Intrinsic frequency response patterns in mechano-sensory neurons of the leech

Abstract

Animals employ mechano-sensory systems to detect and explore their environment. Mechano-sensation encompasses stimuli like constant pressure, surface movement or vibrations at various intensities that need to be segregated in the central nervous system. Besides different receptor structures sensory filtering via intrinsic response properties could provide a convenient way to solve this problem. In leech, three major mechano-sensory cell types can be distinguished according to their stimulus sensitivity into nociceptive, pressure and touch cells. Using intracellular recordings we show that the different mechano-sensory neuron classes in Hirudo medicinalis differentially respond supra-threshold to distinct frequencies of sinusoidal current injections between 0.2 and 20 Hz. Nociceptive cells responded with a low pass filter characteristic, pressure cells as high pass filters and touch cells like an intermediate band pass filter. Each class of mechano-sensory neurons is thus intrinsically tuned to a specific frequency range of voltage oscillation that could help segregate mechano-sensory information centrally.