Essential for the proper localization of brevican (BCAN), mainly as a perineuronal nets (PNNs)-type deposition in the brainstem and cerebellum thereby playing a key role in the formation and structural organization of PNNs (PubMed:22121037). Contributes to the formation and transmission of inhibitory GABAergic synapses between Purkinje cells and deep cerebellar nuclei neurons (PubMed:30125937). Expressed predominantly in brain where it is found mainly throughout the midbrain and hindbrain in a perineuronal net pattern. Expression begins at embryonic day 20 and increases thereafter. Expression continues into adulthood. In deep cerebellar nuclei (DCN) neurons of knockout mice, inhibitory synaptic strengths are reduced as compared to those in wild-type mice, whereas the properties of excitatory synapses are unaffected (PubMed:30125937). A reduction in GABAergic pre-synaptic terminals of Purkinje cells are seen in the DCN neurons (PubMed:30125937). Mice show significantly attenuated perineuronal nets formation in the DCN, a marked decrease of brevican (BCAN) in the brainstem and cerebellum and a reduction in synapse number in the DCN neurons (PubMed:22121037). Belongs to the HAPLN family.