Offline consolidation of spatial memory: Do the cerebellar output circuits play a role? A study utilizing a Morris water maze protocol in male Wistar rats.

To address whether the cerebellum takes part to spatial memory consolidation related to navigation, male Wistar rats were trained daily (4 days), in a Morris water maze to found a submerged escape platform by use of distal cues (place training test). Retention of the allocentric map was evaluated in the probe test (without platform), before the place test. Bilateral shutdown of deep cerebellar nuclei was carried by infusion of the GABA-A agonist muscimol (0.25 µl at 1 µg/µl) immediately after each place test. Histology revealed a dorsal dentate nucleus (DDN) group, with muscimol diffusion confined to dentate nuclei, and a ventromedial/dentate nuclei (VMDN) group, with muscimol additionally involving fastigial, interpositus and vestibular nuclei. In the place test, Vehicle, DDN and VMDN groups reduced latency and distance to the platform over the 4 days and within the single day, indicative of efficient acquisition and working memory; navigational trajectories however differed in that, while Vehicle and DDN groups evolved to use direct paths, VMDN group indulged to navigate in proximity to the platform, suggesting an impairment in refining the spatial map. In the probe test VMDN, unlike Vehicle and DDN animals, failed to develop a preference for the quadrant where the platform was previously located, indicating a consolidation deficit. In conclusion, ventromedial cerebellar related structures may contribute to the process of consolidation of an allocentric spatial memory: their inactivation may have impaired the offline integration of idiothetic information with allothetic signals within the navigational network, leading to a coarse resolution map.