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Possible morphological correlates of capsaicin desensitization
Brain Research, 540 (1991) 279-282 Elsevier
279
BRES 24500
Possible morphological correlates of capsaicin desensitization Elizabeth Kir~ily 1, G. Jancs6 2 and M. Haj6s 2 1Department of Anatomy, Albert Szent-Gy6rgyi Medical University, H-6701 Szeged (Hungary) and 2Departmentof Physiology, Albert Szent-Gy6rgyi Medical University, H-6720Szeged (Hungary) (Accepted 16 October 1990)
Key words: Capsaicin-sensitivenerve fiber; Fine structure; Ureter; Guinea pig; Capsaicin desensitization; In vitro
The changes in the fine structure of axonal profiles of the guinea-pig ureter were examined after exposure to capsaicin in vitro. In the ureters exposed to capsaicin (1-10 gM), about 60%, of all axonal profiles exhibited conspicuous ultrastructural impairment. It is suggested that these alterations might interfere with the release of peptides from these particular nerve endings and therefore contribute significantly to the mechanisms of capsaicin desensitization.
Neurohistological and pharmacological studies have revealed that a population of capsaicin-sensitive primary afferent neurones represents a unique division of the sensory nervous system 5'11-14'21. A continuously accumulating body of evidence indicates not only that capsaicinsensitive afferent fibres are involved in the mediation of reflex and nociceptive responses, but also that they possess a characteristic efferent function 5'8'9'12-14'21. Thus, a distinct feature of these capsaicin-sensitive neurones is the release of peptides from their stimulated peripheral nerve terminals, a mechanism by which they exert a profound and physiologically important regulatory influence on the innervated tissue 5'9'14'21. The occurrence of capsaicin-sensitive primary afferent nerve fibres has been demonstrated in most viscera, including the urogenital system 2'6'7'17'19. In vitro studies on the guinea-pig ureter provided evidence for substance P and calcitonin gene-related peptide-mediated contractile responses which depend on the integrity of the capsaicinsensitive afferent nerves 1'7. The failure of the isolated organ to respond to repeated administration of capsaicin, a phenomenon generally referred to in the current literature as capsaicin desensitization, was a common finding in these experiments. Indeed, upon repeated application capsaicin failed either to elicit a release of neuropeptides 3'~7 or to affect ureteric motility 1. Although several hypotheses have been put forward to explain this effect, the mechanisms of capsaicin desensitization are still unclear 3"4'1°'12"13"15'22. Therefore, the aim of the present experiments was to unravel possible morphological alterations induced by capsaicin under
conditions identical with those used in the in vitro studies, which might contribute to the cellular mechanisms of capsaicin desensitization. Adult male guinea-pigs weighing 400-450 g were used. The animals were anaesthetized with pentobarbitone sodium (40 mg/kg) and the ureters were dissected out. Segments 2-3 mm in length were cut from the organ and placed into small chambers containing Krebs' solution (composition in mM: NaCI 119, N a H C O 3 25, KH2PO 4 1.2, MgSO 4 1.5, KCI 4.7, CaCI 2 2.5, glucose 11) gassed with a mixture of 95% oxygen and 5% carbon dioxide. After a preincubation period of 20 min at 37 °C, capsaicin at concentrations in the range 30 nM-10 /~M or an equivalent amount of its solvent was added to the specimens. After 6 min, the incubation solution was replaced with fresh physiological solution and the specimens were incubated for a further period of 60 rain, whereafter they were fixed in an aldehyde fixative containing 2% paraformaldehyde and 1% glutaraldehyde in 0.1 M phosphate buffer, p H 7.4. Specimens were immersed for another 6 h in the same fixative and then post-fixed in a 2% buffered solution of osmium tetroxide for 2 h at 4 °C, dehydrated in graded alcohols, and finally embedded in Araldite. Ultrathin sections were cut on a Reichert ultrotome, stained with uranyl acetate and lead citrate and examined under a Jeol 100B electron microscope. In control specimens, unmyelinated nerve fibres and different populations of axon profiles containing round clear and large dense-core vesicles were observed in all layers of the ureter. Bundles of unmyelinated axons
Correspondence: G. Jancs6, Department of Physiology, Albert Szent-Gy6rgyi Medical University, D6m t6r 10, H-6720 Szeged, Hungary. 0006-8993/91/$03.50 © 1991 Elsevier Science Publishers B.V. (Biomedical Division)
280
m
C
'~i!i~i~
li t
~
Fig. 1. Electron micrographs illustrating the effects of capsaicin (b,c) or its vehicle (a) on the fine structure of submucosal nerve elements of the guinea-pig ureter, a: the fine structure of the axons and axon terminals appears to be intact after incubation with the vehicle, b: following incubation with capsaicin (1 /~M), many osmiophilic degenerating axonal profiles (arrowheads) can be seen. c: detail of a small blood vessel. Note that m a n y paravascular nerve elements exhibit degeneration (arrowhead) after exposurc to capsaicin (1 /~M). Scale bars: a,b: 0.5 a m ; c: 1 1tin.
281 TABLE I The effect of capsaicin exposure on the proportion of degenerating ureteric axonal profiles
Counts of axonal profiles were made on electron micrographs taken randomly of all layers of the ureter. For each concentration, percentage values were calculated by counting 400-600 axonal profiles in specimensobtained from 3 guinea-pigs. Capsaicin concentration (/~M) -
0.03 1.0 3.0 10.0
Degeneratingaxonal profiles (%)
2.4 1.3 56.6 56.8 70.3
surrounded by perineurial cells were frequently encountered in the adventitia. Axon profiles situated in between the circular and longitudinal muscle layers contained either clear or clear and large dense-core vesicles. Axons and axon terminals observed in the submucosa were found either in bundles running in between the connective tissue elements or in close association with small blood vessels. A few intraepithelial nerve terminals were also found. As illustrated in Fig. la, incubation with Krebs' solution containing the vehicle in an amount equivalent to that contained in a 10 /tM solution of capsaicin had little if any effect on the fine structure of these nerve elements; axons exhibiting moderate swelling were observed only occasionally and these comprised less than 3% of the total axonal population. Exposure to capsaicin at a concentration of 30 nM failed to cause significant structural changes in the ureter except for a moderate swelling of occasional axons. In contrast, marked fine structural alterations were noted in all specimens incubated with capsaicin at concentrations of 0.3 /~M or higher. These consisted of prominent degenerative changes of nerve fibres and terminals. Many axons contained conspicuous osmiophilic debris and/or were markedly swollen (Fig. lb,c). Some degenerating axons, especially in the submucosa, were in close apposition to small blood vessels. Degenerating axons were as a rule intermingled with nerve fibres and terminals of various types virtually unaffected by capsaicin treatment (see Fig. lb). As shown in Table I, there was little difference in the proportion of nerve fibres exhibiting degenerative changes after exposure to capsaicin concentrations of 1 or 3 ~M. The higher incidence of degenerating nerve elements after incubation with 10 /~M capsaicin was mainly accounted for by an increased number of degenerating axons in the muscle and adventitial layers (data not shown). Changes were not noted in the fine structure of non-neural elements, including smooth muscle cells.
The present findings confirm and extend previous reports on the capsaicin-sensitive innervation of the guinea-pig ureter 19'2°. The structural changes observed in the present experiments are somewhat different from those demonstrated in a previous study, in which a short incubation period and a capsaicin concentration two orders of magnitude higher were used 2°. Thus, although axonal swelling was found in both studies, osmiophilic degenerative changes indicative of more severe structural damage have not been observed previously. This may be explained, at least in part, by the longer period of incubation employed in the present study, which might have promoted the development of more marked structural alterations. The close association of many degenerating nerve fibres with small blood vessels may provide the morphological substrate for the capsaicin-sensitive sensory control of ureteric vascular permeability 19. More importantly, the present findings provide a possible morphological basis for the desensitizing effect of capsaicin. Several hypotheses have been put forward to explain the mechanisms of in vitro capsaicin desensitization. It has been suggested that the depletion of peptide stores in sensory nerve terminals by capsaicin may be responsible for this phenomenon 4. However, subsequent investigations showed a quantitatively similar release of substance P-like immunoreactivity both by a combination of potassium and the calcium agonist BAY K 8644 and by a desensitizing concentration of capsaicin. Therefore, it has been concluded that peptide depletion is unlikely to account for capsaicin desensitization 3. The present findings provide new insight into the possible mechanisms of capsaicin desensitization. We suggest that a single exposure to desensitizing concentrations of capsaicin elicits incipient structural changes in afferent nerve endings, which result in impairment of the mechanisms involved in the release of peptide(s) from these particular nerve terminals. Accordingly, the repeated administration of capsaicin fails to evoke sensory receptor potentialcoupled efferent responses 14 mediated by sensory neuropeptides 5'~4. This assumption is in keeping with and supported by previous experimental data showing that the capsaicin-induced release of peptides from afferent nerve terminals is not affected by prior experimental manipulations causing neuropeptide release 3"4"15, whereas prior exposure to capsaicin prevents neuropeptide release by these same manipulations 1'3"4"15. In addition, our finding that ureteric nerve elements were apparently unaffected by exposure to a non-desensitizing concentration of 30 nM capsaicin 18 also suggests a causal relationship between the capsaicin desensitization of and structural damage to afferent nerve terminals. Altered transmembrane fluxes of calcium ions are
282 likely to c o n t r i b u t e to the d e v e l o p m e n t of these structural changes ")'22. This n o t i o n is strongly s u p p o r t e d by recent o b s e r v a t i o n s d e m o n s t r a t i n g a protective effect of R u t h e n i u m red, an i n o r g a n i c dye with calcium e n t r y - b l o c k i n g properties, against the desensitizing action of capsaicin ~' z2. F u r t h e r studies are in progress to elucidate w h e t h e r Ruthenium
red
prevents
c a p s a i c i n - i n d u c e d structural
1 Amann, R., Skofitsch, G. and Lembeck, F., Species-related differences in the capsaicin-sensitive innervation of the rat and guinea-pig ureter, Naunyn-Schmiedeberg's Arch. Pharmacol., 338 (1988) 407-410. 2 Chung, K., Schwen, R.J. and Coggeshall, R.E., Ureteral axon damage following subcutaneous administration of capsaicin in adult rats, Neurosci. Lett., 53 (1985) 221-226. 3 Dray, A., Hankins, M.W. and Yeats, J.C., Desensitization and capsaicin-induced release of substance P-like immunoreactivity from guinea-pig ureter in vitro. Neuroscience, 31 (1989) 479483. 4 Hakanson, R., Beding, B., Ekman, R., Heilig, M., Wahlestedt, C. and Sundler, F., Multiple tachykinin pools in sensory nerve fibres in the rabbit iris, Neuroscience, 21 (1987) 943-950. 5 Holzer, P., Local effector functions of capsaicin-sensitive sensory nerve endings: involvement of tachykinins, calcitonin generelated peptide and other neuropeptides, Neuroscience, 24 (1988) 739-768. 6 Hoyes, A.D. and Barber, P., Degeneration of axons in the ureteric and duodenal nerve plexuses of the adult rat following in vivo treatment with capsaicin, Neurosci. Lett., 25 (1981) 19-24. 7 Hua, X.-Y., Saria, A., Gamse, R., Theodorsson-Norheim, E., Brodin, E. and Lundberg, J.M., Capsaicin-induced release of multiple tachykinins (substance P, neurokinin A and eledoisinlike material) from guinea-pig spinal cord and ureter, Neuroscience, 19 (1986) 313-319. 8 Jancs6, G., Intracisternal capsaicin: selective degeneration of chemosensitive primary sensory afferents in the adult rat, Neurosci. Lett., 27 (1981) 41-45. 9 Jancs6, G., Sensory nerves as modulators of inflammatory reactions. In L.A. Chahl, J. Szolcs~inyi and E Lembeck (Eds.), Antidromic Vasodilatation and Neurogenic Inflammation, Akad6miai Kiad6, Budapest, 1984, pp. 207-222. 10 Jancs6, G., Karcsu, S., Kir~ily, E~, Szebeni, A., T6th, L., B~icsy, E., Jo6, F. and Pfirducz, A., Neurotoxin-induced nerve cell degeneration: possible involvement of calcium, Brain Research, 295 (1984) 211-216. 11 Jancs6, G. and Kir~ily, E., Distribution of chemosensitive primary sensory afferents in the central nervous system of the rat, J. Comp. Neurol., 190 (1980) 781-792. 12 Jancs6, G., Kir~ily, E., Such, G., Jo6, F. and Nagy, A.,
damage,
and whether
the
d e v e l o p m e n t of capsaicin
desensitization is c o r r e l a t e d with such fine structural alterations.
This work was supported in part by a grant from the Hungarian Academy of Sciences (OTKA 1104). We thank Krisztina Moh~lcsi for skilful technical assistance.
Neurotoxic effect of capsaicin in mammals, Acta Physiol. Hung., 69 (1987) 295-313. 13 Jancs6, N., Desensitization with capsaicin and related acylamides as a tool for studying the function of pain receptors. In R.K.S. Lim (Ed.), Pharmacology of Pain, Pergamon Press, Oxford, 1968, pp. 33-55. 14 Maggi, C.A. and Meli, A., The sensory-efferent function of capsaicin-sensitive sensory neurones, Gen. Pharmacol., 19 (1988) 1-43. 15 Maggi, C.A, Patacchini, R., Giuliani, S., Santicioli, P. and Meli, A., Evidence for two independent modes of activation of the 'efferent' function of capsaicin-sensitive nerves, Eur. J. PharmacoL, 15 (1988) 367-373. 16 Maggi, C.A., Patacchini, R., Santicioli, P., Giuliani, S,, Geppetti, P. and Meli, A., Protective action of Ruthenium red toward capsaicin desensitization of sensory fibers, NeuroscL Lett., 88 (1988) 201-205. 17 Santicioli, P., Maggi, C.A., Gepetti, P., Del Bianco, E., Theodorsson, E. and Meli, A., Release of calcitonin generelated peptide-like immunoreactivity (CGRP-LI) from organs of the genitourinary tract in rats, Neurosci. Lett., 92 (1988) 197-201. 18 Santicioli, P., Maggi, C.A. and Meli, A., Functional evidence for the existence of a capsaicin-sensitive innervation in the rat urinary bladder, J. Pharm. Pharmacol., 38 (1986) 446-451. 19 Saria, A., Lundberg, J.M., Hua, X. and Lembeck, E, Capsaicin-induced substance P release and sensory control of vascular permeability in the guinea-pig ureter, Neurosci. Lett., 41 (1983) 167-172. 20 Sikri, K.L., Hoyes, A.D., Barber, P. and Jagessar, H., Substance P-like immunoreactivity in the intramural nerve plexuses of the guinea-pig ureter: a light and electron microscOpical study, J. Anat., 133 (1981) 425-442. 21 Szolcsfinyi, J., Capsaicin-sensitive chemoceptive neural system with dual sensory-efferent function. In L.A, Chahl, J. Szoics~inyi and E Lembeck (Eds.), Antidromic Vasodilatation and Neurogenic Inflammation, Akad6miai Kiad6, Budapest, 1984, pp. 26-52. 22 Wood, J.N., Winter, J., James, J.F., Rang, H.P., Yeats, J. and Bevan, S., Capsaicin-induced ion fluxes in dorsal root ganglionic cells in culture, J. Neurosci., 8 (1988) 3208-3220.
279
BRES 24500
Possible morphological correlates of capsaicin desensitization Elizabeth Kir~ily 1, G. Jancs6 2 and M. Haj6s 2 1Department of Anatomy, Albert Szent-Gy6rgyi Medical University, H-6701 Szeged (Hungary) and 2Departmentof Physiology, Albert Szent-Gy6rgyi Medical University, H-6720Szeged (Hungary) (Accepted 16 October 1990)
Key words: Capsaicin-sensitivenerve fiber; Fine structure; Ureter; Guinea pig; Capsaicin desensitization; In vitro
The changes in the fine structure of axonal profiles of the guinea-pig ureter were examined after exposure to capsaicin in vitro. In the ureters exposed to capsaicin (1-10 gM), about 60%, of all axonal profiles exhibited conspicuous ultrastructural impairment. It is suggested that these alterations might interfere with the release of peptides from these particular nerve endings and therefore contribute significantly to the mechanisms of capsaicin desensitization.
Neurohistological and pharmacological studies have revealed that a population of capsaicin-sensitive primary afferent neurones represents a unique division of the sensory nervous system 5'11-14'21. A continuously accumulating body of evidence indicates not only that capsaicinsensitive afferent fibres are involved in the mediation of reflex and nociceptive responses, but also that they possess a characteristic efferent function 5'8'9'12-14'21. Thus, a distinct feature of these capsaicin-sensitive neurones is the release of peptides from their stimulated peripheral nerve terminals, a mechanism by which they exert a profound and physiologically important regulatory influence on the innervated tissue 5'9'14'21. The occurrence of capsaicin-sensitive primary afferent nerve fibres has been demonstrated in most viscera, including the urogenital system 2'6'7'17'19. In vitro studies on the guinea-pig ureter provided evidence for substance P and calcitonin gene-related peptide-mediated contractile responses which depend on the integrity of the capsaicinsensitive afferent nerves 1'7. The failure of the isolated organ to respond to repeated administration of capsaicin, a phenomenon generally referred to in the current literature as capsaicin desensitization, was a common finding in these experiments. Indeed, upon repeated application capsaicin failed either to elicit a release of neuropeptides 3'~7 or to affect ureteric motility 1. Although several hypotheses have been put forward to explain this effect, the mechanisms of capsaicin desensitization are still unclear 3"4'1°'12"13"15'22. Therefore, the aim of the present experiments was to unravel possible morphological alterations induced by capsaicin under
conditions identical with those used in the in vitro studies, which might contribute to the cellular mechanisms of capsaicin desensitization. Adult male guinea-pigs weighing 400-450 g were used. The animals were anaesthetized with pentobarbitone sodium (40 mg/kg) and the ureters were dissected out. Segments 2-3 mm in length were cut from the organ and placed into small chambers containing Krebs' solution (composition in mM: NaCI 119, N a H C O 3 25, KH2PO 4 1.2, MgSO 4 1.5, KCI 4.7, CaCI 2 2.5, glucose 11) gassed with a mixture of 95% oxygen and 5% carbon dioxide. After a preincubation period of 20 min at 37 °C, capsaicin at concentrations in the range 30 nM-10 /~M or an equivalent amount of its solvent was added to the specimens. After 6 min, the incubation solution was replaced with fresh physiological solution and the specimens were incubated for a further period of 60 rain, whereafter they were fixed in an aldehyde fixative containing 2% paraformaldehyde and 1% glutaraldehyde in 0.1 M phosphate buffer, p H 7.4. Specimens were immersed for another 6 h in the same fixative and then post-fixed in a 2% buffered solution of osmium tetroxide for 2 h at 4 °C, dehydrated in graded alcohols, and finally embedded in Araldite. Ultrathin sections were cut on a Reichert ultrotome, stained with uranyl acetate and lead citrate and examined under a Jeol 100B electron microscope. In control specimens, unmyelinated nerve fibres and different populations of axon profiles containing round clear and large dense-core vesicles were observed in all layers of the ureter. Bundles of unmyelinated axons
Correspondence: G. Jancs6, Department of Physiology, Albert Szent-Gy6rgyi Medical University, D6m t6r 10, H-6720 Szeged, Hungary. 0006-8993/91/$03.50 © 1991 Elsevier Science Publishers B.V. (Biomedical Division)
280
m
C
'~i!i~i~
li t
~
Fig. 1. Electron micrographs illustrating the effects of capsaicin (b,c) or its vehicle (a) on the fine structure of submucosal nerve elements of the guinea-pig ureter, a: the fine structure of the axons and axon terminals appears to be intact after incubation with the vehicle, b: following incubation with capsaicin (1 /~M), many osmiophilic degenerating axonal profiles (arrowheads) can be seen. c: detail of a small blood vessel. Note that m a n y paravascular nerve elements exhibit degeneration (arrowhead) after exposurc to capsaicin (1 /~M). Scale bars: a,b: 0.5 a m ; c: 1 1tin.
281 TABLE I The effect of capsaicin exposure on the proportion of degenerating ureteric axonal profiles
Counts of axonal profiles were made on electron micrographs taken randomly of all layers of the ureter. For each concentration, percentage values were calculated by counting 400-600 axonal profiles in specimensobtained from 3 guinea-pigs. Capsaicin concentration (/~M) -
0.03 1.0 3.0 10.0
Degeneratingaxonal profiles (%)
2.4 1.3 56.6 56.8 70.3
surrounded by perineurial cells were frequently encountered in the adventitia. Axon profiles situated in between the circular and longitudinal muscle layers contained either clear or clear and large dense-core vesicles. Axons and axon terminals observed in the submucosa were found either in bundles running in between the connective tissue elements or in close association with small blood vessels. A few intraepithelial nerve terminals were also found. As illustrated in Fig. la, incubation with Krebs' solution containing the vehicle in an amount equivalent to that contained in a 10 /tM solution of capsaicin had little if any effect on the fine structure of these nerve elements; axons exhibiting moderate swelling were observed only occasionally and these comprised less than 3% of the total axonal population. Exposure to capsaicin at a concentration of 30 nM failed to cause significant structural changes in the ureter except for a moderate swelling of occasional axons. In contrast, marked fine structural alterations were noted in all specimens incubated with capsaicin at concentrations of 0.3 /~M or higher. These consisted of prominent degenerative changes of nerve fibres and terminals. Many axons contained conspicuous osmiophilic debris and/or were markedly swollen (Fig. lb,c). Some degenerating axons, especially in the submucosa, were in close apposition to small blood vessels. Degenerating axons were as a rule intermingled with nerve fibres and terminals of various types virtually unaffected by capsaicin treatment (see Fig. lb). As shown in Table I, there was little difference in the proportion of nerve fibres exhibiting degenerative changes after exposure to capsaicin concentrations of 1 or 3 ~M. The higher incidence of degenerating nerve elements after incubation with 10 /~M capsaicin was mainly accounted for by an increased number of degenerating axons in the muscle and adventitial layers (data not shown). Changes were not noted in the fine structure of non-neural elements, including smooth muscle cells.
The present findings confirm and extend previous reports on the capsaicin-sensitive innervation of the guinea-pig ureter 19'2°. The structural changes observed in the present experiments are somewhat different from those demonstrated in a previous study, in which a short incubation period and a capsaicin concentration two orders of magnitude higher were used 2°. Thus, although axonal swelling was found in both studies, osmiophilic degenerative changes indicative of more severe structural damage have not been observed previously. This may be explained, at least in part, by the longer period of incubation employed in the present study, which might have promoted the development of more marked structural alterations. The close association of many degenerating nerve fibres with small blood vessels may provide the morphological substrate for the capsaicin-sensitive sensory control of ureteric vascular permeability 19. More importantly, the present findings provide a possible morphological basis for the desensitizing effect of capsaicin. Several hypotheses have been put forward to explain the mechanisms of in vitro capsaicin desensitization. It has been suggested that the depletion of peptide stores in sensory nerve terminals by capsaicin may be responsible for this phenomenon 4. However, subsequent investigations showed a quantitatively similar release of substance P-like immunoreactivity both by a combination of potassium and the calcium agonist BAY K 8644 and by a desensitizing concentration of capsaicin. Therefore, it has been concluded that peptide depletion is unlikely to account for capsaicin desensitization 3. The present findings provide new insight into the possible mechanisms of capsaicin desensitization. We suggest that a single exposure to desensitizing concentrations of capsaicin elicits incipient structural changes in afferent nerve endings, which result in impairment of the mechanisms involved in the release of peptide(s) from these particular nerve terminals. Accordingly, the repeated administration of capsaicin fails to evoke sensory receptor potentialcoupled efferent responses 14 mediated by sensory neuropeptides 5'~4. This assumption is in keeping with and supported by previous experimental data showing that the capsaicin-induced release of peptides from afferent nerve terminals is not affected by prior experimental manipulations causing neuropeptide release 3"4"15, whereas prior exposure to capsaicin prevents neuropeptide release by these same manipulations 1'3"4"15. In addition, our finding that ureteric nerve elements were apparently unaffected by exposure to a non-desensitizing concentration of 30 nM capsaicin 18 also suggests a causal relationship between the capsaicin desensitization of and structural damage to afferent nerve terminals. Altered transmembrane fluxes of calcium ions are
282 likely to c o n t r i b u t e to the d e v e l o p m e n t of these structural changes ")'22. This n o t i o n is strongly s u p p o r t e d by recent o b s e r v a t i o n s d e m o n s t r a t i n g a protective effect of R u t h e n i u m red, an i n o r g a n i c dye with calcium e n t r y - b l o c k i n g properties, against the desensitizing action of capsaicin ~' z2. F u r t h e r studies are in progress to elucidate w h e t h e r Ruthenium
red
prevents
c a p s a i c i n - i n d u c e d structural
1 Amann, R., Skofitsch, G. and Lembeck, F., Species-related differences in the capsaicin-sensitive innervation of the rat and guinea-pig ureter, Naunyn-Schmiedeberg's Arch. Pharmacol., 338 (1988) 407-410. 2 Chung, K., Schwen, R.J. and Coggeshall, R.E., Ureteral axon damage following subcutaneous administration of capsaicin in adult rats, Neurosci. Lett., 53 (1985) 221-226. 3 Dray, A., Hankins, M.W. and Yeats, J.C., Desensitization and capsaicin-induced release of substance P-like immunoreactivity from guinea-pig ureter in vitro. Neuroscience, 31 (1989) 479483. 4 Hakanson, R., Beding, B., Ekman, R., Heilig, M., Wahlestedt, C. and Sundler, F., Multiple tachykinin pools in sensory nerve fibres in the rabbit iris, Neuroscience, 21 (1987) 943-950. 5 Holzer, P., Local effector functions of capsaicin-sensitive sensory nerve endings: involvement of tachykinins, calcitonin generelated peptide and other neuropeptides, Neuroscience, 24 (1988) 739-768. 6 Hoyes, A.D. and Barber, P., Degeneration of axons in the ureteric and duodenal nerve plexuses of the adult rat following in vivo treatment with capsaicin, Neurosci. Lett., 25 (1981) 19-24. 7 Hua, X.-Y., Saria, A., Gamse, R., Theodorsson-Norheim, E., Brodin, E. and Lundberg, J.M., Capsaicin-induced release of multiple tachykinins (substance P, neurokinin A and eledoisinlike material) from guinea-pig spinal cord and ureter, Neuroscience, 19 (1986) 313-319. 8 Jancs6, G., Intracisternal capsaicin: selective degeneration of chemosensitive primary sensory afferents in the adult rat, Neurosci. Lett., 27 (1981) 41-45. 9 Jancs6, G., Sensory nerves as modulators of inflammatory reactions. In L.A. Chahl, J. Szolcs~inyi and E Lembeck (Eds.), Antidromic Vasodilatation and Neurogenic Inflammation, Akad6miai Kiad6, Budapest, 1984, pp. 207-222. 10 Jancs6, G., Karcsu, S., Kir~ily, E~, Szebeni, A., T6th, L., B~icsy, E., Jo6, F. and Pfirducz, A., Neurotoxin-induced nerve cell degeneration: possible involvement of calcium, Brain Research, 295 (1984) 211-216. 11 Jancs6, G. and Kir~ily, E., Distribution of chemosensitive primary sensory afferents in the central nervous system of the rat, J. Comp. Neurol., 190 (1980) 781-792. 12 Jancs6, G., Kir~ily, E., Such, G., Jo6, F. and Nagy, A.,
damage,
and whether
the
d e v e l o p m e n t of capsaicin
desensitization is c o r r e l a t e d with such fine structural alterations.
This work was supported in part by a grant from the Hungarian Academy of Sciences (OTKA 1104). We thank Krisztina Moh~lcsi for skilful technical assistance.
Neurotoxic effect of capsaicin in mammals, Acta Physiol. Hung., 69 (1987) 295-313. 13 Jancs6, N., Desensitization with capsaicin and related acylamides as a tool for studying the function of pain receptors. In R.K.S. Lim (Ed.), Pharmacology of Pain, Pergamon Press, Oxford, 1968, pp. 33-55. 14 Maggi, C.A. and Meli, A., The sensory-efferent function of capsaicin-sensitive sensory neurones, Gen. Pharmacol., 19 (1988) 1-43. 15 Maggi, C.A, Patacchini, R., Giuliani, S., Santicioli, P. and Meli, A., Evidence for two independent modes of activation of the 'efferent' function of capsaicin-sensitive nerves, Eur. J. PharmacoL, 15 (1988) 367-373. 16 Maggi, C.A., Patacchini, R., Santicioli, P., Giuliani, S,, Geppetti, P. and Meli, A., Protective action of Ruthenium red toward capsaicin desensitization of sensory fibers, NeuroscL Lett., 88 (1988) 201-205. 17 Santicioli, P., Maggi, C.A., Gepetti, P., Del Bianco, E., Theodorsson, E. and Meli, A., Release of calcitonin generelated peptide-like immunoreactivity (CGRP-LI) from organs of the genitourinary tract in rats, Neurosci. Lett., 92 (1988) 197-201. 18 Santicioli, P., Maggi, C.A. and Meli, A., Functional evidence for the existence of a capsaicin-sensitive innervation in the rat urinary bladder, J. Pharm. Pharmacol., 38 (1986) 446-451. 19 Saria, A., Lundberg, J.M., Hua, X. and Lembeck, E, Capsaicin-induced substance P release and sensory control of vascular permeability in the guinea-pig ureter, Neurosci. Lett., 41 (1983) 167-172. 20 Sikri, K.L., Hoyes, A.D., Barber, P. and Jagessar, H., Substance P-like immunoreactivity in the intramural nerve plexuses of the guinea-pig ureter: a light and electron microscOpical study, J. Anat., 133 (1981) 425-442. 21 Szolcsfinyi, J., Capsaicin-sensitive chemoceptive neural system with dual sensory-efferent function. In L.A, Chahl, J. Szoics~inyi and E Lembeck (Eds.), Antidromic Vasodilatation and Neurogenic Inflammation, Akad6miai Kiad6, Budapest, 1984, pp. 26-52. 22 Wood, J.N., Winter, J., James, J.F., Rang, H.P., Yeats, J. and Bevan, S., Capsaicin-induced ion fluxes in dorsal root ganglionic cells in culture, J. Neurosci., 8 (1988) 3208-3220.