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H P Clamann

Publications and source records attributed to H P Clamann.

11 recordsLinked to original sources
PubMed1991

The influence of noise on quantal EPSP size obtained by deconvolution in spinal motoneurons in the cat.

1. The amplitudes of quantal components that make up single-fiber excitatory postsynaptic potentials (EPSPS) were determined by a deconvolution technique and by simulation studies and were compared with the background noise. 2. A strong correlation was found between the sizes of EPSP quantal components and the standard deviation of the noise from which the data were extracted by deconvolution. A similar correlation was then shown in published data from several other laboratories. 3. EPSPS having amplitudes less than 100 microV were recorded that had little or no variance in their amplitudes. Most of these EPSPS showed a much smaller peak variance than would be expected if they fluctuated among amplitudes in steps of approximately 100 microV--the proposed mean value for the amplitude of the quantal EPSP. 4. Deconvolution of simulated data with the maximum likelihood algorithm resulted in the suppression of components less than 1.5 SD of the background noise. The remaining components were approximately equally spaced. No way was found to detect this error, and rejection of deconvolved data with components less than 1.5 noise SD did not eliminate it. The resulting erroneous data showed a strong correlation between the amplitudes of the components obtained and the noise standard deviation. 5. It is concluded that at least some EPSPS generated by single Ia-afferents on motoneurons are composed of quantal components significantly less than 100 microV and that deconvolution procedures are not capable of detecting such small components.

Action Potentials↗
PubMed1989

Force output of cat motor units stimulated with trains of linearly varying frequency.

1. A relation between stimulation frequency and muscle force is usually determined with stimulus trains of constant frequency and described as a single-valued sigmoid curve. This relationship fails to explain a number of features of rate coding. 2. Single motor units were isolated in medial gastrocnemius or soleus muscles of cats deeply anesthetized with pentobarbital sodium. Motor units were classified as fast or slow. Each unit was stimulated with a train whose frequency varied linearly from less than 3 pulses per second (pps) to 20% above the unit's fusion frequency and back to about 3 pps with a period of 5 s. 3. All motor units showed a marked hysteresis during frequency-varying stimulation. A greater force was produced when frequency was decreasing than when it was increasing. The force output of each unit remained nearly maximal as stimulus frequency declined from its maximum to about one-half of the unit's fusion frequency; force rapidly declined with further decreases in frequency. The force-frequency relation could change with each trial as frequency increased but was highly reproducible when frequency decreased. This suggested a strategy by which central nervous system (CNS) control could maximize the force at any discharge rate and produce a predictable force-frequency relation. 4. Posttetanic potentiation, motor unit slowing, and a preload which causes a motor unit to operate on the negatively sloping portion of the length-tension curve may each contribute to the observed hysteresis under certain circumstances. None can explain why hysteresis was consistently seen in all motor units. A time-dependent rate of tension development and decay together with a catchlike property can account for all of the properties of hysteresis and appeared to be the primary cause of hysteresis in fully potentiated motor units.

Animals↗
PubMed1989

Variance analysis of excitatory postsynaptic potentials in cat spinal motoneurons during posttetanic potentiation.

1. Fluctuations in the peak amplitudes of composite excitatory postsynaptic potentials (EPSPs) in cat spinal motoneurons were analyzed during posttetanic potentiation (PTP). Each of a series of identical tetanic stimulus trains delivered to a muscle nerve was followed by 45 test stimuli applied at 2-s intervals. The mean peak amplitude and mean peak variance were calculated for EPSPs evoked by all those stimuli following a tetanus with the same time interval. It was assumed that the variance arises primarily from the probabilistic all-or-none behavior of single synaptic boutons and background noise due to spontaneous synaptic activity and thermal noise in the recording system. The variance was corrected for the contribution from additive Gaussian background noise. 2. If it is assumed that individual synaptic boutons behave independently, corrected mean peak variance and mean peak amplitude are related by a parabolic function. The expected parabolic relationship was seen in 9 of 31 cases studied, and the parameters of the best parabolic fit to the data allowed estimation of some synaptic properties. From these parameters, the mean amplitude of the unit EPSP (v) was estimated to be 102.1 +/- 57.4 (SD) microV. An average of 3.7 boutons comprised each Ia-motoneuron contact system. 3. On average, only 27% of all synaptic boutons given off by the stimulated Ia fibers to one motoneuron were active and releasing transmitter during unpotentiated reflex transmission. The remaining 73% of the synapse population was intermittently silent. The population of boutons which took part in synaptic transmission could be divided into two subpopulations, one with a release probability P = 1 and a second with a mean release probability P = 0.13 +/- 0.086. 4. We conclude that synaptic boutons connecting Ia afferents to motoneurons exist in two populations, one having a high and one a low probability of transmitter release. Transmitter release is quantal, resulting in a unit EPSP of approximately 100 microV measured at the motoneuron soma.

Analysis of Variance↗
PubMed1988

Nonlinear force addition of newly recruited motor units in the cat hindlimb.

The present experiments were designed to examine the interaction of simultaneously active motor units. Pairs of medial gastrocnemius (MG) or soleus (Sol) units were stimulated individually and then together with constant frequency trains of 5-40 pulses per second. Stimulating two units asynchronously produced a smoother contraction than synchronous stimulation, but rarely a force increase. This contrasts with similar experiments on whole muscle bundles. A force increase may require that adjacent muscle fibers be active. The combined force of two motor units exceeded the algebraic sum of their separate forces by 12% in MG and 5% in Sol on average. The force a unit could sustain after a second unit fell silent was greater than the force the unit produced alone (21% in MG and 8% in Sol). We conclude that motor units produce more force when interacting than alone. During derecruitment the units remaining active produce more force than when recruited.

Animals↗
PubMed1979

Relation between force and fatigability of red and pale skeletal muscles in man.

Experiments were performed to test the effect of muscular fatigue on the relationship between smoothed rectified electrical activity (SREMG) and force in human muscles of different fiber compositions. Fatigue was shown to be produced by failure of a mechanism distal to the neuromuscular junction in three muscles tested: biceps brachii, triceps brachii, and adductor pollicis. Fatigue produced changes in SREMG in first dorsal interosseous, suggesting an effect at or proximal to the neuromuscular junction. Fatigue produced changes in the SREMG-force relationship only at high force levels in the pale triceps and biceps brachii, but produced a change throughout the force range in the red adductor pollicis. It is suggested that muscle units composed of pale fibers fatigue selectively in mixed muscles containing many such units, while fatigue effects are more difficult to produce and are distributed more uniformly in predominantly red muscles.

Adult↗
PubMed1977

The relation between size of motoneurons and their position in the cat spinal cord.

Experiments were performed to test whether motoneurons in the plantaris and medial gastrocnemius muscles of the cat are arranged in the spinal cord according to their sizes. It was found that motoneurons are randomly distributed with respect to size in their motor nuclei. Evidence is also presented that motoneuron density in these pools is irregular, and that there is considerable variability of position of medial gastrocnemius and plantaris motor pools from animal to animal.

Action Potentials↗
PubMed1976

Electrical measurement of axon diameter and its use in relating motoneuron size to critical firing level.

1. Action potentials of single plantaris motoneurons were recorded monophasically from fine ventral root filaments. A resistor was placed in shunt across the recording electrodes and its value was varied until the size of the action potentials was reduced by one-half. At this point the resistance of the filament was taken to be equal to that of the shunt, and the quotient of action-potential amplitude divided by filament resistance was proportional to the axonal action current. 2. The measurement of axonal action currents depends on the assumption that the filament-electrode system obeys Ohm's law. Tests were performed which validated this assumption. It was then shown that the axonal action currents varied as the square of conduction velocity over the range of alpha and gamma motoneurons. 3. A direct correlation was established between the critical firing levels of motoneurons and the sizes of the impulses in their axons after the recorded sizes had been normalized in accordance with the resistances of the ventral root filaments in which they were located. Since both the CFL and axonal diameter were related to impulse size, they were related to each other (Fig. 6). 4. Evidence is cited justifying the conclusion that the dimater of a motor axon is directly related to the size of its soma. Thus, it may be inferred that the critical firing level of a motoneuron is a function of its size.

Action Potentials↗