AFFERENTS OF THE LAMPREY STRIATUM WITH SPECIAL REFERENCE TO THE DOPAMINERGIC SYSTEM - A COMBINED TRACING AND IMMUNOHISTOCHEMICAL STUDY

The origin of afferents to the striatum in lamprey (Lampetra fluviatil is) was studied by using fluorescein-coupled dextran-amines (FDA). Inj ection of FDA into the striatum retrogradely labeled several cell popu lations in the forebrain and the rostral rhombencephalon. No retrograd e labeled cells were seen in the mesencephalon. A dopamine-specific an tiserum was used to determined the distribution of dopaminergic perika rya and fibers. Many dopamine-immunoreactive (DA-ir) fibers were prese nt throughout the brain, but the highest density of labeled fibers was in the mediobasal prosencephalon, especially in the striatum, the lat eral hypothalamic area, and the neurohypophysis. Most DA-ir cells were located in the mediobasal diencephalon (preoptic region, nucleus comm issurae postopticae, hypothalamus, and nucleus tuberculi posterioris). In the mesencephalon, only a few immunopositive cells were observed i n the tectum opticum. In the rhombencephalon, DA-ir cells were observe d in the isthmic region, dorsally to the descending trigeminal tract, and caudally to the posterior rhombencephalic reticular nucleus. The r ostralmost spinal cord received many descending DA-ir fibers from the brainstem. Along the spinal cord, DA-ir neurons were also found, some of which projected to the medioventral surface, forming a prominent pl exus. On the basis of double-labeling experiments, it is shown that th e dopaminergic input to the striatum originates from the nucleus tuber culi posterioris. Thus, the striatum receives inputs from different st ructures, including a strong dopaminergic innervation from the diencep halon. Much of the dopaminergic system in Lampetra fluviatilis is basi cally similar to that seen in some teleosts, but it presents differenc es with other anamniote (elasmobranch) as well as amniote groups. (C) 1997 Wiley-Liss, Inc.