“Interactions between two rhythmic circuits with distinct periods are maintained over a range of temperatures”
Behaviors need to be maintained over a variety of termperatures, whether you are referring to humans or fruit flies. But how the nervous system maintains control under varying temperatures is unclear. Mr. Powell described his work with the crab, Cancer borealis, and changes in neuronal firing rhythms he finds with changes to temperature.
Nearly all biological processes are affected by temperature. It is therefore remarkable that poikilotherms and their nervous systems can maintain activity across a wide range of temperatures. In the crab C. borealis, there are two central pattern generators (CPGs), the fast pyloric (filtering, ~1Hz cycle frequency) and slower gastric mill (chewing, ~0.1 Hz cycle frequency) sub-circuits within the stomatogastric nervous system. These two CPGs are coupled, and it was unknown if two coupled CPGs would maintain coupling across a range of temperatures.
In these experiments, GMRs were evoked between 7 and 21°C, however spontaneous rhythms were observed at temperatures as high as 31°C. Both spontaneous and evoked GMR frequencies increased with temperature, a phenomenon previously documented in the pyloric rhythm. Across this temperature range both the pyloric and gastric mill rhythm have similar apparent Q10s. Certain versions of GMRs are known to have an integer number of pyloric cycles per gastric mill cycle, termed integer coupling (Nadim et al. 1998; Bartos et al. 1999). We found that both spontaneous and evoked GMRs maintain integer coupling at baseline temperatures (11°C). Interestingly, with evoked gastric mill rhythms, integer coupling did not significantly vary with temperature (p = 0.88, N = 10), although the phase coherence between PD and LG neurons decreased with increasing temperature above 17°C (rho = -0.98, p < 1e-4, N = 10, Spearman rank correlation test). Evoked rhythms generated at higher temperatures were generally shorter in duration than those evoked at lower temperature within the same preparation (9/10 preps).