Quantitative Evaluation of Synaptophysin‐Like Immunoreactive Nerve Terminals or Varicosities in Anterior Pituitary of Normal and Adrenalectomized Rats

Abstract

Our previous studies have demonstrated the presence of substantial amounts of peptidergic nerve ®bres in the anterior pituitary of monkeys, dogs and rats. The nerve ®bres increase in number following adrenalectomy and ovariectomy. Furthermore, typical synapses between nerve ®bres and anterior pituitary glandular cells have been demonstrated in the dog and rat, strongly suggesting the existence of some direct neural regulation. However, it is dif®cult to evaluate the functional importance of synapses or nerve terminals 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. Nerve terminals or varicosities were identi®ed by their synaptophysin (SYN)-like 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 under the electron microscope to be localized in the nerve terminals or varicosities. Synapse-like contracts between the nerve terminals or varicosities and the glandular cells could be identi®ed. The number of SYN-like immunoreactive nerve terminals or varicosities was then counted under the light microscope. There were as many as 12424.2t2941.5 and 20700.4t6128 (meantSD) nerve terminals or varicosities per anterior pituitary of normal and adrenalectomized rats, respectively. The increase in number following adrenalectomy was statistically signi®cant. It is concluded that nerve ®bres may play an important role in the regulation of the anterior pituitary.

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