Strain differences in pH-sensitive K+ channel-expressing cells in chemosensory and nonchemosensory brain stem nuclei

Transient upregulation of TASK-1 expression in the hypoglossal nucleus during chronic intermittent hypoxia is reduced by serotonin 2A receptor antagonist

Hypoglossal motoneurons innervate genioglossus muscle, the contraction of which is critical in the maintenance of upper airway patency in patients with obstructive sleep apnea. As a potassium channel distributed in hypoglossal motoneurons, TWIK-related acid-sensitive K+ channel-1 (TASK-1) could be inhibited by 5-HT. This study aimed to investigate if TASK-1 expression in hypoglossal nucleus could be influenced by chronic intermittent hypoxia (CIH) and 5-HT_2A receptors antagonist. Two hundred twenty-eight rats were exposed to CIH or normoxia (NO) in the presence and absence of 5-HT _2A receptor antagonist (MDL-100907) microinjected into the hypoglossal nucleus. The expression of 5-HT and TASK-1 in the hypoglossal nucleus were detected by immunohistochemistry and reverse transcription quantitative polymerase chain reaction on the 1st, 3rd, 7th, 14th and 21st day of CIH exposure. The mean optical density (MOD) of 5-HT in the XII nucleus was significantly increased in the CIH and CIH + MDL group than the NO group on the 7th and 21st day ( p < 0.05). Compared with the NO group, the MOD and gene expression of TASK-1 in the CIH group was significantly increased on the 7th and 14th day ( p < 0.05), then normalized on the 21st day. The TASK-1 expression in the CIH + MDL group was significantly lower than the CIH + PBS and CIH group on the 7th and 14th day ( p < 0.05). The CIH-induced transiently upregulation of the TASK-1 expression in the hypoglossal nucleus could be reversed by 5-HT _2A receptor antagonist, indicating that the modulation of the TASK-1 expression in response to CIH involves 5-HT and 5-HT _2A receptors, and this CIH effect might be 5-HT _2A receptor-dependent.

RNASeq-derived transcriptome comparisons reveal neuromodulatory deficiency in the CO₂ insensitive brown Norway rat

Raphé-derived serotonin (5-HT) and thyrotropin-releasing hormone (TRH) play important roles in fundamental, homeostatic control systems such as breathing and specifically the ventilatory CO2 chemoreflex. Brown Norway (BN) rats exhibit an inherent and severe ventilatory insensitivity to hypercapnia but also exhibit relatively normal ventilation at rest and during other conditions, similar to multiple genetic models of 5-HT system dysfunction in mice. Herein, we tested the hypothesis that the ventilatory insensitivity to hypercapnia in BN rats is due to altered raphé gene expression and the consequent deficiencies in raphé-derived neuromodulators such as TRH. Medullary raphé transcriptome comparisons revealed lower expression of multiple 5-HT neuron-specific genes in BN compared to control Dahl salt-sensitive rats, predictive of reduced central nervous system monoamines by bioinformatics analyses and confirmed by high-performance liquid chromatography measurements. In particular, raphé Trh mRNA and peptide levels were significantly reduced in BN rats, and injections of the stable TRH analogue Taltirelin (TAL) stimulated breathing dose-dependently, with greater effects in BN versus control Sprague-Dawley rats. Importantly, TAL also effectively normalized the ventilatory CO2 chemoreflex in BN rats, but TAL did not affect CO2 sensitivity in control Sprague-Dawley rats. These data establish a molecular basis of the neuromodulatory deficiency in BN rats, and further suggest an important functional role for TRH signalling in the mammalian CO2 chemoreflex.