Location and dynamic properties of the spike generator in an insect mechanosensory neuron

Abstract

1.The cereal bristle hairs of the cockroach, Periplaneta americana, are each innervated by one mechanosensory cell and 1–5 chemosensory cells. In transepithelial recordings, chemo- and mechanosensory spikes could be discriminated from each other by their relative amplitude. 2. When current steps were applied via the sensory hair, trains of impulses were triggered whatever the polarity of the current. 3. All responses adapted to the current, but the time course of adaptation was fitted by a power law for outward currents and an exponential law for inward currents. 4. During application of outward currents, the spikes showed a negative initial phase on which a small positive component was superimposed; strong polarizations produced purely negative spikes. More classical spikes with a positive initial phase were induced by inward currents. 5. The present work supports the hypothesis of a direct excitability of the apical dendrite in cereal bristle mechanoreceptors and confirms previous results suggesting that spikes are normally triggered within that region during mechanical stimulations. It is also established, for the first time, that adaptation to currents may be different in the apical dendrite and in more basal regions of the same mechanosensory neuron.