2.3 Drugs and treatment
The ICV-STZ procedure was used as previously described(Cui, Song et al., 2018; Zhao, Cui et al., 2021). After 7 days of recovery from surgery, streptozotocin (Sigma‒Aldrich, Cat# S0130, MO, USA) was administered on day 1 and day 3 at 3:00-5:00 PM at a dose of 3 mg kg-1dissolved in 4 ± 1 μl artificial cerebrospinal fluid (aCSF; Tocris Bioscience, Cat# 3525/25 ML, Bristol, UK) according to body weight. Streptozotocin was slowly injected into the lateral ventricle using a Hamilton microsyringe fixed to the syringe pump (RWD Life Science Co Ltd., Shenzhen, China) and connected to the injection cannula at a rate of 0.8 μl min-1. The needle was left in place for an additional 3 min to allow for diffusion. The vehicle treatment was with aCSF.
1-Methyl-DL-tryptophan (1-MT; Sigma‒Aldrich, Cat# 860646, MO, USA) was dissolved in 1 M HCl and adjusted the pH to 6.5 using NaOH, then diluted using 0.9% sterile physiological saline to the final treatment concentration(Lawson, Parrott et al., 2013). 1-MT was injected once daily into the PrL or IL bilaterally (1 μl per side) at a rate of 0.2 μl min-1 at 9:00-11:00 AM from day 1 to day 8. The injection cannula was kept in place for another 2 min to allow the drug to diffuse from the tip entirely. According to O’Connor et al., the effective dose of 1-MT in the brain to produce antidepressant effects is 50 μg ml-1(O’Connor, Lawson et al., 2009).