- Email: [email protected]
Comparison of behavioral responses to noxious cold and heat in mice
Brain Research 845 Ž1999. 117–121 www.elsevier.comrlocaterbres
Short communication
Comparison of behavioral responses to noxious cold and heat in mice Don E. Lee
a,b
, Susan J. Kim
a,b
, Min Zhuo
a,b,)
a
b
Department of Anesthesiology, Washington UniÕersity Medical Center, Washington UniÕersity in St. Louis, St. Louis, MO 63110, USA Department of Anatomy and Neurobiology, Washington UniÕersity Medical Center, Washington UniÕersity in St. Louis, St. Louis, MO 63110, USA Accepted 3 August 1999
Abstract We investigated behavioral responses to noxious cold and heat stimuli in mice. Similar to the hot-plate test, mice showed licking or jumping responses on a cold-plate Ž08C.. The sensitivity to noxious heat Ž558C. was not correlated to the sensitivity to noxious cold, indicating that nociceptive processing of cold and heat are different. Behavioral responses to noxious cold are inhibited by systemic morphine or intrathecal administration of morphine. Lesion of the medial frontal cortex, including the anterior cingulate cortex, or selective activation of two types of opioid receptors in the anterior cingulate cortex produces dose-dependent antinociceptive effects on behavioral responses to noxious cold stimuli. These results suggest that activation of opioid receptors in the anterior cingulate cortex can produce powerful antinociception. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Cold pain; Heat pain; Anterior cingulate cortex; Opioid; Mouse
The sensation of temperature is processed through peripheral thermoreceptive fibers w10x. Increasing the skin temperature causes a warm sensation and heat pain if the temperature goes above 458C w10x. In contrast, cooling the skin temperature induces a cold sensation, which is usually not painful. However, when the temperature is further decreased to 08C for about 10 s, a cold and painful sensation can be induced w16x. The existence of cold receptors in the skin has been reported in both animals w5–7,12x and humans w1,6x. Electrophysiological and psychological studies suggest that cold sensation and cold pain are mediated through different signal transduction systems. In the periphery, cold sensation is mediated by small myelinated A d fibers w1,2x, and cold pain is mediated by unmyelinated C fibers w8x. Unlike heat pain, behavioral responses of animals to noxious cold stimuli are less understood. In the present study, we used a cold-plate ŽCP. test to study behavioral responses of adult mice to noxious cold. Male C57r6j mice, 3–4 weeks old, weighing 9–23 g were used ŽJackson.. Mice were kept in the animal facility
)
Corresponding author. Department of Anesthesiology, Washington University Medical Center, Washington University in St. Louis, St. Louis, MO 63110, USA. Fax: q 1-314-862-1571; e-mail: [email protected]
with free access to water and food before the experiments. Behavioral experiments were carried out in a quiet environment and performed during the day. Room temperature was always maintained at 208C. The CP test was performed on ice in a plastic container Ž21 cm Ždiameter. = 21 cm Žheight... The temperature of the ice surface was monitored with a digital thermometer and maintained at 08C by placing ice around the container. Jumping or licking were considered nociceptive responses. The time between the placement of a mouse on the CP and the first jumping or licking of the hindpaw was measured with a digital timer. Mice were removed from the plate after the first response. The hot-plate ŽHP. test was measured with a controlled metal plate ŽColumbia Instruments; Columbus, OH.. The nociceptive response was licking or lifting a hindpaw off the HP, and the latency of response was recorded with a digital timer. Mice were removed from the HP immediately after the first response. In most experiments, a metal plate temperature was maintained at 558C. In some experiments, mice were tested with different temperatures Ž44, 46, 48, 50, 52 and 558C.. A cut-off time of 60 s was used to minimize tissue damage to the hindpaw skin for both the HP and CP tests. Intrathecal injection of drugs was carried out as described w18x. To avoid possible stress during injection, mice were always anesthetized with halothane Ž2%. and recovered from anesthesia within 2–3 min. The injection
0006-8993r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 6 - 8 9 9 3 Ž 9 9 . 0 1 9 5 6 - 3
118
D.E. Lee et al.r Brain Research 845 (1999) 117–121
was monitored by observing the moving of air behind the solution. The effects of intrathecally injected drugs were evaluated 10–15 min after the injection. Lesions of the anterior cingulate cortex were performed as described by using the suction method w11x. Microinjections of opioids into the cingulate cortex were performed unilaterally with a 30-gauge needle. At the end of experiments, the same volume of ink was injected to determine the injection sites. Data were presented as mean values "1 S.E.M. Statistical comparisons were made with the use of ANOVAs ŽDunnett or Newman–Keuls test for post-hoc comparison.. Student’s test was applied for comparisons between paired groups. In all cases, P - 0.05 was considered significant. In a total of 37 mice tested, 30 of them showed jumping responses after 30.4 " 2.3 s Žrange 12–59 s. on the CP. In the other seven mice, no responses were observed within 60 s. The overall mean response latency was 34.5 " 2.7 s Ž n s 37.. Fig. 1A shows the distribution of response latencies. The HP test was also performed in these mice. Unlike the CP test, less individual variability was observed. The average HP Ž558C. latency was 14.5 " 0.9 s Ž n s 37. Žranging from 14.1 to 22.5 s., which is significantly less than that of the CP test Ž P - 0.001.. The distribution of the HP latency is shown in Fig. 1B. We also plotted CP latencies against HP latencies and found no correlation between them Žg s y0.162; P ) 0.05.. In five mice which did not respond on the CP within 60 s, their average HP latency was 11.1 " 0.9 s Žranging 8.4–13.5 s.. In 10 mice, HP latencies at other temperatures Ž44, 46, 48, 50 and 528C. were also tested. The average CP latency in the same mice was 29.1 " 5.7 s and is similar to the average HP latency at 508C Ž27.0 " 3.0 s; Fig. 1D.. To test if the CP response can be inhibited by systemic morphine, morphine was injected intraperitoneally. At a dose of 0.1 mgrkg, CP latency was not significantly affected Ž n s 7.. At a dose of 10 mg, CP responses were all inhibited. The estimated effective dose 50 ŽED50 : dose producing 50% inhibition of the CP response. was 2.2 mgrkg Ž1.0–6.3 mgrkg. ŽFig. 1E.. The inhibitory effect of morphine was reversed by i.p. naloxone Ž1 mgrkg, n s 5.. For comparison, the effect of morphine on HP latency was also measured in the same mice. The HP response was similarly inhibited, with an estimated ED50 of 2.4 mgrkg Ž1.9–6.7 mgrkg. which was not significantly different from that for the CP test. Nociceptive heat transmission and behavioral nociceptive responses to noxious heat can be inhibited by morphine at the level of the spinal cord w17x. We next tested if the CP response was also inhibited by morphine injected intrathecally. Intrathecal injections of morphine produced a dose-dependent inhibition in the CP test. The estimated ED50 was 4.1 mg Ž1.5–6.1 mg.. At a dose of 10 mg, CP responses were completely inhibited in all six mice Žlatency greater than 60 s.. In the HP test, the ED50 was 2.9 mg Ž1.7–5.0 mg. ŽFig. 1F.. There was no significant difference in ED50 s between the HP and CP tests.
In addition to the spinal cord, many supraspinal structures are also important for pain transmission and analgesia w3,4x. The anterior cingulate cortex may play a role in the affective pain response system and may contribute to various functions of the cortex, including the perception of pain. In humans, noxious thermal stimuli induce a significant response in the anterior cingulate cortex w13,15x. To test if the anterior cingulate cortex and adjacent areas may be important for transmission andror regulation of behavioral responses to noxious cold, we lesioned the medial frontal cortex area, including the anterior cingulate cortex. In six mice, lesions of the medial frontal cortex produced significant increases in CP latencies Žfrom 15.8 " 3.2 to 35.4 " 6.0 s; Fig. 2A and B.. Similar to a previous report in rats w11x, behavioral responses in the HP test in the same mice were also significantly increased Žfrom 12.2 " 0.9 to 36.9 " 6.8 s; Fig. 2B.. Although opiate receptors are found in the anterior cingulate cortex, and activation of these receptors inhibit excitatory glutamatergic synaptic transmission in the anterior cingulate cortex w9,14x, it remains unclear if activation of these opiate receptors could be antinociceptive or analgesic. We thus investigated the involvement of different subtypes of opiate receptors in the CP test. Microinjection of a selective m opioid receptor agonist Damgo Ž0.2–200 ngr0.5 ml. produced a dose-dependent inhibition of the CP response. The estimated ED50 for inhibition of CP response was 2.4 ng Ž0.6–6.5 ng.. A similar inhibitory effect was observed in the HP test. The estimated ED50 for inhibition was 6.2 ng Ž3.1–12.2 ng.. A selective d-receptor agonist DPDPE Ž20 ng–2 mgr0.5 ml. was injected into the cingulate cortex. DPDPE produced a dose-dependent inhibition of the CP response with an estimated ED50 of 0.17 mg Ž0.09–0.31 mg., which was significantly greater than that of Damgo Ž P - 0.01.. The HP response was also inhibited by DPDPE. The estimated ED50 was 11.8 mg Ž2.1–2898.2 mg., which is significantly greater than that of DPDPE in the CP test. These results indicate that DPDPE in the anterior cingulate cortex is more effective in inhibiting cold pain than heat pain transmission. A selective k-receptor agonist, Ž" .-trans-Ž1S,2 S .-U-50488 methanesulfonate, however, affected neither HP or CP response latencies at the high dose tested ŽFig. 2C–D.. Our results demonstrate that behavioral responses to noxious cold differ from that to noxious heat. Mice show greater individual differences in the CP than HP test. Behavioral nociceptive thresholds for cold and heat pain are not parallel in the same mice. While cold nociceptive thresholds are higher in some mice, heat nociceptive thresholds remain the same as other animals. These findings indicate that transmission andror modulation of cold pain differ from that of heat pain. Differences in peripheral primary afferent fibers as well as central sensory synapses could affect behavioral responses to cold or hot stimuli. Behavioral responses to noxious cold were inhibited by morphine injected intrathecally or intraperitoneally, indi-
D.E. Lee et al.r Brain Research 845 (1999) 117–121
119
Fig. 1. Behavioral responses of mice to noxious cold and heat. ŽA. Distribution of response latencies in the CP test Ž n s 37.; ŽB. Distribution of response latencies in the HP test in the same mice shown in ŽA.; ŽC. CP latencies were not correlated with HP latencies. CP latencies were plotted against HP latencies; ŽD. Behavioral response to thermal stimuli at different temperatures. Response latencies at different temperatures including cold and hot were measured in the same mice. ŽE. Dose-dependent inhibition of CP response by systemic injection morphine Ži.p.. Žfilled squares.. HP responses were also measured Žopen squares.; ŽF. Dose-dependent effect inhibition of CP response by intrathecal administration of morphine Ži.th.. Žfilled squares.. HP responses were also measured Žopen squares.. Data are presented as mean value "1 S.E.M.
cating that activation of opioid receptors inhibits transmission of cold pain. Furthermore, activation of different opioid receptors within the anterior cingulate cortex produces different effects. Damgo equally inhibited CP and HP responses, and DPDPE more strongly inhibited CP than HP response. Damgo is more potent than DPDPE in
inhibiting CP and HP responses, suggesting that cold and heat pain could be affected by different subpopulations of opioid receptors within the anterior cingulate cortex. The antinociceptive effect produced by opioid receptor agonists may be due to at least two different mechanisms: Ž1. inhibiting supraspinal pain transmission through decreas-
120
D.E. Lee et al.r Brain Research 845 (1999) 117–121
Fig. 2. Role of the anterior cingulate cortex in behavioral response to noxious cold and heat. ŽA. Histological reconstruction of lesions in the medial frontal cortex, including the anterior cingulate cortex. Cg1: cingulate cortex, area 1; Cg2: cingulate cortex, area 2; M1: primary motor cortex; M2: secondary motor cortex. ŽB. Both CP and HP response latencies were significantly increased after the lesion. ŽC. Effects of local microinjection of three different opioid receptor agonists on CP latencies. ŽD. Effects of local microinjection of three different opioid receptor agonists on HP latencies; Data are presented as mean value "1 S.E.M. ŽE. Site for the microinjection of opioid receptor agonists in the anterior cingulate cortex. Symbols are the same as those used in ŽC. and ŽD..
ing excitatory synaptic transmission andror enhancing inhibitory synaptic transmission within the anterior cingulate cortex w14x; and Ž2. activating descending modulatory
systems from the anterior cingulate cortex and thus inhibiting nociceptive transmission at the level of the spinal cord. These results are consistent with a previous in vitro elec-
D.E. Lee et al.r Brain Research 845 (1999) 117–121
trophysiological study w14x and provide the first evidence that activation of opiate receptors within the anterior cingulate cortex can inhibit a behavioral response to noxious cold and heat.
w9x
w10x
References w1x H. Adriaensen, J. Gybels, H.O. Handwerker, J. Van Hees, Response properties of thin myelinated ŽA-d . fibers in human skin nerves, J. Neurophysiol. 49 Ž1983. 111–122. w2x I. Darian-Smith, K.O. Johnson, R. Dykes, ‘‘Cold’’ fiber population innervating palmar and digital skin of the monkey: response to cooling pulses, J. Neurophysiol. 36 Ž1973. 325–346. w3x H.L. Fields, M.M. Heinricher, P. Mason, Neurotransmitters in nociceptive modulatory circuits, Annu. Rev. Neurosci. 14 Ž1991. 219– 245. w4x G.F. Gebhart, A.I. Randich, Brainstem modulation of nociception, in: W.R. Klemm, R.P. Vertes ŽEds.., Brainstem Mechanisms of Behavior, Wiley, New York, 1990, pp. 315–352. w5x H. Hensel, A. Iggo, Analysis of cutaneous warm and cold fibers in primates, Pfluegers Arch. 329 Ž1971. 1–8. w6x H. Hensel, K.K.A. Boman, Afferent impulses in cutaneous sensory nerves in human subjects, J. Neurophysiol. 23 Ž1960. 564–578. w7x A. Iggo, Cutaneous thermoreceptors in primates and subprimates, J. Physiol. ŽLondon. 200 Ž1969. 403–430. w8x R.H. LaMotte, J.G. Thalhammer, Response properties of high-
w11x
w12x
w13x
w14x w15x
w16x
w17x
w18x
121
threshold cutaneous cold receptors in the primate, Brain Res. 244 Ž1982. 279–287. A. Mansour, S.J. Watson. Anatomical distribution of opioid receptors in mammalians: an overview, in: A. Herz, H. Akil, E.J. Simon ŽEds.., Handbook of Experimental Pharmacology, Springer, Berlin, 1992, pp. 79–106. R.A. Meyer, J.N. Campbell, S.N. Raja, Peripheral neural mechanisms of nociception, in: P.D. Wall, R. Melzack ŽEds.., Textbook of Pain, 3rd edn., Churchill Livingstone, New York, 1994, p. 13. L.N. Pastoriza, T.J. Morrow, K.L. Casey, Medial frontal cortex lesions selectively attenuate the hot plate response: possible nocifensive apraxia in the rat, Pain 64 Ž1996. 11–17. E. Perl, Myelinated afferent fibers innervating the primate skin and their response to noxious stimuli, J. Physiol. ŽLondon. 197 Ž1968. 593–615. J.D. Talbot, S. Marrett, A.C. Evans, E. Meyer, M.C. Bushnell, G.H. Duncan, Multiple representations of pain in human cerebral cortex, Science 251 Ž1991. 1355–1358. E. Tanaka, R.A. North, Opioid actions on rat anterior cingulate cortex neurons in vitro, J. Neurosci. 14 Ž1994. 1106–1113. B.A. Vogt, S. Derbyshire, A.K.P. Jones, Pain processing in four regions of human cingulate cortex localized with co-registered PET and MR imaging, Eur. J. Neurosci. 8 Ž1996. 1461–1473. S. Wolf, J.D. Hardy, Studies on pain. Observations on pain due to local cooling and on factors involved in the ‘cold pressor’ effect, J. Clin. Invest. 20 Ž1941. 521–533. T.L. Yaksh, A.B. Malmberg, Central pharmacology of nociceptive transmission, in: P.D. Wall, R. Melzack ŽEds.., Textbook of Pain, 3rd edn., Churchill Livingstone, New York, 1994, p. 165. M. Zhuo, NMDA receptor-dependent long term hyperalgesia after tail amputation in mice, Eur. J. Pharmacol. 349 Ž1998. 211–220.
Short communication
Comparison of behavioral responses to noxious cold and heat in mice Don E. Lee
a,b
, Susan J. Kim
a,b
, Min Zhuo
a,b,)
a
b
Department of Anesthesiology, Washington UniÕersity Medical Center, Washington UniÕersity in St. Louis, St. Louis, MO 63110, USA Department of Anatomy and Neurobiology, Washington UniÕersity Medical Center, Washington UniÕersity in St. Louis, St. Louis, MO 63110, USA Accepted 3 August 1999
Abstract We investigated behavioral responses to noxious cold and heat stimuli in mice. Similar to the hot-plate test, mice showed licking or jumping responses on a cold-plate Ž08C.. The sensitivity to noxious heat Ž558C. was not correlated to the sensitivity to noxious cold, indicating that nociceptive processing of cold and heat are different. Behavioral responses to noxious cold are inhibited by systemic morphine or intrathecal administration of morphine. Lesion of the medial frontal cortex, including the anterior cingulate cortex, or selective activation of two types of opioid receptors in the anterior cingulate cortex produces dose-dependent antinociceptive effects on behavioral responses to noxious cold stimuli. These results suggest that activation of opioid receptors in the anterior cingulate cortex can produce powerful antinociception. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Cold pain; Heat pain; Anterior cingulate cortex; Opioid; Mouse
The sensation of temperature is processed through peripheral thermoreceptive fibers w10x. Increasing the skin temperature causes a warm sensation and heat pain if the temperature goes above 458C w10x. In contrast, cooling the skin temperature induces a cold sensation, which is usually not painful. However, when the temperature is further decreased to 08C for about 10 s, a cold and painful sensation can be induced w16x. The existence of cold receptors in the skin has been reported in both animals w5–7,12x and humans w1,6x. Electrophysiological and psychological studies suggest that cold sensation and cold pain are mediated through different signal transduction systems. In the periphery, cold sensation is mediated by small myelinated A d fibers w1,2x, and cold pain is mediated by unmyelinated C fibers w8x. Unlike heat pain, behavioral responses of animals to noxious cold stimuli are less understood. In the present study, we used a cold-plate ŽCP. test to study behavioral responses of adult mice to noxious cold. Male C57r6j mice, 3–4 weeks old, weighing 9–23 g were used ŽJackson.. Mice were kept in the animal facility
)
Corresponding author. Department of Anesthesiology, Washington University Medical Center, Washington University in St. Louis, St. Louis, MO 63110, USA. Fax: q 1-314-862-1571; e-mail: [email protected]
with free access to water and food before the experiments. Behavioral experiments were carried out in a quiet environment and performed during the day. Room temperature was always maintained at 208C. The CP test was performed on ice in a plastic container Ž21 cm Ždiameter. = 21 cm Žheight... The temperature of the ice surface was monitored with a digital thermometer and maintained at 08C by placing ice around the container. Jumping or licking were considered nociceptive responses. The time between the placement of a mouse on the CP and the first jumping or licking of the hindpaw was measured with a digital timer. Mice were removed from the plate after the first response. The hot-plate ŽHP. test was measured with a controlled metal plate ŽColumbia Instruments; Columbus, OH.. The nociceptive response was licking or lifting a hindpaw off the HP, and the latency of response was recorded with a digital timer. Mice were removed from the HP immediately after the first response. In most experiments, a metal plate temperature was maintained at 558C. In some experiments, mice were tested with different temperatures Ž44, 46, 48, 50, 52 and 558C.. A cut-off time of 60 s was used to minimize tissue damage to the hindpaw skin for both the HP and CP tests. Intrathecal injection of drugs was carried out as described w18x. To avoid possible stress during injection, mice were always anesthetized with halothane Ž2%. and recovered from anesthesia within 2–3 min. The injection
0006-8993r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 6 - 8 9 9 3 Ž 9 9 . 0 1 9 5 6 - 3
118
D.E. Lee et al.r Brain Research 845 (1999) 117–121
was monitored by observing the moving of air behind the solution. The effects of intrathecally injected drugs were evaluated 10–15 min after the injection. Lesions of the anterior cingulate cortex were performed as described by using the suction method w11x. Microinjections of opioids into the cingulate cortex were performed unilaterally with a 30-gauge needle. At the end of experiments, the same volume of ink was injected to determine the injection sites. Data were presented as mean values "1 S.E.M. Statistical comparisons were made with the use of ANOVAs ŽDunnett or Newman–Keuls test for post-hoc comparison.. Student’s test was applied for comparisons between paired groups. In all cases, P - 0.05 was considered significant. In a total of 37 mice tested, 30 of them showed jumping responses after 30.4 " 2.3 s Žrange 12–59 s. on the CP. In the other seven mice, no responses were observed within 60 s. The overall mean response latency was 34.5 " 2.7 s Ž n s 37.. Fig. 1A shows the distribution of response latencies. The HP test was also performed in these mice. Unlike the CP test, less individual variability was observed. The average HP Ž558C. latency was 14.5 " 0.9 s Ž n s 37. Žranging from 14.1 to 22.5 s., which is significantly less than that of the CP test Ž P - 0.001.. The distribution of the HP latency is shown in Fig. 1B. We also plotted CP latencies against HP latencies and found no correlation between them Žg s y0.162; P ) 0.05.. In five mice which did not respond on the CP within 60 s, their average HP latency was 11.1 " 0.9 s Žranging 8.4–13.5 s.. In 10 mice, HP latencies at other temperatures Ž44, 46, 48, 50 and 528C. were also tested. The average CP latency in the same mice was 29.1 " 5.7 s and is similar to the average HP latency at 508C Ž27.0 " 3.0 s; Fig. 1D.. To test if the CP response can be inhibited by systemic morphine, morphine was injected intraperitoneally. At a dose of 0.1 mgrkg, CP latency was not significantly affected Ž n s 7.. At a dose of 10 mg, CP responses were all inhibited. The estimated effective dose 50 ŽED50 : dose producing 50% inhibition of the CP response. was 2.2 mgrkg Ž1.0–6.3 mgrkg. ŽFig. 1E.. The inhibitory effect of morphine was reversed by i.p. naloxone Ž1 mgrkg, n s 5.. For comparison, the effect of morphine on HP latency was also measured in the same mice. The HP response was similarly inhibited, with an estimated ED50 of 2.4 mgrkg Ž1.9–6.7 mgrkg. which was not significantly different from that for the CP test. Nociceptive heat transmission and behavioral nociceptive responses to noxious heat can be inhibited by morphine at the level of the spinal cord w17x. We next tested if the CP response was also inhibited by morphine injected intrathecally. Intrathecal injections of morphine produced a dose-dependent inhibition in the CP test. The estimated ED50 was 4.1 mg Ž1.5–6.1 mg.. At a dose of 10 mg, CP responses were completely inhibited in all six mice Žlatency greater than 60 s.. In the HP test, the ED50 was 2.9 mg Ž1.7–5.0 mg. ŽFig. 1F.. There was no significant difference in ED50 s between the HP and CP tests.
In addition to the spinal cord, many supraspinal structures are also important for pain transmission and analgesia w3,4x. The anterior cingulate cortex may play a role in the affective pain response system and may contribute to various functions of the cortex, including the perception of pain. In humans, noxious thermal stimuli induce a significant response in the anterior cingulate cortex w13,15x. To test if the anterior cingulate cortex and adjacent areas may be important for transmission andror regulation of behavioral responses to noxious cold, we lesioned the medial frontal cortex area, including the anterior cingulate cortex. In six mice, lesions of the medial frontal cortex produced significant increases in CP latencies Žfrom 15.8 " 3.2 to 35.4 " 6.0 s; Fig. 2A and B.. Similar to a previous report in rats w11x, behavioral responses in the HP test in the same mice were also significantly increased Žfrom 12.2 " 0.9 to 36.9 " 6.8 s; Fig. 2B.. Although opiate receptors are found in the anterior cingulate cortex, and activation of these receptors inhibit excitatory glutamatergic synaptic transmission in the anterior cingulate cortex w9,14x, it remains unclear if activation of these opiate receptors could be antinociceptive or analgesic. We thus investigated the involvement of different subtypes of opiate receptors in the CP test. Microinjection of a selective m opioid receptor agonist Damgo Ž0.2–200 ngr0.5 ml. produced a dose-dependent inhibition of the CP response. The estimated ED50 for inhibition of CP response was 2.4 ng Ž0.6–6.5 ng.. A similar inhibitory effect was observed in the HP test. The estimated ED50 for inhibition was 6.2 ng Ž3.1–12.2 ng.. A selective d-receptor agonist DPDPE Ž20 ng–2 mgr0.5 ml. was injected into the cingulate cortex. DPDPE produced a dose-dependent inhibition of the CP response with an estimated ED50 of 0.17 mg Ž0.09–0.31 mg., which was significantly greater than that of Damgo Ž P - 0.01.. The HP response was also inhibited by DPDPE. The estimated ED50 was 11.8 mg Ž2.1–2898.2 mg., which is significantly greater than that of DPDPE in the CP test. These results indicate that DPDPE in the anterior cingulate cortex is more effective in inhibiting cold pain than heat pain transmission. A selective k-receptor agonist, Ž" .-trans-Ž1S,2 S .-U-50488 methanesulfonate, however, affected neither HP or CP response latencies at the high dose tested ŽFig. 2C–D.. Our results demonstrate that behavioral responses to noxious cold differ from that to noxious heat. Mice show greater individual differences in the CP than HP test. Behavioral nociceptive thresholds for cold and heat pain are not parallel in the same mice. While cold nociceptive thresholds are higher in some mice, heat nociceptive thresholds remain the same as other animals. These findings indicate that transmission andror modulation of cold pain differ from that of heat pain. Differences in peripheral primary afferent fibers as well as central sensory synapses could affect behavioral responses to cold or hot stimuli. Behavioral responses to noxious cold were inhibited by morphine injected intrathecally or intraperitoneally, indi-
D.E. Lee et al.r Brain Research 845 (1999) 117–121
119
Fig. 1. Behavioral responses of mice to noxious cold and heat. ŽA. Distribution of response latencies in the CP test Ž n s 37.; ŽB. Distribution of response latencies in the HP test in the same mice shown in ŽA.; ŽC. CP latencies were not correlated with HP latencies. CP latencies were plotted against HP latencies; ŽD. Behavioral response to thermal stimuli at different temperatures. Response latencies at different temperatures including cold and hot were measured in the same mice. ŽE. Dose-dependent inhibition of CP response by systemic injection morphine Ži.p.. Žfilled squares.. HP responses were also measured Žopen squares.; ŽF. Dose-dependent effect inhibition of CP response by intrathecal administration of morphine Ži.th.. Žfilled squares.. HP responses were also measured Žopen squares.. Data are presented as mean value "1 S.E.M.
cating that activation of opioid receptors inhibits transmission of cold pain. Furthermore, activation of different opioid receptors within the anterior cingulate cortex produces different effects. Damgo equally inhibited CP and HP responses, and DPDPE more strongly inhibited CP than HP response. Damgo is more potent than DPDPE in
inhibiting CP and HP responses, suggesting that cold and heat pain could be affected by different subpopulations of opioid receptors within the anterior cingulate cortex. The antinociceptive effect produced by opioid receptor agonists may be due to at least two different mechanisms: Ž1. inhibiting supraspinal pain transmission through decreas-
120
D.E. Lee et al.r Brain Research 845 (1999) 117–121
Fig. 2. Role of the anterior cingulate cortex in behavioral response to noxious cold and heat. ŽA. Histological reconstruction of lesions in the medial frontal cortex, including the anterior cingulate cortex. Cg1: cingulate cortex, area 1; Cg2: cingulate cortex, area 2; M1: primary motor cortex; M2: secondary motor cortex. ŽB. Both CP and HP response latencies were significantly increased after the lesion. ŽC. Effects of local microinjection of three different opioid receptor agonists on CP latencies. ŽD. Effects of local microinjection of three different opioid receptor agonists on HP latencies; Data are presented as mean value "1 S.E.M. ŽE. Site for the microinjection of opioid receptor agonists in the anterior cingulate cortex. Symbols are the same as those used in ŽC. and ŽD..
ing excitatory synaptic transmission andror enhancing inhibitory synaptic transmission within the anterior cingulate cortex w14x; and Ž2. activating descending modulatory
systems from the anterior cingulate cortex and thus inhibiting nociceptive transmission at the level of the spinal cord. These results are consistent with a previous in vitro elec-
D.E. Lee et al.r Brain Research 845 (1999) 117–121
trophysiological study w14x and provide the first evidence that activation of opiate receptors within the anterior cingulate cortex can inhibit a behavioral response to noxious cold and heat.
w9x
w10x
References w1x H. Adriaensen, J. Gybels, H.O. Handwerker, J. Van Hees, Response properties of thin myelinated ŽA-d . fibers in human skin nerves, J. Neurophysiol. 49 Ž1983. 111–122. w2x I. Darian-Smith, K.O. Johnson, R. Dykes, ‘‘Cold’’ fiber population innervating palmar and digital skin of the monkey: response to cooling pulses, J. Neurophysiol. 36 Ž1973. 325–346. w3x H.L. Fields, M.M. Heinricher, P. Mason, Neurotransmitters in nociceptive modulatory circuits, Annu. Rev. Neurosci. 14 Ž1991. 219– 245. w4x G.F. Gebhart, A.I. Randich, Brainstem modulation of nociception, in: W.R. Klemm, R.P. Vertes ŽEds.., Brainstem Mechanisms of Behavior, Wiley, New York, 1990, pp. 315–352. w5x H. Hensel, A. Iggo, Analysis of cutaneous warm and cold fibers in primates, Pfluegers Arch. 329 Ž1971. 1–8. w6x H. Hensel, K.K.A. Boman, Afferent impulses in cutaneous sensory nerves in human subjects, J. Neurophysiol. 23 Ž1960. 564–578. w7x A. Iggo, Cutaneous thermoreceptors in primates and subprimates, J. Physiol. ŽLondon. 200 Ž1969. 403–430. w8x R.H. LaMotte, J.G. Thalhammer, Response properties of high-
w11x
w12x
w13x
w14x w15x
w16x
w17x
w18x
121
threshold cutaneous cold receptors in the primate, Brain Res. 244 Ž1982. 279–287. A. Mansour, S.J. Watson. Anatomical distribution of opioid receptors in mammalians: an overview, in: A. Herz, H. Akil, E.J. Simon ŽEds.., Handbook of Experimental Pharmacology, Springer, Berlin, 1992, pp. 79–106. R.A. Meyer, J.N. Campbell, S.N. Raja, Peripheral neural mechanisms of nociception, in: P.D. Wall, R. Melzack ŽEds.., Textbook of Pain, 3rd edn., Churchill Livingstone, New York, 1994, p. 13. L.N. Pastoriza, T.J. Morrow, K.L. Casey, Medial frontal cortex lesions selectively attenuate the hot plate response: possible nocifensive apraxia in the rat, Pain 64 Ž1996. 11–17. E. Perl, Myelinated afferent fibers innervating the primate skin and their response to noxious stimuli, J. Physiol. ŽLondon. 197 Ž1968. 593–615. J.D. Talbot, S. Marrett, A.C. Evans, E. Meyer, M.C. Bushnell, G.H. Duncan, Multiple representations of pain in human cerebral cortex, Science 251 Ž1991. 1355–1358. E. Tanaka, R.A. North, Opioid actions on rat anterior cingulate cortex neurons in vitro, J. Neurosci. 14 Ž1994. 1106–1113. B.A. Vogt, S. Derbyshire, A.K.P. Jones, Pain processing in four regions of human cingulate cortex localized with co-registered PET and MR imaging, Eur. J. Neurosci. 8 Ž1996. 1461–1473. S. Wolf, J.D. Hardy, Studies on pain. Observations on pain due to local cooling and on factors involved in the ‘cold pressor’ effect, J. Clin. Invest. 20 Ž1941. 521–533. T.L. Yaksh, A.B. Malmberg, Central pharmacology of nociceptive transmission, in: P.D. Wall, R. Melzack ŽEds.., Textbook of Pain, 3rd edn., Churchill Livingstone, New York, 1994, p. 165. M. Zhuo, NMDA receptor-dependent long term hyperalgesia after tail amputation in mice, Eur. J. Pharmacol. 349 Ž1998. 211–220.