Hypothalamus and Hunger Regulation

Lateral Hypothalamus (LH) and Ventromedial Hypothalamus (VMH)

  • Lateral Hypothalamus (LH):

    • Memory hack: LH = Lunch (triggers eating, hunger "ON" switch).

    • Early lesion studies: Destroying LH in rats caused them to stop eating, highlighting its role as a hunger "ON" switch.

    • Stimulation of LH caused overeating, further supporting its role in initiating eating.

  • Ventromedial Hypothalamus (VMH):

    • Memory hack: VMH = Vomit (stops eating, hunger "OFF" switch).

    • Early lesion studies: Destroying VMH caused rats to overeat and gain massive weight, suggesting its role as a hunger "OFF" switch.

    • Stimulation of VMH caused rats to stop eating, reinforcing its role in satiety.

Evidence Against the Simple "On/Off" Model

  • Not absolute control:- LH-lesioned rats sometimes resumed eating with special diets.

    • VMH-lesioned rats sometimes stopped overeating, and weight stabilized.

  • Complex Networks:- Hypothalamus works with other brain regions and multiple hormones.

    • Hunger and satiety result from interacting signals, not just two centers.

  • Broader Behavioral Effects:- LH lesions affect arousal and reward systems.

    • VMH lesions may disrupt metabolism and fat storage.

Genetic Conditions Related to Hunger

  • ob gene:- Results in no leptin production.

  • db gene:- Leptin is produced, but brain receptors are insensitive to it.

Physiological Signals for Hunger

  • Stomach contractions.

  • Blood glucose drop.

  • Hormones: Ghrelin, Insulin.

  • Hypothalamus (lateral).

Physiological Signals for Satiety (Stopping Eating)

  • Stretch receptors in stomach.

  • Blood glucose rises.

  • Hormones: Leptin, CCK, Peptide YY.

  • Ventromedial hypothalamus.

Leptin and Appetite Regulation

  • Leptin: "Satiety hormone" secreted by fat cells.

  • Mechanism: Increased fat stores \rightarrow increased leptin levels \rightarrow signals hypothalamus to reduce appetite and increase energy expenditure.

  • Role: Long-term regulator of body weight.

  • Discovery: Identified via mouse experiment (1994) involving the ob gene.

Gene Definitions

  • ob gene: Encodes for the production of leptin. A mutation in this gene leads to a deficiency in leptin, resulting in severe obesity.

  • db gene: Encodes for the leptin receptor. A mutation in this gene means the body cannot respond to leptin signals, also leading to severe obesity.