Multimodal convergence of presynaptic afferent inhibition in insect proprioceptors

In the leg motor system of insects, several proprioceptive sense organs pro vide the CNS with information about posture and movement. Within one sensor y organ, presynaptic inhibition shapes the inflow of sensory information to the CNS. We show here that also different proprioceptive sense organs can exert a presynaptic inhibition on each other. The afferents of one leg prop rioceptor in the stick insect, either the position-sensitive femoral chordo tonal organ or the load-sensitive campaniform sensilla, receive a primary a fferent depolarization (PAD) from two other leg proprioceptors, the campani form sensilla and/or the coral hairplate. The reversal potential of this PA D is about -59 mV, and the PAD is associated with a conductance increase. T he properties of this presynaptic input support the hypothesis that this PA D acts as presynaptic inhibition. The PAD reduces the amplitude of afferent action potentials and thus likely also efferent transmitter release and sy naptic efficacy. These findings imply that PAD mechanisms of arthropod prop rioceptors might be as complex as in vertebrates.