Analysis of a nonlinear cascade model for sensory encoding by modification of ion channels

Mechanotransconduction is often modeled as a three-stage process in which the input stimulus is first transformed by mechanical components, then transduced into an intracellular receptor current, and finally encoded into a train of action potentials. In the cockroach tactile spine, a rapidly adapting sensory organ, the dynamic behavior is controlled by the encoding stage. It has been previously shown that a nonlinear cascaded model can account for much of the dynamic response. Here, the authors describe the dissection of the cascade by the use of phentolamine, a drug which appears to selectively modify the behavior of sodium channels in the encoder region of the neuron. Phentolamine raised the threshold of the neuron and slowed its discharge rate to a constant white noise stimulus, but did not prevent system identification. Preliminary results suggest that the nonlinear static component of the cascade is unaffected by this drug, while the nonlinear dynamic components are changed. These results may be due to the ionic processes involved in action potential encoding.