The nucleus locus coeruleus (LC) is a major source of noradrenergic projections to the spinal dorsal horn. There is considerable evidence that the bulbospinal noradrenergic system plays a significant role in pain modulation. In the superficial dorsal horn of the spinal cord, noradrenaline was reported to act on the presynaptic terminals of primary afferent fibers (Aδ and C fibers) to reduce glutamate release, and on the presynaptic terminals of inhibitory interneurons to facilitate GABA and glycine releases. Furthermore, it produces an outward current postsynaptically by the activation of potassium channels. Recently, we developed an in vivo patch-clamp recording technique from LC neurons to study the modulatory role at the synaptic level. Male adult rats were anesthetized with urethane and the animal was fixed in a stereotaxic frame. After a craniotomy was performed, the cerebellum was removed to expose the dorsal surface of the brain stem. The patch pipette was advanced into the LC by using a micromanipulator. After established a gigaohm seal formation, cell-attached and whole-cell patch-clamp recordings were made from LC neurons under current- and voltage-clamp conditions. Under cell-attached conditions, LC neuron tested fired spontaneously. Cutaneous noxious stimuli applied to the contralateral hindpaw transiently increased the frequency of the spontaneous action potentials. Under current-clamp conditions, the resting membrane potential was ranged from -45 to -60 mV, and spontaneous firing was also detected at the similar frequency compared with those obtained from cell-attached and extracellular recordings. Under voltage-clamp conditions at a holding potential of -70 mV, LC neurons exhibited spontaneous excitatory postsynaptic currents (EPSCs). Spontaneous inhibitory postsynaptic currents (IPSCs) could be recorded at a holding potential of 0 mV. This newly-developed recording technique, thus enabled us to analyze in detail excitatory and inhibitory synaptic responses evoked in LC neurons in vivo and is therefore useful to elucidate the synaptic transmission in the LC in response to natural noxious stimulation and the plastic changes occurred in chronic pain models.

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　Symptoms of pain in chronic pain patients are known to influence by ambient temperature (AT) change and some of these patients also show temperature unadaptability. These clinical features suggest that alteration of autonomic thermoregulatory systems might be underlying in development and maintenance of chronic pain. In this study, we examined effects of AT change exposure to the pain intensity and autonomic thermoregulatory function in chronic pain patients with impaired cold sensitivity. Two upper extremity neuropathic pain patients who have impaired cold sensitivity in whole body were participated in the present study. The subject sat a chair in an artificial climate chamber (27°C, 50% RH) during the experiment. After the baseline measurements, room temperature was decreased to 15°C in 25 min (cold exposure) and then increased to 40°C in 15 - 20 min (heat exposure). Pain intensity and thermal sensation (cold-cool-warm-hot feeling) during the exposure were frequently measured on a numerical rating scale. Skin temperature, skin blood flow (SBF), and sweating in both hands, and tympanic temperature were also measured continuously throughout the experimental period. In one patient, SBF showed lower baseline value in the affected limb than the healthy limb. During cold exposure, both patients showed increase in their pain intensity in the affected limb, but not expressed any cold feeling in spite of lowering tympanic temperature. Cold exposure decreased SBF in both hands of patients. During heat exposure, both patients expressed hot feeling as an ambient temperature gradually rises, but did not show any change in pain intensity. Heat exposure increased sweating, SBF in both hands of patients. The present study indicated that lowering ambient temperature increased pain intensity in the affected limb of two patients irrespective of impaired cold sensitivity. In these subjects, however, SBF and sweating responded in a different manner to the ambient temperature changes. This could reflect differences in autonomic thermoregulatory function between these patients.

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　D-serine (DS) is an endogenous ligand that especially binds to glycine binding site on N-methyl D-aspartate (NMDA) receptor, a key excitatory neuro-transmitter receptor in the central nervous system. When glia cell is activated in spinal cord after peripheral nerve injury, gliotransmitter such as inflammatory cytokines (IL-β, TNF-α, IL-6 etc), ATP, and glutamate are released to neuronal synaptic membrane, suggesting that they modulate synaptic transmission in spinal pain transmission. In this study, we investigated the effect of DS that it is known for gliotransmitter releasing from astrocyte in spinal cord using electrophysiology and immunohistochemistry methods, and we identified the difference of its role between normal and peripheral nerve injury model.
　When exogenous NMDA was applied to spinal slices at a holding potential of −50 mV, the amplitude of NMDA induced inward current was increased in the presence of DS. Moreover, DS induced transient outward currents were observed at a holding potential of 0 mV, and this current was inhibited by glycine receptor antagonist, strychnine (2 µM), suggesting that the DS-induced outward current is mediated by glycine receptor. In addition, we examined these effects of DS after 10 days operation of spare nerve injury (SNI). Compared with naïve rats, the activation of NMDA receptor by DS was augmented, but inhibitory effect mediated by glycine receptor was decreased in SNI model rats. Finally, we investigated the activation of pERK in spinal cord after SNI. As the result, pERK immuno-positive cell were upregulated in injury side, but not in intact side. In the present study, we have demonstrated that DS in spinal dorsal horn neuron has two distinct actions, one is an excitatory action mediated by NMDA receptor, the other is an inhibitory action mediated by glycine receptor. Interestingly, the excitatory action by DS after peripheral nerve injury was more sensitive than physiological condition, whereas its inhibitory action after peripheral nerve injury was less than naïve one. These findings may play an important role for the development of neuropathic pain.

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　Background and purposes: Photophobia is characteristic and important sign of the migraine headache. Recently, we found that the response of dura-sensitive neuron to photic stimulation was enhanced after dura inflammation. Some previous papers also have reported that neurons located in the dorsal horn of the C₂ spinal cord (C₂ neurons) receive photic inputs suggesting that C₂ neurons somehow involved in photophobia.
　However, how the C₂ neurons are involved in photophobia associated with migraine is unknown. Therefore, the change in neuronal excitability of C₂ nociceptive neurons was analyzed in rat model with dural inflammation.
　Methods: The Sprague-Dawley rats were anesthetized with pentobarbital sodium (50 mg/kg, i.p.) and the small hole was made in the frontal bone, and 10% mustard oil (MO) was applied to the dura surface around the transverse sinus (migraine rat). Photic stimulation was applied to the eye in migraine and vehicle-treated rats, and c-Fos like immunoreactive (LI) cells and pERK-immunoreactive (IR) cells in C₂ were precisely analyzed. To identify trigeminal ganglion (TG) neurons innervating the retina, the fluorogold (FG) solution (4% in distilled water, 10 µl) was injected to the retina using a 31-gauge needle. Substance P (SP), calcitonin generelated peptide (CGRP), TRPV1 immunoreactivities were also detected in the ratina.
　Results: Following MO application to the dura, a large number of c-Fos-LI cells was expressed in the transition zone between subnuclei interpolaris and caudalis (Vi/Vc) zone bilaterally and was also in the ipsilateral C₂. Photic stimulation to the eye in migraine rat caused an expression of pERK-IR cells in C₂, and many of them also showed c-Fos immunoreactivity. FG-labeled trigeminal ganglion cells were observed in the first branch-innervated area of the TG following FG injection into the retina. Many SP, CGRP and TRPV1 immunoreactivities were detected in nerve fibers in the retina.
　The present findings suggested that C₂ neurons are involved in photophobia associated with migraine, and also suggested that the unmyelinated trigeminal afferents innervating the retina might be one of the sources of photic information in photophobia.

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　We evaluated the effect of magnetic stimulation on neuropathic pain using a unique magnetic stimulation apparatus. This system produced an alternating magnetic field of an appropriate uniform intensity that we applied to a rat model of chronic constrictive nerve injury (CCI). We performed an experiment on rats that showed reduction in the paw withdrawal threshold to mechanical stimuli, thermal hyperalgesia and cold hypersensitivity 2 weeks after nerve injury. Animals that underwent CCI were divided into three groups: non-stimulation control (NSC, n=8), low-strength magnetic stimulation (LSM, n=9), and high-strength magnetic stimulation (HSM, n=9). Alternating magnetic stimulation was delivered to the lateral sides of both femurs, operated and unoperated, near the sciatic nerves, at different intensities (ca. 25 mT and 70 mT; 50 Hz) for 30 min every 5 days. Treatment with magnetic stimulation reversed the decreased withdrawal threshold of mechanical allodynia, the effect being more significant in the HSM group as compared to the NSC group on day 5. Magnetic stimulation improved the paw withdrawal latency to thermal stimuli on day 1, though the effect was not significant. Magnetic stimulation had no obvious effect on cold hypersensitivity.
　In conclusion, alternating magnetic stimulation improved neuropathic pain in CCI rats. The advantage of magnetic stimulation is that since it is non-invasive, it could be a suitable method for the non-pharmacological treatment of chronic pain.

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