Temozolomide (TMZ, Temodal®, SP Europe, Belgium) is an alkylating agent intended for the treatment of recurrent malignant glioma. In a dosage finding experiment we found a dose of 25 mg/kg body weight to be effective in suppressing adult neurogenesis by more than 80% after monocyclic (3 days) of treatment (Figure 1A ).
Consequently, to suppress adult neurogenesis, mice from the treatment group (TMZ) received injections of TMZ at 25 mg/kg (i.p., 2,5 mg/ml in 0.9% NaCl), whereas the control group (CTR) received sham injections of saline only. This regimen was given on the first three days of a week for 4 weeks to resemble paradigms used for glioma treatment in humans (Figure 1B ). Behavioral testing was performed 4 weeks after the final TMZ injection.
For adult-born granule cells to become recruitable the sequence of proliferation, differentiation and maturation requires approximately up to 28 days. Thus, suppressing adult neurogenesis for at least 4 weeks combined with a reconstitution period of 4 more weeks ensured that most of the cells borne immediately before onset of TMZ treatment would have been already used or eliminated by apoptosis. Using intercalating convalescence times, we minimized the risk of confounding side effects during behavioral testing.
It has recently been shown that 6–8 weeks old, adult generated granule cells become selectively recruited during acquisition of a spatial learning task [21] (link). Therefore, our primary aim was to minimize the number of potentially recruitable adult-born neurons exactly at that time, when the new granule cells should be of particularly high relevance for task acquisition. Because we suppressed proliferation for at least 4 weeks and behavioral testing began an additional 4 weeks later, at the time-point of the behavioral analysis the subpopulation of 5–7 week old adult generated neurons is primarily affected by TMZ. An immediate recovery of the stem cell niche seemed unlikely as it was found that after wiping out proliferation in the SGZ by irradiation reconstitution occurs only slow and on a prolonged timescale [38] (link). Consequently, at the time, when the mice were learning the water maze task only very few (or no) new granule cells were available to be functionally integrated into existing circuits.
Consequently, to suppress adult neurogenesis, mice from the treatment group (TMZ) received injections of TMZ at 25 mg/kg (i.p., 2,5 mg/ml in 0.9% NaCl), whereas the control group (CTR) received sham injections of saline only. This regimen was given on the first three days of a week for 4 weeks to resemble paradigms used for glioma treatment in humans (
For adult-born granule cells to become recruitable the sequence of proliferation, differentiation and maturation requires approximately up to 28 days. Thus, suppressing adult neurogenesis for at least 4 weeks combined with a reconstitution period of 4 more weeks ensured that most of the cells borne immediately before onset of TMZ treatment would have been already used or eliminated by apoptosis. Using intercalating convalescence times, we minimized the risk of confounding side effects during behavioral testing.
It has recently been shown that 6–8 weeks old, adult generated granule cells become selectively recruited during acquisition of a spatial learning task [21] (link). Therefore, our primary aim was to minimize the number of potentially recruitable adult-born neurons exactly at that time, when the new granule cells should be of particularly high relevance for task acquisition. Because we suppressed proliferation for at least 4 weeks and behavioral testing began an additional 4 weeks later, at the time-point of the behavioral analysis the subpopulation of 5–7 week old adult generated neurons is primarily affected by TMZ. An immediate recovery of the stem cell niche seemed unlikely as it was found that after wiping out proliferation in the SGZ by irradiation reconstitution occurs only slow and on a prolonged timescale [38] (link). Consequently, at the time, when the mice were learning the water maze task only very few (or no) new granule cells were available to be functionally integrated into existing circuits.
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