Parabrachial Opioidergic Projections to Preoptic Hypothalamus Mediate Behavioral and Physiological Thermal Defenses

Maintaining stable body temperature through environmental thermal stressors requires detection of temperature changes, relay of information, and coordination of physiological and behavioral responses. Studies have implicated areas in the preoptic hypothalamic area (POA) and the parabrachial nucleus (PBN) as nodes in the thermosensory neural circuitry and indicate the opioid system within the POA is vital in regulating body temperate. In the present study we identify neurons projecting to the POA from PBN expressing the opioid peptides Dynorphin (Dyn) and Enkephalin (Enk). We determine that warm-activated PBN neuronal populations overlap with both Dyn and Enk expressing PBN populations. We demonstrate that Dyn and Enk expressing neurons are partially overlapping subsets of a glutamatergic population in the PBN. Using optogenetic approaches we selectively activate projections in the POA from PBN Dyn, Enk, and VGLUT2 expressing neurons. Our findings demonstrate that Dyn, Enk, and VGLUT2 expressing PBN neurons are critical for physiological and behavioral heat defense.