Uthors suggest that the 'primary rod pathway' is accountable for response generation at lower stimulus

Uthors suggest that the “primary rod pathway” is accountable for response generation at lower stimulus intensities ( 1 Rh/rod/s), but a direct excitatory input from rods to cone OFF bipolar cells mediated via ionotropic glutamate receptors (“tertiary rod pathway’) is involved in OFF response generation at higher stimulus intensities ( 10 Rh/rod/s). The authors clarify the enhanced OFF 545395-94-6 Description responses at greater intensities after APB therapy as getting due to a reduction on the inhibitory glycinergic input from AII amacrine cells to cone OFF BCs. An enhancement of the APB-resistant OFF responses, obtained with higher stimulus intensity (350 Rh/rod/s) in situations of dark adaptation has also been seen by Yang et al. [104]. The authors have found that strychnine partially blocks APB-induced increments of GC OFF responses, consistent together with the notion that glycine mediates the inhibition from rod ON BCs to cone OFF BCs and OFF GCs. The authors suggest that APB-resistant OFF responses most likely originate in the “secondary rod pathway”, because “in mouse retinas the tertiary pathway is rare”. Constant with this suggestion would be the final results of Wang [158], who has located variations in the time traits on the OFF responses originating from APB-sensitive vs. APB-insensitive pathways. The OFF responses with the APBinsensitive pathway have drastically shorter latency and are capable of following substantially larger stimulus frequencies, that is a characteristic sign of cone responses. The author concluded that “APB sensitive and insensitive rod 9000-92-4 Cancer pathways can convey unique types of details signaling light decrements inside the dark-adapted retina”. In contrast for the above cited final results [103, 104], other authors reported that APB decreases [159] or does not alter [160] the ganglion cell OFF responses at higher stimulus intensities in dark adapted mouse retina. Volgyi et al. [160] describe 3 physiological groups of rod-driven OFF GCs: highsensitivity, intermediate-sensitivity and low-intermediatesensitivity. APB eliminates the light responses only from the high-sensitivity OFF cells, although it has no effects on the responses in the other groups. The authors propose that the responses of high-sensitivity OFF GCs are mediated mainly by the “primary rod pathway”, the responses of intermediate-sensitivity OFF GCs originate mostly in “secondary rod pathway”, though the low-intermediatesensitivity cells acquire rod signals via “tertiary rod pathway”. The latter cells survive in the Cx36 KO mouse retina, where the gap junctions between neighbouring AII cells and amongst rods and cones are disrupted and as a result each the “primary” and “secondary” rod pathways are eliminated. Volgyi et al. [160] have identified that some OFF GCs receive mixed input from main and secondary pathways, other cells get mixed input from primary and tertiary pathways, but OFF cells by no means get convergent inputs from all 3 pathways. Summary. It appears that the scotopic OFF responses of mammalian ganglion cells are due completely to input from the ON channel inside the lowest intensity range (exactly where they may be mediated by “primary” rod pathway). Nonetheless, the nature of518 Existing Neuropharmacology, 2014, Vol. 12, No.Elka Popovainteractions in between the ON and OFF pathways at ganglion cell level remains largely unsolved in the higher scotopic variety, where the responses are mediated by “secondary” and “tertiary” rod pathways. Some data indicate that the ON channel inhibits the activity.