From neurotransmitters to neurotrophic factors to neurogenesis

New neurons continue to be produced in adult mammals, including humans, predominantly in the anterior subventricular zone of the lateral ventricle and the subgranular zone of the dentate gyrus. This update focuses on the emerging concept that adult CNS neurogenesis can be regulated by targeting neurotransmitter receptors, which, in turn, drive expression of crucial neurotrophic and growth factors. Such an approach might enable the development of pharmacological treatments that harness the endogenous potential of the CNS to replace lost cells in neurological disorders such as stroke and Alzheimer's and Huntington's diseases. This review samples in vivo studies in adult mammals from 2006 to mid-2008. It also provides some considerations for navigating toward translation to human disorders. Among them are the formidable problems of scaling up production of new neurons within the two "niches" of the brain and delivering sufficient numbers to distant degenerating regions for cell replacement. However, an expedition can only succeed if started.