Two second messengers mediate amino acid responses in olfactory sensory neurons of the salamander, Necturus maculosus.

Odor transduction mediated by the adenylyl cyclase/cAMP pathway has been well studied, but it is still uncertain whether this pathway mediates the transduction of all odors in vertebrates. We isolated olfactory sensory neurons from the salamander Necturus maculosus and used calcium imaging with the indicator dye fura-2 to examine olfactory responses elicited by amino acids. The properties of approximately two-thirds of the odor responses suggested they were mediated by the adenylyl cyclase/cAMP pathway, but one-third of the responses were not mimicked by cAMP analogs nor blocked by inhibition of adenylyl cyclase, suggesting that these odor responses were mediated differently. Responses that were unaffected by inhibition of adenylyl cyclase were blocked by neomycin, an inhibitor of phospholipase C, implying that they were transduced by activation of phospholipase C. Some cells which responded to more than one amino acid appeared to employ both pathways, but each was used to transduce different odors. In addition, many responses that were mediated by the adenylyl cyclase/cAMP pathway were enhanced following inhibition of phospholipase C, suggesting that the phospholipase C pathway has a role not only in odor transduction, but also in the modulation of olfactory responses.