TY - JOUR
T1 - Failure to form a stable topographic map during optic nerve regeneration : abnormal activity-dependent mechanisms
AU - Dunlop, Sarah
AU - Stirling, R.V.
AU - Rodger, Jennifer
AU - Symonds, A.C.E.
AU - Bancroft, Wesley
AU - Tee, Lisa
AU - Beazley, Lyn
PY - 2003
Y1 - 2003
N2 - Visually evoked responses in the optic tectum are mediated by glutamate receptors. During development, there is a switch from Nmethyl-D-aspartate (NMDA)- to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-mediated activity as the retinotectal map refines and visual function ensues. A similar pattern is seen in goldfish as the map refines during optic nerve regeneration. Here we examined glutamate receptors during optic nerve regeneration in the lizard, Ctenophorus ornatus, in which an imprecise retinotopic map forms transiently but degrades, leaving animals blind via the experimental eye. Receptor function was examined using NMDA and AMPA/kainatc antagonists during in vitro tectal recording of visually evoked post-synaptic extracellular responses. Expression of NR1 (NMDA) and GluR2 (AMPA) receptor subtypes was examined immunohistochemically. In unoperated control animals, responses were robust and AMPA/kainate receptor-mediated. When the imprecise map was present, responses were difficult to evoke and insecure; periods of spontaneous activity as well as inactivity were also noted. Although AMPA/kainate-mediated activity persisted and GluR2 immunoreactivity increased transiently, NMDA receptor-mediated activity was also consistently detected and NR1 expression increased. In the long term, when the map had degraded, responses were readily evoked and predominantly AMPA/kainate receptor-mediated although some NMDA-mediated activity and NR1 expression remained. We suggest that the asynchronous activity reaching the optic tectum results in an inability to recapitulate the appropriate functional sequences of expression of NMDA and AMPA/kainate receptors necessary to refine the retinotectal map. (C) 2003 Elsevier Inc. All rights reserved.
AB - Visually evoked responses in the optic tectum are mediated by glutamate receptors. During development, there is a switch from Nmethyl-D-aspartate (NMDA)- to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-mediated activity as the retinotectal map refines and visual function ensues. A similar pattern is seen in goldfish as the map refines during optic nerve regeneration. Here we examined glutamate receptors during optic nerve regeneration in the lizard, Ctenophorus ornatus, in which an imprecise retinotopic map forms transiently but degrades, leaving animals blind via the experimental eye. Receptor function was examined using NMDA and AMPA/kainatc antagonists during in vitro tectal recording of visually evoked post-synaptic extracellular responses. Expression of NR1 (NMDA) and GluR2 (AMPA) receptor subtypes was examined immunohistochemically. In unoperated control animals, responses were robust and AMPA/kainate receptor-mediated. When the imprecise map was present, responses were difficult to evoke and insecure; periods of spontaneous activity as well as inactivity were also noted. Although AMPA/kainate-mediated activity persisted and GluR2 immunoreactivity increased transiently, NMDA receptor-mediated activity was also consistently detected and NR1 expression increased. In the long term, when the map had degraded, responses were readily evoked and predominantly AMPA/kainate receptor-mediated although some NMDA-mediated activity and NR1 expression remained. We suggest that the asynchronous activity reaching the optic tectum results in an inability to recapitulate the appropriate functional sequences of expression of NMDA and AMPA/kainate receptors necessary to refine the retinotectal map. (C) 2003 Elsevier Inc. All rights reserved.
U2 - 10.1016/j.expneurol.2003.08.013
DO - 10.1016/j.expneurol.2003.08.013
M3 - Article
C2 - 14769373
SN - 0014-4886
VL - 184
SP - 805
EP - 815
JO - Experimental Neurology
JF - Experimental Neurology
IS - 2
ER -