A 3.7 kb Fragment of the MouseScn10aGene Promoter Directs Neural Crest But Not Placodal Lineage EGFP Expression in a Transgenic Animal

Abstract

Under physiological conditions, the voltage-gated sodium channel Na v 1.8 is expressed almost exclusively in primary sensory neurons. The mechanism restricting Na v 1.8 expression is not entirely clear, but we have previously described a 3.7 kb fragment of the Scn10a promoter capable of recapitulating the tissue-specific expression of Na v 1.8 in transfected neurons and cell lines (Puhl and Ikeda, 2008). To validate these studies in vivo, a transgenic mouse encoding EGFP under the control of this putative sensory neuron specific promoter was generated and characterized in this study. Approximately 45% of dorsal root ganglion neurons of transgenic mice were EGFPpositive (mean diameter ϭ 26.5 m). The majority of EGFP-positive neurons bound isolectin B4, although a small percentage (ϳ10%) colabeled with markers of A-fiber neurons. EGFP expression correlated well with the presence of Na v 1.8 transcript (95%), Na v 1.8-immunoreactivity (70%), and TTX-R I Na (100%), although not all Na v 1.8-expressing neurons expressed EGFP. Several cranial sensory ganglia originating from neurogenic placodes, such as the nodose ganglion, failed to express EGFP, suggesting that additional regulatory elements dictate Scn10a expression in placodal-derived sensory neurons. EGFP was also detected in discrete brain regions of transgenic mice. Quantitative PCR and Na v 1.8-immunoreactivity confirmed Na v 1.8 expression in the amygdala, brainstem, globus pallidus, lateral and paraventricular hypothalamus, and olfactory tubercle. TTX-R I Na recorded from EGFP-positive hypothalamic neurons demonstrate the usefulness of this transgenic line to study novel roles of Na v 1.8 beyond sensory neurons. Overall, Scn10a-EGFP transgenic mice recapitulate the majority of the Na v 1.8 expression pattern in neural crest-derived sensory neurons.

Identification of substances which regulate activity of corticotropin-releasing factor-producing neurons in the paraventricular nucleus of the hypothalamus

“…The possible existence of TTX-resistant sodium channels (Na v 1.5, Na v 1.8 and Na v 1.9) 48 might also be taken into consideration. Among these channels, Na v 1.8 is reported to be expressed in the PVN; however, its sodium channel current ( I Na ) accounts for less than 2% of the total I Na 49 . In addition, we sequentially screened multiple substances; however, GPCR itself can be modulated by specific substances via some mechanisms, such as desensitization/resensitization 50 and heterodimerization 51 , 52 .…”

Conditional knockout of NaV1.6 in adult mice ameliorates neuropathic pain

“…Compensatory dysregulation of other molecules may have occurred during development, for example, the TTX-S current was up-regulated in Na V 1.8-null mutant mice 6 , and Na V 1.7 knockout was reported to increase met-enkephalin expression 49 . Additionally, Na V 1.8 expression has been reported in CNS nuclei of naïve mice 50 , thus Na V 1.8-Cre driven Na V 1.6 knockout in these neurons may confound the effects of Na V 1.6 deletion in primary afferents. Moreover, normal neuropathic pain has also been reported to be retained following Na V 1.8 knockout, Na V 1.7/Na V 1.8 double knockout or genetic ablation of Na V 1.8-positive neurons 5 , 6 , 51 .…”

Na v 1.8 neurons are involved in limiting acute phase responses to dietary fat

“…Of note, Voltage-gated sodium channels, such as Na v 1.7, are expressed in the brain including in neurons involved in energy balance [46] . One study reported widespread expression for Na v 1.8 in the mouse brain including the hypothalamus [47] . However, we have examined the brain of Na v 1.8-Cre-tdTomato reporter mice and found no evidence of any Cre activity in the hypothalamus (not shown).…”