Yesenia Castillo Ocampo, María Colón ¹, Anixa Hernández ¹, Pablo Lopez ², and James T. Porter ¹

1 Department of Basic Sciences, Ponce Research Institute, Ponce Health Sciences University, Ponce

2 Department of HIV, Ponce Research Institute, Ponce Health Sciences University, Ponce

Our laboratory recently found an increase of GluN1 subunit expression at ventral hippocampus (vHPC)-toinfralimbic cortex (IL) synapses after auditory fear conditioning (AFC) suggesting that AFC increases the number of NMDA receptors at this synapse. In addition to changes in the number of NMDA receptors, synaptic transmission can also be altered by changes in the expression of GluN2 subunits. GluN2B has larger single-channel conductance and slower decay kinetics which alters the basal state of synapses and affects the induction of synaptic plasticity. Since increases in GluN2B expression contributes to various forms of synaptic plasticity and memory formation, we hypothesized that the expression of GluN2B would increase after AFC. Ventral hippocampal synapses were labeled with channelrhodopsin-EYFP in male and female rats. On the first day, animals were exposed to AFC with paired tones and foot shocks or pseudoconditioning with unpaired tones and shocks (PSEUDO). The next day animals were exposed to two tones to measure fear recall. Then animals were sacrificed and synaptosomes were isolated from IL and GluN2B was labeled with fluorescent antibody.Then, we used FACS to identify double-labeled (EYFP+/GluN2B+) synaptosomes which represent presynaptic vHPC inputs and postsynaptic, membranebound GluN2B. We found increased GluN2B expression on vHPC-to-IL synapses in the males exposed to AFC compared to the PSEUDO group. In contrast, the female AFC and PSEUDO groups expressed similar levels of GluN2B on the vHPC-to-IL synapses. In conclusion, the data suggest that AFC induces sexdependent changes in the expression of GluN2B subunit on vHPC-to-IL with increased GluN2B expression in the males. These changes in NMDA synaptic communication may contribute to altered fear expression after an aversive event.

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