Spinal cord injury (SCI) launches a complex cascade of events that leads to progressive damage and loss of function. Compromise of plasma membrane integrity due to the mechanical impact is an acute event that may contribute to cellular dysfunction. Therefore, the objective of this study was to better understand the extent of acute plasma membrane damage associated with SCI as a function of injury severity and membrane defect size. Fluorescent cell-impermeant dyes were injected into the cerebrospinal fluid of adult male rats prior to contusion injury, and the anatomical location of cell bodies and axons taking up the dye within 10 min following SCI was quantified. Lucifer yellow uptake was assessed as a function of impact force (experimental groups: sham, 100 kdyn, 150 kdyn, and 200 kdyn force). In a separate group of animals, FITC-conjugated dextran molecules of various sizes (3 kDa and 10 kDa with a 1.6-nm and 2.7-nm radius, respectively) were used to approximate the size of membrane defects following moderate injury (150 kdyn force). Quantification revealed that cellular uptake of lucifer yellow was positively correlated with the force of the mechanical impact, indicating that the severity of injury is related to the degree of acute membrane failure. In addition, after moderate injury, cell bodies and axons (located up to 2 mm and 3 mm from the epicenter, respectively) took up significantly more of the 3-kDa and 10-kDa dextran permeability marker compared to sham controls. Permeable neuronal cell bodies exhibited a morphological appearance characterized by pericellular blebbing, suggesting that plasma membrane compromise is associated with pathophysiological cellular alterations. Collectively, these results enhance our understanding of acute SCI and provide targets for developing novel treatment strategies.

The peripheral taste system remains plastic during adulthood. Sectioning the chorda tympani (CT) nerve, which sends sensory information from the anterior tongue to the CNS, causes degeneration of distal fibers and target taste buds. However, taste function is restored after about 40 days in young adult rodents. We tested whether aging impacts the reappearance of neural responses after unilateral CT nerve injury. Taste bud regeneration was minimal at day 50–65 after denervation, and most aged animals died before functional recovery could be assessed. A subset (n=3/5) of old rats exhibited normal CT responses at day 85 post-sectioning, suggesting the potential for efficient recovery. The aged taste system is fairly resilient to sensory receptor loss and major functional changes in normal aging. However, injury to the taste system reveals a surprising vulnerability in old rodents. The gustatory system provides an excellent model to study mechanisms underlying delayed recovery from peripheral nerve injury. Strategies to accelerate recovery and restore normal function will be of interest as the elderly population continues to grow.