Relationship of afferentation with soma size of nucleus gracilis neurons after bilateral dorsal column lesion in the rat

Soma diameter and number of boutons on the soma were positively correlated at all NG levels and survival times, and imply a mechanism which regulates the interaction of quantity of presynaptic afferent fibers upon, and size of, the postsynaptic cell body.

Abstract

The effect of bilateral dorsal column lesion on the afferentation and diameter of neurons in the nucleus gracilis (NG) of the rat was studied during 120 postoperative days. After bilateral, low thoracic lesion of the dorsal column, the animals were killed 1, 2, 3, 7, 14, 30, 45, 60, 90, or 120 days later, and cells in the rostral, middle, or caudal NG were selected and measured for soma diameter and number of boutons on these same somas. The results showed significant reduction in soma diameter during the first 2 weeks postoperatively compared with normals, and also significant changes (increases or decreases in diameter) in survival times during 120 postoperative days. Soma diameter and number of boutons on the soma were positively correlated at all NG levels and survival times. Extrapolations of those values to total surface area and total surface area of soma covered by boutons, show that (i) neither normal nor deafferented soma are totally innervated, and (ii) normal innervation values are maintained in parallel with fluctuations in the total surface area of the soma. These results emphasize the dynamic changes occurring upon and in the postsynaptic cell after deafferentation, and imply a mechanism which regulates the interaction of quantity of presynaptic afferent fibers upon, and size of, the postsynaptic cell body.