Caloric stimulation of ampullar receptors: a new method to produce mechanically-evoked responses in frog semicircular canals

A microthermistor positioned close to the exposed posterior semicircular ca nal in isolated labyrinth preparations of the frog was used to stimulate th e sensory organ. Our results indicated that, depending on the position of t he heater, the induced endolymphatic convection currents may result in eith er excitatory or inhibitory cupular deflections and thus in a modulation of ampbullar receptor resting activity. Other possible thermal-dependent mech anisms, such as a direct action of the stimulus on vestibular sensors or en dolymphatic volume changes, had, in the present experimental conditions, a minor role. Caloric stimulation could therefore represent a novel method to stimulate the semicircular canals 'in situ'. (C) 1999 Elsevier Science B.V . All rights reserved.