Rats (Rattus norvegicus)

Carmen & Carolina

They came to us as the result of a scientific experiment of a collegue of us. Mag. Vivienne Bromout wrote her PhD thesis about the change of hormones in humans during the raising of animals. There have already been data of the famous "grey goose mothers " started by Konrad Lorenz. Now, Vivienne asked if the change in hormone levels shouldn't be even more significant if a person raises an animal which is evolutionary closer related to us than a bird, so she chose rats to be the right animal for that experiment. Every person taking part in that experiment had to raise a baby rat by hand and take urine probes of him/herself during a 30 days period to measure the amount of hormones and calculate hormone curves.

We took part in the experiment because we were interested in the development of baby rats. Here you can read a short diary:

Day 1/ 15.04.2002: In the morning we receive our baby rats. They are just 9 days old, their eyes are still closed and they just have very little, cosy hair on their bodies. To keep them warm, we carry them in little bags close to our bodies. They have to be fed with cat baby milk. They are able to crawl around, shake their bodies and scratch themselves. Whenever they find something, they start sucking and give tiny little squieks. Most of the time they sleep and dream a lot, so they are moving nearly all the time during sleeping. In the beginning, we feed them every 3 to 4 hours. That is not too easy because they don't drink from a squirt, but only suck the milk from our hands.	Carmen at her first day with us (at an age of 9 days)
A hand full of rat...	Day 2/ 16. 04. 2002:Their eyes are still closed, but they sense light and dark, since they immediately crawl into the direction of a light source. The fine, tiny hairs are easy to see on their bodies but they are still very short and thin.
Day 3/ 17. 04. 2002: The little ears, which were closely attached to the body, start to unfold, the fur becomes more dense and the little claws develop. The little paws look more rat-like, the vibrisses (tactile hairs) are quite long already. Sometimes they already show the first rat-like behaviour, like cleaning theirs heads. Since they are still blind, it is to assume that this behaviour is hereditary and doesn't need to be learnt.	They like sleeping in our warm hands...
Under the heating lamp	Day 4/ 18. 04. 2002: They yawn for the first time. On the tail, the first fine hair appears. The eyes seem as if they should open any moment now.
Day 5/ 19. 04. 2002: Carefully, the little eyes open and for the first time, they gaze into the world curiously. First, it's just a needle - head sized little black spot, then they rest of the eyes is opening quite quickly. The shape of their head starts to get more rat­like. They are able to lift their bodies, standing on their hind legs to sniff around.	The eyes are opening !
They gain weight quite quickly...	Day 8/ 22.04.2002:They start cleaning themselves (although yet still not very well­ coordinated). When sucking milk, they very often swallow the wrong way which indicates that we should start with non liquid food (it's quite pitiful to watch - they strech and bend through their back and we can't help them; massaging the belly doesn't really help). The little teeth are already easy to feel and see. They don't want to stay in their bags, actually they would prefer to explore the world around them all the day.
Day 9/ 23.04. 2002: They start drinking milk from a plate and chewing on cornflakes. For that reason, we offer them banana milk, something they immediately love a lot. Unfortunately they lean into the milk with their whole body when drinking, so we have two banana-smelling baby rats :-). We don't manage to clean all their fur, so they start looking very tousled.	Banana milk ! !
Big banana belly..	Day 10/ 24. 04. 2002: Meanwhile they also eat banana pieces. They like banana a lot and eat so much, that as an result their little bellies hang to the ground and they hardly can move any more. Playing and running around is still quite exhausting: sometimes they just fall down sleeping in the middle of their playtime !
Day 15/ 29. 04. 2002:The first fights among the two rat sisters ! As soon as they are in their box together, you can only see a little squieking ball rolling around :-). Now, the hair is soft and fluffy, they don't have the thick hair yet, which protects the adults from cold and wet. That's why they still need to be warmed. We slowly start to wean them from milk. They do already eat from a little plate, but it's still milk (with banana or apples). They should start eating solid food to train their teeth.	Food !
First day in the cage....	Day 18/ 01. 05. 2002: The box is getting too small for them so we move them into a cage. They like it a lot, running around and exploring every corner. There, we also offer them corn food for the first time, which they also like. Unfortunately it turns out that they can break out of the cage, sliding through between the bars. Luckily, they don't show any intention of breaking out, seems they like their cage. It would't be necessary to warm them any more, but during nighttime, we still offer them the heating lamp so they can decide themselves.
Day 20/ 03. 05. 2002: First little "rat drama": Carolina's teeth grow the wrong way, she can't use them as she should and so they are growing too long. After a visit at the vet's we know that this will be a life-long problem, the teeth have to be cut every two weeks. Poor little rat ! Meanwhile, there is an "outdoor-time" every day - an adventure they love a lot. Chairs, sofas and other pieces of furniture are still too big to climb up or down but once they have, after trying for quite a time, found a way they from then on take it without hesitating. There are already big differences in character visible between the two of them: Carmen is less anxious than Carolina and Carolina likes hugging and snuggling a lot more than Carmen.	Adventurous baby rat !
Something new - playing with hay :-)	Day 30/ 13. 05. 2002: Now, the experiment is officially done. Of course, Carmen and Carolina are staying with us - so the fun is just starting ! We just could'nt give them away - we absolutely fell in love with the two of them !

Results of the "Rat-Raising Experiment:": Vivien analyzed our collected urine-samples by an enzyme immuno assay: Estrogen: this steroid hormone is responsible for the female cycle as well as for the secondary sexual attributes (estrogens do also occur in men) Progesterone: the luteale hormone, a gestagen, is produced in the ovary and the placenta and influences the uterus Testosterone: the male sexual hormone is produced in the Leydig cells (females do produce testosterone in small amounts in the ovary); it is mainly responsible for the male sexual attributes (like beard, body features etc.) Cortisole: this Glucocorticoide is produced in the cortex of the suprarenal gland and is segregated during stress phases.

Vivien found the highest peaks in the rising of the stress level - especially during the first days, when the rat babies still had to be fed around the clock - by a rise of cortisole. Normally, coristole levels rise and fall together with wake-sleep-rhytms. This rhytm was strongly disturbed by the feeding times during night. Later, as the rats were already eating by themselves, the cortisole levels were still quite high - of course, because it is quite a task to be responsible for such a little baby rat ! The sex hormones estrogen and progesterone also showed - compared to the preliminary control phase - higher values during the "rat raising time". I myself felt my hormones getting crazy - similar to how it must be for a young mother during the first weeks with her new-born baby. One more interesting thing was that as Florian and I both raised one baby rat each, our hormone curves were strongly synchronized - so there also seems to be a synchronization of hormones between couples. Here are two of the curves Vivien calculated for the hormone results: Cortisole: see the strong incline at the beginning of the rat raising. As soon as the rats were independent, the cortisole level declined again - the stressy time was over ! Estrogen and progesterone: Progesterone levels changed a lot more during the rat raising time than during the control time. Estrogen didn't change due to a hormonal contraception method.

Carmen Carolina