Quiz 4 Neurosci

Adult Neurogenesis

  • Introduction
      - Discusses the ability of the adult brain to generate new neurons (adult neurogenesis).
      - This topic was established in the late 1990s to early 2000s, making it a recent finding in neuroscience.
      - Aim: To explore discoveries on adult neurogenesis, factors influencing it, and mechanisms involved.

  • Establishment of Neurogenesis in Adults
      - Historically thought that only developing brains could generate new neurons.
      - Evidence has confirmed neurogenesis in the adult brain, especially in the hippocampus.
      - Other areas where neurogenesis has been identified:
        - Olfactory system (olfactory bulbs).
        - Basal ganglia (caudate nucleus).
        - Spinal cord has some evidence of neurogenesis.

  • Methods of Identification
      - The compound BrdU (bromo-deoxy-uridine) is used to identify new neurons.
        - BrdU integrates into the DNA of dividing cells, marking newly born cells.
        - This method distinguishes between new neurons and mature, differentiated neurons.
      - Example study:
        - Comparison of hippocampal sections from exercising and non-exercising adult animals using BrdU staining.
        - Exercise notably increased the number of BrdU-positive neurons in the hippocampus.

Factors Influencing Adult Neurogenesis

  • Animal Studies vs. Human Studies
      - Initial evidence for neurogenesis derived from studies on rodents and non-human primates.
      - Difficulties in studying neurogenesis in humans due to ethical constraints.

  • Human Evidence Alongside Animal Studies
      - Late 1990s, cancer patients used BrdU for tumor growth monitoring, leading to neurogenesis findings post-mortem in their hippocampi.
      - Presence of BrdU-positive neurons confirmed neurogenesis in adult humans, indicating regenerative potential of adult brains.

  • Major Factors Promoting Neurogenesis
      - Environmental enrichment: Stimulated living conditions lead to increased neurogenesis.
        - Study: Mice in enriched conditions (toys, running wheels, social interaction) had a 60% increase in new neurons compared to mice in standard conditions.
      - Difficulty in performing similar studies on humans due to ethical and methodological challenges.

  • Component Analysis of Environmental Enrichment
      - Various components involved in environmental enrichment help dissect their individual contributions to neurogenesis:
        - Physical activity (exercise).
        - Learning opportunities (cognitive engagement).
        - Social interaction.
      - Research explored specific components (like exercise) influencing new neuron generation independently.

Effects of Exercise on Neurogenesis

  • Exercise Findings
      - Study by van Praag et al. (1999) highlighted the impact of exercise on neuron proliferation and survival.
      - Experimental conditions included:
        - Control (standard housing).
        - Enriched condition (exercise, social interaction).
        - Learning tasks (Morris water maze).
        - Swimming tasks without learning.
      - Findings:
        - Exercise led to increased proliferation and survival of new neurons.
        - Contextual stress from tasks may inhibit neurogenesis in non-exercised animals.
        - Confirmed that tasks engaging the hippocampus can enhance neurogenesis.

  • Role of Stress in Neurogenesis
      - Stress inhibits neurogenesis through increased glucocorticoids (cortisol).
        - Elevated cortisol levels inhibit stem cell production in the hippocampus and promote neurodegeneration.
      - Chronic cortisol activation can lead to neuron death in the hippocampus due to high glucocorticoid receptor concentrations.

Mechanisms of Exercise-Induced Neurogenesis

  • Growth Factors
      - Exercise elevates growth factors such as brain-derived neurotrophic factor (BDNF).
        - BDNF supports existing neuron survival and promotes new neuron production.
      - Comparison between BDNF and fertilizer (e.g., Miracle-Gro analogy for plant growth).
      - Exercise correlates with reduced progression of neurodegenerative diseases (e.g., Alzheimer's, Parkinson's) via increased BDNF levels.

Introduction to Stem Cells and Stem Cell Research

  • Overview of Stem Cells
      - Characteristics of stem cells include self-renewal and multipotency (ability to differentiate into various cell types).
      - Early embryonic development involves pluripotent stem cells, which can turn into any body cell.
      - Pluripotent cells transition to multipotent stem cells over time, limiting them to specific tissue families.

  • Induced Pluripotent Stem Cells (iPSCs)
      - Discovery of iPSCs in 2006, which reprograms differentiated adult cells (like skin cells) back into pluripotent cells.
      - Methodology involves introducing specific genes associated with stem cells using viral transfection.
        - Retroviruses act as delivery vehicles for stem cell genes, reestablishing pluripotency in differentiated cells.

Applications of iPSCs in Disease Treatment

  • Case Study: Sickle Cell Anemia
      - iPSCs used to reprogram skin cells from sickle cell mice, correct genetic mutations, and differentiate back into healthy blood stem cells.
      - Successful trials resulted in curing sickle cell anemia in mouse models, despite initial complications like tumor development.

  • Modeling of Diseases
      - iPSCs allow modeling diseases (e.g., Alzheimer's, ALS) by transforming patient-specific skin cells into affected cell types (neurons).
      - This enables studying disease progress, structure, and potential treatments in vitro without invasive procedures in living patients.

Ethical Considerations and Future of iPSC Research

  • Ethical Implications
      - iPSCs circumvent issues around embryonic stem cell use, avoiding harvesting from embryos, which is ethically contentious.
      - Changing political landscapes affect regulations on stem cell research funding.
      - Emerging ethical dilemmas introduced by potential genetic manipulation of sperm/egg cells leading to designer babies.

  • Long-Term Implications
      - Challenges include tumorigenesis from viral insertion methods and potential limitations on the pluripotent capabilities of reprogrammed cells.
      - Ongoing research aims to refine gene delivery methods to avoid integration into DNA and potential malignancies.

Overview of Brain Development

  • Major Development Stages
      - Neural Plate to Neural Tube: Initial formation occurs around 18 days after conception.
      - Stages of brain development classified into 6 key processes:
        1. Neurogenesis - Begins after the neural tube forms; peak between 3 to 5 months gestation.
        2. Cell Migration - Neurons migrate to their specific locations guided by radial glial cells.
        3. Differentiation - Neurons specialize based on gene expression, influenced by their environments.
        4. Synaptogenesis - Formation of synapses begins prenatally, completing around two years of age.
        5. Apoptosis - Surplus neurons compete for survival, leading to selective cell death mediated by neurotrophic factors.
        6. Synaptic Rearrangement - Fine-tuning of neural connections based on activity.

  • Neural Tube Defects
      - Examples include spina bifida and anencephaly, leading to significant malformation and serious health issues if not surgically corrected.

Developmental Sex Determination

  • Sexual Differentiation
      - Genotypic sex (XX or XY) is determined at conception based on sperm chromosome contribution.
      - Gonads are initially symmetrical; differentiation occurs around 6 weeks gestation:
        - Presence of SRY gene on Y chromosome leads to testes formation; its absence results in ovaries.
      - Hormonal influences from the gonads (testosterone or lack thereof) lead to organizational changes in brain structure.

  • Genetic versus Phenotypic Sex
      - The phenotypic sex encompasses the visible sexual characteristics shaped by hormonal environment.
      - The brain’s development is shaped by hormones from gonads, leading to structural differences influencing sexual behavior.

  • Conditions Affecting Sexual Development
      - Congenital Adrenal Hyperplasia: High androgen exposure in genetic females leads to ambiguous genitalia and masculinized behaviors.
      - Androgen Insensitivity Syndrome: Genetic males with dysfunctional receptors develop female physical characteristics due to unresponsive androgen signaling.

Epigenetics Overview

  • Definition and Mechanism
      - Epigenetics is the study of how environmental factors regulate gene expression without altering DNA sequences.
      - Mechanisms include DNA methylation (typically silencing genes) and histone modification (modifying accessibility for transcription).

  • Impact on Health
      - Environmental influences (maternally mediated behavior, nutrition, drug exposure) provide profound effects on gene expression with lasting repercussions on health outcomes.

  • Maternal Effects
      - Variation in maternal behaviors impacts offspring glucocorticoid receptor density, which correlates to stress response resilience.
      - Mice offspring of high maternal care exhibit enhanced stress responses due to effective negative feedback in the HPA axis.

  • Dietary Effects
      - Studies reveal that maternal diets influence genetic outcomes for offspring, such as how BPA impacts the agouti gene expression concerning coat color and health.
      - Nutritional interventions can reverse detrimental effects on gene expression, demonstrating the significance of diet on health outcomes.

  • Human Relevance
      - Epigenetic studies reflect how twins diverge over time despite identical DNA, showing that environmental factors shape gene expression.
      - Tools to measure epigenetics have implications for assessing risk factors and biological age, allowing deeper insights into personal health management.