Martinello Katiuscia, Sucapane Antonietta, Fucile Sergio
IRCCS Neuromed, Via Atinense, 86077 Pozzilli, Italy.
Department of Physiology and Pharmacology, Sapienza University of Rome, P.le Aldo Moro, 5, 00185 Rome, Italy.
Life (Basel). 2022 Aug 2;12(8):1178. doi: 10.3390/life12081178.
Rat dorsal root ganglion (DRG) neurons express 5-hydroxytryptamine receptors (5-HT3Rs). To elucidate their physiological role in the modulation of sensory signaling, we aimed to quantify their functional expression in newborn and adult rat DRG neurons, as well as their ability to modulate the Ca-dependent neurotransmitter release, by means of electrophysiological techniques combined with fluorescence-based Ca imaging. The selective 5-HT3R agonist mCPBG (10 μM) elicited whole-cell currents in 92.5% of adult DRG neurons with a significantly higher density current than in responding newborn cells (52.2%), suggesting an increasing serotoninergic modulation on primary afferent cells during development. Briefly, 5-HT3Rs expressed by adult DRG neurons are permeable to Ca ions, with a measured fractional Ca current (i.e., the percentage of total current carried by Ca ions, Pf) of 1.0%, similar to the value measured for the human heteromeric 5-HT3 receptor (P = 1.1%), but lower than that of the human homomeric 5-HT3 receptor (P = 3.5%). mCPBG applied to co-cultures of newborn DRG and spinal neurons significantly increased the miniature excitatory postsynaptic currents (mEPSCs) frequency in a subset of recorded spinal neurons, even in the presence of Cd, a voltage-activated Ca channel blocker. Considered together, our findings indicate that the Ca influx through heteromeric 5-HT3Rs is sufficient to increase the spontaneous neurotransmitter release from DRG to spinal neurons.
大鼠背根神经节（DRG）神经元表达5-羟色胺受体（5-HT3Rs）。为了阐明它们在感觉信号调制中的生理作用，我们旨在通过结合基于荧光的钙成像的电生理技术，量化它们在新生和成年大鼠DRG神经元中的功能表达，以及它们调节钙依赖性神经递质释放的能力。选择性5-HT3R激动剂mCPBG（10μM）在92.5%的成年DRG神经元中引发全细胞电流，其电流密度明显高于反应性新生细胞（52.2%），这表明在发育过程中，初级传入细胞上的5-羟色胺能调制增加。简而言之，成年DRG神经元表达的5-HT3Rs对钙离子具有通透性，测得的钙电流分数（即钙离子携带的总电流百分比，Pf）为1.0%，与人类异聚体5-HT3受体测得的值相似（P = 1.1%），但低于人类同聚体5-HT3受体（P = 3.5%）。将mCPBG应用于新生DRG和脊髓神经元的共培养物中，即使在存在电压激活钙通道阻滞剂镉的情况下，也能显著增加一部分记录的脊髓神经元中的微小兴奋性突触后电流（mEPSCs）频率。综合考虑，我们的研究结果表明，通过异聚体5-HT3Rs的钙内流足以增加从DRG到脊髓神经元的自发性神经递质释放。
