Figure 9.

Low-magnification photomicrographs of the fifth arcuate, or A5, nucleus, revealed with immunostaining for tyrosine hydroxylase, in (a) the southern African hedgehog (Atelerix frontalis) [19], (b) Beecroft’s scaly-tailed squirrel (Anomalurus beecrofti) [44], (c) the Cape mountain zebra (Equus zebra zebra) [pers. obs.], and (d) the lar gibbon (Hylobates lar) [58]. Note that across mammalian species this columnar nucleus appears to be invariably present and is consistently located in the same region of the brain, that being ventrolateral to the subcoeruleus, diffuse portion (A7d), and dorsolateral to the superior olivary nuclear complex (SON). Insets in each image show a high-magnification image of the neurons that form the A5 nucleus in each species. In all images, dorsal is to the top and medial to the left. Scale bars in (a–d) = 1 mm and apply to each specific image. Scale bar in inset (d) = 25 µm and applies to all insets.