Multifunctional neuron CC6 in Aplysia exerts actions opposite to those of multifunctional neuron CC5

The controls of somatic and autonomic functions often appear to be organize d into antagonistic systems. This issue was explored in the bilaterally pai red C cluster neuron, CC6, which was found to have properties that suggeste d that it might function antagonistically to the previously identified mult iaction neuron, CC5. Similar to CC5, CC6 is an interganglionic neuron that sends its sole axon to the ipsilateral and contralateral pedal and pleural ganglia. Synaptic inputs to CC6 were opposite to those of CC5. For example, CC6 receives inhibitory inputs from mechanical touch to the lips and tenta cles and is excited by firing of C-PR, a neuron involved in the control of a head extension response. Also during rhythmic buccal mass movements CC6 r eceives synaptic inputs that are out of phase with those received by CC5. C C6 is inhibited during a fictive locomotor program, whereas CC5 is excited, but unlike CC5, the inputs to CC6 are not rhythmic. CC6 has extensive mono - and polysynaptic outputs to many identified and unidentified neurons loca ted in various central ganglia. Firing of CC6 evoked ipsilateral contractio n of the transverse muscles of the neck, whereas CC5 contracts longitudinal neck muscles. CC6 monosynaptically inhibits the pedal artery shortener neu ron, whereas CC5 monosynaptically excites the pedal artery shortener neuron . Specific motor neurons in the pedal ganglion receive synaptic inputs of o pposite sign from CC5 and CC6. Although the inputs and most of the effects of CC6 were opposite to those of CC5, both cells were found to produce poly synaptic excitation of the abdominal ganglion neuron RBhe, a cell whose act ivity excites the heart. CC5 and CC6 appear to be multifunctional neurons t hat form an antagonist pair.