4.3. Intranasal Administration

Intranasal administration was performed as previously described by Kim et al. (2012) [40]. Briefly, rats were anesthetized with an intramuscular injection of a mixture of ketamine (3.75 mg/100 g body weight) and xylazine hydrochloride (0.5 mg/100 g per body weight). A nose drop containing 500 ng of OPN peptide dissolved in PBS (20 μL) was carefully placed in each nostril of anesthetized animals (supine 90° angle) using a pre-autoclaved pipet tip (T-200-Y, Axygen, CA, USA). The procedure was repeated until the entire dosage was administered at 2 min intervals between applications.