How brain cells drive, quench your thirst un­cov­ered

Iran Daily - - Health -

Sci­en­tists have iden­ti­fied a set of neu­rons deep in the brain that con­trols the crit­i­cal in­stinct of thirst.

When the re­searchers used op­to­ge­net­ics, or light stim­u­la­tion, to in­hibit these brain cells, mice re­duced their wa­ter con­sump­tion, ac­cord­ing to the study pub­lished in is­sue of the US jour­nal Science.

In con­trast, ac­ti­va­tion of the neu­rons cause the mice to drink even though they are wa­ter sa­ti­ated, xin­ re­ported.

The re­searchers made these find­ings by look­ing at a cer­tain re­gion of the brain, the me­dian pre­op­tic nu­cleus (MNPO), which pre­vi­ously has been linked to the sen­sa­tion of thirst.

Liqun Luo, a pro­fes­sor of bi­ol­ogy at Stan­ford, who co-led the study with his col­league, Karl Deis­seroth, a pro­fes­sor of bio­engi­neer­ing and of psy­chi­a­try and be­hav­ioral sciences, said, “Vast ma­jor­ity of be­hav­ioral ex­per­i­ments are done by mak­ing an­i­mals thirsty, and use wa­ter as re­ward to train an­i­mals for spe­cific tasks. So thirst has a very strong mo­ti­va­tional drive.

“How­ever, as the an­i­mals become less thirsty, their per­for­mance de­te­ri­o­rates.

“My (team was) in­ter­ested in ask­ing why wa­ter is so re­ward­ing to thirsty an­i­mals and why the mo­ti­va­tion is lost when they are less thirsty.”

The team uti­lized a new method de­vel­oped by them­selves, called TRAP2, which al­lows them to cap­ture neu­ronal pop­u­la­tions that are ac­ti­vated by a spe­cific stim­u­lus — in this case, wa­ter depri­va­tion.

Luo said, “These ex­per­i­ments sug­gested that ac­ti­va­tion of these neu­rons pro­vides a thirst mo­ti­va­tional drive.

“Fur­ther­more, we can train mice to turn off op­to­ge­netic stim­u­la­tion of these neu­rons by press­ing a lever, sug­gest­ing that ac­ti­va­tion of these neu­rons is aver­sive to mice, and they work to turn off the stim­u­la­tion.

“These ex­per­i­ments pro­vide neu­ro­bi­o­log­i­cal sup­port for a psy­cho­log­i­cal the­ory known as ‘drive re­duc­tion the­ory of mo­ti­va­tion’.

“The the­ory was pro­posed in the 1940s as a uni­fy­ing the­ory to ex­plain mo­ti­vated be­hav­ior, but went out of fashion later on for lack­ing neu­ro­bi­o­log­i­cal sup­port.

“In essence, a de­vi­a­tion of home­osta­sis (such as wa­ter depri­va­tion), cre­ates a neg­a­tive drive (thirst), which mo­ti­vated be­hav­ior to re­duce this neg­a­tive drive (search for wa­ter and drink) to re­store home­osta­sis.

“In an­other words, thirst makes the an­i­mals feel bad, and wa­ter is re­ward­ing to thirst an­i­mals be­cause it makes them feel less bad and thus re­ward­ing.”


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