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The effect of galanin on wide-dynamic range neuron activity in the spinal dorsal horn of rats
Regulatory Peptides 101 Ž2001. 179–182 www.elsevier.comrlocaterregpep
The effect of galanin on wide-dynamic range neuron activity in the spinal dorsal horn of rats Long-Chuan Yu a,b,) , Shi-Lian Xu a , Wei Xiong a , Thomas Lundeberg b a
Department of Physiology, College of Life Sciences, and National Laboratory of Biomembrane and Membrane Biotechnology, Peking UniÕersity, Beijing, 100871, People’s Republic of China b Department of Physiology and Pharmacology, and Department of Medical Rehabilitation, Karolinska Institutet, 171 77 Stockholm, Sweden Received 19 February 2001; received in revised form 6 May 2001; accepted 30 May 2001
Abstract The present study investigated the effect of galanin on wide-dynamic range ŽWDR. neuron activity in the dorsal horn of the spinal cord of rats. The evoked discharge of WDR neurons was elicited by transdermic electrical stimulation applied on the ipsilateral hindpaw of rats. Galanin was administered directly on the spinal dorsal surface of L3–L5. The evoked discharge frequency of the WDR neurons decreased significantly after the administration of galanin and the effect lasted for more than 30 min. Furthermore, the inhibitory effect of galanin on the evoked discharge frequency of WDR neurons was blocked by following administration of the galanin antagonist galantide, indicating that the inhibitory effect of galanin on the activity of WDR neurons was induced by activating galanin receptors in the dorsal horn of the spinal cord. The results suggest that galanin has an inhibitory role in the transmission of presumed nociceptive information in the dorsal horn of the spinal cord in rats. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Galanin; Galantide; Galanin receptor; Wide-dynamic range ŽWDR. neuron; Dorsal horn; Anti-nociception
1. Introduction Galanin is a 29-amino acid peptide Ž30 in human., originally isolated from the porcine intestine w1x. Galanin is widely present in the central and peripheral nervous system, including dorsal root ganglion ŽDRG. cells and spinal interneurons w2,3x. Galanin-like immunoreactivity is densely distributed in the superficial layers of the spinal dorsal horn w2x, suggesting that the neuropeptide may be involved in the transmission or modulation of nociceptive information in dorsal horn of the spinal cord. It has been suggested that galanin is an endogenous analgesic having an anti-nociceptive action in the central nervous system w4–7x. We recently demonstrated that intrathecal administration of galanin increased the response latency to noxious thermal and mechanical stimulation in rats with mononeuropathy w6x. Furthermore, we found an interaction between galanin and opioid peptides in the transmission or modulation of nociceptive information in the spinal cord of rats
)
Corresponding author. Department of Physiology, College of Life Sciences, Peking University, Beijing 100871, People’s Republic of China. Tel.: q86-10-6275-1867; fax: q86-10-6275-1850. E-mail address: [email protected] ŽL.-C. Yu..
with mononeuropathy w8,9x. The present study was performed to investigate the effect of galanin on the evoked discharge frequency of the wide-dynamic range ŽWDR. neuron in dorsal horn of the spinal cord of rats.
2. Materials and methods 2.1. Animals and surgery Experiments were performed on 16 adult male Sprague–Dawley rats weighing 200–250 g ŽExperimental Animal Center of Beijing Medical University, Beijing, China.. The rats were housed in cages with free access to food and water. All experiments were conducted according to the guidelines of the animal ethical committee of Karolinska Institutet and every effort was made to minimize animal suffering. Animals were anesthetized with intraperitoneal pentobarbital sodium Ž45 mgrkg; maintained with intermittent dose of 10 mgrkgrh. and a cannula was inserted into the trachea. The dorsal L3–L5 region of the spinal cord was exposed by laminectomy. The vertebral column was stabilized by vertebral and hip clamps. The spinal cord between
0167-0115r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 0 1 1 5 Ž 0 1 . 0 0 2 8 7 - 7
180
L.-C. Yu et al.r Regulatory Peptides 101 (2001) 179–182
L3 and L5 was placed on a curved metal saddle, gently lifted 0.5 mm from the vertebral canal, and then covered with 0.9% saline Ž37 8C.. The animals were immobilized by intraperitoneal gallamine triethiodide Ž100 mgrkgrh. and received artificial respiration Žfrequency: 90; tidal volume: 4–5 ml.. In order to maintain the rat’s body temperature within physiological levels, a heating plate was placed under the rat so that the rectal temperature remained between 35 8C and 36.5 8C. At the end of the experiments, the rats were killed with an overdose of pentobarbital sodium. 2.2. Recording and stimulation Extra-cellular recording of lumbar dorsal horn unit was performed with a glass microelectrode filled with 3 M NaCl Ž3–8 M V . and advanced by a manual hydraulic micro-driver. Recording sites ranged from 70 to 1100 mm below the dorsal surface at L3–L5 levels of the spinal cord. The evoked discharges were displayed on an oscilloscope after being passed through magnifiers. The output of the magnifier was also entered into a computer that was programmed to construct histograms. Stimulation was delivered through fine stainless needle electrodes inserted through the skin of the ipsilateral hindpaw Ž4 V, 0.33 Hz, 3 ms wide pulses, 20 stimulirtrial.. The electrical stimulation was delivered, and the microelectrode was advanced to find the neuron which responded to both lightly brushing and pinching of the skin, and to a greater degree to pinch than the others, those neurons were confirmed to be WDR neurons w10–12x. Then electrical stimulation was applied again, and the evoked responses of individual neuron were observed. Stable extra-cellular recordings were obtained from the WDR neuron at L3–L5 levels of the spinal dorsal horn. The number of the WDR neuron’s discharge was recorded and used to plot the frequency histograms. Each histogram had 128 dots, and each dot’s duration was 11 ms, making the duration of each histogram about 1.5 s. After 20 histogram pictures recorded, the sum of the number of discharges was calculated.
2.4. Chemicals Solutions for administration were prepared with sterilized saline, each with a volume of 10 ml of Ž1. 0.5 or 1 nmol of galanin Žrat–galanin, Tocris, Ballwin, USA.; Ž2. 1 nmol of galantide ŽTocris.; Ž3. 10 ml of 0.9% saline as a control. 2.5. Statistical analysis The discharge frequency of the WDR neuron was recorded and used to plot the frequency histograms. Each histogram was 1.5 s. After having recorded 20 histograms, they were piled up and the sum of the discharges calculated. The discharge frequency was presented as mean " standard error of the mean ŽS.E.M... The discharge frequencies recorded during subsequent experiment were expressed as percentage changes of the basal level of each neuron’s discharge frequency. The difference between groups was determined by two-way analysis of variance ŽANOVA..
3. Results 3.1. The effect of galanin on the eÕoked discharge frequency of WDR neurons Twenty-four WDR neurons were recorded. The evoked discharge frequency was recorded before and 2, 5, 10, 15, 20, 25, 30 min after the administration of 0.5 Ž n s 6. or 1 nmol of galanin Ž n s 10., or 10 ml of 0.9% saline as a control Ž n s 8.. Compared with the saline group, the evoked discharge frequency of WDR neurons decreased significantly after administration of 1 nmol of galanin Ž F s 52.03, P - 0.001., while 0.5 nmol of galanin had no significant effect Ž F s 0.05, P s 0.83.. The results are shown in Fig. 1.
2.3. Experimental protocol Once a WDR neuron was determined, electrical stimulation was applied again and the evoked discharges were recorded. Trigger inputs were used to make the stimulation and recording synchronous. Each neuron was recorded for 30 min after the chemical applied to the dorsal surface of the spinal cord. The neuron discharge frequency was recorded at 2, 5, 10, 15, 20, 25 and 30 min after the administration. Each time for recording lasted for 30 s. After recording for 30 min, the effect of the chemical was washed away. At least, a 30 min rest period was allowed for the next neuron discharge recording.
Fig. 1. Effects of administration of 0.5 and 1 nmol of galanin to dorsal surface of the L3–L5 spinal cord on the discharge of wide-dynamic range ŽWDR. neurons in rats. Results are presented as mean"S.E.M. The statistical difference between groups was evaluated by two-way analysis of variance ŽANOVA., ) ) ) P - 0.001 compared with the control group.
L.-C. Yu et al.r Regulatory Peptides 101 (2001) 179–182
Fig. 2. Blockade effect of galantide on the galanin-induced inhibition on the discharge frequency of wide-dynamic range ŽWDR. neurons. Results are presented as mean"S.E.M. The statistical difference between groups was evaluated by two-way analysis of variance ŽANOVA., ) ) ) P - 0.001 compared with the control group.
3.2. The effect of galantide on the galanin-induced decrease in the eÕoked discharge frequency of WDR neurons The discharges of 16 WDR neurons were observed. After that, 1 nmol of galanin was directly applied on the dorsal surface of the L3–L5 spinal cord, the evoked discharge frequency of the WDR neuron decreased. Five minutes later, 1 nmol of galantide was applied directly on the surface of L3–L5 dorsal surface of the spinal cord Ž n s 5., or administered 10 ml of 0.9% saline as a control Ž n s 7.. Compared with the control group, the galanin-induced decreases in WDR neuron discharge were blocked significantly after administration of galantide Ž F s 23.20, P - 0.001.. The results are shown in Fig. 2.
4. Discussion The present study demonstrated that the evoked discharge frequency of the WDR neuron decreased significantly after intrathecal administration of galanin, and that the effect lasted for more than 30 min. The results suggest that galanin plays an inhibitory role on the transmission of presumed nociception in the spinal cord of rats. Kask et al. w13x have reported that galanin has an inhibitory action on neuronal activity. Intrathecal injection of 0.316 nmol of galanin also produced a prolonged depression of the flexor reflex in rats w14x. In a recent study, the effects of galanin on magnocellular neurosecretory cells were examined. Application of galanin or of the N-terminal fragment galanin1–16 produced a reversible membrane hyperpolarization with an IC 50 near 10 nM. These effects were associated with an increase in membrane conductance, with a reversal potential near y70 mV, and were not blocked by tetrodotoxin, indicating that the receptors mediating these effects are located postsynaptically. The reversal potential of the galanin-mediated effect was unaffected
181
by reducing extracellular chloride or by intracellular chloride injection, indicating that the effects of galanin are not mediated by modulation of chloride conductance. In contrast, reducing the external concentration of potassium ions from 3 to 1 mM shifted the reversal potential of the responses to y85 mV, suggesting the involvement of potassium conductance. When tested on spontaneously active magnocellular neurosecretory cells, the hyperpolarizing effects of galanin were associated with a suppression of firing in both continuously active and phasically active neurons. These results suggest that galanin may be a potent endogenous modulator of firing pattern in central nervous system cells w15x. In rats with sciatic nerve axotomy, galantide Žan antagonist of galanin. enhanced the nociceptive reflex in spinalized rats with much greater potency than in intact rats w16x. In rats with sciatic nerve ligation, intrathecal administration of galanin produced dose-dependent increases in the hindpaw withdrawal latency to noxious thermal and mechanical, supporting the finding in spinalized rats that galanin produces an inhibitory effect on the transmission of presumed nociceptive information in the spinal cord w6x. Recent studies in our laboratory demonstrated that intraperiaqueductal grey administration of galanin also resulted in a dose-dependent anti-nociception in intact rats and in rats with mononeuropathy w5,7x. The above results suggest that galanin has an anti-nociceptive effect not only in the spinal cord but also in the brain. Galantide is a selective antagonist of galanin receptor w17x. In the present study, the galanin-induced inhibition on the evoked discharge frequency of WDR neurons was blocked by following administration of galantide, indicating that the inhibitory effect of galanin on the activity of WDR neuron was induced by activating galanin receptors in the dorsal horn of the spinal cord. The results of the present study show that galanin is involved in the modulation of the transmission of presumed nociceptive information in the dorsal horn of the spinal cord in rats, and that the anti-nociceptive effect of galanin is mediated by activation of the galanin receptor.
Acknowledgements This study was supported by funds from the Karolinska Institutet Foundation, the National Natural Science Foundation of China ŽNSFC..
References w1x Tatemoto K, Rokaeus A, Jornvall H, McDonald TJ, Mutt V. Galanin —a novel biologically active peptide from porcine intestine. FEBS Lett 1983;164:124–8. w2x Ch’ng JLC, Christofides ND, Anand P, Gibson SJ, Allen YS, Su
182
w3x
w4x
w5x
w6x
w7x
w8x
w9x
L.-C. Yu et al.r Regulatory Peptides 101 (2001) 179–182 HC, et al. Distribution of galanin immunoreactivity in the central nervous system and the response of galanin-containing neuronal pathways to injury. Neuroscience 1985;16:343–54. Merchenthaler I, Lopez FJ, Negro-Vilar A. Anatomy and physiology of central galanin-containing pathways. Prog Neurobiol 1993;40: 711–69. Hokfelt T, Zhang X, Wiesenfeld-Hallin Z. Messenger plasticity in primary sensory neurons following axotomy and its functional implications. Trends Neurosci 1994;17:22–30. Wang D, Lundeberg T, Yu LC. Antinociceptive effects of galanin in periaqueductal grey of rats with experimentally induced mononeuropathy. Neuroscience 2000;96:767–71. Yu LC, Lundeberg S, An H, Wang FX, Lundeberg T. Effects of intrathecal galanin on nociceptive responses in rats with mononeuropathy. Life Sci 1999;64:1145–53. Wang D, Ye HH, Yu LC, Lundeberg T. Intra-periaqueductal grey administration of galanin increases nociceptive response latency in rats, an effect reversed by naloxone. Brain Res 1999;834:152–4. Zhang YP, Lundeberg T, Yu LC. Interaction of galanin and morphine in the spinal antinociception in rats with mononeuropathy. Brain Res 2000;852:485–7. Zhang YP, Yu LC, Lundeberg T. An interaction of opioids and galanin in dorsal horn of the spinal cord in mononeuropathic rats. Regul Pept 2000;86:89–94.
w10x Jiang MC, Cleland CL, Gebhart GF. Intrinsic properties of deep dorsal horn neurons in the L6–S1 spinal cord of the intact rat. J Neurophysiol 1995;74:1819–27. w11x Sotgiu ML, Biella G. Contralateral inhibitory control of spinal nociceptive transmission in rats with chronic peripheral nerve injury. Neurosci Lett 1998;253:21–4. w12x Yu LC, Zheng EM, Lundeberg T. Calcitonin gene-related peptide 8–37 inhibits the evoked discharge frequency of wide-dynamic range neuron in dorsal horn of the spinal cord in rats. Regul Pept 1999;83:21–4. w13x Kask K, Langel U, Bartfai T. Galanin—a neuropeptide with inhibitory actions. Cell Mol Neurobiol 1995;15:653–73. w14x Wiesenfeld-Hallin Z, Villar MJ, Hokfelt T. The effects of intrathecal galanin and C-fiber stimulation on the flexor reflex in the rat. Brain Res 1989;486:205–13. w15x Papas S, Bourque CW. Galanin inhibits continuous and phasic firing in rat hypothalamic magnocellular neurosecretory cells. J Neurosci 1997;17:6048–56. w16x Wiesenfelt-Hallin Z, Xu XJ, Langel U, Bedecs K, Hokfelt T, Bartfai T. Galanin mediated control of pain: enhanced role after nerve injury. Proc Natl Acad Sci U S A 1992;89:3334–7. w17x Bartfai T, Fisone G, Langel U. Galanin and galanin antagonists: molecular and biochemical perspectives. Trans Pharmacol Sci 1992; 13:312–7.
The effect of galanin on wide-dynamic range neuron activity in the spinal dorsal horn of rats Long-Chuan Yu a,b,) , Shi-Lian Xu a , Wei Xiong a , Thomas Lundeberg b a
Department of Physiology, College of Life Sciences, and National Laboratory of Biomembrane and Membrane Biotechnology, Peking UniÕersity, Beijing, 100871, People’s Republic of China b Department of Physiology and Pharmacology, and Department of Medical Rehabilitation, Karolinska Institutet, 171 77 Stockholm, Sweden Received 19 February 2001; received in revised form 6 May 2001; accepted 30 May 2001
Abstract The present study investigated the effect of galanin on wide-dynamic range ŽWDR. neuron activity in the dorsal horn of the spinal cord of rats. The evoked discharge of WDR neurons was elicited by transdermic electrical stimulation applied on the ipsilateral hindpaw of rats. Galanin was administered directly on the spinal dorsal surface of L3–L5. The evoked discharge frequency of the WDR neurons decreased significantly after the administration of galanin and the effect lasted for more than 30 min. Furthermore, the inhibitory effect of galanin on the evoked discharge frequency of WDR neurons was blocked by following administration of the galanin antagonist galantide, indicating that the inhibitory effect of galanin on the activity of WDR neurons was induced by activating galanin receptors in the dorsal horn of the spinal cord. The results suggest that galanin has an inhibitory role in the transmission of presumed nociceptive information in the dorsal horn of the spinal cord in rats. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Galanin; Galantide; Galanin receptor; Wide-dynamic range ŽWDR. neuron; Dorsal horn; Anti-nociception
1. Introduction Galanin is a 29-amino acid peptide Ž30 in human., originally isolated from the porcine intestine w1x. Galanin is widely present in the central and peripheral nervous system, including dorsal root ganglion ŽDRG. cells and spinal interneurons w2,3x. Galanin-like immunoreactivity is densely distributed in the superficial layers of the spinal dorsal horn w2x, suggesting that the neuropeptide may be involved in the transmission or modulation of nociceptive information in dorsal horn of the spinal cord. It has been suggested that galanin is an endogenous analgesic having an anti-nociceptive action in the central nervous system w4–7x. We recently demonstrated that intrathecal administration of galanin increased the response latency to noxious thermal and mechanical stimulation in rats with mononeuropathy w6x. Furthermore, we found an interaction between galanin and opioid peptides in the transmission or modulation of nociceptive information in the spinal cord of rats
)
Corresponding author. Department of Physiology, College of Life Sciences, Peking University, Beijing 100871, People’s Republic of China. Tel.: q86-10-6275-1867; fax: q86-10-6275-1850. E-mail address: [email protected] ŽL.-C. Yu..
with mononeuropathy w8,9x. The present study was performed to investigate the effect of galanin on the evoked discharge frequency of the wide-dynamic range ŽWDR. neuron in dorsal horn of the spinal cord of rats.
2. Materials and methods 2.1. Animals and surgery Experiments were performed on 16 adult male Sprague–Dawley rats weighing 200–250 g ŽExperimental Animal Center of Beijing Medical University, Beijing, China.. The rats were housed in cages with free access to food and water. All experiments were conducted according to the guidelines of the animal ethical committee of Karolinska Institutet and every effort was made to minimize animal suffering. Animals were anesthetized with intraperitoneal pentobarbital sodium Ž45 mgrkg; maintained with intermittent dose of 10 mgrkgrh. and a cannula was inserted into the trachea. The dorsal L3–L5 region of the spinal cord was exposed by laminectomy. The vertebral column was stabilized by vertebral and hip clamps. The spinal cord between
0167-0115r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 0 1 1 5 Ž 0 1 . 0 0 2 8 7 - 7
180
L.-C. Yu et al.r Regulatory Peptides 101 (2001) 179–182
L3 and L5 was placed on a curved metal saddle, gently lifted 0.5 mm from the vertebral canal, and then covered with 0.9% saline Ž37 8C.. The animals were immobilized by intraperitoneal gallamine triethiodide Ž100 mgrkgrh. and received artificial respiration Žfrequency: 90; tidal volume: 4–5 ml.. In order to maintain the rat’s body temperature within physiological levels, a heating plate was placed under the rat so that the rectal temperature remained between 35 8C and 36.5 8C. At the end of the experiments, the rats were killed with an overdose of pentobarbital sodium. 2.2. Recording and stimulation Extra-cellular recording of lumbar dorsal horn unit was performed with a glass microelectrode filled with 3 M NaCl Ž3–8 M V . and advanced by a manual hydraulic micro-driver. Recording sites ranged from 70 to 1100 mm below the dorsal surface at L3–L5 levels of the spinal cord. The evoked discharges were displayed on an oscilloscope after being passed through magnifiers. The output of the magnifier was also entered into a computer that was programmed to construct histograms. Stimulation was delivered through fine stainless needle electrodes inserted through the skin of the ipsilateral hindpaw Ž4 V, 0.33 Hz, 3 ms wide pulses, 20 stimulirtrial.. The electrical stimulation was delivered, and the microelectrode was advanced to find the neuron which responded to both lightly brushing and pinching of the skin, and to a greater degree to pinch than the others, those neurons were confirmed to be WDR neurons w10–12x. Then electrical stimulation was applied again, and the evoked responses of individual neuron were observed. Stable extra-cellular recordings were obtained from the WDR neuron at L3–L5 levels of the spinal dorsal horn. The number of the WDR neuron’s discharge was recorded and used to plot the frequency histograms. Each histogram had 128 dots, and each dot’s duration was 11 ms, making the duration of each histogram about 1.5 s. After 20 histogram pictures recorded, the sum of the number of discharges was calculated.
2.4. Chemicals Solutions for administration were prepared with sterilized saline, each with a volume of 10 ml of Ž1. 0.5 or 1 nmol of galanin Žrat–galanin, Tocris, Ballwin, USA.; Ž2. 1 nmol of galantide ŽTocris.; Ž3. 10 ml of 0.9% saline as a control. 2.5. Statistical analysis The discharge frequency of the WDR neuron was recorded and used to plot the frequency histograms. Each histogram was 1.5 s. After having recorded 20 histograms, they were piled up and the sum of the discharges calculated. The discharge frequency was presented as mean " standard error of the mean ŽS.E.M... The discharge frequencies recorded during subsequent experiment were expressed as percentage changes of the basal level of each neuron’s discharge frequency. The difference between groups was determined by two-way analysis of variance ŽANOVA..
3. Results 3.1. The effect of galanin on the eÕoked discharge frequency of WDR neurons Twenty-four WDR neurons were recorded. The evoked discharge frequency was recorded before and 2, 5, 10, 15, 20, 25, 30 min after the administration of 0.5 Ž n s 6. or 1 nmol of galanin Ž n s 10., or 10 ml of 0.9% saline as a control Ž n s 8.. Compared with the saline group, the evoked discharge frequency of WDR neurons decreased significantly after administration of 1 nmol of galanin Ž F s 52.03, P - 0.001., while 0.5 nmol of galanin had no significant effect Ž F s 0.05, P s 0.83.. The results are shown in Fig. 1.
2.3. Experimental protocol Once a WDR neuron was determined, electrical stimulation was applied again and the evoked discharges were recorded. Trigger inputs were used to make the stimulation and recording synchronous. Each neuron was recorded for 30 min after the chemical applied to the dorsal surface of the spinal cord. The neuron discharge frequency was recorded at 2, 5, 10, 15, 20, 25 and 30 min after the administration. Each time for recording lasted for 30 s. After recording for 30 min, the effect of the chemical was washed away. At least, a 30 min rest period was allowed for the next neuron discharge recording.
Fig. 1. Effects of administration of 0.5 and 1 nmol of galanin to dorsal surface of the L3–L5 spinal cord on the discharge of wide-dynamic range ŽWDR. neurons in rats. Results are presented as mean"S.E.M. The statistical difference between groups was evaluated by two-way analysis of variance ŽANOVA., ) ) ) P - 0.001 compared with the control group.
L.-C. Yu et al.r Regulatory Peptides 101 (2001) 179–182
Fig. 2. Blockade effect of galantide on the galanin-induced inhibition on the discharge frequency of wide-dynamic range ŽWDR. neurons. Results are presented as mean"S.E.M. The statistical difference between groups was evaluated by two-way analysis of variance ŽANOVA., ) ) ) P - 0.001 compared with the control group.
3.2. The effect of galantide on the galanin-induced decrease in the eÕoked discharge frequency of WDR neurons The discharges of 16 WDR neurons were observed. After that, 1 nmol of galanin was directly applied on the dorsal surface of the L3–L5 spinal cord, the evoked discharge frequency of the WDR neuron decreased. Five minutes later, 1 nmol of galantide was applied directly on the surface of L3–L5 dorsal surface of the spinal cord Ž n s 5., or administered 10 ml of 0.9% saline as a control Ž n s 7.. Compared with the control group, the galanin-induced decreases in WDR neuron discharge were blocked significantly after administration of galantide Ž F s 23.20, P - 0.001.. The results are shown in Fig. 2.
4. Discussion The present study demonstrated that the evoked discharge frequency of the WDR neuron decreased significantly after intrathecal administration of galanin, and that the effect lasted for more than 30 min. The results suggest that galanin plays an inhibitory role on the transmission of presumed nociception in the spinal cord of rats. Kask et al. w13x have reported that galanin has an inhibitory action on neuronal activity. Intrathecal injection of 0.316 nmol of galanin also produced a prolonged depression of the flexor reflex in rats w14x. In a recent study, the effects of galanin on magnocellular neurosecretory cells were examined. Application of galanin or of the N-terminal fragment galanin1–16 produced a reversible membrane hyperpolarization with an IC 50 near 10 nM. These effects were associated with an increase in membrane conductance, with a reversal potential near y70 mV, and were not blocked by tetrodotoxin, indicating that the receptors mediating these effects are located postsynaptically. The reversal potential of the galanin-mediated effect was unaffected
181
by reducing extracellular chloride or by intracellular chloride injection, indicating that the effects of galanin are not mediated by modulation of chloride conductance. In contrast, reducing the external concentration of potassium ions from 3 to 1 mM shifted the reversal potential of the responses to y85 mV, suggesting the involvement of potassium conductance. When tested on spontaneously active magnocellular neurosecretory cells, the hyperpolarizing effects of galanin were associated with a suppression of firing in both continuously active and phasically active neurons. These results suggest that galanin may be a potent endogenous modulator of firing pattern in central nervous system cells w15x. In rats with sciatic nerve axotomy, galantide Žan antagonist of galanin. enhanced the nociceptive reflex in spinalized rats with much greater potency than in intact rats w16x. In rats with sciatic nerve ligation, intrathecal administration of galanin produced dose-dependent increases in the hindpaw withdrawal latency to noxious thermal and mechanical, supporting the finding in spinalized rats that galanin produces an inhibitory effect on the transmission of presumed nociceptive information in the spinal cord w6x. Recent studies in our laboratory demonstrated that intraperiaqueductal grey administration of galanin also resulted in a dose-dependent anti-nociception in intact rats and in rats with mononeuropathy w5,7x. The above results suggest that galanin has an anti-nociceptive effect not only in the spinal cord but also in the brain. Galantide is a selective antagonist of galanin receptor w17x. In the present study, the galanin-induced inhibition on the evoked discharge frequency of WDR neurons was blocked by following administration of galantide, indicating that the inhibitory effect of galanin on the activity of WDR neuron was induced by activating galanin receptors in the dorsal horn of the spinal cord. The results of the present study show that galanin is involved in the modulation of the transmission of presumed nociceptive information in the dorsal horn of the spinal cord in rats, and that the anti-nociceptive effect of galanin is mediated by activation of the galanin receptor.
Acknowledgements This study was supported by funds from the Karolinska Institutet Foundation, the National Natural Science Foundation of China ŽNSFC..
References w1x Tatemoto K, Rokaeus A, Jornvall H, McDonald TJ, Mutt V. Galanin —a novel biologically active peptide from porcine intestine. FEBS Lett 1983;164:124–8. w2x Ch’ng JLC, Christofides ND, Anand P, Gibson SJ, Allen YS, Su
182
w3x
w4x
w5x
w6x
w7x
w8x
w9x
L.-C. Yu et al.r Regulatory Peptides 101 (2001) 179–182 HC, et al. Distribution of galanin immunoreactivity in the central nervous system and the response of galanin-containing neuronal pathways to injury. Neuroscience 1985;16:343–54. Merchenthaler I, Lopez FJ, Negro-Vilar A. Anatomy and physiology of central galanin-containing pathways. Prog Neurobiol 1993;40: 711–69. Hokfelt T, Zhang X, Wiesenfeld-Hallin Z. Messenger plasticity in primary sensory neurons following axotomy and its functional implications. Trends Neurosci 1994;17:22–30. Wang D, Lundeberg T, Yu LC. Antinociceptive effects of galanin in periaqueductal grey of rats with experimentally induced mononeuropathy. Neuroscience 2000;96:767–71. Yu LC, Lundeberg S, An H, Wang FX, Lundeberg T. Effects of intrathecal galanin on nociceptive responses in rats with mononeuropathy. Life Sci 1999;64:1145–53. Wang D, Ye HH, Yu LC, Lundeberg T. Intra-periaqueductal grey administration of galanin increases nociceptive response latency in rats, an effect reversed by naloxone. Brain Res 1999;834:152–4. Zhang YP, Lundeberg T, Yu LC. Interaction of galanin and morphine in the spinal antinociception in rats with mononeuropathy. Brain Res 2000;852:485–7. Zhang YP, Yu LC, Lundeberg T. An interaction of opioids and galanin in dorsal horn of the spinal cord in mononeuropathic rats. Regul Pept 2000;86:89–94.
w10x Jiang MC, Cleland CL, Gebhart GF. Intrinsic properties of deep dorsal horn neurons in the L6–S1 spinal cord of the intact rat. J Neurophysiol 1995;74:1819–27. w11x Sotgiu ML, Biella G. Contralateral inhibitory control of spinal nociceptive transmission in rats with chronic peripheral nerve injury. Neurosci Lett 1998;253:21–4. w12x Yu LC, Zheng EM, Lundeberg T. Calcitonin gene-related peptide 8–37 inhibits the evoked discharge frequency of wide-dynamic range neuron in dorsal horn of the spinal cord in rats. Regul Pept 1999;83:21–4. w13x Kask K, Langel U, Bartfai T. Galanin—a neuropeptide with inhibitory actions. Cell Mol Neurobiol 1995;15:653–73. w14x Wiesenfeld-Hallin Z, Villar MJ, Hokfelt T. The effects of intrathecal galanin and C-fiber stimulation on the flexor reflex in the rat. Brain Res 1989;486:205–13. w15x Papas S, Bourque CW. Galanin inhibits continuous and phasic firing in rat hypothalamic magnocellular neurosecretory cells. J Neurosci 1997;17:6048–56. w16x Wiesenfelt-Hallin Z, Xu XJ, Langel U, Bedecs K, Hokfelt T, Bartfai T. Galanin mediated control of pain: enhanced role after nerve injury. Proc Natl Acad Sci U S A 1992;89:3334–7. w17x Bartfai T, Fisone G, Langel U. Galanin and galanin antagonists: molecular and biochemical perspectives. Trans Pharmacol Sci 1992; 13:312–7.