Grueneberg Glomeruli in the Olfactory Bulb are Activated by Odorants and Cool Temperature

Neurons of the Grueneberg ganglion respond to cool temperatures as well as to distinct odorants and extend axonal processes to the olfactory bulb of the brain. Analyses of transgenic mice, in which Grueneberg ganglion neurons and their axons are labeled, revealed that these axons innervated nine distinct glomeruli distributed in a characteristic topographical pattern in dorsal, lateral, ventral, and medial regions of rather posterior areas in the bulb. To assess activation of these glomeruli (hereinafter designated as Grueneberg glomeruli) upon stimulation of Grueneberg ganglion neurons, mice were exposed to the odorant 2,3-dimethylpyrazine (2,3-DMP) and the expression of the activity-dependent marker c-Fos in juxtaglomerular cells of the relevant glomeruli was monitored. It was found that all of these glomeruli were activated, irrespective of their localization in the bulb. To verify that the activation of juxtaglomerular cells in Grueneberg glomeruli was indeed based on stimulation of Grueneberg ganglion neurons, the 2,3-DMP-induced responses in these glomeruli were investigated in mice lacking the cyclic nucleotide-gated channel CNGA3 which is critical for chemo- and thermosensory signal transduction in Grueneberg ganglion neurons. This approach revealed that elimination of CNGA3 led to a reduction of the odorant-induced activity in Grueneberg glomeruli, indicating that the activation of these glomeruli is based on a preceding stimulation of the Grueneberg ganglion. Analyzing whether Grueneberg glomeruli in the bulb might also process thermosensory information, it was found that upon exposure to coolness, Grueneberg glomeruli were activated. Investigating mice lacking CNGA3, the activation of these glomeruli by cool temperatures was attenuated.