Neurotransmitter actions on transient amacrine and ganglion cells of the turtle retina.
We obtained intracellular recordings from transient, On-Off amacrine and ganglion cells of the turtle retina. We tested the ability of neurotransmitter agonists and antagonists to modify the responses to light stimuli. The metabotropic glutamate agonist, 2-amino-phosphonobutyric acid (APB), selectively blocked On responses, whereas the amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA) receptor antagonist, GYKI, blocked both On and Off responses. Although GYKI appeared to block excitation completely, suggesting an absence of N-methyl-d-aspartate (NMDA)-mediated responses, it was found that in the presence of ionotropic gamma-aminobutyric acid (GABA) blockers, the excitatory postsynaptic potential (EPSP) was prolonged. The late component of the EPSP was blocked by the NMDA antagonist, D-2-amino-5-phosphopentanoic acid (D-AP5). Picrotoxin (PTX) and bicuculline (BCC) induced a mean hyperpolarization of -6.4 mV, suggesting a direct effect of GABA on transient amacrine and ganglion cells, since antagonism of a GABA-mediated inhibition of release of glutamate by bipolars would depolarize third-order neurons. The acetylcholine agonist, carbachol, or the nicotinic agonist, epibatidine, depolarized all On-Off neurons. This action was blocked by d-tubocurarine. Cholinergic inputs to On-Off neurons increase their excitability without altering the pattern of light responsiveness.
Vigh
Jozsef
J
Department General Zoology and Comparative Neurobiology, University of Pecs, H7601 Pecs, Hungary.
Witkovsky
Paul
P
D000109:Acetylcholine / Q000378:metabolism; D000200:Action Potentials / Q000187:drug effects; D025042:Amacrine Cells / Q000502:physiology*; D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D001569:Benzodiazepines / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000502:physiology; D016202:N-Methylaspartate / Q000502:physiology; D009474:Neurons / Q000502:physiology; D018377:Neurotransmitter Agents / Q000502:physiology*; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors; D012160:Retina / Q000166:cytology* / Q000378:metabolism*; D012165:Retinal Ganglion Cells / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014426:Turtles / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000502:physiology
D000613:Aminobutyrates; D018691:Excitatory Amino Acid Antagonists; D018377:Neurotransmitter Agents; D018091:Receptors, AMPA; C061950:GYKI 52466; D001569:Benzodiazepines; D018698:Glutamic Acid; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D016202:N-Methylaspartate; C012729:2-amino-4-phosphonobutyric acid; D000109:Acetylcholine