Somatostatin neurons in prefrontal cortex initiate sleep-preparatory behavior and sleep via the preoptic and lateral hypothalamus.

The prefrontal cortex (PFC) enables mammals to respond to situations, including internal states, with appropriate actions. One such internal state could be 'tiredness'. Here, using activity tagging in the mouse PFC, we identified particularly excitable, fast-spiking, somatostatin-expressing, γ-aminobutyric acid (GABA) (PFCSst-GABA) cells that responded to sleep deprivation. These cells projected to the lateral preoptic (LPO) hypothalamus and the lateral hypothalamus (LH). Stimulating PFCSst-GABA terminals in the LPO hypothalamus caused sleep-preparatory behavior (nesting, elevated theta power and elevated temperature), and stimulating PFCSst-GABA terminals in the LH mimicked recovery sleep (non-rapid eye-movement sleep with higher delta power and lower body temperature). PFCSst-GABA terminals had enhanced activity during nesting and sleep, inducing inhibitory postsynaptic currents on diverse cells in the LPO hypothalamus and the LH. The PFC also might feature in deciding sleep location in the absence of excessive fatigue. These findings suggest that the PFC instructs the hypothalamus to ensure that optimal sleep takes place in a suitable place.

Dopamine agonists for the treatment of pituitary tumours: From ergot extracts to next generation therapies.

Dopamine agonists are a key tool in the therapeutic arsenal of endocrinologists worldwide. They exert their effects by binding to dopamine-2 (D2) receptors expressed by pituitary tumour cells to modulate hormonal secretion and tumour size. They are the established first-line treatment for prolactinomas which express high levels of D2 receptors. Growing data support their use as an adjuvant treatment option for other pituitary tumours including growth hormone, adrenocorticotrophic hormones, thyroid hormone secreting adenomas and nonfunctional pituitary tumours, all of which have been shown to express D2 receptors as well, albeit to varying extents. For those pituitary tumours inadequately treated by dopamine agonist alone, combined agonism of D2 and somatostatin receptors represent a new frontier in clinical development. Here we review the development and role of dopamine agonist for the treatment of prolactinomas, the literature supporting their adjuvant use for the treatment of all other pituitary tumours, and recent progress in the development of the next generation of chimeric compounds that target D2 and other receptor subtypes highly expressed on pituitary tumour cells.

Organization of Cortical and Thalamic Input to Inhibitory Neurons in Mouse Motor Cortex.

Intracortical inhibition in motor cortex (M1) regulates movement and motor learning. If cortical and thalamic inputs target different inhibitory cell types in different layers, then these afferents may play different roles in regulating M1 output. Using mice of both sexes, we quantified input to two main classes of M1 interneurons, parvalbumin+ (PV+) cells and somatostatin+ (SOM+) cells, using monosynaptic rabies tracing. We then compared anatomic and functional connectivity based on synaptic strength from sensory cortex and thalamus. Functionally, each input innervated M1 interneurons with a unique laminar profile. Different interneuron types were excited in a distinct, complementary manner, suggesting feedforward inhibition proceeds selectively via distinct circuits. Specifically, somatosensory cortex (S1) inputs primarily targeted PV+ neurons in upper layers (L2/3) but SOM+ neurons in middle layers (L5). Somatosensory thalamus [posterior nucleus (PO)] inputs targeted PV+ neurons in middle layers (L5). In contrast to sensory cortical areas, thalamic input to SOM+ neurons was equivalent to that of PV+ neurons. Thus, long-range excitatory inputs target inhibitory neurons in an area and a cell type-specific manner, which contrasts with input to neighboring pyramidal cells. In contrast to feedforward inhibition providing generic inhibitory tone in cortex, circuits are selectively organized to recruit inhibition matched to incoming excitatory circuits.SIGNIFICANCE STATEMENT M1 integrates sensory information and frontal cortical inputs to plan and control movements. Although inputs to excitatory cells are described, the synaptic circuits by which these inputs drive specific types of M1 interneurons are unknown. Anatomical results with rabies tracing and physiological quantification of synaptic strength shows that two main classes of inhibitory cells (PV+ and SOM+ interneurons) both receive substantial cortical and thalamic input, in contrast to interneurons in sensory areas (where thalamic input strongly prefers PV+ interneurons). Further, each input studied targets PV+ and SOM+ interneurons in a different fashion, suggesting that separate, specific circuits exist for recruitment of feedforward inhibition.

Exploring mitigating role of zinc nanoparticles on arsenic, ammonia and temperature stress using molecular signature in fish.

BACKGROUND: The pollution and climate change in aquatic ecosystems are major problems threatening the aquatic organisms for existence in the recent timeline, which promotes the extinction of the fish species. However, the present study dealt with zinc nanoparticles (Zn-NPs) in mitigating arsenic, ammonia and high temperature stresses in Pangasianodon hypophthalmus. MATERIALS AND METHODS: To studying different gene expressions, an experiment was conducted to mitigate the multiple stressors using dietary Zn-NPs at 0, 2, 4, and 6 mg kg-1 diets. In the present investigation, the gene expressions studies were performed for growth hormone regulator 1 (GHR1), growth hormone regulator ß (GHRß), growth hormone (GR) in liver and gill tissue as well as myostatin (MYST) and somatostatin (SMT) in the muscle tissue. The anti-oxidative genes CAT, SOD and GPx in liver and gill tissues were also analysed. Expression studies for stress responsive heat shock protein gene (HSP70), DNA damage inducible protein, inducible nitric oxide synthase (iNOS), immune related genes such as interleukin (IL), tumour necrosis factor (TNFα), toll like receptor (TLR) and immunoglobulin were performed. At the end of the experiment the fish were infected with Aeromonas hydrophila to evaluate the immunomodulatory role of Zn-NPs. RESULTS: In the present investigation, the growth hormone regulator 1 (GHR1), growth hormone regulator ß (GHRß), growth hormone (GR) in liver and gill as well as myostatin (MYST) and somatostatin (SMT) in muscle were noticeably altered, whereas, Zn-NPs at 4 mg kg-1 diet improved gene expressions. The anti-oxidant gene viz. CAT, SOD and GPx in liver and gill tissues were upregulated by stressors such as As, NH3, NH3+T. As+T and As+NH3+T. Therefore, anti-oxidant genes were noticeably improved with dietary Zn-NPs diet. The stress protein gene (HSP70), DNA damage inducible protein, inducible nitric oxide synthase (iNOS) was significantly upregulated, whereas, Zn-NPs diet was applied to the corrected gene regulation. Similarly, immune related genes such as interleukin (IL), tumour necrosis factor (TNFα), toll like receptor (TLR) and immunoglobulin were highly affected by stressors. Dietary Zn-NPs at 4 mg kg-1 diet was improved all the immune related gene expression and mitigate arsenic, ammonia and high temperature stress in fish. CONCLUSION: The present investigation revealed that Zn-NPs at 4.0 mg kg-1 diet has enormous potential to modulates arsenic, ammonia and high temperature stress, and protect against pathogenic infections in fish.

Target-specific projections of amygdala somatostatin-expressing neurons to the hypothalamus and brainstem.

Somatostatin neurons in the central nucleus of the amygdala (CeA/Sst) can be parsed into subpopulations that project either to the nucleus of the solitary tract (NST) or parabrachial nucleus (PBN). We have shown recently that inhibition of CeA/Sst-to-NST neurons increased the ingestion of a normally aversive taste stimulus, quinine HCl (QHCl). Because the CeA innervates other forebrain areas such as the lateral hypothalamus (LH) that also sends axonal projections to the NST, the effects on QHCl intake could be, in part, the result of CeA modulation of LH-to-NST neurons. To address these issues, the present study investigated whether CeA/Sst-to-NST neurons are distinct from CeA/Sst-to-LH neurons. For comparison purposes, additional experiments assessed divergent innervation of the LH by CeA/Sst-to-PBN neurons. In Sst-cre mice, two different retrograde transported flox viruses were injected into the NST and the ipsilateral LH or PBN and ipsilateral LH. The results showed that 90% or more of retrograde-labeled CeA/Sst neurons project either to the LH, NST, or PBN. Separate populations of CeA/Sst neurons projecting to these different regions suggest a highly heterogeneous population in terms of synaptic target and likely function.

Hippocampal and thalamic afferents form distinct synaptic microcircuits in the mouse infralimbic frontal cortex.

The selection of goal-directed behaviors is supported by neural circuits located within the frontal cortex. Frontal cortical afferents arise from multiple brain areas, yet the cell-type-specific targeting of these inputs is unclear. Here, we use monosynaptic retrograde rabies mapping to examine the distribution of afferent neurons targeting distinct classes of local inhibitory interneurons and excitatory projection neurons in mouse infralimbic frontal cortex. Interneurons expressing parvalbumin, somatostatin, or vasoactive intestinal peptide receive a large proportion of inputs from the hippocampus, while interneurons expressing neuron-derived neurotrophic factor receive a large proportion of inputs from thalamic regions. A similar dichotomy is present among the four different excitatory projection neurons. These results show a prominent bias among long-range hippocampal and thalamic afferent systems in their targeting to specific sets of frontal cortical neurons. Moreover, they suggest the presence of two distinct local microcircuits that control how different inputs govern frontal cortical information processing.

Depleting hypothalamic somatostatinergic neurons recapitulates diabetic phenotypes in mouse brain, bone marrow, adipose and retina.

AIMS/HYPOTHESIS: Hypothalamic inflammation and sympathetic nervous system hyperactivity are hallmark features of the metabolic syndrome and type 2 diabetes. Hypothalamic inflammation may aggravate metabolic and immunological pathologies due to extensive sympathetic activation of peripheral tissues. Loss of somatostatinergic (SST) neurons may contribute to enhanced hypothalamic inflammation. METHODS: The present data show that leptin receptor-deficient (db/db) mice exhibit reduced hypothalamic SST neurons, particularly in the periventricular nucleus. We model this finding, using adeno-associated virus delivery of diphtheria toxin subunit A (DTA) driven by an SST-cre system to deplete these neurons in Sstcre/gfp mice (SST-DTA). RESULTS: SST-DTA mice exhibit enhanced hypothalamic c-Fos expression and brain inflammation as demonstrated by microglial and astrocytic activation. Bone marrow from SST-DTA mice undergoes skewed haematopoiesis, generating excess granulocyte-monocyte progenitors and increased proinflammatory (C-C chemokine receptor type 2; CCR2hi) monocytes. SST-DTA mice exhibited a 'diabetic retinopathy-like' phenotype: reduced visual function by optokinetic response (0.4 vs 0.25 cycles/degree; SST-DTA vs control mice); delayed electroretinogram oscillatory potentials; and increased percentages of retinal monocytes. Finally, mesenteric visceral adipose tissue from SST-DTA mice was resistant to catecholamine-induced lipolysis, displaying 50% reduction in isoprenaline (isoproterenol)-induced lipolysis compared with control littermates. Importantly, hyperglycaemia was not observed in SST-DTA mice. CONCLUSIONS/INTERPRETATION: The isolated reduction in hypothalamic SST neurons was able to recapitulate several hallmark features of type 2 diabetes in disease-relevant tissues.

A neural circuit for excessive feeding driven by environmental context in mice.

Despite notable genetic influences, obesity mainly results from the overconsumption of food, which arises from the interplay of physiological, cognitive and environmental factors. In patients with obesity, eating is determined more by external cues than by internal physiological needs. However, how environmental context drives non-homeostatic feeding is elusive. Here, we identify a population of somatostatin (TNSST) neurons in the mouse hypothalamic tuberal nucleus that are preferentially activated by palatable food. Activation of TNSST neurons enabled a context to drive non-homeostatic feeding in sated mice and required inputs from the subiculum. Pairing a context with palatable food greatly potentiated synaptic transmission between the subiculum and TNSST neurons and drove non-homeostatic feeding that could be selectively suppressed by inhibiting TNSST neurons or the subiculum but not other major orexigenic neurons. These results reveal how palatable food, through a specific hypothalamic circuit, empowers environmental context to drive non-homeostatic feeding.

Leptin Modulates the Response of Brown Adipose Tissue to Negative Energy Balance: Implication of the GH/IGF-I Axis.

The growth hormone (GH)/insulin-like growth factor I (IGF-I) axis is involved in metabolic control. Malnutrition reduces IGF-I and modifies the thermogenic capacity of brown adipose tissue (BAT). Leptin has effects on the GH/IGF-I axis and the function of BAT, but its interaction with IGF-I and the mechanisms involved in the regulation of thermogenesis remains unknown. We studied the GH/IGF-I axis and activation of IGF-I-related signaling and metabolism related to BAT thermogenesis in chronic central leptin infused (L), pair-fed (PF), and control rats. Hypothalamic somatostatin mRNA levels were increased in PF and decreased in L, while pituitary GH mRNA was reduced in PF. Serum GH and IGF-I concentrations were decreased only in PF. In BAT, the association between suppressor of cytokine signaling 3 and the IGF-I receptor was reduced, and phosphorylation of the IGF-I receptor increased in the L group. Phosphorylation of Akt and cyclic AMP response element binding protein and glucose transporter 4 mRNA levels were increased in L and mRNA levels of uncoupling protein-1 (UCP-1) and enzymes involved in lipid anabolism reduced in PF. These results suggest that modifications in UCP-1 in BAT and changes in the GH/IGF-I axis induced by negative energy balance are dependent upon leptin levels.

Diversity of Receptive Fields and Sideband Inhibition with Complex Thalamocortical and Intracortical Origin in L2/3 of Mouse Primary Auditory Cortex.

Receptive fields of primary auditory cortex (A1) neurons show excitatory neuronal frequency preference and diverse inhibitory sidebands. While the frequency preferences of excitatory neurons in local A1 areas can be heterogeneous, those of inhibitory neurons are more homogeneous. To date, the diversity and the origin of inhibitory sidebands in local neuronal populations and the relation between local cellular frequency preference and inhibitory sidebands are unknown. To reveal both excitatory and inhibitory subfields, we presented two-tone and pure tone stimuli while imaging excitatory neurons (Thy1) and two types of inhibitory neurons (parvalbumin and somatostatin) in L2/3 of mice A1. We classified neurons into six classes based on frequency response area (FRA) shapes and sideband inhibition depended both on FRA shapes and cell types. Sideband inhibition showed higher local heterogeneity than frequency tuning, suggesting that sideband inhibition originates from diverse sources of local and distant neurons. Two-tone interactions depended on neuron subclasses with excitatory neurons showing the most nonlinearity. Onset and offset neurons showed dissimilar spectral integration, suggesting differing circuits processing sound onset and offset. These results suggest that excitatory neurons integrate complex and nonuniform inhibitory input. Thalamocortical terminals also exhibited sideband inhibition, but with different properties from those of cortical neurons. Thus, some components of sideband inhibition are inherited from thalamocortical inputs and are further modified by converging intracortical circuits. The combined heterogeneity of frequency tuning and diverse sideband inhibition facilitates complex spectral shape encoding and allows for rapid and extensive plasticity.SIGNIFICANCE STATEMENT Sensory systems recognize and differentiate between different stimuli through selectivity for different features. Sideband inhibition serves as an important mechanism to sharpen stimulus selectivity, but its cortical mechanisms are not entirely resolved. We imaged pyramidal neurons and two common classes of interneurons suggested to mediate sideband inhibition (parvalbumin and somatostatin positive) in the auditory cortex and inferred their inhibitory sidebands. We observed a higher degree of variability in the inhibitory sideband than in the local frequency tuning, which cannot be predicted from the relative high homogeneity of responses by inhibitory interneurons. This suggests that cortical sideband inhibition is nonuniform and likely results from a complex interplay between existing functional inhibition in the feedforward input and cortical refinement.

Developmental divergence of sensory stimulus representation in cortical interneurons.

Vasocative-intestinal-peptide (VIP+) and somatostatin (SST+) interneurons are involved in modulating barrel cortex activity and perception during active whisking. Here we identify a developmental transition point of structural and functional rearrangements onto these interneurons around the start of active sensation at P14. Using in vivo two-photon Ca2+ imaging, we find that before P14, both interneuron types respond stronger to a multi-whisker stimulus, whereas after P14 their responses diverge, with VIP+ cells losing their multi-whisker preference and SST+ neurons enhancing theirs. Additionally, we find that Ca2+ signaling dynamics increase in precision as the cells and network mature. Rabies virus tracings followed by tissue clearing, as well as photostimulation-coupled electrophysiology reveal that SST+ cells receive higher cross-barrel inputs compared to VIP+ neurons at both time points. In addition, whereas prior to P14 both cell types receive direct input from the sensory thalamus, after P14 VIP+ cells show reduced inputs and SST+ cells largely shift to motor-related thalamic nuclei.

A GABAergic neural circuit in the ventromedial hypothalamus mediates chronic stress-induced bone loss.

Homeostasis of bone metabolism is regulated by the central nervous system, and mood disorders such as anxiety are associated with bone metabolism abnormalities, yet our understanding of the central neural circuits regulating bone metabolism is limited. Here, we demonstrate that chronic stress in crewmembers resulted in decreased bone density and elevated anxiety in an isolated habitat mimicking a space station. We then used a mouse model to demonstrate that GABAergic neural circuitry in the ventromedial hypothalamus (VMH) mediates chronic stress-induced bone loss. We show that GABAergic inputs in the dorsomedial VMH arise from a specific group of somatostatin neurons in the posterior region of the bed nucleus of the stria terminalis, which is indispensable for stress-induced bone loss and is able to trigger bone loss in the absence of stressors. In addition, the sympathetic system and glutamatergic neurons in the nucleus tractus solitarius were employed to regulate stress-induced bone loss. Our study has therefore identified the central neural mechanism by which chronic stress-induced mood disorders, such as anxiety, influence bone metabolism.

Hyperactivated PTP1B phosphatase in parvalbumin neurons alters anterior cingulate inhibitory circuits and induces autism-like behaviors.

Individuals with autism spectrum disorder (ASD) have social interaction deficits and difficulty filtering information. Inhibitory interneurons filter information at pyramidal neurons of the anterior cingulate cortex (ACC), an integration hub for higher-order thalamic inputs important for social interaction. Humans with deletions including LMO4, an endogenous inhibitor of PTP1B, display intellectual disabilities and occasionally autism. PV-Lmo4KO mice ablate Lmo4 in PV interneurons and display ASD-like repetitive behaviors and social interaction deficits. Surprisingly, increased PV neuron-mediated peri-somatic feedforward inhibition to the pyramidal neurons causes a compensatory reduction in (somatostatin neuron-mediated) dendritic inhibition. These homeostatic changes increase filtering of mediodorsal-thalamocortical inputs but reduce filtering of cortico-cortical inputs and narrow the range of stimuli ACC pyramidal neurons can distinguish. Simultaneous ablation of PTP1B in PV-Lmo4KO neurons prevents these deficits, indicating that PTP1B activation in PV interneurons contributes to ASD-like characteristics and homeostatic maladaptation of inhibitory circuits may contribute to deficient information filtering in ASD.

Neurochemical characterization of the hypothalamus of the early fetal and newborn alpaca Vicugna pacos.

In this study we performed a neurochemical characterization of the hypothalamus in the developing alpaca (Vicugna pacos) with the aim of revealing the distributions of immunoreactive (-ir) cells containing parvalbumin (PV), calbindin (CB), calretinin (CR), the somatostatin (SOM), the enzyme aromatase P450 (P450Arom), the estrogen receptor α (ER-α), and estrogen receptor ß (ER-ß) in embryonal stages, early fetal age, and in the newborn. This analysis has been carried out on embryos at 20, 30, 45 days, fetuses at 90 days, and newborn alpaca. Our immunohistochemical results revealed no cells-ir throughout the embryonic hypothalami of 20, 30, and 45 days. On the fetal stage of 90 days, SOM-ir cells were observed in the lateral hypothalamus and the ventromedial nuclei of the tuberal region. We checked for the presence of P450Arom-ir cells in the periventricular area and dorsomedial hypothalamic nucleus of the tuberal region. In these fetal stages, no PV-ir, CB-ir, CR-ir or ERs-ir cells were identified. In the newborn, the PV-ir, CB-ir, CR-ir, and SOM-ir cells were detected in both the anterior and tuberal hypothalamic area. The P450Arom-ir cells the ER-α-ir and ER-ß-ir cells were found in the anterior hypothalamus. Our results offer a contribution in the future purpose to obtain a time-expression pattern of the considered markers in alpaca during gestation and represents a foundation for future investigations on the alpaca brain to define the cross talk between PV, CB, CR, P450Arom, SOM, and ERs in the hypothalamus, the strategic region for the control of the reproductive behavior.

Assemblies of Perisomatic GABAergic Neurons in the Developing Barrel Cortex.

The developmental journey of cortical interneurons encounters several activity-dependent milestones. During the early postnatal period in developing mice, GABAergic neurons are transient preferential recipients of thalamic inputs and undergo activity-dependent migration arrest, wiring, and programmed cell-death. Despite their importance for the emergence of sensory experience and the role of activity in their integration into cortical networks, the collective dynamics of GABAergic neurons during that neonatal period remain unknown. Here, we study coordinated activity in GABAergic cells of the mouse barrel cortex using in vivo calcium imaging. We uncover a transient structure in GABAergic population dynamics that disappears in a sensory-dependent process. Its building blocks are anatomically clustered GABAergic assemblies mostly composed by prospective parvalbumin-expressing cells. These progressively widen their territories until forming a uniform perisomatic GABAergic network. Such transient patterning of GABAergic activity is a functional scaffold that links the cortex to the external world prior to active exploration. VIDEO ABSTRACT.

Diabetes Type 2 and Kisspeptin: Central and Peripheral Sex-Specific Actions.

Kisspeptin (KP) plays a major role in the regulation of reproduction governed by the hypothalamic-pituitary-gonadal (HPG) axis. However, recent findings suggest that the KP system is present not only centrally (at the level of the hypothalamus), but also in the peripheral organs crucial for the control of metabolism. The KP system is sexually differentiated in the hypothalamus, and it is of particular interest to study whether sex-specific responses to type 2 diabetes (DM2) exist centrally and peripherally. As collection of data is limited in humans, animal models of DM2 are useful to understand crosstalk between metabolism and reproduction. Sex-specific variations in the KP system reported in animals suggest a need for the development of gender specific therapeutic strategies to treat DM2.

Effects of Somatostatin and Vitamin C on the Fatty Acid Profile of Breast Cancer Cell Membranes.

BACKGROUND: Vitamin C (Vit C) is an important physiological antioxidant with growing applications in cancer. Somatostatin (SST) is a natural peptide with growth inhibitory effect in several mammary cancer models. OBJECTIVE: The combined effects of SST and Vit C supplementation have never been studied in breast cancer cells so far. METHODS: We used MCF-7 and MDA-MB231 breast cancer cells incubated with SST for 24h, in the absence and presence of Vit C, at their EC50 concentrations, to evaluate membrane fatty acid-profiles together with the follow-up of EGFR and MAPK signaling pathways. RESULTS: The two cell lines gave different membrane reorganization: in MCF-7 cells, decrease of omega-6 linoleic acid and increase of omega-3 fatty acids (Fas) occurred after SST and SST+Vit C incubations, the latter also showing significant increases in MUFA, docosapentaenoic acid and mono-trans arachidonic acid levels. In MDA-MB231 cells, SST+Vit C incubation induced significant membrane remodeling with an increase of stearic acid and mono-trans-linoleic acid isomer, diminution of omega-6 linoleic, arachidonic acid and omega-3 (docosapentaenoic and docosadienoic acids). Distinct signaling pathways in these cell lines were studied: in MCF-7 cells, incubations with SST and Vit C, alone or in combination significantly decreased EGFR and MAPK signaling, whereas in MDA-MB231 cells, SST and Vit C incubations, alone or combined, decreased p- P44/42 MAPK levels, and increased EGFR levels. CONCLUSION: Our results showed that SST and Vit C can be combined to induce membrane fatty acid changes, including lipid isomerization through a specific free radical-driven process, influencing signaling pathways.

Glucose stimulates somatostatin secretion in pancreatic δ-cells by cAMP-dependent intracellular Ca2+ release.

Somatostatin secretion from pancreatic islet δ-cells is stimulated by elevated glucose levels, but the underlying mechanisms have only partially been elucidated. Here we show that glucose-induced somatostatin secretion (GISS) involves both membrane potential-dependent and -independent pathways. Although glucose-induced electrical activity triggers somatostatin release, the sugar also stimulates GISS via a cAMP-dependent stimulation of CICR and exocytosis of somatostatin. The latter effect is more quantitatively important and in mouse islets depolarized by 70 mM extracellular K+ , increasing glucose from 1 mM to 20 mM produced an ∼3.5-fold stimulation of somatostatin secretion, an effect that was mimicked by the application of the adenylyl cyclase activator forskolin. Inhibiting cAMP-dependent pathways with PKI or ESI-05, which inhibit PKA and exchange protein directly activated by cAMP 2 (Epac2), respectively, reduced glucose/forskolin-induced somatostatin secretion. Ryanodine produced a similar effect that was not additive to that of the PKA or Epac2 inhibitors. Intracellular application of cAMP produced a concentration-dependent stimulation of somatostatin exocytosis and elevation of cytoplasmic Ca2+ ([Ca2+]i). Both effects were inhibited by ESI-05 and thapsigargin (an inhibitor of SERCA). By contrast, inhibition of PKA suppressed δ-cell exocytosis without affecting [Ca2+]i Simultaneous recordings of electrical activity and [Ca2+]i in δ-cells expressing the genetically encoded Ca2+ indicator GCaMP3 revealed that the majority of glucose-induced [Ca2+]i spikes did not correlate with δ-cell electrical activity but instead reflected Ca2+ release from the ER. These spontaneous [Ca2+]i spikes are resistant to PKI but sensitive to ESI-05 or thapsigargin. We propose that cAMP links an increase in plasma glucose to stimulation of somatostatin secretion by promoting CICR, thus evoking exocytosis of somatostatin-containing secretory vesicles in the δ-cell.

Fine Control of Sound Frequency Tuning and Frequency Discrimination Acuity by Synaptic Zinc Signaling in Mouse Auditory Cortex.

Neurons in the auditory cortex are tuned to specific ranges of sound frequencies. Although the cellular and network mechanisms underlying neuronal sound frequency selectivity are well studied and reflect the interplay of thalamocortical and intracortical excitatory inputs and further refinement by cortical inhibition, the precise synaptic signaling mechanisms remain less understood. To gain further understanding on these mechanisms and their effects on sound-driven behavior, we used in vivo imaging as well as behavioral approaches in awake and behaving female and male mice. We discovered that synaptic zinc, a modulator of neurotransmission and responsiveness to sound, sharpened the sound frequency tuning of principal and parvalbumin-expressing neurons and widened the sound frequency tuning of somatostatin-expressing inhibitory neurons in layer 2/3 of the primary auditory cortex. In the absence of cortical synaptic zinc, mice exhibited reduced acuity for detecting changes in sound frequencies. Together, our results reveal that cell-type-specific effects of zinc contribute to cortical sound frequency tuning and enhance acuity for sound frequency discrimination.SIGNIFICANCE STATEMENT Neuronal tuning to specific features of sensory stimuli is a fundamental property of cortical sensory processing that advantageously supports behavior. Despite the established roles of synaptic thalamocortical and intracortical excitation and inhibition in cortical tuning, the precise synaptic signaling mechanisms remain unknown. Here, we investigated these mechanisms in the mouse auditory cortex. We discovered a previously unknown signaling mechanism linking synaptic zinc signaling with cell-specific cortical tuning and enhancement in sound frequency discrimination acuity. Given the abundance of synaptic zinc in all sensory cortices, this newly discovered interaction between synaptic zinc and cortical tuning can provide a general mechanism for modulating neuronal stimulus specificity and sensory-driven behavior.

Early Excitatory Activity-Dependent Maturation of Somatostatin Interneurons in Cortical Layer 2/3 of Mice.

GABAergic interneurons perform distinct functions during cortical development in the mouse brain. Among the diverse GABAergic neurons present in the brain, early-born somatostatin (SST)-expressing inhibitory interneurons, which are innervated by other interneurons and local pyramidal cells (PCs), act in a neural computational role in circuitry regulation. The synapses between the SST+ interneurons and other cells form gradually during development. Here, we traced the developmental course of the electrophysiological properties of SST+ interneurons at layer 2/3 of the neocortical secondary motor area (M2) in mouse, and the synaptic connectivity between SST+ interneurons and PCs. Also, we used toxin-mediated and genetic method to suppress the activities of PCs, and demonstrate that decreasing excitatory input at early stage (before P1) rather than late stage (after P8) would delay the functional maturation of SST+ interneurons. In conclusion, our results indicate that early functional activity of PCs is crucial for the intrinsic maturation of SST+ interneurons, following which these interneurons participate in local circuitry.