Spatial compartmentalization of AMPA glutamate receptor subunits at the calyx of Held synapse

The mature calyx of Held ending on principal neurons of the medial nucleus of the trapezoid body (MNTB) has very specialized morphological and molecular features that make it possible to transmit auditory signals with high fidelity. In a previous work we described an increased localization of the ionotropic α‐amino‐3‐hydroxy‐5‐methyl‐4 isoxazolepropionic acid (AMPA) glutamate receptor (GluA) subunits at postsynaptic sites of the calyx of Held‐principal cell body synapses from postnatal development to adult. The aim of the present study was to investigate whether the pattern of the synaptic distribution of GluA2/3/4c and ‐4 in adult MNTB principal cell bodies correlated with preferential subcellular domains (stalks and swellings) of the calyx. We used a postembedding immunocytochemical method combined with specific antibodies to GluA2/3/4c and GluA4 subunits. We found that the density of GluA2/3/4c in calyceal swellings (19 ± 1.54 particles/μm) was higher than in stalks (10.93 ± 1.37 particles/μm); however, the differences for GluA4 were not statistically significant (swellings: 13.84 ± 1.39 particles/μm; stalks: 10.42 ± 1.24 particles/μm). Furthermore, GluA2/3/4c and GluA4 labeling co‐localized to some extent in calyceal stalks and swellings. Taking these data together, the distribution pattern of GluA subunits in postsynaptic specializations are indicative of a spatial compartmentalization of AMPA subunits in mature calyx‐principal neuron synapses that may support the temporally precise transmission required for sound localization in the auditory brainstem. J. Comp. Neurol. 518:163–174, 2010. © 2009 Wiley‐Liss, Inc.     

The impact of violence exposure on aggressive behavior through social information processing in adolescents

The purpose of this study was to determine whether exposure to violence (EV) in several contexts predicts aggressive behavior through social information processing (SIP) in adolescents. Six hundred and fifty adolescents between the ages of 12 and 17 participated in a 3-wave longitudinal study. The participants completed measures of proactive and reactive aggression at all waves, SIP measures at Time 1 and Time 2, and violence exposure at Time 1. It was expected that SIP would mediate the predictive relationship between EV and aggressive behavior. We found that total Time 1 EV predicted Time 3 reactive aggression. The influence of EV on proactive aggression was direct. Slight differences emerged, however, for victimization and witnessing violence. Witnessing was associated with reactive aggression via both hostile attribution and response selection, whereas victimization predicted reactive aggression via hostile attribution only. Results also suggested that the types of exposure that are most relevant for the development of aggressive behavior are community and school violence. Finally, male adolescents experienced more EV than female adolescents in all contexts except in the home. The findings indicate that intervention in social-cognitive mechanisms is important to reduce aggressive behavior in adolescents who have been exposed to violence.