In the brain of Blennius incognitus the distribution of biogenic amines was investigated by means of formaldehyde-induced fluorescence (FIF). The telencephalon of Blennius is devoid of fluorescent perikarya. Fluorescent telencephalic fibers and terminals contain either dopamine (DA), noradrenaline (NA), or an indolamine. Two diencephalic nuclei display fluorescent perikarya, the nucleus recessus lateralis and the nucleus recessus posterioris; both nuclear regions contain DA. Only occasionally single green-fluorescent perikarya are found within the ependymal lining of the caudal portion of the recessus lateralis. Four fluorescent nuclei, two catecholamine-containing nuclei and one indolamine-containing nucleus, are present in the tegmentum of the midbrain and in the medulla oblongata. Three of these nuclei, N1 and N3, consist of large, green-fluorescent neurons, which apparently contain NA. N2, located medial to the nucleus isthmi, is formed by several clusters of small neurons, which show a yellow indolamine fluorescence. Caudal to the calamus scriptorius another green-fluorescent nucleus (N4) is visible.
