Early Phase and Technological Setup
In the initial project phase (from September 2018), we recruited personnel, purchased key equipment, and built the necessary experimental infrastructure. Notably, we established an advanced optogenetics-capable electrophysiology setup for ex vivo and in vivo recordings and trained the team in thermoregulatory physiology, tracing, and behavioral assays.
Aim 1: Molecular Sensors of Brain Temperature
We focused on the TRPM2 ion channel, previously implicated in thermoregulation (Song et al., Science 2016). Our ERC-funded work demonstrated that TRPM2 functions as a synaptic temperature sensor within deep brain circuits. This is a novel finding, shifting the paradigm from whole-cell thermosensitivity to temperature-dependent synaptic plasticity. The manuscript is currently under consideration at Neuron.
In parallel, we initiated a project to identify thermoregulation-related neuropeptides. A graduate student implemented a microdialysis system in freely moving mice, enabling the collection of hypothalamic interstitial fluid and CSF. Using ELISA and targeted mass spectrometry (in collaboration with the Haefeli group), we identified several candidate peptides with heat-responsive release profiles. These are currently undergoing validation.
Aim 2: Thermoregulatory Circuit Mapping
To dissect output pathways of hypothalamic thermoregulatory neurons, we focused on a POA cell population we now term Acclimation-Activated Neurons (AANs). Using histological tracing and optogenetics, we mapped their projections to distinct downstream areas, including the paraventricular hypothalamic nucleus (PVH)—a region not previously linked to thermoregulation. In vivo stimulation of defined AAN outputs selectively activated peripheral thermal effectors, including brown adipose tissue (BAT) and tail vasculature. These data demonstrate functional pathway selectivity, a feature that had been hypothesized but not previously demonstrated.
Aim 3: Mechanisms of Heat Acclimation
We hypothesized that the same POA circuits involved in acute thermoregulation might also orchestrate long-term adaptation. Using in vivo imaging and genetic perturbation, we found that AANs exhibit increased activity after repeated heat exposure, whereas neighboring non-AAN neurons do not—indicating cell-type-specific plasticity. Inhibition of AANs blocked the development of heat acclimation. Conversely, optogenetic or chemogenetic activation of AANs was sufficient to induce heat tolerance without prior heat exposure. These findings reveal, for the first time, a central neuronal mechanism underlying heat acclimation. A manuscript is currently in preparation.
