Walking and flying in locusts are exemplary rhythmical behaviors generated by
central pattern generators (CPG) that are tuned in intact animals by phasic
sensory inputs. Although these two behaviors are mutually exclusive and
controlled by independent CPGs, leg movements during flight can be coupled to
the flight rhythm. To investigate potential central coupling between the
underlying CPGs, we used the muscarinic agonist pilocarpine and the amines
octopamine and tyramine to initiate fictive flight and walking in deafferented
locust preparations. Our data illustrate that fictive walking is readily
evoked by comparatively lower concentrations of pilocarpine, whereas higher
concentrations are required to elicit fictive flight. Interestingly, fictive
flight did not suppress fictive walking so that the two patterns were produced
simultaneously. Frequently, leg motor units were temporally coupled to the
flight rhythm, so that each spike in a step cycle volley occurred
synchronously with wing motor units firing at flight rhythm frequency.
Similarly, tyramine also induced fictive walking and flight, but mostly
without any coupling between the two rhythms. Octopamine in contrast readily
evoked fictive flight but generally failed to elicit fictive walking. Despite
this, numerous leg motor units were recruited, whereby each was temporarily
coupled to the flight rhythm. Our results support the notion that the CPGs for
walking and flight are largely independent, but that coupling can be entrained
by aminergic modulation. We speculate that octopamine biases the whole motor
machinery of a locust to flight whereas tyramine primarily promotes walking
