Figure 5.

Ilp4 expression in cortex glia is necessary for LTM

(A) The scheme above memory graphs indicates the time course of temperature treatments. Blocking exocytosis in cortex glia using Shi^ts for 6 h (n = 19; F_2,56 = 8.65, p = 0.0006) or only 2 h (n = 14, F_2,41 = 3.93, p = 0.028) after conditioning yielded a LTM defect. Blocking cortex glia for 6 h after 5× massed training had no effect on 24-h memory performance (n = 25, F_2,74 = 2.24, p = 0.11).

(B) Ilp4 knockdown in adult cortex glia disrupted LTM, tested 24 h after 5× spaced training (n = 18, F_2,53 = 4.24, p = 0.020) but did not affect memory tested 24 h after 5× massed training (n = 16, F_2,47 = 0.38, p = 0.68).

(C) Immunostaining against GFP (green) and Ilp4 (red) performed on brains from 54H02-GAL4 > UAS-mCD8::GFP flies revealed localization of Ilp4 in cortex glia. Scale bar, 10 μm.

(D) Co-expression of Ilp4 RNAi and constitutively active Akt1 (myr-Akt1) restores normal memory as opposed to Ilp4 RNAi expression alone (n = 14–18, F_4,78 = 6.36, p = 0.0002).

(E) After 30 s of 50 μM nicotine stimulation (red line), the glucose concentration was sustainably increased in cortex glia. Decreasing the expression levels of Ilp4 and InR in adult cortex glia lowered the nicotine-induced glucose elevation (n = 15/16, F_2,46 = 4.40, p = 0.02).

(F) Spaced training failed to elicit a faster decrease in glucose concentration in MB neurons upon knockdown of Ilp4 in cortex glia at the adult stage (n = 11, t₂₀ = 0.11, p = 0.91).

Data were collected in parallel with the data presented in Figure 1C. All data are presented as mean ± SEM. Asterisks illustrate the significance level of the t test, or of the least significant pairwise comparison following an ANOVA, with the following nomenclature: ∗p < 0.05; ∗∗p < 0.01; ns: not significant, p > 0.05. See also Figure S5.