Gestational and neonatal iron deficiency alters apical dendrite structure of CA1 pyramidal neurons in adult rat hippocampus

Abstract

The hippocampus develops rapidly during the late fetal and early postnatal periods. Fetal/neonatal iron deficiency anemia (IDA) alters the genomic expression, neurometabolism and electrophysiology of the hippocampus during the period of IDA and, strikingly, in adulthood despite neonatal iron treatment. To determine how early IDA affects the structural development of the apical dendrite arbor in hippocampal area CA1 in the offspring, pregnant rat dams were given an iron-deficient (ID) diet between gestational day 2 and postnatal day (P) 7 followed by rescue with an iron-sufficient (IS) diet. Apical dendrite morphology in hippocampus area CA1 was assessed at P15, P30 and P70 by Scholl analysis of Golgi-Cox-stained neurons. Messenger RNA levels of nine cytoplasmic and transmembrane proteins that are critical for dendrite growth were analyzed at P7, P15, P30 and P65 by quantitative real-time polymerase chain reaction. The ID group had reduced transcript levels of proteins that modify actin and tubulin dynamics [e.g. cofilin-1 (Cfl-1), profilin-1 (Pfn-1), and profilin-2 (Pfn-2)] at P7, followed at P15 by a proximal shift in peak branching, thinner third-generation dendritic branches and smaller-diameter spine heads. At P30, iron treatment since P7 resulted in recovery of all transcripts and structural components except for a continued proximal shift in peak branching. Nevertheless, at P65-P70, the formerly ID group showed a 32% reduction in 9 mRNA transcripts, including Cfl-1 and Pfn-1 and Pfn-2, accompanied by 25% fewer branches, that were also proximally shifted. These alterations may be due to early-life programming of genes important for structural plasticity during adulthood and may contribute to the abnormal long-term electrophysiology and recognition memory behavior that follows early iron deficiency.

Fig. 1

a Proscribed area of CA1 from which Golgi-Cox-stained neurons were selected for analysis. CC = Corpus callosum; DG = dentate gyrus. b Schematic of neuron tracing over Scholl rings with the soma abutting ring 1. The asterisk marks the point of maximal length. The arrow marks the proximal aspect of a third-generation branch immediately after bifurcation from the second-generation branch.

Fig. 2

Dendrite branching distributions at P15 (a), P30 (b) and P70 (c). Average crossings are shown at each ring in intervals 31 μm apart, starting from the soma. The IS group is represented by black squares and ID and FID groups by open triangles. Peak branching distance for the IS group is labeled with a black arrow and with a dashed arrow for the ID group.

Fig. 3

Representative images of third-generation dendrite branches in P15 IS (a) and higher magnification of the highlighted area (rectangular box, b) and P15 ID (c, d). Arrows denote the bifurcation of the thirdgeneration branch from the second generation. Arrowheads illustrate the smaller third-generation branch widths and spine head diameters in the ID compared to the IS animal. Scale bar = 20 μm.

Fig. 4

Representative images of coronal sections of hippocampus with immunohistochemical staining for Crmp-1, Cxcr4, RhoA, Rac1, Cfl-1 and Cdc42 at P65 IS (af) and FID (a′f′). Arrows denote cell body layer of CA1 pyramidal cells. Scale bar = 100 μm.

Fig. 5

The proposed effects of early-life IDA on expression of factors regulating actin and tubulin dynamics in rat hippocampus (derived from ref. [17, 18, 19, 20, 21, 22, 23, 29, 31]. The dotted arrows show the direction of regulatory change at P7 while ID and solid arrows show directional changes at P65 following resolution of iron deficiency.