Morris Water Maze and Contextual Fear Conditioning Tasks to Evaluate Cognitive Functions Associated With Adult Hippocampal Neurogenesis

New neurons are continuously generated and functionally integrated into the dentate gyrus (DG) network during the adult lifespan of most mammals. The hippocampus is a crucial structure for spatial learning and memory, and the addition of new neurons into the DG circuitry of rodents seems to be a key element for these processes to occur. The Morris water maze (MWM) and contextual fear conditioning (CFC) are among the most commonly used hippocampus-dependent behavioral tasks to study episodic-like learning and memory in rodents. While the functional contribution of adult hippocampal neurogenesis (AHN) through these paradigms has been widely addressed, results have generated controversial findings. In this review, we analyze and discuss possible factors in the experimental methods that could explain the inconsistent results among AHN studies; moreover, we provide specific suggestions for the design of more sensitive protocols to assess AHN-mediated learning and memory functions.

Superior Verbal Memory Outcome After Stereotactic Laser Amygdalohippocampotomy

Objective: To evaluate declarative memory outcomes in medically refractory epilepsy patients who underwent either a highly selective laser ablation of the amygdalohippocampal complex or a conventional open temporal lobe resection. Methods: Post-operative change scores were examined for verbal memory outcome in epilepsy patients who underwent stereotactic laser amygdalohippocampotomy (SLAH: n = 40) or open resection procedures (n = 40) using both reliable change index (RCI) scores and a 1-SD change metric. Results: Using RCI scores, patients undergoing open resection (12/40, 30.0%) were more likely to decline on verbal memory than those undergoing SLAH (2/40 [5.0%], p = 0.0064, Fisher's exact test). Patients with language dominant procedures were much more likely to experience a significant verbal memory decline following open resection (9/19 [47.4%]) compared to laser ablation (2/19 [10.5%], p = 0.0293, Fisher's exact test). 1 SD verbal memory decline frequently occurred in the open resection sample of language dominant temporal lobe patients with mesial temporal sclerosis (8/10 [80.0%]), although it rarely occurred in such patients after SLAH (2/14, 14.3%) (p = 0.0027, Fisher's exact test). Memory improvement occurred significantly more frequently following SLAH than after open resection. Interpretation: These findings suggest that while verbal memory function can decline after laser ablation of the amygdalohippocampal complex, it is better preserved when compared to open temporal lobe resection. Our findings also highlight that the dominant hippocampus is not uniquely responsible for verbal memory. While this is at odds with our simple and common heuristic of the hippocampus in memory, it supports the findings of non-human primate studies showing that memory depends on broader medial and lateral TL regions.

Orexin (hypocretin) mediates light-dependent fluctuation of hippocampal function in a diurnal rodent

Environmental lighting conditions play a central role in cognitive function, but the underlying mechanisms remain unclear. Utilizing a diurnal rodent model, the Nile grass rat (Arvicanthis niloticus), we previously found that daytime light intensity affects hippocampal function in this species in a manner similar to its effects in humans. Compared to animals housed in a 12:12 h bright light-dark (brLD) cycle, grass rats kept in a 12:12 h dim light-dark (dimLD) cycle showed impaired spatial memory in the Morris water maze (MWM) and reduced CA1 apical dendritic spine density. The present study explored the neural substrates mediating the effects of daylight intensity on hippocampal function focusing on the hypothalamic orexin (hypocretin) system. First, animals housed in dimLD were treated with daily intranasal administration of orexin A peptide over five training days of the MWM task. Compared to vehicle controls, this treatment led to superior spatial memory accompanied by increased phosphorylation of Ca²⁺ /calmodulin-dependent protein kinase II α and glutamate receptor 1 within the CA1. To assess the role of hippocampal orexinergic signaling, an adeno-associated viral vector (AAV) expressing an orexin receptor 1 (OX1R) shRNA was injected into the dorsal hippocampus targeting the CA1 of animals housed in brLD. AAV-mediated knockdown of OX1R within the hippocampus resulted in deficits in MWM performance and reduced CA1 apical dendritic spine density. These results are consistent with the view that the hypothalamic orexinergic system underlies the modulatory role of daytime illumination on hippocampal function in diurnal mammals.

The effect of complicated febrile convulsion on hippocampal function and its antiepileptic treatment significance

BACKGROUND

This study aimed to explore the effects of complex febrile seizures on hippocampal function and the significance of antiepileptic therapy.

METHODS

A total of 150 children with complex febrile seizures admitted to our hospital from July 2017 to July 2020 were included in the study. The VPA group was given sodium valproate treatment; the LEV group was given levetiracetam treatment; and the observation group was given basic treatment. The efficacy of the patients was evaluated after medication. A complex febrile seizure young mouse model was constructed, and the hippocampal cell morphology and BCL-2 expression of the mice pups were analyzed. A Morris water maze was used to detect the changes in cognitive function of the young mice with complex febrile seizures.

RESULTS

After treatment, the recurrence-free rate of the VPA group was significantly higher than that of the observation group (P=0.0045). After 1 month and 6 months, the improvement rate of EEG in VPA group was significantly higher than that in observation group (P<0.05). After treatment, the levels of BCL-2 in the VPA group and the LEV group decreased and were significantly lower than the observation group during the same period (P<0.05), and the M/C of the two groups was significantly higher than the observation group (P<0.05). The neuronal cells in the hippocampus of the young rats in the VPA group and the LEV group were regular, the matrix was more uniform, and nuclear pyknotic cells were occasionally seen. The pathological changes were less obvious than the model group, followed by the degree of pathological changes (0.92±1.31, 0.94±1.24). The incubation period of pups in the model group was significantly higher than that of the normal group, VPA group, and LEV group (P<0.05), and the number of crossing the station area was significantly less than that of the normal group, VPA group, and LEV group (P<0.05).

CONCLUSIONS

Antiepileptic drugs are effective in preventing the recurrence of complicated febrile seizures (CFS), and the main mechanism may be related to the targeted regulation of BCL-2 on the apoptosis of the hippocampus in the nervous system.

Hippocampal volume, function, and related molecular activity in anorexia nervosa: A scoping review

INTRODUCTION

Anorexia nervosa (AN) is a serious and persistent eating disorder, characterized by severe dietary restriction and weight loss, with a third of patients developing a  severe-enduring form. The factors contributing to this progression are poorly understood, although there is evidence for impairments in neural structures such as the hippocampus, an area particularly affected by malnutrition and chronic stress.

AREAS COVERED

This study aimed to map the evidence for alterations in hippocampal volume, function, and related molecular activity in anorexia nervosa. PubMed, PsycINFO, and Web of Science were searched for studies related to hippocampal function and integrity using a range of methodologies, such as neuropsychological paradigms, structural and functional magnetic resonance imaging, and analysis of blood components.

EXPERT OPINION

Thirty-nine studies were included in this review. The majority were neuroimaging studies, which found hippocampus-specific volumetric and functional impairments. Neuropsychological studies showed evidence for a specific memory and learning impairments. There was some evidence for molecular abnormalities (e.g. cortisol), although these were few studies. Taken together, our review suggests that the hippocampus might be a particular region of interest when considering neurobiological approaches to understanding AN. These findings warrant further investigation and may lead to novel treatment approaches.

Effects of Bisphenol A Exposure during Pregnancy and lactation on Hippocampal Function in Newborn Rats

Bisphenol A (BPA) is widely used in industrial production. It is closely related to the growth and development of the nervous system, and can enter the fetal circulation through the placental barrier, and can be secreted through breast milk. The development of nervous system is very important in fetus and neonatal period. The purpose of this study is to investigate the effects of different doses of BPA on learning and memory function of nervous system in rats. Pregnant rats were randomly divided into three treatment groups (control group, 5 mg/kg/d, 50 mg/kg/d). All animals received BPA from the discovery of pregnancy to 21 days after birth. Results had shown that after high concentration BPA exposure, the increase of PS amplitude and f-EPSP slope in hippocampal CA1 area of male offspring was lower than that of control group. High concentration of BPA could inhibit Nestin, Cyclin D1, bcl-2 and Rac1 in male offspring rats and the expression of bax and RhoA was promoted by BPA. In summary, our study indicated that BPA exposure during pregnancy and lactation could impair the hippocampal function of male offspring by affecting the growth and apoptosis of hippocampal neurons, which might be due to the abnormal regulation of RhoA and Rac1.

Fetal iron deficiency alters the proteome of adult rat hippocampal synaptosomes

Fetal and neonatal iron deficiency results in cognitive impairments in adulthood despite prompt postnatal iron replenishment. To systematically determine whether abnormal expression and localization of proteins that regulate adult synaptic efficacy are involved, we used a quantitative proteomic approach (isobaric tags for relative and absolute quantitation, iTRAQ) and pathway analysis to identify dysregulated proteins in hippocampal synapses of fetal iron deficiency model. Rat pups were made iron deficient (ID) from gestational day 2 through postnatal day (P) 7 by providing pregnant and nursing dams an ID diet (4 ppm Fe) after which they were rescued with an iron-sufficient diet (200 ppm Fe). This paradigm resulted in a 40% loss of brain iron at P15 with complete recovery by P56. Synaptosomes were prepared from hippocampi of the formerly iron-deficient (FID) and always iron-sufficient controls rats at P65 using a sucrose gradient method. Six replicates per group that underwent iTRAQ labeling and LC-MS/MS analysis for protein identification and comparison elucidated 331 differentially expressed proteins. Western analysis was used to confirm findings for selected proteins in the glutamate receptor signaling pathway, which regulates hippocampal synaptic plasticity, a cellular process critical for learning and memory. Bioinformatics were performed using knowledge-based Interactive Pathway Analysis. FID synaptosomes show altered expression of synaptic proteins-mediated cellular signalings, supporting persistent impacts of fetal iron deficiency on synaptic efficacy, which likely cause the cognitive dysfunction and neurobehavioral abnormalities. Importantly, the findings uncover previously unsuspected pathways, including neuronal nitric oxide synthase signaling, identifying additional mechanisms that may contribute to the long-term biobehavioral deficits.

Neuroinflammation alters the hippocampal pattern of behaviorally induced Arc expression

Neuroinflammation is associated with a variety of neurological and pathological diseases, such as Alzheimer's disease (AD), and is reliably detected by the presence of activated microglia. In early AD, the highest degree of activated microglia is observed in brain regions involved in learning and memory. To investigate whether neuroinflammation alters the pattern of rapid de novo gene expression associated with learning and memory, we studied the expression of the activity-induced immediate early gene Arc in the hippocampus of rats with experimental neuroinflammation. Rats were chronically infused with lipopolysaccharide (LPS) (0.25 mug/h) into the fourth ventricle for 28 d. On day 29, the rats explored twice a novel environment for 5 min, separated by 45 or 90 min. In the dentate gyrus and CA3 regions of LPS-infused rats, Arc and OX-6 (specific for major histocompatibility complex class II antigens) immunolabeling and Arc fluorescence in situ hybridization revealed both activated microglia (OX-6 immunoreactivity) and elevated exploration-induced Arc expression compared with control-infused rats. In contrast, in the CA1 of LPS-infused rats, where there was no OX-6 immunostaining, exploration-induced Arc mRNA and protein remained similar in both LPS- and control-infused rats. LPS-induced neuroinflammation did not affect basal levels of Arc expression. Behaviorally induced Arc expression was altered only within the regions showing activated microglia (OX-6 immunoreactivity), suggesting that neuroinflammation may alter the coupling of neural activity with macromolecular synthesis implicated in learning and plasticity. This activity-related alteration in Arc expression induced by neuroinflammation may contribute to the cognitive deficits found in diseases associated with inflammation, such as AD.