Negative geotaxis: An early age behavioral hallmark to VPA rat model of autism:

Background: Negative geotaxis (NG) is an important parameter, commonly used in study of different CNS diseases and neurodevelopmental disorders. Neurobehavioural change following brain injury was easily identified by negative geotaxis. Purpose: Although NG is evaluated in the settings of ASD, most of the studies are conducted for short duration (1-3 day) and the overall trend of acquisition of NG is not evaluated. In this context, we wanted to evaluate the trend of acquisition of negative geotaxis as a behavioural marker of autism in Valproic acid (VPA) model of ASD. Methods: Dams in the VPA group were treated with intraperitoneal injections of VPA 600 mg/kg single dose on gestational day 12.5, while the control animals received normal saline of similar volume. Developmental parameters {body weight (PND 8, 10 & 12), body length (PND 4, 5, 6 8, 10), eye opening (PND 10, 12, 14, 15 and 16) and motor development (grid walking test on PND 20)} were monitored. Negative geotaxis test was performed at PND 6, 10, 15 and 17. Results: The results of the present experiments demonstrate that VPA exposed rats exhibited delayed developmental parameters, aberration of the pattern of acquisition of negative geotaxis, enhanced negative geotaxis in early postnatal period (PND 6) and enhanced negative geotaxis in absence of visual clues (PND 17). Conclusion: NG can be a valuable biomarker in early detection of autistic behavior and in absence of visual clues. The abberant negative geotaxis developmental pattern can serve as a marker to detect ASD. Thus NG can serve as an important early age biomarker of ASD. Further studies are required to validate this finding.