Domitol

Rats were anesthetized with a combination of 0.15 mg/kg of medetomidine (Domitol; Nippon Zenyaku Kogyo Co., Ltd., Fukushima, Japan), 2 mg/kg of midazolam (Dormicum; Astellas Pharma Inc., Tokyo, Japan), and 2.5 mg/kg of butorphanol (Vetorphale; Meiji Seika, Ltd., Tokyo, Japan). In addition, preoperative antibiotic (20,000 U/kg penicillin G; Meiji Seika) was administered subcutaneously. We then surgically induced posterolateral lumbar fusion (Kaito et al., 2013 (link), Morimoto et al., 2014 , Wang et al., 2003 (link)). A posterior midline skin incision was made, followed by 2 separate paramedian incisions in the lumbar fascia 3 mm from the midline, through which the transverse processes were exposed. The L4 and L5 transverse processes were decorticated using a high-speed burr.
A commercially available absorbable collagen sponge (CollaCote; Zimmer Dental Inc., CA, USA) was cut into 5 × 10 mm fragments and placed in a sterile tube. Phosphate-buffered saline (PBS) or rhBMP-2 (50 μg in PBS) was applied to the sponge just before implantation on each side of the spine. We chose 50 μg rhBMP-2 because this corresponded to a high clinical dose (1500 μg/mL) (Morimoto et al., 2014 ). The fascia and skin incisions were closed using a 4-0 absorbable suture. The rats were housed in separate cages and allowed to eat and drink ad libitum while their condition was monitored daily.