Grueneberg ganglion neurons respond to cool ambient temperatures

The Grueneberg ganglion (GG) - a neuronal cell cluster of unknown function localized to the vestibule of the anterior nasal cavity - is considered as a chemosensory compartment based on the expression of olfactory receptors and the olfactory marker protein. Axonal projection of GG neurons to so-called 'necklace glomeruli' in the olfactory bulb of the brain, which are thought to be important for suckling behaviour in rodent pups, has led to the hypothesis that the GG might be involved in mother/child interactions. To survey potential activation of GG neurons in living animals during the course of mother/child interactions, expression of the activity-dependent gene c-Fos in the GG of neonatal mouse pups was monitored in the presence and absence of the dam. It was found that GG neurons were only activated in the absence of the mother. Moreover, GG activation was independent from olfactory cues as revealed by naris occlusion. Searching for stimuli eliciting GG activity in pups separated from the dam, cool ambient temperatures were found to induce strong c-Fos expression in GG neurons whereas warmer temperatures did not. These coolness-induced responses were only observed in a distinct subset of GG neurons characterized by the expression of the olfactory receptor V2r83. Finally, GG responsiveness to coolness was remarkably reduced in older stages. In summary, these findings suggest that the GG of neonatal mice is activated by cool ambient temperatures to which they are exposed in the absence of their dam, indicating that the GG might function as a thermosensor.