Optimum properties of injectable test solutions for intrathecal administration to conscious rats

Lysozyme elicits pain during nerve injury by neuronal Toll-like receptor 4 activation and has therapeutic potential in neuropathic pain

The role of neuronal Toll-like receptor 4 (TLR4) in nerve injury is being pursued actively. However, the endogenous activation of neuronal TLR4 during neuroinflammation, in absence of the participation of glial TLR4, remains elusive. Here, we identified lysozyme as an endogenous activator of neuronal TLR4 signaling during nerve injury. Upon nerve injury, enhanced expression of lysozyme promoted neuronal hyperexcitability and neuropathic pain. Injections of lysozyme in healthy rats increased their mechanical and thermal pain sensitivity. Likewise, infusion of spinal cord slices with lysozyme increased neuronal excitability typical of neuropathic pain. Our results also showed that lysozyme activated excitability of both Aδ- and C-fibers. Thus, in addition to the discovery of lysozyme as an endogenous ligand for regulating neuronal TLR4 signaling, this study also lays the foundation of our understanding of its role in nervous system pathologies, providing multiple avenues for treating neuroinflammation.

Editor's Highlight: Formulation and Toxicology Evaluation of the Intrathecal AYX1 DNA-Decoy in Sprague Dawley Rats

The longevity of pain after surgery is debilitating and limits the recovery of patients. AYX1 is a double-stranded, unprotected, 23 base-pair oligonucleotide designed to reduce acute post-surgical pain and prevent its chronification with a single intrathecal perioperative dose. AYX1 mimics the DNA sequence normally bound by EGR1 on chromosomes, a transcription factor transiently induced in the dorsal root ganglia-spinal cord network following a noxious input. AYX1 binds to EGR1 and prevents it from launching waves of gene regulation that are necessary to maintain pain over time. A formulation suitable for an intrathecal injection of AYX1 was developed, including a specific ratio of AYX1 and calcium so the ionic homeostasis of the cerebrospinal fluid is maintained and no impact on neuromuscular control is produced upon injection. A GLP toxicology study in naïve Sprague Dawley rats was conducted using 3 dose levels up to the maximum feasible dose. Clinical observations, neurobehavioral observations, clinical pathology and histopathology of the nervous system and peripheral tissues were conducted. An additional nonGLP study was conducted in the spared nerve injury model of chronic neuropathic pain in which EGR1 is induced in the dorsal root ganglia and spinal cord. Similar testing was performed, including a modified Irwin test to assess a potential impact of AYX1 on autonomic nervous system responses, locomotion, activity, arousal, sensorimotor, and neuromuscular function. No AYX1-related adverse events were observed in any of the studies and the no-observed-adverse-effect-level was judged to be the maximum feasible dose.

Minimally invasive technique for intrathecal administration of morphine in rats: practicality and antinociceptive properties

The intrathecal (IT) route of administration represents a means to reduce the dose of morphine administered for analgesia, potentially minimizing interactions between opioid effects and experimental outcomes. Perceived technical difficulty, and previously described invasive methods, may limit its use. This report describes a minimally invasive technique for IT administration of morphine by direct transcutaneous lumbosacral puncture in rats; and assesses antinociceptive properties of morphine in anaesthetized rats. Rats ( n = 28) anaesthetized with sevoflurane (inspired fraction of sevoflurane: F_iSevo = 2.4%) were randomly allocated to receive: IT morphine (0.2 mg/kg); subcutaneous (SC) morphine (3 mg/kg); SC buprenorphine (0.05 mg/kg); or SC or IT sodium chloride (NaCl). After a wash-in period (40 min), thermal nociceptive stimuli were applied at nine locations corresponding to different rostrocaudal dermatomes of the rat. Nociceptive stimulation cycles were repeated at all locations after successive decrement of F_iSevo by 15%. Presence or absence of gross purposeful movement (GPM) was recorded for each individual stimulation. IT injection of morphine by direct puncture with a 25 G hypodermic needle is easily performed (successful first attempt: 82%) without complications. IT morphine reduced the frequency of GPM following nociceptive thermal stimulation in a way comparable with SC buprenorphine or morphine. It was not possible to delimit any rostral spinal spread of morphine. This report describes a refined and effective technique of administering morphine IT in rats using readily available materials. IT doses being markedly smaller than the systemic equivalent, analgesia could be provided whilst minimizing the potential interactions of non-analgesic opioid effects with research protocols.

Possible harmful effects on central nervous system cells in the use of physiological saline as an irrigant during neurosurgical procedures

BACKGROUND

Physiologic saline is routinely used as an irrigant in neurosurgery especially in Japan. Cerebrospinal fluid (CSF) differs from physiologic saline in its concentration of inorganic salts, osmolality, and pH and is completely different insofar as it contains glucose, protein, cholesterol, and other lipids. The present study was designed to compare the possible functional and morphologic deleterious influence of these differences on cultured rat neural cells using saline (S), Ringer's solution with glucose (Lactec G, LG; Otsuka Pharmaceutical Co.; Tokyo, Japan) and without glucose (Lactec, L; Otsuka Pharmaceutical Co.), and an artificial CSF (ACSF).

METHODS

Primary cultured rat neurons and astrocytes were divided into five groups according to the medium used, the four experimental groups (ACSF, L, LG, and S) and one control group (C). At various time points up to 24 hours, the rhodamine 123 uptake by neuronal or astrocytic cellular mitochondria was evaluated as cell function assessment. Morphologic assessment for both neuron and astrocyte culture was carried out with scanning electron microscopy (SEM) at the 24-hour time point.

RESULTS

SEM showed little difference between the C and ACSF groups, whereas morphologic deterioration was particularly severe in the S group for both neurons and astrocytes. In the case of neuronal mitochondrial activity, the L and S groups demonstrated respectively severe and some deterioration, particularly in the mitochondria of the neuronal processes. The deleterious effects in mitochondrial activity of the S group were even more apparent in the astrocytic cells.

CONCLUSION

These results suggest that physiologic saline, when used as an irrigant in neurologic surgery, might in some circumstances cause damage to exposed and compromised neural cells.