Mutations of the Caenorhabditis elegans brain-specific inorganic phosphatetransporter eat-4 affect habituation of the tap-withdrawal response without affecting the response itself

The studies reported here were designed to investigate the role of the muta tion eat-4 in the response to tap and in habituation in the nematode Caenor habditis elegans. In C. elegans eat-4 has been found to affect a number of glutamatergic pathways. It has been hypothesized to positively regulate glu taminase activity and therefore glutamatergic neurotransmission. In the eat -4(ky5) loss-of-function worms, there is presumably insufficient glutamate available for sustained transmission. In the experiments reported here eat- 4 worms showed no differences from wild-type in the magnitude of response t o a single tap, indicating that the neural circuit underlying the response was intact and functional in the mutant worms. However, when eat-4 worms we re given repeated taps the resulting habituation was different from that se en in wild-type worms: eat-4 worms habituate more rapidly and recover more slowly than wild-type worms at all interstimulus intervals tested. In addit ion, eat-4 worms do not show dishabituation. The same transgene rescues pha ryngeal activity defects and both the habituation and dishabituation defici ts seen in the eat-4 worms. Our results suggest that neurotransmitter regul ation plays a role in habituation and may play a role in dishabituation.