RESUMEN
Ever since the seminal studies of Hans Selye, activation of hypothalamus-pituitary-adrenal (HPA) axis is emblematic of stress. Consequently, the lack of HPA axis responses following the undisputable psychological stress of a panic attack stands out as one of the most intriguing findings of contemporary psychiatry. On the other hand, the defensive behaviors and aversive emotions produced by stimulation of the dorsal periaqueductal gray matter (DPAG) have been proposed as a model of panic attacks. Therefore, we examined whether the plasma levels of 'stress hormones' corticotropin and prolactin show any change following the DPAG-evoked freezing and flight behaviors of the rat. Rats bearing an electrode into the DPAG and an intra-atrial catheter were stimulated at 9:00 a.m., 18-24 h after the catheter implantation. Blood samples were withdrawn just before 1-min stimulation of DPAG, immediately after (5 or 15 min) and throughout 3 to 27 h following stimulation. In another experiment, samples were withdrawn either before or following a prolonged stimulation (5 min) of the DPAG with flight threshold intensity. Hormones were measured by either chemiluminescent or double-antibody immunoassays. Hormone plasma levels following freezing and flight behaviors were compared to those of resting or restraint-stressed rats. Data show that stress hormones remain unaltered following the DPAG-evoked defensive behaviors. Not even the 5-min stimulation of DPAG with the flight threshold intensity changed corticotropin plasma levels significantly. As far as we known, this is the first demonstration of the lack of stress hormone responses following the intense emotional arousal and physical exertion of a fear-like behavior in rats. Data add new evidence of DPAG involvement in spontaneous panic attacks.
Asunto(s)
Adaptación Psicológica/fisiología , Trastorno de Pánico/etiología , Estrés Fisiológico/fisiología , Hormona Adrenocorticotrópica/sangre , Animales , Mapeo Encefálico , Estimulación Eléctrica , Reacción de Fuga/efectos de los fármacos , Reacción de Fuga/fisiología , Reacción Cataléptica de Congelación/efectos de los fármacos , Reacción Cataléptica de Congelación/fisiología , Masculino , Modelos Biológicos , Monosacáridos de Poliisoprenil Fosfato/farmacología , Prolactina/sangre , Ratas , Ratas Wistar , Estimulación QuímicaRESUMEN
Microsomal membrane preparations from rat livers, when incubated with labelled sugar-nucleotides, were shown to synthesize labelled oligosaccharide-lipids in the presence of excess exogenous dolichyl phosphate. Under the incubation conditions defined in the present study, dolichyl pyrophosphoryl(DolPP)GlcNAc2-Man5, DolPPGlcNAc2Man9 and DolPPGlcNAc2Man9Glc3 were the principal oligosaccharide-lipids formed by both control and vitamin A-deficient membranes. However, deficient membranes synthesized 3.2 +/- 0.8 times as much oligosaccharide-lipids and 2.6 +/- 0.7 times as much dolichyl phosphate mannose (DolPMan) and dolichyl phosphate glucose (DolPGlc) as the controls. The transfer of the oligosaccharide chain from the dolichol carrier to the endogenous protein acceptors in vitamin A-deficient microsomes (microsomal fractions) was only 57.5 +/- 9.5% of that of controls. After endo-beta-N-acetylglucosaminidase treatment, only one oligosaccharide species was isolated from both control and vitamin A-deficient microsomal glycoproteins, and was characterized as GlcNAcMan9Glc3. We conclude that the decreased incorporation of labelled mannose and glucose from sugar-nucleotides into the glycoproteins must be due to decreased transfer of GlcNAc2Man9Glc3 from the dolichol carrier to the protein acceptors. This conclusion was further substantiated by the finding that control membranes transferred 4-6 times as much labelled oligosaccharides from exogenously added dolichol-linked substrate (DolPPGlcNAc2Man9Glc3) to endogenous microsomal protein acceptors as compared with the vitamin A-deficient membranes. Attempts to reverse this defect by addition of retinol or retinyl phosphate (a source of retinyl phosphate mannose) to the incubations were unsuccessful.
Asunto(s)
Glicoproteínas/biosíntesis , Microsomas Hepáticos/metabolismo , Vitamina A/metabolismo , Animales , Cromatografía Líquida de Alta Presión , Diterpenos , Fosfatos de Dolicol/farmacología , Glicosilación , Membranas Intracelulares/efectos de los fármacos , Membranas Intracelulares/metabolismo , Masculino , Microsomas Hepáticos/efectos de los fármacos , Oligosacáridos/análisis , Monosacáridos de Poliisoprenil Fosfato/farmacología , RatasRESUMEN
Dolichol phosphate-mannose (dol-P-mannose) has been shown previously to stimulate the reaction: dolichol phosphate + UDP-[3H]GlcNAc----[3H]GlcNAc-P-P-polyprenols (Kean, E. L. (1982) J. Biol. Chem. 257, 7952-7954). Further studies on this phenomenon are described, using microsomes from the retina of the embryonic chick as the major source of enzyme. Neither dolichol-P-glucose nor retinyl-P-mannose showed this stimulatory activity. Phosphatidylglycerol also stimulated this same process and was most active among a variety of phospholipids which were tested, in accord with previous reports. The presence of GDP-2-deoxy-2-fluoro-D-mannose or GTP had no effect on the reaction. The apparent activation constant for dolichol-P-mannose was 2.2 microM, and for phosphatidylglycerol, 401 microM. The major product (90% or greater) obtained under basal and stimulatory conditions was GlcNAc-P-P-dolichol and the site of the stimulatory effect was the glucosaminyltransferase catalyzing the formation of this compound. The effects of stimulation on the kinetic properties were similar for both activators: increases in the Vmax of the reactions of 7-10-fold; increases in apparent Km for UDP-GlcNAc of 5-7-fold; a 3-fold decrease in apparent Km for dolichol-phosphate. When present together, a mutual inhibition of stimulation was observed compared to the additive effect from dol-P-mannose or phosphatidylglycerol alone. Although a substrate for the reaction, dolichol phosphate repressed the stimulation by dolichol-P-mannose but not that by phosphatidylglycerol. Dol-P-glucose, while not an activator of the reaction, acted as a negative modifier of the stimulation by dol-P-mannose by acting as a competitive inhibitor of the stimulation. The stimulatory phenomenon was observed in microsomes prepared from a variety of tissues from the embryonic chick and from postnatal tissue after partial delipidation. The addition of pyrophosphatase inhibitors did not bring about stimulation of GlcNAc-lipid synthesis, but did enhance the effect. These studies extend the previous observations of the participation of dolichol-P-mannose and phosphatidylglycerol as allosteric activators of GlcNAc-lipid synthesis and indicate additional aspects of metabolic regulation of the dolichol pathway.