Central projections of C4-C8 dorsal root ganglia in the rat studied by anterograde transport of WGA-HRP

Morphological analysis for neuronal pathway from the hindbrain ependymocytes to the hypothalamic kisspeptin neurons

Hindbrain ependymocytes are postulated to have a glucose-sensing role in regulating gonadal functions. Previous studies have suggested that malnutrition-induced suppression of gonadotropin secretion is mediated by noradrenergic inputs from the A2 region in the solitary tract nucleus to the paraventricular nucleus (PVN), and by corticotropin-releasing hormone (CRH) release in the hypothalamus. However, no morphological evidence to indicate the neural pathway from the hindbrain ependymocytes to hypothalamic kisspeptin neurons, a center for reproductive function in mammals, currently exists. The present study aimed to examine the existence of a neuronal pathway from the hindbrain ependymocytes to kisspeptin neurons in the arcuate nucleus (ARC) and anteroventral periventricular nucleus (AVPV). To determine this, wheat-germ agglutinin (WGA), a trans-synaptic tracer, was injected into the fourth ventricle (4V) in heterozygous Kiss1-tandem dimer Tomato (tdTomato) rats, where kisspeptin neurons were visualized by tdTomato fluorescence. 48 h after the WGA injection, brain sections were taken from the forebrain, midbrain and hindbrain and subjected to double immunohistochemistry for WGA and dopamine β-hydroxylase (DBH) or CRH. WGA immunoreactivities were found in vimentin-immunopositive ependymocytes of the 4V and the central canal (CC), but not in the third ventricle. The WGA immunoreactivities were detected in some tdTomato-expressing cells in the ARC and AVPV, DBH-immunopositive cells in the A1–A7 noradrenergic nuclei, and CRH-immunopositive cells in the PVN. These results suggest that the hindbrain ependymocytes have neuronal connections with the kisspeptin neurons, most probably via hindbrain noradrenergic and CRH neurons to relay low energetic signals for regulation of reproduction.

A single GABA neuron receives contacts from myelinated primary afferents of two adjacent peripheral nerves. A possible role in neuropathic pain

GAD67-EGFP mice were used in a series of experiments to provide anatomical evidence for the role of the reduction in myelinated primary afferent input to GABA spinal neurons in the production of neuropathic pain following peripheral L5 nerve injury. First, we confirmed that L5 injury in these mice produced mechanical and thermal hyperalgesia in the ipsilateral foot. Second, we injected a mixture of cholera toxin subunit-B (CTb) and isolectin B4 (IB4) in the sciatic nerve to selectively label its myelinated and unmyelinated primary afferents. Results showed that primary afferents of sciatic nerve extend from L2-L6 spinal segments. Third, we determined the central terminations of myelinated primary afferents of L4 and L5 spinal nerves following CTb injection in either nerve. The myelinated primary afferents of both nerves terminated in the corresponding and two to three rostral spinal segments with some fibers descending to terminate in the segment caudal to the level at which they entered indicating an intermingling of their terminals at the dorsal horn of the spinal cord. Fourthly, we injected CTb in L5 nerve and CTb HRP-conjugate in L4 nerve. Confocal microscopy and subsequent image analyses showed that individual EGFP-labeled neurons in L4 segment receive myelinated primary afferent contacts from both L4 and L5 nerves. Eliminating inputs from L5 nerve following its injury would result in less involvement of spinal GABA neurons which would very likely initiate neuronal sensitization in L4 segment. This could lead to the development of hyperalgesia in response to the stimulation of the adjacent uninjured L4 nerve.

Longitudinal projections of primary afferents from the single dorsal root ganglion of the cervical or lumbosacral enlargements in chickens

Central projections originated from a single dorsal root ganglion (DRG) were studied in the chicken focusing on the rostrocaudal extension of primary afferents in each lamina by using anterograde labeling by lectin-HRP injection into either the 15th or the 24th DRG. In the injection into the 15th DRG, labeled fibers (LFs) were found in a wide rostrocaudal range of laminas IV (the spinal segment (SS) 1-20) and V (SS 4-18) and in a narrow range of other laminas. In the injection into the 24th DRG, LFs were distributed in a similar rostrocaudal range in all laminas except for laminas VIII and IX. LFs in laminas VIII and IX were restricted in the tracer injected segment. LFs in the lateral funiculus derived from both the enlargements projected into the rostral lamina III in addition to the lower medulla oblongata. There was little overlap in the extent of the primary terminal areas from both the enlargements.

Prooxidant-induced c-Src/nuclear factor kappa B-coupled signalling in sensory ganglia mediates cutaneous hyperalgesia

BACKGROUND

Persistent pain resulting from peripheral injury/inflammation is associated with altered sensitivity to cutaneous stimuli, which can manifest as hyperalgesia. The role of oxidant stress in the development, progression and maintenance of hyperalgesia is still not understood. Furthermore, there appears to be a relationship between c-Src kinase in the pain pathway and oxidative stress.

METHODS

We have used a novel prooxidant inflammatory pain model that involves potassium peroxychromate (PPC), a unique prooxidant that produces the same reactants as activated phagocytes. This model was used to investigate the role of oxidant-activated c-Src in mediating hyperalgesia. We compared the effects of PP2 (a Src family kinase inhibitor) and c-Src siRNA on behavioural hyperalgesia with sodium stibogluconate (SSG) (a non-receptor tyrosine phosphatase inhibitor) and AG 1478 (a receptor tyrosine kinase inhibitor).

RESULTS

PP2 and c-Src siRNA attenuated PPC-induced thermal hyperalgesia, while SSG enhanced it. AG 1478 had no effect. PP2 decreased the levels of IL-1β, c-Src/inhibitory kappa B kinase complex formed and prostaglandin E2 produced in the dorsal root ganglia (DRG) ipsilateral to the inflamed paw, while SSG increased the levels of these parameters. c-Src siRNA decreased Src expression and activity in the DRG ipsilateral to the inflamed paw.

CONCLUSIONS

These results confirm that prooxidant-activated c-Src plays a role in initiating and maintaining hyperalgesia by regulating a stimulus-response coupling between the inflamed tissue and the DRG in the pain pathway. Our data also suggest that oxidant-induced dysregulation of c-Src/nuclear factor kappa B coupling may contribute to our understanding of the transition from acute to chronic dysfunctional pain state seen in many human diseases.

Cutaneous and electrically evoked glutamate signaling in the adult rat somatosensory system

Glutamate neurotransmission plays critical roles in normal central nervous system (CNS) function, neurodegenerative diseases, and neurotrauma. We determined whether glutamate signaling could be evoked within the anesthetized normal adult rat CNS with clinically relevant peripheral stimulation and recorded (at >1Hz) with glutamate-sensitive, ceramic microelectrode arrays (MEAs). Basal glutamate levels and both forelimb cutaneous and electrical stimulation-evoked glutamate release were measured within the cuneate nucleus, a relay of the mammalian dorsal columns somatosensory system. The MEAs with triangular, sharp-point tips were more effective at tissue penetration than the flat, blunt tips. Basal glutamate levels of 2.1±4.4μM (mean±SD, n=10 animals) were detected from 150μm to 1200μm below the brainstem dorsal surface. Cutaneous evoked glutamate signals showed an amplitude of 1.1±1.1μM and a duration of 7.3±6.5s (26 signals, n=6). Electrically evoked signals, like cutaneous ones, were both rapid and slowly rising. Electrically evoked signals, especially those evoked by stimulation trains, were more reproducible and had an amplitude of 1.2±1.4μM, duration of 19.4±17.3s, and latency from stimulus onset of 21.3±21.5s (25 signals, n=4). In contrast to cutaneous stimulation, glutamate signals evoked by electrical stimulation had longer durations and were recorded primarily in the middle and ventral cuneate nuclei. Importantly, both cutaneous and electrical stimulation of the contralateral forelimb and hindlimbs did not evoke glutamate signaling. With the use of MEAs, these results show, for the first time, somatosensory-pathway specific changes in glutamate levels during peripheral cutaneous and electrical stimulation.

Acute and chronic changes in dorsal horn innervation by primary afferents and descending supraspinal pathways after spinal cord injury

Sprouting of peptidergic nociceptive and descending supraspinal projections to the dorsal horn following spinal cord injury (SCI) has been proposed as a mechanism of neuropathic pain. To identify structural changes that could initiate or maintain SCI pain, we used a complete transection model in rats to examine how structural remodeling in the dorsal horn rostral to the lesion relates to distance from injury, laminar region, and duration of injury. The major classes of C-fiber primary afferents differed greatly in their susceptibility to structural and chemical changes and their ability to undergo plasticity. Peptidergic primary afferents showed a widespread loss throughout the dorsal horn of segments approaching the injury site. Some of this loss may have been due to decreased neuropeptide expression. The reduction in peptidergic fibers was transient, indicating compensatory sprouting and perhaps also increased neuropeptide expression within the cord. Nonpeptidergic afferents expressing GFRalpha1 were largely unaffected by SCI. In contrast, in GFRalpha2-expressing nonpeptidergic afferents SCI caused a permanent loss of dorsal horn innervation. Unexpectedly, GFRalpha2 was transiently induced throughout deeper laminae but this was not due to upregulation of GFRalpha2 in dorsal root ganglia. We also observed permanent sprouting of catecholamine terminals of supraspinal origin. This was restricted to the superficial laminae. Our results show that SCI caused a loss of sensory input as well as structural remodeling such that the balance of nociceptive inputs and descending modulation was permanently altered. These changes may contribute to mechanisms rostral to the site of SCI that trigger and maintain neuropathic pain.

Loss and spontaneous recovery of forelimb evoked potentials in both the adult rat cuneate nucleus and somatosensory cortex following contusive cervical spinal cord injury

Varying degrees of neurologic function spontaneously recovers in humans and animals during the days and months after spinal cord injury (SCI). For example, abolished upper limb somatosensory potentials (SSEPs) and cutaneous sensations can recover in persons post-contusive cervical SCI. To maximize recovery and the development/evaluation of repair strategies, a better understanding of the anatomical locations and physiological processes underlying spontaneous recovery after SCI is needed. As an initial step, the present study examined whether recovery of upper limb SSEPs after contusive cervical SCI was due to the integrity of some spared dorsal column primary afferents that terminate within the cuneate nucleus and not one of several alternate routes. C5-6 contusions were performed on male adult rats. Electrophysiological techniques were used in the same rat to determine forelimb evoked neuronal responses in both cortex (SSEPs) and the cuneate nucleus (terminal extracellular recordings). SSEPs were not evoked 2 days post-SCI but were found at 7 days and beyond, with an observed change in latencies between 7 and 14 days (suggestive of spared axon remyelination). Forelimb evoked activity in the cuneate nucleus at 15 but not 3 days post-injury occurred despite dorsal column damage throughout the cervical injury (as seen histologically). Neuroanatomical tracing (using 1% unconjugated cholera toxin B subunit) confirmed that upper limb primary afferent terminals remained within the cuneate nuclei. Taken together, these results indicate that neural transmission between dorsal column primary afferents and cuneate nuclei neurons is likely involved in the recovery of upper limb SSEPs after contusive cervical SCI.

Ultrastructure and synaptology of the paratrigeminal nucleus in the rat: primary pharyngeal and laryngeal afferent projections

The paratrigeminal nucleus (PTN) receives primary afferent projections from the aerodigestive tract and orofacial regions and plays a role in the integration of visceral and somatic information. This study describes the fine structure of the rat PTN and the synaptology of primary afferent projections from the pharynx and larynx. Injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or cholera toxin-HRP (CT-HRP) were made into the wall of the pharynx or larynx to label primary afferent axon terminals. Light microscopic observations demonstrated that afferent axons terminated bilaterally in overlapping fields in the PTN. Electron microscopic observations of the PTN revealed that there were three distinct classes of neurons, based on morphology and axosomatic contacts. The most abundant neurons, Type 1, were fusiform in shape and received very few or no axosomatic contacts. Type 2 neurons contained prominent Nissl substance (rough endoplasmic reticulum) and few axosomatic contacts, while Type 3 neurons had many axosomatic synapses. Terminals containing round, clear vesicles and forming asymmetric contacts (round asymmetric, RA) with dendrites were the predominant synaptic type in the PTN. Primary afferent terminals from the pharynx and larynx were of the RA type and formed synaptic contacts with small-diameter (<1 microm) dendrites. Visceral primary afferent inputs from the pharynx and larynx overlap with trigeminal somatic afferents in the PTN and have similar synaptic morphology. The results support the concept that the PTN provides an anatomical substrate for mediating viscerovisceral and somatovisceral reflexes via efferent connections with autonomic centers in the brainstem.

Adult rat forelimb dysfunction after dorsal cervical spinal cord injury

Repairing upper extremity function would significantly enhance the quality of life for persons with cervical spinal cord injury (SCI). Repair strategy development requires investigations of the deficits and the spontaneous recovery that occurs when cervical spinal cord axonal pathways are damaged. The present study revealed that both anatomically and electrophysiologically complete myelotomies of the C4 spinal cord dorsal columns significantly increased the adult rat's averaged times to first attend to adhesive stickers placed on the palms of their forepaws at 1 week. Complete bilateral myelotomies of the dorsal funiculi and dorsal hemisection, but not bilateral dorsolateral funiculi injuries, also similarly increased these times at 1 week. These data extend a previous finding by showing that a forepaw tactile sensory deficit that occurred in the adult rat after bilateral C4 spinal cord dorsal funiculi injury is due to damage of the dorsal columns. Averaged times to first attend to the stickers also decreased to those of sham-operated rats at 3 and 4 weeks post-dorsal hemisection with weekly testing. In contrast, a separate group of rats with dorsal hemisections had significantly increased times when tested only at 4 weeks. These data indicate that frequent assessment of this particular behavior in rats with dorsal hemisections extinguishes it and/or engenders a learned response in the absence of sensory axons in the dorsal columns and dorsolateral funiculi. This finding contrasted with weekly testing of grid walking where increased forelimb footfall numbers persisted for 4 weeks post-dorsal hemisection.

Central sprouting of uninjured small fiber afferents in the adult rat spinal cord following spinal nerve ligation

Partial nerve injury results in chronic pain that is difficult to treat effectively. To investigate the anatomic basis of this phenomenon we used wheat germ agglutinin-horseradish peroxidase (WGA-HRP) to label the central projections of uninjured small fibers (Adelta and C) in a well-established model of neuropathic pain created by selective spinal nerve ligation in the adult. We found extensive sprouting of uninjured WGA-HRP-labeled afferents into the central termination field in lamina II of dorsal horn normally occupied by L5 afferents whose peripheral axons had been ligated distal to the dorsal root ganglion. The formation of new projections by uninjured fibers into a functionally but not anatomically deafferented field in the adult may play a role in the development of chronic pain.

Central projection of unmyelinated (C) primary afferent fibers from gastrocnemius muscle in the guinea pig

We have demonstrated the central projections of muscle C or group IV afferent fibers in the guinea pig by tracing arborizations in the spinal cord. C afferent fibers from the gastrocnemius muscle (GCM) were electrophysiologically identified by conduction velocity (less than 1 m/second). A single neuron in the lumbar 5 dorsal root ganglion (L5 DRG) was intracellularly labeled with Phaseolus vulgaris leucoagglutinin (PHA-L). After iontophoretic injection of PHA-L, we processed the lumbar cord and L5 DRG for PHA-L immunohistochemistry. Six muscle C afferent fibers from 40 animals were labeled, and whole trajectories were recovered. Labeled fibers were reconstructed by tracing of the arbor in serial parasagittal sections. The GCM C afferents projected rostrocaudally for two or three segments and ran at the surface of the dorsal funiculus, giving off collaterals into laminae I and II and sometimes into parts of lamina III. We determined, based on the branching pattern and form of the terminal plexus, that the branching of muscle C afferent fibers showed an intermediate pattern that fell morphologically between the terminal patterns of somatic and visceral afferents. The numbers and sizes of fiber swellings and terminal swellings were measured on all collateral branches. We found that the area of distribution of the terminal swellings of muscle C afferent fibers is larger than that of somatic terminals but that the density of terminal swellings in the terminal area was lower than that of the somatic terminals.

Central projections of thoracic splanchnic and somatic nerves and the location of sympathetic preganglionic neurons in Xenopus laevis

The central and peripheral organization of thoracic visceral and somatic nervous elements was studied by applying dextran amines to the proximal cut ends of the thoracic splanchnic and somatic nerves in Xenopus laevis. Many labeled dorsal root ganglion cells of visceral afferents, and all somatic afferents, were located in a single ganglion of one spinal segment, and the two types of cells were distributed topographically within the ganglion. The labeled sympathetic preganglionic neurons were located predominantly in the same area of the thoracic spinal gray as in other frogs and in mammals. The labeled visceral afferents projected to Lissauer's tract and the dorsal funiculus. The visceral fibers of the tract ascended to the level of the subcerebellar area, supplying collateral branches to the lateral one-third of the dorsal horn and to the area of brainstem nuclei, including lateral cervical and descending trigeminal nucleus, and descended to the filum terminale. The visceral fibers of the dorsal funiculus were distributed to the dorsal column nucleus and the solitary tract. A similar longitudinal projection was also seen in the somatic afferents. The dual central pathway of thoracic primary afferents in the anuran spinal cord is a property held in common with mammals, but the widespread rostrocaudal projection through Lissauer's tract may be a characteristic of the anuran central nervous system. In frogs, the direct transmission of primary afferent information to an extremely wide area of the central nervous system may be important for prompt assessment of environmental factors and control of body functions.

Distribution of sensory neurons of ventral and dorsal cervical cutaneous nerves in dorsal root ganglia of adult rat--a double-label study using DiO and DiI

To examine distribution of sensory neurons of ventral and dorsal cervical cutaneous nerves in dorsal root ganglia (DRGs), DiO and DiI tracers were applied at the proximal section of nerves (transverse superficial cervical and anterior supraclavicular nerves were selected as ventral cervical cutaneous nerves; dorsal cutaneous branches of second, third and fourth cervical nerves were selected as dorsal cervical cutaneous nerves). Located distributions were observed in DRGs of C2, C3, and C4 (25/46 DRGs). Sensory neurons of the ventral cervical cutaneous nerves were distributed in dorso-lateral or dorso-medial portions; neurons of dorsal cervical cutaneous nerves were distributed in ventro-medial or ventro-lateral portions of DRGs. Moreover, sensory neurons of transverse superficial cervical and anterior supraclavicular nerves were mainly distributed from the caudal half of C2 to whole part of C4 DRGs. Results show that there is a tendency for located distribution in two group sensory neurons; also, sensory neurons of ventral cervical cutaneous nerves have a segmental distribution, which has been verified in the brachial and lumbar plexus.

The Distribution of &mgr; and delta Opioid Binding Sites Belonging to a Single Cervical Dorsal Root in the Superficial Dorsal Horn of the Rat Spinal Cord: A Quantitative Autoradiographic Study

Numerous studies have demonstrated a dense concentration of opioid receptors in the superficial layers (laminae I - II) of the spinal cord. These receptors are located both pre- and postsynaptically at this level. The purpose of this study was to assess the distribution of opioid receptors belonging to a single (C7) dorsal root. Thus, quantitative autoradiography of &mgr; ([3H]Tyr-d-Ala-Gly-NMe-Phe-Gly-ol; [3H]DAMGO) and delta ([3H]Tyr-d-Thr-Gly-Phe-Leu-Thr; [3H]DTLET) opioid binding sites was performed for several experimental groups: control rats with intact dorsal roots and lesioned rats with a unilateral dorsal rhizotomy of (a) the C7 root alone, (b) the three successive roots rostral and caudal to the spared C7 root, and (c) the seven roots C4 - Th2. By subtracting results of the 'C7 cut' group from the 'intact' group or by subtracting results of the C4 - Th2 cut group from the C7 spaced group, it was possible to measure the distribution of &mgr; and delta opioid binding sites belonging to the C7 root. The combination of these two methods of calculation allowed us to demonstrate a significant distribution over two segments rostral and one segment caudal to the segment of entry. For [3H]DAMGO, the distribution was 10% (P < 0.05) in the C5, 27%, (P < 0.001) in the C6, 38% (P < 0.001) in the C7 and 14% (P < 0.05) in the C8 segment. For [3H]DTLET, the distribution was 11% (P=0.05) in the C5, 27%, (P < 0.01) in the C6, 37% (P < 0.001) in the C7 and 18% (P < 0.05) in the C8 segment. It is also noted that rostral distributions spread more densely and further than the caudal ones.

Plasticity of &mgr; and delta Opioid Receptors in the Superficial Dorsal Horn of the Adult Rat Spinal Cord Following Dorsal Rhizotomies: A Quantitative Autoradiographic Study

The aim was to study the regulation of &mgr; and delta opioid binding sites in the superficial layers (laminae I - II) of the dorsal horn of the adult rat spinal cord 1, 2, 4 and 12 weeks after unilateral dorsal rhizotomies of various extents. Using quantitative autoradiography and highly selective tritiated opioid ligands, we have shown that the decrease in [3H]Tyr*-d-Ala-Gly-NMe-Phe-Gly-ol ([3H]DAMGO) (&mgr; sites) and [3H]Tyr*-d-Thr-Gly-Phe-Leu-Thr ([3H]DTLET) (delta sites) binding in the side ipsilateral to the lesion as compared to the intact side is related to the number of dorsal roots cut. In the segment central to the lesion, 1 week after the lesion, ipsilateral/contralateral side binding ratios for [3H]DAMGO were 0.70, 0.49, 0.36 and 0.25 when 1, 3, 5 and 7 roots respectively were sectioned. For [3H]DTLET, the ratios were 0.71, 0.54, 0.42 and 0.39. The time-related analysis of binding ratios showed that, in partially deafferented spinal segments after long-term deafferentation (12 weeks postlesion) there were greater numbers of &mgr; and delta binding sites than in cases of short-term deafferentation (1 - 2 weeks). By contrast, in spinal segments considered as completely deafferented, there was no difference in the remaining &mgr; and delta binding sites at 12 weeks as compared to 1 week postlesion. Consequently, it is deduced that the partial recovery of &mgr; and delta binding observed after long-term partial deafferentation could be associated with neuronal plasticity (probably collateral sprouting) of fine diameter primary afferent fibres arising from intact dorsal roots.

Mu and delta opioid receptor-like immunoreactivity in the cervical spinal cord of the rat after dorsal rhizotomy or neonatal capsaicin: an analysis of pre- and postsynaptic receptor distributions

Opioid compounds have powerful analgesic properties when administered to the spinal cord. These effects are exerted through mu and delta opioid receptors, and both pre- and postsynaptic mechanisms have been implicated. To specifically address the relative pre- and postsynaptic contribution to spinal opioid analgesia, we have quantitatively assessed the pre- vs. postsynaptic distribution of the mu-opioid (MOR-1, MOP(1)) and delta-opioid receptors (DOR-1, DOP(1)). We also examined the rostro-caudal arborization of MOR-1 and DOR-1 immunoreactive primary sensory neurons, using an isolated dorsal root preparation. These results were compared to those obtained by labeling for calcitonin gene-related peptide (CGRP), a neuropeptide whose expression in the spinal cord is restricted to the terminals of small diameter primary sensory neurons. We estimate that approximately one half of MOR-1 and two thirds of DOR-1 immunoreactivity in the cervical spinal cord is located on primary afferent fibers. These fibers have a broad rostro-caudal distribution, extending at least three segments rostral and caudal to their segment of entry. Regardless of marker used, the rostral projection was greatest, however, the distribution of CGRP-immunoreactive fibers differed somewhat in that they had a much smaller projection to the most caudal segments examined. Our results suggest that presynaptic delta opioid actions predominate, but that there are mixed pre- and postsynaptic inhibitory effects exerted by opioid analgesics that act at the spinal cord mu opioid receptor.

A beta-fiber intensity stimulation of chronically constricted median nerve induces c-fos expression in thalamic projection neurons of the cuneate nucleus in rats with behavioral signs of neuropathic pain

This study was aimed to investigate the possible involvement of neurons in the cuneate nucleus (CN) in the processing of A beta afferent inputs evoked by electrical stimulation of constricted median nerve in rats with behavioral signs of neuropathic pain. Immunohistochemical localization of Fos protein was used to examine the neuronal activation, and the combination of Fos immunohistochemistry with the retrograde labeling of Fluoro-Gold (FG) injected into the ventrobasal complex of the thalamus was used to characterize the activated neurons. Two weeks after unilateral median nerve constriction injury, the rats exhibited behavioral signs of neuropathic pain in the affected forepaws. In rats after nerve injury but without electrical stimulation, some Fos-like immunoreactive (Fos-LI) neurons were detected in the dorsal horn of the seventh cervical segment (C7) but none was found in the CN. Similar features were also noted when the stimulation of the intact median nerve served as an additional control. After A beta-fiber intensity stimulation of the previously constricted median nerve, an increase in number of Fos-LI neurons occurred in the medial half of the ipsilateral C7 dorsal horn as well as in the ipsilateral CN. In the latter, the Fos-LI neurons were located in the median nerve projection territory throughout the nucleus. Most of the Fos-LI neurons were distributed in the middle region of the CN, with about 78% of them emitting FG fluorescence indicating that they were cuneothalamic projection neurons. The results of this study suggest that the dorsal column-medial lemniscal system may contribute to the transmission and modulation of A beta-fiber mediated neuropathic pain signals.

The trigeminal nerve. Part I: An over-view

The trigeminal nerve is the largest and most complex of twelve cranial nerves. Its vast size and influence are greatly appreciated when one attempts to diagnose and treat patients suffering from orofacial pain and temporomandibular joint disorders. Without a thorough knowledge of the trigeminal nerve, the efficacy of diagnostic and therapeutic procedures will be very disappointing. This is the first of a four-part series of articles about the trigeminal nerve, a basic over-view of both the gross and neuroanatomical structures is presented.

Complete compensation in skilled reaching success with associated impairments in limb synergies, after dorsal column lesion in the rat

Each of the dorsal columns of the rat spinal cord conveys primary sensory information, by way of the medullary dorsal column nucleus, to the ventrobasal thalamus on the contralateral side; thus the dorsal columns are an important source of neural input to the sensorimotor cortex. Damage to the dorsal columns causes impairments in synergistic proximal or whole-body movements in cats and distal limb impairments in primates, particularly in multiarticulated finger movements and tactile foviation while handling objects, but the behavioral effects of afferent fiber lesions in the dorsal columns of rodents have not been described. Female Long-Evans rats were trained to reach with a forelimb for food pellets and subsequently received lesions of the dorsomedial spinal cord at the C2 level, ipsilateral to their preferred limb. Reaching success completely recovered within a few days of dorsal column lesion. Nevertheless, a detailed analysis of high-speed video recordings revealed that rotatory limb movements (aiming, pronation, supination, etc.) were irreversibly impaired. Compensation was achieved with whole-body and alternate limb movements. These results indicate the following: (1) in the absence of the dorsal columns, other sensorimotor pathways support endpoint success in reaching; (2) sensory input conveyed by the dorsal columns is important for both proximal and distal limb movements used for skilled reaching; and (3) detailed behavioral analyses in addition to endpoint measures are necessary to completely describe the effects of dorsal column lesions.

Pre- and postsynaptic distribution of cannabinoid and mu opioid receptors in rat spinal cord

In vitro receptor binding and quantitative autoradiography were used to assess the pre- and postsynaptic distribution of cannabinoid receptors in the cervical dorsal horn of the rat spinal cord. An extensive unilateral dorsal rhizotomy was performed across seven or eight successive spinal segments from C3 to T1 or T2. The densities of cannabinoid and mu opioid receptors in the central (C6) spinal segment were assessed 2, 4, 8, and 16 days post rhizotomy and compared with those of untreated rats. Rhizotomy induced approximately a 50% ipsilateral loss in the [3H]CP55,940 binding to spinal cannabinoid receptors that was maximal at 8 days post-rhizotomy. By comparison, the binding of [3H][d-Ala2-MePhe4, Gly-ol5]enkephalin (DAMGO) to mu receptors was depleted approximately 60% in near-adjacent sections. By contrast, changes in [3H]CP55,940 binding contralateral to the deafferentation were largely absent at all post-lesion delays. These data suggest that under conditions in which a spinal segment is completely deafferented, approximately 50% of cannabinoid receptors in the cervical (C6) dorsal horn reside presynaptically on central terminals of primary afferents. The present data provide anatomical evidence for presynaptic as well as postsynaptic localization of cannabinoid receptors in the spinal dorsal horn.

Direct projections from nucleus X to the external cortex of the inferior colliculus in the rat

Direct projections from nucleus X to the external cortex of the inferior colliculus (ICe) were found in the rat by the retrograde single- and double-labeling methods. The projections are bilateral with a clear contralateral dominance. Some of these projections are made by axon collaterals of projection fibers from nucleus X to the ventrobasal thalamus. On the other hand, projection fibers from nucleus X to the cerebellum send no axon collaterals to ICe.

Transneuronal labeling of a nociceptive pathway, the spino-(trigemino-)parabrachio-amygdaloid, in the rat

Transneuronal tracing of a nociceptive pathway, the spino-(trigemino)-parabrachio-amygdaloid pathway, was performed using an alpha-herpes virus, the Bartha strain of pseudorabies virus (PRV). Microinjection of PRV into the central nucleus of the amygdala (Ce) resulted in progressive retrograde and transneuronal infection of a multisynaptic circuit involving neurons in the brainstem and spinal cord as detected immunocytochemically. At short survival (26 hr), retrogradely labeled neurons were concentrated in the external lateral nucleus of the parabrachial complex (elPB) but were absent from both the trigeminal nucleus caudalis (TNC) and the spinal cord. At longer survivals (52 hr), labeled cells were present in lamina I of both the TNC and spinal dorsal horn. Retrograde labeling from the Ce with Fluoro-gold demonstrated that elPB neurons have long dendrites extending laterally into the terminal field of spinal and trigeminal afferents, where transneuronal passage of PRV to these afferents could occur. Even longer survivals (76 hr) resulted in a columnar pattern of cell labeling in the TNC and spinal dorsal horn that extended from lamina I into lamina II. At this longest survival, primary sensory neurons became infected. Bilateral excitotoxic lesions of the elPB blocked almost all viral passage from the Ce to superficial laminae of the TNC and spinal dorsal horn. These results demonstrate that nociceptive input to the amygdala is relayed from neurons in lamina I through the elPB. We propose that this modular arrangement of lamina I and II neurons may provide the basis for spinal processing of peripheral input to the amygdala.

Ultrastructural study of phenylethanolamine-N-methyltransferase, corticotropin-releasing factor and neurotensin immunoreactive neurons in the external cuneate nucleus of the gerbil

The present study examined the existence of catecholamine-, corticotropin-releasing factor (CRF)- and neurotensin (NT)-containing neurons in the external cuneate nucleus (ECN) of the gerbil using single label pre-embedding immunocytochemistry in an attempt to shed light on the increasing evidence for autonomic involvement of the ECN. Peroxidase immunoreactivity of phenylethanolamine-N-methyl-transferase (PNMT), CRF or NT was identified in the heterogeneous population of the ECN neurons characterized by a deeply infolded nucleus. The label was localized in their somata, dendrites, myelinated axons and axon terminals. The immunolabelled dendrites were contacted by spherical (S) and flattened (F) types of presynaptic boutons containing spherical and flattened synaptic vesicles, respectively. The PNMT-labelled dendrites, however, were postsynaptic to an additional type of axon terminals containing pleomorphic (P) synaptic vesicles. Among the immunoreactive axon terminals, the PNMT-labelled boutons consisted of two types: S and F; in the CRF- and NT-labelled axon terminals, only the S type was observed. The catecholamine-containing ECN neurons differed from the CRF- and NT-immunoreactive neurons in their synaptic organization. The latter two were considered to be of the same cell population because of their similarities in ultrastructural features and synaptic relations. In view of a high frequency (48% for PNMT, 50% for CRF and 46% for NT) of the F-typed boutons associated with the three categories of immunolabelled neurons in the ECN, it is possible that they are under considerable inhibitory control. The presence of catecholamine, CRF and NT in the ECN suggests that the nucleus may be involved in the integration of proprioception-, exercise- or stress-evoked autonomic responses.

Synaptophysin immunoreactivity and distributions of calcium-binding proteins highlight the functional organization of the rat's dorsal column nuclei

The mammalian dorsal column nuclei (DCN) are principally composed of the cuneate (CN) and gracile (GN) nuclei. Data presented here support previously published anatomical and functional evidence that the longitudinal organization of the CN and GN reflect the complex role of the DCN in somatosensory processing. The CN is organized longitudinally into three parts. Within the middle portion of this nucleus, primary afferent projections and cuneothalamic cells are concentrated. Although traditional cytoarchitectonic analyses had failed to detect this tripartite organization in rats, we found evidence for it, with a functional middle region, extending approximately 0.2-0.9 mm caudal to the obex, characterized by precise somatotopy of primary afferent terminations and corresponding somatotopy of cytochrome oxidase (CO) blotches. Additional evidence is presented here consistent with a functionally distinct middle region within the rat's CN: (1) patches of dense synaptophysin (a synaptic-vesical-associated protein)-immunoreactivity (SYN-IR) are limited to the middle CN region, coincident with the dense CO blotches; (2) neurons immunoreactive for the calcium-binding proteins calbindin-D28 (CB), calretinin (CR) and parvalbumin (PV) are concentrated in the middle CN region. Furthermore, in adult rats subjected to perinatal forepaw removal, (1) the patterns of SYN-IR in the middle region of the CN are disrupted, as had previously been shown for the patterns of CO blotches; (2) in contrast, however, distributions of CN cells with PV-, CB- and CR-IR are unaffected. Evidence for a tripartite division in the GN is also presented, based on the distributions of cells with PV-, CB- and CR-IR.

The isolated mammalian spinal cord

This review considers: spinal cord slices; isolated spinal cord sagitally or transversely hemisected; whole spinal cord; respiration control--[brain-stem spinal cord; brain-stem spinal cord with attached lungs]; nociception--[spinal cord with tail]; fictive locomotion--[spinal cord with one hind limb; spinal cord with two hind limbs]. Much of the functional circuitry of the CNS can be studied in the isolated spinal cord with the additional advantage that the isolated spinal cord can be perfused with known concentrations of ions, neurotransmitters, agonists, antagonists, and anaesthetics. These can be washed away, the circuitry allowed to recover and other drugs or different concentrations applied. Future preparations including the complete spinal cord, the two hind limbs, and a sagittal section of the complete brain will allow greater understanding of the multiple sensory and motor pathways and their interactions in the CNS.

Cervical primary afferent input to vestibulospinal neurons projecting to the cervical dorsal horn: an anterograde and retrograde tracing study in the cat

Vestibulospinal neurons in the caudal half of the medial and descending vestibular nuclei terminate in the cervical spinal cord, not only in the ventral horn and intermediate zone but also in the dorsal horn. The purpose of the present study was to examine whether the areas containing these vestibulospinal neurons are reached by cervical primary afferents. In one group of experiments, wheat germ agglutinin-horseradish peroxidase conjugate and horseradish peroxidase were pressure injected into spinal ganglia C2-C8 and revealed anterogradely labeled fibers and boutons in the caudal part (caudal to the dorsal cochlear nucleus) of the ipsilateral medial and descending vestibular nuclei. This projection was verified in experiments in which wheat germ agglutinin-horseradish peroxidase conjugate was microiontophoretically injected into the caudal half of either the medial or the descending vestibular nuclei and revealed retrogradely labeled cells only in ipsilateral spinal ganglia C2-C7, with a maximum of cells in C3. In another group of experiments, after microiontophoretic injections of Phaseolus vulgaris leucoagglutinin or Biocytin into either the medial or the descending vestibular nuclei, anterogradely labeled fibers and boutons were present in the cervical spinal cord, mainly bilaterally in the dorsal horn (laminae I-VI) but also, to a lesser extent, in the ventral horn and intermediate zone. The existence of a loop that relays cervical primary afferent information to vestibulospinal neurons projecting to the cervical spinal cord, in particular the dorsal horn, may have implications for vestibular control over local information processing in the cervical dorsal horn.

Efferent connections from the external cuneate nucleus to the medulla oblongata in the gerbil

The present study revealed the efferent projections from the external cuneate nucleus (ECN) to various medullary nuclei in the gerbil as demonstrated in fresh living brainstem slices by using in vitro anterogradely tracing with the dextran-tetramethyl-rhodamine-biotin. The tracer-labelled ECN axon terminals were observed (1) in most of the vital autonomic-related nuclei: the nucleus solitary tractus, nucleus ambiguus, rostroventrolateral reticular nucleus and C2 adrenergic area, (2) in the reticular formation: the medullary, parvocellular, intermediate, gigantocellular, dorsal paragigantocellular and lateral paragigantocellular reticular nuclei and medullary linear nucleus, and (3) in sensory nuclei: the cuneate nucleus, spinal trigeminal nuclei caudalis and interpolaris, paratrigeminal nucleus, medial and spinal vestibular nuclei, inferior olive and prepositus hypoglossal nucleus. These new findings are discussed in relation to possible roles of the ECN in cardiovascular, respiratory and sensorimotor controls.

Light and electron microscopic immunocytochemical localization of AMPA-selective glutamate receptors in the rat spinal cord

alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-type glutamate receptors are probably the most widespread excitatory neurotransmitter receptors of the central nervous system, and they play a role in most normal and pathological neural activities. However, previous detailed studies of AMPA subunit distribution have been limited mainly to the brain. Thus, a comprehensive study of AMPA receptor subunit distribution was carried out on sections of rat spinal cord and dorsal root ganglia, which were immunolabeled with antibodies made against peptides corresponding to C-terminal portions of the AMPA receptor subunits: GluR1, GluR2/3, and GluR4. In the spinal cord, labeling was most prominent in the superficial dorsal horn, motoneurons, and nuclei containing preganglionic autonomic neurons. Immunostaining also was observed in neurons in other regions including those known to contain Renshaw cells and Ia inhibitory cells. Although overall immunostaining was lighter with antibody to GluR1 than with GluR2/3 and 4, there were neurons that preferentially stained with antibody to GluR1. These "GluR1 intense" neurons were usually fusiform and most concentrated in lamina X. In dorsal root ganglia, immunostaining of ganglion cell bodies was moderate to dense with antibody to GluR2/3 and light to moderate with antibody to GluR4. Possible neuroglia in the spinal cord (mainly GluR2/3 and 4) and satellite cells in dorsal root ganglia (GluR4) were immunostained. Electron microscopic studies of the superficial dorsal horn and lateral motor column showed staining that was restricted mainly to postsynaptic densities and associated dendritic and cell body cytoplasm. In dorsal horn, colocalization of dense-cored vesicles with clear, round synaptic vesicles was observed in unstained presynaptic terminals apposed to stained postsynaptic densities. Subsynaptic dense bodies (Taxi-bodies) were associated with some stained postsynaptic densities in both the superficial dorsal horn and lateral motor column. Based on several morphological features including vesicle structure and presence of Taxi-bodies, it is likely that at least some of the postsynaptic staining seen in this study is apposed to glutamatergic input from primary sensory afferent terminals.

The mutability of low-affinity nerve growth factor receptor (p75NGFR) expression in the rat cuneate nucleus following perinatal injury and adult deafferentations: comparisons with cytochrome oxidase

In normal adult rats, intense immunostaining for the 75 kDa low-affinity receptor for nerve growth factor and other neurotrophins (p75NGFR) is concentrated in the middle region of the cuneate nucleus (CN), distributed in a blotchy pattern similar to that of cytochrome oxidase (CO) activity. In the adult rats, partial dorsal rhizotomies (centered around the 7th and 8th cervical spinal segments) resulted in the complete disappearance of p75NGFR-like immunoreactivity within the ipsilateral CN, but did not affect the distribution of the CO blotches. Perinatal (postnatal day 1-8) damage to the ipsilateral forepaw and subsequent rearing to adulthood also resulted in significant disruption of the topographical expression of p75NGFR-like immunoreactivity within the CN, as well as--as previously reported--disruption of the CO blotches. Although the patterns of staining in intact adult rats are similar for CO staining and for p75NGFR-like immunoreactivity within the CN, the CO staining appears to be primarily associated with postsynaptic cells, while the p75NGFR-like immunostaining appears to be associated with primary afferent terminals.

Surgical management of refractory craniomandibular pain using radiofrequency thermolysis: a report of thirty patients

Radiofrequency thermolysis has traditionally been used to treat pain disorders of differing etiologies primarily in the low back and cervical areas. This paper describes the use and results of a different and simplified approach to surgical management of extracapsular disorders, namely, temporal tendinitis, Ernest Syndrome, and occipital myalgia-neuralgia where conservative attempts have failed. A brief discussion of the pain disorders are addressed along with the methods of differential diagnosis, conservative therapy, and traditional surgical treatment. Finally, surgical management using radiofrequency thermolysis is described with results of treatment in 30 patients showing a 96% success rate.

Distribution of primary afferent fibers projecting from hindlimb cutaneous nerves to the medulla oblongata in the cat and rat

The dorsal column nuclear complex, one of the most important relays for tactile perception, has well been known to be somatotopically organized. Topographical arrangements of terminal sites of individual cutaneous nerves within the dorsal column nuclei, however, have not been examined systematically, although many studies have been done upon primary afferents to the medulla oblongata, including the dorsal column nuclear complex. Thus, in the present study, distribution of primary afferent fibers projecting from the hindlimb cutaneous nerves to the medulla oblongata was examined in the cat and rat by means of the transganglionic transport method with horseradish peroxidase. Cutaneous primary afferent fibers projecting from the hindlimb to the medulla oblongata were distributed mainly in the ipsilateral gracile nucleus. Terminal labeling in the gracile nucleus was seen at all rostrocaudal levels of the nucleus, occasionally including the nuclear part straddling the midline (the median or accessory nucleus). The labeled axon terminals in the gracile nucleus were more densely distributed in the middle and caudal parts of the nucleus than in the rostral part. Although the fields of termination of the hindlimb cutaneous nerves overlapped in the gracile nucleus, the foci of the terminal labeling of the nerves innervating the distal parts of the hindlimb were located more medially or dorsomedially than those of the nerves innervating the proximal parts. Terminal labeling was further found in a small zone immediately medial to the rostromedial border of the external cuneate nucleus. This hitherto undescribed zone (U zone) contained a small cluster of medium-sized neurons in the cat. Although no particular cell cluster was found in the U zone of the rat, convergence of the primary afferent fibers of the cutaneous nerve from the hindlimb appeared to occur as in the U zone of the cat.

Synaptic relationships between GABA-immunoreactive boutons and primary afferent terminals in the rat cuneate nucleus

The present study examined the synaptic relation between the primary afferent terminals and intrinsic neuronal elements in the rat cuneate nucleus. For this purpose, experimental degeneration after multiple cervicothoracic dorsal rhizotomies or anterograde transport of wheatgerm agglutinin conjugated to horseradish peroxidase were used to identify the primary afferent terminals, while immunogold postembedding staining was employed to identify the GABA-immunoreactive boutons. The combined procedure allowed us to demonstrate a direct synaptic relationship between the primary afferent terminals and GABA-immunoreactive boutons. At least two types of synaptic relation were observed between the primary afferent terminals, identified by their degenerating features or labeled by wheatgerm agglutinin conjugated to horseradish peroxidase, and the immunogold-labeled GABA-immunoreactive boutons (i) a GABA-immunoreactive bouton making a simple presynaptic contact with the primary afferent terminal; and (ii) a synaptic glomerular complex in which the centrally located primary afferent terminal was postsynaptic to a GABA-immunoreactive bouton and presynaptic to dendrites closely associated with it; both terminals were sometimes presynaptic to a common dendrite. It is speculated from this study that the incoming impulses from the forelimb area are modulated by the GABA-immunoreactive boutons in the cuneate nucleus of the rat.

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.

Regulation of opioid binding sites in the superficial dorsal horn of the rat spinal cord following loose ligation of the sciatic nerve: comparison with sciatic nerve section and lumbar dorsal rhizotomy

The aim of the present study was to quantify time-related modifications in mu and delta opioid binding sites in the superficial layers (laminae I and II) of the L4 lumbar segment in a rat model of mononeuropathy induced by loose ligation of the sciatic nerve. We have shown a 28% (P < 0.01) and 24% (P < 0.01) decrease in ipsi/contralateral side binding ratios for tritiated (Tyr*-D-Ala-Gly-NMe-Phe-Gly-ol) ([3H]DAMGO) and tritiated (Tyr*-D-Thr-Gly-Phe-Leu-Thr) ([3H]DTLET) respectively, at two weeks postlesion which correspond to the delay of maximal hyperalgesia and of maximal alteration of fine diameter primary afferent fibers. In contrast, no change in [3H]U.69593 specific binding could be detected at this postlesion delay. For longer survival delays (four, eight and 15 weeks postlesion), mu and delta binding ratios return towards control values (approximately equal to 1), probably reflecting the occurrence of a long-term neuroplasticity (i.e. a new equilibrium in the metabolism of primary neurons, or collateral sprouting from intact primary afferents) following loose nerve ligation. In addition, a comparison of the results obtained in this model with those measured after sciatic nerve section and lumbar dorsal rhizotomy was performed in order to compare the degree of loss in opioid binding sites in these three types of lesion. The section of the sciatic nerve induced at eight days postlesion an 18% (P < 0.01) and 28% (P < 0.01) decrease in binding ratio for [3H]DAMGO and [3H]DTLET, respectively. At two weeks postlesion the loss was 24% (P < 0.01) for the two ligands, and at longer delays (four and 12 weeks), a progressive recovery in binding ratio was observed. Thus, it appears that both sciatic nerve lesions we have studied result in mu and delta binding modifications which have similar intensity and similar time course from two to 12-15 weeks postlesion. In contrast, the unilateral rhizotomy of nine consecutive dorsal roots (T13-S2), which is known to induce a massive degeneration of fine diameter primary afferent fibers, is followed by a dramatic decrease in binding ratios for [3H]DAMGO (53%, P < 0.001) and [3H]DTLET (45%, P < 0.001) at two weeks postlesion. These data suggest that the more deprived the dorsal horn is of fine diameter primary afferent fibers, the more dramatic is the opioid binding loss in the ipsilateral side as compared to the contralateral side.(ABSTRACT TRUNCATED AT 400 WORDS)

Long-range afferents in the rat spinal cord. II. Arborizations that penetrate grey matter

1. The caudal extent of the collateral arborizations of entering sensory fibres in rat spinal cord was investigated by two methods: bulk labelling of peripheral nerves by injection of horseradish peroxidase conjugated to cholera toxin (B-HRP) and by antidromic stimulation using small currents from microelectrodes in the spinal cord while recording from single units in peripheral nerve or dorsal root. 2. The results show that injection of B-HRP into the sural or sciatic nerve labelled sural afferents in the grey matter three to four segments caudal to their root entry and sciatic nerve fibres were located in S4, the most caudal segment examined, four to six segments caudal to their root entry. 3. Detailed mapping with microelectrode stimulation showed that the parent descending fibres from filaments dissected from the L1 dorsal root coursed more than 20 mm, seven to eight segments caudal to the entry point in the dorsal columns and sent branches into the grey matter. Single units from the sural nerve were also followed caudally into the S2 and S3 spinal cord segments and also issued collateral branches into the grey matter. 4. The present results suggest that there is close agreement in the caudal penetration of long-ranging afferents by using complementary anatomical and electrophysiological methods.

Forelimb motor performance following cervical spinal cord contusion injury in the rat

The purpose of this study was to examine the degree, persistence, and nature of forelimb behavioral deficits following cervical spinal cord contusion injury in the rat. Forelimb reaching and pellet retrieval, forehead adhesive sticker removal, and vibrissae-induced forelimb placing were examined for 16 weeks following a weight-drop injury (10.0 g-2.5 cm) at the C4-C5 spinal level. Nine of 13 rats studied were unable to perform the pellet retrieval task due to pronounced forelimb extension hypometria. However, these animals did carry out the forehead sticker removal and vibrissae-induced placing tasks. Therefore, the loss of reaching ability related to pellet retrieval was not due to generalized paralysis. This interpretation was further supported by evaluation of the rostrocaudal extent of relative motoneuron loss from 1-mm divisions through the lesion zone. The extent of motoneuron pathology ranged from 2 to 6 mm but was largely confined to the C4-C5 spinal segments. Morphometric assessments of axonal sparing revealed that pellet retrieval performance during the last month of observation was significantly correlated with fiber sparing in the dorsal columns and ventral white matter, whereas no significant correlation could be demonstrated with regard to dorsolateral white matter. While there were no conspicuous differences in qualitative assessments of damage to interneuron pools (i.e., laminae V to VII) between the nonreaching and retrieval-recovered rats, the possibility of combined white and gray matter pathology contributing to this deficit still exists. These initial findings thus demonstrate that the weight-drop contusion injury model can be adopted to studies of cervical spinal cord trauma in the rat. Such lesions yield permanent deficits in forelimb function lending to future studies of possible therapeutic interventions. Furthermore, performance deficits observed at 1 week postinjury in the placing and forehead sticker removal tasks can be predictive of any potential for long-range spontaneous recovery in pellet retrieval ability.

Reappearance of calcitonin gene-related peptide-like immunoreactivity in the dorsal horn in the long-term dorsal root transected rat

Calcitonin gene-related peptide (CGRP)-immunoreactive (IR) fibers in the rat dorsal horn superficial laminae vanish almost completely 3 weeks following unilateral dorsal rhizotomy. After a prolonged survival (20 weeks) of dorsal rhizotomy there is, however, a reappearance of CGRP-IR fibers in the corresponding laminae of the dorsal horn. The density of such IR fibres showed a clear gradient with the lowest number found in the midlesion region and an increase in density towards the neighboring, intact segments. In normal as well as lesioned rats, no neurons intrinsic to the dorsal horn contained detectable levels of CGRP-like immunoreactivity (LI). Furthermore, no cells could, by use of in situ hybridization, be demonstrated to contain detectable levels of mRNA encoding for CGRP in the dorsal horn. Based on these findings, we suggest that the CGRP-IR fibers observed following long-term survival of dorsal rhizotomy derive from proliferating collateral branches of primary afferents of neighboring intact segments.

Fos-like immunoreactivity in the rat superficial dorsal horn induced by formalin injection in the forepaw: effects of dorsal rhizotomies

As previously described at the lumbar spinal level, we found that 2 h after subcutaneous formalin injection in the distal part of the fore-limb, Fos-like immunoreactivity (FLI) was induced in the ipsilateral cervical enlargement. Not surprisingly, as the injection site corresponds to the distal part of the C6-C8 dorsal root dermatomes, maximal labelling which predominated in the superficial laminae, was observed in the C6-C8 segments and to a lesser extent in C5. Similar experiments were performed on rats which underwent various types of unilateral dorsal rhizotomies (DRh) 7 days before formalin injection. In animals with C4, C5, T1 and T2 DRh sparing C6-C8 the rostrocaudal distribution was similar to the intact one. But, in animals having C4-T2 DRh sparing one single root, C7, the segmental FLI distribution was modified: it was slightly increased in C7, decreased in C6 and significantly decreased in C8. As expected, no FLI was found in animals with C4 to T2 DRh. The spared root model provides information about the segmental distribution in the cervical spinal cord of the input brought by a single root following stimulation of the distal forelimb, i.e., maximal distribution in the entry segment, but also in the two rostral and one caudal segments.

Time-related decreases in mu and delta opioid receptors in the superficial dorsal horn of the rat spinal cord following a large unilateral dorsal rhizotomy

The aim of the present study was to measure the time-related modifications of mu and delta opioid binding sites in the superficial layers of the dorsal horn of the rat spinal cord after a C4-T2 unilateral dorsal rhizotomy. Using specific ligands, namely [3H]DAMGO for mu sites and [3H]DTLET for delta sites, and a quantitative autoradiographic analysis, we have observed: (a) a decrease in binding on the ipsilateral side to the lesion as early as the first day postrhizotomy, the maximal loss being attained at 8 days postlesion, (b) after 8 days postlesion, the residual binding remains stable over the period of analysis (90 days), (c) the loss of mu receptors (71-74%) is significantly more pronounced than the loss of delta receptors (57-62%) and (d) affinities of postsynaptic mu and delta receptors are similar to those of the total receptor population in the superficial layers of the dorsal horn. Comparison of these results with the degeneration of primary afferent fibers reported in literature favors the localization of the majority of mu and delta opioid binding sites on fine diameter primary afferent fibers.

Organization of cutaneous primary afferent fibers projecting to the dorsal horn in the rat: WGA-HRP versus B-HRP

Primary afferent projections from cutaneous afferents in the forelimb and hindlimb digits to the dorsal horn (DH) were examined using 4 tracers: (1) 25% free horseradish peroxidase (HRP), (2) 2.5% wheat-germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), (3) a mixture of 25% free HRP and 2.5% WGA-HRP (WGA-HRP/HRP) or (4) 0.1% HRP conjugated to cholera toxin (B-HRP). The tracer was injected intracutaneously into the digits. Three to 4 days later, the rats were perfused transcardially, transverse sections (60-microns thick) were cut and the HRP was reacted using the tetramethyl benzidine (TMB) method. The location of the label was reconstructed by camera lucida drawings. In rats which received an injection of HRP alone, no label was detected in the DH. Rats injected with WGA-HRP had projection patterns similar to those injected with WGA-HRP/HRP. Patterns of labelling with WGA-HRP differed markedly from those with B-HRP. WGA-HRP labelled cutaneous afferents projecting to Rexed's laminae I-III, with the densest label in lamina II; in contrast, B-HRP labelled cutaneous afferents projecting to laminae II-V, with the densest label in laminae III-IV. These results indicate that, for cutaneous primary afferents projecting to the DH, WGA-HRP and B-HRP labelled different subpopulations of fibers, with the B-HRP-labelled subpopulation biased toward afferents of larger diameter. Rostrocaudally, the extent of the densest fiber projections, whether labelled by WGA-HRP or by B-HRP, was essentially the same, but the extent of the less densely labelled projections was much greater with B-HRP than with WGA-HRP. Comparisons of the projection maps from each of the five digits, using either WGA-HRP or B-HRP, indicated that, as seen in transverse sections through the DH, there was extensive overlapping among the labelled cutaneous afferent fibers from adjacent, or even non-adjacent digits.

Ultrastructural characterization of substance-P-immunoreactive synaptic terminals in the cat's normal and rhizotomized trigeminal subnucleus caudalis

Deafferenting injuries often cause transient or permanent physiological alterations within the central projection field of affected primary afferent fibers. Aberrant sensory perceptions, dysesthesias, and hyperalgesias represent the clinical sequelae of such injuries; however, the results of experimental deafferentations have been subject to a variety of interpretations (Rodin and Kruger, 1984b). Neurochemical studies show an increased sensitivity of partially deafferented neurons to substance P (SP). Our previous studies (Hoffmann et al., 1991) documented, primarily at the light-microscopic level, a moderate transient loss of SP-immunoreactive (SPIR) boutons in the trigeminal subnucleus caudalis (Vc)--a loss that seemed to preferentially affect the slightly larger, possibly complex boutons with multiple contacts. However, despite the elimination of the trigeminal input, the larger boutons reappeared. In the present study, therefore, we examined Vc using electron-microscopic immunocytochemistry, in order to document these changes over time and to clarify the structure and relationships of this population of boutons. SPIR boutons occurred in lamina I and II degrees of the substantia gelatinosa of Vc, ranged in size from 1 to 5 microns in diameter, and displayed mixed populations of clear and dense-core vesicles. Most formed single or multiple axodendritic junctions, but a significant number engaged in axoaxonic contacts with both SPIR-labeled and unlabeled terminals. A small number appeared to be the central element of a typical glomerulus, particularly in lamina II degrees. Three to seven days following an ipsilateral retrogasserian rhizotomy, synaptic degeneration was evident in the substantia gelatinosa and often involved glomerular terminals. However, most of these were SPIR-negative and occurred primarily in lamina II degrees. Those SPIR boutons that displayed degenerative features often made single or multiple axodendritic contacts, and in some instances were scalloped. By 30 days, most remaining SPIR boutons were small, with a lower incidence of contacts; however, some of these were axoaxonic. In addition, many SPIR terminals were only very lightly stained--a feature not encountered to such an extent in the contralateral Vc. At 45 days, complex SPIR boutons were again evident in the field, and some showed densely packed vesicles. An increased incidence of clusters of two to four SPIR axoaxonic contacts was also observed. Finally, almost all SPIR boutons encountered at this stage were intensely stained. It is suggested that these alterations represent a compensatory neuroplastic response on the part of overlapping cervical and cranial primary afferents to the partial deafferentation resulting from the interruption of the trigeminal root.(ABSTRACT TRUNCATED AT 400 WORDS)

A direct projection from the medial vestibular nucleus to the cervical spinal dorsal horn of the rat, as demonstrated by anterograde and retrograde tracing

Phaseolus vulgaris leucoagglutinin and wheat germ agglutinin-horseradish peroxidase were iontophoretically injected into different parts of the vestibular nuclear complex (VNC) of the rat. Injections centered into the caudal part of the medial vestibular nucleus revealed a vestibulospinal projection predominantly to the dorsal horn of the cervical spinal cord, besides the expected projection to the intermediate zone (IZ) and ventral horn (VH). While most of the anterogradely labelled fibres could be localized in laminae III to V, some scattered fibres were also seen in laminae I and VI. Lamina II remained free of labelling. The dorsal horn (DH) area with detectable anterograde labelling showed a rostrocaudal extension from C1-C6. Injections into other parts of the VNC labelled fibres and terminals in the IZ and VH while the DH remained almost free of labelling. Additionally, fluorogold and wheat germ agglutinin-horseradish peroxidase were pressure- or iontophoretically injected at different levels into the spinal cord to confirm the projection to the dorsal horn by means of retrograde tracing. Labelled neurons in the area of the medial vestibular nucleus (MVN), from which anterograde labelling in the DH was obtained, were only detectable after fluorogold and wheat germ agglutinin-horseradish peroxidase injections into the cervical spinal cord, in particular its DH. This projection from the caudal medial vestibular nucleus to the dorsal horn of the cervical spinal cord probably enables the VNC to influence sensory processing in the DH, in addition to its well-established influence on posture and locomotion via projections to the intermediate zone and ventral horn.

A novel spinal pathway and other connections to the spinocerebellum in the pigeon

Avian dorsal column nuclei do not project to the cerebellum. Injections of fluorescent tracers into the spinocerebellum of homing pigeons (Columba livia) disclosed a group of neurons located rostral to the dorsal column nuclei which receives spinal primary afferents, as confirmed by double-labeling experiments. Since this group has some similarities to the mammalian group x (location medial to the restiform body, spinal afferents, efferents to the cerebellum), this name was adopted for the pigeon. Further brainstem nuclei projecting to anterior or posterior spinocerebellum and with some relevance to transmission of spinal signals are described.

Central projections of the sciatic, saphenous, median, and ulnar nerves of the rat demonstrated by transganglionic transport of choleragenoid-HRP (B-HRP) and wheat germ agglutinin-HRP (WGA-HRP)

The central projections of the rat sciatic, saphenous, median, and ulnar nerves were labeled by injecting each nerve with 0.05 mg B-HRP, or 0.5 mg WGA-HRP, or a mixture of both. The B-HRP labeled large dorsal root ganglion cells (30-50 microns) and, correspondingly, 98% of axons labeled in a rootlet were meyelinated; although all sizes of myelinated axons were labeled, a greater proportion fell in the large ranges (2-6.5 microns axon diameter) than in the small ranges (0.5-2 microns). Primary afferents labeled with B-HRP were distributed in laminae I, III, IV, and V of the dorsal horn and extended into the intermediate grey and the ventral horn; Clarke's column and the respective dorsal column nuclei were also densely labeled. Motoneurons of the nerve were densely labeled by B-HRP, including extensive regions of their dendritic trees. In contrast, WGA-HRP labeled small dorsal root ganglion cells (15-25 microns) and in the dorsal rootlets, 84% of the labeled axons were nonmyelinated; the small population of labeled myelinated afferents mainly fell within the smaller ranges (0.5-2.0 microns). Terminal fields of WGA-HRP labeled afferents were restricted to the superficial dorsal horn (laminae I-III), and to limited regions in the dorsal column nuclei. Sciatic nerve projections traced by labeling with B-HRP alone or in combination with WGA-HRP were more extensive than previously described when using either native HRP or WGA-HRP. Afferents to the dorsal horn extended from L1-S1, to Clarke's nucleus from T8-L1, to the ventral horn from L2-L5, and extended throughout the medial and dorsal region of the gracilie nucleus. Motoneurons were found from L4-L6. Using the same tracers, saphenous projections extended in the superficial dorsal horn from caudal L1 to rostral L4, in the deep dorsal horn to mid L4 and along the length of the central part of the gracilie nucleus. The median nerve projected to the internal basilar nucleus from C1-C6, the dorsal horn from C3-T2, Clarke's nucleus from T1-T6, the external cuneate nucleus, and a large central area throughout the length of the cuneate nucleus. Motoneurons were located in dorsolateral and ventrolateral nuclear groups from C4 through C8. The ulnar nerve projections were less extensive but also included the internal basilar nucleus from C1-C6, the medial region of the dorsal horn from C4-T1, Clarke's nucleus from T1-T6, the external cuneate nucleus, and the medial part of the cuneate nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)