ABSTRACT
Excitatory postsynaptic potentials (e.p.s.p.s), membrane resting potentials, and intensity of birefringence were measured from the two principal planta retractor muscles (PPRMs) of the first pair of prolegs during metamorphosis of Galleria mellonella. This was done to determine whether cessation of efferent nerve impulses to these single fibres signals their degeneration.
E.p.s.p.s were elicited reflexively by brushing the insect’s last abdominal segment. Though they become attenuated, e.p.s.p.s can be recorded until 11-12 hr. after pupal ecdysis. By this time the membrane resting potential has dropped from c. 55 mV. to less than 18 mV., and the intensity of birefringence has become minimal.
Continuous electromyographic records taken during the initial 18 hr. after pupal ecdysis suggest that the PPRMs are being excited regularly as they degenerate.
No ‘sparing effect’ on the degeneration of the PPRMs could be detected when programmed, current-limited stimuli were administered to pupae via chronically implanted electrodes.
Removing all acknowledged endocrines by transecting newly emerged pupae has negligible effect on the decrease of the PPRM birefringence, but greatly retards the degradation of the membrane resting potential and e.p.s.p.s. This retardation can be alleviated by injecting the steriod hormone 20-hydroxyecdysone.
