EXPRESSION OF C-fos PROTEIN IN SEROTONERGIC NEURONS OF RAT BRAINSTEM FOLLOWING ELECTRO-ACUPUNCTURE

The Involvement of Descending Pain Inhibitory System in Electroacupuncture-Induced Analgesia

Chronic pain is a major health problem, which can impair quality of life and reduce productivity. Electroacupuncture (EA), a modality of medicine based on the theories of Traditional Chinese Medicine (TCM), presents great therapeutic effects on chronic pain. Its clinical application has gained increasing popularity, and in parallel, more research has been performed on the mechanisms of EA-induced analgesia. The past decades have seen enormous advances both in neuronal circuitry of needle-insertion and in its molecular mechanism. EA may block pain by activating the descending pain inhibitory system, which originates in the brainstem and terminates at the spinal cord. This review article synthesizes corresponding studies to elucidate how EA alleviate pain via the mediation of this descending system. Much emphasis has been put on the implication of descending serotonergic and noradrenergic pathways in the process of pain modulation. Also, other important transmitters and supraspinal regions related to analgesic effects of EA have been demonstrated. Finally, it should be noticed that there exist some shortcomings involved in the animal experimental designed for EA, which account for conflicting results obtained by different studies.

Mechanisms of electroacupuncture-induced analgesia on neuropathic pain in animal model

Neuropathic pain remains as one of the most difficult clinical pain syndromes to treat. Electroacupuncture (EA), involving endogenous opioids and neurotransmitters in the central nervous system (CNS), is reported to be clinically efficacious in various fields of pain. Although multiple experimental articles were conducted to assess the effect of EA-induced analgesia, no review has been published to assess the efficacy and clarify the mechanism of EA on neuropathic pain. To this aim, this study was firstly designed to evaluate the EA-induced analgesic effect on neuropathic pain and secondly to guide and help future efforts to advance the neuropathic pain treatment. For this purpose, articles referring to the analgesic effect of acupuncture on neuropathic pain and particularly the work performed in our own laboratory were analyzed. Based on the articles reviewed, the role of spinal opioidergic, adrenergic, serotonergic, cholinergic, and GABAergic receptors in the mechanism of EA-induced analgesia was studied. The results of this research demonstrate that μ and δ opioid receptors, α₂-adrenoreceptors, 5-HT_1A and 5-HT₃ serotonergic receptors, M₁ muscarinic receptors, and GABA_A and GABA_B GABAergic receptors are involved in the mechanisms of EA-induced analgesia on neuropathic pain.

Electroacupuncture for refractory obsessive-compulsive disorder: a pilot waitlist-controlled trial

A large proportion of obsessive-compulsive disorder (OCD) patients are refractory to pharmacological and cognitive-behavioral therapy. The aim of this pilot, waitlist-controlled trial was to evaluate the effectiveness of electroacupuncture (EA) as add-on therapy for treatment-resistant OCD. Nineteen patients with treatment-resistant OCD were assigned to EA treatment for 12 sessions (5 sessions per week, n = 10) or waitlist for controls (n = 9) while continuing their current anti-OCD medications. The clinical outcomes were measured using the Yale-Brown Obsessive-Compulsive Scale and the Clinical Global Impression-Severity at baseline and end point. EA additional treatment produced significantly greater improvements at end point compared with the waitlist group in reducing both Yale-Brown Obsessive-Compulsive Scale (10.2 +/- 4.2 vs. 18.8 +/- 7.4, p = 0.004) and Clinical Global Impression-Severity scores (3.0 +/- 1.1 vs. 4.4 +/- 1.1, p = 0.002). As an additional therapy, EA is effective in alleviating OCD symptoms of treatment-resistant patients. A large-scale controlled study is warranted.

Antidepressive-like effects of electroacupuncture in rats

Here, we investigate the effects of electroacupunture on the depressive-like symptoms in learned helplessness and forced swim tests in rats. Electroacupuncture stimulation (EA) was provided at ST-36 (Zusanli) and SP-6 (Sanyinjiao) acupoints. A positive control group was treated with imipramine. To verify the effects of EA over serotonergic system, other additional groups received daily, for three days, p-chlorophenylalanine and after two days, were submitted to behavioral tests. EA, like imipramine, enhanced the successful active avoidance in the learned helplessness and diminished the time spent in immobility position in the forced swim test, without affecting the number of squares crossed in the open field test. The administration of p-chlorophenylalanine abolished the antidepressive-like effect of EA. EA generates a clear antidepressant effect in two different animal models of depression, and this effect is related, at least in part, to the serotonergic system.

The central serotonergic system mediates the analgesic effect of electroacupuncture on ZUSANLI (ST36) acupoints

Evidence in the past decade indicates that the mechanisms of anti-nociception of electroacupuncture (EAc) involve actions of neuropeptides (i.e., enkephalin and endorphin) and monoamines (i.e., serotonin and norepinephrine) in the central nervous system. Our present results using a subcutaneous injection of formalin to test pain sensation in mice provide further understanding of the involvement of serotonin in the actions of EAc-induced analgesia. Our observations show that (1) EAc at three different frequencies (2, 10 and 100 Hz) elicited an anti-nociceptive effect as determined by behavioral observations of reduced hindpaw licking; (2) exogenously intracerebroventricular administration of 5-hydroxytryptamine (5-HT) exhibited an analgesic effect, which partially mimicked the analgesic actions of EAc; (3) the anti-nociception of EAc at different frequencies was attenuated after reduced biosynthesis of serotonin by the administration of the tryptophan hydroxylase inhibitor, P-chlorophenylalanine, and (4) the 5-HT(1A) and 5-HT(3) receptor antagonists, pindobind-5-HT(1A) and LY-278584, respectively, blocked three different frequencies of EAc-induced analgesic effects, but the anti-nociceptive effect of 100 Hz EAc was potentiated by the 5-HT(2) receptor antagonist, ketanserin. These observations suggest that 5-HT(1A) and 5-HT(3) receptors partially mediate the analgesic effects of EAc, but that the 5-HT(2) receptor is conversely involved in the nociceptive response.

Fos expression in serotonergic neurons in the rat brainstem following noxious stimuli: an immunohistochemical double-labelling study

In order to detect whether there were different expression patterns of Fos protein induced by somatic or visceral noxious stimulation in the serotonergic neurons in the rat brainstem, an immunohistochemical double-labelling technique for serotonin (5-HT) and Fos was employed after subcutaneous or stomach injection of formalin. The two stimuli were matched in pilot experiments to produce maximum Fos expression. The expression of Fos protein in 5-HT-containing neurons (5-HT/Fos co-localized neurons) could be observed in the ventrolateral subdivision of the midbrain periaqueductal grey, interpeduncular nucleus, paramedian raphe nucleus, all of the brainstem raphe nuclei, the alpha part of the gigantocellular reticular nucleus and the lateral paragigantocellular reticular nucleus. The locations of the 5-HT/Fos co-localized neurons in the brainstem of animals subjected to somatic noxious stimulation were similar to those subjected to visceral noxious stimulation. However, the number and proportion of the 5-HT/Fos co-localized neurons in the median raphe nucleus and nucleus raphe obscurus of the rat subjected to visceral noxious stimulation were statistically greater than those in rats subjected to somatic noxious stimulation. These results suggest that serotonergic neurons in median raphe nucleus and nucleus raphe obscurus have a tendency to higher neuronal activity after visceral noxious stimulation.

Suppressive effects of Neiting acupuncture on toothache: an experimental analysis on Fos expression evoked by tooth pulp stimulation in the trigeminal subnucleus pars caudalis and the periaqueductal gray of rats

To clarify the antinociceptive mechanism of acupuncture on acute pain, c-fos protein (Fos) expression induced by tooth pulp stimulation was immunohistochemically examined in the spinal trigeminal subnucleus pars caudalis (spVc) and the periaqueductal gray (PAG) of rats with or without Neiting acupuncture. The central projection of trigeminal ganglion neurons innervating in the tooth pulp was examined by tract-tracing method with horseradish peroxidase-conjugated wheat germ agglutinin (WGA-HRP). Central terminals from the first maxillary molar tooth were labeled transganglionically in the dorsomedial part of spVc with WGA-HRP. Numerous numbers of Fos-immunoreactive (Fos-ir) cells were found in the spVc and PAG by stimulation of the tooth pulp with acetic acid or saline. Neiting acupuncture significantly reduced the Fos expression in the spVc induced by tooth pulp stimulation. On the other hand, Neiting acupuncture evoked many Fos-ir cells in the PAG. The present results suggest that Neiting acupuncture activated PAG neurons that sent descending inhibitory fibers to medullo-spinal nociceptive neurons, and reduced the number of Fos-expressed neurons in the trigeminal subnucleus pars caudalis mediating noxious information from teeth to the higher central nervous system.

Activation of serotonin-immunoreactive cells in the dorsal raphe nucleus in rats exposed to an uncontrollable stressor

The dorsal raphe nucleus (DRN) and its serotonergic terminal regions have been suggested to be part of the neural substrate by which exposure to uncontrollable stressors produces poor escape responding and enhanced conditioned fear expression. Such stressor exposure is thought to selectively activate DRN serotonergic neurons in such a way as to render them transiently sensitized to further input. As a result of this sensitized state, behavioral testing procedures are thought to cause excess serotonergic activity in brain regions that control these behaviors. The present studies were conducted to investigate activity in the DRN following exposure to escapable and yoked, inescapable tailshock. Neural activity was characterized using immunohistochemistry to detect the immediate early gene product Fos in serotonin-immunoreactive cells in the DRN. Inescapable tailshock led to greater serotonergic neural activity than did escapable tailshock, supporting the hypothesis that uncontrollable stressors preferentially activate serotonergic neurons in the DRN.