Probes for SST

Forming long-term memories is crucial for adaptive behavior and survival in changing environments. The molecular consolidation processes which underlie the formation of these long-term memories are dependent on protein synthesis in excitatory and SST-expressing neurons. A centrally important, parallel process to this involves the removal of the memory constraint quinone reductase 2 (QR2), which has been recently shown to enhance memory consolidation for novel experiences in the cortex and hippocampus, via redox modulation. However, it is unknown within which cell type in the cortex removal of QR2 occurs, nor how this affects neuronal function. Here, we use novel taste learning in the mouse anterior insular cortex (aIC) to show that similarly to mRNA translation, QR2 removal occurs in excitatory and SST-expressing neurons. Interestingly, both novel taste and QR2 inhibition reduce excitability specifically within SST, but not excitatory neurons. Furthermore, reducing QR2 expression in SST, but not in PV or excitatory neurons, is sufficient to enhance taste memory. Thus, QR2 mediated intrinsic property changes of SST interneurons in the aIC is a central removable factor to allow novel taste memory formation. This previously unknown involvement of QR2 and SST interneurons in resetting aIC activity hours following learning, describes a molecular mechanism to define cell circuits for novel information. Therefore, the QR2 pathway in SST interneurons provides a fresh new avenue by which to tackle age-related cognitive deficits, while shedding new light onto the functional machinations of long-term memory formation for novel information.

We elucidated neural mechanisms underlying sighing. Photostimulation of parafacial (pF) neuromedin B ( NMB) or gastrin releasing peptide (GRP) or preBötC NMBR or GRPR neurons elicited ectopic sighs with latency inversely related to time from the preceding endogenous sigh. Of particular note, ectopic sighs could be produced without involvement of these peptides or their receptors in preBötC. Moreover, chemogenetic or optogenetic activation of preBötC SST neurons induced sighing, even in the presence of NMBR or GRPR antagonists. We propose that an increase in the excitability of preBötC NMBR or GRPR neurons not requiring activation of their peptide receptors activates partially overlapping pathways to generate sighs, and that preBötC SST neurons are a downstream element in the sigh generation circuit that converts normal breaths into sighs.

Activity in the dorsal vagal complex (DVC) is essential to gastric motility regulation. We and others have previously shown that this activity is greatly influenced by local GABAergic signaling primarily due to somatostatin-expressing GABAergic neurons (SST). To further understand the network dynamics associated with gastric motility control in the DVC, we focused on another neuron prominently distributed in this complex, neuropeptide-Y (NPY) neurons. However, the effect of these neurons on gastric motility remains unknown. Here we investigate the anatomical and functional characteristics of the NPY neurons in the nucleus tractus solitarius (NTS) and their interactions with SST neurons using transgenic mice of both sexes. We sought to determine if NPY neurons influence the activity of gastric projecting neurons, synaptically interact with SST neurons, and affect end-organ function. Our results using combined neuroanatomy and optogenetic in vitro and in vivo show that NPY neurons: are part of the gastric vagal circuit as they are trans-synaptically labeled by a viral tracer from the gastric antrum; are primarily excitatory as optogenetic activation of these neurons evoke EPSCs in gastric-antrum projecting neurons; are functionally coupled to each other and reciprocally connected to SST neurons, whose stimulation has a potent inhibitory effect on the action potential firing of the NPY neurons; and affect gastric tone and motility as reflected by their robust optogenetic response in vivo. These findings indicate that interacting NPY and SST neurons are integral to the network that controls vagal transmission to the stomach.Significance StatementThe brainstem neurons in the dorsal nuclear complex are essential for regulating vagus nerve activity that affects the stomach via tone and motility. Two distinct non-overlapping populations of predominantly excitatory neuropeptide Y (NPY) neurons and predominantly inhibitory somatostatin (SST) neurons form reciprocal connections with each other in the nucleus of the tractus solitarius (NTS) and with premotor neurons in the dorsal motor nucleus of the vagus to control gastric mechanics. Light activation and inhibition of NTS. NPY neurons increased and decreased gastric motility, respectively, while both activation and inhibition of NTS SST neurons enhanced gastric motility.

The hypothalamus plays a key role in coordinating fundamental body functions. Despite recent progress in single-cell technologies, a unified catalog and molecular characterization of the heterogeneous cell types and, specifically, neuronal subtypes in this brain region are still lacking. Here, we present an integrated reference atlas, 'HypoMap,' of the murine hypothalamus, consisting of 384,925 cells, with the ability to incorporate new additional experiments. We validate HypoMap by comparing data collected from Smart-Seq+Fluidigm C1 and bulk RNA sequencing of selected neuronal cell types with different degrees of cellular heterogeneity. Finally, via HypoMap, we identify classes of neurons expressing glucagon-like peptide-1 receptor (Glp1r) and prepronociceptin (Pnoc), and validate them using single-molecule in situ hybridization. Collectively, HypoMap provides a unified framework for the systematic functional annotation of murine hypothalamic cell types, and it can serve as an important platform to unravel the functional organization of hypothalamic neurocircuits and to identify druggable targets for treating metabolic disorders.

Background The central amygdala (CeA) is a bilateral hub of pain and emotional processing with well-established functional lateralization. We reported that optogenetic manipulation of neural activity in the left and right CeA has opposing effects on bladder pain. Methods To determine the influence of calcitonin gene-related peptide (CGRP) signaling from the parabrachial nucleus (PBN) on this diametrically opposed lateralization, we administered CGRP and evaluated the activity of CeA neurons in acute brain slices as well as the behavioral signs of bladder pain in the mouse. Results We found that CGRP increased firing in both the right and left CeA neurons. Furthermore, we found that CGRP administration in the right CeA increased behavioral signs of bladder pain and decreased bladder pain-like behavior when administered in the left CeA. Conclusions These studies reveal a parabrachial-to-amygdala circuit driven by opposing actions of CGRP that determines hemispheric lateralization of visceral pain.

Exposure to irregular lighting schedules leads to deficits in affective behaviors. The retino-recipient perihabenular nucleus (PHb) of the dorsal thalamus has been shown to mediate these effects in mice. However, the mechanisms of how light information is processed within the PHb remains unknown. Here, we show that the PHb contains a distinct cluster of GABAergic neurons that receive direct retinal input. These neurons are part of a larger inhibitory network composed of the thalamic reticular nucleus and zona incerta, known to modulate thalamocortical communication. In addition, PHbGABA neurons locally modulate excitatory-relay neurons, which project to limbic centers. Chronic exposure to irregular light-dark cycles alters photo-responsiveness and synaptic output of PHbGABA neurons, disrupting daily oscillations of genes associated with inhibitory and excitatory PHb signaling. Consequently, selective and chronic PHbGABA manipulation results in mood alterations that mimic those caused by irregular light exposure. Together, light-mediated disruption of PHb inhibitory networks underlies mood deficits.