DOPAMINERGIC NEURON-B20 GENERATES RHYTHMIC NEURONAL-ACTIVITY IN THE FEEDING MOTOR CIRCUITRY OF APLYSIA

We have identified a buccal neuron (B20) that exhibits dopamine-like h istofluorescence and that can drive a rhythmic motor program of the fe eding motor circuitry of Aplysia. The cell fires vigorously during epi sodes of patterned buccal activity that occur spontaneously, or during buccal programs elicited by stimulation of identified cerebral comman d-like neurons for feeding motor programs. Preventing B20 from firing, or firing B20 at inappropriate times, can modify the program driven b y the cerebral feeding command-like neuron CBI-2. When B20 is activate d by means of constant depolarizing current it discharges in phasic bu rsts, and evokes a sustained coordinated rhythmic buccal motor program . This program incorporates numerous buccal and cerebral neurons assoc iated with aspects of feeding responses. The B20-driven program can be reversibly blocked by the dopamine-antagonist ergonovine. suggesting that dopamine may be causally involved in the generation of the progra m. Although firing of B20 evokes phasic activity in cerebral command-l ike neurons, the presence of the cerebral ganglion is not necessary fo r B20 to drive the program. The data are consistent with the notion th at dopaminergic neuron B20 is an element within the central pattern ge nerator for motor programs associated with feeding.