DRD1 and schizophrenia: As an animal model of schizophrenia, HRM shows abnormal dopaminergic function, including reduced DA D1 and D2 receptors (D1R and D2R) in the striatum, reduced D1R- and D2R-mediated locomotor response (Matsuzaki et al., 2007), and increased expression of D2R in the striatum (Varela et al., 2015); and it also shows altered dopaminergic fiber densities in different brain areas, such as increase in the densities of tyrosine hydroxylase-immunoreactive (TH-IR) neurons in the hippocampus but decrease TH-IR neurons in the shell of the nucleus accumbens (Nullmeier et al., 2014).