No abstract

Methylphenidate (MPH) is a psychostimulant that blocks reuptake of dopamine and norepinephrine via their transporters. Currently, MPH is used for the treatment of narcolepsy and is the most common medication used for the treatment of Attention Deficit Hyperactivity Disorder. It is also misused and abused due to its ability to increase attention, decrease appetite, and when injected, create a “high”. Various psychoactive medications, such as antidepressants, opioids, and other psychostimulants have been shown to alter the rate of neurogenesis or the “birth” or new neurons in the dentate gyrus of the hippocampus. Therefore, our lab postulated that long‐term exposure to MPH may also affect neurogenesis rate. In these studies, 25 day old Swiss‐Webster mice received twice daily injections of saline, 1 mg/kg, or 10 mg/kg MPH for 28 days; the 1 mg/kg MPH and 10 mg/kg MPH represent therapeutic and potential abusive doses, respectively. Three days after the final MPH injection, mice were injected with 5‐ethinyl‐2’‐deoxyuridine (EdU), a thymidine analog that incorporates into the DNA of dividing cells. In order to determine both the rate of neurogenesis and the long‐term survival of the new cells, mice were sacrificed at either 1 day post EdU injection or 28 days after EdU injection. Brains were sectioned on the cryostat and mounted on slides. Slides were stained using a Click‐iT EdU imaging kit, and neurons were double‐labeled using immunohistochemistry for the neuronal marker NeuN. Neurons within the dentate gyrus were counted to create a ratio of EdU+ /NeuN+ (or newly produced neurons to total neurons). Our preliminary data suggests that low dose (1 mg/kg) MPH has no effect on neurogenesis rate. However, high dose (10 mg/kg) MPH produces a higher ratio of newly synthesized neurons. Additionally, it appears that these neurons are maintained 28 days post injection. These effects may be relevant to the therapeutic action of MPH and/or its propensity for abuse.