3 and a fraction mayor may not respond to treatment. On the behavioral
level, animal research shows that a variety of experimental conditions
can induce de- pression. The same is true in the field of treatment,
where pharmacologically highly different drugs can equally alleviate
depression in animals and hu- mans. The question as to whether this is
due to a heterogeneity of depressive subjects based on different
pathogenetic mechanisms is open to discussion. We can look for common
features of all possible causal factors in the hope of finding a single
basic mechanism. Many divergent findings may also be ex- plained as
peripheral changes of a highly complicated dynamic system. In the field
of psychopharmacology, a circular reasoning has become evident in the
sense that originally the clinical antidepressive response was founded
on empirical grounds only. In a second step, an attempt was made to
characterize some clinically active compounds pharmacologically, and in
a third, further compounds were developed based on aspects of the
pharmaco- logical profiles. Moreover, the post hoc development of a
pharmacological screening method has the serious disadvantage of
delaying breakthroughs into new fields.