Faculty Bibliography

Nerve injury elicits both universal and limited responses. Among the former is regenerative growth, which occurs in most peripheral neurons, and among the latter is the long-term hyperexcitability that appears selectively in nociceptive sensory neurons. Since positive injury signals communicate information from the site of an injury to the cell body, we hypothesize that a nerve injury activates both universal and limited positive injury signals. Studies in Aplysia indicate that protein kinase G is a limited signal that is responsible for the induction of long-term hyperexcitability. Given that long-term hyperexcitability contributes to chronic pain after axotomy in rodent neuropathic pain models, we investigated its underlying basis in the rat peripheral nervous system. Using biochemical assays, Western blots, and immunocytochemistry we found that the Type 1alpha protein kinase G is the predominant isoform in the rat periphery. It is present primarily in axons and cell bodies of nociceptive neurons, including populations that are isolectin B4-positive, isolectin B4-negative, and those that express transient receptor potential vanilloid receptor-1. Surprisingly, protein kinase G is not present in the facial nerve, which overwhelmingly contains axons of motor neurons. Crushing the sciatic nerve or a cutaneous sensory nerve activates protein kinase G in axons and results in its retrograde transport to the neuronal somata in the DRG. Preventing the activation of protein kinase G by injecting Rp-8-pCPT-cGMPS into the crush site abolished the transport. The protein kinase A inhibitor Rp-8-pCPT-cAMPS had no effect. Extracellular signal-related kinases 42/44 are also activated and transported after nerve crush, but in both motor and sensory axons. Chronic pain has been linked to long-term hyperexcitability following a nerve inflammation in several rodent models. We therefore injected complete Freund's adjuvant into the hindpaw to induce an inflammation and found that protein kinase G was activated in the sural nerve and transported to the DRG. In contrast, the extracellular signal-related kinases in the sensory axons were not activated by the complete Freund's adjuvant. These studies support the idea that the extracellular signal-related kinases are universal positive axonal signals and that protein kinase G is a limited positive axonal signal. They also establish the association between protein kinase G, the induction of long-term hyperexcitability, and chronic pain in rodents.

The purpose of this study is to re-examine the probable directive effect of the distal stump of a severed peripheral nerve on regenerating axons. Forssman postulated the existence of such a directive influence and Cajal interpreted it as chemotactic in nature. This view was subsequently refuted by Weiss and Taylor. In our study the proximal stumps of transected rodent sciatic nerve were inserted into the single inlet end of a Y-shaped autogenous inferior vena cava graft. Into one limb of the double outlet end, namely the common iliac nerve bifurcation, the distal stump of the same sciatic nerve was inserted, while the counter limb was ligated in one group, left open in the second group, inserted with a segment of autogenous tendon in the third, and grafted with a segment of autogenous nerve in the fourth group. Both outlets were left unoccupied in yet another group as the control. The vena cava conduit was prepared so that a 1.5 cm gap existed between the proximal stumps of the sciatic nerve and the distal sciatic nerve stumps and the tendon grafts respectively. The grafted sciatic nerves were explored and biopsied after 12 weeks. The direction of nerve tissue regeneration in each group was analyzed histologically. Predilection of the regenerating nerve fibers toward the distal stumps was observed in each of the test groups. These results indicate the existence of a guiding influence at the distal stump toward the regeneration nerve fibers

We have developed an innovative way to establish a functional bridge around a spinal lesion. We disconnected the T13 nerve from its muscle targets, leaving the proximal end intact. The cut end was inserted either into an intact spinal cord, to assess regeneration of T13 axons into the cord and synapse formation with spinal neurons, or caudal to a hemisection at L2/3, to assess restoration of function below the injury. Four to 28 weeks later, anterograde tracers indicated that axons from the inserted T13 nerve regenerated into the ventral horn, the intermediate zone, and dorsal horn base, both in intact and hemisected animals. Antibodies to cholinergic markers showed that many regenerating axons were from T13 motoneurons. Electrical stimulation of the T13 nerve proximal to the insertion site 4 weeks or more after insertion into the intact cord evoked local field potentials in the intermediate zone and ventral horn, which is where T13 axons terminated. Stimulation of T13 in 71% of the animals (8 hemisected, 7 intact) evoked contraction of the back or leg muscles, depending on the level of insertion. Animals in which T13 was inserted caudal to hemisection had significantly less spasticity and muscle wasting and greater mobility at the hip, knee, ankle, and digits in the ipsilateral hindlimb than did animals with a hemisection only. Thus, T13 motor axons form novel synapses with lumbosacral motor circuits. Because the T13 motor neurons retain their connections to the brain, these novel circuits might restore voluntary control to muscles paralyzed below a spinal lesion.

Over the last two decades, the autogenous venous nerve conduit (AVNC) has been established as an effective treatment modality for the repair of nerve gaps less than 3 cm. In this study, the spatial-temporal progression of Schwann-cell migration and peripheral-nerve regeneration across a 10-mm gap bridged by a venous conduit was examined, using immunoctyochemical techniques. Histologic analysis revealed that the process of nerve regeneration through an AVNC occurs in four phases: the hematoma phase, cellular migration phase, axonal advancement phase, and myelination and maturation phase. The authors found that: 1) the lumen of the vein conduit remains patent throughout the process of nerve regeneration; 2) Schwann cells migrate into the vital space of the vessel lumen from the proximal and distal nerve stumps; 3) axonal growth into the conduit lags behind Schwann-cell migration; 4) Schwann cells migrate to the regenerating axons to form mature nodes of Ranvier when the distal stump is present; and 5) mechanical injury alone is sufficient to induce axonal outgrowth from the proximal nerve stump.

The purpose of the study was to determine the feasibility of preserving ovarian function after heterotopic transplantation by means of microvascular anastomosis of the transplanted vascular pedicles to a set of preselected vessels. Six groups of 10 Sprague-Dawley inbred rats were used in this study. Group I underwent bilateral ovariectomy operation and served as the ovariectomy control. Group II underwent bilateral ovariectomy followed by heterotopic isogenic ovarian implantation. Group III underwent bilateral ovariectomy and isogenic heterotopic ovarian transplantation by means of microvascular anastomosis. Group IV served as the laparotomy sham-operated control. Group V served as the ovarian donor for group II. Group VI served as the donor of the ovarian-kidney vascular pedicle complex for group III. Postoperative ovarian estradiol levels were measured, and histological characteristics were elucidated in groups I, II, III, and IV. The results demonstrated that the estradiol level of the transplantation group was comparable to that of the sham operation group and was significantly higher than that of the implantation group. Histologically normal ovarian architecture was observed in the sham group (IV) and also in the transplantation group (III). Altered architecture was observed in the implantation group (II). These findings indicate that extraabdominal heterotopic ovarian transplantation with microvascular anastomosis led to normal ovarian hormonal function and was effective in preserving oocyte production capacity.

A new extended rat-ear flap model, with both an axial and a random component, is described. The flap is based on an axial supply by the posterior auricular artery and the posterior facial vein. The random portion, consisting of the rat dorsum, is capable of being supercharged at two separate sites-in the scapular and pelvic regions. There are several advantages to this composite flap. It is a combined axial and random flap. When used as a free flap, the viability of the axial portion serves as an indicator for anastomotic patency. The random portion allows for the investigation of the effects of pharmaceutical manipulation or surgical intervention, e.g., flap supercharging. The results indicate that the axial supply alone can cover approximately 50 percent of the extended rat-ear flap. Moreover, adding supercharging perforators to the random portion significantly increases the area of flap survival. Of interest, an axial vascular supply, coupled with more distal dorsal perforators (pelvic) than proximal (scapular) perforators, may increase survival for the so-called "watershed" area in the middle of the random portion of the flap. Additionally, this study also investigated the relative importance of arterial supply vs. venous drainage, using the extended rat-ear flap model. The flap was either supercharged with both the perforators of the scapular and pelvic arteries, or both scapular and pelvic veins. The results of the study suggests that augmenting venous drainage provides statistically significant improvement (87 percent vs. 51.6 percent) in increasing flap survival, when compared to augmenting the arterial supply. Arterial supercharging provided no improvement in flap survival, when compared to no supercharging (axial vessels + arterial supercharging, 51.6 percent vs. axial vessels alone, 49.9 percent). The results also suggest that providing adequate venous outflow is more important than providing additional arterial blood, and that impaired venous outflow may contribute to some cases of flap failure. However, it should be kept in mind that the best flap survival occurs with both arterial and and venous supercharging.

The purpose of this study was to examine the effect of Lactosorb absorbable plates on bone healing across cranial bone defects in the rabbit skull. Two 10-mm diameter parietal skull defects were created in each of 20 rabbits, with one defect being placed on either side of the sagittal suture. In 10 rabbits, an absorbable plate was placed across both the inner and outer cortices of the left defect, and in the other 10 rabbits, an absorbable plate was placed across the outer cortex only of the left defect. The right defect always served as the control side, with no plate being placed across it. Rabbits were killed an average of 25 weeks postoperatively. Areas of reossification in the experimental and control defects of each rabbit were then measured, examined histologically, and compared. Growth across defects spanned by one plate was also compared with growth across defects spanned by two plates. Histologic and statistical analyses revealed no significant differences in reossification between the control and experimental defects in each animal and between the defects spanned by one versus two plates. This study suggests that these copolymer absorbable plates neither inhibit nor facilitate reossification across 10-mm diameter rabbit cranial defects