Fast Localization and Sectioning of Mouse Locus Coeruleus

Immunohistochemistry of Brain Tissues

Immunohistochemistry (IHC) is the basis of histological or pathological analysis and is widely used to enable the detection and characterization of proteins in various organ tissues, including brain tissues. IHC is commonly performed on formalin-fixed paraffin-embedded (FFPE) tissues because of their easy storage and versatility. IHC is a key method for providing more accurate analysis of localization and function of neurons, neuroendocrine cells, and neural stem cells in the brain and other nervous systems. The related cells such as glial cells and neurovascular units have also been analyzed by IHC. Visualization of antibody-antigen interactions can be performed primarily in one of the following ways: chromogenically stained IHC and fluorescently stained IHC. In chromogenically stained IHC, an antibody is chemically conjugated to an enzyme, such as peroxidase, that can be reacted with a suitable substrate to give a colored product. In fluorescently stained IHC, the antibodies are finally tagged with fluorescent chemicals such as fluorescein isothiocyanate (FITC) or rhodamine. Here, we describe the standard methods of IHC applied to brain slice sections. Furthermore, an automated immunostainer is presented as another option for standardized immunohistochemistry.

Neonatal bilateral whisker trimming in male mice age-dependently alters brain neurotransmitter levels and causes adolescent onsets of social behavior abnormalities

Tactile perception via whiskers is important in rodent behavior. Whisker trimming during the neonatal period affects mouse behaviors related to both whisker-based tactile cognition and social performance. However, the molecular basis of these phenomena is not completely understood. To solve this issue, we investigated developmental changes in transmitters and metabolites in various brain regions of male mice subjected to bilateral whisker trimming during the neonatal period (10 days after birth [BWT10 mice]). We discovered significantly lower levels of 3-methoxy-4-hydroxyphenyl glycol (MHPG), the major noradrenaline metabolite, in various brain regions of male BWT10 mice at both early/late adolescent stages (at P4W and P8W). However, reduced levels of dopamine (DA) and their metabolites were more significantly identified at P8W in the nuclear origins of monoamine (midbrain and medulla oblongata) and the limbic system (frontal cortex, amygdala, and hippocampus) than at P4W. Furthermore, the onset of social behavior deficits (P6W) was observed later to the impairment of whisker-based tactile cognitive behaviors (P4W). Taken together, these findings suggest that whisker-mediated tactile cognition may contribute toprogressive abnormalities in social behaviors in BWT10 mice accompanied by impaired development of dopaminergic systems.

Dexmedetomidine Ameliorated Cognitive Dysfunction Induced by Intestinal Ischemia Reperfusion in Mice with Possible Relation to the Anti-inflammatory Effect Through the Locus Coeruleus Norepinephrine System

Cognitive impairment is a common central nervous system complication that occurs following surgery or organs damage outside the nervous system. Neuroinflammation plays a key role in the molecular mechanisms of cognitive impairment. Dexmedetomidine alleviates neuroinflammation and reduces cognitive dysfunction incidence; however, the mechanism by which dexmedetomidine alleviates cognitive dysfunction remains unclear. This study evaluated the effect of dexmedetomidine on attenuation of early cognitive impairment induced by intestinal ischemia–reperfusion in mice and examined whether the locus coeruleus norepinephrine (LCNE) system participates in the anti-inflammatory effect of dexmedetomidine. The superior mesenteric artery was clamped for 45 min to induce intestinal ischemia reperfusion injury. Dexmedetomidine alone or combined with DSP-4, a selective locus coeruleus noradrenergic neurotoxin, was used for pretreatment. Postoperative cognition was assessed using the Morris water maze. Serum and hippocampal levels of IL-1β, TNF-α, norepinephrine (NE), and malondialdehyde (MDA) were assessed by enzyme-linked immunosorbent assay. Immunofluorescence, immunohistochemistry, and hematoxylin and eosin staining were used to evaluate the expression of tyrosine hydroxylase (TH) in the locus coeruleus, hippocampal microglia, and intestinal injury. Pretreatment with dexmedetomidine alleviated intestinal injury and decreased the serum and hippocampal levels of NE, IL-1β, TNF-α, and MDA at 24 h after intestinal ischemia reperfusion, decreased TH-positive neurons in the locus coeruleus, and ameliorated cognitive impairment. Similarly, DSP-4 pre-treatment alleviated neuroinflammation and improved cognitive function. Furthermore, α2-adrenergic receptor antagonist atipamezole or yohimbine administration diminished the neuroprotective effects and improved cognitive function with dexmedetomidine. Therefore, dexmedetomidine attenuated early cognitive dysfunction induced by intestinal ischemia–reperfusion injury in mice, which may be related to its anti-inflammatory effects through the LCNE system.

Activation of locus coeruleus-spinal cord noradrenergic neurons alleviates neuropathic pain in mice via reducing neuroinflammation from astrocytes and microglia in spinal dorsal horn

Background

The noradrenergic neurons of locus coeruleus (LC) project to the spinal dorsal horn (SDH), and release norepinephrine (NE) to inhibit pain transmission. However, its effect on pathological pain and the cellular mechanism in the SDH remains unclear. This study aimed to explore the analgesic effects and the anti-neuroinflammation mechanism of LC-spinal cord noradrenergic pathway (LC:SC) in neuropathic pain (NP) mice with sciatic chronic constriction injury.

Methods

The Designer Receptors Exclusively Activated by Designer Drugs (DREADD) was used to selectively activate LC:SC. Noradrenergic neuron-specific retro–adeno-associated virus was injected to the spinal cord. Pain threshold, LC and wide dynamic range (WDR) neuron firing, neuroinflammation (microglia and astrocyte activation, cytokine expression), and α2AR expression in SDH were evaluated.

Results

Activation of LC:SC with DREADD increased the mechanical and thermal nociceptive thresholds and reduced the WDR neuron firing. LC:SC activation (daily, 7 days) downregulated TNF-α and IL-1β expression, upregulated IL-4 and IL-10 expression in SDH, and inhibited microglia and astrocytes activation in NP mice. Immunofluorescence double staining confirmed that LC:SC activation decreased the expression of cytokines in microglia of the SDH. In addition, the effects of LC:SC activation could be reversed by intrathecal injection of yohimbine. Immunofluorescence of SDH showed that NE receptor α2B-AR was highly expressed in microglia in CCI mice.

Conclusion

These findings indicate that selective activation of LC:SC alleviates NP in mice by increasing the release of NE and reducing neuroinflammation of astrocytes and microglia in SDH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02489-9.

Effects of norepinephrine on microglial neuroinflammation and neuropathic pain

Norepinephrine (NE) is an important neurotransmitter in the central nervous system. NE is released from locus coeruleus neurons and is involved in a variety of physiological and pathological processes. Neuroinflammation is a common manifestation of many kinds of neurological diseases. The activation of microglia directly affects the status of neuroinflammation. Several kinds of adrenergic receptors, which anchor on microglia and can be regulated by NE, affect the activation of microglia and neuroinflammation. NE influences chronic pain, anxiety, and depression by regulating the activation of microglia.

Comparisons of neuroinflammation, microglial activation, and degeneration of the locus coeruleus-norepinephrine system in APP/PS1 and aging mice

BACKGROUND

The role of microglia in Alzheimer's disease (AD) pathogenesis is becoming increasingly important, as activation of these cell types likely contributes to both pathological and protective processes associated with all phases of the disease. During early AD pathogenesis, one of the first areas of degeneration is the locus coeruleus (LC), which provides broad innervation of the central nervous system and facilitates norepinephrine (NE) transmission. Though the LC-NE is likely to influence microglial dynamics, it is unclear how these systems change with AD compared to otherwise healthy aging.

METHODS

In this study, we evaluated the dynamic changes of neuroinflammation and neurodegeneration in the LC-NE system in the brain and spinal cord of APP/PS1 mice and aged WT mice using immunofluorescence and ELISA.

RESULTS

Our results demonstrated increased expression of inflammatory cytokines and microglial activation observed in the cortex, hippocampus, and spinal cord of APP/PS1 compared to WT mice. LC-NE neuron and fiber loss as well as reduced norepinephrine transporter (NET) expression was more evident in APP/PS1 mice, although NE levels were similar between 12-month-old APP/PS1 and WT mice. Notably, the degree of microglial activation, LC-NE nerve fiber loss, and NET reduction in the brain and spinal cord were more severe in 12-month-old APP/PS1 compared to 12- and 24-month-old WT mice.

CONCLUSION

These results suggest that elevated neuroinflammation and microglial activation in the brain and spinal cord of APP/PS1 mice correlate with significant degeneration of the LC-NE system.