Discovery of Novel Hippocampal Neurogenic Agents by Using an in Vivo Stable Isotope Labeling Technique

Abstract

Neurogenesis occurs in discrete regions of adult mammalian brain, including the subgranular zone of the hippocampus. Hippocampal neurogenesis is enhanced by different classes of antidepressants, but screening for neurogenic actions of novel antidepressants has been inefficient because of limitations of 5-bromo-2Ј-deoxyuridine labeling techniques. We describe an efficient in vivo method for measuring hippocampal neurogenesis involving incorporation of the stable isotope, 2 H, into genomic DNA during labeling with 2 H 2 O (heavy water). Male rodents received 8 to 10%2 H 2 O in drinking water; DNA was isolated from hippocampal progenitor cells or neurons. Label incorporation into progenitor cells of Swiss-Webster mice revealed subpopulation kinetics: 16% divided with t 1/2 of 2.7 weeks; the remainder did not divide over 1 year. Progenitor cell proliferation rates in mice were strain-dependent. Chronic antidepressant treatment for 3 weeks, with 2 H 2 O administered during the final week, increased progenitor cell proliferation across all the strains tested. Fluoxetine treatment increased 2 H incorporation into DNA of gradient-enriched neurons or flowsorted neuronal nuclei 4 weeks after 2 H 2 O labeling, representing the survival and differentiation of newly divided cells into neurons. By screening 11 approved drugs for effects on progenitor cell proliferation, we detected previously unrecognized, dose-dependent enhancement of hippocampal progenitor cell proliferation by two statins and the anticonvulsant topiramate. We also confirmed stimulatory activity of other anticonvulsants and showed inhibition of progenitor cell proliferation by isotretinoin and prednisolone. In conclusion, stable isotope labeling is an efficient, high-throughput in vivo method for measuring hippocampal progenitor cell proliferation that can be used to screen for novel neurogenic drugs.

Early Pharmacotherapy Restores Neurogenesis and Cognitive Performance in the Ts65Dn Mouse Model for Down Syndrome

“…This conclusion is supported by the finding that in Ts65Dn mice treatment with fluoxetine restored the expression of the 5-HT1A receptor and that this effect was accompanied by rescue of proliferation. In agreement with previous studies, fluoxetine increased proliferation (Malberg et al, 2000;Clark et al, 2006;Shankaran et al, 2006) and upregulated the expression of the 5-HT1A receptor (Lund et al, 1992) also in the hippocampus of euploid mice, although these effects were smaller than in Ts65Dn mice. In animals with a normal serotonergic system, treatments longer than that used here (13 d) may be required to elicit more overt effects.…”

“…Consequently, no rational basis exists on which to devise therapeutic strategies aimed at improving neurogenesis in DS. Accumulating evidence shows that antidepressants increase neurogenesis in the dentate gyrus and subventricular zone of the lateral ventricle (Malberg et al, 2000;Shankaran et al, 2006). This raises the exciting possibility of pharmacologically improving neurogenesis with drugs that are usable by humans to correct brain pathologies characterized by reduced neuron production/neurodegeneration.…”

A gene expression network model of type 2 diabetes links cell cycle regulation in islets with diabetes susceptibility

“…The proliferation rate of islet cells was measured using a recently developed heavy water ( 2 H 2 O) labeling technique (Busch et al 2004;Shankaran et al 2006Shankaran et al , 2007. Briefly, the incorporation of deuterium ( 2 H) from 2 H 2 O into the deoxyribose moiety of deoxyribonucleotides in cells replicating their DNA is measured by gas chromatography/mass spectrometry (GC/MS).…”

Ethosuximide Induces Hippocampal Neurogenesis and Reverses Cognitive Deficits in an Amyloid-β Toxin-induced Alzheimer Rat Model via the Phosphatidylinositol 3-Kinase (PI3K)/Akt/Wnt/β-Catenin Pathway

“…Thus, ETH also causes neuronal differentiation in the hippocampal region of the rat brain. It has previously been shown that established AEDs, such as topiramate, valproate, and carbamazepine, enhance neurogenesis in the adult rodent hippocampus (27,28,(73)(74)(75). Similarly, commonly used new generation AEDs like lamotrigine and topiramate have been found to promote the survival of newborn neurons in the hippocampal region in experimental temporal lobe epilepsy (74).…”