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

Affinity-purified antibodies raised against the peptide sequence H3 (349-358) receptor specifically recognized two protein species with Mr 62,000 and 93,000 in adult mouse forebrain membranes. Both immunoreactive species were suppressed greatly by preincubation of the antibody with the respective peptide. Immunohistochemical analysis using affinity-purified anti-H3 (349-358) antibodies yielded a high degree of coincidence with ligand-autoradiographical information, with high levels detected in the CA3 and dentate gyrus of the hippocampus, laminae V of the cerebral cortex, the olfactory tubercle, Purkinje cell layer of the cerebellum, substantia nigra, globus pallidus, thalamus and striatum. This study suggests further biochemical evidence for multiple H3 receptor subtypes and the widespread distribution of the H3 receptor in the mammalian brain.

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 β-tubulin III, vimentin and Bcl-2. Store-operated Ca2 + 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 Ca2 + sensor and store-operated Ca2 + 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.

No abstract

Stargazer (stg) mutant mice fail to express stargazin [transmembrane AMPA receptor regulatory protein ␥2 (TARP␥2)] 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) ␣4 and ␤3 subunits were consistently upregulated, GABAR ␦ expression appeared to be variably reduced, whereas GABAR ␣1, ␤2, and ␥2 subunits and the GABAR synaptic anchoring protein gephyrin were essentially unaffected. We established that the ␣4␤␥2 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 ␣4␤␦-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 TARP␥2 is expressed in the dentate, we find that TARP␥2 was neither detected in stg nor control DG. We report that TARP␥8 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 TARP␥8 expression are likely to arise as a consequence of failed expression of TARP␥2 elsewhere in the brain, resulting in hyperexcitable inputs to the dentate.