Developing text-messaging support for fathers after perinatal loss

BACKGROUND

Perinatal loss is a devastating occurrence for expecting parents. Although both parents are affected, research on fathers' grief has not resulted in effective support services for fathers.

AIM

To describe a multi-stage co-design process for developing text messaging support for fathers experiencing perinatal loss.

METHODS

Co-designed text messages were developed in collaboration with a perinatal bereavement organisation, mothers and fathers with lived experience of perinatal loss, and clinicians working with bereaved parents. Bereaved parents responded to a survey about bereaved fathers' information needs (stage 1). A qualitative descriptive data analysis created topics for the generation of text messages (stage 2). Parents with lived experience and clinicians evaluated the messages on importance and clinical fit (stage 3). Messages were revised (stage 4), followed by parent and clinician evaluation and final message revision (stage 5).

FINDINGS

There were 959 survey respondents; the majority agreed that support for fathers would have been useful; 539 provided comments. Qualitative analysis created twelve topics within three themes, leading to the generation of 64 text messages. Messages were evaluated by 27 lived experience parents and 19 clinicians as important (91.6%) and understandable (91.3%), and 92.5% of clinicians agreed the messages fitted clinical guidelines. Message revision resulted in 59 messages across three themes. The final evaluation by 12 parents and 14 clinicians led to a final revised set of 52 messages.

CONCLUSION

Text-based support for bereaved fathers can be developed in a co-design process to accord with clinical practice, from topics suggested parents with lived experience.

Equipping fathers to support distressed mothers: What do mothers want fathers to know and do?

ISSUE ADDRESSED

Up to one in five new mothers experience depression or anxiety, and their partners are often the first line of social and practical support. However, many fathers are unprepared for their role as support person. The SMS4dads program (www.sms4dads.com) provides text-based support to new fathers but lacks specific messages addressing maternal mental distress.

METHODS

A mixed methods process engaged mothers with lived experience of perinatal mental distress to identify message content for co-designing texts in SMS4dads. Participants completed surveys derived from research literature and parenting websites using the theoretical framework of support domains: emotional or affectionate support, informational support, tangible support and positive social interaction. Mothers also indicated the most appropriate timing of support: at the point of identifying the distress (emerging), with ongoing symptoms (persistent) or during recovery (easing). Free text comments from mothers were linked to survey topics to provide examples of wording suitable for text messages to fathers.

RESULTS

Fifty-five mothers with lived experience completed the surveys. All support items were more often endorsed as helpful rather than not helpful by mothers. Emotional support was thought helpful in the early stages, tangible support was valued with ongoing symptoms and social interaction appreciated as symptoms eased.

CONCLUSIONS

Mothers experiencing perinatal depression and anxiety require a range of supportive actions by their partners, including household tasks and baby-care, encouragement, listening and managing relationships with family and friends. SO WHAT?: Information provided by distressed mothers can provide guidance to professionals when designing information for fathers/partners. Digital delivery of this co-designed information to fathers across urban and rural areas may enhance the competence of fathers working to support mothers experiencing mental distress in the perinatal period.

Developing a text message intervention for fathers with partners experiencing perinatal depression or anxiety

BACKGROUND

Support from fathers to their partners is important to reduce distress in mothers during the perinatal period when conditions such as depression and anxiety can be common. The SMS4dads digital platform delivers text messages to fathers but has not previously addressed specific messages to fathers with partners who are experiencing perinatal depression and/or anxiety (PNDA).

AIM

To develop messages, in collaboration with experienced parents and clinicians, that are suitable for fathers whose partner is experiencing PNDA.

METHODS

Messages designed to enhance the quality of partner support for mothers experiencing PNDA were drafted by the SMS4dads team based on suggestions from mothers with lived experience of PNDA. Mothers and fathers with lived experience and expert clinicians rated the messages for importance and understanding. Clinicians additionally rated clinical relevance. Open response comments from parents and clinicians were collated for each message. Re-drafted messages were screened again and checked for literacy level.

RESULTS

Forty-one draft messages received a total of 170 ratings from 24 parents and 164 ratings from 32 clinicians. Over three quarters of parents and clinicians agreed or strongly agreed that messages were understandable (parents 85.6%; clinicians 77.4%), important (parents 86.3%; clinicians 86.6%), and 85.5% of clinicians rated the messages as clinically relevant. Comments from clinicians (n = 99) and parents (n = 46) were reviewed and guided message development. Thirty re-drafted messages were screened and 16 edited based on a second round of ratings and comments from parents and clinicians.

CONCLUSION

Messages for fathers whose partners are experiencing depression and anxiety can be developed and evaluated in collaboration with lived experience of parents and clinicians.

Mental health screening of fathers attending early parenting services in Australia

Paternal perinatal depression and anxiety is a common, though under-recognized mental health condition experienced by men during their transition to fatherhood. An opportunity to screen for paternal mental health issues occurs when parents present for assistance with the care of their baby at early parenting services (EPSs). There are 10 EPSs located across Australia that provide specialist, multidisciplinary interventions to support parents experiencing complex parenting difficulties. Using structured telephone interviews, this qualitative study explored the views of 18 professional staff from nine EPSs regarding screening, referral processes and acceptability of screening fathers for mental health issues. A thematic analysis revealed that most EPSs screened fathers for depression. Participants agreed screening was important and that routine approaches to screening would help normalize the process for both men and services. Despite this, no uniform, comprehensive approach to identifying the mental health needs of fathers was found. EPSs provide a unique opportunity to address the mental health needs of fathers. Results from this study point to the need for a national approach to the development of father-specific screening guidelines for EPSs to improve family well-being, in parallel to those informing the Australian National Perinatal Mental Health Initiative for mothers.

SCREENING DADS FOR DEPRESSION IN AUSTRALIAN EARLY PARENTING CENTRES

For the majority of men, becoming a father is a time of joy that enhances their personal growth and wellbeing. However, similar to the experience of some women, this time can be overwhelming when adjusting to the necessary demands of parenthood and can undermine men's mental health.

The differential diagnosis of longitudinally extensive transverse myelitis

Longitudinally extensive transverse myelitis refers to florid and widespread inflammation of the spinal cord causing T2 hyperintensity on spinal magnetic resonance imaging that is seen to extend over three or more vertebral segments. Whilst rare, longitudinally extensive transverse myelitis is clinically important as it can lead to catastrophic morbidity, and a group of these patients are at risk of further attacks. Early identification and establishment of the underlying aetiology is vital in order to initiate appropriate therapy and optimize outcomes. Whilst longitudinally extensive transverse myelitis is classically associated with neuromyelitis optica, there are many other causes. These include other inflammatory aetiologies, infection, malignancy and metabolic disturbance. Some of these are readily treatable. Laboratory and radiological investigations can help to differentiate these causes. Treatment of longitudinally extensive transverse myelitis hinges on distinguishing inflammatory and non-inflammatory aetiologies and identifying patients who are at high risk of a recurrent course.

Modeling spatiotemporal covariance for magnetoencephalography or electroencephalography source analysis

We propose a new model to approximate spatiotemporal noise covariance for use in neural electromagnetic source analysis, which better captures temporal variability in background activity. As with other existing formalisms, our model employs a Kronecker product of matrices representing temporal and spatial covariance. In our model, spatial components are allowed to have differing temporal covariances. Variability is represented as a series of Kronecker products of spatial component covariances and corresponding temporal covariances. Unlike previous attempts to model covariance through a sum of Kronecker products, our model is designed to have a computationally manageable inverse. Despite increased descriptive power, inversion of the model is fast, making it useful in source analysis. We have explored two versions of the model. One is estimated based on the assumption that spatial components of background noise have uncorrelated time courses. Another version, which gives closer approximation, is based on the assumption that time courses are statistically independent. The accuracy of the structural approximation is compared to an existing model, based on a single Kronecker product, using both Frobenius norm of the difference between spatiotemporal sample covariance and a model, and scatter plots. Performance of ours and previous models is compared in source analysis of a large number of single dipole problems with simulated time courses and with background from authentic magnetoencephalography data.

Dopaminergic modulation and rod contribution in the generation of oscillatory potentials in the tiger salamander retina

The roles of rod and cone input and of dopamine in the generation of oscillatory potentials were studied in tiger salamander retina. Under scotopic conditions, oscillations were elicited with a green, but not a red stimulus. With mesopic background illumination, both stimuli caused oscillations. Addition of quinpirole to a mesopic retina eliminated oscillations while SKF-38393 had no effect. Similarly, addition of sulpiride to a light-adapted retina elicited oscillatory activity, but SCH 22390 had no effect. These results suggest that oscillatory potentials are elicited through activation of the rod pathway and are modulated by dopamine through D2-receptors.

A high frequency resonance in the responses of retinal ganglion cells to rapidly modulated stimuli: a computer model

Brisk Y-type ganglion cells in the cat retina exhibit a high frequency resonance (HFR) in their responses to large, rapidly modulated stimuli. We used a computer model to test whether negative feedback mediated by axon-bearing amacrine cells onto ganglion cells could account for the experimentally observed properties of HFRs. Temporal modulation transfer functions (tMTFs) recorded from model ganglion cells exhibited HFR peaks whose amplitude, width, and locations were qualitatively consistent with experimental data. Moreover, the wide spatial distribution of axon-mediated feedback accounted for the observed increase in HFR amplitude with stimulus size. Model phase plots were qualitatively similar to those recorded from Y ganglion cells, including an anomalous phase advance that in our model coincided with the amplification of low-order harmonics that overlapped the HFR peak. When axon-mediated feedback in the model was directed primarily to bipolar cells, whose synaptic output was graded, or else when the model was replaced with a simple cascade of linear filters, it was possible to produce large HFR peaks but the region of anomalous phase advance was always eliminated, suggesting the critical involvement of strongly non-linear feedback loops. To investigate whether HFRs might contribute to visual processing, we simulated high frequency ocular tremor by rapidly modulating a naturalistic image. Visual signals riding on top of the imposed jitter conveyed an enhanced representation of large objects. We conclude that by amplifying responses to ocular tremor, HFRs may selectively enhance the processing of large image features.

Simultaneously detected biomagnetic signals and NMR

We have obtained 1H NMR spectra simultaneously with high temporal resolution biomagnetic signals such as the magnetocardiogram (MCG) and magnetomyogram (MMG). The NMR spectra are acquired at measurement fields of 2-50 microT, with corresponding proton Larmor frequencies of 80-2000 Hz. Our measurements demonstrate a method suitable for MR imaging with concurrent measurement of biomagnetic signals that can provide sub-millisecond temporal resolution. The narrow line widths, reduction in susceptibility noise and enhanced spectral resolution at ultra low fields provide a new and extremely sensitive measurement method that may enable direct imaging of biological currents by detecting the phase or frequency shifts produced by magnetic fields arising from those currents. The results of our simultaneous measurements of NMR with MCG and MMG are compared to results from a current phantom to investigate the exciting potential of direct MRI of bioelectric currents.

MUSIC seeded multi-dipole MEG modeling using the Constrained Start Spatio-Temporal modeling procedure

The Constrained Start Spatio-Temporal modeling program (CSST) is an objective multi-dipole, multi-start MEG/EEG analysis procedure that randomly selects from 100 to 100,000 initial dipole configurations, and runs a nonlinear simplex search on each of these configurations employing a reduced Chi-square statistic as the minimization criterion, to obtain a set of dipole configurations that best fit the data [Ranken, 2002]. A parallel version of CSST is implemented in IDL and MPI, making CSST usable on a single computer, or on a Linux cluster. We have now developed a multi-resolution version of MUSIC [Mosher, 1992] [Mosher, 1998] that provides an 80% or more reduction in the number of forward calculations needed to obtain results comparable to a 160,000 point MUSIC scan, on a 2 mm grid that defines a brain volume. The multi-resolution MUSIC scan provides an improved set of initial dipole estimates for the CSST analysis. In preliminary tests on real and simulated MEG data, with model orders ranging between 5 and 7 dipoles, the best performance improvements were obtained by mixing in 1 to 3 dipole locations randomly drawn from the best MUSIC locations, with randomly selected locations from the brain volume to complete the selected model order. We have also developed an improved method for sampling the brain volume for initial configurations. These improvements have led to a 75% reduction in the number of starting configurations required to obtain 5-10 best solutions with equal or lower reduced Chi-square values, when compared to the best solutions from the previous version of CSST.

The influence of brain tissue anisotropy on human EEG and MEG

The influence of gray and white matter tissue anisotropy on the human electroencephalogram (EEG) and magnetoencephalogram (MEG) was examined with a high resolution finite element model of the head of an adult male subject. The conductivity tensor data for gray and white matter were estimated from magnetic resonance diffusion tensor imaging. Simulations were carried out with single dipoles or small extended sources in the cortical gray matter. The inclusion of anisotropic volume conduction in the brain was found to have a minor influence on the topology of EEG and MEG (and hence source localization). We found a major influence on the amplitude of EEG and MEG (and hence source strength estimation) due to the change in conductivity and the inclusion of anisotropy. We expect that inclusion of tissue anisotropy information will improve source estimation procedures.

Scattered-light imaging in vivo tracks fast and slow processes of neurophysiological activation

We imaged fast optical changes associated with evoked neural activation in the dorsal brainstem of anesthetized rats, using a novel imaging device. The imager consisted of a gradient-index (GRIN) lens, a microscope objective, and a miniature charged-coupled device (CCD) video camera. We placed the probe in contact with tissue above cardiorespiratory areas of the nucleus of the solitary tract and illuminated the tissue with 780-nm light through flexible fibers around the probe perimeter. The focus depth was adjusted by moving the camera and microscope objective relative to the fixed GRIN lens. Back-scattered light images were relayed through the GRIN lens to the CCD camera. Video frames were digitized at 100 frames per second, along with tracheal pressure, arterial blood pressure, and electrocardiogram signals recorded at 1 kHz per channel. A macroelectrode placed under the GRIN lens recorded field potentials from the imaged area. Aortic, vagal, and superior laryngeal nerves were dissected free of surrounding tissue within the neck. Separate shocks to each dissected nerve elicited evoked electrical responses and caused localized optical activity patterns. The optical response was modeled by four distinct temporal components corresponding to putative physical mechanisms underlying scattered light changes. Region-of-interest analysis revealed image areas which were dominated by one or more of the different time-course components, some of which were also optimally recorded at different tissue depths. Two slow optical components appear to correspond to hemodynamic responses to metabolic demand associated with activation. Two fast optical components paralleled electrical evoked responses.

Continuous image and electrophysiological recording with real-time processing and control

Collecting continuous video together with multichannel electrophysiological data and other experimental modalities requires high bandwidth and storage capacities, as well as accurate synchronization to detect correlations between different recorded events. Often, experiments are highly complex, with many variables requiring immediate analysis and feedback during the course of the experiment. In addition, output channels require real-time control with high time resolution. We have explored several approaches to a system that can perform the above functions. The design of our system considered a number of issues, including time intervals between control and acquisition events, longest continuous recording period, data transfer bottleneck considerations, file archiving and format, and real-time display and processing. To demonstrate the system, we describe an experiment for characterizing rapid evoked scattered light changes in neural tissue, in vivo, using simultaneous electronic image acquisition and electrophysiological recording.

Conductivity tensor mapping of the human brain using diffusion tensor MRI

Knowledge of the electrical conductivity properties of excitable tissues is essential for relating the electromagnetic fields generated by the tissue to the underlying electrophysiological currents. Efforts to characterize these endogenous currents from measurements of the associated electromagnetic fields would significantly benefit from the ability to measure the electrical conductivity properties of the tissue noninvasively. Here, using an effective medium approach, we show how the electrical conductivity tensor of tissue can be quantitatively inferred from the water self-diffusion tensor as measured by diffusion tensor magnetic resonance imaging. The effective medium model indicates a strong linear relationship between the conductivity and diffusion tensor eigenvalues (respectively, final sigma and d) in agreement with theoretical bounds and experimental measurements presented here (final sigma/d approximately 0.844 +/- 0.0545 S small middle dots/mm(3), r(2) = 0.945). The extension to other biological transport phenomena is also discussed.

A focusing image probe for assessing neural activity in vivo

We describe a compact, focusing image probe to record rapid optical changes from neural tissue. A gradient index (GRIN) lens served as a relay lens from tissue to a microscope objective which projected an image onto a CCD camera. The microscope objective and camera assembly was adjusted independently from the GRIN lens, allowing focus changes without disturbing the probe/tissue interface; firm contact minimized movement and specular reflectance. Fiber optics around the probe perimeter provided diffuse illumination from a 780 nm laser, or 660 and 560 nm light emitting diodes. To characterize depth-of-field, we imaged a black suture through increasing tissue thicknesses. Light modulation by the suture remained detectable down to 900 microm using 780 nm illumination. We acquired images from cardiorespiratory areas of the rat dorsal medulla, at different depths and illumination wavelengths. Images illuminated at 560 nm were dominated by vasculature flow patterns, while 660 nm illumination revealed different spatial patterns which preceded vascular flow by 40 ms and may represent cardiac-related neural activity. Using 780 nm light, image sequences triggered by the cardiac R-wave showed vascular perfusion changes with delayed and broader responses at deeper levels. Electrical stimulation within the vagal bundle caused fast optical changes which track the electrical response, with a different spatial distribution from hemodynamic signals.

Bayesian inference applied to the electromagnetic inverse problem

We present a new approach to the electromagnetic inverse problem that explicitly addresses the ambiguity associated with its ill-posed character. Rather than calculating a single "best" solution according to some criterion, our approach produces a large number of likely solutions that both fit the data and any prior information that is used. Whereas the range of the different likely results is representative of the ambiguity in the inverse problem even with prior information present, features that are common across a large number of the different solutions can be identified and are associated with a high degree of probability. This approach is implemented and quantified within the formalism of Bayesian inference, which combines prior information with that of measurement in a common framework using a single measure. To demonstrate this approach, a general neural activation model is constructed that includes a variable number of extended regions of activation and can incorporate a great deal of prior information on neural current such as information on location, orientation, strength, and spatial smoothness. Taken together, this activation model and the Bayesian inferential approach yield estimates of the probability distributions for the number, location, and extent of active regions. Both simulated MEG data and data from a visual evoked response experiment are used to demonstrate the capabilities of this approach.

Diffusion imaging with hyperpolarized 3He Gas

We used MRI of hyperpolarized 3He to demonstrate some novel aspects of gas diffusion. Two different techniques were used. First, a slice was burned into a one-dimensional image by inverting the spins in the slice and diffusion was studied by measuring the magnetization as it filled the depleted slice. A diffusion coefficient was determined by the fit of these data. Second, one-dimensional diffusion images were made using a Stejskal-Tanner PGSE method. This was done with and without a temperature gradient present, showing that the effect of temperature can be dynamically monitored by such diffusion images. Copyright 1997 Academic Press. Copyright 1997Academic Press

Retinotopic organization of human visual cortex: departures from the classical model

Retinotopic mapping strategies similar to those used for invasive electrophysiological studies to identify multiple visual areas in monkeys have been adapted for noninvasive studies in humans, using magnetic recordings of brain activity in conjunction with anatomical magnetic resonance imaging. The retinotopic organization of the primary visual area (V1) in the left hemisphere of human subjects was examined by presenting a small patterned stimuli near the vertical and horizontal meridians in the lower right visual field. In contrast with the classical model of V1 retinotopy, our results suggest that the representation of the horizontal meridian does not necessarily correspond in a one-to-one manner with the base of the calcarine fissure and that some lower field stimuli can activate regions in the lower bank of the fissure. The results also indicate significant individual variability in the details of how V1 maps around the calcarine fissure.

Neuromagnetic source imaging with FOCUSS: a recursive weighted minimum norm algorithm

The paper describes a new algorithm for tomographic source reconstruction in neural electromagnetic inverse problems. Termed FOCUSS (FOCal Underdetermined System Solution), this algorithm combines the desired features of the two major approaches to electromagnetic inverse procedures. Like multiple current dipole modeling methods, FOCUSS produces high resolution solutions appropriate for the highly localized sources often encountered in electromagnetic imaging. Like linear estimation methods, FOCUSS allows current sources to assume arbitrary shapes and it preserves the generality and ease of application characteristic of this group of methods. It stands apart from standard signal processing techniques because, as an initialization-dependent algorithm, it accommodates the non-unique set of feasible solutions that arise from the neuroelectric source constraints. FOCUSS is based on recursive, weighted norm minimization. The consequence of the repeated weighting procedure is, in effect, to concentrate the solution in the minimal active regions that are essential for accurately reproducing the measurements. The FOCUSS algorithm is introduced and its properties are illustrated in the context of a number of simulations, first using exact measurements in 2- and 3-D problems, and then in the presence of noise and modeling errors. The results suggest that FOCUSS is a powerful algorithm with considerable utility for tomographic current estimation.

Mapping function in the human brain with magnetoencephalography, anatomical magnetic resonance imaging, and functional magnetic resonance imaging

Integrated analyses of human anatomical and functional measurements offer a powerful paradigm for human brain mapping. Magnetoencephalography (MEG) and EEG provide excellent temporal resolution of neural population dynamics as well as capabilities for source localization. Anatomical magnetic resonance imaging (MRI) provides excellent spatial resolution of head and brain anatomy, whereas functional MRI (fMRI) techniques provide an alternative measure of neural activation based on associated hemodynamic changes. These methodologies constrain and complement each other and can thereby improve our interpretation of functional neural organization. We have developed a number of computational tools and techniques for the visualization, comparison, and integrated analysis of multiple neuroimaging techniques. Construction of geometric anatomical models from volumetric MRI data allows improved models of the head volume conductor and can provide powerful constraints for neural electromagnetic source modeling. These approaches, coupled to enhanced algorithmic strategies for the inverse problem, can significantly enhance the accuracy of source-localization procedures. We have begun to apply these techniques for studies of the functional organization of the human visual system. Such studies have demonstrated multiple, functionally distinct visual areas that can be resolved on the basis of their locations, temporal dynamics, and differential sensitivity to stimulus parameters. Our studies have also produced evidence of internal retinotopic organization in both striate and extrastriate visual areas but have disclosed organizational departures from classical models. Comparative studies of MEG and fMRI suggest a reasonable but imperfect correlation between electrophysiological and hemodynamic responses. We have demonstrated a method for the integrated analysis of fMRI and MEG, and we outline strategies for improvement of these methods. By combining multiple measurement techniques, we can exploit the complementary strengths and transcend the limitations of the individual neuro-imaging methods.

Temporal dynamics of visual-evoked neuromagnetic sources: effects of stimulus parameters and selective attention

Results are reviewed from several neuromagnetic studies which characterize the temporal dynamics of neural sources contributing to the visual evoked response and effects of attention on these sources. Different types of pattern-onset stimuli (< or = 2 degrees) were presented sequentially to a number of field locations in the right visual field. Multiple dipole models were applied to a sequence of instantaneous field distributions constructed at 10 ms intervals. Best-fitting source parameters were superimposed on Magnetic Resonance images (MRI) of each subject to identify the anatomical structure(s) giving rise to the surface patterns. At least three sources, presumably corresponding to different visual areas, were routinely identified from 80-150 ms following the onset of visual stimulation. This observation was consistent across subjects and studies. The temporal sequence and strength of activation of these sources, however, were dependent upon the specific stimulus parameters used to evoke the response (e.g., eccentricity) and on the relevance of the stimulus to the subject. In addition, our results provide evidence for the recurrence of activity in striate and extrastriate regions, following the initial cycle of responses.

Reversible opening of the blood-brain barrier by anti-bacterial antibodies

The leukocyte adhesion molecule CR3 (CD11b/CD18, Mac-1) promotes leukocyte transmigration into tissues by engaging an unknown cognate ligand on the surface of vascular endothelial cells. Filamentous hemagglutinin (FHA), an adhesin of the bacterium Bordetella pertussis, binds to CR3. We hypothesized that FHA mimics the native ligand for the CR3 integrin on endothelial cells and predicted that anti-FHA antibodies should bind to endothelial cells, interfere with leukocyte recruitment, and induce endothelial permeability. Anti-FHA monoclonal antibodies bound to cerebral microvessels in sections from human brain and upon intravenous injection into rabbits. Antibody binding correlated with the ability to recognize two polypeptides in extracts of human cerebral vessels that were also bound by CD18. In vivo, antibody binding not only interfered with transmigration of leukocytes into cerebrospinal fluid but also induced a dose-dependent reversible increase in blood-brain barrier permeability sufficient to improve delivery of intravenously administered therapeutic agents to brain parenchyma.

Interactions between the subunits of transducin and cyclic GMP phosphodiesterase in Rana catesbiana rod photoreceptors

In bullfrog (Rana catesbiana) rods the activity of cyclic GMP (cGMP) phosphodiesterase was stimulated 10 times by washing disc membranes with an isotonic, GTP-containing buffer. This stimulation was maintained following hydrolysis of GTP and after removal of guanine nucleotides. At least 60-70% of the inhibitory gamma subunit of cGMP phosphodiesterase (P gamma) was physically released from membranes by these washing procedures. When cGMP phosphodiesterase was activated by a hydrolysis-resistant GTP analogue, P gamma was found in the supernatant complexed with the transducin alpha subunit (T alpha) using three chromatography systems. When GTP was used to activate cGMP phosphodiesterase, P gamma was also found in the supernatant complexed with GDP.T alpha. This complex was also isolated using the same three chromatography systems, indicating that P gamma remained tightly bound to T alpha even after bound GTP was hydrolyzed. Interaction with the beta,gamma subunits of transducin, which remained associated with disc membranes, was required for the release of P gamma from the GDP.T alpha complex, which resulted in the deactivation of active cGMP phosphodiesterase. We conclude that during activation of cGMP phosphodiesterase, P gamma is complexed with T alpha (both GTP and GDP forms) in the supernatant and that, following GTP hydrolysis, beta,gamma subunits of transducin are necessary for the release of P gamma from the complex and the resulting inactivation of cGMP phosphodiesterase in frog photoreceptors.

Control of Ca2+ in rod outer segment disks by light and cyclic GMP

Photons absorbed in vertebrate rods and cones probably cause electrochemical changes at the photoreceptor plasma membrane by changing the cytoplasmic concentration of a diffusible transmitter substance, reducing the Na+ current flowing into the outer segment of the cell in the dark, to produce the observed membrane hyperpolarization that is the initial excitatory response. Cyclic GMP has been proposed as the transmitter because a light-activated cyclic GMP phosphodiesterase (PDE) has been found in rod disk membranes and because intracellularly injected cyclic GMP reduces rod membrane potentials. Free Ca2+ has also been proposed because increasing external [Ca2+] quickly and reversibly reduces the dark current and divalent cationophores increase the Ca2+ sensitivity. Ca2+ efflux from rod outer segments (ROS) of intact retinas occurs simultaneously with light responses. Vesicles prepared from ROS disk membranes become more permeable on illumination, releasing trapped ions or molecules, but intact outer segment disks have not previously been found to store sufficient Ca2+ in darkness and to release enough in light to meet the theoretical requirements for control of the dark current by varying cytoplasmic Ca2+ (refs 14-18). We now report experiments that show the required Ca2+ storage and release from rod disk membranes suspended in media containing high-energy phosphate esters and electrolytes approximating the cytoplasmic composition of live rod cells. Cyclic GMP stimulates Ca2+ uptake by ROS disks in such media.

Intestinal parasitic infestation among parturients in Trinidad and Tobago

1. In this limited survey, 42.5% of parturients were found to be infested with intestinal parasites. 2. Hookworm, Trichuris and Entamoeba infestations were the most common. 3. Race, social class and locality influenced in the incidence of the different types of infestations. 4. Those infested with hookworm had longer labor, smaller babies and higher incidence of prematurity.