Long-term stimulation of the anteromedial thalamus increases hippocampal neurogenesis and spatial reference memory in adult rats

Subthalamic nucleus but not entopeduncular nucleus deep brain stimulation enhances neurogenesis in the SVZ-olfactory bulb system of Parkinsonian rats

Introduction

Deep brain stimulation (DBS) is a highly effective treatment option in Parkinson's disease. However, the underlying mechanisms of action, particularly effects on neuronal plasticity, remain enigmatic. Adult neurogenesis in the subventricular zone-olfactory bulb (SVZ-OB) axis and in the dentate gyrus (DG) has been linked to various non-motor symptoms in PD, e.g., memory deficits and olfactory dysfunction. Since DBS affects several of these non-motor symptoms, we analyzed the effects of DBS in the subthalamic nucleus (STN) and the entopeduncular nucleus (EPN) on neurogenesis in 6-hydroxydopamine (6-OHDA)-lesioned hemiparkinsonian rats.

Methods

In our study, we applied five weeks of continuous bilateral STN-DBS or EPN-DBS in 6-OHDA-lesioned rats with stable dopaminergic deficits compared to 6-OHDA-lesioned rats with corresponding sham stimulation. We injected two thymidine analogs to quantify newborn neurons early after DBS onset and three weeks later. Immunohistochemistry identified newborn cells co-labeled with NeuN, TH and GABA within the OB and DG. As a putative mechanism, we simulated the electric field distribution depending on the stimulation site to analyze direct electric effects on neural stem cell proliferation.

Results

STN-DBS persistently increased the number of newborn dopaminergic and GABAergic neurons in the OB but not in the DG, while EPN-DBS does not impact neurogenesis. These effects do not seem to be mediated via direct electric stimulation of neural stem/progenitor cells within the neurogenic niches.

Discussion

Our data support target-specific effects of STN-DBS on adult neurogenesis, a putative modulator of non-motor symptoms in Parkinson's disease.

Systematic review of rodent studies of deep brain stimulation for the treatment of neurological, developmental and neuropsychiatric disorders

Deep brain stimulation (DBS) modulates local and widespread connectivity in dysfunctional networks. Positive results are observed in several patient populations; however, the precise mechanisms underlying treatment remain unknown. Translational DBS studies aim to answer these questions and provide knowledge for advancing the field. Here, we systematically review the literature on DBS studies involving models of neurological, developmental and neuropsychiatric disorders to provide a synthesis of the current scientific landscape surrounding this topic. A systematic analysis of the literature was performed following PRISMA guidelines. 407 original articles were included. Data extraction focused on study characteristics, including stimulation protocol, behavioural outcomes, and mechanisms of action. The number of articles published increased over the years, including 16 rat models and 13 mouse models of transgenic or healthy animals exposed to external factors to induce symptoms. Most studies targeted telencephalic structures with varying stimulation settings. Positive behavioural outcomes were reported in 85.8% of the included studies. In models of psychiatric and neurodevelopmental disorders, DBS-induced effects were associated with changes in monoamines and neuronal activity along the mesocorticolimbic circuit. For movement disorders, DBS improves symptoms via modulation of the striatal dopaminergic system. In dementia and epilepsy models, changes to cellular and molecular aspects of the hippocampus were shown to underlie symptom improvement. Despite limitations in translating findings from preclinical to clinical settings, rodent studies have contributed substantially to our current knowledge of the pathophysiology of disease and DBS mechanisms. Direct inhibition/excitation of neural activity, whereby DBS modulates pathological oscillatory activity within brain networks, is among the major theories of its mechanism. However, there remain fundamental questions on mechanisms, optimal targets and parameters that need to be better understood to improve this therapy and provide more individualized treatment according to the patient's predominant symptoms.

Voluntary exercise during puberty promotes spatial memory and hippocampal DG/CA3 synaptic transmission in mice

Physical exercise has been shown to have an impact on memory and hippocampal function across different age groups. Nevertheless, the influence and mechanisms underlying how voluntary exercise during puberty affects memory are still inadequately comprehended. This research aims to examine the impacts of self-initiated physical activity throughout adolescence on spatial memory. Developing mice were exposed to a 4-wk voluntary wheel running exercise protocol, commencing at the age of 30 d. After engaging in voluntary wheel running exercise during development, there was an enhancement in spatial memory. Moreover, hippocampal dentate gyrus and CA3 neurons rather than CA1 neurons exhibited an increase in the miniature excitatory postsynaptic currents and miniature inhibitory postsynaptic currents. In addition, there was an increase in the expression of NR2A/NR2B subunits of N-methyl-D-aspartate receptors and α1GABAA subunit of gamma-aminobutyric acid type A receptors, as well as dendritic spine density, specifically within dentate gyrus and CA3 regions rather than CA1 region. The findings suggest that voluntary exercise during development can enhance spatial memory in mice by increasing synapse numbers and improving synaptic transmission in hippocampal dentate gyrus and CA3 regions, but not in CA1 region. This study sheds light on the neural mechanisms underlying how early-life exercise improves cognitive function.

Continuous deep brain stimulation of the nucleus accumbens reduces food intake but does not affect body weight in mice fed a high-fat diet

Obesity is an enormous health problem, and many patients do not respond to any of the available therapies. Deep brain stimulation (DBS) is currently investigated as a potential treatment for morbid obesity. In this study, we tested the hypothesis that high-frequency DBS targeting the nucleus accumbens (NAc) shell region reduces food intake and weight gain in mice fed a high-fat diet. We implanted male C57BL/6J mice with bilateral electrodes and a head-mounted microstimulator enabling continuous stimulation for up to 5 weeks. In successfully operated animals (n = 9 per group, high-frequency vs. sham stimulation), we investigated immediate and long-term stimulation effects on metabolic and behavioral phenotypes. Here we show that stimulation acutely induced a transient reduction in energy expenditure and locomotor activity but did not significantly affect spontaneous food intake, social interaction, anxiety or exploratory behaviors. In contrast, continuous stimulation over 5 weeks led to a decrease in food intake and thigmotaxis (the tendency to stay near walls in an open lit arena). However, chronic stimulation did not substantially change weight gain in mice fed a high-fat diet. Our results do not support the use of continuous high-frequency NAc shell DBS as a treatment for obesity. However, DBS can alter obesity-related parameters with differing short and long-term effects. Therefore, future research should employ time and context-sensitive experimental designs to assess the potential of DBS for clinical translation in this area.

Urinary Tract Infections Impair Adult Hippocampal Neurogenesis

Simple Summary

Urinary tract infections are associated with features of cognitive decline and memory deficits, where the underlying correlation or mechanism is still not clear. In this study, we investigate the effect of urinary tract infections on cognitive functions in rodents and whether it is associated with adult hippocampal neurogenesis, a process that is detrimental for memory formation. We have shown that urinary tract infection affects the time spent exploring a novel arm in the Y-maze test. This was accompanied with a decrease in the proliferation of neural stem cells at an early time point post infection and a persistent decrease in neurogenesis at a later time point (34 days). We also detected decreased levels of neurotrophic factors important for neurogenesis and an elevated expression of interleukin 1β in the hippocampus. Treatment with either anti-inflammatory drugs or anti-biotics does not recover proliferation of neural stem cells. Here, we present hippocampal neurogenesis as a possible contributor to cognitive changes associated with urinary tract infections. Given the significant increase in urinary tract infection occurrence, it is important to address some of the detrimental effects that such an infection can have at the level of the brain.

Abstract

Previous studies have suggested a link between urinary tract infections (UTIs) and cognitive impairment. One possible contributing factor for UTI-induced cognitive changes that has not yet been investigated is a potential alteration in hippocampal neurogenesis. In this study, we aim to investigate the effect of UTI on brain plasticity by specifically examining alterations in neurogenesis. Adult male Sprague Dawley rats received an intra-urethral injection of an Escherichia coli (E. coli) clinical isolate (10⁸ CFU/mL). We found that rats with a UTI (CFU/mL ≥ 10⁵) had reduced proliferation of neural stem cells (NSCs) at an early time point post infection (day 4) and neurogenesis at a later time point (day 34). This was associated with the decreased expression in mRNA of BDNF, NGF, and FGF2, and elevated expression of IL-1β in the hippocampus at 6 h post infection, but with no changes in optical intensity of the microglia and astrocytes. In addition, infected rats spent less time exploring a novel arm in the Y-maze test. Treatment with an anti-inflammatory drug did not revert the effect on NSCs, while treatment with antibiotics further decreased the basal level of their proliferation. This study presents novel findings on the impact of urinary tract infections on hippocampal neurogenesis that could be correlated with cognitive impairment.

Multiple Sessions of Entorhinal Cortex Deep Brain Stimulation in C57BL/6J Mice Increases Exploratory Behavior and Hippocampal Neurogenesis. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2021;2021:6390-6393. [PMID: 34892574 DOI: 10.1109/embc46164.2021.9629978]

Deep brain stimulation (DBS) has been a medical intervention for a variety of nervous system diseases and mental diseases. The input of DBS in the entorhinal cortex (EC) regulates the neurophysiological activities in its downstream regions, such as the dentate gyrus (DG) area. EC DBS may play a role in the treatment of diseases through hippocampal neurogenesis. This study we examined the effect of multiple sessions of EC DBS on the regulation of hippocampal neurogenesis. 4-month-old male C57BL/6J mice received bilateral multiple sessions of EC DBS (130 Hz, 90 μs, 100 μA, 1 h/d, 21 days), and the DBS parameters used are close to the high-frequency DBS parameters in clinical studies. The open field test (OFT) was used to test the exploratory behavior of mice, and hippocampal neurogenesis was detected by immunofluorescence staining with anti-doublecortin (DCX). We found that multiple sessions of EC DBS were tolerated in C57BL/6J mice, significantly increased exploratory behavior and the number of DCX-positive neurons in the DG area.Clinical Relevance- Hippocampal neurogenesis may be part of the reason for DBS to improve memory, and the results of this study show that multiple sessions of EC DBS increases exploratory behavior and hippocampal neurogenesis, which is conducive to the application of DBS in nervous system diseases and mental diseases related to memory impairment.