Biology Reference
In-Depth Information
did not fit into the Selye's paradigm concerning stress. However, these findings can on
the other hand be considered as an important step in suggesting that the brain may also
influence the immune system.
11.3 Extending the Pioneer's Findings and the Discovery of
Neural-Immune Connection
In recent decades, the mentioned pioneer findings have been greatly extended by a
range of refined techniques and explorations concerning how psychosocial stimuli
and challenges can decisively contribute to cardiovascular, metabolic and immuno-
logical disturbances and disorders. Of particular importance are James P Henry's fas-
cinating studies of mice colonies along 1960-90s
[22]
. By imposing various kinds of
prolonged psychosocial challenges, he could induce either defence or defeat reac-
tions in the animals, showing how sustained psychosocial stress could elicit neuro-
hormonal response patterns which, in the long run, could induce disorders closely
mimicking man's primary hypertension, and the metabolic syndrome. He further
showed how genetics, sex and earlier experience could decisively influence the out-
come
[23,24]
. In addition, induced defeat reaction led in some cases to an increase of
an endemic type of mammillary tumours. However, his brief report of these obser-
vations was refused by leading cancer journal, because at this time, it was thought
to be impossible that a mental state could have anything to do with local tumour
development.
Later, other studies opened the door for such mechanisms, and in 1975 Ader and
Cohen published a paper introducing the term psychoneuroimmunology
[25]
. In
1981, Felten and co-workers discovered a network of nerves which could influence
cells of the immune system. Thus, nerves were found in the thymus and spleen termi-
nating near clusters of lymphocytes, macrophages and mast cells, all of which help
control immune function. This discovery provided one of the first indications of how
neuro-immune interactions occur
[26]
.
Henry's approach to explore the effects of psychosocial stimuli in group-living
animals has also been most successfully applied to primates where, particularly, the
studies of Kaplan and co-workers in cynomolgus monkeys have shown how prolonged
induction of defeat reactions could induce coronary atherosclerotic changes, even when
diet was kept unchanged
[27]
. As previously mentioned, the findings that psychosocial
stress can affect the development of the metabolic syndrome and atherosclerosis and
even cause myocardial infarction have later been confirmed in humans
[2,5,6,28]
.
In general, the fields of psychoneuroendocrinology and psychoneuroimmunology
have expanded tremendously and a vast number of studies add to present knowledge
of how the central nervous system can influence the function of peripheral organ sys-
tems, including the immune system
[29]
. The development of brain imaging methods
has also increased the possibility of studying brain function in awake human sub-
jects, including how the brain is activated during acute mental stress and how psy-
chosocial stress is perceived and processed
[30]
.
