EXPERIMENTAL PATHOLOGY Microglial activation as a measure of stress in mouse brains exposed acutely (60 minutes) and long-term (2 years) to mobile telephone radiofrequency fields JOHN W. FINNIE,ZHAO CAI,JIM MANAVIS,STEPHEN HELPS AND PETER C. BLUMBERGS Hanson Institute Centre for Neurological Diseases, Institute of Medical and Veterinary Science, SA Pathology, Adelaide, South Australia Summary Aim: To determine whether acute or long-term exposure of the brain to mobile telephone radiofrequency (RF) fields produces activation of microglia, which normally respond rapidly to any change in their microenvironment. Methods: Using a purpose designed exposure system at 900 MHz, mice were given a single, far-field whole body exposure at a specific absorption rate (SAR) of 4 W/kg for 60 min (acute) or on five successive days per week for 104 weeks (long-term). Control mice were sham-exposed or freely mobile in a cage to control for any stress caused by immobilisation in the exposure module. Positive control brains subjected to a stab wound were also included to confirm the ability of microglia to react to any neural stress. Brains were perfusion-fixed with 4% paraformaldehyde and representative regions of the cerebral cortex and hippocam- pus immunostained for ionised calcium binding adaptor molecule (Iba1), a specific microglial marker. Results: There was no increase in microglial Iba1 expression in brains short or long-term exposed to mobile telephony microwaves compared to control (sham-exposed or freely moving caged mice) brains, while substantial microglial activation occurred in damaged positive control neural tissue. Conclusion: Acute (60 minutes) or longer duration (2 years) exposure of murine brains to mobile telephone RF fields did not produce any microglial activation detectable by Iba1 immunostaining. Key words: Mobile telephony, brain, microglial activation. Received 13 July, revised 3 September, accepted 13 September 2009 INTRODUCTION Most studies conducted to date suggest that any adverse neurological effects from exposure to mobile telephone radiofrequency (RF) fields are subtle and probably tran- sient. 1,2 We have previously shown that acute (60 minutes) exposure to mobile telephony microwaves produces no significant disruption of blood-brain barrier (BBB) per- meability 3,4 or neural stress using the immediate early gene, c-fos. 5 Moreover, long-term (2 year) exposure also did not increase BBB permeability 4,6 or c-fos expression. 7 Since microglia function as intrinsic sensors in the brain, responding rapidly to changes in their microenvironment, 8 we used activation of these glia to detect any perturbation of neural tissue resulting from exposure to mobile telephone RF fields. Microglia form a vast network in the brain, with a constitutive homeostatic surveillance role. They respond more rapidly than any other neuroparenchymal element to a wide variety of insults and their activation may occur without any other obvious neuropathological alterations. Microglia are also the principal immune effector cell of the brain. 8,9 The extensive arborisations of microglia are actively motile, with a continuous and high degree of extension and retraction. Therefore, they are able to regularly and effecti- vely scan the extracellular space of the neural parenchyma and, when microlesions are detected by microglial processes, these glia show directed movement towards the injury site. When the microglial milieu is altered, these cells acquire a reactive profile manifest by proliferation and neuroprotec- tive morphological, immunophenotypical and functional changes. Microglia are also closely integrated with neuronal function. 8,9 Resting microglia constitutively express ionised calcium binding adaptor molecule (Iba1), which is a specific immunohistochemical marker for these glial cells, and this protein is up-regulated during microglial activation. In contrast to some other microglial markers, Iba1 is expressed in many microglial subpopulations, 10 and we found this marker to be superior to other microglial markers tested in our formalin-fixed, paraffin-embedded murine brains. In the central nervous system, calcium ions are important signal mediators, this activity being exerted by their association with various calcium-binding proteins. Iba1 is a 17 kDa EF hand calcium-binding protein, which is the product of a gene located within a segment of the major histocompatibility complex class III region. 11 While the function of Iba1 is not well understood, it appears to be involved in the membrane ruffling required for cell motility and phagocytosis by microglia/macrophages. 12 This paper reports the results of a study designed to determine whether acute (60 min) or long-term (2 years) exposure of the brain to mobile telephone RF fields produces any microglial activation using Iba1 immunostaining. MATERIALS AND METHODS In a purpose-designed exposure system with precisely determined dosimetry, 13 exposed mice received either an acute (60 min) or long-term (on five successive days per week for 104 weeks) far-field, whole body exposure of 4 W/kg at 900 MHz. This specific absorption rate (SAR) is a Pathology (February 2010) 42(2), pp. 151–154 Print ISSN 0031-3025/Online ISSN 1465-3931 # 2010 Royal College of Pathologists of Australasia DOI: 10.3109/00313020903494086 Pathology Downloaded from informahealthcare.com by 223.84.131.151 on 05/20/14 For personal use only.