We have been investigating the effects of mutations in 3 genes on habituation to tap. These mutations, suggested to us by Leon Avery, are
eat-4,
avr-14 and
avr-15; all have been hypothesized to be involved in inhibitory glutamate transmission . In earlier work (Wicks and Rankin, 1997) we showed that the most likely site of habituation was the chemical synapses from the touch cells onto the interneurons, and that these synapses were most likely to be inhibitory (Wicks and Rankin, 1995). The
eat-4 gene is thought to encode a transporter required for glutamate neurotransmission (Lee and Avery, pers. comm.). Our results suggest that, although the initial levels of responding are normal in
eat-4 animals, habituation of the tap withdrawal reflex is broadly affected suggesting that glutamate transmission may be involved in habituation of the touch receptors. Habituation of
eat-4 animals is very rapid compared to wild-type worms. Recovery from habituation in
eat-4 animals is also delayed. The
avr-15 gene is thought to encode the a glutamate-gated chloride channel subunit. Avery (pers. comm.) has hypothesized that the
eat-4 is involved in glutamate transport in the pre-synaptic neurons and that
avr-15 affects the post-synaptic inhibitory glutamate receptor. Avr-15 worms respond normally to tap, but show a slightly slower rate of habituation than for wild-type worms. We have also begun testing
avr-14 worms (hypothesized to interact with
avr-15; C. Johnson, pers. comm.) as well as the
avr-14;
avr-15 double strain. With the
avr-14;
avr-15 double we see a slower rate of habituation and a more rapid rate of recovery than for wild-type worms.