Effects of oxygen on the cercal receptors of the cockroach Periplaneta americana

• 1.1. The activity of the cercal nerve XI and giant interneurons of the cockroach Periplaneta americana is much more intense in situ than in vitro, despite perfusion of the sixth abdominal ganglion by oxygenated saline.
• 2.2. The background cercal nerve activity increases in vitro upon oxygenation from a negligible level. It persists for about 10 min following cessation of oxygenation. The activity in situ remains unaffected.
• 3.3. Oxygenation also substantially increases the frequency of sensory spikes evoked during mechanical stimulation of cercal receptors in vitro, as well as the frequency of generated EPSPs in the interneurons which integrate the cercal activity. The latter effect is apparently due to the increased frequency of afferent spikes.
• 4.4. The intense activity detected in vitro in oxygenated preparations appears to be closer to that existing in situ.