Epsilon Archive for Student Projects

Abstract

Maternal behaviour is crucial for the development of the rat pups’ behaviour and stress
responses later in life. There are numerous studies evaluating the effects of the dams’
behaviours on the pups, but not many addressing what can be made for wellbeing of the rat
dams when breeding. Few studies have addressed the question of how the commonly used
rearing environment effects the dams’ behaviour and in the long run how it effect the rats
reared to become our research models. In this study, rats were therefore reared in two
different cage systems; one cage type with elevated top and enriched by a shelf and climbable
netting (RT) was compared to the type of cage most commonly used today, the makrolon type
IV cage (M IV). Dams were equipped with telemetrical devices to measure activity, blood
pressure and heart rate, and direct observations of their maternal behaviour were made. Urine
corticosterone/creatinine quote was measured and behavioural tests (defensive withdrawal
test, elevated plus maze test and open field with novel object) were performed in both dams
and pups. The dams in the RT cages showed more activity and a transient increase in blood
pressure, and a tendency towards less urine corticosterone levels. They also spent less time
licking/grooming and arched back nursing their young. The pups showed differences in urine
corticosterone levels as well as in the behavioural tests, where the RT pups had significantly
less corticosterone excretion, and showed less fearful and anxiety-like behaviours in the
behavioural tests. There were greater differences between the groups of female pups than
between the male ones, pointing to the female pups being more sensitive to improvements of
the environment. We have shown that the rat dams’ activity increases and stress decreases in
the RT enriched cage, and that the rat pups from the RT cages show less stress response, less
fearful and less anxiety-like behaviours even though the dams spend less time
licking/grooming and arched back nursing them. These findings support the argument that an
enriched optimised environment and voluntary maternal separation give mentally healthier
rats, possibly better as a model for mentally healthy humans.