c-Fos Expression In Neurons Research Articles

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.

Schizophrenia-Like Dopamine Release Abnormalities in a Mouse Model of NMDA Receptor Hypofunction.

Amphetamine-induced augmentation of striatal dopamine and its blunted release in prefrontal cortex (PFC) is a hallmark of schizophrenia pathophysiology. Although N-methyl-D-aspartate receptor (NMDAR) hypofunction is also implicated in schizophrenia, it remains unclear whether NMDAR hypofunction leads to dopamine release abnormalities. We previously demonstrated schizophrenia-like phenotypes in GABAergic neuron-specific NMDAR hypofunctional mutant mice, in which Ppp1r2-Cre dependent deletion of indispensable NMDAR channel subunit Grin1 is induced in corticolimbic GABAergic neurons including parvalbumin (PV)-positive neurons, in postnatal development, but not in adulthood. Here, we report enhanced dopaminomimetic-induced locomotor activity in these mutants, along with bidirectional, site-specific changes in in vivo amphetamine-induced dopamine release: nucleus accumbens (NAc) dopamine release was enhanced by amphetamine in postnatal Ppp1r2-Cre/Grin1 knockout (KO) mice, whereas dopamine release was dramatically reduced in the medial PFC (mPFC) compared to controls. Basal tissue dopamine levels in both the NAc and mPFC were unaffected. Interestingly, the magnitude and distribution of amphetamine-induced c-Fos expression in dopamine neurons was comparable between genotypes across dopaminergic input subregions in the ventral tegmental area (VTA). These effects appear to be both developmentally and cell-type specifically modulated, since PV-specific Grin1 KO mice could induce the same effects as seen in postnatal-onset Ppp1r2-Cre/Grin1 KO mice, but no such abnormalities were observed in somatostatin-Cre/Grin1 KO mice or adult-onset Ppp1r2-Cre/Grin1 KO mice. These results suggest that PV GABAergic neuron-NMDAR hypofunction in postnatal development confers bidirectional NAc hyper- and mPFC hypo-sensitivity to amphetamine-induced dopamine release, similar to that classically observed in schizophrenia pathophysiology.

Activation of astrocytic PAR1 receptors in the rat nucleus of the solitary tract regulates breathing through modulation of presynaptic TRPV1.

In the rat nucleus of the solitary tract (NTS), activation of astrocytic proteinase-activated receptor 1 (PAR1) receptors leads to potentiation of neuronal synaptic activity by two mechanisms, one TRPV1-dependent and one TRPV1-independent. PAR1-dependent activation of presynaptic TRPV1 receptors facilitates glutamate release onto NTS neurons. The TRPV1-dependent mechanism appears to rely on astrocytic release of endovanilloid-like molecules. A subset of NTS neurons excited by PAR1 directly project to the rostral ventral respiratory group. The PAR1 initiated, TRPV1-dependent modulation of synaptic transmission in the NTS contributes to regulation of breathing. Many of the cellular and molecular mechanisms underlying astrocytic modulation of synaptic function remain poorly understood. Recent studies show that G-protein coupled receptor-mediated astrocyte activation modulates synaptic transmission in the nucleus of the solitary tract (NTS), a brainstem nucleus that regulates crucial physiological processes including cardiorespiratory activity. By using calcium imaging and patch clamp recordings in acute brain slices of wild-type and TRPV1-/- rats, we show that activation of proteinase-activated receptor 1 (PAR1) in NTS astrocytes potentiates presynaptic glutamate release on NTS neurons. This potentiation is mediated by both a TRPV1-dependent and a TRPV1-independent mechanism. The TRPV1-dependent mechanism appears to require release of endovanilloid-like molecules from astrocytes, which leads to subsequent potentiation of presynaptic glutamate release via activation of presynaptic TRPV1 channels. Activation of NTS astrocytic PAR1 receptors elicits cFOS expression in neurons that project to respiratory premotor neurons and inhibits respiratory activity in control, but not in TRPV1-/- rats. Thus, activation of astrocytic PAR1 receptor in the NTS leads to a TRPV1-dependent excitation of NTS neurons causing a potent modulation of respiratory motor output.

Increased acetylcholine and glutamate efflux in the prefrontal cortex following intranasal orexin-A (hypocretin-1).

Orexin/hypocretin neurons of the lateral hypothalamus and perifornical area are integrators of physiological function. Previous work from our laboratory and others has shown the importance of orexin transmission in cognition. Age-related reductions in markers of orexin function further suggest that this neuropeptide may be a useful target for the treatment of age-related cognitive dysfunction. Intranasal administration of orexin-A (OxA) has shown promise as a therapeutic option for cognitive dysfunction. However, the neurochemical mechanisms of intranasal OxA administration are not fully understood. Here, we use immunohistochemistry and invivo microdialysis to define the effects of acute intranasal OxA administration on: (i) activation of neuronal populations in the cortex, basal forebrain, and brainstem and (ii) acetylcholine (ACh) and glutamate efflux in the prefrontal cortex (PFC) of Fischer 344/Brown Norway F1 rats. Acute intranasal administration of OxA significantly increased c-Fos expression, a marker for neuronal activation, in the PFC and in subpopulations of basal forebrain cholinergic neurons. Subsequently, we investigated the effects of acute intranasal OxA on neurotransmitter efflux in the PFC and found that intranasal OxA significantly increased both ACh and glutamate efflux in this region. These findings were independent from any changes in c-Fos expression in orexin neurons, suggesting that these effects are not resultant from direct activation of orexin neurons. In total, these data indicate that intranasal OxA may enhance cognition through activation of distinct neuronal populations in the cortex and basal forebrain and through increased neurotransmission of ACh and glutamate in the PFC.

Effect of Daily Light on c-Fos Expression in the Suprachiasmatic Nucleus under Jet Lag Conditions.

Jet-lag symptoms arise from temporal misalignment between the internal circadian clock and external solar time when traveling across multiple time zones. Light is known as a strong timing cue of the circadian clock. We here examined the effect of daily light on the process of jet lag by detecting c-Fos expression in the master clock neurons in the suprachiasmatic nucleus (SCN) under 8-hr phase-advanced jet lag condition. In WT mice, c-Fos-immunoreactivity was found at 1–2 hours on the first day after light/dark (LD) phase-advance. This induction was also observed on the second and third days, although their levels were diminished day by day. In contrast, c-Fos induction in the SCN of V1a–/–V1b–/– mice, which show virtually no jet lag symptoms even after 8-hr phase-advance, was only detected on the first day. These results indicate that external light has affected SCN neuronal activity for 3 days after LD phase-advance in WT mice suggesting the continuous progress of activity change of SCN neurons under jet lag conditions. Noteworthy, limited c-Fos induction in V1a–/–V1b–/– SCN is also consistent with the rapid reentrainment of the SCN clock in mutant mice after 8-hr LD phase-advance.

Calcimimetic R568 inhibits tetrodotoxin-sensitive colonic electrolyte secretion and reduces c-fos expression in myenteric neurons

AimsCalcium-sensing receptor (CaSR) is expressed on neurons of both submucosal and myenteric plexuses of the enteric nervous system (ENS) and the CaSR agonist R568 inhibited Cl− secretion in intestine. The purpose of this study was to localize the primary site of action of R568 in the ENS and to explore how CaSR regulates secretion through the ENS. Materials and methodsTwo preparations of rat proximal and distal colon were used. The full-thickness preparation contained both the submucosal and myenteric plexuses, whereas for the “stripped” preparation the myenteric plexus with the muscle layers was removed. Both preparations were mounted onto Ussing chambers and Cl− secretory responses were compared by measuring changes in short circuit current (Isc). Two tissue-specific CaSR knockouts (i.e., neuron-specific vs. enterocyte-specific) were generated to compare the effect of R568 on expression of c-fos protein in myenteric neurons by immunocytochemistry. Key findingsIn full-thickness colons, tetrodotoxin (TTX) inhibited Isc, both in proximal and distal colons. A nearly identical inhibition was produced by R568. However, in stripped preparations, while the effect of TTX on Isc largely remained, the effect of R568 was nearly completely eliminated. In keeping with this, R568 reduced c-fos protein expression only in myenteric neurons of wild type mice and mutant mice that contained CaSR in neurons (i.e., villinCre/Casrflox/flox mice), but not in myenteric neurons of nestinCre/Casrflox/flox mice in which neuronal cell CaSR was eliminated. SignificanceThese results indicate that R568 exerts its anti-secretory effects predominantly via CaSR-mediated inhibition of neuronal activity in the myenteric plexus.

Cerebral Structures Responsible for the Formation of Autonomic Reflexes Related to Realization of Motivated Operant Movements by Rats

We studied changes in the levels of Fos immunoreactivity and NADPH diaphorase reactivity in the autonomic nuclei and catecholaminergic (CA) groups of brainstem cells in rats that realized food-procuring movements by the forelimb. Fos-immunoreactivity in the medullary nuclei of the autonomic nervous system, ANS (Sol, IRt, CVL/RVL), of these animals was appreciably higher than that in control rats. Under such conditions, a considerable part of motoneurons in the brainstem autonomic motor nuclei (10, Amb, and RAmb) were activated. In the motor nuclei of the vagus nerve, large Fos-immunoreactive (Fos-ir) neurons were observed. In rats, therefore, intense autonomic reactions closely related to realization of a motor program develop during sessions of operant food-procuring movements. The expression of protein c-Fos in brainstem CA neurons during the performance of operant movements was intensified, mostly on the contralateral side. In the brainstem CA groups А5 and А6 (LC/SC), we observed a maximum number of Fos-ir neurons, as compared with the control values. These cell groups are formed mostly of noradrenergic neurons that are the main sources of descending inhibitory inputs to the spinal thorasic and lumbar intermediolateral sympathetic nuclei. Therefore, the ANS can directly influence the functioning of muscle spindles and proprioceptors and can, as a result, influence the realization of motor program.

Acute Administration of the Nonpathogenic, Saprophytic Bacterium, Mycobacterium vaccae, Induces Activation of Serotonergic Neurons in the Dorsal Raphe Nucleus and Antidepressant-Like Behavior in Association with Mild Hypothermia.

Peripheral immune activation can have profound physiologic and behavioral effects. One mechanism through which immune activation may affect physiology and behavior is through actions on brainstem neuromodulatory systems, such as serotonergic systems. To test this hypothesis, in Experiment 1, adult male BALB/c mice were implanted with telemetric recording devices and then immunized with Mycobacterium vaccae NCTC 11659 (0.1mg, s.c.; Days -28, -14; N=36). On Day 1, mice received an acute challenge with M. vaccae (0.1mg, s.c.) or borate-buffered saline vehicle. Core body temperature and locomotor activity recordings were conducted during a 36h period beginning 24h prior to challenge; 12h following acute challenge, mice were either tested in a 6-min forced swim test, or served as home cage controls (n=9 per group). In Experiment 2, the protocol was repeated, but with the aim of assessing c-Fos expression in brainstem serotonergic neurons, assessed 90min following exposure to forced swim (N=32; n=8 per group). In Experiment 1, acute M. vaccae challenge in M. vaccae-immunized mice, relative to vehicle-challenged controls, decreased locomotor activity and core body temperature measured 3h following challenge, as measured by continuous telemetric recordings, and decreased immobility in the forced swim test measured 12h following challenge. In Experiment 2, acute M. vaccae challenge in M. vaccae-immunized mice decreased home cage locomotion, in alignment with findings in Experiment 1, as measured by video-based behavioral analysis, and, among mice exposed to the forced swim test, increased c-Fos expression in subsets of serotonergic neurons within the dorsal raphe nucleus (DR) measured 13.5h following challenge. Together, these data are consistent with the hypothesis that acute peripheral immune activation with a heat-killed preparation of M. vaccae transiently induces mild hypothermia in association with suppression of locomotor activity, activates subsets of serotonergic neurons in the DR, and induces antidepressant-like behavioral responses.

Paeoniflorin attenuates postoperative pain by suppressing Matrix Metalloproteinase‐9/2 in mice

Recent studies have implicated that matrix metalloproteinase (MMP)-9 and MMP-2 play key roles in neuropathic pain due to their facilitation of inflammatory cytokine maturation and induction of neuroinflammation. However, the role of MMP-9/2 in postoperative pain is still unclear. We previously suggested that the natural compound paeoniflorin inhibited microglia activation induced by morphine treatment. In the present study, we demonstrated that paeoniflorin could alleviate postoperative pain via specific inhibition of matrix metalloproteinases (MMPs). Mice received a plantar incision surgery and their mechanical allodynia was assessed with von Frey filaments. The activity of MMP-9/2 was determined by gelatin zymography. Cell signalling was assayed by western blot and immunohistochemistry. The expression of MMP-9/2 was significantly increased in mice spinal cords with plantar incision surgery. Paeoniflorin remarkably suppressed the activity of MMP-9/2 and relieved plantar incision-induced mechanical allodynia. Interestingly, the administration of paeoniflorin blocked the maturation of interleukin-1β, which is a critical substrate of MMPs. Thereafter, paeoniflorin markedly suppressed microglia activation, inhibited the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and the expression of neuronal c-Fos. These results indicated that MMP-9/2 activation in spinal microglia plays a key role in incision-induced mechanical allodynia in mice. Moreover, utilizing paeniflorin blockage of the microglia MMP-9/2 activity might represent a valuable alternative for treating postoperative pain. Our results provided direct evidence for the first time that paeoniflorin can inhibit plantar incision-induced microglia TLR4/MMP-9/2/IL-1β signalling pathway and suppress postoperative pain. Thus, regulation of microglia MMP-9/2 may provide a new strategy for ameliorating postoperative pain.

Dopamine D1 receptor subtype mediates acute stress-induced dendritic growth in excitatory neurons of the medial prefrontal cortex and contributes to suppression of stress susceptibility in mice.

Dopamine in prefrontal cortices is implicated in cognitive and emotional functions, and the dysfunction of prefrontal dopamine has been associated with cognitive and emotional deficits in mental illnesses. These findings have led to clinical trials of dopamine-targeting drugs and brain imaging of dopamine receptors in patients with mental illnesses. Rodent studies have suggested that dopaminergic pathway projecting to the medial prefrontal cortex (mPFC) suppresses stress susceptibility. Although various types of mPFC neurons express several dopamine receptor subtypes, previous studies neither isolated a role of dopamine receptor subtype nor identified the site of its action in mPFC. Using social defeat stress (SDS) in mice, here we identified a role of dopamine D1 receptor subtype in mPFC excitatory neurons in suppressing stress susceptibility. Repeated social defeat stress (R-SDS) reduces the expression of D1 receptor subtype in mPFC of mice susceptible to R-SDS. Knockdown of D1 receptor subtype in whole neuronal populations or excitatory neurons in mPFC facilitates the induction of social avoidance by SDS. Single social defeat stress (S-SDS) induces D1 receptor-mediated extracellular signal-regulated kinase phosphorylation and c-Fos expression in mPFC neurons. Whereas R-SDS reduces dendritic lengths of mPFC layer II/III pyramidal neurons, S-SDS increases arborization and spines of apical dendrites of these neurons in a D1 receptor-dependent manner. Collectively, our findings show that D1 receptor subtype and related signaling in mPFC excitatory neurons mediate acute stress-induced dendritic growth of these neurons and contribute to suppression of stress susceptibility. Therefore, we propose that D1 receptor-mediated dendritic growth in mPFC excitatory neurons suppresses stress susceptibility.

Effects of GABA microinjection into dorsal raphe nucleus on behavior and activity of lateral habenular neurons in mice

The dorsal raphe nucleus (DRN) is a key site for 5-hydroxytryptamine (5-HT) synthesis and release. DRN dysfunction has been implicated in several stress-related disorders, including depression and anxiety. The lateral habenular nucleus (LHb) has been shown to inhibit the activity of DRN 5-HT neurons, and thus the LHb-DRN pathway plays an important role in the pathogenesis of depression. Although it is known that the LHb also receives the projection from the 5-HT neuron in the DRN, whether 5-HT neurons in the DRN can influence activity of the LHb in vivo and whether this effect is related to the induced behavioral changes have not been investigated. In the current study, we determined how injecting γ-aminobutyric acid (GABA) into the DRN to inhibit 5-HT neurons affected behavior and the changes in the activity of LHb neurons in mice. We found that GABA injection into the DRN induced depression-like behavior in mice, as indicated by increased immobility time, and decreased climbing time in the forced swimming test and the tail suspension test, decreased time spent in the center and total distance moved in the open field test. Using extracellular single unit recording, we showed that the firing rate of LHb neurons decreased after GABA microinjection into the DRN. Further, c-Fos expression in LHb neurons was inhibited. Together our results indicate that inhibition of DRN 5-HT neurons can cause decreased LHb activity and depression-like behavior in mice, however this depression-like behavior could be independent of the LHb activity. The observed decrease in LHb activity is probably due to the presence of a negative feedback loop between the DRN and the LHb, which may play a role in maintaining emotional homeostasis.

The protective effects of electro-acupuncture in thoracic surgery on trauma stressed rats involve the rostral ventrolateral medulla and supraoptic nucleus.

The present study was designed to explore whether the rostral ventrolateral medulla (RVLM) and supraoptic nucleus (SON) were involved in the protective effects of electro-acupuncture (EA) in thoracic surgery on trauma-stressed rats. The rats were randomly divided into a non-stressed group (Control), surgical trauma-stressed group (Trauma), and Neiguan EA applied on the surgical trauma-stressed group (Trauma+EA-PC 6). RVLM neuron discharge was observed by using an in vivo electrophysiological method, and micro-dialysis combining high-performance liquid chromatography with fluorometric detection (HPLC-FD) was used to assess expression of amino acids in the RVLM. Immunohistochemical methods were used to assess c-Fos expression in SON neurons. The trauma of surgical stress was shown to dramatically increase the discharge frequency of RVLM neurons and promote the release of glutamate and taurine in the RVLM. The expression of c-Fos was also significantly increased in the SON of traumatized rats. EA application at Neiguan acupoints significantly suppressed trauma-induced increase of discharge frequency of the RVLM neurons, almost completely suppressed the trauma-induced increase of glutamate release but only very slightly reduced the trauma-enhanced taurine release, and inhibited the increase of c-Fos expression in these SON neurons of traumatized rats. These results indicate that Neiguan EA may improve cardiac function by modulating neurons in the RVLM and the SON in surgically traumatized rats. The taurine-mediated negative feedback may be involved in the protective effect of EA on cardiac function.

The phosphodiesterase 10A selective inhibitor, TAK-063, induces c-Fos expression in both direct and indirect pathway medium spiny neurons and sub-regions of the medial prefrontal cortex in rats

TAK-063, a selective phosphodiesterase 10A (PDE10A) inhibitor, produces potent antipsychotic-like and pro-cognitive effects in rodents via balanced activation of striatal direct and indirect pathway medium spiny neurons (MSNs). Brain activity modulation by TAK-063 has been characterized using pharmacological magnetic resonance imaging and electroencephalography in animals, revealing modulation of activity in the prefrontal cortex (PFC) where there is little or no PDE10A expression. To understand the specific brain regions and cells affected by TAK-063 in rats, we assessed neural activation in the striatal complex and PFC using immunofluorescence staining to measure c-Fos expression. TAK-063 at 0.3 and 3mg/kg induced a dose-dependent increase in the number of c-Fos immunoreactive cells in the striatal complex. Furthermore, TAK-063 increased the number of MSNs expressing c-fos mRNA in both the D1 receptor-expressing direct pathway and D2 receptor-expressing indirect pathway of the striatal complex. TAK-063 (0.3 and 3mg/kg) induced c-Fos expression in the anterior cingulate cortex (ACC) and prelimbic cortex (PrL), but not the infralimbic, dorsal peduncular, primary motor or anterior insular cortices. These findings suggest that administration of TAK-063 activates similar numbers of direct and indirect pathway MSNs, resulting in activation predominantly in medial PFC sub-regions, such as the ACC and PrL.

The effect of restraint stress on masseter mechanical hyperalgesia and the activity of neurons and astrocytes in the spinal trigeminal nucleus caudalis in rats

Objective: To investigate the effect of restraint stress on masseter mechanical hyperalgesia and the activity of neurons and astrocytes in the spinal trigeminal nucleus caudalis (Vc). Methods: The animals were randomly divided into the control group, 1-, 3-, 5-, 7-, 9-, 11-and 14-day stress groups, with 10 rats in each group. The body weight increase and behavior tests were used to testify the animal model. The mechanical sensitivity of masseter of the rat before and after the stress was measured with Von Frey filaments. Histological examinations were used to evaluate the expression of neuronal c-fos and astrocytic glial fibrillary acidic protein (GFAP). Results: Restraint stress resulted in remarkable mechanical allodynia in the masseter muscle. The head withdrawal threshold was significantly lower in the 7-, 9-, 11-and 14-day stress groups ([0.071±0.011], [0.059±0.020], [0.052±0.011], [0.033±0.011] N) than that in the control group ([0.120±0.025] N) (P<0.05). Compared to the control group, the rats in the 1-day stress group showed a significant increase of c-fos in neurons of the Vc and then declined to normal level after 1 week gradually. The GFAP expression in astrocytes of the Vc was significantly increased in the 7-, 9-, 11-and 14-day stress groups (4.3±1.0, 4.5±0.6, 4.6±0.5, 4.8±1.3) compared with the control group (2.0±0.8) (P<0.05). Conclusions: Chronic restraint stress could lower the threshold of mechanical allodynia in the masseter muscle and activate the neurons and astrocytes in Vc. The activation of neurons and astrocytes plays an important role in the masseter hyperalgesia induced by restraint stress in rats.

Topical dura mater application of CFA induces enhanced expression of c-fos and glutamate in rat trigeminal nucleus caudalis: attenuated by KYNA derivate (SZR72)

BackgroundMigraine is a debilitating neurological disorder where trigeminovascular activation plays a key role. We have previously reported that local application of Complete Freund’s Adjuvant (CFA) onto the dura mater caused activation in rat trigeminal ganglion (TG) which was abolished by a systemic administration of kynurenic acid (KYNA) derivate (SZR72). Here, we hypothesize that this activation may extend to the trigeminal complex in the brainstem and is attenuated by treatment with SZR72.MethodsActivation in the trigeminal nucleus caudalis (TNC) and the trigeminal tract (Sp5) was achieved by application of CFA onto the dural parietal surface. SZR72 was given intraperitoneally (i.p.), one dose prior CFA deposition and repeatedly daily for 7 days. Immunohistochemical studies were performed for mapping glutamate, c-fos, PACAP, substance P, IL-6, IL-1β and TNFα in the TNC/Sp5 and other regions of the brainstem and at the C1-C2 regions of the spinal cord.ResultsWe found that CFA increased c-fos and glutamate immunoreactivity in TNC and C1-C2 neurons. This effect was mitigated by SZR72. PACAP positive fibers were detected in the fasciculus cuneatus and gracilis. Substance P, TNFα, IL-6 and IL-1β immunopositivity were detected in fibers of Sp5 and neither of these molecules showed any change in immunoreactivity following CFA administration.ConclusionThis is the first study demonstrating that dural application of CFA increases the expression of c-fos and glutamate in TNC neurons. Treatment with the KYNA analogue prevented this expression.

Evidence for a histaminergic input from the ventral tuberomammillary nucleus to the solitary tract nucleus involved in arterial pressure regulation.

The tuberomammillary nucleus (TMN) of the posterior hypothalamus has a high density of histaminergic neurons, the projection fibers of which are present in many areas of the brain, including the nucleus tractus solitarius (NTS), which controls arterial pressure (AP). In this study, we investigated whether the TMN–NTS pathway is involved in central cardiovascular regulation. Bicuculline, a gamma‐aminobutyric acid type A (GABAA) receptor antagonist, was microinjected into the ventral TMN of anesthetized rats and its effects on AP and heart rate (HR) were observed. We also evaluated the effect of cetirizine, an H1 receptor antagonist, microinjected into the NTS on cardiovascular responses induced by electrical stimulation of the TMN. Both AP and HR increased following bicuculline microinjection into the ventral TMN. Similar pressor and tachycardic responses were observed after electrical stimulation of the ventral TMN. Microinjection of cetirizine into the NTS partially inhibited the pressor response but had no effect on HR. Finally, the treadmill test was associated with a high level of c‐Fos expression in both ventral TMN and NTS neurons. These results suggest that the TMN–NTS pathway is involved in regulation of AP, presumably under a high‐arousal phase, such as that during exercise.

Suprachiasmatic vasopressin to paraventricular oxytocin neurocircuit in the hypothalamus relays light reception to inhibit feeding behavior.

Light synchronizes the body's circadian rhythms by modulating the master clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. In modern lifestyles that run counter to normal circadian rhythms, the extended and/or irregular light exposure impairs circadian rhythms and, consequently, promotes feeding and metabolic disorders. However, the neuronal pathway through which light is coupled to feeding behavior is less elucidated. The present study employed the light exposure during the dark phase of the day in rats and observed its effect on neuronal activity and feeding behavior. Light exposure acutely suppressed food intake and elevated c-Fos expression in the AVP neurons of SCN and the oxytocin (Oxt) neurons of paraventricular nucleus (PVN) in the hypothalamus. The light-induced suppression of food intake was abolished by blockade of the Oxt receptor in the brain. Retrograde tracer analysis demonstrated the projection of SCN AVP neurons to the PVN. Furthermore, intracerebroventricular injection of AVP suppressed food intake and increased c-Fos in PVN Oxt neurons. Intra-PVN injection of AVP exerted a stronger anorexigenic effect than intracerebroventriclar injection. AVP also induced intracellular Ca2+ signaling and increased firing frequency in Oxt neurons in PVN slices. These results reveal the novel neurocircuit from SCN AVP to PVN Oxt that relays light reception to inhibition of feeding behavior. This light-induced neurocircuit may serve as a pathway for forming the circadian feeding rhythm and linking irregular light exposure to arrhythmic feeding and, consequently, obesity and metabolic diseases.

The Inhibitory Effects of Nesfatin-1 in Ventromedial Hypothalamus on Gastric Function and Its Regulation by Nucleus Accumbens.

Aim: The aim of this study was to investigate the effect of nesfatin-1 signaling in the ventromedial hypothalamus (VMH) on gastric functions, as well as the regulation of these effects by nucleus accumbens (NAc) projections to VMH.Methods: The expression of c-fos in nesfatinergic VMH neurons induced by gastric distension (GD) was measured using the double fluoro-immunohistochemical staining. The firing rates of neurons were monitored with single-unit extracellular electric discharge recording. The projection of nesfatinergic neurons from NAc to VMH was observed by fluorogold retrograde tracer combined with fluoro-immunohistochemical staining. The effect of nesfatin-1 in VMH or electric stimulation in NAc on gastric function was studied by measuring food intake, gastric acid output, gastric motility, and gastric emptying, and the ability of the melanocortin-3/4 receptor antagonist SHU9119 or the anti-nesfatin-1 antibody to block nesfatin-1 in the VMH was assessed.Results: Expression of c-fos was observed in VMH nesfatinergic neurons following GD in rats. Further, nesfatin-1 delivery to single GD-responsive neurons changed the firing rates of these neurons in the VMH. In awake, behaving rats, intra-VMH administration of nesfatin-1 inhibited food intake, gastric acid output, gastric motility, and gastric emptying. These effects were abolished by SHU9119. Fluorogold retrograde tracing showed nesfatinergic neural projection from the NAc to the VMH. Electrical stimulation of NAc modified the firing rates of the VMH neurons and inhibited food intake and gastric functions. The pretreatment with an anti-nesfatin-1 antibody in the VMH reversed the effects of NAc electrical stimulation on the VMH neuronal firing rates and gastric function.Conclusions: Nesfatin-1 in the VMH inhibited food intake, gastric acid output, gastric motility, and gastric emptying. A nesfatinergic pathway between NAc and VMH transmitted metabolism-regulating signals.

Propofol produces preventive analgesia via GluN2B-containing NMDA Receptor/ERK1/2 Signaling Pathway in a rat model of inflammatory pain.

Propofol, an intravenous anesthetic, has been shown to offer superior analgesic effect clinically. Whether propofol has preventive analgesic property remains unexplored. The present study investigated the antinociceptive effect of propofol and underlying molecular and cellular mechanisms via pre-emptive administration in a formalin-induced inflammatory pain model in rats. Male adult Sprague–Dawley rats were randomly allocated into four groups: naïve (Group Naïve), formalin injection only (Group Formalin), and formalin injection at 30 min (Group P-30 min) or 2 h (Group P-2 h) after intravenous infusion of propofol (0.6 mg kg−1 min−1) for 1 h. Nociceptive responses and protein expression of phosphorylated- or pan-GluN2B, ERK1/2, p38 mitogen-activated protein kinase, and c-Jun N-terminal kinase in the spinal dorsal horn were evaluated. Alteration of intracellular Ca2+ concentration induced by N-methyl-D-aspartate (NMDA) receptor agonists with or without pre-treatment of propofol was measured using fluorometry in SH-SY5Y cells while neuronal activation in the spinal dorsal horn by immunofluorescence. Pre-emptive propofol reduced pain with a delayed response to formalin and a reduction in hypersensitivity that lasted at least for 2 h. The formalin-induced activation of spinal GluN2B and ERK1/2 but not p38 or c-Jun N-terminal kinase was also diminished by propofol treatment. Preconditioning treatment with 3 µM and 10 µM of propofol inhibited Ca2+ influx mediated through NMDA receptors in SH-SY5Y cells. Propofol also reduced the neuronal expression of c-Fos and p-ERK induced by formalin. This study shows that pre-emptive administration of propofol produces preventive analgesic effects on inflammatory pain through regulating neuronal GluN2B-containing NMDA receptor and ERK1/2 pathway in the spinal dorsal horn.

Effect of dezocine on c-fos expression in neurons in midbrain periaqueductal gray in a rat model of incisional pain

Objective To evaluate the effect of dezocine on the c-fos expression in neurons in the midbrain periaqueductal gray in a rat model of incisional pain. Methods Thirty-six pathogen-free healthy adult male Wistar rats, weighing 250-300 g, were divided into 3 groups (n=12 each) using a random number table: control group (group C), incisional pain group (group I) and dezocine group (group D). A 1 cm longitudinal incision was made through skin, fascia and muscle of the plantar aspect of the right hind paw in sevoflurane-anesthetized rats.In group C, the rats were only anesthetized and underwent no operation.In group I, 0.9% sodium chloride solution 2 ml was injected via the caudal vein at 15 min before the model was established.In group D, dezocine 1 mg/kg (diluted to 2 ml in 0.9% sodium chloride solution) was injected via the caudal vein at 15 min before the model was established.At 24 h before operation (T0) and 2, 6 and 24 h after operation (T1-3), the mechanical paw withdrawal threshold (MWT) and cumulative pain score were measured.After measurement of the pain threshold at T3, the whole brain was removed for determination of the c-fos expression in neurons in the midbrain periaqueductal gray by immunohistochemistry. Results Compared with group C, the MWT was significantly decreased, cumulative pain scores were increased, and the expression of c-fos in neurons in the midbrain periaqueductal gray was up-regulated at T1-3 in I and D groups (P<0.05). Compared with group I, the MWT was significantly increased, the cumulative pain score was decreased, and the expression of c-fos protein in neurons in the midbrain periaqueductal gray was down-regulated at T1-3 in group D (P<0.05). Conclusion Dezocine mitigates incisional pain through inhibiting the expression of c-fos in neurons in the midbrain periaqueductal gray of rats. Key words: Analgesics, opioid; Pain, postoperative; Periaqueductal gray; Proto-oncogene proteins c-fos