Neurons differentiating from murine neural crest in culture exhibit sensory or sympathetic-like calcium currents

The microtubular cytoskeleton of olfactory neurons derived from patients with schizophrenia or with bipolar disorder: Implications for biomarker characterization, neuronal physiology and pharmacological screening

Schizophrenia (SZ) and Bipolar Disorder (BD) are highly inheritable chronic mental disorders with a worldwide prevalence of around 1%. Despite that many efforts had been made to characterize biomarkers in order to allow for biological testing for their diagnoses, these disorders are currently detected and classified only by clinical appraisal based on the Diagnostic and Statistical Manual of Mental Disorders. Olfactory neuroepithelium-derived neuronal precursors have been recently proposed as a model for biomarker characterization. Because of their peripheral localization, they are amenable to collection and suitable for being cultured and propagated in vitro. Olfactory neuroepithelial cells can be obtained by a non-invasive brush-exfoliation technique from neuropsychiatric patients and healthy subjects. Neuronal precursors isolated from these samples undergo in vitro the cytoskeletal reorganization inherent to the neurodevelopment process which has been described as one important feature in the etiology of both diseases. In this paper, we will review the current knowledge on microtubular organization in olfactory neurons of patients with SZ and with BD that may constitute specific cytoskeletal endophenotypes and their relation with alterations in L-type voltage-activated Ca(2+) currents. Finally, the potential usefulness of neuronal precursors for pharmacological screening will be discussed.

Rolling Nagoya mouse strain (PROD-rol/rol) with classic piebald mutation

Ataxic rolling Nagoya (PROD-rol/rol) mice, which carry a mutation in the α1 subunit of the Ca_v2.1 channel (Cacna1a) gene, were discovered in 1969. They show white spots on agouti coat and have a mutation in the piebald spotting (s) locus. However, mutation analysis of the s locus encoding the endothelin receptor type B (Ednrb) gene in PROD-rol/rol mice had not been performed. Here, we examined the genomic and mRNA sequences of the Ednrb gene in PROD-rol/rol and wild-type rolling Nagoya (PROD-s/s) and studied the expression patterns of Ednrb and Cacna1a genes in these mice in comparison with C57BL/6J mice. Polymerase chain reaction analyses revealed two silent nucleotide substitutions in the coding region and insertion of a retroposon-like element in intron 1 of the Ednrb gene. Expression analyses demonstrated similar localizations and levels of Ednrb and Cacna1a expression in the colon between PROD-rol/rol and PROD-s/s mice, but the expression levels of both genes were diminished compared with C57BL/6J mice. Microsatellite genotyping showed that at least particular regions of chromosome 14 proximal to the Ednrb locus of the PROD strain were derived from Japanese fancy piebald mice. These results indicated that PROD-rol/rol mice have two mutant genes, Ednrb and Cacna1a. As no PROD strain had an intact Ednrb gene, using congenic rolling mice would better serve to examine rolling Nagoya-type Ca_v2.1 channel dysfunctions.

Mitochondrial Ca(2+) signals in autophagy

Macroautophagy (autophagy) is a lysosomal degradation pathway that is conserved from yeast to humans that plays an important role in recycling cellular constituents in all cells. A number of protein complexes and signaling pathways impinge on the regulation of autophagy, with the mammalian target of rapamycin (mTOR) as the central player in the canonical pathway. Cytoplasmic Ca(2+) signaling also regulates autophagy, with both activating and inhibitory effects, mediated by the canonical as well as non-canonical pathways. Here we review this regulation, with a focus on the role of an mTOR-independent pathway that involves the inositol trisphosphate receptor (InsP(3)R) Ca(2+) release channel and Ca(2+) signaling to mitochondria. Constitutive InsP(3)R Ca(2+) transfer to mitochondria is required for autophagy suppression in cells in nutrient-replete media. In its absence, cells become metabolically compromised due to insufficient production of reducing equivalents to support oxidative phosphorylation. Absence of this Ca(2+) transfer to mitochondria results in activation of AMPK, which activates mTOR-independent pro-survival autophagy. Constitutive InsP(3)R Ca(2+) release to mitochondria is an essential cellular process that is required for efficient mitochondrial respiration, maintenance of normal cell bioenergetics and suppression of autophagy.

Differential effects of capsaicin on rat visceral sensory neurons

Nodose neurons play an important role in the regulation of visceral function. Recent studies demonstrated that about 80% of these neurons contain messenger RNA for the capsaicin receptor, a heat-sensitive ion channel. Nodose neurons express voltage-sensitive sodium currents that can be differentiated based on their sensitivity to tetrodotoxin. Considering the potential role of tetrodotoxin-resistant sodium currents in somatosensory neurons, sodium channel expression and sodium currents were studied in nodose neurons. The results were correlated with the response to capsaicin. Nodose neurons contain messenger RNA for the tetrodotoxin-resistant sodium channel PN3. Consistent with these findings, about half of the neurons predominantly expressed tetrodotoxin-resistant sodium currents. In 54% (47/87) of the cells, capsaicin triggered an increase in intracellular calcium. Similarly, in 42% (18/43) of the cells, capsaicin elicited an inward current. There was no relationship between cell size (r=0.07) or sodium current properties (r=0.14) and the response to capsaicin. Micromolar concentrations of capsaicin inhibited voltage-dependent sodium, calcium and potassium currents. This effect was use dependent and did not involve the capsaicin receptor. In conclusion, capsaicin changed the excitability of visceral sensory neurons by blocking voltage-dependent ion channels, an effect that may contribute to the analgesic properties of capsaicin.

Spontaneous calcium transients are required for neuronal differentiation of murine neural crest

We have shown that cultured mouse neural crest (NC) cells exhibit transient increases in intracellular calcium. Up to 50% of the cultured NC-derived cells exhibited calcium transients during the period of neuronal differentiation. As neurogenic activity declined, so did the percentage of active NC-derived cells and their calcium spiking frequency. The decrease in calcium transient activity correlated with a decreased sensitivity to thimerosal, which sensitizes inositol 1,4,5-triphosphate receptors. Thimerosal increased the frequency of oscillations in active NC-derived cells and induced them in a subpopulation of quiescent cells. As neurogenesis ended, NC-derived cells became nonresponsive to thimerosal. Using the expression of time-dependent neuronal traits, we determined that neurons exhibited spontaneous calcium transients as early as a neuronal phenotype could be detected and continued through the acquisition of caffeine sensitivity, soon after which calcium transient activity stopped. A subpopulation of nonneuronal NC-derived cells exhibited calcium transient activity within the same time frame as neurogenesis in culture. Exposing NC-derived cells to 20 mM Mg(2+) blocked calcium transient activity and reduced neuronal number without affecting the survival of differentiated neurons. Using lineage-tracing analysis, we found that 50% of active NC-derived cells gave rise to clones containing neurons, while inactive cells did not. We hypothesize that calcium transient activity establishes a neuronal competence for undifferentiated NC cells.