As part of DugDug’s ongoing series on leading researchers in psychology, we have had the unique privilege of interviewing Diana Keith, a doctoral candidate at the Department of Psychology at Columbia University. Her recent paper, titled Time of day influences the voluntary intake and behavioral response to methamphetamine and food reward was published in the journal Pharmacology, Biochemistry, and Behavior.
Please tell us about your background and research interests.
My initial interests in drug abuse research were sparked when I worked for Dr. Deborah Frank at Boston University School of Medicine. Her work focused on understanding the effects of cocaine on infants and children who were exposed to the drug in utero. Largely because of Dr. Frank’s research, we now know that many of the claims made about “crack babies” were greatly exaggerated. Watching Dr. Frank systematically dispel drug myths inspired me to become a drug researcher. In an effort to gain more skills, I accepted a position at the Alcohol and Drug Abuse Research Center at McLean Hospital in Boston, where I worked on studies investigating the effects of progesterone, the main component of birth control, on the response to nicotine and cocaine. Then, I was accepted to the Ph.D. behavioral neuroscience program at Columbia University, where I’m conducting my dissertation research under the mentorship of Drs. Carl Hart (an expert on substance abuse) and Rae Silver (an expert on circadian rhythms). My work uses both animal and human models to understand the role of the circadian system on effects produced by methamphetamine, marijuana, and opiates.
What led you to this particular study?
A finding from one of our earlier studies intrigued me, which led me to pursue this line of research. In the study, methamphetamine users reported feeling intoxicated after taking a low dose of the drug at night but reported no intoxication when the same dose was taken during the day. This was the first time this has been seen in the study of human drug abuse, though the finding would not surprise most circadian rhythm experts. In fact, most prescriptions include instructions to take medications at a certain time of day because we know that 24 hr (or circadian) rhythms in hormones, proteins, and metabolism can influence how the medications work. However, there has been very little research on the effects of circadian rhythms on the response to abused drugs. Such circadian effects might be a useful tool to understand mechanisms that regulate the brain’s response to methamphetamine.
What were your findings?
Our data show that drug effects are influenced by the time of day. More specifically, we found that mice wanted methamphetamine more, ingested more, and were more hyperactive after taking the drug during the human equivalent of night. In other words, methamphetamine may produce one effect late in the evening and a different effect in the morning. We also found similar results with another reward, peanut butter- a high fat treat. The mice ate more when it was available at night.
How can we use these findings?
These are initial findings so it is difficult to speculate too far beyond them. Nonetheless, they will help shape deeper questions about the role of circadian rhythms on drug effects. One important question that we have is: are drug users are more vulnerable to drug overdose at night due to an increase in drug sensitivity? We hope to be able to shed light on this question with future research.
Our findings with peanut butter were also interesting. The results show similar circadian effects on the intake of high-fat foods and abused drugs. This leads to a number of questions about the similarity in the mechanisms influencing different types of rewards.
What do you plan to do next with this?
These were some of the first circadian experiments in animals in which voluntary intake of drugs and palatable foods were measured. In future work, we will test other voluntary intake conditions and further separate the effects of palatable food from those of methamphetamine. We will also examine the neural changes associated with drug anticipation.
In addition, the animal experiments are specifically designed to test, under laboratory-controlled conditions, the kinds of questions one would want to ask about human drug use. These findings will be used to design experiments with human drug users as research participants, where similar questions will be investigated.
Any advice for people getting into your field?
For undergraduates who are interested in studying drugs of abuse, I would recommend they carefully study both the animal and human literature on the effects of drugs. This would enhance their ability to have a comprehensive understanding of drug abuse and related issues.