Abstracts

Rationale: The overall diagnosis of autism spectrum disorder (ASD) varies widely from very mild to severe social and cognitive impairments. Autism behavioral manifestations are delayed and generally do not emerge until 12 to 18 months of age. Although the ratio of males to females with ASD tends to vary, it is widely accepted that ASD is approximately four times more common in males. Recently we found in a novel postnatal model of ASD that handling and social behaviors are modified. We hypothesized that continuous subconvulsive activity in early postnatal life contributes to autistic behavior and changes in the seizure threshold.  Methods: To further validate our postnatal model of ASD, subconvulsive daily step-up doses of kainic acid (KA) were administered subcutaneously to male and female rat pups for 15 days beginning on postnatal (P) day 6 to elevate glutamate levels and neuronal activity in early life. A battery of behavioral tests was conducted which included the elevated plus maze, alternating T-maze, object recognition, and forced swim test. The latency to seizures was tested with flurothyl or a single unilateral intrahippocampal convulsive dose of KA administered 24 h after the last systemic subconvulsive treatment.   Results: At the end of the treatment protocol, only males displayed significant asocial traits in the social interaction 3 chamber test. Males with ASD exhibited less interest in novel objects and were less exploratory in the object recognition test by spending less time with old and new objects (4.09s ± 1.85 vs. 11.82s ± 2.85, p = 0.038). Similarly, ASD males were less mobile and spent more time freezing compared to sex matched controls. In the spontaneous alternating T-Maze test, males showed a strong trend towards repetitive behavior irrespective of treatment. Interestingly ASD females were more active in the elevated plus maze and open field. After administering a convulsive dose of KA to PBS injected controls vs. the ASD group, there was a delayed onset to seizure behavioral manifestations and a significant reduction in seizure severity score (KAih: 4.2 ± 0.2 vs. ASD+KAih: 2.2 ± 0.05, p<0.01). The onset to wet dog shakes (WDS) and fore limb clonus (FLC) in the ASD group was also delayed and with fewer episodes. In contrast, when flurothyl was administered, to test the seizure threshold, no differences in clonic or tonic-clonic seizures were observed in males. However, ASD females exhibited an accelerated onset to tonic-clonic convulsions revealing a significant interaction between sex and treatment. In the forced swim test the male ASD group exhibited less depressive-like behavior. The total distance of forced swimming and time mobile over a 5-min period was significantly elevated (197s ± 22.88 vs. 101s ± 22.74, p=0.019).  Conclusions: These findings suggest that continuous excitation of low-affinity KA binding sites in early postnatal life leads to increased hyperactivity in females and an ASD phenotype in males during the juvenile period. The delayed onset to seizure behavior after a single high dose of KA in males and females is likely due to desensitization of the receptor within the limbic system, whereas the accelerated seizure threshold in females in response to flurothyl may be due to their hyperactive state. The aberrant results we report in the forced swim test may represent ADHD-like behavior that often manifests in patients diagnosed with ASD. Since males were more susceptible to developing autistic behaviors and cognitive pathologies our postnatal model for autism was further validated. Funding: None