Anatomy, physiology and pharmacology of the periaqueductal gray contribution to antinociceptive controls.
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Analgesia↗
Biomedical subjects
A I Basbaum
Publications and source records attributed to A I Basbaum.
Beta 2-adrenergic mechanisms in experimental arthritis.
We have studied (i) the contribution of specific adrenergic receptors to the proinflammatory effects of the sympathetic nervous system in experimental arthritis and (ii) the phases of the disease during which the sympathetic nervous system influences joint injury. Severity of joint injury was measured radiographically 28 days after induction of adjuvant arthritis in control rats and in rats treated with a variety of sympatholytic agents at various times during the course of the disease. Rats treated with a nonspecific catecholamine depletor (reserpine) or a beta-adrenergic receptor antagonist (propranolol) had a delayed onset and significantly less severe joint injury than saline-treated controls when treatment began prior to injection of the adjuvant and continued to day 28 after the injection. When administered over the same treatment period, neither nonselective (phenoxybenzamine) nor selective [prazosin (alpha 1) and yohimbine (alpha 2)] alpha-adrenergic receptor antagonists affected the onset or severity of joint injury. Metoprolol, a beta 1 antagonist, was also without effect. In contrast, two beta 2 antagonists (butoxamine and ICI 118,551) significantly retarded disease onset and reduced the severity of joint injury. When reserpine or butoxamine treatment was initiated after the onset of clinically apparent arthritis, it was still possible to favorably influence the course of the disease. These data indicate an important contribution of the beta 2-adrenergic receptor to joint injury in experimental arthritis.
Animals↗
Leukotriene B4 decreases the mechanical and thermal thresholds of C-fiber nociceptors in the hairy skin of the rat.
1. We have recently shown that leukotriene B4 (LTB4), a product of the 5-lipoxygenase pathway of arachidonic acid metabolism, sensitizes nociceptors to mechanical stimuli. The present study examined whether LTB4 also induces a heat sensitization of cutaneous C-fiber nociceptors. The C-fiber nociceptors studied had von Frey hair thresholds greater than 5 g and were characterized according to their responses to noxious heat and chemical stimuli, including glacial acetic acid, bradykinin, and capsaicin. Thirty-four of the C-fibers that were activated by intense thermal stimulation were also activated by topical application of glacial acetic acid. They were classified as C-polymodal nociceptors (2, 28). Those that were activated by intense mechanical and thermal stimulation, but were unresponsive to acid, were classified as C-mechanoheat nociceptors (27). 2. Ninety-four percent of C-polymodal nociceptors and 60% of C-mechanoheat nociceptors were sensitized by LTB4. All C-fiber nociceptors that showed a decrease of their heat threshold also had a decrease of their mechanical threshold. LTB4 (75 ng) lowered the average heat threshold from 45 degrees C to 35 degrees C and produced an average decrease in the mechanical threshold of 86%. 3. The magnitude of the LTB4-evoked decrease in thermal threshold was similar to that produced by 75 ng of prostaglandin E2 (PGE2). These data demonstrate that LTB4 sensitizes C-mechanoheat nociceptors to both mechanical and thermal stimuli. 4. We conclude that LTB4 may contribute to the component of hyperalgesia that is resistant to nonsteroidal anti-inflammatory agents.
Action Potentials↗
The fiber caliber of 5-HT immunoreactive axons in the dorsolateral funiculus of the spinal cord of the rat and cat.
Although there is considerable evidence that the analgesic action of electrical brain stimulation is mediated in part by serotonergic (5-HT) axons in the dorsolateral funiculus (DLF) of the spinal cord, studies in the rat have questioned the existence of this pathway. In this study, we used antisera directed against a conjugate of 5-HT and bovine serum albumin (BSA) to identify immunoreactive 5-HT axons in the DLF of the rat and cat. Both light and electron-microscopic studies were performed so that the fiber caliber of the labeled axons could also be determined. We found a rich complement of immunoreactive 5-HT axons in the DLF of both rat and cat. Although these could be seen without difficulty in the normal cat, in the rat it was necessary to make a lesion of the DLF to build up the staining rostrally. Ultrastructural analysis established that almost all of the labeled axons (in rat and cat) were unmyelinated. We conclude that there are indeed 5-HT immunoreactive axons in the DLF of the rat and cat. These presumably derive from neurons of the medullary nucleus raphe magnus (NRM), which have been implicated in the descending controls exerted by opiates and electrical brain stimulation. The results suggest that previous physiological studies of the properties of the opiate-responsive, spinally projecting NRM neurons were not made from those that are 5-HT containing.
Animals↗
Anatomical introduction to analgesia: correlation of activity of neurons of the superficial dorsal horn with pain and analgesia.
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Analgesia↗
Autoradiographic evidence of serotonin1 binding sites on primary afferent fibres in the dorsal horn of the rat spinal cord.
Spinal serotonin1 (5-HT1)(labelled by [3H]5-HT), 5-HT1A (labelled by [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([3H]8-OH-DPAT)), mu- (labelled by [3H]Tyr-D-Ala-Gly-(Me)Phe-Gly-ol ([3H]DAGO) and [3H]naloxone) and delta-opiate (labelled by [3H]Tyr-D-Ser-Gly-Phe-Leu-Thr [( 3H]DSTLE] receptor binding sites were studied in adult rats using quantitative autoradiography after either neonatal treatment with capsaicin or unilateral cervical dorsal rhizotomy. Both treatments produced a significant loss of 5-HT (-20 to -30%) and opiate (-30 to -45%) binding sites within the superficial layers of the dorsal horn, suggesting they are partly located presynaptically on primary afferent fibres. Thus, 5-HT, as well as opiates, might generate analgesia by acting--at least partly--on primary afferent nociceptive fibres at the spinal level.
Afferent Pathways↗
A new microdissection technique for regional biochemical analysis of the rat spinal cord: serotonin, norepinephrine, dopamine and uric acid.
This report described a new microdissection procedure to evaluate the regional distribution of neuromediators in the rat spinal cord. Different segments are first divided into sagittal slices. From these, different grey and white matter regions can be microdissected. This permits selective biochemical measurements in different laminae, including the area around the central canal. White and grey matter can also be differentially analysed. Using HPLC with electrochemical detection, we report on the regional analysis of biogenic amines as well as uric acid. An increase in 5-hydroxytryptamine (5-HT) levels was observed from cervical to lumbar segments. 5-HT levels were highest in the motoneurone samples (lamina IX) of the lumbar cord. The next highest levels were found in lamina X, followed by the intermediate grey matter laminae and the dorsal horn. Small amounts of 5-HT were detected in the white matter. Interestingly, the ratio of 5-hydroxyindoleacetic acid (5-HIAA) to 5-HT was greatest in the white matter and least in the motoneurone sample. Norepinephrine (NE) levels were higher in the thoracic than in the cervical or the lumbar cord. The highest levels were found in the lamina X in thoracic segments. With this exception, no marked laminar difference in NE levels was observed. Dopamine (DA) levels were highest in the dorsal horn of the cervical and the thoracic cord, the next highest levels were found in the intermediate grey matter and lamina X in the same segments. The distribution of uric acid (UA) was comparable to that of NE: UA levels were highest in the thoracic cord, but no marked laminar difference was observed. On the other hand, UA levels in white matter generally exceeded those in the grey matter. These data indicate the value of a sagittal regional microdissection of the spinal cord. The ability to separately analyse different laminae of the cord (as well as differentiating grey and white matter) should prove useful in future studies of experimentally evoked changes in neurotransmitters within functionally distinct regions of the spinal cord.
Animals↗
Wheat germ agglutinin-apoHRP gold: a new retrograde tracer for light- and electron-microscopic single- and double-label studies.
In this report, we describe a new colloidal-gold-labelled retrograde tracer, wheat germ agglutinin (WGA) conjugated to enzymatically inactive horseradish peroxidase (apoHRP). This protein gold complex (WGAapoHRP-Au) is a sensitive marker for retrograde tracing of the projections of CNS neurons at the light-microscopic (LM) level when a silver-enhancement procedure is used to detect the gold in the tracer. For electron-microscopic (EM) analysis, the silver-enhanced sections undergo a further gold-toning step. This protects against rapid oxidation and dissolution of the silver precipitate during the osmication procedure. A major advantage of WGAapoHRP-Au is that it can be used in a variety of multiple-labelling studies. When the retrograde transport of the new tracer is combined with that of the fluorescent dye, True Blue, neurons that have bifurcating axons can be readily demonstrated. Simultaneous immunofluorescent detection of the cytochemistry of the double-retrogradely labelled neurons is also possible. In contrast to a WGA-HRP gold complex, the new complex has no enzymatic activity. Thus HRP-based techniques (e.g., anterograde transport of WGA-HRP or peroxidase-antiperoxidase immunocytochemistry) can be performed on tissue that contains retrogradely labelled neurons marked with WGAapoHRP-Au without having to pretreat tissue so as to destroy endogenous HRP enzyme activity. At the EM level, the gold is readily distinguished from DAB immunoreaction product. This makes both LM and EM double-labelling studies possible. The great sensitivity of the new tracer, its compatibility with a variety of aldehyde fixatives, its ease of detection, and the fact that it can be simultaneously used with several fluorescent and HRP-based immunocytochemical and tracing techniques make WGAapoHRP-Au a valuable tool for LM and EM characterization of CNS cytochemistry and connectivity.
3,3'-Diaminobenzidine↗
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.
Afferent Pathways↗
Cytochemical studies of the neural circuitry underlying pain and pain control.
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Animals↗
The distribution of substance P-, enkephalin- and dynorphin-immunoreactive neurons in the medulla of the rat and their contribution to bulbospinal pathways.
This study examined the medullary distribution of peptide-containing neurons at the origin of bulbospinal pathways in the rat. Antisera directed against substance P, methionine-enkephalin-arg-gly-leu and dynorphin B were used on sections in which spinally projecting brainstem neurons had been identified by the retrograde transport of a protein-gold complex that was injected into the spinal cord. Both the relative numbers and distribution of the different peptide-immunoreactive spinally projecting neurons differed. Methionine-enkephalin-immunoreactive neurons were twice as numerous as the substance P-immunoreactive cells and seven times more numerous than the dynorphin B-positive neurons. The methionine-enkephalin cells were found in all medullary raphé nuclei, and in the ventromedial and ventrolateral medullary reticular formation. Caudally, the methionine-enkephalin cells were concentrated laterally; more rostrally they were located more medially. Three major loci of methionine-enkephalin-immunoreactive cells were found: (1) the nucleus reticularis paragigantocellularis lateralis, at levels caudal to the facial nucleus, (2) the B3 cell group (nucleus raphé magnus and the nucleus reticularis magnocellularis, pars alpha) and the most rostral part of the B1 and B2 cell groups (nuclei raphé pallidus and obscurus), (3) a dense cluster of cells that flanks the dorsal surface of the dorsal accessory olive (referred to as the nucleus interfascicularis hypoglossi, pars dorsalis). Substance P-like cells were seen in all raphé nuclei except for the most anterior portion of the B3 cell group. Substance P-immunoreactive cells were also seen in both the ventromedial (nuclei reticularis ventralis and magnocellularis) and ventrolateral medulla (nucleus reticularis paragigantocellularis lateralis). Finally there was a dense concentration of substance P neurons in the nucleus interfascicularis hypoglossi, pars ventralis. The distribution of dynorphin-immunoreactive neurons differed significantly from that of methionine-enkephalin and substance P. Dynorphin cells were almost exclusively found in the ventrolateral medulla (nucleus reticularis paragigantocellularis lateralis), at all levels between the lateral reticular nucleus and the caudal pole of the facial nucleus. The proportion of each of these peptidergic-immunoreactive cells at the origin of bulbospinal pathways differed considerably. Substance P spinally projecting neurons were more numerous than methionine-enkephalin spinally projecting neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Leukotriene and prostaglandin sensitization of cutaneous high-threshold C- and A-delta mechanonociceptors in the hairy skin of rat hindlimbs.
Single C- and A-delta fibers were isolated from dissected filaments of the saphenous nerve in pentobarbital anesthetized rats and the corresponding cutaneous receptive fields mapped with calibrated von Frey hairs. Nociceptors were characterized by their responses to noxious mechanical, thermal and chemical stimuli, including intradermal injections of leukotriene B4, prostaglandin E2, bradykinin and capsaicin. Leukotriene B4 decreased the mean mechanical threshold by a maximum of 80% within 10 min and for more than 3 h after intradermal injection of 75 ng of leukotriene B4. The degrees of sensitization of a fiber by leukotriene B4 and prostaglandin E2 were highly correlated. A potentiation effect also was observed, in that injection of prostaglandin E2 or leukotriene B4 1 h after the other eicosanoid further lowered the mechanical threshold of a sensitized fiber, whereas fibers that were not sensitized by leukotriene B4 were unaffected by prostaglandin E2. The sensitizing action of leukotriene B4 and prostaglandin E2 was directed to multiple classes of cutaneous nociceptors including 73% of C-polymodal, 60% of C-mechano-heat, 42% of C-mechano-cold nociceptors and 70% of A-delta high-threshold mechanonociceptors. The pain-evoking substances bradykinin and capsaicin activated 81% and 88%, respectively, of the sensitized C-polymodal nociceptors, 17% and 84% of the sensitized-C-mechano-heat nociceptors, 12% and 37% of the sensitized C-mechano-cold nociceptors, and 17% and none of the sensitized A-delta high-threshold mechanociceptors. The responses of C-fibers to bradykinin and capsaicin were highly correlated.(ABSTRACT TRUNCATED AT 250 WORDS)
Afferent Pathways↗
Distinct cellular and regional localization of immunoreactive protein kinase C in rat brain.
Monoclonal antibodies raised against highly purified protein kinase C were used to localize protein kinase C in the rat brain. Using various monoclonal antibodies, at least three distinct antibody-staining patterns were found. One monoclonal antibody exclusively labeled astroglial elements, including astrocytes, tanycytes, and cerebellar radial glia. Another monoclonal antibody exclusively labeled neural cells, including cortical and hippocampal pyramidal dendrites and Purkinje cells of the cerebellum. A third monoclonal antibody (which inhibited protein kinase C activity) intensely stained more limited brain regions, particularly thalamic neurons, and also stained astroglial structures in brain, spinal cord, and cerebellum. The possibility that the three staining patterns reflect the differential regional and cellular localization of related, but distinct, enzymes of protein kinase C is discussed.
Animals↗
Contribution of the nervous system to the pathophysiology of rheumatoid arthritis and other polyarthritides.
Some clinical features of rheumatoid arthritis (RA) (for example, preferential joint involvement and bilateral symmetry), taken together with the strong evidence of neurogenic inflammatory processes, suggest that the nervous system contributes to the inflammatory component of RA and other polyarthritides. The authors propose that the increased risk and severity of disease in particular joints reflects a greater innervation of those joints by unmyelinated afferent and sympathetic efferent fibers. Release of the proinflammatory peptide, substance P, from the peripheral terminals of nociceptive joint afferent fibers, through interactions with many nonneural cells, exacerbates the inflammatory process. Release of mediators from sympathetic efferents (including norepinephrine) also contributes to the inflammation, either through an independent mechanism or by acting in concert with the nociceptive afferent-derived substances. Therapies directed at interruption of the nervous system contribution to the pathophysiology of these diseases should offer a new direction to treatment.
Animals↗
Bulbospinal projections in the primate: a light and electron microscopic study of a pain modulating system.
The projections of the nucleus raphe magnus (NRM) and the immediately adjacent reticular formation were studied in the macaque monkey following injections of the rostroventral medulla with 3H-leucine and examination of the resultant labeled axons and terminals by light and electron microscopic autoradiography. Five monkeys had accurately placed injections, which resulted in fiber pathway labeling that coursed caudally, laterally, and dorsally to project to laminae I, II, and V of subnucleus caudalis of the trigeminal and then traveled in the dorsolateral funiculus of the cord and terminated in similar laminae of the spinal dorsal horn at cervical levels. The pathway was only lightly labeled caudal to the cervical enlargement and could not be readily discerned above background in the thoracic or lumbar cord. Electron microscopy revealed that axons and terminals serving this system constitute a heterogeneous population. Large-diameter myelinated axons (3-6-micron diameter), small myelinated axons (0.75-3-micron diameter), and clusters of nonmyelinated axons were labeled. Terminals in laminae I, II, and V contained mixtures of clear round and granular vesicles or clear pleomorphic and granular vesicles or formed the central element in synaptic glomeruli. The labeled profiles formed asymmetrical or symmetrical synapses on medium and small dendrites; labeled axosomatic synapses were not observed. In rare instances there were contacts between labeled profiles and vesicle-containing structures, which were probably dendritic, but whether the NRM axon was pre- or postsynaptic to such structures could not be determined. It was concluded that the NRM in the monkey is organized in a manner quite similar to that previously described in the cat. The wide variety of fiber types and synaptic terminals serving this system suggests that different classes of neurons participate in it, probably using several transmitter substances that result in varying postsynaptic effects on neurons located in the trigeminal complex and dorsal horn.
Animals↗
The neurotoxic effect of gold sodium thiomalate on the peripheral nerves of the rat. Insights into the antiinflammatory actions of gold therapy.
Although gold is one of the few therapeutic agents that has been proven effective in producing remission in patients with rheumatoid arthritis, its mechanism of action is unknown. Since nociceptive afferent and sympathetic efferent fibers of the peripheral nervous system contribute to the pathophysiology of inflammation, and since a known side effect of gold therapy is a polyneuropathy, we tested the hypothesis that gold is toxic to small-diameter peripheral nerve fibers in the rat. We found that prolonged treatment with gold, at the same dosage reported to be effective against adjuvant-induced arthritis in the rat, produced a significant decrease in the numbers of unmyelinated, but not of myelinated, axons. Gold treatment also elevated nociceptive thresholds in both articular and nonarticular structures. These results suggest that gold produces an antiinflammatory effect on arthritis by a neurotoxic effect on the peripheral nerves involved in neurogenic inflammation.
Animals↗
The contribution of pain to disability in experimentally induced arthritis.
We examined the differential effects of disease severity and pain on morbidity (as measured by weight loss and decrease in activity) in rats with adjuvant-induced arthritis. We found that eliminating nociceptive messages from affected extremities, although not significantly affecting the course of the disease, attenuated the morbidity observed in arthritic rats. When pain was factored out, the severity of the arthritis had no significant effect on the same measures of morbidity. These findings suggest that treatment of pain may reduce morbidity, and thereby may have significant benefits beyond that provided by slowing of the disease process.
Animals↗
Benzidine dihydrochloride as a chromogen for single- and double-label light and electron microscopic immunocytochemical studies.
Although very sensitive chromogens have been adapted for localization of horseradish peroxidase in anterograde and retrograde tracing studies, they have not been successfully applied in immunocytochemical studies. This report describes a protocol which uses benzidine dihydrochloride (BDHC) as the chromogen for light (LM) and electron microscopic (EM) immunocytochemical studies. The protocol is comparable to that used for tetramethylbenzidine, except that the pH of the reaction is above 6.0. At the LM level, the BDHC reaction product is bluish-green and crystalline. Both the color and form of the product are readily distinguished from the reddish-brown DAB reaction product. LM double-labeling studies are therefore feasible. The use of BDHC also increases significantly the sensitivity of the immunoreaction. Higher fixative concentrations can be used, less detergent is necessary, and higher primary antibody dilutions are possible. By osmicating at 45 degrees C in an s-collidine buffer it is possible to preserve the soluble BDHC reaction product for EM analysis. Immunoreactive cells are particularly well labeled with this new protocol. The BDHC crystals are easily detected at the EM level and can be distinguished from flocculent DAB reaction product. This feature makes EM double-labeling studies possible.
3,3'-Diaminobenzidine↗