GABAergic regulation of Locus coeruleus activity in necdin-deficient mice, an animal model of Prader-Willi syndrome.

BACKGROUND: Prader-Willi syndrome (PWS) is a neurodevelopmental disorder caused by loss of paternally expressed genes on chromosome 15q11-13, including NDN, which encodes necdin. Necdin deficiency has been linked to impaired visuospatial memory, social recognition, and stress regulation-features also seen in PWS. Previous work showed that necdin-deficient (Ndn + m/-p) mice exhibit reduced activity of noradrenergic neurons in the locus coeruleus (LC), a nucleus essential for arousal and stress responses. However, the mechanisms underlying LC hypoactivity remain unclear. Because GABAergic signaling is critical for LC excitability, this study examined the role of GABA(A) ​and GABA(B) ​receptor-mediated inhibition in Ndn + m/-p mice. METHODS: Electrophysiological recordings from brainstem slices of wild-type (WT) and Ndn + m/-p mice were used to measure spontaneous firing rates (SFRs) of LC noradrenergic neurons. The effects of bicuculline (GABA(A)​ antagonist) and CGP54626 (GABA(B)​ antagonist) were tested. Whole-cell patch-clamp recordings assessed receptor-mediated currents. Western blotting quantified receptor subunit expression in peri-LC tissue. Immunocytochemistry and ELISA examined GABA(B)​ receptor expression and GABA release in cultured astrocytes. RESULTS: LC-NE neurons in Ndn + m/-p mice exhibited significantly reduced baseline SFR compared with WT. Bicuculline did not alter firing in either genotype, whereas CGP54626 significantly increased SFR in WT but not in Ndn + m/-p neurons, indicating impaired GABA(B) receptor-mediated tonic inhibition. Whole-cell patch-clamp experiments confirmed intact GABA(A) receptor-mediated inward currents in both genotypes, while no GABA(B) receptor-mediated phasic currents were detected. Western blot analysis revealed comparable expression of GABA(A) receptor α2 subunit and GABA(B)R1 in peri-LC tissue between WT and Ndn + m/-p mice, suggesting functional rather than expression-level deficits. GFAP-positive cell density in the LC region was unchanged in vivo; however, in astrocyte cultures, Ndn + m/-p astrocytes exhibited greater proliferation by DIV 19 and consistently secreted higher levels of GABA, with significant elevations at later culture stages. CONCLUSION: Necdin deficiency selectively disrupts GABA(B) receptor-mediated tonic inhibition of LC-NE neurons while preserving GABA(A) receptor function. Elevated astrocytic proliferation and GABA release may further enhance ambient inhibition, contributing to LC hypoactivity and the neurobehavioral phenotypes of PWS. These findings identify GABA(B) receptor dysfunction and astrocytic dysregulation as potential mechanistic targets for therapeutic intervention in PWS.