Caloric evoked motile responses of mammalian vestibular sensory cells

Evokation of caloric nystagmus in microgravity argues against thermal convection as a sufficient explanation for a caloric nystagmic response. By contrast, caloric nystagmus observed in weightlessness suggests a gravity independent mechanism. Here we demonstrate that direct caloric stimulation of isolated living vestibular hair cells from the guinea pig evoked mechanical responses of the sensory cells. Heating of the mechanoreceptor cells from 37 degrees C to 42 degrees C resulted in elongation cooling of the cells from 37 degrees C to 30 degrees C induced shortening of vestibular hair cells. The observed mechanism might contribute to the caloric evokation of a nystagmus both on earth and in orbit.