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The ventral midline thalamus contributes to hippocampo-cortical interactions supporting systems-level consolidation of memories. Recent hippocampus-dependent memories rely on hippocampal connectivity remodeling. Remote memories are underpinned by neocortical connectivity remodeling. After a ventral midline thalamus lesion, recent spatial memories are formed normally but do not last. Why these memories do not endure after the lesion is unknown. We hypothesized that a lesion could interfere with hippocampal and/or neocortical connectivity remodeling. To test this hypothesis, in a first experiment male rats were subjected to lesion of the reuniens and rhomboid (ReRh) nuclei, trained in a water maze, and tested in a probe trial 5 or 25 days post-acquisition. Dendritic spines were counted in the dorsal hippocampus and medial prefrontal cortex. Spatial learning resulted in a significant increase of mushroom spines in region CA1. This modification persisted between 5 and 25 days post-acquisition in Sham rats, not in rats with ReRh lesion. Furthermore, 25 days after acquisition, the number of mushroom spines in the anterior cingulate cortex (ACC) had undergone a dramatic increase in Sham rats; ReRh lesion prevented this gain. In a second experiment, the increase of c-Fos expression in CA1 accompanying memory retrieval was not affected by the lesion, be it for recent or remote memory. However, in the ACC, the lesion had reduced the retrieval-triggered c-Fos expression observed 25 days post-acquisition. These observations suggest that a ReRh lesion might disrupt spatial remote memory formation by preventing persistence of early remodeled hippocampal connectivity, and spinogenesis in the ACC.

published in Photodiagnosis and Photodynamic Therapy, 8(2):149, 2011; International audience; Bladder PDT, the first FDA indication, has been abandoned in favour of photodiagnosis with ALA or derivatives. Major drawback of this treatment modality is prolonged and severe irritative bladder symptoms, due to lack of selectivity of the drug and generalized urothelial necrosis. Low fluence rates are known to potentiate therapeutic efficacy due to an oxygen sparing regime. We have evaluated the effect of low fluence rate PDT on therapeutic outcome and side effects in rat tumor bearing bladders. Bladders were instilled with 8 mM hexylaminolevulinate and illuminated with 635 nm light to a total light dose of 20 or 15 J/cm2 at 100 or 15 mW/cm2, 5 rats per group. Fluence rates of 15 mW/cm2 did not provoke enhancement of cardiac and respiratory rhythms as opposed to 100 mW/cm2, neither was hematuria observed post treatment. Macroscopic aspects of bladders at 100 mW/cm2 show thickened bladders with hemorrhagic areas whereas 15 J/cm2 does not alter macroscopic features. Pathology revealed the absence of viable superficial tumors, irrespective of irradiation conditions. Inflammatory volume was calculated to be 96 a.u. for high fluence high light dose, reduced to 18 a.u. when reducing the light dose and 12 a.u. for the low fluence rates, irrespective of the light dose. Normal urothelial is preserved over the total bladder in case of 15 mW/cm2, whereas major portions of the bladder show absence of reduction of cell layers at 100 mW/cm2. Low fluence rate PDT does not hamper therapeutic efficacy and minimizes local side effects in rats.