The imaginal ecdysis of the cricket ( Teleogryllus oceanicus )

1. The activities of individual motor neurons have been recorded by electromyography from the muscles of unrestrained, successfully ecdysing crickets. 2. As the behavior progresses, each muscle becomes involved in stereotyped patterns of contractions corresponding to a sequence ofmotor programs (Carlson, 1977). For example, muscle 71d participates in 3 programs: (1) Pushups (A1, Fig. 3), (2) Proximal Leg-segment Extrication (B7, Fig. 3), and (3) Distal Leg-segment Extrication (B11, Fig. 3). These motor programs are recruited in tandem, and involve 3 different modes of coordination (Figs. 5A, 7C, 8-bout 55). 3. In this study, 3 motor programs were selected for intensive analysis: (1) Pushups — bilaterally symmetric contractions of front leg muscles; (2) Abdominal Peristalsis (B1, Fig. 3) — longitudinally sequential contractions of abdominal intersegmental muscles; and (3) Proximal Legsegment Extrication — bilaterally alternating contractions of the leg muscles. 4. The entire 4 h period of ecdysis can be recorded bilaterally from right and left muscles 71d, and the motor output underlying all 3 motor programs in which they participate is interrupted by regular interbout intervals (Figs. 4A, 7A, 8, 9). 5. Abdominal peristaltic waves (Fig. 6A, E) occur between bouts of rhythmical contractions by thoracic motor programs (Fig. 9C2), and thus occur at the bout frequency of other programs. 6. During Leg Extrication, the strengths of successive contractions by muscles 71d vary in register with each bout cycle. The strongest contractions occur near the centers of bouts, and are produced by longer bursts of higher frequency impulses (Fig. 7C). Additional motor neurons may be recruited during strong contractions, subject to the “size principle” (see Henneman, 1965). 7. While motor neuron activation varies sinusoidally within each bout cycle, the period of successive burst changes only vary gradually (Fig. 7B, C, 8). This fact implies that the bout generating oscillator does not influence the contraction generating oscillator as it modulates motor neuron activity. The motor neurons must therefore be independent of the oscillator which drives the alternating contractions that extricate the legs. 8. An hypothesis is presented in which “non-spiking interneurons”, are the major components of central oscillators underlying rhythmical contractions, and a series of these, located in each of the segmental ganglia, generate bouts of activity. 9. During a major peak in the intensity of the behavior, which occurs during the Ecdysial Phase, concurrent peaks in bout, burst, and intraburst impulse frequencies of the neurons involved in Proximal Leg-segment Extrication occur (Fig. 10). As interbout intervals shrink, and the burst frequency increases, additional bursts are recruited during each bout, and a second motor neuron is recruited (Fig. 8). 10. Since sensory feedback from areas of newly exposed cuticle are known to accelerate the bout oscillator (Carlson, 1977), it is hypothesized that acceleration of the burst frequency and concurrent increases in average firing rates for motor neurons, which accompany the major intensity peak of the Ecdysial Phase result from sensory feedback. 11. Sensory feedback provides immediate control of the strength of contractions by individual muscles during Pushups (Figs. 5C, 9B1, 9C1), and prolongs motor programs (compare Fig. 9A2 with 9B2, 9C2), without disrupting coordination. 12. It is concluded that a multilayered system of central control which includes more than 48 motor programs, a temporal bout structure, and 4 functionally distinct behavioral phases, cooperates with sensory feedback mechanisms to permit the successful completion of the nearly 4 h of stereotyped behavior which results in the ecdysis of the cricket.