Loss of striatal bradykinin B2 receptor alters anxiety and motivational behaviors in male mice

The kallikrein–kinin system (KKS) has been extensively studied in peripheral tissues, but its role in the central nervous system (CNS) remains poorly understood. The bradykinin B2 receptor (B2R) is constitutively expressed in the brain, where it may modulate neuronal differentiation, neuroplasticity, and behavioral aspects. Here, we investigated the functional role of striatal B2R by conditionally deleting the Bdkrb2 gene in the dorsal striatum of adult male mice (Bdkrb2(flox/flox)) using bilateral stereotaxic injections of an AAV8 that induces Cre and tdTomato expression. Mice lacking B2R in the dorsal striatum displayed several context-dependent behavioral alterations, such as reduced anxiety-like behavior and decreased sucrose preference. Moreover, these animals showed enhanced voluntary wheel running, suggesting alterations in motivation-related behavioral output. Immunofluorescence analysis revealed that among dTomato-positive neurons, approximately 17% co-expressed DARPP-32, indicating that a subset of the transduced cells corresponds to dopaminoceptive medium spiny neurons. Together, these findings show that dorsal striatal B2R deletion alters anxiety-related and motivational/hedonic behaviors in male mice and suggest that these effects may involve striatal neuronal populations, including a subset of dopaminoceptive neurons.