scholarly journals Synaptic potentials evoked in cat dorsal spinocerebellar tract neurones by impulses in single group I muscle afferents.

1989 ◽  
Vol 415 (1) ◽  
pp. 423-431 ◽  
Author(s):  
B Walmsley
Keyword(s):  
Muscle Afferents ◽  
Single Group ◽  
Synaptic Potentials ◽  
Group I ◽  
Spinocerebellar Tract

Nonuniform release probabilities underlie quantal synaptic transmission at a mammalian excitatory central synapse

1988 ◽  
Vol 60 (3) ◽  
pp. 889-908 ◽  
Author(s):  
B. Walmsley ◽  
F. R. Edwards ◽  
D. J. Tracey
Keyword(s):  
Muscle Afferents ◽  
Single Fiber ◽  
Binomial Model ◽  
Release Probability ◽  
Group I ◽  
Unique Nature ◽  
Compound Binomial ◽  
Compound Binomial Model ◽  
Spinocerebellar Tract ◽  
Active Release

1. Excitatory postsynaptic potentials (EPSPs) evoked by impulses in single group I muscle afferents were recorded in dorsal spinocerebellar tract (DSCT) neurons in the spinal cords of anesthetized cats. Fluctuations in the amplitude of these single-fiber EPSPs were determined from measurements of EPSP peak amplitude and contaminating noise (800-4600 trials). 2. In a previous study at this connection, we found that these single-fiber EPSPs fluctuated in amplitude between approximately equal, or quantal, increments. However, these quantal fluctuations could not be described by simple binomial statistics (39). In the present study we have applied further analysis procedures to the same single-fiber EPSPs to formulate a more appropriate probabilistic model of transmission at this connection. 3. In the first stage we have demonstrated that each single-fiber EPSP is composed of the sum of a number (3-30) of uniform quantal events, and that there is extremely little variability in the amplitude of the single quantal event. 4. In a further procedure, we have demonstrated that these quantal fluctuations can be described by a compound binomial model in which each underlying quantal event is associated with a particular, but independent, release probability. The results of this analysis indicate that the probability of transmitter release varies considerably between release sites at this connection. (The use of such a compound binomial model reemphasized previous warnings concerning the interpretation of the results of all statistical models of quantal release. Problems regarding the non-unique nature of N, the total population of quantal events, and other such difficulties are discussed.) 5. A model of transmission at this connection is proposed, in which there are a number of "active" release sites, exhibiting generally high release probabilities, and a number of "reserve" release sites, with zero, or close to zero, release probability. The physiological consequences of such a scheme are discussed.

Specific and nonspecific mechanisms involved in generation of PAD of group Ia afferents in cat spinal cord

1984 ◽  
Vol 52 (5) ◽  
pp. 921-940 ◽  
Author(s):  
I. Jimenez ◽  
P. Rudomin ◽  
M. Solodkin ◽  
L. Vyklicky
Keyword(s):  
Spinal Cord ◽  
Muscle Afferents ◽  
Potassium Ions ◽  
Single Group ◽  
Individual Group ◽  
Afferent Nerves ◽  
Group I ◽  
Stimulation Of ◽  
Anesthetized Cat ◽  
Site Stimulation

In the spinal cord of the anesthetized cat, we measured the changes in extracellular concentration of potassium ions [K+]e and the negative DC shifts produced by stimulation of muscle, cutaneous and mixed afferent nerves, together with alterations in the threshold of single group Ia fibers that were tested at the same site as the potassium measurements. This approach provided information on the extent to which the excitability changes of single Ia-fibers can be correlated with the changes in [K+]e occurring at the same site. Stimulation of the tibial (TIB) nerve and of the cutaneous sural (SU), and superficial peroneous (SP) nerve (100-Hz trains lasting 30-60 s) with stimulus strengths of 10-15 times threshold increased the concentration of [K+]e in the dorsal horn by 2-5 mmol/l above the resting value of 3 mmol/l. This was in clear contrast with the very small [K+]e increases produced at the same site during stimulation of muscle nerves, such as the posterior biceps and semitendinosus (PBSt), gastrocnemius soleus (GS), and deep peroneus (DP), which were generally smaller than 0.25 mmol/l. Stimulation of the PBSt and GS muscle nerves did produce small, but clear, increases of [K+]e (up to 0.3 mmol/l) in the region of the intermediate nucleus, where these fibers synapse with second order cells. These changes were nevertheless smaller than those produced at the same site by stimulation of the TIB, SU, and SP nerves. The peak amplitudes of the [K+]e transients produced by long-lasting 100-Hz trains applied to cutaneous and/or to muscle nerves showed a linear relationship with the amplitudes of the slow negative DC shifts, which were simultaneously recorded from the NaCl barrel of the potassium electrode assembly. Stimulus trains (100 Hz) applied to group I muscle afferents (PBSt and DP) very effectively reduced the threshold for intraspinal activation of individual group I GS fibers but produced negligible negative DC shifts at the same site. On the other hand, 100-Hz stimulus trains applied to the SU and SP nerves produced large negative DC shifts, even with low-stimulus strengths (2 X T, where T is threshold), but had much smaller effects on the threshold of group Ia GS fibers. Increasing the intensity of the stimuli applied to cutaneous and mixed nerves above 2 X T strength further reduced the threshold of the Ia-fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses of cortical neurons (areas 3a and 4) to ramp stretch of hindlimb muscles in the baboon

1976 ◽  
Vol 39 (3) ◽  
pp. 484-500 ◽  
Author(s):  
J. Hore ◽  
J. B. Preston ◽  
P. D. Cheney
Keyword(s):  
Cortical Neurons ◽  
Muscle Length ◽  
Muscle Afferents ◽  
Muscle Stretch ◽  
Hindlimb Muscles ◽  
Group I ◽  
Hindlimb Muscle ◽  
Area 3A ◽  
Group Ii Muscle Afferents ◽  
Group Ii

1. A study was made of the response of single cortical units in areas 3a and 4 to electrical stimulation of hindlimb muscle nerves and to ramp stretch of hindlimb muscles in baboons anesthetized with chloralose.2. Stimulation of hindlimb muscle nerves revealed a group I projection primarily to area 3a but with some input into adjacent area. 4. A major group II projection was found in area 4 adjacent to area 3a. A small number of area 3a neurons receive convergence from both group I and group II muscle afferents.3a. On the basis of their response pattern to ramp stretch, units were classified into one of six categories and their cytoarchitectonic location was determined. Units in area 3a had hynamic sensitivities equivalent to that of the primary spindle afferents. Although the discharge of some area 3a neurons also reflected differences in muscle length, most area 3a neurons had low position sensitivities. One unit type in area 3a did not respond to maintained muscle stretch and signaled only velocity of stretch.4. Units in area 4 had position sensitivities equivalent to that of primary and secondary spindle afferents. Although the discharge of some area 4 units reflected different velocities of muscle stretch, these units had dynamic sensitivities similar to those of secondary spindle afferents rather than those of primary afferents. One type of unit in area 4 had no dynamic component to muscle stretch and signaled only muscle length.5. The results demonstrate that there is a transfer of dynamic and position sensitivity from spindle afferents to cortical neurons. Furthermore, data processing has occurred because some units respond only to the steady-state length of muscle, while other units encode only the dynamic phase of stretch. This behavior is different from the responses to ramp stretch of either group I or group II muscle afferents in the baboon.6. The results demonstrate that single units in cerebral cortex can encode the information transmitted to the central nervous system by muscle spindle afferents. The purpose for which this information is used remains undetermined.

Declining inhibition elicited in cat lumbar motoneurons by repetitive stimulation of group II muscle afferents

1993 ◽  
Vol 70 (5) ◽  
pp. 1805-1810 ◽  
Author(s):  
J. Lafleur ◽  
D. Zytnicki ◽  
G. Horcholle-Bossavit ◽  
L. Jami
Keyword(s):  
Muscle Afferents ◽  
Repetitive Stimulation ◽  
Excitatory Postsynaptic Potential ◽  
Constant Input ◽  
Rapid Reduction ◽  
Group I ◽  
Constant Strength ◽  
Group I Afferents ◽  
Group Ii ◽  
Stimulation Of

1. The aim of the present experiments was to verify whether group II inputs from gastrocnemius medialis (GM) muscle could elicit declining inhibitions similar to those observed during GM contractions in a variety of lumbar motoneurons of the cat spinal cord. Motoneurons were recorded intracellularly in chloralose- or pentobarbitone-anesthetized preparations during electrical stimulation of GM nerve with repetitive trains. 2. With strengths in the group I range, repetitive stimulation evoked the usual Ia excitation in homonymous motoneurons and excitatory postsynaptic potential (EPSP) amplitudes remained constant throughout the stimulation sequence. In synergic plantaris motoneurons lacking an excitatory connection with Ia afferents from GM, the same stimulation, kept at a constant strength throughout the stimulation sequence, elicited rapidly decreasing inhibitory potentials reminiscent of those evoked by GM contractions. 3. In motoneurons of pretibial flexors, quadriceps, and posterior biceps-semitendinosus, the stimulation strength required to observe declining inhibitions resembling those produced by GM contractions was 4-8 times group I threshold, engaging group II in addition to group I fibers. 4. These results show that input from GM group II plus group I afferents can elicit inhibitory effects in a variety of motoneurons. Such observations support the hypothesis that messages from spindle secondary endings and/or nonspecific muscle receptors activated during contraction might contribute to the widespread inhibition caused by GM contractions. 5. Inasmuch as constant input in group II and group I afferents evoked declining inhibitory potentials, the origin of the decline must be central, which suggests that the rapid reduction of contraction-induced inhibitions also depended on a central mechanism.

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