Expression of c-fos-like protein as a marker for neuronal activity following noxious stimulation in the rat

Central and Peripheral Mechanism of Acupuncture Analgesia on Visceral Pain: A Systematic Review

Background/Aims

Despite the wide use of acupuncture for the management of visceral pain and the growing interest in the pathophysiology of visceral pain, there is no conclusive elucidation of the mechanisms behind the effects of acupuncture on visceral pain. This systematic review aims to provide an integrative understanding of the treatment mechanism of acupuncture for visceral pain.

Methods

Electronic and hand searches were conducted to identify studies that involved visceral pain and acupuncture.

Results

We retrieved 192 articles, out of which 46 studies were included in our review. The results of our review demonstrated that visceral pain behaviors were significantly alleviated in response to acupuncture treatment in groups treated with this intervention compared to in sham acupuncture or no-treatment groups. Changes in the concentrations of β-endorphin, epinephrine, cortisol, and prostaglandin E2 in plasma, the levels of c-Fos, substance P, corticotropin-releasing hormone, P2X3, acetylcholinesterase (AchE), N-methyl-D-aspartate (NMDA) receptors, and serotonin in the gut/spinal cord, and the neuronal activity of the thalamus were associated with acupuncture treatment in visceral pain.

Conclusions

Acupuncture reduced visceral pain behavior and induced significant changes in neuronal activity as well as in the levels of pain/inflammation-related cytokines and neurotransmitters in the brain-gut axis. Further researches on the thalamus and on a standard animal model are warranted to improve our knowledge on the mechanism of acupuncture that facilitates visceral pain modulation.

The accessible chromatin landscape of the murine hippocampus at single-cell resolution

Here we present a comprehensive map of the accessible chromatin landscape of the mouse hippocampus at single-cell resolution. Substantial advances of this work include the optimization of a single-cell combinatorial indexing assay for transposase accessible chromatin (sci-ATAC-seq); a software suite, scitools, for the rapid processing and visualization of single-cell combinatorial indexing data sets; and a valuable resource of hippocampal regulatory networks at single-cell resolution. We used sci-ATAC-seq to produce 2346 high-quality single-cell chromatin accessibility maps with a mean unique read count per cell of 29,201 from both fresh and frozen hippocampi, observing little difference in accessibility patterns between the preparations. By using this data set, we identified eight distinct major clusters of cells representing both neuronal and nonneuronal cell types and characterized the driving regulatory factors and differentially accessible loci that define each cluster. Within pyramidal neurons, we identified four major clusters, including CA1 and CA3 neurons, and three additional subclusters. We then applied a recently described coaccessibility framework, Cicero, which identified 146,818 links between promoters and putative distal regulatory DNA. Identified coaccessibility networks showed cell-type specificity, shedding light on key dynamic loci that reconfigure to specify hippocampal cell lineages. Lastly, we performed an additional sci-ATAC-seq preparation from cultured hippocampal neurons (899 high-quality cells, 43,532 mean unique reads) that revealed substantial alterations in their epigenetic landscape compared with nuclei from hippocampal tissue. This data set and accompanying analysis tools provide a new resource that can guide subsequent studies of the hippocampus.

The immediate effects of weaning stress on the hypothalamus-pituitary-adrenal alteration of newly weaned piglets

This study was conducted to examine the effects of weaning stress on gene expression of specific markers in hypothalamus-pituitary-adrenal (HPA) axis and neuronal activity in the newly weaned piglets. Twelve 28-days-old, newly weaned crossbred (Landrace × Yorkshire × Duroc) male piglets from 6 l (2 piglets/l) were randomly categorized into two groups: (a) weaning stress: piglets were separated from their dams, relocated and mixed with the unacquainted domestic piglets for 2 hr (stress, n = 6); (b) no-stress: piglets stayed with their dams in the farrowing house (NS; n = 6). After weaning stress, all piglets were electrically euthanized and the blood samples/HPA tissues were collected for subsequent analysis, including plasma cortisol and mRNA expression of c-fos, c-jun, corticotropin-releasing hormone (CRH), CRH receptor 1 (CRHR-1) and adrenocorticotropin hormone receptor (MC2R). Results: Weaning stress significantly (p < 0.05) increased the plasma cortisol level and suppressed the expression of c-fos and CRH in hypothalamus. In addition, weaning stress enhanced the mRNA abundance of c-jun and CRHR-1 in the pituitary gland. No significant differences in the gene expression of MC2R and CRHR-1 were observed in the adrenal gland between treatment groups. Taken together, HPA involved in weaning stress and CRHR-1 and c-jun could be potential markers to evaluate the activation of HPA axis.

Sensitization of nociceptors and dorsal horn neurons contributes to pain in sickle cell disease

Sickle cell disease (SCD) describes a group of disorders associated with a point mutation in the beta chain of hemoglobin. The mutation leads to the creation of sickle hemoglobin (HbS) and causes distortion of erythrocytes through polymerization under low oxygen, resulting in characteristic sickle red blood cells. Vaso-occlusion episodes caused by accumulation of sRBCs results in ischemia-reperfusion injury, reduced oxygen supply to organs, oxidative stress, organ damage and severe pain that often requires hospitalization and opioid treatment. Further, many patients suffer from chronic pain, including hypersensitivity to heat and cold stimuli. Progress towards the development of novel strategies for both acute and chronic pain in patients with SCD has been impeded by a lack of understanding the mechanisms underlying pain in SCD. The purpose of this review is to highlight evidence for the contribution of peripheral and central sensitization that leads to widespread, chronic pain and hyperalgesia. Targeting the mechanisms that initiate and maintain sensitization in SCD might offer effective approaches to manage the severe and debilitating pain associated with this condition.

Reversible Functional Changes Evoked by Anodal Epidural Direct Current Electrical Stimulation of the Rat Auditory Cortex

Rat auditory cortex was subjected to 0.1 mA anodal direct current in seven 10-min sessions on alternate days. Based on the well-known auditory cortex control of olivocochlear regulation through corticofugal projections, auditory brainstem responses (ABRs) were recorded as an indirect test of the effectiveness and reversibility of the multisession protocol of epidural stimulation. Increases of 20-30 dB ABR auditory thresholds shown after epidural stimulation reverted back to control levels 10 min after a single session. However, increases in thresholds revert 4 days after multisession stimulation. Less changes in wave amplitudes and threshold shifts were shown in ABR recorded contralaterally to the electrically stimulated side of the brain. To assess tissue effects of epidural electric stimulation on the brain cortex, well characterized functional anatomical markers of glial cells (GFAP/astrocytes and Iba1/microglial cells) and neurons (c-Fos) were analyzed in alternate serial sections by quantitative immunocytochemistry. Restricted astroglial and microglial reactivity was observed within the cytoarchitectural limits of the auditory cortex. However, interstitial GFAP overstaining was also observed in the ventricular surface and around blood vessels, thus supporting a potential global electrolytic stimulation of the brain. These results correlate with extensive changes in the distribution of c-Fos immunoreactive neurons among layers along sensory cortices after multisession stimulation. Quantitative immunocytochemical analysis supported this idea by showing a significant increase in the number of positive neurons in supragranular layers and a decrease in layer 6 with no quantitative changes detected in layer 5. Our data indicate that epidural stimulation of the auditory cortex induces a reversible decrease in hearing sensitivity due to local, restricted epidural stimulation. A global plastic response of the sensory cortices, also reported here, may be related to electrolytic effects of electric currents.

Expression of aggressiveness modulates mesencephalic c-fos activation during a social interaction test in Japanese quail (Coturnix japonica)

It is well known that during a social conflict, interactions are dependent on the animal's propensity to behave aggressively as well as the behavior of the opponent. However, discriminating between these two confounding factors was difficult. Recently, a Social Interaction (SI) test using photocastrated males as non-aggressive stimuli was proposed as a useful tool to evaluate aggressiveness. The avian Intercollicular- Griseum centralis complex (comparable to mammalian periaqueductal gray) has been reported as a crucial node in the descending pathways that organize behavioral and autonomic aspects of defensive responses and aggressiveness. Herein, using the SI test, we evaluated whether mesencephalic areas are activated (expressed c-fos) when photostimulated adult males are confronted with non-responsive (non-aggressive) opponents. Furthermore, we also examined whether mesencephalic activation is related to male performance during the SI test (i.e., aggressive vs. non-aggressive males) in birds reared in enriched or in standard environments. Five mesencephalic areas at two anatomic levels (intermediate and rostral) and locomotion during SI testing were studied. Aggressive males showed increased c-fos expression in all areas studied, and moved at faster speeds in comparison to their non-aggressive and control counterparts. Non-aggressive males and the test controls showed similar c-fos labeling. In general, rearing condition did not appear to influence c-fos expression nor behavior during the SI test. Findings suggest that mesencephalic activation is involved when males are actively expressing aggressive behaviors. This overall phenomenon is shown regardless of both the environmental stimuli provided during the birds´ rearing and the potentially stressful stimuli during the SI trial.

c-Fos expression response to olanzapine, amisulpride, aripiprazole, and quetiapine single administration in the rat forebrain: Effect of a mild stress preconditioning

Antipsychotics have been shown to stimulate different forebrain areas, whereas some of them are sensitive to stress. In the present study, effect of a single administration of olanzapine (OLA), amisulpride (AMI), aripiprazole (ARI), and quetiapine (QUE) on the activity of cells in the striatal dorsolateral (stDL) area, the periventricular zone (peVZ), the septal ventrolateral (seVL) nucleus, and the accumbens nucleus shell (shACC) and core (coACC) was investigated in male rats preconditioned with a mild stress complex (CMS) for 20 days. The objective of the study was to extend the anatomical-functional knowledge on the mechanism of selected antipsychotics with the goals: 1) to analyze the ability of the selected antipsychotics to induce c-Fos protein expression in the above mentioned forebrain structures and to map the pattern of their topography and 2) to find out whether longer-lasting mild stress preconditioning may modify the impact of the selected antipsychotics on the activity of cells in the forebrain areas in adult rats. Ten groups of rats were used. CMS complex contained five stressors: cage crowding, air-puff noising, wet bedding, predator stress, and forced swimming. AMI (20 mg/kg), OLA (5 mg/kg), QUE (15 mg/kg), and ARI (10 mg/kg/b.w.) were administered intraperitoneally and 90 min later the animals transcardially perfused by fixative. c-Fos was visualized by ABC complex. In unstressed animals, OLA and ARI elevated c-Fos expression in all areas studied, AMI and QUE in all areas except stDL, seVL and coACC, shACC FL-2 (shACC posterior level), respectively. CMS potentiated the effect of AMI in coACC, and QUE in shACC FL-2 and suppressed the effect of AMI in peVZ, and ARI in peVZ and seVL. The present data provide new insights into activity of cells in response to CMS challenge, which might be helpful in understanding the diverse clinical effects of atypical antipsychotics.

Blue light exposure in vitro causes toxicity to trigeminal neurons and glia through increased superoxide and hydrogen peroxide generation

Today the noxiousness of blue light from natural and particularly artificial (fluorescent tubes, LED panels, visual displays) sources is actively discussed in the context of various ocular diseases. Many of them have an important neurologic component and are associated with ocular pain. This neuropathic signal is provided by nociceptive neurons from trigeminal ganglia. However, the phototoxicity of blue light on trigeminal neurons has not been explored so far. The aim of the present in vitro study was to investigate the cytotoxic impact of various wavebands of visible light (410-630 nm) on primary cell culture of mouse trigeminal neural and glial cells. Three-hour exposure to narrow wavebands of blue light centered at 410, 440 and 480 nm of average 1.1 mW/cm² irradiance provoked cell death, altered cell morphology and induced oxidative stress and inflammation. These effects were not observed for other tested visible wavebands. We observed that neurons and glial cells processed the light signal in different manner, in terms of resulting superoxide and hydrogen peroxide generation, inflammatory biomarkers expression and phototoxic mitochondrial damage. We analyzed the pathways of photic signal reception, and we proposed that, in trigeminal cells, in addition to widely known mitochondria-mediated light absorption, light could be received by means of non-visual opsins, melanopsin (opn4) and neuropsin (opn5). We also investigated the mechanisms underlying the observed phototoxicity, further suggesting an important role of the endoplasmic reticulum in neuronal transmission of blue-light-toxic message. Taken together, our results give some insight into circuit of tangled pain and photosensitivity frequently observed in patients consulting for these ocular symptoms.

Peripheral Inflammation Accelerates the Onset of Mechanical Hypersensitivity after Spinal Cord Injury and Engages Tumor Necrosis Factor α Signaling Mechanisms

Previously, we showed that noxious stimulation of the tail produces numerous detrimental effects after spinal cord injury (SCI), including an earlier onset and increased magnitude of mechanical hypersensitivity. Expanding on these observations, this study sought to determine whether localized peripheral inflammation similarly impacts the expression of mechanical hypersensitivity after SCI. Adult rats received a moderate contusion injury at the thoracic level (Tl0) or sham surgery, and were administered complete Freund's adjuvant (CFA) or vehicle in one hindpaw 24 hours later. Examination of locomotor recovery (Basso, Beattie, and Bresnahan [BBB] score) showed no adverse effect of CFA. Mechanical testing with von Frey hairs was done at time-points ranging from 1 h to 28 days after CFA or vehicle treatment, and rats were sacrificed at 1, 7, or 28 days for cellular assessment. Unlike vehicle-treated SCI rats where mechanical hypersensitivity emerged at 14 days, CFA-treated SCI rats showed mechanical hypersensitivity as early as 1 h after CFA administration, which lasted at least 28 days. CFA-treated sham subjects also showed an early onset of mechanical hypersensitivity, but this was maintained up to 7 days after treatment. Cellular assessments revealed congruent findings. Expression levels of c-fos, tumor necrosis factor α (TNFα), TNF receptors, and members of the TNFα signaling pathway such as caspase 8 and phosphorylated extracellular related kinase (pERK) were preferentially upregulated in the lumbar spinal cord of SCI-CFA rats. Meanwhile, c-jun was significantly increased in both CFA-treated groups. Overall, these results together with our previous reports, suggest that peripheral noxious input after SCI facilitates the development of pain by mechanisms that may require TNFα signaling.

The Medial Septum Is Insulin Resistant in the AD Presymptomatic Phase: Rescue by Nerve Growth Factor-Driven IRS1 Activation

Basal forebrain cholinergic neurons (BFCN) are key modulators of learning and memory and are high energy-demanding neurons. Impaired neuronal metabolism and reduced insulin signaling, known as insulin resistance, has been reported in the early phase of Alzheimer's disease (AD), which has been suggested to be "Type 3 Diabetes." We hypothesized that BFCN may develop insulin resistance and their consequent failure represents one of the earliest event in AD. We found that a condition reminiscent of insulin resistance occurs in the medial septum of 3 months old 3×Tg-AD mice, reported to develop typical AD histopathology and cognitive deficits in adulthood. Further, we obtained insulin resistant BFCN by culturing them with high insulin concentrations. By means of these paradigms, we observed that nerve growth factor (NGF) reduces insulin resistance in vitro and in vivo. NGF activates the insulin receptor substrate 1 (IRS1) and rescues c-Fos expression and glucose metabolism. This effect involves binding of activated IRS1 to the NGF receptor TrkA, and is lost in presence of the specific IRS inhibitor NT157. Overall, our findings indicate that, in a well-established animal model of AD, the medial septum develops insulin resistance several months before it is detectable in the neocortex and hippocampus. Remarkably, NGF counteracts molecular alterations downstream of insulin-resistant receptor and its nasal administration restores insulin signaling in 3×Tg-AD mice by TrkA/IRS1 activation. The cross-talk between NGF and insulin pathways downstream the insulin receptor suggests novel potential therapeutic targets to slow cognitive decline in AD and diabetes-related brain insulin resistance.

Functional Organization of the Sympathetic Pathways Controlling the Pupil: Light-Inhibited and Light-Stimulated Pathways

Pupil dilation is mediated by a sympathetic output acting in opposition to parasympathetically mediated pupil constriction. While light stimulates the parasympathetic output, giving rise to the light reflex, it can both inhibit and stimulate the sympathetic output. Light-inhibited sympathetic pathways originate in retina-receptive neurones of the pretectum and the suprachiasmatic nucleus (SCN): by attenuating sympathetic activity, they allow unimpeded operation of the light reflex. Light stimulates the noradrenergic and serotonergic pathways. The hub of the noradrenergic pathway is the locus coeruleus (LC) containing both excitatory sympathetic premotor neurones (SympPN) projecting to preganglionic neurones in the spinal cord, and inhibitory parasympathetic premotor neurones (ParaPN) projecting to preganglionic neurones in the Edinger-Westphal nucleus (EWN). SympPN receive inputs from the SCN via the dorsomedial hypothalamus, orexinergic neurones of the latero-posterior hypothalamus, wake- and sleep-promoting neurones of the hypothalamus and brain stem, nociceptive collaterals of the spinothalamic tract, whereas ParaPN receive inputs from the amygdala, sleep/arousal network, nociceptive spinothalamic collaterals. The activity of LC neurones is regulated by inhibitory α₂-adrenoceptors. There is a species difference in the function of the preautonomic LC. In diurnal animals, the α₂-adrenoceptor agonist clonidine stimulates mainly autoreceptors on SymPN, causing miosis, whereas in nocturnal animals it stimulates postsynaptic α₂-arenoceptors in the EWN, causing mydriasis. Noxious stimulation activates SympPN in diurnal animals and ParaPN in nocturnal animals, leading to pupil dilation via sympathoexcitation and parasympathetic inhibition, respectively. These differences may be attributed to increased activity of excitatory LC neurones due to stimulation by light in diurnal animals. This may also underlie the wake-promoting effect of light in diurnal animals, in contrast to its sleep-promoting effect in nocturnal species. The hub of the serotonergic pathway is the dorsal raphe nucleus that is light-sensitive, both directly and indirectly (via an orexinergic input). The light-stimulated pathways mediate a latent mydriatic effect of light on the pupil that can be unmasked by drugs that either inhibit or stimulate SympPN in these pathways. The noradrenergic pathway has widespread connections to neural networks controlling a variety of functions, such as sleep/arousal, pain, and fear/anxiety. Many physiological and psychological variables modulate pupil function via this pathway.

How Senses Work Together: Cross-Modal Interactions between Primary Sensory Cortices

On our way through a town, the things we see can make us change the way we go. The things that we hear can make us stop or walk on, or the things we feel can cause us to wear a warm jacket or just a t-shirt. All these behaviors are mediated by highly complex processing mechanisms in our brain and reflect responses to many important sensory inputs. The mammalian cerebral cortex, which processes the sensory information, consists of largely specialized sensory areas mainly receiving information from their corresponding sensory modalities. The first cortical regions receiving the input from the outer world are the so called primary sensory cortices. Strikingly, there is convincing evidence that primary sensory cortices do not work in isolation but are substantially affected by other sensory modalities. Here, we will review previous and current literature on this cross-modal interplay.

Transient photoreception in the hindbrain is permissive to the life history transition of hatching in Atlantic halibut

In nonmammalian vertebrates, photoreception takes place in the deep brain already early in development, but knowledge is lacking about the functions of these nonvisual photoreceptive systems. Prior to hatching, Atlantic halibut has a transient bilateral cluster of photoreceptive cells in the hindbrain. The cluster is imbedded in a neuronal network projecting to the narrow belt of hatching glands in the yolk sac. In halibut, hatching is inhibited in light and activated by transfer to darkness and c-fos analysis during hatching shows that the hindbrain cluster and hatching glands have neural activation. Unexpectedly, the hindbrain cluster expresses dual photopigments, vertebrate ancient opsin and melanopsin. Evolutionarily, these opsins are believed to belong to different classes of photopigments found in rhabdomeric and ciliary photoreceptors. The concept that an organism develops transient light sensitivity to target critical aspects of life history transitions as hatching provides a fascinating landscape to investigate the timing of other biological events.

A Group of Descending Glutamatergic Neurons Activated by Stress in Corticolimbic Regions Project to the Nucleus Accumbens

The nucleus accumbens (NAc) is the major component of the ventral striatum that regulates stress-induced depression. The NAc receives dopaminergic inputs from the ventral tegmental area (VTA), and the role of VTA-NAc neurons in stress response has been recently characterized. The NAc also receives glutamatergic inputs from various forebrain structures including the prelimbic cortex (PL), basolateral amygdala (BLA), and ventral hippocampus (vHIP), whereas the role of those glutamatergic afferents in stress response remains underscored. In the present study, we investigated the extent to which descending glutamatergic neurons activated by stress in the PL, BLA, and vHIP project to the NAc. To specifically label the input neurons into the NAc, fluorescent-tagged cholera toxin subunit B (CTB), which can be used as a retrograde neuronal tracer, was injected into the NAc. After two weeks, the mice were placed under restraint for 1 h. Subsequent histological analyses indicated that CTB-positive cells were detected in 170~680 cells/mm² in the PL, BLA, and vHIP, and those CTB-positive cells were mostly glutamatergic. In the PL, BLA, and vHIP regions analyzed, stress-induced c-Fos expression was found in 20~100 cells/mm². Among the CTB-positive cells, 2.6% in the PL, 4.2% in the BLA, and 1.1% in the vHIP were co-labeled by c-Fos, whereas among c-Fos-positive cells, 7.7% in the PL, 19.8% in the BLA, and 8.5% in the vHIP were co-labeled with CTB. These results suggest that the NAc receives a significant but differing proportion of glutamatergic inputs from the PL, BLA, and vHIP in stress response.

Na+, K+-ATPase inhibition causes hyperactivity and impulsivity in mice via dopamine D2 receptor-mediated mechanism

Hyperactivity and impulsivity are common symptoms in several psychiatric disorders. Although dysfunction of Na⁺, K⁺-ATPase has been reported to be associated with the psychiatric disorders, it is not clear whether inhibition of Na⁺, K⁺-ATPase causes behavioral effects, including hyperactivity and impulsivity, in mice. Here, we evaluated the effect of intracerebroventricular (icv) injection of ouabain, an inhibitor of Na⁺, K⁺-ATPase, on hyperactivity and impulsivity in mice. At seven days after icv injection, ouabain-injected mice displayed the increase in the distance traveled in the open field arena in the open field test and the increase in the number of head-dipping behavior in the cliff avoidance test. Chlorpromazine or haloperidol, typical antipsychotics, reduced the hyperactivity and impulsivity in ouabain-injected mice. On the other hand, neither lithium carbonate nor valproate, established mood-stabilizing drugs, improved hyperactivity and impulsivity in our mouse model. Furthermore, ouabain-injected mice exhibited the increase in the number of c-fos-positive cells in the nucleus accumbens and the prefrontal cortex but not in the ventral tegmental area, which was reduced by haloperidol. These results suggest that the dysfunction of Na⁺, K⁺-ATPase causes hyperactivity and impulsivity via hyperactivation of dopamine D2 receptor-mediated signaling pathway, causing disturbed neuronal circuits in mice.

Detecting genome-wide directional effects of transcription factor binding on polygenic disease risk

Biological interpretation of genome-wide association study data frequently involves assessing whether SNPs linked to a biological process, for example, binding of a transcription factor, show unsigned enrichment for disease signal. However, signed annotations quantifying whether each SNP allele promotes or hinders the biological process can enable stronger statements about disease mechanism. We introduce a method, signed linkage disequilibrium profile regression, for detecting genome-wide directional effects of signed functional annotations on disease risk. We validate the method via simulations and application to molecular quantitative trait loci in blood, recovering known transcriptional regulators. We apply the method to expression quantitative trait loci in 48 Genotype-Tissue Expression tissues, identifying 651 transcription factor-tissue associations including 30 with robust evidence of tissue specificity. We apply the method to 46 diseases and complex traits (average n = 290 K), identifying 77 annotation-trait associations representing 12 independent transcription factor-trait associations, and characterize the underlying transcriptional programs using gene-set enrichment analyses. Our results implicate new causal disease genes and new disease mechanisms.

Dependence of c-fos Expression on Amplitude of High-Frequency Spinal Cord Stimulation in a Rodent Model

OBJECTIVES

Clinical high-frequency spinal cord stimulation (hfSCS) (>250 Hz) applied at subperception amplitudes reduces leg and low back pain. This study investigates, via labeling for c-fos-a marker of neural activation, whether 500 Hz hfSCS applied at amplitudes above and below the dorsal column (DC) compound action potential (CAP) threshold excites dorsal horn neurons.

MATERIALS AND METHODS

DC CAP thresholds in rats were determined by applying single biphasic pulses of SCS to T₁₂ -T₁₃ segments using pulse widths of 40 or 200 μsec via a ball electrode placed over the left DC and increasing amplitude until a short latency CAP was observed on the L₅ DC and sciatic nerve. The result of this comparison allowed us to substitute sciatic nerve CAP for DC CAP. SCS at T₁₂ -T₁₃ was applied continuously for two hours using: sham or hfSCS at 500 Hz SCS, 40 μsec pulse width, and 50, 70, 90, or 140% CAP threshold. Spinal cord slices from T₁₁ -L₁ were immunolabeled for c-fos, and the number of c-fos-positive cells was quantified.

RESULTS

500 Hz hfSCS applied at 90 and 140% CAP threshold produced substantial (≥6 c-fos + neurons on average per slice per segment) c-fos expression in more segments between T₁₁ and L₁ than did sham stimulation (p < 0.025, 90% CAP; p < 0.001, 140% CAP, Fisher's Exact Tests) and resulted in more c-fos-positive neurons on average per slice per segment ipsilateral to than contralateral to the SCS electrode at 70, 90, and 140% CAP threshold (p < 0.01, Wilcoxon Signed Rank Tests).

CONCLUSIONS

The finding of enhanced c-fos expression in the ipsilateral superficial dorsal horn provides evidence for activation/modulation of neuronal circuitry associated with subperception hfSCS.

A Functionally Defined In Vivo Astrocyte Population Identified by c-Fos Activation in a Mouse Model of Multiple Sclerosis Modulated by S1P Signaling: Immediate-Early Astrocytes (ieAstrocytes)

Astrocytes have prominent roles in central nervous system (CNS) function and disease, with subpopulations defined primarily by morphologies and molecular markers often determined in cell culture. Here, we identify an in vivo astrocyte subpopulation termed immediate-early astrocytes (ieAstrocytes) that is defined by functional c-Fos activation during CNS disease development. An unbiased screen for CNS cells showing c-Fos activation during experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis (MS), was developed by using inducible, TetTag c-Fos reporter mice that label activated cells with a temporally stable, nuclear green fluorescent protein (GFP). Four-dimensional (3D over time) c-Fos activation maps in the spinal cord were produced by combining tissue clearing (iDISCO) and confocal microscopy that identified onset and expansion of GFP+ cell populations during EAE. More than 95% of the GFP+ cells showed glial fibrillary acidic protein (GFAP) immunoreactivity-in contrast to absent or rare labeling of neurons, microglia, and infiltrating immune cells-which constituted ieAstrocytes that linearly increased in number with progression of EAE. ieAstrocyte formation was reduced by either astrocyte-specific genetic removal of sphingosine 1-phosphate receptor 1 (S1P1) or pharmacological inhibition by fingolimod (FTY720), an FDA-approved MS medicine that can functionally antagonize S1P1. ieAstrocytes thus represent a functionally defined subset of disease-linked astrocytes that are the first and predominant CNS cell population activated during EAE, and that track with disease severity in vivo. Their reduction by a disease-modifying agent supports their therapeutic relevance to MS and potentially other neuroinflammatory and neurodegenerative diseases.

Single oral administration of flavan 3-ols induces stress responses monitored with stress hormone elevations in the plasma and paraventricular nucleus

We previously confirmed that postprandial alterations in the circulation and metabolism after a single oral dose of flavan 3-ols (mixture of catechin and catechin oligomers) were involved in an increase in sympathetic nervous activity. However, it is well known that, in response to various stresses, activation of the hypothalamic-pituitary-adrenal (HPA) axis occurs together with sympathetic nerve activity, which is associated with activation of the sympathetic-adrenal-medullary (SAM) axis. In this study, we examined whether the HPA axis was activated after a single dose of flavan 3-ols. We administered an oral dose of 10 or 50 mg/kg flavan 3-ols to male ICR mice, removed the brains, and fixed them in paraformaldehyde-phosphate buffer. Other animals that were treated similarly were decapitated, and blood was collected. In the paraventricular nucleus (PVN), c-fos mRNA expression increased significantly at 15 min after administration of either 10 or 50 mg/kg flavan 3-ols. Corticotropin-releasing hormone (CRH) mRNA expression levels significantly increased at 240 min after administration of 10 mg/kg flavan 3-ols, and at 60 min after administration of 50 mg/kg flavan 3-ols. Plasma corticosterone levels were also significantly increased at 240 min after ingestion of 50 mg/kg flavan 3-ols. In this experiment, we confirmed that the ingestion of flavan 3-ols acted as a stressor in mammals with activation both the SAM and HPA axes.

Brainstem Nuclei Associated with Mediating Apnea-Induced Respiratory Motor Plasticity

The respiratory control system is plastic. It has a working memory and is capable of retaining how respiratory stimuli affect breathing by regulating synaptic strength between respiratory neurons. For example, repeated airway obstructions trigger a form of respiratory plasticity that strengthens inspiratory activity of hypoglossal (XII) motoneurons. This form of respiratory plasticity is known as long-term facilitation (LTF) and requires noradrenaline released onto XII motoneurons. However, the brainstem regions responsible for this form of LTF remain unidentified. Here, we used electrophysiology, neuropharmacology and immunohistochemistry in adult rats to identify the brainstem regions involved in mediating LTF. First, we show that repeated airway obstructions induce LTF of XII motoneuron activity and that inactivation of the noradrenergic system prevents LTF. Second, we show that noradrenergic cells in the locus coeruleus (LC), which project to XII motoneurons, are recruited during LTF induction. Third, we show that targeted inactivation of noradrenergic LC cells during LTF induction prevents LTF. And lastly, we show that the nucleus tractus solitarius (NTS), which has known projections to the LC, is critical for LTF because its inactivation prevents LTF. Our results suggest that both the LC and NTS are involved in mediating apnea-induced LTF, and we hypothesize that a NTS → LC → XII circuit mechanism mediates this form of respiratory motor plasticity.

NPTX2 is a key component in the regulation of anxiety

Anxiety disorders significantly impair quality of life. However, limited knowledge of the underlying mechanisms impedes the development of effective therapeutics. Previous studies have suggested that the expression of the Nptx2 gene is associated with anxiety, but the neurobiological processes underlying this association remain unclear. We generated multiple mouse models with knockout or overexpression of Nptx2 in specific brain regions and during different developmental stages to assess anxiety, adult neurogenesis, and glucocorticoid-related gene expression. Our results provide evidence that Nptx2 expression in the adult hippocampus regulates anxiety in mice. Eliminating Nptx2 expression in either the developing mouse brain or in adulthood leads to increased anxiety levels. The increase in anxiety was evident in hippocampus-specific Nptx2 knockout mice, but not in an amygdala specific knockouts. Gene expression analysis revealed increased expression of glucocorticoid receptor target genes in Nptx2 knockout mice after acute stress. Overexpression of Nptx2 in the hippocampus alleviates stress-induced anxious behaviors and reverses the changes in expression of glucocorticoid receptor related genes. In conclusion, we demonstrate that Nptx2 in the hippocampus performs a critical role in modulating anxiety, hippocampal cell proliferation, and glucocorticoid receptor related gene expression. Our results suggest Nptx2 may be a potential target for anxiolytic therapeutics.

NPAS4 recruits CCK basket cell synapses and enhances cannabinoid-sensitive inhibition in the mouse hippocampus

Experience-dependent expression of immediate-early gene transcription factors (IEG-TFs) can transiently change the transcriptome of active neurons and initiate persistent changes in cellular function. However, the impact of IEG-TFs on circuit connectivity and function is poorly understood. We investigate the specificity with which the IEG-TF NPAS4 governs experience-dependent changes in inhibitory synaptic input onto CA1 pyramidal neurons (PNs). We show that novel sensory experience selectively enhances somatic inhibition mediated by cholecystokinin-expressing basket cells (CCKBCs) in an NPAS4-dependent manner. NPAS4 specifically increases the number of synapses made onto PNs by individual CCKBCs without altering synaptic properties. Additionally, we find that sensory experience-driven NPAS4 expression enhances depolarization-induced suppression of inhibition (DSI), a short-term form of cannabinoid-mediated plasticity expressed at CCKBC synapses. Our results indicate that CCKBC inputs are a major target of the NPAS4-dependent transcriptional program in PNs and that NPAS4 is an important regulator of plasticity mediated by endogenous cannabinoids.

Growth Differentiation Factor 5 Improves Neurogenesis and Functional Recovery in Adult Mouse Hippocampus Following Traumatic Brain Injury

The aim of this study was to investigate the therapeutic effect of growth differentiation factor 5 (GDF-5) on traumatic brain injury (TBI) in mice. We utilized a controlled cortical impact to establish a mouse TBI model, and then stereotaxically administered 25 or 100 ng GDF-5 into the bilateral hippocampal dentate gyrus (DG) of each of the animals. Seven days after the injury, some of the animals were sacrificed for immunohistochemical and immunofluorescence examination of 5-bromo-2'-deoxyuridine (BrdU), Sox-2, doublecortin (DCX) and phosphorylated cAMP response element binding protein (p-CREB). Dendrite quantification was also performed using DCX positive cells. Activation of newborn neurons was assessed 35 days after the injury. The remaining animals were subjected to open field, Y maze and contextual fear conditioning tests 2 months after TBI. As a result, we found that post-injury stereotaxical administration of GDF-5 can improve neural stem cell proliferation and differentiation in the DG of the hippocampus, evidenced by the increase in BrdU, Sox-2, and DCX-labeled cells, as well as the improvement in dendrite arborization and newborn neuron activation in response to GDF-5 treatment. Mechanistically, these effects of GDF-5 may be mediated by the CREB pathway, manifested by the recovery of TBI-induced dephosphorylation of CREB upon GDF-5 administration. Behavioral tests further verified the effects of GDF-5 on improving cognitive and behavioral dysfunction after TBI. Collectively, these results reveal that direct injection of GDF-5 into the hippocampus can stimulate neurogenesis and improve functional recovery in a mouse TBI model, indicating the potential therapeutic effects of GDF-5 on TBI.

Decreased level of histone acetylation in the infralimbic prefrontal cortex following immediate extinction may result in deficit of extinction memory

In the last few decades, there has been exponential increase in studies aiming to trace the molecular mechanism of fear extinction with a hope to minimize the return of fear after exposure therapy required for operational treatment of anxiety disorders. The present study explored how the timing of extinction training after developing a specific fear, affects the consequent return of the extinguished fear and the role of histone acetylation in controlling the circuitry, thereof. It was found that rats undergone extinction training 10 min. after fear memory acquisition (Immediate Extinction) had deficits in retention of extinction memory as compared to one which underwent extinction 24 h after fear acquisition (Delayed Extinction). When the differences were sorted at the circuitry level the relative activity of the infralimbic prefrontal cortex (IL) to prelimbic cortex (PL) was found to be lower in the immediate extinction group as compared to the delayed extinction group as evidenced by the c-fos expression in the mPFC of these groups. Further investigation showed that acetylation of histone H3/H4 along with the levels of CREB binding protein (CBP) which is a histone acetyltransferase (HAT), was associated with neuronal activation and was significantly lower in the IL of the immediate extinction group than the delayed extinction group. In conclusion, the observed deficits in the immediate extinction group may be the result of compromised activation of IL, which in turn may be associated with changes in histone acetylation.

Effects of centrally administered glucagon-like peptide-2 on blood pressure and barosensitive neurons in spontaneously hypertensive rats

The central administration of glucagon-like peptide-2 (GLP-2) decreases blood pressure in rats. In the present study, we investigated the hypotensive effects of GLP-2 using spontaneously hypertensive rats (SHRs), an animal model of hypertension. The central administration of GLP-2 (0.6 μg) decreased mean arterial pressure (MAP) in SHRs (-24.1 ± 4.5%; P < 0.05), but not in normotensive Wistar-Kyoto (WKY) rats (-10.6 ± 7.4%; P > 0.05), whereas GLP-2 (6 μg) decreased MAP in WKY rats (-23.5 ± 4.2%; P < 0.05) and SHRs (-46.7 ± 11.6%; P < 0.01) under anesthesia with urethane and α-chloralose. Histological analyses revealed that the central administration of GLP-2 (6 μg) induced Fos immunoreactivity (Fos-IR) in the hypothalamic and medullary areas in WKY rats and SHRs. However, the distribution of Fos-IR in GABAergic neurons in the rostral ventrolateral medulla (RVLM) differed between WKY rats and SHRs. GLP-2 directly modulated the excitability of RVLM neurons in brainstem slices from SHRs, but not WKY rats. These results suggest that neuronal activity through the activation of GLP-2 receptors in the RVLM contributes to lowering blood pressure in SHRs.

Prolactin-induced and neuronal activation in the brain of mother mice

Nursing has important consequences on mothers. To separate the prolactin-mediated and the neuronally-mediated actions of nursing, neurons directly affected by prolactin were visualized using pSTAT5 immunohistochemistry in relation to Fos-expressing neurons in suckled mother mice. In response to pup exposure following 22-h pup deprivation, we found a markedly elevated number of pSTAT5-containing neurons in several brain regions, including the lateral septum, medial amygdaloid nucleus, subparafascicular area, caudal periaqueductal gray, dorsal raphe, lateral parabrachial nucleus, nucleus of the solitary tract, and the periventricular, medial preoptic, paraventricular, arcuate and ventromedial nuclei of the hypothalamus. Pup exposure also induced Fos expression in all of these brain regions except the arcuate and ventromedial hypothalamic nuclei. Bromocriptine treatment known to reduce prolactin levels eliminated pSTAT5 from most brain regions while it did not affect Fos activation following suckling. The degree of colocalization for pSTAT5 and Fos ranged from 8 to 80% in the different brain regions suggesting that most neurons responding to pup exposure in mother mice are driven either by prolactin or direct neuronal input from the pups, while the number of neurons affected by both types of inputs depends on the examined brain area. In addition, both pSTAT5 and Fos were also double-labeled with estrogen receptor alpha (ERα) in mother mice, which revealed a very high degree of colocalization between pSTAT5 and ERα with much less potential interaction between Fos- and ERα-containing neurons suggesting that estrogen-sensitive neurons are more likely to be affected by prolactin than by direct neuronal activation.

Central amygdala lesions inhibit pontine nuclei acoustic reactivity and retard delay eyeblink conditioning acquisition in adult rats

In delay eyeblink conditioning (EBC) a neutral conditioned stimulus (CS; tone) is repeatedly paired with a mildly aversive unconditioned stimulus (US; periorbital electrical shock). Over training, subjects learn to produce an anticipatory eyeblink conditioned response (CR) during the CS, prior to US onset. While cerebellar synaptic plasticity is necessary for successful EBC, the amygdala is proposed to enhance eyeblink CR acquisition. In the current study, adult Long-Evans rats received bilateral sham or neurotoxic lesions of the central nucleus of the amygdala (CEA) followed by 1 or 4 EBC sessions. Fear-evoked freezing behavior, CS-mediated enhancement of the unconditioned response (UR), and eyeblink CR acquisition were all impaired in the CEA lesion rats relative to sham controls. There were also significantly fewer c-Fos immunoreactive cells in the pontine nuclei (PN)-major relays of acoustic information to the cerebellum-following the first and fourth EBC session in lesion rats. In sham rats, freezing behavior decreased from session 1 to 4, commensurate with nucleus-specific reductions in amygdala Fos+ cell counts. Results suggest delay EBC proceeds through three stages: in stage one the amygdala rapidly excites diffuse fear responses and PN acoustic reactivity, facilitating cerebellar synaptic plasticity and the development of eyeblink CRs in stage two, leading, in stage three, to a diminution or stabilization of conditioned fear responding.

Neuronal activity regulates neurotransmitter switching in the adult brain following light-induced stress

The discovery that neurotransmitter identity is regulated by activity in the adult mammalian brain during a stress response raises questions about the extent and function of this plasticity. Specific synapses are associated with the release of a particular neurotransmitter or transmitters on the basis of evidence obtained under a single set of conditions. Transmitter switching endows the connectome with greater plasticity: Activity-dependent revision of signaling provides another dimension of flexibility to regulate normal behavior. Changes in transmitter identity are also positioned to contribute to diseases of the nervous system. Neurotransmitter imbalance has long been implicated in common neurological and psychiatric disorders, provoking interest in transmitter switching as a therapeutic tool for patients.

Neurotransmitter switching in the adult mammalian brain occurs following photoperiod-induced stress, but the mechanism of regulation is unknown. Here, we demonstrate that elevated activity of dopaminergic neurons in the paraventricular nucleus of the hypothalamus (PaVN) in the adult rat is required for the loss of dopamine expression after long-day photoperiod exposure. The transmitter switch occurs exclusively in PaVN dopaminergic neurons that coexpress vesicular glutamate transporter 2 (VGLUT2), is accompanied by a loss of dopamine type 2 receptors (D2Rs) on corticotrophin-releasing factor (CRF) neurons, and can lead to increased release of CRF. Suppressing activity of all PaVN glutamatergic neurons decreases the number of inhibitory PaVN dopaminergic neurons, indicating homeostatic regulation of transmitter expression in the PaVN.

Investigation of candidate long noncoding RNAs and messenger RNAs in the immediate phase of spinal cord injury based on gene expression profiles

Spinal cord injury (SCI) is a serious devastating condition and it has a high mortality rate and morbidity rate. The early pathological changes in the immediate phase of SCI may play a major part in the development of secondary injury. Alterations in the expression of many long noncoding RNAs (lncRNAs) have been shown to play fundamental roles in the diseases of the central nervous system. However, the roles of lncRNAs and messenger RNAs (mRNAs) in the immediate phase of SCI are not clear. We examined the expression of mRNAs and lncRNAs in a rat model at 2 h after SCI and identified the differentially expressed lncRNAs (DE lncRNAs) and differentially expressed mRNAs (DE mRNAs) using microarray analysis. 772 DE lncRNAs and 992 DE mRNAs were identified in spinal cord samples in the immediate phase following SCI compared with control samples. Moreover, Gene Ontology (GO) term annotation results showed that CXCR chemokine receptor binding, neutrophil apoptotic process, neutrophil migration, neutrophil extravasation, macrophage differentiation, monocyte chemotaxis and cellular response to interleukin-1 (IL-1) were the main significantly enriched GO terms. The results of Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the DEGs were enriched in toll-like receptor signaling pathway, p53 signaling pathway, MAPK signaling pathway and Jak-STAT signaling pathway. IL6, MBOAT4, FOS, TNF, JUN, STAT3, CSF2, MYC, CCL2 and FGF2 were the top 10 high-degree hub nodes and may be important targets in the immediate phase of SCI. The current study on provides novel insights into how lncRNAs and mRNAs regulate the pathogenesis of the immediate phase after SCI.

Genetic Reporters of Neuronal Activity: c-Fos and G-CaMP6

The majority of 20th century investigations into anesthetic effects on the nervous system have used electrophysiology. Yet some fundamental limitations to electrophysiologic recordings, including the invasiveness of the technique, the need to place (potentially several) electrodes in every site of interest, and the difficulty of selectively recording from individual cell types, have driven the development of alternative methods for detecting neuronal activation. Two such alternative methods with cellular scale resolution have matured in the last few decades and will be reviewed here: the transcription of immediate early genes, foremost c-fos, and the influx of calcium into neurons as reported by genetically encoded calcium indicators, foremost GCaMP6. Reporters of c-fos allow detection of transcriptional activation even in deep or distant nuclei, without requiring the accurate targeting of multiple electrodes at long distances. The temporal resolution of c-fos is limited due to its dependence upon the detection of transcriptional activation through immunohistochemical assays, though the development of RT-PCR probes has shifted the temporal resolution of the assay when tissues of interest can be isolated. GCaMP6 has several isoforms that trade-off temporal resolution for signal to noise, but the fastest are capable of resolving individual action potential events, provided the microscope used scans quickly enough. GCaMP6 expression can be selectively targeted to neuronal populations of interest, and potentially thousands of neurons can be captured within a single frame, allowing the neuron-by-neuron reporting of circuit dynamics on a scale that is difficult to capture with electrophysiology, as long as the populations are optically accessible.

c-Fos mapping of brain regions activated by multi-modal and electric foot shock stress

Real-world stressors are complex and multimodal, involving physical, psychological, and social dimensions. However, the brain networks that mediate stress responses to these stimuli need to be further studied. We used c-Fos mapping in mice to characterize brain circuits activated by exposure to a single episode of multimodal stress (MMS), and compared these to circuits activated by electric foot shocks (EFS). We focused on characterizing c-Fos activity in stress-relevant brain regions including the paraventricular nucleus (PVN) of the hypothalamus and the bed nucleus of the stria terminalis (BNST). We also assessed stress-induced activation of CRH-positive neurons in each of these structures. MMS and EFS activated an overlapping network of brain regions with a similar time course. c-Fos expression within the PVN and the BNST peaked 30–60 min after exposure to both MMS and EFS, and returned to baseline levels within 24 h. Quantification of c-Fos expression within BNST subregions revealed that while c-Fos expression peaked in all subregions 30–60 min after MMS and EFS exposure, the neuronal density of c-Fos expression was significantly higher in the dorsomedial and ventral BNST relative to the dorsolateral BNST. Our preliminary assessment indicated that a great majority of MMS or EFS-activated neurons in the PVN were CRH-positive (>87%); in contrast, about 6–35% of activated neurons in the BNST were CRH-positive. Our findings indicate that both MMS and EFS are effective at activating stress-relevant brain areas and support the use of MMS as an effective approach for studying multidimensional stress in animal models. The results also reveal that the PVN and BNST are part of a common neural circuit substrate involved in neural processing related to stress.

Activation of the subthalamic nucleus suppressed by high frequency stimulation: A c-Fos immunohistochemical study

Deep brain stimulation applied at high frequency (HFS) to the subthalamic nucleus (STN) is used to ameliorate the symptoms of Parkinson's disease. The mechanism by which this is achieved remains controversial. In particular, it is uncertain whether HFS has a suppressive or excitatory action locally within the STN. Brief exposure of rats to ether anesthesia evokes pathological burst firing and associated expression of the immediate early gene c-Fos in STN neurons. We used this ether model of STN activation to test the effect of a range of HFS parameters on c-Fos expression evoked by the anesthetic. The elevated baseline of c-Fos expression afforded the possibility of detecting further excitatory, or suppressive effects of STN HFS. Four HFS protocols were examined; 130, 200 and 260 Hz with 60 µs, and 130 Hz with 90 µs pulse width (HFS intensity:150-300 µA). All HFS protocols were applied for 20 min while the animals were exposed to ether. Ether-evoked expression of c-Fos immunoreactivity was suppressed by HFS at 200 and 260 Hz with a pulse width of 60 µs, and by 130 Hz when the pulse width was increased to 90 µs. HFS at 130 Hz with the 60 µs pulse width had no significant effect and HFS alone caused negligible c-Fos expression in the STN. These findings suggest that HFS of the STN causes significant suppression of evoked neuronal activity. It remains to be determined whether this locally suppressive property of HFS is associated with the efficacy of STN deep brain stimulation to relieve the symptoms of Parkinson's disease.

Relevance of deprivation studies in understanding rapid eye movement sleep

Rapid eye movement sleep (REMS) is a unique phenomenon essential for maintaining normal physiological processes and is expressed at least in species higher in the evolution. The basic scaffold of the neuronal network responsible for REMS regulation is present in the brainstem, which may be directly or indirectly influenced by most other physiological processes. It is regulated by the neurons in the brainstem. Various manipulations including chemical, elec-trophysiological, lesion, stimulation, behavioral, ontogenic and deprivation studies have been designed to understand REMS genesis, maintenance, physiology and functional significance. Although each of these methods has its significance and limitations, deprivation studies have contributed significantly to the overall understanding of REMS. In this review, we discuss the advantages and limitations of various methods used for REMS deprivation (REMSD) to understand neural regulation and physiological significance of REMS. Among the deprivation strategies, the flowerpot method is by far the method of choice because it is simple and convenient, exploits physiological parameter (muscle atonia) for REMSD and allows conducting adequate controls to overcome experimental limitations as well as to rule out nonspecific effects. Notwithstanding, a major criticism that the flowerpot method faces is that of perceived stress experienced by the experimental animals. Nevertheless, we conclude that like most methods, particularly for in vivo behavioral studies, in spite of a few limitations, given the advantages described above, the flowerpot method is the best method of choice for REMSD studies.

Acute Impact of Selected Pyridoindole Derivatives on Fos Expression in Different Structures of the Rat Brain

The impacts of three pyridoindole derivatives (PDs), designated as PD144, PD143, and PD104, which have previously been shown to have antidepressant (PD144) and anxiolytic (PD143, PD104) properties, were investigated on the Fos expressions in 11 different rat brain areas, including the medial prefrontal cortex, striatum, septum, accumbens nucleus (shell, core), bed nucleus of the stria terminalis, hypothalamic paraventricular nucleus, central amygdala, locus coeruleus, dorsal raphe nucleus, and the solitary tract nucleus. Control rats received vehicle, while the other three groups the PDs in a dose of 25 mg/kg/b.w. The animals were transcardially perfused with a fixative 90 min after the treatments. Coronal sections of 40-µm thickness were processed for Fos-immunostaining by avidin-biotin-peroxidase complex and visualized by nickel-intensified diaminobenzidine complex. Fos-labeled sections were counterstained with neuropeptides including corticoliberine (CRH), oxytocin (OXY), vasopressin (AVP), and vasoactive intestinal polypeptide (VIP) and processed for immunofluorescence staining using Alexa Fluor 555 dye. In all the three groups of animals, the upregulation of PDs-induced Fos expression only in 2 of 11 brain areas was investigated, namely, in the hypothalamic paraventricular nucleus (PVN) and the central amygdaloid nucleus (CeA). The other brain structures studied were devoid of Fos expression. Counterstaining of the Fos-labeled CeA-containing sections with VIP antibody revealed that the Fos expression stimulated by the PDs was upregulated in all the CeA subdivisions (lateral, ventral, capsular), except the medial one. Dual immunoprocessings showed Fos/CRH-labeling in both the PVN and the amygdala and Fos/OXY in the PVN. No Fos/AVP colocalizations were seen in the PVN. The obtained data provide the first view on the intracerebral effects of three new PDs derivatives, which effects were restricted only to the PVN and CeA areas. The present data may help to improve our understanding of the impact of the selected PDs on the brain and to anticipate possible behavioral and neuroendocrine consequences.

Hypothalamic ΔFosB prevents age-related metabolic decline and functions via SNS

The ventral hypothalamus (VHT) integrates several physiological cues to maintain glucose homeostasis and energy balance. Aging is associated with increased glucose intolerance but the underlying mechanisms responsible for age-related metabolic decline, including neuronal signaling in the VHT, remain elusive. We have shown that mice with VHT-targeted overexpression of ∆FosB, a splice variant of the AP1 transcription factor FosB, exhibit increased energy expenditure, leading to decreased adiposity. Here, we show that VHT-targeted overexpression of ∆FosB also improves glucose tolerance, increases insulin sensitivity in target organs and thereby suppresses insulin secretion. These effects are also observed by the overexpression of dominant negative JunD, demonstrating that they occur via AP1 antagonism within the VHT. Furthermore, the improved glucose tolerance and insulin sensitivity persisted in aged animals overexpressing ∆FosB in the VHT. These beneficial effects on glucose metabolism were abolished by peripheral sympathectomy and α-adrenergic, but not β-adrenergic, blockade. Taken together, our results show that antagonizing AP1 transcription activity in the VHT leads to a marked improvement in whole body glucose homeostasis via activation of the SNS, conferring protection against age-related impairment in glucose metabolism. These findings may open novel avenues for therapeutic intervention in diabetes and age-related glucose intolerance.

Downregulation of KCNMB4 expression and changes in BK channel subtype in hippocampal granule neurons following seizure activity

A major challenge is to understand maladaptive changes in ion channels that sets neurons on a course towards epilepsy development. Voltage- and calcium-activated K+ (BK) channels contribute to early spike timing in neurons, and studies indicate that the BK channel plays a pathological role in increasing excitability early after a seizure. Here, we have investigated changes in BK channels and their accessory β4 subunit (KCNMB4) in dentate gyrus (DG) granule neurons of the hippocampus, key neurons that regulate excitability of the hippocampus circuit. Two days after pilocarpine-induced seizures, we found that the predominant effect is a downregulation of the β4 accessory subunit mRNA. Consistent with reduced expression, single channel recording and pharmacology indicate a switch in the subtype of channels expressed; from iberiotoxin-resistant, type II BK channels (BK α/β4) that have higher channel open probability and slow gating, to iberiotoxin-sensitive type I channels (BK α alone) with low open probability and faster gating. The switch to a majority of type I channel expression following seizure activity is correlated with a loss of BK channel function on spike threshold while maintaining the channel’s contribution to increased early spike frequency. Using heterozygous β4 knockout mice, we find reduced expression is sufficient to increase seizure sensitivity. We conclude that seizure-induced downregulation of KCNMB4 is an activity dependent mechanism that increases the excitability of DG neurons. These novel findings indicate that BK channel subtypes are not only defined by cell-specific expression, but can also be plastic depending on the recent history of neuronal excitability.

Hyperalgesia and sensitization of dorsal horn neurons following activation of NK-1 receptors in the rostral ventromedial medulla

Neurons in the rostral ventromedial medulla (RVM) project to the spinal cord and are involved in descending modulation of pain. Several studies have shown that activation of neurokinin-1 (NK-1) receptors in the RVM produces hyperalgesia, although the underlying mechanisms are not clear. In parallel studies, we compared behavioral measures of hyperalgesia to electrophysiological responses of nociceptive dorsal horn neurons produced by activation of NK-1 receptors in the RVM. Injection of the selective NK-1 receptor agonist Sar9,Met(O2)11-substance P (SSP) into the RVM produced dose-dependent mechanical and heat hyperalgesia that was blocked by coadministration of the selective NK-1 receptor antagonist L-733,060. In electrophysiological studies, responses evoked by mechanical and heat stimuli were obtained from identified high-threshold (HT) and wide dynamic range (WDR) neurons. Injection of SSP into the RVM enhanced responses of WDR neurons, including identified neurons that project to the parabrachial area, to mechanical and heat stimuli. Since intraplantar injection of capsaicin produces robust hyperalgesia and sensitization of nociceptive spinal neurons, we examined whether this sensitization was dependent on NK-1 receptors in the RVM. Pretreatment with L-733,060 into the RVM blocked the sensitization of dorsal horn neurons produced by capsaicin. c-Fos labeling was used to determine the spatial distribution of dorsal horn neurons that were sensitized by NK-1 receptor activation in the RVM. Consistent with our electrophysiological results, administration of SSP into the RVM increased pinch-evoked c-Fos expression in the dorsal horn. It is suggested that targeting this descending pathway may be effective in reducing persistent pain.NEW & NOTEWORTHY It is known that activation of neurokinin-1 (NK-1) receptors in the rostral ventromedial medulla (RVM), a main output area for descending modulation of pain, produces hyperalgesia. Here we show that activation of NK-1 receptors produces hyperalgesia by sensitizing nociceptive dorsal horn neurons. Targeting this pathway at its origin or in the spinal cord may be an effective approach for pain management.

Differential induction of c-Fos and phosphorylated ERK by a noxious stimulus after peripheral nerve injury

PURPOSE

In this study, we compared induction of c-Fos and phosphorylated extracellular signal-regulated kinase (p-ERK) in the spinal dorsal horn after peripheral nerve injury.

MATERIALS AND METHODS

We examined the spinal dorsal horn for noxious heat-induced c-Fos and p-ERK protein-like immunoreactive (c-Fos- and p-ERK-IR) neuron profiles after tibial nerve injury. The effect of administration of a MEK 1/2 inhibitor (PD98059) on noxious heat-induced c-Fos expression was also examined after tibial nerve injury.

RESULTS

A large number of c-Fos- and p-ERK-IR neuron profiles were induced by noxious heat stimulation to the hindpaw in sham-operated animals. A marked reduction in the number of c-Fos- and p-ERK-IR neuron profiles was observed in the medial 1/3 (tibial territory) of the dorsal horn at 3 and 7 days after nerve injury. Although c-Fos-IR neuron profiles had reappeared by 14 days after injury, the number of p-ERK-IR neuron profiles remained decreased in the tibial territory of the superficial dorsal horn. Double immunofluorescence labeling for c-Fos and p-ERK induced by noxious heat stimulation to the hindpaw at different time points revealed that a large number of c-Fos-IR, but not p-ERK-IR, neuron profiles were distributed in the tibial territory after injury. Although administration of a MEK 1/2 inhibitor to the spinal cord suppressed noxious heat-induced c-Fos expression in the peroneal territory, this treatment did not alter c-Fos induction in the tibial territory after nerve injury.

CONCLUSIONS

ERK phosphorylation may be involved in c-Fos induction in normal nociceptive responses, but not in exaggerated c-Fos induction after nerve injury.

Sacral Neuromodulation for Fecal Incontinence: A Review of the Central Mechanisms of Action

OBJECTIVE

Fecal incontinence (FI) has a devastating effect on the quality of life and results in social isolation. Sacral neuromodulation (SNM) is proven to be an effective, minimal invasive treatment modality for FI. Despite the increasing application of SNM, the exact mechanisms of action remain unclear. The initial assumption of peripheral motor neurostimulation is not supported by increasing evidence, which report effects of SNM outside the pelvic floor. A new hypothesis states that afferent signals to the brain are essential for a successful therapy. This study aimed to review relevant studies on the central mechanism of SNM in FI.

METHODS

Clinical and experimental studies on the central mechanisms, both brain and spinal cord, of SNM for FI up to December 2015 were evaluated.

RESULTS

In total, 8 studies were found describing original data on the central mechanism of SNM for FI. Four studies evaluated the central effects of SNM in a clinical setting and 4 studies evaluated the central effects of SNM in an experimental animal model. Results demonstrated a variety of (sub)cortical and spinal changes after induction of SNM.

CONCLUSION

Review of literature demonstrated evidence for a central mechanism of action of SNM for FI. The corticoanal pathways, brainstem, and specific parts of the spinal cord are involved.

Whole-brain metallomic analysis of the common marmoset (Callithrix jacchus)

Despite the importance of transition metals for normal brain function, relatively little is known about the distribution of these elemental species across the different tissue compartments of the primate brain. In this study, we employed laser ablation-inductively coupled plasma-mass spectrometry on PFA-fixed brain sections obtained from two adult common marmosets. Concurrent cytoarchitectonic, myeloarchitectonic, and chemoarchitectonic measurements allowed for identification of the major neocortical, archaecortical, and subcortical divisions of the brain, and precise localisation of iron, manganese, and zinc concentrations within each division. Major findings across tissue compartments included: (1) differentiation of white matter tracts from grey matter based on manganese and zinc distribution; (2) high iron concentrations in the basal ganglia, cortex, and substantia nigra; (3) co-localization of high concentrations of iron and manganese in the primary sensory areas of the cerebral cortex; and (4) high manganese in the hippocampus. The marmoset has become a model species of choice for connectomic, aging, and transgenic studies in primates, and the application of metallomics to these disciplines has the potential to yield high translational and basic science value.

The genetic audiogenic seizure hamster from Salamanca: The GASH:Sal

The hamster has been previously described as a paroxysmal dystonia model, but our strain is currently recognized as a model of audiogenic seizures (AGS). The original first epileptic hamster appeared spontaneously at the University of Valladolid, where it was known as the GPG:Vall line, and was transferred to the University of Salamanca where a new strain was developed, named GASH:Sal. By testing auditory brainstem responses, the GASH:Sal exhibits elevated auditory thresholds that indicate a hearing impairment. Moreover, amplified fragment length polymorphism analysis distinguished genetic differences between the susceptible GASH:Sal hamster strain and the control Syrian hamsters. The GASH:Sal constitutes an experimental model of reflex epilepsy of audiogenic origin derived from an autosomal recessive disorder. Thus, the GASH:Sal exhibits generalized tonic-clonic seizures, characterized by a short latency period after auditory stimulation, followed by wild running, a convulsive phase, and finally stupor, with origin in the brainstem. The seizure profile of the GASH:Sal is similar to those exhibited by other models of inherited AGS susceptibility, which decreases after six months of age, but the proneness across generations is maintained. The GASH:Sal can be considered a reliable model of audiogenic seizures, suitable to investigate current antiepileptic pharmaceutical treatments as well as novel therapeutic drugs. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

c-Fos and Arc/Arg3.1 expression in auditory and visual cortices after hearing loss: Evidence of sensory crossmodal reorganization in adult rats

Cross-modal reorganization in the auditory and visual cortices has been reported after hearing and visual deficits mostly during the developmental period, possibly underlying sensory compensation mechanisms. However, there are very few data on the existence or nature and timeline of such reorganization events during sensory deficits in adulthood. In this study, we assessed long-term changes in activity-dependent immediate early genes c-Fos and Arc/Arg3.1 in auditory and neighboring visual cortical areas after bilateral deafness in young adult rats. Specifically, we analyzed qualitatively and quantitatively c-Fos and Arc/Arg3.1 immunoreactivity at 15 and 90 days after cochlea removal. We report extensive, global loss of c-Fos and Arc/Arg3.1 immunoreactive neurons in the auditory cortex 15 days after permanent auditory deprivation in adult rats, which is partly reversed 90 days after deafness. Simultaneously, the number and labeling intensity of c-Fos- and Arc/Arg3.1-immunoreactive neurons progressively increase in neighboring visual cortical areas from 2 weeks after deafness and these changes stabilize three months after inducing the cochlear lesion. These findings support plastic, compensatory, long-term changes in activity in the auditory and visual cortices after auditory deprivation in the adult rats. Further studies may clarify whether those changes result in perceptual potentiation of visual drives on auditory regions of the adult cortex.

The PTZ kindling mouse model of epilepsy exhibits exploratory drive deficits and aberrant activity amongst VTA dopamine neurons in both familiar and novel space

Recurrent seizures that define epilepsy are often accompanied by psychosocial problems and cognitive deficits with incompletely understood aetiology. We therefore used the pentylenetetrazol (PTZ) kindling model of epilepsy in mice to examine potential seizure-associated neuropathologies, focusing on motivation, memory and novel-environment-induced activation of midbrain dopaminergic neurons. In addition to recurrent seizures, we found that PTZ kindling led to a strong suppression of novelty-driven exploration while largely sparing fear-driven exploration. The deficits in exploratory drive may be relevant for other cognitive impairments since reduced unassisted rearing in a learning arena correlated with poorer spatial memory of object location. Using c-Fos immunofluorescence as a marker of neuronal activity, we observed that dopamine neurons within the ventral tegmental area (VTA) of PTZ kindled mice demonstrate hyperactivity at baseline and hypoactivity in response to a novel environment compared to saline-injected cagemate controls. These data extend previous findings of PTZ kindling-mediated disruptions of hippocampal processes important for novel environment recognition and learning by demonstrating PTZ kindling also induces motivational deficits that are associated with reduced stimulus-evoked activation of VTA dopamine neurons. More broadly, these data help understand the aetiology of complex behavioural changes in the PTZ kindling model, and may assist in the development of superior diagnoses and treatments for epilepsy.

Left-right functional asymmetry of ventral hippocampus depends on aversiveness of situations

Many studies suggest that animals exhibit lateralized behaviors during aversive situations, and almost all animals exhibit right hemisphere-dominant behaviors associated with fear or anxiety. However, which brain structure in each hemisphere underlies such lateralized function is unclear. In this study, we focused on the hippocampus and investigated the effects of bilateral and unilateral lesions of the ventral hippocampus (VH) on anxiety-like behavior using the successive alleys test. We also examined the expression of c-fos in the VH, which was induced by an aversive situation. Results revealed that consistent right VH dominance trended with the anxiety level. Weaker anxiety induced both right and left VH functions, whereas stronger anxiety induced right VH function. From these results, we conclude that animals are able to adaptively regulate their behaviors to avoid aversive stimuli by changing the functional dominance of their left and right VH.

Tryptophan overloading activates brain regions involved with cognition, mood and anxiety

Tryptophan is the only precursor of serotonin and mediates serotonergic activity in the brain. Previous studies have shown that the administration of tryptophan or tryptophan depletion significantly alters cognition, mood and anxiety. Nevertheless, the neurobiological alterations that follow these changes have not yet been fully investigated. The aim of this study was to verify the effects of a tryptophan-enriched diet on immunoreactivity to Fos-protein in the rat brain. Sixteen male Wistar rats were distributed into two groups that either received standard chow diet or a tryptophan-enriched diet for a period of thirty days. On the morning of the 31st day, animals were euthanized and subsequently analyzed for Fos-immunoreactivity (Fos-ir) in the dorsal and median raphe nuclei and in regions that receive serotonin innervation from these two brain areas. Treatment with a tryptophan-enriched diet increased Fos-ir in the prefrontal cortex, nucleus accumbens, paraventricular hypothalamus, arcuate and ventromedial hypothalamus, dorsolateral and dorsomedial periaqueductal grey and dorsal and median raphe nucleus. These observations suggest that the physiological and behavioral alterations that follow the administration of tryptophan are associated with the activation of brain regions that regulate cognition and mood/anxiety-related responses.