FMRFAMIDE AND GABA PRODUCE FUNCTIONALLY OPPOSITE EFFECTS ON PREY-CAPTURE REACTIONS IN THE PTEROPOD MOLLUSK CLIONE-LIMACINA

The effects of FMRFamide and gamma-aminobutyric acid (GABA) on prey-ca pture reactions in Clione and on cerebral A and B neurons, which contr ol opposite movements of prey capture appendages, have been studied. F MRFamide hyperpolarized A neurons and depolarized and increased spike activity in B neurons. FMRFamide thus had a reciprocal effect on A and B neurons, triggering buccal cone withdrawal. In addition, FMRFamide inhibited swimming, acceleration of which is a component of feeding ar ousal. Many neurons throughout the central nervous system showed FMRFa mide immunoreactivity. Dense networks of immunoreactive fibers were lo calized in the head wall, buccal mass and in buccal cones, adjacent to striated longitudinal muscle cells. In wings, immunoreactive processe s were found mainly in association with smooth retractor muscles. GABA depolarized and activated A neurons but hyperpolarized and inhibited B neurons. The overall effect of GABA thus resulted in extrusion of bu ccal cones. Both direct GABA responses and inhibitory postsynaptic pot entials (IPSPs) induced in B neurons by A neuron activity were chlorid e-mediated. However, picrotoxin and bicuculline did not block IPSPs or direct GABA responses in B cells.