ACTIVITY OF HYPOTHALAMO-NEUROHYPOPHYSIAL COMPLEX OF EUROPEAN EEL (ANGUILLA ANGUILLA L) ASSESSED BY USE OF AN IN SITU STAINING TECHNIQUE AND BY AUTORADIOGRAPHY

Activity of the hypothalamo-neurohypophysial complex of Anguilla anguilla L., acclimatised to different environmental conditions and after sudden changes of environment, has been investigated by the use of an in situ staining technique for neurosecretion and by autoradiography. Changes in background colour from black to white and vice versa; from darkness to black or white; from black or white to darkness; electric fishing with and without subsequent transportation, and cold temperature shock all resulted in a change, usually a decrease, in stainability of all or part of the complex within 4 hr, whereas a change from fresh to seawater and vice versa; intraperitoneal, or subarachnoid injections of NaCl or distilled water, overcrowding and transportation had no effect on stainability of the complex, though the injection experiments were short-term (1-3 hr). Changes in background colouration had no effect on the amount of stainable neurosecretion in the pre-optic nucleus or tracts of hypophysectomised eels. Preliminary experiments using autoradiography, after administration of 35S-cysteine or 14C-serine, indicated that the complex may be more active in eels acclimatised to freshwater, or transferred from seawater to freshwater, than in those acclimatised to seawater. The techniques and results are critically assessed and it is concluded inter alia that most stressful situations cause a rapid initial depletion of stainability of the complex though normal levels are restored within 24 hr. © 1969.