Abstract
Methamphetamine addicts demonstrate impaired hippocampal-dependent cognitive function that could result from methamphetamine-induced maladaptive plasticity in the hippocampus. Reduced adult hippocampal neurogenesis observed in a rodent model of compulsive methamphetamine self-administration partially contributes to the maladaptive plasticity in the hippocampus. The potential mechanisms underlying methamphetamine-induced inhibition of hippocampal neurogenesis were identified in the present study. Key aspects of the cell cycle dynamics of hippocampal progenitors, including proliferation and neuronal development, were studied in rats that intravenously self-administered methamphetamine in a limited access (1h/day: short access (ShA)-4 days and ShA-13 days) or extended access (6h/day: long access (LgA)-4 days and LgA-13 days) paradigm. Immunohistochemical analysis of Ki-67 cells with 5-chloro-2'-deoxyuridine (CldU) demonstrated that LgA methamphetamine inhibited hippocampal proliferation by decreasing the proliferating pool of progenitors that are in the synthesis (S)-phase of the cell cycle. Double S-phase labeling with CldU and 5-iodo-2'-deoxyuridine (IdU) revealed that reduced S-phase cells were not due to alterations in the length of the S-phase. Further systematic analysis of Ki-67 cells with GFAP, Sox2, and DCX revealed that LgA methamphetamine-induced inhibition of hippocampal neurogenesis was attributable to impairment in the development of neuronal progenitors from preneuronal progenitors to immature neurons. Methamphetamine concomitantly increased hippocampal apoptosis, changes that were evident during the earlier days of self-administration. These findings demonstrate that methamphetamine self-administration initiates allostatic changes in adult neuroplasticity maintained by the hippocampus, including increased apoptosis, and altered dynamics of hippocampal neural progenitors. These data suggest that altered hippocampal plasticity by methamphetamine could partially contribute to methamphetamine-induced impairments in hippocampal function.