Expression of amino acid receptors and neural peptides in the weaver mouse brain

In the present study, we conducted: (i) in situ hybridization in order to investigate the expression of kainate and GABAA receptor subunits and the pre-proenkephalin and prodynorphin peptides in the brain of weaver mouse (a genetic model of dopamine deficiency) and (ii) immunocytochemistry in order to study the somatostatin-positive cells in weaver striatum. Our results indicated: (i) increases in mRNA levels of KA2 and GluR6 kainate receptor subunits, of α4 and β3 GABAA receptor subunits and of pre-proenkephalin and prodynorphin in 6-month-old weaver striatum; (ii) a decrease in α1 and β2 GABAA subunit mRNAs in 6-month-old weaver globus pallidus; (iii) increases in KA2, α4 and β3 and decreases in α2 and β2 mRNAs in the 6-month-old weaver somatosensory cortex; and (iv) an increase in somatostatin-immunopositive cells in 3-month-old weaver striatum. We suggest that: (i) in striatum, the alterations are induced by the induction of the transcription factor ΔfosB (for GluR6, pre-proenkephalin and prodynorphin mRNAs) and the suppression of transcription factors like NGF-IB (nerve growth factor inducible B; for the KA2 mRNA), in response to dopamine depletion; (ii) in striatum and cortex, the alterations in the expression of the GABAA subunits indicate an increase of extrasynaptic versus a decrease of synaptic GABAA receptors; and (iii) in globus pallidus, the increased striatopallidal GABAergic transmission leads to a decrease in the number of GABAA receptors. Our results further clarify the regulatory role of dopamine in the expression of amino acid receptors and striatal neuropeptides.