CHANGES OF SYNAPTIC TERMINAL NUMBER OF PRIMARY AFFERENT FIBERS IN SPINAL CORD LAMINA II OF MORPHINE DEPENDENT RAT-AN EM QUANTITATIVE STUDY

Objective\ Whether the primary afferent fibers given rise by sensory neuron in dorsal root ganglion of rat could make collateral sprouting and form new synapses in spinal lamina Ⅱ under the morphine dependence was explored with EM quantitative method. Methods\ The number of synaptic terminals in the unit area of neuropil of L\-4 spinal lamina Ⅱ was compared between morphine dependent and control rats,because there was no significant change in the crosscut area of L\-4 spinal lamina Ⅱ of two groups of animal,which was estimated by aid of LM stereological method. Results\ The number of synaptic terminals from primary afferent fibers in spinal lamina Ⅱ in morphine dependent group was significantly more than that in control group,among which the number of synaptic terminals from unmyelinated afferent fibers increased 61%.The number of synaptic terminals from myelinated afferent fibers was 70% more than that in control group.In particular,the number of synaptic terminals containing dense\|core vescles from the primary afferent fibers went up 98% over that of control group. Conclusion\ Morphine may promote the collateral sprouting and synaptogenesis of primary afferent fibers in spinal lamina Ⅱ.\;