Calcium compartments in brain

A review of concepts and methods for FTIR imaging of biomarker changes in the post-stroke brain

Stroke represents a core area of study in neurosciences and public health due to its global contribution toward mortality and disability. The intricate pathophysiology of stroke, including ischemic and hemorrhagic events, involves the interruption in oxygen and nutrient delivery to the brain. Disruption of these crucial processes in the central nervous system leads to metabolic dysregulation and cell death. Fourier transform infrared (FTIR) spectroscopy can simultaneously measure total protein and lipid content along with a number of key biomarkers within brain tissue that cannot be observed using conventional techniques. FTIR imaging provides the opportunity to visualize this information in tissue which has not been chemically treated prior to analysis, thus retaining the spatial distribution and in situ chemical information. Here we present a review of FTIR imaging methods for investigating the biomarker responses in the post-stroke brain.

Distinctive calcium isotopic composition of mice organs and fluids: implications for biological research

The stable calcium (Ca) isotopes offer a minimally invasive method for assessing Ca balance in the body, providing a new avenue for research and clinical applications. In this study, we measured the Ca isotopic composition of soft tissues (brain, muscle, liver, and kidney), mineralized tissue (bone), and blood (plasma) from 10 mice (5 females and 5 males) with three different genetic backgrounds and same age (3 months old). The results reveal a distinctive Ca isotopic composition in different body compartments of mice, primally controlled by each compartment's unique Ca metabolism and genetic background, independent of sex. The bones are enriched in the lighter Ca isotopes (δ44/40Cabone =  - 0.10 ± 0.55 ‰) compared to blood and other soft tissues, reflecting the preferential incorporation of lighter Ca isotopes through bone formation, while heavier Ca isotopes remain preferentially in blood. The brain and muscle are enriched in lighter Ca isotopes (δ44/40Cabrain =  - 0.10 ± 0.53 ‰; δ44/40Camuscle = 0.19 ± 0.41 ‰) relative to blood and other soft tissues, making the brain the isotopically lightest soft tissues of the mouse body. In contrast, the kidney is enriched in heavier isotopes (δ44/40Cakidney = 0.86 ± 0.31 ‰) reflecting filtration and reabsorption by the kidney. This study provides important insight into the Ca isotopic composition of various body compartments and fluids.

Brain extracellular space of the naked mole-rat expands and maintains normal diffusion under ischemic conditions

Brain extracellular space (ECS) forms a conduit for diffusion, an essential mode of molecular transport between brain vasculature, neurons and glia. ECS volume is reduced under conditions of hypoxia and ischemia, contributing to impaired extracellular diffusion and consequent neuronal dysfunction and death. We investigated the ECS volume fraction and diffusion permeability of the African naked mole-rat (NM-R; Heterocephalus Glaber), a rodent with a remarkably high tolerance for hypoxia and ischemia. Real-Time Iontophoretic and Integrative Optical Imaging methods were used to evaluate diffusion transport in cortical slices under normoxic and ischemic conditions, and results were compared to values previously collected in rats. NM-R brains under normoxic conditions had a smaller ECS volume fraction than rats, and a correspondingly decreased diffusion permeability for macromolecules. Surprisingly, and in sharp contrast to rats, the NM-R ECS responded to ischemic conditions at the center of thick brain slices by expanding, rather than shrinking, and preserving diffusion permeabilities for small and large molecules. The NM-R thick slices also showed a blunted accumulation of ECS potassium compared to rats. The remarkable dynamic response of the NM-R ECS to ischemia likely demonstrates an adaptation for NM-R to maintain brain function in their extreme nest environment.

Longitudinal biometal accumulation and Ca isotope composition of the Göttingen minipig brain

Biometals play a critical role in both the healthy and diseased brain's functioning. They accumulate in the normal aging brain, and are inherent to neurodegenerative disorders and their associated pathologies. A prominent example of this is the brain accumulation of metals such as Ca, Fe and Cu (and more ambiguously, Zn) associated with Alzheimer's disease (AD). The natural stable isotope compositions of such metals have also shown utility in constraining biological mechanisms, and in differentiating between healthy and diseased states, sometimes prior to conventional methods. Here we have detailed the distribution of the biologically relevant elements Mg, P, K, Ca, Fe, Cu and Zn in brain regions of Göttingen minipigs ranging in age from three months to nearly six years, including control animals and both a single- and double-transgenic model of AD (PS1, APP/PS1). Moreover, we have characterized the Ca isotope composition of the brain for the first time. Concentration data track rises in brain biometals with age, namely for Fe and Cu, as observed in the normal ageing brain and in AD, and biometal data point to increased soluble amyloid beta (Aβ) load prior to AD plaque identification via brain imaging. Calcium isotope results define the brain as the isotopically lightest permanent reservoir in the body, indicating that brain Ca dyshomeostasis may induce measurable isotopic disturbances in accessible downstream reservoirs such as biofluids.

Kisspeptin preserves mitochondrial function by inducing mitophagy and autophagy in aging rat brain hippocampus and human neuronal cell line

It has become amply clear that mitochondrial function defined by quality, quantity, dynamics, homeostasis, and regulated by mitophagy and mitochondrial biogenesis is a critical metric of human aging and disease. As a consequence, therapeutic interventions that can improve mitochondrial function can have a profound impact on human health and longevity. Kisspeptins are neuropeptides belonging to the family of metastasis suppressors that are known to regulate functions like fertility, reproduction, and metabolism. Using SKNSH cell line, hippocampus explant cultures and hippocampus of aging Wistar rat models, we show that Kisspeptin-10 (Kp) induces autophagy and mitophagy via calcium, Ca²⁺/CaM-dependent protein kinase kinase β (CaMKKβ), AMP-activated protein kinase (AMPK), and Unc-51 like autophagy activating kinase (ULK1) signaling pathway that is independent of mammalian target of rapamycin (mTOR). Intriguingly, Kp administration in vivo also results in the enhancement of mitochondrial number, complex I activity, and Adenosine Triphosphate (ATP) levels. This study uncovers potential effects of Kp in protecting mitochondrial health and as a possible therapeutic intervention to hippocampus associated impairments such as memory, cognitive aging, and other diseases linked to mitochondrial dysfunction.

Age- and region-dependent patterns of Ca2+ accumulations following status epilepticus

Elevated Ca(2+) concentrations have been implicated in cell death mechanisms following seizures, however, the age and brain region of intracellular Ca(2+) accumulations [Ca(2+)](i), may influence whether or not they are toxic. Therefore, we examined regional accumulations of (45)Ca(2+) by autoradiography from rats of several developmental stages (P14, P21, P30 and P60) at 5, 14, and 24h after status epilepticus. To determine whether the uptake was intracellular, Ca(2+) was also assessed in hippocampal slices with the dye indicator, Fura 2AM at P14. Control animals accumulated low homogeneous levels of (45)Ca(2+); however, highly specific and age-dependent patterns of (45)Ca(2+) uptake were observed at 5h. (45)Ca(2+) accumulations were predominant in dorsal hippocampal regions, CA1/CA2/CA3a, in P14 and P21 rats and in CA3a and CA3c neurons of P30 and P60 rats. Selective midline and amygdala nuclei were marked at P14 but not at P21 and limbic accumulations recurred with maturation that were extensive at P30 and even more so at P60. At 14 h, P14 and P21 rats had no persistent accumulations whereas P30 and P60 rats showed persistent uptake patterns within selective amygdala, thalamic and hypothalamic nuclei, and other limbic cortical regions that continued to differ at these ages. For example, piriform cortex accumulation was highest at P60. Fura 2AM imaging at P14 confirmed that Ca(2+) rises were intracellular and occurred in both vulnerable and invulnerable regions of the hippocampus, such as CA2 pyramidal and dentate granule cells. Silver impregnation showed predominant CA1 injury at P20 and P30 but CA3 injury at P60 whereas little or no injury was found in extrahippocampal structures at P14 and P20 but was modest at P30 and maximal at P60. Thus, at young ages there was an apparent dissociation between high (45)Ca(2+) accumulations and neurotoxicity whereas in adults a closer relationship was observed, particularly in the extrahippocampal structures.

Long-term decrease in calbindin-D28K expression in the hippocampus of epileptic rats following pilocarpine-induced status epilepticus

Acquired epilepsy (AE) is characterized by spontaneous recurrent seizures and long-term changes that occur in surviving neurons following an injury such as status epilepticus (SE). Long-lasting alterations in hippocampal Ca(2+) homeostasis have been observed in both in vivo and in vitro models of AE. One major regulator of Ca(2+) homeostasis is the neuronal calcium binding protein, calbindin-D28k that serves to buffer and transport Ca(2+) ions. This study evaluated the expression of hippocampal calbindin levels in the rat pilocarpine model of AE. Calbindin protein expression was reduced over 50% in the hippocampus in epileptic animals. This decrease was observed in the pyramidal layer of CA1, stratum lucidum of CA3, hilus, and stratum granulosum and stratum moleculare of the dentate gyrus when corrected for cell loss. Furthermore, calbindin levels in individual neurons were also significantly reduced. In addition, the expression of calbindin mRNA was decreased in epileptic animals. Time course studies demonstrated that decreased calbindin expression was initially present 1 month following pilocarpine-induced SE and lasted for up to 2 years after the initial episode of SE. The results indicate that calbindin is essentially permanently decreased in the hippocampus in AE. This decrease in hippocampal calbindin may be a major contributing factor underlying some of the plasticity changes that occur in epileptogenesis and contribute to the alterations in Ca(2+) homeostasis associated with AE.

Diazoxide prevents mitochondrial swelling and Ca2+ accumulation in CA1 pyramidal cells after cerebral ischemia in newborn pigs

Diazoxide (DIAZ), an opener of mitochondrial ATP-sensitive K(+) channels (mK(ATP)), protects neurons against hypoxic/ischemic stress in vivo, however, direct evidence showing mitochondrial effects of DIAZ in postischemic neurons is lacking. We investigated if DIAZ affects mitochondrial alterations after global ischemia/reperfusion (I/R) in CA1 pyramidal neurons by using oxalate-pyroantimonate electron cytochemistry. Anesthetized piglets were either non-treated, or treated with DIAZ (3 mg/kg, iv), I/R, DIAZ+I/R, or 5-hydroxy-decanoate (5HD)+DIAZ+I/R (n=6, 6, 11, 5, 7, respectively). Ischemia (10 min) was induced by intracranial pressure (ICP) elevation. After 5-30 min of reperfusion, the brains were fixed for ultrastructural studies. Relative volumes of Ca(2+)-containing deposits and mitochondria in CA1 pyramidal cells were determined by point counting on electron micrographs. I/R resulted in maximal increases in mitochondrial volume (from 7.14+/-0.63% to 9.74+/-0.57%*), and Ca(2+) levels (from 5.86+/-1.11% to 11.39+/-1.35%*; mean+/-S.E.M., *p<0.05) at 10-15-min reperfusion time. In this interval, pretreatment with DIAZ virtually abolished mitochondrial swelling (6.88+/-0.49%) and Ca(2+) accumulation (5.15+/-0.82%) evoked by I/R. The protective effect of DIAZ was reduced by 5HD, an inhibitor of mK(ATP), resulting in a calcium accumulation similar to that after IR (10.44+/-1.98%). Thus, DIAZ might preserve mitochondrial integrity in CA1 pyramidal cells after I/R, at least in part mediated by mK(ATP).

Long-term behavioral and morphological consequences of nonconvulsive status epilepticus in rats

The aims of the present study were to ascertain whether nonconvulsive status epilepticus (NCSE) could give rise to long-term behavioral deficits and permanent brain damage. Two months after NCSE was elicited with pilocarpine (15 mg/kg i.p.) in LiCl-pretreated adult male rats, animals were assigned to either behavioral (spontaneous behavior, social interaction, elevated plus-maze, rotorod, and bar-holding tests) or EEG studies. Another group of animals was sacrificed and their brains were processed for Nissl and Timm staining as well as for parvalbumin and calbindin immunohistochemistry. Behavioral analysis revealed motor deficits (shorter latencies to fall from rotorod as well as from bar) and disturbances in the social behavior of experimental animals (decreased interest in juvenile conspecific). EEGs showed no apparent abnormalities. Quantification of immunohistochemically stained sections revealed decreased amounts of parvalbumin- and calbindin-immunoreactive neurons in the motor cortex and of parvalbumin-positive neurons in the dentate gyrus. Despite relatively inconspicuous manifestations, NCSE may represent a risk for long-term deficits.