I. Hack et al., An alternative pathway for rod signals in the rodent retina: Rod photoreceptors, cone bipolar cells, and the localization of glutamate receptors, P NAS US, 96(24), 1999, pp. 14130-14135
Citations number
42
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
In the mammalian retina, extensive processing of spatiotemporal and chromat
ic information occurs. One key principle in signal transfer through the ret
ina is parallel processing. Two of these parallel pathways are the ON- and
OFF-channels transmitting light and dark signals. This dual system is creat
ed in the outer plexiform layer, the first relay station in retinal signal
transfer. Photoreceptors release glutamate onto ON- and OFF-type bipolar ce
lls, which are functionally distinguished by their postsynaptic expression
of different types of glutamate receptors, namely ionotropic and metabotrop
ic glutamate receptors. in the current concept, rad photoreceptors connect
only to rod bipolar cells (ON-type) and cone photoreceptors connect only to
cone bipolar cells (ON- and OFF-type). We have studied the distribution of
(RS)-alpha-aminoJhydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutama
te receptor subunits at the synapses in the auter plexiform layer of the ro
dent retina by immunoelectron microscopy and serial section reconstruction.
We report a non-classical synaptic contact and an alternative pathway for
rod signals in the retina. Rod photoreceptors made synaptic contact with pu
tative OFF-cone bipolar cells that expressed the AMPA glutamate receptor su
bunits GluR1 and GluR2 on their dendrites. Thus, in the retina of mouse and
rat, an alternative pathway for rod signals exists, where rod photorecepto
rs bypass the rod bipolar cell and directly excite OFF-cone bipolar cells t
hrough an ionotropic sign conserving AMPA glutamate receptor.