title: Inner plexiform circuits in the carp retina: effects of cholinergic agonists, GABA, and substance P on the ganglion cells.
abstract: Th effects on ganglion cell light responses and spontaneous activity of neurotransmitter candidates, applied by nebulizer spray and iontophoresis, were studied in the isolated carp retina. ACh, GABA, and substance P had strong effects on the ganglion cells; dopamine and the amino acids aspartate, glutamate, and glycine and only weak effects. ACh and substance P exerted their actions even when synaptic transmission was blocked by cobalt chloride, suggesting postsynaptic receptors for those agents on the ganglion cell membrane. The 3 amino acids and dopamine do not appear to act directly on the ganglion cells. The pharmacological sensitivity of ganglion cells was correlated with their physiological response type. About three-quarters of ON/OFF and half of other transiently responding ganglion cells were excited by micromolar concentrations of cholinergic agonists; most ON-center sustained ganglion cells were insensitive. The light response of some of the ACh-sensitive cells could be suppressed by cholinergic antagonists. Substance P generally excited ganglion cells with an ON-component in their light response. GABA inhibited cells of all response types, but affected least the OFF-center tonic cells. In view of these observations, and of corroborating histological evidence, we propose that ACh, GABA, and substance P are neurotransmitters that are released by amacrine cells and affect receptors located on ganglion cells.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D002347:Carps; D004298:Dopamine / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology; D018698:Glutamic Acid; D005998:Glycine / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D010277:Parasympathomimetics / Q000494:pharmacology*; D010775:Photic Stimulation; D012160:Retina / Q000166:cytology / Q000502:physiology*; D013373:Substance P / Q000494:pharmacology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D005971:Glutamates; D018377:Neurotransmitter Agents; D010277:Parasympathomimetics; D001224:Aspartic Acid; D013373:Substance P; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D000109:Acetylcholine; D005998:Glycine; D004298:Dopamine