The effects of temperature on action potential encoding in the cockroach tactile spine

1. The effect of temperature was observed on the encoding of action potentials from membrane current in the sensory neuron of the cockroach tactile spine. Electrical stimulation was employed, with the tip of a current-passing microelectrode adjacent to the axon where it leaves the soma. Action potentials were detected by extracellular electrodes placed further along the axon. 2. The dynamic properties of encoding were studied by measuring the frequency response function between randomly varying input current and the resulting train of action potentials. 3. Temperature was carefully controlled by mounting the preparation on a thermoelectric servo-controlled stage. The temperature sensor was a fine thermocouple placed against the wall of the tactile spine and within the same pool of saline solution. 4. Temperatures in the range 10 to 35 °C were used. Temperatures outside this range caused failure of action potential production or conduction. The sensitivity of the encoder to electric current did not change appreciably with temperature, but there was an increase in the response to higher frequencies as the temperature was raised, representing more rapid adaptation. 5. Comparison with earlier work on transduction of mechanical stimuli indicates that generation of the receptor current is the step with the most thermal sensitivity. 6. Conduction velocity in the afferent axon increased with temperature by amounts which agree with previous findings and predictions. The mean rate of firing in the receptor increased strongly with temperature, but the reasons for this are not clear.