Dual role of calbindin-D28Kin vesicular catecholamine release from mouse chromaffin cells

Can Brain Health Be Supported by Vitamin D-Based Supplements? A Critical Review

This review presents recent knowledge on the neuroprotective effects of vitamin D and their usefulness as oral supplementation when combined with other molecules, such as curcumin. A critical look at the effectiveness of vitamin D in this field is also provided. Vitamin D plays a crucial role in neuroprotection and in the cognitive decline associated with aging, where vitamin D’s levels are related to the levels of several neurotrophic factors. An important role of vitamin D has also been observed in the mechanism of neuroinflammation, which is the basis of several aging conditions, including cognitive decline and neurodegeration; furthermore, the neuroprotective effect of vitamin D in the cognitive decline of aging has recently been reported. For this reason, many food supplements created for humans contain vitamin D alone or combined with other molecules with antioxidant properties. However, recent studies also explored negative consequences of the use at a high dosage of vitamin D. Vitamin D in tissues or brain cells can also modulate calbindin-D28K, parvalbumin, and calretinin, and is involved in immune function, thanks also to the combination with curcumin. Curcumin acts as a free radical scavenger and antioxidant, inhibiting lipid peroxidation and oxidative DNA damage. In particular, curcumin is a potent immune-regulatory agent and its administration has been reported to attenuate cognitive impairments. These effects could be exploited in the future to control the mechanisms that lead to the brain decay typical of neurodegenerative diseases.

Calbindin-D28k and calretinin in chicken inner retina during postnatal development and neuroplasticity by dim red light

Members of the family of calcium binding proteins (CBPs) are involved in the buffering of calcium (Ca2+) by regulating how Ca2+ can operate within synapses or more globally in the entire cytoplasm and they are present in a particular arrangement in all types of retinal neurons. Calbindin D28k and calretinin belong to the family of CBPs and they are mainly co-expressed with other CBPs. Calbindin D28k is expressed in doubles cones, bipolar cells and in a subpopulation of amacrine and ganglion neurons. Calretinin is present in horizontal cells as well as in a subpopulation of amacrine and ganglion neurons. Both proteins fill the soma at the inner nuclear layer and the neuronal projections at the inner plexiform layer. Moreover, calbindin D28k and calretinin have been associated with neuronal plasticity in the central nervous system. During pre and early postnatal visual development, the visual system shows high responsiveness to environmental influences. In this work we observed modifications in the pattern of stratification of calbindin immunoreactive neurons, as well as in the total amount of calbindin through the early postnatal development. In order to test whether or not calbindin is involved in retinal plasticity we analyzed phosphorylated p38 MAPK expression, which showed a decrease in p-p38 MAPK, concomitant to the observed decrease of calbindin D28k. Results showed in this study suggest that calbindin is a molecule related with neuroplasticity, and we suggest that calbindin D28k has significant roles in neuroplastic changes in the retina, when retinas are stimulated with different light conditions.

Differential alterations of synaptic plasticity in dentate gyrus and CA1 hippocampal area of Calbindin-D28K knockout mice

Regulation of the intracellular calcium concentration ([Ca(2+)](i)) is of critical importance for synaptic function. Therefore, neurons buffer [Ca(2+)](i) using intracellular Ca(2+)-binding proteins (CaBPs). Previous evidence suggests that Calbindin-D(28K) (CB), an abundantly expressed endogenous fast CaBP, plays an important role in neuronal survival, motor coordination, spatial learning paradigms and some forms of synaptic plasticity. In the present study, the role of CB in synaptic transmission and plasticity was further investigated using extracellular recordings of synaptic activity in cell- and dendritic layers of dentate gyrus (DG) and CA1 area in hippocampal slices from wild-type, heterozygous and homozygous CB knockout mice. The results demonstrate a consistent failure to maintain long-term potentiation (LTP) in hippocampal DG and CA1 area of knockout mice. Compared to wild-type mice, the paired-pulse ratio of EPSPs recorded in DG is significantly lower in slices from knockout mice, whereas it is significantly higher in CA1 area. The amplitude of the population spike recorded in CA1 area of wild-type mice steadily increases following tetanic stimulation, whereas it steadily decreases in knockout mice. The combined results demonstrate that the absence of CB results in an impairment of LTP maintenance in both hippocampal DG and CA1 area, whereas paired-pulse facilitation and cellular excitability in CA1 area are differentially affected. These results support the role of CB as a critical determinant for several forms of synaptic plasticity in hippocampal DG and CA1 area. It is hypothesized that CB functions as a postsynaptic Ca(2+) buffer as well as a presynaptic Ca(2+) sensor.

Three distinct modes of exocytosis revealed by amperometry in neuroendocrine cells

Neurotransmission requires Ca(2+)-dependent release of secretory products through fusion pores that open and reclose (partial membrane distention) or open irreversibly (complete membrane distention). It has been challenging to distinguish between these release modes; however, in the work presented here, we were able to deduce different modes of depolarization-evoked exocytosis in neuroendocrine chromaffin and PC12 cells solely by analyzing amperometric recordings. After we determined the quantal size (Q), event half-width (t(50)), event amplitude (I(peak)), and event decay time constant (τ(decay)), we fitted scatter plots of log-transformed data with a mixture of one- and two-dimensional Gaussian distributions. Our analysis revealed three distinct and differently shaped clusters of secretory events, likely corresponding to different modes of exocytosis. Complete membrane distention, through fusion pores of widely varying conductances, accounted for 70% of the total amount of released catecholamine. Two different kinds of partial membrane distention (kiss-and-run and kiss-and-stay exocytosis), characterized by mode-specific fusion pores with unitary conductances, accounted for 20% and 10%, respectively. These results show that our novel one- and two-dimensional analysis of amperometric data reveals new release properties and enables one to distinguish at least three different modes of exocytosis solely by analyzing amperometric recordings.

Is there convincing biological or behavioral evidence linking vitamin D deficiency to brain dysfunction?

Vitamin D insufficiency is common in the United States; the elderly and African-Americans are at particularly high risk of deficiency. This review, written for a broad scientific readership, presents a critical overview of scientific evidence relevant to a possible causal relationship between vitamin D deficiency and adverse cognitive or behavioral effects. Topics discussed are 1) biological functions of vitamin D relevant to cognition and behavior; 2) studies in humans and rodents that directly examine effects of vitamin D inadequacy on cognition or behavior; and 3) immunomodulatory activity of vitamin D relative to the proinflammatory cytokine theory of cognitive/behavioral dysfunction. We conclude there is ample biological evidence to suggest an important role for vitamin D in brain development and function. However, direct effects of vitamin D inadequacy on cognition/behavior in human or rodent systems appear to be subtle, and in our opinion, the current experimental evidence base does not yet fully satisfy causal criteria. Possible explanations for the apparent inconsistency between results of biological and cognitive/behavioral experiments, as well as suggested areas for further research are discussed. Despite residual uncertainty, recommendations for vitamin D supplementation of at-risk groups, including nursing infants, the elderly, and African-Americans appear warranted to ensure adequacy.

Relationship between amperometric pre-spike feet and secretion granule composition in chromaffin cells: an overview

Amperometry is a simple and powerful technique to study exocytosis at the single cell level. By positioning and polarizing (at an appropriate potential at which the molecules released by the cell can be oxidized) a carbon fiber microelectrode at the top of the cell, each exocytotic event is detected as an amperometric spike. More particularly, a portion of these spikes has previously been shown to present a foot, i.e. a small pedestal of current that precedes the spike itself. Among the important number of works dealing with the monitoring of exocytosis by amperometry under different conditions, only a few studies focus on amperometric spikes with a foot. In this work, by coupling our previous and recent experiments on chromaffin cells (that release catecholamines after stimulation) with literature data, we bring more light on what an amperometric foot and particularly its features, represents.

Neonatal exposure to brominated flame retardant BDE-47 reduces long-term potentiation and postsynaptic protein levels in mouse hippocampus

BACKGROUND

Increasing environmental levels of brominated flame retardants raise concern about possible adverse effects, particularly through early developmental exposure.

OBJECTIVE

The objective of this research was to investigate neurodevelopmental mechanisms underlying previously observed behavioral impairments observed after neonatal exposure to polybrominated diphenyl ethers (PBDEs).

METHODS

C57Bl/6 mice received a single oral dose of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on postnatal day (PND) 10 (i.e., during the brain growth spurt). On PND17-19, effects on synaptic plasticity, levels of postsynaptic proteins involved in long-term potentiation (LTP), and vesicular release mechanisms were studied ex vivo. We investigated possible acute in vitro effects of BDE-47 on vesicular catecholamine release and intracellular Ca(2+) in rat pheochromocytoma (PC12) cells.

RESULTS

Field-excitatory postsynaptic potential (f-EPSP) recordings in the hippocampal CA1 area demonstrated reduced LTP after exposure to 6.8 mg (14 micromol)/kg body weight (bw) BDE-47, whereas paired-pulse facilitation was not affected. Western blotting of proteins in the postsynaptic, triton-insoluble fraction of hippocampal tissue revealed a reduction of glutamate receptor subunits NR2B and GluR1 and autophosphorylated-active Ca(2+)/calmodulin-dependent protein kinase II (alphaCaMKII), whereas other proteins tested appeared unaffected. Amperometric recordings in chromaffin cells from mice exposed to 68 mg (140 micromol)/kg bw BDE-47 did not reveal changes in catecholamine release parameters. Modest effects on vesicular release and intracellular Ca(2+) in PC12 cells were seen following acute exposure to 20 microM BDE-47. The combined results suggest a post-synaptic mechanism in vivo.

CONCLUSION

Early neonatal exposure to a single high dose of BDE-47 causes a reduction of LTP together with changes in postsynaptic proteins involved in synaptic plasticity in the mouse hippocampus.