Nature vs Nurture in Rats

A discussion on Nature vs Nurture in rats and the roll of epigenetics

A cool, calm and collected rat is likely to have been licked as a pup by its mother. Via this simple process of licking - a rat mother can effect the expression of its pups genes, which in turn changes the behaviour of its offspring as an adult. Not all mothers are caring though and non nutured pups grow up to be anxious and risk avoiding.

The rat behaviour is not a result of genetics but of epigenetics. Pups who are removed from their non licking mothers will, like their adopted brothers and sisters, acquire this confident behaviour and visa versa.

We are used to thinking of the genetic code as a strict set of rules inherited from parents via sperm and eggs however it is more malleable than first perceived. Above the DNA sequence is the epignome - chemical tags (eg. Methyl groups.) which attach to the DNA turning on and off genes.

Unlike the physical genes - these tags can quickly change as the result of the environment. The epignome allows genetic adaptation without having to wait for slow mutation or natural selection. Essential the DNA acts like a shopping list and the epigenome pulls out what is required creating very different out comes from the same starting points.

The return of the nature nurture debate - are we/rats at the mercy of our genes or the environment? The epigenome allows the parental rat to pass on information after fertilisation. The licking behaviour of the mother Rat essentially tells her pups something about the world they will grow up in. Her behaviour actually programs the pups' DNA in a way that will make them more likely to succeed.

But why not lick? Anxiousness is a result of raised levels of corticol - in the short term is causes the freeing of stored energy preparing for flight or fight but in the long term causes heart disease, diabetes, depression and low social status - even in rats. In a highly nutrient rich and low risk level environment this is definitely a bad thing. However when food is scarce and danger high - The anxious, guarded behaviour of the low-nurtured rat is an advantage. The low nurtured rat is more likely to keep a low profile and respond quickly to stress. In the same environment, a relaxed rat might be a little too relaxed. It may be more likely to let down its guard and be eaten by a predator or take the food from a rat trap like the Goodnature traps.

The differences in behaviour are due to a change in a glucocortocoid receptor (GR) gene during development. At birth, the epigenome tags cause the gene to be inactive. If a rat mother is attentive towards her pups, the pups’ GR gene gradually becomes free of its epigentic tags. This allows access to the gene for the cell's gene 'processing machinery' and the gene is thus more active - the more GR produced.

During stressful situations cortisol is produced resulting in the flight or fight physiological response. Cortisol also travels to an area of the brain called the hippocampus, where it binds to GRs. When enough is bound, the hippocampus sends out signals that turn off the stress circuit, shutting down both the Fight or Flight response and cortisol production. Nurtured pups with higher levels of GR are better at detecting cortisol, and they recover from stress more quickly.Those that were not given attention, and do not express the GR gene, respond poorly to stress and stay in a high level of alertness - ie rat trap aware!