Multifactorial motor behavior assessment for real-time evaluation of emerging therapeutics to treat neurologic impairments.

Integrating multiple assessment parameters of motor behavior is critical for understanding neural activity dynamics during motor control in both intact and dysfunctional nervous systems. Here, we described a novel approach (termed Multifactorial Behavioral Assessment (MfBA)) to integrate, in real-time, electrophysiological and biomechanical properties of rodent spinal sensorimotor network activity with behavioral aspects of motor task performance. Specifically, the MfBA simultaneously records limb kinematics, multi-directional forces and electrophysiological metrics, such as high-fidelity chronic intramuscular electromyography synchronized in time to spinal stimulation in order to characterize spinal cord functional motor evoked potentials (fMEPs). Additionally, we designed the MfBA to incorporate a body weight support system to allow bipedal and quadrupedal stepping on a treadmill and in an open field environment to assess function in rodent models of neurologic disorders that impact motor activity. This novel approach was validated using, a neurologically intact cohort, a cohort with unilateral Parkinsonian motor deficits due to midbrain lesioning, and a cohort with complete hind limb paralysis due to T8 spinal cord transection. In the SCI cohort, lumbosacral epidural electrical stimulation (EES) was applied, with and without administration of the serotonergic agonist Quipazine, to enable hind limb motor functions following paralysis. The results presented herein demonstrate the MfBA is capable of integrating multiple metrics of motor activity in order to characterize relationships between EES inputs that modulate mono- and polysynaptic outputs from spinal circuitry which in turn, can be used to elucidate underlying electrophysiologic mechanisms of motor behavior. These results also demonstrate that proposed MfBA is an effective tool to integrate biomechanical and electrophysiology metrics, synchronized to therapeutic inputs such as EES or pharmacology, during body weight supported treadmill or open field motor activities, to target a high range of variations in motor behavior as a result of neurological deficit at the different levels of CNS.

Assessment of Neurological Toxicity of Hydroxyethyl Starch 130/0.4 Injected in the Intrathecal Space in Rats.

Objective: Epidural blood patch is the procedure of choice to relieve postdural puncture headache. Hydroxyethyl-starch (HES) has been proposed as a patch in some circumstances such as in the case of hematological disease due to the theoretical risk of neoplastic seeding to the central nervous system. Acute neurological HES toxicity has been excluded by a previous animal study, but the long-term neurological toxicity has not been evaluated. Methods: Rats were randomly assigned to one of three groups: no intrathecal injection, 20 µL of intrathecal saline, or a 20-µL intrathecal HES (6% hydroxyethyl starch 130/0.4) administered via a cervical puncture. Clinical daily rat activity was measured before and after dural puncture by actinometry. The rats were killed at day 28, and the spinal cord was surgically removed and stained with hematoxylin-phloxine-saffron for gross and microscopic examination. Results: Eleven rats underwent dural puncture without injection, 11 were injected with normal saline, and 12 received intrathecal HES. No clinical or actimetric changes (total distance traveled, number of direction changes, and number of rearings) were observed up to one month after injection. Nonspecific histopathological changes were equally observed in all groups. Conclusions: The results of the current study indicate that intrathecal injection of HES in rats does not induce any clinical or histopathological evidence of long-term neuronal toxicity. Further safety studies in animals are warranted before HES might be considered a safe alternative to the classic epidural blood patch.

Objective methods for the assessment of the spinal and supraspinal effects of opioids.

BACKGROUND AND PURPOSE: Opioids are potent analgesics. Opioids exert effects after interaction with opioid receptors. Opioid receptors are present in the peripheral- and central nervous system (CNS), but the analgesic effects are primarily mediated via receptors in the CNS. Objective methods for assessment of opioid effects may increase knowledge on the CNS processes responsible for analgesia. The aim of this review was to provide an overview of the most common objective methods for assessment of the spinal and supraspinal effects of opioids and discuss their advantages and limitations. METHOD: The literature search was conducted in Pub Med (http://www.ncbi.nlm.nih.gov/pubmed) from November 2014 to June 2016, using free-text terms: "opioid", "morphine" and "oxycodone" combined with the terms "pupillometry," "magnetic resonance spectroscopy," "fMRI," "BOLD," "PET," "pharmaco-EEG", "electroencephalogram", "EEG," "evoked potentials," and "nociceptive reflex". Only original articles published in English were included. RESULTS: For assessment of opioid effects at the supraspinal level, the following methods are evaluated: pupillometry, proton magnetic resonance spectroscopy, functional resonance magnetic imaging (fMRI), positron emission tomography (PET), spontaneous electroencephalogram (EEG) and evoked potentials (EPs). Pupillometry is a non-invasive tool used in research as well as in the clinical setting. Proton magnetic resonance spectroscopy has been used for the last decades and it is a non-invasive technique for measurement of in vivo brain metabolite concentrations. fMRI has been a widely used non-invasive method to estimate brain activity, where typically from the blood oxygen level-dependent (BOLD) signal. PET is a nuclear imaging technique based on tracing radio labeled molecules injected into the blood, where receptor distribution, density and activity in the brain can be visualized. Spontaneous EEG is typically quantified in frequency bands, power spectrum and spectral edge frequency. EPs are brain responses (assessed by EEG) to a predefined number of short phasic stimuli. EPs are quantified by their peak latencies and amplitudes, power spectrum, scalp topographies and brain source localization. For assessment of opioid effects at the spinal level, the following methods are evaluated: the nociceptive withdrawal reflex (NWR) and spinal EPs. The nociceptive withdrawal reflex can be recorded from all limbs, but it is standard to record the electromyography signal at the biceps femoris muscle after stimulation of the ipsilateral sural nerve; EPs can be recorded from the spinal cord and are typically recorded after stimulation of the median nerve at the wrist. CONCLUSION AND IMPLICATIONS: The presented methods can all be used as objective methods for assessing the centrally mediated effects of opioids. Advantages and limitations should be considered before implementation in drug development, future experimental studies as well as in clinical settings. In conclusion, pupillometry is a sensitive measurement of opioid receptor activation in the CNS and from a practical and economical perspective it may be used as a biomarker for opioid effects in the CNS. However, if more detailed information is needed on opioid effects at different levels of the CNS, then EEG, fMRI, PET and NWR have the potential to be used. Finally, it is conceivable that information from different methods should be considered together for complementary information.

Cortical and spinal assessment - a comparative study using encephalography and the nociceptive withdrawal reflex.

BACKGROUND: Standardized objective methods to assess the analgesic effects of opioids, enable identification of underlying mechanisms of drug actions in the central nervous system. Opioids may exert their effect on both cortical and spinal levels. In this study actions of morphine at both levels were investigated, followed by analysis of a possible correlation between the cortical processing and spinal transmission. METHODS: The study was conducted after a double-blinded, two-way crossover design in thirty-nine healthy participants. Each participant received 30mg morphine or placebo as oral solution in randomized order. The electroencephalogram (EEG) was recorded during rest and during immersion of the hand into ice-water. Electrical stimulation of the sole of the foot was used to elicit the nociceptive withdrawal reflex and the reflex amplitude was recorded. RESULTS: Data from thirty subjects was included in the data analysis. There was no change in the activity in resting EEG (P>0.05) after morphine administration as compared to placebo. During cold pressor stimulation, morphine significantly lowered the relative activity in the delta (1-4Hz) band (P=0.03) and increased the activity in the alpha (8-12Hz) band (P=0.001) as compared to placebo. The reflex amplitudes significantly decreased after morphine administration (P=0.047) as compared to placebo. There was no correlation between individual EEG changes during cold pressor stimulation and the decrease in the reflex amplitude after morphine administration (P>0.05). CONCLUSIONS: Cold pressor EEG and the nociceptive reflex were more sensitive to morphine analgesia than resting EEG and can be used as standardized objective methods to assess opioid effects. However, no correlation between the analgesic effect of morphine on the spinal and cortical assessments could be demonstrated.

Assessment of cord dorsum potentials from caudal nerves in anesthetized clinically normal adult dogs without or during neuromuscular blockade.

OBJECTIVE: To assess the feasibility of measuring cord dorsum potentials (CDPs) in anesthetized clinically normal dogs after caudal nerve stimulation, determine the intervertebral site of maximum amplitude and best waveform of the CDP, and evaluate the effects of neuromuscular blockade. ANIMALS: 8 male and 4 female dogs (age, 1 to 5 years). PROCEDURES: Dogs were anesthetized, and CDPs were recorded via needles placed on the dorsal lamina at intervertebral spaces L1-2 through L7-S1. Caudal nerves were stimulated with monopolar electrodes inserted laterally to the level of the caudal vertebrae. Dogs were tested without and during neuromuscular blockade induced with atracurium besylate. The CDP latency and amplitude were determined from the largest amplitude tracings. RESULTS: CDPs were recorded in 11 of 12 dogs without neuromuscular blockade and in all dogs during neuromuscular blockade. The CDP was largest and most isolated at the L4-5 intervertebral space (3 dogs) or the L5-6 intervertebral space (9 dogs); this site corresponded to the segment of insertion of the first caudal nerve. Onset latencies ranged from 2.0 to 4.7 milliseconds, and there was no effect of neuromuscular blockade on latencies. Amplitudes of the CDPs were highly variable for both experimental conditions. CONCLUSIONS AND CLINICAL RELEVANCE: CDPs were recorded from all dogs tested in the study; neuromuscular blockade was not critical for successful CDP recording but reduced muscle artifact. This technique may be useful as a tool to assess the caudal nerve roots in dogs suspected of having compressive lumbosacral disease or myelopathies affecting the lumbar intumescence.

Effect of vascular endothelial growth factor treatment in experimental traumatic spinal cord injury: in vivo longitudinal assessment.

Vascular endothelial growth factor (VEGF) is thought to provide neuroprotection to the traumatically injured spinal cord. We examined whether supplementing the injured environment with VEGF(165) via direct intraspinal injection into the lesion epicenter during the acute phase of spinal cord injury (SCI) results in improved outcome. The effect of treatment was investigated using longitudinal multi-modal magnetic resonance imaging (MRI), neurobehavioral assays, and end-point immunohistochemistry. We observed on MRI that rats treated with VEGF(165) after SCI had increased tissue sparing compared to vehicle-treated animals at the earlier time points. However, these favorable effects were not maintained into the chronic phase. Histology revealed that VEGF(165) treatment resulted in increased oligodendrogenesis and/or white matter sparing, and therefore may eventually lead to improved functional outcome. The increase in spared tissue as demonstrated by MRI, coupled with the possible remyelination and increased neurosensory sensitivity, suggests that VEGF(165) treatment may play a role in promoting plasticity in the sensory pathways following SCI. However, VEGF-treated animals also demonstrated an increased incidence of persistent allodynia, as indicated on the von Frey filament test.

Sexual dimorphism and hormone responsiveness in the spinal cord of the socially monogamous prairie vole (Microtus ochrogaster).

Prairie voles (Microtus ochrogaster) are exceptional among rodents in that many aspects of their brain and behavior are not masculinized by exogenous aromatizable androgens. However, the sexually differentiated endpoints studied to date rely on estrogenic mechanisms in other mammals. We examined whether sexual differentiation of an androgen receptor-dependent sex difference would be similarly distinct in prairie voles. Male mammals have more and larger motoneurons projecting to perineal muscles than do females. This sex difference normally arises from males' perinatal androgen exposure and can be eliminated by treating developing females with androgens. Gross dissection revealed bulbospongiosus muscles in adult male, but not female, prairie voles. Retrograde tracing from males' bulbocavernosus muscles and the external anal sphincter from both sexes revealed sexually dimorphic populations of labeled motoneurons in the ventral horn of the lumbar spinal cord. Similar to other rodents, males had twice as many motoneurons as females, although no sex difference in motoneuron size was detected. Unexpectedly, prenatal or early postnatal exposure to testosterone propionate had no effect on adult females' motoneuron number or size. In adulthood, gonadectomy alone or followed by chronic testosterone treatment also had no effect on females' motoneuron size or number, although castration reduced motoneuron size in males. Comparing gonadally intact weanlings confirmed that the sex difference in motoneuron number exists before adulthood. As with some other sexually dimorphic traits, and perhaps related to their unique social organization, sexual differentiation of the prairie vole spinal cord differs from that found in most other laboratory rodents.

The incidence and management of tolerance in intrathecal baclofen therapy.

STUDY DESIGN: Retrospective study. OBJECTIVES: To study the incidence and management of tolerance in patients treated with intrathecal baclofen (ITB) therapy. SETTING: Department of neurology and neurosurgery, University Medical Center Groningen, The Netherlands. METHODS: Medical records of all patients who had received an implantable ITB pump at our clinic during 1991-2005 were reviewed. RESULTS: A total of 37 patients (representing 116 pump years) were included. Mean follow-up time was 38 months (range 3-120 months). Baclofen dose increased in the first 18 months after implantation (P<0.05), and then stabilized around a mean dose of 350 microg per day. Eight patients (22%) developed tolerance, defined as a dose increase of >100 microg per year. No predictive factors for development of tolerance could be determined. Three different treatment regimens for tolerant patients were analyzed. Altering the infusion mode from simple to complex continuous (n=6) had no effect on the development of tolerance. Pulsatile bolus infusion (n=1) and a drug holiday (n=2) were both effective in reducing the daily baclofen dose. Patients who needed surgical revision of the pump system because of mechanical failures (n=11) showed a significant dose decrease during the first month after revision, indicating that the preoperative dose increase most likely had been caused by the pump failure. Pump-related complications occurred once per 10.5 years of ITB treatment. Drug-related side effects had an annual risk of 13.8%. The reported events were mostly mild. CONCLUSIONS: ITB therapy is effective and safe, also in the long term and causes tolerance in only 22% of the treated patients.

A re-assessment of minocycline as a neuroprotective agent in a rat spinal cord contusion model.

This study was initiated due to an NIH "Facilities of Research--Spinal Cord Injury" contract to support independent replication of published studies that could be considered for a clinical trial in time. Minocycline has been shown to have neuroprotective effects in models of central nervous system injury, including in a contusive spinal cord injury (SCI) model at the thoracic level. Beneficial effects of minocycline treatment included a significant improvement in locomotor behavior and reduced histopathological changes [Lee, S.M., Yune, T.Y., Kim, S.J., Park, D.O.W., Lee, Y.K., Kim, Y.C., Oh, Y.J., Markelonis, G.J., Oh, T.H., 2003. Minocycline reduces cell death and improves functional recovery after traumatic spinal cord injury in the rat. J Neurotrauma. 20, 1017-1027.] To verify these important observations, we repeated this study in our laboratory. The NYU (MASCIS) Impactor was used to produce a moderate cord lesion at the vertebral level T9-T10 (height 12.5 mm, weight 10 g), (n=45), followed by administration of minocycline, 90 mg/kg (group 1: minocycline IP, n=15; group 2: minocycline IV, n=15; group 3: vehicle IP, n=8; group 4: vehicle IV, n=7) immediately after surgery and followed by two more doses of 45 mg/kg/IP at 12 h and 24 h. Open field locomotion (BBB) and subscores were examined up to 6 weeks after SCI and cords were processed for quantitative histopathological analysis. Administration of minocycline after SCI did not lead to significant behavioral or histopathological improvement. Although positive effects with minocycline have been reported in several animal models of injury with different drug administration schemes, the use of minocycline following contusive SCI requires further investigation before clinical trials are implemented.

A re-assessment of erythropoietin as a neuroprotective agent following rat spinal cord compression or contusion injury.

This study was initiated due to an NIH "Facilities of Research--Spinal Cord Injury" contract to support independent replication of published studies that appear promising for eventual clinical testing. We repeated a study reporting the beneficial effects of recombinant human erythropoietin (rhEPO) treatment after spinal cord injury (SCI). Moderate thoracic SCI was produced by two methods: 1) compression due to placement of a modified aneurysm clip (20 g, 10 s) at the T3 spinal segment (n=45) [followed by administration of rhEPO 1000 IU/kg/IP in 1 or 3 doses (treatment groups)] and 2) contusion by means of the MASCIS impactor (n = 42) at spinal T9 (height 12.5 cm, weight 10 g) [followed by the administration of rhEPO 5000 IU/kg/IP for 7d or single dose (treatment groups)]. The use of rhEPO following moderate compressive or contusive injury of the thoracic spinal cord did not improve the locomotor behavior (BBB rating scale). Also, secondary changes (i.e. necrotic changes followed by cavitation) were not significantly improved with rhEPO therapy. With these results, although we cannot conclude that there will be no beneficial effect in different SCI models, we caution researchers that the use of rhEPO requires further investigation before implementing clinical trials.

Transient allodynia pain models in mice for early assessment of analgesic activity.

BACKGROUND AND PURPOSE: The most common preclinical models of neuropathic pain involve surgical ligation of sensory nerves, which is especially difficult in mice. Transient models of chemically sensitized allodynia are potentially useful for rapidly characterizing the analgesic profile of compounds and conducting mechanistic studies. EXPERIMENTAL APPROACH: Increasing doses of NMDA, sulprostone (an EP1/EP3 prostaglandin receptor agonist) or phenylephrine (an alpha (1) adrenoceptor agonist) were injected intrathecally (i.t.) or i.p., and animals were subsequently assessed for allodynia. The effects of receptor antagonists and analgesic compounds on allodynia were also assessed. KEY RESULTS: A comparison of total body doses that cause allodynia following spinal or systemic administration indicated that NMDA induces allodynia in the spinal cord while sulprostone and phenylephrine act through a peripheral mechanism. Inhibition of the allodynia with receptor antagonists indicated that each agent induces allodynia by a distinct mechanism. The three models were benchmarked using compounds known to be active in neuropathic pain patients and nerve injury animal models, including gabapentin, amitriptyline and clonidine. CONCLUSIONS AND IMPLICATIONS: These transient allodynia models are a useful addition to the toolbox of preclinical pain models. They are simple, rapid and reproducible, and will be especially useful for characterizing the pain phenotype of knockout mice.

Application of magnetic resonance diffusion anisotropy imaging for the assessment neuroprotecting effects of MPEP, a selective mGluR5 antagonist, on the rat spinal cord injury in vivo.

Magnetic resonance diffusion anisotropy imaging (DAI) of the rat spinal cord after contusion using weight-drop method was used to study the neuroprotecting effect of 2-methyl-6-(phenylethynyl)-pyridine (MPEP), an mGluR5 receptor antagonist. Eighteen rats were used, divided into 3 groups of 6 animals: a reference group without any operation, a control group with injury and a test group with injury and MPEP. DAI was performed at 4.7 T at 1 h, 24 h, 48 h and 7 day after the injury. Locomotor function was evaluated using Basso, Beattie and Bresnahan (BBB) open field locomotor activity test each day starting one day after the injury. DAI results confirm positive effect of MPEP on the limitation of secondary excitotoxic injury in the spinal cord.

Contemporary assessment and management of neuropathic pain.

Preclinical studies have increased our understanding of the pathophysiology of neuropathic pain at the anatomic, cellular, and molecular levels. These lines of investigation have enabled more logical uses of older therapies for neuropathic pain and have contributed to our understanding of the potential mechanisms underlying the efficacy of newer remedies. The identification of receptor systems and the development of genetically modified animal models for the study of neuropathic pain have greatly increased our understanding of effective clinical treatments. This review focuses on the central and peripheral nervous system changes believed to be important in the initiation and perpetuation of neuropathic pain. Currently used medications, as well as medications that are on the horizon, are highlighted.

Propofol and sevoflurane in subanesthetic concentrations act preferentially on the spinal cord: evidence from multimodal electrophysiological assessment.

BACKGROUND: Animal experiments in recent years have shown that attenuation of motor responses by general anesthetics is mediated at least partly by spinal mechanisms. Less is known about the relative potency of anesthetic drugs in suppressing cortical and spinal electrophysiological responses in vivo in humans, particularly those, but not only those, connected with motor responses. Therefore, we studied the effects of sevoflurane and propofol in humans using multimodal electrophysiological assessment. METHODS: We studied nine healthy volunteers in two sessions during steady state sedation with 0.5, 1.0, and 1.5 microg/l (targeted plasma concentration) propofol or 0.2 and 0.4 vol% (end-tidal) sevoflurane. Following a 15-min equilibration period, motor responses to transcranial magnetic stimulation and peripheral (H-reflex, F-wave) stimulation were recorded, while electroencephalography and auditory evoked responses were recorded in parallel. RESULTS: At concentrations corresponding to two thirds of C(50 awake), motor responses to transcranial magnetic stimulation were reduced by approximately 50%, H-reflex amplitude was reduced by 22%, F-wave amplitude was reduced by 40%, and F-wave persistence was reduced by 25%. No significant differences between sevoflurane and propofol were found. At this concentration, the Bispectral Index was reduced by 7%, and the middle-latency auditory evoked responses were attenuated only mildly (N(b) latency increased by 11%, amplitude P(a)N(b) did not change). In contrast, the postauricular reflex was suppressed by 77%. CONCLUSIONS: The large effect of both anesthetics on all spinal motor responses, compared with the small effect on electroencephalography and middle-latency auditory evoked responses, assuming that they represent cortical modulation, may suggest that the suppression of motor responses to transcranial magnetic stimulation is largely due to submesencephalic effects.

Assessment of nicotinic acetylcholine receptor-mediated release of [(3)H]-norepinephrine from rat brain slices using a new 96-well format assay.

The study of the modulatory effects of nicotinic acetylcholine receptor (nAChR) agonists on neurotransmitter release from tissue slices has been hampered by laborious and limiting superfusion techniques. A new methodology was developed utilizing 96-well filter plates. This new method produced comparable results to previously published data, yet expanded throughput to permit more complete pharmacological characterization. Rat brain slices, preloaded with [(3)H]-norepinephrine ([(3)H]-NE), were distributed onto 96-well filter plates. Following a 5 min preincubation, the slices were incubated for 5 min with nicotinic agonists or antagonists. (-)-Nicotine (NIC) and 1,1-dimethyl-4-phenylpiperazine (DMPP) evoked release of [(3)H]-NE from a number of brain regions and spinal cord, with the highest response seen in the hippocampus. Concentration-response curves revealed a rank order of potency of (+/-)-epibatidine>>anatoxin-a>A-85380>DMPP=NIC=(-)-cytisine in the hippocampus, thalamus, and frontal cortex. EC(50) values were approximately 0.005, 0.2, 1, 5, 5 and 5 microM, respectively. Concentration-inhibition curves of nicotine evoked [(3)H]-NE release from hippocampal and thalamic slices resulted in a rank order of potency of mecamylamine>hexamethonium>d-tubocurare>DHbetaE. Schild analysis revealed apparent noncompetitive antagonism of [(3)H]-NE release from hippocampus by mecamylamine, hexamethonium, and DHbetaE. In contrast, DHbetaE antagonism of [(3)H]-dopamine release from striatal slices using a similar methodology was competitive.

An assessment of neurotoxicity of aroclors 1016, 1242, 1254, and 1260 administered in diet to Sprague-Dawley rats for one year.

As part of a comparative chronic toxicity/oncogenicity study of different Aroclors (1016, 1242, 1254, and 1260), neurotoxicity was assessed in male and female Sprague-Dawley rats using functional observational battery (FOB) and motor activity tests, and histopathologic evaluation of selected nervous system tissues. Doses varied by Aroclor and ranged from 25 to 200 ppm in the diet. Animals were evaluated prior to initiation of dosing and at 13, 26, 39, and 52 weeks of exposure. Clinical signs, body weights, and feed consumption were evaluated weekly. Data analysis of FOB and motor activity results revealed several instances where Aroclor-treated groups were different from control. However, these were considered incidental, as they lacked any consistent dose- or time-related pattern that would suggest Aroclor-induced neurotoxicity. The nonremarkable findings during each of the four assessments were supported by the absence of any treatment-related clinical signs or mortality. Decreased body weight gain was evident in the male 100 ppm Aroclor 1254 dose group and in all female Aroclor 1254 dose groups late in the study (when a linear relationship was assumed between body weight and time), correlating with decreased feed consumption. Although a variety of incidental, spontaneous, degenerative changes were found in nervous tissue evaluated histopathologically, these changes were seen with similar incidence and severity in treated and control groups. No lesions were found that could be attributed to Aroclor-related neurotoxicity. In summary, 52 weeks of exposure to Aroclors 1016, 1242, 1254, or 1260 mixed in the diet did not yield any functional or morphologic changes indicative of PCB-induced neurotoxicity.

Neurotoxicological assessment after intracisternal injection of liposomal bupivacaine in rabbits.

UNLABELLED: Experiments were performed on rabbits randomly assigned to intracisternally receive 0.3 mL of plain bupivacaine 5 mg/mL, liposomal bupivacaine 5 mg/mL, bupivacaine-free liposomes, or isotonic phosphate-buffered saline. Mechanical ventilation was initiated or intravenous dopamine was infused when respiratory depression or hypotension occurred. Seven days after the injection, the whole spinal cord was removed and histopathologic characteristics were studied on transverse sections. All preparations were devoid of phosphatidylcholine hydrolysis or oxidation compounds. Solutions without bupivacaine produced transient irritative signs that required sedation in most rabbits. Despite the similar duration of respiratory depression in groups receiving liposomal or plain bupivacaine, liposomes produced significantly prolonged motor blockade (126 vs 70 min). Correction of hypotension after plain bupivacaine required a longer dopamine infusion and larger doses than after liposomal bupivacaine (28 vs 18 min and 74 vs 47 mg). Necrosis was observed in the cervical area of two rabbits (one in the liposomal bupivacaine group and another in the phosphate buffer group). No demyelinated areas were noted in spinal cord examinations. We conclude that liposomal bupivacaine leads to a less severe sympathetic block and to a prolonged motor block, whereas histologic changes are not significantly different among groups. IMPLICATIONS: Multilamellar liposomes containing bupivacaine administered intracisternally to rabbits produce spinal cord histopathologic changes not significantly different from those observed with plain bupivacaine. Sustained release of bupivacaine from liposomes is suggested by the prolonged motor blockade and the reduced severity of arterial hypotension. Use of these liposomes could prolong the local anesthetic effects of bupivacaine.

Histological assessment of rodent CNS tissues to EPR oximetry probe material.

The effects of the paramagnetic oxygen sensing material, lithium phthalocyanine (LiPc) and fusinite were assessed in the brain of Mongolian gerbils and the spinal columns of rats respectively, to determine if there are histologically discernible changes in the tissue surrounding the probe material. This information is essential for the evaluation of the role of EPR oximetry in the measurements of pO2 in the CNS; the technique has great potential value for such measurements because it reports on the pO2 accurately and sensitively and, after the initial placement, measurements can be made repeatedly without invasive procedures or anesthesia. Histologic assessments demonstrated the inert nature of both the fusinite and LiPc EPR probes in rodent CNS tissue over relatively long (2 month) time periods. The fusinite suspensions and LiPc crystals (size range of approximately 100-200 microns) remained well localized to the point of injection and created mild acute tissue reaction on implantation (which appeared to resolve quickly) and virtually no tissue reaction at later times. The majority of the implanted fusinite and LiPc material was present extracellularly in the brain and spinal cord. MRI provided an accurate, noninvasive assessment of probe placement and was able to investigate pathologic effects (hemorrhage, edema, necrosis) associated with the probe placement and treatment effects.