Divergent effect of the selective D3 receptor agonist pd-128,907 on locomotor activity in Roman high- and low-avoidance rats: relationship to NGFI-A gene expression in the Calleja islands

Rationale

The inbred Roman high- (RHA-I) and low-avoidance (RLA-I) rats, differing in dopaminergic activity and novelty/substance-seeking profiles, may be a suitable model to study the implication of the dopaminergic system in vulnerability to drug abuse. Differences in D₃ receptor binding recently described between the two strains (Guitart-Masip M, Johansson B, Fernández-Teruel A, Cañete T, Tobeña A, Terenius L, Giménez-Llort L, Neuroscience 142:1231–1243, 2006b) may be important in shaping the aforementioned differences in novelty seeking.

Objective

The aim of the present work was to study the effect of D₃ receptor activation on novelty-induced locomotor activity in these two strains of rats.

Materials and methods

We administered saline and PD-128,907 (0.01 and 0.1 mg/kg), a putative D₃ receptor agonist, to the Roman rats and studied the locomotor activity when animals were placed in a novel environment. Thereafter, by means of in situ hybridization, nerve growth factor inducible clone A (NGFI-A) mRNA was measured in the striatum and the Calleja islands of these animals.

Results

We found that RLA-I rats showed stronger locomotor inhibition than RHA-I rats after PD-128,907 administration. Moreover, RLA-I rats showed stronger reduction of NGFI-A mRNA in the Calleja islands than RHA-I rats.

Conclusions

These results, together with previous findings, suggest that differences in D₃ receptor expression in the Calleja islands may contribute to the divergent behavioral effect of PD-128,907 administration in the two strains of Roman rats.