On the Suggested Ionoregulatory Role of the Teleost Caudal Neurosecretory System.

Abstract

Summary Urophysectomized Tilapia mossambica showed no significant difference in ability to handle a salt load, nor in serum sodium or calcium levels, nor in hematocrit values. Urophysectomized Fundulus kansae revealed no significant difference in serum or urine sodium levels, nor in urine flow. These negative results raise questions concerning the putative ionoregulatory role of the caudal neurosecretory system in fishes. Note added in proof: Fridberg and Nishioka at Berkeley have begun an examination of the terminal spinal cord region in the long-term "depedunculated" (urophysectomized) Tilapia. Ordinary histologic preparations reveal the re-formation of recognizable caudal neurohemal areas, mostly within the tissue of the spinal cord. Electronmicroscope observations indicate reorganization of the normal relationship between caudal neurosecretory axons and capillaries. Accordingly, the possibility must be admitted that urophysial function is restored in Tilapia kept for long periods after urophysectomy, and the negative data obtained should be reviewed in this context. The unexpected regenerative ability of the caudal system is now under intensive study.