Chapter 16 Behavior

Hypothalamic neurons bring the body back to optimal ranges by a mechanism with three steps, what are they?

1. Humoral response: hypothalamic neurons respond to sensory signals by stimulating or inhibiting release of pituitary hormones into the blood stream 2. visceromotor response: neurons in hypothalamus respond to sensory signals by adjusting the balance of sympathetic and parasmpathetic outputs of ANS 3. Somatic motor response: Hypothalamic neurons (lateral hypothalamus) respond to sensory signals by inciting an appropriate somatic motor behavioral response.

Describe the body's reactions during the process of eating a meal and becoming satiated.

1. cephalic phase: sight and smell of food trigger many physiological processes that anticipate arrival of breakfast. Parasymp and enteric activated, secretion of saliva and digestive juices. 2. Gastric phase: responses grow much more intense when you start chewing, swallowing and filling stomach with food. 3. Substrate phase: as stomach fills the partially digested food moves to intestines, nutrients absorbed into blood.

What is the purpose of orexin produced by lateral hypothalamus neurons?

A peptide. These cells also receive direct input from arcuate nucleus. Orexin is an orexigenic peptide (stimulate feeding behavior). Levels of MCH and orexin rise in brain when leptin levels low. Orexin promotes meal initation whereas MCH prolongs consumption. Orexin plays a role in regulation of wakefulness. Mutating orexin genes leads to weightloss and excessive daytime sleepiness. Sleep inhibits eating. Insomnia and obesity go together.

How do the alphaMSH and CART neurons trigger the humoral response?

Activating neurons in paraventricular nucleus of hypothalmus, release of hypophysiotropic hormones that regulate secretion of TSH and ACTH from anterior pituitary. Periventricular nucleus also control activity of sympathetic dividion of ANS with direct axonal projections to neurons in lower brain stem and to preganglionic neurons in SPC. The alphaMSH and CART neurons can also project axons directly down to intermediolateral gray matter of SPC.

What is the role of CCK in feeding?

Administering CCK inhibits meal frequency and size. Present in some cells that line intestines and some neurons of enteric NS. Released in response to stimulation of intestines by certain types of food, fatty ones. Major action of CCK as a satiety peptide is exerted on the vagal sensory axons. CCK acts synergistically with gastric distension to inhibit feeding behavior. Also in some neurons of CNS.

Describe how leptin works.

After much eating, leptin released into bloodstream by fat cells, activate liptin receptors in neurons of arcuate nucleus of hypothalamus, near base of third ventricle. Arcuate neurons activated by rise in blood leptin levels contain peptide neurotransmitters called alphaMSH and CART, these peptides in brain vary in proportion ot level of leptin in blood.

What can bilateral lesions of the lateral hypothalamus cause? how about ventromedial hypothalamus?

Anorexia (lateral hypothalamic syndrome). Obesity (ventromedial hypothalamic syndrome).

Where are neurons important for temp regulation?

Anterior hypothalamus.

Where do the alphaMSH and CART neurons project to?

Areas that facilitate the humoral, visceromotor and somatic motor response.

How are alphaMSH and AgRP antagonistic NTs?

Both bind to MC4 receptor on postsynaptic neurons, but alphaMSH activates while AgRP inhibits. Activation of MC4 on lateral hypothalamic neurons inhibits feeding, inhibiting receptors stimulating feeding.

How is hypertonicity of blood sensed?

By neurons in region lacking BBB: vascular organ of the lamina terminalis (OVLT). When blood hypertonic, water leaves cells, water loss reansduced by OVLT neurons into change in AP firing frequency. OVLT neurons 1) directly excite magnocellular neurosecretory cells that secrete vasopressin 2) stimulate osmometric thirst, motivation to drink water. Lesions completely prevent behavioral and humoral responses to dehydration. Not to responses to loss of blood volume

Describe the release process of insulin.

Cephalic phase: parasymp innervation of pancreas stimulates beta cells to release insulin. In response, blood glucose levels fall slightly, this change is detected by neurons in brain, increase drive to eat (acivation of NPY/AgRP). gastric phase when food in stomach, insulin secretion increases by gastrointestinal hormones like CCK. insulin release is at max when food absorbed in intestines and blood glucose levels rise, during substrate phase.

What is the somatic motor response to increased leptin?

Decrease feeding behavior.

lower ST leads to what?

Depression, reduced satiety. Antidepressent drugs elevate ST and effectively treat bulima nervousa patients.

In general mechanisms by which natural rewards reinforce particular behaviors is mediated by what NT?

Dopamine.

desruction of dopamine axons passing thru the lateral hypothalamus does what?

Failed to reduce "do it cuz it feels good" responses to food even though animals stop eating. Food on rat with lesion on lateral hypothalamus will eat food like it is delicious. Dopamine depleted animals behave like they like the food but dont go searching for it. Stimulate dopamine axons in lateral hypothalamis of normal rats produce craving for food without increasing like it so eat it impact.

Electrical stimulation of the lateral hypothalamic area triggers what?

Feeding behavior.

What is the body's humoral response to increased leptin?

Increased secretion of TSH and ACTH: increase metabolic rate of cells in body.

What happens if you inject brain with alphaMSH/CART?

Mimics response to increased leptin levels. Therefore these are said to be anorectic peptides: diminish appetite. Injecting drugs that block these peptides increases hunger.

What is the role of ghrelin?

Released by stomach into blood when stomach empty. Administration of ghrelin increases hunger by activating NPY/AgRP-containing neurons of arcuate nucleus

What is the role of insulin in feeding?

Released into blood by beta cells of pancreas. glucose transport into other cells (not neurons) of body requires insulin. Important for anabolism when glucose into liver, muscle, fat for storage and catabolism when glucose liberated from storgae. Levels of glucose tightly regulated by levels of insulin. blood glucose levels increased when insulin levels decreased. Blood glucose fall when insulin levels rise.

What NT provides a link between food and mood?

ST

When are ST levels low?

ST levels in hypothalamus low during fasting state, spike during a meal especially in response to carbs.

After a meal what signals occur?

Sitiety signals rise throughout meal and last for a time after, but slowly disapate and orexigenic signals increase slowly until drive to eat occurs again.

What happens if you inject brain with MCH?

Stimulates feeding behaviors. Mice that lack this peptide show decreased feeding behaviors, increased metabolic rate, and are lean.

What does a rise in leptin do?

Stimulates release of alphaMSH and CART from arcuate nucleus neurons. These anoretcic peptides act on brain by activating MC4 receptor to inhibit feeding behavior and increase metabolism.

What is the role of gastric distension and fullness?

Stomach innervated by mechanosensory axons and most ascend to brain via vagus nerve. Vagus nerve has mix of sensory and motor axons, originates in medulla, meanders thru much of body cavity. Vagal sensory axon activate neurons in nucleus of the solitary tract in medulla. These signals inhibit feeding.

Drugs that elevate ST in brain are appetite _____.

Suppressants

Dopamine is involved in learning, T or F?

T

Drugs that block dopamine receptors reduced self-stimulation, suggesting what?

The animals were trying to release dopamine.

What is the postabsorptive state?

The fasting state. stored glycogen and triglycerides broken down to provide body with supply of molecules as fuel Catabolism.

What is the prandial state?

The fed state. Blood is filled with nutrients. Energy is stored as glycogen and triglycerides (fat) (anabolism).

What is the lipostatic hypothesis?

The idea that the brain monitors the amount of body fat and acts to defend this energy store against changes. (eat more when skinny, eat less when fat). Suggests that there is communication between fat and brain.

Deviations for optimal ranges are sensed in where?

The periventricular zone of hypothalamus

How is feeding behavior inhibited?

Via connections of the arcuate nucleus neurons with cells in lateral hypothalamus.

What is thirst triggered by decreased blood volume called?

Volumetric thirst. Vasopressin (from posterior pituitary) acts directly on kidneys to increase water retention and inhibit urine production.

When is feeding stimulated?

When neurons in hypothalamus detect drop in level of hormones released by fat cells. These cells are concentrated in the periventricular zone, lateral hypothalamus.

What do the group of neurons,MCH, in the lateral hypothalamus that receive direct input from leptin-sensitive cells of arcuate nucleus do?

Widespread connections in brain, innervate most of cerebreal cortex: invovled in organizing and initiating goal-driven behaviors like seeking food. MCH system is in a strategic postion to inform cortex of leptin levels in blood and therfore contribute significantly to motivating for food sreach.

Insulin acts on the _____ and _____ nuclei of the hypothalamus.

arcuate and ventromedial. Acts similarly to leptin to regulate feeding.

What physiological signals trigger drinking?

decreased blood volume, increased concentration of dissolved substances.

Where are the regions in the brain most associated with reward and self-stimulation?

dopaminergic axons arising in the ventral tegmental area, projecting though the lateral hypthalamus to several forebrain regions.

How does chocolate chip cookies make you happier?

increase in blood tryptophan and brain serotonin b/c ST derived from dietary tryptophan.

What is the visceromotor response to increased leptin?

increase tone of sympathetic division of ANS, raises metabolic rate, raise body temp.

What is the primary stimulus for insulin release?

increased blood glucose. Rise of insulin, with increased blood glucose levels, is a satiety signal and causes you to stop eating.

What protein is coded for by the ob gene and is responsible for hormonal signaling to brain about adiposity?

leptin. Released by fat cells. Regulates body made by acting directly on neurons of hypothalamus that decrease appetite and increase energy expenditure. Leptin deficiency stimulates hunger. Suppress energy expenditure.

Dopamine neurons signals errors in what?

reward prediction: events that are better than expected cause dopamine neurons to come to life, what that are worse than expected cause them to be inhibited and those that occur as expected cause no change in firing, even if events still provide hedonic reward (still tastes good even if expect it)

What triggers release of vasopression in volumetric thirst?

rise in blood levels of angiotensin 2 in response to reduced blood flow to kidneys. Acts on neurons of subfornical organ in telencephalon, stimulate magnocellular neurosceretory cells of hypothalams release vasopressin. Mechanoreceptors in walls of major blood vessles and heart signal loss of blood pressure which accomanies loss of blood volume. Signals to hypothalamus via vegas nerve

What is diabetes insipids?

selective loss of vasopressin-secreting neurons of the hypothalamus. Body works against brain. Loss of vaspopressin, kidney pass too much water from blood to urine. Dehydration, strong motivation to drink, passes quickly. Extreme thirst large amounts of pale pee.

Motivated behaviors are generated by what?

somatic motor system

What does a fall in leptin do?

stimulates release of NPY and AgRP from arcuate nucleus neurons and release of MCH and orexin from neurons in lateral hypothalamic area. Orexigenic peptides act on brain to simulate feeding behavior and decrease metabolism.

Reduced blood volume does what?

stimulates sympathetic division of ANS, helps correct drop in BP by constricting arterioles Powerfully motivates animals to seek and consume water. lateral hypothalamus involved in this behavior.

What does a decrease in leptin do?

turn off responses mediated by alphaMSH/CART neurons and simulates another type of arcuate nucleus neurons that contain NPY and AgRP: also have connections with paraventriculat nucleus and lateral hypothalamus. NPY and AgRP inhibit secretion of TSH and ACTH. Activate parasympathetic diviion of ANS and stimulate feeding behavior: Orexigenic peptides.