Enables GTPase activator activity. Involved in regulation of dendrite morphogenesis. Acts upstream of or within several processes, including motor learning; neuron remodeling; and positive regulation of synapse assembly. Located in postsynapse and synaptic cleft. Is expressed in several structures, including brain; lung; skeletal muscle; and testis. Orthologous to human ADGRB3 (adhesion G protein-coupled receptor B3). [provided by Alliance of Genome Resources, Apr 2022]