Identification of 5-HT Receptor Subtypes Enhancing Inhibitory Transmission in the Rat Spinal Dorsal Horn in vitro

Abstract

Background5-hydroxytryptamine (5-HT) is one of the major neurotransmitters widely distributed in the CNS. Several 5-HT receptor subtypes have been identified in the spinal dorsal horn which act on both pre- and postsynaptic sites of excitatory and inhibitory neurons. However, the receptor subtypes and sites of actions as well as underlying mechanism are not clarified rigorously. Several electrophysiological studies have been performed to investigate the effects of 5-HT on excitatory transmission in substantia gelatinosa (SG) of the spinal cord. In the present study, to understand the effects of 5-HT on the inhibitory synaptic transmission and to identify receptor subtypes, the blind whole cell recordings were performed from SG neurons of rat spinal cord slices.ResultsBath applied 5-HT (50 μM) increased the frequency but not amplitudes of spontaneous inhibitory postsynaptic currents (sIPSCs) in 58% of neurons, and both amplitude and frequency in 23% of neurons. The frequencies of GABAergic and glycinergic mIPSCs were both enhanced. TTX (0.5 μM) had no effect on the increasing frequency, while the enhancement of amplitude of IPSCs was eliminated. Evoked-IPSCs (eIPSCs) induced by focal stimulation near the recording neurons in the presence of CNQX and APV were enhanced in amplitude by 5-HT. In the presence of Ba2+ (1 mM), a potassium channel blocker, 5-HT had no effect on both frequency and amplitude. A 5-HT2A receptor agonist, TCB-2 mimicked the 5-HT effect, and ketanserin, an antagonist of 5-HT2A receptor, inhibited the effect of 5-HT partially and TCB-2 almost completely. A 5-HT2C receptor agonist WAY 161503 mimicked the 5-HT effect and this effect was blocked by a 5-HT2C receptor antagonist, N-desmethylclozapine. The amplitudes of sIPSCs were unaffected by 5-HT2A or 5-HT2C agonists. A 5-HT3 receptor agonist mCPBG enhanced both amplitude and frequency of sIPSCs. This effect was blocked by a 5-HT3 receptor antagonist ICS-205,930. The perfusion of 5-HT2B receptor agonist had no effect on sIPSCs.ConclusionsOur results demonstrated that 5-HT modulated the inhibitory transmission in SG by the activation of 5-HT2A and 5-HT2C receptors subtypes located predominantly at inhibitory interneuron terminals, and 5-HT3 receptors located at inhibitory interneuron terminals and soma-dendrites, consequently enhanced both frequency and amplitude of IPSCs.

Presynaptic Inhibitory Effects of Fluvoxamine, a Selective Serotonin Reuptake Inhibitor, on Nociceptive Excitatory Synaptic Transmission in Spinal Superficial Dorsal Horn Neurons of Adult Mice

“…Moreover, intrinsic GABAergic neurons also express 5-HT 3 receptors (35,36), activation of which has been shown to increase the release of GABA (37). More recently, Xie et al have shown that the 5-HT 3 receptor agonist mCPBG increases both the amplitude and frequency of GABAergic and glycinergic sIPSCs in SG neurons of rat spinal cord slices (38). Thus, increased GABA and/or glycine could act on primary afferent terminals to reduce nociceptive synaptic transmission.…”

Glutaminase 1 is a potential biomarker for chronic post-surgical pain in the rat dorsal spinal cord using differential proteomics

“…The dorsal spinal cord then acts as an important pain modulation center, as it provides a place for the brainstem descending suppression system to execute its action and also regulates the transmission of nociceptive information through the intermediate neurons (Singh and Tao 2012;Takazawa and MacDermott 2010;Yang and Ma 2011). Many studies have shown that a large amount of pain-associated molecules act in the dorsal spinal cord, especially those associated with nerve pathological pain (Quan-Xin et al 2012;Wei et al 2013;Xie et al 2012;Zhu et al 2013). Besides, various neurotransmitters and neurotransmitter receptors in the dorsal spinal cord could be altered during the nerve pathological pain (Paul et al 2012;Rahman et al 2007;Wan et al 2004).…”

Effect of methysergide on pudendal inhibition of micturition reflex in cats

“…Therefore, it is possible that the pudendal afferent firing might be transmitted to the brain and activate the raphe nuclei that drives the descending 5-HT pathway to activate 5-HT 2 excitatory receptors on inhibitory spinal interneurons (GABAergic/glycinergic) that in turn suppress the micturition reflex. This possibility is supported by various evidence: (1) activation of presynaptic 5-HT 2A receptors on the GABAergic interneuron can enhances GABA release (Fink and Göthert, 2007), (2) 5-HT 2A receptors are present on the GABAergic or glycinergic neurons in the spinal dorsal horn (Wang et al, 2009; Xie et al, 2012) and contribute to spinal antinociception (Liu et al, 2007; Song et al, 2011), and (3) spinal 5-HT 2A receptors are involved in the antinociceptive effect induced by transcutaneous electrical nerve stimulation (Radhakrishnan et al, 2003). However, methysergide did not completely block PNS inhibition in the AA irritated bladder raising the possibility that pudendal neuromodulation is mediated in part by non-5-HT mechanisms.…”