Consolidating p17

We expected naloxone to impair extinction acquisition in P24 rats because previous findings showed that P24 rats essentially are like adult rats in extinction.Whether naloxone attenuates extinction in P17 rats was our primary question of interest.This effect was dependent on central rather than peripheral μ-opioid receptors (Experiment 2), and neither pre-test nor post-extinction injection of naloxone had effects on extinction (Experiments 3 and 4).

consolidating p17-65

Specifically, pretest injection of the γ-aminobutryic acid (GABA) receptor inverse agonist FG7142 has no effect on extinction in postnatal day (P)17 rats, although it reverses extinction in P24 rats as reported by Kim and Richardson in an earlier paper.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).Rats that received a pre-extinction injection of naloxone exhibited substantially higher levels of CS-elicited freezing at test (drug-free) compared with rats that had received saline.Pavlovian conditioned fear is typically acquired by pairing an initially neutral conditioned stimulus (CS; e.g., tone) with an aversive unconditioned stimulus (US; e.g., shock).The formation of an association between the CS and the US is inferred when subsequent presentations of the CS elicits various conditioned fear responses (CR; e.g., freezing).

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