Pre- and postnatal development of noradrenergic projections to the rat spinal cord: an immunocytochemical study

Using immunocytochemistry with a specific antiserum against noradrenaline, the pre- and postnatal development of noradrenergic (NA) projections to the rat spinal cord was studied from embryonic day 16 (E16) to adulthood (the day following nocturnal mating being considered as E0). In this study, pregnant animals were pre-treated with the MAO inhibitor pargyline (200 mg/kg i.p.), whereas postnatal animals received 100 mg/kg. In vibratome sections, noradrenaline-immunoreactive (NA-IR) axons were seen to invade the spinal cord at E16, at cervical and upper thoracic levels, from the ventral funiculus. At E18, small caliber NA-IR fibers were present in the ventral horn at all cord levels, and some fibers were seen in the intermediolateral cell column (IML) at thoracic level. The growth of axons towards the dorsal horn became noticeable by postnatal day 0 (P0). At P3, fine beaded and radially orientated NA-IR fibers were observed at all levels. The pattern of NA innervation of the dorsal horn was similar to that of the adult by P7. The segregation of noradrenaline immunoreactivity in the ventral and dorsal horns, the IML and the periependymal area was more obvious at all levels by P14 and P20. From P30 the NA innervation was similar to that found in the adult spinal cord. Thus, noradrenaline, like serotonin, was present early in the spinal cord before the onset of specific functions. In addition to and prior to its transmitter function, it might play a trophic role in the neurogenesis of the spinal cord.