Tyrosine hydroxylase-like immunoreactivity in the brain of the teleost fish Tinca tinca

The distribution of tyrosine hydroxylase-like immunoreactivity has been studied in the central nervous system of the tench (Tinca tinca) using a monoclonal antibody and the avidin-biotin-immunoperoxidase technique. Immunoreactive elements were found in all brain subdivisions. Thus, catecholaminergic neurons and fibers were detected in most nuclei of the ventral telencephalon and in the pars centralis and lateralis of the dorsal telencephalon. The diencephalon was the brain subdivision where largest density of immunoreactive elements were found, mainly located in the periventricular region. The mesencephalon and metencephalon only demonstrated immunoreactive fibers, and no immunoreactive cell bodies were observed in these regions. The myelencephalon showed three groups of immunoreactive neurons located at isthmal level, in the central medullary area, and at the medullary-spinal cord transition area. The distribution of catecholaminergic elements in the tench brain revealed a general pattern shared by most teleosts. The number and distribution of catecholaminergic elements was similar to those described in other teleostean species in the caudal region of the brain. However, noticeable differences were found in areas related to the integration of different sensory information, specially in the telencephalon and diencephalon, suggesting a relationship among the functional level of each sensorial system and the complexity of the catecholaminergic innervation of their integration regions. Additionally, this study revealed the presence of an important number of cerebrospinal fluid-contacting cells in the organum paraventricularis expressing tyrosine hydroxylase that in most investigated teleostean species were tyrosine hydroxylase-immunonegative despite they contained catecholamines. This data argues for distinct evolutionary patterns in the hypothalamic catecholaminergic system among different teleostean species.