title: Retinal input to efferent target amacrine cells in the avian retina.
abstract: The bird visual system includes a substantial projection, of unknown function, from a midbrain nucleus to the contralateral retina. Every centrifugal, or efferent, neuron originating in the midbrain nucleus makes synaptic contact with the soma of a single unique amacrine cell, the target cell (TC). By labeling efferent neurons in the midbrain, we have been able to identify their terminals in retinal slices and make patch-clamp recordings from TCs. TCs generate Na+-based action potentials (APs) triggered by spontaneous EPSPs originating from multiple classes of presynaptic neurons. Exogenously applied glutamate elicited inward currents having the mixed pharmacology of NMDA, kainate, and inward rectifying AMPA receptors. Exogenously applied GABA elicited currents entirely suppressed by GABAzine and therefore mediated by GABAA receptors. Immunohistochemistry showed the vesicular glutamate transporter, vGluT2, to be present in the characteristic synaptic boutons of efferent terminals, whereas the GABA synthetic enzyme, GAD, was present in much smaller processes of intrinsic retinal neurons. Extracellular recording showed that exogenously applied GABA was directly excitatory to TCs and, consistent with this, NKCC, the Cl- transporter often associated with excitatory GABAergic synapses, was identified in TCs by antibody staining. The presence of excitatory retinal input to TCs implies that TCs are not merely slaves to their midbrain input; instead, their output reflects local retinal activity and descending input from the midbrain.
authors.affiliation: Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, California 95616, USA.
authors.forename: Sarah H
authors.initials: SH
authors.lastname: Lindstrom
authors.forename: Nason
authors.initials: N
authors.lastname: Azizi
authors.forename: Cynthia
authors.initials: C
authors.lastname: Weller
authors.forename: Martin
authors.initials: M
authors.lastname: Wilson
mesh_terms: D000200:Action Potentials; D025042:Amacrine Cells / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002645:Chickens / Q000033:anatomy & histology*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018682:GABA Agents / Q000494:pharmacology; D005968:Glutamate Decarboxylase / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology; D066298:In Vitro Techniques; D007546:Isoquinolines / Q000378:metabolism; D007608:Kainic Acid / Q000494:pharmacology; D008636:Mesencephalon / Q000166:cytology; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018722:Nicotinic Agonists / Q000494:pharmacology; D010320:Parvalbumins / Q000378:metabolism; D018408:Patch-Clamp Techniques / Q000379:methods; D017981:Receptors, Neurotransmitter / Q000378:metabolism; D012160:Retina / Q000166:cytology*; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D064506:Solute Carrier Family 12, Member 2; D050599:Vesicular Glutamate Transport Protein 2 / Q000378:metabolism; D014795:Visual Pathways / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018682:GABA Agents; D007546:Isoquinolines; D018722:Nicotinic Agonists; D010320:Parvalbumins; D017981:Receptors, Neurotransmitter; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D050599:Vesicular Glutamate Transport Protein 2; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D016202:N-Methylaspartate; C017475:lucifer yellow; D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2; D007608:Kainic Acid