Corticotropin-releasing factor in the basolateral amygdala enhances memory consolidation via an interaction with the beta-adrenoceptor-cAMP pathway: dependence on glucocorticoid receptor activation

Abstract

Extensive evidence indicates that stress hormone effects on the consolidation of emotionally influenced memory involve noradrenergic activation of the basolateral complex of the amygdala (BLA). The present experiments examined whether corticotropin-releasing factor (CRF) modulates memory consolidation via an interaction with the beta-adrenoceptor-cAMP system in the BLA. In a first experiment, male Sprague Dawley rats received bilateral infusions of the CRF-binding protein ligand inhibitor CRF(6-33) into the BLA either alone or together with the CRF receptor antagonist alpha-helical CRF(9-41) immediately after inhibitory avoidance training. CRF(6-33) induced dose-dependent enhancement of 48 h retention latencies, which was blocked by coadministration of alpha-helical CRF(9-41), suggesting that CRF(6-33) enhances memory consolidation by displacing CRF from its binding protein, thereby increasing "free" endogenous CRF concentrations. In a second experiment, intra-BLA infusions of atenolol (beta-adrenoceptor antagonist) and Rp-cAMPS (cAMP inhibitor), but not prazosin (alpha(1)-adrenoceptor antagonist), blocked CRF(6-33)-induced retention enhancement. In a third experiment, the CRF receptor antagonist alpha-helical CRF(9-41) administered into the BLA immediately after training attenuated the dose-response effects of concurrent intra-BLA infusions of clenbuterol (beta-adrenoceptor agonist). In contrast, alpha-helical CRF(9-41) did not alter retention enhancement induced by posttraining intra-BLA infusions of either cirazoline (alpha(1)-adrenoceptor agonist) or 8-br-cAMP (cAMP analog). These findings suggest that CRF facilitates the memory-modulatory effects of noradrenergic stimulation in the BLA via an interaction with the beta-adrenoceptor-cAMP cascade, at a locus between the membrane-bound beta-adrenoceptor and the intracellular cAMP formation site. Moreover, consistent with evidence that glucocorticoids enhance memory consolidation via a similar interaction with the beta-adrenoceptor-cAMP cascade, a last experiment found that the CRF and glucocorticoid systems within the BLA interact in influencing beta-adrenoceptor-cAMP effects on memory consolidation.

Figure 1.

Step-through latencies (mean + SEM) in seconds on the 48 h inhibitory avoidance retention test of rats given immediate posttraining infusions into the basolateral amygdala of the CRF-binding protein ligand inhibitor CRF_6–33 (0.01, 0.1, or 1 μg in 0.2 μl) either alone or together with the nonselective CRF receptor antagonist α-helical CRF_9–41 (1 μg). **p < 0.01 compared with the saline group; ^♦♦p < 0.01 compared with the corresponding CRF_6–33 group (n = 10–12 per group).

Figure 2.

Step-through latencies (mean + SEM) in seconds on the 48 h inhibitory avoidance retention test of rats given immediate posttraining infusions into the basolateral amygdala of the CRF-binding protein ligand inhibitor CRF_6–33 (0.01, 0.1, or 1 μg in 0.2 μl) either alone or together with the β-adrenoceptor antagonist atenolol (0.5 μg), the α₁-adrenoceptor antagonist prazosin (0.1 μg), or the cAMP inhibitor Rp-cAMPS (4 μg). *p < 0.05, **p < 0.01 compared with the corresponding saline group; ^♦p < 0.05, ^♦♦p < 0.01 compared with the corresponding CRF_6–33 group (n = 9–13 per group).

Figure 3.

Step-through latencies (mean + SEM) in seconds on the 48 h inhibitory avoidance retention test of rats given immediate posttraining infusions into the basolateral amygdala of the CRF receptor antagonist α-helical CRF_9–41 (1 μg in 0.2 μl) together with the β-adrenoceptor agonist clenbuterol (1, 10, or 100 ng) (A), the α₁-adrenoceptor agonist cirazoline (0.01, 0.1, or 1 μg) (B), or the synthetic cAMP analog 8-br-cAMP (0.1, 0.3, or 1 μg) (C). *p < 0.05, **p < 0.01 compared with the corresponding saline group; ^♦p < 0.05, ^♦♦p < 0.01 compared with the corresponding clenbuterol-alone group (n = 9–13 per group).

Figure 4.

Step-through latencies (mean + SEM) in seconds on the 48 h inhibitory avoidance retention test. A, Rats were given immediate posttraining infusions into the basolateral amygdala of the CRF-binding protein ligand inhibitor CRF_6–33 (0.01, 0.1, or 1 μg in 0.2 μl) either alone or together with the glucocorticoid receptor antagonist RU 38486 (1 ng). B, Rats were given immediate posttraining infusions into the basolateral amygdala of the GR agonist RU 28362 (1, 3, or 10 ng in 0.2 μl) either alone or together with the CRF receptor antagonist α-helical CRF_9–41 (1 μg). *p < 0.05, **p < 0.01 compared with the corresponding vehicle group; ^♦p < 0.05, ^♦♦p < 0.01 compared with the corresponding CRF_6–33- or RU 28362-alone group (n = 8–11 per group).

Figure 5.

Representative photomicrograph illustrating placement of a cannula and needle tip in the basolateral amygdala. The arrow points to the needle tip. The gray area in the diagram represents the different nuclei of the basolateral complex of the amygdala: the lateral nucleus (L), basal nucleus (B), and accessory basal nucleus (AB). CEA, Central nucleus of the amygdala.

Figure 6.

Schematic summarizing CRF and glucocorticoid effects on the β-adrenoceptor–cAMP signaling pathway in the basolateral amygdala in influencing memory consolidation. Norepinephrine (NE) is released after training in emotionally arousing tasks and binds to both β-adrenoceptors and α₁-adrenoceptors at postsynaptic sites. The β-adrenoceptor is coupled directly to adenylate cyclase to stimulate cAMP formation. The α₁-adrenoceptor is known to modulate the response induced by β-adrenoceptor stimulation. CRF may also facilitate the β-adrenoceptor–cAMP response, but independently from the α₁-adrenoceptor-induced modulation. Glucocorticoids enhance memory consolidation via a synergistic interaction with both the CRF and α₁-adrenoceptor systems in potentiation training-induced β-adrenoceptor–cAMP activation. Other studies have demonstrated that cAMP may initiate a cascade of intracellular events involving the activation of cAMP-dependent protein kinase (PKA). Our findings suggest that these effects in the basolateral amygdala are required for regulating memory consolidation in other brain regions. α₁, α₁-Adrenoceptor; α₂, α₂-adrenoceptor; AC, adenylate cyclase; β, β-adrenoceptor; CRF-R, corticotropin-releasing factor receptor.