Figure 4. IGF-1 decreased CA3 oxidative stress and its related hyperexcitability.
(a) Slice culture excitability in response to oxidative stress (OS) was further characterized by classifying evoked potential changes to a single current pulse that normally triggered a half-maximal field potential response where a normal field potential (FP; left) was rated “1”; a FP that included stimulus-related bursting activity (center) was rated “2”; and a stimulus that resulted in spreading depression (right) was rated is a “3”. Relative evoked excitability was determined as a sum of responses seen (e.g., responses of “2” and a “3” yielded an overall excitability score of five). Responses were measured 30 minutes after exposure to hydrogen peroxide (H2O2). (b) Exposure to H2O2 (n = 7) triggered a significant (*p < 0.001) increase in evoked excitability compared to control (n = 8) and this increase was abrogated by acute application of IGF-1 (n = 4) to a non-significant difference from control. IGF-1 exposure alone (n = 4) had no significant impact on slice CA3 area evoked excitability (i.e., showed a response of “1”). (c) 3-day exposure to IGF-1 had a similar impact on slice culture OS-increased excitability mimicked by application of H2O2. H2O2 significantly (*p < 0.001) increased slice excitability (n = 15) compared to control (n = 18). Pretreatment with IGF-1 for 3 days (n = 9) reduced the H2O2-induced increased excitability to a non-significant difference from control. (d-e) Exemplary images of control (d) slice culture OS compared to increased slice OS induced by exposure to menadione (e). Calibration bar, 200 μm. Dotted boxes indicate CA3 areas of interest used for relative OS quantifications (f and g). (f) Exposure to menadione (M; n = 12) triggered a significant (*p < 0.001) increase in OS compared to control (n = 18). Acute treatment with IGF-1 (n = 15) reduced OS from menadione to a non-significant (p = 0.15) difference from control (n =18). Acute IGF-1 exposure alone (n = 18) did not reduced slice culture OS from control. (g) Pretreatment with IGF-1 for 3 days (n = 15) also reduced menadione-induced significant increase in OS (*p < 0.001; n = 12) to a non-significant (p = 0.148) difference from control (n = 15). In addition, IGF-1 pretreatment alone (n = 18) significantly (*p = 0.008) reduced slice culture OS compared to control.