Effects of neonatal capsaicin administration on primary sensory neurons in rat. Relationships between neuronal sizes and their axonal diameters

초록

Recently, it has been known that neonatal capsaicin treatment severely reduces the number of type B spinal ganglia neurons selectively, and also decreases many of the unmyelinated and some of the fine myelinated axons in dorsal roots and peripheral nerves. Using these effects of capsaicin, present study was attempted to clarify the relationships between the sizes of S₁ spinal ganglion cells and the diameters of their axons in dorsal roots and peripheral nerves of the rats. The normal and capsaicin-pretreated adult rats were operated microscopically to remove the somatic and visceral motor axons from their peripheral nerves, and one week later, fixed by transcardiac perfusion techique. The ganglia were embedded in paraffin for light microscopy, and the dorsal roots and peripheral nerves in plastic mixture for electron microscopy. All the ganglion cells and axons were counted, and the diameters of ganglion cells and myelinated axons were measured by computed planimeter. The results obtained were summarized as followings. 1. In dorsal root ganglia, the diameters of neuronal bodies were in the range of 5~45㎛, and averaged 18.22㎛ in a normal group and 20.54㎛ in an experimental group. Neonatal capsaicin-treatment decreased 44.5% of total number of neurons which were small ones less than 17.5% in diameter. 2. In the dorsal roots, the unmyelinated axons decreased 52.496 and myelinated axons, 11.2% in an experimental group. The diameters of myelinated axons were in the range of 0.3~11.0㎛, and averaged 2.72㎛ in a normal group and 3.14㎛ in an experimental group. The perished axons by neonatal capsaicin-treatment were appeared to be less than 2㎛ in diameter. 3. In the peripheral nerves, the unmyelinated axons decreased 55.1% and the myelinated axons, 13.7% in an experimental group. The diameters of myelinated axons were in the range of 0.5~11.5㎛, and averaged 3.07㎛ in a normal group and 3.26㎛ in an experimental group. The perished axons were less than 3㎛ in diameter. 4. Therefore, it is borne out that the small ganglia cells less than 17.5㎛ in diameter give rise to the unmyelinated axons to the dorsal roots and peripheral nerves, and myelinated axons less than 2pm in diameter to the dorsal root and those less than 3㎛ in diameter to the peripheral nerve.

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