News tips from the Journal of Neuroscience

1. Calcium Buffering by Mitochondria Prolongs Synaptic Responses
Yuliya V. Medvedeva, Man-Su Kim, and Yuriy M. Usachev

Mitochondria can transform brief stimulation into long-lasting responses by rapidly sequestering and slowly releasing calcium, according to Medvedeva et al. Activation of presynaptic TRPV1 channels in cultures of dorsal root ganglion and spinal neurons induced a biphasic calcium response in the axonal boutons: upon capsaicin application, cytoplasmic calcium concentration rapidly increased; then, after washout, the calcium concentration decreased to a plateau level that lasted for ~15 min before returning to baseline. These changes were paralleled by increased glutamate release, which increased EPSC frequency in postsynaptic neurons for the duration of the calcium plateau. Although calcium influx through TRPV1 channels produced the initial calcium increase, release from mitochondria was responsible for the plateau phase. Furthermore, blocking calcium uptake by mitochondria not only eliminated the plateau but also increased the amplitude of the initial calcium response, suggesting that mitochondria both limit the amplitude and prolong the duration of the response.

2. Depolarization Unmasks Latent Hippocampal Stem Cells
Tara L. Walker, Amanda White, Debra M. Black, Robyn H. Wallace, Pankaj Sah, and Perry F. Bartlett

Although neurons are generated in the hippocampus throughout life, researchers have been unable to isolate the stem cells capable of generating new neurons from adult hippocampus. To assay for stem cells, dissociated neurons are grown in suspension culture, which causes stem cells and progenitors to form neurospheres. Walker et al. reasoned that because neuronal activity increases adult neurogenesis, such activity might activate otherwise latent stem cells. Indeed, depolarizing cultured mouse hippocampal neurons with KCl increased the number of neurospheres formed. Some of the largest of these (about eight per hippocampus) contained multipotent stems cells that could be passaged several times and produced neurons upon differentiation. In contrast, KCl did not increase the number of neurospheres formed from neonatal hippocampus (which formed many neurospheres in the absence of activity), and although depolarization increased thenumber of neurospheres produced from aged hippocampus, these were only small neurospheres that did not contain stem cells.