Cellular dehydration caused by stimuli such as hypertonic NaCl or mannitol cause a sustained shrinkage of osmosensitive cells, and in osmosensitive neurons this is transduced into a proportional change in firing rate. The basal firing rate of these neurons may encode an effective set point for osmoregulation. In the brain, these osmoreceptors seem to be predominantly in the SFO, MnPO, and OVLT. From selective lesion and other evidence, it appears that these regions act in a synergistic manner, such that optimal drinking and/or AVP secretion occurs when all three of these interconnected regions are functional. Some data suggest that there may be species differences in the details of this integrated functioning of the lamina terminalis.