Parabrachial neurons: their connections and role in maintaining body temperature, wakefulness, and appetite

The brain receives sensory information to maintain body homeostasis. Much of this sensory information flows through the parabrachial nucleus in the brainstem to the forebrain. The parabrachial nucleus is divided into subpopulations of neurons that express different genes, and relay different types of information to different targets in the forebrain. We began by investigating the projection from the parabrachial nucleus to the insular cortex, and whether this projection mediates wakefulness. We first identified the anatomy and genetic identity of the neurons in the parabrachial nucleus that send this projection. We then specifically stimulated this projection but found it did not wake mice.

We then tested if specifically ablating these parabrachial neurons would cause loss of wakefulness, but found these mice had normal amounts of wakefulness and activity. We then examined if parabrachial ablation would impair other physiological functions. Despite previous research indicating that the parabrachial nucleus controls appetite, we instead found that mice ate normal amounts of food and gained weight at a normal pace. Lastly, we exposed mice to warm and cold temperatures. Control mice maintained their body temperature when placed in cold conditions, but the body temperature of mice with parabrachial ablations rapidly plunged. We identified a subpopulation of parabrachial neurons that express the proteins FoxP2 and Gastrin-Releasing Peptide as necessary for maintaining body temperature in the cold.