To understand characteristics of pain system in the elderly, we investigated the nocifensive behavior to heat stimulation and activity of nociceptive neurons in the lumbar spinal dorsal horn of aged and young rats. The paw withdrawal latency was significantly shorter and paw-licking occurrence was lower in aged rats than those of young rats. The responses of nociceptive neurons to noxious thermal stimulation as well as the spontaneous firing rate were significantly higher in the aged as compared to young rats. Furthermore, the size of high threshold receptive field area of wide dynamic range neurons was larger and that of low threshold area was smaller in aged rats than in young rats. The increased nociceptive neuronal activity in aged rats may cause shorter paw withdrawal latencies to a noxious heat stimulus. Reversible local anesthetic block of descending pathways resulted in a dramatic increase in neuronal activity in young rats but had little effect in aged rats. There was also a significant loss of serotoninergic and noradrenergic fibers in the spinal dorsal horn. These results demonstrate an age-related plasticity in spinal nociceptive processing that is related to impairment of descending modulating pathways.

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   The mechanism of pain relief by low-power laser (Ga-Al-As diode laser, 16.2 mW) irradiation was studied using the patch-clamp technique in cultured mouse dorsal root ganglion neurons as sociated with C-fiber. Bradykinin (BK) and laser stimulation was limited to the process or the cell body using a specially developed separator. The action potentials of the cell body after BK application to the process were reversibly suppressed by 2 min irradiation of the process. K⁺ channel opening elicited by BK was reversibly suppressed by irradiation of the cell body. After irradiation of the cell body was performed without BK stimulation, the resting potential was depolarized by a potential of 2 - 3 mV, and the rate of the spike evoked by the depolarization pulse was increased. However, when irradiation was limited to the process, the rate of the spike was not increased. The inward current evoked by the depolarization pulse was not suppressed by irradiation of the cell body. BK-evoked inward currents evoked by BK application to the process were suppressed by irradiation of the process. When BK was applied to the process and irradiation of the cell body was performed, the BK-induced action potentials were not suppressed. When 1,2-dioctanoyl-sn-glycerol, a potent protein kinase C (PKC) activator, was applied concomitantly with BK to the process, the suppressive effects of laser irradiation were not observed. These results suggest that the increase in spike rate following the irradiation of the cell body without BK can be ascribed to depolarization due to inhibition of K⁺ channel opening, and the suppressive effects of laser irradiation on BK-evoked action potentials may come from suppression of the PKC-pathway in the process.Laser irradiation of the process is thus recommended for the treatment of BK-induced pain.

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   Purpose: To assess the level of analgesia using a peripheral nerve stimulator during spinal anesthesia.
   Methods: Forty patients receiving spinal anesthesia with hyperbaric 0.5% tetracaine were included. The spread of sensory blockade was assessed by cold sensation to an alcohol–soaked sponge, pain after pinprick, pain after 50 Hz (10 mA) tetanic stimulation and pain after 100 Hz (10 mA) tetanic stimulation.
   Results: There was no significant difference between the analgesic levels assessed by tetanic stimulation at frequencies of 50 Hz and 100 Hz. The analgesic level assessed by tetanic stimulation was two segments lower than that assessed by cold and one segment lower than that assessed by pinprick. In some cases, oozing occurred at pinprick points. There was no complication associated with tetanic stimulation.
   Conclusion: Tetanic stimulation using a peripheral nerve stimulator was a simple and safe method to assess the level of spinal anesthesia.

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   Background: Patients often enter clinical situations feeling a variety of emotions. It is important to relieve these emotions because there is a negative correlation between a patient's emotions and pain. In this study, we evaluated the correlation between pain and emotions such as anxiety and depression. We also examined whether a reduction in anxiety or depression could diminish pain by using the 5-HT_1A agonist tandospirone citrate as an anxiolytic agent.
   Subjects and methods: A total of 270 patients were enrolled in two studies. These included 250 patients with dental phobia in Studies 1 and 2 (Study 1: 71 males, 107 females; Study 2: 33 males, 39 females), and 20 patients with no dental phobia in Study 2 only (10 males, 10 females). Anxiety was evaluated using the Spielberger State and Trait Anxiety Inventory (STAI) and depression was evaluated using the Zung Self-Rating Depression Scale (SDS). Venipuncture and cannulation were performed on the median cubital vein using a 22-gauge needle. Pain caused by the needle was measured immediately after the puncture using the Visual Analogue Scales (VAS). In Study 1, anxiety and depression were evaluated and the degree of trait anxiety, state anxiety and depression before venipuncture in the three groups was classified. We then compared these results with the VAS results in each group. In Study 2, anxiety was evaluated using the STAI measured previously (STAI-1). Subjects were divided into four groups as follows: no treatment group (NT: n=25, 11 males, 14 females); Mecobalamin group (ME: n=25, 12 males, 13 females); Tandospirone group (TA: n=22, 10 males, 12 females); and no dental phobia group (NP: n=20, 10 males, 10 females). The subjects in the ME and TA groups were given 1.5 mg of Mecobalamin or 30 mg of Tandospirone, respectively, and anxiety was examined sixty minutes after the medication was administered (STAI-2). The second evaluation was followed immediately by venipuncture, and pain caused by the needle was assessed.
   Results: The VAS for each group in Study 1 increased significantly with regards to degree of trait anxiety and state anxiety, but not with depression. In Study 2, there was no significant change in trait anxiety in any of the four groups. In contrast, state anxiety increased significantly in the NT group, but not in the ME, TA or NP groups. Pain caused by the needle used for venipuncture was significantly lower in the TA group, and was similar to that recorded for the NP group.
   Conclusions: This study demonstrates that anxiety amplifies pain in patients with dental phobia. These results suggest that the suppression of patient anxiety could also lead to the reduction of pain.

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