Figure 5.

Goldfish RGCs respond to specific carbohydrates. a,d-glucose and d-mannose have potent axon-promoting effects. Neither their l-enantiomers nor any other d-sugars are active (tested at 50-100 μm: alt, altrose; all, allose). b, None of the samples affects cell survival. The number of viable RGCs per field is normalized to that of untreated controls. c, The effect of d-mannose on axon outgrowth saturates at 25-50 μm, with an ED₅₀ of ∼10 μm. d, The maximal effects of the factor isolated from bovine vitreous and of glucose are ∼70% that of unfractionated VE <3. Another factor that elutes later from the gel-filtration column (14-17), and which has no activity by itself (Fig. 3d), enhances the effects of glucose and of the carbohydrate isolated from VE <3. e, The membrane-permeable cAMP analog dBcAMP (1 mm) does not augment the effect of glucose. f, The protein kinase A inhibitor KT5720 has little effect on mannose-induced growth.