Alteration of the Respiratory System at the Onset of Locust Flight: I. Abdominal Pumping

Abstract

The respiratory behaviour of Locusta migratoria is altered at the onset of flight. The neuronal processes and some of the mechanisms underlying these alterations were studied by using intracellular recording and staining techniques. It has previously been reported that abdominal pumping ceases for the first seconds of flight. Our data indicate that this phenomenon is not due to inhibition of the respiratory system, since most interneurones and some motoneurones maintain a respiratory rhythm during the onset of flight activity. Likely explanations for the cessation of the abdominal pumping are: (1) increased stiffness of the abdomen due to maintained activation of abdominal muscles and (2) decreased rhythmic modulation in abdominal motor units due to tonic excitatory input. Two major changes occur in the respiratory system at the onset of flight: (1) the rhythm is reset by an activation of inspiratory and inactivation of expiratory neurones, and (2) the respiratory rate is increased. The increase in the respiratory rate at the onset of flight is in part due to an activation of inspiratory interneurones which are capable of accelerating the respiratory rhythm. The changes in the respiratory system coinciding with the initiation of flight suggest a feedforward mechanism linking both behaviours. Tonic interneurones, involved in the initiation of flight and influencing respiration, might be involved in linking respiration and flight. At flight onset, one group of these simultaneously disinhibited respiration and flight and thus contributed both to an increase in the respiratory rate and to an activation of the flight system. Another group evoked flight and had variable effects on respiration. One tonic interneurone had a depressing effect on the respiratory rate. We conclude that respiration is centrally linked to flight in part by the same interneurones controlling the initiation of flight. The existence of such a feedforward mechanism in the locust resembles the situation found in vertebrates, where locomotory and respiratory behaviour can be driven from the same brainstem region.