Organization of adrenergic inputs to the paraventricular and supraoptic nuclei of the hypothalamus in the rat

Abstract Anterograde transport, retrograde transport, and immunohistochemical techniques were used to characterize the organization of neural inputs to the paraventricular (PVH) and supraoptic (SO) nuclei from the C1, C2, and C3 adrenergic cell groups in the rostral medulla. The results are as follows: (1) Phenylethanolamine‐N‐methyltransferase–immunoreactive (PNMT‐IR) fibers and terminals were distributed to all parts of the parvicellular division of the PVH; the dorsal and dorsal medial subdivisions received the most prominent inputs, the lateral and ventral medial parts the least. Sparse terminal fields were found consistently in the magnocellular division of the PVH and in the SO. (2) A combined retrograde transport–immunohistochemical method was used to estimate the number and proportion of cells in the regions of the C1, C2, and C3 cell groups that contribute to the PNMT‐IR innervation of the PVH. On average, 232 ± 37 retrogradely labeled cells in the C1 cell group, 73 ± 32 in the C2 cell group, and 96 ± 26 in the C3 group stained positively for PNMT‐IR. These values comprised 70%, 84%, and 89%, respectively, of all retrogradely labeled neurons in these regions. (3) Fibers and terminals arising from the regions of each of the three adrenergic cell gruops were labeled by local injections of the anterogradely transported plant lectin PHA‐L. Each component projection was found to distribute in a very similar fashion and to mimic the overall distribution of PNMT‐IR; differential projection patterns within the PVH or SO were not seen consistently following deposits in any of the individual adrenergic cell groups or at different rostrocaudal levels of any individual cell group. (4) A dual anterograde tracing (PHA‐L)–immunohistochemical (PNMT) labeling method revealed an appreciable number of varicosities arising from the regions of C1, C2, and C3 cell groups to contain PNMT‐IR. These results suggest that adrenergic inputs to the PVH and So, while arising from distinct medullary cell groups and presumably relaying different types of sensory information, are in a position to influence similar groups of parvicellular neurosecretory and/or autonomic‐related projection neurons.