Preliminary evidence on the role of vestibolo- and neo-cerebellar circuits in the consolidation of spatial memory related to navigation.

To evaluate if the cerebellum takes part in the process of consolidation of the memory traces related to navigation, we tested in a Morris water maze two groups of male rats, chronically implanted for injection into the cerebellar nuclei of saline or muscimol (MU), a GABAA agonist with a transient inhibitory action. During the acquisition phase (Place test) animals were trained to find a submerged escape platform by the use of distal cues in a protocol of 8 trials/day (2 blocks of 4 trials) for 5 days, and injected immediately after. A Probe test was applied before Place test; the time spent in the area where the platform was previously located is an index of consolidation.Based on histology, MU-treated animals were sorted in: (a) dorsal dentate group (DDN) and (b) ventromedial dentate group (VMDN), in which the injected drug reached also the vestibular nuclei. In the place test, the VMDN showed versus controls (C), longer latencies in reaching the platform in the first block of each day, indicating a less efficient retention. In the probe test, C and DDN showed a gradual increase of time spent in reference quadrant up to values around 40% at day 4 while the VMDN remained around the value of 25 %, regarded as casual distribution. Results seem to exclude a role of the cerebellum trough the dentate nucleus in the process of spatial memory consolidation, at least at the time span of our protocol, and suggest that such a role could be exerted trough the vestibular system.