- Email: [email protected]
Roles of central interleukin-1 on stress-induced-hypertension and footshock-induced-analgesia in rats
Neuroscience Letters 311 (2001) 41±44
www.elsevier.com/locate/neulet
Roles of central interleukin-1 on stress-induced-hypertension and footshock-induced-analgesia in rats Chang-Jiang Zou*, Jin-Dong Liu, Yi-Chun Zhou Department of Physiology and Pathophysiology, Health Science Center, Peking University, Beijing 100083, People's Republic of China Received 9 March 2001; received in revised form 29 June 2001; accepted 20 July 2001
Abstract Central interleukin-1 (IL-1) plays an important role in mediating the neural, endocrine, and behavioral responses to stressors. Here we tested whether central IL-1 is involved in stress-induced hypertension or footshock (FS)-inducedanalgesia. We observed that: (1) intracerebral ventricular injection of (ICV) IL-1b induced pressor responses; (2) hypertension induced by IL-1b was blocked by ICV an IL-1 antagonist, IL-1ra; (3) ICV IL-1ra attenuated the pressor response induced by FS but intravenous injection of IL-1ra did not signi®cantly reduce this response; (4) the hypertensive response to conditioned fear stimuli was reversed by ICV IL-1ra; (5) FS-induced-analgesia was attenuated by ICV IL-1ra and this effect disappeared 15 min after ICV IL-1ra. These results suggest that both the pressor response to FS or conditioned fear stimuli and short lasting analgesia induced by FS are mediated by central IL-1. q 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Interleukin-1; Conditioned fear stimuli; Hypertension; Footshock-induced-analgesia
Sharing the characteristics of stress mediators [2], central interleukin-1 (IL-1) plays an important role in mediating the neural, endocrine, and behavioral responses to stressors [10,12,13]. Many stressful stimuli may increase brain IL-1 mRNA and brain IL-1 bioactivity [8,9]. Cardiovascular and endocrine responses to IL-1b are similar to stress responses [10]. For example, both IL-1b and stress raised blood pressure, activate hypothalamic-pituitary-adrenal axis [10]. Immunoreactive IL-1 ®bers exist in some cardiovascular regulatory areas [3,6]. Thus, it seems possible that central IL-1 is involved in stress-induced hypertension (SIH). To test this hypothesis, roles of IL-1b in SIH were studied by intracerebral ventricular injection of (ICV) IL-1b or an IL-1 antagonist (IL-1ra). Experiments were performed on male SD rats (150±300 g) housed 2±3 to a cage and had free access to food and water. After implantation of cerebroventricular cannula, a catheter was inserted into the right external jugular vein and/ or right carotid artery, the mean arterial blood pressure (mABP) and heart rate (HR) or pain threshold (tail ¯ick latency, (TFL)) were measured. And, all data were
* Corresponding author. Tel.: 186-10-62091418; fax: 186-1062091443. E-mail address: [email protected] (C.-J. Zou).
expressed as mean ^ SE and analyzed with ANOVA followed by Neuman test. After the rats were anesthetized with chlorohydrate (0.4 g/kg, intraperitoneally (i.p.)) or urethane (1.4 g/kg, i.p.), a stainless cannula was inserted into the right lateral cerebral ventricle with the tip located at 0.6 mm caudal to the bregma, 1.6 mm lateral to the midline and 4.5 mm below the skull. Chlorohydrate-anesthetized rats were allowed to recover for 2 to 3 days. The drugs, recombinant rat IL-1b (PeproTech EC Ltd, England) and IL-1ra (Health Science Center of Peking University, China), diluted with normal saline to 2.5 mg/ml and 10 mg/ml or 0.5 mg/ml, or the vehicle was administered in a volume of 10 ml over a 1min period via cerebroventricular cannula. After each experiment, the position of the cannula tip was veri®ed with methylene blue injected through the cannula (30G). In urethane anesthetized rats whose rectal temperature was maintained 36.5±37.58C through out the experiment, mABP and HR were directly recorded after insertion of an arterial cannula into the right carotid artery. In some conscious rats, however, arterial pressure and HR were taken through a tail cuff system. In conscious rats, a signi®cant pressor response was observed starting about 10 min after ICV 100 ng IL-1b and lasting about an hour (see Fig. 1a). In urethane anesthetized rats, a signi®cant pressor response was induced in 60±
0304-3940/01/$ - see front matter q 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S03 04 - 394 0( 0 1) 02 14 0- 1
42
C.-J. Zou et al. / Neuroscience Letters 311 (2001) 41±44
Fig. 2. An antagonistic effect of IL-1ra on pressor roles of IL-1b. *0:01 , P , 0:05, **P , 0:01 compared IL-1b injected rats with IL-1b injected but IL-1ra pretreated rats.
Fig. 1. Effects of ICV IL-1b on mABP and HR in conscious rats (A) and in urethane-anesthetized rats (B). W ICV vehicle, n 8; P ICV 25 ng IL-b, n 7; X ICV 100 ng IL-b, n 8 (A) or 7 (B). *0:01 , P , 0:05, **P , 0:01 compared with vehicle-injected rats.
110 min after ICV 25 ng IL-1b (see Fig. 1b). A greater hypertensive response was induced in 30±110 min after ICV 100 ng IL-1b. Both in urethane-anesthetized rats and conscious rats, there were no signi®cant changes in HR. As depicted in Fig. 2, the pressor response induced by ICV IL-1b was almost completely blocked by ICV 0.5 mg IL-1ra. 30 min after ICV or intravenous injection of (IV) vehicle or IL-1ra, continuous electric shocks were given to the hind feet (14V, 50Hz, 1 min). Footshock (FS) increased mABP in both IL-1ra and vehicle injected rats though HR remained unchanged (see Table 1). Although ICV IL-1ra resulted in a transient rise in mABP, the maximal change of FS-inducedhypertension after ICV IL-1ra was signi®cantly smaller than that after ICV vehicle, whereas IV IL-1ra had no signi®cant in¯uence on FS-induced-hypertension. According to Yagi's method [17], 3 to 5 days after the
implantation of the ICV cannula, rats received a habituation session twice a day for 3 days. Rats were transferred to an experimental room, placed in a special holder and left undisturbed for 15 min. Following the 3 days habituation procedure, the next day, rats received a training session. Before training session, the mABP and HR were taken as described above. In training session, rats in the FS group were placed in a special holder for 5 min and given shocks to the hind feet (14 V, 50 Hz, 1 s) every 30 s for 5 min. These rats were kept in the holder for another 5 min. The non-shocked rats received identical habituation sessions and training procedures, but without electric shocks. The next day after training session, 25 min after ICV vehicle or IL-1ra, rats were placed in the special holder and mABP and HR were recorded for 15 min. Conditioned fear stimuli induced hypertension and tachycardia in vehicle injected rats but not in IL-1ra injected rats. Furthermore, conditioned fear stimuli reduced mABP but had no signi®cant in¯uences on HR in IL-1ra injected group. In shocked rats, signi®cant differences existed between the mABP in vehicle-injected rats and IL-1ra injected rats. In non-shocked rats, no signi®cant differences existed in mABP and HR when compared vehicle-injected rats with IL-1ra-injected rats (Fig. 3). Administration of IL-1 and FS may increase pain threshold [1,14]. In¯ammatory analgesia is mediated by IL-1 [15]. So, the involvement of central IL-1 in FS-induced-analgesia was also examined by ICV IL-1ra. Therefore, 2±3 days after implantation of the cerebroventricular cannula, the pain
Table 1 In¯uences of IL-1ra on FS-induced-hypertension a Treatment
ICV IL-1ra ICV NS (n 6)
IV IL-1ra ICV IL-1ra (n 6)
FS after ICV FS after ICV IV NS (n 8) IL-1ra (n 8) (n 7)
IV IL-1ra (n 7)
FS after IV NS (n 7)
MABP before T (mmHg) 108.6 ^ 3.7 107.4 ^ 5.0 105.2 ^ 6.8 113.9 ^ 6.4 110.5 ^ 7.6 113.4 ^ 8.1 112.4 ^ 4.2 Max. changes in mABP 2 3.9 ^ 2.6 11.4 ^ 3.0** 21.3 ^ 3.3 8.2 ^ 3.6** 2 0.3 ^ 0.9 0.9 ^ 0.7 11.1 ^ 3.8 (mmHg) after T a
FS after IV IL1ra (n 7) 116.1 ^ 4.4 10.6 ^ 3.3
Compared with NS injected rats **P , 0:01. FS, footshock; T, treatment; Max., Maximal; ICV, intracerebroventricular injection of; IV, intravenous injection of.
C.-J. Zou et al. / Neuroscience Letters 311 (2001) 41±44
Fig. 3. In¯uences of IL-1ra on emotional stress-induced-hypertension. MABP and HR were recorded at the 3 rd, 8 th and 13 th min after a rat was placed in the holder. W ICV vehicle, n 11; X conditioned fear stimuli were given 25 min after ICV vehicle, n 9; K ICV IL-1ra, n 8; O conditioned fear stimuli were given 25 min after ICV IL-1ra, n 8. *P , 0:05, **P , 0:01 compared with vehicle-injected rats. 1 P , 0:05, 1 1 P , 0:01 also compared with non-shocked control rats.
threshold was assessed by measuring TFL through heat radiation on the tail. Following determination of basal TFL, 1 s duration electric shocks (14 V, 50 Hz) were given to the hind feet every 30 s for 5 min. Then ICV IL1ra or vehicle was immediately administered within a 1 min period and TFL was measured every 5 min for 35 min. Nonshocked rats were treated identical to the shocked rats except, they did not receive FS. In vehicle injected rats, FS increased pain threshold. Compared to non-shocked rats, FS induced signi®cant changes in percentages of TFL in 5±15 min and 25±35 min after FS. In IL-1ra injected rats, signi®cant increases were not observed until 15 min after FS comparing shocked rats with non-shocked rats. Furthermore, a signi®cant difference existed in pain threshold 10 min after FS when compared to vehicle injected rats with IL-1ra injected rats. In non-footshocked rats, there existed no signi®cant differences when compared vehicle-injected rats with IL-1rainjected rats (Fig. 4).
Fig. 4. In¯uences of IL-1ra on FS-induced-analgesia. TFL, the percent of tail ¯ick latency; FS, footshock; icv, ICV vehicle or IL1ra. *P , 0:05, **P , 0:01 compared with vehicle-injected rats. 1 P , 0:05, 1 1 P , 0:01 also compared with non-shocked control rats.
43
Consistent with previous reports [10], pressor responses were induced in conscious rats by ICV IL-1b; however, this pressure elevation may be secondary to an increased body temperature [2,12]. Therefore, we repeated these observations under urethane anesthesia while maintaining constant body temperature. Here, we found that pressor responses were induced by ICV 25 or 100 ng IL-1b. Furthermore, pretreatment with ICV 0.5 mg IL-1ra blocked the pressor response induced by ICV IL-1b. IV IL-1b decreased mABP, this response was suppressed by IV antibodies of IL-1b [4]. The presence of IL-1 receptors and IL-1 mRNA in neurons and glia [12] with our observations suggest that the pressor role of central IL-1b is mediated by central IL-1 receptors. Stressors may activate brain IL-1 [9]. In the present experiment, the pressor response induced by stressful stimuli (FS or conditioned fear stimuli) was attenuated or reversed by ICV IL-1ra. As described above, central IL-1b plays a pressor role via central IL-1 receptors. Thus, our results suggest that central IL-1 is involved in SIH. Although fear-induced-tachycardiac responses did not occur in IL-1ra injected rats, ICV IL-1b did not signi®cantly increase HR, in addition, no signi®cant differences were observed when compared IL-1ra injected shocked-rats with vehicle injected shocked-rats. Thus, these results seem to show that central IL-1 is not very important in fear-induced-tachycardia. As hypertensive rats exhibit a higher pain threshold than normotensive counterparts [16], both hypertension and analgesia can be induced by FS [1,5,14], it seems possible that common central mediators exist in hypertension or analgesia induced by FS. Since ICV IL-1 may increase pain threshold and mABP [1,10] and in¯ammatory analgesia is mediated by IL-1 [15]. Thus, we used ICV IL-1ra to test our hypothesis that central IL-1 is a possible common mediator in hypertension or analgesia induced by FS. In present results, although TFL in 15±35 min after FS in IL1ra injected rats were not signi®cantly different from that in vehicle injected rats, the TFL did not increase until 15 min after FS in IL-1ra injected rats, while TFL was increased immediately after FS in vehicle injected rats. These results suggest that central IL-1 mediates the short lasting analgesia induced by FS. As exposure to inescapable shock produces learned fear responses or enhancement of fear conditioning [7,11], ICV IL-1ra blocks behavioral effects of the enhancement of fear conditioning produced by tail shock [7]. Our results appear to support the hypothesis that central IL-1 is involved in fear learning or conditioning. Surprisingly, hypertension induced by conditioned fear stimuli was not just attenuated but was reversed by ICV IL-1ra. In addition, ICV IL-1b failed to potentiate fear conditioning [8]. The attenuation of IL-1ra to SIH is unlikely due to the in¯uence of fear learning or conditioning. Thus, these results give us a hint that central IL-1 are selectively involved in SIH or FSinduced-analgesia.
44
C.-J. Zou et al. / Neuroscience Letters 311 (2001) 41±44
Since IV the same dose IL-1ra had no signi®cant in¯uence on pressor responses induced by FS, it is unlikely that the attenuation of ICV IL-1ra is due to the leakage of IL-1ra to peripheral circulation. In addition, we also observed that the pressor response to ICV IL-1b lasted longer in urethaneanesthetized rats than that in conscious rats. It seems possibly because the baroceptor re¯ex is less sensitive and/or drug metabolism is slower in urethane-anesthetized rats than that in conscious rats. In a word, our results show that central IL-1 mediates hypertension induced by FS or fear and short lasting analgesia induced by FS. [1] Bianchi, M., Dib, B. and Panerai, A.E., Interleukin-1 and nociception in the rat, J. Neurosci. Res., 53 (1998) 645± 650. [2] Bianchi, M., Sacerdote, P., Locatelli, L., Mantegazza, P. and Panerai, A.E., Corticotrophin releasing hormone, IL-1a, and tumor necrosis factor-a share characteristics of stress mediators, Brain Res., 546 (1991) 139±142. [3] Breder, C.D., Dinarello, C.A. and Saper, C.B., Interleukin-1 immunoreactive innervation of the human hypothalamus, Science, 240 (1988) 321±324. [4] Gardiner, S.M., Kemp, P.A., March, J.E., Wooley, J. and Bennett, T., The in¯uence of antibodies to TNF-a and IL1b on haemodynamic responses to the cytokines, and to lipopolysaccharide, in conscious rats, Br. J. Pharmacol., 125 (1998) 1543±1550. [5] Israel, A., Sosa, B. and Gutierez, C.I., Brain AT(2) receptor mediate vasodepressor response to footshocks: role of kinins and nitric oxide, Brain Res. Bull., 51 (2000) 339±343. [6] Lechan, R.M., Toni, R., Clark, B.D., Cannon, J.G., Shaw, A.R., Dinarello, C.A. and Reichlin, S., Immunoreactive interleukin-1(localization in the rat forebrain, Brain Res., 514 (1990) 135±140. [7] Maier, S.F. and Watkins, L.R., Intracerebroventricular interleukin-1 receptor antagonist blocks the enhancement of
[8]
[9]
[10]
[11] [12] [13]
[14] [15]
[16] [17]
fear conditioning and interference with escape produced by inescapable shock, Brain Res., 695 (1995) 279±282. Maier, S.F., Nguyen, K.T., Deak, T., Milligan, E.D. and Watkins, L.R., Stress, learned helplessness, and brain interleukin-1b, In Danter, R., Wollman, E.E., Yirmiga, R. (Eds.), (Cytokines, Stress, and Depression), KluwerAcadamic/ Plenum Publishers, New York, 1999, pp. 235±250. Minami, M., Kuraishi, Y., Yamaguchi, T., Nakai, S., Hirai, Y. and Satoh, M., Immobilization stress induces interleukin-1b mRNA in the rat hypothalamus, Neurosci. Lett., 123 (1991) 254±256. Nakamori, T., Morimoto, A. and Murakami, N., Effect of a central CRF antagonist on cardiovascular and thermoregulatory responses induced by stress or IL-1b, Am. J. Physiol., 265 (1993) R834±R839. Onaka, T. and Yagi, K., Neural mechanisms underlying neuroendocrine responses to emotional stress, Adv. Neurol. Sci., 41 (1997) 563±573. Rothwell, N.J., Functions and mechanisms of interleukin-1 in the brain, Trends Pharmacol. Sci., 12 (1991) 430±436. Schotanus, K., Meloen, R.H., Puijk, W.C., Berkenbosch, F., Binnekade, R. and Tilders, F.J., Effects of monoclonal antibodies to speci®c epitopes of rat interleukin-1 beta (IL-1 beta) on IL-1 beta-induced ACTH, corticosterone and IL-6 responses in rats, J. Neuroendocrinol., 7 (1995) 255±262. Watkins, L.R. and Mayer, D.J., Organization of endogenous opiate and non-opiate pain control, Science, 216 (1982) 1185±1192. Woolf, C.J., Allchorne, A., Sa®ech-Garabedian, B. and Poole, S., Cytokines, nerve growth factor and in¯ammatory analgesia: the contribution of tumour necrosis factor-a , Br. J. Pharmacol., 121 (1997) 417±424. Zamir, N. and Segal, M., Hypertension-induced analgesia: changes in pain sensitivity in experimental hypertensive rats, Brain Res., 160 (1979) 170±173. Zou, C.J., Onaka, T. and Yagi, K., Roles of adrenoceptors in vasopressin, oxytocin and prolactin responses to conditioned fear stimuli in the rat, J. Neuroendocrinol., 10 (1998) 905±910.
www.elsevier.com/locate/neulet
Roles of central interleukin-1 on stress-induced-hypertension and footshock-induced-analgesia in rats Chang-Jiang Zou*, Jin-Dong Liu, Yi-Chun Zhou Department of Physiology and Pathophysiology, Health Science Center, Peking University, Beijing 100083, People's Republic of China Received 9 March 2001; received in revised form 29 June 2001; accepted 20 July 2001
Abstract Central interleukin-1 (IL-1) plays an important role in mediating the neural, endocrine, and behavioral responses to stressors. Here we tested whether central IL-1 is involved in stress-induced hypertension or footshock (FS)-inducedanalgesia. We observed that: (1) intracerebral ventricular injection of (ICV) IL-1b induced pressor responses; (2) hypertension induced by IL-1b was blocked by ICV an IL-1 antagonist, IL-1ra; (3) ICV IL-1ra attenuated the pressor response induced by FS but intravenous injection of IL-1ra did not signi®cantly reduce this response; (4) the hypertensive response to conditioned fear stimuli was reversed by ICV IL-1ra; (5) FS-induced-analgesia was attenuated by ICV IL-1ra and this effect disappeared 15 min after ICV IL-1ra. These results suggest that both the pressor response to FS or conditioned fear stimuli and short lasting analgesia induced by FS are mediated by central IL-1. q 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Interleukin-1; Conditioned fear stimuli; Hypertension; Footshock-induced-analgesia
Sharing the characteristics of stress mediators [2], central interleukin-1 (IL-1) plays an important role in mediating the neural, endocrine, and behavioral responses to stressors [10,12,13]. Many stressful stimuli may increase brain IL-1 mRNA and brain IL-1 bioactivity [8,9]. Cardiovascular and endocrine responses to IL-1b are similar to stress responses [10]. For example, both IL-1b and stress raised blood pressure, activate hypothalamic-pituitary-adrenal axis [10]. Immunoreactive IL-1 ®bers exist in some cardiovascular regulatory areas [3,6]. Thus, it seems possible that central IL-1 is involved in stress-induced hypertension (SIH). To test this hypothesis, roles of IL-1b in SIH were studied by intracerebral ventricular injection of (ICV) IL-1b or an IL-1 antagonist (IL-1ra). Experiments were performed on male SD rats (150±300 g) housed 2±3 to a cage and had free access to food and water. After implantation of cerebroventricular cannula, a catheter was inserted into the right external jugular vein and/ or right carotid artery, the mean arterial blood pressure (mABP) and heart rate (HR) or pain threshold (tail ¯ick latency, (TFL)) were measured. And, all data were
* Corresponding author. Tel.: 186-10-62091418; fax: 186-1062091443. E-mail address: [email protected] (C.-J. Zou).
expressed as mean ^ SE and analyzed with ANOVA followed by Neuman test. After the rats were anesthetized with chlorohydrate (0.4 g/kg, intraperitoneally (i.p.)) or urethane (1.4 g/kg, i.p.), a stainless cannula was inserted into the right lateral cerebral ventricle with the tip located at 0.6 mm caudal to the bregma, 1.6 mm lateral to the midline and 4.5 mm below the skull. Chlorohydrate-anesthetized rats were allowed to recover for 2 to 3 days. The drugs, recombinant rat IL-1b (PeproTech EC Ltd, England) and IL-1ra (Health Science Center of Peking University, China), diluted with normal saline to 2.5 mg/ml and 10 mg/ml or 0.5 mg/ml, or the vehicle was administered in a volume of 10 ml over a 1min period via cerebroventricular cannula. After each experiment, the position of the cannula tip was veri®ed with methylene blue injected through the cannula (30G). In urethane anesthetized rats whose rectal temperature was maintained 36.5±37.58C through out the experiment, mABP and HR were directly recorded after insertion of an arterial cannula into the right carotid artery. In some conscious rats, however, arterial pressure and HR were taken through a tail cuff system. In conscious rats, a signi®cant pressor response was observed starting about 10 min after ICV 100 ng IL-1b and lasting about an hour (see Fig. 1a). In urethane anesthetized rats, a signi®cant pressor response was induced in 60±
0304-3940/01/$ - see front matter q 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S03 04 - 394 0( 0 1) 02 14 0- 1
42
C.-J. Zou et al. / Neuroscience Letters 311 (2001) 41±44
Fig. 2. An antagonistic effect of IL-1ra on pressor roles of IL-1b. *0:01 , P , 0:05, **P , 0:01 compared IL-1b injected rats with IL-1b injected but IL-1ra pretreated rats.
Fig. 1. Effects of ICV IL-1b on mABP and HR in conscious rats (A) and in urethane-anesthetized rats (B). W ICV vehicle, n 8; P ICV 25 ng IL-b, n 7; X ICV 100 ng IL-b, n 8 (A) or 7 (B). *0:01 , P , 0:05, **P , 0:01 compared with vehicle-injected rats.
110 min after ICV 25 ng IL-1b (see Fig. 1b). A greater hypertensive response was induced in 30±110 min after ICV 100 ng IL-1b. Both in urethane-anesthetized rats and conscious rats, there were no signi®cant changes in HR. As depicted in Fig. 2, the pressor response induced by ICV IL-1b was almost completely blocked by ICV 0.5 mg IL-1ra. 30 min after ICV or intravenous injection of (IV) vehicle or IL-1ra, continuous electric shocks were given to the hind feet (14V, 50Hz, 1 min). Footshock (FS) increased mABP in both IL-1ra and vehicle injected rats though HR remained unchanged (see Table 1). Although ICV IL-1ra resulted in a transient rise in mABP, the maximal change of FS-inducedhypertension after ICV IL-1ra was signi®cantly smaller than that after ICV vehicle, whereas IV IL-1ra had no signi®cant in¯uence on FS-induced-hypertension. According to Yagi's method [17], 3 to 5 days after the
implantation of the ICV cannula, rats received a habituation session twice a day for 3 days. Rats were transferred to an experimental room, placed in a special holder and left undisturbed for 15 min. Following the 3 days habituation procedure, the next day, rats received a training session. Before training session, the mABP and HR were taken as described above. In training session, rats in the FS group were placed in a special holder for 5 min and given shocks to the hind feet (14 V, 50 Hz, 1 s) every 30 s for 5 min. These rats were kept in the holder for another 5 min. The non-shocked rats received identical habituation sessions and training procedures, but without electric shocks. The next day after training session, 25 min after ICV vehicle or IL-1ra, rats were placed in the special holder and mABP and HR were recorded for 15 min. Conditioned fear stimuli induced hypertension and tachycardia in vehicle injected rats but not in IL-1ra injected rats. Furthermore, conditioned fear stimuli reduced mABP but had no signi®cant in¯uences on HR in IL-1ra injected group. In shocked rats, signi®cant differences existed between the mABP in vehicle-injected rats and IL-1ra injected rats. In non-shocked rats, no signi®cant differences existed in mABP and HR when compared vehicle-injected rats with IL-1ra-injected rats (Fig. 3). Administration of IL-1 and FS may increase pain threshold [1,14]. In¯ammatory analgesia is mediated by IL-1 [15]. So, the involvement of central IL-1 in FS-induced-analgesia was also examined by ICV IL-1ra. Therefore, 2±3 days after implantation of the cerebroventricular cannula, the pain
Table 1 In¯uences of IL-1ra on FS-induced-hypertension a Treatment
ICV IL-1ra ICV NS (n 6)
IV IL-1ra ICV IL-1ra (n 6)
FS after ICV FS after ICV IV NS (n 8) IL-1ra (n 8) (n 7)
IV IL-1ra (n 7)
FS after IV NS (n 7)
MABP before T (mmHg) 108.6 ^ 3.7 107.4 ^ 5.0 105.2 ^ 6.8 113.9 ^ 6.4 110.5 ^ 7.6 113.4 ^ 8.1 112.4 ^ 4.2 Max. changes in mABP 2 3.9 ^ 2.6 11.4 ^ 3.0** 21.3 ^ 3.3 8.2 ^ 3.6** 2 0.3 ^ 0.9 0.9 ^ 0.7 11.1 ^ 3.8 (mmHg) after T a
FS after IV IL1ra (n 7) 116.1 ^ 4.4 10.6 ^ 3.3
Compared with NS injected rats **P , 0:01. FS, footshock; T, treatment; Max., Maximal; ICV, intracerebroventricular injection of; IV, intravenous injection of.
C.-J. Zou et al. / Neuroscience Letters 311 (2001) 41±44
Fig. 3. In¯uences of IL-1ra on emotional stress-induced-hypertension. MABP and HR were recorded at the 3 rd, 8 th and 13 th min after a rat was placed in the holder. W ICV vehicle, n 11; X conditioned fear stimuli were given 25 min after ICV vehicle, n 9; K ICV IL-1ra, n 8; O conditioned fear stimuli were given 25 min after ICV IL-1ra, n 8. *P , 0:05, **P , 0:01 compared with vehicle-injected rats. 1 P , 0:05, 1 1 P , 0:01 also compared with non-shocked control rats.
threshold was assessed by measuring TFL through heat radiation on the tail. Following determination of basal TFL, 1 s duration electric shocks (14 V, 50 Hz) were given to the hind feet every 30 s for 5 min. Then ICV IL1ra or vehicle was immediately administered within a 1 min period and TFL was measured every 5 min for 35 min. Nonshocked rats were treated identical to the shocked rats except, they did not receive FS. In vehicle injected rats, FS increased pain threshold. Compared to non-shocked rats, FS induced signi®cant changes in percentages of TFL in 5±15 min and 25±35 min after FS. In IL-1ra injected rats, signi®cant increases were not observed until 15 min after FS comparing shocked rats with non-shocked rats. Furthermore, a signi®cant difference existed in pain threshold 10 min after FS when compared to vehicle injected rats with IL-1ra injected rats. In non-footshocked rats, there existed no signi®cant differences when compared vehicle-injected rats with IL-1rainjected rats (Fig. 4).
Fig. 4. In¯uences of IL-1ra on FS-induced-analgesia. TFL, the percent of tail ¯ick latency; FS, footshock; icv, ICV vehicle or IL1ra. *P , 0:05, **P , 0:01 compared with vehicle-injected rats. 1 P , 0:05, 1 1 P , 0:01 also compared with non-shocked control rats.
43
Consistent with previous reports [10], pressor responses were induced in conscious rats by ICV IL-1b; however, this pressure elevation may be secondary to an increased body temperature [2,12]. Therefore, we repeated these observations under urethane anesthesia while maintaining constant body temperature. Here, we found that pressor responses were induced by ICV 25 or 100 ng IL-1b. Furthermore, pretreatment with ICV 0.5 mg IL-1ra blocked the pressor response induced by ICV IL-1b. IV IL-1b decreased mABP, this response was suppressed by IV antibodies of IL-1b [4]. The presence of IL-1 receptors and IL-1 mRNA in neurons and glia [12] with our observations suggest that the pressor role of central IL-1b is mediated by central IL-1 receptors. Stressors may activate brain IL-1 [9]. In the present experiment, the pressor response induced by stressful stimuli (FS or conditioned fear stimuli) was attenuated or reversed by ICV IL-1ra. As described above, central IL-1b plays a pressor role via central IL-1 receptors. Thus, our results suggest that central IL-1 is involved in SIH. Although fear-induced-tachycardiac responses did not occur in IL-1ra injected rats, ICV IL-1b did not signi®cantly increase HR, in addition, no signi®cant differences were observed when compared IL-1ra injected shocked-rats with vehicle injected shocked-rats. Thus, these results seem to show that central IL-1 is not very important in fear-induced-tachycardia. As hypertensive rats exhibit a higher pain threshold than normotensive counterparts [16], both hypertension and analgesia can be induced by FS [1,5,14], it seems possible that common central mediators exist in hypertension or analgesia induced by FS. Since ICV IL-1 may increase pain threshold and mABP [1,10] and in¯ammatory analgesia is mediated by IL-1 [15]. Thus, we used ICV IL-1ra to test our hypothesis that central IL-1 is a possible common mediator in hypertension or analgesia induced by FS. In present results, although TFL in 15±35 min after FS in IL1ra injected rats were not signi®cantly different from that in vehicle injected rats, the TFL did not increase until 15 min after FS in IL-1ra injected rats, while TFL was increased immediately after FS in vehicle injected rats. These results suggest that central IL-1 mediates the short lasting analgesia induced by FS. As exposure to inescapable shock produces learned fear responses or enhancement of fear conditioning [7,11], ICV IL-1ra blocks behavioral effects of the enhancement of fear conditioning produced by tail shock [7]. Our results appear to support the hypothesis that central IL-1 is involved in fear learning or conditioning. Surprisingly, hypertension induced by conditioned fear stimuli was not just attenuated but was reversed by ICV IL-1ra. In addition, ICV IL-1b failed to potentiate fear conditioning [8]. The attenuation of IL-1ra to SIH is unlikely due to the in¯uence of fear learning or conditioning. Thus, these results give us a hint that central IL-1 are selectively involved in SIH or FSinduced-analgesia.
44
C.-J. Zou et al. / Neuroscience Letters 311 (2001) 41±44
Since IV the same dose IL-1ra had no signi®cant in¯uence on pressor responses induced by FS, it is unlikely that the attenuation of ICV IL-1ra is due to the leakage of IL-1ra to peripheral circulation. In addition, we also observed that the pressor response to ICV IL-1b lasted longer in urethaneanesthetized rats than that in conscious rats. It seems possibly because the baroceptor re¯ex is less sensitive and/or drug metabolism is slower in urethane-anesthetized rats than that in conscious rats. In a word, our results show that central IL-1 mediates hypertension induced by FS or fear and short lasting analgesia induced by FS. [1] Bianchi, M., Dib, B. and Panerai, A.E., Interleukin-1 and nociception in the rat, J. Neurosci. Res., 53 (1998) 645± 650. [2] Bianchi, M., Sacerdote, P., Locatelli, L., Mantegazza, P. and Panerai, A.E., Corticotrophin releasing hormone, IL-1a, and tumor necrosis factor-a share characteristics of stress mediators, Brain Res., 546 (1991) 139±142. [3] Breder, C.D., Dinarello, C.A. and Saper, C.B., Interleukin-1 immunoreactive innervation of the human hypothalamus, Science, 240 (1988) 321±324. [4] Gardiner, S.M., Kemp, P.A., March, J.E., Wooley, J. and Bennett, T., The in¯uence of antibodies to TNF-a and IL1b on haemodynamic responses to the cytokines, and to lipopolysaccharide, in conscious rats, Br. J. Pharmacol., 125 (1998) 1543±1550. [5] Israel, A., Sosa, B. and Gutierez, C.I., Brain AT(2) receptor mediate vasodepressor response to footshocks: role of kinins and nitric oxide, Brain Res. Bull., 51 (2000) 339±343. [6] Lechan, R.M., Toni, R., Clark, B.D., Cannon, J.G., Shaw, A.R., Dinarello, C.A. and Reichlin, S., Immunoreactive interleukin-1(localization in the rat forebrain, Brain Res., 514 (1990) 135±140. [7] Maier, S.F. and Watkins, L.R., Intracerebroventricular interleukin-1 receptor antagonist blocks the enhancement of
[8]
[9]
[10]
[11] [12] [13]
[14] [15]
[16] [17]
fear conditioning and interference with escape produced by inescapable shock, Brain Res., 695 (1995) 279±282. Maier, S.F., Nguyen, K.T., Deak, T., Milligan, E.D. and Watkins, L.R., Stress, learned helplessness, and brain interleukin-1b, In Danter, R., Wollman, E.E., Yirmiga, R. (Eds.), (Cytokines, Stress, and Depression), KluwerAcadamic/ Plenum Publishers, New York, 1999, pp. 235±250. Minami, M., Kuraishi, Y., Yamaguchi, T., Nakai, S., Hirai, Y. and Satoh, M., Immobilization stress induces interleukin-1b mRNA in the rat hypothalamus, Neurosci. Lett., 123 (1991) 254±256. Nakamori, T., Morimoto, A. and Murakami, N., Effect of a central CRF antagonist on cardiovascular and thermoregulatory responses induced by stress or IL-1b, Am. J. Physiol., 265 (1993) R834±R839. Onaka, T. and Yagi, K., Neural mechanisms underlying neuroendocrine responses to emotional stress, Adv. Neurol. Sci., 41 (1997) 563±573. Rothwell, N.J., Functions and mechanisms of interleukin-1 in the brain, Trends Pharmacol. Sci., 12 (1991) 430±436. Schotanus, K., Meloen, R.H., Puijk, W.C., Berkenbosch, F., Binnekade, R. and Tilders, F.J., Effects of monoclonal antibodies to speci®c epitopes of rat interleukin-1 beta (IL-1 beta) on IL-1 beta-induced ACTH, corticosterone and IL-6 responses in rats, J. Neuroendocrinol., 7 (1995) 255±262. Watkins, L.R. and Mayer, D.J., Organization of endogenous opiate and non-opiate pain control, Science, 216 (1982) 1185±1192. Woolf, C.J., Allchorne, A., Sa®ech-Garabedian, B. and Poole, S., Cytokines, nerve growth factor and in¯ammatory analgesia: the contribution of tumour necrosis factor-a , Br. J. Pharmacol., 121 (1997) 417±424. Zamir, N. and Segal, M., Hypertension-induced analgesia: changes in pain sensitivity in experimental hypertensive rats, Brain Res., 160 (1979) 170±173. Zou, C.J., Onaka, T. and Yagi, K., Roles of adrenoceptors in vasopressin, oxytocin and prolactin responses to conditioned fear stimuli in the rat, J. Neuroendocrinol., 10 (1998) 905±910.