ABSTRACT
Microglial cell activation is known to contribute to neuropathic pain following spinal sensory nerve injuries. In this study, I investigated its mechanisms in the case of trigeminal sensory nerve injuries by which microglial cell and p38 mitogen-activated protein kinase (p38 MAPK) activation in the medullary dorsal horn (MDH) would contribute to the facial pain hypersensitivity following mandibular nerve transection (MNT). And also investigated the changes of trigeminal ganglion neurons and ERK, p38 MAPK manifestations. Activation of microglial cells was monitored at 1, 3, 7, 14, 28 and 60 day using immunohistochemical analyses. Microglial cell activation was primarily observed in the superficial laminae of the MDH. Microglial cell activation was initiated at postoperative 1 day, maximal at 3 day, maintained until 14 day and gradually reduced and returned to the basal level by 60 days after MNT. Pain hypersensitivity was also initiated and attenuated almost in parallel with microglial cell activation pattern. To investigate the contribution of the microglial cell activation to the pain hypersensitivity, minocycline, an inhibitor of microglial cell activation by means of p38 MAPK inhibition, was administered. Minocycline dose-dependently attenuated the development of the pain hypersensitivity in parallel with inhibition of microglial cell and p38 MAPK activation following MNT. Mandibular nerve transection induced the activation of ERK, but did not p38 MAPK in the trigeminal ganglion. These results suggest that microglial cell activation in the MDH and p38 MAPK activation in the hyperactive microglial cells play an important role in the development of facial neuropathic pain following MNT. The results also suggest that ERK activation in the trigeminal ganglion contributes microglial cell activation and facial neuropathic pain.
Subject(s)
Animals , Facial Pain , Horns , Hypersensitivity , Mandibular Nerve , Minocycline , Neuralgia , Neurons , p38 Mitogen-Activated Protein Kinases , Protein Kinases , Trigeminal GanglionABSTRACT
Calbindin-D28k (CB), calretinin (CR) and parvalbumin (PV) are the most common calcium-binding proteins (CaBPs). In the present study, FOS immunoreactivity was first induced in neurons of the medullary dorsal horn (MDH) of the rat by noxious orofacial stimulation; CaBPs (CB, CR and PV) in these neurons were then identified by imumunofluorescence histochemistry, and then, in addition, afferents to CaBPs/FOS double-labeled neurons were showed by immunofluorescence histochemical staining for the γ-aminobutyric acid (GABA) , glycine transporter 2 (GlyT2) , enkephalin (ENK) , serotonin (5-HT) or substance P (SP). Under the light microscope,we observed that: (1) neuronal cell bodies exhibiting FOS-immunoreactivity were present throughout all laminae of the MOH, with the highest concentration in lamina Ⅱ; (2) most CB-, CR- and PV-immunoreactive (IR) neurons were located in lamina Ⅱ , but some were also encountered in laminae Ⅰ and Ⅲ; (3) 5-HT-, GABA-, GlyT2-, ENK- and SP-IR fibers and terminals were also chiefly located in laminae Ⅰ and Ⅱ of the MDH; (4) some FOS-IR neurons showed CB-, CR-, or PV-immunoreactivity; (5) 5-HT-, GABA-, GlyT2- and ENK-IR terminals made close contacts with FOS/CB, FOS/CR or FOS/PV double-labeled neurons; (6) SP-IR terminals, as well as 5-HT-, GABA-, GlyT2- or ENK-IR terminals, closely contacted CB-, CR- or PV-containing neurons. Under the electron microscope, 5-HT-, GABA-, GlyT2- and ENK-IR terminals principally made symmetric (inhibitory) synaptic connections with CB-, CR- and PV-containing neurons were observed. These results suggest that 5-HT, GABA, glycine (Gly) and ENK may modulate transmission of orofacial noxious information by inhibiting nociceptive neurons that contain CaBPs in the rat MDH.
ABSTRACT
Objective To investigate the connections between ?\|aminobutyric acid(GABA)\|or glycine (Gly)\|containing terminals and Fos\|positive projection neurons from the medullary dorsal horn (MDH) to the thalamus or parabrachial nuclei(PBN). Methods Tetramethyl rhodamine(TMR) retrograde tracing,combined with immunofluorescence histochemical triple\|staining for TMR/Fos/GABA or TMR/Fos/Gly was used. Results GABA\|or Gly\|immunoreactive terminals were chiefly located in the superficial laminae(laminae Ⅰ and Ⅱ) of the MDH.After orofacial noxious stimulation.Fos\|positive neurons were also mainly observed in the superficial laminae.After injecting TMR into the unilateral thalamus or PBN,TMR retrogradely labeled neurons were mainly distributed in the superficial laminae of the controlateral or ipsilateral MDH,respectively.Some of these TMR\|labeled neurons also exhibited Fos\|immunoreactivities.GABA\| or Gly\|containing terminals made close contacts with Fos positive retrogradely labeled neurons.Conclusion\ In the superficial laminae of the MDH,some of the orofacial nociceptive neurons send project fibers directly to the thalamus or PBN,GABA and Gly might exert their inhibitory effects on these nociceptive projection neurons.\;[
ABSTRACT
After injecting retrograde tracer fiuoro-gold (FG) into the parabrachial region(PB), caudal ventrolateral medulla(CVLM) and the fourth segment of cervical spinal cord (C4), respectively, neurons in laminae I ～ Ⅱ of the medullary dorsalhorn projecting to the above mentioned brain areas were observed. PB received projections from bilateral laminae I and Ⅱ withan ipsilateral dominance; CVLM and C4 received projections from ipsilateral laminae I and Ⅱ. Neurons projecting to C4 werevery sparsely distributed in laminae I and Ⅱ of the medullary dorsal horn. The projecting neurons in outer part of lamina Ⅱwere more than those in inner part of lamina Ⅱ . Combined with immunofluorescence histochemistry for calbindin-D28k(CB) andparvalbumin(PV), it was demonstrated that a part of neurons projecting to PB or CVLM showed CB-like immunoreactivity, butnone of them exhibited PV-like immunoreactivity. There were only a few neurons in lamina Ⅱ projecting to C4 and they exhibitedneither CB- nor PV-like immunoreactivity. The present study provides further evidence for the existence of projecting neurons inlamina Ⅱ and suggests that immunostaining against CB and PV may distinguish two neuronal subpopulations in lamina Ⅱ .
ABSTRACT
Using Nissl method, Kluver and Barrera method and rapid Golgi method, we found that there were large, medium and small-sized neurons in lamina V of medullary dorsal horn Of the cat, the medium-sized neurons were most numerous and the large-sized neurons were least in number. According to the dendritic branching pattern and the number of spines, the lamina Ⅴ neurons could be divided into two categories——the radiate neuron and bushy neuron. The former contained three subcategories: pyramidal, polygonal and bipolar neurons. Spiny and smooth types were found in pyramidal and polygonal neurons. Considering with the results of neurophysiologic research and intracellular injection of HRP by others, we presume that different types of neurons in lamina Ⅴ might also differ functionally. In addition, according to the results of transganglionic transport of HRP from the peripheral and retrograde transport of HRP from the thalamus, it was assumed that some neurons in lamina V received messages from the primary afferent in lamina Ⅴ, Ⅳ, and Ⅲ, and thence, transmitted them to the thalamus.
ABSTRACT
Objective To observe the morphologic features of neurons labeled with green fluorescent protein (GFP) gene recombinant Sindibis virus in the deep part of lamina Ⅲ in the medullary dorsal horn (MDH) of the rat. Methods Neurons were infected and labeled with GFP gene recombinant Sindibis virus injected into lamina Ⅲ.Immunohistchemical staining showed the labeling results.The morphologic features of the GFP labeled neurons were revealed after reconstruction. Results A few GFP-labeled single neurons were found in the distal portions away from the virus injection site within the deep part of lamina Ⅲ of the MDH.According to the morphological features,especially their axons and axonal collaterals,GFP labeled neurons were classified into projection neurons and intrinsic neurons.The axons and their collaterals of the projection neurons entered to the superficial part of lamina Ⅲ,lamina Ⅱ and/or the medullary reticular formation.Most of the axons and their collaterals of the intrinsic neurons extended mainly within lamina Ⅲ.Conclusions According to the morphological features of axons and their axonal collaterals,GFP labeled neurons were classified into projection neurons and intrinsic neurons in the deep part of lamina Ⅲ of the MDH.GFP gene recombinant virus labeling technique is an effective method to investigate the morphological features of neurons.
ABSTRACT
Objective To examine the projection of protein kinase C? isoform(PKC?)\|immunoreactive neurons from the medullary and spinal dorsal horns to the midbrain periaqueductal gray(PAG) in the rat. Methods By using fluoro\|gold(FG) retrograde tracing combined with immunofluorescence histochemical staining for PKC?. Results PKC?\|immunoreactive neurons were observed in laminae Ⅰ,Ⅱ,Ⅲ of the medullary and spinal dorsal horns and lateral spinal nucleus.After injecting FG into the PAG,FG retrogradely labeled neurons were also mainly found in laminae Ⅰ,Ⅱ,Ⅲ of the medullary and spinal dorsal horns and lateral spinal nucleus.Some of these FG\|labeled neurons in laminae Ⅰ,Ⅱ,Ⅲ of the medullary and spinal dorsal horns and lateral spinal nucleus exhibited PKC?\|immunoreactivities.Conclusion\ PKC?\|immunoreactive neurons in the medullary and spinal dorsal horns might be involved in the transmission of nociceptive information from the medullary and spinal dorsal horns to the PAG.\;[