El Comportamiento del Hambre

• These are study notes about the behavior of hunger and thirst

Behavior, Hunger

• Stimulus triggers a rapid response
• Can involve the thalamus, amygdala, the sympathetic nervous system (SNS), and the hypothalamic-pituitary-adrenal axis (HPA axis)
• Stimulus triggers a slow response which includes sensory cortex
• Can involve the hippocampus, hypothalamus, cingulate gyrus, thalamus, and prior sensory experience
• Cytokines increase appetite
• Ghrelin increases appetite and is produced in the fundus of the stomach by oxyntic cells
• Increases GAP secretion
• Receptors located in the arcuate nucleus in the neurons of neuropeptide Y (NPY) and pro-opiomelanocortin (POMC)
• Hunger results in ghrelin which encourages NPY
• Targets the lateral hypothalamic area and leads to food seeking behavior
• Agouti-related peptide (AgRP) and orexin are also involved in hunger
• POMC release triggers alpha-melanocyte-stimulating hormone (α-MSH)
• This acts on the ventromedial nucleus/satiety center
• Lateral hypothalamic nucleus is the center of hunger
• Ventromedial nucleus is the satiety center
• To measure behavior, there must be observable and measurable signs

Limbic system

• Includes emotions and is for survival, maintenance, protection, and reproduction
• Changes in SL can cause reproductive problems, cardiovascular issues, autonomic response issues, gastrointestinal issues, and changes in temperature
• Hypothalamus function includes thermoregulation, control of maintenance and social behavior
• Amygdala responds to somatosensory stimuli, response patterns, and fear
• Cingulate gyrus processes information for motor responses
• Hippocampus is responsible for immediate and spatial memory
• Nucleus accumbens controls motivation and reward
• Brainstem includes the locus coeruleus responsible for central noradrenaline production, the tegmental area that produces dopamine, the raphe nuclei that produce serotonin and gigantocellular neurons which produce acetylcholine
• Food in the stomach stretches the stomach walls which triggers signals to the nucleus of the solitary tract (NPY)
• This is modulated by cholecystokinin (CCK) and neuropeptide Y (NPY)
• Ghrelin induces appetite by stimulating the production and secretion of NPY-AgRP in the arcuate nucleus of the hypothalamus
• Reduce the excitability of POMC-CarT neurons
• It stimulates the dopaminergic reward pathway, increasing the desire to ingest food
• Incretin: glucagon-like peptide 1 (GLP-1) contributes to energy homeostasis, glucose metabolism, gastric secretion and emptying, and insulin secretion
• Oxyntomodulin stimulates gastric acid secretion, activates GLP-1 and GLP-2, induces satiety, reduces weight gain, and increases energy expenditure
• Gastric inhibitory polypeptide (GIP) stimulates vagal afferents that inhibit NPY-AgRP
• It inhibits gastric acid secretion and improves insulin secretion
• Obestatin stimulates vagal afferents that inhibit NPY-AgRP
• Acts in opposition to the action of ghrelin on appetite, is anorexigenic
• Cholecystokinin (CCK) stimulates the gallbladder, bile flow and contraction
• Increases the secretion of pancreatic digestive enzymes
• Vagus nerves in the intestine express CCK1 receptors, inducing short-term satiety
• Vasoactive intestinal peptide (VIP) stimulates vagal afferents that inhibit NPY-AgRP
• Causes smooth muscle relaxation and stimulates pancreatic bicarbonate secretion

Behavior, Thirst

• Organum vasculosum of the lamina terminalis (OVLT), subfornical organ (SFO) and median preoptic nucleus (MnPO) detect changes in osmolarity
• CULT, SFO, and NPOM detect changes in osmolarity which leads to vasopressin (ADH) being released
• Neuroendocrine cells in the supraoptic nucleus (SON) and paraventricular nucleus (PVN)
• Thirst and NPV are polysynaptic pathways
• Gamma-aminobutyric acid (GABA)ergic neurons block the SFO, MnPO, and OVLT
• An elimination of electrolytes increases SRAA
• Angiotensin II is a vasoconstrictor
• Stimulates OVLT which leads to ADH secretion and increases salt appetite
• Short term response triggered by fluids in the oropharynx activating neurons that cause inhibition in 15-20 minutes which involves GABA ergics
• Long term response is from the absorption of fluids to inhibit vagal afferent neurons of the SFO
• This leads to activation of neurons which turn off the hypovolemic thirst reflex using GABA ergics