No alterations in the performance of two interval timing operant tasks after alpha-difluoromethylornithine (DFMO)-induced cerebellar stunting.

The cerebellum is critically involved in temporal processes in the millisecond range and may be involved in longer time estimations (i.e. in the seconds range). Estimates in the millisecond range are impaired after developmentally induced cerebellar alterations, however, little is known about the effects of similar alterations on longer timing performance. Appropriately timed DFMO treatment reliably causes cerebellar stunting in rats, however, its effects on temporal estimation performance are unknown. Here, male and female Sprague-Dawley rats were treated with subcutaneous injections of 500 mg/kg DFMO on postnatal days 5-12, causing a 10% cerebellar weight reduction at adulthood. As adults, subjects were tested under one of two paradigms - a differential reinforcement of low response rate (DRL) task requiring that subjects withhold a lever press response for 10-14 s or a temporal response differentiation (TRD) task requiring that subjects maintain a lever press response for 10-14 s. Training and steady-state performance of the DRL and TRD tasks were not significantly altered by DFMO treatment. Performance after acute challenges with two dopaminergic agonists (2.00-7.50 mg/kg methylphenidate and 0.10-1.00 mg/kg d-amphetamine) was measured after which all subjects underwent behavioral extinction. Generally, performance after methylphenidate and d-amphetamine was similar in control and DFMO-treated rats and DFMO treatment had no differential effects on performance during extinction. These results support findings from an earlier study [Ferguson SA, Paule MG, Holson RR. Neonatal dexamethasoneon day 7 in rats causes behavioral alterations reflective of hippocampal, but not cerebellar, deficits. Neurotoxicol Teratol, 2001; 23:57-69] indicating that developmental cerebellar stunting has few effects on time estimation within the range of seconds.

Neonatal polyamine depletion by alpha-difluoromethylornithine: effects on adenylyl cyclase cell signaling are separable from effects on brain region growth.

Ornithine decarboxylase (ODC) and the polyamines play an essential role in brain cell replication and differentiation. We administered alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, to neonatal rats on postnatal days 5-12, during the mitotic peak of the cerebellum, a treatment regimen that leads to selective growth inhibition and dysmorphology. In adulthood, cell signaling responses mediated through the adenylyl cyclase pathway were evaluated in order to determine if synaptic dysfunction extends to regions that appear to be otherwise unaffected by DFMO. Total adenylyl cyclase catalytic activity, evaluated with the direct enzymatic stimulant, Mn(2+), was significantly elevated in male rats both in the cerebellum and in brain regions showing no growth retardation (cerebral cortex, brainstem); there were no significant effects in females. In contrast, signaling mediated through the G proteins that couple neurotransmitter receptors to adenylyl cyclase showed a deficit in the DFMO group, as evaluated with the response to fluoride; in males, there was no corresponding increase in activity as would have been expected solely from the enhancement of adenylyl cyclase, and in females, there was actually a significant decrease in the response to fluoride. Again, the deficits were not restricted to the cerebellum. Stimulation of adenylyl cyclase by isoproterenol, a beta-adrenergic receptor agonist that acts through G(s), likewise displayed deficits in both males and females, and without distinction by brain region. These results indicate that the ODC/polyamine pathway plays a role in the development of cell signaling, and hence in neurotransmission, above and beyond its role in cell replication and differentiation. Given the fact that numerous drugs and environmental contaminants have been shown to alter ODC and the polyamines in the developing brain, our findings suggest that changes in brain region growth or structure are inadequate to predict the targeting of specific neurotransmitter or signaling pathways, and that gender-selective functional defects may be present despite the absence of morphological differences.

Minimal behavioral effects from developmental cerebellar stunting in young rats induced by postnatal treatment with alpha-difluoromethylornithine.

Postnatal treatment with alpha-difluoromethylornithine (DFMO), a potent inhibitor of ornithine decarboxylase, reduces polyamine levels in rats. Because polyamines are critically involved in growth and development, body and/or brain weights are often decreased by DFMO treatment. Here, rats were injected subcutaneously with 0, 250, 500, or 750 mg/kg of DFMO on postnatal days (PNDs) 5-10. Behavioral assessments included righting reflex, negative geotaxis, forelimb hanging, open field activity, and rotarod performance. Additionally, day of eye opening was recorded and on PND 28, whole and regional brain weights were measured. Cerebellar/whole-brain ratio was decreased in a dose-dependent manner whereas frontal cortex/whole-brain ratio was increased. Eye opening was delayed to a similar extent in all treated groups whereas body weight was unaffected. alpha-difluoromethylornithine treatment had no significant effects on the assessed behaviors. These results indicate that 6 days of DFMO treatment can substantially impact cerebellar development, but this appears to have few effects on these early assessed behaviors. However, potential behavioral alterations may not be apparent until adulthood. Published by Elsevier Science Inc.

Minimal effects from developmental exposure to St. John's wort (Hypericum perforatum) in Sprague-Dawley rats.

Increasing widespread use of St. John's Wort (SJW, Hypericum perforatum) has led to concerns about its use in pregnant women. Behavioral and physiological alterations resulting from developmental treatment were investigated in Sprague-Dawley rats exposed to diets containing 0, 180, 900, 1800 or 4500ppm SJW beginning on gestational day 3 and ending at offspring weaning on postnatal day (PND) 21. These dietary doses span 1-25 times the recommended human dose. Post-weaning behavioral assessments of male and female offspring included: open field activity, acoustic startle, performance of complex and Morris water mazes, and activity in an elevated plus-maze. There were no SJW effects on maternal weight gain or duration of gestation; offspring body weights were similar to controls from PND 2 through PND 56 after which, some treated groups weighed significantly less than the controls. There were no SJW-related behavioral alterations on any measure. Whole and regional brain weights of offspring at adulthood indicated no significant effects of SJW. These results indicate that there are few neurobehavioral alterations resulting from developmental SJW treatment in rats.