Structure of hypothalamic nuclei, the nucleus lateralis tuberis (NLT) and its seasonal changes in relation to ovarian cycle of Labeo rohita

Abstract

Structure and round the year changes in the morphohistology and cytology of
hypothalamic nuclei, the nucleus lateralis tuberis (NLT) were studied in relation
to ovarian cycle of a freshwater carp (Labeo rohita Ham.). The NLT neurons are
paired situated above the pituitary in the lateral and lateroventral wall of the
hypothalamus. These are of two types, the larger a-cells generally placed on the
ventrolateral side of the hypothalamus and the smaller P-cells forming ventromedian
component at the opening of the hypophysis. Both a and P cells pass
through seasonal cyclical changes corresponding to the ovarian cycle of the fish.
During pre-spawning phase of the gonad (February through May), these cells
significantly increase activities in terms of cell size, number and neurosecretory
material concentration reaching peaks during active spawning period (June and
July), followed by sharply loosing activities at the post-spawning period (September
to October) when they get hypotrophied possessing depleted
neurosecretary material (nsm). Thereafter, these neurons remain inactive except
for the increase in number during resting phase of gonad (November to January).