Modulation of network pacemaker neurons by oxygen at the anaerobic threshold
Previous in vitro and in vivo studies showed that the frequency of rhythmic pyloric network activity in the lobster is modulated directly by oxygen partial pressure (PO2). We have extended these results by (1) increasing the period of exposure to low PO2 and by (2) testing the sensitivity of the pyloric network to changes in PO2 that are within the narrow range normally experienced by the lobster (1 to 6 kPa). We found that the pyloric network rhythm was indeed altered by changes in PO2 within the range typically observed in vivo. Furthermore, a previous study showed that the lateral pyloric constrictor motor neuron (LP) contributes to the O2 sensitivity of the pyloric network. Here, we expanded on this idea by testing the hypothesis that pyloric pacemaker neurons also contribute to pyloric O2 sensitivity. A 2-h exposure to 1 kPa PO2, which was twice the period used previously, decreased the frequency of an isolated group of pacemaker neurons, suggesting that changes in the rhythmogenic properties of these cells contribute to pyloric O2 sensitivity during long-term near-anaerobic (anaerobic threshold, 0.7–1.2 kPa) conditions.