ABSTRACT

Aggression and emotionality in two lines of a phenylethanolamine-n-ethyl-transferase (PNMT) overexpressing transgenic mouse model

Dorte Bratbo Sørensen1, Pernille Fraas Johnsen1, Bo Martin Bibby2, Antje Böttner3 & Axel Kornerup Hansen1

1Centre for Bioethics and Risk Assessment, The Royal Veterinary and Agricultural University of Copenhagen, Division of Laboratory Animal Science and Welfare, Ridebanevej 9, 1870 Frederiksberg C, Denmark; 2The Royal Veterinary and Agricultural University of Copenhagen, Department of Mathematics and Physics, Thorvaldsensvej 40, 1870 Frederiksberg C, Denmark & 3Centre for Bioethics and Risk Assessment, Department of Pediatrics, University of Leipzig

PNMT - phenylethanolamin-N-ethyl-transferase - is an enzyme that catalyses the formation of adrenaline from noradrenaline. Transgenic mice with an over-expression of PNMT resulting in a hypersecretion of epinephrine has been developed to study the relation between the sympatho-adrenergic system and obesity, and preliminary observations in two lines showed an extremely high level of offensive aggression compared to their background strain C57BL/6J. Moreover, many studies suggest a relationship between PNMT activity and aggression.
An increase in aggression within groups may seriously reduce the welfare of the animals. To evaluate possibly differences in the expression of the transgene and the influence of PNMT on aggression and emotionality in these two lines of PNMT transgenic mice, single-sex male and female groups were established, consisting of either four wildtypes, four Tg1815 or four Tg1819, each group consisting of littermates. Moreover, single-sex mixed groups consisting of two transgenic mice and two wildtypes were established.
Aggression was assessed measuring number of fights in home cages and open field behaviour was evaluated. Weights of the adrenal glands were measured.
Almost no fights were observed in the female groups. In male groups, Tg1815 showed a significantly higher level of fighting than Tg1819, controls and mixed male groups (p<0.0001). Housing transgenic lines in mixed groups with wildtypes seems to decrease the level of aggression in particularly Tg1815, implying that the individual composition of the group has a great impact on the level of aggression within the group. In the open field, Tg1819 were significantly less active than wildtypes (p<0.0001), but no significant differences were found neither between wildtypes and Tg1815 (p=0.11) nor between the two transgenic lines (p=0.08). Tg1819 showed significantly longer latency to leave the inner circle that wildtypes (p<0.0001) and Tg1815 (p<0.05). Whether the groups were mixed wildtypes and transgenic mice or pure single-line transgenic mice or pure control groups (i.e. the social environment) did not influence locomotion and latency in the open field.
This study clearly demonstrates significant differences in aggression and emotionality, emphasizing the need for phenotypic characterisation of different transgenic lines.
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