Investigating how long-term signals modulate brainstem satiation circuits

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Project Abstract: The size of a meal is carefully regulated to prevent over- or under-feeding. Direct control of meal size is attributed by brainstem areas, such as the caudal nucleus of the solitary tract (cNTS), that directly receive short-term sensory feedback from the GI tract during feeding. In contrast, the indirect controls, which include hypothalamic circuits and leptin, are hypothesized to encode long-term energy balance and regulate meal termination by modulating the potency of these short-term signals sensed in the brainstem. Interactions between these long-term and short-term systems are critical for the control of food intake, but how it is encoded in the dynamics of the underlying brainstem circuits remains unknown. The cNTS contains many cell types that are involved in controlling food intake. Among these cell types, prolactin releasing hormone (PRLH) and glucagon (GCG) neurons are particularly important for meal termination. In my recent studies, I performed the first neural recordings of these two cell types in awake behaving mice. I found unexpectedly that these cells were rapidly activated at the start of a meal by feedforward signals such as taste. These technical and conceptual advances create an opportunity for me to investigate the longstanding question of how signals of long-term energy balance modulate brainstem circuits to control meal termination. I propose here to address this question by investigating how two regulators of long-term energy balance – Agouti-related peptide (AgRP) neurons and leptin – modulate PRLH or GCG neuron dynamics or their control of feeding behavior. Together these results will reveal how long-term systems modulate brainstem circuits to regulate meal size, which is an important determinant of overall food intake and can be dysregulated in conditions like obesity.