DISTRIBUTION OF CATECHOLAMINE-SYNTHESIZING ENZYMES IN GOLDFISH BRAINS - PRESUMPTIVE DOPAMINE AND NOREPINEPHRINE NEURONAL ORGANIZATION

The organization of presumptive dopamine- and norepinephrine-synthesizing neurons in the brains of goldfish is described by using antibodies to tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH) with avidin-biotin immunocytochemical techniques. In the hindbrain, TH-immunoreactive (IR) and DBH-IR cell bodies are located together in the following three regions: (1) dorsomedial medulla in the postobecular region, (2) medullary tegmentum from the level of the greatest expansion of the vagal lobes to the medullospinal transition, and (3) isthmal tegmentum dorsolateral to the medial longitudinal fasciculus. Elsewhere in the brain, TH-IR neurons were visualized in eight distinct forebrain neuronal groups; DBH-IR cell bodies were not observed. Fibers and terminals IR for TH and DBH were most dense in forebrain periventricular regions, i.e. adjacent to the third ventricle, and specifically around the lateral and preoptic recesses. In the telencephalon, a dense innervation of TH- and DBH-IR fibers was noted within the area dorsalis, pars lateralis and pars dorsalis. Within the area dorsalis, pars centralis TH-IR fibers were dense; DBH-IR fibers were not visualized in this region. The presence of both dopamine- and norepinephrine-synthesizing neurons in the isthmal and medullary tegmentum and in the dorsomedial medulla provides evidence indicating that these regions are homologous to the locus ceruleus, medullary reticular nucleus and area postrema, respectively, in tetrapod brains. In addition, the remarkably dense innervation of TH-IR and DBH-IR fibers and terminals in periventricular regions of the hypothalamus and within the telencephalon suggests that there are potential similarities in the catecholaminergic innervation of forebrain regions of teleost and mammalian brains.