Reflex and locomotor changes following unilateral deafferentation of rat hind limb assessed by chronic electromyography

Abstract

A method of chronic electromyographic recording from the soleus and tibialis anterior muscles was employed for assessing the time course of changes in electromyographic activity following unilateral section of dorsal roots L 1–S 1 in the rat (from several minutes after the operation up to 3–5 months postoperatively). The resting, postural activity in the soleus muscle disappears after deafferentation. However, spontaneous tonic electromyographic activity appears within 1–3 days in this muscle. Two to 6 days after dorsal rhizotomy, spontaneous tonic electromyographic activity is present in the deafferented soleus even when the rat is lifted up. Crossed-inhibitory and crossed-excitatory effects upon this activity may be elicited from the non-operated contralateral limb. Various suprasegmental stimuli (e.g. lifting the animal, pinching the skin at the nape of the neck etc.) either inhibit or enhance the spontaneous activity of the deafferented soleus muscle. A week or more after dorsal root section, a paradoxical reaction appears in the deafferented soleus muscle: stretching this muscle turns off the spontaneous electromyography activity. The same phenomenon was also found in the deafferented gastrocnemius muscle. Electromyographic records of walking or running in a treadmill have shown that the muscle electromyographic pattern is practically unchanged even several months after dorsal root section in spite of clinically impaired ambulation (characterized by a distinct tendency to extension). Since most of the deafferentation changes do not appear until several days after dorsal root section, it is suggested that they are not only due to elimination of peripheral feed-back mechanisms. They are most probably the result of developing hypersensitivity of deafferented extensor spinal motoneurones and second order neurones to activity in descending pathways and to contralateral influences.