Opioid Receptors Modulate Inhibition within the Prefrontal Cortex Through Dissociable Cellular and Molecular Mechanisms

Abstract

Aberrant signaling within cortical inhibitory microcircuits has been identified as a common signature of neuropsychiatric disorders. Interneuron (IN) activity is precisely regulated by neuromodulatory systems that evoke widespread changes in synaptic transmission and principal cell output. Cortical interneurons express high levels of opioid receptors, positioning opioid signaling as a critical regulator of inhibitory transmission. However, we lack a complete understanding of how classical opioid receptor systems regulate prefrontal cortex (PFC) microcircuitry. Here, we combine whole-cell patch-clamp electrophysiology, optogenetics, and viral tools to provide an extensive characterization of how the Mu opioid receptor (MOR), Delta opioid receptor (DOR), and Kappa opioid receptor (KOR) regulate inhibitory transmission in male and female mice. We show that across these receptor systems, DOR activation is more effective at suppressing spontaneous inhibitory transmission in layer 2/3 of the prelimbic PFC, while MOR causes a greater acute suppression of electrically-evoked GABA release, and KOR plays a minor role in inhibitory transmission. Cell type-specific optogenetics revealed that MOR and DOR differentially regulate inhibitory transmission from parvalbumin, somatostatin, cholecystokinin, and vasoactive intestinal peptide-expressing INs. Finally, we demonstrate that DOR regulates inhibitory transmission through simultaneous pre- and postsynaptic modifications to IN physiology, whereas MOR function varies between somato-dendritic or presynaptic signaling depending on cell type.

Significance Statement The endogenous opioid system regulates behaviors that rely on prefrontal cortex (PFC) function. Previous studies have described opioid receptor expression within cortical GABAergic interneurons, but a detailed understanding of how the Mu (MOR), Delta (DOR), and Kappa opioid receptor (KOR) regulate different interneuron subtypes and microcircuits has not been reported. We use whole-cell patch-clamp electrophysiology, genetically engineered mice, and optogenetics to assess MOR, DOR, and KOR regulation of PFC inhibitory transmission, demonstrating that MOR and DOR inhibition of interneurons display qualitative and quantitative variation across GABAergic circuits within mouse prelimbic PFC.