Nuclear clefting in dorsal root ganglion neurons: a response to whole body vibration

Normal adult rabbits were studied in a whole body vibration model which simulates the type of environmental exposure associated with vibration-induced low back pain. This model has previously been shown to induce changes in pain-related neuropeptides in the dorsal root ganglion. Following two weeks of daily exposure to whole body vibration, dorsal root ganglia were excised from control and vibrated rabbits and prepared for ultrastructural evaluation. Of over 1,200 cells sampled, 190 appropriately sectioned cells were analyzed: 32 from immobilized controls, 44 from normal controls, and 114 from vibrated animals. Analysis of nuclear contours revealed more prevalent and more extensive clefting of the nuclear membrane in vibrated cells. The membrane lining these clefts was traversed by numerous pores; density of these pores was 46% greater than in adjacent nonclefted segments (p less than .001). Number of clefts per nucleus was increased by 39% in vibrated animals. Cleft area represented 1.19% of nuclear area in vibrated cells compared to 0.74% in controls (p less than .001). Numerous mitochondria and free ribosomes and abundant rough endoplasmic reticulum were located within the cleft spaces of vibrated cells. Pores in the cleft membrane appeared normal, supporting the conclusion that the clefts are structural alterations rather than fixation or sectioning artifacts. Changes in dorsal root ganglion neuropeptides seen in previous studies of vibrated animals may result from increased or redirected cellular synthesis. Ultrastructural changes seen in these vibrated dorsal root ganglion neurons are consistent with such an alteration in metabolism and could reflect increased synthesis of pain-related neuropeptides.