Rhythmic contractile movements of the larval midgut of the silkworm, Bombyx mori

The raidgut of intact larvae of Bombyx mori exhibited active contractile movements. Contraction waves were generated rhythmically at several regions of the midgut. The waves passed in both oral and aboral directions from their sites of origin. Midgut movements were depressed during moulting. The midgut continued to move normally when tetrodotoxin was injected into the larval haemocoel at doses sufficient to paralyze somatic muscle. Ligation of larvae paralyzed with tetrodotoxin behind the second or third body segment resulted in the abolition of the contraction waves in the midgut portion anterior to the ligature. A ligature applied behind other body segments did not hamper midgut motor activity irrespective of whether or not an abdominal ganglion had been extirpated. The frequency of contraction and the rate of food transport in the midgut were increased when larvae were administered serotonin or when their body temperature was raised.