Centripetal activity in fibres in the ventral abdominal vagus nerve of the rat has been studied by recording from fine strands of the divided nerve within the abdomen. 2. In the starved animal, few spontaneously active fibres were located. A proportion of these, however, showed changes in activity in response to changes in F1 oxygen which were typical of arterial chemoreceptor afferent nerves. The resting discharge in these preparations was 0.8-8.0 impulses/sec. In response to extreme hypoxic hypoxia, histotoxic hypoxia or acetylcholine, this discharge increased markedly, with a maximum mean activity of up to 25 impulses/sec. 3. Both the mean/S.D. ratio and statistical comparison with a 'noise' equation were used to assess the apparent random nature of the spike intervals. The former indicated that the spike intervals were random but the latter test was inconclusive. 4. We suggest that this chemoreceptor-like activity originates from the abdominal vagal paraganglia and that these structures may be part of a more generally distributed chemoreceptor system.
