Extracts of the crustacean eyestalk, and particularly of the sinus gla
nd, produce an inhibition of the spontaneous firing rate of motor and
sensitive neurons in two different bioassays. This activity can be asc
ribed to a molecule of low molecular weight, neutral, non-peptidic, so
luble in water and methanol, thermostable, different from GABA but sup
pressed by picrotoxin. Its nature remains to be elucidated.