Neuronal viability or death after dendrite amputation within 200 μm of the perikaryon: Correlation with electrophysiologic and morphological changes and the presence or absence of extracellular calcium

The responses of cultured mammalian spinal neurons to physical trauma were observed following UV laser amputation of primary dendrites within 400 (mu)m of perikarya. The following observations were made. First, neuronal survival is a function of lesion distance from the perikaryon and of process diameter at the lesion site. For an average lesion diameter of 3.2 (mu)m, dendrite transections at 50 (mu)m, 100 (mu)m, and 150 (mu)m were associated with survival probabilities of 31%, 54% and 70% respectively. Second, the fate of the injured cells was definitely established 24 hours after injury and very likely was determined as early as two hours. Third, phase microscopic observation revealed that the early stages of deterioration leading to cell death were associated with increased cytoplasmic phase brightness; this optical effect correlated ultrastructurally with the appearance of numerous, small, electron-lucent vacuoles and swollen mitochondria. Fourth, the magnitude and time course of injury potentials recorded at the somata were a function of the lesion distance and did not return to prelesion levels within 30 minutes after transection. Fifth, at 24 hours after surgery, the average membrane potential of lesioned neurons was 8% below that of control neurons. Sixth, at a lesion distance of approximately 300 (mu)m both anticipated injury potentials and the probability of cell death approach zero. The influence of lesion physical parameters upon neuronal survival after dendrite amputation suggests that neuronal deterioration and death after dendrite amputation trauma depend upon the magnitude of the injury currents reaching the soma. Removal of the calcium from the culture medium, however, does not protect lesioned neurons and actually decreases the probability of survival. It is, therefore, hypothesized that the influx of external sodium after physical trauma may mediate the death of injured neurons both indirectly by triggering the release of endogenous mitochondrial calcium stores, and directly by causing osmotic swelling and irreversible damage to mitochondria.