Role of neuron and non-neuronal cell communication in persistent orofacial pain

It is well known that trigeminal nerve injury causes hyperexcitability in trigeminal ganglion neurons, which become sensitized. Long after trigeminal nerve damage, trigeminal spinal subnucleus caudalis and upper cervical spinal cord (C1/C2) nociceptive neurons become hyperactive and are sensitized, resulting in persistent orofacial pain. Communication between neurons and non-neuronal cells is believed to be involved in these mechanisms. In this article, the authors highlight several lines of evidence that neuron-glial cell and neuron macrophage communication have essential roles in persistent orofacial pain mechanisms associated with trigeminal nerve injury and/or orofacial inflammation.

Effect of carbamazepine and gabapentin on excitability in the trigeminal subnucleus caudalis of neonatal rats using a voltage-sensitive dye imaging technique

BACKGROUND: The antiepileptic drugs carbamazepine and gabapentin are effective in treating neuropathic pain and trigeminal neuralgia. In the present study, to analyze the effects of carbamazepine and gabapentin on neuronal excitation in the spinal trigeminal subnucleus caudalis (Sp5c) in the medulla oblongata, we recorded temporal changes in nociceptive afferent activity in the Sp5c of trigeminal nerve-attached brainstem slices of neonatal rats using a voltage-sensitive dye imaging technique. RESULTS: Electrical stimulation of the trigeminal nerve rootlet evoked changes in the fluorescence intensity of dye in the Sp5c. The optical signals were composed of two phases, a fast component with a sharp peak followed by a long-lasting component with a period of more than 500 ms. This evoked excitation was not influenced by administration of carbamazepine (10, 100 and 1,000 µM) or gabapentin (1 and 10 µM), but was increased by administration of 100 µM gabapentin. This evoked excitation was increased further in low Mg²+ (0.8 mM) conditions, and this effect of low Mg²+ concentration was antagonized by 30 µM DL-2-amino-5-phosphonopentanoic acid (AP5), a N-methyl-D-as-partate (NMDA) receptor blocker. The increased excitation in low Mg²+ conditions was also antagonized by carbamazepine (1,000 µM) and gabapentin (100 µM). CONCLUSION: Carbamazepine and gabapentin did not decrease electrically evoked excitation in the Sp5c in control conditions. Further excitation in low Mg²+ conditions was antagonized by the NMDA receptor blocker AP5. Carbamazepine and gabapentin had similar effects to AP5 on evoked excitation in the Sp5c in low Mg²+ conditions. Thus, we concluded that carbamazepine and gabapentin may act by blocking NMDA receptors in the Sp5c, which contributes to its anti-hypersensitivity in neuropathic pain.

Changes of the level of phosphorelated ERK1/2 in the spinal trigeminal nucleus of migraine model rats / 中华行为医学与脑科学杂志

Objective To explore the role of ERK1/2 in the central pathogenesis of migraine.Methods Healthy adult male SD rats were randomly divided into five groups:normal group (group C),sham operation group(group C),migraine model group(group M),DMSO group (group D)and PD-98059group (PD group),with 12 rats in each group.The extracellular discharge frequency in the spinal trigeminal nucleus was recorded and ERK1/2 phosphorylation was tested.Results (1) The percentage of extracellular discharge frequency change:Two hours after treatment,the percentage of discharge frequency change was (325.9±47.32)％.The percentage of extracellula discharge frequency change in group M (325.9±47.3)％ was higher than that in group N (100.0± 0.0) ％ and group C(107.3± 16.4)％.There was no significant difference in the percentage of discharge frequency change between group D(319.3±42.5) ％ and group M (325.9±47.3) ％.The percentage of discharge frequency change in group PD(218.5±31.7)％ was lower than that in group M(325.9±47.3)％ and group D(319.3± 42.5)％.(2) ERK1/2 phosphorylation:the ERK1/2 phosphorylation in group M and group D was higher than that in group N and group C.There was no significant difference in ERK1/2 phosphorylation between group D and group M.The ERK1/2 phosphorylation in group PD was lower than the other four groups.Conclusion During the process of central sensitization to migraine,neuronal excitability and ERK1/2 phosphorylation were increased.ERK1/2 inhibitor (PD98059) reduced ERK1/2 phosphorylation and neuronal excitability.These indicated that ERK1/2 may play a role in central sensitization of migraine in rats.

Effect of protein kinase C inhibitor on the level of phosphralated extracellular regulated protein kinases in the spinal trigeminal nucleus of migraine model rats / 中华行为医学与脑科学杂志

Objective To explore the effect of protein kinase C inhibitor on the level of phosphralated extracellular regulated protein kinases in the spinal trigeminal nucleus of migraine model rats.Methods Healthy adult male SD rats were randomly divided into four groups:normal group (group C),sham operation group (group C),migraine model group(group M),and H-7group(H-7group),with 18 rats in each group.Dural blood flow and the extracellular discharge frequency in the spinal trigeminal nucleus was recorded.ERK1/2 phosphorylation was tested.Results (1) Dural blood flow:compared with group C((3.8± 1.0)％),the dural blood flow in M group ((78.0±4.2) ％)increased obviously(P＜0.01) ; compared with M group((78.0±4.2)％),the dural blood flow in H-7 group((-24.8±4.9) ％) decreased obviously(P＜0.01).(2) The percentage of extracellular discharge frequency change:two hours after treatment,the percentage of extracellula discharge frequency change in group M ((325.9 ±47.3)％)was higher than that in group C((107.3±16.4)％).The percentage of discharge frequency change in group H-7((136.0±26.5)％) was lower than that in group M((325.9±47.3)％).There was no significant difference in the percentage of discharge frequency change between group H-7((136.0±26.5) ％) and group C((107.3 ± 16.4)％).(2) ERK1/2 phosphorylation:the ERK1/2 phosphorylation in group M was higher than that in group C.The ERK1/2 phosphorylation in group H-7 was lower than than that in group C and group M.Conclusion ERK1/2 is a downstream PKC signal path and PKC may have indirect activation of ERK1/2.

THE RESPONSE AND RELATIONSHIP OF RAT SPINAL TRIGEMINAL NUCLEUS ASTROCYTES AND NEURONS TO PAIN INDUCED BY SUBCUTANEOUS FORMALIN INJECTION / 解剖学报

Objective To investigate the responses of neurons and astrocytes within rat′s spinal trigeminal nucleus(Sp5C) following nocuous pain stimulation induced by subcutaneous formalin injection into the unilateral upper lip. Methods By means of anti\|phospholipase(PLC),anti\|Fos protein and anti\|glial fibrillary acidic protein(GFAP) immunohistochemical method,the distribution of reactive neurons and astrocytes in the Sp5C was observed at different time after formalin injection. Results No immunohistochemical staining was found in normal rat Sp5C.After formalin injection,PLC like immunoreaction(\|LI),Fos\|LI and GFAP\|LI were found in astrocytes while PLC\|LI and Fos\|LI in neurons.The labeled astrocytes and neurons showed similar distribution and close relationship.PLC\|LI and Fos\|LI were found earlier than that in neurons.Conclusion\ The results suggested that the astrocytes in the Sp5C might participate in pain modulation in CNS and actively regulate neuron′s function.

PARVALBUMIN-EXPRESSING NEURONS ON THE CENTRAL PATHWAY OF THE TRIGEMINAL PROPRIOCEPTIVE SENSATION OF THE RAT: A DOUBLE LABELING STUDY / 神经解剖学杂志

Previous studies showed that the Vodm-LRF-including the dorsomedial part of the subnucleus oralis of the spinal trigeminal nucleus and its adjacent lateral reticular formation--contained the second-order neurons on the central pathway of the trigeminal proprioceptive sensation of the rat and the "zone-shaped area"-including the caudolateral part of the supratrigeminal nucleus (Vsup-CL). The dorsomedial part of principal sensory trigeminal nucleus (Vpdm) and two newly found nuclei: the areaventral to the motor trigeminal nucleus (AVM) and the area dorsal to the superior olivary nucleus (ADO)-contained the third order neurons of this pathway. Parvalbumin (PV) is one of the calcium-binding proteins, In this pathway, many PV-like immunoreactive (PV-LI) neurons were observed in Vodm LRF and the "zone-shaped arena", hut there has been no reports so far regarding whether these PV-LI neurons are projection neurons responsible for the transmission of proprioceptive information or the interneurons serving the modulatory function, in the present study, our aim was to solve the problem by a double labeling study by using retrograde tracing method combined with immunofluorescence histochemistry. The results showed that: (1) following the unilateral Fluoro-Gold (FG) injections into the ventral posteromedial nucleus (VPM) of the thalamus and the separated parts of the "zone-shaped area", viz, Vpdm, ADO and AVM, many FG-labeled neurons were always found contralaterally in the "zone-shaped area" and ipsilaterally in the Vodm-LRF, respectively; (2) in either the "zone-shaped area" or the Vodm-LRF, a substantial number of the FG retrogradely labeled neurons showed PV-LI. In the Vsup-CL, Vpdm, AVM and ADO, about 57%, 55%, 11% and 4% of the neurons projecting to the VPM of the thalamus showed pV-LI, respectively. Of the total population of PV-LI neurons in the Vsup-CL, Vpdm. AVM and ADO, about 23%, 79%, 53% and 16% were labeled by FG, respectively. Most of these PV/FG double-labeled neurons were medium- to small-sized, round, piriform or irregular in shape. On the other hand, in the Vodm-LRF, approximately 33%, 34% and 50% of the neurons which projected to the Vpdm, AVM and ADO expressed PV-LI, respectively. The percentage of PV/FG double-labeled neurons to the total number of the PV-LI neurons in Vpdm, AVM or ADO were 26%, 17% or 11%, respectively, The present results indicated that PV might play an important role in the transmission of the trigeminal proprioceptive information of the rat from Vndm-LRF to the contralateral VPM of the thalamus through the "zone-shaped area".

THE PROJECTION OF THE CEREBRAL CORTEX TO THE ORAL SUBNUCLEUS OF SPINAL TRIGEMINAL NUCLEUS IN THE CAT——A STUDY WITH THE HRP RETROGRADE TRACING METHOD / 解剖学报

The cortical distribution of thecells of origin of the corticotrigeminal projection to the oral subnucleus of spinal trigeminal nucleus(Vo)was examined with the HRP retrograde tracing method. The results showed that the coronal gyrus was the main site of origin. The anterior part and the posterior part of the gyrus projected to the dorsomedial portion and the ventrolateral portion of Vo respectively. The amount of labelled cells in the anterior part of the gyrus was much larger than those in the posterior. There were also numerous labelled cells in the anterior parts of orbital gyrus and of the lateral zone of anterior sigmoid gyrus. The most anterior ends of these three gyri joined together forming the so-called "presylvian gyrus" where the labelled cells were most concentrated. In addition, the labelled cells were also scattered in the anterior suprasylvian gyrus, posterior sigmoid gyrus, lateral gyrus and anterior ectosylvian gyrus. All labelled cells were located in the fifth layer of the cortex. Their size varied. The results of the present study did not support that there were projections from the temporal and occipital lobes and proreate gyrus to Vo.

DISTRIBUTION OF GFP-POSITIVE NEURONS AND THE COLOCALIZATION WITH PARVALBUMIN IN THE CAUDAL SPINAL TRIGEMINAL NUCLEUS IN THE GAD67-GFP KNOCK-IN MOUSE / 解剖学报

Objective To observe the distribution of GABA-containing neurons revealed by GFP expression and the colocalization of the GFP with parvalbumin(PV) in the caudal spinal trigeminal nucleus(Vc),the glutamate decarboxylase 67-green fluorescence protein(GAD67-GFP) knock-in mice were used in the present study. Methods Double-labeled techniques were used by in situ hybridization combined with immunohistochemistry for GFP and double immunofluorescence histochemistry for GFP and NeuN(neuronal nuclei protein,a neuronal marker) or PV.The stained sections were observed under light microscope and a confocal laser-scanning microscope. Results 1.Over 90% of GFP-positive neuronal cell bodies in the laminae Ⅰ and Ⅱ of the Vc showed hybridization signals for GAD67 mRNA,and that almost all neuronal cell bodies with GAD67 mRNA signals were GFP-positive;2.GFP-positive neurons were mainly distributed in the laminae Ⅰ and Ⅱ of the Vc and the vast majority of them were small neurons.The considerable number of GFP-positive processes and somata were most densely observed in the lamina Ⅱ of the Vc.The proportion of GFP-positive neurons in the NeuN-labeled neurons of the Vc was about 19.4% and 24.3% in laminae Ⅰ and Ⅱ,respectively;3.Double-labeled neurons for GFP/PV are mainly found in laminae Ⅰ and Ⅱ of the Vc.The proportion of GFP/PV double-labeled neurons was about 62.4% and 12.8% of total population of PV-and GFP-positive neurons in laminae Ⅰ-Ⅱ of the Vc,respectively.Conclusion GABAergic neurons are mainly distributed in the laminae Ⅰ and Ⅱ of the Vc which related closely to transmission of the nociceptive primary afferent information,and the majority of PV-positive neurons are GABAergic neurons.