Genetic identity of thermosensory relay neurons in the lateral parabrachial nucleus

Abstract

The parabrachial nucleus is important for thermoregulation because it relays skin temperature information from the spinal cord to the hypothalamus. Prior work in rats localized thermosensory relay neurons to its lateral subdivision (LPB), but the genetic and neurochemical identity of these neurons remains unknown. To determine the identity of LPB thermosensory neurons, we exposed mice to a warm (36°C) or cool (4°C) ambient temperature. Each condition activated neurons in distinct LPB subregions that receive input from the spinal cord. Most c-Fos+ neurons in these LPB subregions expressed the transcription factor marker FoxP2. Consistent with prior evidence that LPB thermosensory relay neurons are glutamatergic, all FoxP2+ neurons in these subregions colocalized with green fluorescent protein (GFP) in reporter mice for Vglut2, but not for Vgat. Prodynorphin (Pdyn)-expressing neurons were identified using a GFP reporter mouse and formed a caudal subset of LPB FoxP2+ neurons, primarily in the dorsal lateral subnucleus (PBdL). Warm exposure activated many FoxP2+ neurons within PBdL. Half of the c-Fos+ neurons in PBdL were Pdyn+, and most of these project into the preoptic area. Cool exposure activated a separate FoxP2+ cluster of neurons in the far-rostral LPB, which we named the rostral-to-external lateral subnucleus (PBreL). These findings improve our understanding of LPB organization and reveal that Pdyn-IRES-Cre mice provide genetic access to warm-activated, FoxP2+ glutamatergic neurons in PBdL, many of which project to the hypothalamus.

Barrington's nucleus: Neuroanatomic landscape of the mouse “pontine micturition center”

“…Likewise, the goat‐ and rabbit‐anti‐CTb antisera did not produce any labeling above background fluorescence in brain sections from mice without CTb injections, or in regions without established connectivity to the injection site in a given case. The sheep and goat FoxP2 antisera produced the same pattern of labeling we have analyzed and published in the mesopontine tegmentum of rats and mice (Geerling et al, ; Gray, ). Our goat anti‐ChAT and our rabbit, sheep, and mouse anti‐TH antisera all labeled well‐established distributions of cholinergic or catecholaminergic neurons and axons, the one exception being that the mouse anti‐TH antibody densely labeled pial tissue antigens along the periphery of all brain sections, but this did not interfere with identification of TH‐immunoreactive neurons in the subcoeruleus and LC, near Bar.…”

“…Our protocols for double‐ and triple‐immunofluorescence labeling were similar to those described in greater detail in (Geerling et al, ). In brief, we rinsed sections twice in PBS, then placed them in netwells in a primary solution containing PBS with Triton 0.3% X‐100 (PBT) along 2% normal horse serum (NHS) and one to three of the primary antisera listed in Table , which we selected to avoid any same‐species cross‐reactivity and to avoid goat/sheep cross‐reactivity.…”

Warm-Sensitive Neurons that Control Body Temperature

“…Consistent with this possibility, we found that cold and warm-challenge induced pS6 in distinct populations of preoptic neurons (Figure S1D,E). This anatomic segregation is reminiscent of the distinct populations of warm- and cold-activated neurons that have been described in the parabrachial nucleus, a brainstem relay for ascending thermal information that projects to the POA (Geerling et al, 2016; Nakamura and Morrison, 2008, 2010). One implication of these findings is that there should exist an as-yet-unidentified population of cold-sensitive neurons in the POA that receives thermal signals originating from cold-activated sensory fibers.…”

“…The POA also receives abundant input from ascending neural pathways that convey thermal signals from the skin and viscera (Geerling et al, 2016; Nakamura and Morrison, 2007, 2008, 2010). In our experiments, VMPO BDNF/PACAP neurons were activated by environmental warmth within seconds (Figure 2I), which almost certainly reflects activation of cutaneous thermoreceptors rather than much slower changes in intracranial temperature.…”

Kölliker–Fuse GABAergic and glutamatergic neurons project to distinct targets

“…First, inefficiencies in the expression of Cre or recombination with various reporters (Schmidt-Supprian & Rajewsky, 2007; Liu et al, 2013) can increase variability and reduce sensitivity. We mitigated these problems by using IRES-Cre knockin mice and an L10-GFP strain with robust and well-documented Cre-reporting (Vong et al, 2011; Krashes et al, 2014; Geerling et al, 2016). In these mice, GFP labeling was consistent and robust, and conformed to established locations of glutamatergic and GABAergic neurons.…”