Store-operated Ca(2+) entry in proliferating and retinoic acid-differentiated N- and S-type neuroblastoma cells.

Neuroblastoma cell lines are heterogeneous, comprised of at least three distinct cell phenotypes; neuroblastic N-type cells, non-neuronal substrate-adherent S-type cells and intermediate I-type cells. N- and S-type cell populations were enriched from the parental SH-SY5Y neuroblastoma cell line and induced to differentiate by the addition of retinoic acid (RA), a drug used in the treatment of neuroblastoma. N- and S-type cells were identified based on their differential expression of ß-tubulin III, vimentin and Bcl-2. Store-operated Ca(2+) entry (SOCE) was then measured in proliferating and differentiated N- and S-type cell populations and the expression of STIM1, Orai1 and TRPC1, three proteins reported to play a key role in SOCE, was determined. In N-type cells the RA-induced switch from proliferation to differentiation was accompanied by a down-regulation in SOCE. STIM1 and Orai1 expression became down-regulated in differentiated cells, consistent with their respective roles as ER Ca(2+) sensor and store-operated Ca(2+) channel (SOC). TRPC1 became up-regulated suggesting that TRPC1 is not involved in SOCE, at least in differentiated N-type cells. In S-type cells SOCE remained active following the RA-induced switch from proliferation to differentiation and the expression of STIM1 and Orai1 remained unchanged. TRPC1 was not expressed in S-type cells. Our results indicate that differentiation of neuronal cells is associated with a remodelling of SOCE. Therapeutic targeting of SOCE proteins could potentially be a means of promoting neuronal differentiation in the treatment of neuroblastoma.

Immunohistochemical localization of histamine H3 receptors in rodent skin, dorsal root ganglia, superior cervical ganglia, and spinal cord: potential antinociceptive targets.

Activation of histamine H3 receptors (H3Rs) reduces inflammation and nociception, but the existence of H3Rs on peripheral innervation has never been demonstrated. Here we use antibodies to locate H3Rs in whisker pads, hairy and glabrous hind paw skin, dorsal root ganglia (DRGs), and spinal cords of rats, wild type mice, and H3R knockout (H3KO) mice. Although H3Rs have been hypothesized to be on C and sympathetic fibers, H3R-like immunoreactivity (H3R-LI) was only detected on presumptive periarterial A delta fibers and on A beta fibers that terminated in Meissner's corpuscles and as lanceolate endings around hair follicles. The H3R-positive periarterial fibers were thin-caliber and coexpressed immunoreactivity for calcitonin gene-related peptide (CGRP), substance P, acid sensing ion channel 3, and 200 kDa neurofilament protein (NF). H3R-LI was also detected on epidermal keratinocytes and Merkel cells, but not on Merkel endings, C fibers, any other A delta fibers, or sympathetic fibers. In DRGs, H3R-LI was preponderantly on medium to large neurons coexpressing NF-LI and mostly CGRP-LI. In dorsal horn, CGRP-positive fibers with and without H3R-LI ramified extensively in lamina II; many of the former formed a plexus in lamina V. Low levels of H3R-LI were also present on A beta fibers penetrating superficial and into deeper laminae. The distribution of H3R-LI was similar in rats and wild type mice, but was eliminated or strongly reduced in A delta fibers and A beta fibers, respectively, in H3KO mice. Taken with recently published behavioral results, the present findings suggest that periarterial, peptidergic, H3R-containing A delta fibers may be sources of high threshold mechanical nociception.

Aberrant GABA(A) receptor expression in the dentate gyrus of the epileptic mutant mouse stargazer.

Stargazer (stg) mutant mice fail to express stargazin [transmembrane AMPA receptor regulatory protein gamma2 (TARPgamma2)] and consequently experience absence seizure-like thalamocortical spike-wave discharges that pervade the hippocampal formation via the dentate gyrus (DG). As in other seizure models, the dentate granule cells of stg develop elaborate reentrant axon collaterals and transiently overexpress brain-derived neurotrophic factor. We investigated whether GABAergic parameters were affected by the stg mutation in this brain region. GABA(A) receptor (GABAR) alpha4 and beta3 subunits were consistently upregulated, GABAR delta expression appeared to be variably reduced, whereas GABAR alpha1, beta2, and gamma2 subunits and the GABAR synaptic anchoring protein gephyrin were essentially unaffected. We established that the alpha4 betagamma2 subunit-containing, flunitrazepam-insensitive subtype of GABARs, not normally a significant GABAR in DG neurons, was strongly upregulated in stg DG, apparently arising at the expense of extrasynaptic alpha4 betadelta-containing receptors. This change was associated with a reduction in neurosteroid-sensitive GABAR-mediated tonic current. This switch in GABAR subtypes was not reciprocated in the tottering mouse model of absence epilepsy implicating a unique, intrinsic adaptation of GABAergic networks in stg. Contrary to previous reports that suggested that TARPgamma2 is expressed in the dentate, we find that TARPgamma2 was neither detected in stg nor control DG. We report that TARPgamma8 is the principal TARP isoform found in the DG and that its expression is compromised by the stargazer mutation. These effects on GABAergic parameters and TARPgamma8 expression are likely to arise as a consequence of failed expression of TARPgamma2 elsewhere in the brain, resulting in hyperexcitable inputs to the dentate.