Maternal dietary loads of alpha-tocopherol increase synapse density and glial synaptic coverage in the hippocampus of adult offspring.

European Journal of Histochemistry 2014; volume 58:2355 Maternal dietary loads of alpha-tocopherol increase synapse density and glial synaptic coverage in the hippocampus of adult offspring S. Salucci,1 P. Ambrogini,2 D. Lattanzi,2 M. Betti,2 P. Gobbi,1 C. Galati,2 F. Galli,3 R. Cuppini,2 A. Minelli2 face (tripartite synapses) was increased. These findings indicate that gestational and neonatal exposure to supranutritional Tocopherol intake can result in anatomical changes of offspring hippocampus that last through adulthood. These include a surplus of axo-spinous synapses and an aberrant gliasynapse relationship, which may represent the morphological signature of previously described alterations in synaptic plasticity and hippocampus-dependent learning. 1 Department of Earth, Life and Environmental Sciences (DiSTeVA), Section of Morphology, Carlo Bo University of Urbino 2 Department of Earth, Life and Environmental Sciences (DiSTeVA), Section of Physiology, Carlo Bo University of Urbino 3 Department of Internal Medicine, Section of Applied Biochemistry and Nutritional Sciences, University of Perugia, Italy Introduction Abstract An increased intake of the antioxidant
Tocopherol (vitamin E) is recommended in complicated pregnancies, to prevent free radical damage to mother and fetus. However, the anti-PKC and antimitotic activity of
Tocopherol raises concerns about its potential effects on brain development. Recently, we found that maternal dietary loads of
Tocopherol through pregnancy and lactation cause developmental deficit in hippocampal synaptic plasticity in rat offspring. The defect persisted into adulthood, with behavioral alterations in hippocampus-dependent learning. Here, using the same rat model of maternal supplementation, ultrastructural morphometric studies were carried out to provide mechanistic interpretation to such a functional impairment in adult offspring by the occurrence of long-term changes in density and morphological features of hippocampal synapses. Higher density of axo-spinous synapses was found in CA1 stratum radiatum of
Tocopherol-exposed rats compared to controls, pointing to a reduced synapse pruning. No morphometric changes were found in synaptic ultrastructural features, i.e., perimeter of axon terminals, length of synaptic specializations, extension of bouton-spine contact. Gliasynapse anatomical relationship was also affected. Heavier astrocytic coverage of synapses was observed in Tocopherol-treated offspring, notably surrounding axon terminals; moreover, the percentage of synapses contacted by astrocytic endfeet at bouton-spine inter[page 120] Alpha-Tocopherol (
-T), the main form of vitamin E in mammal organisms, is a potent fat-soluble antioxidant and scavenger of hydroperoxyl radicals formed during the lipid peroxidation chain reaction. However,
-T also possess alternative, non-antioxidant, functions1 that occur through the regulation of signaling molecules and the transcriptional control of groups of genes involved in key cellular events such as cell cycle progression and apoptosis, mitochondrial function, xenobiotic and lipid metabolism, etc.2-4 Protein kinase C (PKC) appears to be central to vitamin E signaling;2-6 in fact,
-T can potently inhibit PKC activity, as documented in various in vitro model systems5-7 and in vivo in both the developing8 and adult brain.9
-T is regarded as an important molecule during fetal and early postnatal life, playing fundamental roles in protecting the developing organism against oxidative stress. In fact, free radicals have been indicated as causative agents of pregnancy-related disorders, such as preeclampsia and maternal diabetes, inducing serious complications in both the mother and fetus.10,11 Blood
-T concentrations are reduced in abnormal pregnancies;11-13 moreover, preclinical in vitro evidence pointed to a potential therapeutic role of vitamin E in reducing placental oxidative stress induced by nicotine.14 On the bases of this rationale, an increase of vitamin E intake is recommended in complicated pregnancy to prevent free radical damage to the fetus.15-18 However, beneficial effects of vitamin E in risky pregnancy are currently debated, and the anti-PKC and antimitotic activity of
-T raises important caveat against an indiscriminate use of vitamin E in gestation because of its potential effects on brain development. In fact, PKC plays a pivotal role in brain maturation,19-21 and alterations in its activity and/or expression levels have been proposed as the mechanism underlying the neuroteratogenicity of several chemical or physical agents.22-25 In previous works, we found that maternal supranutritional dietary intake of
-T through pregnancy and lactation in rats markedly Correspondence: Dr. Andrea Minelli, Department of Earth, Life and Environmental Sciences (DiSTeVA), Section of Physiology, University of Urbino Carlo Bo, via Cà le Suore 2, 61029 Urbino, Italy. Tel. +39.0722.304252 – Fax: +39.0722.304226. E-mail: Key words: Vitamin E, CA1 stratum radiatum, axo-spinous synapses, glia-synapse relationship, tripartite synapses, morphometry, electron microscopy. Conflict of interests: the authors declare no conflict of interest, having no commercial relationships to products or companies related to the subject matter of the article. Contributions: all authors gave substantial contributions to the conception and design of the work and to the acquisition, analysis, and interpretation of data. Funding: Carlo Bo University of Urbino, Italy. Received for publication: 11 December 2013. Accepted for publication: 12 March 2014. This work is licensed under a Creative Commons Attribution NonCommercial 3.0 License (CC BYNC 3.0). ©Copyright S. Salucci et al., 2014 Licensee PAGEPress, Italy European Journal of Histochemistry 2014; 58:2355 doi:10.4081/ejh.2014.2355 depresses PKC activity also reducing synaptic long-term potentiation (LTP) in developing hippocampus.8 Importantly, a deficit in hippocampal synaptic plasticity was produced that persisted in adulthood, accompanied by alterations in hippocampus-dependent learning performances.8,26 In particular, adult rats born to tocopherol-supplemented dams performed less efficiently in spatial learning tasks, but displayed improved contextual fear conditioning, thus showing that two kinds of hippocampus-dependent learning abilities display differential sensitivity to the same manipulation of early nutritional environment.26. Collectively, these findings indicated that exposing rats to an excess of
-T during development can lead to long-term electrophysiological and neurobehavioral consequences in adulthood, i.e., when tocopherol intake and
T brain accumulation, as well as PKC activity, have returned to normal levels.8 The possibility that adult offspring of tocopherol-supplemented dams may carry brain structural changes that could help explaining functional and behavioral alterations in adulthood, remains unexplored. Here, using t (...truncated)