The clinical experience of novice students in nursing.

The learning experience of nursing students in their first clinical laboratory in a hospital was examined in a qualitative investigation. Graduate students in a nursing research seminar course participated as co-investigators in the study of clinical learning among sophomore nursing students. Findings revealed that sophomore students in nursing reflected on their role in the clinical setting and in nursing; pursued ways to learn in clinical settings; actively sought mentors; made connections to staff, patients, and peers; and searched for ways to validate the competence of their beginning skills. Parallels of the students' behaviors to the novice-to-expert paradigm were found. The study was valuable for both undergraduate and graduate students involved in the investigation.

The electrical geometry, electrical properties and synaptic connections onto rat V motoneurones in vitro.

1. We have developed a tissue slice preparation which allows the study of the actions of single presynaptic neurones onto single trigeminal motoneurones in the immature rat. Our aim in this first stage of the work has been to assess the validity of this preparation as a model for responses obtained in vivo from trigeminal motoneurones in adult rats. We have quantified the integrative properties of the motoneurones and also the variability in transmission at synapses of single presynaptic neurones onto the motoneurones. This data has then been compared to similar published data obtained from adult (rat) trigeminal motoneurones in vivo. 2. Quantitative reconstructions were made of the morphology of three motoneurones which had been labelled with biocytin by intracellular injection. The neurones gave off six to nine dendrites, of mean length 522 microns (S.D. = 160; n = 22), which branched on average 10.5 times to produce 11.45 end-terminations per dendrite (S.D. = 8.57; n = 22). The mean surface area of the dendrites was 0.92 x 10(4) microns2 (S.D. = 0.67; n = 22), and, for individual cells, the ratio of the combined dendritic surface area to the total neuronal surface area ranged from 98.3 to 99.2% (n = 3). At dendritic branch points the ratio of the summed diameters of the daughter dendrites to the 3/2 power against the parent dendrite to the 3/2 power was 1.09 (S.D. = 0.21; n = 217), allowing branch points to be collapsed into a single cylinder. The equivalent cylinder diameter of the combined dendritic tree remained approximately constant over the proximal 25-40% of the equivalent electrical length of the dendritic tree and then showed tapering. The tapering could be ascribed to termination of dendrites at different electrical distances from the soma. 3. Electrical properties were determined for a total of eighty-seven motoneurones, all with membrane potentials more negative than 60 mV (mean = 66.0 mV; S.D. = 5.2) and spikes which overshot zero (mean spike amplitude = 77 mV; S.D. = 10.5; n = 87). The spikes were followed by after-hyperpolarizations (AHPs) of mean amplitude 2.2 mV (S.D. = 1.7; n = 47), and mean duration 54.1 ms (S.D. = 9.5; n = 47). The mean input resistance of the neurones was 7.5 M omega (S.D. = 2.5; n = 69), the mean membrane time constant was 3.5 ms (S.D. = 2.2; n = 35), and the mean rheobase was 1.6 nA (S.D. = 1.1; n = 56).(ABSTRACT TRUNCATED AT 400 WORDS)

Monosynaptic EPSPs elicited by single interneurones and spindle afferents in trigeminal motoneurones of anaesthetized rats.

1. Our aim has been to quantify the monosynaptic connections of trigeminal interneurones and spindle afferents onto jaw-elevator motoneurones as a step towards identifying common features in organization of monosynaptic inputs onto motoneurones. We have used the intracellular variant of the spike-triggered averaging method to examine the connections of single identified trigeminal interneurones and jaw-elevator muscle spindle afferents onto single jaw-elevator motoneurones. The interneurones examined lay in the region immediately caudal to the trigeminal motor nucleus. The experiments were performed on rats anaesthetized with pentobarbitone, paralysed and artificially ventilated. 2. Ten EPSPs and eight IPSPs were obtained from examining the connections of seventeen interneurones to thirty-six motoneurones, suggesting a functional connectivity of 50% for individual interneurones onto elevator motoneurones. Fourteen EPSPs were obtained from examining the connections of thirteen spindle afferents onto twenty-seven motoneurones, giving a functional connectivity of 52% for individual spindle afferents onto elevator motoneurones. The amplitudes of the EPSPs elicited by interneurones ranged from 7-48 microV (mean = 17, S.D. = 12.5, n = 10) and from 7 to 289 microV (mean = 64, S.D. = 76.0, n = 14) for the spindle-mediated EPSPs; the difference in the two means was not significant (P = 0.07). 3. However, the amplitude of averaged responses obtained by signal averaging methods are dependent on the assumption that the postsynaptic response occurs following every impulse in the presynaptic neurone. We therefore estimated the percentage of sweeps which contained EPSPs triggered by the presynaptic neurone under study. In essence the method used consisted of visual inspection of the individual sweeps comprising an average in order to assess the occurrence of EPSPs within six separate time windows, each of duration +/- 0.3 ms. Five windows were placed at randomly selected times on average and were used to provide an estimate of the frequency of occurrence of randomly triggered EPSPs. The sixth window was centred on the start of the averaged EPSP and the frequency of occurrence of randomly triggered EPSPs was subtracted from the frequency of occurrence of EPSPs in this window to produce an estimate of the incidence of EPSPs triggered by the presynaptic neurone under study. 4. Values of the incidence of occurrence of EPSPs triggered by the presynaptic neurones ranged from 4.3 to 92% for the fifteen averaged EPSPs which could be analysed in this manner (two elicited by interneurones and thirteen by spindle afferents).(ABSTRACT TRUNCATED AT 400 WORDS)

The development of a pH-sensitive contrast agent for NMR 1H imaging.

Fe(III)meso-tetra(4-sulfonatophenyl)porphine (Fe-TPPS4) has been investigated as a potential pH-sensitive nuclear magnetic resonance (NMR) proton image contrast agent. Relaxation rates (1/T1 and 1/T2) of water protons were measured as a function of pH and concentration of Fe-TPPS4 in phosphate-buffered isotonic saline. Transverse relaxation rates (1/T2) did not change appreciably with pH above 6.0. Longitudinal relaxation rates (1/T1) increased significantly between pH 7.75 and 5.75. This effect was more pronounced with the increasing concentration of Fe-TPPS4 from 0.1 to 1.5 mM and is attributed to a pH-dependent equilibrium between the high-spin (S = 5/2) Fe-TPPS4 monomer at low pH and the antiferromagnetically coupled mu-oxodimer O-(FeTPPS4)2 at high pH. The efficacy of this pH-dependent contrast agent is demonstrated in vitro.

Hormonal regulation of capillary fenestrae in the rat adrenal cortex: quantitative studies using objective lens staging scanning electron microscopy.

High magnification studies of the fenestrated capillary endothelium in the zona fasciculata (ZF) of rat adrenal glands were performed using the objective lens stage of an analytical scanning electron microscope (SEM) equipped with a lanthanum hexaboride emitter (LaB6). Resolution of surface substructure of the luminal membrane obtained with specimens decorated with gold/palladium (Au/Pd) was compared with that observed in others sputter coated with tantalum (Ta). High magnification (50,000x) of the fenestrated endothelium demonstrates that tantalum coating of the cryofractured adrenals improves the substructural detail compared to that seen in Au/Pd decorated specimens. The procedures used in specimen preparation, metal deposition and secondary electron imaging (SEI) are described. Quality imaging achieved using the objective lens stage is a result of the elimination of the SE-III component derived from backscattered electrons. Rat adrenals exhibited uniformly patent capillaries. High magnification micrographs of capillary walls were randomly recorded in two morphometric studies of the fenestral content of capillaries in the rat adrenal cortex. Adrenocorticotropic hormone (ACTH), when administered to rats following dexamethasone (DEX) treatment, significantly reduced the fenestrae/micron 2 of endothelial surface and increased the mean size of fenestrae. After hypophysectomy, the number of fenestrae/micron 2 declined over 48 h; within 2 h after ACTH was given to rats hypophysectomized 48 hours earlier, the fenestrae/micron 2 had increased two-fold. These studies indicate that ACTH plays an important role in modulating fenestral content of the capillary endothelium in the adrenal cortex.

Extraction of corticosterone from cell homogenates and subcellular fractions of the rat adrenal cortex. II. ACTH-induced changes in subcellular corticosterone.

Zona fasciculata-reticularis subcellular structures were implicated in corticosterone transport and secretion by noting changes in subcellular corticosterone during a 30-min period following ACTH stimulation. Six decapsulated adrenal homogenate subcellular fractions separated by gradient centrifugation were characterized cytochemically and morphologically. Predominant components in each of six fractions were: floating lipid droplets, 0.125 M sucrose (no organelles), cytosol (0.25 M sucrose supernatant with 0.25-1.2 micron electron dense granules), microsomes (interface between 0.5 M and 1.1 M sucrose layers), mitochondria (boundary between 1.1 M and 2.2 M sucrose layers) and nuclei (centrifuge pellet). Whole glands and most subcellular fractions showed peak corticosterone levels 10 to 15, and 30 min after stimulation. Sucrose and cytosolic fractions contained about 75% of the total corticosterone, responded to stimulation most significantly, and were rich in protein. In these two fractions only cytosol contained structures; these consisted of 0.15-1.2 micron electron dense granules.

A method for the isolation of lipid droplet fractions from decapsulated rat adrenals.

Ultrastructural and cell fractionation studies implicate lipid droplets in the storage of cholesterol and in the secretion of steroids. To evaluate the role of the lipid droplet in steroidogenesis, a discontinuous gradient centrifugation method has been developed for the isolation of both lipid droplet and non-lipid fractions from decapsulated rat adrenal homogenates. Steroids were extracted from the fractions with chloroform/methanol; the cholesterol ester, cholesterol and corticosterone in each extract were purified using a single chromatogram and the purified steroid and sterols were assayed fluorometrically. The lipid droplet fraction contained 85% of the esterified cholesterol and 32% of the free cholesterol found in whole gland extracts. Although adrenal lipid droplet fractions isolated from non-stimulated control animals contained 65-79% of the total corticosterone assayed in extracts of the whole gland, in vivo injections of ACTH did not increase corticosterone in this fraction. On the other hand, the corticosterone measured in non-lipid fraction extracts increased significantly following ACTH treatment. These results suggest that the synthesis/release mechanism for corticosterone is not associated with the lipid droplets but may involve specific components in the non-lipid fraction. The function of lipid droplet corticosterone is unknown.

An improved method for the extraction of corticosterone from cell homogenates and subcellular fractions of the rat adrenal cortex.

An improved technique is described for the extraction and analysis of corticosterone (11 beta,21-dihydroxy-4-pregnene-3,20-dione) from homogenates and subcellular fractions of the rat adrenal cortex. Factors influencing complete extraction of corticosterone were the nature of the organic solvent system and the concentration of the tissue being extracted. The continued activity of steroidogenic enzymes during subcellular fractionation was presented by 0.1 mM 1-benzylimidazole. For optimum extraction, homogenates were diluted 1:12 (v/v) in 0.25 M sucrose, containing 0.1 M potassium hydroxide. Dilute homogenate was mixed with absolute ethanol (1:10, v/v) and extracted three times with diethyl ether (1:5, v/v). Following extraction, corticosterone in each sample was isolated by thin-layer chromatography (TLC), quantitated by radioimmunoassay (RIA), and corrected by measuring the recovery of added H3 corticosterone. With these procedures, 90-100% of corticosterone found in extracts of adrenal homogenates was recovered in extracts of subcellular fractions of the homogenates.

SEM cryofracture study of ovarian follicles of immature rats.

Follicles were examined with the scanning electron microscope (SEM) following preparation of cryofractured specimens of rat ovaries. After perfusion fixation with 2.5% glutaraldehyde buffered at pH 7.4 with 0.1M cacodylate, ovaries were trimmed of fat and decapsulated, fixed for an additional 12 hours, washed in distilled H2O for 20 hours and postfixed in 1% OsO4 in distilled H2O for 30 minutes. Following a brief wash, ovaries were dehydrated in a linear gradient of dist. H2O/ethanol, frozen in Freon 22, cryofractured under liquid nitrogen, brought to 1 degree C in ethanol, and critical point dried from CO2. Follicles cleaved through their oocytes were examined with SEM to determine the ultrastructural characteristics of developing and atretic follicles revealed by cryofracture. Cytoplasmic arrays of parallel sheets, nucleoli and microvilli were prominent structures of cryofractured oocytes. Numerous cytoplasmic projections of granulosa cells and oocyte microvilli penetrated the zonae pellucida of preantral follicles. The numbers of oocyte microvilli were greatly diminished in large antral follicles. Other structures made prominent by cryofracture included cell nuclei, a microvillous border at the granulosa-theca boundary, and numerous holes in the cytoplasm of thecal cells which correspond in size and distribution to the liquid droplets in these cells. The soluble proteins and glycoproteins of the follicular fluid were visualized as a homogeneous granular precipitate. The disappearance of oocyte microvilli and granulosa cell projections from the zonae pellucida and the blebbing of granulosa cells at the surface of the antral cavity appeared characteristic of an early stage of follicular atresia. Increased numbers of holes in thecal cells, oocyte fragmentation, and extensive dissociation and fragmentation of granulosa cells were typical of more advanced stages of atresia.