Modification of the motor reflex responses due to repetition of the peripheral stimulus in the cockroach. II. Conditions of activation of the motoneurones.

The cockroach reacts to an air puff applied to its cerci by a forward escape reflex which decreases or even disappears after a few successive stimuli have been applied (Roeder, 1948). In the preceding paper (Zilber-Gachelin & Chartier, 1973) we have shown that the response is already modified by habituating effects at the first synaptic relay, in the 6th abdominal ganglion (A.G.). The present paper extends this work and studies the effect of the second synaptic relay, the 3rd thoracic ganglion (T.G.), on the abdominal cord to motor nerve transmission. In the final section we study how these properties, combined with those we described in the 6th A.G., can explain the modification of the motor response observed on the isolated reflex loop when repetitive cereal air puffs are delivered. Finally, the bearing of these results on the behaviour of the whole free cockroach is discussed. A brief report of this work has appeared previously (Chartier & Zilber-Gachelin, 1969).