Histology:
One series was mounted onto gelatin-coated slides before being stained for Nissl using cresyl violet. The sections were then dehydrated through increasing concentrations of alcohol (70%; 90%; 100%; 100%) and washed in xylene. Then, the slides were cover-slipped with DPX (Sigma Aldrich, Gillingham, UK) mounting medium. To enhance the fluorescence signal of the mCherry (iDREADDs group) or GFP (control group), additional series were washed three times in PBS and then blocked with 5% normal goat serum (NGS) (Invitrogen, Inchinnan, UK) in Phosphate Buffered Saline with Tritonx-1000 (PBST) for two hours. Both series were then transferred in either a solution of rabbit polyclonal anti-mCherry (Abcam, Cambridge, UK) or chicken polyclonal anti-GFP (Abcam, Cambridge, UK) antibody at a dilution of 1:1000 in PBST with 1% NGS and incubated for 24 hours at room temperature. The sections were then washed three times and transferred to a secondary antibody of either goat-anti-rabbit (Dylight Alexa flour 594, Vector Laboratories, Peterborough, UK) or Alexa Fluor 488 goat-anti-chicken (Invitrogen, Inchinnan, UK) at a dilution of 1:200 in PBST for two hours. The sections were then washed in PBS and mounted onto gelatin-coated slides and cover-slipped using Fluromount (Sigma-Aldrich, Germany).