Anesthetic stimulation of insect water receptors.

Halothane, chloroform, and carbon tetrachloride, in the vapor and liquid phases, stimulate the water receptor of the blowfly Phormia regina. There are three successive phases of response to long-lasting stimulation by halothane: stimulation of the water receptor for the first 19 sec, narcosis for the next 80 sec, and stimulation of all receptors after 80 sec. The behavior of the fly is correlated with these phases. A thirsty fly extends its proboscis and attempts to drink during the first phase, withdraws its proboscis during the second, and extends in a manner characteristic of aversion in the third. A water-satiated fly responds only in the third phase. These results indicate that both the labeled line and the across-fiber hypothesis of sensory coding apply to the blowfly. At the level of sensory transduction the data do not rule out the possibility that streaming potentials are normally involved in stimulation of the water receptor. They are also consistent with a hypothesis that neutral narcotics stimulate the water receptor by facilitating the passage of sodium ions through the dendritic membrane.