Self-administration of drugs observed in ants

Briana Crilley
Science & Tech Correspondent

Recent studies have revealed similarities between invertebrate and mammalian responses to commonly-abused drugs. However, only mammals have been known to display behaviors of self-administration absent of a natural reward—until now.
A research team at The University has discovered the first invertebrate model: ants, specifically Florida carpenter ants.

Lead researchers Brian Entler, Timothy Cannon, Ph.D. and Marc Seid, Ph.D. aimed to demonstrate that self-administration of drugs was not limited to mammals. To do so, they experimented with introducing Florida carpenter ants to varying concentrations of morphine to determine the behavioral and neural outcomes.

Ants were first fed with a sucrose solution absent of morphine. Over the course of six days, the solution’s morphine concentration increased as the sucrose concentration decreased. The final solution contained pure morphine.

During the drug introduction stage, the ants’ interest in the sucrose solution declined as the morphine became more potent. However, when presented with pure morphine, interest escalated. Furthermore, when given the option of a sucrose solution or pure morphine, the latter was selected at large. When non-drugged ants were presented with the same option, greater interest was observed for sucrose as opposed to morphine.

When Entler, Cannon and Seid examined the neural responses, elevated levels of the neurotransmitter dopamine were found in the drugged ants. This is a key finding, as dopamine is known for stimulating reward-seeking behavior.

When asked why Florida carpenter ants were used as the experimental subject and what implications this study provides, Seid responded, “Rats are often used as experimental subjects for experiments, however they are not as social as ants. Ants have a specific social order and are interdependent on one another. I wanted to observe how addiction affects or breaks this social order. Because humans are also social and interdependent, the findings could potentially be analgous to the disruption of social order amongst humans.”

The findings of this study demonstrate ants to be the first invertebrate model of drug self-administration, revealing that such behavior is not limited to mammals, a truly novel discovery.

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