Yasutomo Iwai-Liao

Stress-induced hyperalgesia: animal models and putative mechanisms.

Stress has been shown to affect brain activity and promote long-term changes in multiple neural systems. A variety of environmental and/or stressful stimuli have been shown to produce analgesia, a phenomenon often referred to as stress-induced analgesia (SIA). However, acute and chronic stresses also produce hyperalgesia in various behavioral tests. There are now several animal models in which stress enhances nociceptive responses. The dysfunction of the hypothalamo-pituitary-adrenocortical axis (HPA axis) and multiple neurotransmitter systems in the central nervous system (CNS), including endogenous opioid, serotonergic and noradrenergic systems, has been reported. These stress-induced hyperalgesia models may contribute to a better understanding of chronic pain and provide a more rational basis for drug therapies in a variety of pain syndromes.

The effects of acute and chronic restraint stress on activation of ERK in the rostral ventromedial medulla and locus coeruleus

&NA; Extracellular signal‐regulated kinase (ERK) is a key molecule in numerous cellular and physiological processes in the CNS. Exposure to stressors causes substantial effects on the perception and response to pain. The rostral ventromedial medulla (RVM) and the locus coeruleus (LC) play crucial roles in descending pain modulation system. In the present study, the activation of ERK in the RVM and the LC in rats following acute and chronic restraint stress was examined in order to characterize the mechanisms underlying stress induced analgesic and hyperalgesic responses. Rats were stressed by restraint 6 h daily for 3 weeks. The acute and chronic restraint stresses produced analgesic and hyperalgesic reactions, respectively, to thermal stimuli applied to the tail. The phospho‐ERK‐immunoreactive (p‐ERK‐IR) neurons were observed in the nucleus raphe magnus (NRM), nucleus reticularis gigantocellularis pars alpha (GiA) and LC. In the RVM, the number of p‐ERK‐IR neurons per section in the 3‐week restraint rats (14.3±1.2) was significantly higher than that in the control rats (8.9±0.7) [P<0.01]. About 75% of p‐ERK‐IR neurons in the RVM in the 3‐week restraint rats were serotonergic neurons. Protein levels of tryptophan hydroxylase were significantly increased in the RVM region in the 3‐week restraint rats. On the other hand, the chronic restraint stress significantly decreased p‐ERK‐IR in the LC [P<0.05]. These findings suggest that chronic restraint stress‐induced activation of ERK in the RVM and the suppression in the LC may be involved in the modulation of the pain threshold by chronic stress.

Effects of peripheral inflammation on activation of ERK in the rostral ventromedial medulla.

In the present study, the activation of extracellular signal-regulated kinase (ERK) in the rostral ventromedial medulla (RVM) following the injection of complete Freunds adjuvant (CFA) into the rat hindpaw was examined in order to clarify the mechanisms underlying the dynamic changes in the descending pain modulatory system after peripheral inflammation. Phospho-extracellular signal-regulated kinase-immunoreactive (p-ERK-IR) neurons were observed in the nucleus raphe magnus (NRM) and nucleus reticularis gigantocellularis pars alpha (GiA). Inflammation induced the activation of ERK in the RVM, with a peak at 7 h after the injection of CFA into the hindpaw and a duration of 24 h. In the RVM, the number of p-ERK-IR neurons per section in rats killed at 7 h after CFA injection (14.2 +/- 1.7) was significantly higher than that in the control group (4.5 +/- 0.9) [P < 0.01]. At 7 h after CFA injection, about 60% of p-ERK-IR neurons in the RVM were serotonergic neurons. The percentage of RVM serotonergic neurons that are also p-ERK positive in the rats with inflammation (20.5% +/- 2.3%) was seven times higher than that in control rats (2.7% +/- 1.4%) [P < 0.01]. These findings suggest that inflammation-induced activation of ERK in the RVM may be involved in the plasticity in the descending pain modulatory system following inflammation.

Effects of peripheral inflammation on activation of p38 mitogen-activated protein kinase in the rostral ventromedial medulla.

In the present study, the activation of p38 mitogen-activated protein kinase (p38 MAPK) in the rostral ventromedial medulla (RVM) following the injection of complete Freunds adjuvant (CFA) into the rat hindpaw was examined in order to clarify the mechanisms underlying the dynamic changes in the descending pain modulatory system after peripheral inflammation. Phospho-p38 MAPK-immunoreactive (p-p38 MAPK-IR) neurons were observed in the nucleus raphe magnus (NRM) and nucleus reticularis gigantocellularis pars alpha (GiA). Inflammation induced the activation of p38 MAPK in the RVM, with a peak at 30 min after the injection of CFA into the hindpaw, which lasted for 1 h. In the RVM, the number of p-p38 MAPK-IR neurons per section in rats killed at 30 min after CFA injection (19.4+/-2.0) was significantly higher than that in the naive group (8.4+/-2.4) [p<0.05]. At 30 min after CFA injection, about 40% of p-p38 MAPK-IR neurons in the RVM were serotonergic neurons (tryptophan hydroxylase, TPH, positive) and about 70% of TPH-IR neurons in the RVM were p-p38 MAPK positive. The number of p-p38 MAPK- and TPH-double-positive RVM neurons in the rats with inflammation was significantly higher than that in naive rats [p<0.05]. These findings suggest that inflammation-induced activation of p38 MAPK in the RVM may be involved in the plasticity in the descending pain modulatory system following inflammation.

Fourier Analysis of Maxillary Dental Arch Forms

Our previous principal component analysis conducting on reference points, lines and angles, and a vector-developed polar coordinate system has elucidated that the components of eigenvectors had positive relationships in the curvature of anterior teeth segment, between the protrusion of canines and degree of arch roundness, and in the length-to-width ratio of 62 maxillary dentitions, which were preliminarily classified with reference to the conventional Thompson’s morphological descriptions for dental arch forms. In the present study on morphological characters of the maxillary dentitions, we conducted a Fourier analysis on the previously obtained data. We observed that the amplitude of 2 nd , 3 rd and 4 th Fourier harmonics were closely correlated with the length-to-width ratio, curvature of the anterior teeth segment, and the curvilinear contour of maxillary dental arches. In addition, the relationships between previously estimated data and the constant value and the amplitude of the Fourier series were examined by analysis of correlation coefficients(p＜0.01). The results of the present study suggest that the morphology of maxillary dentitions consists of three essentials-the length-to-width ratio, the curvature of anterior teeth and the curvilinear contour of dental arches.

Classification of Mandibular Dental Arches by Correlation and Principal Component Analyses

PURPOSE To evaluate the morphology of dental arches. METHODS 62 (male: 36, female: 26) paired casts having normal dentitions and occlusion were selected from 396 (age: 18 to 26 years old; male: 257, female: 139) sets of dental study models. The maxillary dentitions were preliminarily classified as square, round-square, round and round V-shaped arches based on the conventional morphological descriptions. Midpoints of the incisor edge (I1(R), I1(L), I2(R), &I2(L)), summits of the cuspids (C(R) & C(L)), buccal cusps of the premolars (P1(R), P1(L), P2(R), & P2(L)), mesial buccal cusps of the first and second molars (M1(R), M1(L), M2(R), & M2(L)), and the midpoint (A) of line I1(R)-I1(L) were designated as reference points. From A, let a vertical line intersected line M2(R)-M2(L) at reference point B. The line A-B intersected CR-CL at reference point E. The following items were evaluated: (1) the protrusion of the cuspids by 1. angle I2(R)-C(R)-P1(R) (angle R) + angle I2(L)-C(L)-P1(L) (angle L); (2) the curvature of the anterior teeth by 2. A-B/C(R)-C(L), 3. 180 degrees-angle C(R)-A-C(L), and 4. A-E/C(R)-C(L); (3) the length to width ratio of the dental arch by 5. A-B/M2(R)-M2(L); (4) the degree of roundness of the maxillary arch by estimation of 6. (rtheta(5)-rtheta(4))(R)+(rtheta(5)-rtheta(4))(L); and (5) an item 7. for the differentiation of type I and type II round-square arches by relating the bilateral contour and position of break line P1-P2-M1-M2 (i) to line P1-M2 (ii). The data of items 1, 2, 3, 4, 5, and 6 were further standardized and summarized into three essential principal components: (1) the curvature of the anterior teeth, (2) the curvilinear contour of the dental arch, and (3) the length-to-width ratio of the dental arch. RESULTS (1) 60% of the maxillary dentitions were round-square arches which showed no prominent principal component; (2) square maxillary arches distinctly showed a small 1. angle R+angle L; (3) round arches were characteristic by small 6 (rtheta(5)-rtheta(4))(R)+(rtheta(5)-rtheta(4))(L) values; and (4) round V-shaped arches had large 2, 3 and 4 values. CONCLUSIONS We concluded that parameters 1, 2, 3, 4, 5, 6 and 7 were summarized into three principal components (first principal component, second principal component and third principal component). Through three principal component analysis, we can quickly evaluate the morphology of the dental arches clinically. This methods is simple and of validity. And we can also obtain the characteristics of maxillary dental arches.

Histological Study of Genesis of the Mice Oral Vestibule

Background: Both the vestibular lamina (VL) and dental lamina (DL) develop from the primary epithelial band of the oral cavity. Previous studies have reported that VL and DL were initiated by certain epithelial-mesenchymal interactions between the primary epithelial band of the oral cavity and underlying mesenchyme; however, the exact mechanisms remain to be elucidated. Aims: Here we studied how the retinoblastoma (Rb) family and E2 promoter binding factor (E2F) regulate signals that control and regulate the proliferation and differentiation of the VL leading to the formation of the oral vestibule. Methods: Immunohistochemical light microscopy by the enhanced polymer one-step staining(EPOS) method and confocal laser scanning microscopy by the LsAB labelled streptavidin biotin (LSAB) method were performed on the developing vestibular lamina(VL) of fetal mice at stages from 11 days after fertilization E11 to E14.The immunohistochemical findings were compared with the findings in the developing dental lamina (DL) and tooth germ. Conventional transmission electron microscopy was performed on the E13 fetuses, in an effort to elucidate the differentiation of keratocytes in the developing VL. Results: We found that: 1) EGF, TGF , EGFR, PCNA, FGF2, pRb, and FGFR1-4 were immunolocalized in the developing tissues. 2) Cytokine expression patterns indicated that the EGF family and FGF2 essentially induced VL generation and cell proliferation. 3) FGFR1 as diffusely localized in the primary epithelial band, but was strongly expressed in the E12-14 VL and DL/enamel organ. By contrast, EGFR internalization was observed in the differentiating E13 VL. 4) Expression of pRb was intensely localized in the suprabasal layer of the E13 VL corresponding to CK-10 expression and keratohyaline-containing structures in the VL stratum germinativum cells. Conclusions: We suggest a mechanism in which FGFR1 regulates pRb to induce proliferation of cells in the VL and DL/enamel organ, and, in particular, to incite keratocyte differentiation and subsequent exfoliation of keratinizing VL cells.