Much evidence indicates that experiences in adolescence can alter the development of social behaviour. We previously demonstrated that male rats exposed to social instability stress in adolescence (SS; 1 h isolation and return to an unfamiliar cagemate daily from postnatal day [PND] 30-45) had reduced social interaction, impaired social recognition, reduced sexual performance, and increased aggression in competition for food reward compared with non-stressed control (CTL) rats. Here, we investigated whether SS affects stellate neuron morphology using the Golgi-Cox method and several markers of synaptic plasticity using western blotting in the medial amygdala (MeA) and lateral septum (LS), sites involved in social behaviour. On PND 46, 24 h after the last stress exposure, SS rats had increased dendritic arborisation, a greater number of dendrite terminals, and a higher average dendrite branch order in the anterodorsal MeA compared with CTL rats. SS rats had reduced dendritic arborization and a reduced total length of dendrite matter in the anteroventral MeA and a reduced number of dendrite terminals in the posterodorsal MeA compared with CTL rats. Moreover, SS rats had a reduced number of dendritic spines in the dorsal LS compared with CTL rats. SS rats had less synaptophysin in the MeA and more CaMKII in the LS than did CTL rats, and did not differ in spinophilin, PSD95, or glucocorticoid receptor protein expression in the MeA and LS. We discuss how changes in neural structure and in markers of synaptic plasticity the MeA and LS of adolescent SS rats compared with CTL rats may underlie their differences in social behaviour.
Keywords: Adolescence; Dendritic arborisation; Lateral septum; Medial amygdala; Social instability; Synaptic plasticity.