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Biomedical subjects

U Tan

Publications and source records attributed to U Tan.

At least 127 records · Page 7Linked to original sources
PubMed1977

Electrocorticographic effects of topically applied ouabain, epinephrine and bicuculline.

The effects of topically applied ouabain, epinephrine and bicuculline on the electrocorticographic activity were studied in unanesthetized cats with high cervical transection. Ouabain in a concentration of 25 X 10(-6) induced single intermittent spikes or paroxysms lasting for about 4-10 min. A 5% solution of bicuculline also induced paroxyms which lasted for many hours and were suppressed by topical epinephrine. Ouabain paroxysms became more vigorous when applied after epinephrine and bicuculline. Topical epinephrine dimished the ouabain discharges and the click evoked cortical responses. It is suggested that the epileptogenic activity of ouabain and bicuculline and its antagonization by epinephrine can be accounted for by the antagonistic effects of these agents on the electrogenic ion pumps such as inhibition and stimulation of the (Na + K) ATPase activity, respectively.

Administration, Topical↗
PubMed1975

Post-tetanic changes in the discharge pattern of the extensor alpha motoneurones.

The after effects of orthodromic tetanization on the discharge pattern of gastrocnemius motoneurones were investigated in decerebrate and spinalized cats. tduring stimulation of intact gastrocnemius nerves at 20 Hz, small motoneurones showed ttion for 8 sec, large motoneurones followed the 20 Hz stimulation in 1:1 order, whereas small motoneurones became silent for about 37 sec. Thereafter, the impulse rate of large motoneurone decreased while that of small motoneurone increased, progressively reaching the pre-tetanic values in about 72 sec. When gastrocnemius nerves were tetanized for 20 sec, potentiation of large motoneurones and depression of small motoneurones lasted for about 120 sec. Post-tetanic potentiation of large motoneurone was still observed during stimulation with 40 Hz but not with 80 Hx. Inhibition of a small tonic motoneurone during repetitive activity of a large motoneurone was observed during stimulation of Group I + II afferents following injection of 0.025 mg/kg strychnine. Another strychnine injection of the same dose reduced this inhibition. It was concluded that large-phasic motoneurones may be highly susceptible to post-tetanic potentiation; and that small-tonic motoneurones may be inhibited by large motoneurones through a recurrent circuit.

Animals↗
PubMed1975

Firing rate and size distribution of the hind limb extensor and flexor motoneuronal units.

Axonal spike size of extensor and flexor motoneurones were subjected to statistical analysis. Extensor motoneurones were isolated in decerebrate cats and the flexor motoneurones in spinalized cats. Smallest spikes were due to gamma motoneurones which could be further classified as small, medium and large. Extensor and flexor alpha motoneuronal units were also divided into these three subgroups. Considering the firing pattern and the cell size extensor alpha units were divided into five types: small-tonic, medium-tonic, large-tonic, large-phasic and largest-phasic. Maximum firing rate of extensor alpha units was directly related to the cell size and was distributed between 5-15, 15-20, 25-40 and 35-55 imp/sec for the small-tonic, medium-tonic, large-tonic and large-phasic motoneurones. Stabilized firing rates were distributed between 5-10, 10-15 and 15-20 imp./sec for the small-tonic, medium-tonic and large-tonic motoneurones. Flexor motoneuronal types and their maximum firing rates were as follows: small-tonic (16 imp./sec), medium-tonic (24 imp./sec), small-phasic (37.5 imp/sec), medium-phasic (30 imp./sec), large-phasic (46 imp./sec) and largest-phasic (only one or two impulses). The functional significance of the results was discussed considering the axonal spike size as an index for the cell size.

Animals↗
PubMedDate not supplied

Correlations between nonverbal intelligence and peripheral nerve conduction velocity in right-handed subjects: sex-related differences.

The speed hypothesis of intelligence was tested in relation to median nerve conduction velocity (NCV) in right-handed subjects. In total, NCV did not significantly correlate with IQ (Cattell's Culture Fair Intelligence test). The motor and sensory median NCVs correlated with IQ positively linearly in men and negatively linearly in women. These results supported the general, unqualified speed hypothesis of intelligence only for men. It was concluded that the conduction speed of the input-output channels of brain as an information processing unit may differentially contribute to nonverbal intelligence, depending upon sex. The male hormone, testosterone, was suggested to be the main factor responsible for sex-related differences in the IQ-NCV relationships.

Adolescent↗
PubMedDate not supplied

The relationship between serum testosterone level and Hoffmann reflex from the long flexor thumb muscle in right-handed young adults.

The relationship between serum testosterone level and Hoffmann (H) reflex from right to left thumb flexors was studied in right-handed young men and women. The subjects were divided into two subgroups: fast and slow in right-hand skill, but no difference in left-hand skill (peg moving). The mean serum testosterone level was found to be significantly lower in subjects with fast right hand than those with slow right hand. The mean H reflex from right was significantly smaller in subjects with fast right hand than those with slow right hand. There was a negative, linear relationship between serum testosterone level and amplitude of H-reflex from right thumb. This was more pronounced in females than males. The H reflex from left was not significantly associated with serum testosterone levels. It was concluded that testosterone may affect the somatomotor system of the left brain during adolescence impairing the right-hand skill especially in females. These results also appear to be in accord with the testosterone theory of cerebral lateralization.

Adolescent↗
PubMedDate not supplied

The relationship between serum testosterone and visuomotor learning in hand skill in right-handed young women.

The relationship between serum testosterone level and motor learning in hand skill was studied in right-handed young women. Hand skill was assessed by a peg moving task. Subjects were required to shift 25 pegs from one of two parallel rows to the corresponding holes as fast as possible, first with right and then with left hand. One trial consisted of the time elapsed to move 25 pegs with one hand. Ten trials were performed by each hand. Peg moving times for the right and left hands linearly decreased at each successive trial (visuomotor learning). Subjects were divided into two subgroups as those having serum testosterone concentrations below and above the mean. The right hand skill and its motor learning was found to be better in subjects with low testosterone than those with high testosterone. The left hand skill was better in subjects with low testosterone than those with high testosterone; there was no significant difference in the left-hand learning in subjects with low and high testosterone (parallel regression lines). Motor learning linearly decreased with testosterone for the right hand, not for the left hand. These results seem to be in accord with the testosterone theory of cerebral lateralization (Geschwind & Behan, 1982).

Adolescent↗
PubMedDate not supplied

The relationship between serum testosterone level and visuomotor learning in right-handed young men.

The relationship between serum testosterone level and visuomotor of learning of hand skill was studied in right-handed young men. Hand skill was assessed by a peg moving task. Peg moving times for the right and left hands linearly decreased at each successive trial (visuomotor learning). The peg moving times for the right and left hands were found to be negatively linearly related to serum testosterone levels: there was a direct relationship between hand skill and testosterone, which was more prominent for the right than the left hand. The slopes of the learning curves for the right hand were found to be equal in subjects with low, normal, and high testosterone. The intercepts of these curves exhibited a shift toward a better hand skill from low- to high-testosterone subjects. The visuomotor learning for the left hand was found to be better in subjects with normal and high testosterone than those with low testosterone. It was concluded that testosterone would favor the visuomotor development especially of the left cerebral hemisphere, probably at puberty; the motor learning of this hemisphere does not seem to be associated with testosterone. Testosterone seems to be advantageous for the visuomotor performance as well as for the motor learning of the right cerebral hemisphere.

Adolescent↗