Abstracts

Rationale: Recently we observed that chronic subconvulsive treatment during the 2nd two weeks of postnatal life leads to autism (ASD) phenotypes in young rat pups apparent in the juvenile weanling period. Impairments observed were in open handling, attention/memory, anxiety, and social behavior. Although aberrant increases in glutamate levels are associated with seizures that result in cascade triggering cell death pathways, here we elicit a subseizure state which may be more specific to downstream excitatory responses that activate post-synaptic metabotropic glutamate receptors (mGluR) and milder forms of ASD. Group I mGluR subtypes such as the mGluR5 variant plays an important role in learning and memory suggesting that positive allosteric modulators (PAMs) may serve to improve cognitive impairment associated with early detectable ASD as well as initial early life seizures. Methods: To induce a postnatal epigenetic model of ASD, daily low doses of kainic acid (KA) (25-100 µg) were administered subcutaneously to rat pups for 15 days beginning on postnatal day 6 to elevate early life neuronal activity without elicitation of seizures. The seizure threshold was subsequently examined with flurothyl at the end of the subconvulsive treatment. Pups were treated with LiCl (80 mg/kg) followed by the mGlu5 receptor PAM, VU0360172 (10 mg/kg), 1 h prior to sacrifice. Dissected brain regions were used to measure inositolmonophosphate (InsP) formation, an indicator of polyphosphoinositde (PI) hydrolysis. Endogenous IsnP levels were measured by ELISA. Fixed brains were histologically evaluated with NeuN, parvalbumin (PV), and Nissl stain. The seizure threshold was examined with flurothyl 24 h after the last subseizure dose of KA. Animals were sacrificed 24 h after their last KA treatment or flurothyl exposure. Results: When flurothyl was administered, control males had faster onset to twitches and clonic seizures than females. After subseizure treatment, no sex-related differences were observed. IP3 hydrolysis was selectively reduced in the medial prefrontal cortex (mPfcx), thalamus, and amygdala. Except for the thalamus, VU0360172, at the dose used, did not potentiate hydrolysis unless the animals were previously exposed to flurothyl. Steady levels were observed in the striatum and piriform/ entorhinal cortex, and no potentiation was observed under any condition in either region. Presumed deficits in IP3-mediated Ca2+ signaling corresponded to selective loss of NeuN antigenicity (in the absence of cell loss) within the medial prefrontal cortex and amygdala that extended from the baslolateral nucleus (BLA) to the entorhinal cortex. Immunolabeling with PV antibodies was preserved among hippocampal interneuons, but significantly reduced in the amygdala subjected to the subconvulsive protocol. Conclusions: Data suggest that metabolism of the extra-hippocampal loop is predominantly affected by subtle but steady release of glutamate triggered by the low dose, early life protocol of KA. Loss of metabolic activity in critical brain regions could be responsible for deficits previously observed in the two-object recognition memory test and social interaction environments. We propose that IP3 receptor activity of the mPfcx, thalamus, and amygdala regions is defective in our model of ASD and not rescued by PAMs. Instead, mGluR5 potentiation with PAMs to improve cognition may be a more effective treatment strategy for children with epilepsy. Funding: No funding