72 



VISION 



Table 5. S-potentials in elasmobranchs. 



Animal 



Peak 



sensitivity 

 (nm) 



Response 

 type 



Reference 



Heterodontus 

 japonic us 



494 



Mustelus manazo 494 



Tamuraetal. (1966) 

 Tamura and Niwa (1967) 



Niwa and Tamura (1975) 



Bipolar Cell Potentials— Bipolar cells are neurons that transmit signals 

 from the photoreceptor cells vertically to the amacrine and ganglion cells. 

 Kaneko (1971) was the first to successfully record from elasmobranch 

 bipolar cells. Using the dogfish Mustelus, he found that bipolar cells 

 exhibited resting potentials of —30 to —40 mV. Photic stimuli evoked a 

 two-phase depolarizing response: the first, a transient depolarization, was 

 followed by a smaller phase of maintained depolarization. Hyperpolarizing 

 responses such as those recorded in other vertebrates (Werblin and Dowling 

 1969) were not reported by Kaneko. 



Similar results were given by Ashmore and Falk (1976) from the bipolars 

 of Raja and Scyliorhinus. Resting potentials of —45 to —60 mV were found 

 with a maximum response to light of 20 mV from the resting potential, i.e., 

 —65 to —85 mV. Responses to centered spots of light consisted of a tran- 

 sient depolarization followed by a sustained depolarization maintained for 

 the duration of stimulation (Figure 19). Again, hyperpolarizing responses 

 were not found. 



Receptive field centers in the dark-adapted preparation were on the order 

 of 150 jum with only a barely detectable antagonistic effect in response to 

 illumination in the periphery. 



To our knowledge, there have been no recordings from elasmobranch 

 amacrine cells. 



