Page 211 - Pagetit

NEUROSCIENCE OF PSYCHOACTIVE SUBSTANCE USE AND DEPENDENCE

The best clinical support for the self-medication hypothesis is provided
by evidence that:
— antidepressant treatment is more effective in reducing substance use
in users suffering from depression than in users who are not, suggesting
that antidepressant medication may replace the need for consumption
of psychoactive substances;
— atypical antipsychotic medications that are most effective against the
negative symptoms and cognitive deficits associated with schizo-
phrenia reduce substance use as though the need for self-medication
has been reduced;
—these studies emphasize the importance of treating comorbid psychiatric
illness, and show that this treatment can be efficacious in managing
substance dependence.
The preclinical and clinical investigations of the factors that may lead to the
high degree of comorbidity are likely to provide valuable information about
the neurobiology of schizophrenia and depression which in turn would lead
to the development of better treatments for these debilitating disorders. If
indeed patients with schizophrenia and depression self-medicate various
symptoms with psychoactive substances, then insights could be gained from
the patients’ patterns of substance use in terms of novel medications that can
be developed that may have beneficial effects for these disorders. Accordingly,
owing to the recent awareness of the comorbidity of substance dependence
with psychiatric disorders, preclinical animal studies have been initiated to
investigate the neurobiological substrates that may explain this comorbidity.
Future studies should continue to directly address the hypotheses of shared
neurobiological substrates using animal models of depression, schizophrenia
and substance dependence, based on the current understanding of the
neurobiology of these three psychiatric disorders. Generally, it would be
fruitful to design research programmes that would explicitly test, with similar
experimental approaches, hypotheses generated in the field of depression
and schizophrenia in animal models of substance dependence and vice versa.
Considering that all psychiatric disorders, including depression,
schizophrenia and substance dependence, involve primarily behavioural
symptoms that reflect underlying neurobiological abnormalities, progress
in understanding these diseases at any level of analysis will certainly involve
a multidisciplinary approach to research. Emphasis should be placed on both
clinical and preclinical studies in the study of specific behavioural dimensions
or psychological processes (e.g. specific symptoms) that are thought to be
affected by the disorder of interest (Geyer & Markou, 1995, 2002). Long-term
prospective studies that follow individuals from an early age would also be
very informative, though difficult in practice.
Another area that requires greater research attention is the role of gender
in the presence of comorbidity among people with substance use disorders.

190

Chapter_6 190 19.1.2004, 11:48