Distribution of choline acetyltransferase-immunoreactive structures in thelamprey brain

The distribution of cholinergic neurons and fibers was studied immunohistoc hemically in the brain of two species of lampreys (Petromyzon marinus and L ampetra fluviatilis), by using an antiserum against choline acetyltransfera se (ChAT). The results obtained in both species were similar, but there app eared some interspecies differences. In the forebrain, cholinergic cells we re present in the striatum, preoptic region, paraventricular nucleus, pinea l and parapineal organs, habenula, and pretectum. The cranial nerve motoneu rons (III, IV, V, VI, VII, IX, and X), the first and second spine-occipital nerves (so), and the ventral horn of the spinal cord showed a strong ChAT immunoreactivity. Additional cholinergic neurons were observed: the mesence phalic M5 nucleus of Schober, two different cell populations in the isthmic region, the efferent component of the eighth nerve, putative preganglionic parasympathetic cells, cells in the solitary tract nucleus, and the rhombe ncephalic reticular formation. Cholinergic fibers were widely distributed i n the brain. Comparison with previous studies in other vertebrates suggests that major cholinergic pathways, like tectal innervation from the isthmic region, are also present in lampreys. Of particular interest was the promin ent projection to the neurohypophysis from cholinergic neurons in the preop tic region and paraventricular nucleus. Present data were analyzed within t he segmental paradigm, as was previously done in other vertebrates. Our res ults reveal that the organization of many cholinergic systems in the lampre y as, for example, in the striatal, preoptic, and isthmic regions, comprise s features of the anamniote brain that remain common to all living amniotes studied so far, thus being conservative to a surprisingly high degree. The refore, the distribution of ChAT-immunoreactive structures in the lamprey b rain is, in general, comparable to that previously described in other verte brate species. J. Comp. Neurol. 431:105-126, 2001. (C) zool Wiley-Liss, Inc .