Embryonic nmjs show no spontaneous synaptic currents. Glutamate applied directly to the postsynaptic muscle has no effect. Homozygous KaiRIA¹ embryos, homozygous KaiRIA² embryos and transheterozygous KaiRIA¹/KaiRIA² embryos have normal gross, epidermal and neuromuscular anatomy but fail to hatch and appear paralysed both within the eggshell and when artificially removed from the eggshell. No peristaltic somatic muscle movements occur. Presynaptic morphology is normal; nerves form normal branches to appropriate muscles. Amplitude of sustained rhythmic currents (SRCs) in CNS motor neurons is unchanged compared to wild type, however the frequency is reduced more than three fold. Incidence of motor neurons showing SRC activity is reduced from more than 90% to around 40%.