Dissecting populations of PrRP neurone in conditional transgenic mice

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In order to survive, we need to balance our energy intake (the food we eat) with metabolic demands. The latter includes the energy we require to keep warm, exercise and maintain body functions. We must ensure that there is adequate energy easily available in the form of glucose and stored in the form of fat, and predict any changes in demand. To do this, the brain and particularly regions of the hypothalamus and brainstem, collect information from other organs regarding whether we have recently eaten, the time of day, how much glucose is in our blood and how much fat is laid down in adipose tissue. All of this information is integrated by specific brain cells and translated into actions, again by peripheral organs: should we eat, produce more warmth, release more energy from stores? Our problem is that we know relatively little about the kinds of brain cell (neurone) which carry out this key integrative function. However, we have demonstrated that a novel brain transmitter, called PrRP, is capable of regulating many of these critical responses to changing energy demands, and that mice lacking the receptor for PrRP are obese. More interestingly, PrRP is produced in distinct populations of neurone in the exact regions of the hypothalamus and brainstem mentioned. However, the problem remains how to study or manipulate these distinct neurones in their different environments. We have a unique opportunity to bring together the very best physiological and behavioural analyses with cutting-edge genetics. Using the latest techniques we will produce transgenic mice with harmless alterations to the genes expressed in PrRP neurones. The first type of mouse will express a fluorescent marker only in PrRP neurones which will allow us to visualise them amongst the millions of cells in the brain. We will then be able to record their electrical activity and determine how they respond to different stimuli. This mouse will also allow us to selectively silence signalling molecules, thus demonstrating the importance of different signals specifically to PrRP neurones. The second mouse will have a small piece of DNA inserted into the PrRP gene to disrupt its expression. We predict that this mouse will be obese because it cannot respond to metabolic signals to produce the normal regulatory responses. However, we can cross this mouse with others which will result in the insert being removed from the PrRP gene in specific populations of PrRP neurone. This will allow us to study mice in which PrRP now functions normally in the brainstem alone and then also in the hypothalamus. Through these studies we will gain important insight into the brain circuitry controlling energy balance and that will perhaps allow us to develop new strategies to fight the burgeoning obesity epidemic.