REGULATION OF DISCHARGE RATE BY INHIBITION, 

 ESPECIALLY BY RECURRENT INHIBITION 



Ragnar Granit 



From the Nobel Institute for Neurophysiology, Karolinska Institutet, 

 Stockhohn 60, Sweden 



Problems of regulation and control in the mammalian preparation present 

 us with the inherent difficulty of how to analyze equihbria. One tries to 

 disturb them — and a chain of events is mobilized to establish a new state of 

 equilibrium. The combinations and pemiutations involved in such readjust- 

 ments are not easily disentangled. In the hope of being able to contribute 

 to the understanding of the role of inhibition in the regulation of activity of 

 the motoneurons it was decided to make a test case out of recurrent inhibition 

 whose circuit is relatively simple and has the advantage of being on the 

 efferent side and hence not subject to as many influences as is the afferent 

 side. It is not possible here to discuss the old work on antidromic inhibition 

 and the early attempts from the beginning of this century to assign a function 

 to the recurrent collaterals of Golgi. A great step forward was taken when 

 Renshaw (1946) discovered the high-frequency discharge to antidromic 

 stimulation of ventral roots in the ceUs which today we call the Renshaw 

 cells, and when Eccles et al. (1954) by different types of experiments found 

 that it paralleled the course of repolarization of the ventral horn cells that 

 was to be expected if antidromic inhibition essentially was recurrent in 

 nature. The work of Brooks and Wilson (1959) and of Wilson (1959) supports 

 the view of the Canberra group; as also does all the work they have done at 

 Canberra since 1954. We make it the basis of our approach that recurrent 

 inhibition repolarizes the motoneurons across an internuncial cell and that it 

 in this respect resembles other polysynaptic inhibitions, a parallel emphasized 

 by Eccles (1957). Most of the work to be considered below is from three 

 papers from the Nobel Institute (Granit et al, 1957, 1960; Granit and 

 Rutledge, 1960). They will be referred to as nos. 1, 2 and 3, respectively. 



In paper no. 1 the decerebrate preparation was used and antidromic 

 stimulation of a number of efferent filaments was made to influence the 

 tonic discharge of a functionally isolated cell in a thin ventral root filament. 

 This technique has been used also in papers nos. 2 and 3. To produce a 

 tonic discharge we stimulate by pull on the gastrocnemius-soleus muscle 

 or cut the nerve to this muscle and tetanize its central stump electrically at a 



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