Smoking and mental health - NCSCT

Neurobiological and behavioural mechanisms linking smoking and mental disorders 3
Additional twin and family studies should be pursued first to determine the
extent to which shared genetic liability contributes to the association.
3.4.2 Evidence from animal studies
In experimental animals, nicotine is reported to alleviate cognitive dysfunction,
and it has been suggested that patients with schizophrenia may find this property
of the drug particularly beneficial. 117,118 There is consistent evidence from
animal studies that nicotine and tobacco smoking enhance pre-pulse inhibition,
a form of sensorimotor gating, and attenuates the impairment in this measure
observed in patients with schizophrenia. 119,120 Nicotine normalises
schizophrenia-like deficits in sensorimotor gating induced by isolation rearing or
the administration of amphetamine. 121 Impaired sensory gating has been linked
to a reduction in the density of the α 7
subtype of the neuronal nicotinic receptor
in the hippocampus, and with genetically linked polymorphisms in this
receptor; 122,123 a recent postmortem study has shown that smoking selectively
increases the expression and density of these receptors in the hippocampus of
patients with schizophrenia. 110 Thus, the available data suggest that nicotine
evokes this beneficial effect by both stimulating the receptors and enhancing
their expression in the brains of patients with schizophrenia. Other studies in
mice have shown that nicotine can reverse sensorimotor deficits evoked by the
administration of a glutamate receptor antagonist, but that this response to
nicotine is not observed in all strains of mice tested. 124 These data are consistent
with the hypothesis that people who smoke may use nicotine as a form of selfmedication
but that its efficacy in this regard may depend on the interactions
between nicotinic and glutamate receptors within the brain, which are genetically
determined.
3.4.3 Evidence from human studies
Wing and colleagues 125 investigated cognitive performance variable among people
with schizophrenia who both do and do not smoke. They found that non-smokers
performed the poorest on measures of sustained attention, processing speed and
response inhibition. Two experimental studies tested the hypothesis that nicotine
can improve cognitive functioning in people with schizophrenia. 118,126 In a study
by Depatie and colleagues, 126 nicotine patches improved the ability of participants
to engage in tasks requiring sustained attention relative to placebo patches,
findings that are consistent with research showing that people with schizophrenia
have a diminished capacity to filter out irrelevant perceptual features of their
environment, and that nicotine, through its action on inhibitory
neurotransmission in the hippocampus, can correct this impairment. 116,127 The
possibility that the beneficial effects of nicotine were related to the reversal of
© Royal College of Physicians 2013 47