DISTRIBUTION OF GALANIN-LIKE IMMUNOREACTIVE ELEMENTS IN THE BRAIN OF THE ADULT LAMPREY LAMPETRA-FLUVIATILIS

Galanin is a brain-gut peptide present in the central nervous system o f vertebrates and invertebrates. The distribution of galanin-like immu noreactive perikarya and fibers in the brain of the river lamprey Lamp etra fluviatilis (Agnatha) has been studied immunocytochemically by us ing antisera against rat and porcine galanin. Galanin-like immunoreact ive perikarya were seen in the telencephalon and mediobasal diencephal on. In the telencephalon, they were present in the nucleus olfactorius anterior: nucleus basalis, and especially, in the nucleus commissurae anterioris. The diencephalon contained most of the immunoreactive neu rons. They were located in the nucleus commissurae praeinfundibularis, nucleus ventralis hypothalami, nucleus commissurae postinfundibularis , nucleus ventralis thalami, and nucleus dorsalis thalami pars medius. Most of the galanin-like immunoreactive infundibular neurons showed a pical processes contacting the cerebrospinal fluid. Immunoreactive fib ers and terminals were widely distributed throughout the neuraxis. In the telencephalon, the richest galaninergic innervation was found in t he nucleus olfactorius anterior, lobus subhippocampalis, corpus striat um, and around the nucleus septi and the nucleus praeopticus. In the d iencephalon, the highest density of galanin-like immunoreactive fibers was seen in the nucleus commissurae postopticae, nucleus commissurae praeinfundibularis, nucleus ventralis hypothalami, nucleus dorsalis hy pothalami, and neurohypophysis. In the mesencephalon and rhombencephal on, the distribution of immunoreactive fibers was heterogeneous, being most pronounced in a region between the nucleus nervi oculomotorii an d the nucleus interpeduncularis mesencephali, in the nucleus isthmi, a nd in the raphe region. A subependymal plexus of immunoreactive fibers was found throughout the ventricular system. The distribution of immu noreactive neurons and fibers was similar to that of teleosts but diff erent to those of other vertebrate groups. The possible hypophysiotrop ic and neuroregulatory roles of galanin are discussed. (C) 1996 Wiley- Liss, Inc.