Serotonin at the laterodorsal tegmental nucleus suppresses rapid-eye-movement sleep in freely behaving rats

Serotonin [5-hydroxytryptamine (5-HT)] is believed to play an important inhibitory role in the regulation of rapid-eye-movement (REM) sleep. 5-HT may exert this effect on neurons of the laterodorsal tegmental (LDT) nuclei that are implicated as important in the generation of REM sleep and phasic REM events such as ponto-geniculo-occipital (PGO) waves and respiratory variability. In rat brainstem in vitro, 5-HT hyperpolarizes and inhibits the bursting properties of LDT neurons assumed to be involved in generating REM sleep and PGO waves. This study tests the hypothesis that in vivo 5-HT at the LDT nuclei suppresses REM sleep and phasic REM events. Ten rats were implanted with bilateral cannulae aimed at the LDT and with electrodes for recording the electroencephalogram, neck electromyogram, PGO waves, and diaphragm electromyogram. During REM sleep, 5-HT (100 nl; 1-1.5 mM), saline, or sham microinjections were performed; repeated microinjections were separated by approximately 1 hr. After the first microinjection, REM sleep as a percent of the total sleep time was reduced with 5-HT (mean percent REM, 19.9 +/- 2.5% for 5-HT vs 26.8 +/- 2.4% for saline; p = 0.02). REM duration was reduced by 37% with 5-HT (p = 0.01), but REM episode frequency was changed less consistently (p = 0.21), suggesting that 5-HT mainly disrupted REM sleep maintenance. Per unit time of REM sleep, 5-HT had no effect on the amount or variability of REM PGO activity (p > 0.740) or on the mean or coefficient of variation of REM respiratory rate (p > 0.11). With subsequent microinjections, the effects of 5-HT on REM sleep were similar. A dose-dependent REM sleep suppression with 5-HT was observed in five rats tested. These data suggest that in vivo 5-HT at the LDT nuclei suppresses REM sleep expression. Although 5-HT did not disproportionately reduce the occurrence of phasic events within REM, total REM phasic activity was reduced because of less REM sleep after 5-HT.

Topography of ligand-induced binding sites, including a novel cation-sensitive epitope (AP5) at the amino terminus, of the human integrin beta 3 subunit

Changes in ligand binding ability of the integrin alpha IIb beta 3 can be monitored by the concomitant expression of ligand-inducible binding sites (LIBS). A new LIBS, the hexapeptide sequence GPNICT (residues 1-6) at the amino terminus of beta 3 recognized by the murine monoclonal antibody (mAb) AP5, is sensitive both to the binding of ligand and to micromolar differences in divalent cation levels. Calcium or magnesium can completely inhibit the binding of AP5 to alpha IIb beta 3 on platelets, with ID50 values of 80 and 1500 microM, respectively. The inhibitory effect of calcium plus magnesium is cumulative. In the presence of 1 mM calcium plus 1 mM magnesium, the peptide RGDW overcomes this inhibition and induces maximal binding of AP5. Maximal AP5 binding is also induced by a molar excess of EDTA. The unique location of the AP5 LIBS was determined by comparing the binding of LIBS-specific mAb to recombinant human-Xenopus beta 3 chimeras produced in a baculovirus expression system. AP5 defines one region at the amino terminus beta 3 1-6. A second region, defined by mAb D3GP3, is probably located within beta 3 422-490, confirming the finding of Kouns et al. (Kouns, W. C., Newman, P.J., Puckett, K. J., Miller, A. A., Wall, C. D., Fox, C. F., Seyer, J. M., and Jennings, L. K. (1991) Blood 78, 3215-3223). The third region, encompassing at most residues 490-690, and perhaps more precisely located within 602-690 (Du X., Gu, M., Weise, J. W., Nagaswami, C., Bennett, J. S., Bowditch, R., and Ginsberg, M. H. (1993) J. Biol. Chem. 268, 23087-23092), is recognized by the four mAb, anti-LIBS2, anti-LIBS3, anti-LIBS6, and P41. Since its exposure is uniquely regulated by both divalent cations and ligand, the amino terminus of beta 3 may be involved in control of ligand binding by divalent cation mobilization.

Variability of integrin alpha 2 beta 1 activity on human platelets

The activity and surface antigenicity of alpha 2 beta 1 on platelets from 27 normal subjects were found to vary significantly. A fourfold range of surface antigen correlates with a 20-fold variation in the ability of nonactivated, washed platelets to adhere to type I collagen and a fivefold variation in the adhesion of platelets to type III collagen. These differences in surface receptor are reflected in significant variation in the lag time required for type I collagen-induced platelet aggregation in platelet-rich plasma. Among the same individuals, no difference was observed in surface levels or activities of two other platelet integrins, the fibronectin receptor alpha 5 beta 1 and the fibrinogen receptor alpha IIb beta 3. In all cases studied, we observed complimentary differences in the incorporation of 125I into surface alpha 2 beta 1, in quantity of surface alpha 2 beta 1 antigens, and in alpha 2 beta 1 collagen receptor activity. Despite variations in these parameters, there was no difference in the electrophoretic mobility or isoelectric point of either integrin subunit among the individuals studied. The wide range of activity and antigenicity of this platelet collagen receptor may result from polymorphism(s) in the alpha 2 beta 1 genes, or the activity of alpha 2 beta 1 may be variably regulated by another gene product. The heterogeneity of platelet alpha 2 beta 1 that we describe in this report certainly explains previous discrepancies concerning the contributions of this integrin to platelet adhesion to collagens. Most importantly, differences in surface collagen receptor activity may correlate with a long-term risk toward thrombosis, impaired hemostasis, and/or cardiovascular disease.

Evaluation of soft tissue response to a poly(urethane urea)

Variations in the performance of vascular prostheses constructed of polyurethanes, and some evidence which suggested that these variations could be due not to the properties of the polymer itself, but to differences in the cellular response to the various microstructures of porous polyurethanes require investigation. Experiments were performed to evaluate quantitatively the extent of the cell behaviour adjacent to a series of polyurethane samples. It was shown that, with Biomer, a polyurethane urea, the profile of cell behaviour as a function of distance from the implant surface and of time following implantation, the response of cells in general and macrophages in particular, varied considerably with different internal microstructure. This supports the suggestion that the cellular response to different structures and susceptibility to degradation are related.

Effect of compliance mismatch on flow disturbances in a model of an arterial graft replacement

Flow disturbances in a model of an interposition graft in an arterial segment were measured using an ultrasound Doppler velocimeter. The effect of the degree of compliance mismatch between a stiff' graft' and compliant 'arterial' segments was investigated. In steady flow, disturbances were detected when the compliance ratio (stiff to compliant segments) was less than or equal to 0.1 and the Reynolds number greater than or equal to 2200. A recirculation zone just downstream of the distal anastomosis was observed at a Reynolds number greater than or equal to 2400. Disturbances were also measured under pulsatile flow which consisted of a time-varying component superimposed on a steady flow component. The time-varying flow component was either quasiphysiological or sinusoidal in shape. The Reynolds number was 500 but the frequency parameter varied from 4.2 to 8.5. Significant disturbances were observed for conduits with compliance ratio less than or equal to 0.19. The disturbance intensity tended to increase as the compliance ratio decreased and the frequency parameter increased. The magnitude of the disturbance was also greater with the quasiphysiological than the sinusoidal input flow waveform.

A two year study of the performance of a small diameter polyurethane (Biomer) arterial prosthesis

The performance of a new compliant microfibrous polyetherurethane urea (Biomer) synthetic artery of our design has been studied in a series of 26 consecutive implants as carotid artery replacements in dogs. A 4 cm length of carotid artery was excised and replaced by a similar length of the synthetic artery. All implants were performed by the same surgeon (LdeC). Twelve interrupted sutures of 6/0 "Prolene" were used to fashion both end-to-end anastomoses. Assessments of patency of the grafts was made using fortnightly Toshiba B scan ultrasound with linked Doppler shift waveform analysis. Twenty-six grafts were implanted. Seventeen grafts have remained patent for periods in excess of 24 months. Five failed acutely (within 2 weeks), 4 failed between the 59th and 201st day. Sixteen of those grafts that remained patent for more than 24 months have been removed for histopathological examination, which has demonstrated a limited extension of a new intima on to the inner surface of the grafts. The new intima is firmly attached and shows no sign of pseudo-intimal hyperplasia. The inner surface, uncovered by neointima, nevertheless, has extensive endothelial cover. Of practical importance are the excellent handling qualities of the graft. It cuts cleanly without fraying and a stitch placed 1 mm from the cut end of the graft will hold securely. There is no needle hole bleeding. The graft has both axial and circumferential compliance similar to that of the natural artery it replaces.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of pressure losses in steady non-Newtonian flow through experimental tapered and cylindrical arterial prostheses

The use of an arterial prosthesis with a tapered lumen has several important advantages; for example, improved stability of flow, increased wall shear and better matching of its size with that of the host vessel. Tapering may, however, lead to increased energy losses, particularly if the angle of taper is large and the flow is high. This study is concerned with the determination of pressure drop for steady and laminar converging flow through rigid wall models of tapered arterial grafts. The angles of taper examined ranged from 0.5 degrees to 1.0 degrees. Aqueous solutions of polyacrylamide, with non-Newtonian viscous properties similar to those of blood, were used. The pressure drops across the tapered tubes were measured and the data were related to the pressure loss in cylindrical tubes of equivalent dimensions. Expressions for the ratio of the pressure drop in a tapered tube to that in a cylindrical tube for steady flow of a power law fluid were derived; there was good agreement between the predicted and the measured pressure drop ratios over a wide range of flows. The results of this study may be applied to the design of tapered arterial grafts. The pressure losses to be expected in tapered bypass grafts having various dimensions can easily be computed.

Viscoelastic behavior of polyurethane vascular prostheses

A method of evaluating the in vitro viscoelastic properties of microfibrous Biomer poly(ether-urethane-urea) vascular prostheses is outlined. Quasi-static and dynamic tests were carried out on Biomer grafts of diameter between 3.4 mm and 3.8 mm and wall thickness between 0.25 mm and 0.55 mm. It is shown that the quasi-static compliance of a Biomer graft may be determined from an equation relating transmural pressure, radius, and longitudinal strains in terms of the graft dimensions and material constants. The dynamic compliance spectra were evaluated as a function of the longitudinal and circumferential strains and temperature. Although the ratio of dynamic compliance to quasi-static compliance was linearly related to the logarithm of frequency it was not significantly affected by strains or temperature over the relevant ranges studied. Employing the usual assumptions of linear isotropic incremental elastic theory the dynamic elastic and viscous moduli were calculated as a function of frequency. Biomer grafts were more viscous than canine carotid and femoral arteries, especially at the higher frequencies. The variation in the ratio of dynamic to static incremental modulus with frequency was similar to that observed in the femoral arteries by Bergel (J. Physiol., 156, 458-469 (1961)).

Polyether-urethane elastomers for small-diameter arterial prostheses

Textile polymers have been used for the manufacture of synthetic arterial prostheses. The extreme rigidity of these polymers has severely limited the nature of the structures that could be fabricated, so that the mechanical properties and structural form of the prostheses bear little resemblance to those of natural arteries. The variety of chemical structures, of mechanical properties and of means of fabrication make it possible to produce a compliant flexible prosthesis having a more delicate structure, thereby acquiring better tissue and blood compatibility and good long-term durability. These, and an acceptable form that encourages good surgical practice, account for the good performance of the prosthesis. By way of illustration, an electrostatically spun microfibrous arterial prosthesis of small diameter is described. It is made of a polyether-urethane urea (Biomer). We report good two-year patency for arterial prostheses of our design used to replace the common carotid artery in dogs.

Infrared diameter gauge for in vitro mechanical testing of vascular grafts

A diameter gauge employing modulated infrared radiation has been developed for in vitro mechanical testing of small diameter vascular grafts. A linear range of greater than 6 mm has been achieved using a 100 mm2 photodiode. The device is immune to ambient illumination. Temperature stability has been greatly improved by using a simple closed-loop control circuit. The pressure-diameter relationship of a polyurethane artery graft, 4 mm internal diameter, has been determined under static and dynamic loading. The results show that the distensibility of the graft is relatively constant up to about 6 Hz but increases rapidly at frequencies greater than 10 Hz.

Ultrasonic scanning of the thyroid gland as a guide to the treatment of the clinically solitary nodule

This study examines the diagnostic accuracy of ultrasonic scanning in the recognition of multinodular goitre in 87 patients referred for examination who were thought by the referring clinician to have a single nodule in the thyroid gland. Twenty-five were found to have multinodular glands, 23 of which were correctly identified by ultrasound. Of those who had truly solitary nodules, ultrasonic scanning enabled us to identify all 23 who had cystic lesions and 35 out of the 39 who had predominantly solid lesions. The clinical significance of these observations in the management of patients with so-called 'single nodules' is discussed.

A sterile 'use-once' clip applicator for skin closure

A sterile disposable applicator for skin clips has been used for the closure of skin incisions in 117 consecutive operations. These have included most of the standard incisions in the head, neck, trunk, and limbs. The instrument has proved satisfactory in use, the skin incisions having healed satisfactorily with much time having been saved in their closure.