“Dissection of dopamine D2 receptor function by conditional mutagenesis into the mouse genome

RUBINSTEIN M

Huerta Grande, Córdoba, Argentina

Congreso; I Reunión Conjunta SAN - Taller de Neurociencia; 2009

SAN y Taller de Neurociencia

Dopamine transmission participates in the extrapyramidal control of locomotor activity, spatio-temporal organization of goal-oriented behaviors, the reinforcing properties of natural rewards and the synthesis and release of pituitary hormones. Efforts to determine the specific contribution of the dopamine D2 receptor (D2R) in these functions have been limited by the fact that pharmacological agents interact with other dopamine receptors –mainly of the D2R-class and in all brain and peripheral areas simultaneously. To dissect the functional roles of D2Rs we have studied mutant mice carrying null Drd2 alleles using a wide battery of neurochemical and behavioral paradigms. Although this analysis revealed several differential phenotypes that helped us to assign specific functions of the DR2 in dopaminergic transmission, we also learned the limitations of the mouse gene knockout technology. Compensatory adaptations of the developing nervous system to the absence of D2Rs was evidenced by a hypolocomotor state that was significantly less severe than that induced by the acute pharmacological blockade of D2R-like in WT mice. Also, the central phenotypes observed in the D2R knockout mice may be difficult to interpret due to the concurrent peripheral deficiencies observed such as high serum prolactin levels, growth hormone deficits and late onset pituitary tumors. In addition, our studies failed to discriminate post- and presynaptic components of D2R stimulation. Improvements to bypass these drawbacks could be achieved through a conditional gene knockout strategy that permits the region- or cell-specific disruption of the D2R gene and/or the temporal control of gene inactivation. To this end, we used the Cre/ loxP system to create a strain of mutant mice in which the critical exon 2 is flanked by two loxP sites. Molecular and behavioral sudies demonstrated that C57Bl/6J congenic (n=10) homozygous Drd2flox/flox mice are overtly indistinguishable from their Drd2+/+ wild-type littermates. Along this talk, I will present recent data obtained after crossing Drd2flox/flox mice with transgenic mice carrying expressing Cre from different promoters that are allowing us to dissect the specific role of the D2R in particular cell-types, brain regions and/or times.