Proceedings of The Physiological Society
Cardiff University (2009) Proc Physiol Soc 17, PC11
Experience-dependent regulation of functional maps and protein expression in visual cortex
S. Jaffer1, V. Vorobyov1, P. C. Kind2, F. Sengpiel1
1. School of Biosciences, Cardiff University, Cardiff, United Kingdom. 2. School of Biomedical Sciences, University of Edinburgh, Edinburgh, United Kingdom.
The primary visual cortex (V1) is a model system for the study of synaptic plasticity. Although some of the receptors associated with ocular dominance (OD) plasticity in cats have been examined, the role of downstream signalling molecules has received scant attention. We therefore examined how glutamate receptor subunits and their downstream signalling molecules and GABA receptor subunits are regulated developmentally and whose expression is dependent on sensory experience. We assessed the functional architecture of VI using optical imaging of intrinsic signals in anaesthestised cats (1.0-2.5% isoflurane in 60% N2O and 40% O2). We obtained OD and orientation maps from cats reared normally (10 days, 3, 5 12 weeks and 1 year old) or in complete darkness (DR) (3, 5 and 12 weeks old, n=2 or 3 per age group). Animals were euthanised and V1 was removed and homogenised, followed by immunoblotting for quantification of protein expression. We found that visual experience is not required for the establishment of OD and orientation maps, since these were distinct in DR cats at 5 weeks. In contrast, in 12 weeks old DR cats, maps were barely discernible; therefore visual experience is required for their maintenance. Developmentally, the expression of NR2B and SAP-102 declined with age while NR2A, pMAPK and mGluR5 peaked at 5 weeks of age. The expression of NR1, GluR1, GluR2/3, PKC, PKARIIβ, PLCβ1, and PLCβ4 did not change throughout development. In contrast, the expression of GABAAα1a, PSD-95, αCaMKII, synGAP and synaptophysin peaked from 3 weeks onwards. DR from birth prevented developmental down-regulation of NR2B and up-regulation of NR2A subunits. In addition, DR from birth increased the expression of GABAAα1a subunits while the expression of synaptophysin was reduced. It appears that DR activates mechanisms associated with both excitatory and inhibitory pathways so as to maintain a homeostatic balance. We also assessed the functional architecture of V1 of cats that had undergone monocular deprivation (MD) by lid suture (under ketamine (30 mg/kg) and xylazine (4 mg/kg) anaesthesia i.m.) for 2 or 7 days (n=2 or 3 respectively). MD for 2 days and 7 days resulted in similar depression of deprived eye responses. In contrast, potentiation of non-deprived eye responses was almost twice as strong after 7 days compared to 2 days of MD. Immunoblotting showed that the AMPA receptor subunit, GluR1, was down-regulated after 2 days of MD while no change in its expression was observed after 7 days of MD relative to control. The expression of αCaMKII was up-regulated after 7 days of MD but not after 2 days of MD while synGAP was down-regulated after 2 days of MD but up-regulated after 7 days of MD relative to control. In contrast to DR, MD regulates signalling molecules downstream of NMDA receptors; it appears that different mechanisms are activated depending on the nature of sensory experience.
Where applicable, experiments conform with Society ethical requirements