Prenatal Stress Induced Spatial Memory Deficit in a Sex-Specific Manner in Mice: Possible Involvement of Hippocampal Insulin Resistance

Introduction: In the present study, the effects of prenatal stress on spatial learning and memory deficit and its relationship with hippocampal insulin resistance was examined in male and female offspring. Method: Female NMRI mice were mate with males overnight and the zero day of pregnancy was detected (Gestational day zero-GD0). The pregnant mice were then randomly divided into stress and control groups. The stress group received stress from the GD0 to GD10. On post natal day 30 (PND30) the offspring were divided into for subgroups namely: male-control, female-control, male-stress, and female-stress. Barnes maze (BM) method was used for spatial learning evaluation. Plasma cortisol and insulin levels were measured at the beginning of the experiments. At the end of the experiments, the animals’ brains were removed and their hippocampus was extracted. The hippocampus was homogenized and its insulin and insulin receptor contents were evaluated. Results: The stressed animals needed more time for reaching to target hole. In addition, they spend more distance for finding the target hole, which was more pronounced in the male offspring. Both plasma and hippocampal insulin content were reduced in stressed groups. Moreover, the hippocampal insulin receptors protein was reduced in the stressed animals. There was a positive relationship between plasma and hippocampal content and memory deficit in the stressed groups. Conclusion: These results indicated that prenatal stress can induce spatial learning and memory deficit in offspring which is associated with plasma and hippocampal insulin and receptor content reduction (hippocampal insulin resistance) in these animals.

Nootropic and Neuroprotective Effects of Ethanol Extract of Hibiscus Sabdariffa L. on Scopolamine-Induced Cognitive Deficit in Mice

The aim of this investigation was to explore the neuroprotective and memory-enhancing effect of Hibiscus sabdariffa L. ethanolic extract on scopolamine-induced learning and memory deficit in young mice. The nootropic and neuroprotective potential of the extract in scopolamine induced amnesic mice was evaluated by elevated plus maze, step-down avoidance, and Morris water maze tests after 14 days of daily administration. The extract significantly enhanced learning, memory function, improved spatial recognition, as well as successfully reversed scopolamine-induced amnesia. Also, it significantly decreased the brain acetylcholinesterase activity and optimized brain catecholamine levels. Histopathological results confirmed the protective effect of the extract on hippocampal and cortical neurons. These findings suggest that ethanolic extract of H. sabdariffa can confer neuroprotection and augment memory. In conclusion, H. sabdariffa can be used in the management of amnesia and neurodegenerative diseases involving learning, memory, and cognitive dysfunctions.

The Effect of Different Doses of Melatonin on Learning and Memory Deficit in Alzheimer Model of Rats

Background: Alzheimer Disease (AD) is an age-related neurodegenerative disorder with a progressive impairment of cognitive function. The pineal gland hormone melatonin (MEL) has been known as a protection agent against AD. However, the effect of melatonin in various doses is inconsistent. Objectives: In this study, we aimed to investigate two doses of MEL on learning and memory in the amyloid-βeta (Aβ)-induced AD in the rats. Materials & Methods: Forty-eight male Wistar rats were used in the experiment and randomly divided control, sham, vehicle, AD, AD+MEL10 mg/kg, and AD+MEL 20 mg/kg groups. Intracerebroventricular injection of Aβ1–42 was used to develop the animal model of AD. Also, MEL-treated groups received an intraperitoneal injection of MEL for 4 next weeks. The Morris Water Maze (MWM) and Passive Avoidance Learning (PAL) tests were used to examine animals’ learning and memory. The brain of animals was removed for immunohistochemistry for anti- Amyloid Precursor Protein (APP). Results: Intra-peritoneal injection of MEL significantly improve learning and memory in MWM (P=0.000) and PAL test (P=0.000), but there were no significant changes in the two groups that received the melatonin (P>0.05). Histopathological analysis revealed that the clearance of APP deposition in the AD+MEL20 group was considerable compared with the AD+MEL10 group (P=0.000). Conclusion: Our findings indicate that 10 and 20 mg/kg doses of melatonin have similar results on learning and memory in the AD model. But 20 mg/kg of melatonin has significantly more effect on the clearance of APP deposition.

A Low-Cost Analytical Method for the Morris Water Maze Task using ImageJ

The Morris water maze, which has been used for more than 30 years, is one of the most famous learning and memory tasks among animals. This method is robust and reliable, and it can be carried out anywhere with little effort. Nowadays, there are many companies creating analysis software to easily analyze the Morris water maze results. However, these softwares are costly and may be difficult for researchers in developing countries especially with limited research funds. Only escape latency and time spent in the target quadrant can be manually obtained after video review. To resolve this problem and to extend the ability to detect learning and memory impairment in the Morris water maze, we provide a novel low-cost analysis method using common office tools combined with ImageJ software to analyze learning and memory impairment in rat or mouse models. In this study, we used the 2-vessel occlusion (2VO) rats and sham-operated control rats as learning and memory deficit rats and normal rats, respectively. Taken together, travel distance, swimming speed, and swimming traces can be acquired from this method, which will help researchers to investigate further impairment of learning and memory in animal models.