Hydrostatic pressure receptors and depth usage 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 [1], 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 [2]. 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 [3]. 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.