The Distribution of Primary Nitric Oxide Synthase- and Parvalbumin- Immunoreactive Afferents in the Dorsal Funiculus of the Lumbosacral Spinal Cord in a Dog

1. The aim of the present study was to examine the distribution of unmyelinated, small-diameter myelinated neuronal nitric oxide synthase immunoreactive (nNOS-IR) axons and large-diameter myelinated neuronal nitric oxide synthase and parvalbumin-immunoreactive (PV-IR) axons in the dorsal funiculus (DF) of sacral (S1-S3) and lumbar (L1-L7) segments of the dog.2. nNOS and PV immunohistochemical methods were used to demonstrate the presence of nNOS-IR and PV-IR in the large-diameter myelinated, presumed to be proprioceptive, axons in the DF along the lumbosacral segments.3. Fiber size and density of nNOS-IR and PV-IR axons were used to compartmentalize the DF into five compartments (CI-CV). The first compartment (CI) localized in the lateralmost part of the DF, containing both unmyelinated and small-diameter myelinated nNOS-IR axons, is homologous with the dorsolateral fasciculus, or Lissauer tract. The second compartment (CII) having similar fiber organization as CI is situated more medially in sacral segments. Rostrally, in lower lumbar segments, CII moves more medially, and at upper lumbar level, CII reaches the dorsomedial angle of the DF and fuses with axons of CIV. CIII is the largest in the DF and the only one containing large-diameter myelinated nNOS-IR and PV-IR axons. The largest nNOS-IR and PV-IR axons of CIII (8.0-9.2 mum in diameter), presumed to be stem Ia proprioceptive afferents, are located in the deep portion of the DF close to the dorsal and dorsomedial border of the dorsal horn. The CIV compartment varies in shape, appearing first as a small triangular area in S3 and S2 segments, homologous with the Philippe-Gombault triangle. Beginning at S1 level, CIV acquires a more elongated shape and is seen throughout the lumbar segments as a narrow band of fibers extending just below the dorsal median septum in approximately upper two-thirds of the DF. The CV is located in the basal part of the DF. In general, CV is poor in nNOS-IR fibers; among them solitary PV-IR fibers are seen.4. The analysis of the control material and the degeneration of the large- and medium-caliber nNOS-IR fibers after unilateral L7 and S1 dorsal rhizotomy confirmed that large-caliber nNOS-IR and and PV-IR axons, presumed to be proprioceptive Ia axons, and their ascending and descending collaterals are present in large number in the DF of the lumbosacral intumescence. However, in the DF of the upper lumbar segments, the decrease in the number of nNOS-IR and PV-IR fibers is quite evident.

Traumatic injury of the spinal cord and nitric oxide

In the current report, we summarize our findings related to the involvement of nitric oxide (NO) in the pathology of spinal cord trauma. We initially studied the distribution of nitric oxide synthase (NOS)-immunolabeled and/or nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd; which is highly colocalized with NOS)-stained somata and fibers in the spinal cord of the rabbit. Segmental and laminar distribution of NADPHd-stained neurons in the rabbit revealed a large number of NADPHd-stained neurons in the spinal cord falling into six categories, N1-N6, while others could not be classified. Large numbers of NADPHd-stained neurons were identified in the superficial dorsal horn and around the central canal. Four morphologically distinct kinds of NADPHd-stained axons 2.5-3.5 microm in diameter were identified throughout the white matter in the spinal cord. Moreover, a massive occurrence of axonal NADPHd-staining was detected in the juxtagriseal layer of the ventral funiculus along the rostrocaudal axis. The prominent NADPHd-stained fiber bundles were identified in the mediobasal and central portion of the ventral funiculus. The sulcomarginal fasciculus was found in the basal and medial portion of the ventral funiculus in all cervical and thoracic segments. Since the discovery that NO may act as a neuronal transmitter, an increasing interest has focused on its ability to modulate synaptic function. NO passes through cell membranes without specific release or uptake mechanisms inducing changes in signal-related functions by several means. In particular, the activation of the soluble guanylyl cyclases (sGC), the formation of cyclic guanosine 3',5'-monophosphate (cGMP) and the action of cGMP-dependent protein kinases has been identified as the main signal transduction pathways of NO in the nervous system including spinal cord. It is known that the intracellular level of cGMP is strictly controlled by its rate of synthesis via guanylyl cyclases (GC) and/or by the rate of its degradation via 3',5'-cyclic nucleotide phosphodiesterases (PDE). GC can be divided into two main groups, i.e., the membrane-bound or particular guanylyl cyclase (pGC) and the cytosolic or sGC. In the spinal cord, the activation of pGC has only been demonstrated for natriuretic peptides, which stimulate cGMP accumulation in GABA-ergic structures in laminae I-III of the rat cervical spinal cord. These neurons are involved in controlling the action of the locomotor circuit. In view of the abundance of NO-responsive structures in the brain, it is proposed that NO-cGMP signaling will be part of neuronal information processing at many levels. In relation to this, we found that surgically induced Th7 constriction of 24 h duration stimulated both the constitutive NOS activity and cGMP level by 120 and 131%, respectively, in non-compartmentalized white matter of Th8-Th9 segments, located just caudally to the site of injury. NO-mediated cGMP formation was only slightly increased in the dorsal funiculus of Th5-Th9 segments. There are some other sources that may influence the NO-mediated cGMP formation in spinal cord. A high level of glutamate produced at the site of the lesion and an excessive accumulation of intracellular Ca2+ may stimulate NOS activity and create suitable conditions for NO synthesis and its adverse effect on white matter. An increased interest has focused on the role of NO at the site of injury and in areas located close to the epicenter of the impact site and, in these connections an upregulation of NOS was noted in neurons and interneurons. However, the upregulation of NOS expression was also seen in interneurons located just rostrally and caudally to the lesion. A quantitative analysis of laminar distribution of multiple cauda equina constriction (MCEC) induced NADPHd-stained neurons revealed a considerable increase in these neurons in laminae VIII-IX 8h postconstriction, and a highly statistically significant increase of such neurons in laminae VII-X 5 days postconstriction in the lumbosacral segments. Concurrently, the number of NADPHd-stained neurons on laminae I-II in LS segments was greatly reduced. It is concluded that a greater understanding of NO changes after spinal cord trauma is essential for the possibility of targeting this pathway therapeutically.

Neuronal Nitric Oxide Synthase Immunopositivity in Motoneurons of the Rabbit's Spinal Cord After Transient Ischemia/Reperfusion Injury

1. Motoneurons in the spinal cord are especially vulnerable to ischemic injury and selectively destroyed after transient ischemia. To evaluate the role of nitric oxide (NO) in the pathophysiology of the spinal cord ischemia, the expression of neuronal nitric oxide synthase (nNOS) in the motoneurons of the lumbosacral spinal cord was examined in the rabbit model of transient abdominal aorta occlusion. 2. The aim of the present study was to find if there is any consensus between the duration of transient abdominal aorta occlusion, nNOS positivity of the motoneurons and neurological hind limb impairment. 3. According to the degree of neurological damage (i.e., from the group with almost no sign of damage to a group with fully developed paraplegia), the experimental animals were divided into three groups. The respective spinal cord segments of each experimental group were compared to the control group. 4. Spinal cord ischemia (15 min) was induced by Fogarty arterial embolectomy catheter occlusion of abdominal aorta with a reperfusion period of 7 days. On seventh day, the sections of lumbosacral segments were immunohistochemically treated and L1-L7, and S1-S2 segment sections were monitored using light microscopy.

The Effect of a Spinal Cord Hemisection on Changes in Nitric Oxide Synthase Pools in the Site of Injury and in Regions Located Far Away from the Injured Site

1. The present study was designed to examine the nitric oxide synthase activities (constitutive and inducible) in the site of injury in response to Th10-Th11 spinal cord hemisection and, to determine whether unilateral disconnection of the spinal cord influences the NOS pools on the contra- and ipsilateral sides in segments located far away from the epicentre of injury. 2. A radioassay detection was used to determine Ca(2+)-dependent and inducible nitric oxide synthase activities. Somal, axonal and neuropil neuronal nitric oxide synthase was assessed by immunocytochemical study. A quantitative assessment of neuronal nitric oxide synthase immunoreactivity was made by an image analyser. The level of neuronal nitric oxide synthase protein was measured by the Western blot analysis. 3. Our data show the increase of inducible nitric oxide synthase activity and a decrease of Ca(2+)-dependent nitric oxide synthase activity in the injured site analysed 1 and 7 days after surgery. In segments remote from the epicentre of injury the inducible nitric oxide synthase activity was increased at both time points. Ca(2+)-dependent nitric oxide synthase activity had decreased in L5-S1 segments in a group of animals surviving for 7 days. A hemisection performed at thoracic level did not cause significant difference in the nitric oxide synthase activities and in the level of neuronal nitric oxide synthase protein between the contra- and ipsilateral sides in C6-Th1 and L5-S1 segments taken as a whole. Significant differences were observed, but only when the spinal cord was analysed segment by segment, and/or was divided into dorsal and ventral parts. The cell counts in the cervicothoracic (C7-Th1) and lumbosacral (L5-S1) enlargements revealed changes in neuronal nitric oxide synthase immunoreactivity on the ipsilateral side of the injury. The densitometric area measurements confirmed the reduction of somal, neuropil and axonal neuronal nitric oxide synthase immunoreactive staining in the ventral part of rostrally oriented segments. 4. Our findings provide evidence that the changes in nitric oxide synthase pools are limited not only to impact zone, but spread outside the original lesion. The regional distribution of nitric oxide synthase activity and neuronal nitric oxide synthase immunoreactivity, measured segment by segment shows that nitric oxide may play a significant role in the stepping cycle in the quadrupeds.

Nitrergic Proprioceptive Afferents Originating from Quadriceps Femoris Muscle are Related to Monosynaptic Ia-Motoneuron Stretch Reflex Circuit in the Dog

1. The aim of the present study was to examine the occurrence of the neuronal nitric oxide synthase immunoreactivity in the stretch reflex circuit pertaining to the quadriceps femoris muscle in the dog. 2. Immunohistochemical processing for neuronal nitric oxide synthase and histochemical staining for nicotinamide adenine dinucleotide phosphate diaphorase were used to demonstrate the presence of neuronal nitric oxide synthase in the proprioceptive afferents issuing in the quadriceps femoris muscle. The retrograde tracer Fluorogold injected into the quadriceps femoris muscle was used to detect the proprioceptive afferents and their entry into the L5 and L6 dorsal root ganglia. 3. A noticeable number of medium-sized intensely nitric oxide synthase immunolabelled somata (1000-2000 microm(2) square area) was found in control animals in the dorsolateral part of L5 and L6 dorsal root ganglia along with large-caliber intraganglionic nitric oxide synthase immunolabelled fibers, presumed to be Ia axons. Before entering the dorsal funiculus the large-caliber nitric oxide synthase immunolabelled fibers of the L5 and L6 dorsal roots formed a massive medial bundle, which upon entering the dorsal root entry zone reached the dorsolateral part of the dorsal funiculus and were distributed here in a funnel-shaped fashion. The largest nitric oxide synthase immunolabelled fibers, 8.0-9.2 microm in diameter, remained close to the dorsal horn, while medium-sized fibers were seen dispersed across the medial portion of the dorsal funiculus. Single, considerably tapered nitric oxide synthase immunolabelled fibers, 2.2-4.6 microm in diameter, were seen to proceed in ventrolateral direction until they reached the mediobasal portion of the dorsal horn and the medial part of lamina VII. In lamina IX, only short fragments of nitric oxide synthase immunoreactive fibers and their terminal ramifications could be seen. Nitric oxide synthase immunolabelled terminals varying greatly in size were identified in control material at the base of the dorsal horn, in the vicinity of motoneurons ventrally and ventrolaterally in L5 and L6 segments and in Clarke's column of L3 and L4 segments. Injections of the retrograde tracer Fluorogold into the quadriceps femoris muscle and cut femoral nerve, combined with nitric oxide synthase immunohistochemistry of the L5 and L6 dorsal root ganglia, confirmed the existence of a number of medium-sized nitric oxide synthase immunoreactive and Fluorogold-fluorescent somata presumed to be proprioceptive Ia neurons (1000-2000 microm(2) square area) in the dorsolateral part of both dorsal root ganglia. L5 and L6 dorsal rhizotomy caused a marked depletion of nitric oxide synthase immunoreactivity in the medial bundle of the L5 and L6 dorsal roots and in the dorsal funiculus of L5 and L6 segments. 4. The analysis of control material and the degeneration of the large- and medium-caliber nitric oxide synthase immunoreactive Ia fibers in the dorsal funiculus of L5 and L6 segments confirmed the presence of nitric oxide synthase in the afferent limb of the monosynaptic Ia-motoneuron stretch reflex circuit related to the quadriceps femoris muscle.

Effect of ischemia in vivo and oxygen-glucose deprivation in vitro on NOS pools in the spinal cord: comparative study

1. This study was performed to compare both the Ca(2+)-dependent nitric oxide synthase (NOS) activity and the neuronal nitric oxide synthase immunoreactivity (nNOS-IR) in the rabbit lumbosacral spinal cord after 15 min abdominal aorta occlusion (ischemia in vivo) and oxygen-glucose deprivation of the spinal cord slices for 45 and 60 min (ischemia in vitro). All ischemic periods were followed by 15, 30 and 60 min reoxygenation in vitro. 2. Catalytic nitric oxide synthase activity was determined by the conversion of (L)-[(14)C]arginine to (L)-[(14)C]citrulline. Neuronal nitric oxide synthase immunoreactivity in the spinal cord was detected by incubation of sections with polyclonal sheep-nNOS-primary antibody and biotinylated anti-sheep secondary antibody. 3. Our results show that ischemia in vivo and the oxygen-glucose deprivation of spinal cord slices in vitro result in a time-dependent loss of constitutive NOS activity with a partial restoration of enzyme activity during 15 and 45 min ischemia followed by 30 min of reoxygenation. A significant decrease of enzyme activity was found during 60 min ischemia alone, which persisted up to 1 h of oxygen-glucose restoration. The upregulation of neuronal nitric oxide synthase was observed in the ventral horn motoneurons after all ischemic periods. The remarkable changes in optical density of neuronal nitric oxide synthase immunoreactive motoneurons were observed after 45 and 60 min ischemia in vitro followed by 30 and 60 min reoxygenation. 4. Our results suggest that the oxygen-glucose deprivation followed by reoxygenation in the spinal cord is adequately sensitive to monitor ischemia/reperfusion changes. It seems that 15 min ischemia in vivo and 45 min ischemia in vitro cause reversible changes, while the decline of Ca(2+)-dependent nitric oxide synthase activity after 60 min ischemic insult suggests irreversible alterations.

Immunohistochemical, Histochemical and Radioassay Analysis of Nitric Oxide Synthase Immunoreactivity in the Lumbar and Sacral Dorsal Root Ganglia of the Dog

In this study, immunohistochemistry for neuronal nitric oxide synthase (bNOS-IR), nicotinamide adenine dinucleotide phosphate diaphorase histochemistry (NADPHd) and nitric oxide synthase radioassay were used to study the occurrence, number and distribution pattern of nitric oxide synthesizing neurons in the lumbar (L1-L7) and sacral (S1-S3) dorsal root ganglia of the dog. Nitric oxide synthase immunolabelling was present in a large number of small- (area <1,000 microm(2)) and medium-sized (area 1,000-2,000 microm(2)) as well as in a limited number of large-sized (area >2000 microm(2)) neurons. Although neuronal nitric oxide synthase immunolabelling and histochemical staining provided intense staining of multiple small- and medium-sized neurons in all lumbar and sacral dorsal root ganglia, immuno-labelled or histochemically stained somata exhibited little topographic distribution in individual dorsal root ganglia. Great heterogeneity was noticed in the immunolabelling of medium-sized nitric oxide synthase immunopositive neurons ranging from lightly immuno-labelled somata to heavily immunoreactive ones with completely obscured nuclei. Both staining procedures proved to be highly effective in visualizing intraganglionic fibers of various diameters. In general, the largest fibers revealed at the peripheral end of lumbar and sacral dorsal root ganglia were larger, 6.49-9.35 mum in diameter, while those running centrally and proceeding into the dorsal roots were about 30% reduced, ranging between 5.32 and 8.67 microm in diameter. Peripherally, the occurrence of nitric oxide synthase detected in axonal profiles, and confirmed histochemically, in the specimens of the femoral and sciatic nerves, is the first indication of the presence of nitric oxide synthase in the peripheral processes of somata located in L4-S2 dorsal root ganglia. Large and thin central nitric oxide synthase immunoreactive processes of L1-S3 dorsal root ganglion neurons segregate shortly before entering the spinal cord, the former making a massive medial bundle in the dorsal root accompanied by a slim lateral bundle penetrating Lissauer's tract. Quantitative assessment of the distribution of bNOS-IR and/or NADPHd-stained neurons showed a peculiar pattern in relation to spinal levels. Apparent incongruity was found in the total number of NADPHd-stained versus bNOS-IR neurons, demonstrating a clear prevalence of small bNOS-IR somata in all lumbar ganglia, while medium-sized NADPHd-stained somata clearly prevailed all along the rostrocaudal axis with a peak in L5 ganglion. While the number of small bNOS-IR neurons clearly outnumbered NADPHd-stained and NADPHd-unstained somata in S1-S3 ganglia, an inverse relation appeared comparing the total number of medium-sized NADPHd-stained and NADPHd-unstained somata compared with the number of moderate and intense bNOS-IR neurons. Densitometry of bNOS-IR and NADPHd-stained neurons in lumbar and sacral ganglia revealed two distinct subsets of densitometric profiles, one relating to more often found medium-sized bNOS immuno-labelled and the other, characteristic for moderately bNOS immunoreactive somata of the same cell size. Considerable differences in catalytic nitric oxide synthase activity, determined by conversion of [(3)H]arginine to [(3)H]citrulline were obtained in lumbosacral dorsal root ganglia all along the lumbosacral intumescence, the lowest (0.898+/- 0.2 dpm/min/microg protein) being in the L4 dorsal root ganglion and the highest (4.194+/-0.2 dpm/min/microg protein) in the S2 dorsal root ganglion.

The evidence for nitric oxide synthase immunopositivity in the monosynaptic Ia-motoneuron pathway of the dog

In this study, nitric oxide synthase immunohistochemistry supported by nicotinamide adenine dinucleotide phosphate diaphorase histochemistry was used to demonstrate the nitric oxide synthase immunoreactivity in the monosynaptic Ia-motoneuron pathway exemplified by structural components of the afferent limb of the soleus H-reflex in the dog. A noticeable number of medium-sized intensely nitric oxide synthase immunoreactive somata (1000-2000 microm(2) square area) and large intraganglionic nitric oxide synthase immunoreactive fibers, presumed to be Ia axons, was found in the L7 and S1 dorsal root ganglia. The existence of nitric oxide synthase immunoreactive fibers (6-8 microm in diameter, not counting the myelin sheath) was confirmed in L7 and S1 dorsal roots and in the medial bundle of both dorsal roots before entering the dorsal root entry zone. By virtue of the funicular organization of nitric oxide synthase immunoreactive fibers in the dorsal funiculus, the largest nitric oxide synthase immunoreactive fibers represent stem Ia axons located in the deep portion of the dorsal funiculus close to the dorsomedial margin of the dorsal horn. Upon entering the gray matter of L7 and S1 segments and passing through the medial half of the dorsal horn, tapered nitric oxide synthase immunoreactive collaterals of the stem Ia fibers pass through the deep layers of the dorsal horn and intermediate zone, and terminate in the group of homonymous motoneurons in L7 and S1 segments innervating the gastrocnemius-soleus muscles. Terminal fibers issued in the ventral horn intensely nitric oxide synthase immunoreactive terminals with long axis ranging from 0.7 to >or=15.1 microm presumed to be Ia bNOS-IR boutons. This finding is unique in that it focuses directly on nitric oxide synthase immunopositivity in the signalling transmitted by proprioceptive Ia fibers. Nitric oxide synthase immunoreactive boutons were found in the neuropil of Clarke's column of L4 segment, varying greatly in size from 0.7 to >or=15.1 microm in length x 0.7 to 4.8 microm wide. Subsequent to identification of the afferent nitric oxide synthase immunoreactive limb of the monosynaptic Ia-motoneuron pathway on control sections, intramuscular injections of the retrograde tracer Fluorogold into the gastrocnemius-soleus muscles, combined with nitric oxide synthase immunohistochemistry of L7 and S1 dorsal root ganglia, confirmed the existence of a number of medium-sized nitric oxide synthase immunoreactive somata (1000-2000 microm(2) square area) in the dorsolateral part of both dorsal root ganglia, presumed to be proprioceptive Ia neurons. Concurrently, large nitric oxide synthase immunoreactive fibers were detected at the input and output side of both dorsal root ganglia. S1 and S2 dorsal rhizotomy caused a marked depletion of nitric oxide synthase immunoreactivity in the medial bundle of S1 and S2 dorsal roots and in the dorsal funiculus of S1, S2 and lower lumbar segments. In addition, anterograde degeneration of large nitric oxide synthase immunoreactive Ia fibers in the dorsal funiculus of L7-S2 segments produces direct evidence that the afferent limb of the soleus H-reflex is nitric oxide synthase immunoreactive and presents new immunohistochemical characteristics of the monosynaptic Ia-motoneuron pathway, unseparably coupled with the performance of the stretch reflex.

Experimental cauda equina compression induces HSP70 synthesis in dog

The heat shock protein 70 (HSP70) is a key component of the stress response induced by various noxious conditions such as heat, oxygen stress, trauma and infection. In present study we have assessed the consequences of the compression of lower lumbar and sacral nerve roots caused by a multiple cauda equina constrictions (MCEC) on HSP70 immunoreactivity (HSP70-IR) in the dog. Our data indicate that constriction of central processes evokes HSP70 up-regulation in the spinal cord (L7, S1-Co3) as well as in the corresponding dorsal root ganglion cells (DRGs) (L7-S1) two days following injury. A limited number of bipolar or triangular HSP-IR neurons were found in the lateral collateral pathway (LCP) as well as in the pericentral region (lamina X) of the spinal cord. In contrast, a high number of HSP70 exhibiting motoneurons with fine processes appeared in the ventral horn (laminae VIII-IX) of lumbosacral segments. Concomitantly, close to them a few lightly HSP70-positive neuronal somata or cell bodies lacking the HSP70-IR occurred. In the DRGs, HSP70 expression was mildly up-regulated in small and medium-sized neurons and in satellite cells. On the contrary, DRGs from intact or sham-operated dogs did not reveal HSP70 specific neuronal staining. In conclusion, we have demonstrated that the MCEC in dogs mimicking the cauda equina syndrome in clinical settings evokes expression of HSP70 synthesis in specific neurons of the lumbo-sacro-coccygeal spinal cord segments and in small and medium sized neurons of corresponding DRGs. This suggests that HSP70 may play an active role in neuroprotective processes partly by maintaining intracellular protein integrity and preventing the neuronal degeneration in this experimental paradigm.

Cauda equina syndrome and nitric oxide synthase immunoreactivity in the spinal cord of the dog

The development of the cauda equina syndrome in the dog and the involvement of spinal nitric oxide synthase immunoreactivity (NOS-IR) and catalytic nitric oxide synthase (cNOS) activity were studied in a pain model caused by multiple cauda equina constrictions. Increased NOS-IR was found two days post-constriction in neurons of the deep dorsal horn and in large, mostly bipolar neurons located in the internal basal nucleus of Cajal seen along the medial border of the dorsal horn. Concomitantly, NOS-IR was detected in small neurons close to the medioventral border of the ventral horn. High NOS-IR appeared in a dense sacral vascular body close to the Lissauer tract in S1-S3 segments. Somatic and fiber-like NOS-IR appeared at five days post-constriction in the Lissauer tract and in the lateral and medial collateral pathways arising from the Lissauer tract. Both pathways were accompanied by a dense punctate NOS immunopositive staining. Simultaneously, the internal basal nucleus of Cajal and neuropil of this nucleus exhibited high NOS-IR. A significant decrease in the number of small NOS immunoreactive somata was noted in laminae I-II of L6-S2 segments at five days post-constriction while, at the same time, the number of NOS immunoreactive neurons located in laminae VIII and IX was significantly increased. Moreover, high immunopositivity in the sacral vascular body persisted along with a highly expressed NOS-IR staining of vessels supplying the dorsal sacral gray commissure and dorsal horn in S1-S3 segments. cNOS activity, based on a radioassay of compartmentalized gray and white matter regions of lower lumbar segments and non-compartmentalized gray and white matter of S1-S3 segments, proved to be highly variable for both post-constriction periods.

Premotor nitric oxide synthase immunoreactive pathway connecting lumbar segments with the ventral motor nucleus of the cervical enlargement in the dog

In this study we investigate the occurrence and origin of punctate nitric oxide synthase immunoreactivity in the neuropil of the ventral motor nucleus in C7-Th1 segments of the dog spine, which are supposed to be the terminal field of an ascending premotor propriospinal nitric oxide synthase-immunoreactive pathway. As the first step, nitric oxide synthase immunohistochemistry was used to distinguish nitric oxide synthase-immunoreactive staining of the ventral motor nucleus. Dense, punctate nitric oxide synthase immunoreactivity was found on control sections in the neuropil of the ventral motor nucleus. After hemisection at Th10-11, axotomy-induced retrograde changes consisting in a strong upregulation of nitric oxide synthase-containing neurons were found mostly unilaterally in lamina VIII, the medial part of lamina VII and in the pericentral region in all segments of the lumbosacral enlargement. Concurrently, a strong depletion of the punctate nitric oxide synthase immunopositivity in the neuropil of the ventral motor nucleus ipsilaterally with the hemisection was detected, thus revealing that an uncrossed ascending premotor propriospinal pathway containing a fairly high number of nitric oxide synthase-immunoreactive fibers terminates in the ventral motor nucleus. Application of the retrograde fluorescent tracer Fluorogold injected into the ventral motor nucleus and analysis of alternate sections processed for nitric oxide synthase immunocytochemistry revealed the presence of Fluorogold-labeled and nitric oxide synthase-immunoreactive axons in the ventrolateral funiculus and in the lateral and medial portions of the ventral column throughout the thoracic and upper lumbar segments. A noticeable number of Fluorogold-labeled and nitric oxide synthase-immunoreactive somata detected on consecutive sections were found in the lumbosacral enlargement, mainly in laminae VIII-IX, the medial part of lamina VII and in the pericentral region (lamina X), ipsilaterally with the injection of Fluorogold into the ventral motor nucleus. In summary, the present study provides evidence for a hitherto unknown ascending premotor propriospinal nitric oxide synthase-immunoreactive pathway connecting the lumbosacral enlargement with the motoneurons of the ventral motor nucleus in the dog.

The Effect of Cauda Equina Constriction on Nitric Oxide Synthase Activity

Nitric oxide synthase (NOS) activity was studied in the gray and white matter regions of the spinal cord 2 and 5 days after multiple cauda equina constrictions of the central processes of L7-Co5 dorsal root ganglia neurons. The results show considerable differences in enzyme activity in the thoracic, upper lumbar, lower lumbar, and sacral segments. Increased NOS activity was observed at 2 days after multiple cauda equina constrictions in the dorsal, lateral, and ventral columns of the lower lumbar segments and in the ventral column of the upper lumbar segments. The values returned to control levels within 5 postconstriction days. In the lateral columns of thoracic segments taken 2 and 5 days after surgery, NOS activity was enhanced by 54% and 55% and in the upper lumbar segments by 130% and 163%, respectively. Multiple cauda equina constrictions performed surgically for 2 and 5 days caused a significant increase in NOS activity predominantly in the gray matter regions of thoracic segments. A quite different response was found 5 days postconstriction in the upper lumbar segments, where the enzyme activity was significantly decreased in the dorsal horn, intermediate zone, and ventral horn. No such extreme differences could be seen in the lower lumbar segments, where NOS activity was significantly enhanced only in the ventral horn. The data correspond with a higher number of NOS immunoreactive somata, quantitatively evaluated in the ventral horn of the lower lumbar segments at 5 days after multiple cauda equina constrictions. While the great region-dependent heterogeneity in NOS activity seen 2 and 5 days after multiple cauda equina constrictions is quite apparent and suggestive of an active role played by nitric oxide in neuroprotective or neurotoxic processes occurring in the gray and white matter of the spinal cord, the extent of damage or the degree of neuroprotection caused by nitric oxide in compartmentalized gray and white matter in this experimental paradigm would be possible only using longer postconstriction periods.

Localization and distribution patterns of nicotinamide adenine dinucleotide phosphate diaphorase exhibiting axons in the white matter of the spinal cord of the rabbit

The funicular distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-exhibiting axons was examined in the white matter of the rabbit spinal cord by using horizontal, parasaggital, and transverse sections. Four morphologically distinct kinds of NADPHd-exhibiting axons (2.5-3.5 microm in diameter) were identified in the sulcomarginal fasciculus as a part of the ventral column in the cervical and upper thoracic segments and in the long propriospinal bundle of the ventral column in Th3-L3 segments. Varicose NADPHd-exhibiting axons of the sympathetic preganglionic neurons, characterized by widely spaced varicosities, were found in the ventral column of Th2-L3 segments. A third kind of NADPHd-positive ultrafine axons, 0.3-0.5 microm in diameter with numerous varicosities mostly spherical in shape, was identified in large number within Lissauer's tract. The last group of NADPHd-exhibiting axons (1.0-1.5 microm in diameter) occurred in the Lissauer tract. Most of these axons were traceable for considerable distances and generated varicosities varying in shape from spherical to elliptical forms. The majority of NADPHd-exhibiting axons identified in the cuneate and gracile fascicles were concentrated in the deep portion of the dorsal column. An extremely reduced number of NADPHd-exhibiting axons, confirmed by a computer-assisted image-processing system, was found in the dorsal half of the gracile fascicle. Axonal NADPHd positivity could not be detected in a wide area of the lateral column consistent with the location of the dorsal spinoccrebellar tract. Numerous, mostly thin NADPHd-positive axonal profiles were detected in the dorsolateral funiculus in all the segments studied and in a juxtagriscal portion of the lateral column as far as the cervical and lumbar enlargements. A massive occurrence of axonal NADPHd positivity was detected in the juxtagriseal layer of the ventral column all along the rostrocaudal axis of the spinal cord. The prominent NADPHd-exhibiting bundles containing thick, smooth, nonvaricose axons were identified in the mediobasal and central portion of the ventral column. First, the sulcomarginal fasciculus was found in the basal and medial portion of the ventral column in all cervical and upper thoracic segments. Second, more caudally, a long propriospinal bundle displaying prominent NADPHd positivity was localized in the central portion of the ventral column throughout the Th3-L3 segments.

Peripheral axotomy affects nicotinamide adenine dinucleotide phosphate diaphorase and nitric oxide synthases in the spinal cord of the rabbit

Using nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry and nitric oxide synthase (NOS) immunocytochemistry combined with radioassay of calcium-dependent NOS activity, we examined the occurrence of NADPHd staining and NOS immunoreactivity (NOS-IR) in the dorsal root ganglia (DRG) neurons, dorsal root afferents, and axons projecting via gracile fascicle to gracile nucleus 14 days after unilateral sciatic nerve transection in the rabbit. Mild to moderate NADPHd staining and NOS-IR appeared in a large number of small and medium-sized to large neurons in the ipsilateral L4-L6 DRG, accompanied by enhanced NOS-IR of thick myelinated fibers in the ipsilateral L4-L6 dorsal roots. A noticeable increase in the density of punctate NADPHd staining occurred throughout laminae I-IV in the ipsilateral medial part of the dorsal horn in L4-L6 segments. Concurrently, a statistically significant decrease in the number of small NADPHd-exhibiting neurons in laminae I-II and, in contrast to this, a statistically significant increase of medium-sized to large NADPHd-stained somata in the ipsilateral laminae III-VI of L4-L6 segments were found. A detailed compartmentalization of L4-L6 segments into gray and white matter regions disclosed substantially increased catalytic NOS activity and inducible NOS mRNA levels in the dorsal horn and dorsal column ipsilaterally to the peripheral injury. A noticeable increase in the number of thick myelinated NADPHd-exhibiting and NOS-IR axons was noted in the ipsilateral gracile fascicle, terminating in dense, punctate NADPHd staining in the neuropil of the gracile nucleus. These observations indicate that the de novo-synthesized NOS in the lesioned primary afferent neurons resulting after sciatic nerve transection may be involved in an increase in NADPHd staining and NOS-IR in the ipsilateral dorsal roots and dorsal horn of L4-L6 segments, whence NOS could be supplied to ascending axons of the gracile fascicle.

The case for the bulbospinal respiratory nitric oxide synthase-immunoreactive pathway in the dog

Previous investigations from our laboratory have documented that the neuropil of the phrenic nucleus contains a dense accumulation of punctate nicotinamide adenine dinucleotide phosphate diaphorase staining. In this study we investigated the occurrence and origin of punctate nitric oxide synthase immunoreactivity in the neuropil of the phrenic nucleus in C3-C5 segments, supposed to be the terminal field of the premotor bulbospinal respiratory nitric oxide synthase-immunoreactive pathway in the dog. As the first step, nitric oxide synthase immunohistochemistry was used to characterize nitric oxide synthase-immunoreactive staining of the phrenic nucleus and nitric oxide synthase-containing neurons in the dorsal and rostral ventral respiratory group and in the Bötzinger complex of the medulla. Dense punctate nitric oxide synthase immunoreactivity was found on control sections in the neuropil of the phrenic nucleus. Several thin bundles of nitric oxide synthase-immunoreactive fibers were found to enter the phrenic nucleus from the lateral and ventral column. Nitric oxide synthase-containing neurons were revealed in the dorsal respiratory group of medulla corresponding to the ventrolateral nucleus of the solitary tract and in the rostral ventral respiratory group beginning approximately 1 mm caudal to the obex and reaching to 650 microm rostral to the obex. Axotomy-induced retrograde changes, consisting in a strong upregulation of nitric oxide synthase-containing neurons, were found in the dorsal and rostral ventral respiratory group contralateral to the hemisection performed at the C2-C3 level. Concurrently, a strong depletion of the punctate nitric oxide synthase immunopositivity in the neuropil of the phrenic nucleus ipsilaterally with the hemisection was detected, thus revealing that a crossed premotor bulbospinal respiratory pathway contains a fairly high number of nitric oxide synthase-immunopositive fibers terminating in the phrenic nucleus. The use of the retrograde fluorescent tracer Fluorogold injected into the phrenic nucleus and an analysis of sections cut through the dorsal and rostral ventral respiratory group and Bötzinger complex of medulla and processed for nitric oxide synthase immunocytochemistry revealed that approximately 73.8% of crossed premotor bulbospinal respiratory nitric oxide synthase-immunoreactive axons originate in the rostral ventral respiratory group and 26.2% is given by nitric oxide synthase-containing neurons of the dorsal respiratory group. A few premotor nitric oxide synthase-immunoreactive axons originating from the Bötzinger complex were found. In summary, the present study provides evidence for a hitherto unknown premotor bulbospinal respiratory nitric oxide synthase-immunoreactive pathway connecting the bulbar respiratory centers with the motor neurons of the phrenic nucleus in the dog.

The regional distribution of nitric oxide synthase activity in the spinal cord of the dog

The aim of this study was to examine the distribution of calcium-dependent nitric oxide synthase activity (cNOS) in the white and gray matter in cervical, thoracic, lumbar and sacral segments of the spinal cord and cauda equina of the dog. The enzyme's activity, measured by the conversion of [3H]arginine to [3H]citrulline revealed considerable region-dependent differences along the rostrocaudal axis of the spinal cord in general and in cervical (C1, C2, C4, C6 and C8) and lumbar (L1-L3, L4-L7) segments in particular. In the non-compartmentalized spinal cord, the cNOS activity was lowest in the thoracic and highest in the sacral segments. No significant differences were noted in the gray matter regions (dorsal horn, intermediate zone and ventral horn) and the white matter columns (dorsal, lateral and ventral) in the upper cervical segments (C1-C4), except for a significant increase in the ventral horn of C4 segment. In C6 segment, the enzyme's activity displayed significant differences in the intermediate zone, ventral and lateral columns. Surprisingly, extremely high cNOS activity was noted in the dorsal horn and dorsal column of the lowest cervical segment. Comparing the enzyme's activity in upper and lower lumbar segments of the spinal cord, cNOS activity prevailed in L4-L7 segments in the dorsal horn and in all the above mentioned white matter columns.

Neuropathic pain is associated with alterations of nitric oxide synthase immunoreactivity and catalytic activity in dorsal root ganglia and spinal dorsal horn

Previous experiments have suggested that nitric oxide may play an important role in nociceptive transmission in the spinal cord. To assess the possible roles of neuronal nitric oxide synthase (nNOS) in spinal sensitization after nerve injury, we examined the distribution of nNOS immunoreactivity in dorsal root ganglia (DRGs) and dorsal horn of the corresponding spinal segments. NOS catalytic activity was also determined by monitoring the conversion of [3H]arginine to [3H]citrulline in the lumbar (L4-L6) spinal cord segments and DRGs in rats 21 days after unilateral loose ligation of the sciatic nerve. Behavioral signs of tactile and cold allodynia developed in the nerve-ligated rats within 1 week after surgery and lasted up to 21 days. Immunocytochemical staining revealed a significant increase (approximately 6.7-fold) of nNOS-immunoreactive neurons and fibers in the DRGs L4-L6. No significant changes were detected in the number of nNOS-positive neurons in laminae I-II of the spinal segments L4-L6 ipsilateral to nerve ligation. However, an increased number of large stellate or elongated somata in deep laminae III-V of the L5 segment expressed high nNOS immunoreactivity. The alterations of NOS catalytic activity in the spinal segments L4-L6 and corresponding DRGs closely correlated with nNOS distribution detected by immunocytochemistry. No such changes were detected in the contralateral DRGs or spinal cord of sham-operated rats. The results indicate that marked alterations of nNOS in the DRG cells and in the spinal cord may contribute to spinal sensory processing as well as to the development of neuronal plasticity phenomena in the dorsal horn.

Effect of spinal cord compression on cyclic 3',5'-guanosine monophosphate in the white matter columns of rabbit

Changes in the level of cyclic 3',5'-guanosine monophosphate (cGMP) were studied one day after a surgically induced spinal cord constriction performed at the Th7 segment level in the dorsal, lateral and ventral white matter columns and in the non-compartmentalized white matter of Th5-Th6 segments, i.e., above the site of the spinal cord constriction and in Th8-Th9 segments, located below the spinal cord constriction. The midthoracic spinal cord constriction caused a significant decrease in the level of cGMP in the ventral column of Th5-Th6 segments and a significant increase in the lateral column of Th8-Th9 segments. The level of cGMP in the dorsal column, located either rostrally or caudally to the site of the spinal cord injury, remained unchanged. In addition, no significant changes in the level of cGMP were found in the non-compartmentalized white matter of Th5-Th6 and Th8-Th9 segments in response to constriction of the Th7 segment.

Cauda equina syndrome

Single or double-level compression of the lumbosacral nerve roots located in the dural sac results in a polyradicular symptomatology clinically diagnosed as cauda equina syndrome. The cauda equina nerve roots provide the sensory and motor innervation of most of the lower extremities, the pelvic floor and the sphincters. Therefore, in a fully developed cauda equina syndrome, multiple signs of sensory disorders may appear. These disorders include low-back pain, saddle anesthesia, bilateral sciatica, then motor weakness of the lower extremities or chronic paraplegia and, bladder dysfunction. Multiple etiologies can cause the cauda equina syndrome. Among them, non-neoplastic compressive etiologies such as herniated lumbosacral discs and spinal stenosis and spinal neoplasms play a significant role in the development of the cauda equina syndrome. Non-compressive etiologies of the cauda equina syndrome include ischemic insults, inflammatory conditions, spinal arachnoiditis and other infectious etiologies. The use of canine, porcine and rat models mimicking the cauda equina syndrome enabled discovery of the effects of the compression on nerve root neural and vascular anatomy, the impairment of impulse propagation and the changes of the neurotransmitters in the spinal cord after compression of cauda equina. The involvement of intrinsic spinal cord neurons in the compression-induced cauda equina syndrome includes anterograde, retrograde and transneuronal degeneration in the lumbosacral segments. Prominent changes of NADPH diaphorase exhibiting, Fos-like immunoreactive and heat shock protein HSP72 were detected in the lumbosacral segments in a short-and long-lasting compression of the cauda equina in the dog. Developments in the diagnosis and treatment of patients with back pain, sciatica and with a herniated lumbar disc are mentioned, including many treatment options available.

The regional changes of the catalytic NOS activity in the spinal cord of the rabbit after repeated sublethal ischemia

The regional distribution of catalytic NOS activity was studied in the lumbosacral segments of the spinal cord of the rabbit during single (8-min), twice (8-, 8-min) and thrice repeated (8-, 8-, 9-min) sublethal ischemia followed each time by 1 h of reperfusion. Single ischemia/reperfusion induced a significant increase of cNOS activity in almost all spinal cord regions, with the exception of non-significant increase in the dorsal horn. Sublethal ischemia repeated twice produced a significant decrease of enzyme activity in the intermediate zone and ventral horn and an increase in the white matter columns. Within thrice repeated ischemia, the activity of cNOS in the gray matter regions was similar to that found after a single ischemia/reperfusion. For all the animals subjected to single and twice repeated sublethal ischemic insults, there was no neurological impairment. Following thrice repeated ischemic insults, four out of five of the experimental animals recovered only partially and one was completely paraplegic. Our results do not indicate a cumulative effect of repeated sublethal ischemia on cNOS activity and, consequently, on NO production. The NO generated during thrice repeated ischemia/reperfusion appears to have a detrimental effect on the neurological outcome.

Effect of midthoracic spinal cord constriction on catalytic nitric oxide synthase activity in the white matter columns of rabbit

The distribution and changes of catalytic nitric oxid synthase (cNOS) activity in the dorsal, lateral and ventral white matter columns at midthoracic level of the rabbit's spinal cord were studied in a model of surgically-induced spinal cord constriction performed at Th7 segment level and compared with the occurrence of nicotinamide adenine dinucleotide phosphate diaphorase expressing and neuronal nitric oxide synthase immunoreactive axons in the white matter of the control thoracic segments. Segmental and white-column dependent differences of cNOS activity were found in the dorsal (141.5 +/- 4.2 dpm/microm protein), lateral (87.3 +/- 11.5 dpm/microm protein) and ventral (117.1 +/- 7.6 dpm/microm protein) white matter columns in the Th5-Th6 segments and in the dorsal (103.3 +/- 15.5 dpm/microm protein), lateral (54.9 +/- 4.9 dpm/microm protein), and ventral (86.1 +/- 6.8 dpm/microm protein) white matter columns in the Th8-Th9 segments. A surgically-induced constriction of Th7 segment caused a disproportionate response of cNOS activity in the rostrally (Th5-Th6) and caudally (Th8-Th9) located segments in both lateral and ventral white matter columns. While a statistically significant decrease of cNOS activity was detected above the constriction site in the ventral columns, a considerable, statistically significant increase of cNOS activity was noted in the white lateral columns below the site of constriction. It is reasoned that the changes of cNOS activity may have adverse effects on nitric oxide (NO) production in the white matter close to the site of constriction injury, thus broadening the scope of the secondary mechanisms that play a role in neuronal trauma.

Regional changes of cyclic 3',5'-guanosine monophosphate in the spinal cord of the rabbit following brief repeated ischemic insults

The regional distribution of cyclic 3',5'-guanosine monophosphate was studied in the lumbosacral segments of the spinal cord of the rabbit under physiological conditions and following brief repeated sublethal ischemic insults. While the basal cGMP level in the gray matter was about 0.120 nmol cGMP/mg wet. wt., the level of cGMP in non-compartmentalized white matter was about half of this value. The highest level of cGMP in the compartmentalized gray matter was found in the dorsal horns, about 0.180 nmol cGMP/mg wet. wt., whereas the level of cGMP was greatly reduced in the ventral horns, reaching one half of the previous value. Multiple sublethal ischemic insults, repeated at 1-h intervals, caused a statistically significant decrease of cGMP in all gray matter regions. While the post-ischemic and post-reperfusion level of cGMP in the dorsal horns remained relatively high in comparison with the intermediate zone and ventral horns, the changes of cGMP level detected in the white matter columns differed considerably and resulted in a statistically significant cGMP increase in the dorsal and ventral columns and, vice versa, a statistically significant decrease of cGMP was found in the lateral columns.

Catalytic nitric oxide synthase activity in the white and gray matter regions of the spinal cord of rabbits

The latest research reveals that nitric oxide as a gas messenger may diffuse into the surrounding extracellular fluid and act locally upon neighboring target cells. However, several observations raise the possibility that nitric oxide may also be released at a greater distance from the neuronal cell body. The catalytic nitric oxide synthase (cNOS) activity was therefore studied in the cervicothoracic and lumbosacral segments of the spinal cord of rabbits, including the white matter of dorsal columns (DC), lateral columns (LC) and ventral columns (VC), as well as the gray matter of dorsal horns (DH), intermediate zone (IZ) and ventral horns (VH). Lower cNOS activity was found in the white matter of both cervicothoracic (47%) and lumbosacral (30%) regions, whereas that detected in the gray matter of the lumbosacral part of the spinal cord was considerably higher (70%). Enzyme activity varied from 43.4 to 77.2 dpm/microg protein in the cervicothoracic segments of the gray matter in the descending order: DH>VH>IZ. Similar cNOS activity was found in the white matter of the cervicothoracic segments (42.1-62.8 dpm/microg protein). When the activity of cNOS was compared in the lumbosacral segments, the highest enzyme activity was found in DH of the gray matter (198.7 dpm/microg protein) and the lowest cNOS in DC (45.8 dpm/microg protein) of the white matter. It was concluded that the white matter of the spinal cord contains similar cNOS activity in comparison to the gray matter.

Segmental and laminar distributions of nicotinamide adenine dinucleotide phosphate-diaphorase-expressing and neuronal nitric oxide synthase-immunoreactive neurons versus radioassay detection of catalytic nitric oxide synthase activity in the rabbit spinal cord

The distributions of neuronal nitric oxide synthase-immunoreactive neurons and of nicotinamide adenine dinucleotide phosphate-diaphorase activity were studied in the C6, Th2, L1, L5, S2 and S3 segments and laminae in the rabbit spinal cord and compared with the catalytic nitric oxide synthase activity, determined by monitoring the conversion of [3H]arginine to [3H]citrulline in the same segments and laminae. Morphologically, a heterogeneous population of nicotinamide adenine dinucleotide phosphate-diaphorase-expressing and neuronal nitric oxide synthase-immunoreactive neurons was detected in the superficial and deep dorsal horn and the pericentral region in all segments studied, and in the intermediolateral cell column of the thoracic and lumbosacral segments. A disproportionate distribution of both neuronal categories which had a significantly higher number of nicotinamide adenine dinucleotide phosphate-diaphorase-expressing rather than neuronal nitric oxide synthase-immunoreactive cell bodies was found in all segments. The catalytic nitric oxide synthase activity was distributed unequally in the C6, Th2, L1, L5, S2 and S3 segments, with a comparatively low value in the Th2 segment (70 +/- 5.1 d.p.m./microg protein) in comparison with the S3 segment, where the highest level (140 +/- 5.5 d.p.m./microg protein) was found. A close correlation between the number of neuronal nitric oxide synthase-immunoreactive somata and catalytic nitric oxide synthase activity was revealed in the dorsal horn (laminae I-VI). Whereas a low number of neuronal nitric oxide synthase-immunoreactive somata in laminae VII-X was found in the L5, S2 and S3 segments, the values of catalytic nitric oxide synthase activity in the same laminae and segments were found to be exceedingly high. These findings indicate that the occurrence of many neuronal nitric oxide synthase-immunoreactive fibers (mainly axons), and dense, punctate, non-somatic neuronal nitric oxide synthase immunopositivity in the neuropil staining of the same laminae and segments, can substantially enhance catalytic nitric oxide synthase activity.

Phospholipid composition in spinal cord regions after ischemia/reperfusion

Ischemia-reperfusion induced changes in concentration of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI) and sphingomyelin (SM) in the gray matter taken in toto, white matter, dorsal horns, intermediate zone and ventral horns of the rabbit's spinal cord were studied and compared with neurohistopathological changes. With the exception of PI concentration in the dorsal horns, ischemia of 25 min caused significant degradation of all phospholipids. While short-lasting recirculation (1 h) did not returned the levels of phospholipids to control values, postischemic recirculation for 3 h sharply increased the resynthesis of all phospholipids, but only the concentration of PE, PS, and PI in the dorsal horns and PC in the intermediate zone significantly improved and returned close to control values. Corresponding neurohistopathological changes resulting after the same reperfusion periods are given.

Regional changes of membrane phospholipid concentrations in rabbit spinal cord following brief repeated ischemic insults

Changes in the concentration of membrane-bound phospholipids following single (25-min) spinal cord ischemia and 3 h of reperfusion were determined. These were compared with the changes following brief repeated (8-, 8-, and 9-min) ischemia followed each time by reperfusion for 1 h, or the same periods of ischemia followed by 8 h, 8 h, and 24 h of reperfusion, respectively. Phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), and sphingomyelin (SM) were assayed in regions of the spinal cord of the rabbit, including gray matter, white matter, dorsal horns, intermediate zone, and ventral horns. The brief repeated ischemia with 1-h reperfusions produced more extensive degradation of phospholipids in almost all regions compared with the equivalent time of ischemia (25 min) in a single period. After a lengthy reperfusion after repeated ischemia, the phospholipids were resynthesized with the exception of the phosphatidylinositol in the gray matter. The resynthesis was most pronounced in the dorsal horns and in the white matter.

[Changes in phospholipids after repeated induced sublethal spinal cord ischemia in rabbits]

BACKGROUND

Degradation of membrane bound phospholipids in CNS during ischaemia begins with extreme rapidity. Sublethal ischaemia influences ischaemic tolerance in the affected neurons and is stressful enough to induce neuronal changes such as postischaemic hypoperfusion, transient suppression of protein synthesis and induction of stress (HSP) proteins. It seems, that the nature of factors responsible for ischaemic tolerance may involve the activation of multiple different systems.

MAIN PURPOSE

The aim of this study was to investigate the changes of phospholipids in gray matter regions of spinal cord following sublethal ischaemia repeated in long intervals of reperfusion.

METHODS

Male rabbits, weight range 2.5-3.5 kg were used in the experiment. They were divided in following groups : 1. control animals; 2. animals subjected to 25 min ischaemia; 3. animals subjected to 25 min ischaemia and 3 h of reperfusion; 4. animals subjected to sublethal (8-8-9 min) ischaemia repeated in long-lasting (8-8-24 h) intervals of reperfusion. Phospholipids were separated by thin layer chromatography, lipidic phosphorus was assessed spectrophotometrically.

RESULTS

Sublethal ischaemia repeated in long-lasting intervals of reperfusion increased the concentration of phospholipids to control levels in all gray matter regions. The resynthesis in the dorsal horns, of PC and PE in the ventral horns and of PC in the intermediate zone.

CONCLUSIONS

An excessive renewal of phospholipids after sublethal ischaemia repeated in longer intervals of reperfusion was most pronounced in the eh dorsal horns of the spinal cord and can be the result of many defensive cellular mechanisms.

Lipid peroxidation and phospholipid composition in rat brain regions after ischemia and in early perfusion periods

Lipid peroxidation products (LPPs) and phospholipid composition were studied in a model of four-vessel occlusion in rats in homogenates of cortex, striatum and hippocampus after 30 min forebrain ischemia and following 1, 5, 10, 15, 30 and 180 min of recirculation. Major modification of LPPs was found after shorter reperfusion time, 5 min in hippocampus and 15 min in cortex and striatum when compared to control, while a slight decrease in the level of LPPs in the striatum and hippocampus was detected after longer (30 and 180 min) intervals. However, significant decrease was found in the homogenates of cortex. The results obtained from enhanced iron-dependent peroxidation in homogenates of frontal and occipital cortex indicated marked susceptibility to lipid peroxidation in the tissue subjected to 30 min ischemia and after 15 min of recirculation. The level of DG + PA was significantly higher during ischemia in the striatum, while increased hydrolysis of PI and DG + PA concentrations in the cortex, PI and PE levels in the striatum and PE and PS in the hippocampus after 30 min of ischemia were found. After 15 min of reperfusion considerably higher degradation of almost all phospholipids was found within all brain regions studied. The irreversibility of changes in PS, PE and SM was noted in the hippocampus after longer reperfusion periods. Our results indicate that the correlation between the lipid peroxidat ion product formation and phospholipid hydrolysis does exist, and, moreover, early reperfusion period seems to be highly critical in the development of ischemia-reperfusion induced neuronal damage.

Regional distribution of phospholipids and polyphosphatidyl inositides in the rabbit's spinal cord

The plasticity of the membrane phospholipids in general and stimulated phosphoinositides turnover in particular are the subjects in a variety of neural paradigms studying the molecular mechanisms of neuronal changes under normal and pathological conditions. The regional modifiability of phospholipids (SM, PC, PS, PI, PA + DG, PE), polyphosphatidylinositides (PI, PIP, PIP2) and diacylglycerol-dependent incorporation of CDP-choline into phosphatidylcholine in the gray matter, white matter, dorsal horns, intermediate zone and ventral horns of the rabbit's spinal cord was studied. We have found 1. a significant increase in the concentration of SM, PC, PS, DG + PA and PE in the white matter in comparison to the gray one, 2. the highest concentration of the outer membrane leaflet-bound phospholipids in the dorsal horns and the inner membrane phospholipids in the intermediate zone in comparison to the gray matter, 3. a substantial amount of labeled polyphosphatidylinositides (poly-PI(s)) in the spinal cord white matter with descending order PIP > PI > PIP2, 4. similar incorporation of myo-2-[3H]inositol into all poly-PI(s) in ventral horns and intermediate zone, but a different, lower incorporation into PI and PIP and higher into PIP2 in the dorsal horns, 5. higher diacylglycerol-dependent incorporation of CDP-choline into PC in the regionally undivided gray matter than in the white matter taken as a whole, 6. the high proportion of diacylglycerol-dependent incorporation of CDP-choline into PC in both the ventral and dorsal horns, whereas that in the intermediate zone remained low.

Neuroprotective effect of graded postischemic reoxygenation in spinal cord ischemia in the rabbit

Early ischemia/reperfusion-induced changes of four phospholipid compounds bound to the inner cell membrane leaflet, i.e., phosphatidic acid, inositol phospholipids, serine phospholipids, and ethanolamine plasmalogens, were studied in a model of spinal cord ischemia in the rabbit during normoxic and graded postischemic reoxygenation. Light and electron microscopic analysis after normoxic reoxygenation disclosed neuronal membrane argyrophilia of the interneuronal pool located in lamina VII of L4-L6 segments. The number of small neurons (10-25 microm in diameter) affected by somatodendritic argyrophilia was greatly reduced, and concomitantly the ultrastructure of the endoplasmic reticulum, mitochondria, and Golgi complexes remained almost undamaged when graded postischemic reoxygenation had been applied. A statistically significant increase of phosphatidylserine and ethanolamine plasmalogen levels, and a decrease of phosphatidic acid, were detected after a short-lasting graded postischemic reoxygenation. The formation of thiobarbituric acid-reactive substances was significantly reduced during 60 min of graded postischemic reoxygenation and remained close to control or ischemic levels. The present data indicate that graded postischemic reoxygenation, which is considered to be neuroprotective, can prevent neuronal argyrophilia and the development of reperfusion-induced alterations of organelles. Moreover, reoxygenation can positively modify ischemia-induced changes of some membrane-bound phospholipids.

Ischemia-reperfusion injury in the spinal cord of rabbits strongly enhances lipid peroxidation and modifies phospholipid profiles

The effect of spinal cord ischemia (10, 20, and 40 min) and post-ischemic reperfusion (10, 30, and 60 min) on lipid peroxidation and phospholipids was investigated. Spinal cord ischemia was accompanied by lipolytic processes with significant changes in concentration of lipid peroxidation products (LPP). Reestablishment of the blood supply after 10 min ischemia was accompanied by significantly increased levels of thiobarbituric acid reactive substances (TBA-RS) after 10 and 30 min of reperfusion. Following 20 and 40 min ischemia a significant increase was observed at all reperfusion periods. Ischemia itself significantly reduced the concentration of phosphatidyl inositol (IP), phosphatidyl ethanolamine (EP) and ethanolamine plasmalogens (Epls). Significant changes were observed in concentration of phosphatidyl serine (SP) too, but only after 20 and 40 min of ischemia. The concentration of phosphatidic acid (PA) was significantly reduced only after 10 min of ischemia. The onset of reperfusion after ischemia was accompanied by a diverse pattern of changes in PA, IP, Epls and SP, while the concentration of EP remained at the above mentioned ischemic intervals.

Effect of stobadine on lipid peroxidation and phospholipids in rabbit spinal cord after ischaemia

Stobadine, a drug with the pyridoindol structure, was compared with thiopental and pentobarbital for its ability to inhibit stimulated peroxidation in homogenates of spinal cord in vitro. The antioxidative capacity of the drug exceeded that of barbiturates more than 100-fold. Stobadine was also shown to inhibit the increase in formation of TBA-RS in homogenates of rabbit spinal cord, subjected to 20 min ischaemia, to the level comparable with controls. Administration of the drug (6 mg kg-1) to animals 5 min before 20 min ischaemia had no effect on level of lipid peroxidation products in the spinal cord; however, it slowed down stimulated Fe(2+)-dependent peroxidation after in vitro incubation of the homogenates and increased the concentration of phosphatidylserine and ethanolamine plasmalogens, as compared with non-treated animals. Application of stobadine 2 min before the release of an aortic occlusion increased the antiradical capacity in homogenates of spinal cord and revealed an ameliorating effect on the composition of phospholipids.

Effect of liposomes on lipid peroxidation and total phospholipids in rabbit ischemic spinal cord model

The effect of spinal cord ischemia (induced by abdominal aorta ligation for 20 minutes) on lipid peroxidation and TPL composition was investigated and discussed in our previous articles. It is known, that partially reduced species of oxygen can be formed under aerobic conditions. For that reason, the effect of ligation release for 60 minutes was observed in experimental animals treated with the selected liposomes. Administration of CP, (CP+SA) and (CP+Chol) liposomes applied 30 minutes before 20 minutes ischemia revealed an ameliorating effect on in vivo and in vitro Fe-dependent peroxidation manifested by TBA-RS accumulation. Combined use of (CP+SA) liposomes with lipophylic form of stobadine (DP 1031) was not more effective. Application of CP liposomes directly before the ligation release slightly increased the antiradical capacity in spinal cord homogenates comparing with not-treated animals. Accumulation of TBA-RS was accompanied by TPL degradation during recirculation period but values of TPL after liposomal treatment were unaffected.

Effect of partial ischemia on phospholipids and postischemic lipid peroxidation in rabbit spinal cord

Rabbit spinal cord, subjected to severe partial ischemia induced by abdominal aorta ligation tightly below the renal arteries, was analyzed for phospholipid composition and levels of lipid peroxidation products after 10, 20, and 40 min of the insult. Under conditions when spinal cord blood flow was decreased below 5% of control, concentrations of inositol and ethanolamine phospholipids were decreased by 30% and 10%, respectively. Phosphatidic acid concentration was also altered during ischemia. No accumulation of thiobarbituric acid reactive substances (TBA-RS), conjugated dienes and fluorescent lipid soluble material was found throughout the ischemic period. Pattern of TBA-RS, conjugated diene, and fluorophore formation during postischemic in vitro incubation without and with a peroxidation couple (Fe2+, ascorbic acid) showed increased susceptibility to postischemic lipid peroxidation in tissues after 20 and 40 min of ischemia.

Effects of incomplete ischemia and subsequent recirculation on free palmitate, stearate, oleate and arachidonate levels in lumbar and cervical spinal cord of rabbit

The effect of severe incomplete ischemia, induced by abdominal aorta ligation for 40 minutes, and subsequent recirculation for one and four days on accumulation of free fatty acids was studies in the lumbar and cervical part of rabbit spinal cord. Changes in free fatty acid levels were determined separately in gracile fascicle (Fg), dorsal part (Dp, without Fg) and ventral part (Vp) of both spinal cord regions. In lumbar spinal cord increases in free fatty acid levels, especially that of arachidonate, were observed in Fg, Dp and Vp a the end of the ischemic period. During recirculation all values were similar to nonischemic controls. In cervical spinal cord a slight increase in free fatty acid levels was found in Fg after four days of recirculation, and in Dp arachidonate and stearate levels were most markedly elevated after one day of recirculation. No changes at any interval were found in Vp of cervical spinal cord. The present results indicate that the experimental insult induced typical ischemic injury to spinal cord tissue demonstrated by fatty acid liberation from membrane lipids. This injury may affect neurotransmission and other processes and free fatty acids themselves impair tissue metabolism (inhibition of oxidative phosphorylation, edema precipitation, synthesis of eicosanoids) and thus restrict the possibilities to enhance recovery in the recirculation period.