Epidural and Intrathecal Drug Delivery in Rats and Mice for Experimental Research: Fundamental Concepts, Techniques, Precaution, and Application

Acute Extrinsic Activation of the RANKL Pathway Decreases Wound Healing and Functional Recovery After Spinal Cord Injury in Mice

Manipulating wound healing-associated signaling after SCI presents a promising avenue for increasing the recovery of function after injury. This study explores the potential of targeting molecular regulators of wound healing, initially identified in nonneural tissues, to enhance outcomes after SCI. Astrocytes, pivotal in central nervous system wound healing, play a crucial role in tissue remodeling and recovery. However, the optimal manipulation of astrogliosis for beneficial outcomes remains elusive. Previous research demonstrated a transcriptional response in astrocytes resembling epithelial-to-mesenchymal transitions (EMTs) after CNS injury. Here, we investigate the extrinsic manipulation of wound healing through the Receptor Activator of Nuclear-factor Kappa-Β (RANK) pathway, known for its involvement in nonneural tissue remodeling and linked to EMT pathway. Using a severe thoracic spinal cord contusion mouse model, we demonstrate that acute activation of the RANK pathway with RANK ligand (RANKL) adversely affects tissue remodeling, resulting in larger lesion volumes and delayed recovery of posture and locomotion. These findings suggest that early perturbations in the tight molecular regulation of tissue remodeling negatively impact the wound-healing process after SCI. The study provides a proof-of-concept demonstration that exogenous nonneural remodeling ligands can modify astrocyte responses and functional recovery after SCI, raising questions about the optimal time frame for beneficial remodeling interventions during injury progression. These insights open new avenues for therapeutic strategies aimed at improving functional outcomes following SCI.

Modulation of pain sensitivity by Ascl1- and Lhx6-dependent GABAergic neuronal function in streptozotocin diabetic mice

Painful diabetic neuropathy commonly affects the peripheral nervous system in individuals with diabetes. However, the pathological processes and mechanisms underlying diabetic neuropathic pain remain unclear. We aimed to identify the overall profiles and screen for genes potentially involved in pain mechanisms using transcriptome analysis of the dorsal root ganglion of diabetic mice treated with streptozotocin (STZ). Using RNA sequencing, we identified differentially expressed genes between streptozotocin-treated diabetic mice and controls, focusing on altered GABAergic neuron-related genes and inflammatory pathways. Behavioral and molecular analyses revealed a marked reduction in GABAergic neuronal markers (GAD65, GAD67, VGAT) and increased pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) in the diabetic group compared with controls. Intrathecal administration of lentiviral vectors expressing transcription factors Ascl1 and Lhx6 reversed pain hypersensitivity and restored normal expression of GABAergic genes and inflammatory mediators. Protein-protein interaction network analysis revealed five key proteins influenced by Ascl1 and Lhx6 treatment, including those in the JunD/FosB/C-fos signaling pathway. These findings suggest that Ascl1 and Lhx6 mitigate diabetic neuropathic pain by modulating GABAergic neuronal function, pro-inflammatory responses, and pain-related channels (TRPV1, Nav1.7). These results provide a basis for developing transcription factor-based therapies targeting GABAergic neurons for diabetic neuropathic pain relief.

Esketamine alleviates depressive-like behavior in neuropathic pain mice through the METTL3-GluA1 pathway

Esketamine, a newly developed antidepressant, is the subject of this research which seeks to explore its impact on depressive symptoms in neuropathic pain mice and the potential molecular mechanisms involved. Through transcriptome sequencing and bioinformatics analysis combined with in vivo studies, it was identified that esketamine markedly boosts the levels of the m6A methyltransferase METTL3 and the AMPA receptor GluA1 subunit. Esketamine activates METTL3, allowing it to bind with GluA1 mRNA, promoting m6A modification, thereby enhancing GluA1 expression at synapses. Through this mechanism, esketamine may reduce depressive-like behavior in neuropathic pain mice, providing new insights into the potential applications of esketamine and novel therapeutic avenues for neuropathic pain and depressive behavior.

Ultrasound as a reliable guide for lumbar intrathecal injection in rats: A pilot study

Lumbar intrathecal administration provides an ideal route for drug delivery into the central nervous system, especially when dorsal root ganglions are the main target for the therapy in rat model of chronic pain. Two main methods of lumbar intrathecal administrations are chronic catheter implantation and the acute needle puncture. Chronic catheter implantation involves surgical manipulation to insert micro indwelling catheter into the intrathecal space. However, this method is invasive, produces inflammatory reactions, and generates more surgical stress. Acute needle puncture is less invasive and cheaper however is technically challenging to perform. We performed an ultrasound-guided lumbar intrathecal injection in six male Sprague Dawley rat cadavers, on average weighing 250-300 grams. Fresh rat cadavers were positioned in a sternal recumbent position, vertebrae were palpated and scanned using a linear probe ultrasound. A 25G needle insertion was advanced with real-time ultrasound guidance, and placement was confirmed prior to dye injection (Methylene blue, Sigma Aldrich). Cadavers were then dissected, and the vertebrae were visually inspected for dye staining. All three cadavers that underwent intrathecal injection with sagittal and axial plane ultrasound guidance showed positive dye staining within the intrathecal space, confirming successful acute intrathecal administration. There was one successful intrathecal injection under sagittal plane-only ultrasound guidance. Ultrasound is a useful, operator-dependent tool to guide acute needle puncture intrathecal administration.

Irisin alleviates CFA-induced inflammatory pain by modulating macrophage polarization and spinal glial cell activation

Although the potent anti-inflammatory effects of irisin have been documented in various inflammatory disorders, its efficacy against inflammatory pain remains unexplored. Herein, we examined the therapeutic effects of irisin in a mouse model of inflammatory pain induced by complete Freund's adjuvant (CFA). Mice were divided into three groups: normal control, CFA-injected (CFA), and CFA plus irisin-treated (CFA+Irisin). The irisin-treated group exhibited a gradual reduction in mechanical allodynia and thermal hyperalgesia when compared with the CFA group. Moreover, treatment with irisin significantly upregulated the expression of M2 macrophage markers (interleukin [IL]-4 and IL-10) and downregulated M1 macrophage markers (IL-1β, IL-6, and tumor necrosis factor-α) in the local paw tissue, dorsal root ganglion, and spinal cord tissue. However, there was no significant difference in the total number of F4/80+ macrophages in the paw tissue and dorsal root ganglion, indicating phenotypic exchange. Treatment with irisin also downregulated the expression of the glial cell activation-related markers Iba-1 and GFAP in the spinal cord tissue. To elucidate the underlying mechanisms, we detected the expression of Toll-like receptor 4 (TLR4), MyD88, and interferon regulatory factor 5 (IRF5) in paw tissues, dorsal root ganglion, and spinal tissues, revealing that irisin could downregulate the expression of these proteins. Irisin alleviated inflammatory pain by modulating local tissue inflammation and peripheral and central neuroinflammation and reducing glial cell activation and M2 macrophage polarization by modulating the TLR4-MyD88-IRF5 signaling pathway. Accordingly, irisin is a promising candidate for treating inflammatory pain in various diseases.

CT myelography by intrathecal injection of contrast medium though percutaneous administration route visualizes compressed cervical spinal cord in a mouse

BACKGROUND

Chronic compressive myelopathy (CCM) is a major cause of spinal cord disorders in the elderly, in which the spinal cord is compressed by bony or soft tissue structures. Although computed tomography myelography (CTM) has been clinically used for the diagnosis of CCM, a method of CTM in rodents remains to be developed.

NEW METHOD

A 50 μl Hamilton syringe attached to a disposable needle was percutaneously inserted into the subarachnoid space (cisterna magna) between the occipital bone and C1 lamina in an anesthetized adult mouse, followed by the injection of contrast medium and CT imaging.

RESULTS

CTM clearly visualized the shape of the spinal cord of intact mice and tiptoe-walking Yoshimura (Twy) mice without any health issues.

COMPARISON WITH EXISTING METHOD(S)

Unlike histology, the current method functions in live mice, directly depicts the compressed spinal cord, and provides clinically related image information. Furthermore, the intrathecal administration of contrast medium through the percutaneous route makes CTM less invasive and takes less time than a conventional intrathecal injection method.

CONCLUSIONS

The CTM method used in the present study enables clear visualization of the shape of the dural sac and spinal cord and is useful when conducting experiments on CCM and other spinal diseases in rodents.

Specific transcription factors Ascl1 and Lhx6 attenuate diabetic neuropathic pain by modulating spinal neuroinflammation and microglial activation in mice

Gamma-aminobutyric acid (GABA) neuronal system-related transcription factors (TFs) play a critical role in GABA production, and GABA modulates diabetic neuropathic pain (DNP). The present study investigated the therapeutic effects of intrathecal delivery of two TFs achaete-scute homolog 1 (Ascl1) and LIM homeobox protein 6 (Lhx6) in a mouse model of DNP and elucidated their underlying mechanisms. GABA-related specific TFs, including Ascl1, Lhx6, distal-less homeobox 1, distal-less homeobox 5, the Nkx2.1 homeobox gene, and the Nkx2.2 homeobox gene, were investigated under normal and diabetic conditions. Among these, the expression of Ascl1 and Lhx6 was significantly downregulated in mice with diabetes. Therefore, a single intrathecal injection of combined lenti-Ascl1/Lhx6 was performed. Intrathecal delivery of lenti-Ascl1/Lhx6 significantly relieved mechanical allodynia and heat hyperalgesia in mice with DNP. Ascl1/Lhx6 delivery also reduced microglial activation, decreased the levels of pro-inflammatory cytokines including tumor necrosis factor-α and interleukin (IL)-1β, increased the levels of anti-inflammatory cytokines including IL-4, IL-10, and IL-13, and reduced the activation of p38, c-Jun N-terminal kinase, and NF-κB in the spinal cord of mice with DNP, thereby reducing DNP. The results of this study suggest that intrathecal Ascl1/Lhx6 delivery attenuates DNP via upregulating spinal GABA neuronal function and inducing anti-inflammatory effects.