4/7/15 – Lecture 20 – Hunger and Eating Behaviors- Goal: to understand what drives hunger and how this influences eating behaviors- All living organisms need energyo ATP is the energy current of the cell ATP comes from different sources (fats, glucose, and amino acids) which come from foodso Getting energy from food depends on 3 processes Digestion – the breakdown of food starting in the mouth (chewing and saliva) and ending in the small intestine Absorption – the process of moving nutrients into the bloodstream from the gut Uptake – the process by which cells of the body take up nutrients for use in producingATP- Control of Appetiteo KEY POINT – the hypothalamus regulates hunger and satietyo The Hypothalamus – in the forebrain – controls DAY TO DAY functions (body temperature, hunger, thirst, fatigue, sleep, circadian cycles, and stress responses) Major site of integration between the nervous system and the endocrine system (the glands that secrete hormones throughout our bodies)- Nervous system = quick responses- Endocrine system = long and lasting responses Connects to many other brain/cortical structures that influence behavior- Hypothalamic Hunger and Satiety Centerso Lateral Hypothalamus (LH) – hunger centero Ventromedial Hypothalamus (VMH) and Paraventricular Nucleus (PVN) – satiety centerso Arcuate Nucleus (AN) – regulates both hunger and satiety- They Hypothalamic Appetite Circuito One set of arcuate nucleus cells releases melanocyte stimulating hormones (MSH excitatory neurons) onto satiety center neurons in the VMH and PVN and activates themo Another set of arcuate nucleus neurons releases neuropeptide Y (NPYexcitatory neurons) onto LH hunger center neurons, activating themo NPY neurons also inhibit satiety center neuronso VMH and PVN satiety neurons release the hormone CRHo LH hunger neurons release orexin In all cases, the neurotransmitters activate neurons in the frontal cortex and other brain regions that allow the organism to engage in the appropriate behaviors- Walking away, throwing food out in the case of satiety, searching for food in the case of hungero What activates the different arcuate nucleus neurons? – Satiety and hunger signals Major SATIETY Signals- Cholecystokinin (CCK) – a peptide released by the stomach when it has food in ito Stomach has stretch receptors/mechanical receptors to know its full (not the whole reason)o Stomach also senses the nutrients that are being digested by chemoreceptors- Glucose – blood levels rise during absorption- Insulin – released by pancreas during absorptiono Activates neurons that activate our satiety pathways- Serotonin – increased by absorption of tryptophan (an amino acid)- Leptin – released by fat cells when they are taking up fato Defects in Leptin Signaling Result in Severe Obesity Ob/ob mice have mutation in their leptin gene and exhibit hyperphagia (hugely increased eating) and obesity Db/db mice have a mutation in their leptin receptor gene andalso exhibit hyperphagia (hugely increased eating) and obesity Most human obesity is environmental (not genetic) and leptin levels are normal or even elevated in most obese humans Major HUNGER Signals- Ghrelin – a peptide released by the stomach when it is empty- Low glucose- Endocannabinoids – endogenous cannabinoids (their production in the hypothalamus is inhibited by leptin)o Hypothalamic Appetite Circuit CCK, insulin, high glucose, serotonin and leptin all activate MSH neurons in the arcuate nucleus, which in turn releases MSH and activate VMH and PVN satiety center neurons that release CRH that influences cortical neurons to generate satiety behaviors Ghrelin and low glucose activate NYP neurons in the arcuate nucleus, which in turn release NPY and activate LH hunger center neurons that release orexin that influences cortical neurons to generate feeding behaviorso Endocannabinoids and “the munchies” Endocannabinoids inhibit CCK release by the stomach, decreasing satiety Endocannabinoids inhibit CRH neurons, decreasing satiety Endocannabinoids stimulate hunger neurons, increasing hunger Leptin inhibits endocannabinoids, increasing satiety If eating behavior is so tightly regulated, why are so manypeople overweight or obese!?!?- What are some factors influencing when we eat besides hunger??o Memoryo Work Scheduleso Family traditions or routineso Cultural normso Personal preferences and habitso FOOD AVAILABILITY (most determinate for developed countries) What is some factors that influences how much we eat besides satiety signals??- Social influences – people consume 60% more when eating with others but can decrease consumption too so as not to appear gluttonous- “Cafeteria Effect” – eating one food decreased the desire for that food but having other foods available will cause you to continue eating because your desire for them has not been reduced as much- “Appetizer Effect” – eating a small amount of food first often increases hunger- Cultural Norms – how long our meals are, eating until we’re not hungry anymore (Europeans) vs eating until we’re full (Americans)- External/ Visual Cues – plate/portion size (eating until the plate is clean), supersizing, economy size, etc. - Taste and Enjoyment 4 Brain Regions that Influence Eating Behaviors- Amygdala – regulates emotions; provides input to hypothalamus about food aversions, emotional states, stress, etc.- Hippocampus & Medial Temporal Lobe – memory storage; provides input to hypothalamus about how recently we are, how filling it was, how nutritious and good tasting it was, and learned cravings, etc.- Inferior Frontal Lobe – receives input from the olfactory bulb about smells and taste, provides input to hypothalamus about pleasurable sensory information related to food- Reward Centers – provides input to the hypothalamus about pleasure Reward Systems of the Brain and Eating Behaviors- Neurons in the ventral tegmental area release dopamine in response to pleasurable experiences onto neurons in the nucleus accumbens- Dopamine stimulation of neurons in the nucleus accumbens increases in anticipation of the actual stimuluso Dopamine release is thus involved in the “wanting” aspects of and motivation for rewardo Binding of dopamine to its receptors on nucleus accumbens neurons is associated with “liking” Smell and other anticipatory cues triggered often activate thereward