On the other hand, the P/Q type channel blocker ω-agatoxin IVA (agatoxin [AgTX], 500 nM) had a larger effect on the GABAergic transmission (blocking ∼55% of the initial peak transmission) than did CTX, but it had a much smaller effect on the nicotinic transmission (reducing, but not abolishing, the peak response by ∼40%) than did CTX (Figures 6B–6D). These results indicate that the contributions of N and P/Q channels to ACh release were very different from their contribution to GABA release, though the detailed roles Dactolisib solubility dmso of specific Ca2+ channels subtypes in ACh and GABA

releases remain to be elucidated. Taken together, the above results suggest that ACh and GABA releases from SACs are regulated differentially, providing evidence that ACh and GABA were released from two different populations of synaptic vesicles (see Discussion). The present study demonstrated that ACh and GABA were coreleased from SACs to mediate fast synaptic transmission in two distinct synaptic circuits. The release of the two transmitters was regulated differentially and FG-4592 price presumably from two different vesicle populations. The ACh release required higher extracellular Ca2+ and repetitive

excitation, forming a silent and facilitating surround that enables a DSGC to encode motion sensitivity without compromising spatial resolution. In contrast, the GABA release required lower extracellular Ca2+ and was less sensitive to repetitive stimulation, forming a reliable and spatially extended (leading) inhibition which, together with asymmetric GABAergic connectivity between SACs and DSGCs, ensures robust direction selectivity. The motion-sensitive cholinergic transmission to a DSGC was suppressed in the null direction, Ribose-5-phosphate isomerase resulting in a functionally asymmetric cholinergic excitation which, in turn, enhances direction selectivity. Together, these findings resulted

in an integrated model of ACh-GABA cotransmission and motion-direction codetection (Figure 7, see below for detail). Although ACh release in the retina has been studied with radioactive isotopes since 1970s (Masland and Ames, 1976, Masland and Mills, 1979, Massey and Neal, 1979a and Massey and Neal, 1979b), the synaptic mechanism and synaptic circuitry of cholinergic transmission have remained poorly understood. Our dual patch-clamp recordings from SACs and DSGCs clearly detected fast nicotinic synaptic transmission, which consisted of a fast initial peak component followed by a much smaller and prolonged/slow component (Figure 1). The fast nicotinic component was found reliably in >90% of the pair recordings (>60 pairs in various directions), demonstrating the presence of classic fast nicotinic transmission at SAC-DSGC synapses.