Consolidating p17

The present study further investigates extinction in the developing rat by examining the involvement of the endogenous opioid system.Along with GABAergic and NMDA neurotransmission, endogenous opioids regulate extinction in the adult rat (Hernandez and Powell 1980, Mc Nally and Westbrook 2003a).Not only are these findings important theoretically, the observed developmental differences in extinction also have significant clinical implications.In contrast to suggestions that fear acquired early in development has enduring effects that are resistant to extinction (1999), these preclinical studies suggest that fear acquired early in development may be more permanently extinguished if treated early compared with later in development.Early models of associative learning suggested that extinction was due to the “unlearning” or “erasure” of the original CS–US association (e.g., Rescorla and Wagner 1972).However, it is now more widely accepted that the reduced CR following extinction reflects new learning of a CS–no US association that inhibits the expression of the original CS–US association (e.g., Bouton 2002).Pre-extinction injection of naloxone significantly impaired the acquisition of extinction in both P17 and P24 rats (Fig. A mixed-design analysis of variance (ANOVA) of the extinction data yielded significant main effects of Block (Table 1 displays the baseline freezing levels for each group in all experiments).

Therefore, follow-up experiments in this study focused on extinction in P17 rats.The primary evidence for this view comes from behavioral studies that show performance to an extinguished CS can recover without any retraining (e.g., spontaneous recovery, renewal, and reinstatement).Additionally, we know that extinction involves inhibition because reducing γ-amino butyric acid (GABA) inhibitory activity by pretest injections of the GABA receptor inverse agonist FG7142 reverses extinction (Kandel 2001).There was a main effect of Drug ( It was demonstrated in Experiment 1 that pre-extinction systemic injection of naloxone significantly impairs extinction learning in P17 and P24 rats.The result with the P24 rat is consistent with previous findings with adult rats and further shows that P24 rats are adult-like in terms of extinction.

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