Neuronal Cell Death during Development

A central problem in developmental neurobiology is the understanding of the regulation of neuron survival and death. The neurotrophic theory provides a basis for understanding several features of neuronal development, including the question of why, in many populations of developing neurons, only a proportion of the original number of postmitotic cells survives. It is well known that in many regions of the nervous system large numbers (approx. 50%) of postmitotic neurons degenerate and die by a process of naturally occurring neuronal death. It has been repeatedly demonstrated that in most populations of neurons this normal cell loss occurs during the period when neurons are establishing synaptic connections with their targets. This temporal coincidence, together with the demonstration that manipulations of the availability of putative synaptic targets alters the number of surviving innervating neurons, led to the proposal that neurons compete for a target-derived factor that is supplied in limiting amounts by the targets and thus adjusting neuron numbers so as to provide sufficient innervations for their targets. However, there is growing evidence that other mechanisms may be involved in regulating cell death.

First Few Days After Stroke

When someone is suspected of having had a stroke, tests will be done to confirm this or to rule it out. Often a brain scan will be done – either CT or MRI. ‘CT’ is short for computed tomography. Introduced in the 1970s, CT scanning revolutionized the investigation of brain disease, because it was now possible to see what was going on inside the brain without difficult, painful and hazardous tests. It has improved enormously, giving much clearer pictures much more quickly. ‘MRI’ stands for magnetic resonance imaging. This method is better than CT scans at showing up very small infarcts, particularly if the doctor thinks the problem is in the cerebellum or the brain stem. The reason for this is that CT scan pictures get distorted, but this is not a difficulty with MRI. The MRI scans can also show up the arteries very clearly (magnetic resonance angiography), and can therefore be used to see where the root of the problem might be. Other tests may be needed, such as an arteriogram, an echocardiogram or lumbar puncture, and we discuss these too. The results obtained from the investigations will indicate which treatment is likely to be the best for any particular person. This includes rehabilitation as well as drugs to help recovery.