Abstracts

Rationale: Although select genes have been identified in cases of severe ASD, they do not yet account for the mild and more functional ASD cases that are not pervasive until years after birth. We hypothesized that continuous subconvulsive activity in early postnatal life may contribute to the development of autistic pathologies. For example, subconvulsive postnatal activity may affect critical descending inhibitory pathways such as the amygdala cortical complex (AMG/Cx). Methods: To establish a valid ASD model, daily subconvulsive step-up doses of kainic acid (KA) were administered subcutaneously to rat pups for 15 days beginning on postnatal (P) day 6. At 24 h after the last subconvulsive treatment, a single convulsive dose of KA was administered to ASD (ASD+KA) and naïve rat pups (1xKA) to compare cellular consequences of subconvulsive vs. convulsive activity in early postnatal life. Brains were histologically evaluated with cresyl violet Nissl staining for neuronal integrity, NeuN and cFos as markers for activated neurons, and parvalbumin (PV) immunohistochemistry. Results: The ASD group had increased numbers of hyperbasophilic neurons within the AMG/Cx that correlated with reduced NeuN antigenicity revealing an increased average gap width extending from the basolateral amygdala (BLA), basomedial amygdala (BMA), and central amygdala (CEA) to the piriform and entorhinal cortices, but in the absence of cell loss (142 ± 5 µm vs. 216 ± 8 µm, p<0.01). Serial hippocampal sections were devoid of injury in contrast to juveniles with 1xKA. Few cells were cfos⁺ in control AMG/Cx, whereas the ASD group had many scattered cfos⁺ cells within the AMG/Cx and dorsal blade of the dentate gyrus (DG), presumably GABAergic interneurons (2.33 ± 1.8 vs. 34.3 ± 4.4). A prominent cfos+ cluster was also observed within the BMA (45.5 ± 1.5, p<0.002). After ASD+KA, extremely dark cfos expression was apparent within large cells of the hilus, resembling GABAergic mossy cell distribution. Eosinophilia was also detected deep within the hilus, but belonged to a different cell population. Interneurons expressing PV were dramatically reduced in number and immunodensity but only in ASD and ASD+KA treated groups<./p>