Involvement of CRFR₁ in the Basolateral Amygdala in the Immediate Fear Extinction Deficit

Impaired extinction efficiency due to immediate post-conditioning interval is restored by a post-conditioning bilateral infusion of CRFR₁ antagonist NBI30775 in the BLA. Animals were separated into groups (A) balanced for anxiety-like behavior on the elevated plus maze (B). After successful fear conditioning they received a bilateral infusion of NBI30775 or vehicle immediately at the end of the session (C) and were given an extinction training session 30 min later (D). Animals infused with the 10-µg dose of NBI30775 showed significantly reduced freezing levels during the first testing session 48 h post-conditioning (E). Both 1- and 10-µg doses showed significantly reduced freezing levels when tested 1 week later (F). A separate group of animals were fear conditioned and received NBI or vehicle afterward and were left undisturbed until testing 48 h later. Treated animals showed similar levels of freezing in the test, suggesting that infusion of NBI does not affect memory consolidation (G). BL, baseline freezing during the first 3 min pretone. Data depicted as mean percentage of time spent freezing ± SEM. *Significant difference (p < 0.05) with the DMSO vehicle group; n = 6–10/group.

Infusion of CRF agonist CRF_6–33 in the BLA immediately before delayed extinction session alters extinction efficacy. Animals were separated into groups (A) balanced for anxiety-like behavior on the elevated plus maze (B), successfully fear conditioned to a similar level (C), and infused with CRF_6–33 or saline 30 min before a delayed (24 h) extinction session. Treated animals showed significantly increased freezing levels compared with vehicle (D). BL, baseline freezing during the first 3 min pretone. Data depicted as percentage of time spent freezing ± SEM. *Significant difference (p < 0.05) with the CRF agonist CRF_6–33 group (0.1 µg/0.2 µl); n = 5–6/group.

Immediate extinction impairment is associated with reduced phosphorylation of the AMPA GluA1 Ser⁸⁴⁵ subunit. Animals were separated into groups (A) balanced for anxiety-like behavior on the elevated plus maze (B), fear conditioned and sacrificed (X) immediately after various context B (CtxB) exposures either 30 min or 24 h after training, with each group showing similar levels of freezing during CtxB exposure (C). Phosphorylation of AMPA GluA1 Ser⁸⁴⁵ was significantly decreased in animals exposed to CS presentations 30 min post-conditioning but not in those with a delayed (24 h) exposure (D) compared with the home cage controls (HC). There were no significant differences in the phosphorylation levels of AMPA GluA1 Ser⁸³¹ (E) or total GluA1 receptor protein (F). Data depicted as percentage of control group ± SEM. *Significant difference (p < 0.05) with HC group; n = 6/group.

GluA1 Ser⁸⁴⁵ phosphorylation levels are reversed with administration of NBI. Animals were separated into groups (A) balanced for anxiety-like behavior on the elevated plus maze (B) and received a post-conditioning infusion of either the CRFR₁ antagonist NBI30775 or vehicle and an immediate extinction session 30 min later (C). Treatment with NBI30775 restored GluA1 Ser⁸⁴⁵ phosphorylation to vehicle home cage (HC) levels (D,E) but had no effect on GluA1 Ser⁸³¹ (D,F) or on its own (G). Data depicted as percentage of vehicle HC control group (hatched bar and also dotted line) ± SEM. *Significant difference (p < 0.05) with the vehicle-treated HC group; n = 8–12/group.