Intro into Neuroscience-Hunger and Thirst

What is homeostasis?

The maintenance of a stable, balanced internal environment

What is the main homeostatic mechanism?

NEGATIVE FEEDBACK SYTEMS.

If you deviate from ______, compensatory action begins.

If you deviate from a SET POINT, your body tries to compensate and keep things balanced

Motivation is...

Factors that initiate, sustain, or direct behavior

What drives physiological motivation?

Homeostatic systems

What are the 2 systems involved in thermoregulation?

1. Preoptic Area: A part of the hypothalamus where lesions result in impaired physiological response, but not behavioral response. Physiological responses include sweating, constriction/dilation of blood vessels, and respiration. Lateral Hypothalamus: Lesions here result in the loss of behavioral regulation of temperature. Behavioral responses include shivering and heat-seeking/avoiding behaviors.

What is hypovolemic thirst?

1. Hypovolemic thirst is thirst stimulated by LOW OR LOSS OF EXTRACELLULAR/INTRAVASCULAR (WATER) VOLUME. Your outside cells have less water, and you get low blood pressure. Baroreceptors detect this drop. Arteries constrict to raise BP. NOTE: CONCENTRATION is not changed

Vasopressin and Renin are released due to hypovolemic thirst. What are their functions, respectively?

2. Vasopressin (ADH) - Released from posterior pituitary, blood vessel constriction, less blood flow to bladder, more water retention. Renin - Released from the kidneys when blood volume decreases, plays a major role in the Angiotensin cascade

Which of your organs helps resolve hypovolemic thirst?

4. SUBFORNICAL ORGAN; Angiotensin II acts here to signal to other brain sites (such as the POA) to initiate drinking

What is osmotic thirst?

5. Osmotic thirst is thirst stimulated by HIGH EXTRACELLULAR SOLUTE CONCENTRATION. Water can leave the cell, but salt cannot. When water leaves the cell, the cell shrinks

What neurons respond to a rise in blood osmotic pressure? Where are they found?

6. OSMOSENSORY NEURONS, which are found in the anterior hypothalamus (OVLT). They respond to increased osmotic pressure by causing the posterior pituitary to release ADH/Vasopressin

Which of your organs helps resolve osmotic thirst?

7. OVLT

What is the principal energy source, which is also used by your brain?

8. GLUCOSE. Your body even uses a process called glycogenesis to convert glucose to glycogen for storage

If absolutely necessary, what other form of energy will your brain be willing to use?

9. FAT- but only if your brain is starving and there is no other glucose left. Lipids and fat tissue are generally for longer-term storage of energy.

What is glycogen, and how is it made?

Your body makes glycogen through a process called glycogenesis to convert glucose into glycogen for short-term storage in the liver. Glycogenesis involves the use of insulin.

Increased insulin levels lead to _______, whereas increased glucagon levels lead to _______

a. Increased insulin levels lead to more glycogen production and less glucose, whereas increased glucagon levels lead to more glucose production and less glycogen

What is Leptin?

b. Leptin is produced by adipocytes (fat cells) and is secreted into the bloodstream. A deficit in leptin production results in a false-low report of body fat, causing animals to overeat. Obese rats and people are leptin-resistant.

What would weight loss do to leptin levels?

10. Decrease leptin levels, leads to hypothalamus signaling your body to increase food intake and use less energy.

What would weight gain do to leptin levels?

11. Increase leptin levels, food intake will go down, and use more energy.

What is Ghrelin?

GHRELIN is released by STOMACH endocrine cells. This is an appetite stimulant that RISES DURING FASTING and DROPS AFTER EATING.

When you are full after eating food, do you have high or low ghrelin and leptin levels?

12. Low Ghrelin levels, high Leptin levels

What disorder do some obese people have with a problem with peripheral signals?

13. PRADER-WILLI SYNDROME is when people have abnormally elevated ghrelin levels. These people eat as if they were starving. Main question to ask over the phone to see if the caller's child has Prader-Willi- "Do you have a lock on the fridge?" People with Prader-Willi will eat as much as they can, even if it's rotten food. Imagine having this and trying to diet and maintain a healthy weight.

Where in the brain would lesions cause overeating?

14. If you have lesions in the VENTROMEDIAL HYPOTHALAMUS, obesity may result. In an experiment, VMH lesioned rats overeat until they become obese. Stability and a new SET POINT is made at this heavier weight. Thus, even if you are a scientist and force-feed VMH lesioned rats, the rats, when the force feeding stops, will drop back down to the new set point, as opposed to the original, healthy set-point.

Lesions in what part of your brain would cause refusal to eat?

15. LATERAL HYPOTHALAMUS. a. LH lesioned animals stop eating, and stabilize their weight at a new lower level because of a new, lower set point. b. Perhaps anorexics have a lower set point

NPY/AgRP neurons produce neuropeptide Y and agouti-related peptide. What do these do?

16. They STIMULATE appetite and LOWER metabolism. Weight gain

What do POMC neurons do?

1. POMC/CART neurons produce pro-opiomelanocortin (POMC) and CART, which do two things for weight loss: a. INHIBIT appetite and RAISE metabolism

VMH lesions destroy the ____

2. Anorexigenic Paraventricular Nucleus (PVN)

LH lesions destroy the ____

Orexigenic Lateral Hypothalamus (LH)

High calorie diets cause __________ and ___________

3. Hypothalamic scarring and microglial activation

Overeating leads to hypothalamic inflammation, which:

Inhibits neurogenesis, resets your set point

Izzy was obese and died of heart failure. How did he get up to 757 pounds?

17. Izzy might have had leptin deficiency or VMH lesion. We don't exactly know, but it is certain he had a high set point from weight gain that made it hard to diet.

You are still trying to lose weight (summer is coming soon). Why do diets fail for most people?

18. The first week of the diet is probably decently successful. People reduce caloric intake drastically, and see they've lost a lot of weight, 6 pounds. Eating this same amount of food the second week, people see a much less drop in weight, maybe 2 pounds. This happens because your BASAL METABOLIC RATE (the energy required to fuel the brain/body and maintain temperature) falls to PREVENT losing weight. Your body is working against your diet because it is scared you will die! The better strategy, instead of cutting 1000 calories the first week, may be to cut 100 calories the first two weeks, and another 100 the next, and so on, so your body doesn't get used to it. Exercise is helpful, too (but not as essential as reduced intake)!

What are effective treatments for obesity?

a. -Eat less, modify behavior to avoid temptation to pig out, and exercise b. -Giving a cannabinoid receptor antagonist. However, if you block cannabinoids, you get suicidal thoughts. Not a viable option. c. -If you treat obesity as an addiction, for instance, REDUCING D2 receptors and DECREASING IN PREFRONTAL METABOLISM, the treatment may be somewhat effective. d. -GASTRIC BYPASS SURGERY is the best, in which GHRELIN IS REDUCED and PYY AND GLP-1 IS INCREASED, reducing hunger. 25% average weight loss in patients is long lasting, reduces mortality, and has many health benefits

(True or False): Increasing Leptin and decreasing Ghrelin levels are an effective method for treating obesity

4. FALSE

What is anorexia nervosa? What are some symptoms?

19. ANOREXIA NERVOSA is the refusal to maintain body weight, coupled with fear of weight gain, body image disturbance, amenorrhea, etc. It can be a restricting or a binge-eating/purging type. It is 10x more common in woman than in men

What is bulimia? What are some symptoms?

20. BULIMIA is recurrent binge eating with recurrent inappropriate, compensatory behavior. It often goes on for at least 2x/week for 3 months. Symptoms include thinning of bones, brittle hair and nails, drop in body temperature, low blood pressure, slow breathing, etc.

Teenage girls with anorexia have (larger/smaller) Insula and (larger/smaller) Orbitofrontal Cortex (OFC)

5. Larger, larger

What are some treatments for anorexia or bulimia?

6. For anorexia or bulimia, SEROTONIN is LOW. Treating this eating disorder as a mood disorder might be successful. Antidepressants and anti-schizophrenic drugs (like Olazapine) produces some benefit. Dopamine might be involved in some way as well.