Following fasting, satiety is observed within two hours after reintroducing food and accompanied by neuronal activation in distinct areas of the brain including the hypothalamic paraventricular nucleus and dorsomedial nucleus, parabrachial nucleus, medial and commissural subdivisions of the nucleus tractus solitarius (NTS), central nucleus of the amygdala (CeA) and bed nucleus of the stria terminalis (BNST) that have all been associated with the regulation of food intake by affecting autonomic and reward centers in the brain. In addition to these regions, we observed in our preliminary studies striking cfos activation in the parasubthalamic nucleus (PSTN), a poorly characterized nucleus in the brain that we hypothesize comprises a major node in the satiety circuitry. To test this hypothesis, we will elucidate how refeeding-activated PSTN neurons are integrated into the central nervous system using classic neuroanatomical tracing techniques (retrograde and anterograde), and to test the functionality of these neurons in the regulation of appetite, the use of DREADDs to activate or inhibit PSTN activity. Anatomical maps will be constructed of the projection pathways of refeeding-activated PSTN neurons including the topography of neurons in the PSTN that project to known appetite regulating centers and whether activated neurons have a single, dedicated projection field or multiple projection fields. The functionality of this circuitry will e tested by activating or inhibiting PSTN neuronal perikarya using AAV expressing DREADDs fused to mCherry injected bilaterally into the PSTN that either expresses hM3Dq to activate PSTN neurons or hM4Di to silence PSTN neurons in response to the systemic administration of clozapine-N-oxide (CNO). Behavioral readouts used will include measuring food and water intake and locomotor activity in automated cages using a fasting-refeeding paradigm, and by operant conditioning to study reward feeding. We propose that these studies will lead to new insights about how appetite is suppressed and better understanding about the mechanisms underlying the regulation of food intake.
Understanding the mechanisms by which the central nervous system controls food intake is essential to identifying new approaches to prevent the significant morbidities associated with disorders of appetite and satiety affecting both children and adults such as anorexia nervosa and obesity. We propose that anatomical and functional characterization of neurons in the parasubthalamic nucleus (PSTN) that are activated at the point of satiety when fasting animals have been refed, will uncover new and important information about how appetite is regulated.