Conventional definitions of drug addiction are focused on characterizing the neurophysiological and behavioral responses of mammals. Although mammalian models have been invaluable in studying specific and complex aspects of addiction, invertebrate systems have proven advantageous in investigating how drugs of abuse corrupt the most basic motivational and neurochemical systems. It has recently been shown that invertebrates and mammals have remarkable similarities in their behavioral and neurochemical responses to drugs of abuse. However, until now only mammals have demonstrated drug seeking and self-administration without the concurrent presence of a natural reward, e.g. sucrose. Using a sucrose-fading paradigm, followed by a two-dish choice test, we establish ants as an invertebrate model of opioid addiction. The ant species Camponotus floridanus actively seeks and self-administers morphine even in the absence of caloric value or additional natural reward. Using HPLC equipped with electrochemical detection, the neurochemicals serotonin, octopamine and dopamine were identified and subsequently quantified, establishing the concurrent neurochemical response to the opioid morphine within the invertebrate brain. With this study, we demonstrate dopamine to be governing opioid addiction in the brains of ants. Thus, this study establishes ants as the first non-mammalian model of self-administration that is truly analogous to mammals.
The authors declare no competing or financial interests.
B.V.E. and M.A.S. were responsible for experimental design, methodology, analysis and manuscript preparation. J.T.C. was responsible for experimental design, analysis and drug oversight. B.V.E. ran all experiments with the help of undergraduate researchers.
This research was funded via internal grants from The University of Scranton.
Neurochemical data are available upon request via email.
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.140616.supplemental
- Received March 21, 2016.
- Accepted July 5, 2016.
- © 2016. Published by The Company of Biologists Ltd