Convection-enhanced delivery into the rat brainstem

OBJECT: Convection-enhanced delivery (CED) can be used safely to achieve high local infusate concentrations within the brain and spinal cord. The use of CED in the brainstem has not been previously reported and may offer an alternative method for treating diffuse pontine gliomas. In the present study the authors tested CED within the rat brainstem to assess its safety and establish distribution parameters. METHODS: Eighteen rats underwent stereotactic cannula placement into the pontine nucleus oralis without subsequent infusions. Twenty rats underwent stereotactic cannula placement followed by infusion of fluorescein isothiocyanate (FITC)-dextran at a constant rate (0.1 microl/minute) until various total volumes of infusion (V(i)s) were reached: 0.5, 1, 2, and 4 microl. Additional rats underwent FITC-dextran infusion (V, 4 microl) and were observed for 48 hours (five animals) or 14 days (five animals). Serial (20-microm thick) brain sections were imaged using confocal microscopy with ultraviolet illumination, and the volume of distribution (Vd) was calculated using computer image analysis. Histological analysis was performed on adjacent sections. No animal exhibited a postoperative neurological deficit, and there was no histological evidence of tissue disruption. The Vd increased linearly (range 15.4-55.8 mm3) along with increasing Vi, with statistically significant correlations for all groups that were compared (p < 0.022). The Va/Vi ratio ranged from 14 to 30.9. The maximum cross-sectional area of fluorescence (range 9.8-20.9 mm2) and the craniocaudal extent of fluorescence (range 2.8-5.1 mm) increased with increasing Vi. CONCLUSIONS: Convection-enhanced delivery can be safely applied to the rat brainstem with substantial and predictable V(d)s. This study provides the basis for investigating delivery of various candidate agents for the treatment of diffuse pontine gliomas.     

Overcoming peripheral nerve gap defects using an intact nerve bridge in a rabbit model

This study investigated the intact nerve bridge technique for overcoming peripheral nerve gap defects in a rabbit model. To create the intact nerve bridge, a 1-cm segment of the peroneal nerve is resected leaving a gap defect. The proximal and distal peroneal nerve stumps are sutured 1 cm apart, in an end-to-side fashion, to the intact tibial nerve epineurium. Four experimental groups were used (n = 10): primary repair of resected segment; intact nerve bridge; nerve autograft; and gap in situ control. Evaluation after 12 weeks included measurement of isometric muscle contraction force, axonal counting, wet muscle weights, and histologic examination. The results of this study support two main conclusions, in a rabbit model: (a) regenerating axons can use the epineurium of an intact nerve to bridge a gap defect; (b) there is no significant difference in the functional recovery between standard nerve autografts and the intact nerve bridge technique.     

Using intact nerve to bridge peripheral nerve defects: an alternative to the use of nerve grafts

This preliminary study was conducted to determine whether a regenerating peripheral nerve in a rat model can use the epineurium of an intact nerve to bridge a nerve gap defect. To create the intact nerve bridge a 1-cm segment of the peroneal nerve is resected leaving a gap defect. The proximal and distal peroneal nerve stumps are sutured 1-cm apart, in an end-to-side fashion, to the epineurium of the intact tibial nerve. The following experimental groups were used (n = 12): group A, immediate primary repair of resected segment; group B, intact nerve bridge technique; group C, nerve autograft; and group D, gap in situ control. Evaluation 12 weeks after surgery included measurement of the tibialis anterior muscle contraction force, axonal counting, wet weight of the tibialis anterior muscle, and histologic examination. The results of this animal study support 3 main conclusions: regenerating axons can use the epineurium of an intact nerve to bridge a gap in nerve continuity; when using functional recovery to assess regeneration, there is no significant difference between standard nerve autografts and the intact nerve bridge technique; and based on histologic examination, the intact nerve bridge technique does not injure the intact tibial nerve used to bridge the gap defect. Taken together, the results of this preliminary animal study suggest that the intact nerve bridge technique may be a potential alternative to standard nerve autografts in appropriate circumstances. Further investigation in a higher animal model is warranted before considering clinical application of the intact nerve bridge technique.     

Spatially controlled delivery of neurotrophic factors in silk fibroin-based nerve conduits for peripheral nerve repair

Restoration with sufficient functional recovery after long-gap peripheral nerve damage remains a clinical challenge. Silk has shown clinical promise for numerous tissue engineering applications due to its biocompatibility, impressive mechanical properties, and Food and Drug Administration approval. The aim of this study was to evaluate the efficacy of silk fibroin--based nerve guides containing glial cell line-derived neurotrophic factor (GDNF) in a long-gap sized (15 mm) rat sciatic nerve defect model. Four groups of nerve conduits were prepared: (1) silk conduits with empty silk microspheres, (2) silk conduits with GDNF-loaded silk microspheres uniformly distributed in the conduit wall, (3) silk conduits with GDNF-loaded silk microspheres in a controlled manner with the highest GDNF concentration at the distal end, and (4) isograft. After 6 weeks, the nerve grafts were explanted, harvested, and fixed for histologic analysis. Nerve tissue stained with the S-100, and neuroendocrine marker PGP 9.5 antibodies demonstrated a significantly increased density of nerve tissue in the GDNF-treated groups compared with the empty microsphere (control) group (P < 0.05). GDNF-treated animals with a higher concentration of GDNF in the distal portion possessed a significantly higher density of PGP 9.5 protein middle conduit part than comparison to GDNF uniform-treated animals (P < 0.05). Silk-based nerve conduits possess optimal mechanical and degradative properties, rendering them potentially useful in peripheral nerve repair. This study demonstrates that novel, porous silk fibroin--based nerve conduits, infused with GDNF in a controlled manner, represent a potentially viable conduit for Schwann cell migration and proliferation in the regeneration of peripheral nerves.     

Convection-enhanced delivery: from mechanisms to clinical drug delivery for diseases of the central nervous system

The evolution of cancer chemotherapy has been a major advance in medical science in the late 20th century. However, patients with malignant gliomas have not benefitted much. The blood-brain barrier (BBB), which always hinders the entry of therapeutic agents into the central nervous system (CNS), may at least partly be responsible. Convection-enhanced delivery (CED), a method for distributing large and small molecular weight compounds bypassing the BBB, enables robust distribution of the infused molecules at the site of infusion. CED is promising as an effective treatment not only for malignant gliomas but also for multiple CNS disorders because this method can effectively distribute multiple molecules that are potentially effective against different diseases. Although the method is quite simple, several problems require solution in developing novel CED-based strategies, including what, where, when, and how to infuse. This review discusses basic considerations when developing CED-based strategies for CNS diseases, focusing mainly on brain tumors.     

Anatomy and microanatomy of peripheral nerve.

The anatomy of the peripheral nervous system is presented, with special emphasis on the connective tissue sheaths and their relationship to the nerves' blood supply. The microanatomy of nerve fibers is also presented, with a focus on pathologic changes caused by compression and ischemic injuries. The article highlights neuropathologic findings relevant to the surgical management of peripheral nerve injury and entrapment.     

Techniques of peripheral nerve repair.

At present, the principles of microsurgical reconstruction of the peripheral nerve incorporate a clear understanding of the pathophysiology of the peripheral nerve, accurate preoperative assessment of the lesion, aggressive early treatment to avoid irreversible atrophy of the end organ, use of nontraumatic microtechniques for optimal alignment of individual fascicular bundles, introduction of a minimum amount of foreign material at the suture line, resection of the scar-producing epineurium, total avoidance of tension at the suture line, and placement of the nerve repair in a well-vascularized soft tissue bed. If tension is eliminated, a minimal amount of suture material is required to repair the nerve ends, because the bundles are maintained in anatomical alignment by a fibrin clot. We have reviewed the various nerve repair methods, stressing that with strict attention to microsurgical technique, the surgeon can hope to maximize reinnervation. Although the importance of all aspects of careful surgical technique cannot be overemphasized, we believe that it is unlikely that improved clinical results will come from further refinements in microsurgical techniques. We are not limited by a working knowledge and understanding of the details of the neurobiology and the neurochemistry of nerve regeneration.     

A comparison of peripheral nerve regeneration in acellular muscle and nerve autografts.

Regeneration of the rat sciatic nerve through acellular muscle and nerve autografts was evaluated 6-28 days postoperatively by the sensory pinch test, immunocytochemical staining for neurofilaments, and light and electron microscopy. Data points generated by the pinch test were plotted against postoperative time periods and by the use of regression analysis the initial delay period for muscle grafts was determined to 10.3 days. This value was similar to that previously published for acellular nerve grafts (9.5 days), but significantly longer than that for fresh nerve grafts (3.6 days). The calculated regeneration rate (slope of the regression line) for muscle grafts (1.8 mm/day) did not differ significantly (p > 0.05) from that calculated for acellular nerve grafts (2.1 mm/day) or for fresh nerve grafts (1.5 mm/day). The front of regenerating axons shown by axonal neurofilament staining confirmed the pinch test results. Both types of acellular grafts were repopulated with host non-neuronal cells and the muscle graft contained occasional ectopic muscle fibres. Remnants of graft basal laminae were evident at the ultrastructural level. These results indicate the suitability of either acellular muscle or nerve grafts for nerve repair despite their prolonged initial delay periods compared with conventional fresh nerve grafts.     

Percussive injury to peripheral nerve in rats.

Weights were dropped on rat sciatic nerves. Teased fibers and light and electron micrographs of nerves removed between 10 minutes and 2 weeks later were examined. Axonal alterations were seen 10 minutes after injury, and subsequently interruption of axonal continuity with preservation of the basal lamina was apparent. Dissolution of myelin began within 30 minutes and progressed. At 14 days, a segment of some large fibers was devoid of myelin and, by 2 weeks, remyelination had commenced. Demyelination of significant number of fibers was always accompanied by Wallerian degeneration of other fibers of the same nerve. Percussive injury of nerves caused a mixed lesion in which the early and late pathological features were clearly distinguishable from those following crush or compression by a cuff. Any explanation of the transient interruption of function that has been described following such an injury is at present speculative.     

Tremor and peripheral nerve entrapment. Case report

A patient is described in whom pain, paresthesias, weakness, and resting tremor gradually developed 8 years after an ulnar nerve transposition. Electromyography revealed that the tremor occurred at 4 to 5 Hz, was abolished by voluntary muscle contraction, and was localized to ulnar-innervated muscles. Ulnar nerve conduction was focally slowed at the elbow; therefore, ulnar neurolysis was performed and a fusiform neuroma-in-continuity was found. Mechanically tapping the neuroma elicited repetitive discharges at 4 to 5 Hz in the intrinsic muscles of the hand; these discharges were abolished by anesthetic block proximal to the neuroma. Although the pain, paresthesias, and weakness were abolished by the neurolysis, the tremor persisted. Possible neurophysiological mechanisms underlying the appearance of tremor with peripheral nerve entrapment are discussed.     

End-to-side nerve suture--a technique to repair peripheral nerve injury.

End-to-side nerve suture (ETSNS) has until recently been extensively researched in the laboratory animal (rat and baboon). Lateral sprouting from an intact nerve into an attached nerve does occur, and functional recovery (sensory and motor) has been demonstrated. We have demonstrated conclusively that ETSNS in the human is a viable option in treating peripheral nerve injuries, including injuries to the brachial plexus. Among the many advantages of this new technique are: (i) simple and short operation; (ii) shorter recovery time--suture is done closer to the target organs; (iii) nerve grafts to bridge injured gaps are eliminated, reducing the morbidity of nerve surgery to a minimum; (iv) innervation of paralysed muscles, for which there was previously thought to be no hope of recovery, opens up many new treatment options; and (v) certain aspects of nerve function and regeneration, unknown until recently, open new horizons and understanding. ETSNS has given us new dimensions in the management of peripheral nerve injuries.     

End-to-side nerve repair in peripheral nerve injury

In peripheral nerve injury, end-to-side neurorrhaphy has been reported as an alternative in cases that the proximal nerve stump is not accessible. Several hypotheses have been proposed to explain peripheral nerve regeneration after end-to-side neurorrhaphy. Recent evidence suggests that nerve regeneration occurs by collateral sprouting. Although a great number of humoral factors have been identified, molecular mechanism of nerve regeneration after end-to-side neurorrhaphy has not been completely clarified yet. The goal of this technique is to provide satisfactory functional recovery for the recipient nerve, without any deterioration of the donor nerve function. End-to-side technique has been investigated in detail in both experimental and clinical studies. Only a limited number of reported cases in clinical practice, until today, can reveal that end-to-side technique may become a viable means of repairing peripheral nerves in certain clinical situations.     

Local anaesthetic delivery regimens for peripheral nerve catheters: a systematic review and network meta-analysis

There are numerous possible techniques for delivering local anaesthetic through peripheral nerve catheters. These include continuous infusions, patient-controlled boluses and programmed intermittent boluses. The optimal delivery regimen of local anaesthetic is yet to be conclusively established. In this review, we identified prospective trials of delivery regimens through peripheral nerve catheters. Our primary outcome was visual analogue scale scores for pain at 48 h. Secondary outcomes were: visual analogue scores at 24 h; patient satisfaction scores; rescue opioid use; local anaesthetic consumption; and nausea and vomiting. Network meta-analysis was used to compare these outcomes. Predefined sub-group analyses were performed. Thirty-three studies enrolling 1934 participants were included. In comparison with continuous infusion, programmed intermittent boluses improved visual analogue pain scores at both 48 and 24 h, the weighted mean difference (95%CI) being −0.63 (−1.12 to −0.14), p = 0.012 and −0.48 (−0.92 to −0.03), p = 0.034, respectively. Programmed intermittent boluses also improved satisfaction scores, the weighted mean difference (95%CI) being 0.70 (0.10–1.31), p = 0.023, and reduced rescue opioid use, the weighted mean difference (95%CI) in oral morphine equivalent at 24 h being −23.84 mg (−43.90 mg to −3.77 mg), p = 0.020. Sub-group analysis revealed that these findings were mostly confined to lower limb and truncal catheter studies; there were few studies of programmed intermittent boluses for upper limb catheters. Programmed intermittent boluses may provide optimal delivery of a local anaesthetic through peripheral nerve catheters. Further research is warranted, particularly to delineate the differences between upper and lower limb catheter locations, which will help clarify the clinical relevance of these findings.