Electrophysiology of the olfactory nerve of the pike, Esox lucius: A pilotstudy on optimal experimental conditions

Electrophysiological recordings in the olfactory nerve of the European pike Esox lucius were done as early as at the beginning of the 20th century, bu t since then, the nerve has not been extensively studied. It contains 4 to 6 millions unmyelinated sensory axons, with a relatively homogenous populat ion of sizes, more than 95% have diameters of about 0.2 mum. The aim of our work concerned the keeping conditions under which reproducible electrophys iological responses can be obtained, and some of the electrophysiological p roperties of these unmyelinated sensory axons. Particular attention has bee n given to the dissection of the pike olfactory nerve. We have adapted the technique described by von Muralt et al. (1976) to obtain the nerves more q uickly and to prolong their survival. For the latter aim, we have found tha t a medium, used to keep excised Xenopus oocytes for many days, kept 69% of the nerves functional for up to 3 days. The diphasic compound action poten tial (CAP) of the pike olfactory nerve propagated at a velocity of 12+/-0.5 cm/s (n = 37) and was suppressed by tetrodotoxin (10 muM), known to block voltage-activated sodium channels. Nerve CAP kinetics were noticeably modif ied when tested after about 3 h in the medium at room temperature. However, the nerves produced consistent CAP during 30-60 min in the recording chamb er in air. White preliminary, our results indicate that the olfactory nerve of the European pike, Esox lucius, by its survivability may be a suitable model for electrophysiological and pharmacological studies of unmyelinated sensory axons.