Cortical field potentials were recorded by electrodes implanted chronically on the surface and at a 2.0 mm depth in various cortical areas in the left hemisphere in the rat during self-paced movements of the right forelimb. A surface-negative (s-N), depth-positive (d-P) cortical field potential appeared about 1.0 s (range: 0.5–1.5 s) before movement onset in the rostral (RFA) and caudal (CFA) forelimb areas of the motor cortex, and the somatosensory cortex, but not in the occipital cortex. Bipolar recording of electromyographic activities induced by the electrical stimulation of various cortical loci was also performed by pairs of steel electrodes inserted in the face, trunk, forelimb and hindlimb muscles on both sides. The stimulation of the forelimb motor cortex activated the face and/or forelimb muscles, while that of the somatosensory cortex generally activated several body part muscles including the forelimb muscle. Stronger stimulus intensity was requested to elicit the activities of most of the ipsilateral muscles to the cortex stimulated than the contralateral ones. The minimum intensity for inducing the forelimb muscle activity was lowest in the CFA among cortical areas producing the activity. The stimulation of cortical loci in which the s-N, d-P potential was recorded could induce muscle activities in the forelimb contralateral to the stimulation. It is suggested that the s-N, d-P potential is the readiness potential for activating muscles to initiate movement in the rat forelimb.

抄録全体を表示

Stimulation of the vestibular system has been reported to elicit ventilatory and circulatory changes in humans. The purpose of this study was to clarify the characteristics of vestibular-mediated ventilatory and circulatory responses in male endurance runners at the onset of passive chair rotation, which selectively stimulates the semicircular canals. Fourteen runners and 14 male untrained subjects participated. The vestibular stimulus test, which consists of 180° chair rotations (left or right half-turns on an earth-vertical axis) for a duration of 2 s, was carried out on each subject. Inspiratory minute ventilation, tidal volume, respiratory frequency, heart rate, and blood pressure were measured by breath-by-breath and beat-to-beat techniques before, during, and after the chair rotation for a total of 60 s. It was found in this study that (i) the relative change of minute ventilation response in the endurance runners was significantly (P < 0.05) greater than in the untrained subjects during and after the rotation, and that (ii) no significant group differences were observed in heart rate and mean blood pressure responses during and after the rotation. In conclusion, vestibular-mediated ventilatory response, but not circulatory response, at the onset of the chair rotation in the endurance runners was significantly greater than that in the untrained subjects. The results from the present study suggest that an increase in vestibulo-ventilatory response would be attributed to an adaptation to long-term endurance training.

抄録全体を表示

The present study examined the rheological blood velocity profile in the conduit femoral artery during rhythmic muscle contractions at different muscle forces. Eight healthy volunteers performed one-legged, dynamic knee-extensor exercise at work rates of 5, 10, 20, 30, and 40 W at 60 contractions per minute. The time and space-averaged, amplitude-weighted mean (V_mean) and maximum (V_max) blood flow velocities in the common femoral artery were measured during the cardiosystolic phase (CSP) and cardiodiastolic phase (CDP) by the Doppler ultrasound technique. The V_max/V_mean ratio was used as a flow profile index, in which a ratio of ∼1 indicates a “flat velocity flow profile” and a ratio significantly >1 indicates a “parabolic velocity flow profile.” At rest, the V_max/V_mean ratio was ∼1.3 and ∼1.8 during the CSP and CDP, respectively. The V_max/V_mean ratio was higher (p < 0.01) during the CDP than during the CSP, both at rest and at all work rates. The V_max/V_mean ratio during the CSP was higher (p < 0.01) at 30 and 40 W compared to at rest. The V_max/V_mean ratio during the CDP was lower (p < 0.05) at 5 and 10 W compared to at rest. There was a positive linear correlation between blood flow and incremental work rates during both the CSP and CDP, respectively. Thus under resting conditions, the findings indicate a “steeper” parabolic velocity profile during the CDP than during the CSP. The velocity profile during the CDP furthermore shifts to being less “steep” during rhythmic muscle contractions at lower intensities, but to being reelevated and normalized as at rest during higher intensities. The “steepness” of the parabolic velocity profile observed during the CSP at rest increased during muscle contraction at higher intensities. In conclusion, the blood velocity in the common femoral artery is parabolic both at rest and during exercise for both the CSP and CDP, indicating the persistence of laminar flow. The occurrence of any temporary slight disturbance or turbulence in the flow at the sight of measurement in the common femoral artery does consequently not induce a persisting “disturbed” and fully flat “plug-like” velocity profile. Instead, the “steepness” of the parabolic velocity profile is only slightly modified, whereby blood flow is not impaired. Thus the blood velocity profile, besides being influenced by the muscle contraction-relaxation induced mechanical “impedance,” seems also to be modulated by the cardiac- and blood pressure-phases, consequently influencing the exercise blood flow response.

抄録全体を表示

We examined the effects of habitual moderate exercise on central information processing in older individuals using the reaction time (RT) and P3 component of event-related brain potentials (ERP). The present study was designed to assess cognitive function by comparing groups of 20 older individuals (69.20 ± 1.3 years active group) who regularly engage in moderate physical activity with 20 subjects (66.90 ± 1.1 years inactive group) who do comparatively little exercise. Subjects performed a somatosensory oddball task composed of pressing a button with their right foot as fast as possible following an electrical stimulus applied to the right index finger, and not responding to an electrical stimulus applied to the left index finger. Electroencephalogram (EEG) was recorded at the frontal (Fz), central (Cz), and parietal (Pz) sites according to the International 10–20 system referenced to linked earlobes. The RT was faster for the active group than for the inactive group, and the P3 amplitude of the active group was significantly larger than that of the inactive group. Moreover, the P3 amplitude for the active group was maximum at Pz and significantly larger than at Fz and Cz, but for the inactive group it was identical between Fz and Pz. The results suggest that habitual moderate exercise exerts positive influences in older adults not only on response processing, but also on cognitive processing.

抄録全体を表示

A complex balance between extrinsic neural and intrinsic mechanisms is responsible for regulating atrioventricular (AV) conduction. We hypothesized that atrial excitation interval is shortened during dynamic exercise by extrinsic cardiac autonomic activity and that if AV conduction time responds inversely to fluctuation in atrial rhythm, ventricular excitation interval will be maintained at the predetermined cardiac cycle length. To examine such inverse relationship between PP interval and the subsequent change in PR interval (ΔPR), we analyzed the beat-to-beat changes in PP, PR, and RR intervals during stair-stepping exercise for 10 min in 11 sedentary and 9 trained subjects. In the sedentary group, the average PR interval significantly shortened during exercise, in parallel with the reduction in the average PP and RR intervals. The variance of PP and RR intervals was also significantly decreased during exercise. The reduction in the variance of RR interval was, however, much greater than that of PP interval, implying that AV conduction time changes inversely to fluctuation in atrial excitation rhythm. Indeed, the variance of PR interval was augmented during exercise and there was a clear inverse relationship between PP and ΔPR intervals. Although trained subjects were characterized by their lower heart rate response during dynamic exercise, the responses in the variability of PP, PR, and RR intervals were fundamentally identical with those in sedentary subjects. We conclude that the AV nodal mechanism that operates at a higher level of heart rate during dynamic exercise may cancel fluctuation in atrial excitation interval and keep ventricular excitation rhythm at the predetermined cardiac cycle length.

抄録全体を表示

We examined the effect of the Ca²⁺ concentration in the endolymph ([Ca]_e) or in the endolymphatic surface cells ([Ca]_i) on the endocochlear potential (EP) by using an endolymphatic or perilymphatic perfusion technique, respectively. (i) A large increase in [Ca]_e up to ∼10⁻³ M with a fall in the EP was induced by transient asphyxia (∼2 min) or by the intravenous administration of furosemide (60 mg/kg), and a significant correlation was obtained between the EP and p[Ca]_e (= −log [Ca]_e, r = 0.998). (ii) Perfusion of the endolymph with 10 mM EGTA for 5 min neither produced any significant change in the EP nor altered the asphyxia-induced change in EP (ΔEP_asp), suggesting that neither [Ca]_e nor the Ca²⁺ concentration gradient across the stria vascularis contributed directly to the generation of the EP in the condition of low [Ca]_e. In contrast, endolymphatic perfusion with high Ca²⁺ (more than 10 mM) produced a decrease in EP and a significant correlation was obtained between the EP and the Ca²⁺ concentration of perfusion solution (r = 0.982), suggesting that Ca²⁺ permeability may exist across the stria vascularis. (iii) The administration of a Ca²⁺ chelator, EGTA-acetoxymethyl ester (AM, 0.3 mM), to the endolymph, which produced a gradual increase in EP, suppressed significantly, by 60–80%, ΔEP_asp or furosemide-induced changes in EP. In contrast, perilymphatic administration of 0.5 mM EGTA-AM caused no significant suppression of the ΔEP_asp. These findings suggest that [Ca]_i plays an important role in generating/maintaining a large positive EP.

抄録全体を表示

The position of the neuromuscular junction of the human masseter muscle has estimated from the low frequency component of the surface electromyogram. Monopolar surface electromyograms were recorded in response to clenching from eight sites with the reference electrode placed on the tip of the nose in six healthy male subjects. Component of the slow wave was separated from the raw recordings using digital filter, and the difference of the polarity and magnitude with the sites was examined. The base line of the recordings deflected either negatively or positively depending on the recording sites. These deflections coincided with bursts of muscular action potentials. Deflection of the slow wave component was largely negative over the inferior masseter close to the mandibular ramus but shifted to positive over the superior part. The greatest magnitude of the muscular action potential coincided with the most negative deflection of the slow wave. The phase of the muscular action potential burst also reversed near the site of the polarity change of the slow wave. These findings suggest that the slow wave, as detected by this method, originates mainly from the synaptic potential at the meuromuscular junction and that this is located on the inferior part of the muscle close to the mandibular ramus.

抄録全体を表示

We previously reported that the intrathoracic pressure (ITP) decreases and the transmural pressure of the aortic wall (TMP) increases during 4.5 s of microgravity (μG) induced by free drop. To examine the ITP response to a longer period of μG in the absence of the respiratory rate (RR) decrease, i.e., bradypnea, which occurs at the onset of μG, we measured the aortic blood pressure at the diaphragma level (AP) and ITP. We then calculated the TMP at the aortic arch level during 20 s of μG induced by parabolic flight in anesthetized rats (n = 7) with either spontaneous ventilation (SPN-V) or controlled ventilation (CONT-V). In the SPN-V group, the bradypnea was observed in all rats after the onset of the μG (RR change −13.9 ± 2.9/min). The ITP during μG (−9.3 ± 0.9 mmHg) was significantly lower than that during 1 G (−7.7 ± 0.9 mmHg), and the TMP was significantly increased during μG (112 ± 6 mmHg) compared to 1 G (103 ± 5 mmHg). Similar changes in ITP and TMP were observed in the CONT-V group: During μG and 1G, respectively, the ITP was −8.4 ± 0.6 mmHg and −5.9 ± 0.7 mmHg, and the TMP was 112 ± 6 mmHg and 101 ± 6 mmHg, whereas no change in RR was observed because of the controlled ventilation. These results show that the ITP decreases and the TMP increases during μG, and they are not affected by a disturbance of respiratory rhythm.

抄録全体を表示

An intracisternal injection of the GABA_A receptor antagonist bicuculline into conscious rats increased arterial pressure and decreased hindquarter resistance. Propranolol attenuated only the resistance response, but ganglionic block abolished both responses. These findings suggest that central GABA_A receptor blockade induces an autonomic pressor action with hindquarter vasodilatation.

抄録全体を表示

Corrections to Vol. 54, No. 5, pp. 431-448 (2004)

p. 435, right column, 2nd paragraph: 12th line should read: "even with currents as high as 500 μA after this lesion" ("500 A" should be "500 μA".)

p. 438, left column, 2nd paragraph: 4th line should read: "rent intensity less than 100 μA) induced a large tran-" ("100 A" should be "100 μA".)

p. 440, left column, 3rd paragraph: 3rd line should read: "nodulus and uvula with a latency of 6–10.5 ms in" ("–" and "1" are overlapping.)

p. 442, left column, 3rd paragraph: 6th line should read "from one 30° downward. This stimulus caused" ("30¡" should be "30°".)

Corrected full-text is shown in PDF.

抄録全体を表示