ORGANIZATION OF THE LAMPREY STRIATUM - TRANSMITTERS AND PROJECTIONS

The purpose of the present study is to characterize the striatum of th e lamprey by immunohistochemical and tracing techniques. Cells immunor eactive for GABA and substance P (SP), and positive for acetylcholines terase, are present in the lamprey striatum. Immunoreactive (ir) fiber s were detected by antisera raised against SP, dopamine, enkephalin an d serotonin. These immunoreactive fibers were mainly located in the pe riventricular neuropil that borders the striatum and in which GABAergi c striatal neurons distributed their dendritic arbors. Putative connec tions between the striatum, the ventral part of the lateral pallium, a nd the diencephalic motor centers involved in the control of locomotio n were studied by using fluorescein-coupled dextran amines (FDA) as a tracer. The striatum projects to the ventral part of the lateral palli um (lpv), where GABA-ir cells and SP-ir fibers were also present. The lpv in turn projects to the ventral thalamus, which has descending con nections to the reticulospinal cells involved in the control of locomo tion. These results, together with previous findings of histaminergic and neurotensin projections, suggest that the lamprey striatum and its inputs with regard to neurotransmitters/modulators are very similar t o those of modern amniotes, including primates, and are thus conserved to a high degree. (C) 1997 Elsevier Science B.V.