49
Neuroscience Letters, 124 (1991) 49-51 © 1991 Elsevier Scientific Publishers Ireland Ltd. 0304-3940/91/$ 03.50 ADONIS 030439409100004C NSL 07597
Effect of neurokinin A, substance P and calcitonin gene related peptide in peripheral hyperalgesia in the rat paw Meire N a k a m u r a - C r a i g and Balvinder K a u r Gill Department of Pharmacology, WellcomeResearch Laboratories, Beckenham, Kent ( U.K.) (Received 27 August 1990; Revised version received 5 December 1990; Accepted 7 December 1990)
Key words: Peripheral hyperalgesia; Neurokinin A; Substance P; Calcitonin gene-related peptide The effect of neurokinin A (NKA), substance P (SP) and calcitonin gene-related peptide (CGRP) in peripheral hyperalgesia was studied in rats using a modification of the Randall-Selitto paw test. NKA was l0 times more potent than SP which was 500 times more potent than CGRP in inducing hyperalgesia in the rat paw, suggesting that NKA and SP but not CGRP could have an important role in acute hyperalgesic conditions. Furthermore, sensitization induced by several injections of subthreshold doses of NKA or CGRP suggest that these neuropeptides along with SP could participate as mediators or modulators of chronic pain.
The hypothesis that SP participates in the nociceptive process has been well investigated and there appears to be enough evidence to support this theory. SP has a preferential excitatory effect on the nociceptive neurones in the dorsal horn of the spinal cord [7, 9, 11, 18]. Recently we suggested that SP may participate as a neuromodulator in peripheral inflammatory pain probably associated with chronic conditions [14]. N K A has been shown to be distributed in parallel with SP in the dorsal horn of the spinal cord and its pharmacology has resembled SP in many ways [17]. A similar distribution is also described for CGRP [6]. Furthermore there are suggestions that NKA and CGRP are also involved in nociception [4, 8, 10, 19]. The present study investigates the possible involvement of NKA and CGRP in peripheral pain. The possibility that NKA and CGRP produce sensitization as does SP in the rat paw by repeated administration of a subthreshold dose [13], has also been investigated. Male Wistar rats (150-170 g) were used throughout. Hyperalgesia was measured by a modification of the Randall-Selitto test [2]. In this test, a constant pressure of 20 mmHG is applied to the hind paw of rats (using a syringe and plunger) and is discontinued when the animals present a behavioural response, characterized by a reduction of escape movements and a change of respiratory frequency. The observation is made whilst the rat is held into the experimental position by the experiCorrespondence: M. Nakamura-Craig, Department of Pharmacology, Wellcome Research Laboratories, Langley Court, Beckenham, Kent BR3 3BS, U.K.
menter. In control animals the time taken for such a response to occur is very reproducible (34.8 + O.12, n = 20) but is less after injection of a hyperalgesic stimulus. Measuring the reaction time before and after injection of a hyperalgesic stimulus subcutaneously into the rat paw (subplantar, s.pl.), provides an assessment of the degree of hyperalgesi~i (expressed as the difference between the two times, d reaction time, seconds). Indomethacin (2 mg/kg, p.o.) was given 30 rain before injection of the hyperalgesic substances. The experimenter was unaware of the group treatments during the test period. All results are presented as means___S.E.M. The level of statistical significance was determined with Student's t-test for paired samples and differences with P < 0.05 were considered statistically significant. The number of animals in each experimental group was 5. A comparison of hyperalgesia induced by SP, NKA and CGRP is shown in Fig. 1. The figure shows the hyperalgesic potency at 30 min after the subplantar injections of NKA, SP and CGRP, when the hyperalgesic effect is maximal, the EDs0 and 95 % confidence limits being 0.35 (0-3.62), 3.49 (2.57-5.12) and 1555 nmol/ paw, respectively. The SP antagonist, [D-Arg 1, D-Pro 2, DTrp 7,9, Leull]Sp (SPAt, 3.34 nmol/paw) 10 rain before SP reduced the hyperalgesia induced by 3.71 nmol/paw at 30 min from 18.2__.0.06 s to 1.2___0.32 s (93.4%). The hyperalgesia induced by NKA (4.41 nmol/paw, 21.1 +0.15 s) and CGRP (2.63 nmol/paw, 8.8 +_0.87 s) at 30 min was not affected by the SPAt, 3.34 nmol/paw (19.2 _ 0.78 s and 11.0 +-0.34 s, respectively). Multiple subthreshold injections of NKA (0.4 fmol/
50
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Neuroscience Letters, 124 (1991) 49-51 © 1991 Elsevier Scientific Publishers Ireland Ltd. 0304-3940/91/$ 03.50 ADONIS 030439409100004C NSL 07597
Effect of neurokinin A, substance P and calcitonin gene related peptide in peripheral hyperalgesia in the rat paw Meire N a k a m u r a - C r a i g and Balvinder K a u r Gill Department of Pharmacology, WellcomeResearch Laboratories, Beckenham, Kent ( U.K.) (Received 27 August 1990; Revised version received 5 December 1990; Accepted 7 December 1990)
Key words: Peripheral hyperalgesia; Neurokinin A; Substance P; Calcitonin gene-related peptide The effect of neurokinin A (NKA), substance P (SP) and calcitonin gene-related peptide (CGRP) in peripheral hyperalgesia was studied in rats using a modification of the Randall-Selitto paw test. NKA was l0 times more potent than SP which was 500 times more potent than CGRP in inducing hyperalgesia in the rat paw, suggesting that NKA and SP but not CGRP could have an important role in acute hyperalgesic conditions. Furthermore, sensitization induced by several injections of subthreshold doses of NKA or CGRP suggest that these neuropeptides along with SP could participate as mediators or modulators of chronic pain.
The hypothesis that SP participates in the nociceptive process has been well investigated and there appears to be enough evidence to support this theory. SP has a preferential excitatory effect on the nociceptive neurones in the dorsal horn of the spinal cord [7, 9, 11, 18]. Recently we suggested that SP may participate as a neuromodulator in peripheral inflammatory pain probably associated with chronic conditions [14]. N K A has been shown to be distributed in parallel with SP in the dorsal horn of the spinal cord and its pharmacology has resembled SP in many ways [17]. A similar distribution is also described for CGRP [6]. Furthermore there are suggestions that NKA and CGRP are also involved in nociception [4, 8, 10, 19]. The present study investigates the possible involvement of NKA and CGRP in peripheral pain. The possibility that NKA and CGRP produce sensitization as does SP in the rat paw by repeated administration of a subthreshold dose [13], has also been investigated. Male Wistar rats (150-170 g) were used throughout. Hyperalgesia was measured by a modification of the Randall-Selitto test [2]. In this test, a constant pressure of 20 mmHG is applied to the hind paw of rats (using a syringe and plunger) and is discontinued when the animals present a behavioural response, characterized by a reduction of escape movements and a change of respiratory frequency. The observation is made whilst the rat is held into the experimental position by the experiCorrespondence: M. Nakamura-Craig, Department of Pharmacology, Wellcome Research Laboratories, Langley Court, Beckenham, Kent BR3 3BS, U.K.
menter. In control animals the time taken for such a response to occur is very reproducible (34.8 + O.12, n = 20) but is less after injection of a hyperalgesic stimulus. Measuring the reaction time before and after injection of a hyperalgesic stimulus subcutaneously into the rat paw (subplantar, s.pl.), provides an assessment of the degree of hyperalgesi~i (expressed as the difference between the two times, d reaction time, seconds). Indomethacin (2 mg/kg, p.o.) was given 30 rain before injection of the hyperalgesic substances. The experimenter was unaware of the group treatments during the test period. All results are presented as means___S.E.M. The level of statistical significance was determined with Student's t-test for paired samples and differences with P < 0.05 were considered statistically significant. The number of animals in each experimental group was 5. A comparison of hyperalgesia induced by SP, NKA and CGRP is shown in Fig. 1. The figure shows the hyperalgesic potency at 30 min after the subplantar injections of NKA, SP and CGRP, when the hyperalgesic effect is maximal, the EDs0 and 95 % confidence limits being 0.35 (0-3.62), 3.49 (2.57-5.12) and 1555 nmol/ paw, respectively. The SP antagonist, [D-Arg 1, D-Pro 2, DTrp 7,9, Leull]Sp (SPAt, 3.34 nmol/paw) 10 rain before SP reduced the hyperalgesia induced by 3.71 nmol/paw at 30 min from 18.2__.0.06 s to 1.2___0.32 s (93.4%). The hyperalgesia induced by NKA (4.41 nmol/paw, 21.1 +0.15 s) and CGRP (2.63 nmol/paw, 8.8 +_0.87 s) at 30 min was not affected by the SPAt, 3.34 nmol/paw (19.2 _ 0.78 s and 11.0 +-0.34 s, respectively). Multiple subthreshold injections of NKA (0.4 fmol/
50
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28
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~
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I
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