Gamma-Aminobutyric Acidergic Projections From the Dorsal Raphe to the Nucleus Accumbens Are Regulated by Neuromedin U

Abstract

Introduction Neuromedin U (NMU) is a neuropeptide enriched in the nucleus accumbens shell (NAcSh), a brain region associated with reward. While NMU and its receptor, NMU Receptor 2 (NMUR2), have been studied for its ability to regulate food reward, NMU has not been studied in the context of drugs of abuse (e.g. cocaine). Furthermore, the neuroanatomical pathways which express NMUR2 and its ultrastructural localization are unknown. Methods Immunohistochemistry was used to determine the synaptic localization of NMUR2 in the NAcSh and characterize which neurons express this receptor (n=17). The functional outcome of NMU on NMUR2 was examined using microdialysis (n=16). The behavioral effects of NMU microinjection directly to the NAcSh was investigated using cocaine-evoked locomotion (n=93). The specific effects of NMUR2 knockdown on cocaine-evoked locomotion was evaluated using viral-mediated RNAi (n=40). Results NMUR2 is localized to presynaptic GABAergic nerve terminals in the NAcSh originating from the dorsal raphe nucleus. Furthermore, NMU microinjection to the NAcSh decreased local GABA concentrations. Next, we evaluated the effects of NMU microinjection on behavioral sensitization to cocaine. When repeatedly administered throughout the sensitization regimen, NMU attenuated cocaine-evoked hyperactivity. Additionally, shRNA-mediated knockdown of presynaptic NMUR2 in the NAcSh using a retrograde viral vector potentiated cocaine sensitization. Conclusions Together, these data reveal that NMUR2 modulates a novel GABAergic pathway from the dorsal raphe nucleus to the NAcSh to influence behavioral responses to cocaine.

Regulation of motivation for food by neuromedin U in the paraventricular nucleus and the dorsal raphe nucleus

“…Brains were extracted, cryoprotected and sliced into sections as previously described (9). Sections were analyzed for Fos expression as previously described (31). …”

“…For viral tracing of signaling pathways, guide cannulae were implanted based on Kasper et al 2016 (31). PVN coordinates were adjusted for a 10° outside angle and set at (A/P −0.18, M/L +0.15, D/V −0.82) from bregma; DRN coordinates were adjusted for a 30° outside angle, with internal cannula inserted at (A/P −0.71, M/L +0.32, D/V +0.83) from bregma.…”

“…Immunohistochemistry for NMUR2 was performed as previously published (9, 31) and validation of the specificity of the NMUR2 antibody was also previously published (9, 31). Briefly, sections of brain were washed 3X in 1X PBS, 5 minutes/wash, to remove residual sodium azide, and incubated in 1% SDS for 5 minutes for antigen unmasking.…”

Brain region‐specific neuromedin U signalling regulates alcohol‐related behaviours and food intake in rodents

“…Alcohol‐mediated behaviours are mandated via alcohol's ability to activate the nucleus accumbens (NAc) shell (for review). In addition, this area contains NMU, the expression of NMUR2 has been identified on GABA terminals in NAc, and the NMUR2 protein has been detected within NAc . We therefore hypothesise that activation of NMUR2 in NAc shell attenuates acute, as well as chronic effects of alcohol in rodents.…”

“…It is well‐known for its ability to reduce food intake and decrease the motivation to consume foods (for review). NMU receptors 2 (NMUR2) located in the arcuate nucleus, paraventricular nucleus, and dorsal raphe nucleus are key players for NMU's anorexigenic properties . An additional study has established that NMU infusion into the third ventricle attenuates both the acute effects of alcohol in mice and alcohol intake in a chronic rat model of alcohol use .…”