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Possible role of the histaminergic system in autonomic and cardiovascular responses to neuropeptide Y
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Neuropeptides Neuropeptides 43 (2009) 21–29 www.elsevier.com/locate/npep
Possible role of the histaminergic system in autonomic and cardiovascular responses to neuropeptide Y Mamoru Tanida a,b,c,*, Jiao Shen b,c, Katsuya Nagai b,c a
Department of Biomedical Sciences, College of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan b ANBAS Corporation, Kita-ku, Osaka 531-0072, Japan c Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan Received 20 May 2008; accepted 30 September 2008 Available online 8 November 2008
Abstract Previous studies have demonstrated that neuropeptide Y (NPY) affects blood pressure (BP) in anesthetized rats. Here, we examined the effects of the third cerebral ventricular (3CV) injection of various doses of NPY on renal sympathetic nerve activity (RSNA) and BP in anesthetized rats. 3CV injection of NPY suppressed RSNA and BP in a dose-dependent manner. Moreover, suppressing effects of NPY on RSNA and BP were eliminated by lateral cerebral ventricular (LCV) preinjection of thioperamide, an antagonist of histaminergic H3-receptor, not diphenhydramine, an antagonist of histaminergic H1-receptor. In addition, 3CV injection of NPY accelerated gastric vagal nerve activity (GVNA) and inhibited brown adipose tissue sympathetic nerve activity (BAT-SNA) of anesthetized rats, and lowered brown adipose tissue temperature (BAT-T) of conscious rats. Thus, these evidences suggest that central NPY affects autonomic nerves containing RSNA, GVNA or BAT-SNA, and BP by mediating central histaminergic H3-receptors. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: NPY; Histamine-H1-receptor; Renal sympathetic nerve; Stomach; Brown adipose tissue; Blood pressure
1. Introduction Neuropeptide Y (NPY), orexins, leptin, and ghrelin (Konturek et al., 2004) are recently identified feedingrelated neurotransmitters. NPY, a 36 amino acid peptide isolated from the porcine brain (Tatemoto et al., 1982), is an orexigenic neuropeptide distributed widely and abundantly within the mammalian brain, particularly in the hypothalamus (Chronwall et al., 1985). Intracisternal injection of NPY reduces blood pressure (BP) in anesthetized rats (Fuxe et al., 1983); however, *
Corresponding author. Address: Department of Biomedical Sciences, College of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan. Tel.: +81 77 561 3378; fax: +81 77 561 6569. E-mail address: [email protected] (M. Tanida). 0143-4179/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.npep.2008.09.007
intracerebroventricular (ICV) injection elevates or lowers BP of anesthetized rats (Hu and Dunbar, 1997) or conscious rats (Aguirre et al., 1990). Thus, NPY seems to evoke a cardiovascular response dependant on the NPY injection site or the state of consciousness. The third ventricle is approximate to the hypothalamic autonomic center. We previously observed that 1D4 injection, an anti-BIT/SHPS-1 monoclonal antibody, reacts with the extracellular domain of BIT/SHPS-1 and stimulates its tyrosine phosphorylation, increasing the renal sympathetic nerve activity (RSNA), which participates in BP regulation (Handa and Johns, 1985), and decreasing the gastric vagal nerve activity (GVNA) in urethaneanesthetized rats (Taniguchi et al., 2006). Moreover, 1D4 injection into the third cerebral ventricular (3CV) elevated brown adipose tissue temperature (BAT-T) (Taniguchi et al., 2006), which is modulated by
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sympathetic neural activity (Morrison, 2004). However, it is unknown whether NPY injection into the 3CV affects RSNA, GVNA, or BAT-T. Histaminergic neurons are located in the tuberomamillary nucleus (TMN) of the hypothalamus and widely project to various regions in the brain (Watanabe et al., 1984). Histamine released from histaminergic neurons functions as a modulator of feeding behavior, the sleep-wake cycle, and blood pressure (BP) (Brown et al., 2001). We observed that a small dose of histamine injection into the lateral cerebral ventricle (LCV) decreased RSNA and BP in anesthetized rats (Tanida et al., 2007b). When low-dose histamine is released from the presynapse, the presynaptic histaminergic H3-receptor exhibits a higher affinity and automatically inhibits histamine production (Arrang et al., 1983). This suggests that the histaminergic system modulates autonomic nerves via the histamine receptors. In contrast, NPY forms direct synapses with histaminergic cells in the TMN (Tamiya et al., 1989), and injection of NPY into the ICV alters the hypothalamic histamine release (Ishizuka et al., 2006). However, the role of the histaminergic system in the sympathetic and cardiovascular responses to NPY is unknown. In the present study, we examined the effects of NPY injection into the 3CV on RSNA, GVNA, BAT-SNA, and BP of urethane-anesthetized rats and BAT-T in conscious rats. Moreover, we examined the effects of histaminergic receptor antagonists on NPY-mediated RSNA and BP changes.
2. Methods 2.1. Animals Male Wistar rats (n = 44), weighing 280–320 g, were used. Rats were housed in a room maintained at 24 ± 1 °C and illuminated for 12 h (07:00–19:00) everyday. Food and water were freely available. Rats were adapted to the environment for at least one week prior to the experiment. All animal care and handling procedures were approved by the Institutional Animal Care and Use Committee of Osaka University. 2.2. General animal preparation On the day of the experiment, food was removed 5 h prior to surgery. Under anesthesia induced by intraperitoneal (IP) injection of 1 g/kg urethane (when it was insufficient, 0.2–0.3 g/kg of urethane was added), a polyethylene catheter was inserted into the left femoral vein for intravenous injection, and another catheter was inserted into the left femoral artery for BP determination. The rat was then cannulated through the trachea and fixed in a stereotaxic apparatus. Body temperature
was maintained at 37.0–37.5 °C using a heating pad and monitored with a thermometer inserted into the rectum. For recording RSNA, the left renal nerve was exposed retroperitoneally through a left flank incision using a dissecting microscope. For recording BATSNA, the left sympathetic nerve innervating interscapular brown adipose tissue was exposed through a left dorsal incision. For recording GVNA, the gastric branch of the ventral subdiaphragmatic vagal nerve was identified and exposed on the oesphagus after incision of the abdomen midline (Niijima, 1991). The distal end of the respective nerve was ligated, and then hooked up to a pair of silver wire electrodes for recording efferent nerve activity. The recording electrodes were immersed in a pool of liquid paraffin oil or a mixture of warm vaseline and liquid paraffin oil, to prevent dehydration and for electrical insulation, respectively. The rat was allowed to stabilize for 30–60 min after being placed on the recording electrodes. Electrical changes in RSNA, GVNA and BAT-SNA were amplified 2000–5000 times with a band path of 100–1000 kHz, and monitored by an oscilloscope. Raw data of the nerve activity was converted to standard pulses by a window discriminator, which separated discharge from electrical background noise which remained post mortem. Both the discharge rates and the neurogram were sampled with a Power-Lab analog-to-digital converter for recording and data analysis on a computer. Data were obtained as described previously (Tanida et al., 2005). The catheter in the left femoral artery was connected to a BP transducer (DX-100, Nihon Kohden, Japan), and the output signal of the transducer was amplified in a BP amplifier (AP641G, Nihon Kohden, Japan). Two needle electrodes were placed under the skin at the right arm and left leg to record an electrocardiogram (ECG). The ECG signal was amplified with a bioelectric amplifier (AB-620G, Nihon Kohden, Japan). The BP and ECG were monitored with an oscilloscope, sampled with the Power-Lab, and stored on a hard disk for off-line analysis to calculate mean arterial pressure (MAP) and heart rate (HR). 2.3. Telemetry recording To measure the BAT-T, Telemetry System (Star Medical Co., Japan) was used as described previously (Taniguchi et al., 2006). In some rats (n = 8), seven days before the 3CV injection of NPY, a capsule containing a temperature sensor, battery and transmitter was implanted above the BAT fat pad under pentobarbital anesthesia (35 mg/kg, IP). The output signals mediating a receiver were converted from analog-to-digital and monitored and stored on a PC. The data were analyzed by 16ch-Eight Star program (Star Medical Corp., Japan). On the experimental day, the rats were made to fast 4 h prior to stimulation to avoid evoking diet-
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induced thermogenesis. With the animal conscious, baseline measurement of BAT-T was made for 5 min just before 3CV injection of NPY (1 nmol/10 ll aCSF) or aCSF. After the injection, these parameters were recorded for 60 min. 2.4. Intracerebroventricular cannulation One week before the experiment, a brain cannula (length; 3 cm) made of polyethylene tubing (PE-10; Clay Adams, Parsippany, NJ) and fitted with a tip of a microsyringe for injection was inserted into the third cerebral ventricle (A-P, 1.0 mm caudal to the bregma; L, 0 mm lateral to the midline; V, 7.0 mm below the skull surface) or the left lateral cerebral ventricle (A-P, 1.5 mm caudal to the bregma; L, 2.0 mm lateral to the midline; V, 3.0 mm below the skull surface) under pentobarbital anesthesia (35 mg/kg, IP) as previously described (Yamamoto et al., 1988). The cannula implanted into the brain was securely fixed by dental cement and synthetic resin. When injections were given to rats, the microsyringe for injection was directly connected to the cannula. 2.5. Experimental protocol Baseline measurements of RSNA, GVNA, BATSNA MAP, and HR were made 5 min prior to 3CV injection of NPY (0.01, 0.1, 1 nmol/10 ll artificial cerebrospinal fluid, aCSF) or aCSF (10 ll). After the start of the stimulation, these parameters were recorded for 60 min. The effects of diphenhydramine hydrochloride (5 lg/10 ll), a histaminergic H1-antagonist, or thioperamide maleate (2 lg/10 ll), a histaminergic H1antagonist, dissolved in aCSF on changes in RSNA and BP elicited by NPY were examined. In regard to injection dose of thioperamide, our preliminary study determined it which unaffected RSNA and BP (Supplementary Fig. 1). These antagonists were administered into the lateral cerebral ventricle 15 min prior to the 3CV injection of NPY. At the end of the experiment, hexamethonium chloride (10 mg/kg) was administered intravenously to ensure that post-ganglionic efferent sympathetic nerve activity had been recorded. 2.6. Data analyses The RSNA, GVNA, BAT-SNA, MAP, HR and BAT-T data measured during each 5 min period after injection of aCSF or NPY were analyzed by digital signal processing and appropriate statistical analyses. All data were expressed as means ± SEM. Mann–Whitney U-test was used to compare basal levels in the each groups. Percent changes from the baseline values were calculated for the RSNA, GVNA and BAT-SNA. Absolute value changes from the baseline were calculated for
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MAP, HR and BAT-T. Two-way analysis of variance (ANOVA) was applied to compare group responses of the RSNA, GVNA, BAT-SNA, MAP, and HR. To perform statistical analysis of the dose response to 3CV NPY, ANOVA, followed by multiple comparisons using Dunnett’s multiple range tests, was used. To compare group responses of BAT-T, ANOVA and post-hoc test (Fisher’s PLSD) were performed. P < 0.05 was considered statistically significant.
3. Results Injection of artificial cerebrospinal fluid (aCSF) into the 3CV did not affect RSNA, MAP or HR (Fig. 1A), and there was no difference among the basal (0 min) values of RSNA, MAP, and HR (Fig. 1, Table 1). However, they were significantly suppressed following NPY (1 nmol) injection and gradually decreased to reach their lowest levels after 60 min (Fig. 1B–D). The lowest levels attained were 75.3 ± 15.7% (RSNA), 13.2 ± 6.2 mmHg (MAP), and 21 ± 8 beats/min (HR). Lower dose (0.01 and 0.1 nmol) injections of NPY into the 3CV also decreased RSNA, MAP, and HR 60 min following the injection (Fig. 2A–C), but the maximum suppressive responses occurred after 1 nmol NPY of the injection. In contrast, thioperamide pretreatment eliminated the effects of NPY (Fig. 2A–C), whereas diphenhydramine did not. Injection of aCSF did not affect GVNA or BAT-SNA (Fig. 3A); however, both were significantly changed by 1 nmol of NPY. Following the injection of 1 nmol of NPY, GVNA increased gradually (Fig. 3B) to reach its highest level (127.8 ± 6%) 45 min after the injection. In contrast, BAT-SNA decreased gradually following NPY injection (Fig. 3C) and reached its lowest level (22.7 ± 9.5) 50 min after the injection. There was no difference between the absolute basal (0 min) GVNA and BAT-SNA values (Fig. 3, Table 1). Injection of aCSF did not affect BAT-T, whereas it was significantly suppressed by NPY (1 nmol) (Fig. 4A). Following the injection, BAT-T decreased gradually (Fig. 4B) and reached its lowest level ( 0.46 ± 0.25 °C) 20 min after the injection. The basal (0 min) values of BAT-T were 37.7 ± 0.3 °C (aCSF-group) and 38.4 ± 0.5 °C (NPYgroup).
4. Discussion The present study showed that the injection of NPY into the 3CV evoked significant decreases in RSNA and BP in a dose-dependent manner (Fig. 1). We found that the suppressing effects of NPY on RSNA and BP were abolished by pretreatment with a lateral cerebral
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Fig. 1. Effects of 3CV injection of NPY (1 nmol) on renal sympathetic nerve activity (RSNA), blood pressure (BP) and heart rate (HR). Representative trace data from recordings of RSNA and BP (A) before and after the 3CV injection of aCSF or NPY (1 nmol) was described. The arrows indicate the time of injection. Time-course data of RSNA (B), MAP (C) and HR (D) after 3CV injection of aCSF or NPY (1 nmol) are expressed as mean + SEM. Numbers of animals used are shown in the parentheses. *Significant differences between aCSF group and NPY group (P < 0.05).
ventricular (LCV) injection of thioperamide, an H3receptor antagonist, but not by diphenhydramine, an H1-receptor antagonist, suggesting that the responses induced by NPY were mediated by central histaminergic
receptors. In addition, injection of NPY into the 3CV caused a decrease in BTA-SNA and an increase in GVNA. NPY has hyperphagic action via the central nervous system (Konturek et al., 2004), and there is a
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Table 1 Basal-levels of autonomic nerve activation and cardiovascular parameters in experimental Groups
aCSF NPY 1 nmol
RSXA
MAP
HR
GVNA
BAT-SNA
(spike/5 s)
(mmHg)
(beats/min)
(spike/5 s)
(spike/5 s)
(number of rats)
(number of rats)
(number of rats)
(number of rats)
(number of rats)
120.5 ± 17.3 (4) 141.3 ± 12.6 (4)
87.0 ± 9.0 (4) 90.1 ± 5.4 (4)
378 ± 32 (4) 346 ± 45 (4)
259.9 ± 29.7 (4) 227.7 ± 30.0 (4)
164.3 ± 48.2 (4) 217.7 ± 38.4 (4)
RSNA, renal sympathetic nerve activity; MAP, mean arterial pressure; HR, heart rate; GVNA, gastric vagal nerve activity, BAT-SNA, brown adipose tissue sympathetic nerve activity. Data are shown as means ± SEM.
close relationship between parasympathetic nerves and feeding regulation (Shen et al., 2005a,b). To the best of our knowledge, this is the first study to provide evidence in animals that NPY injected into the 3CV significantly elevates parasympathetic nerve outflow to the digestive organs, including the stomach. Animal studies have confirmed that central administration of NPY may suppress (Fuxe et al., 1983; Aguirre et al., 1990; Matsumura et al., 2000) or elevate (Hu and Dunbar, 1997; Vallejo and Lightman, 1986) BP and HR, suggesting complex and biphasic actions of NPY on central cardiovascular functions. In general, previous reports investigating the central actions of NPY on cardiovascular function suggest that a variety of factors might affect NPY actions. Some of the confounding factors may be alertness, the area injected, and the rat breed. Scott et al. observed that NPY lowered BP in conscious rats (Scott et al., 1989) and we found that NPY lowered RSNA and BP of anesthetized rats and BAT-T of conscious rats. These results suggest that alertness might not be associated with the cardiovascular effects of NPY. With respect to the injection area, previous studies that injected NPY into the various brain areas reported that NPY injection into the cisterna reduced (Fuxe et al., 1983), whereas injection into the lateral ventricle elevated (Hu and Dunbar, 1997) BP. Thus, these results suggest that cardiovascular responses to NPY may be dependent on the brain area of NPY action. In Sprague–Dawley rats, NPY injection into the 3CV significantly increases BP and HR (Vallejo and Lightman, 1986). We used Wistar rats in the present study, which may explain our contradictory results. However, further investigation is required to develop the relationship between NPY and various rat breeds. Histaminergic neurotransmission in the brain consists of histamine release from the presynaptic histaminergic neurons via the H3-receptor and histamine binding with the H1-receptor expressed in the postsynaptic histaminergic neurons (Arrang et al., 1983). Our previous study showed that thioperamide, but not diphenhydramine, eliminated the suppressing effects of low-dose histamine on RSNA and BP in anesthetized rats (Tanida et al., 2007b). This work suggested that
the presynaptic H3-receptor mediating auto-inhibition of histamine release from the histaminergic neurons to the synaptic clefts might cause renal sympathetic inhibition and BP reduction. In this study, we found that the suppressing effects of NPY on RSNA and BP were abolished by pretreatment with thioperamide (Fig. 2). Furthermore, our preliminary evidence that thioperamide abolished NPY-induced GVNA activation and BAT-SNA suppression was confirmed (Supplementary Fig. 2). Thus, this evidence suggests that the central histaminergic system, including the H3receptor, is involved in the autonomic and cardiovascular response to NPY. Moreover, NPY-containing neurons connect with histaminergic neurons in the TMN (Tamiya et al., 1989) and express NPY-Y1 receptor mRNA (Kishi et al., 2005). It appears that NPY directly affects histaminergic neurons via the NPY/Y1 pathway and regulates histamine release thereby altering the autonomic and cardiovascular functions. In this respect, Ishizuka et al. reported that central injection of NPY accelerates histamine release in the hypothalamus (Ishizuka et al., 2006), which is in accordance with our previous observation that low-dose histamine causes RSNA and BP suppression (Tanida et al., 2007b). At present, the reason for this discrepancy is unknown. However, it is possible that the NPY-Y1 and H3-receptors expressed in the histaminergic neurons might interact with each other through an intracellular cascade and affect the regulation of histamine release. NPY-containing fibers connect with the dorsal motor nucleus of the vagus (Buchan et al., 1991), and efferent vagal neurons project to the stomach (Zhang et al., 2000). Moreover, hypothalamic injection of NPY suppresses gastric acid secretion modulated by autonomic nerves (Humphreys et al., 1992), indicating a possible role of NPY in parasympathetic control. We found that NPY injection into the 3CV increased GVNA in urethane-anesthetized rats (Fig. 3). Based on previous reports that parasympathetic excitation evokes an increase in food intake (Shen et al., 2005b), a close relationship between parasympathetic nerves supplying the stomach and feeding behavior is suggested. In fact, an increase in the central NPY level induces hyperphagia (Konturek et al., 2004). In contrast, parasympathetic
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Fig. 2. Effects of histaminergic receptors antagonists (diphenhydramine or thioperamide) on changes in RSNA, MAP and HR following 3CV injection of NPY. Bars in A–C show RSNA, MAP and HR values 60 min after injection of three doses (0.01, 0.1, and 1 nmol) of NPY and aCSF. Effect of pretreatment with diphenhyrdramine (diphen) or thioperamide (thiop) is added to bar graphs in A–C. Four rats are used in each group. *Significant differences between aCSF and NPY-injections (P < 0.05).
nerves innervating the pancreas and the liver modulate glucose metabolism via insulin release or glycogen synthesis. Generally, parasympathetic nerve activation reduces blood glucose level and mediates an increase in these factors (Yamano et al., 2001). A preliminary study demonstrated that NPY injected into the brain of rats, elevated neural activity of the celiac parasympathetic nerve projecting to the pancreas but inhibited hyperglycemia due to 2-deoxy-D-glucose injection (unpublished data). This suggests that NPY might act on the brain and affect parasympathetic nerves to control appetite and blood glucose level. We have shown, along with others (Egawa et al., 1991), that a central injection of NPY suppresses BTA-SNA in anesthetized rats. Brown adipose tissue functions as a thermogenic organ that produces heat in the mitochondria via the activation of uncoupling protein-1, which shunts the energy obtained from the oxidation of free fatty acids into heat; this heat is then stored in the vessels and is distributed throughout the body (Argyropoulos and Harper, 2002). Thermogenesis is evoked by the acceleration of BAT-SNA secondary to the commands from the brain (Morrison, 2004). Thus, our data that NPY injection into the 3CV lowered BAT-T in conscious rats is consistent with this idea. Egawa et al. reported that microinjection of NPY into the hypothalamic paraventricular nucleus significantly suppresses BTA-SNA, indicating that NPY affects BAT-SNA through the paraventricular nucleus (Egawa et al., 1991). Various nuclei in the hypothalamus, such as the suprachiasmatic and the paraventricular nucleus, project to the brown adipose tissue via sympathetic nerves (Bamshad et al., 1999). We have previously shown that the suprachiasmatic nucleus supplies efferent projections to the paraventricular nucleus (Buijs et al., 2001) and that bilateral lesions of the suprachiasmatic nucleus abolish the effects of L-carnosine, a dipeptide released from the muscle into the blood, on BAT-SNA (Tanida et al., 2007a). Moreover, NPY-Y1 receptor mRNA was localized in both nuclei (Kishi et al., 2005), suggesting that NPY might act directly on the hypothalamic nuclei and change BAT-SNA and BATT for thermoregulation. Microinjection investigations that are focused on the specific hypothalamic regions of NPY-Y1 receptor localization may be helpful to determine a detailed neural pathway within the hypothalamus. With regard to autonomic and cardiovascular responses to NPY, the recovery responses after NPY injection are unknown. Generally, the effects of acute stimulation on autonomic nerves are immediate, but whether the effect of NPY is intermediate is unknown. Our preliminary data showed that the effect of NPY injection on GVNA and BAT-SNA returned to baseline 2-3 h after the injection (Supplementary Fig. 2), suggesting that NPY has a relatively short acting effect on auto-
M. Tanida et al. / Neuropeptides 43 (2009) 21–29
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Fig. 3. Effects of 3CV injection of NPY (1 nmol) on GVNA and BAT-SNA. Representative trace data from recordings of GVNA and BAT-SNA (A) before and after the 3CV injection of aCSF or NPY (1 nmol) was described. The arrows indicate the time of injection. Time-course data of GVNA (B) and BAT-SNA (C) after 3CV injection of aCSF or NPY (1 nmol) are expressed as mean + SEM. Numbers of animals used are shown in the parentheses. *Significant differences between aCSF group and NPY group (P < 0.05).
nomic nerves. On the other hand, it is thought that blood levels of NPY leaking from the brain might affect sympathetic and cardiovascular responses to central NPY. Thus, we investigated the effect of an intravenous injection of NPY on RSNA and BP and found no effect on sympathetic and cardiovascular actions (Supplementary Fig. 3). Based on this evidence, there may be a minimal effect of NPY leaked from the brain.
In conclusion, we demonstrated that NPY dosedependently lowers RSNA and BP with a central mechanism through histaminergic H3-receptors. In addition, autonomic and thermoregulatory responses to NPY were confirmed through the elevation of GVNA and reductions in BAT-SNA and the BAT-T. Thus, NPY affects autonomic nerves and lowers BP and BAT-T via a central mechanism.
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Fig. 4. Effects of 3CV injection of NPY (1 nmol) on BAT-T in conscious rats. Representative trace data from recordings of BAT-T (A) before and after the 3CV injection of aCSF or NPY (1 nmol) was described. The arrows indicate the time of injection. Time-course data of BAT-T (B) after 3CV injection of aCSF or NPY (1 nmol) is expressed as mean + SEM. Numbers of animals used are shown in the parentheses. *Significant differences between aCSF group and NPY group (P < 0.05).
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/ j.npep.2008.09.007.
References Aguirre, J.A., Fuxe, K., Agnati, L.F., von Euler, G., 1990. Centrally injected neuropeptide Y (13–36) produces vasopressor effects and
antagonizes the vasodepressor action of neuropeptide Y (1–36) in the awake male rat. Neuroscience Letters 118, 5–8. Argyropoulos, G., Harper, M.E., 2002. Uncoupling proteins and thermoregulation. Journal of Applied Physiology 92, 2187–2198. Arrang, J.M., Garbarg, M., Schwartz, J.C., 1983. Auto-inhibition of brain histamine release mediated by a novel class (H3) of histamine receptor. Nature 302, 832–837. Bamshad, M., Song, C.K., Bartness, T.J., 1999. CNS origins of the sympathetic nervous system outflow to brown adipose tissue. American Journal of Physiology 276, R1569–R1578. Brown, R.E., Stevens, D.R., Haas, H.L., 2001. The physiology of brain histamine. Progress in neurobiology 63, 637–672. Buchan, A.M., Kwok, Y.N., Pederson, R.A., 1991. Anatomical relationship between neuropeptide-containing fibers and efferent vagal neurons projecting to the rat corpus. Regulatory Peptide 34, 1–12. Buijs, R.M., Chun, S.J., Niijima, A., Romijn, H.J., Nagai, K., 2001. Parasympathetic and sympathetic control of the pancreas: a role for the suprachiasmatic nucleus and other hypothalamic centers that are involved in the regulation of food intake. Journal of Comparative Neurology 431, 405–423. Chronwall, B.M., DiMaggio, D.A., Massari, V.J., Pickel, V.M., Ruggiero, D.A., O’Donohue, T.L., 1985. The anatomy of neuropeptide-Y-containing neurons in rat brain. Neuroscience 15, 1159– 1181. Egawa, M., Yoshimatsu, H., Bray, G.A., 1991. Neuropeptide Y suppresses sympathetic activity to interscapular brown adipose tissue in rats. American Journal of Physiology 260, R328–R334. Fuxe, K., Agnati, L.F., Harfstrand, A., Zini, I., Tatemoto, K., Pich, E.M., Hokfelt, T., Mutt, V., Terenius, L., 1983. Central administration of neuropeptide Y induces hypotension bradypnea and EEG synchronization in the rat. Acta Physiologica Scandinavica 118, 189–192. Handa, R.K., Johns, E.J., 1985. Interaction of the renin-angiotensin system and the renal nerves in the regulation of rat kidney function. Journal of Physiology 369, 311–321. Hu, Y., Dunbar, J.C., 1997. Intracerebroventricular administration of NPY increases sympathetic tone selectively in vascular beds. Brain Research Bulletin 44, 97–103. Humphreys, G.A., Davison, J.S., Veale, W.L., 1992. Hypothalamic neuropeptide Y inhibits gastric acid output in rat: role of the autonomic nervous system. American Journal of Physiology 263, G726–G732. Ishizuka, T., Nomura, S., Hosoda, H., Kangawa, K., Watanabe, T., Yamatodani, A., 2006. A role of the histaminergic system for the control of feeding by orexigenic peptides. Physiology and Behavior 89, 295–300. Kishi, T., Aschkenasi, C.J., Choi, B.J., Lopez, M.E., Lee, C.E., Liu, H., Hollenberg, A.N., Friedman, J.M., Elmquist, J.K., 2005. Neuropeptide Y Y1 receptor mRNA in rodent brain: distribution and colocalization with melanocortin-4 receptor. Journal of Comparative Neurology 482, 217–243. Konturek, S.J., Konturek, J.W., Pawlik, T., Brzozowski, T., 2004. Brain-gut axis and its role in the control of food intake. Journal of Physiology and Pharmacology 55, 137–154. Matsumura, K., Tsuchihashi, T., Abe, I., 2000. Central cardiovascular action of neuropeptide Y in conscious rabbits. Hypertension 36, 1040–1044. Morrison, S.F., 2004. Central pathways controlling brown adipose tissue thermogenesis. News in physiological sciences 19, 67–74. Niijima, A., 1991. Effect of umami taste stimulations on vagal efferent activity in the rat. Brain Research Bulletin 27, 393–396. Scott, NA., Webb, V., Boublik, J.H., Rivier, J., Brown, M.R., 1989. The cardiovascular actions of centrally administered neuropeptide Y. Regulatory Peptide 25, 247–258. Shen, J., Niijima, A., Tanida, M., Horii, Y., Maeda, K., Nagai, K., 2005a. Olfactory stimulation with scent of grapefruit oil affects
M. Tanida et al. / Neuropeptides 43 (2009) 21–29 autonomic nerves, lipolysis and appetite in rats. Neuroscience Letters 380, 289–294. Shen, J., Niijima, A., Tanida, M., Horii, Y., Maeda, K., Nagai, K., 2005b. Olfactory stimulation with scent of lavender oil affects autonomic nerves, lipolysis and appetite in rats. Neuroscience Letters 383, 188–193. Tamiya, R., Hanada, M., Narita, N., Kawai, Y., Tohyama, M., Takagi, H., 1989. Neuropeptide Y afferents have synaptic interactions with histaminergic (histidine decarboxylase-immunoreactive) neurons in the rat brain. Neuroscience Letters 99, 241–245. Tanida, M., Gotoh, H., Taniguchi, H., Otani, H., Shen, J., Nakamura, T., Tsuruoka, N., Kiso, Y., Okumura, N., Nagai, K., 2007a. Effects of central injection of L-carnosine on sympathetic nerve activity innervating brown adipose tissue and body temperature in rats. Regulatory Peptide 144, 62–71. Tanida, M., Kaneko, H., Shen, J., Nagai, K., 2007b. Involvement of the histaminergic system in renal sympathetic and cardiovascular responses to leptin and ghrelin. Neuroscience Letters 413, 88–92. Tanida, M., Niijima, A., Shen, J., Nakamura, T., Nagai, K., 2005. Olfactory stimulation with scent of essential oil of grapefruit affects autonomic neurotransmission and blood pressure. Brain Research 1058, 44–55. Taniguchi, H., Tanida, M., Okumura, N., Hamada, J., Sano, S., Nagai, K., 2006. Regulation of sympathetic and parasympathetic
29
nerve activities by BIT/SHPS-1. Neuroscience Letters 398, 102– 106. Tatemoto, K., Carlquist, M., Mutt, V., 1982. Neuropeptide Y–a novel brain peptide with structural similarities to peptide YY and pancreatic polypeptide. Nature 296, 659–660. Vallejo, M., Lightman, S.L., 1986. Pressor effect of centrally administered neuropeptide Y in rats: role of sympathetic nervous system and vasopressin. Life Sciences 38, 1859–1866. Watanabe, T., Taguchi, Y., Shiosaka, S., Tanaka, J., Kubota, H., Terano, Y., Tohyama, M., Wada, H., 1984. Distribution of the histaminergic neuron system in the central nervous system of rats; a fluorescent immunohistochemical analysis with histidine decarboxylase as a marker. Brain Research 295, 13–25. Yamamoto, H., Nagai, K., Nakagawa, H., 1988. Time-dependent involvement of autonomic nervous system in hyperglycemia due to 2-deoxy-D-glucose. American Journal of Physiology 255, E928– E933. Yamano, T., Niijima, A., Iimori, S., Tsuruoka, N., Kiso, Y., Nagai, K., 2001. Effect of L-carnosine on the hyperglycemia caused by intracranial injection of 2-deoxy-D-glucose in rats. Neuroscience Letters 313, 78–82. Zhang, X., Renehan, W.E., Fogel, R., 2000. Vagal innervation of the rat duodenum. Journal of Autonomic Nervous System 79, 8–18.
Neuropeptides Neuropeptides 43 (2009) 21–29 www.elsevier.com/locate/npep
Possible role of the histaminergic system in autonomic and cardiovascular responses to neuropeptide Y Mamoru Tanida a,b,c,*, Jiao Shen b,c, Katsuya Nagai b,c a
Department of Biomedical Sciences, College of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan b ANBAS Corporation, Kita-ku, Osaka 531-0072, Japan c Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan Received 20 May 2008; accepted 30 September 2008 Available online 8 November 2008
Abstract Previous studies have demonstrated that neuropeptide Y (NPY) affects blood pressure (BP) in anesthetized rats. Here, we examined the effects of the third cerebral ventricular (3CV) injection of various doses of NPY on renal sympathetic nerve activity (RSNA) and BP in anesthetized rats. 3CV injection of NPY suppressed RSNA and BP in a dose-dependent manner. Moreover, suppressing effects of NPY on RSNA and BP were eliminated by lateral cerebral ventricular (LCV) preinjection of thioperamide, an antagonist of histaminergic H3-receptor, not diphenhydramine, an antagonist of histaminergic H1-receptor. In addition, 3CV injection of NPY accelerated gastric vagal nerve activity (GVNA) and inhibited brown adipose tissue sympathetic nerve activity (BAT-SNA) of anesthetized rats, and lowered brown adipose tissue temperature (BAT-T) of conscious rats. Thus, these evidences suggest that central NPY affects autonomic nerves containing RSNA, GVNA or BAT-SNA, and BP by mediating central histaminergic H3-receptors. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: NPY; Histamine-H1-receptor; Renal sympathetic nerve; Stomach; Brown adipose tissue; Blood pressure
1. Introduction Neuropeptide Y (NPY), orexins, leptin, and ghrelin (Konturek et al., 2004) are recently identified feedingrelated neurotransmitters. NPY, a 36 amino acid peptide isolated from the porcine brain (Tatemoto et al., 1982), is an orexigenic neuropeptide distributed widely and abundantly within the mammalian brain, particularly in the hypothalamus (Chronwall et al., 1985). Intracisternal injection of NPY reduces blood pressure (BP) in anesthetized rats (Fuxe et al., 1983); however, *
Corresponding author. Address: Department of Biomedical Sciences, College of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan. Tel.: +81 77 561 3378; fax: +81 77 561 6569. E-mail address: [email protected] (M. Tanida). 0143-4179/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.npep.2008.09.007
intracerebroventricular (ICV) injection elevates or lowers BP of anesthetized rats (Hu and Dunbar, 1997) or conscious rats (Aguirre et al., 1990). Thus, NPY seems to evoke a cardiovascular response dependant on the NPY injection site or the state of consciousness. The third ventricle is approximate to the hypothalamic autonomic center. We previously observed that 1D4 injection, an anti-BIT/SHPS-1 monoclonal antibody, reacts with the extracellular domain of BIT/SHPS-1 and stimulates its tyrosine phosphorylation, increasing the renal sympathetic nerve activity (RSNA), which participates in BP regulation (Handa and Johns, 1985), and decreasing the gastric vagal nerve activity (GVNA) in urethaneanesthetized rats (Taniguchi et al., 2006). Moreover, 1D4 injection into the third cerebral ventricular (3CV) elevated brown adipose tissue temperature (BAT-T) (Taniguchi et al., 2006), which is modulated by
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sympathetic neural activity (Morrison, 2004). However, it is unknown whether NPY injection into the 3CV affects RSNA, GVNA, or BAT-T. Histaminergic neurons are located in the tuberomamillary nucleus (TMN) of the hypothalamus and widely project to various regions in the brain (Watanabe et al., 1984). Histamine released from histaminergic neurons functions as a modulator of feeding behavior, the sleep-wake cycle, and blood pressure (BP) (Brown et al., 2001). We observed that a small dose of histamine injection into the lateral cerebral ventricle (LCV) decreased RSNA and BP in anesthetized rats (Tanida et al., 2007b). When low-dose histamine is released from the presynapse, the presynaptic histaminergic H3-receptor exhibits a higher affinity and automatically inhibits histamine production (Arrang et al., 1983). This suggests that the histaminergic system modulates autonomic nerves via the histamine receptors. In contrast, NPY forms direct synapses with histaminergic cells in the TMN (Tamiya et al., 1989), and injection of NPY into the ICV alters the hypothalamic histamine release (Ishizuka et al., 2006). However, the role of the histaminergic system in the sympathetic and cardiovascular responses to NPY is unknown. In the present study, we examined the effects of NPY injection into the 3CV on RSNA, GVNA, BAT-SNA, and BP of urethane-anesthetized rats and BAT-T in conscious rats. Moreover, we examined the effects of histaminergic receptor antagonists on NPY-mediated RSNA and BP changes.
2. Methods 2.1. Animals Male Wistar rats (n = 44), weighing 280–320 g, were used. Rats were housed in a room maintained at 24 ± 1 °C and illuminated for 12 h (07:00–19:00) everyday. Food and water were freely available. Rats were adapted to the environment for at least one week prior to the experiment. All animal care and handling procedures were approved by the Institutional Animal Care and Use Committee of Osaka University. 2.2. General animal preparation On the day of the experiment, food was removed 5 h prior to surgery. Under anesthesia induced by intraperitoneal (IP) injection of 1 g/kg urethane (when it was insufficient, 0.2–0.3 g/kg of urethane was added), a polyethylene catheter was inserted into the left femoral vein for intravenous injection, and another catheter was inserted into the left femoral artery for BP determination. The rat was then cannulated through the trachea and fixed in a stereotaxic apparatus. Body temperature
was maintained at 37.0–37.5 °C using a heating pad and monitored with a thermometer inserted into the rectum. For recording RSNA, the left renal nerve was exposed retroperitoneally through a left flank incision using a dissecting microscope. For recording BATSNA, the left sympathetic nerve innervating interscapular brown adipose tissue was exposed through a left dorsal incision. For recording GVNA, the gastric branch of the ventral subdiaphragmatic vagal nerve was identified and exposed on the oesphagus after incision of the abdomen midline (Niijima, 1991). The distal end of the respective nerve was ligated, and then hooked up to a pair of silver wire electrodes for recording efferent nerve activity. The recording electrodes were immersed in a pool of liquid paraffin oil or a mixture of warm vaseline and liquid paraffin oil, to prevent dehydration and for electrical insulation, respectively. The rat was allowed to stabilize for 30–60 min after being placed on the recording electrodes. Electrical changes in RSNA, GVNA and BAT-SNA were amplified 2000–5000 times with a band path of 100–1000 kHz, and monitored by an oscilloscope. Raw data of the nerve activity was converted to standard pulses by a window discriminator, which separated discharge from electrical background noise which remained post mortem. Both the discharge rates and the neurogram were sampled with a Power-Lab analog-to-digital converter for recording and data analysis on a computer. Data were obtained as described previously (Tanida et al., 2005). The catheter in the left femoral artery was connected to a BP transducer (DX-100, Nihon Kohden, Japan), and the output signal of the transducer was amplified in a BP amplifier (AP641G, Nihon Kohden, Japan). Two needle electrodes were placed under the skin at the right arm and left leg to record an electrocardiogram (ECG). The ECG signal was amplified with a bioelectric amplifier (AB-620G, Nihon Kohden, Japan). The BP and ECG were monitored with an oscilloscope, sampled with the Power-Lab, and stored on a hard disk for off-line analysis to calculate mean arterial pressure (MAP) and heart rate (HR). 2.3. Telemetry recording To measure the BAT-T, Telemetry System (Star Medical Co., Japan) was used as described previously (Taniguchi et al., 2006). In some rats (n = 8), seven days before the 3CV injection of NPY, a capsule containing a temperature sensor, battery and transmitter was implanted above the BAT fat pad under pentobarbital anesthesia (35 mg/kg, IP). The output signals mediating a receiver were converted from analog-to-digital and monitored and stored on a PC. The data were analyzed by 16ch-Eight Star program (Star Medical Corp., Japan). On the experimental day, the rats were made to fast 4 h prior to stimulation to avoid evoking diet-
M. Tanida et al. / Neuropeptides 43 (2009) 21–29
induced thermogenesis. With the animal conscious, baseline measurement of BAT-T was made for 5 min just before 3CV injection of NPY (1 nmol/10 ll aCSF) or aCSF. After the injection, these parameters were recorded for 60 min. 2.4. Intracerebroventricular cannulation One week before the experiment, a brain cannula (length; 3 cm) made of polyethylene tubing (PE-10; Clay Adams, Parsippany, NJ) and fitted with a tip of a microsyringe for injection was inserted into the third cerebral ventricle (A-P, 1.0 mm caudal to the bregma; L, 0 mm lateral to the midline; V, 7.0 mm below the skull surface) or the left lateral cerebral ventricle (A-P, 1.5 mm caudal to the bregma; L, 2.0 mm lateral to the midline; V, 3.0 mm below the skull surface) under pentobarbital anesthesia (35 mg/kg, IP) as previously described (Yamamoto et al., 1988). The cannula implanted into the brain was securely fixed by dental cement and synthetic resin. When injections were given to rats, the microsyringe for injection was directly connected to the cannula. 2.5. Experimental protocol Baseline measurements of RSNA, GVNA, BATSNA MAP, and HR were made 5 min prior to 3CV injection of NPY (0.01, 0.1, 1 nmol/10 ll artificial cerebrospinal fluid, aCSF) or aCSF (10 ll). After the start of the stimulation, these parameters were recorded for 60 min. The effects of diphenhydramine hydrochloride (5 lg/10 ll), a histaminergic H1-antagonist, or thioperamide maleate (2 lg/10 ll), a histaminergic H1antagonist, dissolved in aCSF on changes in RSNA and BP elicited by NPY were examined. In regard to injection dose of thioperamide, our preliminary study determined it which unaffected RSNA and BP (Supplementary Fig. 1). These antagonists were administered into the lateral cerebral ventricle 15 min prior to the 3CV injection of NPY. At the end of the experiment, hexamethonium chloride (10 mg/kg) was administered intravenously to ensure that post-ganglionic efferent sympathetic nerve activity had been recorded. 2.6. Data analyses The RSNA, GVNA, BAT-SNA, MAP, HR and BAT-T data measured during each 5 min period after injection of aCSF or NPY were analyzed by digital signal processing and appropriate statistical analyses. All data were expressed as means ± SEM. Mann–Whitney U-test was used to compare basal levels in the each groups. Percent changes from the baseline values were calculated for the RSNA, GVNA and BAT-SNA. Absolute value changes from the baseline were calculated for
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MAP, HR and BAT-T. Two-way analysis of variance (ANOVA) was applied to compare group responses of the RSNA, GVNA, BAT-SNA, MAP, and HR. To perform statistical analysis of the dose response to 3CV NPY, ANOVA, followed by multiple comparisons using Dunnett’s multiple range tests, was used. To compare group responses of BAT-T, ANOVA and post-hoc test (Fisher’s PLSD) were performed. P < 0.05 was considered statistically significant.
3. Results Injection of artificial cerebrospinal fluid (aCSF) into the 3CV did not affect RSNA, MAP or HR (Fig. 1A), and there was no difference among the basal (0 min) values of RSNA, MAP, and HR (Fig. 1, Table 1). However, they were significantly suppressed following NPY (1 nmol) injection and gradually decreased to reach their lowest levels after 60 min (Fig. 1B–D). The lowest levels attained were 75.3 ± 15.7% (RSNA), 13.2 ± 6.2 mmHg (MAP), and 21 ± 8 beats/min (HR). Lower dose (0.01 and 0.1 nmol) injections of NPY into the 3CV also decreased RSNA, MAP, and HR 60 min following the injection (Fig. 2A–C), but the maximum suppressive responses occurred after 1 nmol NPY of the injection. In contrast, thioperamide pretreatment eliminated the effects of NPY (Fig. 2A–C), whereas diphenhydramine did not. Injection of aCSF did not affect GVNA or BAT-SNA (Fig. 3A); however, both were significantly changed by 1 nmol of NPY. Following the injection of 1 nmol of NPY, GVNA increased gradually (Fig. 3B) to reach its highest level (127.8 ± 6%) 45 min after the injection. In contrast, BAT-SNA decreased gradually following NPY injection (Fig. 3C) and reached its lowest level (22.7 ± 9.5) 50 min after the injection. There was no difference between the absolute basal (0 min) GVNA and BAT-SNA values (Fig. 3, Table 1). Injection of aCSF did not affect BAT-T, whereas it was significantly suppressed by NPY (1 nmol) (Fig. 4A). Following the injection, BAT-T decreased gradually (Fig. 4B) and reached its lowest level ( 0.46 ± 0.25 °C) 20 min after the injection. The basal (0 min) values of BAT-T were 37.7 ± 0.3 °C (aCSF-group) and 38.4 ± 0.5 °C (NPYgroup).
4. Discussion The present study showed that the injection of NPY into the 3CV evoked significant decreases in RSNA and BP in a dose-dependent manner (Fig. 1). We found that the suppressing effects of NPY on RSNA and BP were abolished by pretreatment with a lateral cerebral
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Fig. 1. Effects of 3CV injection of NPY (1 nmol) on renal sympathetic nerve activity (RSNA), blood pressure (BP) and heart rate (HR). Representative trace data from recordings of RSNA and BP (A) before and after the 3CV injection of aCSF or NPY (1 nmol) was described. The arrows indicate the time of injection. Time-course data of RSNA (B), MAP (C) and HR (D) after 3CV injection of aCSF or NPY (1 nmol) are expressed as mean + SEM. Numbers of animals used are shown in the parentheses. *Significant differences between aCSF group and NPY group (P < 0.05).
ventricular (LCV) injection of thioperamide, an H3receptor antagonist, but not by diphenhydramine, an H1-receptor antagonist, suggesting that the responses induced by NPY were mediated by central histaminergic
receptors. In addition, injection of NPY into the 3CV caused a decrease in BTA-SNA and an increase in GVNA. NPY has hyperphagic action via the central nervous system (Konturek et al., 2004), and there is a
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Table 1 Basal-levels of autonomic nerve activation and cardiovascular parameters in experimental Groups
aCSF NPY 1 nmol
RSXA
MAP
HR
GVNA
BAT-SNA
(spike/5 s)
(mmHg)
(beats/min)
(spike/5 s)
(spike/5 s)
(number of rats)
(number of rats)
(number of rats)
(number of rats)
(number of rats)
120.5 ± 17.3 (4) 141.3 ± 12.6 (4)
87.0 ± 9.0 (4) 90.1 ± 5.4 (4)
378 ± 32 (4) 346 ± 45 (4)
259.9 ± 29.7 (4) 227.7 ± 30.0 (4)
164.3 ± 48.2 (4) 217.7 ± 38.4 (4)
RSNA, renal sympathetic nerve activity; MAP, mean arterial pressure; HR, heart rate; GVNA, gastric vagal nerve activity, BAT-SNA, brown adipose tissue sympathetic nerve activity. Data are shown as means ± SEM.
close relationship between parasympathetic nerves and feeding regulation (Shen et al., 2005a,b). To the best of our knowledge, this is the first study to provide evidence in animals that NPY injected into the 3CV significantly elevates parasympathetic nerve outflow to the digestive organs, including the stomach. Animal studies have confirmed that central administration of NPY may suppress (Fuxe et al., 1983; Aguirre et al., 1990; Matsumura et al., 2000) or elevate (Hu and Dunbar, 1997; Vallejo and Lightman, 1986) BP and HR, suggesting complex and biphasic actions of NPY on central cardiovascular functions. In general, previous reports investigating the central actions of NPY on cardiovascular function suggest that a variety of factors might affect NPY actions. Some of the confounding factors may be alertness, the area injected, and the rat breed. Scott et al. observed that NPY lowered BP in conscious rats (Scott et al., 1989) and we found that NPY lowered RSNA and BP of anesthetized rats and BAT-T of conscious rats. These results suggest that alertness might not be associated with the cardiovascular effects of NPY. With respect to the injection area, previous studies that injected NPY into the various brain areas reported that NPY injection into the cisterna reduced (Fuxe et al., 1983), whereas injection into the lateral ventricle elevated (Hu and Dunbar, 1997) BP. Thus, these results suggest that cardiovascular responses to NPY may be dependent on the brain area of NPY action. In Sprague–Dawley rats, NPY injection into the 3CV significantly increases BP and HR (Vallejo and Lightman, 1986). We used Wistar rats in the present study, which may explain our contradictory results. However, further investigation is required to develop the relationship between NPY and various rat breeds. Histaminergic neurotransmission in the brain consists of histamine release from the presynaptic histaminergic neurons via the H3-receptor and histamine binding with the H1-receptor expressed in the postsynaptic histaminergic neurons (Arrang et al., 1983). Our previous study showed that thioperamide, but not diphenhydramine, eliminated the suppressing effects of low-dose histamine on RSNA and BP in anesthetized rats (Tanida et al., 2007b). This work suggested that
the presynaptic H3-receptor mediating auto-inhibition of histamine release from the histaminergic neurons to the synaptic clefts might cause renal sympathetic inhibition and BP reduction. In this study, we found that the suppressing effects of NPY on RSNA and BP were abolished by pretreatment with thioperamide (Fig. 2). Furthermore, our preliminary evidence that thioperamide abolished NPY-induced GVNA activation and BAT-SNA suppression was confirmed (Supplementary Fig. 2). Thus, this evidence suggests that the central histaminergic system, including the H3receptor, is involved in the autonomic and cardiovascular response to NPY. Moreover, NPY-containing neurons connect with histaminergic neurons in the TMN (Tamiya et al., 1989) and express NPY-Y1 receptor mRNA (Kishi et al., 2005). It appears that NPY directly affects histaminergic neurons via the NPY/Y1 pathway and regulates histamine release thereby altering the autonomic and cardiovascular functions. In this respect, Ishizuka et al. reported that central injection of NPY accelerates histamine release in the hypothalamus (Ishizuka et al., 2006), which is in accordance with our previous observation that low-dose histamine causes RSNA and BP suppression (Tanida et al., 2007b). At present, the reason for this discrepancy is unknown. However, it is possible that the NPY-Y1 and H3-receptors expressed in the histaminergic neurons might interact with each other through an intracellular cascade and affect the regulation of histamine release. NPY-containing fibers connect with the dorsal motor nucleus of the vagus (Buchan et al., 1991), and efferent vagal neurons project to the stomach (Zhang et al., 2000). Moreover, hypothalamic injection of NPY suppresses gastric acid secretion modulated by autonomic nerves (Humphreys et al., 1992), indicating a possible role of NPY in parasympathetic control. We found that NPY injection into the 3CV increased GVNA in urethane-anesthetized rats (Fig. 3). Based on previous reports that parasympathetic excitation evokes an increase in food intake (Shen et al., 2005b), a close relationship between parasympathetic nerves supplying the stomach and feeding behavior is suggested. In fact, an increase in the central NPY level induces hyperphagia (Konturek et al., 2004). In contrast, parasympathetic
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Fig. 2. Effects of histaminergic receptors antagonists (diphenhydramine or thioperamide) on changes in RSNA, MAP and HR following 3CV injection of NPY. Bars in A–C show RSNA, MAP and HR values 60 min after injection of three doses (0.01, 0.1, and 1 nmol) of NPY and aCSF. Effect of pretreatment with diphenhyrdramine (diphen) or thioperamide (thiop) is added to bar graphs in A–C. Four rats are used in each group. *Significant differences between aCSF and NPY-injections (P < 0.05).
nerves innervating the pancreas and the liver modulate glucose metabolism via insulin release or glycogen synthesis. Generally, parasympathetic nerve activation reduces blood glucose level and mediates an increase in these factors (Yamano et al., 2001). A preliminary study demonstrated that NPY injected into the brain of rats, elevated neural activity of the celiac parasympathetic nerve projecting to the pancreas but inhibited hyperglycemia due to 2-deoxy-D-glucose injection (unpublished data). This suggests that NPY might act on the brain and affect parasympathetic nerves to control appetite and blood glucose level. We have shown, along with others (Egawa et al., 1991), that a central injection of NPY suppresses BTA-SNA in anesthetized rats. Brown adipose tissue functions as a thermogenic organ that produces heat in the mitochondria via the activation of uncoupling protein-1, which shunts the energy obtained from the oxidation of free fatty acids into heat; this heat is then stored in the vessels and is distributed throughout the body (Argyropoulos and Harper, 2002). Thermogenesis is evoked by the acceleration of BAT-SNA secondary to the commands from the brain (Morrison, 2004). Thus, our data that NPY injection into the 3CV lowered BAT-T in conscious rats is consistent with this idea. Egawa et al. reported that microinjection of NPY into the hypothalamic paraventricular nucleus significantly suppresses BTA-SNA, indicating that NPY affects BAT-SNA through the paraventricular nucleus (Egawa et al., 1991). Various nuclei in the hypothalamus, such as the suprachiasmatic and the paraventricular nucleus, project to the brown adipose tissue via sympathetic nerves (Bamshad et al., 1999). We have previously shown that the suprachiasmatic nucleus supplies efferent projections to the paraventricular nucleus (Buijs et al., 2001) and that bilateral lesions of the suprachiasmatic nucleus abolish the effects of L-carnosine, a dipeptide released from the muscle into the blood, on BAT-SNA (Tanida et al., 2007a). Moreover, NPY-Y1 receptor mRNA was localized in both nuclei (Kishi et al., 2005), suggesting that NPY might act directly on the hypothalamic nuclei and change BAT-SNA and BATT for thermoregulation. Microinjection investigations that are focused on the specific hypothalamic regions of NPY-Y1 receptor localization may be helpful to determine a detailed neural pathway within the hypothalamus. With regard to autonomic and cardiovascular responses to NPY, the recovery responses after NPY injection are unknown. Generally, the effects of acute stimulation on autonomic nerves are immediate, but whether the effect of NPY is intermediate is unknown. Our preliminary data showed that the effect of NPY injection on GVNA and BAT-SNA returned to baseline 2-3 h after the injection (Supplementary Fig. 2), suggesting that NPY has a relatively short acting effect on auto-
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Fig. 3. Effects of 3CV injection of NPY (1 nmol) on GVNA and BAT-SNA. Representative trace data from recordings of GVNA and BAT-SNA (A) before and after the 3CV injection of aCSF or NPY (1 nmol) was described. The arrows indicate the time of injection. Time-course data of GVNA (B) and BAT-SNA (C) after 3CV injection of aCSF or NPY (1 nmol) are expressed as mean + SEM. Numbers of animals used are shown in the parentheses. *Significant differences between aCSF group and NPY group (P < 0.05).
nomic nerves. On the other hand, it is thought that blood levels of NPY leaking from the brain might affect sympathetic and cardiovascular responses to central NPY. Thus, we investigated the effect of an intravenous injection of NPY on RSNA and BP and found no effect on sympathetic and cardiovascular actions (Supplementary Fig. 3). Based on this evidence, there may be a minimal effect of NPY leaked from the brain.
In conclusion, we demonstrated that NPY dosedependently lowers RSNA and BP with a central mechanism through histaminergic H3-receptors. In addition, autonomic and thermoregulatory responses to NPY were confirmed through the elevation of GVNA and reductions in BAT-SNA and the BAT-T. Thus, NPY affects autonomic nerves and lowers BP and BAT-T via a central mechanism.
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Fig. 4. Effects of 3CV injection of NPY (1 nmol) on BAT-T in conscious rats. Representative trace data from recordings of BAT-T (A) before and after the 3CV injection of aCSF or NPY (1 nmol) was described. The arrows indicate the time of injection. Time-course data of BAT-T (B) after 3CV injection of aCSF or NPY (1 nmol) is expressed as mean + SEM. Numbers of animals used are shown in the parentheses. *Significant differences between aCSF group and NPY group (P < 0.05).
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/ j.npep.2008.09.007.
References Aguirre, J.A., Fuxe, K., Agnati, L.F., von Euler, G., 1990. Centrally injected neuropeptide Y (13–36) produces vasopressor effects and
antagonizes the vasodepressor action of neuropeptide Y (1–36) in the awake male rat. Neuroscience Letters 118, 5–8. Argyropoulos, G., Harper, M.E., 2002. Uncoupling proteins and thermoregulation. Journal of Applied Physiology 92, 2187–2198. Arrang, J.M., Garbarg, M., Schwartz, J.C., 1983. Auto-inhibition of brain histamine release mediated by a novel class (H3) of histamine receptor. Nature 302, 832–837. Bamshad, M., Song, C.K., Bartness, T.J., 1999. CNS origins of the sympathetic nervous system outflow to brown adipose tissue. American Journal of Physiology 276, R1569–R1578. Brown, R.E., Stevens, D.R., Haas, H.L., 2001. The physiology of brain histamine. Progress in neurobiology 63, 637–672. Buchan, A.M., Kwok, Y.N., Pederson, R.A., 1991. Anatomical relationship between neuropeptide-containing fibers and efferent vagal neurons projecting to the rat corpus. Regulatory Peptide 34, 1–12. Buijs, R.M., Chun, S.J., Niijima, A., Romijn, H.J., Nagai, K., 2001. Parasympathetic and sympathetic control of the pancreas: a role for the suprachiasmatic nucleus and other hypothalamic centers that are involved in the regulation of food intake. Journal of Comparative Neurology 431, 405–423. Chronwall, B.M., DiMaggio, D.A., Massari, V.J., Pickel, V.M., Ruggiero, D.A., O’Donohue, T.L., 1985. The anatomy of neuropeptide-Y-containing neurons in rat brain. Neuroscience 15, 1159– 1181. Egawa, M., Yoshimatsu, H., Bray, G.A., 1991. Neuropeptide Y suppresses sympathetic activity to interscapular brown adipose tissue in rats. American Journal of Physiology 260, R328–R334. Fuxe, K., Agnati, L.F., Harfstrand, A., Zini, I., Tatemoto, K., Pich, E.M., Hokfelt, T., Mutt, V., Terenius, L., 1983. Central administration of neuropeptide Y induces hypotension bradypnea and EEG synchronization in the rat. Acta Physiologica Scandinavica 118, 189–192. Handa, R.K., Johns, E.J., 1985. Interaction of the renin-angiotensin system and the renal nerves in the regulation of rat kidney function. Journal of Physiology 369, 311–321. Hu, Y., Dunbar, J.C., 1997. Intracerebroventricular administration of NPY increases sympathetic tone selectively in vascular beds. Brain Research Bulletin 44, 97–103. Humphreys, G.A., Davison, J.S., Veale, W.L., 1992. Hypothalamic neuropeptide Y inhibits gastric acid output in rat: role of the autonomic nervous system. American Journal of Physiology 263, G726–G732. Ishizuka, T., Nomura, S., Hosoda, H., Kangawa, K., Watanabe, T., Yamatodani, A., 2006. A role of the histaminergic system for the control of feeding by orexigenic peptides. Physiology and Behavior 89, 295–300. Kishi, T., Aschkenasi, C.J., Choi, B.J., Lopez, M.E., Lee, C.E., Liu, H., Hollenberg, A.N., Friedman, J.M., Elmquist, J.K., 2005. Neuropeptide Y Y1 receptor mRNA in rodent brain: distribution and colocalization with melanocortin-4 receptor. Journal of Comparative Neurology 482, 217–243. Konturek, S.J., Konturek, J.W., Pawlik, T., Brzozowski, T., 2004. Brain-gut axis and its role in the control of food intake. Journal of Physiology and Pharmacology 55, 137–154. Matsumura, K., Tsuchihashi, T., Abe, I., 2000. Central cardiovascular action of neuropeptide Y in conscious rabbits. Hypertension 36, 1040–1044. Morrison, S.F., 2004. Central pathways controlling brown adipose tissue thermogenesis. News in physiological sciences 19, 67–74. Niijima, A., 1991. Effect of umami taste stimulations on vagal efferent activity in the rat. Brain Research Bulletin 27, 393–396. Scott, NA., Webb, V., Boublik, J.H., Rivier, J., Brown, M.R., 1989. The cardiovascular actions of centrally administered neuropeptide Y. Regulatory Peptide 25, 247–258. Shen, J., Niijima, A., Tanida, M., Horii, Y., Maeda, K., Nagai, K., 2005a. Olfactory stimulation with scent of grapefruit oil affects
M. Tanida et al. / Neuropeptides 43 (2009) 21–29 autonomic nerves, lipolysis and appetite in rats. Neuroscience Letters 380, 289–294. Shen, J., Niijima, A., Tanida, M., Horii, Y., Maeda, K., Nagai, K., 2005b. Olfactory stimulation with scent of lavender oil affects autonomic nerves, lipolysis and appetite in rats. Neuroscience Letters 383, 188–193. Tamiya, R., Hanada, M., Narita, N., Kawai, Y., Tohyama, M., Takagi, H., 1989. Neuropeptide Y afferents have synaptic interactions with histaminergic (histidine decarboxylase-immunoreactive) neurons in the rat brain. Neuroscience Letters 99, 241–245. Tanida, M., Gotoh, H., Taniguchi, H., Otani, H., Shen, J., Nakamura, T., Tsuruoka, N., Kiso, Y., Okumura, N., Nagai, K., 2007a. Effects of central injection of L-carnosine on sympathetic nerve activity innervating brown adipose tissue and body temperature in rats. Regulatory Peptide 144, 62–71. Tanida, M., Kaneko, H., Shen, J., Nagai, K., 2007b. Involvement of the histaminergic system in renal sympathetic and cardiovascular responses to leptin and ghrelin. Neuroscience Letters 413, 88–92. Tanida, M., Niijima, A., Shen, J., Nakamura, T., Nagai, K., 2005. Olfactory stimulation with scent of essential oil of grapefruit affects autonomic neurotransmission and blood pressure. Brain Research 1058, 44–55. Taniguchi, H., Tanida, M., Okumura, N., Hamada, J., Sano, S., Nagai, K., 2006. Regulation of sympathetic and parasympathetic
29
nerve activities by BIT/SHPS-1. Neuroscience Letters 398, 102– 106. Tatemoto, K., Carlquist, M., Mutt, V., 1982. Neuropeptide Y–a novel brain peptide with structural similarities to peptide YY and pancreatic polypeptide. Nature 296, 659–660. Vallejo, M., Lightman, S.L., 1986. Pressor effect of centrally administered neuropeptide Y in rats: role of sympathetic nervous system and vasopressin. Life Sciences 38, 1859–1866. Watanabe, T., Taguchi, Y., Shiosaka, S., Tanaka, J., Kubota, H., Terano, Y., Tohyama, M., Wada, H., 1984. Distribution of the histaminergic neuron system in the central nervous system of rats; a fluorescent immunohistochemical analysis with histidine decarboxylase as a marker. Brain Research 295, 13–25. Yamamoto, H., Nagai, K., Nakagawa, H., 1988. Time-dependent involvement of autonomic nervous system in hyperglycemia due to 2-deoxy-D-glucose. American Journal of Physiology 255, E928– E933. Yamano, T., Niijima, A., Iimori, S., Tsuruoka, N., Kiso, Y., Nagai, K., 2001. Effect of L-carnosine on the hyperglycemia caused by intracranial injection of 2-deoxy-D-glucose in rats. Neuroscience Letters 313, 78–82. Zhang, X., Renehan, W.E., Fogel, R., 2000. Vagal innervation of the rat duodenum. Journal of Autonomic Nervous System 79, 8–18.