Homosynaptic depression and transmitter turnover in spinal monosynaptic pathway

1977 ◽  
Vol 40 (1) ◽  
pp. 95-105 ◽  
Author(s):  
R. Capek ◽  
B. Esplin
Keyword(s):  
Transmitter Release ◽  
Motor Nerve ◽  
Drug Effects ◽  
Medial Gastrocnemius ◽  
Lateral Gastrocnemius ◽  
Homosynaptic Depression ◽  
Dorsal Root Reflex ◽  
Frequency Of Stimulation ◽  
Fractional Release ◽  
Stimulation Of

1. The transmission in the spinal monosynaptic pathway was studied during repetitive stimulation of a motor nerve by 10 stimuli at 2, 5, or 10 Hz in spinal cats. Initially, the amplitudes of the monosynaptic responses rapidly declined, reaching a plateau after a few stimuli. The level of the plateau was inversely related to the frequency of stimulation. 2. This depression of monosynaptic response was seen only when the same pathway was stimulated; the response elicited from the lateral gastrocnemius was not depressed when preceded by stimulation of the medial gastrocnemius nerve and vice versa. Pretreatment with semicarbazide left the homosynaptic depression unchanged while suppressing the dorsal root reflex. The participation of a depolarization of primary afferents in the described depression is, therefore, unlikely. 3. The decrease of transmitter release by successive volleys, which is the cause of the observed depression, could conceivably be related to the depletion of transmitter stores. 4. A procedure is described, based on this assumption, which allows the calculation of transmitter turnover. The input-output relation in the spinal monosynaptic pathway is used to convert the amplitudes of monosynaptic responses to the amounts of transmitter, both relative to the maximum response. The changes of transmitter release are analyzed under the assumption that each volley releases instantaneously a constant fraction of the transmitter store available for release and that this store is replenished at a constant fraction of the depleted part per second. 5. The values of fractional release per volley were about 0.4, irrespective of frequency of stimulation. 6. The values of fractional replenishment per second ranged from about 1 to 5 on the average, depending directly on the frequency of stimulation. 7. It is suggested that the described procedure might be useful in analyzing drug effects on synaptic transmission.

Recurrent inhibition to and from motoneurons innervating the flexor digitorum and flexor hallucis longus muscles of the cat

1990 ◽  
Vol 63 (3) ◽  
pp. 395-403 ◽  
Author(s):  
T. M. Hamm
Keyword(s):  
Tibialis Anterior ◽  
Recurrent Inhibition ◽  
Medial Gastrocnemius ◽  
Flexor Hallucis Longus ◽  
Flexor Digitorum Longus ◽  
Lateral Gastrocnemius ◽  
Hindlimb Muscles ◽  
Inhibitory Postsynaptic Potentials ◽  
Flexor Digitorum ◽  
Stimulation Of

1. Recurrent inhibitory postsynaptic potentials (IPSPs) to and from motoneurons innervating the flexor digitorum longus (FDL) and flexor hallucis longus (FHL) muscles of the cat were investigated to determine whether recurrent inhibitory projections involving these motoneurons are similar--as would be consistent with the Ia and anatomic synergism of FDL and FHL--or are dissimilar, as are the activities of these muscles during locomotion (O'Donovan et al. 1982). 2. Composite recurrent IPSPs were recorded in several species of motoneurons innervating hindlimb muscles in response to stimulation of a number of muscle nerves in cats allowed to become unanesthetized after ischemic decapitation. 3. No recurrent IPSPs from stimulation of the FDL nerve were observed in motoneurons innervating FDL, FHL, lateral gastrocnemius-soleus (LG-S), medial gastrocnemius (MG), plantaris (Pl), tibialis anterior (TA), or extensor digitorum longus (EDL). 4. The recurrent IPSPs produced by stimulation of FHL were larger and found more frequently in LG-S than in FDL motoneurons. Recurrent inhibition from FHL was also greater in Pl than in FDL motoneurons. 5. The recurrent IPSPs produced by stimulation of LG-S, PL, and MG were larger in FHL than in FDL motoneurons, and those from LG-S and MG were found more frequently in FHL than in FDL motoneurons. 6. Stimulation of the TA nerve produces recurrent IPSPs in FDL but not in FHL motoneurons. A few FDL and FHL cells (6 of 23 and 9 of 34, respectively) received small (less than 0.5 mV) recurrent IPSPs from stimulation of the EDL nerve.(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)

Modulation of synaptic transmission at Ia-afferent connections on motoneurons during high-frequency afferent stimulation: dependence on motor task

1991 ◽  
Vol 65 (6) ◽  
pp. 1313-1320 ◽  
Author(s):  
H. R. Koerber ◽  
L. M. Mendell
Keyword(s):  
High Frequency ◽  
Frequency Control ◽  
Motor Task ◽  
Low Frequency ◽  
Medial Gastrocnemius ◽  
High Frequency Stimulation ◽  
Lateral Gastrocnemius ◽  
Low Frequency Stimulation ◽  
Frequency Stimulation ◽  
Stimulation Of

1. Monosynaptic excitatory postsynaptic potentials (EPSPs) were evoked in medial gastrocnemius motoneurons by maximal group Ia stimulation of the heteronymous lateral gastrocnemius-soleus nerve in anesthetized cats. Three different patterns of high-frequency stimulation were delivered to the nerve, and the EPSPs were averaged in register (1, 2, . . ., n) for each. 2. One pattern ("Burst") consisted of 32 shocks delivered every 2 s at an interstimulus interval of 6 ms (167 Hz). The second pattern ("Stepping") was a frequency-modulated burst of 52 shocks derived from a recording of a spindle during stepping and was delivered every 2 s. The third pattern ("Paw Shake") was from an extensor spindle afferent recorded during rapid paw shake and was delivered in groups of six bursts with an interburst interval of 75 ms and a 3-s pause between groups of six bursts. The EPSPs in each burst were averaged in register (1, 2, . . ., n) so that the relative amplitude of each EPSP in the burst could be ascertained. The EPSP produced by low-frequency stimulation of the nerve (18 Hz) was also recorded for each motoneuron. 3. The initial EPSP in most bursts was larger than the EPSP measured as a result of low-frequency stimulation. This potentiation, defined as the ratio of the amplitude of the initial EPSP of the response to that of the low-frequency control, was found to vary systematically as a function of amplitude of the control EPSP as well as the stimulus paradigm used.(ABSTRACT TRUNCATED AT 250 WORDS)

Reinnervated muscles fail to produce stretch reflexes

1994 ◽  
Vol 71 (2) ◽  
pp. 817-820 ◽  
Author(s):  
T. C. Cope ◽  
S. J. Bonasera ◽  
T. R. Nichols
Keyword(s):  
Surgical Repair ◽  
Motor Units ◽  
Synaptic Integration ◽  
Medial Gastrocnemius ◽  
Nerve Section ◽  
Lateral Gastrocnemius ◽  
The Common ◽  
Decerebrate Cats ◽  
Recovery Of Motor Function ◽  
Stimulation Of

1. We studied the stretch-evoked reflex organization of hind limb muscles in two decerebrate cats 36 mo after unilateral section and immediate surgical repair of the common nerve supplying the lateral gastrocnemius (LG) and soleus (S) muscles. 2. The production of considerable reflex force by reinnervated muscles in response to electrical stimulation of uninjured nerves indicated substantial functional recovery of motor units. However, reduction in the responsiveness of reinnervated muscles to stretch of the untreated medial gastrocnemius (MG) muscle indicated some deficit in recovery of normal synaptic integration. 3. Stretch failed to elicit autogenic excitation of the reinnervated S and LG. This failure was observed whether the reinnervated muscles were quiescent or contracting in other reflexes. 4. The heterogenic reflex organization of reinnervated muscles was abnormal. Stretch of the reinnervated S failed to evoke heterogenic reflexes both in the untreated MG and in the reinnervated LG. Stretch of the reinnervated LG failed to produce excitation of MG. 5. These findings demonstrate deficiencies in proprioceptive feedback from reinnervated muscles and lead us to expect incomplete recovery of motor function after nerve section.

Plasticity of the extensor group I pathway controlling the stance to swing transition in the cat

1995 ◽  
Vol 74 (6) ◽  
pp. 2782-2787 ◽  
Author(s):  
P. J. Whelan ◽  
G. W. Hiebert ◽  
K. G. Pearson
Keyword(s):  
Medial Gastrocnemius ◽  
Lateral Gastrocnemius ◽  
Group I ◽  
Excitatory Pathways ◽  
Extensor Muscles ◽  
Stimulus Train ◽  
Control Response ◽  
Control Limb ◽  
Adult Cats ◽  
Stimulation Of

1. This study examines whether the efficacy of polysynaptic group I excitatory pathways to extensor motoneurons are modified after axotomy of a synergistic nerve. Previously, it has been shown that stimulation of extensor nerves at group I strength can extend the stance phase and delay swing. Stimulation of the lateral gastrocnemius and soleus (LG/S) nerve prolongs stance for the duration of the stimulus train, whereas stimulation of the medial gastrocnemius (MG) nerve moderately increases stance. Our hypothesis was that after axotomy of the LG/S nerve the efficacy of the MG group I input would increase. 2. This idea was tested in 10 adult cats that had their left LG/S nerves axotomized for 3-28 days. On the experimental day the cats were decerebrated and the left (experimental) and right (control) LG/S and MG nerves were stimulated during late stance as the animals were walking on a motorized treadmill. A significant increase in the efficacy of the left MG nerve occurred 5 days after axotomy of the LG/S nerve when compared with the control response. By contrast, the previously cut LG/S nerve showed a reduction in efficacy after 3 days compared with the control limb. 3. Functionally, this plasticity may be an important mechanism by which the strength of the group I pathway is calibrated to different loads on the extensor muscles.

A differential synaptic input to the motor nuclei of triceps surae from the caudal and lateral cutaneous sural nerves

1989 ◽  
Vol 61 (2) ◽  
pp. 291-301 ◽  
Author(s):  
L. A. LaBella ◽  
J. P. Kehler ◽  
D. A. McCrea
Keyword(s):  
Electrical Stimulation ◽  
Stimulus Intensity ◽  
Triceps Surae ◽  
Medial Gastrocnemius ◽  
Lateral Gastrocnemius ◽  
Motor Nuclei ◽  
Adult Cats ◽  
Predominant Effect ◽  
Sural Nerves ◽  
Stimulation Of

1. Postsynaptic potentials (PSPs) were recorded in 115 triceps surae motoneurons of 10 chloralose-anesthetized adult cats (spinal cord intact), upon electrical stimulation of the caudal and lateral cutaneous sural nerve branches (CCS and LCS, respectively). 2. With twice threshold (2T) stimulation of CCS, excitatory PSPs (EPSPs) were the predominant effect in 95% of all medial gastrocnemius (MG) motoneurons tested (min. central latency 1.5 ms; mean 2.4 ms). In only a few MG cells was the EPSP followed by an inhibitory postsynaptic potential (IPSP) and in only one cell was an IPSP the sole effect. Increasing the stimulus intensity to 5T tended to enhance both the later EPSP and IPSP components, with less change in the amplitude or latency of the earliest EPSPs. 3. In lateral gastrocnemius (LG) and soleus (SOL) motoneurons, 2T CCS stimulation led to either inhibition or no potential change in the majority of cells tested: EPSPs were the predominant effect in only 15 and 30% of LG and SOL cells, respectively (min. central latency 2.5 ms; mean 3.0 ms) and rarely occurred without subsequent inhibition. Again, increasing the stimulus intensity to 5T had more of an effect on later rather than earlier PSP components. 4. A predominance of depolarization in MG motoneurons but not in SOL motoneurons is in agreement with previous findings that CCS excitation is more powerful in "fast type" triceps surae motoneurons. However, the strong predominance of hyperpolarizing effects of CCS stimulation in the present LG population is evidence that such an organization does not transcend triceps surae motor nuclei as a whole. 5. Postsynaptic effects of LCS stimulation at 2T were frequently weak or absent but increasing the stimulus intensity to 5T produced predominant inhibition in 71% of all triceps surae motoneurons studied (n = 107). Of the few cells which did receive excitation from this nerve, most were MG, a few were SOL, and none were LG. These EPSPs occurred more frequently at 5T than at lower stimulation strengths. 6. The results indicate that excitation produced by electrical stimulation of the ipsilateral CCS nerve occurs preferentially in the MG portion of triceps surae and with the shortest central latencies. Effects of LCS stimulation are largely inhibitory throughout the motor nuclei comprising triceps surae but even here, the presence of excitation occurs more frequently in MG. A comparison of these results with those in other reports is discussed.

Reduction in postsynaptic inhibition during maintained electrical stimulation of different nerves in the cat hindlimb

1994 ◽  
Vol 71 (6) ◽  
pp. 2281-2293 ◽  
Author(s):  
C. J. Heckman ◽  
J. F. Miller ◽  
M. Munson ◽  
K. D. Paul ◽  
W. Z. Rymer
Keyword(s):  
Electrical Stimulation ◽  
Steady State ◽  
Time Course ◽  
Initial Period ◽  
Input Resistance ◽  
Medial Gastrocnemius ◽  
Rapid Phase ◽  
Afferent Pathways ◽  
Lateral Gastrocnemius ◽  
Stimulation Of

1. Steady-state postsynaptic potentials (PSPs) were generated by prolonged (approximately 1 s) high-frequency (100-200 Hz) electrical stimulation of nerves in the cat hindlimb. The characteristics of these steady-state PSPs were compared for two polysynaptic afferent pathways (ipsilateral cutaneous sural vs. contralateral peroneal nerves), two animal preparations (decerebrate vs. chloralose), and two motoneuron pools (medial gastrocnemius vs. lateral gastrocnemius-soleus). 2. PSPs from both nerves usually (36 of 51 cases) contained a mixture of depolarizing and hyperpolarizing components. In all 36 cases where the PSP contained a hyperpolarizing component, a consistent qualitative pattern emerged during prolonged stimulation: the hyperpolarization reached a peak approximately 20 ms after stimulation onset and then decayed with a biphasic time course that consisted of an initial rapid phase (20–40 ms) and a later slower phase (200–400 ms) before the steady-state value was reached. This pattern occurred regardless of the differences in polysynaptic afferent pathways, animal preparations, and motoneuron pools. 3. The consistency of this overall pattern was remarkable, given the existence of several quantitative differences among the PSPs. These differences include the following: hyperpolarizing components were least common in the sural and peroneal PSPs in the decerebrate preparation. And only these sural and peroneal PSPs tended to have prolonged afterpotentials after stimulus cessation. The steady-state sural PSPs in the decerebrate preparation tended to generate the largest PSPs and, moreover, these PSPs did not follow the overall trend of having a statistically significant relation between the amplitude of the initial hyperpolarization and the amount of its decay. Finally, transient sural PSPs in lateral gastrocnemius-soleus motoneurons in the decerebrate preparation tended to have the largest hyperpolarizations. 4. To determine whether the decay of the hyperpolarization and the subsequent dominance of depolarization was due to a decreased inhibition or an increased excitation, injected current pulses were utilized to measure the changes in the cell's input resistance during the course of the synaptic input. A strong decrease in input resistance accompanied the initial period of maximal hyperpolarization (50% with respect to the resting input resistance). Input resistance then returned toward resting values as hyperpolarization faded and depolarization became dominant. However, there remained a persistent decrease in input resistance during the final phase of the PSP that amounted to < 10% of the initial decrease. These findings indicated that much of the reduction in hyperpolarization reflected a progressive decrease in synaptic efficacy for the inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of preventing reinnervation on axotomized spinal motoneurons in the cat. II. Changes in group Ia synaptic function

1989 ◽  
Vol 62 (2) ◽  
pp. 325-333 ◽  
Author(s):  
S. Vanden Noven ◽  
M. J. Pinter
Keyword(s):  
Electrical Stimulation ◽  
Rise Time ◽  
Mean Amplitude ◽  
Synaptic Function ◽  
Medial Gastrocnemius ◽  
Lateral Gastrocnemius ◽  
Epsp Amplitude ◽  
Time To Peak ◽  
Postoperative Time ◽  
Stimulation Of

1. Composite excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation of heteronymous group Ia afferents have been studied at various postoperative times in axotomized motoneurons that were denied the opportunity to reinnervate muscle. 2. The medial gastrocnemius (MG) nerve was transected and sutured onto the surface of the normally innervated lateral gastrocnemius (LG) muscle. The denervated MG muscle was excised thereby eliminating access of regenerating MG motor axons to vacant end-plates. 3. The mean amplitude of monosynaptic Ia EPSPs evoked by electrical stimulation of the LG-soleus (LGS) nerve and recorded in axotomized MG motoneurons showed an initial decline at 20 days postoperative (DPO) that was not significant. At 44 DPO, mean amplitude had declined significantly to 43% of the control mean amplitude. At 90 DPO, mean EPSP amplitude was not significantly different from control. At the latest postoperative time (150-180 DPO), mean amplitude was significantly less than the control amplitude. 4. Mean EPSP rise time (time-to-peak) was significantly increased (27%) at the earliest postoperative times (20-44 DPO). At later postoperative times (90-180), mean EPSP rise time was not significantly different from mean control rise time. 5. "Partial responses" superimposed on EPSPs were not observed at any postoperative time. 6. Mean posttetanic potentiation (PTP) of the LGS EPSP was significantly depressed at 20 DPO. At later postoperative times, PTP did not differ significantly from mean control PTP. 7. The possibility is considered that postaxotomy alterations in the electrical properties of motoneurons may explain these complex variations of mean EPSP amplitude and rise time.

Reflex increase in ventilation by muscle receptors with nonmedullated fibers (C fibers)

1972 ◽  
Vol 32 (2) ◽  
pp. 189-193 ◽  
Author(s):  
Madhu Kalia ◽  
J. M. Senapati ◽  
B. Parida ◽  
A. Panda
Keyword(s):  
Gastrocnemius Muscle ◽  
Medial Gastrocnemius ◽  
Lateral Gastrocnemius ◽  
Group Iii ◽  
C Fibers ◽  
Group I ◽  
Natural Stimulation ◽  
Antidromic Stimulation ◽  
Sensory Endings ◽  
Stimulation Of

The reflex increase in ventilation (Ve) produced by natural stimulation of certain sensory receptors in gastrocnemius muscle was studied in dogs anesthetized with Na pentobarbital. Reflex increase in Ve occurred when the endings of group III fibers and nonmedullated fibers were stimulated (by stretching, pressing, or squeezing the muscle locally), whereas the endings of group I and group II fibers were blocked by repetitive antidromic stimulation. Stimulation of endings of nonmedullated fibers alone also increased Ve after all the medullated fibers were blocked either by cooling the medial gastrocnemius nerve to 5 C or by stimulating lateral gastrocnemius nerve repetitively. It was concluded that there were sensory endings of nonmedullated fibers in muscles which are stimulated by stretching, pressing, or squeezing the muscle locally; these endings produce reflex hyperventilation. antidromic stimulation; gastrocnemius muscle

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