Ventilation and underlying neural rhythmogenesis were investigated on the behavioural, neuroanatomical and neurophysiological level in different locust species (Locusta migratoria, Schistocerca gregaria, Schistocerca americana, Taeniopoda eques).Staining with CoCl 2 revealed the anatomy of putative ventilatory interneurones in the metathoracic ganglion. One possible ventilatory intersegmental interneurone could be characterised due to the position of the soma and the anatomical structure.Possible receptor cells exposed on the surface of the ganglion which might detect respiratory gases in the hemolymph were stained with dextrane-linked fluorescein and revealed neurite -like endings reaching into the ganglion. Their function might be detection of changing partial pressures in the surrounding medium.In an isolated locust nerve cord preparation (mesothoracic -first abdominal ganglion) efferent ventilatory patterns could be recorded without interference from sensory feedback and were compared to patterns in intact animals. A wide range of ventilatory patterns occurred depending on temperature, physiological condition of the used animal and on oxygen supply of the tissue. Two extreme pattern (with transient forms) occurr: continuous, often high frequency ventilation and low frequency discontinuous ventilation (typical insect "group ventilation") with long pauses between two burst groups. Clear discontinuous ventilatory patterns occurred regularly when the ventral tracheal supply of the ganglion was maintained. By comparing results from various insect species it could be demonstrated that regular ventilatory patterns are produced in the isolated locust CNS. Experimental change of partial pressures of O 2 and CO 2 in the ambient athmosphere showed a significant correlation to ventilatory frequencies for the isolated CNS (in intact animals: Taeniopoda eques and Schistocerca americana). Increased concentration of CO 2 raises the frequency and increased oxygen lowers the frequency. This is clear evidence for the presence of internal oxygen receptors of the CNS that could be a separate type of chemoreceptors as well as oxygen sensitive neurons. Exposure to increased levels of oxygen elicited clear ventilatory rhythms causing excitatory input from (a) presynaptic cell(s) in one identified interneurone. With intracellular recording and staining with Lucifer Yellow ventilatory interneurones in the metathoracic ganglion from the region of the fused abdominal neuromeres (mainly first fused neuromer) were studied. Experiments were made in semiintact
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