Differential Responses to Drugs and Sweet Tastes

Overview

Young adults who exhibit "bipolar phenotype" (BPP), defined as occasional episodes of mood elevation and heightened activity, are at risk for several psychiatric disorders, including problem use of drugs and alcohol. Mood elevation has been linked to higher alcohol consumption and alcohol use disorders. Individuals with BPP show elevated lifetime prevalence of alcohol use disorders (between 39%-61%), figures that exceed those reported in both major depression and schizophrenia. Recently, the investigators demonstrated in a controlled laboratory study that individuals with BPP (but not meeting criteria for full Bipolar I Disorder), report dampened responses to a single dose of alcohol, compared to placebo. In the current study, the investigators seek to extend these findings to determine if young adults reporting BPP, based on a questionnaire, will exhibit reduced responses to other rewarding stimuli, such as d-amphetamine and sweet tastes. The investigators hypothesize that the BPP individuals will exhibit dampened subjective responses to stimulant and sweet taste rewards compared to healthy controls.

This study will extend the understanding of risk factors for drug or alcohol misuse, or other reward-related behaviors. The investigators previously showed that individuals who report occasional feelings of high energy and excitability experience less effect from a single dose of alcohol, compared to people who have not experienced these effects. Now the investigators wish to determine if this dampened response also occurs with other rewards, namely feelings of wellbeing after a dose of amphetamine, or liking of a sweet solution. Individuals who exhibit the BPP (i.e., periods of excitability) also are more likely to develop alcohol problems, substance misuse, and weight gain and obesity. Therefore, the investigators will test the working hypothesis that young adults who report having these experiences, based on a questionnaire measure (i.e., BPP individuals) will show dampened subjective responses to both single oral doses of amphetamine or sweet palatable tastes. The investigators will also obtain objective measures (e.g. Respiratory Sinus Arrhythmia and heart rate) to amphetamine and sweet taste, to establish whether the dampened subjective response extends to physiological indices as well. This study will extend the previous literature regarding the blunted effects of alcohol in BPP individuals and will suggest possible mechanisms that promote broader addictive behaviors in individuals with mood disturbance. Importantly, the investigators are proposing to test individuals at a relatively young age, 18-19 years. This is important to identify a risk factor, that is thought to pre-date use of drugs. In older participants, it would be difficult to separate the role of the pre-existing trait from the effect of habitual drug or alcohol use that escalates markedly after age 20.