A transgenic rat containing in its genome a nucleotide sequence encoding a Ga subunit protein, which Ga protein subunit is uncoupled from regulation by Regulators of G-Protein Signaling (RGS) proteins, which Gx subunit protein is eventually the dominant-negative G188S mutant of Gax9, which nucleotide sequence is operatively associated with a neuron-specific expression control sequence, wherein the transgenic rat expresses the GA subunit protein in neural cells resulting in extended D-protein coupled receptor signaling mediated by the Ga subunit protein.