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 fluviatilis) was studied by using fluorescein-coupled dextran-amines (FDA). Injection of FDA into the striatum retrogradely labeled several cell populations in the forebrain and the rostral rhombencephalon. No retrograde labeled cells were seen in the mesencephalon. A dopamine-specific antiserum was used to determined the distribution of dopaminergic perikarya and fibers. Many dopamine-immunoreactive (DA-ir) fibers were present throughout the brain, but the highest density of labeled fibers was in the mediobasal prosencephalon, especially in the striatum, the lateral hypothalamic area, and the neurohypophysis. Most DA-ir cells were located in the mediobasal diencephalon (preoptic region, nucleus commissurae postopticae, hypothalamus, and nucleus tuberculi posterioris). In the mesencephalon, only a few immunopositive cells were observed in the tectum opticum. In the rhombencephalon, DA-ir cells were observed in the isthmic region, dorsally to the descending trigeminal tract, and caudally to the posterior rhombencephalic reticular nucleus. The rostralmost 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 plexus. On the basis of double-labeling experiments, it is shown that the dopaminergic input to the striatum originates from the nucleus tuberculi posterioris. Thus, the striatum receives inputs from different structures, including a strong dopaminergic innervation from the diencephalon. Much of the dopaminergic system in Lampetra fluviatilis is basically similar to that seen in some teleosts, but it presents differences with other anamniote (elasmobranch) as well as amniote groups.