INHIBITION IN THE NEURO-ENDOCRINE SYSTEMS 

 OF INVERTEBRATES* 



William G. Van der Kloot 

 Department of Pharmacology, New York University School of Medicine 



Our present familiarity with inhibition has come about by collecting and 

 comparing data taken from a wide range of animals. By exploiting the riches 

 of the animal kingdom, preparations have been found in which the cellular 

 events in inhibition could be studied precisely and in detail. Comparative 

 studies also give information on another level, as they have begun to show 

 the manifold ways in which animals use inhibition. 



My purpose is to point out how frequently inhibition has been used in the 

 evolution of invertebrate neuroendocrine systems. There are two objectives. 

 First, to discuss preparations which deserve further study, especially by physi- 

 cal and chemical methods. Second, to look for the pressures which led to 

 selection for inhibitory hnks in the control of endocrine function — appreci- 

 ating that we know more of the cellular details of inhibition than of its 

 biological utility. The examples will illustrate the use of seemingly conventional 

 inhibitory neurons, the existence of inhibitory hormones that are released by 

 neurosecretory cells, and the long-term inhibition of entire sections of the 

 central nervous system. At the outset, a few words of caution — perhaps of 

 conciliation— are needed. If at times my definition of inhibition seems 

 stretched beyond the usual hmits, it is the fault of the animals discussed, who 

 do unusual things. 



INHIBITION OF A PART OF THE CENTRAL 

 NERVOUS SYSTEM 



The first example is of an inhibition persisting for weeks or months that is 

 enforced by profound chemical changes in the nerve cells. For these reasons, 

 inhibition of this type can be of only limited general usefulness to animals. 

 It is worth considering, nonetheless, because it shows that nerve cells can be 

 deprived of excitability for long periods of time, during the course of a life- 

 cycle, and eventually restored to normal activity. 



The animal which shows this progression is the Cecropia silkworm. At the 



♦ The original studies reported in this paper were supported by grants from the Institute 

 of Neurological Diseases and Blindness, Public Health Service. 

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