Redundancy of olfactory sensory pathways for odor-aversion memory in the terrestrial slug Limax valentianus

Abstract

Terrestrial slugs Limax valentianus (Férussac 1822) (12-16 weeks post hatching) have been maintained in our laboratory at 19°C for at least nine generations as a closed colony. They have been fed only on a diet of humidified powder mixture consisting of 521·g rat chow (Oriental Yeast, Tokyo, Japan), 500·g wheat starch (Wako Pure Chemicals, Osaka, Japan) and 21·g vitamins (Oriental Yeast). Accepted 1 April 2008 SUMMARY Terrestrial slugs have the ability to learn and remember a food odor paired with an aversive stimulus. Olfaction in slugs involves the tips of two pairs of tentacles, the superior and the inferior tentacles. Sensory nerves in both pairs of the tentacles transmit olfactory information to the structure in the CNS, the procerebrum where learning and memory formation occur. We investigated the role of each pair of tentacles in odor-aversion learning, and examined the ability of slugs to recall memory after selective surgical amputation. Our results show that memory formation was not altered by the amputation of either one of the pairs before or after odor-aversion learning, while the odor sensibility of the slugs was maintained. These data suggest that either pair of tentacles is sufficient for the acquisition and retrieval of aversive olfactory memory.

Olfactory Memory Storage and/or Retrieval Requires the Presence of the Exact Tentacle Used During Memory Acquisition in the Terrestrial SlugLimax

“…We previously showed that the memory acquired with two pairs of tentacles can even be retrieved using either one of the superior or inferior tentacles, and that the memory can be acquired and retrieved using either one of the superior or inferior tentacles (Yamagishi et al, 2008). These findings do not contradict our present results, because the same pairs of superior or inferior tentacles were functional both during the acquisition and retrieval of the memory in that study (Yamagishi et al, 2008).…”

“…These findings do not contradict our present results, because the same pairs of superior or inferior tentacles were functional both during the acquisition and retrieval of the memory in that study (Yamagishi et al, 2008). Friedrich and Teyke (1998), using an anesthetic agent, reported that the terrestrial snail Helix is unable to retrieve an appetitive olfactory memory if a different side (right or left) of the superior and inferior tentacles is allowed to function during memory acquisition and retrieval.…”

“…The slugs were conditioned and tested in an experimental setup that does not use a shading box, as described previously (Yamagishi et al, 2008) with slight modification. Briefly, the slugs were first divided into two separate groups; one is conditioned (conditioned group) and the other is not (control group).…”

Effects of tentacle amputation and regeneration on the morphology and activity of the olfactory center of the terrestrial slug Limax valentianus

“…In one group, the slugs were conditioned with carrot juice six days after amputation of the inferior tentacle. It has been demonstrated previously that the amputated tentacles do not regenerate in a recovery period as short as six days (Yamagishi et al, 2008). However, the superior tentacles, amputated 34 days before, showed regeneration to some extent at this time (R.M., unpublished observations).…”

“…The tentacle amputation of the slugs (12-13 weeks post hatching) was performed under anesthesia, as described previously (Yamagishi et al, 2008;Matsuo et al, 2010b -1 Hepes, pH 7.0) was injected into the body cavity to improve the recovery from anesthetization. After surgery, two to five (usually three) slugs were transferred to a plastic container and maintained with free access to the humidified powder mixture until the next procedure -that is, in vitro LFP recording or histological analysis.…”