Alterations in Noradrenergic Innervation of the Brain Following Dorsal Bundle Lesions in Neonatal Rats
Document Type
Article
Publication Date
1-1-1986
Description
Several seemingly conflicting sets of data have been reported on the regenerative capacity of central noradrenergic neurons, following transection of the ascending noradrenergic fiber tract in neonatal rats (Iacovitti et al., Dev Brain Res 1: 21-33, 1981; Jonsson and Sachs, Brain Res Bull 9: 641-650, 1982). In order to more fully investigate changes in noradrenergic neurons in the brain after such a transection, rats were lesioned at various times after birth, sometimes in conjunction with administration of the neurotoxin, 6-hydroxydopa (6-OHDOPA). Animals were sacrifced at 7, 10, 14, 28, 42 or 56 days after birth, in order to assess the pattern of noradrenergic neuronal damage, as well as the recovery rate. Dorsal bundle lesions were associated with neocortical and hippocampal hypoinnervation by noradrenergic fibers, and sprouting of a collateral fiber group, with production of noradrenergic hyperinnervation of the cerebellum and pons-medulla. Recovery of the norepinephrine (NE) content to control levels occurred in the neocortex at 8 weeks, when the dorsal bundle was lesioned at birth. When the lesion was produced at a later time (3 days or 5 days after birth), less recovery in the neocortex and hippocampus was found. Histofluorescent fiber number, as observed with a glyoxylic acid method, correlated with NE changes. It appears that 6-OHDOPA (20 μg/g IP) does not modify long-term recovery from a dorsal bundle lesion, when rats are co-treated at 3 days after birth. However, the length of the proximal noradrenergic fiber stump may be an important factor affecting the capacity for recovery from injury. These results suggest that a shorter fiber stump, as produced with a dorsal bundle lesion at the level of the pons, may be associated with a greater degree of recovery from injury. Also, the younger the rat at the time of injury, the greater appears to be the capacity for regeneration. These results demonstrate that regeneration can occur in one part of the brain without modification of a collateral hyperinnervation of a different part of the brain. Therefore, our findings discount a programming of central noradrenergic fibers to express a specific number of nerve terminal arborizations, (i.e., the "pruning hypothesis").
Citation Information
Klisans-Fuenmayor, Dolores; Harston, Craig T.; and Kostrzewa, Richard M.. 1986. Alterations in Noradrenergic Innervation of the Brain Following Dorsal Bundle Lesions in Neonatal Rats. Brain Research Bulletin. Vol.16(1). 47-54. https://doi.org/10.1016/0361-9230(86)90011-0 PMID: 3082466 ISSN: 0361-9230