Retinoid hyposignaling contributes to aging-related decline in hippocampal function in short-term/working memory organization and long-term declarative memory encoding in mice.

An increasing body of evidence indicates that the vitamin A metabolite retinoic acid (RA) plays a role in adult brain plasticity by activating gene transcription through nuclear receptors. Our previous studies in mice have shown that a moderate downregulation of retinoid-mediated transcription contributed to aging-related deficits in hippocampal long-term potentiation and long-term declarative memory (LTDM). Here, knock-out, pharmacological, and nutritional approaches were used in a series of radial-arm maze experiments with mice to further assess the hypothesis that retinoid-mediated nuclear events are causally involved in preferential degradation of hippocampal function in aging.

The hippocampus plays a critical role at encoding discontiguous events for subsequent declarative memory expression in mice.

The hypothesis that hippocampal activity at encoding is causally related to subsequent declarative memory expression is tested in the mouse, by using lidocaine inactivation of the hippocampus in combination with c-fos neuroimaging analysis. We employed a two-stage radial maze paradigm of spatial discrimination, which was previously shown to dissociate between declarative and nondeclarative expression of memory related to the same acquired material. In Stage 1 (encoding), mice learnt the constant location of food among a set of six arms (three baited, three unbaited) by being submitted repeatedly to discontiguous experiences with each arm separately ("go/no-go" discrimination).

Differential effect of retinoic acid and triiodothyronine on the age-related hypo-expression of neurogranin in rat.

Given the important role of retinoids and thyroid hormone for optimal brain functioning and the tenuous relationship between retinoic acid (RA) and triiodothyronine (T3) signalings, we compared the effects of RA or T3 administrations on RA and T3 nuclear receptors (RAR, RXR and TR) and on their target genes, neuromodulin (GAP43) and neurogranin (RC3) in 24-month-old rats. Quantitative real time PCR and western blot analysis allowed us to verify that retinoid and thyroid signalings and GAP43 and RC3 expression are affected by age. By in situ hybridization we observed a decreased expression of RC3 in hippocampus, striatum and cerebral cortex.

[Mucocele: a cause of exophthalmos originating blindness].

Inflammatory exophthalmos with visual loss due to optic atrophy is reported in a 45-year-old man. Computed tomography showed an ethmoido-frontal mucocel. This single case stresses the severe complication of a mucocel like optic nerve head atrophy.