Histochemical Distribution of Non-Haem Iron in the Human Brain

Abstract

The detailed anatomical distribution of iron in the post-mortem human brain has been studied using Perl’s and Turnbull’s methods with the diaminobenzidine intensification procedure for the demonstration of non-haem Fe³⁺ and Fe²⁺ respectively. Attention to methodological procedures has revealed that even brief immersion of tissue in routinely used fixatives causes a reduction of staining intensity in areas of high iron content and, often, loss of staining in areas of low iron content. Optimal staining is obtained using frozen section briefly fixed for 5 min in 4% formalin and Perl’s stain (Fe³⁺) with diaminobenzidine intensification. Highest levels of stainable iron were found in the extrapyramidal system with the globus pallidus, substantia nigra zona reticulata, red nucleus and myelinated fibres of the putamen showing highest staining reactivity. Moderate staining intensity with Perl’s technique was found in the majority of forebrain, midbrain and cerebellar structures with the striatum, thalamus, cortex and deep white matter, substantia nigra zona compacta, and cerebellar cortex showing consistent staining patterns with intensification of Perl’s stain. The brain-stem and spinal cord generally only showed staining with the intensification procedure and even this was of low intensity. Microscopically the non-heam iron appears to be found predominantly in glial cells as fine cytoplasmic granules which in heavily stained areas coalesce to fill the entire cell. Iron-positive granules appear to be free in the neuropil and also around blood vessels in the globus pallidus, striatum and substantia nigra. The neuropil shows a fibrous impregnation when stained for iron which is, in part, derived from glial processes, myelinated fibres and fibre bundles. Neurones, in general, show only very low reactivity for iron, and this is difficult to discern due, often, to the higher reactivity of the surrounding neuropil. In the globus pallidus and substantia nigra zona reticulata, neurones with highly stainable iron content are found with granular cytoplasmic iron reactivity similar to that seen in the local glial cells. Our results are comparable with those of early workers, but with the use of intensification extend the distribution of non-haem iron to areas previously reported as negative. No apparent correlation of iron staining with known neurotransmitter systems is seen and the predilection for the extrapyramidal system is not easily explained, though the non-haem iron in the brain appears to be as a storage form in the iron storage protein ferritin. The localization of iron in the brain provides a foundation for the study of iron in certain neurodegenerative diseases such as Parkinson’s disease, where iron has been implicated in the pathogenesis.

High-field MRI of brain cortical substructure based on signal phase

“…In the cortex, regional variations in T 2 have been attributed to cortical variation in iron concentration, rather than to blood volume differences (43). Perl's iron stains of brain sections from a rhesus monkey (44) and humans (45,46) indicate a GM iron concentration that varies across cortical layers, with deeper layers having the highest iron concentration. Similarity with the MRI phase data are illustrated in Fig.…”

Cellular and subcellular localizations of nonheme ferric and ferrous iron in the rat brain: a light and electron microscopic study by the perfusion-Perls and -Turnbull methods

“…Fe(III) and Fe(II), are extensively distributed throughout the brain, are especially highly concentrated in the diencephalon, basal ganglia, brain stem, and cerebellum, s i m i l a r t o p r e v i o u s o b s e r v a t i o n s f o r F e ( I I I ) i n various mammalian and human brains (Hill and Switzer, 1984;Connor et al, 1990;Morris et al, 1992;Gilissen et al, 1998).…”

“…Progressive iron accumulation with age in specific brain regions has long been known in humans and other mammals (Hill and Switzer, 1984;Morris et al, 1992). Recent magnetic resonance imaging (MRI) studies of the human brain also demonstrated such increased iron accumulation with age in these brain regions (Drayer et al, 1986;Xu et al, 2008).…”

Gender and Iron Genes May Modify Associations Between Brain Iron and Memory in Healthy Aging

“…MRI can measure brain iron levels through the effect of iron on transverse relaxation rates (R 2 ) (Bartzokis et al, 1993;Bartzokis et al, 1994;Vymazal et al, 1996a;Yao et al, 2009). The bulk of brain iron is stored in ferritin molecules (Floyd and Carney, 1993;Morris et al, 1992) and an in vivo MRI method called field-dependent relaxation rate (R 2 ) increase (FDRI) can measure their iron content (Bartzokis et al, 1993;Bartzokis et al, 1994). Briefly, FDRI is the difference in measures of brain R 2 obtained with two different fieldstrength MRI instruments.…”