Abstracts

Rationale: Children with epilepsy are more likely to develop Attention Deficit Hyperactivity Disorder (ADHD) than children without epilepsy, but it is unknown whether seizures can cause changes consistent with ADHD, such as impairments in visuospatial attention or loss of prefrontal cortex (PFC) dopaminergic receptors. In the current study, these correlates of ADHD were assessed following transient perinatal hypoxia in rats to determine whether early life seizures can alter visuospatial attention and dopamine receptors in the PFC. Methods: Male and female Sprague Dawley rats received hypoxia on postnatal day 10-12 by lowering O₂ to 5-7% by infusion of N₂ gas into an airtight chamber. After 12 min, O₂ was lowered by ~1%/min. Animals were monitored for seizures, and removed from the chamber upon apnea. Control animals were kept in the same chamber under normoxic conditions. Two weeks later, animals were perfused and brains were processed for immunocytochemistry. Coronal sections labeled with DRD4 antibody, to identify D4 dopamine receptors, were incubated in fluorescent secondary antibody, and the PFC was imaged using a Leica SP2 laser scanning confocal microscope. The number of DRD4 immunopositive receptors per unit volume was quantified using offline measurement software (Imaris). A second cohort of animals was tested for attention using the 5-arm maze. Animals were partially food deprived during the six phase testing period. During Phase l (habituation), all five arms were baited, illuminated and remained open. During Phases ll, lll and lV (acquisition) the number of arm choices gradually increased with one arm lit and baited. During Phases V and VI (visuo-spatial attention), all doors remained opened and one arm was lit for a duration of 2sec (Phase V) and 0.5, 1 or 2sec (Phase VI), during a 10sec (Phase V) or random (5-35sec, Phase VI) delay. Results: Initial anatomical measures from a subset of animals (n=6) show a tendency for DRD4 receptor density in the PFC to be reduced following perinatal hypoxia (t(4)=2.77, p=0.056). Repeated measures analysis of task acquisition showed a significant main effect for phase (F(3,36)=52.94, p<0.05), and a significant phase by condition interaction (F(3,36)=3.19, p<0.05), which showed that the rate of task acquisition was faster for hypoxic animals than for controls (n=14). When the task was switched to a measure of attention (Phases V and VI), there was a significant main effect for condition (F(1,4)=9.52, p<0.05), with hypoxic animals making significantly fewer errors than controls (n=6). Conclusions: Together, these results suggest that the PFC dopaminergic system and visuospatial attention are altered by early life seizures in this model, but not in the ways that were predicted. While initial anatomical evidence does support a decrease in PFC DRD4 density, more animals will be needed to confirm this finding. However, behavioral measures showed a surprising result that hypoxic animals outperformed controls in basic task acquisition and measures of visuospatial attention. Interpretations and follow-up data will be discussed.