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Effects of H‐reflex up‐conditioning on GABAergic terminals on rat soleus motoneurons
Author(s) -
Pillai Shreejith,
Wang Yu,
Wolpaw Jonathan R.,
Chen Xiang Yang
Publication year - 2008
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.2008.06370.x
Subject(s) - gabaergic , conditioning , neuroscience , soleus muscle , chemistry , reflex , glutamate decarboxylase , biology , anatomy , inhibitory postsynaptic potential , biochemistry , skeletal muscle , enzyme , statistics , mathematics
To explore the role of spinal cord plasticity in motor learning, we evaluated the effects of H‐reflex operant conditioning on GABAergic input to rat spinal motoneurons. Previous work indicated that down‐conditioning of soleus H‐reflex increases GABAergic input to soleus motoneurons. This study explored the effect of H‐reflex up‐conditioning on GABAergic input. Of nine rats exposed to H‐reflex up‐conditioning, up‐conditioning was successful (H‐reflex increase ≥ 20%) in seven and failed (change < 20%) in two. These rats and eight naive control (i.e. unconditioned) rats were injected with cholera toxin subunit B‐conjugated Alexa fluor 488 into the soleus muscle to retrogradely label soleus motoneurons. Sections containing soleus motoneurons were processed for GAD 67 [one of the two principal forms of the GABA‐synthesizing enzyme glutamic acid decarboxylase (GAD)] with an ABC‐peroxidase system. Two blinded independent raters counted and measured GABAergic terminals on these motoneurons. Unlike successful down‐conditioning, which greatly increased the number of identifiable GABAergic terminals on the motoneurons, up‐conditioning did not significantly change GABAergic terminal number. Successful up‐conditioning did produce slight but statistically significant increases in GABAergic terminal diameter and soma coverage. These results are consistent with other data indicating that up‐ and down‐conditioning are not mirror images of each other, but rather have different mechanisms. Although the marked changes in GABAergic terminals with down‐conditioning probably contribute to H‐reflex decrease, the modest changes in GABAergic terminals associated with up‐conditioning may be compensatory or reactive plasticity, rather than the plasticity responsible for H‐reflex increase. As a variety of spinal and supraspinal GABAergic neurons innervate motoneurons, the changes found with up‐conditioning may be in terminals other than those affected in successful down‐conditioning.