P50 amplitude reduction: A nicotinic receptor-mediated deficit in first-degree relatives of schizophrenia patients

Rationale: Impaired P50 gating is a putative index of genetically mediated nicotinic dysfunction in schizophrenia. However, assessment is confounded, in patients, by differential effects of smoking, symptoms, and treatment. Objectives: This double-blind placebo-controlled study was designed to tease apart the relationships among P50, acute and chronic nicotine exposure, and familial risk. Methods and results: Experiment 1: To assess the putative effects of genetic vulnerability without other confounds, 14 unaffected relatives of schizophrenia patients and 15 controls, all nonsmokers, were tested with/without 7 mg transdermal nicotine. Family members had reduced P50 amplitude to an initial auditory stimulus, but normal P50 gating. Nicotine decreased P50 amplitude in controls; family members had a mixed response: eight decreased and six increased P50 amplitude with nicotine. Experiment 2: To assess chronic nicotine use and short-term withdrawal as a model of nicotinic dysfunction, 26 healthy smokers (14 abstinent for >12 h) received 21 mg transdermal nicotine. Chronic nicotine use, alone, did not alter P50 amplitude or gating. Short-term withdrawal resulted in decreased P50 amplitude, with no effect on P50 gating. Nicotine increased P50 amplitude in abstinent smokers and decreased it in nonabstinent smokers. Conclusions: Familial vulnerability to schizophrenia reduces P50 amplitude. Nicotinic modulation of this deficit mirrors the effect of nicotine during smoking abstinence and suggests an "inverted-U" relationship between P50 amplitude and endogenous nicotinic activity. P50 amplitude may, therefore, be a sensitive marker of nicotinic dysfunction in individuals with familial risk for schizophrenia, which is mediated through mechanisms (e.g., α₄β₂ receptors) that are distinct from those (e.g., α₇ receptors) that mediate P50 gating.