Altered blood-brain barrier development by early-life stress in an altricial mammal

The blood-brain barrier (BBB) develops following neurulation and continues its differentiation in postnatal life. Should BBB development be delayed it will make the brain prone to damage due to the noxious agents, such as high potassium and glutamate levels, circulating in the blood stream.

The study here reported aimed to ascertain the effects of stress in uterus or during postnatal life on BBB development. Twelve Wistar rats and their pups (10 per litter) were used. Prenatal stress, 20min forced swimming in 32°C water, was done from embryonic day (E) 10 to E20. Controls were kept in the same environment without any stress manipulation. After delivery, half of each litter underwent postnatal stress, 180min maternal separation, from postnatal day (P) 2 to P20. On P1, P10, P20 and P33 pups were anesthetized and given an intracardiac (ic) administration of 2% Evans Blue (EB, 0.4mL/100g bw). After 10min of EB administration, pups were perfused with 4% paraformaldehyde (PFA). As a control for the possible hypoxia effects, due to the thoracic opening, EB was also given ip (2.5mL/100g bw). Brains were immersed in 4% PFA, 24hrs later sectioned in 2mm coronal or sagittal slices and photographed. Photographs were analyzed for optical density with the Image J software.

EB administration procedure (ic vs. ip) did not affect BBB development in controls. At P1, prenatal stressed pups showed BBB permeability to EB in the olfactory bulb (F1–7=2.53, p<0.05) and visual cortex (F1–7=3.33, p<0.005). At P10 BBB permeability of the postnatal stressed pups showed leakage in olfactory bulb (F1–7=2.53, p<0.05) pons (F1–7=2.30, p<0.05), orbitofrontal cx (F1–7=2.19, p<0.05), entorhinal cx (F1–7=3.03, p<0.05), auditory cx (F1–7=3.23, p<0.05). Prenatal stress effects on BBB function were observed mainly in P20, BBB was highly permeable in the orbitofrontal cx (F1–7=2.19, p<0.05), cingulate cx (F1–7=4.53, p<0.001), primary motor, visual and auditory cortices (motor: F1–6=4.56, visual: F1–7=3.33, auditory: F1–6=3.23, all significant at p<0.05), hippocampus (F1–7=3.05, p<0.01), basal ganglia (F1–7=2.46, p<0.05) and olfactory bulb (F1–7=2.53, p<0.05).

By P33, BBB of both stressed and control pups showed complete functionality, EB was observed only in those brain regions without BBB (e.g. pineal gland and choroid plexus). The pre-postnatal stress group did not differ from controls in the EB penetration to the whole brain at any of the ages studied.

Supported by DGAPA, UNAM, project IN220102.