Abstract
The effects of the neuropeptide FMRFa on spontaneous excitatory postsynaptic currents (sEPSCs) and inhibitory postsynaptic currents (sIPSCs), as well as on evoked EPSCs and IPSCs, in two types of neurons within the central optic lobe of cuttlefish were examined using the whole-cell voltage-clamp technique. FMRFa (1-10 micro m) did not affect cell membrane resting potentials, but reversibly reduced both the frequency and amplitude of sEPSCs in neurons within the medulla region of the optic lobe while increasing the frequency and amplitude of their sIPSCs. For centrifugal neurons in the inner granule cell layer of the optic lobe, FMRFa (1-10 micro m) decreased both the frequency and amplitude of sEPSCs. In the presence of tetrodotoxin (0.5 micro m), neither the interevent interval, nor amplitude distributions of the miniature EPSCs or the miniature IPSCs, were affected by FMRFa, implying a presynaptic action of FMRFa on the optic lobe neurons. Bath application of the neuropeptide also abolished or reduced in amplitude the evoked EPSCs and increased the amplitude of evoked IPSCs in optic lobe neurons, showing that FMRFa induced similar effects on evoked as on spontaneous postsynaptic currents. These results demonstrate the complex range of modulatory effects FMRFa can have within central nervous system circuits.
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