Opposing effects of α2- and ß-adrenergic receptor stimulation on quiescent neural precursor cell activity and adult hippocampal neurogenesis.

Norepinephrine regulates latent neural stem cell activity and adult hippocampal neurogenesis, and has an important role in modulating hippocampal functions such as learning, memory and mood. Adult hippocampal neurogenesis is a multi-stage process, spanning from the activation and proliferation of hippocampal stem cells, to their differentiation into neurons. However, the stage-specific effects of noradrenergic receptors in regulating adult hippocampal neurogenesis remain poorly understood. In this study, we used transgenic Nestin-GFP mice and neurosphere assays to show that modulation of α2- and ß-adrenergic receptor activity directly affects Nestin-GFP/GFAP-positive precursor cell population albeit in an opposing fashion. While selective stimulation of α2-adrenergic receptors decreases precursor cell activation, proliferation and immature neuron number, stimulation of ß-adrenergic receptors activates the quiescent precursor pool and enhances their proliferation in the adult hippocampus. Furthermore, our data indicate no major role for α1-adrenergic receptors, as we did not observe any change in either the activation and proliferation of hippocampal precursors following selective stimulation or blockade of α1-adrenergic receptors. Taken together, our data suggest that under physiological as well as under conditions that lead to enhanced norepinephrine release, the balance between α2- and ß-adrenergic receptor activity regulates precursor cell activity and hippocampal neurogenesis.

Culturing and expansion of precursor cells from the adult hippocampus.

It is now well established that a resident population of neural precursor cells continues to generate new neurons in the adult hippocampus throughout life. Numerous studies have suggested that these newborn neurons preferentially participate in the functional hippocampal circuitry that leads to enhancement of learning, cognition and mood. Therefore, understanding the molecular mechanisms that regulate the activity of these endogenous precursor cells is paramount to develop novel regenerative strategies for the treatment of neurological and psychiatric disorders. The neurosphere assay has been instrumental in discovering the presence of stem and precursor cell population from several brain regions. In this chapter, we describe this assay to specifically isolate and culture neural stem and precursor cell populations from the adult hippocampus of mice. In addition, we provide methods to conduct detailed assays to examine their functional properties such as proliferation, self-renewal, and differentiation.