Hypothalamo-neurohypophysial neurosecretory system and its vasculature in the freshwater catfish Mystus vittatus (Bloch).

The architectural pattern of the hypothalamo-neurohypophysial (HN) system of M. vittatus basically resembles that of other catfishes described earlier (Sathyanesan 1969 a, b). Some of the neurons of the nucleus preopticus of the hypophysectomised fish exhibit degeneration, whereas the viable ones were degranulated. The neurosecretory tract (NT) is in close association with the ependymal lining, both in the third ventricle and infundibular recess extending into the neurohypophysis. The pituicytes of the neurohypophysis are in close association with the NT which is of functional significance. In this species the NT entering the pituitary could be demonstrated with aldehyde fuchsin (AF), Palmgren's silver impregnation technique, alkaline and acid phosphatase and ascorbic acid tests. At least some among them may constitute separate tracts and their origin needs to be confirmed. As all those tracts pass through the infundibular base they come in direct contact among themselves as well as with the nucleus lateralis tuberis (NLT) neurons which lie on their pathway. In M. vittatus, in addition to the presence of neuro-adeno interface vasculature which is the median eminence (ME) equivalent of the teleosts, there is morphological evidence for the presence of a ME of tetrapodan type. The presence of strong alkaline and acid phosphatase and ascorbic acid activity in both the sites further supports the above view. However, additional ultrastructural evidence is needed to prove the functional status of the extra-hypophysial ME.