Hypophysiotropic Neurons in the Hypothalamus of the Catfish <i>Clarias batrachus: </i>A Cobaltous Lysine and HRP Study

Abstract

Seven hypothalamic nuclei and several isolated perikarya that send projections to the pituitary gland were identified following administration of cobaltous lysine or horseradish peroxidase (HRP) to severed hypophysial stalks of previously hypophysectomized catfish, Clarias batrachus. Retrogradely labelled neurons were identified in the nucleus preopticus periventricularis, suprachiasmatic nucleus, paraventricular and supraoptic divisions of the magnocellular nucleus preopticus (NPO) and nucleus lateralis tuberis. A few neurons in the paraventricular subdivision of the NPO, however, remained unfilled; these may project to extrahypophysial sites. Three other nuclei contributing to the innervation of the pituitary gland include the paraventricular organ, nucleus recessus lateralis (NRL) and nucleus recessus posterioris (NRP), all of which contain cerebrospinal fluid-contacting aminergic neurons. These three neuronal aggregations were retrogradely labelled with cobaltous lysine but not with HRP. Isolated neurons displaying hypophysial connections were identified in the organon vasculosum laminae terminalis area, in the nucleus hypothalamics ventromedialis, and in the vicinity of the NRL and NRP. Thus the present study reveals that hypothalamic projections to the pituitary gland of catfish have their origin in several peptidergic and aminergic nuclei and perikarya hitherto unreported.

Development of the serotoninergic system in the central nervous system of a shark, the lesser spotted dogfish Scyliorhinus canicula

“…The earliest serotoninergic fibers course along the hypothalamic floor at about the time of the appearance of hypothalamic serotoninergic cells, suggesting that cells of the paraventricular organ give rise to the serotoninergic innervation of the median eminence and neurointermediate lobe, as has been described in teleosts after application of tracer techniques (Prasada Rao et al, 1993;Holmqvist and Ekström, 1995). The late appearance of these fibers during dogfish ontogeny is probably related to late maturation of the hypophysis, as reported in teleosts (Ekström et al, 1985;McLean and Fetcho, 2004a).…”

Actual problems of the cerebrospinal fluid-contacting neurons

“…CSFcontacting neurons of this nucleus labeled retrogradely with cobaltous lysine in the catfish were found to project to the pituitary stalk (Prasada Rao et al, 1993). These observations demonstrate that the region around the posterior recess-first of all, its catecholaminergic neurons-furnish the pituitary with afferents.…”

“…These observations demonstrate that the paraventricular organ is a source of pituitary afferents in the goldfish. The CSF-contacting neurons of the paraventricular organ and nucleus recessi lateralis of the catfish, Clarias batrachus, send fibers retrogradly labeled with cobaltous lysine to the pituitary stalk (Prasada Rao et al, 1993).…”

Galanin-like immunoreactivity in the brain and pituitary of the "four-eyed" fish, Anableps anableps

“…Such GAL-ir cells were not found in any other fish species, except for the goldfish (Prasada Rao et al 1996). A direct innervation of the pituitary from NPO and NLT components has been demonstrated by immunocytochemical and tracer techniques (Fryer and Maler 1981;Fryer et al 1985;Rama Krishna and Subhedar 1989;Anglade et al 1993;Prasada Rao et al 1993). As the NPO is known to be involved in the control of hormonal regulation by the pituitary and to influence gonadal maturation in teleosts (Peter and Fryer 1983), it is likely that the NPO (which contains GAL-like peptide) is responsible for such functions in A. anableps.…”