Survival and function of bursa-derived cells in bursectomized chickens

Chicken given heterologous antibodies to μ chains as embryos and again following bursectomy at hatching were rendered permanently agammaglobulinemic, whereas treatment with anti-μ alone resulted in transient hypogammaglobulinemia. These and other observations indicate that sites other than the bursa of Fabricius are unable to serve as sources of immunoglobulin-producing cells. Agammaglobulinemia did not develop in birds bursectomized at 1, 14, or 35 days after hatch during an observation period of 21–125 wk. Some bursectomized birds developed 10 × normal IgM levels but were very deficient in IgG; this pattern persisted throughout life. B lymphocytes, identified by surface immunoglobulins in high density, were permanently deficient in bursectomized animals despite development of hypergammaglobulinemia and high levels of antibodies to ferritin following hyperimmunization. In experiments employing embryonic bursectomy, the level of the circulating pool of B lymphocytes was shown to be dependent upon the time allowed for the bursa to function before removal.     

Effects of feeding a Fusarium toxin-contaminated diet to infectious bursal disease virus-infected broilers on the protein turnover of the bursa of Fabricius and spleen

Two experiments were carried out to examine the effects of feeding an uncontaminated control diet (CON) or a Fusarium toxin-contaminated diet (FUS; 10.7 mg deoxynivalenol [DON]/kg diet) to growing broilers, which were either uninfected or infected with infectious bursal disease virus (IBDV) beginning at 1 day post hatch. Broilers had been infected at three weeks post hatch with either a classical virulent infectious bursal disease virus (IBDV-IM, Exp. 1) or a very virulent IBDV (vvIBDV, Exp. 2) strain. The effects of the DON-contaminated diet in combination with the virus-infection on the bursa of Fabricius and spleen were determined at 3 and 6-7 days post infection. The transient development of the bursa oedema and the bursa atrophy was not significantly affected by the diet after infection with the different IBDV-strains. The histopathological lesions were more severe in IBDV-IM-infected birds at 6 days post infection when additionally exposed to the FUS diet as compared to the FUS-free feed. Most parameters of the bursa of Fabricius and spleen protein turnover (e.g. fractional protein synthesis rate, protein, DNA and RNA content and derived indices) were significantly and interactively influenced by infection and stage of infection. The vvIBDV-infected birds responded with a more pronounced depressing effect on the fractional protein synthesis rate after feeding the DON-containing FUS diet when compared to their IBDV-IM-infected counterparts, where the opposite effect was observed. It can be concluded that feeding a FUS diet to IBDV-infected broilers might modulate the virulence-dependent pathogenesis of an IBDV infection.     

Properties of reticulum cell sarcomas in SJL/J mice: II. Fate of labeled tumor cells in normal and irradiated syngeneic mice

Transplantable reticulum cell sarcoma (RCS) cells were labeled with ³H-uridine or ³H-thymidine in vitro and injected intravenously into normal and irradiated syngeneic SJL/J mice. RCS cells exhibited typical B cell migration characteristics in peripheral lymphoid organs in both normal and irradiated recipients, localizing in follicles in a pattern resembling that of labeled normal bone marrow cells. However, over the first 72 hr after transfer, RCS cells diluted their label much less in irradiated than in normal recipients, reflecting their inability to proliferate in the irradiated hosts. The presence of unlabeled tumor cells did not significantly affect the distribution of labeled normal bone marrow or lymph node cells in the recipients. Thus, RCS fails to grow in irradiated recipients in spite of undisturbed homing characteristics and in the absence of any evidence of cytotoxic influences from the host.     

IgG Fc receptor-bearing cells during early lymphoid cell development in the chicken

Cells from intraembryonic mesenchyme, yolk sac, bursa of Fabricius, and thymus from chicken embryos at different stages of development were studied for the presence of IgG Fc receptors by EA-rosette formation and binding of heat-aggregated chicken IgG (agg IgG). Cells with Fc receptors were found in high frequency in the intraembryonic mesenchyme as early as on the third day of incubation, in the yolk sac on the 7th day, in the bursa on the 10th day, and in the thymus on the 16th day of embryonic development. In the bursa the number of agg IgG binding cells increased with the age of the embryo and remained high after hatching, whereas in the thymus the peak value (76%) was observed on the 16th embryonic day, and after hatching only about 10% of the cells expressed the agg IgG receptors. The results also suggest that the appearance of IgG Fc receptors precedes the expression of B-L (Ia-like) antigens and of cytoplasmic and surface immunoglobulins on early lymphoid cells of the chicken embryo.     

Transfer of agammaglobulinemia in the chicken. I. Generation of suppressor activity by injection of bursa cells

Spleen cells from adult agammaglobulinemic (bursectomized) chickens taken 1 to 3 weeks after an injection of histocompatible bursa cells can inhibit the adoptive antibody response to B. abortus of normal spleen or bursa cells in irradiated recipients. Spleen cells from Aγ chickens not injected with bursa cells generally do not. Moreover, bursectomized chickens which have been reconstituted with spleen cells within the first week after hatching do not respond with suppressor cell formation upon bursa cell injection. This apparent “autoimmunization” with bursa cells induces suppressor T cells which are only minimally sensitive to treatment with mitomycin C or to 5000 R γ irradiation. The suppressor activity is neither induced nor potentiated by concanavalin A in vivo. It is much stronger in spleen than in thymus cells and appears to be macrophage independent and to require intact cells. The cell component which stimulates the suppressor activity is more pronounced on bursa than on spleen cells, and is at most present to a very limited extent on bone marrow, thymus, or peritoneal exudate cells. It is better represented in comparable cell numbers of Day 17 than of Day 14 embryonic bursa. The inducing cell component is present in the membrane fraction of disrupted bursa cells. Immunization with bursa cells from B locus histoincompatible chickens leads to suppressor activity against histocompatible bursa cells. Although the removal of Ig-bearing cells from bursa greatly diminishes its immunizing capacity, injection of serum IgM and IgG does not induce suppressor cells. It is suggested that tolerance to a B-cell antigen is lacking in adult Aγ chickens, resulting in an autoimmune response upon exposure to B cells. The B-cell antigen may be a cell surface-specific form of Ig, a complex of Ig and a membrane component, or a differentiation antigen which appears simultaneously with Ig during ontogeny.     

Time-course of the alterations in prostanoid production and in contractile responses of mesenteric beds isolated from streptozotocin diabetic rats.

The prostanoid production and the effect of indomethacin on the noradrenaline-induced contractions were studied in the mesenteric bed of rats at different times (1-8 weeks) after the administration of streptozotocin (STZ). The production of prostacyclin (measured as 6-keto-PGF1alpha) and prostaglandin (PG) E2 was unchanged one week after STZ, but it was reduced to 50% of control values 4 weeks after STZ without further changes 8 weeks after the treatment. The release of thromboxane (TX) A2 (measured as TXB2) and PGF2alpha, increased by 100% one week after STZ and returned to basal values at 3 weeks. TX release was below control values 8 weeks after STZ. The ratio 6-keto-PGF1alpha/TXB2 was reduced one week after STZ, recovered to control values at 4 weeks and augmented at 8 weeks. Indomethacin (10 microM) reduced the contractile responses to noradrenaline in the controls, whereas in STZ-treated rats this effect was observed solely 8 weeks after the treatment. Since this recovery coincided with an increase of the vasodilator/vasoconstrictor prostanoid ratio, a time-dependent compensation of the vascular alterations caused by STZ can be proposed from the present results.     

Ability of chicken B cells from different compartments to respond to TNP-Ficoll

The responsiveness of chicken B cells from various compartments to T-independent antigens was studied by immune transfers of spleen and bursa cells into immunosuppressed recipients. Bursa cells from 8- to 10-wk-old donors failed to respond to trinitrophenylated Ficoll (TNP-F) even when thymus cells or splenic T cells were added. Spleen cells from the same donors transferred responses, as judged both by anti-TNP plaque-forming cells (PFC) per spleen and serum anti-TNP titers. In contrast, responses to TNP-Brucella abortus (TNP-BA) were transferred at least as well as by bursa as by spleen cells. Rabbit anti-chicken T cell serum plus complement treatment of the spleen cells reduced their ability to transfer responses to sheep erythrocytes, but either did not affect or enhanced serum antibody responses to TNP-BA and TNP-F. In intact animals, responsiveness to i.v. injected TNP-F was found to develop slowly after hatching in the chicken. At the age of 2 and 3 mo, PFC/spleen on day 4 after TNP-F injection were only 20% and 40%, respectively, of the adult response. Thymectomy at hatching further delayed this development, resulting in 12% and 45% of the adult control response at ages of 3 and 4 mo. It is concluded that responsiveness to the TI-2 antigen, TNP-F, develops slower than that to the TI-1 antigen, TNP-BA, and is restricted to the splenic B cell compartment. In addition, this development appears to be faster in the presence rather than in the absence of the thymus. In view of the previously shown effect of thymus on bursa development, these data suggest that the maturation of TI-1 antigen (TNP-F)-respondent chicken B cells requires residence in both the bursa and spleen before the development of responsiveness to such antigens.     

Some effects of thyroidectomy on growth, heat production and the thermoregulatory ability of the immature fowl (Gallus domesticus)

1. 1.|The effect of thyroidectomy at 12 days of age on weight gain, and on heat production and thermoregulatory ability of 4- to 5-week-old chickens at temperatures within and below the thermo-neutral zone was investigated.

2. 2.|Despit the absence of thyroid tissue, as demonstrated with radioiodine, a small amount of thyroxine was found in the plasma of some thyroidectomized (TX) birds.

3. 3.|Thyroidectomy depressed weight gain; pair-fed controls grew significantly faster than TX birds.

4. 4.|Resting heat production of TX birds at thermoneutrality (30°C) was depressed by 18% (P < 0.001) and body temperature by 0.4°C (P < 0.001).

5. 5.|At 12°C heat production of TX birds was similar to that of controls but the body temperature of TX birds was 0.7°C lower (P < 0.001).

6. 6.|Thyroidectomized birds were unable to regulate body temperature at 5°C even if thyroxine was provided on the day before and at the time of cold-exposure. This inability to thermoregulate was probably due to inadequate insulation and poor nutritional status.

EA rosette forming lymphoid cells: distribution as to cell types and organs from chickens of different developmental stages.

The interaction of chicken spleen cells with sheep erythrocytes coated with chicken antibody (EA complexes) was studied using a rosette assay. The results reported in this paper indicate that subpopulations of chicken lymphocytes, monocytes, and heterophils have a receptor for EA. The formation of rosettes between chicken lymphoid cells and sheep erythrocytes (SRBC) was dependent upon the concentration of antibody used to sensitize the SRBC. In a developmental study of rosette-forming lymphocytes (RFL), the bursa was the first site of appearance of large numbers of RFL. The percentage of RFL in the bursa reached a peak at 17 days of embryonic life, and declined to a low by hatching. The percentage of RFL in the spleen, however, began to increase at the time of hatching and by 6 weeks of age the spleen far surpassed the bursa in percentage RFL. At no age were significant numbers of RFL detected in the thymus.     

Factors affecting piping plover hatching success on Long Island,New York

Low hatching success may limit progress towards reaching productivity goals for Atlantic Coast piping plover (Charadrius melodus) recovery, despite management strategies to protect eggs from predators and decrease human disturbance of birds on nests. We measured piping plover hatching success on Eastern Long Island beaches and identified the major causes of egg failure to better understand why eggs that were otherwise intact (not depredated or destroyed by tidal flooding) failed to hatch. We documented egg and nest fates, dissected contents of unhatched eggs to determine viability, and recorded human and predator activity near a subset of plover nests on Suffolk County Parks properties. The low hatching success we recorded (0.60) in 2006 and 2007 would require higher chick survival rates than are typically observed for piping plovers to meet recovery targets for productivity. Few eggs showed signs of poor viability and overall egg hatchability was comparable to other ground nesting birds. Most egg failure was due to either depredation at unexclosed nests or nest abandonment by adults. The best predictor of nest abandonment was the maximum number of red fox tracks (Vulpes vulpes) counted on nearby transects (β = −1.16, 95% CI: −2.0 to −0.3) and we found evidence that plovers abandoned eggs in response to predation risk (e.g., a fox circling a nest exclosure). Adults from abandoned nests may have deserted eggs or been depredated. In either case, intact and viable eggs were abandoned. Nest abandonment was not related to human activity near nests, which were buffered from human disturbance by symbolic string fencing. Our results suggest that depredation and nest abandonment (e.g., desertion or death of adults) due to predator disturbance, not human disturbance or poor egg viability, contributed to the low hatching success we recorded. Active predator removal in addition to modification of predator exclosure use and design may be necessary to prevent direct (egg depredation) and indirect (nest abandonment) negative effects of predators on hatching success. © 2010 The Wildlife Society.     

The refractive development of the eye of the American kestrel (Falco sparverius): a new avian model

Summary Most measures of avian visual performance are carried out on commonly available domestic species such as the chicken, and most of the data on avian induced refractive error deals with chickens. Raptors are predatory birds in which good visual resolving ability is particularly important. Behavioral studies indicate that the eyes of raptors have two to three times the resolving ability of the human eye. The domestic chicken is precocial at hatching whereas most raptors are semi-altricial. This study was an effort to determine if the effect of early visual deprivation on the refractive development of the chicken eye can be reproduced in the American kestrel, a species which is not domesticated and in which the need for acute vision is particularly important.Visual deprivation was achieved by unilaterally applying translucent plastic goggles over the eyes of kestrels two days after hatching. Refractive error was measured using a retinoscope and trial lenses. Ocular growth was monitored by A-scan ultrasonography, and frozen ocular sections of sacrificed birds. The effect of the experimental manipulation on the contralateral control eye and body weight was evaluated each day over a 42-day period. The goggles did not significantly affect the normal changes in body weight or the normal pattern of ocular growth and refractive development in the untreated eyes. An analysis of the refractive state changes as a result of form deprivation was made each week for 6 weeks after hatching on both the treated and untreated eyes in a separate group of experimental birds. Visual form deprivation caused a significant myopic shift in refractive error and a significant increase in the vitreous chamber depth in the treated eyes at 3 and 6 weeks of age. However, the amount of myopia produced is much less than that induced in chicks, and in certain cases hyperopia is produced. The kestrels recover from myopia and hyperopia within 10 days of goggle removal, after 3 to 4 weeks of deprivation.This study is the first indication that chickens may not be a representative bird model for studying form deprivation myopia. First, myopia is not always produced in kestrels in response to form deprivation. Second, kestrels are severely myopic at hatching and therefore, the direction of emmetropization is opposite to that found in hatchling chicks.     

Progesterone antagonism of androgen-dependent marking in gerbils

The role of progesterone (P) as an androgen antagonist in Mongolian gerbil territorial marking was assessed in the present investigation. Twenty-seven mature males were observed for two consecutive weeks in a marking apparatus. On the basis of the average of the two sessions, subjects were matched and assigned to one of three groups. All animals were orchidectomized and tested three weeks after surgery. Three days after a single postoperative session a schedule of hormonal replacement was initiated. Group 1 was administered 640 μg testosterone propionate (TP). Group 2 received 640 μg TP followed immediately by 3 mg P. A third group received 640 μg TP followed by a 1 mg injection of P. Subjects were tested for marking 24 hr after the injection for a cumulative period of 6 wk.Results indicated that (a) castration drastically reduced marking; (b) TP alone and TP + 1 mg P restored the behavior; (c) TP + 3 mg P inhibited its restoration; and (d) a significant interaction was present between hormonal therapy and the 6-wk testing interval. However, all three hormonal treatments restored sebaceous gland dimensions. Results are discussed in terms of a model of hormone-gene action.     

Comparison of plasma ACTH and corticosterone levels after embryo bursectomy

Plasma levels of both adrenocorticotropic hormone (ACTH) and corticosterone (B) were determined in embryos (day 15 of incubation), chicks (day 3 after hatch) and young chickens (8 weeks). Experimental animals were bursectomized at 80 hr of incubation, i.e., before any anlage of the bursa of Fabricius could develop. Bursectomized (BFX) animals were compared to sham-operated controls (T), in basal, resting condition and 7 (ACTH) or 14 min (B) after ether stress was delivered for 30 sec. Basal B and ACTH levels seemed not to be significantly modified in BFX embryos, chicks and chickens. Hypophysial and adrenocortical response to stress appeared more precociously in BFX embryos (day 15 of incubation) than in intact ones (day 19). The non stress-responsive period that was observed for one week after hatch of T birds did not appear in 3-day-old BFX chicks whose both B and ACTH stress-induced levels were as high as in intact adults. In contrast, adrenocortical and pituitary corticotropic responses to stress were markedly impaired (by 50%) in adult BFX chickens as compared to intact controls.     

A novel method to bursectomize avian embryos and obtain quail----chick bursal chimeras. II. Immune response of bursectomized chicks and chimeras and post-natal rejection of the grafted quail bursas

Two methods to bursectomize chick embryos before hemopoietic cell seeding of the bursa of Fabricius were compared in this work: section of the tail region at E3 including the presumptive bursal territory, and selective removal of the bursa at E5. Hatching ability is better with the former method, but survival rate and effectiveness of bursectomy are favored with the second, novel technique. Moreover, selective removal of the bursa at E5 can be followed by in situ engraftment of a quail bursa and construction of quail-chick bursal chimeras. The immune response of bursaless birds and bursal chimeras has been studied. Total absence of the bursa does not prevent a few B cells from differentiating and nonspecific Ig (IgM and/or IgG) from being secreted. As reported previously, bursaless birds, however, are unable to mount an immune response by producing specific antibodies. This immune function is restored by the graft of a quail bursa. The microenvironment of the bursa, although heterospecific, allows the expansion of the B cell population and generates the repertoire of the B cell antigen receptors. This process takes place during late embryonic and early postnatal life because the grafted quail bursal stroma is subjected to immune rejection from 2 to 3 wk after birth in all chimeras, which are, however, perfectly immunocompetent.     

Relationship between the expression of class I antigen and reactivity of chicken thymocytes

The expression of major histocompatibility complex (MHC) class I antigens in ontogenesis and the distribution of B-F⁺ cells, defined by means of a monoclonal antibody, were studied by indirect membrane immunofluorescence tests on suspensions of thymus, bursa, spleen, peripheral blood lymphocytes (PBL) and red blood cells (RBC) from 18-day-old chicken embryos and chickens from 1–90 days after hatching. At 18 days of incubation and at the first day after hatching, RBC, PBL, and the cells from bursa and thymus are negative. The percentage of positive PBL and bursal cells increases up to 9 days after hatching. By 2 weeks after hatching almost 100 % of the RBC, PBL, bursa, and spleen cells were positive whereas the thymus showed only 20% positive cells. Analysis on 4-m-thick, frozen acetone-fixed tissue sections of thymus showed that medullary cells are positive, while the cortical area is negative. The graft-versus-host (GvH) competence of these thymus subpopulations was compared after sorting by the fluorescence-activated cell sorter and injection into MHC incompatible embryos. GvH reactivity was associated primarily with the B-F⁺ population. Double staining studies with peanut agglutinin (PNA)-fluorescein isothiocyanate and a rabbit-anti-Ig tetramethyl isothiocyanate-conjugate proved that the PNA^– thymocytes are identical with B-F⁺ thymocytes.Abbreviations used in this paper: FACS fluorescence-activated cell sorter - FCS fetal calf serum - FITC-Ig fluorescein isothiocyanate-conjugated immunoglobulin - GvH graft-versus-host - HAT hypoxanthineaminopterin-thymidine - HBSS Hanks' balanced salt solution - IIF indirect immunofluorescence - MCA monoclonal antibody - MHC major histocompatibility complex - NWL normal white Leghorn - OS Obese strain - PBL peripheral blood lymphocytes - PBS phosphate-buffered saline - PNA peanut agglutinin - RBC red blood cells - TRITC-Ig tetramethyl isothiocyanate-conjugated immunoglobulin     

Antagonism of central estrogen action by intracerebral implants of tamoxifen

In order to determine the neural site(s) of estradiol (E2) priming of receptive behavior in female Long-Evans rats, we attempted to inhibit the behavioral effects of peripheral injections of E2 by administering the E2 antagonist tamoxifen (TX) to particular brain regions. Crystalline TX was administered unilaterally or bilaterally via 28-gauge cannulae into the ventromedial hypothalamic nucleus (VMN), the preoptic area (POA), or the interpeduncular region (IP) 1 hr prior to the first of three daily E2 benzoate injections. Subjects were tested for the presence or absence of behavioral estrus 5 hr after a 200-micrograms progesterone injection given 4 days after the initial hormone treatment. Results of this experiment showed that TX inhibits lordosis when directed toward the VMN, but not when directed toward the POA or IP. The quality of the lordosis response and the proportion of subjects showing solicitation behavior were both lower in VMN subjects treated with TX than in POA or IP subjects given the same treatment. Unilateral implants were as effective as bilateral implants in inhibiting the behavior of VMN subjects. A second experiment measured uptake of radiolabeled E2 by nuclei of hypothalamic (HYP) and POA tissue following bilateral TX administration to the VMN or POA. TX was capable of inhibiting uptake of [3H]E2 into nuclei of cells located near the implant site. Most subjects which showed behavioral inhibition also showed a reduction in uptake of [3H]E2 by HYP tissue. These data support the hypothesis that exposure of the VMN to E2 is necessary for the priming of estrous behavior in the female rat.     

Migratory patterns of B lymphocytes: II. Fate of cells from central lymphoid organs in the chicken

Studies were made of the fate of ³H-nucleoside-labeled chicken bursa, thymus and bone marrow cells after intravenous injection into 8-day-old, irradiated chickens. A higher rate of proliferation of bursa cells was indicated by the fact that bursa cells incorporated more ³H-thymidine and ³H-adenosine than thymus cells, while ³H-uridine incorporation was similar for these two cell types. Homing patterns in recipient spleen tissue were similar for all three nucleoside-labeled bursa cells. Bursa cells localized in follicular and periellipsoidal areas, whereas thymus cells preferentially homed to periarteriolar sheaths. Bone marrow cells were found in all these locations. Bursa cells from chickens aged 4 weeks and older showed a greater tendency to home to the spleen than did bursa cells from 8-day-old donor chickens. Homing to other tissues appeared independent of donor age.     

Formation of Paul-Bunnell antibodies by cultures of lymphocytes from infectious mononucleosis.

Short-term cultures of peripheral blood lymphocytes obtained from 20 infectious mononucleosis patients 2–4 weeks after the onset of the disease were studied for formation of heterophile antibodies. In studying pooled supernatant fluids of lymphocytes from three patients cultured for 3–20 days, lytic antibodies for red blood cells of bovine (BRBC) and sheep (SRBC) origin were demonstrated. These hemolysins were shown to be of IgM nature and Paul-Bunnell specificity. Subsequently, plaque-forming cell (PFC) assays were performed with lymphocyte cultures of 15 patients. Significant numbers (60–750/2 × 10⁷ cells) of PFC secreting antibodies against BRBC were demonstrated in lymphocyte cultures of 12 patients. The number of PFC apparently reached its peak after 5 to 10 days of culturing. No or a very few PFC were observed in the lymphocytes that were not cultured or in lymphocytes cultured for 3 weeks or longer. Lymphocyte cultures prepared in a similar fashion from normal individuals or patients suffering from sore throat and submandibular lymphadenopathy of other than infectious mononucleosis origin did not produce PFC. Production of lytic zones by antibodies to BRBC secreted by PFC was inhibited by preincubation of lymphocytes of infectious mononucleosis patients with solubilized Paul-Bunnell antigen but not with other heterophile antigens, indicating that antibodies involved in the PFC formation are of Paul-Bunnell specificity. An increased number of PFC against BRBC were obtained in two of three lymphocyte cultures after cultivation with BRBC or solubilized Paul-Bunnell antigen.     

Antisense Morpholino Oligonucleotides Reduce Neurofilament Synthesis and Inhibit Axon Regeneration in Lamprey Reticulospinal Neurons

The sea lamprey has been used as a model for the study of axonal regeneration after spinal cord injury. Previous studies have suggested that, unlike developing axons in mammal, the tips of regenerating axons in lamprey spinal cord are simple in shape, packed with neurofilaments (NFs), and contain very little F-actin. Thus it has been proposed that regeneration of axons in the central nervous system of mature vertebrates is not based on the canonical actin-dependent pulling mechanism of growth cones, but involves an internal protrusive force, perhaps generated by the transport or assembly of NFs in the distal axon. In order to assess this hypothesis, expression of NFs was manipulated by antisense morpholino oligonucleotides (MO). A standard, company-supplied MO was used as control. Axon retraction and regeneration were assessed at 2, 4 and 9 weeks after MOs were applied to a spinal cord transection (TX) site. Antisense MO inhibited NF180 expression compared to control MO. The effect of inhibiting NF expression on axon retraction and regeneration was studied by measuring the distance of axon tips from the TX site at 2 and 4 weeks post-TX, and counting the number of reticulospinal neurons (RNs) retrogradely labeled by fluorescently-tagged dextran injected caudal to the injury at 9 weeks post-TX. There was no statistically significant effect of MO on axon retraction at 2 weeks post-TX. However, at both 4 and 9 weeks post-TX, inhibition of NF expression inhibited axon regeneration.