Effects of localized low-temperature pulses on the cockroach circadian pacemaker

The hypothesis that the circadian pacemaker that controls the activity rhythm in the cockroach, Leucophaea maderae, is composed of mutually coupled optic lobe oscillators was investigated using localized low-temperature pulses. Following section of one optic tract cooling the intact optic lobe for 6 h (7.5 degrees C) beginning at activity onset consistently caused a phase delay of several hours. Cooling the neurally isolated lobe had little or no effect. The results suggested the low-temperature phase delays the rhythm via a phase shift in an oscillator in the optic lobe. To determine if optic lobe oscillators were coupled, low-temperature pulses were given to one optic lobe of intact animals. If the treated lobe was isolated by optic tract section 4 days after the pulse, the rhythm (driven by the untreated lobe) was delayed; but if the tract was cut 0.5 h after the pulse the phase shift was prevented. The interaction between the optic lobes in intact animals was also found to reduce the delay caused by a low-temperature pulse. These results suggest the cockroach circadian pacemaker is composed of two mutually coupled optic lobe oscillators.