Glucocorticoid receptor‐immunoreactivity in C1, C2, and C3 adrenergic neurons that project to the hypothalamus or to the spinal cord in the rat

A combined retrograde transport‐double immunohistochemical staining method was used to determine the extent to which rat liver glucocorticoid receptor‐immunoreactivity (GR‐ir) is contained within phenylethanolamine‐N‐methyltransferase (PNMT)‐ir neurons that project to the paraventricular nucleus of the hypothalamus (PVH) or the spinal cord. The results confirmed that cells in the C1, C2, and C3 adrenergic cell groups each contribute to the adrenergic innervation of the PVH, and indicated that the great majority of retrogradely labeled neurons in each group (80% overall) also express GR‐ir. Following injections in the upper thoracic segments of the spinal cord, the bulk of adrenergic neurons that were retrogradely labeled were found in the C1 cell group, though 31% of the total number PNMT‐ir cells that could be retrogradely labeled following spinal injections were localized in the C2 and C3 regions. Of these spinally projecting PNMT‐ir neurons, 62% displayed GR‐ir. The results suggest all three medullary adrenergic cell groups contribute projections to the spinal cord and/or the PVH, and that the capacity to express the GR phenotype is a common, though perhaps not universal, attribute of PNMT‐ir neurons. No pronounced differences in the expression GR‐ir were observed in adrenergic neurons as a function of their location or efferent projections. Brainstem adrenergic neurons may play a role in integrating neuronal and hormonal controls of adrenal function via ascending and descending projections.