The Control of the Locust Spermatheca

The coordination of reproductive events in female locusts involves the interaction between sensory cells, reflex loops, and central pattern generators. Neurochemicals have also been identified as being important for initiating and/or modulating the activities of reproductive tissues. The present thesis investigates the association of neurochemicals with the spermatheca and the neural control of the spermatheca via a central pattern generator (CPG) that is coordinated with other reproductive events. Crustacean cardioactive peptide (CCAP)-like immunoreactivity is present in the innervation to the spermatheca of adult locusts. CCAP enhances basal tonus, spontaneous and neurally-evoked contractions and may function as a neuromodulator/neurotransmitter at the locust spermatheca. No locustatachykinin (LomTK)-like immunoreactivity is present in the innervation to the spermatheca, or on the spermatheca itself, whereas allatostatin-like immunoreactivity is present. LomTK1 is a stimulator of spermathecal contractions, but allatostatin 1 does not lead to any changes in spermathecal contractions. It is likely that LomTK acts as a neurohormone on the spermatheca, while the role of allatostatin remains unknown. Tyramine-like immunoreactivity is present in the nerves that project to the spermatheca and throughout all of its regions. Quantification of tyramine revealed that there is more tyramine than octopamine present in the spermatheca, and that tyramine can be released from the spermatheca by electrical stimulation of the ventral ovipositor nerve (VON). Physiological assays reveal that both tyramine and octopamine increase spermathecal contractions. Tyramine may be a co-transmitter with octopamine at the locust spermatheca. There is likely a central pattern generator (CPG) that controls the spermathecal muscle activity, that is regulated by descending inhibition. Extracellular nerve and electromyographic recordings demonstrate that this CPG appears to be localized within the VIIth and VIIIth abdominal ganglia and is found to integrate with the CPG that regulates oviposition digging in locusts.Ph