Hyperosmotic activation of transmitter release from presynaptic terminals onto retinal ganglion cells.
A method for evoking neurotransmitter release without light stimulation has been developed and applied to a retinal slice preparation of the tiger salamander (Ambystoma Tigrum). This method utilizes a micropipette containing hyperosmotic levels of sucrose in Ringer, positioned within the inner plexiform layer (IPL) under visual control. Intermittent pressure (between 0.1 and 2 bars) applied to the pipette evoked release of neurotransmitters which were evaluated with whole-cell recording (WCR) technique applied to cells in the ganglion cell layer. Pharmacological studies were used to characterize the properties of the hyperosmotic sucrose-evoked response (HSER) and in some cases, we compared the HSER with synaptic currents evoked by light stimulation. The HSER typically consisted of both inhibitory and excitatory components with a reversal potential in between that for chloride (approximately -60 mV) and non-specific cation channels (approximately 0 mV). Relatively pure inhibition or excitation could be revealed through pharmacological techniques by blocking the inhibition with picrotoxin/strychnine or by blocking the glutamatergic neurotransmission with D-AP7 (D-2-amino-7-phosphonoheptanoate) and NBQX (2,3-dihydroxy-6-nitro-sulfamoyl -benzo (F) quinoxaline). A comparison of light-evoked responses (LER) and the HSER suggested that they activate the same pool of releasable neurotransmitter.
Yu
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Department of Physiology, University of Minnesota, Minneapolis 55455, USA.
Miller
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D015763:2-Amino-5-phosphonovalerate / Q000031:analogs & derivatives*; D000559:Ambystomatidae; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D003292:Convulsants / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D008027:Light; D008564:Membrane Potentials / Q000187:drug effects; D018377:Neurotransmitter Agents / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009924:Organ Culture Techniques; D009997:Osmotic Pressure; D018408:Patch-Clamp Techniques; D010852:Picrotoxin / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000378:metabolism*; D011810:Quinoxalines / Q000494:pharmacology; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000502:physiology*; D013331:Strychnine / Q000494:pharmacology; D013395:Sucrose / Q000494:pharmacology
D015763:2-Amino-5-phosphonovalerate; D000596:Amino Acids; D000927:Anticonvulsants; D002104:Cadmium; D003035:Cobalt; D003292:Convulsants; D018691:Excitatory Amino Acid Antagonists; D018377:Neurotransmitter Agents; D010852:Picrotoxin; D011810:Quinoxalines; D013331:Strychnine; D013395:Sucrose; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; C031231:2-amino-7-phosphonoheptanoic acid