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what is the key region of the brain for metabolic control?

the arcuate nucleus of the hypothalamus
particularly true for control of appetite


where do signals to the arcuate nucleus come from? how does it exert control?

receives hormonal input from the periphery in the form of insulin, leptin, ghrelin and others
signals to the periphery in turn to exert metabolic control


what are the types of neurons in the arcuate nucleus? what does each type do to appetite? What NT do they release and what is the receptor for the NT?

POMC neurons = anorexigenic (appetite-suppressing) - release alpha-MSH (melanocyte-stimulating hormone) to activate downstream neurons that express MC4 receptor

NPY neurons = orexigenic (appetite-stimulating) - release several NT, including NPY


how do NPY neurons inhibit appetite?

1: by inhibiting downstream neurons that the POMC neurons activate
2: by inhibiting POMC neurons


how do fuel sources affect activation of appetite?

POMC neurons can be activated by glucose
NPY neurons can be activated by FA


how do pancreatic beta cells sense glucose? (review)

1: glucose enters cell via GLUT2 channel
2: glucokinase phosporylates glucose to glucose-6-phosphate
3: glucose metabolized through glycolysis - citric acid cycle begins
4: electron transport chain in mitochondria generates ATP from the NADH and FADH2 generated by citric acid cycle
5: ATP can inhibit plasma membrane K channel => membrane depolarization
6: depolarization activates V-G Ca channel => Ca enters cell
7: Ca entry triggers secretion of insulin via fusion of vesicles with plasma membrane

in step 3, the amount of glucose-6-phosphate made depends on the amount of glucose present (since the Km of the kinase is in the physiological range, it should be able to convert all the glucose that comes into the cell), and the GLUT2 transporter is not regulated, so the amount of glucose entering the cell should always be directly proportional to the amount in the blood


How do POMC neurons sense glucose levels?

use part of pathway that pancreatic beta cells use - part where ATP inhibits K channel
inhibition => depolarization of plasma membrane => action potential


what are potassium, sodium, and calcium levels inside and outside of cells?

K: high in cytoplasm (>100 mM) and low in cells (100 mM)

Ca: very low in cytoplasm (<100 nM) and high extracellularly (1-2 mM) plus lots of Ca in ER


how do NPY neurons sense FA levels?

despite that brain doesn't synthesize or oxidize FA, NPY neurons have enzymes from the FA synthesis/oxidation pathways including CAT-1, ACC, FAS, and AMPK
interplay between ACC and CAT-1 regulates NPY activity:
- low CAT-1 activity is anorexigenic => decreased NPY activity
- high CAT-1 activity is orexigenic => increased NPY activty


what does it mean for something to be anorexigenic?

it decreases appetite and increases energy utilization


what does it mean for something to be orexigenic?

it increases appetite and decreases energy utilization


what does CAT-1 do? (review)

converts Acyl-CoA to carnitine-CoA
first step in FA transport into mitochondiral matrix for oxidation


what does ACC do? (review)

produces malonyl-CoA
key step in FA synthesis
the malonyl-CoA inhibits CAT-1 activity => inhibited FA oxidation


what does FAS do? (review)

uses malonyl-CoA to synthesize FA
high activity depletes malonyl-CoA => increased CAT-1 activity (since malonyl-CoA inhibits CAT-1) => increased FA oxidation


what does AMPK do? (review)

can phosphorylate ACC => reduced ACC activity => decreased malonyl-CoA levels => increased CAT-1 activity => increased FA oxidation


how do neuronal ACC inhibitors affect appetite?

increase neuronal CAT-1 activity
increases appetite


how do neuronal FAS inhibitors affect appetite?

decrease neuronal CAT-1 activity
decreases appetite


how do neuronal CAT-1 inhibitors affect appetite?

decrease neuronal CAT-1 activity
decreases appetite


how do neuronal AMPK activators affect appetite?

increase neuronal CAT-1 activity
increases appetite


what is leptin? what cells secrete it?

peptide hormone secreted by adipose tissue


how do leptin levels relate to fat?

blood leptin levels are proportional to adipose tissue mass


where does leptin act?

on the arcuate nucleus of the hypothalamus


what is the action of leptin on arcuate nucleus neurons?

inhibits NPY neurons
activates POMC neurons


what are the affects of leptin on neuronal circuitry?

appears to affect two aspects:
1: direct neural signaling in the short-term
2: neuronal wiring patterns in the long-term - creates more stimulatory POMC synapses and less stimulatory NPY synapses


what is the end result of leptin activity?

decreased appetite (anorexigenic) and increased energy expenditure
keeps amount of adipose tissue within a certain range


what happens in individuals that don't produce leptin? can this be treated?

this is rare, but does happen
will result in morbid obesity
but can be treated with leptin


what mutations can occur in the leptin pathway (beside not producing leptin)?

mutations in:
1: leptin receptor
2: alpha-MSH (the NT released from POMC neurons)
3: MC4R (major alpha-MSH receptor on neurons down-stream of POMC neurons)


what are the blood levels of leptin in most people with obesity?

most have higher than normal blood leptin levels


how does leptin's creation of a set-point affect the ability of diets to be effective?

dieting causes loss of adipose tissue => decrease in leptin levels => increased NPY and decreased POMC neuron activity => hunger
plus longer-term wiring patterns in brain still geared toward heavier set point
dieter therefore fighting against strong biological desire to eat more and strong biological desire to reduce energy expenditure


what type of hormone is ghrelin and what organ secretes it?

peptide hormone secreted by the stomach