Neurobiology. Neuronal self-reliance

Endogenous neural stem/progenitor cells stabilize the cortical microenvironment after traumatic brain injury

Although a myriad of pathological responses contribute to traumatic brain injury (TBI), cerebral dysfunction has been closely linked to cell death mechanisms. A number of therapeutic strategies have been studied in an attempt to minimize or ameliorate tissue damage; however, few studies have evaluated the inherent protective capacity of the brain. Endogenous neural stem/progenitor cells (NSPCs) reside in distinct brain regions and have been shown to respond to tissue damage by migrating to regions of injury. Until now, it remained unknown whether these cells have the capacity to promote endogenous repair. We ablated NSPCs in the subventricular zone to examine their contribution to the injury microenvironment after controlled cortical impact (CCI) injury. Studies were performed in transgenic mice expressing the herpes simplex virus thymidine kinase gene under the control of the nestin(δ) promoter exposed to CCI injury. Two weeks after CCI injury, mice deficient in NSPCs had reduced neuronal survival in the perilesional cortex and fewer Iba-1-positive and glial fibrillary acidic protein-positive glial cells but increased glial hypertrophy at the injury site. These findings suggest that the presence of NSPCs play a supportive role in the cortex to promote neuronal survival and glial cell expansion after TBI injury, which corresponds with improvements in motor function. We conclude that enhancing this endogenous response may have acute protective roles after TBI.

Susceptibility of developing cochlear nucleus neurons to deafferentation-induced death abruptly ends just before the onset of hearing

To investigate the ability of developing cochlear nucleus (CN) neurons to survive in the absence of afferent input, left cochlear removals were performed on gerbils at 2 day intervals from postnatal (P)3 to P11, and at P18 and P93. After a 3 month postsurgical survival period, Nissl-stained frontal sections through the brainstem were analyzed under the light microscope. CN volume, anteroventral cochlear nucleus (AVCN) neuron cross-sectional area, and total number of neurons in the CN were measured on both sides of the brain. Mean volume reduction of the deafferented CN relative to the intact CN ranged between 76% in the P3 group to 33% in the P11 group and did not differ significantly between P11 and P93. Cochlear removal at all ages reduced AVCN neuron cross-sectional area by approximately 40% in the deafferented CN relative to the intact CN, except for the P93 group where neuron atrophy was significantly less severe (23% mean reduction). Massive loss of CN neurons (>50% of the intact side) was observed following cochlear removal performed during the first postnatal week. However, between P7 and P9, neurons in all areas of the CN lose susceptibility to deafferentation-induced neuron death. No significant neuron loss was observed following cochlear removal after P7. This study shows that an abrupt transition in the ability of CN neurons to survive in the absence of afferent input is coincident with events leading to the onset of hearing.

Interleukin-1 beta suppresses apoptosis in CD34 positive bone marrow cells through activation of the type I IL-1 receptor

Interleukin-1 is a pleiotropic cytokine that has been shown previously to suppress active cell death in T cells. Two cell surface receptors for interleukin-1 have been identified and their genes cloned, type I (IL-RI) and type II (IL-RII) receptors. In the present study, we provide evidence for a role of interleukin-1 beta in the short-term suppression of cell death both in purified CD34+/Lin- bone marrow precursors and in the GM-CSF dependent cell line TF-1. Several lines of evidence suggest that the biologic effects of IL-1 beta are mediated by activation of type I IL-1 receptors (IL-1RI) and induction of GM-CSF production. First, neutralizing antibodies to IL-1RI but not IL-1RII drastically abrogated cell survival induced by IL-1 beta in CD34+/Lin- cells and TF-1 cells. Second, neutralizing antibodies against GM-CSF abrogate cell survival supported by IL-1 both in CD34+/Lin- bone marrow cells and in the cell line TF-1. Furthermore, exposure of TF-1 cells to IL-1 beta results in a transient accumulation of GM-CSF mRNA, with a peak at 3 h, which was dramatically decreased by neutralizing anti-IL-1R1 antibodies. In contrast, neutralizing anti-IL-1RII did not change the IL-1 induced cell survival of bone marrow cells and was followed by a paradoxical increase in viable cell numbers, in c-myc and c-myb mRNA accumulation in IL-1 treated TF-1 cells. Together our results indicate that the increase in cell survival induced IL-1 beta occurs through binding to IL-1RI and the subsequent production of endogenous GM-CSF. IL-1RII does not appear to be involved in signal transduction in primary CD34+/Lin- cells but could negatively regulate the response to IL-1 beta in TF-1 cells.

Characterization of the signaling interactions that promote the survival and growth of developing retinal ganglion cells in culture

The signaling mechanisms that control the survival of CNS neurons are poorly understood. Here we show that, in contrast to PNS neurons, the survival of purified postnatal rat retinal ganglion cells (RGCs) in vitro is not promoted by peptide trophic factors unless their intracellular cAMP is increased pharmacologically or they are depolarized by K+ or glutamate agonists. Long-term survival of most RGCs in culture can be promoted by a combination of trophic factors normally produced along the visual pathway, including BDNF, CNTF, IGF1, an oligodendrocyte-derived protein, and forskolin. These results suggest that neurotransmitter stimulation and electrical activity enhance the survival of developing RGCs and raise the question of whether the survival control mechanisms of PNS and CNS neurons are different.