Evidence that certain retinal bipolar cells use both glutamate and GABA

J Comp Neurol. 2004 Oct 18;478(3):207-18. doi: 10.1002/cne.20221.


Retinal bipolar neurons release the excitatory transmitter, glutamate. However, certain bipolar cells contain GABA, raising the question whether a neuron might release both transmitters and, if so, what function might the inhibitory transmitter play in a particular circuit? Here we identify a subset of cone bipolar cells in cat retina that contain glutamate, plus its vesicular transporter (VGLUT1), and GABA, plus its synthetic enzyme (GAD(65)) and its vesicular transporter (VGAT). These cells are negative for a marker of ON bipolar cells and restrict their axons to the OFF strata of the inner synaptic layer. They do not colocalize with the neurokinin 3 receptor that stains a type (or two) of OFF bipolar cells. By "targeted injection," we identified two types of OFF bipolar cell with the machinery to make and package both transmitters. One of these types costratifies with a dopamine plexus.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Carbocyanines / pharmacokinetics
  • Cats
  • Cell Count / methods
  • Dendrites / metabolism
  • Dendrites / ultrastructure
  • Glutamate Decarboxylase / metabolism
  • Glutamic Acid / metabolism*
  • Immunohistochemistry / methods
  • Isoenzymes / metabolism
  • Membrane Transport Proteins
  • Microscopy, Immunoelectron / methods
  • Neurons / classification
  • Neurons / metabolism*
  • Neurons / ultrastructure
  • Receptors, Neurokinin-3 / metabolism
  • Retina / cytology*
  • Retinal Cone Photoreceptor Cells / physiology
  • Tyrosine 3-Monooxygenase / metabolism
  • Vesicular Glutamate Transport Protein 1
  • gamma-Aminobutyric Acid / metabolism*


  • 3,3'-dihexadecylindocarbocyanine
  • Carbocyanines
  • Isoenzymes
  • Membrane Transport Proteins
  • Receptors, Neurokinin-3
  • Vesicular Glutamate Transport Protein 1
  • Glutamic Acid
  • gamma-Aminobutyric Acid
  • Tyrosine 3-Monooxygenase
  • Glutamate Decarboxylase
  • glutamate decarboxylase 2