cortex

Project number:

202

Project title:

Changes in visual cortex in Albino Rats

Project supervisor:

Klaus Peter Hoffmann

Project description:

What: The study aims at a characterization of molecular changes in the visual system of albinos. The first step is a characterization of the tyrosinase mutation of the albino ferret and Wistar rat with a molecular genetic approach.

One part of the project involves the specification of the expression patterns of KCC2 and NKCC1 chloride-cotransporters that play an important role in synaptic signal transmission by the use of Western Blotting for protein expression level and for the mRNA expression level by the use of quantitative RT-PCR.
Additionally, an overall genetic approach using proteomics and gene expression profiles will reveal possible candidate proteins/genes that are altered due to albinism. As the genetic heterogenity may occur between different strains independent of the albino genotype, recombinant strains of Long Evans and Wistar rats will be used for the comparative analysis of possible molecular changes.

Why:

To understand the electrophysiological basis of the functional changes in the visual cortex in albinos we studied the physiological characteristics and transmembrane currents of pyramidal neurons in 350 µm thick slices of visual cortex from pigmented and albino rats using whole-cell and gramicidin perforated patch clamp recordings and found that the resting membrane potential was significantly positiver and the rheobase was significantly lower in neurons of layers II/III and V in albinos as compared to pigmented rats. No significant differences were found in the input resistance, time constant, and chronaxy. Whereas the AMPA receptor mediated currents were not significantly different the maximum GABAA receptor (GABAAR) mediated currents and miniature inhibitory postsynaptic currents showed significantly lower amplitudes in neurons of layer V in visual cortex of albinos as compared to pigmented rats. The reversal potential of the GABAAR mediated currents (EGABA) was significantly shifted to more positive values in albinos. Pharmacological experiments showed, that this shift is caused by an increased action of the inward chloride cotransporter NKCC1 and reduced action of the outward chloride cotransporter KCC2 in albino rats.

How:

1)The mutation in the tyrosinase gene of the albino Wistar rat in comparison to the pigmented Long Evans rat will be revealed. Additionally, the albino ferret will be genotyped as well.
2)The neuronal chloride homeostasis in the albino visual system will be compared with those of the pigmented rat and strain differences will be examined.
3)An overall screening will reveal if there are changes in gene/protein expression profiles that could contribute to anatomical, physiological and behavioural changes known to be present in albinos.

Possible cortex partners for rotation:

Professor Kalia, Helsinki: Cooperation on distribution and function of KCC2 and NKCC1 chloride co-transporter. Professor Sten Grillner: Basic properties of sensorimotor circuits