Abstract
Abstract: :
Purpose: The experimental aim was to characterize the AMPA (α–amino–3–hydroxy–5–methyl–4–isoxazole–propionic acid) and KA (kainate) receptor–mediated currents on dendrites of morphologically identified off–cone bipolar cells in the rabbit retina and to determine their differential contribution to excitatory inputs of cells. Methods: Whole–cell currents were recorded from off–cone bipolar cells in the rabbit retinal slice preparation that was superfused with a Ringer’s solution containing 2 mM Co2+ to synaptically isolate cells. Sulforhodamine B was included in recording pipettes to label cells during recordings in order to correlate the cell’s morphology with its physiology. These off–cone bipolar cells were identified based on the distinct stratification of their axon terminals within sublamina–a of the retinal inner plexiform layer. KA and S–AMPA were applied by pressure ejection through a glass pipette positioned near the cell’s dendrites; the specific AMPA antagonist SYM2206 and KA antagonist NS102 were applied in the Ringer’s solution as it bathed the retina. Results: Consistent with our previous studies off–cone bipolar cells consisted of five morphological types: CBa1–2n and CBa2n had narrow field diameter axon terminals and CBa1, CBa1–2 and CBa2 had medium–field diameter axon terminals. The application of 200 µM kainate activated inward currents under negative holding potentials and outward currents under positive holding potentials in all off–cone bipolar cells tested. Superfusion with the AMPA antagonist, SYM2206 (100 µM), completely blocked the KA– and S–AMPA– activated currents of CBa1–2n and CBa2n. However, superfusion with SMY2206 blocked a major portion of the KA–activated currents of CBa1, CBa1–2 and CBa2 and an application of NS102 at a saturating concentration eliminated the remaining current. Conclusions:The CBa1–2n and CBa2n bipolar cells most likely possess only AMPA receptors on their dendrites; whereas, the dendrites of CBa1, CBa1–2 and CBa2 appear to possess a mixture of AMPA and KA receptors.
Keywords: bipolar cells • excitatory neurotransmitters • receptors: pharmacology/physiology