ABSTRACT
The immediate early gene product activity-regulated cytoskeleton-associated protein (Arc or Arg3.1) is a major regulator of long-term synaptic plasticity with critical roles in postnatal cortical development and memory formation. However, the molecular basis of Arc function is undefined. Arc is a hub protein with interaction partners in the postsynaptic neuronal compartment and nucleus. Previous in vitro biochemical and biophysical analysis of purified recombinant Arc showed formation of low-order oligomers and larger particles including retrovirus-like capsids. Here, we provide evidence for naturally occurring Arc oligomers in the mammalian brain. Using in situ protein crosslinking to trap weak Arc-Arc interactions, we identified in various preparations a prominent Arc immunoreactive band on SDS-PAGE of molecular mass corresponding to a dimer. While putative trimers, tetramers and heavier Arc species were detected, they were of lower abundance. Stimulus-evoked induction of Arc expression and dimer formation was first demonstrated in SH-SY5Y neuroblastoma cells treated with the muscarinic cholinergic agonist, carbachol, and in primary cortical neuronal cultures treated with brain-derived neurotrophic factor (BDNF). In the dentate gyrus (DG) of adult anesthetized rats, induction of long-term potentiation (LTP) by high-frequency stimulation (HFS) of medial perforant synapses or by brief intrahippocampal infusion of BDNF led to a massive increase in Arc dimer expression. Arc immunoprecipitation of crosslinked DG tissue showed enhanced dimer expression during 4 h of LTP maintenance. Mass spectrometric proteomic analysis of immunoprecipitated, gel-excised bands corroborated detection of Arc dimer. Furthermore, Arc dimer was constitutively expressed in naïve cortical, hippocampal and DG tissue, with the lowest levels in the DG. Taken together the results implicate Arc dimer as the predominant low-oligomeric form in mammalian brain, exhibiting regional differences in its constitutive expression and enhanced synaptic activity-evoked expression in LTP.
ABSTRACT
An "establishing shot" prefaces a scene in a movie with a wide shot of the scene's location. It is meant to help viewers process a shift to a new location. Establishing shots can depict the actors in the space in which they will be acting, the exterior of a building, or the larger geographic context of the scene. While use of an establishing shot is standard filmmaking practice, some argue that establishing shots are unnecessary. This study sought to investigate how effective four types of establishing shots are at helping viewers process location shifts. Pupil diameter was recorded using a MangoldVision eye tracking system as a measure of arousal and cognitive load. Oxygenation levels in the prefrontal cortex provided an additional measure of cognitive load assessed through functional near infrared spectroscopy (fNIRS). We expected scene transitions to be followed by transient increases in pupil diameter and oxygenation levels, suggesting increased cognitive load and arousal. We predicted that participants should experience less cognitive load and arousal after a transition to a new scene when that scene has been prefaced with an establishing shot and that these effects would be greatest for establishing shots that depict actors. We found that geographic establishing shots produced significantly lower average pupil diameter than all other establishing shot types and the use of no establishing shot. Actors establishing shots elicited significantly lower average pupil diameter values than the use of no establishing shot. Maximum and average oxygenation values for the actors establishing shot condition were significantly higher than for the exterior establishing shot condition. An alpha level of 0.05 was used for all analyses. These results suggest differences between pupil diameter and fNIRS in terms of the psychological phenomenon they measure, and may inform the design of future films.
