Effects of ghrelin on neuronal activity in the ventromedial nucleus of the hypothalamus in infantile rats: An in vitro study

Ghrelin is an endogenous ligand for the growth hormone (GH) secretagogue (GHS) receptor (GHS-R) and a potent stimulant for GH secretion even in infantile rats before puberty. Although the ventromedial nucleus of the hypothalamus (VMH) might be a site of action for ghrelin to induce GH release, the electrophysiological effect of ghrelin on VMH neurons in infantile rats remains to be elucidated. Thus, the purpose of the present study was to investigate the effect of ghrelin on VMH neurons using hypothalamic slices of infantile rats. Ghrelin excited a majority of VMH neurons in a concentration-dependent manner. VMH neurons that were excited by GH releasing peptide-6 (GHRP-6), a synthetic GHS, were also excited by ghrelin and vice versa. Repeated application of ghrelin to the same VMH neuron decreased progressively the excitatory responses depending on the number of times it was administered. The excitatory effect of ghrelin on VMH neurons in normal artificial cerebrospinal fluid (ACSF) persisted in low Ca²⁺-high Mg²⁺ ACSF. The present results indicate that (1) ghrelin excites a majority of VMH neurons dose-dependently and postsynaptically and (2) the excitatory effects of ghrelin are mimicked by GHRP-6 and desensitized by repeated applications of ghrelin.     

Alloreactivity against IE-encoded antigens: evidence of the discrepancy between graft rejection and reactivity of IE-reactive T cells.

Participation of IE antigens (Ag) in immune response as the transplantation Ag was examined. IE- B10.A(4R)(4R; Kk, IAk, IE-, Db) mice could not reject skin graft from IE Ag alone-disparate B10.A(2R) (2R; Kk, IAk, IEk, Db) mice despite intravenous (iv) injection of 2R spleen cells (SC) before or after skin grafting, indicating that graft rejection could not be caused across IE Ag-barrier alone. Furthermore, 4R SC could not induce lethal graft-versus-host disease (GVHD) in supralethally (950 rad) irradiated 2R mice. On the other hand, infiltration of lymphoid cells was observed at the site of transplanted 2R skin in 4R mice. SC of 4R mice unprimed or primed with 2R skin or 2R SC showed the capability to proliferate in vitro in response to 2R Ag. In immunofluorescence analysis of lymph node cells (LNC) of 4R mice injected iv with 2R SC 7 days earlier, IE-reactive CD4+Vbeta 11+ T cells did not change in number, but slightly increased the expression of interleukin-2 receptor (IL-2R). In 2R mice irradiated with 670 rad and injected iv with 4R SC 7 days earlier, 4R-derived CD4+V beta 11+ T cells proliferated, changed to blastoid form, and showed a markedly increased expression of IL-2R. To further investigate the influence of IE alloantigens on transplantation immunity, IL-2 production and anti-class I CTL activity were assayed. The 4R SC capable of recognizing IEk and Dk Ag of B10.BR (Kk, IAk, IEk, Dk) generated levels of both IL-2 and CTL activities higher than those of 2R SC capable of recognizing Dk Ag alone. These results strongly suggest that IE alloantigens indirectly act as the transplantation Ag by the stimulation of IE-reactive CD4+ helper T cells resulting in the differentiation of class I-restricted CD8+ T cells.     

Low responsiveness of human neonatal lymphocytes to a B-cell mitogen, Staphylococcus aureus Cowan I (SpA CoI)

Responses of neonatal and adult lymphocytes to various mitogens were studied. Lymphocytes from umbilical cord blood (UCB) responded well to both phytohemagglutinin and concanavalin A, and also to pokeweed mitogen and Staphylococcus aureus Protein A. The responses of UCB lymphocytes to these mitogens were not significantly lower than those of adult peripheral blood lymphocytes (PBL). In contrast, UCB lymphocytes showed only a minimal response to killed Staphylococcus aureus Cowan I (SpA CoI), a potent B-cell mitogen for human PBL, although the proportion of B cells in UCB was not less than that in PBL. The low level of response of lymphocytes from UCB to SpA CoI was not ascribed to differences in dose response or kinetics. Purified B cells from UCB were not stimulated by SpA CoI either, suggesting tht the low responsiveness was not due to the suppressive effect of T cells or macrophages, but to some intrinsic defect in B cells in UCB. These results suggest that the B cells in neonates may be more immature than the T cells.     

Immune deficiency in the X-linked lymphoproliferative syndrome. I. Epstein-Barr virus-specific defects

Eleven males with XLP were evaluated for EBV-specific antibodies during periods of 2 to 7 yr. Variable responses to EBV-specific antigens were found. All 11 patients had subnormal anti-EBNA titers, which probably reflected a T cell deficiency. The patients showed four different patterns in their anti-VCA response: 1) two boys who had experienced malignant lymphoma mounted no antibodies at all; 2) two patients showed intermittent anti-VCA titers; 3) four males had persistently elevated anti-VCA titers; and 4) three patients showed normal anti-VCA titers. ADCC against EBV-infected cells was abnormally low in six patients and was elevated in two patients given gamma-globulin. ADCC titers did not correlate with anti-VCA titers. However, most patients with XLP failed to effect regression of autologous EBV-infected lymphoblastoid cell lines, indicating a deficiency in long-lived T cell-mediated immunity to EBV.     

OmpF channel permeability of quinolones and their comparison with β-lactams

The diffusion rates of nalidixic acid, ofloxacin and ofloxacin's two optically active isomers through OmpF channels were measured in proteoliposomes and compared with the rates of beta-lactams. The four quinolones showed high diffusion rates, exceeding that of cephaloridine and being comparable to imipenem. There was no significant difference in diffusion rate between nalidixic acid and ofloxacin, or between the two optically active isomers. The diffusion rates of enoxacin and norfloxacin were also estimated to be higher than many beta-lactams.     

fist: an Arabidopsis mutant with altered cell division planes and radial pattern disruption during embryogenesis

A T-DNA-tagged, embryo-defective Arabidopsis thaliana mutant, fist, was identified and shown to exhibit defects in nuclear positioning and cell division orientation beginning at the four-cell stage of the embryo proper. Cell division orientation was randomised, with each embryo exhibiting a different pattern. Periclinal divisions did not occur after the eight-cell embryo proper stage and fist embryos lacked a histologically distinct protoderm layer. Terminal embryos resembled globular-stage embryos, but were a disorganised mass containing 30–100 cells. Some terminal embryos (5%) developed xylem-like elements in outer surface cells, indicating that the fist mutation affects radial pattern. A soybean β-conglycinin seed storage protein gene promoter, active in wild-type embryos from heart stage to maturity, was also active in terminal fist embryos despite their disorganised globular state. This indicated that some pathways of cellular differentiation in fist embryos proceed independently of both organised division plane orientation and normal morphogenesis. Endosperm morphogenesis in seeds containing terminal fist embryos was arrested at one of three distinct developmental stages and appeared unlinked to fist embryo morphogenesis. The β-conglycinin seed storage protein gene promoter, normally active in cellularised wild-type endosperm, was inactive in fist endosperm, indicating abnormal development of fist endosperm at the biochemical level. These data indicate that the fist mutation, either directly or indirectly, results in defects in cell division orientation during the early stages of Arabidopsis embryo development. Other aspects of the fist phenotype, such as defects in endosperm development and radial pattern formation, may be related to abnormal cell division orientation or may occur as pleiotropic effects of the fist mutation. Received: 15 July 1997 / Accepted: 9 September 1997     

Identification of two novel arginine binding DNAs.

RNA tertiary structure is known to play critical roles in RNA-protein recognition and RNA function. To examine how DNA tertiary structure might relate to RNA structure, we performed in vitro selection experiments to identify single-stranded DNAs that specifically bind arginine, and compared the results with analogous experiments performed with RNA. In the case of RNA, a motif related to the arginine binding site in human immunodeficiency virus TAR RNA was commonly found, whereas in the case of DNA, two novel motifs and no TAR-like structures were found. One DNA motif, found in approximately 40% of the cloned sequences, forms of hairpin structure with a highly conserved 10 nucleotide loop, whereas the second motif is especially rich in G residues. Chemical interference and mutagenesis experiments identified nucleotides in both motifs that form specific arginine binding sites, and dimethylsulfate footprinting experiments identified single guanine residues in both that are protected from methylation in the presence of arginine, suggesting possible sites of arginine contact or conformational changes in the DNAs. Circular dichroism experiments indicated that both DNAs undergo conformational changes upon arginine binding and that the arginine guanidinium group alone is responsible for binding. A model for the G-rich motif is proposed in which mixed guanine and adenine quartets may form a novel DNA structure. Arginine binding DNAs and RNAs should provide useful model systems for studying nucleic acid tertiary structure.