Spatial Conditioning in the Flesh Fly, Sarcophaga crassipal pis: Disruption of Learning by Cold Shock and Protection by Rapid Cold Hardening

We have developed a new paradigm for examining classical conditioning in the flesh fly, Sarcophaga crassipalpis, and specifically apply it as a sensitive measurement for sublethal effects of cold shock. When water was applied as a conditioned stimulus to the right tarsus and reinforced with a brief opportunity to feed on a sucrose-water solution, flies quickly learn to discriminate stimulation of the right from the left tarsus. Further analyses revealed that the discrimination has a strong spatial component. Flies also retain this spatial discrimination over four days as indicated by the fact that the number of correct responses increases with continued training over that time. Cold shock (-10°C for 3 min) applied 30 and 60 min after first training interfered with learning. But, cold shock applied 120 min before or 90 min after conditioning did not significantly affect learning. The spatial memory we have identified therefore has a sensitive period during which it can be disrupted with cold shock. Furthermore, we demonstrate that the disruptive effect of cold shock on learning formation can be prevented by rapid cold hardening, a brief pre-exposure to a less severe low temperature.