Individual EPSPs produced by single triceps surae Ia afferent fibers in homonymous and heteronymous motoneurons

1976 ◽  
Vol 39 (4) ◽  
pp. 679-692 ◽  
Author(s):  
J. G. Scott ◽  
L. M. Mendell
Keyword(s):  
Spinal Cord ◽  
The Other ◽  
Triceps Surae ◽  
Relative Location ◽  
Spatial Effects ◽  
Epsp Amplitude ◽  
Ia Afferent ◽  
Afferent Fibers ◽  
The Mean ◽  
The Individual

1. The individual EPSPs evoked by the action of single Ia fibers from cat triceps surae (MG, LG, SOL) were recorded in homonymous and heteronymous motoneurons innervating these same three muscles. 2. In general, Ia fibers projected to a greater percentage of homonymous than heteronymous motoneurons. One class of Ia afferent evoked EPSPs in virtually all homonymous motoneurons; the other had a substantially lower projection frequency. Possible difficulties introduced by the limited resolution of the averaging technique are discussed. 3. Individual EPSPs were larger on the average if evoked a) in SOL rather than in MG or LG motoneurons, b) by LG rather than by MG or SOL afferent fibers, or c) in homonymous rather than in heteronymous motoneurons. The mean EPSP was larger in homonymous than in heteronymous motoneurons because the largest EPSPs (greater than 150 muV) were found mainly in homonymous motoneurons. 4. Rise times of EPSPs were only slightly shorter in homonymous than in heteronymous motoneurons, suggesting that other factors besides relative location of Ia terminals account for the observed EPSP amplitude differences. Rise times in SOL motoneurons were longer than those in MG or LG. 5. LG afferent fibers tended to produce larger EPSPs in rostral than in caudal LG motoneurons, and MG afferents produced larger EPSPs in caudal than in rostral MG motoneurons. These spatial effects were in accord with the more rostral entry of LG than MG Ia afferents into the spinal cord. The differential projection of SOL afferents to MG and SOL motoneurons which overlap spatially in the spinal cord suggests a species specificity in addition to a location specificity.

Analysis of individual Ia-afferent EPSPs in a homonymous motoneuron pool with respect to muscle topography

1984 ◽  
Vol 51 (1) ◽  
pp. 64-74 ◽  
Author(s):  
S. M. Lucas ◽  
T. C. Cope ◽  
M. D. Binder
Keyword(s):  
Afferent Fiber ◽  
Afferent Input ◽  
The Other ◽  
Medial Gastrocnemius ◽  
Excitatory Postsynaptic Potential ◽  
Epsp Amplitude ◽  
Ia Afferent ◽  
Branch Group ◽  
Intramuscular Nerve ◽  
The Mean

The spike-triggered averaging technique (26) was used to determine whether the synaptic input from medial gastrocnemius (MG) Ia-afferent fibers to homonymous motoneurons is "topographically weighted" (22) by means of differences in projection frequency, excitatory postsynaptic potential (EPSP) amplitude, or a combination of both factors. Motoneurons were classified as either "same branch" or "other branch," depending on whether a Ia-afferent fiber and motor axon were contained in the same or different intramuscular nerve branches. No difference was found in the projection frequency of Ia-afferents to the same branch and other branch motoneurons (95 versus 94%, respectively). The mean EPSP amplitude was larger in the same branch group of motoneurons (92 +/- 8 (SE) microV; n = V; n = 97) than in the other branch group (77 +/- 7 microV; n = 79). This difference was most striking in high-rheobase (greater than or equal to 10 nA) motoneurons, for which the mean EPSP amplitude in the same branch group was 82 +/- 12 microV (n = 48), whereas that in the other branch group was 52 +/- 5 microV (n = 37). In 60 cases it was possible to compare the EPSPs produced by a same branch afferent and an other branch afferent in the same motoneuron. The same branch afferent produced the larger EPSP in 73% (44/60) of the cases. Moreover, the mean ratio of the same branch to the other branch EPSP amplitudes was 1.7, which was both statistically significant and consistent with analogous results from our preceding study of aggregate EPSPs (22). Mean rise times and half-widths of EPSPs in the same branch group were not significantly different from those in the other branch group. Furthermore, no significant differences in rise times or half-widths between the two groups were evident when motoneurons were segregated according to their rheobase values. This suggests that the segregation of Ia-afferent and motor axons across the intramuscular nerve branches is not reflected in the locations of Ia terminals on the motoneuron somadendritic surface and that other factors must account for observed EPSP amplitude differences. Our data suggest that the topographic weighting of homonymous Ia-afferent input to cat MG motoneurons is mediated by a gradient of EPSP amplitude rather than by a gradient of Ia connectivity and also suggest that the effect is most prominent in high-rheobase motoneurons.

Influence of synaptic identity on single-Ia-afferent connectivity and EPSP amplitude in the adult cat: homonymous versus heteronymous connections

1992 ◽  
Vol 68 (4) ◽  
pp. 1046-1052 ◽  
Author(s):  
C. B. Webb ◽  
T. C. Cope
Keyword(s):  
Spinal Cord ◽  
Conduction Velocity ◽  
Triceps Surae ◽  
Medial Gastrocnemius ◽  
Separate Experiment ◽  
Excitatory Postsynaptic Potential ◽  
Epsp Amplitude ◽  
Ia Afferent ◽  
Ia Afferents ◽  
Entry Points

1. This study makes use of the pattern of synaptic connections between motoneurons and Ia afferents of triceps surae muscles in the cat to test the relative importance of synaptic identity, neuronal size, and neuronal topography as determinants of Ia-afferent connectivity and excitatory postsynaptic potential (EPSP) amplitude. 2. The synaptic actions of single-Ia medial gastrocnemius (MG) afferents were measured by intracellular recording in MG and lateral gastrocnemius (LG) motoneurons. The spike-triggered averaging technique was used to measure EPSPs generated by homonymous or heteronymous Ia afferents and motoneurons, i.e., neurons supplying the same or different muscles, respectively. In agreement with earlier studies, the pooled sample showed that the number of functional connections and the size of EPSPs were both significantly greater for homonymous than for heteronymous neurons. 3. Afferent conduction velocity, motoneuron conduction velocity, rheobase current, and position of the motoneuron relative to the spinal cord afferent entry were all correlated with EPSP amplitude, but the amplitude difference between homonymous and heteronymous connections remained significant after the statistical removal analysis of covariance (ANCOVA) of the contribution of these variables. Stepwise multiple-regression analysis showed that synaptic identity explained the greatest fraction of the variance in EPSP amplitude (9%), with significant but smaller fractions accounted for by rheobase current or motoneuron conduction velocity. 4. In a separate experiment, the monosynaptic affects from both homonymous and heteronymous single-Ia afferents were examined in each of 88 MG or LG motoneurons. The single-Ia afferents used in this portion of the study were sampled from both MG and LG muscles and selected for similar conduction velocities and spinal cord entry points.(ABSTRACT TRUNCATED AT 250 WORDS)

Monosynaptic EPSPs in primate lumbar motoneurons

1993 ◽  
Vol 70 (4) ◽  
pp. 1585-1592 ◽  
Author(s):  
J. S. Carp
Keyword(s):  
Input Resistance ◽  
Triceps Surae ◽  
Medial Gastrocnemius ◽  
Macaca Nemestrina ◽  
Synaptic Connectivity ◽  
Lateral Gastrocnemius ◽  
Mean Values ◽  
Epsp Amplitude ◽  
The Mean ◽  
Stimulation Of

1. Homonymous and heteronymous monosynaptic composite excitatory postsynaptic potentials (EPSPs) were evaluated by intracellular recordings from 89 motoneurons innervating triceps surae (n = 59) and more distal (n = 30) muscles in 14 pentobarbital-anesthetized monkeys (Macaca nemestrina). 2. Homonymous EPSPs were found in all motoneurons tested. The mean values +/- SD for maximum EPSP amplitude of triceps surae motoneurons were 2.5 +/- 1.3, 1.8 +/- 1.3 and 4.5 +/- 2.0 mV for medial gastrocnemius, lateral gastrocnemius, and soleus motoneurons, respectively. Heteronymous EPSPs were almost always smaller than their corresponding homonymous EPSPs. 3. Triceps surae EPSP amplitude was larger in motoneurons with higher input resistance. However, this relationship was weak, suggesting that factors related to input resistance play a limited role in determining the magnitude of the EPSP. 4. The mean ratio +/- SD of the amplitude of the EPSP elicited by combined stimulation of all triceps surae nerves to the amplitude of the algebraic sum of the three individual EPSPs was 0.95 +/- 0.05. This ratio was greater in motoneurons with lower rheobase. 5. Some patterns of synaptic connectivity in the macaque are consistent with previously reported differences between primates and cat (e.g., heteronymous EPSPs elicited by medial gastrocnemius nerve stimulation in soleus motoneurons are small in macaque and other primates but large in cat). However, no overall pattern emerges from a comparison of the similarities and differences in EPSPs among species in which they have been studied (i.e., macaque, baboon, and cat). That is, there are no two species in which EPSP properties are consistently similar to each other, but different from those of the third species.(ABSTRACT TRUNCATED AT 250 WORDS)

On the capture of interstellar matter by stars

1940 ◽  
Vol 36 (3) ◽  
pp. 314-322 ◽  
Author(s):  
R. d'E. Atkinson
Keyword(s):  
Radial Velocity ◽  
The Other ◽  
Interstellar Matter ◽  
Centre Of Gravity ◽  
Compelling Reason ◽  
Other Hand ◽  
The Mean ◽  
The One ◽  
The Individual ◽  
Capture Radius

The derivation given by Hoyle and Lyttleton for an accretion formula proposed by them is examined. A number of arguments against its validity are put forward, especially that on the one hand their capture radius depends on the theorem that if the velocity of certain masses of gas after collision is less than the velocity of escape at the point, they will not in fact escape, while on the other hand it is clear (and is now admitted) that the gas cannot in fact move with this velocity at all. It is also shown that since, ex hypothesi, the individual molecules will all, on the average, retain their hyperbolic velocities, there is not the compelling reason for their capture that there appeared to be in Hoyle and Lyttleton's argument, where only the mean radial velocity of the centre of gravity of the mass was considered. Further, it seems improbable that the temperature of the interstellar matter can be low enough for the initial assumptions of their theory to hold.

EFFECT OF AMPICILLIN ADMINISTRATION ON THE EXCRETION OF TWELVE OESTROGENS IN PREGNANCY URINE

1975 ◽  
Vol 80 (3) ◽  
pp. 551-557 ◽  
Author(s):  
H. Adlercreutz ◽  
F. Martin ◽  
M. J. Tikkanen ◽  
M. Pulkkinen
Keyword(s):  
Enterohepatic Circulation ◽  
Basic Mechanism ◽  
The Other ◽  
Control Value ◽  
The Third ◽  
Urinary Levels ◽  
Pregnancy Urine ◽  
The Mean ◽  
The Individual ◽  
In Pregnancy

ABSTRACT The excretion of twelve oestrogens in urine, pooled daily from a group of pregnant women, was determined before, during and after ampicillin administration (2 g/day, for 3 days). On the second day of ampicillin administration total oestrogen excretion fell to 67 % of the mean control value, oestriol excretion to 69% and that of the other eleven individual oestrogens to an average of 62 % of the mean control values. In general, on the third day of treatment and on the two post-treatment days this decrease tended to be corrected. The patterns of change in the urinary levels of the individual metabolites provided no clear lead to the basic mechanism of ampicillin impairment of oestrogen excretion. However, as the drug affected all their excretion in more or less the same way as it did that of oestriol, it is possible that ampicillin interferes primarily with their enterohepatic circulation in the mother as has been established with reasonable certainty in the case of oestriol.

Ammonium decreases excitatory synaptic transmission in cat spinal cord in vivo

1989 ◽  
Vol 62 (6) ◽  
pp. 1461-1473 ◽  
Author(s):  
W. Raabe
Keyword(s):  
Spinal Cord ◽  
Synaptic Transmission ◽  
Action Potentials ◽  
Conduction Block ◽  
Excitatory Synaptic Transmission ◽  
Excitatory Postsynaptic Potential ◽  
Presynaptic Terminals ◽  
Ia Afferent ◽  
Afferent Fibers ◽  
Low Threshold

1. Glutamine is thought to be a precursor of the pool of glutamate that is used as synaptic transmitter. NH4+ inhibits glutaminase, the enzyme presumed to cleave glutamine into glutamate in synaptic terminals. Therefore a decrease by NH4+ of excitatory synaptic transmission in hippocampus was suggested to be due to the inability to utilize glutamine as a precursor for glutamate and subsequent transmitter depletion. This study reexamines the effects of NH4+ on excitatory synaptic transmission. 2. The effects of NH4+ on excitatory synaptic transmission from low-threshold afferent fibers, presumably Ia-afferent fibers, to motoneurons was investigated in the spinal cord of anesthetized cats in vivo. 3. Action potentials of low-threshold afferent fibers were recorded at the entry of the dorsal roots into the spinal cord. An extracellular electrode within a motoneuron nucleus recorded the action potential of low-threshold afferent fibers and the extracellular monosynaptic excitatory postsynaptic potential, i.e., the focal synaptic potential (FSP). This extracellular electrode also recorded the antidromic field potential (AFP) in response to ventral root stimulation. Electrodes on the ventral roots recorded the monosynaptic reflex (MSR) and the monosynaptic excitatory postsynaptic potential in motoneurons electrotonically conducted into the ventral roots (VR-EPSP). 4. Intravenous infusion of ammonium acetate (AA) reversibly decreased MSR, VR-EPSP, and FSP, i.e., decreased excitatory synaptic transmission. 5. The decrease of VR-EPSP and FSP was accompanied initially by a decrease of conduction and, eventually, a conduction block in presynaptic terminals of low-threshold afferent fibers. 6. The decreases of VR-EPSP and FSP were also accompanied by the transient appearance of a reflex discharge, triggered by VR-EPSPs of decreased amplitude, and changes of the AFP indicating increased invasion of motoneuron somata by antidromic action potentials. 7. It is suggested that NH4+ depolarizes intraspinal Ia-afferent fibers and motoneurons. This depolarization initially decreases and then blocks conduction of action potentials into the presynaptic terminals of Ia-afferent fibers. The conduction block prevents the release of excitatory transmitter and decreases excitatory synaptic transmission. 8. The suggested depolarizing action of NH4+ may be due to K+-like ionic properties of NH4+ and/or an inhibition of K+-uptake into astrocytes. 9. The conduction block in presynaptic terminals of low-threshold afferent fibers can fully explain the decrease of excitatory synaptic transmission by NH4+. Because of the conduction block in presynaptic terminals, this study does not permit a conclusion as to an inhibition by NH4+ fo the utilization of glutamine as a precursor for glutamate used as synaptic transmitter.

SERUM GAMMA GLOBULIN LEVELS IN NORMAL INFANTS

PEDIATRICS ◽  
1955 ◽  
Vol 16 (5) ◽  
pp. 575-584
Author(s):  
O. Orlandini T. ◽  
A. Sass-Kortsak ◽  
J. H. Ebbs
Keyword(s):  
Cord Blood ◽  
Blood Level ◽  
Serum Protein ◽  
Gamma Globulin ◽  
Decay Curve ◽  
The Other ◽  
Turnover Rates ◽  
The Mean ◽  
The Individual ◽  
Breast Fed

Changes of serum gamma globulin levels with age are described in a group of 140 normal infants from birth to 2 years of age. The mean cord blood level of gamma globulin is significantly higher than the level in the mother's blood. This relation is, however, by no means constant in the individual pairs, as one-third of the 28 pairs showed the opposite relationship. The gamma globulin level drops soon after birth, reaching about one-third of the birth value at 1 month of age. After very little change between 1 and 3 months, the levels start to rise and adult values are closely approximated by 2 years of age. Breast-fed newborns show as rapid a decrease in gamma globulin levels as do artificially fed newborns. Colostrum does not, therefore, seem to contribute significantly to the serum gamma globulin levels in humans. The above described changes in serum gamma globulin levels with age appear to be different in direction, timing, and extent, from changes observed in the other serum protein fractions. The decrease of serum gamma globulin in the first month of life has the characteristics of a simple exponential decay. Comparison of this decay curve with that of passively acquired antibodies, and consideration of available data on gamma globulin turnover rates, warrant the hypothesis that there is practically no gamma globulin formation in the first month of life.

From individual to collective vigilance in wild boar (Sus scrofa)

1992 ◽  
Vol 70 (8) ◽  
pp. 1632-1635 ◽  
Author(s):  
Pierre-Yves Quenette ◽  
Jean-François Gerard
Keyword(s):  
Wild Boar ◽  
Group Size ◽  
Sus Scrofa ◽  
Functional Approach ◽  
The Other ◽  
Motor Variability ◽  
Proximate Causation ◽  
Vigilance Behaviour ◽  
The Mean ◽  
The Individual

Vigilance behaviour of captive wild boars at feeding points was investigated using films. Results show that individual vigilance decreased with increasing group size, especially between solitary individuals and groups of 2. Moreover, the collective vigilance was, whatever the group size, below the individual vigilance in solitary animals. The study of the motor variability of vigilance behaviour allows three types of movement to be distinguished. The mean durations of each type vary largely, but are almost constant whatever the group size. On the other hand, the relative proportions of the vigilance acts change according to group size. Although previous studies of vigilance are in keeping with the functional approach of behaviour, these data are interpreted in terms of proximate causation. A mechanism based on allelomimesis is proposed to explain the results.

Potentiation of transmission at Ia-motoneuron connections induced by repeated short bursts of afferent activity

1985 ◽  
Vol 54 (6) ◽  
pp. 1541-1552 ◽  
Author(s):  
B. M. Davis ◽  
W. F. Collins ◽  
L. M. Mendell
Keyword(s):  
High Frequency ◽  
Afferent Fiber ◽  
Low Frequency ◽  
Mean Amplitude ◽  
Medial Gastrocnemius ◽  
Epsp Amplitude ◽  
Ia Afferent ◽  
Enhanced Transmission ◽  
Test Stimulation ◽  
The Mean

Single medial gastrocnemius Ia-afferent fibers and motoneurons to which they projected were simultaneously impaled in anesthetized cats. Each Ia-afferent fiber was electrically stimulated once every 2 s with short high-frequency bursts (32 shocks at 167 Hz) followed by 1-11 test shocks. The resulting motoneuron excitatory postsynaptic potentials (EPSPs) were recorded and averaged in register. The interval between the end of one burst and the beginning of the next was 2 s; therefore, the amplitude of the first EPSP in the burst was considered to be a measure of efficacy of transmission 2 s after the burst. At most connections (23/29) the mean amplitude of the first EPSP in the burst was equal to or larger than the mean amplitude of control EPSPs produced by low-frequency (18-Hz) stimulation. Enhancement of transmission was maximum 50-100 ms after the burst, and the amplitude of the test EPSP delivered at this time was always greater than that of the control. The period of enhanced transmission appeared to decay more rapidly at connections with small EPSPs. The greatest amount of EPSP amplitude enhancement at 50 or 100 ms after the burst was observed at connections at which EPSP amplitude increased during the burst. The shape (rise time, half width) of potentiated EPSPs was the same as control EPSPs averaged during low-frequency (18-Hz) stimulation. Multiple shocks delivered at low frequency between bursts revealed that enhanced transmission following the high-frequency burst is very sensitive to the effects of low-frequency test stimulation. Furthermore, increasing the number of shocks during the interval between bursts reduced the enhancement of the first EPSP in the burst. We suggest that modulation of synaptic transmission after high-frequency bursts differs across Ia-motoneuron connections. These time-dependent changes associated with short bursts of firing (which are similar in frequency to those observed in Ia-fibers supplying hind-limb muscles during stepping) emphasize the necessity to consider the history of the discharge pattern of the group Ia fiber in assessing efficacy at individual Ia-motoneuron connections.

Sign in / Sign up

Export Citation Format

Share Document