INHIBITORY INTERACTION IN THE RETINA 



245 



Fig. 2. Silver-impregnated section of Liniuliis compound eye. Unstained eccentric 

 cells (£■); pigment shrouded retinular cells {R); rhabdom (/-); distal process 

 (D.P.); retinular cell axons (R. ax.); eccentric cell axons {E. ax.); axonal branches 

 (B); neuropile (N); blood vessel ih.v.). 



(Inset) — Osmium-fixed ommatidium in cross-section. Eccentric cell (E). The 

 border of a retinular cell (R) is indicated by a white line. (From RatlifT, 1961). 



effects exerted on it by neighboring ommatidia. It is reasonable to suppose 

 that the inhibitory interaction is mediated synaptically in the knots of neuro- 

 pile that are located within the plexus. 



Inhibition of a receptor unit by the activity of its neighbors is illustrated in 

 Fig. 6. In the experiment from which this record was obtained a single fiber 

 was dissected from the optic nerve and the ommatidium from which this fiber 

 originated was located and illuminated by a small spot of light confined to 

 its facet. After allowing a few seconds for the discharge to subside to its 

 steady level, a region of the eye near this "test" receptor was illuminated as 

 indicated by the signal above the time marks. This stimulation of the nearby 

 ommatidia produced a marked slowing of the discharge of the test receptor, 

 persisting as long as the neighboring elements were illuminated. When the 

 illumination on them was turned off, the discharge of the test receptor rose 

 again to its original value, with a very slight, but distinct, overshoot. There 

 was a slight delay in the onset of the inhibitory action which can be attributed. 



