Genetic identity of warm and cool thermosensory relay neurons in the mouse parabrachial nucleus

Abstract

The parabrachial nucleus relays skin temperature from the spinal cord to the hypothalamus. Relay neurons for warm and cool thermosensation were localized in rats to the lateral parabrachial nucleus (LPB), but we need more information about their genetic identity for chemogenetic and optogenetic experiments. To determine the developmental‐genetic and neurotransmitter phenotype of these neurons, we analyzed transcription factor expression in Cre‐reporter mice after exposure to warm (36 C) or cool (4 C) ambient temperature. In both conditions, Fos‐activated neurons were found in a continuum of LPB subnuclei known to receive input from the spinal cord. Most Fos+ neurons also expressed FoxP2, a marker for glutamatergic LPB neurons derived from the rhombic lip. These FoxP2+ neurons were GFP+ in reporter mice for vglut2, but not vgat. Dynorphin neurons, visualized using pdyn‐cre reporter mice, formed a caudally skewed subset of these FoxP2+ neurons. After warm exposure, many dynorphin neurons became Fos+ in the dorsal lateral (PBdL) and central lateral subnuclei (PBcL). After cool exposure, non‐dynorphin Fos+ neurons were prominent rostrally, arcing around the external lateral PB. Most cool‐induced Fos was clustered densely here, in a far‐rostral subpopulation of FoxP2+ neurons we designated as the rostral external lateral subnucleus (PBreL). These findings shed new light on the genetic organization of LPB and suggest that pdyn‐cre mice may allow experimental access to warm thermosensory relay neurons in the caudal LPB in order to investigate their role in thermoregulation, sleep, and other homeostatic functions.