A photographic perspective on the origins, form, course and relations of the acetylcholinesterase-containing fibres of the dorsal tegmental pathway in the rat brain.

The dorsal tegmental pathway in the rat brain has been studied using acetylcholinesterase (AChe) staining alone, after lesions, and combined with the horseradish-peroxidase (HRP) tracing method. This paper characterises in photographs, diagrams and text the origins, form, extent and relations of its visible AChe-staining fibres in 3 planes. This record should provide a template for further investigations. The pathway largely takes origin from ChAT-containing pedunculopontine (PPTg) and laterodorsal (LDT) nuclei; some non-cholinergic cell groups may also contribute, notably locus coeruleus (LC). It takes the form of a horizontally disposed fan which radiates from the pontomesencephalic area to the forebrain. Its lateral portion is bunched and consists mainly of cholinergic fibres whereas the cholinergic status of its fully unfurled intermediate and partly unfurled medial contingents (which mainly accompany the central tegmental tract) is more doubtful. The changing form and relations of PPTg and LDT are adumbrated including that of the microcellular nucleus (MI) to the former and of Barrington's detrusor nucleus (B) which is unstained, to the latter. Functional overlapping between non-cholinergic and cholinergic nuclei in the peribrachial region are noted and some correlations adduced.