Social environment affects synaptic structure in the glomerulus of the accessory olfactory bulb of the hamster

The accessory olfactory bulb (AOB) is the primary center of the vomeronasal chemosensory system. The effects of differential rearing on the numerical density and size of synapse as well as neuronal size were examined in the AOB of adult hamster. At 30 days from birth, male littermates were assigned to one of three experimental conditions. (1) the IC (isolated condition), where a male animal was housed alone, (2) the NC (neighbor condition), where one male was separated from two females by wire shields, and (3) the SC (social condition), where two males and two females were housed together. After 2 months of differential rearing, the AOBs of male littermates from each experimental set were prepared for morphological examination. The lengths of synaptic contact zones and the density of synapses in the glomeruli of the AOB as well as the area of somata of mitral/tufted cells were measured with an image analyzer. The synaptic contact zone was longer in the SC compared with both the IC and the NC while there was no difference in the synaptic density among the three groups. The somal area of mitral/tufted cells was larger in both the SC and the NC compared with the IC. These results indicate that the exposure to different rearing conditions induces differential morphological changes in both synapses and somata in the AOB of adult hamster.