Increased chymotrypsin-like and trypsin-like proteasome activities in aggregate containing brain regions of the HD94 mice. A, Immunohistochemistry with anti-N-terminal htt (CAG53b) or anti-ubiquitin antibodies revealed the presence of aggregates in the cortex and the striatum, but not in the cerebellum, of HD94 mice. Both nuclear (empty arrows) and neuropil aggregates (black arrows) can be detected. Cx, Cortex; St, striatum; Cb, cerebellum; ML, molecular layer; PCL, Purkinje cell layer; GCL, granule cell layer. Scale bar, 20 μm. B, The chymotrypsin-like, trypsin-like, and post-glutamyl peptidase activities of the proteasome were assayed in brain extracts of control and HD94 mice by incubating with fluorogenic substrates as described in Materials and Methods. The chymotrypsin-like and trypsin-like activities (shown in arbitrary units) were significantly (^*p < 0.01) increased in the cortex and striatum of HD94 mice with respect to control littermates.