Synaptic efficacy of inhibitory synapses in hypoglossal motoneurons after transection of the hypoglossal nerves.

In cat hypoglossal motoneurons after axotomy the synaptic efficacy of inhibitory synapses made by the lingual nerve afferent fibers was studied. The amplitude of the short- and the long-lasting inhibitory postsynaptic potential produced in tongue protruder motoneurons 24 days after axotomy by stimulation of the lingual nerve was significantly reduced in size as compared with the control on the unoperated side. In most protruder motoneurons 40 days after axotomy a large excitatory postsynaptic potential and a spike was produced by stimulation of either the ipsilateral or the contralateral lingual nerve. We have demonstrated that the decline of synaptic efficacy of inhibitory synapses for the short-lasting inhibitory postsynaptic potential was more prominent than that for the long-lasting inhibitory potential in the motoneuron 24 days after axotomy. After the cut axons of protruder motoneurons were re-united to tongue muscles, we have demonstrated that the decline of synaptic efficacy of inhibitory synapses for the short-lasting inhibitory postsynaptic potential was less prominent than that in axotomized protruder motoneurons.