S25_NEUR3003_Day9

NEUR 3003: Neuroscience of Behavior

• Reminders: Annotated bibliographies due on Sunday (2/9)

Course Topics

• Homeostasis: The balance of physiological processes and maintenance of an organism's internal environment.

• Hunger: Understanding the neural drives related to food intake.

Learning Objectives

• Describe and identify the central neural drive for food intake.

• Explain the mediators that affect meal size, duration, and timing (both short- and long-term).

• Predict changes in food intake based on lesions or pharmacological manipulations.

Homeostasis

• Definition: Regulation ensuring physiological processes function within a narrow internal range (Bear, Neuroscience, Exploring the Brain).

Historical Background

• Claude Bernard (1849): First described the regulation of the internal environment.

• Walter Bradford Cannon (1926): Coined the term "homeostasis"; introduced "fight or flight" (1915).

• Joseph Barcroft (1932): Integrated brain function into the homeostasis concept.

Homeostasis Mechanisms

• Stressor: Factors disrupting homeostasis such as heat, cold, hunger, or threats.

• Stress Response: Physiological adaptations aiming to restore homeostasis.

Role of the Hypothalamus

• Functions: Acts as a master regulator of critical body processes including:

  • Sleep and wakefulness

  • Feeding and energy metabolism

  • Fluid and electrolyte balance

  • Blood composition and volume

  • Stress response

  • Body temperature

  • Heart rate and blood pressure

  • Reproduction

Why Do We Eat?

• Discussion Prompt: Reasons for food consumption.

Motivations for Eating (Hervey 1969)

• Energy restoration through glucose intake.

• Factors influencing meal initiation:

  • Anticipatory (permissive influences)

  • Feedback mechanisms to maintain homeostasis.

What Is Hunger?

• Definition: A motivational state driving food intake.

• Key Factors:

  • Glucose homeostasis is the ultimate reason for hunger.

  • Influences include food's incentive value, time of day, and memory of last meal.

• Hormonal and neural signals from the gut influence hunger.

Regulation of Eating Behavior

• Arcuate Nucleus: Central driver with two first-order neuron classes:

  • MSH/CART Neurons: Anorexigenic (suppress food intake).

  • NPY/AgRP Neurons: Orexigenic (stimulate food intake).

Second-Order Neurons

• Regions include Paraventricular nucleus (PVN), Lateral Hypothalamus (LHA), and Peri-fornical area (PFA).

• Peptides:

  • Orexin: Promotes meal initiation.

  • MCH: Prolongs consumption.

Role of Orexin in Feeding Behavior

• Exogenous orexin increases food intake.

• Orexin may have roles in the rewarding aspects of food.

Meal Onset Signals

• Ghrelin: Released by an empty stomach; induces food intake.

Meal Offset and Satiety Signals

• Endocrine Signals: Stop feeding behavior, with compounds like:

  • Cholecystokinin (CCK): From the small intestine (within-meal satiety).

  • Peptide YY (PYY) and GLP-1: From the large intestine (between-meal satiety).

Meal Regulation Determinants

• Factors influencing meals include:

  • Gastric emptying

  • Digestion rates

  • Nutrient sensing.

Engagement Discussion

• Ozempic: A GLP1 receptor agonist helping manage body mass and glucose levels.

• Potential experiment design to explore its effects on food intake and central drive for food.

The Rodent Feeding Circuit

• Leptin, GLP-1, and NPY/AgRP feedback relation.

• Circuit interactions among different brain areas controlling food intake.

Longer Term Energy Balance

• Insulin:

  • Essential for glucose uptake in cells, signaling satiety post-meal.

Interaction of Leptin and Insulin

• Leptin and insulin influence hypothalamic pathways that regulate eating and energy expenditure.

Integration of Energy Balance Signals

• Interaction between adiposity signals, satiety signals, and energy metabolism.

Factors Influencing Energy Balance

• Various elements, such as diet composition, physical activity, and genetics, play roles in energy intake and expenditure.

Review: Terms and Their Purposes

• Pairing terms (NPY/AgRP, POMC/CART, Insulin, Orexin, etc.) with their physiological functions in relation to hunger and satiety signaling.

Hunger Games Analysis

• Reflection on Katniss Everdeen's homeostatic challenges in water scarcity and weather extremes during the Quarter Quell.