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February 29, 2012
Key Hormone Helps Brain Control How Much We Eat and How Much Energy We Have

Yale University researchers have discovered a key cellular mechanism that may help the brain control how much we eat, what we weigh, and how much energy we have.

Three MCH neurons in the hypothalamus region are highlighted in green. In animals, these neurons are associated with high calorie intake and lower energy levels. Yale researchers have shown how the effects of these key cells are reversed.

The findings, published in the Feb. 28 issue of the Journal of Neuroscience, describe the regulation of a family of cells that project throughout the nervous system and originate in an area of the brain call the hypothalamus, which has been long known to control energy balances.

Behavioral adaptation to a naturally occurring event (energy
homeostasis, predation, reproduction), or during an experimental
task in a laboratory, results from the integration of external and
internal signals.

Scientists are closely investigating the role of melanin-concentrating hormone (MCH) neurons in controlling food intake and energy. Previous studies have shown that MCH makes lab animals eat more, sleep more, and have less energy. In contrast, other hypothalamic neurons use the thyrotropin-releasing hormone (TRH) as a neurotransmitter, and these neurons reduce food intake and body weight, and increase physical activity.

Increasing Arousal

Interestingly, neurotransmitters involved in cognitive functions are also responsible for tuning of arousal. Activation of neurons producing acetylcholine and monoamines neurotrans mitters have long been associated with an increased arousal and vigilance, as well as increased responsiveness of cortical and thalamic cells to sensory stimuli. This means that stimulation of these regions during arousal also excites the neurons and consequently stimulating the body's energy levels.

The MCH system is the target of these ascending and descending arousal and cognitive-promoting neuronal popula tions from the brainstem and forebrain structures.

The Yale study of brains of mice shows that the two systems appear to act in direct opposition, to help the organism keep these crucial functions in balance.

Although TRH is normally an excitatory neurotransmitter, the Yale study shows that in mice TRH inhibits MCH cells by increasing inhibitory synaptic input. In contrast, TRH had little effect on other types of neurons also involved in energy regulation.

"That these two types of neurons interact at the synaptic level gives us clues as to how the brain controls the amount of food we eat, and how much we sleep," said Anthony van den Pol, senior author and professor of neurosurgery at Yale School of Medicine.


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