Abstracts

Rationale: Age-dependent variations in behavioral characteristics and brain histological analysis of the rats with kainic acid-induced seizures have been described. In immature rats, immobility, ataxia, repetitive scratching and tonic/clonic seizures are predominant with no significant neuronal damage, while behavioral changes in adult ones consist of immobility, wet-dog shakes, automatism and clonus with widespread neuronal damage with a predilection for limbic structures. Involvement of the maturation process can be implied from these age-specific features. The blood brain barrier (BBB), which consists of a specialized range of mechanisms that prevent the infiltration of many blood constituents into the brain, undergoes changes with development. The BBB in young animals has morphological barriers which later disappear in adulthood. The BBB may therefore have a vital role in the protection of the young brain from seizure-induced injury. To study the role of the BBB during development, the behavioral and histological effects from alteration of BBB in immature rats with seizures induced by kainic acid (KA) was studied. Bile salts were used to alter the BBB permeability. Methods: Ten Sprague Dawley rat pups of age P16-17 weighing between 26 and 52 g were used in this study. After anesthesia with isoflurane, intracranial injections were done with either 2 mM of bile salt (dehydrocholic acid) in aCSF or pure aCSF (control group) stereostatically in the right CA1. One hour after the injection, kainic acid (10mg/kg) was then injected intraperitoneally so as to induce seizures. The animals were then placed in a plastic container and the behavioral changes were closely monitored. Thirty minutes after the onset of seizures, rats received diazepam (5mg/kg) to stop the seizure. After two weeks rats were killed with a lethal dose of pentobarbital, and the brains were removed, sectioned at 40 µm on a freezing microtome, and stained using thionin for cell counting. Results: Bile salts were shown to disrupt the BBB on the side of the injection by Evens blue injection. Both the group with the disrupted BBB and the controls manifested similar behavioral changes which included immobility, ataxia, swimming, automatism, and tonic-clonic seizures. No obvious difference in behavioral features between groups was noted in seizure characteristic or latency to seizure onset. However, histological changes were noted. Using a semiquantitative scale to assess cell lose we found a significant decrease in CA3 cell counts in rats with a disrupted BBB versus rats with a normal BBB (p = 0.014). No differences were noted in CA1 and hilar cell counts. Conclusions: These results indicate that the intact BBB in immature rats limits neuronal damage following status epilepticus. The BBB may play an important role in protecting the immature brain from seizure-induced injury.