Age effects on the regulation of adult hippocampal neurogenesis by physical activity and environmental enrichment in the APP23 mouse model of Alzheimer disease.

An active lifestyle is to some degree protective against Alzheimer's disease (AD), but the biological basis for this benefit is still far from clear. We hypothesize that physical and cognitive activity increase a reserve for plasticity by increasing adult neurogenesis in the hippocampal dentate gyrus (DG). We thus assessed how age affects the response to activity in the murine APP23 model of AD compared with wild type (WT) controls and studied the effects of physical exercise (RUN) and environmental enrichment (ENR) in comparison with standard housing (CTR) at two different ages (6 months and 18 months) and in both genotypes. At 18 months, both activity paradigms reduced the hippocampal human Abeta1-42/Abeta1-40 ratio when compared with CTR, despite a stable plaque load in the hippocampus. At this age, both RUN and ENR increased the number of newborn granule cells in the DG of APP23 mice when compared with CTR, whereas the levels of regulation were equivalent to those in WT mice under the same housing conditions. At 6 months, however, neurogenesis in ENR but not RUN mice responded like the WT. Quantifying the number of cells at the doublecortin-positive stage in relation to the number of cells on postmitotic stages we found that ENR overproportionally increased the number of the DCX-positive "late" progenitor cells, indicative of an increased potential to recruit even more new neurons. In summary, the biological substrates for activity-dependent regulation of adult hippocampal neurogenesis were preserved in the APP23 mice. We thus propose that in this model, ENR even more than RUN might contribute to a "neurogenic reserve" despite a stable plaque load and that age affects the outcome of an interaction based on "activity."

Prenatal ethanol exposure reduces the expression of the transcriptional factor Pax6 in the developing rat brain.

Prenatal ethanol exposure (PEE) induces functional and structural disorders in the developing central nervous system (CNS). The relationship between radial glial cells (RGCs) and migrating neuroblasts is crucial for the establishment of normal CNS laminated structures. Pax6, a transcription factor involved in mammalian neuronal developmental processes, could be affected by PEE, as it is already known to occur in amphibians. From gestational day 10 to 18 (G10-G18), pregnant Wistar rats were subjected to an intraperitoneal injection of a daily ethanol (EtOH) 3.5 g/kg dose. Control pregnant rats received equivalent volumes of saline solution. Fetal weights and cerebral cortex thickness were significantly lower in G18 PEE than in control fetuses, and neural tube defects were found in the G18 PEE fetuses. Cortical expression of vimentin (an RGC cytoskeletal marker), S-100b protein (a neurotrophic factor and cytosolic marker of RGCs during embryonic development), and 68 kDa neurofilaments (a neuronal cytoskeletal marker) were also decreased in G18 PEE fetuses. At G14, a reduction in Pax6 cortical expression was found. Our results suggest that PEE reduces Pax6 expression in undifferentiated mammalian CNS cells. This could be one of the factors that induce RGCs and neuronal alterations at end-gestation. These alterations could be involved in the pathophysiology of neurodevelopmental disorders observed in the children affected by the fetal alcohol syndrome.

A low chronic ethanol exposure induces morphological changes in the adolescent rat brain that are not fully recovered even after a long abstinence: an immunohistochemical study.

Little is known about the morphological effects of alcoholism on the developing adolescent brain and its consequences into adulthood. We studied here the relationship between two neurotransmitter systems (the serotoninergic and nitrergic) and the astrocytic and neuronal cytoskeleton immediately and long after drinking cessation of a chronic, but low, ethanol administration. Adolescent male Wistar rats were exposed to ethanol 6.6% (v/v) in drinking water for 6 weeks and studied after ending exposure or after a 10-week recovery period drinking water. Control animals received water. Brain sections were processed by immunohistochemistry using antibodies to serotonin (5-HT); glial fibrillary acidic protein (GFAP); astroglial S-100b protein; microtubule associated protein-2 (MAP-2); 200 kDa neurofilaments (Nf-200); and neuronal nitric oxide synthase (nNOS). The mesencephalic dorsal and median raphe nucleus (DRN; MRN) and three prosencephalic areas closely related to cognitive abilities (CA1 hippocampal area, striatum and frontal cortex) were studied by digital image analysis. 5-HT immunoreactivity (-ir) decreased in the DRN and recovered after abstinence and was not changed in the MRN. In the three prosencephalic areas, astrocytes' cell area (GFAP-ir cells) increased after EtOH exposure and tended to return to normality after abstinence, while cytoplasmic astroglial S100b protein-ir, relative area of MAP-2-ir and Nf-200-ir fibers decreased, and later partially recovered. In the striatum and frontal cortex, nNOS-ir decreased only after abstinence. In conclusion, in the adolescent brain, drinking cessation can partially ameliorate the ethanol-induced morphological changes on neurons and astrocytes but cannot fully return it to the basal state.