Effects of pre-training injection of orexin A into dorsal raphe nucleus in passive avoidance acquisition on male rats

Endogenous orexins, especially orexin A, play an important role in spatial learning and memory. A recent study has shown the effect of orexinergic system in hippocampus on avoidance learning. Orexinergic receptors are distributed in dorsal raphe nucleus (DRN). The aim of this study was to evaluate the role of dorsal raphe orexinergic system in passive avoidance learning (PA). Rats were implanted with the cannula aimed at dorsal raphe nucleus. Orexin A or saline were injected into the DRN prior to avoidance training. Pre-training orexin type 1 receptors activation in DRN impaired passive avoidance acquisition but had no effect on PA retention.