Probes for SST

Basolateral amygdala (BLA) principal cells are capable of driving and antagonizing behaviors of opposing valence. BLA neurons project to the central amygdala (CeA), which also participates in negative and positive behaviors. However, the CeA has primarily been studied as the site for negative behaviors, and the causal role for CeA circuits underlying appetitive behaviors is poorly understood. Here, we identify several genetically distinct populations of CeA neurons that mediate appetitive behaviors and dissect the BLA-to-CeA circuit for appetitive behaviors. Protein phosphatase 1 regulatory subunit 1B+ BLA pyramidal neurons to dopamine receptor 1+ CeA neurons define a pathway for promoting appetitive behaviors, while R-spondin 2+ BLA pyramidal neurons to dopamine receptor 2+ CeA neurons define a pathway for suppressing appetitive behaviors. These data reveal genetically defined neural circuits in the amygdala that promote and suppress appetitive behaviors analogous to the direct and indirect pathways of the basal ganglia.

Although neuropeptide Y (NPY) has potent anxiolytic actions within the basolateral amygdala (BLA), selective activation of BLA NPY Y2receptors (Y2R) acutely increases anxiety by an unknown mechanism. Using ex vivo male rat brain slice electrophysiology, we show that the selective Y2R agonist, [ahx5-24]NPY, reduced the frequency of GABAA-mediated miniature inhibitory post synaptic currents (mIPSC) in BLA principal neurons (PN). [ahx5-24]NPY also reduced tonic activation of GABAB receptors (GABABR), which increased PN excitability through inhibition of a tonic, inwardly-rectifying potassium current (KIR ). Surprisingly, Y2R-sensitive GABABR currents were action potential-independent, persisting after treatment with tetrodotoxin. Additionally, the Ca2+-dependent, slow afterhyperpolarizing K+ current (IsAHP ) was enhanced in roughly half of the Y2R-sensitive PNs, possibly from enhanced Ca2+ influx, permitted by reduced GABABR tone. In male and female mice expressing tdTomato in Y2R-expressing cells (tdT-Y2R mice), immunohistochemistry revealed that BLA somatostatin interneurons (SST IN) express Y2Rs, as do a significant subset of BLA PNs. In tdT-Y2R mice, [ahx5-24]NPY increased excitability and suppressed the KIR in nearly all BLA PNs independent of tdT-Y2R fluorescence, consistent with presynaptic Y2Rs on SST INs mediating the above effects. However, only tdT-Y2R-expressing PNs responded to [ahx5-24]NPY with an enhancement of the IsAHP Ultimately, increased PN excitability via acute Y2R activation likely correlates with enhanced BLA output, consistent with reported Y2R-mediated anxiogenesis. Furthermore, we demonstrate: 1) a novel mechanism whereby activity-independent GABA release can powerfully dampen BLA neuronal excitability via postsynaptic GABABRs, and 2) that this tonic inhibition can be interrupted by neuromodulation, here by NPY via Y2Rs.SIGNIFICANCE STATEMENTWithin the basolateral amygdala (BLA), neuropeptide Y (NPY) is potently anxiolytic. However, selective activation of NPY2-receptors (Y2R) increases anxiety by an unknown mechanism. We show that activation of BLA Y2Rs decreases tonic GABA release onto BLA principal neurons (PN), probably from Y2R-expressing somatostatin interneurons some of which co-express NPY. This increases PN excitability by reducing GABAB receptor (GABABR)-mediated activation of G-protein-coupled, inwardly-rectifying K+(GIRK) currents. Tonic, Y2R- sensitive GABABR currents unexpectedly persisted in the absence of action potential firing, revealing, to our knowledge, the first report of substantial, activity-independent GABABR activation. Ultimately, we provide a plausible explanation for Y2R-mediated anxiogenesis in vivo and describe a novel and modulatable means of damping neuronal excitability.