Probes for INS

The bed nucleus of the stria terminalis (BNST) is a critical node involved in stress and reward-related behaviors. Relaxin family peptide receptor 3 (RXFP3) signaling in the BNST has been implicated in stress-induced alcohol seeking behavior. However, the neurochemical phenotype and connectivity of BNST RXFP3-expressing (RXFP3+) cells have yet to be elucidated. We interrogated the molecular signature and electrophysiological properties of BNST RXFP3+ neurons using a RXFP3-Cre reporter mouse line. BNST RXFP3+ cells are circumscribed to the dorsal BNST (dBNST) and are neurochemically heterogeneous, comprising a mix of inhibitory and excitatory neurons. Immunohistochemistry revealed that ~48% of BNST RXFP3+ neurons are GABAergic, and a quarter of these co-express the calcium-binding protein, calbindin. A subset of BNST RXFP3+ cells (~41%) co-express CaMKIIα, suggesting this subpopulation of BNST RXFP3+ neurons are excitatory. Corroborating this, RNAscope™ revealed that ~35% of BNST RXFP3+ cells express vVGluT2 mRNA, indicating a subpopulation of RXFP3+ neurons are glutamatergic. RXFP3+ neurons show direct hyperpolarization to bath application of a selective RXFP3 agonist, RXFP3-A2, while around 50% of cells were depolarised by exogenous corticotrophin releasing factor. In behaviorally naive mice the majority of RXFP3+ neurons were Type II cells exhibiting Ih and T type calcium mediated currents. However, chronic swim stress caused persistent plasticity, decreasing the proportion of neurons that express these channels. These studies are the first to characterize the BNST RXFP3 system in mouse and lay the foundation for future functional studies appraising the role of the murine BNST RXFP3 system in more complex behaviors.

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.

KCNQ2/3 channels, ubiquitously expressed neuronal potassium channels, have emerged as indispensable regulators of brain network activity. Despite their critical role in brain homeostasis, the mechanisms by which KCNQ2/3 dysfunction lead to hypersychrony are not fully known. Here, we show that deletion of KCNQ2/3 channels changed PV+ interneurons', but not SST+ interneurons', firing properties. We also find that deletion of either KCNQ2/3 or KCNQ2 channels from PV+ interneurons led to elevated homeostatic potentiation of fast excitatory transmission in pyramidal neurons. Pvalb-Kcnq2 null-mice showed increased seizure susceptibility, suggesting that decreases in interneuron KCNQ2/3 activity remodels excitatory networks, providing a new function for these channels.

Brain regions that regulate fluid satiation are not well characterized, yet are essential for understanding fluid homeostasis. We found that oxytocin-receptor-expressing neurons in the parabrachial nucleus of mice (OxtrPBN neurons) are key regulators of fluid satiation. Chemogenetic activation of OxtrPBN neurons robustly suppressed noncaloric fluid intake, but did not decrease food intake after fasting or salt intake following salt depletion; inactivation increased saline intake after dehydration and hypertonic saline injection. Under physiological conditions, OxtrPBN neurons were activated by fluid satiation and hypertonic saline injection. OxtrPBN neurons were directly innervated by oxytocin neurons in the paraventricular hypothalamus (OxtPVH neurons), which mildly attenuated fluid intake. Activation of neurons in the nucleus of the solitary tract substantially suppressed fluid intake and activated OxtrPBN neurons. Our results suggest that OxtrPBN neurons act as a key node in the fluid satiation neurocircuitry, which acts to decrease water and/or saline intake to prevent or attenuate hypervolemia and hypernatremia.

Primary afferents are known to be inhibited by kappa opioid receptor (KOR) signaling. However, the specific types of somatosensory neurons that express KOR remain unclear. Here, using a newly developed KOR-cre knockin allele, viral tracing, single-cell RT-PCR, and ex vivo recordings, we show that KOR is expressed in several populations of primary afferents: a subset of peptidergic sensory neurons, as well as low-threshold mechanoreceptors that form lanceolate or circumferential endings around hair follicles. We find that KOR acts centrally to inhibit excitatory neurotransmission from KOR-cre afferents in laminae I and III, and this effect is likely due to KOR-mediated inhibition of Ca2+ influx, which we observed in sensory neurons from both mouse and human. In the periphery, KOR signaling inhibits neurogenic inflammation and nociceptor sensitization by inflammatory mediators. Finally, peripherally restricted KOR agonists selectively reduce pain and itch behaviors, as well as mechanical hypersensitivity associated with a surgical incision. These experiments provide a rationale for the use of peripherally restricted KOR agonists for therapeutic treatment.

A wealth of data has elucidated the mechanisms by which sensory inputs are encoded in the neocortex, but how these processes are regulated by the behavioral relevance of sensory information is less understood. Here, we focus on neocortical layer 1 (L1), a key location for processing of such top-down information. Using Neuron-Derived Neurotrophic Factor(NDNF) as a selective marker of L1 interneurons (INs) and in vivo 2-photon calcium imaging, electrophysiology, viral tracing, optogenetics, and associative memory, we find that L1 NDNF-INs mediate a prolonged form of inhibition in distal pyramidal neuron dendrites that correlates with the strength of the memory trace. Conversely, inhibition from Martinotti cells remains unchanged after conditioning but in turn tightly controls sensory responses in NDNF-INs. These results define a genetically addressable form of dendritic inhibition that is highly experience dependent and indicate that in addition to disinhibition, salient stimuli are encoded at elevated levels of distal dendritic inhibition.