OCTOPAMINE SELECTIVELY MODIFIES THE SLOW COMPONENT OF SENSORY ADAPTATION IN AN INSECT MECHANORECEPTOR

The effects of octopamine were studied on the dynamic behavior of the sensory neuron in the cockroach femoral tactile spine. The neuron is a rapidly adapting mechanoreceptor in which adaptation occurs by elevation of the threshold for action potential encoding. The threshold follows increases or decreases of membrane potential, with a delay that involves two separate exponential components. Previous evidence has associated the slow component with sodium pumping and the fast component with sodium channel inactivation. Octopamine reversibly raised the resting threshold and increased but slowed the slow component. These data indicate that octopamine has specific effects on membrane-ionic processes in insect sensory neurons.