Overall Introduction
Substance use disorders (SUD) are widely prevalent and pose devastating health, financial, and societal costs. The incidence of SU increases across adolescence, making this sensitive developmental period one of both heightened risk and heightened opportunity for prevention and intervention. However, to develop effective interventions, we need to identify novel and modifiable risk factors and mechanisms for SUD. Circadian rhythm and sleep disturbances have strong ties to SU risk, and their effects on intermediary markers of SU risk in adolescence—reward and inhibitory control systems—provides a plausible mechanistic substrate.
The conceptual model for CARRS is that adolescent development is associated with enhanced reward function relative to cognitive control, phase delay in endogenous circadian rhythms, and lower homeostatic sleep drive. Environmental and social factors interact with these developmental processes, often resulting in late sleep timing, short sleep duration, and circadian misalignment—each of which is associated with increased substance use in teens and young adults. The CARRS Center will determine how these factors interact to increase vulnerability for substance use, what mechanisms underlie these associations, and begin to develop interventions to lower this risk.
Project 1: Circadian rhythms and homeostatic sleep regulation during adolescence: Implications for reward, cognitive control, and substance use risk
Project 1 (P1) will recruit healthy subjects aged 13-15 and utilize a laboratory based constant routine paradigm to rigorously characterize endogenous circadian rhythms and homeostatic sleep drive in individual subjects by controlling for the influences of physical activity, posture, meals, and light levels. We will also examine the individual and combined effects of sleep and circadian rhythm disruptions that teens experience on a daily basis, and perform a brief, in laboratory sleep restriction. This will allow us to determine how both environmental and genetic factors associated with sleep and circadian rhythm phenotypes correlate with measures of brain activity, reward and cognitive control, and in combination with P2, on the development of substance use (SU), to better define the important and direct associations proposed in the CARRS conceptual model.
Project 2: Circadian rhythms, sleep, and substance use risk during adolescence: Observational, experimental, and longitudinal studies
Project 2 (P2) will test the hypothesis that individual differences in sleep and circadian characteristics (i.e. late versus early sleep) during adolescence are associated with behavioral, and neural indicators of reward function and cognitive control, which in turn are associated with increased risk for SU. Further, P2 tests an experimental intervention that manipulates sleep and circadian rhythms (properly aligning them with school time) using timed light and darkness and a behavioral sleep intervention in teens with late or disrupted rhythms to directly examine its impact on reward function, providing an early assessment of the potential for chronotherapeutic intervention.
Project 3: Molecular rhythms and substance abuse vulnerability in adolescents
Project 3 (P3) will provide translational studies in both human subjects and rodent models to help determine the mechanistic details of how circadian rhythm and sleep disruptions alter reward circuitry. We will measure molecular rhythms in peripheral samples from human subjects recruited through P1/2 and combine this data with the thorough rhythm, sleep, cognition, and reward data collected in those projects. We will also determine how molecular rhythm measures in rodents correlate with sleep and circadian phenotypes, as well as behavioral and electrophysiological data collected in P4/5. We will also use rodents to provide detailed gene and protein expression in brain regions of interest in response to specific manipulations of sleep and circadian rhythms. Finally, we are testing potential pharmacological interventions on molecular rhythms in human and rodent cells which will inform future clinical studies aimed at shifting or stabilizing rhythms.
Project 4: Determining the role of adolescent sleep and circadian factors on risk for substance use in a rat model
Project 4 (P4) aims to determine the effects individual differences in chronotype, circadian misalignment, and acute and chronic sleep disruption on behavioral indices of addiction risk and corticolimbic neural activity in adolescent rats. We will determine how sleep and circadian phenotypes relate to impulsivity and execute function on the 5-choice serial reaction time task (5-CSRTT) and if rats with extreme chronotypes (early vs. late) exhibit differences in nicotine or THC self-administration. Moreover, we will determine how manipulations of circadian rhythms and sleep alter behavior in these tasks and we will test how corticolimbic activity is altered during behavior using in vivo fiber photometry. Results of these studies will be integrated with human neuroimaging data obtained in P1 and 2, and with the molecular and ex vivo electrophysiological results obtained in P3 and 5. Importantly, these studies help establish the direct and causal link between sleep/circadian abnormalities and substance use.
Project 5: Regulation of nucleus accumbens neurons by sleep and circadian rhythm
Project 5 (P5) will focus on rodent models to determine the cellular and synaptic mechanisms within the cortico-limbic circuit through which natural variations in phenotypes as well as sleep and circadian disruptions alter reward processing. We will focus on the nucleus accumbens (NAc) which is a reward-processing “hub” in the ventral striatum sensitive to both sleep and circadian disruptions. Accordingly, P5 will test the hypothesis that sleep and circadian rhythm target aspects of NAc synaptic transmission and neural modulation to regulate reward-motivated behaviors. We will determine whether naturally occurring “early” and “late” chronotypes are associated with different diurnal variation of AMPAR transmission in NAc neurons. Next, we will determine whether circadian disruptions without changes in sleep alter the diurnal variation of membrane excitability and/or postsynaptic AMPAR levels in the NAc MSNs. Finally, we will determine the effects of acute and chronic sleep restrictions on adenosine and cholinergic transmission in the NAc, and the behavioral consequences in natural or drug self-administration. The expected outcome of P5 will integrate and extend findings from behavioral (P4) and molecular genetic (P3) studies, which together will provide mechanistic insights to inform and further develop human studies (P1&2).