Overlap in the distribution of cholinergic and catecholaminergic neurons in the upper brainstem of the ferret

Abstract

The distribution of catecholaminergic and cholinergic neurons in the upper brainstem of the ferret were mapped by staining immunohistochemically two adjacent series of sections of brainstem for tyrosine hydroxylase and choline acetyltransferase, respectively. As in other species, large numbers of tyrosine‐hydroxylase‐positive neurons are localized in the ventral tegmental area (A10), the substantia nigra (A9), and in A8. Tyrosine‐hydroxylase‐positive neurons in the dorsolateral pontine tegmentum (A4, A6, and A7‐the locus coeruleus complex) of the ferret are rather diffusely distributed, as has been observed in other carnivore species such as the cat and the dog, but unlike in the cat, these cells in the ferret display a relative uniformity in size and morphology. Choline‐acetyltransferase‐positive neurons which extend in the ferret's pedunculopontine tegmental nucleus and ventral parabrachial area (Ch5) are relatively large cells that stain intensely for choline acetyltransferase, and their dendrites form prominent bundles in regions where unstained fibre tracts are prevalent. Choline‐acetyltransferase‐positive neurons distributed in the laterodorsal tegmental nucleus (Ch6) are smaller than the cholinergic cells of Ch5, and they stain less intensely for choline acetyltransferase. Rostrally, there is little overlap between the catecholaminergic cell groups A8, A9, and A10 and the cholinergic cell groups of Ch5 and Ch6. Caudally, the Ch5 neurons extend some considerable extent into the locus coeruleus complex. In the region of overlap, no cells with staining for both tyrosine hydroxylase and choline acetyltransferase were observed, as was ascertained with a double staining method employing a combination of tyrosine hydroxylase immunofluorescence and choline acetyltransferase peroxidase‐antiperoxidase immunohistochemistry. In conclusion, the ferret has a typically carnivore pattern for the distribution of catecholaminergic cells in the upper brainstem, and there is a significant overlap between the catecholaminergic and cholinergic cell groups in the dorsolateral pontine tegmentum.