Nonetheless, we expected that if CeA CRF secretion has a critical temporal involvement in facilitating the consolidation of contextual fear memory, then inhibition of CeA CRF using CRF ASO will likely impair contextual memory during the early, but not later, post-training periods. Rats microinjected with CRF ASO into the CeA at 5-min (t17= 3.208,p< 0.01), 9-h (t13= 2.518,p< 0.05), and 24-h (t13= 2.513,p< 0.05) after training exhibited significantly lower levels of contextual freezing than their respective controls. CeA site-specific microinjections of CRF antisense oligonucleotides (CRF ASO) at several post-training time intervals. Rats microinjected with CRF ASO at post-training intervals up to 24-h subsequently exhibited significant impairments in contextual freezing retention in contrast Alvelestat to animals treated 96-h after training. To further establish the validity of the results, CeA fiber-sparing lesions were made at two distinct post-training periods (24-h, 96-h), corresponding respectively to the temporal intervals when CeA CRF ASO administration disrupted or had no significant effects on memory consolidation. Similar to the CeA CRF ASO results, ENPEP CeA Alvelestat lesions made 24-h, but not 96-h, after training induced significant freezing deficits in the retention test. In conclusion, the current results demonstrate: 1) an extended involvement of CeA CRF in contextual memory consolidation and 2) that contextual fear memory storage is not dependent on a functional CeA. Keywords:Central amygdala, corticotropin-releasing factor, contextual fear conditioning, emotional memory consolidation, contextual memory storage, CRF antisense oligonucleotides == 1. Introduction == Memory consolidation is a process in which short-term memories are converted into long-term memories. This process has been demonstrated to be dependent upon the activation of intracellular signaling cascades and the synthesis of new proteins (Dudai, 2004;McGaugh, 2004). Much of our current understanding of memory consolidation is derived from studies using aversive conditioning procedures, such as inhibitory avoidance and pavlovian fear conditioning. In pavlovian fear conditioning, a neutral conditioned stimulus (CS) is paired with an aversive unconditioned stimulus to establish a CS-US association. Subsequent re-exposure to the CS elicits a conditioned response, which indicates a learned association. The amygdala plays an essential role in emotional learning and memory. The basolateral amygdala complex (BLA; including the lateral, basal, and accessory basal nuclei) is a critical region involved in emotional learning (LeDoux, 2000) and a variety of neuromodulators have been shown to influence consolidation at this site, including norepinephrine, glucocorticoids, and corticotropin-releasing factor (CRF) (Par, 2003;McGaugh, 2004;Roozendaal et al., 2008). Specifically, BLA administration of CRF receptor antagonists following both contextual fear conditioning (Hubbard et al., 2007) and inhibitory avoidance training (Roozendaal et al., 2002) has been demonstrated to disrupt memory consolidation. Yet, both of the aforementioned studies reported no impairment when CRF receptor antagonists were injected into the adjacent central nucleus (CeA), which contains the majority of CRF immunoreactive cell bodies within the amygdala (Veening et al., 1984). Furthermore, we recently reported that pre-training microinjections of CRF antisense oligonucleotides (CRF ASO) into the CeA did not disrupt freezing during training, but impaired the retention of contextual freezing when assessed 48-h later (Pitts et al., 2009). In sum, these findings suggest that CeA CRF promotes fear memory consolidation by activating BLA CRF1receptors. Of additional importance, the CeA is widely thought to act as the final output of the amygdala and to be essential for fear expression (Wilensky et al., 2006;Zimmerman et al., 2007;Rodrigues et al., 2009;Jimenez & Maren, 2009). The CeA receives unidirectional projections from the adjacent BLA (Pitknen et al., 1997) and sends projections to several downstream brainstem sites that mediate conditioned fear responses (McDonald, 1998;LeDoux, 2000). While the BLA to CeA serial transmission model has been accepted by many, some studies have produced results which contradict this model (Koo et al., 2004;Pitts et al., 2009). In particular, we previously found no impairment in contextual fear retention when the CeA was inactivated immediately prior to Alvelestat retention testing (Pitts et al., 2009). Thus, in our first study, we investigated the temporal role of CeA CRF in contextual fear memory consolidation by inhibiting CeA CRF with CRF ASO at several post-training intervals. Next, we evaluated the general function of the CeA in fear memory consolidation and retention by inducing fiber-sparing CeA lesions at two distinct post-training intervals (24-h and 96-h) identified in the first experiment to represent ongoing consolidation and post-consolidation periods under our training procedures. Collectively, our results demonstrate: 1) CeA CRF secretion facilitates memory consolidation for at least 24-h after exposure to contextual fear conditioning; and 2) by 96-h after conditioning,.