Forskolin enhanced off-response in the turtle olfactory system.

Olfactory responses appear not only at the onset of odor stimulation, but also at the termination of the stimulation. It is widely considered that the cAMP-pathway is involved in the generation of odor responses. We examined how cAMP affects the generation of off-responses. To explore the role of the cAMP-pathway, odorants were applied to the turtle olfactory epithelium after forskolin at high concentrations which saturated the olfactory response to forskolin. Various odorants induced off-responses after 50 microM forskolin, indicating that off-responses are not induced via the cAMP-dependent pathway. However, the magnitude of the off-response after forskolin varied from 100 to 1400% of those of off-responses in its absence, indicating that forskolin greatly enhanced the off-responses to some odorants. The off-response after 0.1 mM citralva was also enhanced by 3 mM 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (cpt-cAMP). These results suggested that cAMP modulates off-responses in the turtle olfactory system.