Fig. 1.

Basal forebrain system responsivity to insulin in wild-type and AD mice (a–j) Lysates of medial septum from nasal insulin and vehicle-treated 3 months old 3xTg-AD (3xTg + INS and 3xTg + veh, respectively; 30′) and age-matched wild-type (wt + INS and wt + veh, respectively; 30′) mice were analyzed by WB for the level of phosphorylated and total IR (f, g and a, b; respectively), IRS₁^Y608 (f, h and a, c; respectively) IRS₁^S307 (f, i and a, d; respectively) and AKT (f, j and a, e; respectively). The level of pIR^Y1150/1151, pIRS₁^Y608 and pAKT in insulin treated mice were measured by WB using specific antibodies and β-actin, as loading control. The respective ratios over total IR, IRS₁, and AKT levels were calculated and expressed as percentage of the vehicle treated mice. (a–e) Representative WB (a) and bar graphs (b–e) showing the rapid activation of the canonical insulin pathway in the medial septum of wt mice upon insulin administration, with increased phosphorylation of IR^Y1150/1151 (182.2 ± 15.6% of wt + veh; **p < 0.01; Fig. 1b), IRS₁^Y608 (166.9 ± 59.4% of wt + veh; *p < 0.05; Fig. 1c) and AKT (172.6 ± 6.2% of wt + veh; **p < 0.01; Fig. 1e). (f–j) Representative WB (f) and bar graphs (g–j) indicate a blunted insulin response in the medial septum of 3xTg AD mice as a response to nasal stimulation. In fact, level of pIR^Y1150/1151 (86.4 ± 8.8% of 3xTg + veh, p = 0.194; Fig. 1g), pIRS₁ ^Y608 (86.9 ± 9.0% of 3xTg + veh; p = 0.283; Fig. 1h) and pAKT (100.4 ± 6.1% of 3xTg + veh, p = 0.954; Fig. 1j) were unchanged following insulin treatment, a molecular state reminiscent of insulin resistance. On the other hand, insulin administration was able to downregulate the level of inhibitory pIRS₁^S307 in wt mice (83.9 ± 4.9% of wt + veh, *p < 0.05; Fig. 1a, d), but failed to reduce it in AD mice (109.9 ± 10.6% of 3xTg + veh, p = 0.402; Fig. 1f, i)