Neurons in the brain which quench thirst identified.
To maintain homeostasis in the body, physiological imbalances produce motivational drives, one of which is thirst. This thirst produces a drive to seek and consume water, however, just how neural activity creates this motivation remains poorly understood. Now, a study from researchers at Stanford University identifies a subgroup of neurons in mice which drive thirst. The team state that the activity of these neurons decreased as the mice consumed more water, suggesting that they play a direct role in the primordial emotion. The study is published in the journal Science.
Previous research suggests that a certain region of the brain, the median preoptic nucleus (MnPO), contributes to the sensation of thirst, yet the exact underlying mechanisms have remained largely unknown. The current study analyzes RNA expression within the MnPO of mice which have been deprived of water for 48 hours, to identify a cluster of excitatory neurons of interest.
The current study uses TRAP2 to tag active neurons in mice who’ve been without water, then adds light-sensitive genes to turn the tagged neurons off and on by using a fiber optic light. Results show that the researchers can make satiated mice drink. Data findings show that the lab were able to finely control how often these mice went to drink, that is, how often they pressed a lever in order to obtain water, just by changing how often they stimulated thirst neurons.
The team state that they went one step further to show they could train these mice to press a lever to turn off optogenetic activation of thirst neurons, not to get water. They go on to add this suggests that animals drink water in order to feel less bad, that is, they are not so much pursuing something rewarding as trying to alleviate an uncomfortable sensation or reduce an aversive drive. They conclude that similar mechanisms may be at work for other types of natural or pathological motivational drives, such as mating impulses or drug addiction.
The team surmise that their data identifies a distinct population of neurons in a brain region called the median preoptic nucleus which are activated during thirst. For the future, the researchers state that the activity of these neurons integrates the recent history of water intake and adaptively regulates goal-directed behaviour.
Source: Stanford Medicine