Connections of the ventral telencephalon and tyrosine hydroxylase distribution in the zebrafish brain (Danio rerio) lead to identification of an ascending dopaminergic system in a teleost.

We studied the connections and catecholaminergic organization of the subpallium in the zebrafish, in particular to demonstrate the origin of the ascending dopaminergic system of teleosts, by using the tracers DiI or biocytin in combination with tyrosine hydroxylase (TH) immunohistochemistry. Retrogradely labeled cells were found in the olfactory bulb, the area dorsalis telencephali, the preoptic region, the dorsal and ventral thalamus, the posterior tubercle, the preglomerular region, and the medulla oblongata. Moreover, the zebrafish subpallium has strong reciprocal connections with the tuberal hypothalamus. Double-labeled cells (for TH and tracer) were identified in two locations of the rostral posterior tubercle: small round neurons in its periventricular nucleus and large pear-shaped cells adjacent to it. These double-labeled cells of the posterior tubercle presumably represent the teleostean dopaminergic system ascending to the striatum.