Figure 7.

Dark-rearing enhances spontaneous activity and causes GABA to retain an excitatory component. DR3_A-DR4_B, Relative onset plots from two retinas at DR3 and two retinas at DR4. Spontaneous activity is strong (Fig. 3, compare PH3_A to PH3_D), and sometimes propagates smoothly (DR3_B). A, Cellular recruitment at PH2, PH3 (black bars), DR2-3, and DR4 (gray bars). Recruitment is much higher in DR retinas. ^**p < 0.001 (N-K post test, PH2 compared with DR2-3 and PH3, with DR4). B, GABA-induced wave in a DR4 retina (conventions as in Fig. 6 B). In normal rearing conditions, GABA is already inhibitory at that age. C, Bicuculline-induced (2-5 μm) increase in cellular recruitment in DR2-4 retinas. ^***p < 0.0001. Error bars indicate SEM. D, Percentage increase in cellular recruitment induced by bicuculline (2-5 μm) from S26 to PH3 and in DR2-4. The progressive developmental increase in bicuculline efficacy at enhancing spontaneous activity is much weaker in DR conditions, suggesting that GABA has remained excitatory.