The apoptotic pathway evolves over hours to weeks after injury, is an active process requiring energy, is more closely associated with the caspase proteases, and is less clearly linked to inflammatory responses. Primary substrates for the caspases also include cytoskeletal elements as well as the capacity

to activate other processes that can be toxic to the cell.25 Both families of proteases and hence both the necrotic and apoptotic pathways are under complex control of multiple Epigenetic pathway inhibitors modulators, the ultimate balance Inhibitors,research,lifescience,medical of which appear to determine cell survival.25 In addition to these processes, there is a growing appreciation for the role of other factors in the cytotoxic cascades such as the generation Inhibitors,research,lifescience,medical of free radicals, and the disruption of lysosomal membranes with the subsequent release of hydrolytic enzymes into the intracellular environment.24 Inhibitors,research,lifescience,medical The excessive release of neurotransmitters other than glutamate may also play a role

in the elaboration of neurotrauma. For example cholinergic excess may amplify the destructive effects of excitatory amino acid excesses, and may be particularly injurious to brain areas where acetylcholine and excitatory amino acids are densely colocated (ie, hippocampus and frontal cortices).27 The effects of cerebral monoaminergic excesses in the cytotoxic cascade are not understood fully, although in experimental injury models traumatically induced elevations Inhibitors,research,lifescience,medical of cerebral serotonin seem to decrease cerebral glucose use,28,29 and serotonin agonists are not particularly helpful in improving post-traumatic neurobehavioral status or TBI outcome.30,31 Administration

Inhibitors,research,lifescience,medical of catecholamine antagonists impedes recovery from brain injury32-34 and delay emergence from post-traumatic amnesia however in humans,35 suggesting that blocking catecholamine excesses is not an effective means by which to mitigate the cytotoxic cascade after TBI. Neurotransmitter excesses seem to wane over the first several weeks after TBI,36,37 although the time course of their resolution is not characterized fully. TBI in humans produces chronic cerebral cholinergic deficit via injury to ventral forebrain cholinergic nuclei38,39 and their cortical projections.39-41 It is possible that TBI also results in primary or secondary disturbances in monoaminergic systems,42 the effects of which may be amplified by individual genetically mediated variations in catecholamine metabolism.