LACTATE DEHYDROGENASE IN THE RETINA OF THE GUPPY 1 771 



prépondérance of enzyme activity, as well as of E-isozyme activity, in the photo- 

 receptor layer (figs. 17 and 18). When viewed with oil immersion, it can be readily 



I seen that the formazan deposits of sections treated both with and without in- 

 hibitor, are located predominantly in the outer and inner segments of ail three 

 types of cônes. It can be further observed that the outer segments of the rods 

 contain pink stain in the inner, and blue granules in the outer half. Parallel expe- 

 riments with 1) acétone extraction previous to incubation and 2) without lactate 

 in the incubation mixture, again suggests that the blue droplets represent for- 

 mazan absorbed by lipid material and that the pink stain is due to " nothing 

 dehydrogenase ". Thus, the results indicate that the differentiated eye (stage 7) 

 of Lebistes has the same LDH and E-isozyme distribution as the adult eye. 



The E-isozyme bands on starch gel, and the E-isozyme distribution shown by 

 kryostat sections, once established (stage 7), do not change during the remaining 



i embryonic, post-embryonic and growth phases. The only noticeable différence 

 is seen in the generally weaker expression of the E-isozymes in the embryonic 

 phase. 



Discussion 



The distribution of LDH has been studied in the eye of the rabbit and the 

 monkey (Graymore and Kissun, 1969; Lowry et al, 1956). In the rabbit, the 

 photoreceptors stain up very weakly, or not at ail, whereas the inner layers 

 exhibit more LDH activity. In the inner layers of monkey retina, there is less LDH 

 activity than in rabbit retina (fig. 19). Lowry et al. explain this by the différence 

 in blood supply in the two species: the monkey has two sets of vessels, i.e. one in 

 J the choroid and another one on the inner surface of the retina. The latter sends 

 • capillaries as far as the inner nuclear layer. In the rabbit, however, this inner set 

 of vessels is missing over most of the retina. The authors assume that a glycolytic 

 metabolism (LDH) might therefore be required for the inner layers in the rabbit. 

 The blood supply to the eye of Lebistes is furnished almost exclusively by the 

 choroid vessels. There can be seen a few capillaries along the inner surface of the 

 retina, but they do not penetrate it. This condition resembles that of the rabbit 

 eye. However, the LDH activity is most intense in the outer régions of the Lebistes 

 eye, that is, nearest to the choroid blood supply. 



The différence between the LDH activity of rabbit and monkey photo- 

 receptors, reported by Lowry et al. (1956), is difficult to interpret. The rabbit has 

 only rods in the retina, whereas in the monkey it is made up of both rods and 

 cônes; yet they were not analyzed separately. Thus, the fact that LDH activity 

 is higher in the photoreceptors of the monkey may suggest that in mammals 

 LDH is présent predominantly in the cônes, as is the case in Lebistes. 



