All rats were anesthetized by intraperitoneal injections of Pentobarbital (1 mL per 100 g body weight); depth of anesthesia was tested by the absence of reflections after a painful stimulus. During surgery the body temperature was maintained at 37°C with a thermostatically controlled warming pad (Harvard Apparatus, March, GER). After shaving the skull and its fixation in a stereotactic frame (Stoelting Europe, Dublin, IRL), the scalp was lifted with a forceps (Fine Science Tools (FST), Heidelberg, GER) and opened by surgical scissors (FST, Heidelberg, GER). Within the surgical area the periosteum was removed from the surface of the skull with a sharp double-spoon (sharp spoon after Willinger; Intermedical24, Regensburg, GER) over the surgical area. Bleeding vessels were closed with a cautery kit (Bovie Medical, Clearwater, USA) and the skull was cleaned and disinfected with a 3% H
2O
2 solution (Carl Roth, Karlsruhe, GER). Under a surgical microscope (Carl Zeiss Meditec, Oberkochen, GER) the skull was thinned with a Dremel (Dremel Europe, Konijnenberg NL) and a drill (Eickemeyer, Tuttlingen, GER) was used to prepare the cranial window over the parietal cortex located between -2 mm and -6 mm in relation to the Bregma and 1 mm to 5 mm lateral in relation to the sagittal suture. The skull was regularly cleaned with compressed air (CRC Industries UK Ltd, Bridgwater, UK) to avoid soiling of the field in which surgery was conducted. After removing the bone piece carefully, a small syringe needle (B. Braun, Melsungen, GER) was used to make a little incision and remove the dura mater to the edge of the cranial window by using a spring scissor (FST, Heidelberg, GER). In mice, intravital imaging is usually performed throughout the intact dura mater
[
29], thus, an additional preparation without removing the dura mater was attempted in two of the 15 Wistar rats, too. After surgery the cranial window was filled with sterile irrigation (e.g. sodium chloride 0,9%; B. Braun, Melsungen, GER) and sealed by a 7 mm cover glass (Gerhard Menzel, Braunschweig, GER) using the instant glue Roti-coll 1 (Carl Roth, Karlsruhe, GER).