Abstracts

Rationale: Activity-regulated cytoskeletal associated protein (Arc/Arg 3.1) is an immediate-early gene that is rapidly induced by neuronal activity. Arc/Arg3.1 is known to be required for long-lasting forms of synaptic plasticity, learning and memory consolidation. It has been demonstrated that Arc/Arg3.1 selectively regulates trafficking of AMPA-type glutamate receptors (AMPARs) in neurons by accelerating endocytosis and reducing surface expression of GluR2 and GluR3 subunits. We have previously shown that AMPA receptor trafficking is critical to enhanced network excitability following early life hypoxia-induced seizures (HS) in a rat model of neonatal seizures. We hypothesized that Arc/Arg 3.1 activation may be upstream of AMPA trafficking, which occurs between 1-24 hours after seizures. In the present study we evaluated the temporal and spatial pattern of Arc/Arg 3.1 expression in postnatal day (P)10 rats in which seizures were induced either by hypoxia or by pentylenetetrazol (PTZ). Methods: Seizures were induced in male Long Evans rats at P10 either by exposure to graded global hypoxia (15 min to min of 4%O2) (n=4) or PTZ dose (80 mg/kg i.p.) (n=4). Untreated littermates were used as controls (n=2). Rat pups were perfused 2, 4 or 6 hours after seizure onset. 20 M sections were cut from fixed brains and immunostained with Arc/Arg 3.1 antibody (sc-15325, Santa Cruz Biotechnology). Results: Minimal baseline staining of Arc/Arg 3.1 was seen in the cortex and hippocampus in the P10 controls. As early as 2 hours after PTZ injection, Arc/Arg 3.1. neuronal staining was more intense and widespread in the cortex (cingulate cortex, retrosplenial cortex, neocortical layers II-VI and subplate), hippocampus (CA1, CA3 and dentate gyrus), pyriform cortex and hypothalamus (anterior hypothalamic area, arcuate nucleus, dorsomedial and ventromedial). In comparison, at 2 hours after HS, only slight staining was seen in layer II of the cortex, subplate and pyriform. By 4 or 6 hours, immunoreactivity increased and staining was present in the same regions as PTZ-induced seizures. However, hypoxic seizures resulted in a more intense staining in the pyriform cortex, thalamus and hypothalamus (arcuate nucleus, dorsomedial and periventricular). Conclusions: These results suggest a change in Arc/Arg3.1 expression induced by seizures in the immature brain. Further studies are required to understand the molecular pathway that relates Arc/Arg3.1 protein with AMPARs. (Supported by RO1 NS31718, DP1 0D003347, IDDRC ).