Immunocytochemical evidence for hypophysial projections of the cells of the nucleus lateralis tuberis pars lateralis in the rainbow trout (Salmo gairdneri).

In the rainbow trout the pars lateralis is the most prominent part of the nucleus lateralis tuberis (NLT). To demonstrate a morphological relationship between this lateral part of the NLT and the pituitary, immunocytochemistry was applied as a staining method. Experiments were carried out on glutaraldehyde-picric acid-acetic acid-fixed brain sections of mature male and female rainbow trout using the peroxidase-anti-peroxidase immune technique with an antiserum against 27-S-methylglucagon as the first antibody. Most of the cells in the NLT/pars lateralis reacted with the antiserum. Axons from these cells enter the pituitary, extending exclusively in the numerous neurohypophysial digitations in the pars intermedia. No immunoreactive neurohypophysial protrusions were found in those parts of the adenohypophysis where the gonadotropic cells are located, indicating that the lateral part of the NLT is not directly involved in the control of gonadotropin secretion. In addition to cells of the NLT/pars lateralis only prolactin cells in the rostral pars distalis of the adenohypophysis reacted with the antiserum used.