ABSTRACT
The hypothesis that emotions and mental processes are interlinked can be traced back to antiquity. However, the scientific basis of the mechanisms underlying these processes have only recently been uncovered, largely due to the research of Hans Seyle and his collaborators.! These investigators showed that the hypothalamus and the pituitary gland playa crucial role in controlling the release of stress hormones, particularly the glucocorticoids, which not only assist the body in adapting to external and internal stressors but also in modulating immune function. Subsequently, it was shown that the immunotransmitters, the cytokines, and related secretory products from immune cells can communicate with the endocrine and central nervous systems to modulate their functions. 2 It is now generally recognized that the endocrine-immune systems and the brain are functionally linked to provide a co-ordinated response to external and internal stressors. This network is also linked to the central and peripheral sympathetic systems thereby providing a mechanism whereby the nervous system can directly affect the activity of the immune system by activating adrenoceptors that are located on immune cells. Psychoneuroimmunology has now developed into a specialist discipline for the study of the immune-endocrine-neurotransmitterbehavioral network.3,4
Over the past 40 years, evidence has accumulated on the nature of the interactions between the central neurotransmitters and the immune system. The immune system is autoregulated in that most immune cells distinguish normal cells that belong to the body (self) from foreign (non-self) cells so that mounting
an immune response against foreign cells does not require a major contribution from the brain. However, it is now evident that the brain plays a major role in modulating the function of the immune system and, conversely, the immune system plays a major role in the symptoms of patients suffering from major psychiatric disorders such as depression, schizophrenia, and anxiety disorders.5,6 Thus despite the widely held view that the immune system is primarily an autoregulated system concerned with protection of the body against infectious diseases, it is now evident that there is constant 'cross-talk' between the immuneendocrine and neurotransmitter systems.
