Biology of Sodium Appetite (IMAGE)
Caption
Researchers induced salt (Na+) appetite in mice or rats, which led to the discovery of profound changes in certain nerve cells in the hypothalamus (micrographs, upper right). These nerve cells became enlarged and increased their expression of two proteins, DARPP-32 (green) and ARC (blue). These neurons are part of a powerful circuit that sustains addiction behavior, and the increased expression of DARPP-32 and ARC suggests that these neurons more readily respond to reward stimuli. The bright yellow color in these neurons indicates co-localization (the appearance together) of both of those proteins along with orexin, a protein initially linked to appetite stimulation, but in this part of the hypothalamus later found to be critical for addiction-related behaviors. Dopamine-receptor-1 is a nerve-cell-surface receptor protein that signals to the nerve cell that dopamine molecules have attached. One of the effects of dopamine binding to its receptor is that animals, including humans, get a strong reward sensation, which can be coupled to behavioral conditioning -- the binding makes the animal or person want to repeat what led to the dopamine release. Below, the line graphs show that induced salt appetite in mice can be powerfully reduced with drugs that block dopamine-receptor-1, whereas a related instinct, thirst for water, is not affected by such treatment.
Credit
Wolfgang Liedtke, Duke Departments of Medicine and Neurobiology
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