Some animal models of chronically administered
nicotine show a desensitization of central nicotine receptors
and in some cases, an overall decrease in dopamine
release (Kirch et al. 1987; Wonnacott et al. 1990).
Conversely other animal studies have shown that chronic
nicotine administration may demonstrate an increase in
dopamine, or alternatively show no change in dopamine
activity (Lohr & Flynn 1992). In their human study of 265
outpatients with schizophrenia, Ziedonis et al. (1994)
found that heavy smokers had the most positive symptoms
and a significantly lower number of negative symptoms.