Research report
Choline availability alters embryonic development of the hippocampus and septum in the rat

https://doi.org/10.1016/S0165-3806(98)00183-7Get rights and content

Abstract

Choline availability in the diet during pregnancy alters fetal brain biochemistry with resulting behavioral changes that persist throughout the lifetime of the offspring. In the present study, the effects of dietary choline on cell proliferation, migration, and apoptosis in neuronal progenitor cells in the hippocampus and septum were analyzed in fetal brains at different stages of embryonic development. Timed-pregnant rats on day E12 were fed AIN-76 diet with varying levels of dietary choline for 6 days, and, on days E18 or E20, fetal brain sections were collected. We found that choline deficiency (CD) significantly decreased the rate of mitosis in the neuroepithelium adjacent to the hippocampus. An increased number of apoptotic cells were found in the region of the dentate gyrus of CD hippocampus compared to controls (5.5±0.7 vs. 1.9±0.3 apoptotic cells per section; p<0.01). Using a combination of bromodeoxyuridine (BrdU) labeling and an unbiased computer-assisted image analysis method, we found that modulation of dietary choline availability changed the distribution and migration of precursor cells born on E16 in the fimbria, primordial dentate gyrus, and Ammon's horn of the fetal hippocampus. CD also decreased the migration of newly born cells from the neuroepithelium into the lateral septum, thus indicating that the sensitivity of fetal brain to choline availability is not restricted to the hippocampus. We found an increase in the expression of TOAD-64 protein, an early neuronal differentiation marker, in the hippocampus of CD day E18 fetal brains compared to controls. These results show that dietary choline availability alters the timing of the genesis, migration, and commitment to differentiation of progenitor neuronal-type cells in fetal brain hippocampal regions known to be associated with learning and memory processes in adult brain.

Introduction

Choline is an essential nutrient for humans and rats 11, 22. Variations in dietary choline availability during pregnancy have long-lasting behavioral effects in offspring. Prenatal choline supplementation in rats facilitates cognitive function and visuospatial memory, whereas choline deficiency impairs divided attention and accelerates the age-related decline in temporal processing 26, 27, 28, 29, 30, 41. These changes in memory are correlated with decreases in the threshold for induction of long-term potentiation [33]and with biochemical changes. Choline supplementation in pregnant rats decreases choline acetyltransferase activity [13]and increases phospholipase D (PLD) activity in the hippocampus of offspring [20]. Also, it increases the size of the cell body of cholinergic neurons [24]. In contrast choline deficiency increases the activity of cholinergic system, but does not affect the basal level of PLD activity in hippocampus [20]. These long-lasting functional, anatomical, and biochemical alterations may be related to the changes in neurogenesis and differentiation in fetal hippocampus and septum, areas of brain that are important for normal spatial learning and memory 11, 25.

During fetal brain development, progenitor-type cells in the ventricular neuroepithelial layer of the hippocampus and septum undergo cell proliferation and mitosis, daughter cells commit to differentiate along neuronal or glial lineage, and cells migrate to locations in the hippocampus appropriate for their birth date 12, 36, 37. Cells that are produced in excess or are unnecessary die by apoptosis 15, 16, 19, 32. The specialized regions of hippocampus, such as the fimbria, dentate gyrus, and Ammon's horn, which develop from these progenitor cells, are associated with different aspects of the acquisition of memory and learning processes associated with the hippocampus. Thus, neuronal patterning and brain function could be significantly influenced by alterations in the timing of cell division, migration and apoptosis during the development of these regions.

Section snippets

Timed-bred animals

Timed-bred Sprague–Dawley rats (Charles River Breeding, Raleigh, NC) were obtained on days 8–10 of gestation and were maintained in a climate controlled environment and exposed to a 12 h light/dark cycle daily. The rats were provided with AIN-76A diet containing 7.8 mmol/kg (1.1 g/kg) choline chloride (Dyets, Bethlehem, PA) and water ad libitum. On day 12 of gestation, pregnant rats were divided into three treatment groups: supplemented, control, and deficient. Control (CT) animals received an

Neuroanatomy

In coronal sections of embryonic rat brain on days E18–E20, the hippocampal formation is located between the dorsal third ventricle and the lateral ventricle (Fig. 1). By E18 in control brains, the neuroepithelial layer and central CA1–CA3 regions are identifiable and cells migrating from the overlying neuroepithelium have begun to delineate the circular outline of the dentate gyrus adjacent to the fimbria. By day E18 the medial and lateral septal regions are identifiable. By day E20 the

Discussion

This study shows that choline availability during pregnancy affects the development of the hippocampus and septum in fetal rat brain. We found that feeding a choline deficient diet during embryonic days E12–E18 reduced mitosis and the birth of cells in the progenitor neuroepithelial ventricular zone in E18 hippocampus. Choline deficiency also resulted in an increase in apoptosis in a specific region of the hippocampus, namely the dentate gyrus. Feeding a choline supplemented diet increased the

Acknowledgements

This work was funded by a grant from the National Institutes of Health (AG09525).

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