Implantation of PNS graft inhibits the induction of neuronal nitric oxide synthase and enhances the survival of spinal motoneurons following root avulsion

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.

Expression of NADPH-diaphorase and nitric oxide synthase in lumbosacral motoneurons after knee joint immobilisation in the guinea pig

The expression of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) and nitric oxide synthase (NOS) in spinal ventral horn neurons was studied in the guinea pig after right knee joint immobilisation (RKJI). At 1 wk after RKJI, neurons in the ipsilateral ventral horn from L4 to S1 segments showed a moderate reactivity for NADPH-d staining. At 2 wk, NADPH-d labelled neurons were also observed in the contralateral ventral horn. Ipsilateral NOS immunoreactive cells were not detectable until wk 2. The intensity of NADPH-d and NOS labelled neurons in the bilateral ventral horns was sustained, peaking at the 4th wk after RKJI. In guinea pigs subjected to 4 wk of RKJI and subsequently released from the immobilisation for 2 and 4 wk, NADPH-d and NOS reactivity in ventral horn neurons diminished. The expression of NADPH-d positive neurons differed from that of NOS labelled neurons in terms of time interval, cell number and staining intensity, the latter being later, fewer and weaker. It is suggested that the induction and upregulation of NADPH-d and NOS are attributable to reduced activity of muscles acting on the knee joint after RKJI; the changes are reversible. It is speculated that increased levels of NO production are involved in protective mechanisms against possible neuronal degeneration as a consequence of target dysfunction.

Brain-derived neurotrophic factor promotes axonal regeneration and long-term survival of adult rat spinal motoneurons in vivo

This study shows that in adult rat spinal motoneurons brain-derived neurotrophic factor exerts a neuroprotective effect which extends several weeks beyond the duration of treatment. In addition, brain-derived neurotrophic factor strongly enhances regeneration of avulsed motor axons across the border between the central and peripheral nervous systems. Treatment with brain-derived neurotrophic factor is known to rescue adult rat spinal motoneurons from retrograde cell death induced by ventral root avulsion. The present experiments were designed to test whether this survival effect remains over an extended period of time following cessation of treatment and, also, whether brain-derived neurotrophic factor promotes regeneration of avulsed motor axons. After avulsion of a spinal ventral root, four weeks of treatment with brain-derived neurotrophic factor (10 microg/day) or vehicle was initiated. By using different retrograde tracers to obtain pre- and postoperative labelling of avulsed and regenerating motoneurons, respectively, the number of surviving motoneurons as well as the extent of motor axonal regeneration could be analysed. The expression of nitric oxide synthase in the lesioned motoneurons was also studied. In the vehicle-treated rats, only 10% of the avulsed motoneurons remained at 12 weeks postoperatively, 20-40% of which displayed nitric oxide synthase activity. Treatment with brain-derived neurotrophic factor during the initial four postoperative weeks resulted in 45% motoneuron survival and a complete blockage of nitric oxide synthase expression at 12 weeks postoperatively. Brain-derived neurotrophic factor also induced abundant regeneration of the avulsed motor axons, which formed extensive fibre bundles along the surface of the spinal cord and adjacent ventral roots. The long-term effect by brain-derived neurotrophic factor seemed to be even stronger on motor axonal regeneration than on motoneuron survival. The present results indicate a therapeutic potential for brain-derived neurotrophic factor in the early treatment of traumatic injuries to spinal nerves and roots.

Persistent neuronal labeling by retrograde fluorescent tracers: a comparison between Fast Blue, Fluoro-Gold and various dextran conjugates

The permanence of retrograde neuronal labeling by the fluorescent tracers Fast Blue, Fluoro-Gold, Mini-Ruby, Fluoro-Ruby and Fluoro-Emerald was investigated in adult rat spinal motorneurons at 1, 4, 12 and 24 weeks after tracer application to a transected muscle nerve. After 1 week, the largest number of retrogradely labeled motoneurons was found with Mini-Ruby, Fluoro-Gold and Fluoro-Ruby, while Fluoro-Emerald yielded a smaller number of labeled cells. With increasing survival time, all of these tracers exhibited a marked decrease in the number of labeled neurons. Fast Blue also produced very efficient staining after 1 week and, in addition, the number of Fast Blue-labeled cells remained constant over the entire time period studied. Also in embryonic spinal cord tissue exposed to Fast Blue. the label persisted for at least 6 months after transplantation into adult spinal cord. Double-labeling experiments combining Fast Blue with Fluoro-Gold, Mini-Ruby, Fluoro-Ruby or Fluoro-Emerald showed that all these substances were non-toxic and that the time-related decrease in the number of neurons labeled by the latter tracers was due to degradation or leakage of the dyes. Thus, Fast Blue would be the tracer of choice for motoneuronal labeling in long-term experiments, whereas the usage of the other tracers should be restricted to experiments of limited duration.

Age-dependent induction of nitric oxide synthase activity in facial motoneurons after axotomy

The facial nerve was transected in rats at different postnatal ages, from birth to early adulthood. NADPH-diaphorase histochemistry was performed to analyze the induction of nitric oxide synthase, the synthetic enzyme of the free radical nitric oxide, in injured facial motoneurons. In addition, in situ nick-end labeling of DNA fragmentation (TUNEL technique) was performed after axotomy at birth, to verify the occurrence of apoptosis in the damaged facial motoneurons. A striking age-dependency was found in the induction of nitric oxide synthase activity in axotomized facial motoneurons. NADPH-diaphorase positivity was not detectable in these neurons 1 and 2 days after axotomy at birth, when apoptotic changes were evident and marked. In addition, NADPH-diaphorase staining was hardly detectable in the facial nucleus 4 days after axotomies at birth, when extensive motoneuron loss was evident. NADPH-diaphorase positivity was instead induced in the facial motoneurons axotomized from the end of the first postnatal week to adulthood, when the nerve cell loss was less severe than in newborns. However, the time course of the enzyme activity induction varied considerably in relation to the animals' age. These findings are discussed in relation to the role of nitric oxide in motoneuron death or protective response to injury and of oxidative stress in neurodegeneration.

Involvement of nitric oxide in the pathophysiology of acute heat stress in the rat. Influence of a new antioxidant compound H-290/51

The possibility that nitric oxide (NO) is involved in the pathophysiology of brain injury caused by heat stress (HS) was examined using immunohistochemistry of a constitutive isoform of neuronal nitric oxide synthase (c-NOS) in a rat model. In addition, to discover the role of oxidative stress in inducing c-NOS activity in HS, the effect of a new antioxidant H-290/51 on HS-induced expression of c-NOS immunoreactivity was examined. Subjection of conscious young animals to a 4-h HS in a biological oxygen demand (BOD) incubator at 38 degrees C resulted in marked upregulation of c-NOS in the cerebral cortex and hippocampus of stressed rats compared to normal rats kept at room temperature (21 +/- 1 degrees C). The c-NOS immunoreactivity was found in distorted neurons located in the edematous regions not normally showing c-NOS activity. Pretreatment with H-290/51 significantly attenuated the upregulation of c-NOS in animals subjected to HS, and the signs of neuronal distortion and edema were less pronounced. These results suggest that HS has the capacity to induce upregulation of c-NOS, and these effects can be reduced by prior treatment with H-290/51, indicating a possible neuroprotective effect of antioxidants in thermal brain injury.

Botulinum toxin induces nitric oxide synthase activity in motoneurons

Intramuscular injections of botulinum toxin A were made into the snout of 3-month- and 3-week-old rats, resulting in transient paralysis of the facial muscles. Nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry, which is a marker of nitric oxide synthase activity in fixed tissue and, in particular, in injured motoneurons, was studied in the facial nucleus. At variance with control injections of saline, the histochemical staining was found to be induced in facial motoneurons after botulinum toxin injection. The occurrence and persistence of the histochemical positivity in facial motoneurons paralleled that of muscle paralysis. These findings indicate that the enzyme of synthesis of the free radical nitric oxide can be induced in motoneurons after a functional disconnection from the target, which spares the axon and is associated with cell survival.

Expression of neuronal nitric oxide synthase in spinal motoneurons in aged rats

We investigated the expression of nitric oxide synthase (NOS) in motoneurons of aged rats by the nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase (NADPH-d) reaction. The number of NADPH-d positive neurons (i.e. presumed motoneurons) in the motor nucleus at L4-L6 level of the spinal cord was 0.0 +/- 0.0 for 13- to 15-month-old rats, 2.2 +/- 0.8 for 24-month-old rats, and 7.9 +/- 5.4 for 29- to 32-month-old rats. These NADPH-d positive neurons were multipolar in shape and the soma cross-sectional area was 820 +/- 245 mu2 (n = 56; range, 359-1460 mu2) which was similar to the value for alpha-motoneurons. The results indicate that nitric oxide (NO) may be produced by a few motoneurons in the aged rat spinal cord and may lead these neurons to eventual death.

Expression of nitric oxide synthase by motor neurones in the spinal cord of the mutant mouse wobbler

The expression of nitric oxide synthase (NOS) has been studied in the spinal cord of the mutant mouse wobbler, a recessive mutation in which there is motor neurone degeneration, using nicotinamide dinucleotide phosphate-diaphorase (NADPH-d) histochemistry. Abnormal NOS positive large neuronal profiles could be found in the ventral born of affected mutant animals but not their unaffected littermate controls. The number of abnormal profiles observed was dependent upon the age of the animal. A small number of these NOS positive large neuronal profiles were seen at the onset of the disease at 3-4 weeks of age, larger numbers were found in animals aged 5-8 weeks coincident with the main period of motor neurone death, whilst in the spinal cords of older animals aged 9-12 months, when motor neurone death is minimal, none were found. These NOS positive profiles seen in younger wobbler mouse ventral horn had a morphology and size similar to that of degenerating motor neurones seen in Nissl stained preparations. It was concluded that these NOS positive profiles were degenerating motor neurones. These observations provide further evidence that induction of nitric oxide synthase expression may play a role in motor neurone death. Though no NOS positive motor neurones were found in the spinal cords of older wobblers increased numbers of NOS positive varicose axons were observed in the ventral horn often forming tangled accumulations on the border of the grey and white matter.

Involvement of nitric oxide in acute spinal cord injury: an immunocytochemical study using light and electron microscopy in the rat

The possibility that nitric oxide participates in the pathophysiology of spinal cord injury was examined using a constitutive isoform of neuronal nitric oxide synthase immunoreactivity in a rat model. Spinal cord trauma was produced by making an incision into the right dorsal horn of the T10-11 segments. Five h after trauma, a marked upregulation of NOS-immunostained neurons was seen in the perifocal T9 and T12 segments of the cord. The immunolabelling was most pronounced in the dorsal horn of the ipsilateral side. Topical application of an antiserum to nitric oxide synthase (NOS) 2 min after injury prevented the trauma-induced upregulation of NOS-immunoreactivity. In contrast, application of preabsorbed serum or L-NAME, an inhibitor to NOS, was ineffective in reducing the induction of NOS-immunoreactivity. Trauma caused a marked expansion of the cord and resulted in marked cell changes. This expansion and cell reaction was significantly reduced following application of NOS antiserum but it was not seen after application of preabsorbed antiserum or L-NAME. Our results for the first time show that a focal trauma to the spinal cord has the capacity to upregulate neuronal NOS immunoreactivity and that application of NOS antiserum has a neuro protective effect. This indicates that nitric oxide is somehow involved in the pathogenesis of secondary injuries after spinal cord trauma.

Rescue of adult mouse motoneurons from injury-induced cell death by glial cell line-derived neurotrophic factor

Glial cell line-derived neurotrophic factor (GDNF) has been shown to rescue developing motoneurons in vivo and in vitro from both naturally occurring and axotomy-induced cell death. To test whether GDNF has trophic effects on adult motoneurons, we used a mouse model of injury-induced adult motoneuron degeneration. Injuring adult motoneuron axons at the exit point of the nerve from the spinal cord (avulsion) resulted in a 70% loss of motoneurons by 3 weeks following surgery and a complete loss by 6 weeks. Half of the loss was prevented by GDNF treatment. GDNF also induced an increase (hypertrophy) in the size of surviving motoneurons. These data provide strong evidence that the survival of injured adult mammalian motoneurons can be promoted by a known neurotrophic factor, suggesting the potential use of GDNF in therapeutic approaches to adult-onset motoneuron diseases such as amyotrophic lateral sclerosis.

Induction of nitric oxide synthase and motoneuron death in newborn and early postnatal rats following spinal root avulsion

It is well established that immature motoneurons are more vulnerable to axonal injury than the adult ones. Many previous studies used distal axonal injury, such as sciatic nerve transection, to examine the response of immature motoneurons to injury. In the present study, a more severe injury, spinal root avulsion, was performed in newborn and early postnatal rats, and the response of immature spinal motoneurons to the injury was observed. In newborn rats, root avulsion causes motoneuron loss which is similar to that of previous studies by distal axonal injury. During the early postnatal development, motoneuron loss in immature rats is greater following root avulsion when compared to cell loss following distal axonal injury at any given age. Following root avulsion, nitric oxide synthase (NOS) is induced in injured immature motoneurons. The induction and accumulation of NOS in injured motoneurons is much more rapid in the immature animals than in the adult, which is coincident with the more rapid motoneuron loss in the immature animals. Results of the present study indicate an involvement of NOS in neuronal degeneration. However, the precise role of NOS in the response of motoneurons to axonal injury is not clear and needs to be further studied.