Hydrostatic Pressure Receptors and Path Integration in Crustacea and Fish.

The discovery that small changes in hydrostatic pressure were coded by angular acceleration receptors in the crab with a mechanism involving nanometer level displacements of mechanoreceptors by differential compression of cuticular and cellular tissues (Fraser and Macdonald, 1994), has pointed to a set of sensory signals fundamentally involved in navigation in a much broader range of animals. Neural correlates of hydrostatic pressure cycles have been found in a variety of crustacean equilibrium systems (Fraser et al, 2001). A more recent study has also shown that angular acceleration receptors in the semicircular canal system of the shark Scyliorhinus respond to small steps and cycles of hydrostatic pressure (Fraser and Shelmerdine, 2002). In order to investigate rates of changes and absolute changes in hydrostatic pressure detected by these sensory systems, we used pressure chambers together with a tide machine or a voltage controlled pressure regulator to subject balancing system neurones to steps and cycles of hydrostatic pressure, using spike density as a measure of activity. In a variety of species, responses obtained fell into the range expected from the known ranges of depth and rates of change of depth.