Tetrapodlike features of the hypothalamohypophysial vascularization in the air-breathing teleost, Heteropneustes fossilis (Bl.)

Abstract

In Heteropneustes fossilis the midventral floor of the hypothalamus is the site of the formation of median neurosecretory tracts and the uniting place of the median and the main tracts. Hence this area has a close network of neurosecretory axons, and at least some of them seem to terminate in this region. It is also the site of formation of the capillary plexus, which is in close contact with the neurosecretory axons. Thus, it is comparable to the median eminence of the tetrapods. Blood from the primary capillary plexus is conducted into the pituitary by portal vessels, which largely irrigate both pars distalis and pars intermedia. Some of them, along with the direct branches of the median hypophysial arteries, contribute to the formation of the interface vascular plexus lying in between the rostral neurohypophysis and pars distalis. From the interface vascular plexus also, blood vessels penetrate into the glandular pituitary. Thus the rostral neurohypophysis also functions as a median eminence.