GFAP levels are positively associated with neurite outgrowth under growth stimulatory conditions. Histographs showing from different mouse genotypes at PN7 (A) the amount of retinal GFAP (mean±SEM), (B) GFAP levels (mean±SEM) in PN7 retinal explants cultured 7 days with either 10% FBS, 10% EN2, or 10% EN2 w/o HC, and (C) neurites per explant (mean±SEM) in PN7 retinal explants cultured for 7 days with 10% FBS, 10% EN2, or 10% EN2-HC. (A) The amount of GFAP in different mouse genotypes shows titration of GFAP from background levels (Gfap-/-, *P<0.001 versus Gfap+/+ retinas), to half the amount of GFAP (Gfap+/-, *P=0.048 versus Gfap+/+ retinas), to double the amount of GFAP (Tg170.2, **P=0.041 versus Gfap+/+ retinas). (B) In retinal explants cultured for 7 days the same relationship between GFAP levels and genotype was maintained, regardless of culture conditions (*P<0.05), although overall GFAP levels were significantly higher in explants cultured in EN2 versus EN2 w/o HC treated explants (**P<0.03). (C) None of the FBS treated explants had significant neurite outgrowth, indicating that increased GFAP alone does not increase neurite outgrowth. EN2 and EN2 w/o HC treated explants had increased neurites in all strains compared to FBS. In Gfap+/+ and Tg170.2 explants, there were significantly more neurites in EN2 treated explants than EN2 w/o HC treated explants. In Gfap-/- and Gfap+/- explants, this treatment dependent effect was ablated, indicating that one important contribution of HC to increased neurite outgrowth is the increase in GFAP. Bracketed comparisons are significantly different (P<0.05).