Hippocampal Volume and the Spectrum of Metabolites in Adult Gray Rats Rattus norvegicus Selected for Different Attitudes toward Humans and Exposed to Early Social Instability.

Previous magnetic resonance studies of the dorsal hippocampus in male rats selected for aggressive attitude toward humans revealed lower contents of γ-aminobutyric acid (GABA), N-acetylaspartate, and creatinine+phosphocreatinine (Cr+PCr), as well as a higher of phosphorylethanolamine content, as compared to males selected for tame behavior. The effect of early social instability on the hippocampal volume and spectrum of neurometabolites in the dorsal hippocampus was investigated in adult tame, aggressive, and unselected gray rats Rattus norvegicus. Experimental conditions of social instability included early weaning, subsequent housing of behaviorally matched males in pairs until the age of 3 months, and daily replacement of cagemates from days 19 to 25. In the control group, rat pups were weaned at the age of 30 days and then kept by 4–5 animals per cage until the age of 3 months. Control aggressive males were inferior to tame counterparts in hippocampal volumes, both absolute and normalized to individual brain volumes, while early social instability had no effect on these indices. In experimental groups, lower phosphorylethanolamine and higher alanine contents in the dorsal hippocampus, as compared to control animals, were detected in aggressive males only. This fact may be due to a lower level of stress response in these animals, as we observed previously. From the obtained results, it follows that aggressive rats are more sensitive to social instability conditions. Moreover, the early instability conditions and selection for aggressive behavior oppositely affect both phosphorylethanolamine metabolism and integral characteristics of the metabolic profile in the dorsal hippocampus. [ABSTRACT FROM AUTHOR]