Supporting cells of the main olfactory epithelium of larval Xenopus laevis are sensitive to extracellular application of ATP. Nucleotides activate supporting cells. A detailed investigation of these nucleotide-induced responses showed that extracellular nucleotides activate supporting cells via P2Y2/P2Y4-like receptors and initiate a characteristic intraepithelial Ca2+ wave propagating from the apical to the basal part of the olfactory epithelium (see Hassenklöver et al., 2008). Currently, we are exploring possible physiological roles of this intraepithelial signaling.
We recently discovered that nucleotides also evoke Ca2+-signals in basal stem/progenitor cells of the olfactory epithelium (see Hassenklöver et al., 2009). Nucleotides regulate olfactory stem cell proliferation. These Ca2+-signals are mediated by P2Y receptors with a different agonist profile than supporting cells. Blocking purinergic receptors, significantly reduced the number of proliferating cells in the basal cell layer. This implicates that nucleotides modulate the proliferating activity of basal stem/progenitor cell. Possible connections between the purinergic signaling pathways in supporting and basal cells are currently under investigation.
Also supporting and basal cells (but not vomeronasal receptor neurons) of the neuroepithelium of the vomeronasal organ express functional purinergic receptors The vomeronasal organ expresses functional purinergic receptors. (see Dittrich et al., 2013). Thus, the purinergic system of the Xenopus vomeronasal epithelium appears to be very similar to the purinergic system of the MOE, suggesting that purinergic receptors might have similar functional effects in both olfactory subsystems.
The anterior telencephalon consists of the olfactory bulb, the first relay station for olfactory information, and the periventricular zone of the lateral ventricles. The periventricular zone gives rise to new neurons, which integrate into the olfactory bulb circuitry throughout the lifetime of an organism. Cells of the anterior telencephalon are also sensitive to nucleotides. Cells of the olfactory bulb and the periventricular zone of larval Xenopus laevis are both sensitive to extracellular nucleotides. Both regions show differences in the expression of purinergic receptor subtypes. A pharmacological investigation led to the conclusion that olfactory bulb cells express almost exclusively ionotropic P2X receptors, whereas PVZ cells express predominantly P2X, but also metabotropic P1 and P2Y receptors (Hassenklöver et al., 2010). We are currently investigating the physiological function of the telencephalic purinergic system.