An appraisal of low-temperature embedding by progressive lowering of temperature into Lowicryl HM20 for immunocytochemical studies

The progressive lowering of temperature (PLT) method of embedding for electron microscope immunolabelling has been examined with the objective of formulating a standardized protocol which can be applied to a wide variety of samples. The methods described cover fixation, processing of samples by the PLT method, embedding in Lowicryl HM20 and subsequent immunolabelling. Each of the steps in the fixation and embedding protocol has been assessed for its potential to retain both morphology and antigenicity. Comparison of samples embedded in Lowicryl K4M and HM20 at -25 degrees C indicate an increased membrane contrast in HM20 sections, and a further improvement in morphology when samples were embedded in HM20 at -50 degrees C rather than at -25 degrees C. The results of applying the methods described are demonstrated in a range of samples of both mammalian and botanical origin, which includes solid tissues, cells in suspension, and cells grown in vitro as a monolayer culture and embedded in situ. Samples processed by this method have been immunolabelled using a wide range of antibodies recognizing nuclear, cytoplasmic, cell membrane and extracellular matrix antigens.

Genetic transformation of Norway spruce (Picea abies (L.) Karst) using somatic embryo explants by microprojectile bombardment

Stable transformation of Norway spruce tissue has been obtained following bombardment of mature somatic embryos with pRT99gus, a plasmid that contains neo coding for NPTII, and gusA, coding for beta-glucuronidase, both fused to the CaMV 35S promoter. At least 8 lines have been stably transformed (over 15 months in culture) following bombardment and selection on kanamycin. Polymerase chain reaction analyses showed a high frequency of cotransformation of the gusA and neo genes. The frequency of coexpression of the selected and unselected markers was 100%. DNA/DNA hybridization of one transformed line provided conclusive evidence of stable integration and showed copy numbers of over 10 plasmid sequences per genome. None of the transformed lines has remained embryogenic.

Apoptosis in interleukin-3-dependent haemopoietic cells. Quantification by two flow cytometric methods

The murine haemopoietic cell line, BAF3, undergoes apoptosis when the growth factor IL-3 is withdrawn. Two flow cytometric methods for quantifying the apoptotic cells are described. Cell sorting followed by DNA gel electrophoresis, and both light and electron microscopy have been used to identify the apoptotic cells. In the first method the cells are fixed in ethanol, stained with propidium iodide and a DNA histogram recorded. The apoptotic cells give a 'sub-G1' peak. In the second method unfixed cells are incubated with the bis-benzimidazole, Hoechst 33342. The apoptotic cells take up this dye more rapidly. In this latter method, the non-viable cells can also be enumerated by addition of propidium iodide. The value of the method has been demonstrated in a brief study of the effects of a panel of cytokines on growth and apoptosis.

Orthostatic hypotension of prolonged weightlessness: clinical models

Orthostatic intolerance on return from space is a widely known consequence of space travel. Development of countermeasures against this problem is a major priority of the field of space physiology and medicine. The bedrest model is widely used in the investigation of this phenomenon, and has provided important data, but questions remain. In this article, we suggest that the disorders that produce chronic orthostatic hypotension have significant potential as models of microgravity-induced orthostatic intolerance. Understanding the pathophysiology of these syndromes may be useful to those involved in improving the operational aspects of manned space flight; four such syndromes and their possible relevance to space flight are described.

Chronic hypotension. In the shadow of hypertension

Understanding the causes and treatment of chronic hypotension is of benefit to affected patients and may also shed light on the physiology and genetics of mechanisms of blood pressure control. Symptomatic hypotension (almost always with a blood pressure fall greater than or equal to 20/10 mm Hg) may reflect unrecognized medication effects or a variety of other causes. Autonomic neuropathies include those secondary to diabetes, peripheral autonomic impairment (the Bradbury-Eggleston syndrome), central autonomic impairment (the Shy-Drager syndrome), or newly described gene defects such as dopamine-beta-hydroxylase deficiency (which causes the absence of norepinephrine with an accumulation of dopamine). Baroreceptor dysfunction causes wide swings in blood pressure that are unrelated to posture, whereas a variety of stimuli (cough, micturition, or carotid sinus pressure) may precipitate paroxysmal parasympathetic activation, and sympathetic orthostatic hypotension associated with hypovolemia may occur with mitral valve prolapse or as an idiopathic condition. The differentiation of these and other causes of symptomatic hypotension may in many cases lead to beneficial therapy.

Role of cyclic AMP in adenosine inhibition of intracellular calcium rise in human platelets. Comparison of adenosine effects on thrombin- and epinephrine-induced platelet stimulation

Thrombin-induced platelet aggregation is associated with an increase in intracellular calcium. Epinephrine provokes aggregation in the absence of a rise in intracellular calcium. Adenosine has been postulated as an endogenous inhibitor of platelet aggregation. In this study, the authors examine the effect of adenosine on the rise in intracellular calcium and on platelet aggregation, and the role of cyclic AMP (cAMP) in these actions. Human platelets were obtained from citrated plasma containing 5 micrograms/mL of indomethacin. Intracellular calcium was determined by fura-2 fluorescent dye. Adenosine inhibited thrombin-induced platelet aggregation and the rise in intracellular calcium in a dose-dependent manner. At a concentration of 100 mumol/L, adenosine completely inhibited thrombin-induced aggregation, but only partly inhibited the rise in intracellular calcium (55%). Adenosine also partially inhibited the rise in calcium produced by thrombin in both calcium-containing and calcium-free media, suggesting that adenosine inhibits both calcium influx and calcium mobilization. The effects of adenosine on intracellular calcium, as in the case of platelet aggregation, appear to be linked to adenylate cyclase, since they were prevented by the adenylate cyclase inhibitor 2',5'-dideoxyadenosine (1-mmol/L) and were potentiated by phospho-diesterase inhibition with papaverine (1 mumol/L). Adenosine and dibutyryl-cAMP also inhibited epinephrine-stimulated platelet aggregation in a dose-dependent manner. Thus, it appears that adenosine may inhibit platelet aggregation independently of its ability to decrease cytosolic free calcium.

Early efferent innervation of the developing rat cochlea studied with a carbocyanine dye

The olivocochlear pathway in the developing rat was visualized in fixed material. The fluorescent carbocyanine dye 1,1'-Dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) was applied to the cut central axons of the olivocochlear neurones at the floor of the fourth ventricle, and the termination pattern within the cochlea was examined after dye diffusion. From the day of birth (P0) to postnatal day 2 (P2), efferent innervation of the cochlea was exclusively in the region of the inner hair cells. Between P2 and P11, progressive outgrowth of neuronal processes to the outer hair cell region occurred; possible connections with the outer hair cells were occasionally seen at P4 and approached the mature pattern by P6. The efferent innervation of the organ of Corti appeared to mature progressively from the cochlear base to the apex, with outgrowth to the outer hair cells occurring earlier in the basal turn of the cochlea than in the second and third cochlear turns. Numerous blind axonal endings were observed in the spiral lamina especially at early postnatal ages. These findings may be consistent with a sequential pattern of arrival of efferent axons at the organ of Corti and ongoing death of efferent neurones in the brainstem during this period of development.

The roles of health care teams in care of the elderly

In this brief overview of the issues relating to health care teams in geriatric care, some advantages of multidisciplinary team care versus care by an individual practitioner are outlined. An examination of barriers to teamwork and strategies to overcome them follows. Finally, a Canadian program in which medical students and family practice residents participated in interdisciplinary teamwork is described.

Mechanical preprocessing in the mammalian cochlea

The mammalian cochlea responds with exquisite sensitivity to the small fluctuations in air pressure that make up the stimulus of sound. Moreover, it responds to pressure fluctuations that occur extremely rapidly and that vary over a wide range of intensities--in both cases, to an extent outside the capabilities of unaided nerve fibres. Research performed during the past decade has shown that these properties are dependent on a physiological source of mechanical energy that operates probably within the outer hair cells of the organ of Corti. These cells, which are anatomically and functionally similar to the primary receptor cells, the inner hair cells, are believed to function as a source of mechanical power to assist the mechanical sensitivity of the cochlea, by mechanisms that currently are not understood. Several possible mechanisms have been proposed, but each has limitations that may make it an unsuitable candidate. Recent work has also demonstrated the likely role of mechanoelectrical transduction in outer hair cells in controlling the power source and thereby influencing the sensitivity and amplitude range of the cochlea.

Affinity purification of functional receptors for Escherichia coli heat-stable enterotoxin from rat intestine

Active receptors for Escherichia coli heat-stable enterotoxin (ST) were partially purified by ligand-affinity chromatography. The affinity column was prepared by coupling ST to biotin derivatized with an extended N-hydroxysuccinylated spacer arm prior to binding to monomeric avidin immobilized on agarose. Detergent extracts of rat intestinal mucosa membranes were quantitatively depleted of ST binding activity when chromatographed on this affinity matrix. Biotinylated ST-receptor complexes were eluted from affinity columns with 2 mM biotin and these complexes quantitatively dissociated with bile salts. Using this technique, functional ST receptors were purified maximally about 2000-fold, with about 3% of the total activity in crude extracts recovered in these purified preparations. Analysis of affinity-purified preparations by polyacrylamide gel electrophoresis and silver staining demonstrated a major protein subunit of 74 kDa. Affinity cross-linking of these preparations to 125I-ST demonstrated specific labeling predominantly of the 74-kDa subunit. In addition, lower amounts of labeled ST were incorporated into subunits of 164 and 45 kDa, confirming the heterogeneous nature of ST receptors. Purified receptors bound ST in a concentration-dependent fashion, with an IC50 of 10(-9) M. These studies demonstrate that ligand-affinity chromatography can be employed to purify ST receptors. The availability of purified receptors will facilitate further studies of mechanisms underlying ST-induced intestinal secretion.

Dipeptidyl peptidase iv expression identifies a functional sub-population of breast fibroblasts

The immunocytochemical distribution of the cell-surface enzyme dipeptidyl peptidase IV (DPP IV) has been studied in the human breast at the light and ultrastructural level. The presence of the enzyme was demonstrated on the cell membranes of interlobular fibroblasts, whilst intralobular fibroblasts were DPP-IV-negative. A fluorograph, after immunoprecipitation of 35S-methionine-labelled proteins of fibroblasts from primary breast cultures with an anti-serum to DPP IV, demonstrated a band at 135 kDa consistent with the presence of the enzyme. The clear delineation of 2 functionally distinct subpopulations of breast fibroblasts was maintained in benign fibro-adenomas and cystosarcoma phyllodes, both tumour types having growth characteristics of intralobular stroma. This observation has important implications for both normal breast biology and for breast carcinogenesis.

Relationships among health beliefs, self-efficacy, and exercise adherence in patients with coronary artery disease

Management of the pathologic progression of coronary artery disease requires life-style changes in patients, but the level of compliance with medical recommendations is low. Critical care nurses have a unique opportunity to encourage patients to assume responsibility for their health care and life-style behavior. In this study we developed a model to identify the relationships among variables that explained adherence to a recommended exercise regimen. The variables studied included self-efficacy, perceived severity, barriers, benefits, and cues to action.

Shapes of rate-versus-level functions of primary auditory nerve fibres: test of the basilar membrane mechanical hypothesis

Rate-versus level functions (RI functions) for characteristic frequency (CF) stimulation were measured from primary auditory nerve fibres from different spontaneous rate categories in the guinea pig cochlea. Attention was focussed on those fibres that showed clear breakpoints in their RI functions (sloping-saturation fibres). A statistical curve fitting procedure to an empirical equation was used to provide a quantitative estimate of the breakpoint position in individual fibres. It was found that, within the limits of reliability of the curve fitting procedure, the breakpoint position was the same in fibres from the same CF regions in any given animal. This result is consistent with the notion that the breakpoint position is determined by global basilar membrane mechanics and not by processes private to each nerve fibre. However, a subgroup of fibres not easily classifiable as sloping-saturation, showed features of their RI functions suggesting that factors other than basilar membrane mechanics could lead to fibre-to-fibre differences in rate-versus-level behaviour.

Relationship between tone burst discharge pattern and spontaneous firing rate of auditory nerve fibres in the guinea pig

A detailed investigation was carried out of the response of single auditory nerve fibres in the guinea pig to tone bursts. Comparisons were made between the shapes of peri-stimulus-time histograms (PSTHs) of low and high characteristic frequency (CF) fibres grouped according to their spontaneous firing rates (SR). Both low and high CF fibres of high spontaneous rate (greater than 18 spikes/s) exhibited marked rapid adaptation in their PSTH's which became most pronounced at high stimulus intensities. The ratio of onset-to-adapted firing estimated from PSTH data in these fibres increased monotonically as a function of adapted firing rate. The behaviour of fibres with the lowest spontaneous rates (less than 0.5 spikes/s) was markedly different, particularly in fibres from low CF regions. In general, these low-SR fibres showed slower adaptation than high-SR fibres, and a less pronounced onset peak. This was most striking in low CF fibres. Furthermore, the ratio of onset-to-adapted firing rate tended to decrease with increasing stimulus intensity in both low and high CF fibres with low spontaneous firing rates. Low-SR fibres also showed the highest maximum discharge rates to tone burst stimuli. Fibres with medium spontaneous rates between 0.5 and 18 spikes/s displayed intermediate characteristics in their PSTH's. Recent data in the chinchilla (Relkin and Doucet, 1991), suggest that these differences may arise in part from differences in inter-stimulus recovery processes in the different spontaneous rate groups.

[Mechanism of action of adenosine on intracellular calcium and platelet aggregation]

Adenosine inhibits platelet aggregation and elevates the levels of cytoplasmic Ca2+ induced by thrombin, 0.3 U/ml). When given at the maximal (100 microM) concentration, adenosine completely inhibits the aggregation, but only partially (by 55%) suppresses the growth of Ca2+, blocking both its entry and intracellular depot mobilization. Adenosine is likely to affect intracellular Ca2+, by activating adenylate cyclase, since 2',5'-didesoxyadenosine (1 mM) prevents the effect of adenosine, by inhibiting the enzyme, whereas the phosphodiesterase inhibitor papaverine (1 microM) potentiates its effect. When stimulated with adrenaline, 1 microM, adenosine and dibutyryl-cAMP are also able to inhibit platelet aggregation in the absence of cytoplasmic Ca2+ growth.

Cardiovascular excitatory effects of adenosine in the nucleus of the solitary tract

Adenosine is an inhibitory neuromodulator in several brain regions. In the nucleus tractus solitarius (NTS), however, adenosine exerts excitatory cardiovascular effects. The purpose of the present study was to elucidate the involvement of other endogenous mechanisms that could contribute to the final hemodynamic response to adenosine in this nucleus. In normotensive Sprague-Dawley rats, intra-NTS microinjection of adenosine (2.3 nmol/60 nl) decreased blood pressure and heart rate. These effects were blocked by prior administration of the specific adenosine receptor antagonist 1,3-dipropyl-8-p-sulfophenylxanthine (0.92 nmol) and by the two glutamate receptor antagonists kynurenic acid and glutamic diethylester. The specificity of the adenosine-glutamate interaction in the NTS was demonstrated with adrenergic and angiotensin receptor antagonists that did not affect the adenosine response and by experiments with glutamate receptor antagonists that did not affect nicotine actions in the NTS. Furthermore, an increase in glutamate levels was demonstrated during perfusion of adenosine through a microdialysis probe in the NTS of anesthetized rabbits. These findings indicate that adenosine increases the release of glutamate in the NTS and, thus, are at variance with the concept of a "universal" inhibitory effect of adenosine in the central nervous system.

Rate-versus-level functions of primary auditory nerve fibres: evidence for square law behaviour of all fibre categories in the guinea pig

Detailed measurements of rate-versus-level (RI) functions close to threshold were made from single primary auditory nerve fibres in the guinea pig cochlea. For all fibres, a simple square law provided the best statistical fit to the data near threshold, regardless of spontaneous fibrin rate of the fibre. In no case was a better fit obtained with an exponent greater than 2. We conclude that a simple square law is an accurate description of the underlying synaptic drive to all primary auditory nerve fibres. For fibres with very low spontaneous firing rates the best square law fit near threshold frequently led to the formal mathematical estimate of a negative firing rate as the asymptotic value of the spontaneous firing rate. The 'negative spontaneous rate' of low spontaneous rate fibres derived from curve fitting can be conceptualized by postulating that for sound pressures well below threshold in these fibres the underlying synaptic drive lies below a threshold value at a site determining action potential generation.

Dopamine beta-hydroxylase deficiency. A genetic disorder of cardiovascular regulation

Dopamine beta-hydroxylase (DBH) deficiency is a genetic disorder in which affected patients cannot synthesize norepinephrine, epinephrine, and octopamine in either the central nervous system or the peripheral autonomic neurons. Dopamine acts as a false neurotransmitter in their noradrenergic neurons. Neonates with DBH deficiency have had episodic hypothermia, hypoglycemia, and hypotension, but survivors sometimes cope relatively well until late childhood when overwhelming orthostatic hypotension profoundly limits their activities. The hypotension may be so severe that clonic seizures supervene. Most currently recognized patients are young or middle-aged adults. The diagnosis is established by the observation of severe orthostatic hypotension in a patient whose plasma norepinephrine/dopamine ratio is much less than one.