introduction: the antinociceptive effect of morphine is, in part, mediated through the activation of a descending pathway. one of the major components of this pathway is the nucleus raphe magnus (nrm). our previous study demonstrated the involvement of nrm in the analgesic effect of morphine microinjected into the nucleus cuneiformis (ncf) in a descending manner. the aim of the current study wa...

Chronic pain is thought to be partly caused by a loss of GABAergic inhibition and resultant neuronal hyperactivation in the central pain-modulating system, but the underlying mechanisms for pain-modulating neurons in the brain are unclear. In this study, we investigated the cellular mechanisms for activation of brainstem descending pain facilitation in rats under persistent pain conditions. In ...

Descending projections arising from brainstem serotonergic (5HT) neurons contribute to both facilitatory and inhibitory controls of spinal cord "pain" transmission neurons. Unclear, however, are the brainstem networks that influence the output of these 5HT neurons. To address this question, here we used a novel neuroanatomical tracing method in a transgenic line of mice in which Cre recombinase...

The present study investigated the role of calcitonin gene-related peptide (CGRP) on nociception in nucleus raphe magnus (NRM) and the interaction between CGRP and opioid peptides in NRM of rats. CGRP-like immunoreactivity was found at a concentration of 6.0+/-0. 77 pmol/g in NRM tissue of ten samples of rats, suggesting that it may contribute to physiological responses orchestrated by the NRM....

To examine if brain neurons involved in the efferent control of the kidneys possess melanocortin-4 receptor (MC4-R) and/or tryptophan hydroxylase (TPH). Retrograde tracing pseudorabies virus (PRV)-614 was injected into the kidneys in adult male MC4R-green fluorescent protein (GFP) transgenic mice. After a survival time of 3-7 days, spinal cord and brain were removed and sectioned, and processed...

Serotonin in the spinal cord acutely modulates nociceptive transmission and motor reflexes and may also assist functional restoration after spinal cord injury (SCI). It is released there mainly by descending axons of the medulla's nucleus raphe magnus (NRM). We examined whether mechanical allodynia (cutaneous hypersensitivity) after incomplete SCI is sustainably reversed by prolonged, intermitt...

The role of the acetylcholine-mediated system in the organization of postictal antinociception was investigated. For this purpose, nicotinic and muscarinic cholinergic receptor antagonists were microinjected into the nucleus raphe magnus (NRM), a key structure of the endogenous pain inhibitory system. After the tail-flick test baseline recording, male Wistar rats (N=8 per group) were submitted ...

To investigate analgesic neural circuits activated by electroacupuncture (EA) at different sets of acupoints in the brain, goats were stimulated by EA at set of Baihui-Santai acupoints or set of Housanli acupoints for 30 min. The pain threshold was measured using the potassium iontophoresis method. The levels of c-Fos were determined with Streptavidin-Biotin Complex immunohistochemistry. The re...

The present studies in the rat employed a combined retrograde transport-immunocytochemical technique to determine the origin in the brainstem of enkephalin (Enk) projections to spinal sympathetic nuclei, including the intermediolateralis nucleus, pars principalis (ILp). We found that Enk projections to the ILp nucleus are found in such serotonergic-containing areas as the raphe obscurus; raphe ...

It has been shown previously that the muscarinic cholinergic system in the nucleus raphe magnus (NRM) is involved in the modulation of nociception. In this study, we examined the direct actions of muscarine on the NRM neurons in a slice preparation. Muscarine (1-30 microM) produced a dose-dependent hyperpolarization in a subpopulation of the NRM cells that contain 5-hydroxytryptamine (5-HT). In...