BIOGENIC-AMINES MODULATE SYNAPTIC TRANSMISSION BETWEEN IDENTIFIED GIANT INTERNEURONS AND THORACIC INTERNEURONS IN THE ESCAPE SYSTEM OF THE COCKROACH

In the escape system of the cockroach, Periplaneta americana, a population of uniquely identifiable thoracic interneurons (type A or TI(A)s) receive information about wind via chemical synapses from a population of ventral giant interneurons (vGIs). The TI(A)s are involved in the integration of sensory information necessary for orienting the animal during escape. It is likely that there are times in an animal's life when it is advantageous to modify the effectiveness of synaptic transmission between the vGIs and the TI(A)s. Given the central position of the TI(A)s in the escape system, this would greatly alter associated motor outputs. We tested the ability of octopamine, serotonin, and dopamine to modulate synaptic transmission between vGIs and TI(A)s. Both octopamine and dopamine significantly increased the amplitude of vGI-evoked excitatory postsynaptic potentials (EPSPs) in TI(A)s at 10(-4)-10(-2) M, and 10(-3) M, respectively. On the other hand, serotonin significantly decreased the vGI-evoked EPSPs in TI(A)s at 10(-4)-10(-3) M. These results indicate that octopamine, serotonin, and dopamine are capable of modulating the efficacy of transmission of important neural connections within this circuit.