Evidence that dorsal locus coeruleus neurons can maintain their spinal cord projection following neonatal transection of the dorsal adrenergic bundle in rats.

In adult rats, locus coeruleus neurons which extend axons to the spinal cord are found only at mid-rostrocaudal levels of the nucleus, where they are essentially confined to its ventral, wedge-shaped half (Satoh et al. 1980; Westlund et al. 1983; Loughlin et al. 1986). However, during early postnatal development, coeruleospinal cells are found throughout the locus coeruleus (Cabana and Martin 1984; Chen and Stanfield 1987). This developmental restriction of the distribution of coeruleospinal neurons is due to axonal elimination rather than to cell death, since neurons retrogradely labeled through their spinal axons perinatally are still present in the dorsal portion of the locus coeruleus at survival periods beyond the age at which these cells lose their spinal projection (Chen and Stanfield 1987). I now report that if axons ascending from the locus coeruleus are cut by transecting the dorsal adrenergic bundle on the day of birth, a more widespread distribution of coeruleospinal neurons is retained beyond the perinatal period. These results not only indicate that the absence of the normally maintained collateral of a locus coeruleus neuron is sufficient to prevent the elimination of a collateral which would otherwise be lost, but also may imply that during normal postnatal development the presence of the maintained collateral is somehow causally involved in the elimination of the transient collateral.