THE MOTOR INNERVATION OF THE OVIDUCTS AND CENTRAL GENERATION OF THE OVIDUCTAL CONTRACTIONS IN 2 ORTHOPTERAN SPECIES (CALLIPTAMUS SP AND DECTICUS-ALBIFRONS)

The oviducts of the female Decticus albifrons (Orthoptera: Tettigonida e) are innervated by six bilaterally paired neurones, while those of t he female Calliptamus sp, (Orthoptera: Catantopidae) are innervated by three bilaterally paired neurones, located in the seventh abdominal g anglion. Using intracellular recording and staining, five of the six o viductal neurones of D. albifrons and the three oviductal neurones of Calliptamus sp. were physiologically and morphologically identified. A ll three oviductal neurones of Calliptamus sp. have a motor function, In D. albifrons, however, there is evidence for motor function in only three of the five identified oviductal neurones that appear to partic ipate in the generation of the oviductal contractions. The remaining t wo identified neurones of D. albifrons have a branching pattern simila r to that of motor neurones, but their physiological characteristics, large overshooting soma action potentials (30-40 mV) with a long after hyperpolarising phase, are similar to those of the oviductal unpaired median neurones, which are known to modulate the oviductal contraction s. The oviductal muscle exhibits two different modes of contractions: (a) fast and slow myogenic contractions, the fast contractions being p roduced by spontaneous potentials (30-40 mV) generated by some oviduct al muscle fibres; and (b) neurogenic contractions caused by the rhythm ic spiking of the oviductal motor neurones. This motor pattern is prod uced by the oviductal central pattern generator, a neural network resi ding in the last two abdominal ganglia (seventh and terminal abdominal ganglia) of the species examined here. When isolated both anteriorly and posteriorly, the seventh abdominal ganglion generates rhythmic ovi ductal contractions of lower frequency and amplitude than those record ed when the connectives between the genital ganglia are intact. The ov iductal pattern generator is activated through release from descending inhibition, which originates, in Calliptamus sp., from the compound m etathoracic ganglion (fused metathoracic and first three abdominal neu romeres) and in, D. albifrons, from the first free abdominal ganglion (fused second and third abdominal neuromeres).