222 DY Kim and CS Jung Fig. 3. Modulation of b-waves. (A) b-waves were recorded under the control condition, after injecting 100 μM SKF 38393, and after injecting a mixture of 100 μM SKF 38393 and 200 μM MFA. (B) b-waves were re- corded under the control condition, after injecting 30 μM SCH 23390, and after injecting a mixture of 30 μM SCH 23390 and 200 μM MFA. Fig. 4. Modulation of b-waves. (A) b-waves were recorded under the control condition, after injecting 100 μM quinpirole, and after injecting a mixture of 100 μM quinpirole and 200 μM MFA. (B) b-waves were recorded under the control condition, after injecting 200 μM sulpiride, and after injecting a mixture of 200 μM sulpiride and 200 μM MFA. (C) b-waves were recorded under the control condition, after injecting 200 μM dopamine, and after injecting a mixture of 200 μM dopamine and 200 μM MFA. b-wave was enhanced by 44±14% compared to that in the control (n=7, p＜0.05, paired t-test; Fig. 4B). This enhanced peak remained unchanged after a further injection of a mix- ture of 200 μM sulpiride and 200 μM MFA. To investigate the relationship between exogenous NO and DA on b-waves, we injected 200 μM DA first and then injected a mixture of 200 μM DA and 1mM SNP (Fig. 4C). The injection of DA enhanced b-wave amplitude by 57±11%, which was stat- istically significant compared to that in the control (n=8, p＜0.05, paired t-test). This enhanced b-wave peak follow- ing DA administration did not change after a further in- jection of 200 μM DA and 1 mM SNP (Fig. 4C). DISCUSSION Our findings indicate that the b-wave amplitude of ERG retinal activity at the photopic level, as related to gap junc- tions in the goldfish retina, could be mainly dependent on activation by NO- and DA-related agents. We observed enhanced ERG b-waves when the gap junc- tion was blocked by MFA under the photopic level in the goldfish retina. It has been reported that the Cx35/36 gap junction protein is expressed on the dendrites of ON-type bipolar cells in the goldfish retina [6,25]. The Cx35 protein was originally observed in perch and skate, and Cx36, a homolog of Cx35, has been observed in mouse retinas [26,27]. Both CX35 and Cx36 are blocked reversibly by the gap junction blockers MFA and mefloquine [6,28,29]. In our experiment, we used MFA, as it is soluble in water and blocks Cx35/36 gap junction channels. The largest ERG change by 2 mM L-NAME is the a-wave, known to be generated by hyperpolarization of the photo- receptors. Thus, an enhanced a-wave could be seen as a photoreceptor contribution [30]. Intense staining of nicoti- namide dinucleotide phosphate diaphorase (NADPH-d), an enzyme associated with NOS activity, is observed in the photoreceptor and horizontal cells in the goldfish retina