Spatial working memory can be assessed in mice through the spontaneous alternation T-maze test. The T-maze is a T-shaped apparatus featuring a stem (start arm) and two lateral goal arms (left and right arms). The procedure is based on the natural tendency of rodents to prefer exploring a novel arm over a familiar one, which induces them to alternate the choice of the goal arm across repeated trials. During the task, in order to successfully alternate choices across trials, an animal has to remember which arm had been visited in the previous trial, which makes spontaneous alternation T-maze an optimal test for spatial working memory. As this test relies on a spontaneous behaviour and does not require rewards, punishments or pre-training, it represents a particularly useful tool for cognitive evaluation, both time-saving and animal-friendly. We describe here in detail the apparatus and the protocol, providing representative results on wild-type healthy mice.

Type I mucopolysaccharidosis (MPS I) is a lysosomal storage disorder caused by the deficiency of α-L-iduronidase, which results in glycosaminoglycan accumulation in tissues. Clinical manifestations include skeletal dysplasia, joint stiffness, visual and auditory defects, cardiac insufficiency, hepatosplenomegaly, and mental retardation (the last being present exclusively in the severe Hurler variant). The available treatments, enzyme-replacement therapy and hematopoietic stem cell (HSC) transplantation, can ameliorate most disease manifestations, but their outcome on skeletal and brain disease could be further improved. We demonstrate here that HSC gene therapy, based on lentiviral vectors, completely corrects disease manifestations in the mouse model. Of note, the therapeutic benefit provided by gene therapy on critical MPS I manifestations, such as neurologic and skeletal disease, greatly exceeds that exerted by HSC transplantation, the standard of care treatment for Hurler patients. Interestingly, therapeutic efficacy of HSC gene therapy is strictly dependent on the achievement of supranormal enzyme activity in the hematopoietic system of transplanted mice, which allows enzyme delivery to the brain and skeleton for disease correction. Overall, our data provide evidence of an efficacious treatment for MPS I Hurler patients, warranting future development toward clinical testing.

Designing animal-friendly behavioral tests for neuroscience research: The importance of an ethological approach