Jan Arvidsson

Cell loss in lumbar dorsal root ganglia and transganglionic degeneration after sciatic nerve resection in the rat

The effects of sciatic nerve resection on lumbar dorsal root ganglion cells and their central branches have been studied in the adult rat. A quantitative analysis of the lumbar dorsal root ganglia indicated a 15-30% cell loss on the operated side. Argyrophilia indicating transganglionic degeneration was observed in Fink-Heimer stained sections from the lumbar spinal cord and the brainstem. The areas of degeneration argyrophilia were mainly located in the medial part of the ipsilateral L2-L6 dorsal horn laminae I-IV, the tract of Lissauer, the dorsal funiculus and the gracile nucleus. A few degenerating fibers could also be observed in the ipsilateral dorsal horn laminae V and VI, and in the ipsilateral ventral horn as well as in the contralateral dorsal horn and the gracile nucleus. The results confirm and extend previous findings at other levels and in other species. This suggests that cell loss and transganglionic degeneration may be general phenomena affecting a substantial proportion of primary sensory neurons following peripheral nerve injury.

Nerve cell degeneration and death in the trigeminal ganglion of the adult rat following peripheral nerve transection.

SummaryTrigeminal ganglia of normal rats and of adult rats subjected to unilateral transection of the infraorbital nerve were studied by light and electron microscopy. Counts of ganglion cells in ganglia on operated and unoperated sides were made following long postoperative survival times. The ultrastructural changes in ganglia of the operated side were studied from 3 to 70 days postoperatively. The quantitative observations show that a considerable loss of ganglion cells takes place on the operated side. The ultrastructural observations demonstrate the occurrence of ganglion cell degeneration, nerve fibre degeneration and phagocytosis by satellite and Schwann cells. The results are compatible with the view that degeneration of trigeminal afferents in the brain stem following lesions of peripheral trigeminal nerve branches is related to retrograde degeneration of trigeminal ganglion cells.

The reaction of primary sensory neurons to peripheral nerve injury with particular emphasis on transganglionic changes

This paper reviews light- and electron microscopic, histochemical and physiological evidence which demonstrate that peripheral nerve injury in mammals is followed by profound structural and functional changes in the central terminals of the affected primary sensory neurons. Available evidence indicates that at least some of these so-called transganglionic changes are the result of ganglion cell degeneration and death, although other mechanisms are probably in effect as well. Existing data suggest that this ganglion cell death does not effect all types of ganglion cells equally, but do not permit a clearcut answer to the question of which kinds of ganglion cells are affected more than others. Results from studies with microtubule inhibitors and antibodies to nerve growth factor are compatible with the notion that depletion of retrogradely transported trophic factors is involved in the production of certain transganglionic changes. This issue needs further examination, however. Physiological studies indicate marked alterations in certain primary afferent synaptic connections after peripheral nerve lesions. So far, these changes have not been satisfactorily correlated with the structural changes induced by similar lesions. Further studies on the structural and functional response of primary sensory neurons to peripheral nerve injury are likely to contribute to the understanding of the frequent failure to regain normal sensory functions after peripheral nerve lesions in man, as well as of the basic aspects of lesion-induced changes in general in the peripheral and central nervous system.

Transganglionic degeneration in trigeminal primary sensory neurons.

In 16 kittens either the frontal or the inferior alveolar nerve was transected and in 17 adult rats either the supraorbital, the infraorbital or the mental nerve was divided. The postoperative survival periods were kept at 3-28 days for the kittens and 15-26 days for the rats. Sections from the caudal brain stem and the upper part of the cervical cord were impregnated according to the Fink-Heimer method, procedure II. In the kittens degeneration was found after the 8th postoperative day ipsilaterally in both the spinal and main sensory trigeminal nuclei and the spinal trigeminal tract. In the rats degeneration was found in all cases in the same ipsilateral structures as in the kittens. The amount of degeneration was relatively great in the rats, whereas it was very modest in the kittens. A somatotopical pattern was found for the degeneration both within the spinal and the main sensory nuclei. It was in agreement with what has been found in earlier studies, where other techniques have been used. By a comparison with the results of a previous study on the trigeminal nerve in the rat, where partial lesions of the ganglia had been made, it was found that the degeneration in the present study did not cover the whole area receiving primary trigeminal afferents. Possible explanations for this are discussed.

Comprehensive immunofluorescence and lectin binding analysis of vibrissal follicle sinus complex innervation in the mystacial pad of the rat.

The innervation of the vibrissal follicle sinus complexes (FSCs) in the mystacial pad of the rat was examined by lectin binding histofluorescence with the B subunit of Griffonia simplicifolia (GSA) and by immunofluorescence with a wide variety of antibodies for neuronal related structural proteins, enzymes, and peptides. Only anti‐protein gene product 9.5 labeled all sets of innervation. Several types of mechanoreceptors were distributed to specific different targets by medium to large caliber myelinated axons. All were positive for 200 kDa neurofilament subunit, peripherin, and carbonic anhydrase. Their endings expressed synaptophysin. Labeling for the 160 kDa neurofilament subunit, calbindin, and parvalbumin varied. Anti‐Schwann cell protein S100 was completely co‐extensive with the axons, terminal arbors, and endings of the mechanoreceptor afferents including Merkel innervation. At least 15 different sets of unmyelinated innervation were evident based upon distribution and labeling characteristics. They consisted of four basic types: 1) peptidergic; 2) GSA binding; 3) peptidergic and GSA binding; and 4) nonpeptidergic and GSA negative (peptide‐/GSA‐). Previous studies had not revealed that several major sets of unmyelinated innervation were peptide‐/GSA‐. The unmyelinated innervation had detectable peripherin but not 160 kDa or 200 kDa neurofilament subunits. GSA‐positive axons uniquely lacked anti‐S100 immunoreactivity. The dense circumferentially oriented unmyelinated innervation of the inner conical body contained major sets of peptide‐/GSA‐ and GSA innervation as well as a smaller peptidergic GSA component. A small contingent of sympathetic and possibly parasympathetic innervation was affiliated with microvasculature in the FSCs. This study confirms and refutes some previous hypotheses about biochemical and morphological relationships between peripheral innervation and sensory ganglion cells. J. Comp. Neurol. 385:149–184, 1997.

Transganglionic transport of horseradish peroxidase in primary sensory neurons

The cut end of the sciatic nerve of adult rats was exposed to horseradish peroxidase (HRP). The rats were allowed to survive for 12 h--5 days. 12--18 h postoperatively small dorsal root ganglion cells more heavily labeled than large ones. After 48--72 h more large cells were intensely labeled. From 18 h onwards large amounts of HRP labeling was observed ipsilaterally in the superficial laminae of the dorsal horn, from 48 h also in deeper laminae and in the gracile nucleus. The heavy labeling clearly indicates the potential of the present approach for mapping purposes. The findings also indicate that short postoperative survivals can be used for rather selective marking of small cells and fibers.

A quantitative analysis of the microglial cell reaction in central primary sensory projection territories following peripheral nerve injury in the adult rat.

The time course of the microglial cell reaction in central nervous system primary sensory projection territories has been examined following peripheral nerve injury in the adult rat using qualitative and quantitative analysis of immunoreactivity with the monoclonal antibody OX-42, which recognises the complement receptor CR3. The regions examined included the gracile nucleus, the column of Clarke and the spinal cord dorsal horn (superficial and deep laminae separately) after unilateral sciatic nerve transection, and the spinal trigeminal nucleus following unilateral infraorbital nerve transection. In all territories examined a qualitative increase in OX-42 immunoreactivity was observed 24 h postlesion. Further, quantitative analysis revealed an exponential development of the OX-42 immunoreactivity, with a peak at one week postlesion, thereafter showing a slow exponential decline. Our results show that the signal (or signals) that induces the microglial cell response in primary sensory projection territories is rapid in comparison to previously described central degenerative changes following peripheral nerve lesions (transganglionic degeneration). These findings are compatible with the hypothesis that activated microglia play a pathogenetic role in the development of transganglionic degeneration.

Transganglionic transport of wheat germ agglutinin-HRP and choleragenoid-HRP in rat trigeminal primary sensory neurons

Horseradish peroxidase conjugates of either the lectin wheat germ agglutinin (WGA-HRP) or choleragenoid (B-HRP) have been shown to be sensitive neuroanatomical tracers. In the present study a comparison was made between these two conjugates as transganglionic tracers in trigeminal primary sensory neurons following injection into the rat mystacial vibrissae skin. Differences between the two tracers were observed in the labeling of cell bodies in the trigeminal ganglion. Injection of WGA-HRP resulted in labeling of predominantly small cell bodies, whereas B-HRP gave rise to labeling of somewhat larger cell bodies. By increasing the concentration of the injected WGA-HRP solution the number of labeled cells increased substantially, while a corresponding increase in the concentration of B-HRP resulted in a relatively small increase in the number of labeled cells. WGA-HRP injection resulted in labeling of primary afferents mainly in the substantia gelatinosa of the trigeminal subnucleus caudalis. When the concentration of the injected WGA-HRP solution was increased, labeling was also observed in the marginal and magnocellular zones. Following B-HRP injection, labeling was only observed in the magnocellular zone and innermost part of the substantia gelatinosa. This general pattern of labeling was the same when the concentration of the B-HRP solution was increased.

Ultrastructural changes of the central scalloped (C1) primary afferent endings of synaptic glomeruli in the substantia gelatinosa Rolandi of the rat after peripheral neurotomy

SummaryFine structural changes were observed in the dark scalloped central C1 terminals of type I synaptic glomeruli in spinal cord segments C6–C7 of the rat 3 days after cutting the three main forelimb nerves. Twenty-six per cent of the C1 terminals occurring on the ipsilateral side showed a lighter appearance due to a decrease in the number of synaptic vesicles. The number of synaptic vesicles per unit section area was only 42% of that present in normal C1 terminals on the contralateral side. The number of synaptic contacts of C1 terminals with the profiles surrounding them in each glomerulus was diminished and glial envelopment was increased to 15% of C1 terminal contour. Up to day 12, vesicle and synaptic losses were gradually aggravated and glial apposition was increased, but no obvious signs of glial engulfment were observed. From day 3 to day 12, altered C1 terminals increased in number, while those that appeared normal decreased. The latter had disappeared at day 12 and the altered ones at day 15, and from this stage type I glomeruli were no longer present on the treated side. The lack of electron-dense degenerative bouton changes characteristic of Wallerian degeneration offers an explanation for the lack of or minimal amount of argyrophilic structures which has been found consistently in the substantia gelatinosa during transganglionic degeneration. The gradual decay of the C1 terminals raises the question of their fate. Future studies with the use of a stable marker might provide an answer.

Comprehensive immunofluorescence and lectin binding analysis of intervibrissal fur innervation in the mystacial pad of the rat

The innervation of the intervibrissal fur in the mystacial pad of the rat and mouse was examined by immunofluorescence with a wide variety of antibodies for neuronal related structural proteins, enzymes, and peptides as well as for lectin binding histofluorescence with Griffonia simplicifolia (GSA). Anti‐protein gene product 9.5 (PGP) immunofluorescence labeled all sets of axons and endings. The innervation in the upper dermis and epidermis was distributed through a four tiered dermal plexus. From deep to superficial, the second tier was the source of all apparent myelinated mechanorceptors, the third tier of nearly all the peptidergic and GSA binding innervation, and the fourth tier of nonpeptidergic GSA negative innervation (peptide‐/GSA‐). Three types of mechanoreceptors—Merkel, transverse lanceolate, and longitudinal lanceolate endings—innervated guard hair follicles. All had similar labeling characteristics for 160 kDa and 200 kDa neurofilament subunits, peripherin, carbonic anhydrase, synaptophysin, and S100. Palisades of longitudinal lanceolate endings were part of piloneural complexes along circumferentially oriented sets of transverse lanceolate endings, peptidergic free nerve endings (FNEs), and peptide‐/GSA‐ FNEs. The longitudinal lanceolate endings were the only mechanoreceptors in the mystacial pad that had detectable calcitonin gene‐related peptide. The epidermis contained four types of unmyelinated endings: simple free nerve endings (FNEs), penicillate endings, cluster endings and bush endings. Only the simple FNEs were clearly peptidergic. Virtually all others were peptide‐/GSA‐. Each bush ending was actually an intermingled cluster of endings formed by several unmyelinated axons and occasionally an Aδ axon. In contrast to the other unmyelinated innervation to the epidermis, bush endings labeled with an antibody against the Schwann cell protein S100. The necks and mouths of follicles, as well as superficial vasculature, were innervated by a mixture of unmyelinated peptidergic and/or GSA labeled sensory and sympathetic axons. Small presumptive sweat glands were innervated by three sets of peptidergic axons of which one was immunoreactive for somatostatin. Potential functions of the various sets of innervation are discussed. J. Comp. Neurol. 385:185–206, 1997.