355_Motivation_16

What is the somatic motor response to excessive adiposity and high levels of leptin?

3. The somatic motor response is triggered by connections of the arcuate nucleus neurons with cells in the lateral hypothalamus. This response consist in an inhibition of feeding behavior.

What is insulin shock?

A condition related to an overdose of insulin and hypoglycemia which produces sweating, tremor, anxiety, dizziness and double vision. Untreated, it can lead to convulsions, loss of consciousness, and delirium.

What is the lipostatic hypothesis?

A hypothesis based on the idea that the brain monitors the amount of body fat and acts to defend this energy storage against perturbations. This communication suggests a feedback loop between the adipose tissue, the fat, and the hypothalamus in the brain.

What is the substrate phase?

A phase in which nutrients begin to be absorbed into your bloodstream, whilst the stomach fills up and the food partially digested.

What is diabetes insipidus?

A selective loss of vasopressin-secreting neurons which results in the kidneys passing too much water from the blood to the urine. This causes dehydration which motivates drinking, but the water is quickly passed again from the kidneys to the urine, resulting in extreme thirst and frequent urination. The treatment for this is vasopressin replacement.

What is the postprandial state?

A state in which digestion is ongoing.

What is the prandial state?

A state in which the blood is filled with nutrients; prandial is Latin for breakfast.

Why is body weight usually very stable?

Body weight usually return to baseline after starvation or forced feeding due to the maintenance of homeostasis.

Why are αMSH and AgRP antagonistic neurotransmitters?

Both peptides bind competitively to the MC4 receptor. αMSH is the receptor's antagonist and inhibits feeding when bound. AgRP is the receptors antagonist and blocks the αMSH's stimulation at the receptor, which stimulates feeding.

What is the gastric phase?

Chewing, swallowing and digesting of the food happen which increases the physiological responses. Gastric distension signals, such as stomach stretching and innervation of mechanosensory axons that ascend to the brain, activate the nucleus of the solitary tract in the medulla via the vagal sensory axons (vagus nerve) and inhibits feeding. Cholecystokinin (CKK, 1970) is present in cells lining the intestine. It is released in response to food, especially fatty food, acts on the vagal sensory axons to inhibit feeding and works synergistically with gastric distension.

What did Douglas Coleman study?

Douglas Coleman studied genetically obese mice but was most interested in those that lacked pairs of specific gene strains dubbed "ob", which he hypothesized to code for a protein which signals the brain that fat reserves are normal, and db, which codes for a protein creating a satiety signal.

What does the stimulation of the dopamine axon produce?

It produces a craving for food without increasing the hedonic impact.

When does the pancreas starts making insulin?

It produces insulin during the cephalic phase. The increase in insulin decreases blood blood glucose level which is detected by the NPY/AgRP neurons, increasing the drive to eat.

What did the destruction of dopaminergic fibers reveals?

It revealed that it inhibits feeding but not the rewarding aspects of food. The liking of food is unaffected but the wanting is removed, it affects the incentive salience.

What other responses does a reduced blood volume entail?

It stimulates the sympathetic division of the ANS to help correct reduced blood pressure by constricting arteries. It also results in a powerful motivation to drink, in which the lateral hypothalamus is critically important.

Which neurons does a fall in leptin levels stimulate?

It stimulates two other types of arcuate neurons, namely: NPY (neuropeptide Y) and AgRP (agouti-related peptide). NPY and AgRP also have connections to the paraventricular nucleus and the lateral hypothalamus.

What did this connection between body fat and brain suggest?

It suggested a blood borne hormonal signal. This was later confirmed by Douglas Coleman in the 1960s.

What did Coleman's studies suggest on his genetically modified mice?

It suggested that ob/ob mice are lacking a satiety hormone, which was restored by db/db or normal mice, and that db/db mice produce a satiety hormone but are insensitive to it.

What is the look ahead study?

It was a study where more than 5145 randomly assigned overweight participants with type-2 diabetes where subject to intensive lifestyle intervention (ILI) or diabetes support intervention (DSI). ILI participants showed a greater loss of weight kept for a longer number of years.

What was the original belief with dopamine?

It was believed to be the pleasure molecule, serving in hedonic reward and released in response to sensations making them pleasurable.

What did Jeffrey Friedman et al. contribute to the study of the ob gene?

Jeffrey Friedman isolated that the ob gene coded for a protein that they name leptin which is produced by adipocytes (fat cells). Friedman showed that giving leptin to ob/ob mice would reverse body weight and decrease appetite.

What does it mean for weight loss to be considered long term?

LT weight loss is considered to be long term when 10% of the initial loss of weight is maintained for a year. LT weight loss is observed in generally 20% of people

Why do most behaviors occur?

Most occur in order to maintain homeostasis.

Does motivation guarantee action?

No, it does not has we can have conflicting goals which makes us gate the expression of different motivated actions.

What does Rimonobant do to CB1 receptors?

Rimonobant is an inverse agonist at the CB1 receptor which inhibits these receptors and reduces food intake.

Which part of the brain has great importance in motivating us to eat?

The lateral hypothalamus.

What is parabiosis?

The long-term anatomical and physiological union of two animals, similar to Siamese twins. Coleman initially employed parabiosis to fuse a db/db and a normal mouse.

What are the two forms in which we store energy that we got from our meals?

The first form is glycogen which is found in limited reserves, mainly in the liver and the skeletal muscles. The second form is triglycerides which is found in in adipose tissue in virtually limitless quantities.

What is obesity?

The increase of body fat due to a greater intake of energy than expenditure.

What are voluntary movements?

They are movements motivated to occur in order to satisfy a physiological or more abstract need.

What are anorectic peptides?

They are peptides that mimic elevated leptin levels. This inhibits appetite and feeding habits, and is associated with increased energy expenditures. (eg injection of αMSH and CART in the brain.)

What are orexigenic peptides?

They are peptides that mimic low leptin levels. This stimulates appetite and feeding habits, and is associated with decreased energy expenditures. (eg injection of NPY and AgRP in the brain.)

What were the characteristics of ob/ob mice?

They have a mutation of chromosome 6 and lack both ob genes. They are massively obese have marked hyperphagia and mild transient diabetes.

What are the characteristics of db/db mice?

They have a mutation on chromosome 4 and lack both db genes. They develop marked obesity, hyperphagia and severe-life shortening type-2 diabetes.

Why do we eat?

We eat to satisfy a metabolic need or reduce a drive, which is related to wanting. We also eat for its inherent hedonistic effect (pleasure), which is related to liking. Wanting and liking are mediated by separate brain circuits.

What are the effects of the AgRP and NPY neuropeptides?

They have the opposite effects of the αMSH and CART neuropeptides. They - inhibit the secretion of ACTH and TSH by the anterior pituitary, - increase activity in the parasympathetic division of the ANS and - stimulate feeding behaviors.

What does the activation of CB1 receptors do?

They stimulate feeding.

How is blood glucose level regulated by insulin?

When insulin is reduced, blood glucose level is elevated; when insulin rises, blood glucose level is reduced. This is why insulin is used to treat diabetes mellitus, in which there prolong periods of high blood sugar levels.

What is anabolic metabolism?

It is the assembly of macromolecules such as glycogen and triglycerides from smaller precursor molecules.

What are the physiological signals that initiate drinking?

1. Hypovolemia, or a decrease in blood volume. 2. Hypertonicity, or an increase in the concentration of dissolved solutes in the blood.

What are the integrated response to a fall in temperature?

1. It is detected by warm-sensitive neurons in the anterior hypothalamus which activate the humoral response. Thyroid stimulating hormones (TSH) are released by the anterior pituitary and stimulate the release of thyroxin causing a widespread increase in cellular respiration. 2. The visceromotor response consists of a constricting in the skin and the appearance of goosebumps (piloerection). 3. The somatic motor response consists of shivering to generate heat in the muscles and voluntary somatic motor response to seek warm.

What is the humoral response to excessive adiposity and high levels of leptin?

1. The humoral response is triggered by the activation of POMC/CART neurons in the paraventricular nucleus of the medial hypothalamus. This activation triggers the release of hypophysiotropic hormones by the anterior pituitary which causes the secretion of TSH (thyroid stimulating hormones) and ACTH (adrenocorticotropic hormones). This increases the metabolic rate of cells in the body.

What types of stimuli trigger the release of vasopressin?

1. Under cases of lowered blood volumes or pressure, blood levels of angiotensin II goes up. Angiotensin II acts on neurons in the subfornical area which stimulate the magnocellular neurosecretory cells residing in the posterior pituitary to release vasopressin. 2. Release of vasopressin is triggered by mechanoreceptor axons lining the walls of blood vessel and the heart which project to the hypothalamus and signals for loss in blood pressure (due to loss of blood volume).

What is the visceromotor response to excessive adiposity and high levels of leptin?

2. The visceromotor response is triggered by the paraventricular nucleus that has direct axonal projection to the neurons of the lower brain stem and preganglionic neurons in the spinal cord. αMSH and CART neurons also project axons directly down to the intermediolateral gray matter of the spinal cord which allows for direct arcuate control of the sympathetic division. This response consists of an increase in the sympathetic division of the ANS, mostly by raising body temperature, which also increases the metabolic rate of the body.

What is catabolic metabolism?

It is the breaking down of complex macromolecules into simpler molecules.

How does leptin act on the brain?

After being released into the bloodstream by adipocytes, whose release is higher after feeding and high during excessive feeding, it as activates leptin receptors on the arcuate nucleus of the hypothalamus, near the base of the third ventricle. This rise in leptin activates two types of arcuate neurons: CART (Cocaine- and amphetamine-regulated transcript) and POMC (proopiomelanocortin) neurons, from which αMSH (alpha-melanocute-stimulating hormone) is derived.

What is vasopressin?

An antidiuretic hormone (ADH) which acts directly acts on the kidney to increase water retention and inhibit urine production.

By what signals are the effect of leptin are regulated in the short-term?

As leptin levels vary slowly with periods of fasting and overeating, our motivation to eat is helped in part by orexigenic signals generated in response to a post-meal fasting. They build up during fasting and motivate us to eat. Eating is terminated and feeding is inhibited by satiety signals which are build up during eating and begin the process of digestion.

At which temperature are our cells and enzymatic processes fine-tuned to function?

At 37 degrees Celsius.

When do changes in blood insulin levels can be detected?

Before, during and after a meal. It is highest during the substrate phase.

Of what consisted Wolfram Schultz's study in relation to dopamine?

He recorded a electrode placed in the ventral tegmental area of an animal trained to associate light with apple juice.

What type of system is the dopamine part of?

It is part of a diffuse modulatory system.

Of what consisted Olds and Milner's 1950s experiment?

In their electrical self-stimulation experiment, Olds and Milner implanted an electrode in a rat's head and left it in a box, in which a certain corner of the box would send a jolt of electricity to the brain when stepped on. When the rat discovered it, it spend all its time in the corner. Additionally, they redid the experiment with a lever that would send electricity when stepped on. When the rat discovered it, it would step on the lever to the point of shunning food and water until collapsing of exhaustion.

What happened in Schultz's experiment?

Initially, dopaminergic neurons responded to juice but not light. After training dopaminergic neurons responded to light (predictive of reward-learning). Neurons had a reduced response in the absence of an expected reward. Dopamine signals are reward prediction errors. Neuron would fire if the reward was greater than expected, don't fire at all if it was worse than expected and cause no change when expected (only responded to light).

How does the regulation of homeostasis by the hypothalamus work?

Initially, sensory neurons in the periventricular zone of the hypothalamus detect the change in a regulated parameter (temperature, blood pressure, glucose levels) and produce a response. Firstly, hypothalamic neurons stimulate or inhibit the release of pituitary hormones in the bloodstream, this is called the humoral response. Secondly, hypothalamic neurons adjust the parasympathetic or sympathetic response of the autonomic nervous system, this is called the visceral response. Thirdly, hypothalamic neurons from the lateral hypothalamus incite an appropriate somatic motor behavior, this is called the somatic motor response.

What is insulin?

Insulin is an hormone secreted by the beta cells of the pancreas. Insulin is required for the transport of glucose in parts outside of the brain. It is important for anabolic metabolism when glucose is stored in the liver and skeletal muscles, and for catabolic metabolism when glucose is released from energy storage.

What happens with insulin during the gastric phase?

Insulin secretion is stimulated by gastrointestinal hormones such as CCK.

On which part of the brain does insulin directly act upon?

It acts on the arcuate nucleus and the ventromedial hypothalamus.

What is motivation?

It can be thought of as a driving force on behavior.

What can an overdose of insulin cause?

It can cause blood glucose level to plummet (hypoglycemia) which starves the neurons in the brain.

Why does marijuana stimulate appetite?

It does so through THC (Delta-9-tetrahydrocannabinol) which stimulates (CB1) cannabinoid receptor 1 expressed throughout the brain and affect many other functions apart from appetite.

What is the postabsorptive state?

It is a metabolic state achieved after complete digestion and absorption of a meal which takes about 3 to 5 hours. In this state stored glycogen and triglycerides are broken down to provide a continuous supply of energy.

By which part of the brain is hypertonicity of the blood detected?

It is detected by the vascular organ of the lamina terminalis or OVLT, a region of the telencephalon that is lacking a blood-brain barrier.

What is dopamine important for?

It is important for the wanting aspect of feeding as well as the anticipation of food. Rises in dopamine are associated with learning and reinforcing of behaviors. Drugs subject to abuse hijack this natural reward circuitry.

What happens when we eat?

Our energy stores are replenished and our blood is filled with nutrients (prandial state).

What impact does Redux have on the brain?

Redux, a drug used to treat obesity, increases serotonin and therefore are powerful appetite suppressants.

Where are located the neurons that change their firing rate in response to small temperature changes?

They are found throughout he brain and spinal cord, but the most important ones are those in the anterior hypothalamus.

Where where the rats stimulated?

Systematically moving the electrode has shown that the most effective sites are in the trajectory of dopaminergic axons projecting from the (VTA) ventral tegmental area to the (LH) lateral hypothalamus via the medial forebrain bundle. Drugs that block dopamine reduce electrical self-stimulation.

What are the main group of cells that receives direct input from leptin sensitive cells in the arcuate nucleus?

The MCH (melanin-concentrating hormone) expressing cells which prolong consumption and the orexin expressing cells which promote meal initiation. Both cell types have widespread connections with the cortex and the rest of the brain.

What is the cephalic phase?

The anticipation (sight and smell of food) triggers the parasympathetic and enteric divisions of the ANS which generates salivation, increase in digestive juices and insulin secreted from the pancreas. Hunger is triggered by the gherlin hormone (1999) which is concentrated in the stomach and is released into the blood, when it is empty. This activates NPY and AgRP containing neurons which stimulate feeding.

Say, you wake up and find pancakes which you eat until you're full. Which 3 phases can your body's reaction be divided into?

The cephalic phase. The gastric phase. The substrate (or intestinal) phase).

What were the conclusion of the mice studies?

The conclusion was that ob/ob mice lack leptin and db/db mice have mutated leptin receptors, which makes them have lots of leptin.

What happened when Coleman fused a db/db mouse with a ob/ob mouse?

The db/db mouse had an increase in - Body weight - Adipose tissue mass. The ob/ob mouse died of starvation due to low blood sugar and experienced: - a lower food intake - a decrease in adipose tissue mass - an abnormally large quantity of blood insulin.

What happened when Coleman fused a db/db and a normal mouse together?

The db/db mouse had an increase in: - body weight - adipose tissue mass. The normal mouse starved to death due to low blood sugar and had: - a lower food intake - an abnormally large quantity of blood insulin. Coleman hypothesized that the db/db mouse produced a powerful satiety signal.

What is starvation?

The decrease in fat tissue due to a greater energy expenditure than intake.

What happened when Coleman fused a ob/ob mouse with a normal mouse?

The obese mouse lost weight and had: - a lower food intake - a lower blood insulin level - lower blood sugar level The normal mouse experienced no changed.

Eating disorders are commonly associated with which neurotransmitter?

They are associated with an imbalance of serotonin.

Through which system are mood and food connected?

They are connected by the serotonergic system. Serotonin is low during the postabsorptive period, rises when anticipating food and peaks with food intake.

Where are the CB1 receptors involved in regulating appetite?

They are located in the hypothalamus and the olfactory bulb.

What is thirst triggered by hypovolemia called?

Volumetric thirst.

How does the OVLT react in face of a loss of water?

Water loss is transduced by OVLT neurons in an action potential firing frequency which directly excite the magnocellular neurosecretory cells of the posterior pituitary to secrete vasopressin. OVLT neurons also stimulate osmotic thirst by projecting to the lateral hypothalamus.

Why do we eat?

We consume food to provide the brain with glucose and avoid glucodeprivation which can cause coma and death.

How do we avoid glucodeprivation apart from eating?

We do so by have internal reserves and regulation. One reason of our motivation to eat is to maintain energy reserve at an adequate level to avoid energy shortfall.

How do people generally fare when it comes to long-term weight loss?

Without follow-up care, obese individuals tend to regain a third of their weight in a year and return to their baseline weight in 3 to 5 years.