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International Journal of Morphology

versión On-line ISSN 0717-9502

Int. J. Morphol. vol.34 no.4 Temuco dic. 2016

http://dx.doi.org/10.4067/S0717-95022016000400047 

Int. J. Morphol., 34(4):1465-1471, 2016.

 

Expression and Distribution of Kinin B2 Receptor in Medulla and Spinal Cord Tissues of Rats Treated with Capsaicin

 

Expresión y Distribución del Receptor B2 de Cininas en la Médula y Tejido Medular Espinal de Ratones Tratados con Capsaicina

 

Camilla Estevão de França*,**; Carla Guardabassi* & Ricardo Luiz Smith*

* Department of Morphology and Genetics, Universidade Federal de São Paulo, Brasil.

** CNPq Ph.D. fellowship and Canadian Institutes of Health Research.

Correspondence to:


SUMMARY: Kinins are vasoactive peptides that promote pain and inflammation, yet centrally believed to participate to cardiovascular defensive reflexes produced by noxious stimuli. These peptides signal through the activation of two transmembrane G-protein-coupled receptors named B1 and B2 receptors (B1R and B2R). The B2R is constitutive in healthy tissues and animals. The aim of the study was to measure the gene and protein expression of B2R kinin receptors in central and peripheral tissues isolated from control rats and rats were pre-treated with capsaicin on the second day of life (50 mg/kg, s.c.) or two weeks prior to sacrifice (125 mg/kg over three days, s.c.). The same treatment with saline was made in control animals. Levels of mRNA for B2R were measured by quantitative RT-PCR and Qualitative while receptor binding sites were measured on tissue sections with the radioligands 125I-HPP-Hoe 140 (B2R). B2R was expressed in all studied tissues (hypothalamus, paratrigeminal nucleus, nucleus of solitary tract, spinal cord, aorta and liver) and treatment capsaicin neonates when compared to controls, did not affect its level of expression. Capsaicin had no significant effect on the expression of B2R in some tissues on binding sites. The synthesis of B2R kinin receptor is not associated with sensory C-fibre and tissues showed no significant difference indicating that B2R was regulated by distinct mechanisms.

KEY WORDS: Medulla; Spinal Cord; Rats; Kinin receptor B2; Capsaicin.


RESUMEN: Las cininas son péptidos vaso activos que participan de mecanismos de dolor e inflamación, con la promoción de reflejos cardiovasculares defensivos producidos por estímulos nocivos. Estos péptidos señalizan por medio de la activación de dos receptores transmembrana acoplados a proteína G llamados receptores B1 y B2 (B1R y B2R). El B2R es constitutivo en tejidos saludables y en animales. El objetivo de este estudio consistió en tomar las medidas de la expresión del gen y la proteína del receptor B2R de cinina en tejidos centrales y periféricos aislados de ratones control y ratones pre tratados con capsaicina en el segundo día de vida (50 mg/kg, s.c.) o con dos semanas antes del sacrificio (125 mg/kg por tres días, s.c.). El mismo tratamiento fue hecho con solución salina en los animales control. Fueron medidos niveles de mRNA para B2R por RT-PCR en forma cuantitativa y cualitativa, en cuanto los sitios de unión del receptor fueron medidos en secciones de tejido con radioligante 125I-HPP-Hoe 140 (B2R). B2R fue expresado en todos los tejidos estudiados (hipotálamo, núcleo paratrigeminal, núcleo del tracto solitario, médula espinal, aorta e hígado). El tratamiento con capsaicina en ratones neonatos comparados con controles no presentaron afectación del nivel de expresión. Por otro lado, la capsaicina no tuvo efecto significante en la expresión de los sitios de unión de B2R en los tejidos. La síntesis del receptor B2R de cininas no está asociado con fibras C sensoriales así como los tejidos no mostraron diferencias significativas indicando que B2R es regulado por mecanismos distintos.

PALABRAS CLAVE: Médula; Ratones; Receptor B2 de Cinina; Capsaicina.


 

INTRODUCTION

Bradykinin, a potent neuropeptide and a vasoactive peptide, has a wide spectrum of biological activities (Couture & Lindsey, 2000; Leeb-Lundberg et al., 2005). Kinins are biologically active autacoids implicated in the response of the organism to trauma and tissue injury. Under physi-ological conditions, kinin activity is mediated by the interaction of the B2 kinin receptors (Leeb-Lundberg et al.). These are present in organ and arterial smooth muscle cells and in rat and human brain nuclei, such as the paratrigeminal nucleus and the nucleus of the solitary tract (Lindsey et al., 1997; de Sousa Buck et al., 2002). Stimulation of arterial B2 kinin receptor causes resistance to vessel vasodilatation and hypotension (Sharma et al., 2006). On the other hand, stimulation of central kinin receptors leads to blood pressure increases (Lindsey et al., 1997), mediated by central sympathetic mechanisms (Caous et al., 2004). Thus, among other impor-tant functions, such as blood pressure regulation, kinins are characterized as mediators of pain and inflammatory responses, both in the central and in the peripheral nervous systems (Leeb-Lundberg et al.); they are also important mediators in the cascade of the febrile response (Pessini et al., 2006). Additionally, bradykinin apparently plays a role in the rat reproductive tis-sues via the kinin B2 receptor (França et al., 2010). As vascular agents they promote vascular permeability and vasodilatation (Leeb-Lundberg et al.), which are important mechanisms related to the anti-hypertensive action of kinase II inhibitors (Lindsey et al., 1987). In particular, bradykinin and kallidin are powerful algesic and vasoactive peptides generated locally following the proteolytic cleavage of their precursors, high- and low-molecular-weight cultures and in various regions of the brain including the medulla oblongata, the pons, the cerebral cortex and the hippocampus (Damasceno et al., 2015).

Two receptor types, both of the protein G receptor family, are known to mediate kinin effects in different tissues throughout the body (Leeb-Lundberg et al.). The widely distributed B2 receptor is constitutive and mediates the effects of BK and KD, while the B1 receptor, absent or under-expressed in healthy animals, mediates the effects of des-Arg9-BK and des- Arg10-KD (Marceau et al., 1998; Regoli et al., 2001). The B1 receptor, normally not present in healthy tissues, has its expression promoted by inflammatory responses caused by injury, infection, or endogenous and exogenous pyrogens (Lungu et al., 2007). Spinal cord, B2 receptor-binding sites were seen preferentially localized to the superficial laminae of the dorsal horn, the site of first synapse for terminals of primary sensory fibers (Lopes et al., 1995). Most, if not all, studies have restricted their work on brain, at a large macroscopic level, without particular focus on a more cellular localization such as neurons, glial cells and/or vascular tissue (capillary) and neurotoxin for small-diameter primary afferent fibers (C and A delta). There is considerable evidence showing that bradykinin is a major mediator of inflammation following peripheral issue injury, and can stimulate or sensitize peripheral nociceptive afferent terminals to elicit pain and hyperalgesia via the activation of the B2 kinin receptor (Lindsey et al., 1997). Within the brain and the spinal cord, kinins have been extensively studied for their implications in the transmission of nociceptive information (Muto et al., 2012) the control of blood pressure (Scheuren et al., 2016). For a better understanding of the localization rat kinin B2 receptor to gain insight, we analyzed mature RNA and binding sites in neonate normotensive rat strains using of bulbar nucleus, spinal cord and aorta were respectively analyzed for a clearer understanding of this receptor as originates from C and A delta sensory primary fibers.

MATERIAL AND METHOD

Chemicals and materials. HPP-Hoe 140 (3-(4 hydroxyphenyl) propionyl-D-Arg0[Hyp3, Thi5, D-Tic7 Oic8]-BK) was developed from the selective B2 receptor antagonist Hoe 140 (Hock et al., 1991) and it was synthesized by Dr. Witold Neugebauer (Institute of Pharmacology, University of Sherbrooke, Sherbrooke, Quebec, Canada). Autoradiographic [125I]-microscales and Kodak Scientific BIOMAXTM MS (Amersham Pharmacia Biotech Canada). Bacitracin, bovine serum albumin (protease free), captopril, dithiothreitol, magnesium chloride, piperazine- N, N0-bis [2-ethanesulfonic-acid] (PIPES), and 1,10-phenanthroline (Sigma- Aldrich, Canada). Hoe 140 a selective B2 receptor antagonist (Hock et al.) (DArg0[Hyp3,Thi5,D-Tic7,Oic8]-BK, Peninsula Laboratories, San Carlos, CA, USA) and des-Arg9-BK and BK (Bachem Bioscience Inc., King of Prussia, PA, USA). All other chemicals were obtained from standard commercial sources.

Animals. Male Wistar newborn (2 days) and adult rats (weighting 200­250g) (n=4 per group, 8 groups ­ control and capsaicin treated) were purchased from Charles River (St-Constant Quebec, Canada) and CEDEME Bioterio from Federal University of São Paulo, Brazil. The care of animals and research protocols conformed to the guiding principles for animal experimentation as enunciated by the Canadian Council on Animal Care and approved by the CEP ­ Research Ethics Committee of our university.

Tissue preparation. Quantitative Autoradiography and PCR real time: After killing under CO2 inhalation, rats were decapitated and the brains and spinal cords were immediately removed, frozen in 2-methyl butane cooled at 45 to 55 oC in liquid nitrogen, and then stored at 80 oC until use. Matched whole brains and thoracic spinal cords (T8­T12) were mounted together (2 brains or 4 spinal cords per gelatin bloc) and serially cut into 20-µm thick sections on a cryostat with temperature varying between 10 to 12 oC. Sections were thaw-mounted on 0.2 % gelatin/0.033 % chromium potassium sulfate-coated slides and stored at 80 oC. Three thousand total slides were used for the autoradiography analysis. Quantitative autoradiography Iodination of HPP-Hoe 140 and B2 receptor autoradiography were performed according to the method of chloramine T described by Ongali et al. (2003). Sections were thawed at room temperature and preincubated for 30 s in 25 mM PIPES buffer (pH 7.4, 48 oC). Thereafter, slides were incubated for 90 min at room temperature in 25 mM PIPES buffer containing 1 mM 1,10-phenanthroline, 1 mM dithiothreitol, 0.014 % bacitracin, 0.1 mM captopril, 0.2 % bovine serum albumin(protease free), and 7.5 mM magnesium chloride in the presence of 200 pM [125I]HPP-Hoe 140 (specific activity:1212 Ci/mmol). The nonspecific binding was determined in the presence of 1 µM of unlabeled ligand. At the end of the incubation period, slides were transferred sequentially through four rinses of 4 min each in 25 mM PIPES (pH 7.4, 48 oC) and dipped for 15 s in distilled water (48 oC) to remove the excess of salts, and air-dried. Kodak Scientific BIOMAXTM MS1 were juxtaposed onto the slides in the presence of [125I]-microscales and exposed at room temperature for 2 days. The methodology employed was similar to that described previously by Lopes et al., with some modifications. Competition binding assays were carried out under the same assay conditions described above, using 200 pM [125I] HPP-Hoe 140 as radioligand in the presence of increasing concentrations (ranging from 10-16 to 10-5 M) of non-radiolabeled selective agonist (BK) and antagonists (HPP Hoe 140, Hoe 140 and LF16-0687) for B2 receptor.

Image analysis. Densitometric readings were performed using an MCIDTM image analysis system (Imaging Research, St Catharines, Ontario, Canada). The number of replicates analyzed for each brain and spinal cord region was a minimum of 3 per animal. The nomenclature of anatomical structures and their abbreviations are adapted from the atlas of Paxinos & Watson (2013).

Tissue preparation for B2R binding and mRNA expression. Spinal cord segments (T8­T11), brains, thoracic aorta were removed and immediately frozen in 2-methyl butane cooled at - 45 to - 55 oC with liquid nitrogen and kept at - 80 oC for autoradiography. The same tissues (Liver, Pa5, NTS and thoracic Spinal Cord) were removed and put in polyethylene microtubes containing TRizol reagent (Life Technologies, Burlington, Ont., Canada) and then frozen with liquid nitrogen and stored at -80 oC until extraction of total RNA and measurement by real-time polymerase chain reaction (real-time PCR). In vitro receptor autoradiography, used tissues of 4 rats per group were mounted together (2 brains or 4 spinal cords per gelatin bloc) and serially cut into 20-mm thick sections on a cryostat with temperature varying between -10 to ­ 12 oC. Sections were thaw-mounted on 0.2 % gelatin/0.033 % chromium potassium sulfate-coated slides and stored at - 80 oC. 3000 slides were used for the autoradiography analysis. The concentration of the radioligand [125I]HPP-Hoe 140 chosen (200 pM) corresponds to maximal specific binding on the saturation curves (Bmax) in the all tissues analyzed in both treatment capsaicin and control rats on the 2nd day (Fig. 1). The nonspecific binding did not significantly differ between control and Capsaicin treatment.

Gene expression RNA were extracted according to manufactures protocol (Trizol and Qiagen). The SYBR Green System was used for quantification of gene expression. To this end, reactions were performed in a final volume of 20 mL containing 30­100 ng of cDNA or mtDNA, 10 mL of SYBR Green Universal PCR Master Mix 2x and 1 mL of each sense and antisense oligo (10 mM each). The cycling protocol was followed according to the determination of the unit standard 7500 from Applied Biosystems, including the dissociation curve. mRNA reactions were conducted with the following primers: (Table I).

Standard curves for each pair of oligo and cDNA sample group were made to establish the efficiency of these reactions. For the analysis of gene expression only reactions with high efficiency (> 95 %) were used. This allowed us to use the 2-DCt parameter for expressing arbitrary value of relative gene expression for each sample, using as endogenous control b-actin gene (mRNA).

Statistical analysis. The results were presented as the mean ± SEM of four animals per group. Statistical comparison of the data was performed with Graph-Pad Prism computer program using unpaired Student's t-test, or for multiple comparisons, one-way analysis of variance (ANOVA) followed by test T Tukey P <0.05 was considered to be statistically significant and all values are expressed as mean ± SEM.

Fig. 1 - Spinal cord (left), Medulla (right) and AORTA (above): Colored pseudo images of radioautograms
representing the anatomical distribution of B2R in Wistar neonate rats. The nonspecific binding is
represented by NS. (location based in Paxinos & Watson). Vertical bars
in the graphics represent the mean ± standard error.

Table I. Oligonucleotides sentences.

RESULTS

B2 receptor Quantitative autoradiograpy analyses (binding sites). Specific kinin B2 receptor binding sites were measured in control and capsaisin-sensitive treatment rats using [125I]HPP-Hoe 140 as radioligand. Representative autoradiograms reveal that B2 receptor binding sites are distributed throughout all the structures of the gray matter of the spinal cord, medulla oblongata and thoracic aorta (Fig. 1). The specific ligation range of 0,1277±0,04 to 2,303±0,54 fmol/mg (fentomol by miligram of tissue).

B2 receptor binding sites displayed a distribution profile similar to that observed in control animals (Fig. 1). However, specific B2 receptor densities were slightly but significantly in thoracic aorta. Representative autoradiograms showing the distribution of B2 receptor binding sites in the brain of control depicted. Using the B2 iodinated antagonist [125I]HPP-HOE140 as radioligand to quantify and localize kinin B2 receptors in brains specific binding sites were verifed all over the tissue.

Analysis of Gene Expression B2 Receptor. For the analysis of gene expression of B2R was performed RT-PCR (qRT-PCR). The qualitative RT-PCR was used only to confirm the gene expression of this receptor. Figure 2 shows the image of an agarose gel showing the amplified products of approximately 700 base pairs (bp) respectively. Amplification of the B2 receptor gene encoding kinins, from qRT-PCR was obtained from different tissues of Central Nervous System regions (PA5, NTS, hypothalamus, spinal cord) and in peripheral tissues, as well as the thoracic aorta and liver. The liver tissue with intense vascularity was selected as a positive control for the amplification reaction.

Fig. 2. Agarose gel showing the amplification of the kinin B2 receptor. Product ~ 700pb B2 receptor and b actin used as a positive control of reverse transcriptase reaction (RT) and amplification (PCR). (PM - molecular weight; B2 salt / salt - saline control; B2cap / salt - treated capsaicin). PA5 - paratrigeminal core, NTS - nucleus of the solitary tract, HIP - hypothalamus; ME ­ spinal cord, A ­aorta. Above: Analysis of gene expression of kinin B2 receptor after treatment with capsaicin and salt. FIG ­ liver, ME ­ spinal cord, PA5 ­ paratrigeminal core, NTS - nucleus of the solitary tract, AT ­ aorta. (T test non significant).

DISCUSSION

This study showed the distribution of the B2 receptor binding sites of kinins in the spinal cord medulla cores and thoracic aorta, by quantitative autoradiography, as well as using real-time PCR to analyze gene expression of B2 kinin receptor. The kallikrein-kinin system, of which bradykinin is the main representative, has raised interest, in view of the signaling pathways in which this peptide acts. B2 bradykinin receptor has been found in many cell types such as vascular endothelium, primary sensory afferent neurons, vascular smooth muscle and non-vascular, epithelial cells, and perhaps in certain types of leukocytes, which gives bradykinin a wide physiological activities such as vasodilatation, increased vascular permeability, stimulation of sympathetic and sensory nerves connection (Coelho et al., 1997; Caous et al., 2001; Couture & Lindsey). The B2 kinin receptor has constitutive expression being relatively stable, regulated only by the transcription factor affinity for the promoter site of the gene (Pesquero et. al, 1996).

Studies have shown that treatment with capsaicin neonatal rats causes a permanent loss of A delta, C and small diameter fibers (Fitzgerald & Koltzenburg, 1986). To examine the relationship of these projections on the receivers, we used the autoradiography and molecular biology, to see if these losses could alter the expression and location of these receptors.

Treatment with capsaicin was determined to find out if the bradykinin receptor in paratrigeminal nucleus is located on the efferent core fibers. In other instances anatomical structures show that bradykinin also produces a pressor response when microinjected in PA5, demonstrating a functional glutaminergic receptor-mediated pathway in the nucleus, suggesting an excitatory action on the PA5 (Fior et al., 1993). Bilateral terminal fibers, connected to the paratrigeminal core was also observed in solitary tract nucleus, lateral reticular nucleus (LRT), ambiguous nucleus (Amb), rostroventrolateral reticular nucleus (RVL), beeing the vegetative actions explained by its projections (de Sousa Buck et al.; Caous et al., 2008). All binding sites of [125I Tyr8] BK located in the medulla regions mainly of the solitary tract nucleus (NTS) and subnuclear structures project to the core of the spinal trigeminal tract of rats as indicated elsewhere (Privitera et al., 2003). The present results show that treatment of capsaicin does not alter the B2 bradykinin receptor expression, suggesting that the response mediated kinin receptor is localized on sensory afferents affected by the neurotoxin. The change was not significant when compared with the control group, this observation can also be seen in the analysis of some medulla nuclei (PA5, NTS) and spinal cord using qPCR, RT and also in peripheral tissues such as the thoracic aorta and liver, in which the same result was found, with no significant difference between the groups. The distribution of binding sites was located in the spinal cord, aorta and medulla regions. Central pressor effect of bradykinin on the dorsolateral spinal cord was also demonstrated (Fior et al.). On the spinal cord of both control animals and animals treated, the specific connections are preferably in surface Rexed laminae I, II, III, VII and dorsal nucleus with B2 iodinated [125I] HPP-Hoe 140. Similarly the binding sites in the medulla are in the paratrigeminal nucleus, the solitary tract nucleus, spinal vestibular nucleus (SPVE), rostral ventrolateral nucleus (RVL), vestibular caudoventrolateral nucleus (CVL).

We also used the thoracic aorta, a well-vascularized area that possesses a lot of kinin B2 receptor. As a constitutive receptor, it was important to consider whether there would be differences in the expression and quantification of this receptor after capsaicin (França et al.). This hypothesis was supported by the B2 receptor involvement in nociception and antinociception (Calixto et al., 2001; 2004; Couture et al., 2001). The marking ion binding sites was observed in the fibers terminals associated with synaptic buttons in the nucleus ambiguus, and rostral ventrolateral nucleus (RVL) (Finley & Katz, 1992). Among the nuclei of the ventral medulla, for whom PA5 projections, the RVL is the most involved with the control of vasomotor tone (Caous et al., 2001). The spinal vestibular nucleus (SpVe), was analyzed by tracer and highlighted its connections to the spinal cord (Liang et al., 2015). In the spinal cord, the analysis of the binding sites present, suggests that cardiovascular regulation of bradykinin occurs (Ongali et al.). The occurrence of gene expression of B2 kinin receptor mRNA was verified by both in peripheral tissues and the central (PA5, NTS, aorta, liver and spinal cord). In the organ and tissues examined, the mRNA levels encoding for the B2 receptor kinin were analyzed using as internal control, the concentration of the b-actin mRNA. The high expression of RNA encoding for kinin receptors in the liver is due to the high organ irrigation (Couture et al., 2000).

In this study, we examine whether there would be differences in the expression and quantification of this receptor after treatment with capsaicin using qPCR, RT, which was obtained the same result, no significant difference between the groups, as occurred with autoradiography.

Among Central Nervous System structures, NTS, PA5 and spinal cord showed a greater amount of RNA encoding for the B2 kinin receptor. It is possible that the cerebral vasculature contributes to the localization and expression of this receptor. The qPCR-RT methodology and autoradiography used to distinguish respectively the mRNA and B2R kinin location in the medulla nuclei, spinal cord and peripheral tissues.

The results obtained with respect NTS, PA5, aorta and spinal cord have shown no significance with respect to control and treated animals. As noted in studies, the lesions C and A delta fibers do not prevent the actions of BK or alter isotopically-labeled radioligand (binding) the B2 receptor PA5 (Lindsey et al., 1997; Couture & Lindsey). These data plus the results of the present study, suggest that this receptor is not present inafferents fibers sensitive to capsaicin.

ACKNOWLEDGMENTS

The authors thank Dr. Hudson Buck from the Department of Physiology, Santa Casa de Misericordia, for conceding the use of the Image Analysis System (MCID, Imaging Research, São Paulo, Brasil) and for his kind help with quantification. Dr. João Bosco Pesquero to using qRT-PCR.

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Correspondence to:

Ricardo Luiz Smith M.D., PhD

Departamento de Morfologia e Genética
Escola Paulista de Medicina, UNIFESP
Rua Botucatú 740
CEP 04023-900, São Paulo, SP
BRASIL

Email: rlsmith@unifesp.br
camillaef@yahoo.ca

Received: 29-06-2016
Accepted: 17-10-2016

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