Neonatal infraorbital nerve transection in the rat: comparison of effects on substance P immunoreactive primary afferents and those recognized by the lectin Bandierea simplicifolia-I

Consequences of neurite transection in vitro

In order to quantify degenerative and regenerative changes and analyze the contribution of multiple factors to the outcome after neurite transection, we cultured adult mouse dorsal root ganglion neurons, and with a precise laser beam, we transected the nerve fibers they extended. Cell preparations were continuously visualized for 24 h with time-lapse microscopy. More distal cuts caused a more elongated field of degeneration, while thicker neurites degenerated faster than thinner ones. Transected neurites degenerated more if the uncut neurites of the same neuron simultaneously degenerated. If any of these uncut processes regenerated, the transected neurites underwent less degeneration. Regeneration of neurites was limited to distal cuts. Unipolar neurons had shorter regeneration than multipolar ones. Branching slowed the regenerative process, while simultaneous degeneration of uncut neurites increased it. Proximal lesions, small neuronal size, and extensive and rapid neurite degeneration were predictive of death of an injured neuron, which typically displayed necrotic rather than apoptotic form. In conclusion, this in vitro model proved useful in unmasking many new aspects and correlates of mechanically-induced neurite injury.

A5-positive primary sensory neurons are nonpermissive for productive infection with herpes simplex virus 1 in vitro

Herpes simplex viruses 1 and 2 (HSV-1 and HSV-2) establish latency and express the latency-associated transcript (LAT) preferentially in different murine sensory neuron populations, with most HSV-1 LAT expression in A5(+) neurons and most HSV-2 LAT expression in KH10(+) neurons. To study the mechanisms regulating the establishment of HSV latency in specific subtypes of neurons, cultured dissociated adult murine trigeminal ganglion (TG) neurons were assessed for relative permissiveness for productive infection. In contrast to that for neonatal TG, the relative distribution of A5(+) and KH10(+) neurons in cultured adult TG was similar to that seen in vivo. Productive infection with HSV was restricted, and only 45% of cultured neurons could be productively infected with either HSV-1 or HSV-2. A5(+) neurons supported productive infection with HSV-2 but were selectively nonpermissive for productive infection with HSV-1, a phenomenon that was not due to restricted viral entry or DNA uncoating, since HSV-1 expressing β-galactosidase under the control of the neurofilament promoter was detected in ∼90% of cultured neurons, with no preference for any neuronal subtype. Infection with HSV-1 reporter viruses expressing enhanced green fluorescent protein (EGFP) from immediate early (IE), early, and late gene promoters indicated that the block to productive infection occurred before IE gene expression. Trichostatin A treatment of quiescently infected neurons induced productive infection preferentially from non-A5(+) neurons, demonstrating that the nonpermissive neuronal subtype is also nonpermissive for reactivation. Thus, HSV-1 is capable of entering the majority of sensory neurons in vitro; productive infection occurs within a subset of these neurons; and this differential distribution of productive infection is determined at or before the expression of the viral IE genes.

Impaired axonal regeneration by isolectin B4-binding dorsal root ganglion neurons in vitro

The subpopulation of dorsal root ganglion (DRG) neurons recognized by Griffonia simplicifolia isolectin B4 (IB4) differ from other neurons by expressing receptors for glial cell line-derived neurotrophic factor (GDNF) rather than neurotrophins. Additionally, IB4-labeled neurons do not express the laminin receptor, alpha7-integrin (Gardiner et al., 2005), necessary for optimal axonal regeneration in the peripheral nervous system. In cultures of dissociated DRG neurons of adult mice on laminin, robust spontaneous neurite outgrowth from IB4-negative neurons occurs and is strongly enhanced by previous axotomy. In contrast, IB4-labeled neurons show little neurite outgrowth and do not express GAP 43, even after axotomy or culture with GDNF. Moreover, growth of their axons through collagen gels is impaired compared with other DRG neurons. To determine whether the sparse neurite outgrowth of IB4-labeled neurons is attributable to lack of integrin expression, DRG cultures were infected with a herpes simplex 1 vector encoding alpha7-integrin, but its forced expression failed to promote neurite outgrowth in either IB4-labeled or other DRG neurons or in cultured adult retinal ganglion cells. Forced coexpression of both alpha7-integrin and GAP 43 also failed to promote neurite outgrowth in IB4-labeled neurons. In addition, cultured sciatic nerve segments were found to release much lower levels of GDNF, demonstrated by ELISA, than nerve growth factor. These findings together with their impaired intrinsic axonal regeneration capacity may contribute to the known vulnerability of the IB4-labeled population of DRG neurons to peripheral nerve injury.

Tooth extraction-induced internalization of the substance P receptor in trigeminal nucleus and spinal cord neurons: imaging the neurochemistry of dental pain

Although pains arising from the craniofacial complex can be severe and debilitating, relatively little is known about the peripheral and central mechanisms that generate and maintain orofacial pain. To better understand the neurons in the trigeminal complex and spinal cord that are activated following nociceptive stimuli to the orofacial complex, we examined substance P (SP) induced internalization of substance P receptors (SPR) in neurons following dental extraction in the rat. Unilateral gingival reflection or surgical extraction of a rat maxillary incisor or molar was performed and tissues harvested at various time points post-extraction. Immunohistochemical analysis of brainstem and cervical spinal cord sections was performed using an anti-SPR antibody and confocal imaging. Both the number and location of neurons showing SPR internalization was dependent on the location and extent of tissue injury. Whereas extraction of the incisor induced internalization of SPR in neurons bilaterally in nucleus caudalis and the spinal cord, extraction of the molar induced strictly unilateral internalization of SPR-expressing neurons in the same brain structures. Minor tissue injury (retraction of the gingiva) activated SPR neurons located in lamina I whereas more extensive and severe tissue injury (incisor or molar extraction) induced extensive SPR internalization in neurons located in both laminae I and III-V. The rostrocaudal extent of the SPR internalization was also correlated with the extent of tissue injury. Thus, following relatively minor tissue injury (gingival reflection) neurons showing SPR internalization were confined to the nucleus caudalis while procedures which cause greater tissue injury (incisor or molar extraction), neurons showing SPR internalization extended from the interpolaris/caudalis transition zone through the C7 spinal level. Defining the population of neurons activated in orofacial pain and whether analgesics modify the activation of these neurons should provide insight into the mechanisms that generate and maintain acute and chronic orofacial pain.

Changes in neuropeptide expression in the trigeminal ganglion following inferior alveolar nerve section in the ferret

Changes in neuropeptide expression in afferent nerve fibres may play a role in the persistent sensory abnormalities that can be experienced following trigeminal nerve injuries. We have therefore studied changes in the expression of the neuropeptides substance P, calcitonin gene-related peptide, enkephalin, galanin, neuropeptide Y and vasoactive intestinal polypeptide in the trigeminal ganglion following peripheral nerve injury. In anaesthetised adult female ferrets, the left inferior alveolar nerve was sectioned and recovery allowed for three days, three weeks or 12 weeks prior to perfusion-fixation. During a second procedure, one week prior to perfusion, the inferior alveolar nerve was exposed and an injection made central to the injury site using a mixture of 4 % Fluorogold and 4 % isolectin B4 conjugated to horseradish peroxidase to identify cell bodies with axons in the inferior alveolar nerve and cells with unmyelinated axons within this population, respectively. Control animals received tracer injection alone. After harvesting the tissue, sagittal sections were taken from both the right and left ganglia and immunohistochemical staining was used to reveal the presence of peptides and isolectin B4-horseradish peroxidase tracer. Within the Fluorogold-labelled population, cell counts revealed a significant reduction in the proportion of substance P-containing cells at three days (P = 0.0025), three weeks (P = 0.0094) and three months (P = 0.0149) after nerve section, and a significant reduction in the proportion of calcitonin gene-related peptide-containing cells at three days (P = 0.0003) and three weeks (P = 0.007). No significant changes were seen in the expression of the other peptides, or at other time periods. A significant reduction in the number of isolectin B4-horseradish peroxidase-positive cells (with unmyelinated axons) was seen at three days (P = 0.0025), three weeks (P = 0.0074) and three months after the injury (P = 0.0133). These results demonstrate a significant reduction in the expression of some neuropeptides in the early stages after inferior alveolar nerve section. Some of the results differ markedly from those reported previously in other systems, and may be related to the specific nerve studied, species variations or differences between spinal and trigeminal nerves.

GDNF rescues nonpeptidergic unmyelinated primary afferents in streptozotocin-treated diabetic mice

Sensory deficits induced by diabetes commonly affect small unmyelinated peptidergic and nonpeptidergic sensory neurons. The peptidergic population responds to nerve growth factor (NGF), while the nonpeptidergic DRG neurons postnatally switch their dependency from NGF to glial cell line-derived neurotrophic factor (GDNF). Recent studies have demonstrated that deficient NGF support of peptidergic nociceptors is involved in problems with small-fiber diabetic neuropathy. To determine if nonpeptidergic GDNF-responsive neurons are similarly affected by hyperglycemia, diabetes was induced in mice using streptozotocin (STZ). Four weeks following diabetes induction, staining of axon terminals of nonpeptidergic unmyelinated neurons labeled with the isolectin IB4 or enzyme activity for thiamine monophosphatase (TMP) was reduced in lamina IIi of the lumbar dorsal horn, particularly in the medial region which receives distal sciatic afferents. In contrast, NGF-responsive CGRP-immunoreactive (ir) axons showed no or only a slight decrease in spinal terminations. Insulin treatment in diabetic mice failed to improve deficits in IB4/TMP central afferents. To test whether GDNF or NGF could restore spinal deficits in nonpeptidergic afferents, STZ-treated mice were treated intrathecally for 2 weeks with NGF or GDNF. NGF administration enhanced CGRP-ir staining but failed to improve IB4/TMP projections. GDNF treatment had no effect on CGRP-ir projections but restored TMP labeling in lamina IIi. Our results demonstrate that nonpeptidergic unmyelinated sensory neurons are vulnerable to diabetes and that GDNF administration can selectively reverse deficits caused by diabetes in the IB4/TMP subpopulation.

Building blocks of pain: the regulation of key molecules in spinal sensory neurones during development and following peripheral axotomy

The pathways, synapses and molecules involved in pain processing in the newborn are not only required to trigger repair and recuperation but are also involved in the process of forming a mature nervous system. Sensory neurons in the dorsal root ganglion and dorsal horn express a phenomenal array of molecules which contribute to their structural and functional characteristics and many of these are developmentally regulated both pre- and postnatally. In order to understand nociceptive signalling and pain in the neonate we need a clear picture of that regulation. This review concentrates on the changing expression of selected key molecules, receptors and channels in the embryo, neonate and adult, which both characterise the sensory neuron and contribute to its response to painful stimuli in normal and pathological conditions.

IB4-binding DRG neurons switch from NGF to GDNF dependence in early postnatal life

We have tested the role of glial cell line-derived neurotrophic factor (GDNF) in regulating a group of putatively nociceptive dorsal root ganglion (DRG) neurons that do not express calcitonin gene-related peptide (CGRP) and that downregulate the nerve growth factor (NGF) receptor tyrosine kinase, TrkA, after birth. We show that mRNA and protein for the GDNF receptor tyrosine kinase, Ret, are expressed in the DRG in patterns that differ markedly from those of any of the neurotrophin receptors. Most strikingly, a population of small neurons initiates expression of Ret between embryonic day 15.5 and postnatal day 7.5 and maintains Ret expression into adulthood. These Ret-expressing small neurons are selectively labeled by the lectin IB4 and project to lamina IIi of the dorsal horn. Ret-expressing neurons also express the glycosyl-phosphatidyl inositol-linked (GPI-linked) GDNF binding component GDNFR-alpha and retrogradely transport 125I-GDNF, indicating the presence of a biologically active GDNF receptor complex. In vitro, GDNF supports the survival of small neurons that express Ret and bind IB4 while failing to support the survival of neurons expressing TrkA and CGRP. Together, our findings suggest that IB4-binding neurons switch from dependence on NGF in embryonic life to dependence on GDNF in postnatal life and are likely regulated by GDNF in maturity.

Neonatal damage to the rat's infraorbital nerve upregulates both galanin and neuropeptide Y in individual vibrissae-related primary afferent axons

Previous studies in adult animals have suggested that the peptides galanin and neuropeptide Y (NPY) may be upregulated in the same primary afferent neurons after peripheral axotomy. The present study was undertaken to determine whether such upregulation occurred in vibrissae-related primary afferent neurons and their axons after damage to the infraorbital nerve [ION; the trigeminal (V) branch that innervates the vibrissae follicles]. Double-labelling experiments demonstrated that approximately 75% of axotomized V ganglion cells and the central arbors of vibrissae-related primary afferents expressed both galanin and NPY after perinatal, but not adult, nerve damage. However, additional experiments demonstrated that the sensitive periods for lesion-induced upregulation of the two peptides and the period over which they were expressed after neonatal ION transection differed substantially. Staining for both peptides was increased after ION damage on P-0 through P-14, but only galanin staining was increased in vibrissae-related primary afferents after lesions on P-21. Galanin expression was elevated in vibrissae-related primary afferents in rats killed 3, 8, and 15 days after neonatal ION transection, while increased NPY was observed at only the middle time point. The lesion-induced increases in galanin and NPY in vibrissae-related ION primary afferents suggest that these peptides may modulate central V reorganization after such damage.

Sciatic nerve injury in the adult rat: comparison of effects on oligosaccharide, CGRP and GAP43 immunoreactivity in primary afferents following two types of trauma

Using immunocytochemical and morphometric techniques, the localisation of three neuronal oligosaccharide antigens (two lactoseries and one globoseries oligosaccharide) were studied in the spinal cord and dorsal root ganglia of adult rats following unilateral crushing or transection of the sciatic nerve. The expression of CGRP and GAP43 was also studied for comparison. We found that following transection of the nerve the expression of lactoseries oligosaccharides and CGRP was permanently depressed, whilst that of the globoseries antigen (SSEA4) was unaffected. However following crush trauma and subsequent regeneration after 2 months, only the expression of one lactoseries antigen, LA4 remained significantly depressed. Our results suggest that different subsets of sensory neurons vary in the rate of reaction to injury and that one subset of neurons expressing a lactoseries oligosaccharide antigen is particularly susceptible to axotomy-induced changes. Furthermore neurons expressing the globoseries oligosaccharide antigen SSEA4 appear to be relatively unaffected by peripheral axotomy.

Organization of primary afferent axons in the trigeminal sensory root and tract of the rat

A combination of immunocytochemical and electron microscopic methods were employed to assess the organization of the trigeminal (V) spinal tract in adult rats. Immunostaining was employed at the light microscopic level to selectively label large myelinated (by using antibodies against neurofilament protein) and small unmyelinated (by using antibodies against calcitonin gene-related peptide) primary afferents. In addition, the plant lectin Bandeiraea simplicifolia-I was employed to histochemically label small unmyelinated primary afferents. Results from these experiments indicated that larger myelinated axons were distributed throughout the cross-sectional extent of the V spinal tract (TrV), whereas smaller fibers were most numerous just below the pial surface. These results were confirmed with quantitative electron microscopy which demonstrated that the central portion of the V sensory root and TrV were composed primarily of larger myelinated fibers, whereas the periphery of the root and the portion of TrV just below the pial surface contained a higher percentage of smaller myelinated and unmyelinated axons. When considered together with results regarding the birthdates of neurochemically defined classes of V ganglion cells (White et al. [1994] J. Comp. Neurol. 350:397-411), these results suggest that TrV is laid down in a chronotopic fashion with the first axons forming its deeper portion and later arriving axons being added more superficially.

Birth dates and survival after axotomy of neurochemically defined subsets of trigeminal ganglion cells

Trigeminal (V) ganglion cells with different neurochemical phenotypes or different birth dates are affected differently by neonatal axonal transection. The aim of the present study was to determine if V ganglion cell birth date and neurochemical phenotype were correlated and if these two variables could be related to responses to neonatal axonal transection. Immunocytochemistry, histochemistry, and [3H]thymidine labelling were used to determine the birth dates of V ganglion cells recognized by antibodies directed against neurofilament protein (NF), calcitonin gene-related peptide (CGRP), and substance P (SP) and those that bound the lectin Bandierea simplicifolia-I (BS-I). All V ganglion cells were born between embryonic days (E-) 9.5 and 14.5. All ganglion cells were born between E-9.5 and E-14.5. In a normalized population (percentages normalized to equal 100%), over 90% of NF-positive V ganglion cells were born between E-10.5 and E-12.5. The majority of CGRP-positive and SP-positive ganglion cells (> 90%) were generated from E-13.5 to E-14.5 and E-12.5 through E-14.5, respectively. Almost 85% of BS-I-positive ganglion cells were generated on E-12.5 through E-14.5. Previous results and additional data from this study indicated that NF- and BS-I-positive ganglion cells are proportionally more likely to be lost after neonatal axotomy and that SP-positive cells are more likely to remain. The percentage of CGRP-positive cells in the V ganglion was not significantly altered by neonatal infraorbital nerve transection. Overall, these findings do not indicate a strong relationship between cell birth date and the probability of survival after neonatal axonal damage for all V ganglion cell phenotypes.

Long-term age-related consequences of forelimb damage upon expression of primary afferent phenotypes in the cervical dorsal horn

Rats that sustained forelimb removal on either embryonic day 16 (E-16) or the day of birth (P-0), or transection of the brachial plexus in adulthood, had sections through the cervical dorsal horn stained for galanin, calcitonin gene-related peptide (CGRP), or the plant lectin Bandieria simplicifolia-I (BS-I) 35-50 days after these lesions. The results of these experiments demonstrated age-related differences in the effects of peripheral nerve damage upon the distributions of each of these three primary afferent markers in the dorsal horn. Damage to the brachial plexus in adulthood caused a significant increase in the density of galanin immunoreactivity in the medial portion of layers I and II and the appearance of galanin immunoreactivity in layers III and IV of the cervical dorsal horn. Such lesions resulted in significant reductions in the density of CGRP immunoreactivity in layers I and II and of BS-I binding in lamina II. Forelimb removal on the day of birth resulted in no significant change in the density of galanin immunoreactivity in layers I and II, but in the appearance of galanin-immunoreactive fibers in layers III-V. Neonatal forelimb removal resulted in no significant change in the density of CGRP immunoreactivity in layers I and II, but in a significant reduction in the density of BS-I binding in the medial portion of lamina II. Removal of the forelimb on E-16 caused a significant increase in the density of galanin immunoreactivity in layers III-V, but had no significant effect on the density or distribution of either CGRP immunoreactivity or BS-I binding in the cervical dorsal horn. These results suggest that peripheral nerve damage at all ages may cause an up-regulation of galanin in a wider distribution of ganglion cell types than was previously thought to be the case, and that there are different sensitive periods for lesion-induced, long-term changes in the innervation of the dorsal horn by CGRP- and BS-I-positive primary afferent axons.

Evidence for survival of the central arbors of trigeminal primary afferents after peripheral neonatal axotomy: experiments with galanin immunocytochemistry and Di-I labelling

Studies employing axoplasmic transport techniques have suggested that the central arbors of vibrissae-related primary afferents are rapidly and permanently lost from the trigeminal (V) brainstem complex after transection of the intraorbital nerve (ION). The present study reexamined this issue using immunocytochemistry for galanin (GAL) and anterograde labelling with Di-I to evaluate V brainstem organization in rats that sustained damage to the ION or individual vibrissae follicles in infancy or adulthood. After adult nerve damage, GAL-positive fibers are increased in layers I and II of V subnucleus caudalis (SpC). This was apparent by 3 days after the lesion. In rats that sustained nerve damage at birth (P0), GAL immunoreactivity (IR) appeared throughout the V brainstem complex and had a patchy distribution similar to that of vibrissae-related V primary afferents in normal rats. Increased GAL-IR in rostral portions of the V brainstem complex was observed in rats that sustained ION damage as late as P14. Additional experiments in which nerve damage was followed by destruction of the V ganglion demonstrated that this GAL-IR was contained in primary afferents. Damage to single vibrissa follicles or to a row of follicles produced a single patch or row of GAL-IR terminals in the somatotopically appropriate portion of the ipsilateral V brainstem complex. Di-I labelling in neonatally nerve-damaged rats demonstrated that primary afferent axons filled the central territory normally innervated by this nerve and that their terminal distribution was patchy. These results suggest that the V ganglion cells that survive neonatal axotomy may retain somatotopically organized projections to the V brainstem complex for at least a limited postnatal period.

Transganglionic transport and binding of the isolectin B4 from Griffonia simplicifolia I in rat primary sensory neurons

The isolectin B4 from Griffonia simplicifolia I binds to a subpopulation of rat small-diameter dorsal root ganglion neurons, and to fibres and presumed terminals in laminae I-II of the spinal cord dorsal horn. In the present study we investigated B4 and B4 conjugated to horseradish peroxidase as potential transganglionic tracers of somatic primary afferent neurons after injection into a peripheral nerve. We also tried to identify the specific subpopulation of dorsal root ganglion neurons that bind and ganglion neurons that bind and transport B4. Following injection of B4 or B4-horseradish peroxidase into the sciatic nerve, labelled presumed terminals that reached peak labelling at two days were found exclusively in regions of the spinal cord gray matter known to receive unmyelinated primary afferent fibres. Almost all dorsal root ganglion cells that transported B4-horseradish peroxidase also bound B4. Cell counts showed that 51% of the dorsal root ganglion neurons were B4-positive and cell area measurements that these were all in the small size range. An extensive overlap was found between B4 and fluoride-resistant acid phosphatase (85%), and between B4 and calcitonin gene-related peptide (59%). Seventeen per cent of the B4-positive cells were substance P-immunoreactive and 9% were immunoreactive to somatostatin. Minimal overlap was seen between B4-positive cells and cells positive for RT97 (3%), a selective marker of primary afferent neurons with myelinated axons. All somatostatin-immunoreactive cells and almost all (95%) of the fluoride-resistant acid phosphatase-positive cells were contained within the B4-positive population. This comprised also 58% of the cells immunoreactive to calcitonin gene-related peptide and 42% of those immunoreactive to substance P. The results obtained show that B4 binds to a subpopulation of unmyelinated primary afferent neurons, and that B4 and B4-horseradish peroxidase can be used as selective transganglionic tracers of this specific cell subpopulation.

Neonatal infraorbital nerve damage and the development of eating behavior in the rat

It has been previously shown that bilateral infraorbital nerve (ION) transection in adult rats has little effect upon body weight regulation or eating behavior. However, in neonatal mouse, unilateral ION cut produces a profound decrease in body weight, beginning around the time of weaning. To help clarify the role of the ION in the development and sensorimotor control of eating solid food in rodents, the present experiment examined the effects of unilateral, neonatal ION transection in rats, upon body weight regulation and post-weaning eating behaviors. Comparison of normal and lesioned groups of rats, up to postnatal day (PND) 61, revealed no significant difference in mean adjusted (for sex) body weight. In addition, no significant differences were detected between the groups on post-weaning (PND 26 to PND 61) measures of mean adjusted (for weight) food intake, responsiveness to food, biting ability or inefficiency of mandibulation. At the end of the experiment, the effectiveness of the lesion was histologically evaluated. A significant 48.5% mean reduction in the cross-sectional area of the ophthalmic-maxillary portion of the trigeminal ganglion was observed on the lesioned side, relative to the intact side. There appears to be a differential influence of unilateral, neonatal ION cut upon eating in rat and mouse.

Quantitative analysis of central terminal projections of visceral and somatic unmyelinated (C) primary afferent fibers in the guinea pig

In guinea pigs, intracellular labeling of the dorsal root ganglion (DRG) cells with Phaseolus vulgaris-leucoagglutinin (PHA-L) was used to demonstrate the central projections of somatic and visceral afferent C-fibers. The terminations of the afferent fibers were analyzed qualitatively and quantitatively with the aid of camera lucida drawings. Terminal branches of C-fibers of both somatic and visceral origin were, in general, distributed in accord with the organization of the neuropil in lamina of the spinal cord. Terminal boutons arranged from longitudinally coursing fibers were distributed in lamina I, while boutons in lamina II were scattered in an apparent random fashion. The synaptic enlargements were counted in gray matter of the spinal dorsal horn and measured on each terminal branch of a fiber. All synaptic boutons (over one thousand) of somatic fibers were found in the superficial dorsal horn (laminae I and II). More than 60% of the synaptic enlargements of the visceral afferents also were localized superficially (lamina I and adjacent dorsal funiculus) while 10-20% of the visceral enlargements appeared in deeper layers of the spinal cord. Boutons of somatic C-fibers were larger than those of visceral origin. Quantitative data of the unmyelinated afferent fibers are discussed in the context of the sensory functions of myelinated afferent fibers.

Selective sparing of later-born ganglion cells after neonatal transection of the infraorbital nerve

A combination of [3H]thymidine labelling and retrograde tracing with either horseradish peroxidase (HRP) or true blue (TB) was used to determine whether V primary afferent neurons born on different embryonic (E) days were differentially susceptible to neonatal transection of the infraorbital nerve (ION). In one experiment, rat fetuses were exposed to [3H]thymidine on E-8.5, 9.5, 10.5, 11.5, 12.5, 13.5, 14.5, or 15.5, the left infraorbital nerve (ION) was transected on the day of birth, and both the regenerate and intact IONs were labelled with HRP when the animals reached adulthood. The percentage of HRP labelled cells that were also heavily labelled by [3H]thymidine was calculated for both the intact ganglion and that ipsilateral to the damaged nerve for each animal. A consistently higher percentage of double labelled cells on the lesioned rather than on the intact side for a given E-day was taken as an indication that cells born on the day in question had an increased probability of survival relative to the entire population of V ganglion cells that contributed axons to the ION. Cells born late in gestation on E-12.5 through 14.5 were significantly more likely than early born (E-9.5 through 11.5) cells to survive neonatal axotomy. In a second experiment, fetuses were exposed to [3H]thymidine on either E-9.5, E-10.5, or E-14.5, the vibrissa pads on both sides of the face were injected with TB within 6 hours of birth, and the ION was transected 6-8 hours later.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective labelling of primary sensory afferent terminals in lamina II of the dorsal horn by injection of Bandeiraea simplicifolia isolectin B4 into peripheral nerves

The I-B4 isolectin from Bandeiraea simplicifolia exhibits specific binding to a subpopulation of rat dorsal root ganglion neurons of small diameter which terminate in the substantia gelatinosa of the dorsal horn. Recent double-labelling experiments in the rat have demonstrated that only primary afferents which innervate the skin are recognized by the I-B4 lectin [Plenderleith and Snow (1993) Neurosci. Lett. (in press)]. As the I-B4 lectin appears to bind selectively to a subset of small-diameter primary afferents with cutaneous peripheral projections, we sought to determine whether it could be used as a transganglionic tracer which selectively labels the spinal terminations of cutaneous afferents in superficial dorsal horn. We now report that the I-B4-horseradish peroxidase conjugate labels synaptic terminals in lamina II of the dorsal horn following the injection of the conjugate into the sciatic and saphenous nerves in the rat. Electron-microscopic examination of the dorsal horn revealed many examples of labelled synaptic terminals and unmyelinated axons, but in no cases was label observed in myelinated axons. No label was observed outside of the substantia gelatinosa; thus the I-B4 isolectin is unique among lectins used for transganglionic tracing in that it does not retrogradely label motoneurons. These results, together with previous studies of lectin binding properties of primary sensory afferents, suggest that injection of I-B4 conjugates into peripheral nerves enables the visualization of the central terminations of cutaneous C-fibres. Transganglionic labelling with the I-B4 isolectin from Bandeiraea simplicifolia should facilitate further examination of synaptic relationships of nociceptive cutaneous afferents in the superficial dorsal horn.

Neonatal sciatic nerve section results in thiamine monophosphate but not substance P or calcitonin gene-related peptide depletion from the terminal field in the dorsal horn of the rat: the role of collateral sprouting

The expression of substance P, calcitonin gene-related peptide (CGRP) and thiamine monophosphatase in the sciatic nerve terminal field of the lumbar dorsal horn of the rat was examined following neonatal sciatic nerve section and ligation. The total terminal field from L3 to L5 was mapped from semi-serial sections on the treated side and compared to equivalent maps on the contralateral intact side. To obtain a detailed time course of events, data were obtained 4, 7, 10, 15-20 and 40-60 days after sciatic nerve section. At 4-7 days thiamine monophosphate was depleted from the cut nerve terminals resulting in a gap in dorsal horn thiamine monophosphate stain similar to that seen after adult nerve section. In contrast, substance P and CGRP-containing terminals showed only a transient fall in expression in the first week following nerve section and then staining was no different from that seen on the control side. The depletion of peptides normally observed after adult nerve section did not occur. This phenomenon was only observed if the sciatic nerve was cut at birth. Nerve section at 10 days of age resulted in the same pattern of peptide depletion as is observed in the adult. A week after neonatal sciatic nerve section, thiamine monophosphate-containing nerve terminals from nearby intact nerves begin to sprout into the sciatic nerve territory in the dorsal horn. This, together with some recovery of thiamine monophosphate from the remaining sciatic terminals themselves, results in a slow filling in of the gap in the thiamine monophosphate stain. Resection of the cut sciatic nerve, together with adjacent intact nerves, re-establishes the depletion. Substance P and CGRP terminals from nearby intact nerves also sprout into the deafferented sciatic field and this can be demonstrated by the larger than normal area of depletion following section of these nerves when adult. Furthermore, resection of the neonatally cut sciatic nerve when adult also causes some depletion of substance P and CGRP within the sciatic field, indicating a degree of recovery or up-regulation of peptides in surviving cut afferents. However, even after resection of the cut sciatic nerve and nearby intact nerves, substance P and CGRP staining remained in the terminal region. We conclude that while central collateral sprouting does take place in both substance P and CGRP-containing afferents following peripheral nerve section, it cannot account for the lack of depletion of peptides observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Normal development and effects of neonatal infraorbital nerve damage upon the innervation of the trigeminal brainstem complex by primary afferent fibers containing calcitonin gene-related peptide

Immunocytochemistry was used to study the normal development and response to infraorbital nerve (ION) damage of the innervation of the trigeminal (V) brainstem complex by axons recognized by an antibody directed against calcitonin gene-related peptide (CGRP). CGRP-like immunoreactivity (CGRPLI) was present in axons that occupied the outer V spinal tract (TrV) at all levels of the V brainstem complex. Almost no fibers terminated within V nucleus principalis (PrV), but there was dense CGRPLI in the supratrigeminal nucleus. There was also very little CGRPLI within rostral V subnucleus oralis (SpO). However, in the caudal one-half of the nucleus, a dense elongated patch of immunoreactivity was consistently present just medial to TrV. Only occasional CGRP-positive axons could be seen within V subnucleus interpolaris (SpI), but the paratrigeminal nucleus contained dense immunoreactivity. Trigeminal subnucleus caudalis (SpC) also contained CGRPLI that was very dense in lamina I and the outer portion of lamina II. Scattered terminals were also present in layers III and IV and dense terminal clusters were in lamina V. CGRP-immunoreactive neurons were present in the V ganglion by embryonic (E-) day 16 and immunoreactive axons could be seen in the V brainstem complex on E-17. At birth, CGRP-positive axons in the V brainstem complex had achieved a distribution very similar to that in adult rats. The major difference between the patterns of labelling in neonates and adults was the presence of relatively large numbers of CGRP-positive fibers in ventral PrV and SpO of the former animals. The disappearance of these fibers was completed by the middle of the third postnatal week. Transection of the ION on the day of birth had little effect upon CGRP in SpO, SpI, and SpC, but it did result in an increase in CGRP-positive fibers in PrV ipsilateral to the damaged nerve. When considered together with previous findings, these results suggest that CGRP-positive axons express this peptide well after they have entered the V brainstem complex and that the central terminal field of these fibers is not substantially altered by a manipulation which results in the death of nearly 60% of all V primary afferent neurons.

The distribution of binding by isolectin I-B4 from Griffonia simplicifolia in the trigeminal ganglion and brainstem trigeminal nuclei in the rat

The distribution of binding by the isolectin I-B4 from Griffonia simplicifolia in the rat trigeminal system has been investigated. This lectin binds to a sub-population of small-diameter trigeminal ganglion neurons. Double-labelling studies revealed that this lectin bound to all the trigeminal ganglion neurons containing somatostatin, whereas it bound to less than 25% of those containing calcitonin gene-related peptide or substance P. In the brainstem this lectin gave terminal-like staining in only the sub-nucleus caudalis of the trigeminal nuclei. In this nucleus, staining was most dense in the inner part of lamina II. Morphometric studies suggest that this lectin and that from the soybean recognize the same population of cells. The relationship of this data to those obtained in other studies using markers binding to glycoconjugates with a terminal alpha-galactose is discussed.

Sub-populations of smaller diameter trigeminal primary afferent neurons defined by expression of calcitonin gene-related peptide and the cell surface oligosaccharide recognized by monoclonal antibody LA4

Immunocytochemistry has been used to examine the trigeminal ganglion cell populations in the rat which expresses calcitonin gene-related peptide (CGRP) and the oligosaccharide antigen recognized by the monoclonal antibody LA4. Calcitonin gene-related peptide and LA4 identify two large but mainly separate populations of trigeminal ganglion cells. Depending on the method of assessment used, CGRP-immunoreactive cells represent 29-37% of trigeminal ganglion cells while LA4 labels 26-40% of the cells, but with only 8% overlap between the two populations. Both CGRP and LA4 label predominantly small diameter cells (mean diameters 23 microns and 25 microns respectively) but with CGRP cells exhibiting a greater range of diameters than LA4 cells. The cell sizes indicate that small diameter CGRP-immunoreactive cells and most LA4-immunoreactive cells are likely to have unmyelinated axons, and together the two populations can account for the great majority of unmyelinated trigeminal primary afferent neurons. Centrally, CGRP and LA4 show distinct patterns of staining. Thus although both antigens are found in lamina II of subnucleus caudalis of the spinal trigeminal nucleus, CGRP is most abundant in lamina I and lamina II outer while LA4 immunoreactivity is most dense in lamina II inner. In addition CGRP-, but not LA4-, immunoreactive fibres occur in the magnocellular portion of caudalis. Previous studies have show that in rat dorsal root ganglion cells CGRP coexists with most other known neuropeptides and can therefore be used as a general marker for peptide-containing primary afferents. In contrast LA4 labels a cell population which is probably largely identical to that identified by the presence of fluoride resistant acid phosphatase or by the binding of lectins such as Griffonia simplicifolia isolectin B4 and this population does not contain neuropeptides. Our results thus provide further evidence that unmyelinated primary afferents can be divided into peptide and non-peptide containing subpopulations and that these populations innervate distinct regions of laminae I and II.

Birthdates of trigeminal ganglion cells contributing axons to the infraorbital nerve and specific vibrissal follicles in the rat

Prenatal labelling with [3H]-thymidine was combined with retrograde tracing techniques in adult rats to determine the birthdates of the trigeminal (V) ganglion cells that contributed axons to the infraorbital nerve (ION) and the generation of the subsets of ION cells that innervated specific vibrissae follicles (C-1 and C-5). The V ganglion cells contributing axons to the ION are born between embryonic (E-, E-0 = the day of conception) days 9.5 and 14.5. The percentages (normalized so that they total 100%) of the total V ganglion population born on E-9.5 through E-14.5 were 5.8, 25.7, 19.8, 23.4, 21.0, and 4.4%, respectively. The distribution of birthdates for the V ganglion cells that were retrogradely labelled from the ION closely matched that for the ganglion as a whole. All of these neurons were also born on E-9.5 through E-14.5, and the percentages born on each day were 6.3, 23.6, 18.1, 24.0, 23.6, and 4.4%. Finally, a similar distribution of birthdates was obtained for the V ganglion cells that were retrogradely labelled after injection of retrograde tracers into either the C-1 or C-5 vibrissae follicles. We were unable to detect any distinctive spatial distributions for either all V ganglion or ION cells born on a specific embryonic day. Furthermore, neurons with a given birthdate and that innervated a given follicle were distributed throughout the entire region containing all of the ganglion cells supplying the follicle in question. Therefore, it appears that the V ganglion cells contributing axons to the ION are born over the entire period of ganglion neurogenesis and further that the organization of the ION's innervation of the periphery is not a function of cell birthdate.