Neural activity and survival in the developing nervous system

Recent evidence suggests that blockade of normal excitation in the immature nervous system may have profound effects on neuronal survival during the period of natural cell death. Cell loss following depression of electrical activity in the central nervous system (CNS) may explain the neuropsychiatric deficits in humans exposed to alcohol or other CNS depressants during development. Thus, understanding the role of electrical activity in the survival of young neurons is an important goal of modern basic and clinical neuroscience. Here we review the evidence from in vivo and in vitro model systems that electrical activity participates in promoting neuronal survival. We discuss the potential role of moderate elevations of intracellular calcium in promoting survival, and we address the possible ways in which activity and conventional trophic factors may interact.     

Ecological cues, gestation length, and birth timing in African buffalo (Syncerus caffer)

We examined annual variation in the timing of conception andparturition in the African buffalo (Syncerus caffer) and thesynchrony of birth timing with resource cues, using 8 yearsof monthly birth, rainfall, and vegetation data, measured asNormalized Difference Vegetation Index (NDVI). Monthly birthshad the strongest significant correlations with NDVI and rainfalllevels 12 and 13 months in the past, respectively. In addition,the synchrony of current year births corresponds most stronglyto the synchrony of the previous year's NDVI distribution. Becausethe gestation period of buffalo has been estimated to be around11 months, these findings suggest that improved protein levels,occurring approximately a month after the first green flushof the wet season, are either a trigger for conception or conceptionhas evolved to be synchronous with correlated environmentalcues that ensure females enter a period of peak body conditionaround the time of conception and/or parturition. With a gestationperiod of approximately 340 days, parturition occurs to takeadvantage of the period when forage has its highest proteincontent. A comparative analysis of gestation periods withinthe subfamily Bovinae indicates that African buffalo have aprotracted gestation for their body size, which we suggest isan adaptation to their seasonal environment. We also found thatinterannual variation in the birth distribution suggests a degreeof plasticity in the date of conception, and variation in thenumber of calves born each year suggest further synchrony ata timescale longer than a single year.