Distribution of somatic and visceral primary afferent fibres within the thoracic spinal cord of the cat

Analysis of calcitonin gene-related peptide-like immunoreactivity in the cat dorsal spinal cord and dorsal root ganglia provide evidence for a multisegmental projection of nociceptive C-fiber primary afferents

Recent studies have suggested that calcitonin gene-related peptide (CGRP) can be used as a marker for a subpopulation of nociceptive primary afferents. Consequently, CGRP-immunoreactive (CGRP-IR) primary afferents have been reported to project many segments rostral to their segment of entry and to send collaterals into the superficial and deep laminae of the dorsal horn. This study reports that some CGRP-IR primary afferents of sacral origin project rostral through the ipsilateral lumbar enlargement in the cat. The ultrastructure of these multisegmentally projecting primary afferent axons and terminals identified in a partially denervated cat was examined and compared to the ultrastructure of CGRP-IR afferents from an intact cat. Retrograde transport of wheatgerm agglutinin-colloidal gold injected into the cat L4 spinal cord resulted in labeling of primary afferent cell bodies in the ipsilateral L4-S1 dorsal root ganglia (DRG). Analysis of every fourth section through the ipsilateral S1 DRG revealed as many as 1,000 retrogradely labeled neuronal cell bodies. One third of these cell bodies were double labeled for CGRP-like immunoreactivity. The number of single- and double-labeled cells increased in ganglia closer to the injection site (L4-L7). At the ultrastructural level, in the lumbosacral dorsal spinal cord of a normal cat, most CGRP-IR axons were unmyelinated, while the rest were small myelinated axons. In both the superficial dorsal horn and lamina V, CGRP-IR varicosities were dome shaped, scallop shaped, or elongated. The CGRP-IR varicosities contained small agranular vesicles and frequently a few dense core vesicles. These labeled varicosities formed asymmetric synapses on unlabeled dendritic spines, shafts, or neuronal somata. One cat received multiple unilateral dorsal rhizotomies (S1-L4) and an ipsilateral hemisection (mid L4). CGRP-IR axons and terminals were found within each of the rhizotomized segments, although their density was greatly reduced compared to that in the intact animals. In Lissauer's tract the majority (greater than 90%) of CGRP-IR fibers were unmyelinated. In laminae I and V, the remaining CGRP-IR varicosities were mainly the dome-shaped varicosities morphologically similar to those observed in the normal spinal cords. They contained small agranular vesicles and a few dense core vesicles and formed asymmetric synapses on unlabeled dendritic shafts and spines. These data demonstrate that unmyelinated, presumably C-fiber nociceptive primary afferents and some small myelinated A-delta nociceptive primary afferents of sacral origin project rostral through the cat lumbar enlargement and make synaptic connections in both the superficial and deep laminae of the cat dorsal spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Relays from the spinal cord and solitary nucleus through the parabrachial nucleus to the forebrain in the cat

Projections from the spinal cord and solitary nucleus to the lateral parabrachial nucleus (PBN1) in the cat were directly compared using double anterograde tracing methods. The two inputs were found to overlap within a well-circumscribed zone in the rostral 2/3 of PBN1. This zone was flanked ventrally by a zone receiving only solitary nucleus input and dorsally by a zone receiving only spinal input. Other authors have shown that neurons within these three recipient zones (overlap area, solitary nucleus and spinal cord) project to different forebrain targets (hypothalamus, amygdala and thalamus, respectively). This orderly input-output organization is likely to provide part of the framework for PBN's complex involvement in the coordination of respiratory and cardiovascular activities and their association with pain, visceral sensation and emotion.

Visceral pain: a review of experimental studies

This paper reviews clinical and basic science research reports and is directed toward an understanding of visceral pain, with emphasis on studies related to spinal processing. Four main types of visceral stimuli have been employed in experimental studies of visceral nociception: (1) electrical, (2) mechanical, (3) ischemic, and (4) chemical. Studies of visceral pain are discussed in relation to the use and 'adequacy' of these stimuli and the responses produced (e.g., behavioral, pseudoaffective, neuronal, etc.). We propose a definition of an adequate noxious visceral stimulus and speculate on spinal mechanisms of visceral pain.

The effects of electrical stimulation of A and C visceral afferent fibres on the excitability of viscerosomatic neurones in the thoracic spinal cord of the cat

Single unit electrical activity has been recorded from viscerosomatic neurons in the lower thoracic spinal cord of decerebrate spinalized cats. The responses of the cells to electrical stimulation of afferent fibres in the splanchnic (SPLN) nerve and the effects of repetitive stimulation of somatic and visceral afferent C-fibres have been studied. Four groups of viscerosomatic neurones could be distinguished according to the type of visceral afferent input of the cells: (1) A-only cells (32.9%), driven only by stimulation of A delta afferent fibres in the SPLN nerve; (2) C-only cells (3%), driven only by stimulation of C afferent fibres in the SPLN nerve; (3) A + C cells (45.7%), driven by both A delta and C afferent fibres in the SPLN nerve; and (4) A + C? cells (18.6%), driven by A delta visceral afferents and showing signs of responsiveness to C-fibres though lacking a distinct response volley to visceral C-fibre activation. Two cells of the A + C group and located in lamina I of the dorsal horn responded to SPLN nerve stimulation in a manner consistent with the afferent fibre composition of the nerve, that is, showed evidence of strong monosynaptic links with SPLN afferent C-fibres and weaker responses to SPLN A delta afferents. Excitability changes of viscerosomatic neurones ('wind up', 'wind down' and changes in background activity) were also observed in the majority of neurones following electrical stimulation of somatic and of visceral afferent C-fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcitonin gene-related peptide immunoreactivity in the cat lumbosacral spinal cord and the effects of multiple dorsal rhizotomies

This study determined the extent of the rostral projection of calcitonin gene-related peptide-like immunoreactive (CGRP-IR) primary afferents in the cat lumbosacral spinal cord. To do this we examined the distribution of CGRP-like immunoreactivity (CGRP-LI) contralateral and ipsilateral to multiple dorsal rhizotomies. In the contralateral dorsal spinal cord, CGRP-IR fibers were mostly observed in Lissauer's tract, the dorsal columns, and laminae I, II, and V. Fewer CGRP-IR fibers were observed in laminae III, IV, and VI and the area around the central canal. The location of the CGRP-LI suggests that the afferents arose from nociceptors. Unilateral dorsal rhizotomies of five consecutive segments in the lumbar enlargement caused a substantial although incomplete loss of CGRP-LI in the rhizotomized dorsal spinal cord ipsilateral to the lesions. The majority of the remaining CGRP-IR fibers were located in Lissauer's tract, the dorsal columns, and the lateral part of laminae I and V. Ventral rhizotomies or an ipsilateral hemisection in the most rostral rhizotomized segment, in addition to the dorsal rhizotomies, had no noticeable effect upon the density or location of the remaining CGRP-LI. These results suggest that the majority of the CGRP-LI within the rhizotomized region of spinal cord was contained within branches of small-diameter primary afferents that entered the spinal cord through intact dorsal roots located caudal to the rhizotomized segments of spinal cord. It is concluded that CGRP-IR small-diameter primary afferents are capable of projecting at least five segments beyond their segment of entry and supplying collaterals to the superficial and deeper layers of the dorsal horn involved in the processing of nociceptive information.

Expression of c-fos protein in interneurons and projection neurons of the rat spinal cord in response to noxious somatic, articular, and visceral stimulation

This study used immunocytochemistry to examine the pattern of noxious-stimulus evoked expression of the proto-oncogene c-fos in the spinal cord of the rat. Both noxious somatic and joint stimulation in awake rats evoked the expression of c-fos protein in similar areas of the lumbar spinal cord. C-fos-immunoreactive neurons were found in laminae I and outer II, in the lateral part of the neck of the dorsal horn, and in laminae VII, VIII, and X. All of the labelled neurons were located ipsilateral to the injured hindpaw, except for lamina VIII where bilateral labelling was recorded. The c-fos-immunoreactive neurons in lamina I extended from the L3 segment to the rostral sacral cord; staining in outer lamina II was only found at the L4 segment. The more deeply located cells, of the dorsal and medioventral horns, had the most extensive rostrocaudal spread; they were found from L1 through the rostral sacral segments. The pattern of c-fos-immunoreactivity produced by visceral stimulation, in anesthetized rats, differed in several ways from that produced by somatic stimulation. First, there was considerable bilateral, symmetrical labelling of cells. Second, there was a much more extensive rostrocaudal spread of the labelling, from cervical through sacral cord. Third, the greatest rostrocaudal spread was found for neurons in the superficial dorsal horn; labelled cells in the neck of the dorsal horn and in lamina X were restricted to segments at the thoracolumbar junction, which is also where the superficial dorsal horn cells were most concentrated. Fourth, there were very few labelled neurons in the outer part of the substantia gelatinosa. To determine whether any neurons that express the c-fos protein in response to noxious stimulation project to supraspinal sites, we combined the immunocytochemical localization of c-fos with the localization of a retrogradely transported protein-gold complex that was injected into the thalamic and brainstem targets of the major ascending spinal pathways. In rats that received the somatic noxious stimulus, 90% of all of the c-fos projection neurons were recorded in four major areas of the cord: lamina I (37%), the lateral part of the neck of the dorsal horn (24%), laminae VIII (9%), and X (29%). The remainder were scattered throughout the spinal gray. With the exception of lamina VIII, which contained c-fos projection neurons contralateral to the inflamed paw, all of the c-fos projection neurons were located ipsilateral to the injured paw.(ABSTRACT TRUNCATED AT 400 WORDS)

The cells of origin of the hypoglossal afferent nerves and central projections in the cat

The cells of origin for the hypoglossal afferent nerves of the cat and their central projections were examined using the transganglionic and somatopetal transport of horseradish peroxidase (HRP). Primary afferent neurons from the hypoglossal nerve were located in the trigeminal ganglion, the superior ganglion of glossopharyngeal and vagal nerves, and the first 3 cervical ganglia. The central projections of hypoglossal afferents were organized in a selective manner according to their cells of origin. The primary afferent nerves originating from the trigeminal ganglion terminated in the subnucleus dorsalis (Vpd) of the principal nucleus (Vp), lateral margin of the caudal pars interpolaris (Vi), interstitial nucleus and laminae I and V of the pars caudalis (Vc). The projection of the afferent nerves for glossopharyngeal and vagal origins are similarly organized in the Vi and Vc to those of trigeminal origin, but differed in that they terminated ipsilaterally in the caudal half of the solitary nucleus and bilaterally in the commissural nucleus. The primary afferents arising from the first 3 cervical ganglia terminated in laminae I and V of the corresponding cervical cord segments.

Responses of neurons in nucleus ventralis posterolateralis of the cat thalamus' to hypogastric inputs

Recordings were made from 68 units in the nucleus ventralis posterolateralis (VPL) of the cat thalamus, which responded to stimulation of hypogastric afferents. These units also received nociceptive inputs from the contralateral integument. Units which responded exclusively to hypogastric afferent inputs were not found. Thirty seven of the units were nociceptive specific (NS), and the remaining 31 were wide dynamic range (WDR) units. All of these units were located in the shell region of the lateral subdivision of the caudal VPL. NS units responding to hypogastric afferent inputs had a circumscribed cutaneous receptive field on the contralateral abdomen, gluteal region, tail or hind limb. These areas corresponded to tactile dermatomes T13-S2. Similarly, the cutaneous receptive fields of WDR units receiving hypogastric afferent inputs were distributed in the contralateral abdomen, gluteal region, tail and hind limb, with the sole exception of one unit, whose receptive field also included a part of the lower thorax. These findings extend the previous findings that the shell region of the caudal VPL of the cat thalamus constitutes a thalamic link in a visceral pain pathway, and that the visceral and cutaneous pathways share a common projection locus in the VPL.

Characterization of superficial T13-L2 dorsal horn neurons encoding for colorectal distension in the rat: comparison with neurons in deep laminae

Fifty-five neurons responsive to colorectal distension located in the superficial spinal dorsal horn (0.0-0.3 mm ventral to the cord dorsum) of the T13-L2 spinal segments of pentobarbital-anesthetized, physiologically intact or spinalized (C1 transection), decerebrate rats were characterized. These neurons could be separated into three groups based upon their response to an 80 mm Hg, 20 s colorectal distension: (1) short latency-abrupt (SL-A) neurons (n = 22) that were excited by colorectal distension at a short latency (less than 1 s) and abruptly terminated responses following the termination of the distending stimulus; (2) short latency-sustained (SL-S) neurons (n = 26) that were excited by colorectal distension at a short latency (less than 1 s) and demonstrated sustained responses (greater than 4 s) following termination of the distending stimulus; and (3) INHIB neurons (n = 7) that were spontaneously active and were inhibited by colorectal distension. All 55 neurons had convergent cutaneous receptive fields (i.e. were 'viscerosomatic'), exhibiting excitatory responses to noxious (pinch/heat) and/or non-noxious (brush) stimuli. Neurons excited by colorectal distension also demonstrated monotonic, accelerating responses to graded colorectal distension, were excited by the intraarterial administration of bradykinin, could be antidromically activated by electrical stimulation in the caudal ventrolateral medulla and were subject to tonic descending inhibitory modulation as evidenced by more vigorous responses to distension when rats were reversibly spinalized using a cold block.(ABSTRACT TRUNCATED AT 250 WORDS)

The pelvic innervation in the rat: different spinal origin and projections in Sprague-Dawley and Wistar rats

WGA-HRP was applied to the pelvic and pudendal nerves of Sprague-Dawley and Wistar rats to compare the segmental levels of the resulting labeling. L6 and S1 were the segments at which the sacral parasympathetic nucleus and the denser primary afferents occurred in Sprague-Dawley rats. The levels found in Wistar rats were S1 and S2, thus indicating a disparity between both strains of rats in the spinal level of the sacral parasympathetic nucleus and the primary afferents.

Brain natriuretic peptides: differential localization of a new family of neuropeptides

Brain natriuretic peptide (BNP) is a recently discovered neuropeptide, isolated from the porcine brain, that is highly homologous to atriopeptin (AP), the atrial natriuretic peptide. We used a set of highly selective antisera against the two peptides to map their differential distribution immunohistochemically in the rat central nervous system. BNP immunoreactivity has a distinct distribution, involving many central autonomic and endocrine control structures that contain little if any AP immunoreactivity. AP and BNP belong to a family of neuropeptides that may be important in central cardiovascular control.

Visceral and somatic afferent origin of calcitonin gene-related peptide immunoreactivity in the lower thoracic spinal cord of the rat

The origin of calcitonin gene-related peptide in the thoracic spinal cord of the rat was investigated by radioimmunoassay and immunohistochemistry. In transverse sections from normal animals there was a dense staining of calcitonin gene-related peptide-immunoreactivity in laminae I, II and V of the dorsal horn. In parasagittal sections this was found to consist of rostrocaudally orientated fibres in laminae I and II and longitudinal bundles of fibres interspersed with a plexus of immunoreactivity in lamina V. After sectioning the thoracic spinal nerves there was a significant reduction in immunoreactivity in the dorsal horn of the spinal cord which was seen as a marked reduction of staining in lamina II and in the bundles of fibres in lamina V. Section of the splanchnic nerve slightly reduced staining in lamina I and virtually abolished the plexuses of immunoreactivity in lamina V. However, measurement of calcitonin gene-related peptide in samples from coeliac-ganglionized rats revealed an increase in immunoreactivity in regions of the spinal cord containing lamina V. These results provide evidence of a visceral and somatic afferent origin of calcitonin gene-related peptide in the thoracic spinal cord of the rat.

Neurotensin receptors in the human spinal cord: a quantitative autoradiographic study

The anatomical localization of neurotensin receptors in the human spinal cord was examined in 12 cases aged 4-68 years using quantitative autoradiographic methods following the incubation of fresh, unfixed cryostat sections with 4 nM [3H]neurotensin. Characterization of the pharmacological specificity of the [3H]neurotensin binding sites in the human spinal cord from displacement studies with neurotensin and various neurotensin fragments indicated that, whereas 1.0 microM neurotensin and the carboxy-terminal fragment neurotensin almost completely displaced [3H]neurotensin binding (4 nM), the amino-terminal fragments neurotensin and neurotensin1-11 were weak inhibitors. This requirement for the carboxy-terminal fragment neurotensin is consistent with [3H]neurotensin binding to specific neurotensin receptors in the human spinal cord. In all cases the autoradiograms demonstrated that neurotensin receptors were distributed in a similar fashion in the gray matter of the cervical, thoracic, lumbar, sacral and coccygeal regions of the human spinal cord. At all 21 spinal levels examined, the highest density of neurotensin receptors was localized in lamina II of the dorsal horn. Within lamina II the receptors were especially concentrated in the deeper inner segment (IIi) where they formed a dense band lying immediately dorsal to lamina III. The density of receptors in this inner region of lamina II (23.5 fmol/mg) was almost double that in the outer segment of lamina II (12.2 fmol/mg), which showed the next highest density of receptors, and more than three times that in the adjacent lamina I (6.9 fmol/mg) and lamina III (7.1 fmol/mg). A moderate density of receptors was present in the intermediomedial (8.0 fmol/mg) and intermediolateral (8.0 fmol/mg) nuclei of lamina VII, and in lamina IX (4.4 fmol/mg). The density of labelling in the remaining laminae of the spinal cord was very low. These results indicate that neurotensin receptors are mainly localized in somatic and visceral sensory and motor regions of the human spinal cord and suggest that neurotensin may play a role in modulating sensory-motor functions in the human spinal cord.

The postnatal ontogeny of substance P-immunoreactive fibers in the sympathetic preganglionic nuclei of the rat

The ontogeny of substance P (SP)-containing fibers and puncta is described in laminae VII and X of the rat thoracolumbar spinal cord from the day of birth until postnatal day (P) 60. As SP fibers and puncta innervate and demarcate the distribution of preganglionic sympathetic nuclei, strong temporal and weak rostrocaudal ontogenetic gradients exist. Additionally, a heterogeneous segmental SP ontogenetic pattern is observed in sympathetic nuclei. On the day of birth, SP fibers are present in an unorganized fashion in sympathetic nuclei with the exception of the nucleus intercalatus which is clearly outlined. From P0 to P4 SP fibers and puncta are established along a 'ladder-like' pattern and from P6 to P15 SP fibers and puncta steadily accumulate in sympathetic nuclei at all spinal levels. By P15 the nuclei intermediolateralis, pars principalis and funicularis, and the nucleus intercalatus are clearly outlined by SP immunoreactivity while the central autonomic region (lamina X) contains heterogeneous bands of SP immunoreactivity. From P20 to P30, SP fibers and puncta accumulate in each autonomic nucleus and longitudinal SP connections form between each adjacent nucleus intermediolateralis pars principalis. Along the spinal midline the nucleus intercalatus pars paraependymalis and the dorsal commissural nucleus emerge from the central autonomic region as separate SP-innervated nuclei. On P40 a period of reorganization takes place so that SP fibers within sympathetic nuclei become more diffuse and the nucleus intercalatus becomes more complex in appearance. The adult SP pattern is formed by P60 when the dorsal commissural nucleus dense core becomes the last autonomic region to be SP innervated. In addition, a transient population of immunohistochemically demonstrable cervical-thoracic laminae VII and X SP cell bodies are observed from P2 to P15.

Morphometrical study of the cat thoracic dorsal root ganglion cells in relation to muscular and cutaneous afferent innervation

The sizes of neuronal somata in cat dorsal root ganglia were determined at the different thoracic segmental levels (T1-T13). The intersegmental variations in the average value and class distribution of diameters were analysed. The maximal and minimal average mean cell diameters were 51.1 and 43.3 microns at the T1 and T2 levels, respectively. Caudally, this value gradually increased from T2 to T8 (47.8 microns) and thereafter decreased progressively to T12 (44.7 microns). At T1, large cells (greater than 50 microns in diameter) were 3.3-fold in excess compared to small ones (less than 35 microns in diameter). The proportion of large to small cells strongly decreased to a 0.9 ratio from T1 to T2, then increased again from T2 (0.9) to T8 (2.3). The size distributions of the overall cell populations were compared to those of neurones supplying muscular targets via the external intercostal nerves or cutaneous targets via the lateral branch of the internal intercostal nerves, identified following the retrograde transport of horseradish peroxidase. The size distribution of cells serving cutaneous nerves was similar to that exhibited by the overall population of ganglion cells. In contrast, the size distributions of cells giving rise to muscle afferents tended towards smaller values. In the thoracic dorsal root ganglia, the cell body sizes of the muscular primary afferents were close to those previously reported for the visceral primary afferents.

The projection of the medial and posterior articular nerves of the cat's knee to the spinal cord

We studied the spinal projections of the medial and posterior articular nerves (MAN and PAN) of the knee joint in the cat with the aid of the transganglionic transport of horseradish peroxidase. The afferent fibers of the MAN entered the spinal cord via the lumbar dorsal roots L5 and L6 and those of the PAN entered via the dorsal roots L6 and L7. Within the dorsal root ganglia, most labeled neurons had small to medium diameters. A relatively higher number of medium-size cell bodies were labeled from the PAN than from the MAN. In the spinal cord labeled MAN afferent fibers and terminations were most dense in the L5 and L6 segments, and those of the PAN were most dense in L6 and L7, that is, in the respective segments of entry. Labeled afferent fibers from both nerves projected rostrally at least as far as L1 and caudally as far as S2. Labeled fibers were found in Lissauer's tract as well as in the dorsal column immediately adjacent to the dorsal horn. In the spinal gray matter, both nerves had two main projection fields, one in the cap of the dorsal horn in lamina I, the other in the deep dorsal horn in laminae V-VI and the dorsal part of lamina VII. Both nerves, but particularly the PAN, projected to the medial portion of Clarke's column. No projection was found to laminae II, III, and IV of the dorsal horn or to the ventral horn. Since these findings parallel observations on hindlimb muscle afferent fibers, the present data support the existence of a common pattern for the central distribution of deep somatic afferent fibers.

Bilateral inputs and supraspinal control of viscerosomatic neurones in the lower thoracic spinal cord of the cat

1. Single-unit activity has been recorded from eighty-three viscero-somatic neurones in the lower thoracic spinal cord (T9-T11) of chloralose-anaesthetized cats. These neurones were driven by natural and/or electrical stimulation in their somatic receptive fields and gave excitatory responses to electrical stimulation of the ipsilateral splanchnic nerve. Contralateral visceral inputs were tested by electrical stimulation of the contralateral splanchnic nerve. Tonic and phasic descending influences were tested by reversible spinalization with cold block at T7 and by electrical stimulation in nucleus raphe magnus and the immediately adjacent reticular formation. 2. Most viscero-somatic neurones (89%) gave an excitatory response to stimulation of the contralateral splanchnic nerve and were therefore considered to have bilateral visceral inputs. In this group of neurones three categories of cells were identified depending on whether their responses to ipsilateral splanchnic nerve stimulation were decreased (50%), increased (42%) or unchanged (8%) in the spinal state. Only one cell with an exclusively ipsilateral visceral input was tested for the effects of reversible spinalization. Stimulation of contralateral splanchnic nerve failed to evoke activity in this cell in the spinal state. 3. Sixty-four viscero-somatic neurones with bilateral visceral inputs and four neurones with exclusively ipsilateral visceral inputs were tested with electrical stimulation in nucleus raphe magnus and the adjacent reticular formation. Seventy-eight per cent gave an initial excitatory response which was followed by a period of reduced responsiveness to stimulation of visceral and somatic afferents. Three of the four neurones with an exclusively ipsilateral visceral input had no excitatory drive from the brain stem but their responses to stimulation of visceral and somatic afferents were depressed. 4. The majority (77%) of neurones with bilateral inputs were located in laminae VII and VIII with the remainder in the dorsal horn, predominantly laminae I and V, whereas all but one of the neurones with an exclusively ipsilateral visceral input were located in the superficial dorsal horn, predominantly lamina I, and none in laminae VII and VIII. 5. These results show that the majority of viscero-somatic neurones in the cat's lower thoracic spinal cord receive bilateral visceral inputs and that the transfer of this information is subjected to descending control which includes excitation as well as inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Lamina X of primate spinal cord: distribution of five neuropeptides and serotonin

The distribution of substance P, somatostatin, cholecystokinin, vasoactive intestinal polypeptide, enkephalin and serotonin in axons, terminals and neurons was compared in the area surrounding the central canal (lamina X) at five representative levels of the monkey spinal cord, using peroxidase-antiperoxidase immunocytochemistry. Immunoreactive neurons containing each of the neurochemicals were identified. At the cervical, thoracic and lumbar levels the area lateral to the canal had dense terminal fields immunoreactive for each neurochemical. The dorsal commissural region, the pericanal area, and the ventral commissural area were supplied by some but not all of the substances. In the lower thoracic cord innervation extended into the dorsal midline area and into the ventromedial commissural region. In contrast, in the sacral cord, the dorsal commissural region could be subdivided on the basis of innervation, and the lateral region was densely supplied by only cholecystokinin and serotonin, while the sacral ventral commissure and the pericanal area were supplied by all six neurochemicals. The immunocytochemical mappings were compared with published maps of functional classes of neurons and with the distribution of primary afferents and descending fibers in lamina X. The dense peptidergic and serotonergic innervation in the lateral area and the dorsal commissural area corresponded particularly with the location of projection neurons and primary afferents described in other studies.

The central projection of masticatory afferent fibers to the trigeminal sensory nuclear complex and upper cervical spinal cord

Retrograde and anterograde transport of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) conjugate was used to study the organization of primary afferent neurons innervating the masticatory muscles. HRP applied to the nerves of jaw-closing muscles--the deep temporal (DT), masseter (Ma), and medial pterygoid (MP)--labeled cells in the trigeminal ganglion and the mesencephalic trigeminal nucleus (Vmes), whereas HRP applied to nerves of the jaw-opening muscles--anterior digastric (AD) and mylohyoid (My)--labeled cells only in the trigeminal ganglion. Cell bodies innervating the jaw-closing muscles were found with greater frequency in the intermediate region of the mandibular subdivision, while somata supplying the jaw-opening muscles were predominant posterolaterally. The distribution of their somatic sizes was unimodal and limited to a subpopulation of smaller cells. Projections of the muscle afferents of ganglionic origin to the trigeminal sensory nuclear complex (TSNC) were confined primarily to the caudal half of pars interpolaris (Vi), and the medullary and upper cervical dorsal horns. In the Vi, Ma, MP, AD, and My nerves terminated in the lateral-most part of the nucleus with an extensive overlap in projections, save for the DT nerve, which projected to the interstitial nucleus or paratrigeminal nucleus. In the medullary and upper cervical dorsal horns, the main terminal fields of individual branches were confined to laminae I/V, but the density of the terminals in lamina V was very sparse. The rostrocaudal extent of the terminal field in lamina I differed among the muscle afferents of origin, whereas in the mediolateral or dorsoventral axis, a remarkable overlap in projections was noted between or among muscle afferents. The terminals of DT afferents were most broadly extended from the rostral level of the pars caudalis to the C3 segment, whereas the MP nerve showed limited projection to the middle one-third of the pars caudalis. Terminal fields of the Ma, AD, and My nerves appeared in the caudal two-thirds of the pars caudalis including the first two cervical segments, the caudal half of the pars caudalis and the C1 segment, and in the caudal part of the pars caudalis including the rostral C1 segment, respectively. This rostrocaudal arrangement in the projections of muscle nerves, which corresponds to the anteroposterior length of the muscles and their positions, indicates that representation of the masticatory muscles in lamina I reflects an onion-skin organization. These results suggest that primary muscle afferent neurons of ganglionic origin primarily mediate muscle pain.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurophysiology of gastrointestinal pain

The only non-general sensation that can be evoked from the gastrointestinal (GI) tract is that of pain ranging from mild discomfort to intense pain. However, in certain regions of the gut, such as the rectum and gastro-oesophagus, the feeling of pain can be preceded by non-painful sensations of distension at lower stimulus intensities. GI pain is often dull, aching, ill-defined and badly localized. In some cases, GI pain is projected to areas of the body away from the originating viscus ('referred' pain). These properties indicate that the representation of internal organs within the central nervous system is very imprecise. Behavioural, neurophysiological and clinical evidence shows that most forms of GI pain are mediated by activity in visceral afferent fibres running in sympathetic nerves and that the afferent innervation of the gut mediated by parasympathetic nerves is not primarily concerned with the signalling and transmission of GI pain. As for the encoding mechanism of the peripheral sensory receptor in the gut, there is evidence for the existence of specific visceral nociceptors in some locations (e.g. the biliary system) and for the existence of non-specific 'intensity' type receptors in other locations (e.g. the colon). In any case, the actual number of nociceptive afferent fibres in the gut is very small and this explains why large areas of the GI tract appear to be insensitive or require considerable stimulation before giving rise to painful sensations. The few nociceptive afferents contained in sympathetic nerves can excite many second order neurones in the spinal cord which in turn generate extensive divergence within the spinal cord and brain stem, sometimes involving long supraspinal loops. Such a divergent input can activate many different systems, motor and autonomic as well as sensory, and thus trigger the general reactions that are characteristic of visceral nociception: a diffuse and ill-localized pain sometimes referred to somatic areas, and autonomic and somatic reflexes that result in prolonged motor activity.

Central distribution of efferent and afferent components of the pudendal nerve in rat

Central distribution of efferent and afferent components of the pudendal nerve was examined in the rat by the horseradish peroxidase (HRP) method after HRP application to the central cut end of the pudendal nerve. The pudendal motoneurons were located in the dorsolateral, dorsomedial and lateral groups at L5 and L6. Each of the dorsolateral and dorsomedial groups constituted a slender longitudinal cell column. Pudendal motoneurons in the lateral group were scattered at L5, rostrodorsally to the dorsolateral group. The neurons in the dorsolateral and lateral groups were labelled with HRP applied to the nerve branch innervating the ischiocavernosus and sphincter urethrae muscles. The neurons in the dorsomedial group were labelled with HRP applied to the branch supplying the sphincter ani externus and bulbospongiosus muscles. Some dendrites of pudendal motoneurons in the dorsomedial group extended to the contralateral dorsomedial group. These crossing dendrites were observed not only in male rats but also in female. The average number of the pudendal motoneurons in the dorsolateral and dorsomedial groups were larger in male rats than in female. A few neurons of the intermediolateral nucleus at upper L6 were also labelled with HRP applied to the dorsalis penis (clitoridis) nerve. Axon terminals of the pudendal nerve were distributed, bilaterally with an ipsilateral predominance, to the gracile nucleus, as well as to the dorsal horn and dorsal commissural gray from L4 to S2. A few labelled axons were seen in the intermediolateral nucleus at L6 and S1. Axon terminals from the dorsalis penis nerve were distributed more medially in the dorsal horn than those from the perinealis nerve.

Evidence for a visceral afferent origin of substance P-like immunoreactivity in lamina V of the rat thoracic spinal cord

A visceral afferent origin of substance P-like immunoreactivity in lamina V of the lower thoracic spinal cord of the rat was investigated. In transverse sections from normal animals there was a moderately dense substance P-immunoreactive innervation of lamina V. In some sections there was a dorsoventrally orientated fibre bundle from the superficial dorsal horn entering lamina V. In parasagittal sections, substance P-immunoreactivity in lamina V was found arranged in clusters, with a periodicity in the rostrocaudal axis of 200-600 microns. In some cases these were seen to be continuous with a dorsoventrally orientated fibre bundle from the superficial dorsal horn. After section of the splanchnic nerve there was a consistent reduction in the density of the substance P-like immunoreactivity in lamina V, with fewer clusters on the operated side. Adult rats treated neonatally with capsaicin showed a substantial reduction of substance P-immunoreactivity in laminae I and II and the virtual abolition of staining in lamina V. These results provide evidence of a visceral origin for some of the substance P-like immunoreactivity in lamina V of the rat thoracic spinal cord. In addition, they confirm that most of the substance P-immunoreactivity in the dorsal horn is of primary afferent origin.

Distribution of capsaicin-sensitive urinary bladder afferents in the rat spinal cord

The capsaicin-sensitive afferent innervation of the urinary bladder and the central nervous system distribution of urinary bladder afferents have been studied in the rat. Capsaicin-sensitive primary sensory neurones supplying the urinary bladder have been found in two groups of spinal ganglia located in the Th13-L2 and L6-S1 segments. Capsaicin-sensitive primary sensory afferents from the bladder terminate within Rexed's laminae I, V and X, and in the dorsal gray commissure of the lumbosacral spinal cord. In addition, the results point to a possible vagal sensory innervation of the urinary bladder.

Somatic and visceral inputs to the thoracic spinal cord of the cat: marginal zone (lamina I) of the dorsal horn

1. Single-unit electrical activity has been recorded from fifty-five neurones whose recording sites were located in or immediately adjacent to the marginal zone (lamina I) of the lower thoracic spinal cord (T8-T12) of anaesthetized or decerebrate cats. Their responses to stimulation of somatic and visceral afferent fibres and the sizes of their cutaneous receptive fields have been analysed and compared with the responses and receptive fields of neurones recorded throughout the spinal grey matter. 2. Neurones were classified according to their responses to innocuous stimulation of their somatic receptive fields (i.e. brushing and stroking) or to noxious stimulation (i.e. pinching, squeezing and/or heating above 45 degrees C). 52% of all the neurones recorded in lamina I were driven exclusively by noxious stimulation of the skin (nocireceptive); 33% were driven by both noxious and innocuous stimulation of the skin (multireceptive) and 15% were driven exclusively by innocuous stimulation of the skin (mechanoreceptive). 3. Visceral afferent inputs to these neurones were tested by supramaximal electrical stimulation of the ipsilateral splanchnic nerve (15 V, 0.2 ms, 0.3 Hz). Two types of neurone were distinguished according to their responses to visceral stimulation: (i) somatic neurones, driven only by stimulation of somatic afferent fibres and (ii) viscero-somatic neurones, driven by stimulation of somatic and visceral afferent fibres. Of the neurones recorded in lamina I, 33% were somatic and 67% were viscero-somatic. This proportion was very similar to the percentages of somatic and viscero-somatic neurones recorded throughout the grey matter (37 and 63%, respectively). 4. Viscero-somatic neurones in lamina I had somatic receptive field properties similar to those of viscero-somatic neurones of the entire spinal cord. Half of them were multireceptive, 39% were nocireceptive and 11% were mechanoreceptive. However, somatic neurones in lamina I had receptive field properties different from those of somatic neurones from other laminae: no multireceptive somatic neurones were recorded in lamina I; the vast majority (78%) were nocireceptive and 22% were mechanoreceptive. 5. The majority of somatic and viscero-somatic neurones in lamina I had small somatic receptive fields but, even in this group of cells, viscero-somatic neurones had larger receptive fields than somatic cells. 6. Ascending axonal projections in both dorsolateral funiculi and in the contralateral ventrolateral quadrant were tested in eighteen lamina I neurones. Only one neurone was found to project to the cervical cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Spinal cord projections from hindlimb muscle nerves in the rat studied by transganglionic transport of horseradish peroxidase, wheat germ agglutinin conjugated horseradish peroxidase, or horseradish peroxidase with dimethylsulfoxide

The spinal cord projections of four different groups of hindlimb muscle nerve branches--the medial and lateral gastrocnemius nerves, muscle branches of the deep peroneal nerve, muscle branches of the femoral nerve, and a nerve to the hamstring muscles--were studied with transganglionic transport of horseradish peroxidase (HRP) in the rat. The influence of varying the postoperative survival (3, 6, and 10 days) and of using wheat germ agglutinin-HRP conjugate (WGA-HRP), or HRP with dimethylsulfoxide (DMSO) instead of free HRP was studied for the gastrocnemius nerves. After 3 days' survival following application of HRP to the gastrocnemius nerves, fine granular labeling was found mainly in lamina V in L4-5, and coarse granular labeling was found in Clarke's column as far caudally as L2, and in laminae VI and VII predominantly in Th12-L2. After 6 or 10 days' survival, the fine labeling in lamina V was sparse or absent, whereas the coarse labeling appeared to remain or to be only slightly reduced in Clarke's column and in laminae VI and VII. No labeling suggestive of terminals was observed in laminae I-III from the gastrocnemius nerves. Except for sparse labeling in lamina I in some of the cases and some minor differences rostrocaudally, the spinal distribution of labeling was similar to that from the other nerves investigated. The distribution of labeling obtained after application of WGA-HRP or HRP with DMSO to the gastrocnemius nerves was very similar to that obtained with free HRP after 3 days' survival. The results indicate that the spinal cord projections of hindlimb muscle nerves in the rat distribute mainly in the deep part of the dorsal horn and in the intermediate zone. Furthermore, the lack of labeling suggestive of terminals in laminae I-III from the gastrocnemius nerves suggests, in conflict with earlier findings in the cat, that primary afferent fibers from muscles do not necessarily terminate in these laminae in the rat. The results suggest, furthermore, that fine granular labeling found in lamina V represents fine-calibered afferent fibers. Finally, the similar spinal projection patterns of the different muscle nerves investigated suggest either a less developed or an essentially different somatotopic organization for muscle afferents compared to cutaneous afferents, as revealed in earlier studies.

Projections of visceral and somatic primary afferents to the sacral spinal cord of the domestic fowl revealed by transganglionic transport of horseradish peroxidase

The termination of visceral and somatic primary afferent fibers in the sacral spinal cord of the domestic fowl was studied using transganglionic transport of horseradish peroxidase. Nerve terminals of visceral afferent fibers were found in the lateral edge and base of the dorsal horn and in the dorsal gray commissure in close proximity to parasympathetic preganglionic neurons. Somatic afferents terminated in laminae 2 and 3. The results demonstrate that visceral and somatic afferent fibers in this avian species terminate in different areas of the dorsal horn.

Spinal and trigeminal projections to the nucleus of the solitary tract: a possible substrate for somatovisceral and viscerovisceral reflex activation

This study used the retrograde transport of a protein-gold complex to examine the distribution of spinal cord and trigeminal nucleus caudalis neurons that project to the nucleus of the solitary tract (NST) in the rat. In the spinal grey matter, retrogradely labeled cells were common in the marginal zone (lamina I), in the lateral spinal nucleus of the dorsolateral funiculus, in the reticular part of the neck of the dorsal horn (lamina V), around the central canal (lamina X), and in the region of the thoracic and sacral autonomic cell columns. The pattern of labeling closely resembled that seen for the cells at the origin of the spinomesencephalic tract and shared some features with that of the spinoreticular and spinothalamic tracts. Labeled cells in lamina IV of the dorsal horn were only observed when injections spread dorsally, into the dorsal column nuclei, and are thus not considered to be at the origin of the spinosolitary tract. They are probably neurons of the postsynaptic fibers of the dorsal column. Retrogradely labeled cells were also numerous in the superficial laminae of the trigeminal nucleus caudalis, through its rostrocaudal extent. The pattern of marginal cell labeling appeared to be continuous with that of labeled neurons in the paratrigeminal nucleus, located in the descending tract of trigeminal nerve. Since the NST is an important relay for visceral afferents from both the glossopharyngeal and vagus nerves, we suggest that the spinal and trigeminal neurons that project to the NST may be part of a larger system that integrates somatic and visceral afferent inputs from wide areas of the body. The projections may underlie somatovisceral and/or viscerovisceral reflexes, perhaps with a significant afferent nociceptive component.

Neuronal mechanisms of pain with special emphasis on visceral and deep somatic pain

Pain has several dimensions: the sensory-discriminative, the motivational-affective, the cognitive and the motor and autonomic dimension. Each dimension can be roughly identified with certain brain areas. The sensory-discriminative dimension is also called the "nociceptive dimension" or, briefly, "nociception". 1. Noxious stimuli applied to the skin appear to be encoded quite specifically by certain types of nociceptive afferent units with group III (A) and IV (C) fibers. The impulse activity of these cutaneous primary afferents converges on spinal "nociceptive-specific" neurones, most of which seem to be located in lamina I of the dorsal horn, and together with the nonnociceptive information from the skin on "wide-dynamic range" (multisensory) neurones in the grey matter, most of which are situated in lamina V, but some also in adjacent laminae and lamina I. 2. Many of these "nociceptive-specific" and "wide-dynamic range" neurones project with their axons through the anterolateral tract to the nucleus ventralis posterolateralis (VPL) of the thalamus and also to other thalamic nuclei, to the mesencephalon and to the reticular formation of the brain stem. In the VPL of the thalamus, most neurones with nociceptive input have a wide-dynamic range property, very few are nociceptive-specific. 3. Noxious events leading to deep somatic pain are encoded by thin myelinated (A delta) and unmyelinated afferent fibers (e.g., from skeletal muscle, tendon and joint capsule). Besides these deep somatic "nociceptive" afferent units, other nonnociceptive deep somatic afferent units with fine afferents have been claimed to exist and it is believed that these are involved in functions other than nociception. The specificity of responses of these afferents, with respect to the natural stimuli, is only relative. 4. For the viscera nociceptive spinal visceral afferents, which are only activated when injurious or potentially injurious events in the visceral domain (which may lead to pain) occur, cannot be unambiguously shown to exist. It seems more likely that the activity in the same population of spinal visceral afferents is involved in nociceptive as well as in nonnociceptive sensory functions, in the regulation of visceral organs and in various types of reflexes. 5. No neurones in the spinal grey matter have been found which specifically transmit and process information from fine deep somatic and spinal visceral afferents. This information seems to converge not only on many "wide-dynamic range" (multisensory) spinal neurones but also on some "nociceptive-specific" neurones.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of substance P-like immunoreactive fibers in the thoracic spinal cord of guinea pig

A dorsal-horn fiber system is revealed in the thoracic spinal cord of guinea pig by means of substance P immunocytochemistry. This system has repeated craniocaudal and/or caudo-cranial extensions and possesses five main components: a superficial network, situated beneath the dorsolateral surface of the spinal cord. This network is connected with the dorsal root fibers and the accumulations of substance P-like immunoreactive (SP-LI) fibers in the Lissauer's tract; an accumulation of SP-LI fibers in the Lissauer's tract at the border of the dorsal horn; two collateral SP-LI fascicles (one lateral and one medial) emerging from the SP-LI fiber accumulation in the Lissauer's tract; a transversal fascicle running through laminae III-V, and an SP-LI network in the region of the lateral spinal cord nucleus. These components of the dorsal-horn fiber system show widespread connections with ipsi- and contralateral spinal cord areas, connecting them in cranio-caudal and/or caudo-cranial directions. The SP-LI dorsal-horn system has close relationship with groups of preganglionic sympathetic cells in the intermediate zone of the spinal cord, respective with the vegetative network of this zone. It is suggested that some fibers of the dorsal-horn system that originate from dorsal-root ganglia may represent primary sensory or visceral afferents. It is likely that the dorsal-horn fiber system and the vegetative network of the thoracic spinal cord may represent the morphological basis for the integration of the central and peripheral vegetative nervous systems, and the somatic and vegetative nervous system.

The distribution within the spinal cord of visceral primary afferent axons carried by the lumbar colonic nerve of the cat

Horseradish peroxidase taken up by the sensory axons in the lumbar colonic nerves in 5 cats was observed in the dorsal root ganglia and in the spinal cord in segments L1 through L5. Reaction product was observed in Lissauer's tract, the dorsal columns and laminae I, V, VII and X in a pattern typical of visceral primary afferents from other nerves. A small number of preganglionic neurons were also labeled.

Laminar distribution and somatotopic organization of primary afferent fibers from hindlimb nerves in the dorsal horn. A study by transganglionic transport of horseradish peroxidase in the rat

Primary afferent nerve fibers to the spinal cord in the adult rat were labeled by applying horseradish peroxidase to the cut end of one of the following hindlimb nerves; the tibial, medial plantar, lateral plantar, common peroneal, saphenous, sural, lateral femoral cutaneous or obturator nerve. Maximal labeling intensity was found in the dorsal horn after 36-72 h survival. Labeling was observed in different dorsal horn laminae at different levels within the L1-S1 spinal cord segments, depending on which nerve horseradish peroxidase had been exposed to, probably reflecting the individual composition of afferent fiber types. Although a certain overlap was found, the central projections of the eight different nerves investigated formed well delineated three dimensional compartments within the medial 2/3 to 3/4 of the dorsal horn. This was most clearly discernible in lamina II. Although interindividual differences were present, bilaterally identical operations gave symmetrical projection patterns in the dorsal horn. The results indicate that dorsal horn projections of hindlimb nerves are organized in a highly ordered somatotopic fashion.