EPRI to estimate the in vivo intracerebral reducing ability in adolescent rats subjected to neonatal isolation

Abstract

Purpose: To estimate the in vivo intracerebral reducing ability after acute stress in adolescent rats subjected to early neonatal isolation (NI), by performing temporal electron paramagnetic resonance imaging (EPRI) of the brain. Materials and Methods:An EPRI system operating at an EPR frequency of 700 MHz was used. The intracerebral reducing ability was estimated based on the halflife of the EPR signal of the blood-brain barrier (BBB)-permeable nitroxide radical. The NI treatment was performed for a period of one hour per day over postnatal days 2-9. Six-weekold rats were exposed to acute stress (immobilization for 90 minutes) prior to the EPRI study.Results: Depletion of the intracerebral reducing ability caused by the acute stress was observed; however, this depletion phenomenon did not occur in animals that were not subjected to NI. Conclusion:The results obtained in this study prove that NI induces cerebral vulnerability to acute stress in adolescence. EARLY ADVERSE EXPERIENCE is a pervasive social problem that is frequently associated with significant long-term psychiatric sequelae, such as major depression and anxiety (1). Early neonatal isolation (NI) of rats is an experimental model designed to clarify the mechanisms by which psychiatric disorders occur after an early adverse experience. Previous studies (2-4) demonstrated that the release of corticosterone in the hypothalamic-pituitary-adrenal axis was altered by acute stress in rats that were subjected to early maternal separation and NI. However, other biological evidence related to vulnerability in this model has not been reported. KeyIt is thought that the pathogenesis of many diseases is related to oxidative damage. In vivo antioxidant ability (i.e., reducing ability) is subject to a balance between the amount of oxidants and reductants. An in vivo temporal electron paramagnetic resonance imaging (EPRI) technique was recently developed that can be applied to the brain of a rat that has been intravenously injected with a blood-brain barrier (BBB)-permeable nitroxide radical, 3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (hydroxymethyl-PROXYL) (5,6). With this imaging technique it is possible to measure the decay rates of a nitroxide radical in multiple regions of the brain simultaneously. Nitroxide radicals are reduced to hydroxylamins by reductants (5). The decay rate of the EPR signal intensity (SI) in a selected region of the brain is indicative of the region-specific reducing ability. In this study we used EPRI to estimate the intracerebral reducing ability after acute stress in adolescent rats that had been subjected to early NI. MATERIALS AND METHODS AnimalsSprague-Dawley rats were divided into two groups: control (N ϭ 12) and NI (N ϭ 12). In the NI group the pups were isolated from the dam, nest, and siblings for a period of one hour per day over postnatal days 2-9. Each pup was placed individually into a clean cup in a humidity-controlled environmental chamber maintained at 30°C. After one hour the pups were returned to the home cag...

In vivo evaluation of different alterations of redox status by studying pharmacokinetics of nitroxides using magnetic resonance techniques

“…The role of ROS and antioxidants on ageing is the subject of ongoing research and EPRS studies on young and old rodents revealed that ageing diminishes the ability of the brain to reduce injected nitroxides [20] , [86] . The study on intracerebral reducing ability after acute stress in adult rats showed diminished reducing ability in rats that were subjected to neonatal isolation [118] .…”

Imaging Reactive Oxygen Species-Induced Modifications in Living Systems

“…These findings were confirmed by using an acyl-protected hydroxylamine that undergoes intracellular oxidation to nitroxides ( 150 ), showing that oxidative stress in the hippocampus and striatum in KA-treated animals is enhanced, but not in the cortex. Another set of studies, performed on the effect of various neuroleptics that are known to induce oxidative stress on the brain, revealed diminished ability of various brain areas in treated animals to reduce injected nitroxide ( 149 , 152 , 154 ). The study on intracerebral-reducing ability after acute stress in adult rats showed diminished reducing ability in rats that were subjected to neonatal isolation ( 154 ).…”

“…Another set of studies, performed on the effect of various neuroleptics that are known to induce oxidative stress on the brain, revealed diminished ability of various brain areas in treated animals to reduce injected nitroxide ( 149 , 152 , 154 ). The study on intracerebral-reducing ability after acute stress in adult rats showed diminished reducing ability in rats that were subjected to neonatal isolation ( 154 ). Studies employing ischemia-reperfusion (I/R) injury induced by mid-carotid-artery occlusion using either only MRI ( 13 ) or EPRI/MRI combination ( 52 ) revealed slower reduction rates in brains that have undergone I/R.…”

Oxidative Stress Imaging in Live Animals with Techniques Based on Electron Paramagnetic Resonance

“…Direct EPR imaging with time resolution allowing registering spin probe decay provides 2D or 3D oxidative stress images of tissues such as tumors, heart or brain in vivo (38–41). Spatial resolution in redox imaging with EPR is affected by linewidth of nitroxides (typically ~1 gauss) and their relatively short half-life in vivo .…”

“…The effects of neonatal stress and acute stress on the redox state of the adult rat brain were also studied using EPR redox imaging. It turned out that the intracerebral reducing ability was significantly increased in rats exposed to neonatal stress and significantly depleted in the same rats that had been subjected to acute stress (41). …”