Quantitative evaluation of synaptophysin-like immunoreactive nerve terminals or varicosities in anterior pituitary of normal and adrenalectomized rats

Our previous studies have demonstrated the presence of substantial amounts of peptidergic nerve fibres in the anterior pituitary of monkeys, dogs and rats. The nerve fibres increase in number following adrenalectomy and ovari ectomy. Furthermore, typical synapses between nerve fibres and anterior pit uitary glandular cells have been demonstrated in the dog and rat, strongly suggesting the existence of some direct neural regulation. However, it is d ifficult to evaluate the functional importance of synapses or nerve termina ls in general, unless quantitative data can be provided. The present study therefore aimed to quantify the number of terminals or varicosities in the anterior pituitary of the rat and its changes following adrenalectomy. Nerv e terminals or varicosities were identified by their synaptophysin (SYN)-li ke immunoreactivity. Under the light microscope, SYN-like immunoreactivity appeared mainly as dots, mostly among glandular cells, and some were found distributed along blood vessels. SYN-like immunoreactive dots were found un der the electron microscope to be localized in the nerve terminals or varic osities. Synapse-like contracts between the nerve terminals or varicosities and the glandular cells could be identified. The number of SYN-like immuno reactive nerve terminals or varicosities was then counted under the light m icroscope. There were as many as 12424.2 +/- 2941.5 and 20700.4 +/- 6128 (m ean +/- SD) nerve terminals or varicosities per anterior pituitary of norma l and adrenalectomized rats, respectively. The increase in number following adrenalectomy was statistically significant. It is concluded that nerve fi bres may play an important role in the regulation of the anterior pituitary .