anxiety disorders, panic disorder, obsessive-compulsive disorder, phobias, post-traumatic stress disorder

Stress, neglect and ill-treatment during childhood impair development, and even prenatal stress can impede the establishment and maintenance of neuronal networks in the emotional system - particularly in males. This was the conclusion reached by Professor Katharina Braun from the University of Magdeburg from a study on rats that she is presenting to the Forum of European Brain Researchers in Vienna.

2 day old Octodon degus pup

Stress, neglect and ill-treatment in childhood have lasting effects, resulting in serious and permanent deficits in language acquisition and personality development. Clinical studies have shown that these factors impair children's intellectual and social skills.

A research team led by Professor Katharina Braun at the Department of Zoology and Developmental Neurobiology at the University of Magdeburg in eastern Germany has been investigating the effects of these damaging factors on brain development and behaviour in laboratory rats and degus or brush-tail rats (Octodon degus), a species of rodent closely related to guinea pigs.

Degu infants are developmentally similar to human babies and grow up under family conditions closely resembling those of human infants, making these cute rodents a popular animal for scientific studies "When these animals are born they are at roughly the same stage of development as a human infant," Katharina Braun explains.

By contrast, the developmental stage reached by rat babies at birth is comparable with that of a human baby born prematurely. Moreover, unlike laboratory rats, degu infants are raised jointly by their father and mother and are extremely communicative, carrying on intensive "conversations" using whistling tones.

It appears as if the nerve cells 'remember' the stress the animal was subjected to in the wombThe researchers found that separation from their parents produced changes in the brain activity of the young animals. They discovered that in several regions of the brain, including the emotional centres (cingular cortex), the metabolism slows down. This led Braun to suspect that if this stress-induced reduction in brain activity was maintained over a long period, it might have a negative impact on the structural development of circuits in the brain.

In fact a further study revealed that even mild stress produces structural changes in a young animal's brain. Separating the young rodents from their parents for one hour a day or alternatively giving them a daily injection of salt solution produced different effects on the structure and connections between the nerve cells. Whereas those animals deprived of parental attention for short periods formed more synapses between the nerve cells than animals in the control group, those injected with salt solution formed fewer synapses "This clearly shows that the type of stress is important for the emotional centres in a child's brain," Braun says.

By contrast, animals raised without a father - and thus subjected to greater emotional deprivation, since their "single" mothers did not provide additional care to compensate for the absent father - formed fewer synapses than the control group. "This may indicate," Braun explains, "that more emotionally deprived animals form fewer synapses in the emotional centres of the brain. As a result the emotional development of these animals may be different." Stress coupled with physical discomfort - the prick of the injection - would then be expected to have similarly negative effects.

In fact, the increased growth of synapses in animals deprived of their parents for only short periods of time might even be positive. To find out whether this is the case, the researchers will need to do further studies. "For it is not only the quantity of the synapses but above all their quality in the network that determines later cognitive and emotional capacity," Braun says.

Stress, neglect and ill-treatment in childhood have lasting effects, resulting in serious and permanent deficits in language acquisition and personality development.The researchers also know from their studies of degus and laboratory rats that stress can have different effects at different stages of development. In laboratory rats, for example, there is a period during the first few days after birth when the infants do not produce stress hormones, because their body's stress system is not yet active. "These hormones also have an effect on the brain," Braun explains. If very young rats, whose stress system is still dormant, are separated from their mothers for short periods of time, this does not effect the development of nerve cells and their synapses. This only happens once the animals' stress system becomes active around 10 to 14 days after birth.

The most recent studies conducted by Katharina Braun's research team together with Israeli scientists at the University of Jerusalem have shown that even prenatal stress can influence brain development.

If mother rats are subjected to unpredictable and unavoidable stress during the last trimester of pregnancy their babies also suffer. These rat children are later more timid and more susceptible to depressive or schizophrenic disorders.

The effects of prenatal stress on infant laboratory rats can also be observed in the brain: the number of synapses in the cingular and orbito-frontal cortex - two regions of the brain concerned with emotions - is significantly lower. In addition, the nerve cells of young male rats - though not of females - in the emotional systems of the frontal lobe - the prefrontal cortex - form shorter dendritic arbours. Dendrites are the branched projections of nerve cells which receive information from other nerve cells via the synapses. "The extent to which the dendrites are developed is probably a measure of the brain's capacity to transmit information," Braun explains. The longer the dendrites and the more ramified they are, the greater the amount of information the nerve cells from which they project can receive and process.

The prefrontal cortex is an area of the brain that does not develop fully until long after birth. In humans, for example, the prefrontal cortex does not reach full maturity until about the age of 20, and in rats and other mammals it also develops late. The dendrites of the nerve cells in this area of the brain only begin to grow after birth. "It appears as if the nerve cells 'remember' the stress the animal was subjected to in the womb and, therefore, instead of developing a dendritic arbour with many branches, they grow only short stumps," Braun says. However, little research has been done on how this cell memory functions.

Braun K.
Emotional experience and the synaptic development of limbic circuits.
FENS Abstr., 2006; vol.3, A171.2, · [Abstract]