Medial entorhinal cortex and medial septum contribute to self-motion-based linear distance estimation.

Path integration is a navigation strategy that requires animals to integrate self-movements during exploration to determine their position in space. The medial entorhinal cortex (MEC) has been suggested to play a pivotal role in this process. Grid cells, head-direction cells, border cells as well as speed cells within the MEC collectively provide a dynamic representation of the animal position in space based on the integration of self-movements. All these cells are strongly modulated by theta oscillations, thus suggesting that theta rhythmicity in the MEC may be essential for integrating and coordinating self-movement information during navigation. In this study, we first show that excitotoxic MEC lesions, but not dorsal hippocampal lesions, impair the ability of rats to estimate linear distances based on self-movement information. Next, we report similar deficits following medial septum inactivation, which strongly impairs theta oscillations in the entorhinal-hippocampal circuits. Taken together, these findings demonstrate a major role of the MEC and MS in estimating distances to be traveled, and point to theta oscillations within the MEC as a neural mechanism responsible for the integration of information generated by linear self-displacements.

Effects of combined ferrous sulphate administration and exposure to static magnetic field on spatial learning and motor abilities in rats.

PRIMARY OBJECTIVE: Occupational exposure to static magnetic fields (SMF) increases, in particular due to the widespread use of Magnetic Resonance Imaging (MRI) for medical diagnosis, thus raising health concerns. This study investigated the behavioural effects of 128 mT SMF in rats and examined the hypothesis that iron supplementation (3 mg kg(-1) for 5 days) potentiate the effects of SMF. METHODS: Spatial learning abilities in the water maze, motor co-ordination in the rotarod and motor skills in the stationary beam and suspending string tests were assessed in iron-treated, SMF-exposed and co-exposed SMF-iron rats. RESULTS: Acquisition of the water maze navigation task was unaffected in all groups. SMF-exposed and iron-treated rats showed a deficit in the 7-day retention test. No deficit was found in the rotarod and suspended string tests in all groups. Only iron-treated rats were impaired in the stationary beam test. A combination of iron and SMF treatments did not produce additional degradation of performance in all tests. CONCLUSION: SMF exposure had no massive effect but affected long-term spatial memory. Iron supplementation and 128 mT SMF had no synergistic effects.