An ultrastructural study of the submucous plexus of guinea pig intestine after unilateral vagotomy

Abstract

This study describes the degenerative changes of the axon terminals making synaptic contacts with the neurons in the submucous ganglia of guinea pig small and large intestines following left or right cervical vagotomy. There were no noticeable ultrastructural changes 1 d after the operation. Beginning at the 3rd postoperative day for the small intestines and the 5th day for the large intestines, some of the axon terminals presynaptic to the submucous neurons displayed different stages of degeneration. The most obvious feature of the degenerating terminals was the swelling and vacuolation of mitochondria with disrupted cristae; another change was the clumping of synaptic vesicles. In the animals killed 7 d after vagotomy, besides the above changes, the degenerating axon terminals also showed an accumulation of a variable amount of glycogen-like particles. The changes were most severe in the guinea pigs killed on the 10th postoperative day. The synaptic vesicles in some degenerating terminals were depleted. There were occasional degenerating nerve cell bodies in the submucous ganglia in the period studied. A variable number of lamellated bodies were found in some of the submucous neurons of 10 and 15 d postoperative animals. By 30 d after vagotomy, all the terminals presynaptic to the submucous neurons appeared normal. There was no significant difference in the total number of axon terminals between 10 d and 30 d after operation (P > 0.05). This suggests that either there had been successful reinnervation or new synaptic contacts had been established by sprouting from the unoperated vagus or other intrinsic neurons. The present quantitative studies also showed that the number of degenerating axon terminals in the submucous ganglia of duodenum after left vagotomy was higher than right vagotomy (P < 0.05). This feature was particularly evident in animals killed 10 d after the operation. The larger number of degenerating terminals in the submucous ganglia of duodenum after left vagotomy suggests that the presynaptic axon terminals in the submucous ganglia of different gut regions are not evenly distributed. Finally, the present study showed that the degenerative changes in the small intestine preceded the large intestine.