Lumbar spinal cord explants from neonatal rat display age-related decrease of outgrowth in culture.

Lumbar spinal cord explants, harvested from neonatal rat pups aged between postnatal day 0 (P0) and P7, were cultured for a period of 48 h in the chemically defined medium R(12) [17] (Romijn, H.J., van-Huijen, F., Wolters, P.S., Neurosci Biobehav Rev, 8 (1984) 301-334), embedded in a collagen matrix. The outgrowth into the surrounding matrix was quantified. Age-matched cortical explants were used as controls. Despite adaptations of the culture protocol, outgrowth remained variable. Statistical analysis demonstrated a clear relation between the age of the explant (at the time of explantation) and the number of neurites in the corona surrounding the explant. The number of outgrowing neurites decreased sharply with age. The average number of neurites per explant obeyed to the expression log(N)= -0.652 A+17 (N: the number of neurites per explant; A: the age expressed in gestational days; A epsilon [G23-G30]; G23 signifying gestational day 23, or P0). The observed age-related decrease of outgrowth could not be explained by progressive myelination of the spinal cord white matter, nor by the absence of trophic support from muscle, but may be related to a progressive inability of the spinal neurites to interact with collagen.