RT Journal Article
SR Electronic
T1 Mu Opioid Receptor (Oprm1) Copy Number Influences Nucleus Accumbens Microcircuitry and Reciprocal Social Behaviors
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP JN-RM-2440-20
DO 10.1523/JNEUROSCI.2440-20.2021
A1 Carlee Toddes
A1 Emilia M. Lefevre
A1 Dieter D. Brandner
A1 Lauryn Zugschwert
A1 Patrick E. Rothwell
YR 2021
UL http://www.jneurosci.org/content/early/2021/07/22/JNEUROSCI.2440-20.2021.abstract
AB The mu opioid receptor regulates reward derived from both drug use and natural experiences, including social interaction, through actions in the nucleus accumbens. Here, we studied nucleus accumbens microcircuitry and social behavior in male and female mice with heterozygous genetic knockout of the mu opioid receptor (Oprm1+/-). This genetic condition models the partial reduction of mu opioid receptor signaling reported in several neuropsychiatric disorders. We first analyzed inhibitory synapses in the nucleus accumbens, using methods that differentiate between medium spiny neurons (MSNs) expressing the D1 or D2 dopamine receptor. Inhibitory synaptic transmission was increased in D2-MSNs of male mutants, but not female mutants, while the expression of gephyrin mRNA and density of inhibitory synaptic puncta at the cell body of D2-MSNs was increased in mutants of both sexes. Some of these changes were more robust in Oprm1+/- mutants than Oprm1-/- mutants, demonstrating that partial reductions of mu opioid signaling can have large effects. At the behavioral level, social conditioned place preference and reciprocal social interaction were diminished in Oprm1+/- and Oprm1-/- mutants of both sexes. Interaction with Oprm1 mutants also altered the social behavior of wild-type test partners. We corroborated this latter result using a social preference task, in which wild-type mice preferred interactions with another typical mouse over Oprm1 mutants. Surprisingly, Oprm1-/- mice preferred interactions with other Oprm1-/- mutants, even though these interactions did not produce a conditioned place preference. Our results support a role for partial dysregulation of mu opioid signaling in social deficits associated with neuropsychiatric conditions.SIGNIFICANCE STATEMENTActivation of the mu opioid receptor plays a key role in the expression of normal social behaviors. In this study, we examined brain function and social behavior of female and male mice, with either partial or complete genetic deletion of mu opioid receptor expression. We observed abnormal social behavior following both genetic manipulations, as well as changes in the structure and function of synaptic input to a specific population of neurons in the nucleus accumbens, which is an important brain region for social behavior. Synaptic changes were most robust when mu opioid receptor expression was only partially lost, indicating that small reductions in mu opioid receptor signaling can have a large impact on brain function and behavior.