Selective potentiation of N-type calcium channels by angiotensin II in rat subfornical organ neurones.

1. Here we have characterized Ca(2+) currents in rat subfornical organ neurones, and their modulation by angiotensin II. Currents were of the high voltage-activated (HNA) subtype, as the threshold for activation was near -30 mV (mid-point potential (V(50)) of activation -14 mV). Using Ba(2+) as the charge carrier, little inactivation was observed, and it occurred only at depolarized potentials (V(50) of inactivation -12 mV). More inactivation was observed using Ca(2+) as the charge carrier, indicating that Ca(2+)-dependent inactivation plays a role in regulating Ca(2+) channel function in subfornical organ (SFO) neurones. 2. The net Ba(2+) current could be blocked by Cd(2+) (EC(50) 1.6 microM), confirming that currents are of the HVA variety. By using selective antagonists, we identified the presence of both L- and N-type channels; 20 microM nifedipine blocked 22 +/- 1 % of the current, while omega-conotoxin GVIA blocked 65 +/- 7 %, indicating that these currents make up the net current through Ca(2+) channels. 3. Angiotensin II potentiated the inward current throughout the range of activation. Using depolarizing voltage ramps, 1 nM angiotensin potentiated the peak current by 14 +/- 5 %. We then used selective blockade of the HVA component currents; 20 microM nifedipine failed to prevent the potentiation by angiotensin II (12 +/- 5 %), while blocking N-type channels with omega-conotoxin GVIA blocked the facilitation by ANG (2.3 +/- 2 %). Losartan (1 microM) prevented the actions of ANG on the inward current (1.6 +/- 1 %), indicating that the selective effects of ANG on N-type channels in SFO neurones are mediated by AT(1) receptors.

Circadian force and EMG activity in hindlimb muscles of rhesus monkeys.

Continuous intramuscular electromyograms (EMGs) were recorded from the soleus (Sol), medial gastrocnemius (MG), tibialis anterior (TA), and vastus lateralis (VL) muscles of Rhesus during normal cage activity throughout 24-h periods and also during treadmill locomotion. Daily levels of MG tendon force and EMG activity were obtained from five monkeys with partial datasets from three other animals. Activity levels correlated with the light-dark cycle with peak activities in most muscles occurring between 08:00 and 10:00. The lowest levels of activity generally occurred between 22:00 and 02:00. Daily EMG integrals ranged from 19 mV/s in one TA muscle to 3339 mV/s in one Sol muscle: average values were 1245 (Sol), 90 (MG), 65 (TA), and 209 (VL) mV/s. The average Sol EMG amplitude per 24-h period was 14 microV, compared with 246 microV for a short burst of locomotion. Mean EMG amplitudes for the Sol, MG, TA, and VL during active periods were 102, 18, 20, and 33 microV, respectively. EMG amplitudes that approximated recruitment of all fibers within a muscle occurred for 5-40 s/day in all muscles. The duration of daily activation was greatest in the Sol [151 +/- 45 (SE) min] and shortest in the TA (61 +/- 19 min). The results show that even a "postural" muscle such as the Sol was active for only approximately 9% of the day, whereas less active muscles were active for approximately 4% of the day. MG tendon forces were generally very low, consistent with the MG EMG data but occasionally reached levels close to estimates of the maximum force generating potential of the muscle. The Sol and TA activities were mutually exclusive, except at very low levels, suggesting very little coactivation of these antagonistic muscles. In contrast, the MG activity usually accompanied Sol activity suggesting that the MG was rarely used in the absence of Sol activation. The results clearly demonstrate a wide range of activation levels among muscles of the same animal as well as among different animals during normal cage activity.

Hormonal and neurotransmitter roles for angiotensin in the regulation of central autonomic function.

In this review we present the case for both hormonal and neurotransmitter actions of angiotensin II (ANG) in the control of neuronal excitability in a simple neural pathway involved in central autonomic regulation. We will present both single-cell and whole-animal data highlighting hormonal roles for ANG in controlling the excitability of subfornical organ (SFO) neurons. More controversially we will also present the case for a neurotransmitter role for ANG in SFO neurons in controlling the excitability of identified neurons in the paraventricular nucleus (PVN) of the hypothalamus. In this review we highlight the similarities between the actions of ANG on these two populations of neurons in an attempt to emphasize that whether we call such actions "hormonal" or "neurotransmitter" is largely semantic. In fact such definitions only refer to the method of delivery of the chemical messenger, in this case ANG, to its cellular site of action, in this case the AT1 receptor. We also described in this review some novel concepts that may underlie synthesis, metabolic processing, and co-transmitter actions of ANG in this pathway. We hope that such suggestions may lead ultimately to the development of broader guiding principles to enhance our understanding of the multiplicity of physiological uses for single chemical messengers.

A subthreshold persistent sodium current mediates bursting in rat subfornical organ neurones.

It is widely accepted that while release of amino acid neurotransmitters occurs with relatively high fidelity, peptidergic synapses require clustered bursts of action potentials for optimal transmitter release. Here we describe for the first time the occurrence and mechanisms of bursting by neurones in the subfornical organ (SFO), cells that utilize the peptide angiotensin II (ANG) in neurotransmission in autonomic pathways. In current clamp recording of isolated SFO neurones in vitro, 53 % (n = 74) showed either spontaneous or evoked burst-like discharge patterns. Bursts typically appeared as shifts in bistable membrane potential, with action potentials superimposed on a depolarizing afterpotential (DAP). Similarly, in vivo single unit recordings of identified SFO neurones showed that 9 of 15 neurones fired in bursts. The pattern of bursting, as well as duration of evoked DAPs was strongly dependent upon membrane potential, suggesting that the DAP contributes to burst generation. Based on our previous observation of calcium-sensing receptor (CaR)-activated bursts, we investigated the effects of NPS R-467, an allosteric agonist of the CaR, on evoked DAPs. NPS R-467 (1 microM) potentiated DAP duration throughout the voltage range tested. We observed a dependence of evoked DAPs upon Na+ channels, as shown by sensitivity to tetrodotoxin (0.5 microM) or reduction of external [Na+] from 140 to 40 mM. The duration of DAPs suggested that a persistent Na+ current mediates these events. Voltage-clamp analysis revealed the presence of a subthreshold sodium current, INaP. Pharmacological blockade of INaP with 100 microM lidocaine reduced the duration of evoked DAPs, and inhibited bursting in SFO neurones. Facilitation of INaP with 10 nM anemone toxin (ATX) increased DAP duration and led to marked excitation of bursting cells. These data indicate that INaP is the main current underlying bursting in SFO neurones. Our observations of receptor-mediated facilitation of bursting by SFO neurones represents an intriguing mechanism through which the release of the peptide neurotransmitter ANG may be regulated.

Intrinsic osmosensitivity of subfornical organ neurons.

The constancy of plasma osmolality demands that salt and water concentration within the extracellular fluid be constantly monitored and regulated within a few percentage points. The circumventricular organs in general, and the subfornical organ in particular, have long been proposed to be the site of the osmosensitivity. Isolated subfornical organ neurons of male rats were studied using the whole-cell patch-clamp technique and both action potential frequency and whole cell currents were measured as bath osmolality was changed, from 240 to 330mOsm, by altering the amount of mannitol and maintaining the concentrations of electrolytes constant. Out of 64 cells, 66% responded to changes in bath osmolality in a predictable manner, exhibiting a hyperpolarization and decrease in spike frequency in hypo-osmotic solutions and a depolarization and increase in action potential frequency during hyperosmotic exposure. Cells (34%) defined as non-responders exhibited no significant modulation during identical changes in extracellular osmolality. The responses to changing extracellular osmolality were dose dependent; the activity of subfornical organ neurons was significantly modulated by changes in extracellular osmolality of less than 10mOsm. By regression analysis, this osmosensitivity was approximately 0. 1Hz/mOsm change throughout a +/-10mOsm range and was maintained throughout the range of osmolalities studied (270-330mOsm). The mechanism underlying this osmosensitivity remains unclear, although the non-selective cation conductance and the volume-activated chloride conductance do not seem to be involved.This intrinsic osmosensitivity of subfornical organ within the normal physiological range supports the view that this circumventricular structure plays a role in normal osmoregulation.

Topographic mapping of brain potentials in the newborn infant: the establishment of normal values and utility in assessing infants with neurological injury.

AIM: To demonstrate that quantitative EEG (qEEG) can be used as a non-invasive measure of brain injury by establishing normative data in term infants and contrasting it with other modalities of brain imaging. DESIGN: qEEG during quiet sleep was performed on 13 healthy full-term infants comprising a normal group and on 10 infants with neurological abnormalities identified on brain imaging studies (abnormal group) at 36-47 wk postconceptional age. Quantitative analysis was performed and topographic maps were produced for each patient. The EEG data from the normal group, after spectral analysis, yielded power data in the delta, theta, alpha, and beta frequency bands and coherence information, which then formed the normative database. qEEG from the infants in the abnormal group was then compared to this normative data. RESULTS: The normal group's mean absolute power in the delta, theta, alpha, and beta bands for all EEG leads combined were 278.48+/-83.83, 31.71+/-10.12, 29.20+/-2.04, and 35.76+/-11.35 uv2, respectively. The median frequency was 1.49+/-0.07, 5.45+/-3.46, 9.74+/-5.11, and 18.01+/-3.38 Hz, respectively. The qEEG was abnormal in all 10 study infants, while abnormalities were noted in the clinical EEG in 4 of 10, in the neuroultrasound in 5 of 10, in the CT in one of 6, and in the MRI in 2 of 2 tested. CONCLUSIONS: qEEG appears to be a useful non-invasive method for measuring brain injury as it correlates well with other modalities of brain imaging and, if corroborated by further study, may, in fact, be more sensitive in determining abnormalities in brain function.

The calcium receptor modulates the hyperpolarization-activated current in subfornical organ neurons.

Here we report that neurons of the subfornical organ (SFO), a circumventricular structure devoid of a blood-brain barrier, show time-dependent, inward rectification indicative of the presence of a subthreshold, hyperpolarization-activated inward current (Ih). In whole-cell patch clamp experiments of isolated SFO neurons, we observed a Cs+-sensitive Ih in 47% of cells tested. Furthermore, we show that Ih is involved in the generation of evoked bursts in SFO neurons. An allosteric agonist of the extracellular calcium-sensing receptor (CaR) was found to potentiate Ih consistent with our previous observations of CaR-mediated bursting in SFO neurons. These studies indicate that a proportion of SFO neurons express Ih, and this may be one ionic mechanism through which bursting is regulated by various extracellular messengers.

Human breast cancer specimens: diffraction-enhanced imaging with histologic correlation--improved conspicuity of lesion detail compared with digital radiography.

Seven breast cancer specimens were examined with diffraction-enhanced imaging at 18 keV with a silicon crystal with use of the silicon 333 reflection in Bragg mode. Images were compared with digital radiographs of the specimen, and regions of increased detail were identified. Six of the seven cases (86%) showed enhanced visibility of surface spiculation that correlated with histopathologic information, including extension of tumor into surrounding tissue.

PTS performance by flight- and control-group macaques.

A total of 25 young monkeys (Macaca mulatta) were trained with the Psychomotor Test System, a package of software tasks and computer hardware developed for spaceflight research with nonhuman primates. Two flight monkeys and two control monkeys were selected from this pool and performed a psychomotor task before and after the Bion 11 flight or a ground-control period. Monkeys from both groups showed significant disruption in performance after the 14-day flight or simulation (plus one anesthetized day of biopsies and other tests), and this disruption appeared to be magnified for the flight animal.

Distinguishing interpretation from fact (DIFF): a computerized drill for methodology courses.

It is important for psychologists to distinguish between statements of fact and opinions in the research reports they read or hear. Surprisingly, this basic skill is not readily observed in undergraduate students. A computerized laboratory activity is described that permits students to practice this discrimination, and demonstration data are reported to support the effectiveness of the exercise.

Effects of processing conditions on mammographic image quality.

RATIONALE AND OBJECTIVES: Any given mammographic film will exhibit changes in sensitometric response and image resolution as processing variables are altered. Developer type, immersion time, and temperature have been shown to affect the contrast of the mammographic image and thus lesion visibility. The authors evaluated the effect of altering processing variables, including film type, developer type, and immersion time, on the visibility of masses, fibrils, and speaks in a standard mammographic phantom. MATERIALS AND METHODS: Images of a phantom obtained with two screen types (Kodak Min-R and Fuji) and five film types (Kodak Min-R M, Min-R E, Min-R H; Fuji UM-MA HC, and DuPont Microvision-C) were processed with five different developer chemicals (Autex SE, DuPont HSD, Kodak RP, Picker 3-7-90, and White Mountain) at four different immersion times (24, 30, 36, and 46 seconds). Processor chemical activity was monitored with sensitometric strips, and developer temperatures were continuously measured. The film images were reviewed by two board-certified radiologists and two physicists with expertise in mammography quality control and were scored based on the visibility of calcifications, masses, and fibrils. RESULTS: Although the differences in the absolute scores were not large, the Kodak Min-R M and Fuji films exhibited the highest scores, and images developed in White Mountain and Autex chemicals exhibited the highest scores. CONCLUSION: For any film, several processing chemicals may be used to produce images of similar quality. Extended processing may no longer be necessary.

Inhibition of subfornical organ neuronal potassium channels by vasopressin.

The subfornical organ is one of a specialized group of CNS structures devoid of a significant blood-brain barrier, collectively known as the circumventricular organs. While peptides are normally excluded from access to most regions of the CNS, the subfornical organ contains neurons with a high density of receptors for many circulating peptides, including vasopressin. There is a well-established role for the subfornical organ in stimulating the release of vasopressin, and recent evidence suggests that it may also play an important role in mediating the negative feedback actions of vasopressin. The aim of this study was to determine the direct effects of vasopressin on subfornical organ neurons through patch-clamp studies in a dissociated subfornical organ preparation. In current-clamp studies, bath application of 10 nM vasopressin caused depolarizations in 61%, hyperpolarizations in 11%, and no significant change in membrane potential in 28% of neurons tested. We then sought to determine the specific ion channels involved in regulating the vasopressin-induced excitability of subfornical organ neurons through voltage-clamp studies. Vasopressin (10 nM) decreased the peak outward current at +40 mV by 50% (n=7), which was blocked by pretreatment with a V1 receptor antagonist (n=5). Based on these findings, we carried out a systematic characterization of two subformical organ K+ channels, the delayed rectifier (I(K)) and the transient outward current (I(A)). Through voltage isolation of I(K), we found that vasopressin inhibited the steady-state current, by 33+/-7% (n=9). Vasopressin also inhibited the peak I(A) by 27+/-5% (n=8). These data provide the first evidence of a role for K+ channels in mediating the excitatory effects of vasopressin on subfornical organ neurons. The exact physiological roles and sources of vasopressin which may act on subfornical organ neurons are not completely understood at present.

Control of neuronal excitability by an ion-sensing receptor (correction of anion-sensing)

While most central nervous system (CNS) neurons receive the majority of their input through direct synaptic connections, there is evidence suggesting that they are in fact susceptible to modulation by changes in extracellular ionic composition during both physiological and pathophysiological conditions. In many regions of the CNS, there exists an identified extracellular receptor with the ability to sense levels of cations, most notably calcium. Here we report that activation of this calcium receptor (CaR) in neurons of the subfornical organ (SFO), a forebrain circumventricular structure, results in profound effects on neuronal excitability through metabotropic actions on a non-selective cation channel. Activation of the CaR by NPS R-467, an allosteric agonist of the CaR, evoked depolarizing plateau potentials ranging in duration from 5 to 30 s. Similarly, 5 mm CaCl2 caused depolarization and increased action potential frequency. NPS R-467 was found to activate a non-selective cation channel with a reversal potential of -48 +/- 4 mV, and a slope conductance of 2.54 +/- 11 nS. This current could also be elicited by spermine, a known agonist of the CaR. CaR-mediated activation of this channel was dependent upon both G proteins and intracellular Ca2+ signalling, as disruption of these pathways through inclusion of guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S) and 1,2-bis(2-aminophenoxy)ethane-N,N,N ',N '-tetraacetic acid (BAPTA), respectively, in the recording pipette prevented activation of the current. Microinjection of CaR agonists into the SFO of anaesthetized rats resulted in a significant, site-specific elevation of blood pressure (mean area under curve, 141 +/- 50 mmHg. s). Together, these results indicate that the CaR can play an important role in transducing the effects of changes in the extracellular ionic composition, and that these effects have implications for the neural control of fluid balance.

Effects of spaceflight on rhesus quadrupedal locomotion after return to 1G.

Effects of spaceflight on Rhesus quadrupedal locomotion after return to 1G. Locomotor performance, activation patterns of the soleus (Sol), medial gastrocnemius (MG), vastus lateralis (VL), and tibialis anterior (TA) and MG tendon force during quadrupedal stepping were studied in adult Rhesus before and after 14 days of either spaceflight (n = 2) or flight simulation at 1G (n = 3). Flight simulation involved duplication of the spaceflight conditions and experimental protocol in a 1G environment. Postflight, but not postsimulation, electromyographic (EMG) recordings revealed clonus-like activity in all muscles. Compared with preflight, the cycle period and burst durations of the primary extensors (Sol, MG, and VL) tended to decrease postflight. These decreases were associated with shorter steps. The flexor (TA) EMG burst duration postflight was similar to preflight, whereas the burst amplitude was elevated. Consequently, the Sol:TA and MG:TA EMG amplitude ratios were lower following flight, reflecting a "flexor bias." Together, these alterations in mean EMG amplitudes reflect differential adaptations in motor-unit recruitment patterns of flexors and extensors as well as fast and slow motor pools. Shorter cycle period and burst durations persisted throughout the 20-day postflight testing period, whereas mean EMG returned to preflight levels by 17 days postflight. Compared with presimulation, the simulation group showed slight increases in the cycle period and burst durations of all muscles. Mean EMG amplitude decreased in the Sol, increased in the MG and VL, and was unchanged in the TA. Thus adaptations observed postsimulation were different from those observed postflight, indicating that there was a response unique to the microgravity environment, i.e., the modulations in the nervous system controlling locomotion cannot merely be attributed to restriction of movement but appear to be the result of changes in the interpretation of load-related proprioceptive feedback to the nervous system. Peak MG tendon force amplitudes were approximately two times greater post- compared with preflight or presimulation. Adaptations in tendon force and EMG amplitude ratios indicate that the nervous system undergoes a reorganization of the recruitment patterns biased toward an increased recruitment of fast versus slow motor units and flexor versus extensor muscles. Combined, these data indicate that some details of the control of motor pools during locomotion are dependent on the persistence of Earth's gravitational environment.

Comparison of levels of human immunodeficiency virus type 1 RNA in plasma as measured by the NucliSens nucleic acid sequence-based amplification and Quantiplex branched-DNA assays.

This study compared levels of human immunodeficiency virus type 1 RNA in plasma as measured by the Quantiplex branched-DNA and NucliSens nucleic acid sequence-based amplification assays. RNA was detectable in 118 of 184 samples (64.13%) by the Quantiplex assay and in 171 of 184 samples (92.94%) by the NucliSens assay. Regression analysis indicated that a linear relationship existed between the two sets of values (P < 0.0001), although the Quantiplex and NucliSens values were significantly different (P < 0.001), with the NucliSens values being approximately 0.323 log higher. Spearman correlation analysis indicated that the overall changes in patient viral load patterns were highly correlative between the two assays: r = 0.912, P < 0.0001. The lower limits of sensitivity were determined to be approximately 100 copies/ml and 1,200 to 1,400 copies/ml for the NucliSens and Quantiplex assays, respectively.

Memory monitoring by animals and humans.

The authors asked whether animals and humans would use similarly an uncertain response to escape indeterminate memories. Monkeys and humans performed serial probe recognition tasks that produced differential memory difficulty across serial positions (e.g., primacy and recency effects). Participants were given an escape option that let them avoid any trials they wished and receive a hint to the trial's answer. Across species, across tasks, and even across conspecifics with sharper or duller memories, monkeys and humans used the escape option selectively when more indeterminate memory traces were probed. Their pattern of escaping always mirrored the pattern of their primary memory performance across serial positions. Signal-detection analyses confirm the similarity of the animals' and humans' performances. Optimality analyses assess their efficiency. Several aspects of monkeys' performance suggest the cognitive sophistication of their decisions to escape.