Masamichi Kato

Disturbances of voluntary control of saccadic eye movements in schizophrenic patients

To study whether or not schizophrenic patients have disturbances in voluntary control of saccades, we examined visually elicited saccade and antisaccade tasks in 10 normal control subjects and 12 schizophrenic patients. The latencies of saccades in the schizophrenic patients were not significantly different from those of normal controls. However, 6 of the 12 schizophrenics showed significant abnormalities in the antisaccade task; 6 made more errors and 3 of them showed longer latencies than normal controls. Five of these 6 patients revealed an atrophy of the frontal cortex on computed tomography (CT) scans. These results indicate that many schizophrenics show difficulties in voluntary control of saccades, suggesting a dysfunction of the frontal cortex.

Firing rate of individual motor units in voluntary contraction of abductor digiti minimi muscle in man

Abstract The frequency and variability of discharges of motor units in abductor digiti minimi muscle of 11 human subjects were investigated. In the first series, contraction was performed so as to raise the tension as linearly as possible from 0 to maximum in 2, 3.2, 5, 8, and 10 sec. There was a rise in discharge frequency when the tension was raised; this rise was steeper when the contraction was faster. The frequency at the start of discharge was higher, and the peak value of frequency was also higher at contractions with greater speeds. Irregular fluctuations in the discharge frequency was greater and appeared at earlier stages during the more rapid contractions. In the second series of experiments, the tension was held constant at various levels covering the entire range of contraction. At contractions with larger steady tension the discharge frequency of units was found to be higher and irregularity of discharge was enhanced. The units recruited at smaller tension vary over a greater range of discharge frequencies than those recruited at larger tension.

Recruitment of motor units in voluntary contraction of a finger muscle in man

Abstract The recruitment of motor units during voluntary isometric contraction was studied in the abductor digiti minimi muscle of 13 human subjects trained to increase tension in this muscle almost linearly from zero to maximum. The subjects matched the output of a transducer, measuring the tension in this muscle, to a linear target ramp voltage. The target ramps varied in duration from 2 to 10 sec. When speed of contraction was kept constant there was considerable degree of constancy in the tension at which individual motor units were recruited. The recruitment order of motor units, therefore, appeared to be determined at repeated contractions. However, the order was not rigidly fixed among units whose tension range of recruitment is overlapped, especially among those units recruited at medium to strong contraction. When the contraction was performed more quickly the motor units were recruited at lower tension. Larger population of units were recruited at lower tension range: 45.8% of units were recruited before the tension attained 20% of maximum tension. There is a tendency for motor units with larger action potentials to be recruited at higher tension.

Treadmill walking and overground walking of human subjects compared by recording sole-floor reaction force

In order to clarify differences of treadmill from overground locomotion, experiments were carried out on 10 volunteers (five males and five females). Sole-floor reaction force was recorded from five anatomically discrete points with strain gauge transducers of 14 mm diameter attached firmly to the sole of bare-foot. At first the subject was asked to walk on the laboratory floor at his/her preferred velocity. After the average velocity was obtained, the subject was asked to walk on the treadmill at the same velocity of average overground walking. Stance period at treadmill walking shortened to 93.3% (P < 0.01) of the value at overground walking. Coefficient of variation of stance period was significantly smaller at the treadmill walking than at overground walking. Strain gauge-floor contact times were shorter in the treadmill walking; heel 81.2%, first metatarsal 93.5%, third metatarsal 93.6%, fifth metatarsal 90.6% and at great toe 93.2% of overground locomotion. Cadence during treadmill locomotion was significantly larger than overground walking (106.6%, P < 0.05). These results show that when subjects walk on the treadmill and on laboratory floor at the identical speed, stance period shortened by 6.7% while cadence increased by 6.6% on the treadmill.

Circularly polarized 50-Hz magnetic field exposure reduces pineal gland and blood melatonin concentrations of Long-Evans rats

In order to determine if pigmented rats also exhibit melatonin suppression like that described for albino rats exposed to circularly polarized, 50-Hz, 1-muT magnetic fields for 6 weeks, two experiments were conducted with Long-Evans rats. The field-exposed experimental group received circularly polarized, 50-Hz, 1-muT magnetic fields for 6 weeks, the concurrent sham-exposed control group was exposed to the stray field of 0.02 muT. In addition, prior to the exposure experiment, two cage-control groups were placed in the facility for 6 weeks without activation of the 50-Hz magnetic field generation apparatus. Rats were sacrificed at 12.00 and at 24.00 h for collection of plasma and pineal gland: melatonin was determined by radioimmunoassay. Significant reductions of plasma and pineal gland melatonin contents were observed at 0.02 muT as compared to the control values, and a further reduction was observed at 1 muT. As do albino rats, pigmented rats rats also exhibit melatonin suppression when exposed to time-varying magnetic fields.

Horizontal or vertical 50-Hz, 1-μT magnetic fields have no effect on pineal gland or plasma melatonin concentration of albino rats

Three experiments were carried out on male Wistar-King rats to determine if 6 weeks of exposure to horizontally- or vertically-oriented 1-microT, 50-Hz magnetic fields suppresses melatonin content in plasma and pineal gland, as does 6 weeks of exposure to circularly-polarized, 50-Hz, 1-microT magnetic fields. In each experiment, a concurrent sham-exposed control group was exposed to a stray field of 0.02 microT. In addition, a separate control experiment was completed between the horizontal and vertical field experiments in which cage-controls were housed in the exposure facility for 6 weeks without activation of the magnetic field coils. Subjects were sacrificed at 12:00 or at 24:00 h for collection of plasma and pineal gland; melatonin was determined by radioimmunoassay. In contrast to the results of experiments with rotating-vector magnetic fields, there were no significant differences among 1-microT, 0.02-microT and control groups in melatonin concentration of pineal gland or plasma.

Disruption of fore- and hindlimb coordination during overground locomotion in cats with bilateral serial hemisection of the spinal cord.

In order to investigate if inter-limb propriospinal reflexes participate in coordination of locomotive movements of fore- and hindlimbs, we examined the relations between fore- and hindlimbs during overground locomotion of adult cats with spinal cord lesions. In a group of cats (T-T preparations), the spinal cord was hemisected first at around Th12 and then at intervals of 37-126 days contralaterally at mid-thoracic level, propriospinal tracts being mostly severed in this group. In a second group of cats (C-T preparations), which received hemisections first at around C2 and then at intervals of 21-73 days at mid-thoracic level, propriospinal tracts were left intact at least on one side of the spinal cord. Control observations were also made in intact cats and those with single hemisections at C2 or Th12, or with double unilateral hemisections at Th6 and Th12. Thus, it was found that in both T-T and C-T preparations, step length of the forelimbs was shortened significantly, whereas that of the hindlimbs was significantly lengthened. Furthermore, phase relations between the fore- and hindlimbs were completely lost in these preparations, suggesting that the stepping generator for the forelimbs operates independently of that for the hindlimbs. In other single-hemisected or unilaterally double-hemisected preparations, by contrast, no such changes were observed. The close similarity of the results in T-T and C-T preparations, in spite of different degrees of impairment of propriospinal tracts in them, leads to a conclusion that inter-limb propriospinal reflexes play little role in coordination of locomotive movements of fore- and hindlimbs.

Recovery of postural control following chronic bilateral hemisections at different spinal cord levels in adult cats

Chronic cats with double hemisections of the spinal cord, first at a lower thoracic level followed by a contralateral midthoracic cord at intervals of 0 to 126 days (T-T preparations) or first at an upper cervical followed by a midthoracic at intervals of 15 to 74 days (C-T preparations), eventually recovered quadrupedal standing 7 to 53 days after the second hemisection. For about 7 days following the first hemisection at a lower thoracic level, floor reaction force (FRF) of the hind limb of the hemisected side decreased to 25 to 30% of the normal value, then recovered to the control value. A group of cats whose second hemisection was done within 7 days after the first hemisection needed 24 to 53 (mean 43) days to recover quadrupedal standing, whereas cats whose second hemisection occurred after 10 to 126 days needed 7 to 22 (mean 15) days. During the recovery period many unusual reflexes were elicited which eventually disappeared as the cats resumed standing and walking. Lateral stability of the double-hemisected cats deteriorated significantly, whereas segmental reflexes were augmented. These results indicate the importance of descending impulses over the segmental motoneuron pools to control standing posture and locomotion. It was assumed that the descending impulses were conveyed by polysynaptic pathways which had minimal functions before the hemisections.

Vestibular responses and branching of interstitiospinal neurons

Summary1.Interstitiospinal neurons were activated by antidromic stimulation of the ventromedial funiculus of the spinal cord at C1 and C4 in cerebellectomized cats under chloralose anesthesia. 46% of these neurons responded only at C1 (N cells) and the remaining 54% responded at C4 also (D cells). There is no topographical difference in the location of N and D cells. Conduction velocities of N cells were significantly slower than those of D cells.2.Stimulation of the contralateral whole vestibular nerve evoked firing of 31% of both N and D cells; some responded early enough to suggest disynaptic connections, many responded late. Stimulation of the ipsilateral whole vestibular nerve evoked firing of several cells, one spontaneously discharging D cell was inhibited.3.Stimulation of the contralateral individual semicircular canal nerves evoked firing of 33% of N cells and 13% of D cells. Most of these responses were late. N cells responded not only to the vertical canals but also to the horizontal canal, whereas D cells responded to the horizontal canal, but seldom to the vertical ones. Most canal responding neurons received specific input, only two N cells received convergent input from both the anterior and horizontal canals. Stimulation of the ipsilateral canals did not evoke excitation of any cells tested; one D cell was inhibited by stimulation of the horizontal canal nerve.4.Stimulation of the rostral medial vestibular nucleus evoked characteristic negative field potentials centered in the contralateral interstitial nucleus of Cajal (INC). Approximately 60% of both N and D cells received excitation from the contralateral vestibular nuclei. About 17% of these responding neurons received monosynaptic excitation, most frequently from the rostral medial nucleus. Stimulation of the ipsilateral vestibular nuclei evoked firing of 12% of both N and D cells.5.Twenty-nine neurons were fired antidromically by weak stimuli applied to the ipsilateral vestibular nuclei. Twenty-seven of the 29 were activated only from C1 and were found in the INC (10 cells) and in the reticular formation dorsal to the INC (19 cells). Measurement of the spread of the effect of stimulus current and comparison of latencies to stimulation of the vestibular nuclei and C1 indicated that these neurons have axon collaterals going to the ipsilateral vestibular nuclei. Only one of them received excitation from the contralateral posterior canal, others did not respond to the labyrinth. Some were activated by stimulation of the vestibular nuclei.

Location and vestibular responses of interstitial and midbrain reticular neurons that project to the vestibular nuclei in the cat.

SummaryExperiments were performed on cats anesthetized with a chloralose to locate neurons in and around the interstitial nucleus of Cajal (INC) that project to the vestibular nuclei, and to study labyrinthine inputs to these neurons. Neurons that project to the vestibular nuclei were identified by microstimulation confined to the vestibular nuclei on both sides. All neurons thus identified were activated antidromically from the ipsilateral (but not contralateral) vestibular nuclei. Vestibular projecting neurons were found in the INC and the reticular formation rostral, dorsal and caudal to the INC. About 23% of these neurons were vestibular branching spinal projecting neurons. The median conduction velocity of vestibular projecting neurons was estimated to be in the neighborhood of 12–16 m/s. Stimulation of the contralateral vestibular nerve evoked firing in 29% of neurons projecting to the vestibular nuclei, but not to the spinal cord. Interstitial neurons responded more frequently than reticular neurons (45% vs 11%, χ2 test, p < 0.001). By stimulation of individual semicircular canal nerves, it was shown that vestibular projecting neurons receive excitation from the contralateral vertical canals, but do not receive substantial inputs from the horizontal canal. Stimulation of the ipsilateral vestibular nerve excited 10% of neurons; suppression of activity was observed for six cells and four of the six were excited by stimulation of the contralateral vestibular nerve. Stimulation of ipsilateral individual semicircular canal nerves did not excite any cells tested; the activity of a few cells was suppressed by stimulation of the vertical canal nerves. One neuron received excitation from the contralateral anterior canal and suppression from the ipsilateral posterior canal. Vestibular branching spinal projecting neurons rarely received labyrinthine inputs as already reported (Fukushima et al. 1980a). These results suggest that vestibular projecting neurons may be involved in vertical vestibular reflexes.