J M Mouveroux | PubMed Health

PubMed2001

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.

Age Factors↗

PubMed2000

Intrinsic properties of the developing motor cortex in the rat: in vitro axons from the medial somatomotor cortex grow faster than axons from the lateral somatomotor cortex.

The axons that originate in the medial somatomotor cortex of the rat depart, during development, after those from the lateral somatomotor cortex, yet they arrive in the cervical spinal cord first. Either the medially originating axons elongate faster, or the laterally originating ones pause along the descent pathway. To investigate the presence of an intrinsic difference of the axonal elongation velocity between the lateral and medial somatomotor cortical areas, we cultured explants taken from these areas for 2 days, and measured the length of the outgrowth. After 2 days the explants were surrounded by a radiate corona of axons of which the longest measured 1.95 mm. A significant difference was detected between the medial and lateral somatomotor cortical areas in vitro. Axons originating from explants taken from the medial somatomotor cortical area are, after 2 days in culture, on average 0.16 mm longer than those from the lateral somatomotor cortical area. Though the observed difference is not large enough to allow for the overtaking observed in vivo, it does indicate that intrinsic differences exist within the developing rat somatomotor cortex. This in turn indicates that intrinsic cortical traits not only influence regionalization and targeting behavior of cortical projection neurons, but also their axonal elongation speed.

Animals↗