Choroid plexuses secrete the cerebrospinal fluid in which the brain is immersed. The cells that make them up form a barrier between the blood and the brain, preventing certain toxic molecules from entering it. The remarkable vascularisation of part of a choroid plexus, taken from a 9-day-old rat, can be seen here by means of green
immunofluorescence. The researchers are investigating the ways in which immune cells can enter the brain in the event of infection, for example during childbirth. Although the labelling of monocytes, white blood cells present in the blood, has been removed, this 3D visualisation makes it possible to understand the essential role played by the choroid plexus in the proper functioning of the brain. This image was taken using light sheet microscopy. It is one of the winners of the 2022 La preuve par l’image (LPPI) photography competition.