Chronic cannulation of the intradural or extradural space in the rat

Pregabalin alleviates neuropathic pain via inhibition of the PKCε/TRPV1 pathway

Pregabalin has been increasingly used in recent years, and becoming a first-line medication for the clinical treatment of neuropathic pain. However, the mechanisms underlying pregabalin-induced neuropathic pain alleviation remain unclear. In this study, we aimed to investigate whether PKC epsilon (PKCε)/ transient receptor potential vanilloid subtype 1(TRPV1) signaling pathway participated in pregabalin-induced analgesia during treatment of neuropathic pain using rat models of spared nerve injury (SNI). The left hind paw withdrawal mechanical thresholds (PWMT) of rats were measured preoperatively one day before and on day 1, 4, 7 and 14 after surgery. On day 7 after SNI surgery, the rats received ligation operation were administrated with pregabalin intraperitoneally and were intrathecally injected with PKC Inhibitor BIM Ⅰ or PKC agonist PMA for seven consecutive days, IL-1β and IL-6 expression levels in the spinal cord of rats were then assessed. Furthermore, we analyzed the PKCε, TRPV1, pTRPV1 and Glial fibrillary acidic protein (GFAP) protein levels and the expression of reactive astrocytes and the PKCε, TRPV1 and pTRPV1 positive cells on day 14 after SNI. Our findings indicated that pregabalin could relieve neuropathic pain to a certain extent by suppressing the PKCε/TRPV1 signaling pathway and inhibiting inflammatory processes in the spinal cord.

Harnessing cerebrospinal fluid circulation for drug delivery to brain tissues

Initially thought to be useful only to reach tissues in the immediate vicinity of the CSF circulatory system, CSF circulation is now increasingly viewed as a viable pathway to deliver certain therapeutics deeper into brain tissues. There is emerging evidence that this goal is achievable in the case of large therapeutic proteins, provided conditions are met that are described herein. We show how fluid dynamic modeling helps predict infusion rate and duration to overcome high CSF turnover. We posit that despite model limitations and controversies, fluid dynamic models, pharmacokinetic models, preclinical testing, and a qualitative understanding of the glymphatic system circulation can be used to estimate drug penetration in brain tissues. Lastly, in addition to highlighting landmark scientific and medical literature, we provide practical advice on formulation development, device selection, and pharmacokinetic modeling. Our review of clinical studies suggests a growing interest for intra-CSF delivery, particularly for targeted proteins.

Use of high-resolution thermography as a validation measure to confirm epidural anesthesia in mice: a cross-over study

BACKGROUND

Effective epidural anesthesia is confirmed in humans by sensory assessments but these tests are not feasible in mice. We hypothesized that, in mice, infrared thermography would demonstrate selective segmental warming of lower extremities following epidural anesthesia.

METHODS

We anesthetized 10 C57BL/6 mice with isoflurane and then inserted a PU-10 epidural catheter under direct surgical microscopy at T11-12. A thermal camera (thermal sensitivity ±0.05°C, pixel resolution 320x240 pixels, and spatial resolution 200 μm) recorded baseline temperature of front and rear paws, tail and ears. Thermography was assessed at baseline and 2, 5, 10, and 15 min after an epidural bolus dose of 50 μL bupivacaine 0.25% or 50 μL saline (control) using a cross-over design with dose order randomized and investigators blinded to study drug. Thermal images were recorded from video and analyzed using FLIR software. Effect over time and maximal effect (E_max) were assessed by repeated measures ANOVA and paired t-tests. Comparisons were between bupivacaine and control, and between lower vs upper extremities.

RESULTS

Epidural bupivacaine caused progressive warming of lower compared with upper extremities (P <0.001), typically returning to baseline by 15 min after administration. Mean (±SD) E_max was +3.73 (±1.56) °C for lower extremities compared with 0.56 (±0.68) °C (P=0.03) for upper extremities. Following epidural saline, there was no effect over time (E_max for lower extremities -0.88 (±0.28) °C compared with the upper extremities -0.88 (±0.19) °C (P >0.99).

CONCLUSIONS

Thermography is a useful tool to confirm epidural catheter placement in animals for which subjective, non-noxious, sensory measures are impossible.

Neurosteroid dehydroepiandrosterone sulphate enhances pain transmission in rat spinal cord dorsal horn

BACKGROUND

The neurosteroid dehydroepiandrosterone sulphate (DHEAS) activates the sigma-1 receptor, inhibits gamma-aminobutyric acid A (GABA_A) and glycine receptors, and induces hyperalgesic effects. Although its effects have been studied in various tissues of the nervous system, its synaptic mechanisms in nociceptive pathways remain to be elucidated.

METHODS

The threshold of mechanical hypersensitivity and spontaneous pain behaviour was assessed using the von Frey test in adult male Wistar rats after intrathecal administration of DHEAS. We also investigated the effects of DHEAS on synaptic transmission in the spinal dorsal horn using slice patch-clamp electrophysiology.

RESULTS

Intrathecally administered DHEAS elicited dose-dependent mechanical hyperalgesia and spontaneous pain behaviours (withdrawal threshold: saline; 51.0 [20.1] g, 3 μg DHEAS; 14.0 [7.8] g, P<0.01, 10 μg DHEAS; 6.9 [5.2] g, 15 min after administration, P<0.001). DHEAS at 100 μM increased the frequency of miniature postsynaptic currents in the rat dorsal spinal horn; this increase was extracellular Ca²⁺-dependent but not sigma-1 and N-methyl-d-aspartate receptor-dependent. DHEAS suppressed the frequency of miniature inhibitory postsynaptic currents in a GABA_A receptor- and sigma-1 receptor-dependent manner.

CONCLUSIONS

These results suggest that DHEAS participates in the pathophysiology of nociceptive synaptic transmission in the spinal cord by potentiation of glutamate release and inhibition of the GABA_A receptor.

Evaluation of the neurotoxicity of intrathecal dexmedetomidine on rat spinal cord (electromicroscopic observations)

Background:

Spinal administration of dexmedetomidine has been proposed as an adjuvant in spinal anesthesia. However, there is limited information about its possible neurotoxic effect after its neuraxial administration. Potential spinal neurotoxicity should be investigated in animals before administering drugs through the spinal cord. Our aim was to investigate the neurotoxic effects of intrathecal dexmedetomidine in rats.

Methods:

Two groups were performed: the dexmedetomidine (D) group (n = 10) received 10 μg (0.5 ml), whereas the control (C) group (n = 10) received 0.9% (0.5 ml) sodium chloride through indwelling intrathecal catheter. Seven days after the injection, the medulla spinalis was extracted. Samples were withdrawn from both groups for histologic, electron microscopic examination. The histologic examination was performed separately on each of the four sites. The findings were categorized as follows: 0 - normal neuron; 1 - intermediate neuron damage; and 2 - neurotoxicity.

Results:

Intrathecal administration of dexmedetomidine sensorial block was seen in the dexmedetomidine group and significant differences in the dexmedetomidine group than control group in 15^th and 30^th min (P < 0.05). Histological examination did not show evidence suggestive of neuronal body or axonal lesion, gliosis, or myelin sheath damage in any group. In all animals, there were observed changes compatible with unspecific inflammation at the tip of the needle location. On the four-area scoring histologic examination, the scores of both groups were 0–1, and no statistical difference was observed between the groups.

Conclusions:

A single dose of intrathecal dexmedetomidine did not produce histologic evidence of neurotoxicity.

A new technique for long time catheterization of sacral epidural canal in rabbits

INTRODUCTION

In this study we aimed to develop a simple and practical technique for chronic sacral epidural catheterization of rabbits.

METHODS

We included ten rabbits weighing 2-2.5 kg in the study. After anesthesia and analgesia, we placed an epidural catheter by a 2 cm longitudinal skin incision in the tail above the sacral hiatus region. We confirmed localization by giving 1% lidocaine (leveling sensory loss and motor function loss of the lower extremity). The catheter was carried forward through a subcutaneous tunnel and fixed at the neck.

RESULTS

Chronic caudal epidural catheter placement was succesful in all rabbits. The catheters stayed in place effectively for ten days. We encountered no catheter complications during this period. The localization of the catheter was reconfirmed by 1% lidocaine on the last day. After animals killing, we performed a laminectomy and verified localization of the catheter in the epidural space.

CONCLUSIONS

Various methods for catheterization of the epidural space in animal models exist in the literature. Epidural catheterization of rabbits can be accomplished by atlanto-occipital, lumbar or caudal routes by amputation of the tail. Intrathecal and epidural catheterization techniques defined in the literature necessitate surgical skill and knowledge of surgical procedures like laminectomy and tail amputation. Our technique does not require substantial surgical skill, anatomical integrity is preserved and malposition of the catheter is not encountered. In conclusion, we suggest that our simple and easily applicable new epidural catheterization technique can be used as a model in experimental animal studies.

A comparison of the effects of epidural and spinal anesthesia with ischemia-reperfusion injury on the rat transverse rectus abdominis musculocutaneous flap

The purpose of this study is to compare the effects of spinal and epidural anesthesia on a rat transverse rectus abdominus myocutaneous flap ischemia-reperfusion injury model.Forty Sprague-Dawley rats were divided into 4 experimental groups: group I (n = 10), sham group; group II (n = 10), control group; group III (n = 10), epidural group; and group IV (n = 10), spinal group. After the elevation of the transverse rectus abdominus myocutaneous flaps, all groups except for the sham group were subjected to normothermic no-flow ischemia for 4 hours, followed by a reperfusion period of 2 hours. At the end of the reperfusion period, biochemical and histopathological evaluations were performed on tissue samples.Although there was no significant difference concerning the malonyldialdehyde, nitric oxide, and paraoxonase levels in the spinal and epidural groups, the total antioxidant state levels were significantly increased, and the total oxidative stress levels were significantly decreased in the epidural group in comparison to the spinal group. The pathological evaluation showed that findings related to inflammation, nuclear change rates and hyalinization were significantly higher in the spinal group compared with the epidural group.Epidural anesthesia can be considered as a more suitable method that enables a decrease in ischemia-reperfusion injuries in the muscle flaps.

Intrathecal catheterization alone induces neuroimmune activation in the rat

Intrathecal (i.t.) catheterization in the rat has been used extensively for drug delivery in various experimental paradigms. These indwelling i.t. catheters have been associated with inflammatory processes and tissue reactions external to the spinal cord in numerous clinical and animal studies. The purpose of this study was to determine whether i.t. catheter placement produced glial activation and changes in specific cytokine expression, i.e. neuroimmune activation, within the spinal cord which might cause altered sensory processing. Rats underwent i.t. catheterization or sham surgery and were killed at 3 or 14 days postsurgery (n> or =3 per group). Spinal cord segments were taken at the cervical level, tip of the catheter and distal to the catheter (thoracic levels). Immunohistochemistry was used to examine spinal localization of the cytokines, interleukin (IL)-6, IL-10 and glial activation (OX-42 for microglia and anti-glial fibrillary acidic protein for astrocytes). At 3 and 14 days after i.t. catheterization, there was an elevation in OX-42 and GFAP expression as compared to control (n=3) and sham surgery (n=4) groups. IL-10-like immunoreactivity was significantly increased in both the dorsal and ventral horns 14 days after i.t. placement as compared to the sham and normal groups. Conversely, IL-6-like immunoreactivity was not significantly different from sham or normal groups. These cytokine findings are discussed in the context of a differential role of specific cytokines in the potential generation of pain states or in the production of analgesia. This study demonstrated that i.t. catheterization induces robust neuroimmune activation that manifests as increases in glial markers and specific cytokine expression. This method should be controlled for, or alternate methods used for, drug delivery in nociceptive animal models that require spinally administered agents.

Interventional pain treatments for cancer pain

Cancer pain is prevalent and often multifactorial. For a segment of the cancer pain population, pain control remains inadequate despite full compliance with the WHO analgesic guidelines including use of co-analgesics. The failure to obtain acceptable pain or symptom relief prompted the inclusion of a fourth step to the WHO analgesic ladder, which includes advanced interventional approaches. Interventional pain-relieving therapies can be indispensable allies in the quest for pain reduction among cancer patients suffering from refractory pain. There are a variety of techniques used by interventional pain physicians, which may be grossly divided into modalities affecting the spinal canal (e.g., intrathecal or epidural space), called neuraxial techniques and those that target individual nerves or nerve bundles, termed neurolytic techniques. An array of intrathecal medications are infused into the cerebrospinal fluid in an attempt to relieve refractory cancer pain, reduce disabling adverse effects of systemic analgesics, and promote a higher quality of life. These intrathecal medications include opioids, local anesthetics, clonidine, and ziconotide. Intrathecal and epidural infusions can serve as useful methods of delivering analgesics quickly and safely. Spinal delivery of drugs for the treatment of chronic pain by means of an implantable drug delivery system (IDDS) began in the 1980s. Both intrathecal and epidural neurolysis can be effective in managing intractable cancer-related pain. There are several sites for neurolytic blockade of the sympathetic nervous system for the treatment of cancer pain. The more common sites include the celiac plexus, superior hypogastric plexus, and ganglion impar. Today, interventional pain-relieving approaches should be considered a critical component of a multifaceted therapeutic program of cancer pain relief.

Intrathecal therapy for the management of cancer pain

Inadequately managed cancer pain continues to be a significant problem despite increased awareness, improved knowledge and understanding of pain pathophysiology, and standardized treatment guidelines of this distressing and debilitating symptom complex. Small subsets of patients who are refractory to optimal medical management because of drug toxicity or unsatisfactory analgesia may be candidates for exteriorized or implantable intrathecal drug delivery systems. By delivering opioids and other agents directly to the central nervous system, intrathecal drug administration can offer superior pain relief with less toxicity at a fraction of the systemic dose. With adjuncts such as local anesthetics and clonidine, intrathecal therapy also allows for broader therapeutic options in the most difficult of cases. In general, intrathecal therapy is underused despite evidence of its efficacy, safety, and cost-effectiveness.

Dextran 40 (Rheomacrodex) or Polygeline (Haemaccel) as an epidural patch for post dural puncture headache: a neurotoxicity study in a rat model of Dextran 40 and Polygeline injected intrathecally

BACKGROUND AND OBJECTIVE

Although an epidural autologous blood patch is considered the most effective treatment for post dural puncture headache, which sometimes occurs following spinal or inadvertent spinal anaesthesia, there remains a need for alternative materials for epidural patches. We investigated the potential neurotoxicity of Dextran 40 (Rheomacrodex) and Polygeline (Haemaccel) used for this purpose in a rat model.

METHODS

Repeated boluses of 10% Dextran 40, 3.5% Polygeline or 0.9% saline were injected intrathecally over a period of 1 month in three groups of rats.

RESULTS

No behavioural or clinical derangements were observed in any of the three groups during this period. After sacrifice of the animals at the end of the experiment, no significant differences in the histopathological appearances of the spinal cords in the three groups were observed. No toxic effects diminishing viability of spinal cord cells were evident. Similarly, viability of renal, hepatic and peripheral blood mononuclear cells remained unaffected (98% +/- 2%).

CONCLUSIONS

No deleterious effects, clinical or cellular, were evident in this rat model when Dextran 40 or Polygeline were injected intrathecally. Thus, both substances can be considered as possible alternative materials for epidural patches.

An improved procedure for catheterization of the thoracic spinal subarachnoid space in the rat

Catheterization of the subarachnoid space provides a convenient means to deliver drugs to, or collect cerebrospinal fluid from, the spinal cord in animal experiments, and has been instrumental to our understanding of spinal mechanisms that underlie anesthesia, analgesia, or cardiovascular regulation. Experience gained over the years has revealed several shortcomings of this technique. We report a procedure that encompasses the benefits of direct subarachnoid catheterization of the rat thoracic spinal cord but circumvents the known shortcomings. An intrathecal catheter was fabricated with a small silicon bead at one end of a PE-10 catheter, which was cannulated with a 4/0 suture that served as a guide. Using the L-shape hook of the suture guide as an anchorage, the catheter was advanced into the subarachnoid space until the silicon bead was lodged on a drilled hole (2 x 2 mm) over the lamina proper on the T13 vertebrae. With less surgical trauma, greater precision of placement and firmer anchorage of the catheter, less leakage of cerebrospinal fluid, and minimal mortality or morbidity, our modified procedure for catheterization of the thoracic spinal subarachnoid space in the rat compared favorably to previously reported methods.

Evaluation of Sympathetic Blockade after Intrathecal and Epidural Lidocaine in Rats by Laser Doppler Perfusion Imaging

The widespread use of neuraxial anaesthesia increases the need for animal models to evaluate therapeutic prospects, mechanisms and risks of this technique. As a methodological prerequisite, we characterised the sympathetic blockade after different modes of neuraxial anaesthesia with regard to segments supplying the splanchnic region. Under haemodynamic monitoring, lidocaine 2% or saline were infused via intrathecal (10 microl), lumbar epidural (10 and 30 microl) or thoracic epidural (10 and 30 microl) catheters. Segmental spread of neuraxially infused local anaesthetic was assessed using methylene blue. Mean arterial blood pressure decreased more severely after neuraxial lidocaine in thoracic epidural (10 and 30 microl) compared to high-volume (30 microl anaesthesia animals. Determination of the sympathetic blockade by means of laser Doppler perfusion imaging was restricted to the paws due to a higher density of subcutaneous blood vessels as compared to the abdominal wall (mean +/- SD: 3.93 +/- 0.06 vs. 1.35 +/- 0.05/384 mm(2), p < 0.05). Only high-volume (30 microl) lumbar and thoracic epidural anaesthesia (10 and 30 microl) increased skin perfusion in both hind and front paws. This extensive sympathetic blockade was demonstrated to include splanchnic segments using thermography. Segmental spread of methylene blue did not closely correspond to laser Doppler findings and should be interpreted as minimum rather than exact epidural spread of local anaesthetic.

Anti-allodynic and anti-hyperalgesic effects of nociceptin receptor antagonist, JTC-801, in rats after spinal nerve injury and inflammation

The effects of nociceptin/orphanin FQ (N/OFQ) peptide receptor antagonist JTC-801 on allodynia and hyperalgesia were examined in rats in order to explore the involvement of N/OFQ system in these pathological pain states. Tactile allodynia induced by L5/L6 spinal nerve ligation was reversed by both systemic (3-30 mg/kg) and spinal (22.5 and 45 pg) JTC-801 in a dose-dependent manner. Concerning hyperalgesia induced by formalin injection into the hindpaw, JTC-801 dose-dependently suppressed the second phase, but not the first phase, of the licking behavior. Furthermore, systemic JTC-801 reduced Fos-like immunoreactivity in the dorsal horn of the spinal cord (laminae I/II). In conclusion, N/OFQ receptor antagonist JTC-801 exerted anti-allodynic and anti-hyperalgesic effects in rats, suggesting that N/OFQ system might be involved in the modulation of neuropathic pain and inflammatory hyperalgesia.

Evolving spinal analgesia practice in palliative care

Intraspinal analgesia can be helpful in some patients with intractable pain. Over 15 years palliative care professionals evolved their spinals policy through a repeated series of evaluations, discussions and literature reviews. One hundred intraspinal lines were then reviewed. Notable changes in policy were the switch from epidurals to intrathecals, and the insertion of lines during working hours rather than as emergencies. Our efficacy, and frequency of adverse effects, is equal or better to published studies. Key issues in reducing adverse effects were the improved care of the spinal line exit site, a change from bolus administration to continuous infusions, and modifying line insertion techniques. Current policy is to use continuous infusions of diamorphine and bupivacaine in a 1:5 ratio through externalized intrathecal lines. The lines are effective in approximately two thirds of patients and can be kept in place for up to 18 months. The policy continues to be updated and common documentation is now in place.

Intrathecal bupivacaine protects against extension of lesions in an acute photochemical spinal cord injury model

PURPOSE

The photochemical spinal-cord injury model reproduces extensive secondary lesions that occur after spinal injury. We have evaluated in 27 rats the functional, electrophysiological and anatomical consequences of a photochemical spinal-cord lesion induced before or after intrathecal injection of bupivacaine.

METHODS

After randomization, nine rats received 20 micro L of intrathecal bupivacaine 0.5% 15 min before a photochemical spinal-cord lesion (Group I) and eight rats received 20 micro L intrathecal bupivacaine 15 min after such a lesion (Group II). Ten rats received 20 micro L of saline 15 min before the photochemical injury (control group). Paraplegia was tested on days one, three, five, seven, nine, 12, 15 and 18 using an evaluation of hindlimb movements and an inclined plane stability test. Sensory block was evaluated by the animal's response when each hindlimb was brought into contact with a hot plate. Sympathetic injury was evaluated in terms of bladder voiding dysfunction. On day 18, residual somatosensory evoked potentials (SEP) were measured and the area of the intact spinal cord was determined using a digitalized system.

RESULTS

Early paraplegia recovery was found in the two bupivacaine groups (P < 0.05). On day 12, motor recovery was complete in both bupivacaine groups whereas recovery was not complete on day 18 in the control group. Compared to the control group, inclined plane stability recovered earlier in Groups I and II, from day three to day 15. Sensory and sympathetic block scores were not different in the three groups. Nevertheless, SEP latencies were longer and amplitudes were lower in control group rats compared with the two bupivacaine groups on day 18. The intact spinal-cord cross-sectional area around the lesion was not different in the three groups.

CONCLUSION

Twenty microlitres of intrathecal bupivacaine before or after acute photochemical spinal injury improves hindlimb motor recovery and SEP parameters in rats.

Distribution of intrathecal catheter positions in rat

BACKGROUND

Although drug administration through an intrathecal catheter is widely used in the study of spinal pharmacology, the catheter positions in transverse plane that may cause a limited spread of a solution remain unclear. In the first step to clarify this issue, the distribution of the intrathecal catheter position was investigated in rats.

METHODS

A polyethylene catheter (PE-10) was inserted intrathecally 8.5 cm through the atlanto-occipital membrane, aiming the tip of the catheter to the dorsal surface of the spinal cord. Three or four weeks after the implantation of the catheter, 83 rats were transcardiacally perfused with fixative solution. The catheter positions were investigated longitudinally and transversely by cutting the spinal cord segmentally through the intervertebral disk at different spinal levels.

RESULTS

Seventeen rats were excluded from further data analysis. Transversely, catheters were located in the left lateral subarachnoid space in 23 rats (35%), in the right lateral in 15 (23%), in the dorsal in 22 (33%), and in the ventral in 6 (9%). Longitudinally, catheter position was significantly higher in the ventral group (median, T9) than that in the dorsal group (T11/12) (P<0.01).

CONCLUSION

Chronic intrathecal catheters were variously located in the rat spinal subarachnoid space in the transverse plane, and lateral subarachnoid placement of the catheter (58%) was frequently observed, whereas dorsal subarachnoid placement occurred in 33%.

Subarachnoid Techniques for Cancer Pain Therapy: When, Why, and How?

For cancer patients who obtain inadequate pain relief with conservative treatment, there is a growing list of effective options for subarachnoid therapy. Morphine and bupivacaine have been the most frequently used drugs for intrathecal infusion, and their use has consistently yielded good results. Despite their effectiveness, however, a therapeutic deficit remains, primarily in the treatment of neuropathic cancer pain. Because of this limitation, more recent research has focused on novel compounds for intrathecal therapy such as clonidine, midazolam, ketamine, and SNX-111. In addition to new drug options, there are various catheter delivery systems from which to choose. In reviewing the literature and experience to date with these various medications and delivery systems, we hope to better aid the clinician in tailoring the best treatment for each patient.

Lumbar catheterization of the subarachnoid space with a 32-gauge polyurethane catheter in the rat

Chronic catheterization of the subarachnoid space of rats is an important tool for intrathecal drug delivery in pharmacologic investigations of pain. We describe a technique using direct lumbar insertion of a small 32-gauge polyurethane (PU) catheter without extensive surgery. Location of the catheter was confirmed with 2% lidocaine injection 1 day later, and methylene blue injection after 7-14 days. This method improved recovery of the rat after catheter implantation and reduced neurologic complications.

Complications associated with the use of indwelling epidural catheters in dogs: 81 cases (1996-1999)

OBJECTIVE

To evaluate complications associated with use of indwelling epidural catheters in dogs in a clinical setting.

DESIGN

Retrospective clinical study.

ANIMALS

81 client-owned dogs.

PROCEDURE

Medical records were reviewed for dogs in which a 19-gauge epidural catheter was placed percutaneously at L7-S1 and advanced to the point of maximum efficacy for pain control (between L7 and T4, depending on the procedure). Catheters were used to provide perioperative epidural analgesia during surgeries that included perineal (n = 6), hind limb (33), abdominal (43), thoracic (5), forelimb (2), and cervical (1) procedures.

RESULTS

Catheters were maintained in situ from 1 to 7 days (mean, 2.3 days; median, 2.0 days). Sixty-four dogs did not have complications; 17 dogs had minor complications. Catheter dislodgement was the most common complication (13/80 [16%] dogs). Catheter site contamination without inflammation developed in 2 (2.4%) dogs; inflammation at the catheter site developed in 2 (2.4%) dogs but was not related to duration of time the catheter was in place. Complications were not serious and did not require treatment other than catheter removal. Dogs that dislodged their catheters were significantly younger (mean, 2.9 years; median, 2.0 years) than other dogs (mean, 6.2 years; median, 6.0 years). Dogs that received femoral fracture repair dislodged their catheters more often (62.5%) than dogs undergoing other procedures (10.9%).

CONCLUSIONS AND CLINICAL RELEVANCE

The complication rate associated with temporary epidural catheterization of dogs appears to be low, and complications generally are not serious.

Spinal anaesthesia with gamma hydroxybutyrate. A study in a rat model

Gamma hydroxybutyric acid, a central inhibitory neurotransmitter and a cerebral metabolite of gamma-aminobutyric acid, is present in high concentrations in the mammalian hypothalamus and basal ganglia. Its sodium salt gamma hydroxybutyrate has been effectively used as an intravenous anaesthetic agent, and as an oral sedative, and in the management of the alcohol withdrawal syndrome. In an animal model, using 72 Wistar strain rats allocated to one of six groups of 12 animals each, with implanted lumbar intrathecal catheters, we examined whether gamma hydroxybutyrate, 20% 40 microL (32 mg kg-1) administered alone or combined with fentanyl, gamma hydroxybutyrate 20% 20 microL (16 mg kg-1), fentanyl 0.005% 20 microL (4 mg kg-1) as an intrathecal bolus, provides intraoperative anaesthesia, comparable with that produced by intrathecal lignocaine. We demonstrated that gamma hydroxybutyrate, given by an intrathecal bolus in the rat model, produced reversible segmental antinociception, together with muscular relaxation of the abdominal wall and rear limbs. This is accompanied by moderate sedation without haemodynamic or respiratory depression. This agent may thus be promising for use as a spinal anaesthetic drug.

A sheep model for continuous intrathecal infusion of test substances

Pharmaceutical research and new drug development rely extensively on animal research. The development of novel agents for intrathecal administration requires preclinical studies of toxic effects in an animal model. We have developed a nonrodent animal model for this purpose. Our sheep model: 1 Is an animal whose neural axis is similar to the human 2 Allows for the percutaneous placement of intrathecal catheters 3 Has minimal possibilities of infection because the infusion system is totally implanted 4 Provides continuous infusion of the test agent 5 Generates behavioral, motor, neurological and histopathological information so that safety guidelines can be established prior to preclinical studies.

An investigation of the possible neurotoxic effects of intrathecal midazolam combined with fentanyl in the rat

In previous work, midazolam was injected intrathecally and produced reversible, segmental, spinally mediated anti-nociception sufficient for abdominal surgery in a rat model. The neurotoxic effect of midazolam, alone or combined with fentanyl, injected intrathecally repeatedly on 15 occasions over a period of 1 month, was studied in the same model. We sought to establish whether this would produce neurological damage or neurotoxic injury. Histopathological examination of the excised spinal cord and paraspinal tissues was carried out. Thirty Wistar strain rats with nylon catheters chronically implanted in the lumbar subarachnoid space were divided into five groups: group 1 (n = 6) received 40 microL of midazolam 0.1%; group 2 (n = 6) received 40 microL of fentanyl 0.005%; group 3 (n = 6) received 20 microL of midazolam 0.1% plus 20 microL of fentanyl 0.005%; group 4 (n = 6) received 40 microL of lignocaine 2%; group 5 (n = 6) received 40 microL of phenol in water. All substances were injected through the implanted catheters. The neurological recovery of all the animals in the four groups that received intrathecal midazolam alone, fentanyl alone, midazolam plus fentanyl and lignocaine alone was similar and complete. There were no significant differences in the histological changes in the neural tissues of these groups, despite repeated application of the test substances. Group 5 demonstrated the typical neurolytic lesions of phenol when injected intentionally into the subarachnoid space.

A rat model of chronic lumbar epidural catheterisation

PURPOSE

There are no rodent models of chronic epidural catheterisation which can induce clinically relevant analgesic effects of morphine (potency ratio of intrathecal:epidural = 10 to 30:1). The purpose of this study was to investigate a new rat model of chronic epidural catheterisation by comparing the analgesic effect of epidural and intrathecal morphine.

METHODS

In Sprague-Dawley rats, for epidural catheterisation, a skin incision and muscle dissection were made at T13 level in the midline. The intervertebral ligament was cut to insert an epidural catheter (polyethylene tube; outer diameter 0.14 mm) 2 cm caudally. The distal end of the catheter (0.61 mm) was passed s.c. to exit in the dorsal neck area. For intrathecal catheterisation, the atlanto-occipital membrane was incised to insert a catheter (0.61 mm) 8.5 cm caudally. The effects of morphine (1, 3, 10, 30, or 100 micrograms.10 microliters-1 intrathecally, and 30, 100, or 300 micrograms.5, 10, or 20 microliters-1 epidurally) on thermal escape latency were investigated by a hot box test. Behaviour and motor function were also tested.

RESULTS

A volume of 20 microliters induced greater analgesic effect than 5 and 10 microliters epidural administration. The ED50 of epidural morphine (94.1 micrograms) was 30 times more than that of intrathecal morphine (3.1 micrograms).

CONCLUSION

A new rat model of chronic epidural catheterisation is described, which provides a similar analgesic epidural: intrathecal potency ratio for morphine to that in humans when morphine is administered in a volume of 20 microliters.

The effect of intrathecal administration of magnesium sulphate in rats

Somatosensory evoked potential, locomotion and vocalisation upon tail pinch in rats was studied in order to determine whether intrathecal magnesium sulphate administration causes spinal anaesthesia. In Wistar rats with indwelling intrathecal catheters, cortical somatosensory evoked potential was recorded following stimulation via electrodes inserted into the hind paw under chloral hydrate anaesthesia before and after intrathecal administration of 10 microliters of either magnesium sulphate (12.3% or 24.6%) or lignocaine (4% or 8%). Locomotion and vocalisation after tail pinch were tested following intrathecal administration of the same two drugs in conscious rats. Somatosensory evoked potential amplitude was diminished after administration of lignocaine (p < 0.05) but did not change after magnesium sulphate. Latency of P1 was increased by lignocaine and by magnesium sulphate 12.3% (p < 0.05). Although lower extremity paralysis was observed in both groups, its duration with magnesium sulphate was much longer than with lignocaine. Vocalisation was recognised after magnesium sulphate 12.3%, but was not observed after lignocaine 8% during paralysis (p < 0.05). We believe that magnesium sulphate caused motor paralysis, but not complete analgesia.

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

We devised a versatile intrathecal injection method enabling evaluation of central nervous system (CNS) toxicities in rats, and then explored appropriate physico-chemical properties for injectable test solutions at relatively large dosage volumes. In a preliminary bolus injection study, a 25-gauge needle was inserted into the subarachnoid space through the lateral aspect of the intervertebral portion between the 2nd and 3rd lumbar vertebra under light ether anesthesia. When 3% phthalocyanine blue solution, a vital dye, was injected in order to confirm its transfer to the brain tissue, the dye reached the cerebral ventricle, perivascular spaces and veins of the cerebral cortex. On the basis of these information, a fine polyethylene tube was introduced up to a level around the axis via a 20-gauge needle inserted in advance into the vertebral space by the same way. The needle was then withdrawn from the space leaving the tube filled with a test solution. After a full recovery from anesthesia, the infusion was commenced. Injection volume-versus-speed or osmolality-versus-pH relationship was assessed using solutions with various compositions, followed by monitoring mortality coupled with clinical signs. The tolerable combination of factors for the intrathecal solution without causing death was thought to be an injection volume up to 2 ml/rat with 300 mOsm/kg H2O, pH 3 to 7, at a injection speed of less than 0.5 ml/min, although minor clinical signs were observed. Pathological examination revealed pulmonary edema in dead animals, but no changes in surviving animals. This method applicable to conscious rats is considered to be simple and reliable, and does not require surgical operation and special equipment. The toxicological event in the intrathecal route seems to depend largely on the physico-chemical characteristics of the injectable solution, under these experimental conditions.

Intrathecal granuloma after implantation of a morphine pump: case report and review of the literature

BACKGROUND

Intrathecal morphine pumps are being increasingly used in patients with benign pain who have a longer life expectancy than cancer patients. Newer complications may be encountered.

CLINICAL PRESENTATION

We report a complication that occurred in a 48-year-old woman who presented with intractable lower back pain 18 months after morphine pump implantation. Magnetic resonance imaging of the lumbosacral spine revealed an intrathecal mass around the catheter. At surgery, an inflammatory mass was found without any evidence of neoplasia or infection. This is a very unusual complication of intrathecal morphine pumps. (Related animal and human studies are reviewed in this article.)

CONCLUSION

Long-term use of implantable pumps may carry increased risks that are not observed during the short-term experience of cancer patients. Reimaging is important in evaluating patients who have developed uncontrollable pain and new neurologic findings.

Spinal anaesthesia with midazolam in the rat

PURPOSE

This study examined in an animal model whether intrathecal midazolam, alone or with fentanyl, can achieve anaesthesia sufficient for laparotomy, comparable to lidocaine. Effects on consciousness and whether anaesthesia was segmental were also examined. The haemodynamic and respiratory changes were compared with those of intrathecal lidocaine or intrathecal fentanyl alone.

METHODS

Sixty Wistar strain rats, with nylon catheters chronically implanted in the lumbar subarachnoid theca, were divided into six groups. Group 1 (n = 12) received 75 microL intrathecal lidocaine 2%. Group 2 (n = 12) received 75 microL intrathecal midazolam 0.1%, Group 3 (n = 12) received intrathecal 37.5 microL midazolam 0.1%, plus 37.5 microL fentanyl 0.005%. Group 4 (n = 12) received intrathecal 50 microL fentanyl 0.005%. Group 5 (n = 6) received 75 microL midazolam 0.1% iv. Group 6 (n = 6) received halothane 0.6% in oxygen by inhalation.

RESULTS

Both groups that received intrathecal midazolam, alone or combined with fentanyl, developed effective segmental sensory and motor blockade of the hind limbs and abdominal wall, sufficient for a pain-free laparotomy procedure. Neither of these groups, unlike the group that received intrathecal lidocaine, developed a reduction in blood pressure or change in heart rate at the time of maximal sensory or motor blockade, nor were there changes in the arterial blood gases or respiratory rate.

CONCLUSION

Midazolam, when injected intrathecally, produces reversible, segmental, spinally mediated antinociception, sufficient to provide balanced anaesthesia for abdominal surgery.

Involvement of increased excitatory amino acids and intracellular Ca2+ concentration in the spinal dorsal horn in an animal model of neuropathic pain

Neuropathic pain following nerve injury is believed to involve excitatory amino acids (EAAs) and Ca2+-mediated neuronal plastic changes in the central nervous system (CNS). This study was designed to investigate the changes in glutamate and aspartate contents in the dorsal half of the spinal cord following chronic constrictive injury (CCI) of the rat common sciatic nerve. We also examined the changes in intracellular calcium ion concentration ([Ca2+]i) of the spinal dorsal horn in transverse spinal slices in the same animal model. Thermal and mechanical hyperalgesia were observed on day 2 and thereafter following CCI (P < 0.0001). In the CCI rats to which 0.5 mg/kg of i.p. MK-801 was given 30 min prior to CCI and subsequently three daily treatments with 0.5 mg/kg of i.p. MK-801, the development of thermal and mechanical hyperalgesia was suppressed for a period of up to 7 days; however, hyperalgesia appeared on day 10 and day 14 (P < 0.001). In CCI rats, significant increases were observed in glutamate and aspartate contents on the ipsilateral side of the dorsal horn to nerve ligation on days 4, 7 and 14 (P < 0.001). Moreover, significant increases in [Ca2+]i in the spinal dorsal horn were also observed in the superficial (lamina I-II) and deep layers (lamina V-VI) on the ipsilateral side to nerve ligation on days 4, 7 and 14 after nerve ligation in the spinal slices (P < 0.0001). The treatment with i.p. MK-801 suppressed the increases in the contents of glutamate and aspartate and in [Ca2+]i on days 4 and 7. However, the ipsilateral contents of glutamate and aspartate significantly increased on day 14 (P < 0.001 and 0.003, respectively); the increased [Ca2+]i was also observed on day 14 (P < 0.001), and the spatial pattern of the increased regions was similar to untreated CCI rats. We interpret these results to indicate that neuropathic hyperalgesia induced by CCI in the rat is associated with an increase in glutamate and aspartate contents and the subsequent activation of NMDA receptors, followed by an increase in [Ca2+]i within dorsal horn of the spinal cord.

Antinociceptive synergistic interaction between morphine and n omega-nitro 1-arginine methyl ester on thermal nociceptive tests in the rats

PURPOSE

This study was conducted to demonstrate if subeffective dose of N omega Nitro L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, interacts with morphine when given intrathecally (IT), epidurally (EP), and intravenously (IV) to produce a synergistic antinociceptive effect in normal rats.

METHODS

Chronically catheterized 72 male Wistar rats were used in this study. We measured the tail flick latency in response to thermal stimulation of the tail on a hot plate (53 degrees C), and determined dose-response functions of IT, EP and IV morphine, L-NAME, and morphine co-administered with subeffective doses of L-NAME. The antinociceptive effect was evaluated using the doses for 50% maximum probable effect (ED50). The interaction between morphine and L-NAME was evaluated using an isobolographic approach. ANOVA was used for the statistical analysis. Significance was taken at P < 0.05.

RESULTS

Morphine and L-NAME produced dose-related antinociceptive effects in the IT (ED50 = 1.23 +/- 0.18 micrograms (Mean +/- SEM) and 76.0 +/- 14.5 micrograms), EP (ED50 = 32.6 +/- 2.4 micrograms and 560 +/- 97 micrograms), and IV (ED50 = 563 +/- 71.8 micrograms and 16.0 +/- 4.0 mg) groups, respectively. Co-administration of small doses of L-NAME and morphine produced reductions in the ED50 values for morphine (0.16 +/- 0.03 microgram in IT, 1.18 +/- 0.32 micrograms in EP, and 50.5 +/- 11.4 micrograms in IV groups) (P < 0.01), suggesting a multiplicative interaction of L-NAME with morphine.

CONCLUSION

L-NAME has a synergistic antinociceptive interaction with morphine in response to thermal stimulation when given intrathecally, epidurally or intravenously in rats.

Spinal anaesthesia induced by intrathecal magnesium sulphate

We have demonstrated in a rat model that the intrathecal injection of 0.02 ml of 6.3% magnesium sulphate, a concentration iso-osmolar with rat plasma, will produce a state of spinal anaesthesia and general sedation, lasting approximately 1 h. These effects reversed completely after 6 h, without evidence of neurotoxicity, immediately or during the period 1 week following the injection. The accompanying changes in haemodynamic and respiratory functions were minimal throughout the period of anaesthesia and compare favourably with those induced by an intrathecal bolus of 0.04 ml of 2% lignocaine.

Lumbar catheterization of the spinal subarachnoid space in the rat

The method commonly used for catheterization of the lumbar subarachnoid space in the rat implies inserting the catheter through the atlanto-occipital (A-O) membrane and moving the catheter caudally along the spinal cord. The method is associated with a considerable morbidity. A method for direct catheterization of the lumbar subarachnoid space was therefore developed. Major surgery was avoided by using a catheter-through-needle technique. Of 32 rats, none died. There were no signs of neurological disturbances, and all animals gained weight as normal the first week after implantation. Data from rats catheterized by the A-O method were used for comparison. Of 40 animals, 2 died, 11 showed signs of neurological disturbances, and the mean weight was reduced during the first week after catheterization. The two groups of animals showed different behavioural responses to intrathecal injection of N-methyl-D-aspartate (NMDA, 0.1-1.6 mM, 15 microliters) which is thought to stimulate afferent pathways mediating nociception. Animals with a lumbar catheter showed licking, biting and scratching behaviour in a dose-related manner for concentrations up to 1.6 mM. The animals with A-O catheters showed a maximum level of this behaviour already at 0.4 mM, while 0.5 mM induced convulsions. A possible explanation of this difference in response to NMDA could be a long-lasting pain state in the A-O group, caused by catheter-induced changes in the spinal cord and by the extensive surgery. It is concluded that the direct lumbar catheterization has several advantages compared to the A-O method, decreasing the suffering of the animals, the neurological disturbances and the interference with nociceptive functions of the spinal cord.

Percutaneous chronic epidural catheterization in the rabbit

BACKGROUND

Although several epidural catheterizations in small animals have been reported, all of them were performed surgically and no percutaneous method has been reported. We have established a technique for percutaneous chronic epidural catheterization in rabbits.

METHODS

Following pentobarbital anesthesia, the animals (n = 15) were fixed in a prone position using a fixing apparatus. A 19-gauge Tuohy needle was inserted in the lumbar region at an angle of about 30 degrees to the skin with the paramedian approach and advanced into the epidural space with the loss-of-resistance method. A 23-gauge Nylon catheter was advanced cephalad in the epidural space and the distal tip was extruded from the neck following the subcutaneous tunnelling. The effects of 0.5 ml of 1% lidocaine injected through the catheter were observed for 10 days.

RESULTS

No behavioral or neurological abnormalities were observed after the catheterization except for one case of catheterization in the epidural vessel. Motor paralysis of hind-limbs became manifest at 1-2 min after injection of 0.5 ml of 1% lidocaine through the catheter, and lasted 15-25 min. Autopsy revealed that the catheter was located in the lumbar epidural space in all animals and the distribution of methylene blue was consistent with that of lidocaine.

CONCLUSION

This rabbit model can be used to investigate the effects of epidurally administered drugs.

Intrathecal granuloma complicating chronic spinal infusion of morphine. Report of three cases

Intrathecal morphine delivered by implanted pumps has been used in the treatment of pain caused by terminal cancer. Some authors supports its use in benign pain as well. The authors present three cases in which chronic infiltration of intraspinal narcotic medication was complicated by the formation of a granulomatous mass that became large enough to exert mass effect and induce neurological dysfunction.

Spinal anesthesia attenuates myocardial ischemia during coronary artery spasm induced by intraaortic methacholine in rats

Coronary artery spasm is not rare in patients with coronary artery disease, but the influence of regional anesthesia on spasm-induced myocardial ischemia is not known. We investigated the effects of spinal anesthesia on myocardial ischemia during coronary artery spasm in rats, and compared these with the effects of an alpha- and beta-adrenergic antagonist, and an alpha-adrenergic agonist. An intraaortic catheter was inserted via the right internal carotid artery so that the tip of the catheter was placed near the coronary ostium. An intrathecal catheter was placed at lumbar level. Coronary spasm was induced by the intraaortic injection of methacholine, and we identified the thresholds of myocardial ischemia, defined as the dose of methacholine that induced ST-segment elevation. Subsequently, the thresholds were determined after spinal anesthesia, and after the intraaortic injection of phentolamine and propranolol. The thresholds of myocardial ischemia increased significantly after intrathecal bupivacaine. In contrast, the threshold did not change after the injection of phentolamine. The thresholds increased significantly after the injection of propranolol. Methoxamine significantly decreased the threshold of ischemia. These results demonstrated that spinal anesthesia attenuated myocardial ischemia during methacholine-induced coronary spasm. This effect was equivalent to that of propranolol.

Chronic intrathecal catheterization in the sheep

This paper describes a relatively simple and noninvasive method for the chronic implantation of intrathecal catheters in the sheep. The technique has been carried out on 17 occasions in nine sheep, with 60% of attempted catheterizations producing a correctly positioned, functional catheter. The placement and integrity of the catheters were confirmed by radiography using a contrast medium. Correctly placed catheters have been maintained for up to 16 months without problems.

Leakage of fluid administered epidurally to rats into subcutaneous tissue

Epidural catheters were implanted in rats under halothane/nitrous oxide anaesthesia. Contrast medium (Iopamidol) was injected via the catheter under fluoroscopic control 24-48 h after implantation. In 15 of 20 rats contrast could be seen leaking out of the epidural space, usually after only 25 microliters was administered. Leakage was associated with diminished antinociceptive response to morphine administered via the catheter. Both leakage and decreased response to morphine could be largely prevented by applying a drop of Supa-Glue over the site of entry of the catheter to the epidural space at the time of catheter implantation. Investigators using epidurally cannulated rats should document that leakage does not occur or discard results from rats showing evidence of leakage.

Analgesia and serum concentrations of extradural, subdural and intraperitoneal fentanyl in a rat model

The effects of epidural, subdural and intraperitoneal fentanyl were determined on the tail flick response of the rat using the response latency as a measure of analgesia. Dose-time-response curves were generated for incremental doses of fentanyl administered at constant injection volumes. Serum concentrations at varying doses were determined using a radioimmunoassay technique. It was found that serum concentrations for extradural, subdural and intraperitoneal fentanyl were similar at the low doses, but differed significantly at higher doses suggesting that pharmacokinetic differences may be concentration dependent. Extradural administration of naloxone (0.004 mg) was able to antagonize extradural fentanyl (8.0 micrograms), a dose eight-fold greater than the lowest maximally effective dose. The relationship between serum fentanyl concentrations and administered doses suggest that the analgesic properties of extradural and subdural fentanyl are in part dependent on centrally mediated actions.

Thoracic epidural anesthesia in conscious and anaesthetized rats. Effects on central haemodynamics compared to cardiac beta adrenoceptor and ganglionic blockade

A simple technique for cannulation of the thoracic epidural space in rats was described. 40-50 microliter of epidural bupivacaine 5 mg/ml induced a distribution of sensory analgesia from lower cervical to lower thoracic segments. With this model, effects of thoracic epidural anaesthesia (TEA) on mean arterial pressure (MAP), cardiac output (CO), systemic vascular resistance (SVR), stroke volume (SV), heart rate (HR), central venous pressure (CVP), left ventricular end-diastolic pressure (LVEDP) and maximal increase of pressure in the left ventricle (max dp/dt) were studied in six groups of animals: 1) In conscious animals (n = 10) MAP, CO, SV and HR decreased significantly by 12%, 25%, 10% and 16%, respectively, while SVR increased significantly by 20% during TEA; 2) In chloralose-anaesthetized animals (n = 7) the reduction in CO during TEA was less pronounced and there were no significant changes in SV or SVR; 3) In conscious animals (n = 6) LVEDP, CVP and max dp/dt decreased significantly during TEA; 4) Hexamethonium, when administered to pharmacologically vagotomized conscious animals during TEA (n = 8), induced a significant decrease in SVR (23%) but no change in HR; 5) Changes in haemodynamics after cardiac adrenoceptor blockade with metoprolol, in conscious animals (n = 12), did not differ significantly from those seen during TEA, except for an unchanged SV after metoprolol; 6) 50 microliters of bupivacaine (5 mg/ml) when given i.v. to conscious animals (n = 8) did not affect CO, SV, HR or TPR significantly, while MAP increased slightly but significantly. Thus, in this conscious animal model, TEA almost completely and rather selectively blocked probably mediated by a reflex activation of unblocked sympathetic efferents.(ABSTRACT TRUNCATED AT 250 WORDS)