The call for some shift of focus was in no way a repudiation of the 

 value of anatomical and behavioral studies. Certainly the ultimate test 

 of insights is in their applicability to understanding the behavior of 

 intact animals in their normal environments. However, the major shift 

 indicated at this time was toward more molecular and cellular levels of 

 investigation. 



During the 1960's and 1970' s, modern electrophysiological methods have 

 been applied to analyzing the chemical senses of various elasmobranchs. 

 The first breakthrough came with the recordings of electrical activities 

 of masses of cells in various parts of the shark's brain — the electro- 

 encephalograph (EEG) — which provided a picture of the functions of 

 various surface areas of the brain (Gilbert, Hodgson, and Mathewson, 1964). 

 It was found that variations in EEG patterns could be correlated with 

 chemical stimulation and with behavior patterns of lemon sharks ( Negaprion) , 

 nurse sharks ( Ginglymo stoma ) and bonnet sharks ( Sphyrna tiburo ) . In some 

 of these studies chronically implanted brian electrodes were used, and 

 responses of sharks to pure chemicals were tested in a hydrodynamic tunnel 

 (Hodgson, Mathewson and Gilbert, 1967). 



Very recently, electrophysiological recordings have been made from 

 the olfactory tracts of hammerhead sharks exposed to chemical stimuli. 

 This was done by a student at the University of Hawaii (A. L. Tester, 

 personal communication) . 



Amino acids, short-chain tertiary amines, and purified hemoglobin 

 (human and bovine) have been found especially effective in altering EEG 

 patterns, and in eliciting typical orientation behavior — either klino- 

 taxis or rheotaxis — in lemon and nurse sharks (Hodgson and Mathewson, 

 1971) . Results similar to those obtained under controlled laboratory 

 conditions have been observed with open-sea tests using these purified 

 chemicals, making observations by a remotely-controlled underwater tele- 

 vision camera, (R.F. Mathewson and E.S. Hodgson, personal communication). 



The linking of electrophysiological analysis with field studies of 

 behavior, and the limitation of stimulation to single pure chemical stimuli, 

 bring the study of shark chemical senses to a new level of sophistication 

 and usefulness. Laboratory EEG analysis has good predictive value for 

 behavior of sharks in open sea. Furthermore, the use of single pure chem- 

 icals gives access to future studies on exact chemical mechanisms of 

 stimulation. We can now ask a whole series of new questions about olfaction 

 and taste in sharks: 



1) What is the mechanism of interaction between a chemical 

 stimulant and the receptor cell membrane? 



2) Once more is known about that, it would be possible to 

 investigate specific blocking agents of anti-metabolites 

 which might interfere with these specific processes. In 

 other words, how might the specific mechanism of stimulation 

 be modified, and possibly controlled? 



3) How can we get single cell, or few-fiber experimental prepar- 

 ations, to reveal the action potentials which must certainly 

 be involved in stimulation by chemicals? Additional studies 

 of the ultrastructnre of olfactory nerves, and taste 



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