The dorsal tegmentum of the pontomesencephalic junction of the rat - Immunohistochemistry (choline acetyltransferase, tyrosine hydroxylase, substance P) and NADPH-diaphorase histochemistry in frontal and horizontal sections

37 complete frontal and horizontal series of rat brain were studied to compare the distribution of choline acetyltransferase- (ChAT), tyrosine hydroxylase- (TH), substance P- (SP), calbindin D- (Calb) and NADPH-diaphorase (NADPH-d)-positive cells within the cytoarchitectonic borders of the latero-dorsal tegmental nucleus (L-D) and its neighbourhood. We found the same distribution, number and morphology of NADPH-d-positive cells and ChAT-positive cells. Rostrally, there are no borders between NADPH-d-positive cells of L-D and NADPH-d-positive cells of the lateral part of the dorsal raphe nucleus. Only a few TK-positive cells are intermingled with ChAT/NADPH-d-positive cells at the lateral border of L-D. TH-positive cells are larger or the same size as cholinergic neurons. Locus coeruleus and its rostral part is full of TH-positive cells and their fibres run ventromedially towards L-D. Barrington's nucleus appears in double staining (ChAT and TH or NADPH-d and TH) as an empty area bordered by ChAT- or NADPH-d-positive cells of L-D and TH-positive fibres of the locus coeruleus. Some of these fibres run through the Barrington's nucleus. The shape and size of SP-positive neurons is the same as ChAT- and NADPH-d-positive neurons. SP-positive neurons are sparsely distributed in all parts of L-D, but there are only a few SP-positive cells in its medial part. About 50% of the ChAT- and NADPH-d-positive cells are also SP-positive. Results are expressed by figures in three representative frontal sections and one horizontal section through the dorsal mesopontine tegmentum.