Purchase this article with an account.
S. Deniz, S. A. Picaud, D. Hicks, M. J. Roux; Gaba Evokes Gaba-b-Dependent but No Gaba-a/c Currents in the Cones of the Diurnal Nile Rat Arvicanthis Ansorgei . Invest. Ophthalmol. Vis. Sci. 2010;51(13):3288.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The information processing at the first retinal synapse, involving horizontal cell modulation of cone activity, is not fully understood. Different hypothesis have been but forward, from a conventional transmission targeting ionotropic GABA receptors on cone terminals, to unusual modulations of cone calcium channels through pH changes in the synaptic cleft or ephaptic interactions. As classical rodent models are nocturnal species with few cones, we have examined the GABA-evoked currents in cones from the cone-rich retina of the diurnal nile rat, Arvicanthis ansorgei
Retina slices were prepared from adult Arvicanthis ansorgei. Cones cell bodies were identified through their localization in the outer rows of the outer nuclear layers and their shape, larger and more oval than those of rods. Whole-cell voltage clamp recordings were obtained from cones. Agonists were applied locally through a puff pipette placed in the vicinity of the cone synaptic terminal, while antagonists were bath applied.
At -70 mV, local GABA application (100 µM, 100 ms) evoked an inward current in Arvicanthis cones, whether the intracellular solution set ECl to 0 or -70 mV. When the holding potential was changed between -120 and +20 mV, the current did not reverse, and changed non linearly, with a larger amplitude around -50 mV. The evoked current was not blocked by GABA-A and/or C antagonists bicuculline methiodide (100 µM), TPMPA (50 µM) or picrotoxin (100 µM). No current was evoked by the application of the GABA-A agonist isoguvacine (100 µM), but the application of 100 µM baclofen, a GABA-B agonist, evoked currents similar to those evoked by GABA.
In contrast to what was observed in the mouse retina, Arvicanthis cones do not seem to express functional ionotropic GABA receptors. GABA modulates their activity through GABA-B receptors, which are most probably presynaptic. Our results suggest that GABA transmission in the outer plexiform layers differs between rodents.
This PDF is available to Subscribers Only