Locus Coeruleus Area Research Articles

Sex-specific threat responding and neuronal engagement in carbon dioxide associated fear and extinction: Noradrenergic involvement in female mice

Difficulty in appropriately responding to threats is a key feature of psychiatric disorders, especially fear-related conditions such as panic disorder (PD) and posttraumatic stress disorder (PTSD). Most prior work on threat and fear regulation involves exposure to external threatful cues. However, fear can also be triggered by aversive, within-the-body, sensations. This interoceptive signaling of fear is highly relevant to PD and PTSD but is not well understood, especially in the context of sex. Using female and male mice, the current study investigated fear-associated spontaneous and conditioned behaviors to carbon dioxide (CO2) inhalation, a potent interoceptive threat that induces fear and panic. We also investigated whether behavioral sensitivity to CO2 is associated with delayed PTSD-relevant behaviors. CO2 evoked heterogenous freezing behaviors in both male and female animals. However, active, rearing behavior was significantly reduced in CO2-exposed male but not female mice. Interestingly, behavioral sensitivity to CO2 was associated with compromised fear extinction, independent of sex. However, in comparison to CO2-exposed males, females elicited less freezing and higher rearing during extinction suggesting an engagement of active versus passive defensive coping. Persistent neuronal activation marker ΔFosB immuno-mapping revealed attenuated engagement of infralimbic-prefrontal areas in both sexes but higher activation of brain stem locus coeruleus (LC) area in females. Inter-regional co-activation mapping revealed sex-independent disruptions in the infralimbic-amygdala associations but altered LC associations only in CO2-exposed female mice. Lastly, dopamine β hydroxylase positive (DβH + ve) noradrenergic neuronal cell counts in the LC correlated with freezing and rearing behaviors during CO2 inhalation and extinction only in female but not male mice. Collectively, these data provide evidence for higher active defensive responding to interoceptive threat CO2-associated fear in females that may stem from increased recruitment of the brainstem noradrenergic system. Our findings reveal distinct contributory mechanisms that may promote sex differences in fear and panic associated pathologies.

It is the locus coeruleus! Or… is it?: a proposition for analyses and reporting standards for structural and functional magnetic resonance imaging of the noradrenergic locus coeruleus

The noradrenergic locus coeruleus (LC) is one of the protein pathology epicenters in neurodegenerative diseases. In contrast to PET (positron emission tomography), MRI (magnetic resonance imaging) offers the spatial resolution necessary to investigate the 3–4 mm wide and 1.5 cm long LC. However, standard data postprocessing is often too spatially imprecise to allow investigating the structure and function of the LC at the group level. Our analysis pipeline uses a combination of existing toolboxes (SPM12, ANTs, FSL, FreeSurfer), and is tailored towards achieving suitable spatial precision in the brainstem area. Its effectiveness is demonstrated using 2 datasets comprising both younger and older adults. We also suggest quality assessment procedures which allow to quantify the spatial precision obtained. Spatial deviations below 2.5 mm in the LC area are achieved, which is superior to current standard approaches. Relevant for ageing and clinical researchers interested in brainstem imaging, we provide a tool for more reliable analyses of structural and functional LC imaging data which can be also adapted for investigating other nuclei of the brainstem.

Nicotine suppresses central post-stroke pain via facilitation of descending noradrenergic neuron through activation of orexinergic neuron

Central post-stroke pain (CPSP) is a type of central neuropathic pain, whose underlying mechanisms remain unknown. We previously reported that bilateral carotid artery occlusion (BCAO)-induced CPSP model mice showed mechanical hypersensitivity and decreased mRNA levels of preproorexin, an orexin precursor, in the hypothalamus. Recently, nicotine was shown to regulate the neuronal activity of orexin in the lateral hypothalamus (LH) and suppress inflammatory and neuropathic pain. In this study, we evaluated whether nicotine could suppress BCAO-induced mechanical allodynia through the activation of orexinergic neurons. Mice were subjected to BCAO for 30 min. Mechanical hypersensitivity was assessed by the von Frey test. BCAO mice showed hypersensitivity to mechanical stimuli three days after BCAO surgery. The intracerebroventricular injection of nicotine suppressed BCAO-induced mechanical hypersensitivity in a dose-dependent manner. These effects were inhibited by α7 or α4β2-nicotinic receptor antagonists. After nicotine injection, the level of c-fos, a neuronal activity marker, increased in the LH and locus coeruleus (LC) of Sham and BCAO mice. Increased number of c-Fos-positive cells partly colocalized with orexin A-positive cells in the LH, as well as tyrosine hydroxylase-positive cells in the LC.Orexinergic neurons project to the LC area. Nicotine-induced antinociception tended to cancel by the pretreatment of SB334867, an orexin receptor1 antagonist into the LC. Intra-LH microinjection of nicotine attenuated BCAO-induced mechanical hypersensitivity. Nicotine-induced antinociception was inhibited by intrathecal pre-treatment with yohimbine, an α2 adrenergic receptor antagonist. These results indicated that nicotine may suppress BCAO-induced mechanical hypersensitivity through the activation of the descending pain control system via orexin neurons.

Active vs passive novelty-related strategies: Sex differences in exploratory behaviour and monoaminergic systems

Sex differences are apparent in numerous behavioural characteristics. In order to compare and characterise male and female variability of exploratory behaviour, 365 male and 401 female rats were assessed in a task where a bimodal response distribution had previously been established in males. Female rats had significantly higher exploratory activity, and presented normal distribution of the behaviour, very differently from the bimodal distribution of males. No major effect of litter or oestrous cycle was detected. Several differences between male and female rats were found in monoamine metabolism measured ex vivo. Male rats had lower levels of dopamine (DA) in frontal cortex, and higher levels of 3,4-dihydroxyphenylacetic acid (DOPAC) in raphe area; higher levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in dorsal striatum but lower levels of 5-HT and 5-HIAA in locus coeruleus area, 5-HIAA levels were also lower in hippocampus as compared to females. Males had higher noradrenaline (NA) levels in hippocampus and lower normetanephrine (NMN) levels in striatum, in both brain regions male animals had lower NMN/NA ratio. No sex difference was found in accumbens. The only brain region with an interaction between sex and the expression of exploratory activity was raphe: Here 5-HT levels were lower, and DOPAC levels and DOPAC/DA and 5-HIAA/5-HT ratios higher in low exploring male but not female rats. Conclusively, female rats not only display higher levels of exploration but the population distribution of this behaviour is distinct; this may be related to differences in the monoaminergic systems between female and male animals.

Chemical ablation of locus coeruleus terminals in mice dysregulates behavioral features reminiscent of prodromal Alzheimer’s disease

AbstractBackgroundThe prodromal stages of Alzheimer’s disease (AD), which precede cognitive impairment by decades, are characterized by neuropsychiatric symptoms such as anxiety, agitation, impulsivity, and sleep disturbances that significantly impair quality of life. The brainstem noradrenergic locus coeruleus (LC) modulates behaviors that are reminiscent of these prodromal symptoms. Furthermore, the loss of norepinephrine (NE) terminals in LC‐projecting regions is a prominent feature of early AD, implicating LC dysfunction as a possible contributor to prodromal symptoms. However, the behavioral and pathological consequences of LC terminal loss have not been fully investigated.MethodAdult male and female C57BL/6 mice aged 4‐6 months were administered either saline or the LC‐specific neurotoxin, N‐(2‐chloroethyl)‐N‐ethyl‐bromo‐benzylamine (DSP‐4) (50 mg/kg, i.p.) on day 1 and day 7 (12 animals/group). Performance in behavioral tests that assess arousal (sleep latency), locomotor activity (novelty‐induced and circadian), anxiety (novelty‐suppressed feeding), and associative memory (contextual fear conditioning) commenced one week following the last treatment. In addition, brain sections consisting of LC, hippocampus, and cortical areas were immunostained for tyrosine hydroxylase (TH) to evaluate LC integrity, NE transporter (NET) to determine fiber/terminal density to LC‐projecting regions, and glial fibrillary acidic protein (GFAP) to assess astrogliosis. Fluorescence immunoreactivity (IR) was analyzed with ImageJ.ResultAnimals treated with DSP‐4 displayed significantly increased latency to feed in a novel environment compared to saline‐treated animals, with no treatment differences in the home cage, suggesting elevated neophobic behavior. Furthermore, DSP‐4‐treated animals trended towards decreased locomotor activity in the center of the environment over 1 hour and 23 hours, indicating increased thigmotaxis. No behavioral treatment differences were observed for sleep latency and contextual fear conditioning paradigms. Immunofluorescence revealed no treatment differences in TH IR in the LC but reduced NET IR in LC‐projecting regions of DSP‐4‐treated animals, demonstrating preserved LC cell bodies and LC fiber loss. No significant treatment differences were found for GFAP.ConclusionThese data suggest that chemical ablation of LC terminals with DSP‐4 can contribute to neophobia and anxiogenic responses, implicating LC terminal loss in mediating prodromal symptoms relevant to AD. Further studies are warranted to identify the physiological and molecular mechanisms underlying LC dysfunction for alleviating prodromal AD symptoms.

Dynamic changes of locus coeruleus damage in Parkinson's disease-like mice induced by paraquat

Objective: To observe the dynamic changes of brainstem locus coeruleus (LC) damage in Parkinson' s disease (PD) -like mice by paraquat (PQ) . Methods: In October 2019, 36 male C57BL/6 mice were randomly divided into the exposure group and the control group, with 18 mice in each group. The mice in the exposure group were given intraperitoneal injection of 15 mg/kg PQ, and the mice in the control group were given intraperitoneal injection of 0.9% saline, twice a week for 8 weeks. Neurobehavioral changes (pole climbing test, swimming test, open field test, tail hanging test, high plus maze test and water maze test) were observed at 4 weeks, 6 weeks and 8 weeks, respectively, and the changes of motor ability, emotion and cognitive function were evaluated. The brain tissue of mice were taken and stained with Hematoxylin-Eosin (HE) to observe the pathological changes of LC. Nissl staining was used to detect the changes of neuronal Nissl bodies in LC. Immunohistochemistry (IHC) staining was used to detect the expression of neuron nuclear antigen (NeuN) , dopamine (DA) neurons and norepinephrine (NE) neuron markers tyrosine hydroxylase (TH) , α-synuclein (α-syn) in substantia nigra (SN) and LC. The expression levels of NeuN, TH and α-syn in the midbrain and brainstem were detected by Western blotting. TUNEL staining was used to detect neuronal apoptosis in LC. Results: Compared with the 4th week of PQ exposure group, the time of pole climbing and swimming immobility were gradually increased, the ratio of open arm residence time of high plus maze test and the number of times of the platform and the residence time of platform quadrant in water maze test were gradually decreased (P<0.05) in the exposure group with the progress of exposure time. The results of HE and Nissl staining showed that the neurons in LC gradually arranged loosely, the nucleus were deeply stained, the cytoplasm was pyknosis, and the number of Nissl bodies gradually decreased (P<0.05) in the exposure group with the progress of exposure time. IHC results showed that the number of NeuN and TH positive cells in SN and LC of mice were gradually decreased, and the positive expression of α-syn was gradually increased (P<0.05) in the exposure group with the progress of exposure time. Western blotting results showed that the expression levels of NeuN and TH in the midbrain and brainstem were gradually decreased, and the expression level of α-syn was gradually increased (P<0.05) in the exposure group with the progress of exposure time. TUNEL staining showed that the apoptosis rates of neurons in LC were gradually increased (P<0.05) in the exposure group with the progress of exposure time. Conclusion: PQ induces progressive damage in the LC area of PD-like mice, which may be caused by the abnormal accumulation of pathological α-syn in the LC area.

Proton Pump Inhibitor "Lansoprazole" Inhibits Locus Coeruleus's Neuronal Activity and Increases Rapid Eye Movement Sleep.

Alteration of the bodily CO2 concentration and proton pump activity affects the sleep architecture. The brainstem locus coeruleus (LC) area plays an essential role in rapid eye movement (REM) sleep generation and chemoregulation. Previously, we reported that lansoprazole injections (intraperitoneal) increased REM sleep in the rats. However, it is not known if proton pumps in the LC influence REM sleep. Here, we studied the effects of lansoprazole in the LC on the neuronal activity and REM sleep expression. Male Wistar rats (250-300 g) were surgically prepared for sleep recording and drug microinjections into the LC. We determined the localization of proton pumps and expression levels of cFOS in the LC neurons immunohistochemically. Sleep-wake was recorded before and after the microinjections of drugs/vehicles. Our results demonstrate (i) the presence of proton pumps in the LC neurons, (ii) that the microinjection of lansoprazole into the LC reduced the number of cFOS+ve-TH+ve double-labeled neurons in the LC by 52.6% (p < 0.001) compared to the vehicle and (iii) that low and high doses of lansoprazole significantly increased REM sleep by 32% (p < 0.001) and 60% (p < 0.001), respectively, compared to the vehicle. Our results suggest that the proton pumps modulate the LC's noradrenergic (NE-ergic) neuronal activity and REM sleep. The increased amount of REM sleep can be attributed to the inhibition of the LC NE-ergic activity. Further, the REM sleep amount increased after the lansoprazole microinjections into the LC with a significant increase in the REM sleep episode numbers. Overall, our results suggest that proton pumps in the LC may be involved in REM sleep generation.

The role of anterior insula-brainstem projections and alpha-1 noradrenergic receptors for compulsion-like and alcohol-only drinking.

Compulsion-like alcohol drinking (CLAD), where consumption continues despite negative consequences, is a major obstacle to treating alcohol use disorder. The locus coeruleus area in the brainstem and norepinephrine receptor (NER) signaling in forebrain cortical regions have been implicated in adaptive responding under stress, which is conceptually similar to compulsion-like responding (adaptive responding despite the presence of stress or conflict). Thus, we examined whether anterior insula (aINS)-to-brainstem connections and alpha-1 NERs regulated compulsion-like intake and alcohol-only drinking (AOD). Halorhodopsin inhibition of aINS-brainstem significantly reduced CLAD, with no effect on alcohol-only or saccharin intake, suggesting a specific aINS-brainstem role in aversion-resistant drinking. In contrast, prazosin inhibition of alpha-1 NERs systemically reduced both CLAD and AOD. Similar to systemic inhibition, intra-aINS alpha-1-NER antagonism reduced both CLAD and AOD. Global aINS inhibition with GABAR agonists also strongly reduced both CLAD and AOD, without impacting saccharin intake or locomotion, while aINS inhibition of calcium-permeable AMPARs (with NASPM) reduced CLAD without impacting AOD. Finally, prazosin inhibition of CLAD and AOD was not correlated with each other, systemically or within aINS, suggesting the possibility that different aINS pathways regulate CLAD versus AOD, which will require further study to definitively address. Together, our results provide important new information showing that some aINS pathways (aINS-brainstem and NASPM-sensitive) specifically regulate compulsion-like alcohol consumption, while aINS more generally may contain parallel pathways promoting CLAD versus AOD. These findings also support the importance of the adaptive stress response system for multiple forms of alcohol drinking.

A Novel Methodology Using Dexamethasone to Induce Neuronal Differentiation in the CNS-Derived Catecholaminergic CAD Cells.

The Cath.a-differentiated (CAD) cell line is a central nervous system-derived catecholaminergic cell line originating from tyrosine hydroxylase (TH)-producing neurons located around the locus coeruleus area of the mouse brain. CAD cells have been used as an in vitro model for cellular and molecular studies due to their ability to differentiate under serum-free media conditions. However, the lack of serum-derived survival factors, limits the longevity for differentiated CAD cells to be maintained in healthy conditions; thereby, limiting their use in long-term culture studies. Here, we present a novel differentiation method that utilizes dexamethasone (Dex), a synthetic glucocorticoid receptor agonist. Specifically, we discovered that the addition of 100µM of Dex into the 1% fetal bovine serum (FBS)-supplemented media effectively induced neuronal differentiation of CAD cells, as characterized by neurite formation and elongation. Dex-differentiated CAD cells exited the cell cycle, stopped proliferating, extended the neurites, and expressed neuronal markers. These effects were dependent on the glucocorticoid receptors (GR) as they were abolished by GR knockdown. Importantly, Dex-differentiated CAD cells showed longer survival duration than serum-free differentiated CAD cells. In addition, RNA-sequencing and qPCR data demonstrate that several genes involved in proliferation, neuronal differentiation, and survival pathways were differentially expressed in the Dex-differentiated cells. This is the first study to reveal Dex as a novel differentiation methodology used to generate postmitotic neuronal CAD cells, which may be utilized as an in vitro neuronal model for cellular and molecular neurobiology research.

Neurons in the Locus Coeruleus Modulate the Hedonic Effects of Sub-Anesthetic Dose of Propofol.

Propofol is a worldwide-used intravenous general anesthetic with ideal effects, but hedonic effects of propofol have been reported and cause addictive issue. There is little known about the neurobiological mechanism of hedonic effects of propofol. Increasing researches have shown that the dopaminergic nervous system of the ventral tegmental area (VTA) and the noradrenergic system of locus coeruleus (LC) play a crucial role in hedonic experiences, which are putative sites for mediating the hedonic effects of propofol. In the present study, rat hedonic response scale and place conditioning paradigm were employed to examine the euphoric effects of propofol. In vivo GCaMP-based (AVV-hSyn-GCaMP6s) fiber photometry calcium imaging was used to monitor the real-time neuronal activity in VTA and LC area in rats exhibiting propofol-induced euphoric behaviors. Then DREADDs (designer receptors exclusively activated by designer drugs) modulation using rAAV-hSyn-hM4D(Gi)-EGFP was performed to confirm the neuronal substrate that mediates the euphoric effects of propofol. The score of hedonic facial responses was significantly increased in the 4 mg/kg group compared with that of the 0 mg/kg group. The locomotor activity in the propofol-paired compartment was significantly increased at the 4 mg/kg dose compared with that of the saline-paired group. When compared with the 0 mg/kg group, the place preference increased in the 4 mg/kg group. Administration of 4 mg/kg of propofol triggers reliable increases in GcaMP fluorescence. However, in the VTA GcaMP-expressing rats, administration of 4 mg/kg of propofol did not induce any change of GcaMP signals. The facial score and the place preference, which increased by 4 mg/kg propofol were abolished by chemogenetic inhibition of the neuronal activity in the LC area. Our results suggest that LC noradrenergic neurons, not VTA dopaminergic neurons, are directly involved in the hedonic effects of sub-anesthetic dose of propofol.

Neural circuits of anxiolytic and antidepressant pherine molecules.

In this review, we describe proposed circuits mediating the mechanism of action of pherines, a new class of synthetic neuroactive steroids with demonstrated antianxiety and antidepressant properties, that engage nasal chemosensory receptors. We hypothesize that afferent signals triggered by activation of these peripheral receptors could reach subgroups of olfactory bulb neurons broadcasting information to gamma-aminobutyric acid (GABAergic) and corticotropin-releasing hormone (CRH) neurons in the limbic amygdala. We propose that chemosensory inputs triggered by pherines project to centrolateral (CeL) and centromedial (CeM) amygdala neurons, with downstream effects mediating behavioral actions. Anxiolytic pherines could activate the forward inhibitory GABAergic neurons that facilitate the release of neuropeptide S (NPS) in the locus coeruleus (LC) and GABA in the bed nucleus of the stria terminalis (BNST) and inhibit catecholamine release in the LC and ventral tegmental area (VTA) leading to rapid anxiolytic effect. Alternatively, antidepressant pherines could facilitate the CRH and GABAergic neurons that inhibit the release of NPS from the LC, increase glutamate release from the BNST, and increase norepinephrine (NE), dopamine (DA), and serotonin release from the LC, VTA, and raphe nucleus, respectively. Activation of these neural circuits leads to rapid antidepressant effect. The information provided is consistent with this model, but it should be noted that some steps on these pathways have not been demonstrated conclusively in the human brain.

Autophagy-Based Hypothesis on the Role of Brain Catecholamine Response During Stress.

Stressful events, similar to abused drugs, significantly affect the homeostatic balance of the catecholamine brain systems while activating compensation mechanisms to restore balance. In detail, norepinephrine (NE)- and dopamine (DA)-containing neurons within the locus coeruleus (LC) and ventral tegmental area (VTA), are readily and similarly activated by psychostimulants and stressful events involving neural processes related to perception, reward, cognitive evaluation, appraisal, and stress-dependent hormonal factors. Brain catecholamine response to stress results in time-dependent regulatory processes involving mesocorticolimbic circuits and networks, where LC-NE neurons respond more readily than VTA-DA neurons. LC-NE projections are dominant in controlling the forebrain DA-targeted areas, such as the nucleus accumbens (NAc) and medial pre-frontal cortex (mPFC). Heavy and persistent coping demand could lead to sustained LC-NE and VTA-DA neuronal activity, that, when persisting chronically, is supposed to alter LC-VTA synaptic connections. Increasing evidence has been provided indicating a role of autophagy in modulating DA neurotransmission and synaptic plasticity. This alters behavior, and emotional/cognitive experience in response to drug abuse and occasionally, to psychological stress. Thus, relevant information to address the role of stress and autophagy can be drawn from psychostimulants research. In the present mini-review we discuss the role of autophagy in brain catecholamine response to stress and its dysregulation. The findings here discussed suggest a crucial role of regulated autophagy in the response and adaptation of LC-NE and VTA-DA systems to stress.

Bone-edge electroacupuncture relieves pain by regulating expression of GRK5, β-arrestin 2 and PKCα proteins in locus coeruleus in bone cancer pain rats with morphine tolerance

To observe the effect of bone-edge electroacupuncture (EA) intervention on mechanical pain threshold (PT) and expression of G protein-coupled receptor kinase (GRK5), β-arrestin 2, total and phosphorylated PKC alpha (p-PKCα) proteins in the locus coeruleus (LC) of rats with bone cancer pain induced morphine tolerance, so as to reveal its partial central mechanisms underlying pain relief. Forty SD rats were randomly divided into 5 groups, namely sham bone cancer, bone cancer pain, morphine tolerance, bone-edge EA, and sham EA (n＝ 8 rats in each group). The bone cancer with morphine tolerance model was established by intramedullary injection of MRMT-1 cells into the tibial cavity, and then intraperitoneal injection of morphine hydrochloride injection. After successful establishment of morphine tolerance model, the bone-edge EA (2 Hz/100 Hz，0.5－1.5 mA) was applied to bilateral "Zusanli" (ST36) and "Kunlun" (BL60) for 30 min, once a day for 7 days, after inserting the needle-tip to the tibial bone surface. The ipsilateral mechanical paw withdrawal thresholds (PWTs) were detected dynamically. The expression levels of GRK5, β-arrestin 2, PKCα and p-PKCα in the LC area were measured by Western blot. The PWTs of bone cancer pain rats were decreased on day 10 after inoculation of cancer cells (P<0.01). After i．p. of morphine for 11 days, no analgesic effect and pain tolerance appeared (P>0.05). The PWTs were significantly increased in the bone-edge EA intervention group (P<0.01), not in the sham EA group (P>0.05). In comparison with the sham bone cancer group, the expression of GRK5 protein in morphine tolerance group was significantly decreased (P<0.01); compared with morphine tolerance group, the expression of GRK5 protein in bone-edge EA group was increased(P<0.01). In comparison with the sham bone cancer group, the expression of β-arrestin 2 and p-PKCα in bone cancer group significantly increased (P<0.01). After the intervention, the increased β-arrestin 2 and p-PKCα expressions were reversed in the bone-edge EA group (P<0.01); compared with morphine tolerance group and sham EA group, the expression of PKCα protein was decreased(P<0.01). Bone-edge EA can effectively relieve morphine tolerance in bone cancer pain rats, which may be related to its functions in up-regulating GRK5 protein and down-regulating β-arrestin 2, PKCα and p-PKCα proteins in LC. .

Locus coeruleus connectivity alterations in late-life major depressive disorder during a visual oddball task

The Locus Coeruleus (LC) is the major source of noradrenergic neurotransmission. Structural alterations in the LC have been observed in neurodegenerative disorders and at-risk individuals, although functional connectivity studies between the LC and other brain areas have not been yet performed in these populations. Patients with late-life major depressive disorder (MDD) are indeed at increased risk for neurodegenerative disorders, and here we investigated LC connectivity in late-life MDD in comparison to individuals with amnestic type mild cognitive impairment (aMCI) and healthy controls (HCs). We assessed 20 patients with late-life MDD, 16 patients with aMCI, and 26 HCs, who underwent a functional magnetic resonance scan while performing a visual oddball task. We assessed task-related modulations of LC connectivity (i.e., Psychophysiological Interactions, PPI) with other brain areas. A T1-weighted fast spin-echo sequence for LC localization was also obtained. Patients with late-life MDD showed lower global connectivity during target detection in a cluster encompassing the right caudal LC. Specifically, we observed lower LC connectivity with the left anterior cingulate cortex (ACC), the right fusiform gyrus, and different cerebellar clusters. Moreover, alterations in LC-ACC connectivity correlated negatively with depression severity (i.e., Geriatric Depression Scale and number of recurrences). Reduced connectivity of the LC during oddball performance seems to specifically characterize patients with late-life MDD, but not other populations of aged individuals with cognitive alterations. Such alteration is associated with different measures of disease severity, such as the current presence of symptoms and the burden of disease (number of recurrences).

Alzheimer's disease-like pathology-triggered oxidative stress, alterations in monoamines levels, and structural damage of locus coeruleus neurons are partially recovered by a mix of proteoglycans of embryonic genesis

Alzheimer's disease (AD) pathogenesis includes oxidative damage and perturbations of monoamines. However, as many details of these alterations are not known, we have investigated the changes in monoamine levels as well as the free radical oxidation processes (FRO) in the brainstem of rats that were administered i.c.v. Aβ (25–35) (rat model of AD-like pathology). The level of oxidative stress was found elevated in the brainstem along with the increased concentrations of monoamines, especially norepinephrine in the locus coeruleus (LC) area of the brainstem. This was accompanied by the substantial structural damage of monoaminergic neurons of LC. In addition, we have tested the ability of proteoglycans of embryonic genesis (PEG) that were shown previously to act as neuroprotectors, to restore the AD-triggered alterations in monoaminergic system and FRO. Indeed, PEG reduced the increased FRO and upregulated monoamines in the brainstem of Aβ (25–35) treated animals. Administration of PEG to control animals led to the increase of the antioxidant capacity as well as the intensity of free radical oxidation processes.Our study confirms the important role of the brainstem FRO and monoamine shifts in AD development along with the known aggregation of Ab peptide and Tau hyperphosphorylation. We suggest that at the early stages of AD development, with still functional neurons, regulation of monoamine levels via stabilizing FRO processes can be beneficial. Our data demonstrate the regulatory action of PEG on the monoamine disturbances and the level of oxidative stress in the AD damaged structures, suggesting its possible therapeutic application in AD.

Norepinephrine-Fe(III)-ATP Ternary Complex and Its Relevance to Parkinson's Disease.

The aberrant autoxidation of norepinephrine (NE) in the presence of oxygen, which is accelerated by Fe(III), has been linked to the pathogenesis of the Parkinson's disease (PD). Adenosine triphosphate (ATP), as a neurotransmitter whose release can be stimulated by tissue damage and oxidative stress, is co-stored and often co-released with NE in presynaptic terminals. We have shown previously that ATP inhibits the iron-catalyzed dopamine oxidation, thereby decreasing the production of certain neurotoxins such as 6-hydroxydopamine. Whether ATP plays a similar role in Fe(III)-catalyzed NE oxidation and how it maintains the NE stability have not been investigated. Here, we studied the coordination in a ternary complex among NE, Fe(III), and ATP, and found that Fe(III) is coordinated as a octahedral center by NE and ATP. Voltammetry and mass spectrometry were employed to examine this ternary complex's modulation of the NE autoxidation. NE-Fe(III)-ATP plays a protective role to modulate the autoxidation and Fe(III)-catalyzed oxidation of NE. The ternary complex can be detected in the substantia nigra (SN), locus coeruleus (LC), and striatum regions of C57BL/6 wild-type mice. In contrast, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse brains displayed a significant decrease of the ternary complex in the SN region and an increase in the LC and striatum areas. We posit that the ternary complex is produced by noradrenergic neurons as a protective regulator against neuronal damage and oxidative stress, contributing to the lower vulnerability of LC neurons with respect to that of SN neurons.

Tropomyosin Receptor Kinase B Receptor Activation in the Locus Coeruleus Restores Impairment of Endogenous Analgesia at a Late Stage Following Nerve Injury in Rats

A rat model of neuropathic pain at 6 weeks after spinal nerve ligation (SNL6w) exhibits both mechanical hypersensitivity and impaired noxious stimuli-induced analgesia (NSIA). Repeated treatment with antidepressants can produce antihypersensitivity and restore NSIA. To examine the involvement of a brain-derived neurotrophic factor-mediated mechanism, a tropomyosin receptor kinase B (TrkB) agonist, 7,8-dihydroxyflavone (DHF), was administered to SNL6w rats (5 mg/kg/d for 5 days). Mechanical hypersensitivity was evaluated using the von Frey filament test and paw pressure test. NSIA was examined by measuring the change in the hind paw withdrawal threshold 30 minutes after painful stimulation induced by capsaicin injection into the fore paw. Changes in the concentrations of glutamate and GABA in the locus coeruleus area were measured by in vivo microdialysis. DHF treatment did not affect mechanical hypersensitivity, although it restored NSIA by reducing GABA release in response to the fore paw capsaicin injection. DHF treatment did not alter the baseline concentration of glutamate or GABA. These findings suggest that DHF treatment restored the stimuli–response activity of the locus coeruleus without affecting the tonic activity of the locus coeruleus. The brain-derived neurotrophic factor–TkB signaling is also involved in the NSIA-restoring effect of amitriptyline. PerspectiveThis article demonstrates that repeated treatment with TrkB agonist, DHF, restored endogenous analgesia. Repeated amitriptyline treatment showed similar effect via TrkB-mediated mechanisms, and the effect may be independent from the effect of antihypersensitivity. This effect of TrkB activation is promising for patients with chronic pain with impaired descending inhibition.

High-resolution in vivo imaging of human locus coeruleus by magnetization transfer MRI at 3T and 7T

Locus Coeruleus (LC) is a neuromelanin-rich brainstem structure that is the source of noradrenaline in the cortex and is thought to modulate attention and memory. LC imaging in vivo is commonly performed with a 2D T1-weighted Turbo Spin Echo (TSE) MRI sequence, an approach that suffers from several drawbacks at 3T, including long acquisition times and highly anisotropic spatial resolution. In this study, we developed a high-resolution Magnetization Transfer (MT) sequence for LC imaging at both 7T and 3T and compared its performance to a TSE sequence. Results indicate that LC imaging can be achieved with an MT sequence at both 7 and 3T at higher spatial resolution than the 3T TSE. Furthermore, we investigated whether the currently disputed source of contrast in the LC region with a TSE sequence relates to MT effects or shortened T1 and T2* due to increased iron concentration. Our results suggest that the contrast in the LC area relates to MT effects. To conclude, in this study we managed to image the LC, for the first time, at 7T and at an increased resolution compared to the current state-of-the-art. Imaging the LC is highly relevant for clinical diagnostics as structural tissue properties of the LC may hold promise as a biomarker in neurodegenerative diseases.

Identification of a Group of GABAergic Neurons in the Dorsomedial Area of the Locus Coeruleus.

The locus coeruleus (LC)-norepinephrine (NE) system in the brainstem plays a critical role in a variety of behaviors is an important target of pharmacological intervention to several neurological disorders. Although GABA is the major inhibitory neurotransmitter of LC neurons, the modulation of LC neuronal firing activity by local GABAergic interneurons remains poorly understood with respect to their precise location, intrinsic membrane properties and synaptic modulation. Here, we took an optogenetic approach to address these questions. Channelrhodopsin (ChR2) in a tandem with the yellow fluorescent protein (YFP) was expressed in GABAergic neurons under the control of glutamic acid decarboxylase 2 (GAD2) promoter. Immediately dorsomedial to the LC nucleus, a group of GABAergic neurons was observed. They had small soma and were densely packed in a small area, which we named the dorsomedial LC or dmLC nucleus. These GABAergic neurons showed fast firing activity, strong inward rectification and spike frequency adaptation. Lateral inhibition among these GABAergic neurons was observed. Optostimulation of the dmLC area drastically inhibited LC neuronal firing frequency, expanded the spike intervals, and reset their pacemaking activity. Analysis of the light evoked inhibitory postsynaptic currents (IPSCs) indicated that they were monosynaptic. Such light evoked IPSCs were not seen in slices where this group of GABAergic neurons was absent. Thus, an isolated group of GABAergic neurons is demonstrated in the LC area, whose location, somatic morphology and intrinsic membrane properties are clearly distinguishable from adjacent LC neurons. They interact with each and may inhibit LC neurons as well as a part of local neuronal circuitry in the LC.

Neuropathic and inflammatory pain are modulated by tuberoinfundibular peptide of 39 residues

Nociceptive information is modulated by a large number of endogenous signaling agents that change over the course of recovery from injury. This plasticity makes understanding regulatory mechanisms involved in descending inhibition of pain scientifically and clinically important. Neurons that synthesize the neuropeptide TIP39 project to many areas that modulate nociceptive information. These areas are enriched in its receptor, the parathyroid hormone 2 receptor (PTH2R). We previously found that TIP39 affects several acute nociceptive responses, leading us to now investigate its potential role in chronic pain. Following nerve injury, both PTH2R and TIP39 knockout mice developed less tactile and thermal hypersensitivity than controls and returned to baseline sensory thresholds faster. Effects of hindpaw inflammatory injury were similarly decreased in knockout mice. Blockade of α-2 adrenergic receptors increased the tactile and thermal sensitivity of apparently recovered knockout mice, returning it to levels of neuropathic controls. Mice with locus coeruleus (LC) area injection of lentivirus encoding a secreted PTH2R antagonist had a rapid, α-2 reversible, apparent recovery from neuropathic injury similar to the knockout mice. Ablation of LC area glutamatergic neurons led to local PTH2R-ir loss, and barley lectin was transferred from local glutamatergic neurons to GABA interneurons that surround the LC. These results suggest that TIP39 signaling modulates sensory thresholds via effects on glutamatergic transmission to brainstem GABAergic interneurons that innervate noradrenergic neurons. TIP39's normal role may be to inhibit release of hypoalgesic amounts of norepinephrine during chronic pain. The neuropeptide may help maintain central sensitization, which could serve to enhance guarding behavior.