Morphological alterations in dorsal root ganglion neurons after peripheral axon injury: association with changes in metabolism

Regeneration of sensory nerve branches in extraction socket and surrounding alveolar bone in rat: immunohistochemical observation of the axon and myelin sheath changes

The purpose of this study was to investigate the process and derivation of the distribution of the sensory nerves that appear in the extraction socket and surrounding alveolar bone following tooth extraction. The right mandibular first molar of rats and periodontal ligament were extracted as a single mass, and the mandible was harvested after days 1, 3, 5, and 7 after extraction. Serial sections of 7 µm thickness were prepared for the proximal root (Section A), buccolingual root (Section B), and centrifugal root (Section C) of the first molar. H–E staining and immunohistochemical staining with anti-S100 antibody and anti-NF-L antibody were carried out. The presence of nerve fiber bundles in the blood clot was already evident on post-extraction day 3, and on post-extraction day 7. On day 3, the number of axons in Sections B and C had greatly decreased, indicating that, after extraction, the connection between peripheral nerve tissue and the trigeminal ganglion was temporarily markedly reduced in the region of the alveolar branch. Although the myelin sheaths were regenerating on day 5, the majority of the axons of the alveolar branches extending from the inferior alveolar nerve were seen to be extremely thin and scattered, despite their further regeneration. The above results suggest that the newly myelinated nerves are actually derived from the bone marrow to the extraction socket, so few nerves, rather than being derived from the alveolar branches that had innervated the extracted tooth.

Chromatolysis: Do injured axons regenerate poorly when ribonucleases attack rough endoplasmic reticulum, ribosomes and RNA?

After axonal injury, chromatolysis (fragmentation of Nissl substance) can occur in the soma. Electron microscopy shows that chromatolysis involves fission of the rough endoplasmic reticulum. In CNS neurons (which do not regenerate axons back to their original targets) or in motor neurons or dorsal root ganglion neurons denied axon regeneration (e.g., by transection and ligation), chromatolysis is often accompanied by degranulation (loss of ribosomes from rough endoplasmic reticulum), disaggregation of polyribosomes and degradation of monoribosomes into dust‐like particles. Ribosomes and rough endoplasmic reticulum may also be degraded in autophagic vacuoles by ribophagy and reticulophagy, respectively. In other words, chromatolysis is disruption of parts of the protein synthesis infrastructure. Whereas some neurons may show transient or no chromatolysis, severely injured neurons can remain chromatolytic and never again synthesize normal levels of protein; some may atrophy or die. Ribonuclease(s) might cause the following features of chromatolysis: fragmentation and degranulation of rough endoplasmic reticulum, disaggregation of polyribosomes and degradation of monoribosomes. For example, ribonucleases in the EndoU/PP11 family can modify rough endoplasmic reticulum; many ribonucleases can degrade mRNA causing polyribosomes to unchain and disperse, and they can disassemble monoribosomes; Ribonuclease 5 can control rRNA synthesis and degrade tRNA; Ribonuclease T2 can degrade ribosomes, endoplasmic reticulum and RNA within autophagic vacuoles; and Ribonuclease IRE1α acts as a stress sensor within the endoplasmic reticulum. Regeneration might be improved after axonal injury by protecting the protein synthesis machinery from catabolism; targeting ribonucleases using inhibitors can enhance neurite outgrowth and could be a profitable strategy in vivo. © 2018 Wiley Periodicals, Inc. Develop Neurobiol, 2018

Sensory Neurons, Ion Channels, Inflammation and the Onset of Neuropathic Pain

Neuropathic pain often fails to respond to conventional pain management procedures. here we review the aetiology of neuropathic pain as would result from peripheral neuropathy or injury. We show that inflammatory mediators released from damaged nerves and tissue are responsible for triggering ectopic activity in primary afferents and that this, in turn, provokes increased spinal cord activity and the development of ‘central sensitization’. Although evidence is mounting to support the role of interleukin-1β, prostaglandins and other cytokines in the onset of neuropathic pain, the clinical efficacy of drugs which antagonize or prevent the actions of these mediators is yet to be determined. basic science findings do, however, support the use of pre-emptive analgesia during procedures which involve nerve manipulation and the use of anti-inflammatory steroids as soon as possible following traumatic nerve injury.

Reduction of sample size requirements by bilateral versus unilateral research designs in animal models for cartilage tissue engineering

Advanced tissue engineering approaches for articular cartilage repair in the knee joint rely on translational animal models. In these investigations, cartilage defects may be established either in one joint (unilateral design) or in both joints of the same animal (bilateral design). We hypothesized that a lower intraindividual variability following the bilateral strategy would reduce the number of required joints. Standardized osteochondral defects were created in the trochlear groove of 18 rabbits. In 12 animals, defects were produced unilaterally (unilateral design; n=12 defects), while defects were created bilaterally in 6 animals (bilateral design; n=12 defects). After 3 weeks, osteochondral repair was evaluated histologically applying an established grading system. Based on intra- and interindividual variabilities, required sample sizes for the detection of discrete differences in the histological score were determined for both study designs (α=0.05, β=0.20). Coefficients of variation (%CV) of the total histological score values were 1.9-fold increased following the unilateral design when compared with the bilateral approach (26 versus 14%CV). The resulting numbers of joints needed to treat were always higher for the unilateral design, resulting in an up to 3.9-fold increase in the required number of experimental animals. This effect was most pronounced for the detection of small-effect sizes and estimating large standard deviations. The data underline the possible benefit of bilateral study designs for the decrease of sample size requirements for certain investigations in articular cartilage research. These findings might also be transferred to other scoring systems, defect types, or translational animal models in the field of cartilage tissue engineering.

Correlation between the appearance of neuropeptides in the rat trigeminal ganglion and reinnervation of the healing root socket after tooth extraction

The neuropeptide substance P (SP) modulates bone metabolism. This study examined the temporal appearance of the neuropeptides SP and brain-derived nerve growth factor (BDNF) and their receptors (neurokinin-1 receptor (NK₁-R) and Trk B, respectively) in the rat trigeminal ganglion to investigate the role of neuropeptides in healing after tooth extraction. Rats were anesthetized and their upper right first molars were extracted; the rats were sacrificed 3 hours and 1–21 days after extraction. Their trigeminal ganglion and maxilla were removed, and cryosections were prepared and immunostained using specific antibodies against SP, BDNF, NK₁-R, and Trk B. In the tooth sockets after extraction, new bone and a few SP-­immunoreactive nerve fibers were first seen at day 7, and bone completely filled the sockets at day 21. In the trigeminal ganglion, the proportions of NK₁-R-, BDNF-, and Trk B-immuno­reactive neurons changed similarly, i.e., they initially decreased, increased rapidly to ­maximum levels by day 3, and then decreased gradually to control levels until 21 days. These findings suggest that the appearance of neuropeptides in the trigeminal ganglion, the reinnervation of SP-immunoreactive nerve fibers, and bone repair in the tooth socket during healing after extraction were correlated.

Pathology of lumbar nerve root compression. Part 2: morphological and immunohistochemical changes of dorsal root ganglion

STUDY DESIGN

This study is to investigate the changes of dorsal root ganglion (DRG) induced by mechanical compression using in vivo model.

OBJECTIVES

The effect of axonal flow disturbance induced by nerve root compression was determined in DRG.

SUMMARY OF BACKGROUND DATA

The dorsal root ganglion should not be overlooked when considering the mechanism of low back pain and sciatica, so it is important to understand the morphologic and functional changes that occur in primary sensory neurons of the dorsal root ganglion as a result of nerve root compression. However, few studies have looked at changes of neurons within the dorsal root ganglion caused by disturbance of axonal flow and the axon reaction as a result of mechanical compression of the dorsal root through which the central branches of the primary sensory nerves pass.

METHODS

In mongrel dogs, the seventh lumbar nerve root was compressed for 24 h, one week, or three weeks using a clip with a pressure of 7.5 gf. Morphologic changes of the primary sensory neurons in the dorsal root ganglion secondary to the axon reaction were examined by light and electron microscopy. Changes of immunostaining for substance P (SP), calcitonin gene-related peptide (CGRP), and somatostatin (SOM) in the primary sensory neurons affected by central chromatolysis after nerve root compression were also examined.

RESULTS

Light microscopy showed central chromatolysis of neurons in the dorsal root ganglion from one week after the start of compression. Electron microscopy of the affected neurons revealed movement of the nucleus to the cell periphery and the loss of rough endo-plasmic reticulum and mitochondria from the central region. Immunohistochemical studies showed a marked decrease of SP, CGRP, and SOM staining in small ganglion cells with central chromatolysis when compared with cells from control ganglia.

CONCLUSION

It is important to be aware that in patients with nerve root compression due to lumbar disc herniation or lumbar canal stenosis, dysfunction is not confined to degeneration at the site of compression, but also extends to the primary sensory neurons within the dorsal root ganglion as a result of the axon reaction. Patients with sensory disturbance should therefore be fully informed of the fact that these symptoms will not resolve immediately after surgery.

Paclitaxel induces nucleolar enlargement in dorsal root ganglion neurons in vivo reducing oxaliplatin toxicity

Paclitaxel and oxaliplatin are promising drugs for combination trials but both induce peripheral neurotoxicity. To investigate this toxicity, 10-week-old female Wistar rats were given single intraperitoneal doses of paclitaxel and oxaliplatin, alone or in combination. Neurotoxicity was assessed by L5 dorsal root ganglion morphometry and H-reflex-related sensory nerve conduction velocity. Platinum concentrations in dorsal root ganglia and plasma were measured by inductively coupled plasma mass spectrometry. Dorsal root ganglion nucleolus size was significantly increased following single doses of paclitaxel of 10 and 20 mg kg(-1) at 24 h and 6 days (P<0.02). In contrast, dorsal root ganglion nucleolus size was significantly decreased following single doses of oxaliplatin ranging from 3 to 30 mg kg(-1) at time points ranging from 2 h to 14 days. Sensory nerve conduction velocity was altered after a single dose of oxaliplatin but not after paclitaxel. In combination with oxaliplatin, paclitaxel did not alter the plasma pharmacokinetics or dorsal root ganglion accumulation of oxaliplatin-derived platinum. However, prior paclitaxel inhibited oxaliplatin-induced reductions of dorsal root ganglion nucleolar diameter (P<0.02). Sensory nerve conduction velocity was reduced after oxaliplatin alone (P&<0.05) but unchanged when paclitaxel was given before oxaliplatin. In conclusion, paclitaxel induces nucleolar enlargement in dorsal root ganglion neurons after pharmacologically relevant doses in vivo and reduces oxaliplatin nucleolar damage and neurotoxicity.

Downregulation of TrkA expression in primary sensory neurons after unilateral lumbar spinal nerve transection and some rescuing effects of nerve growth factor infusion

Peripheral nerve injury results in sprouting of sympathetic and sensory nerve terminals around large diameter neurons in the dorsal root ganglia (DRG), but the underlying mechanism is not clear. Current study sought to examine changes of the nerve growth factor (NGF) receptor TrkA in DRG and spinal cord after a spinal nerve transection by an immunohistochemical technique and to investigate effects of NGF on the expression of TrkA protein in the same animal model. In the control rat, TrkA immunoreactivity was localized to about 55 +/ -1% of total neurons in DRG and to laminae I and II of the spinal cord. The percentage of TrkA immunoreactive neurons in DRG and TrkA staining intensity of spinal cord were reduced 1 week after the nerve lesion. The changes became maximal 2 weeks, but recovered partially 4 weeks after the lesion. The size of TrkA immunoreactive neurons dramatically shifted to smaller sizes, becoming more remarkable 4 weeks after the lesion. In the contralateral DRG, the percentage of TrkA immunoreactive neurons also decreased significantly. Exogenous NGF delivered to DRG for 2 weeks partially reversed the reduction of TrkA expression as well as atrophy of TrkA immunoreactive neurons. No TrkA immunoreactive basket was found around neuronal somata. Our data show that unilateral peripheral nerve injury results in dynamic downregulation of TrkA in sensory neurons in bilateral DRG and spinal cord, and that TrkA expression in sensory neurons is partially regulated by target-derived NGF.

Magnitude, laterality, and uniformity of swelling in axotomized spinal motoneurons: lack of evidence for influence by the distal stump

Injury to frog lumbar motor axons produces a coordinated, allometric enlargement of the nucleolus, nucleus, and cell body of the injured neuron. The mechanisms by which swelling is initiated and sustained are not known. In this study, we have sought evidence for a role of the severed distal stump in the magnitude, laterality, and uniformity of the swelling response in frog spinal motoneurons. We find that swelling of motoneuron nucleoli, nuclei, and perikarya after unilateral spinal nerve transection is exclusively ipsilateral and uniform among motoneurons of different sizes. Removal of the severed distal stump does not affect the magnitude, unilaterality, or uniformity of the swelling responses. Thus, the distal stump appears to play no role in initiating swelling following spinal nerve transection.

Electromagnetic fields influence NGF activity and levels following sciatic nerve transection

Pulsed electromagnetic fields (PEMF) have been shown to increase the rate of nerve regeneration. Transient post-transection loss of target-derived nerve growth factor (NGF) is one mechanism proposed to signal induction of early nerve regenerative events. We tested the hypothesis that PEMF alter levels of NGF activity and protein in injured nerve and/or dorsal root ganglia (DRG) during the first stages of regeneration (6-72 hr). Rats with a transection injury to the midthigh portion of the sciatic nerve on one side were exposed to PEMF or sham control PEMF for 4 hr/day for different time periods. NGF-like activity was determined in DRG, in 5-mm nerve segments proximal and distal to the transection site and in a corresponding 5-mm segment of the contralateral nonoperated nerve. NGF-like activity of coded tissue samples was measured in a blinded fashion using the chick DRG sensory neuron bioassay. Overall, PEMF caused a significant decrease in NGF-like activity in nerve tissue (P < 0.02, repeated measures analysis of variance, ANOVA) with decreases evident in proximal, distal, and contralateral nonoperated nerve. Unexpectedly, transection was also found to cause a significant (P=0.001) 2-fold increase in DRG NGF-like activity between 6 and 24 hr postinjury in contralateral but not ipsilateral DRG. PEMF also reduced NGF-like activity in DRG, although this decrease did not reach statistical significance. Assessment of the same nerve and DRG samples using ELISA and NGF-specific antibodies confirmed an overall significant (P < 0.001) decrease in NGF levels in PEMF-treated nerve tissue, while no decrease was detected in DRG or in nerve samples harvested from PEMF-treated uninjured rats. These findings demonstrate that PEMF can affect growth factor activity and levels, and raise the possibility that PEMF might promote nerve regeneration by amplifying the early postinjury decline in NGF activity.

Dorsal root ganglion nerve cells transiently express increased immunoreactivity of the calcium-binding protein S-100beta after sciatic nerve transection

Transiently increased immunoreactivity of the calcium binding protein S-100beta was demonstrated in spinal ganglion nerve cells after sciatic nerve transection. Neuropeptide Y (NPY), normally not seen in these nerve cells, appeared concomitantly. The transiently elevated co-expression of S-100beta and NPY is proposed to reflect an increased demand of neurotrophic and neuroprotective compounds in reactive neurons, tentatively regulating calcium ions.

Mechanisms of enhancement of neurite regeneration in vitro following a conditioning sciatic nerve lesion

To examine the mechanisms responsible for the more rapid nerve regeneration observed after a previous (conditioning) nerve injury, adult rats were subjected to a midthigh sciatic nerve transection by using one of three protocols designed to facilitate or restrict nerve regeneration: 1) ligation, in which transected axons were prevented from regenerating; 2) cut, in which transected axons were permitted to extend into peripheral target tissue but were separated from the denervated peripheral nerve stump; and 3) crush, in which axons could regenerate normally through the denervated distal nerve tract. The affected dorsal root ganglia (DRG) were subsequently removed, dissociated, and cultured for up to 3 days, and the timing of neurite initiation, rate of outgrowth, and arborization pattern of previously injured neurons were compared with control DRG. Our results indicate that conditioning lesions have at least four distinct and differentially regulated effects on neuronal morphogenesis: 1) conditioning lesions promote earlier neurite initiation, 2) prior nerve injury decreases the ability of neurons to extend long neurites following a second axotomy, 3) exposure to the environment of a denervated peripheral nerve stimulates greater initial rates of neurite outgrowth, and 4) conditioning lesions reduces initial neuritic branching frequency, resulting in straighter neurites whose growth cones extend further distances from their cell bodies. The primary effect of all conditioning lesions on cultured DRG neurons appeared to be to advance the timing of morphogenesis, resulting in conditioning-lesioned neurons that exhibited characteristics consistent with control neurons that had been cultured for an additional day or more. A secondary effect of conditioning lesions on neurite outgrowth rates was dependent on the local environment of the axons prior to culturing.

Differential effects of NGF and BDNF on axotomy-induced changes in GABA(A)-receptor-mediated conductance and sodium currents in cutaneous afferent neurons

The effects of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) on injury-induced changes in the electrophysiological properties of adult rat cutaneous afferent dorsal root ganglion (DRG) neurons were examined. Whole cell patch-clamp techniques were used to study gamma-aminobutyric acid-A (GABA(A))-receptor-mediated conductance, voltage-dependent sodium currents, and action potential waveform in cutaneous afferent neurons (35-60 microm diam) cultured from control and axotomized animals. Cutaneous afferent neurons were identified by retrograde labeling with hydroxy-stilbamidine (Fluoro-gold, a fluorescent retrograde axonal tracer); the sciatic nerve was transected 1 wk after Fluoro-gold injection and L4/L5 DRG neurons were cultured 2-3 wk after axotomy. NGF, BDNF, or Ringer (vehicle) solution was delivered in vivo directly to the transected sciatic nerve stump in axotomized rats via an osmotic pump. Recordings were obtained from neurons 5-24 h after culture. Axotomized neurons from rats treated with vehicle solution displayed a twofold increase in GABA-induced conductance and a prominent reduction in the proportion of neurons expressing action potentials that had inflections on the falling phase. The expression of kinetically slow tetrodotoxin (TTX)-resistant sodium current was markedly reduced and an increased expression of kinetically fast TTX-sensitive current was observed in neurons from vehicle-treated, axotomized rats. Treatment with NGF (0.25 microg/microl at 12 microl/day for 14 days) in axotomized animals resulted in an increase in the proportion of neurons expressing TTX-resistant, slow sodium currents and inflected action potentials, but had no effect on GABA-induced conductance. Treatment with BDNF (0.5 microg/microl at 12 microl/day for 14 days) attenuated the axotomy-induced increase in GABA(A)-receptor-mediated conductance while minimally affecting action potential waveform. The observed neurotrophin effects occurred independently of cell size changes. These findings indicate a differential regulation of GABA(A) receptor and sodium channel properties in axotomized rat cutaneous afferent neurons by specific neurotrophic factors.

Enhancement of GABAA receptor-mediated conductances induced by nerve injury in a subclass of sensory neurons

1. The effects of axotomy on the electrophysiologic properties of adult rat dorsal root ganglion (DRG) neurons were studied to understand the changes in excitability induced by traumatic nerve injury. Nerve injury was induced in vivo by sciatic nerve ligation with distal nerve transection. Two to four weeks after nerve ligation, a time when a neuroma forms, lumbar (L4 and L5) DRG neurons were removed and placed in short-term tissue culture. Whole cell patch-clamp recordings were made 5-24 h after plating. 2. DRG neurons were grouped into large (43-65 microns)-, medium (34-42 microns)-, and small (20-32 microns)- sized classes. Large neurons had short duration action potentials with approximately 60% having inflections on the falling phase of their action potentials. In contrast, action potentials of medium and small neurons were longer in duration and approximately 68% had inflections. 3. Pressure microejection of gamma-aminobutyric acid (GABA, 100 microM) or muscimol (100 microM) onto voltage-clamped DRG neurons elicited a rapidly desensitizing inward current that was blocked by 200 microM bicuculline. To measure the peak conductance induced by GABA or muscimol, neurons were voltage-clamped at a holding potential of -60 mV, and pulses to -80 mV and -100 mV were applied at a rate of 2.5 or 5 Hz during drug application. Slope conductances were calculated from plots of whole cell current measured at each of these potentials. 4. GABA-induced currents and conductances of control DRG neurons increased progressively with cell diameter. The mean GABA conductance was 36 +/- 10 nS (mean +/- SE) in small neurons, 124 +/- 21 nS in medium neurons, and 527 +/- 65 nS in large neurons. 5. After axotomy, medium neurons had significantly larger GABA-induced conductances compared with medium control neurons (390 +/- 50 vs. 124 +/- 21; P < 0.001). The increase in GABA conductance of medium neurons was associated with a decrease in duration of action potentials. In contrast, small neurons had no change in GABA conductance or action potential duration after ligation. The GABA conductance of large control neurons was highly variable, and ligation resulted in an increase that was significant only for neurons > 50 microns. The mean action potential duration in large neurons was not significantly changed, but neurons with inflections on the falling phase of the action potential were less common after ligation. There was no difference in resting potential or input resistance between control and ligated groups, except that the resting potential was less negative in small cells after axotomy.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in sensory neuropeptides in dorsal root ganglion and spinal cord of spontaneously diabetic BB rats. A quantitative immunohistochemical study

This study examined the expression of the sensory neuropeptides, calcitonin gene-related peptide (CGRP) and substance P (SP), in the lumbar 4 and 5 dorsal root ganglion (DRG) and spinal cord of spontaneously diabetic BB rats and non-diabetic controls using quantitative immunohistochemical analysis. In both animal groups immunoreactivities for CGRP and SP were widely distributed within the neurons of DRG and in nerve fibres of the dorsal spinal cord. Image analysis of each neuropeptide subpopulation in the DRG showed that in diabetic rats the cell diameter of immunostained CGRP neurons was significantly decreased compared with controls, while no difference could be found for SP-immunoreactive (IR) neurons. The decrease in the CGRP-IR cell diameter appeared to occur mainly in medium to large neurons (30-50 microns diameter; 2.2% controls, < 1% diabetes), this change being parallel to an increased frequency of small-size neurons (< 20 microns diameter) in diabetic rats (62% controls, 69% diabetes; P < 0.05). However, there was no statistical difference in the total number of cells immunostained for either CGRP or SP between control and diabetic rats. The ratio of CGRP or SP neurons compared to total cells in the ganglion was similar in control and diabetic groups. No difference could be observed for peptide immunoreactivity in the dorsal and ventral horns of either control or diabetic animals. The observed changes of perikaryal size in diabetic rats might relate to the reduced axonal calibre and conduction velocity observed in these animals, and indicate that subpopulations of sensory neurons are affected differently by diabetes.

RNA transcription in axotomized dorsal root ganglion neurons

Levels of RNA transcription were examined in L5 sensory ganglion neurons after unilateral crush injuries of the sciatic nerve using an in situ autoradiographic technique. Neuronal transcription increased in a biphasic pattern on the lesioned side within the first two weeks after injury. The timing and pattern of increases in transcription corresponded to previously reported increases RNA synthesis. The data demonstrate a dynamic regulation of RNA transcription in regenerating neuronal populations. This technique may prove to be useful in the study of factors controlling transcriptional activity in injured neurons.

Changes in plasma cytokines associated with peripheral nerve injury

Plasma levels of interleukins 1, 2, 4 and 6 and tumor necrosis factor (TNF) were measured from 0 to 30 days in rats after a unilateral crush of the sciatic nerve at the level of the sciatic notch and after sham operations without nerve crush. Interleukin-6 was observed to peak and return to baseline levels within 24 h and remained at baseline for the duration of the experiment. An initial sharp rise in interleukin-1 and TNF was observed in all animals 1-2 days after the operation. A transient increase in interleukin-1 and TNF was also observed only in nerve-injured animals between 10 and 14 days after injury. A large increase in interleukin-2 appeared only in nerve-injured animals beginning at 11 days after injury and remained elevated for the remaining study period. No alterations in plasma interleukin-4 were observed at any time point. The experiments provide preliminary evidence for significant trauma-induced alterations in plasma cytokines which could provide a basis for some of the diffuse responses of peripheral neurons to trauma. The biphasic nature changes in plasma cytokines suggest that the immune system may participate in tissue reactions involved in the recovery from nerve injury.

Axonal transport and release of transferrin in nerves of regenerating amphibian limbs

Transferrin, a plasma protein required for proliferation of normal and malignant cells, is abundant in peripheral nerves of birds and mammals and becomes more concentrated in this tissue during nerve regeneration. We are testing the hypothesis that this factor is involved in the growth-promoting effect of nerves during the early, avascular phase of amphibian limb regeneration. A sensitive enzyme-linked immunosorbent assay for axolotl transferrin was developed and used to determine whether this protein meets certain criteria expected of the trophic factor(s) from nerves. During limb regeneration adult sciatic nerves greatly increased their content of transferrin, which immunohistochemistry revealed was distributed in both axons and Schwann cells. Using the double ligature method with sciatic nerves in vivo, it was determined that transferrin is carried by fast anterograde axonal transport at all stages of limb regeneration. An approach based on multicompartment organ culture demonstrated that fast-transported transferrin was secreted in physiologically significant amounts at distal ends of regenerating axons. Finally, the concentration of transferrin in the distal region of larval axolotl limb stumps was found to decrease directly and rapidly in response to axotomy. Since transferrin is important for both axonal regeneration and cell cycling, the present data have significance for various aspects of nerve's trophic activity during limb regeneration.

Anterograde horseradish peroxidase tracing and immunohistochemistry of trigeminal ganglion tooth pulp neurons after dental nerve lesions in the rat

The peripheral reorganization of pulpal nerves after tooth injury was studied, in the rat, with anterograde horseradish peroxidase tracing techniques, and combined retrograde Fluorogold tracing and immunohistochemistry was employed to examine the effects of inferior alveolar nerve lesions or tooth injury on some cytochemical characteristics of pulpal trigeminal ganglion nerve cells, namely content of substance P, calcitonin gene-related peptide and the ganglioside GM1 (binding subunit of cholera toxin), as well as affinity to RT 97 (antibody to neurofilament protein) and the lectin Griffonia simplicifolia isolectin I-B4. Anterograde horseradish peroxidase tracing demonstrated that pulpal nerves either disappear or reinnervate novel targets after loss of pulpal tissue. There were no obvious signs of neuroma formation. Retrograde Fluorogold labelling with immunohistochemistry showed that after inferior alveolar nerve lesions with subsequent regeneration, a much higher proportion of Fluorogold cells (15%) were substance P-positive compared to normal (2%). In addition, 3% of the cells were Griffonia simplicifolia isolectin I-B4-positive. Such cells were very rare in controls. Proportions of calcitonin gene-related peptide-, GM1- and RT-97-positive cells were normal. After tooth lesions, the proportions of Fluorogold-positive substance P-, Griffonia simplicifolia isolectin I-B4-, GM1- and RT 97-labelled cells were similar to controls, while the proportion of calcitonin gene-related peptide-positive neurons was reduced. The results show that pulpal deafferentation may change the long-term cytochemical characteristics of affected trigeminal ganglion neurons.

Effects of advancing age on the central response of rat facial neurons to axotomy: light microscope morphometry

Following axotomy, the regrowth of peripheral axons takes longer in older individuals than in young ones. The present study compares central responses of facial motor neurons to a crush injury of the facial nerve in 3-month-old and 15-month-old male rats sampled through 28 days post-crush (dpc). Neuronal somata, nuclei, and nucleoli were measured in 30 microns brain stem sections within subdivisions of the facial nucleus that contain the cell bodies responsible for the movement of the vibrissae. The temporal patterns of change in the size of the three structures were interpreted with reference to the re-establishment of functional connections, i.e., the return of voluntary vibrissae activity, which is delayed by 4 days in the older animals relative to the younger ones. There was no age-related difference in the pattern of somal swelling and recovery, nor was there an age-related difference in the response of nuclei and nucleoli to axotomy through 4 dpc. Both nuclei and nucleoli increased in size in animals of both age groups, but after 4 dpc in the older animals nuclear enlargement was prolonged and the nucleolar increases were less robust compared to the younger animals. The greatest age difference appeared with the re-establishment of functional connections. In the 3-month-old animals, the resumption of whisker activity coincided with vigorous transient increases in the sizes of nuclei and nucleoli; in the 15-month-old animals, there was little nuclear response to functional recovery and a comparatively small increase in nuclear sizes.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of age on enzyme activities in the rat facial nucleus following axotomy: acetylcholinesterase and cytochrome oxidase

Advancing age affects the ability of motor neurons to regrow axons after the facial nerve is crushed. In rats, it requires 14 days after injury for 3-month-old animals to resume normal whisker activity, compared to at least 19 days in 15-month-old animals. The present study examines central enzymatic responses of facial motor neurons to axotomy. During the postoperative period from 1 day through 8 weeks, alternate frozen sections of brain stem are histochemically reacted to demonstrate activities of acetylcholinesterase (AChE) or cytochrome oxidase (COX) and the reactions are quantified using computerized image analyzing densitometry. AChE activity is evaluated separately in perikaryal cytoplasm and neuropil, while COX is assayed in the facial nucleus as a whole. Coincident with the initiation of axon outgrowth the activities of these enzymes decrease in the neurons. For AChE the decrease is greater in the older animals; for COX the decrease is equivalent in both age groups. With regard to the perikaryal AChE and the neuropil AChE, the recovery patterns are different in the two locations. In the perikarya AChE activity begins to recover after 4 days in both age groups; however, AChE activity in the neuropil remains decreased until after functional recovery of whisker activity, when it recovers rapidly in the 3-month-old animals, but more gradually in the 15-month-old animals. In both age groups, COX activity gradually decreases in response to axotomy. In the 3-month-old animals it recovers rapidly following return of whisker activity, while in the 15-month animals COX activity is maintained at the decreased level through 28 days post-crush, before it begins its gradual recovery. The study demonstrates that age differences are most apparent after the reestablishment of functional connections. This age-related deficiency may be related to deficiencies in retrogradely transported signals arising from the reinnervated target or in the older neuron's ability to respond to such signals.

The effect of peripheral nerve section on lectin binding in the superficial dorsal horn of the rat spinal cord

The effect of peripheral nerve section on binding of the plant lectin soybean agglutinin (SBA) to the dorsal horn of the spinal cord has been investigated in the rat. Four, 15 and 43 days after unilateral sciatic nerve section no effect on SBA binding in the L4 segment of the spinal cord was apparent. However 90 days after nerve section a marked decline in SBA binding was observed. It is suggested that the long latency in effect on SBA binding may be due to the slow rate of utilisation of the SBA binding site.