performance in male rats

Glutamate (Glu), the key excitatory neurotransmitter in the central nervous system, is considered essential for brain functioning and has a vital role in learning and memory formation. Earlier it was considered as a harmful agent but later found to be useful for many body functions. However, studies regarding the effects of free l-Glu administration on CNS function are limited. Therefore, current experiment is aimed to monitor the neurobiological effects of free l-Glu in male rats. l-Glu was orally administered to rats for 5-weeks and changes in behavioral performance were monitored. Thereafter, brain and hippocampus were collected for oxidative and neurochemical analysis. Results showed that chronic supplementation of free l-Glu enhanced locomotor performance and cognitive function of animals which may be attributed to the improved antioxidant status and cholinergic, monoaminergic and glutamatergic neurotransmission in brain and hippocampus. Current results showed that chronic supplementation of l-Glu affects the animal behaviour and brain functioning via improving the neurochemical and redox system of brain. Free l-Glu could be a useful therapeutic agent to combat neurological disturbances however this requires further targeted studies.