Olfactory transduction mechanisms in sheep

Inositol 1,4,5-trisphosphate and adenophostin analogues induce responses in turtle olfactory sensory neurons

Using the whole-cell mode of the patch-clamp technique, we recorded inward currents in response to inositol-1,4,5-trisphosphate (IP3) and adenophostin analogues in turtle olfactory sensory neurons. Dialysis of IP3 into the neurons induced inward currents with an increase in membrane conductance in a dose-dependent manner under the voltage-clamp conditions (holding potential -70 mV). The application of Ca2+-free Ringer solution to neurons previously dialysed with IP3 induced inward currents that were reversibly inhibited by application of Na+, Ca2+-free Ringer solution, normal Ringer solution or 10 microM ruthenium red. Dialysis of the adenophostin analogues, novel IP3 receptor ligands, also induced inward currents with an increase in membrane conductance. The magnitude of the responses to the adenophostin analogues varied among these derivatives. The application of Ca2+-free Ringer solution to neurons previously dialysed with the adenophostin analogues induced inward currents that were inhibited by the application of normal Ringer solution. The reversal potential of inward currents induced by an adenophostin analogue was similar to that induced by IP3, suggesting that inward currents induced by the adenophostin analogue were generated by a similar ionic mechanism to that induced by IP3. The present study demonstrated that IP3-mediated transduction pathways exist in turtle olfactory receptor neurons and that adenophostin analogues act as agonists of IP3.

Existence of multiple receptors in single neurons: responses of single bullfrog olfactory neurons to many cAMP-dependent and independent odorants

The responses of single bullfrog olfactory neurons to various odorants were measured with the whole-cell patch clamp which offers direct information on cellular events and with the ciliary recording technique to obtain stable quantitative data from many neurons. A large portion of single olfactory neurons (about 64% and 79% in the whole-cell recording and in the ciliary recording, respectively) responded to many odorants with quite diverse molecular structures, including both odorants previously indicated to be cAMP-dependent (increasing) and independent odorants. One odorant elicited a response in many cells; e.g. hedione and citralva elicited the response in 100% and 92% of total neurons examined with the ciliary recording technique. To confirm that a single neuron carries different receptors or transduction pathways, the cross-adaptation technique was applied to single neurons. Application of hedione to a single neuron after desensitization of the current in response to lyral or citralva induced an inward current with a similar magnitude to that applied alone. It was suggested that most single olfactory neurons carry multiple receptors and at least dual transduction pathways.