Torpor Does Not Influence Spatial Memory in Hibernating Golden-Mantled Ground Squirrels (Spermophilus [Callospermophilus] lateralis).

AbstractMammalian hibernation in ground squirrels is characterized by periods of torpor wherein body temperature approaches ambient temperature and metabolism is reduced to as low as 1/100th of active rates. It is unclear how hibernation affects long-term spatial memory, as tremendous remodeling of neurons is associated with torpor use. Given the suspected links between remodeling and memory formation and retention, we examined long-term spatial memory retention throughout a hibernation season. Animals were trained on a Barnes maze before entering torpor. Animals were tested for memory retention once a month throughout a hibernation season. Results indicate marked variation between individuals. Some squirrels retained memory across multiple torpor bouts, while other squirrels did not. No relationship was found between the number of torpor bouts, duration of bouts, or time spent torpid on long-term memory retention. However, that some squirrels successfully retain memory suggests that the profound remodeling of dendritic spines during torpor does not always lead to memory loss.

Maternal separation increases methamphetamine-induced damage in the striatum in male, but not female rats.

Methamphetamine abuse impacts the global economy through costs associated with drug enforcement, emergency room visits, and treatment. Previous research has demonstrated early life stress, such as childhood abuse, increases the likelihood of developing a substance abuse disorder. However, the effects of early life stress on neuronal damage induced by binge methamphetamine administration are unknown. We aimed to elucidate the effects of early life stress on methamphetamine induced dopamine damage in the striatum. Pups were separated from dams for 3h per day during the first two weeks of development or 15 min for control. In adulthood, rats received either subcutaneous 0.9% saline or 5.0mg/kg METH injections every 2h for a total of four injections. Rectal temperatures were taken before the first injection and 1h after each subsequent injection. Seven days after treatment, rats were euthanized and striatum was collected for quantification of tyrosine hydroxylase (TH) and dopamine transporters (DAT) content by Western blot. Methamphetamine significantly elevated core body temperature in males and decreased striatal DAT and TH content, and this effect was potentiated by early life stress. Females did not exhibit elevated core body temperatures or changes in DAT or TH in either condition. Results indicate maternal separation increases methamphetamine induced damage, and females are less susceptible to methamphetamine induced damage.

Altered locomotor and stereotyped responses to acute methamphetamine in adolescent, maternally separated rats.

RATIONALE: Neonatal maternal separation (MS) has been used to model the effects of early life stress in rodents. MS alters behavioral responses to a variety of abused drugs, but few studies have examined its effects on methamphetamine sensitivity. OBJECTIVES: We sought to determine the effects of MS on locomotor and stereotyped responses to low-to-moderate doses of methamphetamine in male and female adolescent rats. METHODS: Male and female rat pups were subjected to 3 h per day of MS on postnatal days (PN) 2-14 or a brief handling control procedure during the same period. During adolescence (approximately PN 40), all rats were tested for locomotor activity and stereotyped behavior in response to acute methamphetamine administration (0, 1.0, or 3.0 mg/kg, s.c.). RESULTS: MS rats of both sexes exhibited increased locomotor activity in a novel environment, relative to handled controls. MS increased the locomotor response to methamphetamine (METH), and this effect occurred at different doses for male (3.0 mg/kg) and female (1.0 mg/kg) rats. MS also increased stereotyped behavior in response to METH (1.0 mg/kg) in both sexes. CONCLUSIONS: MS enhances the locomotor response to METH in a dose- and sex-dependent manner. These results suggest that individuals with a history of early life stress may be particularly vulnerable to the psychostimulant effects of METH, even at relatively low doses.