Responses of the nematodeCaenorhabditis elegans to controlled chemical stimulation

Abstract

A new method is described for studying the behavioral responses of nematodes to controlled chemical stimulation. The worm is held by the tail with a suction pipet. Behavior is recorded by an array of light sensors connected to a multichannel recorder. Several types of behavior can be detected in addition to the normal backward propagating waves of about 2 Hz that propel untethered worms forward. The most dramatic of these is the reversal bout, consisting of forward propagating waves of about 0.7 Hz, that propel untethered worms backward. The latter waves are easily distinguished from the former by the large amplitude motion caused by the fact that they contain a sharper bend at the tail. This technique was used to demonstrate that a purely temporal change in chemical stimulation can cause a large change in the probability of occurrrence of a reversal bout. These altered probabilities adapt back to the basal level in about one minute. Increased probabilities adapt faster than decreased. Stronger stimulation causes slower adaptation. Since the reversal bout is associated with changes in direction of locomotion, these observations suggest that klinokinesis with adaptation plays a role in the movement of nematodes in chemical gradients.