Social stress and corticosterone regionally upregulate limbic N-methyl- d-aspartatereceptor (NR) subunit type NR 2A and NR 2B in the lizard anolis carolinensis

Abstract

Social aggression in the lizard Anolis carolinensis produces dominant and subordinate relationships while elevating corticosterone levels and monoaminergic transmitter activity in hippocampus (medial and mediodorsal cortex). Adaptive social behavior for dominant and subordinate male A. carolinensis is learned during aggressive interaction and therefore was hypothesized to involve hippocampus and regulation of N-methyl- d-aspartate (NMDA) receptors. To test the effects of social stress and corticosterone on NMDA receptor subunits (NR), male lizards were either paired or given two injections of corticosterone 1 day apart. Paired males were allowed to form dominant–subordinate relationships and were killed 1 day later. Groups included isolated controls, dominant males, subordinate males and males injected with corticosterone. Brains were processed for glutamate receptor subunit immunohistochemistry and fluorescence was analyzed by image analysis for NR 2A and NR 2B in the small and large cell divisions of the medial and mediodorsal cortex. In the small granule cell division there were no significant differences in NR 2A or NR 2B immunoreactivity among all groups. In contrast, there was a significant upregulation of NR 2A and NR 2B subunits in the large pyramidal cell division in all three experimental groups as compared with controls. The results revealed significantly increased NR 2A and NR 2B subunits in behaving animals, whereas animals simply injected with corticosterone showed less of an effect, although they were significantly increased over control. Upregulation of NR 2 subunits occurs during stressful social interactions and is likely to be regulated in part by glucocorticoids. The data also suggest that learning social roles during stressful aggressive interactions may involve NMDA receptor-mediated mechanisms.