Yoichiro Matsui

Peripheral nerve stimulation increases serotonin and dopamine metabolites in rat spinal cord

Extracellular serotonin (5-HT), dopamine (DA), and their metabolites, 5-hydroxyindoleacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA), were assessed in the rat lumbar spinal cord (L3-4) by in vivo microdialysis with high performance liquid chromatography and electrochemical detection (HPLC-ECD). Under urethane-chloralose anesthesia, basal levels of 5-HT and DA in the dialysates were approximately 1.0-1.2 pg/22 microliters sample, 5-HIAA, DOPAC, and HVA were constant at 322.6 +/- 14.9, 8.6 +/- 0.7, and 10.4 +/- 0.4 pg/22 microliters sample (mean +/- SE), respectively. Local application of 100 mM KCl via the dialysis probe increased the 5-HT and DA. Peripheral nerve stimulation that selectively excited the large (A-beta) or small (A-delta) myelinated fibres increased the metabolites. Excitation of the A-beta fibers increased the levels of 5-HIAA to 138%, DOPAC to 155%, and HVA to 143% of the controls. Stimulation of the A-delta fibers increased 5-HIAA to 121%, DOPAC to 120%, and HVA to 124% of the controls. The results suggest that non-nociceptive peripheral nerve stimulation may activate the descending 5-HT and DA systems in the spinal cord.

Neurochemical evidence for inflammation-induced activation of the coeruleospinal modulation system in the rat

By using the microdialysis technique, the concentration of noradrenaline (NA) in the dorsal horn during unilateral hindpaw inflammation was compared between rats receiving bilateral lesions of the locus coeruleus (LC) and non-operated control rats. Bilateral lesions of the LC were made using an anodal current one week before testing. Unilateral hindpaw inflammation was produced by a subcutaneous injection of carrageenan (6 mg in 0.15 ml saline). Under conditions of sodium pentobarbital anesthesia, the microdialysis probe was inserted into the dorsal horn either ipsilateral or contralateral to the site of inflammation. The NA concentration in the dialysate was measured by high-performance liquid chromatography with electrochemical detection. Prior to carrageenan injection, the NA level (baseline level) did not differ between the LC-lesioned and the non-operated groups. After carrageenan injection, in the non-operated rats, the NA level increased significantly compared to the baseline level only in the dorsal horn ipsilateral to the site of inflammation, but not in the dorsal horn contralateral to the site of inflammation. An increase of the NA level was not observed in the LC-lesioned rats and in rats receiving an injection of saline. The result suggests that unilateral hindpaw inflammation produces excitation of descending NA-containing neurons from the LC, resulting in an increase of the NA level in the dorsal horn ipsilateral to the site of inflammation.

Activation of descending noradrenergic system by peripheral nerve stimulation.

Noradrenaline (NA) release in the rat lumbar spinal cord (L3-4) in response to variable intensity, selective stimulation of large (A-beta), small myelinated (A-delta), and unmyelinated (C) afferent fibers was examined by in vivo microdialysis with high performance liquid chromatography and electrochemical detection. Application of 100 mM K+ solution via the dialysis probe increased NA in the dialysate. Thoracic segment transection rostral to the probe depressed the NA level. Transcutaneous stimulation of peripheral nerves had the following effects: 1) High intensity stimulation of afferent A-delta or C fibers increased spinal NA release, which was decreased by thoracic spinal cord transection. 2) Stimulation of afferent A-beta or A-delta fibers at low intensity did not affect the NA level. 3) High intensity stimulation of afferent A-beta fibers depressed NA release in half of the trials. Results indicate that many NA-containing nerve terminals that innervate the lumbar spinal cord originate from supraspinal structures. Somatic neural inputs from afferent C fibers and high-threshold A-delta, but not A-beta nor low-threshold A-delta fibers, activate the descending NA system and release the NA in the spinal cord. The descending NA system may participate in antinociception.

Aδ afferent fiber stimulation activates descending noradrenergic system from the locus coeruleus

We compared the noradrenaline (NA) level in the dorsal horn following electrical stimulation of Aδ afferent nerve fibers in the peripheral nervous system between rats with bilateral lesions of the locus coeruleus (LC) and non-operated control rats by using a microdialysis technique combined with high performance liquid chromatography. Prior to Aδ afferent fiber stimulation, the NA content in the dialysate did not differ between the LC-lesioned and the control rats. During Aδ afferent fiber stimulation, in the LC-lesioned rats, the NA level did not change significantly compared to that before Aδ afferent fiber stimulation, whereas the NA level increased significantly in the control rats. There was a significant difference in the NA levels during Aδ afferent fiber stimulation between the two groups of rats. The result suggests that descending noradrenergic neurons from the LC is involved in the increase of the NA level in the spinal cord dorsal horn produced by Aδ afferent fiber stimulation.

Thalamic- and cerebellar-projecting interpolaris neuron responses to afferent inputs

Thalamic- and cerebellar-projecting interpolaris neuron responses to afferent inputs from the temporomandibular joint (TMJ) and/or the masseter muscle (Mm) were examined in rats. Of 230 neurons tested, 24 could be antidromically stimulated from the contralateral ventral posteromedial thalamic nucleus (VPM), and 27 of 91 neurons tested were stimulated from the ipsilateral posteromedial part of crus II of the cerebellar cortex. None had dual projections. The thalamic-projecting neurons were recorded in the dorsomedial region of the interpolaris; most cerebellar-projecting neurons were at the medial border of the interpolaris. Ten of 24 thalamic- and 17 of 27 cerebellar-projecting neurons received nociceptive information. Afferent inputs from the TMJ and the Mm converged on 6 of 24 thalamic-projecting neurons and on 16 of 27 cerebellar-projecting neurons. In both the thalamic- and cerebellar-projecting neurons, there was no difference between the non-nociceptive and nociceptive neurons in mean antidromic latency. The results suggest that the interpolaris integrates and relays afferent inputs from deep oral structures.

Somatosensory afferent inputs release 5-HT and NA from the spinal cord

Endogenous serotonin (5-HT) and noradrenaline (NA) release by somatosensory afferent inputs was investigated at the level of the spinal cord using in vivo microdialysis technique combined with high performance liquid chromatography and electrochemical detection (HPLC-ECD). Selective stimulation of large myelinated Aβ afferent fibers significantly increased 5-HT release to 151.1 ±10.1% of the control, but did not affect NA release. However, selective stimulation of small myelinated Aδ fibers released NA rather than 5-HT. The NA level enhanced to 128.8±6.4% of the control after Aδ fibers were stimulated with the intensity of 6 times threshold. Stimulation of unmyelinated C fibers unavoidably excited the Aβ and Aδ afferent fibers, causing both 5-HT and NA release from the spinal cord. The results suggest that both innocuous and noxious information may activate serotonergic descending pathways. The noradrenergic descending pathways are only triggered by noxious inputs transmitted by small afferent fibers.

Quantitative relationship between the stimulus intensity and the response magnitude in the tail flick reflex

The purpose of the present study was to investigate the quantitative relation between the stimulus intensity and the response magnitude of the tail flick reflex. The EMG of a tail muscle was recorded from the extensor caudae medialis (ECM) muscle in the side contralateral to heat stimulation, and the area of integrated EMG for 1 sec was measured as the magnitude of EMG activity. The minimum temperature to the onset of the EMG was 42.3 +/- 0.4 degrees C. The relation between the stimulus intensity and the magnitude of an integrated EMG followed a power function with an exponent of about 8.5. The magnitude of an integrated EMG was decreased by about 50% of the control by an intraperitoneal administration of morphine (0.5 mg/kg). These results suggest that tail flick reflex is closely related to painful sensation, and that EMG activity of the ECM muscle is applicable as an electrophysiological indicator to noxious stimulation of the tail and an expressible indicator of the magnitude of pain.

Inhibition of nociceptive responses of wide-dynamic-range neurons by peripheral nerve stimulation

Of 107 neurons from the sacral and coccygeal levels of the spinal cord in anesthetized intact rats examined, 62 wide-dynamic-range (WDR) neurons that responded to noxious heating of the tail were recorded. On the basis of their inhibitory responses through A-beta or A-delta afferent fibers to noxious stimulation, these neurons were classified into one of the following three types: Type I--neurons inhibited only by A-beta afferent nerve impulses; Type II--neurons inhibited only by A-delta afferent nerve impulses; Type III--neurons inhibited by both. The present results are compared with previously reported behavioral results.

Beating activity of heterokaryons between myocardial and non-myocardial cells in culture

Cultured mouse myocardial cells grown as monolayers fused upon treatment with HVJ (Sendai virus). The myocardial cells also fused with quail myocardial cells, neuroblastoma cells and non-excitable cells, such as KB cells. The beating activity of these heterokaryons was studied in the present work. Heterokaryons composed of myocardial cells from different species maintained spontaneous beating activity for 2 days or more. Those of one myocardial and one neuroblastoma cell maintained the activity for 22-26 h, while those of one myocardial and one non-excitable cell, such as KB cell, lost the activity within 2-4 h after addition of HVJ. Heterokaryons that had stopped spontaneous beating did not contract on application of electrical-field stimulation. The ration of non-myocardial cells in the heterokaryons increased in inverse proportion to the decrease in beating activity of the heterokaryons. Study of the rapid disappearance of beating activity in heterokaryons composed of one myocardial and one KB cell showed that both excitability of the cell membrane and myofibril organization were rapidly lost.

Effects of yohimbine on naloxone-induced antinociception in a rat model of inflammatory hyperalgesia

Effects of the alpha2-adrenoceptor antagonist yohimbine on the antinociception produced by a low dose of naloxone were examined in a rat model of carrageenan-induced inflammation. In rats receiving saline prior to naloxone injection, the low dose of naloxone (5 microg/kg, i.p.) significantly prolonged paw withdrawal latency in response to noxious thermal stimuli for both the inflamed and the non-inflamed paws 4 h after carrageenan injection (6.0 mg in 0.15 ml saline). In rats receiving yohimbine, the low dose of naloxone failed to produce prolongation of paw withdrawal latencies 4 h after carrageenan, whereas naloxone produced antinociception 7 days after carrageenan. The results suggest that noradrenergic mechanisms are involved in naloxone-induced antinociception only in the early phase of carrageenan-induced inflammation.