A refined Golgi-Cox method for the staining of embryonic neurons in the mouse brain

The Golgi-Cox stain remains a valuable technique used to investigate the morphology of individual neurons. Despite this, Golgi-Cox staining protocols are predominantly designed to impregnate adult neurons. Protocols optimised for the staining of immature embryonic mouse neurons have been previously developed but have limitations, including being time-consuming and being reliant on the use of expensive commercial kits. Here, we present a simple and inexpensive method for Golgi-Cox staining of embryonic neurons in the mouse brain. We identified that a 60 minute, 4 % paraformaldehyde (PFA) brain fixation step, followed by a wash with distilled water prior to immersion in Golgi-Cox solution was critical to the success of the stain. By altering the duration of the wash step, the visualisation of different populations across the neuraxis of neurons could be emphasised. Shorter washes enabled cortical neurons to be readily distinguished, whereas extending the wash steps was needed to enable subcortical neurons to be delineated.