STRESS, COMPORTEMENT ET MALADIE

For those who have attempted to attach some importance to the problem, the role played by psychological factors in disease usually is reduced to a doctrinal choice between psychoanalytic connotations and a mechanist theory based on the biology of stress. The boundaries of this choice have enormously evolved during these last years and the results of the psychobiologic approach allow us to leave this bipolar quarrel aside. The notion of stress invariably suggests the idea of a common final pathway through which environmental aggressions influence the psychological equilibrium and visceral function. This notion is obsolete. Our organism has specific defence mechanisms according to the nature of the aggression. Each of these systems relies on the close relationship existing between visceral reactions and behaviour. They differ, however, by their trigger mechanisms and the somatic and psychic modalities of expression. The exteroceptive defence system is the best known. It is activated by any external aggression susceptible of endangering the animal's (including man) physical or mental being. The behaviour pattern which arises from this reaction depends on the species, but varies according to the possibilities of prevision and control of the aggression. The same is true for their hormonal and autonomous components. In the interoceptive defence system, it is essentially the gastrointestinal components related to acquired gustative aversion that have been studied. Poisoning due to ingestion of spoiled food provokes an aversion to the aliment responsible, based on its organoleptic characteristics. The mechanisms that intervene differ according to whether the aliment can be expelled by vomiting or by acceleration of intestinal transit. The immunoceptive defence system corresponds to the reactions engaged in the fight against infection. The energy spent on the production of fever can be covered only if all behaviour patterns which are not directly related to thermoregulation stop. The association between fever and modified behaviour patterns is due to the neurogenic action of endogenous pyrogens, through unidentified mechanism. Each of these defence systems functions independently and without reciprocate interference as studied in this setting. Abnormally intense or prolonged activation of one of these systems, however, can sensitize the causal neuronal elements. Sensitization can then provoke converging trigger mechanisms centered on the sensitized system through action by other defence systems. These interactions can play an important role in the pathophysioslogical mechanisms responsible for neurogenic disorders such as the irritable bowel syndrome.