How does your brain decide when you are full?

You probably know the famous adage which says that you have to take your time to eat because it takes 20 minutes for satiety to reach your brain. If this state of affairs was well validated by the scientific approach, which had already highlighted the role of the brain, more precisely the brainstem and some of the cells found there and the afferents of the vagus nerve coming from the tract gastrogastro-intestinal in the occurrence of satiety, considerable limits weigh on these results. Indeed, the classic methodology was to detect a transcription factor on anesthetized animals or on brain slices: “ the classic method in physiology has long been to look at the expression of a family of proteins called cFos, which play the role of transcription factor and which is expressed during the activation of a neuronneuron. Thus, we look at which neurons and how many neurons express cFos and we have an idea of ​​the activation of neuronal populations,” explains Filipe De Vadder, researcher in intestinal physiology at the National Center for Scientific Research (CNRS) who did not participate in the study.

The revolutions: Cre-lox and optogenetic tools

With this initial methodology, it was impossible for biologists to study these same mechanisms on living organisms. movementmovement. Just as isolating the effect of a embarrassedembarrassed especially. It is now possible thanks to revolutionary theoretical and technological advances which give rise to multiple experiments which study our preference for sugar, fear or even the effects of stress, in moving organisms. “ Thanks to the revolution of the Cre-lox system and the tools of theoptogeneticsoptogeneticswe can really manipulate as we wish where the gene we wish to study will be expressed, as well as the closing and opening of the ion channelsion channels for neuronal communication. These are discoveries that deserve a Nobel Prize in my opinion,” suggests Filipe De Vadder.

Satiety is a sequential mechanism

What interests the authors of this study published in the journal Nature, is to know how our neural circuits transform our sensory signals during food intake and control it dynamically, at different time scales. Using the different techniques mentioned above, they demonstrate that neurons sensitive to prolactinprolactin (PLRH) intervene in a very short time scale (of the order of a second) and that they are very sensitive to the contact of food with the mouth and to their taste, while the neurons sensitive to proglucagon detect the activity intestinal muscle and the presence of certain nutrientsnutrients, which will determine long-term satiety. In short, this demonstrates that satiety is a sequential process that involves different cells, different circuits and different signals.

For Filipe De Vadder, this study highlights the power of optogenetics: “ From now on, we can really dissect the different neuronal circuits, control and isolate the expression geneticgenetic and show that a population of cells is specifically responsible for a particular behavior generated by a particular characteristic of a food, enthuses the researcher. Finally, he also notes a positive point in this paper apart from the strictly scientific aspect: In the experiment both males and females are used, which is positive because we do not exclude sex a priori. Recent studies have shown in particular that the criteria for excluding females from studies on mice were unnecessary. “.