Differential expression of glutamatergic receptor subunits in the hippocampus in carioca high- and low-conditioned freezing rats.

Anxiety is an emotional state that affects the quality of human life. Several neurotransmitters are involved in the regulation of anxiety, including glutamate. The major actions of glutamate are mediated by N-methyl-d-aspartate receptors (NMDARs) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). The present study performed a behavioral and neurochemical analysis of Carioca High-conditioned Freezing (CHF) and Carioca Low-conditioned Freezing (CLF) rats compared with control rats. We evaluated thermal nociception, anxiety-like behavior, depressive-like behavior, spatial memory, habituation memory, and the content and localization of different glutamatergic receptor subunits and postsynaptic density-95 (PSD-95), a postsynaptic protein. The CHF group exhibited an anxious-like phenotype, impairments in habituation and spatial memory, and a depressive-like phenotype compared with the control group. In the ventral hippocampus, an increase in the PSD-95, GluN1 and GluA1 subunits and a decrease in the GluN2A subunit of glutamatergic receptors. The CLF group exhibited a less anxious-like phenotype, hyperlocomotion and habituation impairments. Also, CLF animals, presented, in the ventral hippocampus, an increase in the PSD-95, GluN1 and GluA2 subunits and a decrease in the GluN2B subunit. These results suggest that the differential composition of NMDAR and AMPAR subunits may be related to the modulation of different phenotypes in CHF and CLF rats, which may help identify new targets for therapeutic interventions for anxiety disorders and other comorbidities.