RESUMO
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.
RESUMO
Enrichment studies with rodents have demonstrated that cage enhancements can improve animal welfare and performance on common behavioral measures, but few studies have compared more than one type of enrichment or controlled for confounds, and some have revealed undesirable effects including increased aggression. We compared effects on male (n=51) and female (n=52) BALB/cJ mice of three common additions to a standard home cage: shelter, shelter+running wheel, and shelter+novel objects. Mice in all conditions lived in standard sized cages with 3-4 mice per cage. Males evidenced significant condition effects. Shelter increased longevity and maintained low levels of aggression. Adding a running wheel increased aggression over shelter alone, changed behavior in the elevated plus (EP) and open field (OF), and maintained the improved longevity seen in all shelter conditions. Novel objects impacted behavioral measures compared to the standard condition. An Igloo shelter without running wheel creates a very different home cage environment than the same shelter with the running wheel attached. Shelter, with positive impact on animal welfare, minimal effects on some common behavioral measures, and some positive effects on test variance, warrants consideration for routine inclusion with group-housed BALB/cJ males.
