Worm Breeder's Gazette 17(1): 44 (October 1, 2001)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Common imprinting for temperature and odor memories

J.J. Remy^1,2

The AFD neurone and its postsynaptic interneurons AIY and AIZ have been identified as responsible for thermotaxis in C. elegans. It has been shown by the group of Ikue Mori that nematodes are able to learn and memorise temperature (A. Mohri et al., JWM 2000), as they display preference for and move along isotherms corresponding to their breeding temperature. This experience-dependent behavior called isothermal tracking (IT) suggest that sensory inputs present in the environment during early development can influence adult sensory properties. Genetic analysis involved several molecules in this learning process, including recently the neurone specific calcium-sensor 1 (NCS-1) expressed in the AIY interneurone (Gomez et al., Neuron 2001 Apr; 30(1): 241-8). We already suggested that olfactory imprinting (or odor memory) could exist in nematodes (Remy J.J., EWM 2000). More experiments confirmed now that adults worms can be sensitized to odorant molecules that are present during a short period of their early development. For N2 as well as for a number of other of C. elegans strains, we were able to define a critical period during which worms can learn and memorize short odor inputs. Chemotactic assays performed on adults showed that early exposure to an attractive molecule such as beta-citronellol or benzaldehyde, does sensitize worms to these attractants, but sensitization is restricted to the breeding concentration. Moreover, as for temperature memory, this behaviour is dependent on the presence of food and starved worms showed no odor learning ability. Thus olfactory imprinting and temperature memory seem to share at least three common features : short inputs during early development are efficient, memory of the "intensity" of sensory stimulation (heat level or odor concentration), and food-dependence. It is known that the thermosensory AFD and the chemosensory neurones responsible for attraction to volatil attractants, AWA and AWC, cosynapse the same interneurone AIY, suggesting the possibility of common integration of the two sensations. If this is true, then all mutations affecting temperature memory would also affect olfactive memory. We found for instance that the two alleles ot-22 and ks-5 of the thermotaxis mutant ttx-3, a LIM homeobox exclusively expressed in AIY (Hobert O et al., Neuron 1997, 19:345-357), although not affected in their chemotaxis behaviour, are affected in olfactory learning. These observations reinforce and provide new experimental support to the idea of cointegration of thermo and chemosensory inputs in C. elegans (Pierce-Shimomura, IWM 2001).