The role of sensory input in maintaining output from the locust oviposition digging central pattern generator

Summary A quantitative EMG analysis is presented of the effects of deafferentation on the motor program for oviposition digging in the locust Locusta migratoria. We examined the activity of two groups of antagonistic muscles, the opener and closer muscles of the ventral ovipositor valves, in terms of the cycle frequency, burst duration, and relative burst onset times. There were no significant differences between the pattern frequency produced in intact, semi-intact, or deafferented animals within 10 min of the onset of the pattern. Over time, however, the pattern in deafferented animals showed a significant decrease in frequency, which it did not do in intact or semi-intact animals. Seven out of 10 deafferented preparations ceased producing the digging rhythm within 35 min of onset, but none of the semi-intact preparations did so. Mechanosensory hairs cover the ovipositor valves, and are in a position to supply sensory input to the digging pattern generator during the natural behaviour. When nerves carrying sensory axons from these hairs were electrically-stimulated tonically, the motor pattern was restored in deafferented animals. The effects of the stimulation outlasted the stimulation itself for several minutes, and could be repeated several times. We suggest that tonic input is necessary for the maintenance of the digging rhythm, possibly by maintaining levels of some modulatory substance(s) within the CNS.Abbreviations CPG central pattern generator - DUM dorsal unpaired median neuron - EMG electromyogram - LC left ovipositor ventral closer muscle - LCDUR duration of activity of LC - LCFREQ frequency of activity bursts in LC - LCONSET onset of activity in LC relative to LO - LO left ovipositor ventral opener muscle - LODUR duration of activity of LO - LOFREQ frequency of activity bursts of LO - RO right ovipositor ventral opener muscle - RODUR duration of activity in RO - ROFREQ frequency of activityb bursts of RO