Differentiation state determines neural effects on microvascular endothelial cells

Growing evidence indicates that nerves and capillaries interact paracrinely in uninjured skin and cutaneous wounds. Although mature neurons are the predominant neural cell in the skin, neural progenitor cells have also been detected in uninjured adult skin. The aim of this study was to characterize differential paracrine effects of neural progenitor cells and mature sensory neurons on dermal microvascular endothelial cells. Our results suggest that neural progenitor cells and mature sensory neurons have unique secretory profiles and distinct effects on dermal microvascular endothelial cell proliferation, migration, and nitric oxide production. Neural progenitor cells and dorsal root ganglion neurons secrete different proteins related to angiogenesis. Specific to neural progenitor cells were dipeptidyl peptidase-4, IGFBP-2, pentraxin-3, serpin f1, TIMP-1, TIMP-4 and VEGF. In contrast, endostatin, FGF-1, MCP-1 and thrombospondin-2 were specific to dorsal root ganglion neurons. Microvascular endothelial cell proliferation was inhibited by dorsal root ganglion neurons but unaffected by neural progenitor cells. In contrast, microvascular endothelial cell migration in a scratch wound assay was inhibited by neural progenitor cells and unaffected by dorsal root ganglion neurons. In addition, nitric oxide production by microvascular endothelial cells was increased by dorsal root ganglion neurons but unaffected by neural progenitor cells.     

Expression of gp130 and leukaemia inhibitory factor receptor subunits in adult rat sensory neurones: regulation by nerve injury

Members of the interleukin-6 (IL-6) family of cytokines have been implicated as major mediators of the response of the adult nervous system to injury. The basis for an interaction of IL-6 cytokines with adult sensory neurones has been established by analysing the levels and distribution of the two signal-transducing receptor subunits, glycoprotein 130 (gp130) and leukaemia inhibitory factor receptor (LIFR), in the dorsal root ganglion (DRG) of male adult rats before and following nerve injury. All sensory neurones express gp130-immunoreactivity (IR) in the cytoplasm and on the plasma membrane. Levels of gp130 and its intracellular distribution remained unchanged up to 14 days following sciatic nerve axotomy. LIFR-IR was largely absent from the cytoplasm and plasma membrane of sensory neurones, but confined almost exclusively to the nuclear compartment. However, following axotomy, punctate cytoplasmic LIFR-IR was detected which persisted up to 28 days following axotomy. The expression of cytoplasmic LIFR 2 days post-axotomy was proportionally greater in a subset of small diameter sensory neurones which expressed either the sensory neuropeptide CGRP or the cell surface marker isolectin B4. The coexpression of gp130 and LIFR in the same intracellular compartment following axotomy conveys potential responsiveness of injured sensory neurones to members of the IL-6 family of cytokines.     

Oxidized galectin-1 promotes axonal regeneration in peripheral nerves but does not possess lectin properties.

Galectin-1 has recently been identified as a factor that regulates initial axonal growth in peripheral nerves after axotomy. Although galectin-1 is a well-known beta-galactoside-binding lectin, its potential to promote axonal regeneration as a lectin has not been reported. It is essential that the process of initial repair in peripheral nerves after axotomy is well clarified. We therefore undertook to investigate the relation between the structure and axonal regeneration-promoting activity of galectin-1. Recombinant human galectin-1 secreted into the culture supernatant of transfected COS1 cells (rhGAL-1/COS1) was purified under nonreducing conditions and subjected to structural analysis. Mass spectrometric analysis of peptide fragments from rhGAL-1/COS1 revealed that the secreted protein exists as an oxidized form containing three intramolecular disulfide bonds (Cys2-Cys130, Cys16-Cys88 and Cys42-Cys60). Recombinant human galectin-1 (rhGAL-1) and a galectin-1 mutant in which all six cysteine residues were replaced by serine (CSGAL-1) were expressed in and purified from Escherichia coli for further analysis; the purified rhGAL-1 was subjected to oxidation, which induced the same pattern of disulfide linkages as that observed in rhGAL-1/COS1. Oxidized rhGAL-1 enhanced axonal regeneration from the transected nerve sites of adult rat dorsal root ganglion explants with associated nerve stumps (5.0-5000 pg. mL-1), but it lacked lectin activity. In contrast, CSGAL-1 induced hemagglutination of rabbit erythrocytes but lacked axonal regeneration-promoting activity. These results indicate that galectin-1 promotes axonal regeneration only in the oxidized form containing three intramolecular disulfide bonds, not in the reduced form which exhibits lectin activity.     

Developmental potentialities in the nonneuronal population of quail sensory ganglia

Sensory ganglia taken from quail embryos at E4 to E7 were back-transplanted into the vagal neural crest migration pathway (i.e., at the level of somites 1 to 6) of 8- to 10-somite stage chick embryos. Three types of sensory ganglia were used: (i) proximal ganglia of cranial sensory nerves IX and X forming the jugular-superior ganglionic complex, whose neurons and nonneuronal cells both arise from the neural crest; (ii) distal ganglia of the same nerves, i.e., the petrosal and nodose ganglia in which the neurons originate from epibranchial placodes and the nonneuronal cells from the neural crest; (iii) dorsal root ganglia taken in the truncal region between the fore- and hindlimb levels. The question raised was whether cells from the graft would be able to yield the neural crest derivatives normally arising from the hindbrain and vagal crest, such as carotid body type I and II cells, enteric ganglia, Schwann cells located along the local nerves, and the nonneuronal contingent of cells in the host nodose ganglion. All the grafted cephalic ganglia provided the host with the complete array of these cell types. In contrast, grafted dorsal root ganglion cells gave rise only to carotid body type I and II cells, to the nonneuronal cells of the nodose ganglion, and to Schwann cells; the ganglion-derived cells did not invade the gut and therefore failed to contribute to the host's enteric neuronal system. Coculture on the chorioallantoic membrane of aneural chick gut directly associated with quail sensory ganglia essentially reinforced these results. These data demonstrate that the capacity of peripheral ganglia to provide enteric plexuses varies according to the level of the neuraxis from which they originate.     

Calretinin-immunoreactive nerves in the uterus, pelvic autonomic ganglia, lumbosacral dorsal root ganglia and lumbosacral spinal cord

Nerves containing the calcium-binding protein calretinin have been reported in several organs but not in female reproductive organs and associated ganglia. This study was undertaken to determine if nerves associated with the uterus contain calretinin and the source(s) of calretinin-synthesizing nerves in the rat (are they sensory, efferent, or both?). Calretinin-immunoreactive nerves were present in the uterine horns and cervix where they were associated with arteries, uterine smooth muscle, glands, and the epithelium. Calretinin-immunoreactive terminals were apposed to neurons in the paracervical ganglia; in addition, some postganglionic neurons in this ganglion were calretinin positive. Calretinin perikarya were present in the lumbosacral dorsal root ganglia, no-dose ganglia, and lumbosacral spinal cord. Retrograde axonal tracing, utilizing Fluorogold injected into the uterus or paracervical parasympathetic ganglia, revealed calretinin-positive/Fluorogold-labeled neurons in the dorsal root and nodose ganglia. Also, capsaicin treatment substantially reduced the calretinin-positive fibers in the uterus and pelvic ganglia, thus indicating the sensory nature of these fibers. The presence of calretinin immunoreactivity identifies a subset of nerves that are involved in innervation of the pelvic viscera and have origins from lumbosacral dorsal root ganglia and vagal nodose ganglia. Though the exact function of calretinin in these nerves is not currently known, calretinin is likely to play a role in calcium regulation and their function.     

In vitro and in vivo characterization of a novel semaphorin 3A inhibitor,SM-216289 or xanthofulvin

SM-216289 (xanthofulvin) isolated from the fermentation broth of a fungal strain, Penicillium sp. SPF-3059, was identified as a strong semaphorin 3A (Sema3A) inhibitor. Sema3A-induced growth cone collapse of dorsal root ganglion neurons in vitro was completely abolished in the presence of SM-216289 at levels less than 2 mum (IC50 = 0.16 mum). When dorsal root ganglion explants were co-cultured with Sema3A-producing COS7 cells in a collagen gel matrix, SM-216289 enabled neurites to grow toward the COS7 cells. SM-216289 diminished the binding of Sema3A to its receptor neuropilin-1 in vitro, suggesting a direct interference of receptor-ligand association. Moreover, our data suggest that SM-216289 interacted with Sema3A directly and blocked the binding of Sema3A to its receptor. We examined the efficacy of SM-216289 in vivo using a rat olfactory nerve axotomy model, in which strong Sema3A induction has been reported around regenerating axons. The regeneration of olfactory nerves was significantly accelerated by a local administration of SM-216289 in the lesion site, suggesting the involvement of Sema3A in neural regeneration as an inhibitory factor. SM-216289 is an excellent molecular probe to investigate the function of Sema3A, in vitro and in vivo, and may be useful for the treatment of traumatic neural injuries.     

Administration of Hsp70 in vivo inhibits motor and sensory neuron degeneration

The induction of heat shock proteins (Hsps) serves not only as a marker for cellular stress but also as a promoter of cell survival, which is especially important in the nervous system. We examined the regulation of the constitutive and stress-induced 70-kD Hsps (Hsc70 and Hsp70, respectively) after sciatic nerve (SN) axotomy in the neonatal mouse. Additionally, the prevention of axotomy-induced SN cell death by administration of several preparations of exogenous Hsc70 and Hsp70 was tested. Immunohistochemistry and Western blot analyses showed that endogenous levels of Hsc70 and Hsp70 did not increase significantly in lumbar motor neurons or dorsal root ganglion sensory neurons up to 24 hours after axotomy. When a variety of Hsc70 and Hsp70 preparations at doses ranging from 5 to 75 microg were applied to the SN stump after axotomy, the survival of both motor and sensory neurons was significantly improved. Thus, it appears that motor and sensory neurons in the neonatal mouse do not initiate a typical Hsp70 response after traumatic injury and that administration of exogenous Hsc/Hsp70 can remedy that deficit and reduce the subsequent loss of neurons by apoptosis.     

Axotomy-induced apoptosis in adult rat primary sensory neurons

Neuronal death following unilateral axotomy of a sensory nerve has long been inferred from neuronal counts of dorsal root ganglion neurons, using the contralateral ganglia as a control. The counting methods used usually involved the counting of neuronal nucleoli and made assumptions about them which could conceivably be flawed. Very few studies have used direct observations of dying or degenerating neurons to address questions concerning the duration of the period of neuronal death or the mechanisms involved in this process. Here we describe a morphological, morphometric and histochemical study into the nature and duration of sensory neuron death following transection and ligation of the sciatic nerve at mid-thigh level in the adult rat. We show that at least some of this neuronal loss occurs by apoptosis as defined by morphological criteria and in situ end-labelling of damaged DNA. Absolute numbers of apoptotic neurons were counted from serial paraffin sections of ganglia and estimates of neuronal numbers obtained by disector analysis at 1, 2, 3 and 6 months after axotomy. Using this approach we show that axotomy-induced apoptosis begins at around 1 week and continues up to at least 6 months after axotomy.     

Delta/Notch signaling promotes formation of zebrafish neural crest by repressing Neurogenin 1 function

In zebrafish, cells at the lateral edge of the neural plate become Rohon-Beard primary sensory neurons or neural crest. Delta/Notch signaling is required for neural crest formation. ngn1 is expressed in primary neurons; inhibiting Ngn1 activity prevents Rohon-Beard cell formation but not formation of other primary neurons. Reducing Ngn1 activity in embryos lacking Delta/Notch signaling restores neural crest formation, indicating Delta/Notch signaling inhibits neurogenesis without actively promoting neural crest. Ngn1 activity is also required for later development of dorsal root ganglion sensory neurons; however, Rohon-Beard neurons and dorsal root ganglion neurons are not necessarily derived from the same precursor cell. We propose that temporally distinct episodes of Ngn1 activity in the same precursor population specify these two different types of sensory neurons.     

Peripheral choline acetyltransferase in rat skin demonstrated by immunohistochemistry

Conventional choline acetyltransferase immunohistochemistry has been used widely for visualizing central cholinergic neurons and fibers but not often for labeling peripheral structures, probably because of their poor staining. The recent identification of the peripheral type of choline acetyltransferase (pChAT) has enabled the clear immunohistochemical detection of many known peripheral cholinergic elements. Here, we report the presence of pChAT-immunoreactive nerve fibers in rat skin. Intensely stained nerve fibers were distributed in association with eccrine sweat glands, blood vessels, hair follicles and portions just beneath the epidermis. These results suggest that pChAT-positive nerves participate in the sympathetic cholinergic innervation of eccrine sweat glands. Moreover, pChAT also appears to play a role in cutaneous sensory nerve endings. These findings are supported by the presence of many pChAT-positive neuronal cells in the sympathetic ganglion and dorsal root ganglion. Thus, pChAT immunohistochemistry should provide a novel and unique tool for studying cholinergic nerves in the skin.     

Dopamine as trace amine in the dorsal root ganglia

It has been shown that in the chick dorsal root ganglion (DRG) about 8% of neurons, belonging to both the A and B classes of sensory neurons exhibit a clear dopamine immunoreactivity. In the present study are reported the results of measurements, by mean of HPLC-electrochemical detection (HPLC-ED), of DA and of the DA metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the rat DRG and their central nerves. Very low levels of DA, about 10 folds lower than the levels found in the dorsal horn of the spinal cord, were found in the DRG. However the levels of DOPAC and HVA were approximately equivalent to the levels found in the cord. The immunocytochemical study performed in parallel has shown that some dopaminergic-immunoreactive fibers in the DRG are located around the blood vessels. Few dopamine-immunoreactive sensory neurons were identified in the DRG and immunoreactive fibers, not linked to blood vessels, were identified in the dorsal root nerves. The present work indicates that there is a dopaminergic innervation of the blood vessels in the rat DRG but that dopamine may also be, as in the chick, a transmitter of primary afferent fibers.     

The cranial sensory ganglia in culture: Differences in the response of placode-derived and neural crest-derived neurons to nerve growth factor

Explants of cranial sensory ganglia and dorsal root ganglia from embryonic chicks of 4 to 16 days incubation (E4 to E16) were grown for 24 hr in collagen gels with and without nerve growth factor (NGF) in the culture medium. NGF elicited marked neurite outgrowth from neural crest-derived explants, i.e., dorsal root ganglia, the dorsomedial part of the trigeminal ganglion, and the jugular ganglion. This response was first observed in ganglia taken from E6 embryos, reached a maximum between E8 and E11, and gradually declined through E16. Explants in which the neurons were of placodal origin varied in their response to NGF. There was negligible neurite outgrowth from explants of the ventrolateral part of the trigeminal ganglion and the vestibular ganglion grown in the presence of NGF. The geniculate, petrosal, and nodose ganglia exhibited an early moderate response to NGF. This was first evident in ganglia taken from E5 embryos, reached a maximum by E6, and declined through later ages, becoming negligible by E13. Dissociated neuron-enriched cultures of vestibular, petrosal, jugular, and dorsal root ganglia were established from embryos taken at E6 and E9. At both ages NGF elicited neurite outgrowth from a substantial proportion of neural crest-derived neurons (jugular and dorsal root ganglia) but did not promote the growth of placode-derived neurons (vestibular and petrosal ganglia). Our findings demonstrate a marked difference in the response of neural crest and placode-derived sensory neurones to NGF. The data from dissociated neuron-enriched cultures suggest that NGF promotes survival and growth of sensory ganglionic neurons of neural crest origin but not of placodal origin. The data from explant cultures suggest that NGF promotes neurite outgrowth from placodal neurons of the geniculate, petrosal, and nodose ganglia early in their ontogeny. However, we argue that this fibre outgrowth emanates not from the placodal neurons but from neural crest-derived cells which normally give rise only to satellite cells of these ganglia.     

Development of a neuronal pressure sensor

Neuronal sensory systems are capable of performing very complex signal processing functions. Reconstruction of such sensory systems in vitro should enable whole-cell biological sensors to be generated that possess inherent signal processing capabilities. In this paper, the results of preliminary investigations to produce a mechanosensory neuronal network are presented. An in vitro network of rat dorsal root ganglion neurons has been produced on a microelectrode plate revealing an interesting rhythmical pattern of spontaneous discharges. This periodic activity has been shown to be disrupted following the application of a static pressure to the cell culture. These results indicate that neuronal networks represent a practical system that may be used for the development of intelligent, whole-cell, biological sensors.     

Spontaneous activity in afferent and efferent fibers after chronic axotomy: response to potassium channel blockade

Distally propagating spontaneous impulses in acutely and chronically cut rat saphenous nerve were examined to determine (1) the origin(s) of the activity, (2) the fiber types involved, and (3) whether the activity was affected by potassium channel blockade. Under deep pentobarbital anesthesia, six male Sprague-Dawley rats underwent L3 cauda equina section, then unilateral saphenous axotomy. The nerve was then dissected into 30-50 microfilaments and surveyed for spontaneous activity using a modification of the microfilament recording method. Afterward, the nerve was cut back, and a potassium channel blocking agent (gallamine) was administered. The axonal activity was once again surveyed in the same fashion. Twenty-eight rats underwent unilateral saphenous axotomy 1-8 weeks prior to similar recordings, and the neuroma was excised just before microfilament dissection. Spontaneous discharges in these preparations originated from three foci: (1) antidromic activity from in-continuity dorsal root ganglia (DRG), (2) orthodromic activity from sympathetic neurons, and (3) antidromic activation of dichotomizing afferent axons in the peripheral nerve. There was significantly more antidromic activity from DRG in rats with prior axotomies than in control animals (t = 2.38; p less than 0.025), and gallamine produced a significant increase in DRG activity in the chronically lesioned nerve (t = 2.43; p less than 0.005), but not in acutely lesioned controls. However, most of the spontaneous activity in these preparations was from sympathetic efferents. This activity was decreased significantly by chronic axotomy (t = 2.635; p less than 0.01), and it was not affected by potassium channel blockade with gallamine. In two microfilaments, spontaneous antidromic action potentials were observed in conjunction with a clear receptive field on blood vessels in the nearby fascia. Both of these presumably dichotomized axons were found in acutely cut nerve, thus were not the result of retrograde sprouting from a neuroma. It was concluded that (1) chronic axotomy of sensory afferents produced ectopic activity in their respective DRG, (2) gallamine administration increased spontaneous activity from DRG in chronically axotomized rats, (3) ongoing sympathetic efferent activity in rat saphenous nerve was decreased by distal axotomy for up to 8 weeks, and (4) rare branched sensory afferents occasionally exhibit spontaneous activity.     

Intrathecally delivered glial cell line-derived neurotrophic factor produces electrically evoked release of somatostatin in the dorsal horn of the spinal cord

Glial cell line-derived neurotrophic factor (GDNF) is a trophic factor with an established role in sensory neuron development. More recently it has also been shown to support adult sensory neuron survival and exert a neuroprotective effect on damaged sensory neurons. Some adult small-sized dorsal root ganglion (DRG) cells that are GDNF-sensitive sensory neurons express the inhibitory peptide somatostatin (SOM). Thus, we tested the hypothesis that prolonged GDNF administration would regulate SOM expression in sensory neuron cell bodies in the dorsal root ganglia (DRG) and activity-induced release of SOM from axon terminals in the dorsal horn. Continuous intrathecal delivery of GDNF for 11-13 days significantly increased the number of small DRG cells that expressed SOM. Furthermore, GDNF treatment evoked SOM release in the isolated dorsal horn following electrical stimulation of the dorsal roots that was otherwise undetectable in control rats. Conversely capsaicin-induced release of SOM (EC(50) 50 nM) was not modified by GDNF treatment. These results show that GDNF can regulate central synaptic function in SOM-containing sensory neurons.     

Distribution and changes with age of nitric oxide synthase-immunoreactive nerves of the rat urinary bladder, ureter and in lumbosacral sensory neurons

In the distal parts of the urinary tract, nerves containing nitric oxide (NO) are either postganglionic parasympathetic nerves, with cell bodies in the major pelvic ganglia, or sensory nerves with cell bodies in the lumbosacral dorsal root ganglia. We have used indirect immunohistochemical techniques to examine the distribution and regional variation of nerves immunoreactive for neuronal nitric oxide synthase (NOS) in the urinary bladder, distal ureter and in neurons in lumbosacral dorsal root ganglia (L1-L2 & L6-S1) of young adult (3 months) and aged (24 months) male rats. Semi-quantitative estimations of nerve densities were made of NOS fibres innervating the dome, body and base of the urinary bladder and distal ureter. Quantitative studies were also used to examine the effects of age on the percentage of dorsal root ganglion neurons immunoreactive for NOS. The dome and the body regions, in both age groups, contained no NOS-immunoreactive axons. The bladder base and distal ureter in young adults showed sparse to moderate numbers of fibres immunoreactive to NOS within the urothelium and in the subepithelium and muscle coat. In the aged rat there were slight reductions in the densities of NOS-immunoreactive nerves in all three regions. In the lumbosacral dorsal root ganglia, the percentage of NOS-immunoreactive neuronal profiles showed a significant reduction from 4.6 +/- 0.2% in young adult to 2.7 +/- 0.2% (means +/- S.E.M) in aged rats. These findings suggest that the effects of NO on the bladder and distal ureteric musculature and also its expression in dorsal root ganglion neurons are affected in aged rats and that the micturition reflex may be perturbed as a result.     

Egg laying inAplysia

1. Central pathways for bag cell activation were identified by examining the frequency of spontaneous egg laying episodes in animals with central connective lesions. Bilateral lesions of the cerebropleural (but not the cerebropedal) connectives abolished spontaneous egg laying. In contrast, bilateral lesions of all cerebral ganglion peripheral nerves did not abolish spontaneous egg laying, suggesting that sensory input to the cerebral ganglion is not necessary for activating the bag cells. 2. Backfilling either pleuroabdominal connective labelled cell bodies in the cerebral ganglia (via the ipsilateral cerebropleural connective) that could project to the bag cells. Focal extracellular stimulation of these stained clusters activated the bag cells in isolated brains. 3. Central pathways for initiating egg laying behaviors were identified by selectively eliciting bag cell discharges in animals with central connective lesions. Bilateral lesions of the cerebropedal (but not the cerebropleural) connectives completely abolished elicited egg laying behaviors. 4. Pathways for motor output during rhythmic head and neck movements were identified by eliciting bag cell discharges in animals with peripheral nerve lesions. Bilateral lesions of the four tegumentary nerves in combination with the anterior pedal nerve completely abolished elicited egg laying behaviors, indicating that these nerves are necessary for normal motor output. A normal pattern of egg laying behaviors occurred when the four tegumentary and the anterior pedal nerves were left intact and all other pedal ganglion nerves were lesioned bilaterally, indicating that these nerves are also sufficient for normal motor output.(ABSTRACT TRUNCATED AT 250 WORDS)     

The Plasticity of the DRG Neurons Belonging to Different Subpopulations After Dorsal Rhizotomy

SUMMARY 1. The plasticity of sensory neurons following the injury to their axons is very important for prognosis of recovery of afferent fibers with different modality. It is evident that the response of dorsal root ganglion (DRG) neurons after peripheral axotomy is different depending on the deficiency in neurotrophic factors from peripheral region. The loss of cells appears earlier and is more severe in B-cells (small, dark cells with unmyelinated axons) than in A-cells (large, light cells with myelinated axons).2. We studied using immunohistochemical methods the response of DRG neurons to dorsal rhizotomy and combined injury of central and peripheral neuronal processes. A quantitative analysis of DRG neurons tagged by the selective markers isolectin B4 (IB4) and the heavy molecular component of the neurofilament triplet (NF200) antibody, selective for subpopulations of small and large/medium DRG neurons, respectively, was performed after dorsal rhizotomy, peripheral axotomy, and their combination.3. The number of NF200⁺-neurons is reduced substantially after both dorsal rhizotomy and peripheral axotomy, while the decrease of IB4⁺-neurons is observed only in combined injury, i.e., dorsal rhizotomy accompanied with sciatic nerve injury.4. Our results show that distinct subpopulations of DRG neurons respond differently to the injury of their central processes. The number of NF200⁺-neurons decreases to greater degree following dorsal rhizotomy in comparison to IB4⁺-neurons.     

The dorsal root reflex in isolated mammalian spinal cord

1. The dorsal root reflex has been investigated in an isolated preparation of adult mammalian spinal cord. 2. Both evoked and spontaneous activity can be recorded from the cord in the dorsal spinal roots. 3. The spontaneous activity has a characteristic pattern of firing in bursts of action potentials. Spontaneous and evoked activity are optimum at temperatures between 25 and 27 degrees C; little activity can be detected above 35 degrees C. 4. The spontaneous dorsal root activity has been shown to be correlated with negative potentials in the dorsal horn of the cord, and intracellular recordings made from primary afferent fibres have shown spontaneous primary afferent depolarizations (PAD) which underlie the generation of the spontaneous dorsal root activity. 5. The evoked dorsal root reflex has been shown to spread up to 16 spinal segments both rostrally and caudally from the stimulated dorsal root, and to the contralateral side of the cord. 6. The spontaneous dorsal root activity in widely separated segments has been shown by cross-correlation analysis to be linked both ipsi- and contra-laterally. 7. The significance of such a widespread system for the generation of PAD is discussed.     

An ultrastructural classification of the neuronal cell bodies of the rat dorsal root ganglion using zinc iodide-osmium impregnation

Summary Zinc iodide-osmium (ZIO) impregnation of rat dorsal root ganglia differentially stained various elements in the neuronal cells, particularly their Golgi bodies. On the basis of this differential ZIO staining dorsal root ganglion neurones have been classified into seven types. The ultrastructure of these is described and the numbers of each type in the L4 dorsal root ganglion have been determined. Prolonged nerve stimulation did not change the relative numbers of the different cell types suggesting that none of the differences between cell types represents differences in their state of activity. The possibility is discussed that differences in morphology may reflect differences in neurotransmitter function.I.R.D. is supported by the Medical Research Council; P.K. thanks the Mental Health Trust for a project grant