IN-VIVO MODULATION OF INTERACTING CENTRAL PATTERN GENERATORS IN LOBSTER STOMATOGASTRIC GANGLION - INFLUENCE OF FEEDING AND PARTIAL-PRESSUREOF OXYGEN

The stomatogastric ganglion (STG) of the European lobster Homarus gamm arus contains two rhythm-generating networks (the gastric and pyloric circuits) that in resting, unfed animals produce two distinct, yet str ongly interacting, motor patterns. By using simultaneous EMG recording s from the gastric and pyloric muscles in vivo, we found that after fe eding, the gastropyloric interaction disappears as the two networks ex press accelerated motor rhythms. The return to control levels of netwo rk activity occurs progressively over the following 1-2 d and is assoc iated with a gradual reappearance of the gastropyloric interaction. In parallel with this change in network activity is an alteration of oxy gen levels in the blood, In resting, un fed animals, arterial partial pressure of oxygen (PO2) is most often between 1 and 2 kPa and then do ubles within 1 hr after feeding, before returning to control values so me 24 hr later. In vivo, experimental prevention of the arlerial PO2 i ncrease after feeding leads to a slowing of pyloric rhythmicity toward control values and a reappearance of the gastropyloric interaction, w ithout apparent effect on gastric network operation. Using in vitro pr eparations of the stomatogastric nervous system and by changing oxygen levels uniquely at the level of the STG within the range observed in the intact animal, we were able to mimic most of the effects observed in vivo. Our data indicate that the gastropyloric interaction appears only during a ''free run'' mode of foregut activity and that the coord inated operation of multiple neural networks may be modulated by local changes in oxygenation.