Brainstem projections to the medial preoptic region containing the luteinizing hormone-releasing hormone perikarya in the rat. An immunohistochemical and retrograde transport study.

The afferent projections to the anterior medial preoptic area (MPA) from the brainstem have been studied, in female Wistar rats, by retrograde tracing with horseradish peroxidase (HRP). The HRP was injected by iontophoresis into the preoptic region containing the luteinizing hormone-releasing hormone (LHRH) perikarya. The brain sections including the MPA were reacted with diaminobenzidine (DAB) to reveal the injection site; the LHRH cells were then immunohistochemically identified using DAB with ammonium nickel sulphate. When the injection site incorporated the LHRH cells, the brainstem sections were reacted with the DAB nickel solution to detect lysosomal HRP and then immunohistochemically processed to locate the adrenaline-synthesizing cells using DAB alone. The results confirm the brainstem projections to the MPA from the central grey matter, ventral tegmental area, subcoeruleus area, the dorsal raphe nucleus, the lateral parabrachial nucleus, the raphe pontis nucleus, the raphe obscurus nucleus, the region of the paragigantocellular nucleus and the nucleus of the solitary tract. Given the considerable evidence implicating the ascending adrenergic systems in the regulation of LHRH, we focused our attention on the afferents from the locus coeruleus, area postrema and the adrenaline-synthesizing cell groups (C1-3). The only cells which were retrogradely labelled and immunopositive for phenylethanolamine N-methyltransferase were found in C3.