Presynaptic inhibition compared with homosynaptic depression as an explanation for soleus H-reflex depression in humans

Abstract

The H-reflex is depressed for seconds if elicited following a single H-reflex or train of H-reflexes. Presynaptic inhibition from flexor afferents (tibialis anterior) onto soleus Ia afferents elicited by either single or trains of stimuli had no effect on the soleus H-reflex on a time scale of seconds. Postsynaptic inhibition was also excluded by magnetic stimulation tests that showed that the excitability of the motoneuron pool was not changed at latencies within a range of seconds. Homosynaptic depression localized at the presynaptic terminal seems to be the mechanism behind the H-reflex depression in humans.

Simulation system of spinal cord motor nuclei and associated nerves and muscles, in a Web-based architecture

“…15 shows the number of recruited MNs in response to each stimulation pulse. The depression of H-reflex amplitude obtained in the simulations is within the range found experimentally Kohn et al 1997;Meunier et al 2007). It is important to note that the data supplied in the lower panel are impossible to obtain in humans and cats with present technologies.…”

“…Experiments conducted in our laboratory, as well as those published in the literature Kohn et al 1997;Pierrot-Deseilligny and Burke 2005), supplied data used to adjust the threshold for axon firing and the size of motor-unit potentials (MUAP). These parameters were changed in an ad-hoc way (within physiological ranges) until the simulated motor nuclei could generate H-reflexes compatible with those obtained in humans.…”

Web-based neuromuscular simulator applied to the teaching of principles of neuroscience

“…As the EPSP amplitude increases after each presynaptic spike, the AP threshold is reached earlier. The student/instructor can also simulate the opposite effect, i.e., synaptic depression (not shown here) that occurs during long-lasting presynaptic activity (Kandel et al, 2013;Kohn et al, 1997).…”

Absence of effects of contralateral group I muscle afferents on presynaptic inhibition of Ia terminals in humans and cats

“…2B), totaling 20 responses. A reduced H-reflex amplitude (e.g., due to homosynaptic depression; Cisi and Kohn 2007;Kohn et al 1997) suggests that the Ia afferents have been effectively recruited by the brief vibratory stimulus. However, a small contribution from group Ib afferents cannot be excluded (Burke et al 1983).…”

“…An interval of 10 s was used between consecutive H-reflex responses to minimize the effects of homosynaptic depression (Kohn et al 1997). Each trial was repeated 10 times, resulting in 260 H-reflex responses (10 PSI_control and 10 PSI_conditioned by vibration for each of the 13 ISIs).…”