Abstract
GABA was tested for its effects on patterned motor activity (PMA) underlying feeding. Using buccal motoneuron B19 to monitor PMA through intracellular recordings, GABA was found to exert effects at two levels. First, GABA stimulated rhythmic patterned activity resembling fictive feeding, which is under the control of the buccal CPG. In addition, GABA produced a direct inhibition of neuron B19. Both effects were observed when the buccal ganglia were studied in isolation from the rest of the central nervous system, suggesting local interactions with GABA receptors of buccal neurons. Furthermore, these two actions of GABA were found to be pharmacologically distinguishable. The direct hyperpolarization of neuron B19 was mimicked by muscimol, but not baclofen, and involved an increased chloride conductance, which was blocked by picrotoxin. Baclofen duplicated CPG activation by GABA. Picrotoxin had no effect on GABA- or baclofen-induced PMA. These results demonstrate that the Helisoma buccal ganglia have two GABA receptor types which resemble, pharmacologically, mammalian GABAA and GABAB receptors, and that GABA plays a key role in feeding patterned motor activity in Helisoma.
Published Version
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