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Many studies of synaptic transmission have assumed a parametric model to estimate the mean quantal content and size or the effect upon them of manipulations such as the induction of long-term potentiation. Classical tests of fit usually assume that model parameters have been selected independently of the data. Therefore, their use is problematic after parameters have been estimated. We hypothesized that Monte Carlo (MC) simulations of a quantal model could provide a table of parameter-independent critical values with which to test the fit after parameter estimation, emulating Lilliefors's tests. However, when we tested this hypothesis within a conventional quantal model, the empirical distributions of two conventional goodness-of-fit statistics were affected by the values of the quantal parameters, falsifying the hypothesis. Notably, the tests' critical values increased when the combined variances of the noise and quantal-size distributions were reduced, increasing the distinctness of quantal peaks. Our results support two conclusions. First, tests that use a predetermined critical value to assess the fit of a quantal model after parameter estimation may operate at a differing unknown level of significance for each experiment. Second, a MC test enables a valid assessment of the fit of a quantal model after parameter estimation.

This manuscript describes methods for preparing, visualizing, and recording from healthy perirhinal cortex neurons in brain slices from young and aging rats. We focused on perirhinal cortex because of its role in learning, memory, and aging-related cognitive decline. Detailed accounts of our dissection procedures are reported. Procedures that reliably yielded healthy neurons from juvenile rats were not conducive to obtaining healthy, readily-patchable neurons from aging rats, suggesting a procedure-by-age interaction. Performing an intracardiac perfusion, using a temperature-controlled vibratome, matching osmolarity between the cutting and incubation saline, using a slow cutting speed, and incubating slices at a warm temperature for 30 min were important when working with older tissue. Excellent visualization of neurons at depths of up to 100 microm was achieved in slices from all ages (without tissue clearing) avoiding the need to record from surface neurons, which are more likely to have truncated processes. Whole-cell recordings typically remained stable for several hours in neurons prepared from rats at all ages. These procedures should benefit neuroscientists interested in applying visually-guided whole-cell patch-clamp techniques to brain slice experiments using aged tissue. These methods should also facilitate the application of fluorescent imaging technology to brain slices for studying aging-related changes.

Excitatory postsynaptic currents (EPSCs) evoked in hippocampal CA3 pyramidal neurons by extracellular stimulation of the dentate gyrus typically exhibit complex waveforms. They commonly have inflections or notches on the rising phase; the decay phase may exhibit notches or other obvious departures from a simple monoexponential decline; they often display considerable variability in the latency from stimulation to the peak current; and the rise times tend to be long. One hypothesis is that these complex EPSC waveforms might result from excitation via other CA3 pyramidal cells that were recruited antidromically or trans-synaptically by the stimulus due to the complex anatomy of this region. An alternative hypothesis is that EPSC complexity does not emerge from the functional anatomy but rather reflects an unusual physiological property, intrinsic to excitation-secretion coupling in mossy-fiber (mf) synaptic terminals, that causes asynchronous quantal release. We evaluated certain predictions of our anatomic hypothesis by adding a pharmacological agent to the normal bathing medium that should suppress di- or polysynaptic responses. For this purpose we used baclofen (3 microM), a selective agonist for the gamma-aminobutyric acid B receptor. The idea was that baclophen should discriminate against polysynaptic versus monosynaptic inputs by hyperpolarizing the cells, bringing them further from spike threshold and possibly also through inhibitory presynaptic actions. Whole cell recordings were done from visually preselected CA3 pyramidal neurons and EPSCs were evoked by fine bipolar electrodes positioned into the granule cell layer of the dentate. To the extent that the EPSC complexity reflects di- or polysynaptic responses, we predicted baclofen to reduce the number of notches on the rising and decay phases, reduce the variance in latency to peak of the EPSCs, decrease the amplitudes and rise times of the individual and averaged EPSCs, and increase the apparent failures in evoked EPSCs. All of these predictions were confirmed, in support of the hypothesis that these complex EPSC waveforms commonly reflect di- or polysynaptic responses. We also documented a distinctly different, intermittent, form of EPSC complexity, which also is predicted and easily explained by our anatomic hypothesis. In particular, the results were in accord with the suggestion that stimulation of the dentate gyrus might antidromically stimulate axon collaterals of CA3 neurons that make recurrent synapses onto the recorded cell. We conclude that the overall pattern of results is consistent with expectations based on the functional anatomy. The explanation does not demand a special type of intrinsic asynchronous mechanism for excitation-secretion coupling in the mf synapses.

The eyeblink reflex is one of the most extensively studied behaviors in mammals. The active downward force that causes lid closure is controlled by the orbicularis oculi (OO) muscle. To augment our studies on the neurophysiology and plasticity of the rat eyeblink circuit, here we present the first anatomical paper to focus exclusively on identifying and characterizing the OO motoneurons of the rat facial motor nucleus (FMN). One thousand and twenty-nine cells from four animals were retrogradely labeled by injecting the OO muscle with HRP and were imaged conventionally. One hundred and one cells from five animals were labeled by injecting the OO muscle with a 3000 mol. wt. fluorescent dextran and were imaged using confocal laser scanning microscopy (CLSM). The latter method resulted in little tissue shrinkage, bright labeling, and excellent resolution of the soma, dendrites, and axon. Furthermore, it is a histologically simple alternative to HRP for retrograde labeling from the neuromuscular junction. Both methods revealed that the OO motoneurons were distributed over the entire length of the FMN, that they were concentrated along the dorsal crest of the nucleus, and that they were less numerous in the extreme rostral and caudal regions. As measured using the CLSM method, cell body areas were highly variable, ranging from 317 to 1500 microm2, but there was no size gradient along the rostrocaudal extent of the FMN. The neurons exhibited seven primary dendrites on average, which gave rise to bifurcating and even trifurcating secondary dendrites. Using the HRP method, the estimated area of OO motoneurons ranged from 161 to 1381 microm2. The combined methods furnished a detailed characterization of the number, spatial distribution, and morphology of rat OO motoneurons. Moreover, these methods provide a useful way to analyze the circuitry that modulates the rat eyeblink.

We present a comparative analysis of electrotonus in the three classes of principal neurons in rat hippocampus: pyramidal cells of the CA1 and CA3c fields of the hippocampus proper, and granule cells of the dentate gyrus. This analysis used the electrotonic transform, which combines anatomic and biophysical data to map neuronal anatomy into electrotonic space, where physical distance between points is replaced by the logarithm of voltage attenuation (log A). The transforms were rendered as "neuromorphic figures" by redrawing the cell with branch lengths proportional to log A along each branch. We also used plots of log A versus anatomic distance from the soma; these reveal features that are otherwise less apparent and facilitate comparisons between dendritic fields of different cells. Transforms were always larger for voltage spreading toward the soma (V(in)) than away from it (V(out)). Most of the electrotonic length in V(out) transforms was along proximal large diameter branches where signal loss for somatofugal voltage spread is greatest. In V(in) transforms, more of the length was in thin distal branches, indicating a steep voltage gradient for signals propagating toward the soma. All transforms lengthened substantially with increasing frequency. CA1 neurons were electrotonically significantly larger than CA3c neurons. Their V(out) transforms displayed one primary apical dendrite, which bifurcated in some cases, whereas CA3c cell transforms exhibited multiple apical branches. In both cell classes, basilar dendrite V(out) transforms were small, indicating that somatic potentials reached their distal ends with little attenuation. However, for somatopetal voltage spread, attenuation along the basilar and apical dendrites was comparable, so the V(in) transforms of these dendritic fields were nearly equal in extent. Granule cells were physically and electrotonically most compact. Their V(out) transforms at 0 Hz were very small, indicating near isopotentiality at DC and low frequencies. These transforms resembled those of the basilar dendrites of CA1 and CA3c pyramidal cells. This raises the possibility of similar functional or computational roles for these dendritic fields. Interpreting the anatomic distribution of thorny excrescences on CA3 pyramidal neurons with this approach indicates that synaptic currents generated by some mossy fiber inputs may be recorded accurately by a somatic patch clamp, providing that strict criteria on their time course are satisfied. Similar accuracy may not be achievable in somatic recordings of Schaffer collateral synapses onto CA1 pyramidal cells in light of the anatomic and biophysical properties of these neurons and the spatial distribution of synapses.

Confocal laser scanning microscopy was used to visualize Ca2+ transients in a particular type of dendritic spine, known as a thorny excrescence, in hippocampal CA3 pyramidal neurons. These large excrescences or thorns, which serve as the postsynaptic target for the mossy-fiber synaptic inputs, were identified on the basis of their location, frequency, and size. Whole cell recordings were made from superficial CA3 pyramidal neurons in thick hippocampal slices with the use of infrared video microscopy; cells with proximal apical dendrites close to the surface of the slice were selected. Changes in intracellular Ca2+ levels were monitored by imaging changes in fluorescence of the dyes Calcium Green-1 and Fluo-3. Dual-emission fluorescence imaging was also employed with the use of a combination of Fluo-3 and the Ca2+-insensitive dye seminaphthorhodafluor-1. This method was used to decrease the potential influence of background fluorescence on the calculated changes in intracellular Ca2+ concentration ([Ca2+]i). Somatic depolarization produced increases in [Ca2+]i in both the thorn and the immediately adjacent dendrite. Changes in [Ca2+]i were time locked with the onset of depolarization and the decay began immediately after the termination of depolarization. The peak increase in the Ca2+ signal was significantly greater in the thorns than in the adjacent dendritic shafts. With the use of high-temporal-resolution methods (line scans), differences were also seen in the time course of Ca2+ signals in these two regions. The decay time constants of the Ca2+ signal were faster in thorns than in the adjacent dendritic shafts. These observations suggest that voltage-gated Ca2+ channels are localized directly on the dendritic spines receiving mossy-fiber input. Furthermore, Ca2+ homeostasis within thorny excrescences is distinct from Ca2+ regulation in the dendritic shaft, at least over brief time periods, a finding that could have important implications for synaptic plasticity and signaling.

The effects of SB 206284A, 1-[7-(4-benzyloxyphenoxy)heptyl] piperidine hydrochloride, have been investigated in vitro on calcium and sodium currents in rat-cultured dorsal root ganglion (DRG) neurones and potassium-mediated calcium influx in rat synaptosomes. Cardiovascular hemodynamic effects in both anesthetized and conscious rats, and neuroprotective activity in in vivo cerebral ischemia models were also investigated. In the rat DRG cells, SB 206284A caused almost complete block of the sustained inward Ca2+ current (IC50 = 2.4 microM), suggesting that the compound is an effective blocker of slowly inactivating, high-voltage calcium current. SB 206284A reduced locomotor hyperactivity in the gerbil bilateral carotid artery occlusion model without affecting ischemia-induced damage in the hippocampal CA1 region. In the rat middle cerebral artery occlusion model, SB 206284A reduced lesion volume in the posterior forebrain, and in the rat photochemical cortical lesion model, lesion volume was reduced even when treatment was delayed until 4 hours after occlusion. At neuroprotective doses, SB 206284A had no cardiovascular effects. These findings show that SB 206284A is a novel calcium channel antagonist that shows neuroprotective properties.

Conditioned enhancement of the rat eyeblink reflex was studied using as a response measure the electromyogram (EMG) in the orbicularis oculi (oo) muscle, which is responsible for the active force generating eyelid closure. During a reflex eyeblink, the EMG evidences both a short-latency (R1) and a long-latency (R2) component, mediated by different circuits. The R2 response exhibits several experience- or use-dependent modifications. We were interested in the modifiability of the neurophysiologically simpler R1 response. Experiments were designed to determine whether the R1 response can be enhanced by a conditioned stimulus (CS) that has been explicitly paired with an aversive unconditioned stimulus (US). The R1 response was elicited by electrical stimulation of the supraorbital branch of the trigeminal nerve. Following long-delay conditioning, the CS produced a significant R1 enhancement and latency decrease that were dependent upon explicit CS-US pairings. The CS by itself produced no significant EMG response, consistent with a modulatory rather than additive effect. This is the first demonstration that the R1 response can be associatively modulated. Based on other evidence, we hypothesize that the CS-produced enhancement results from a relatively direct projection from the amygdala to the R1 circuit. As an index of aversive conditioning, R1 enhancement may prove to be a useful expression system because it offers high temporal resolution and the underlying circuitry is relatively simple-the shortest path from the fifth nerve to the muscle consisting of only two central synapses.

1. The spread of electrical signals in pyramidal neurons from the CA1 field of rat hippocampus was investigated through multicompartmental modeling based on three-dimensional morphometric reconstructions of four of these cells. These models were used to dissect the electrotonic architecture of these neurons, and to evaluate the equivalent cylinder approach that this laboratory and others have previously applied to them. Robustness of results was verified by the use of wide ranges of values of specific membrane resistance (Rm) and cytoplasmic resistivity. 2. The anatomy exhibited extreme departures from a key assumption of the equivalent cylinder model, the so-called "3/2 power law." 3. The compartmental models showed that the frequency distribution of steady-state electrotonic distances between the soma and the dendritic terminations was multimodal, with a large range and a sizeable coefficient of variation. This violated another central assumption of the equivalent cylinder model, namely, that all terminations are electronically equidistant from the soma. This finding, which was observed both for "centrifugal" (away from the soma) and "centripetal" (toward the soma) spread of electrical signals, indicates that the concept of an equivalent electrotonic length for the whole dendritic tree is not appropriate for these neurons. 4. The multiple peaks in the electrotonic distance distributions, whether for centrifugal or centripetal voltage transfer, were clearly related to the laminar organization of synaptic afferents in the CA1 region. 5. The results in the three preceding paragraphs reveal how little of the electrotonic architecture of these neurons is captured by a simple equivalent cylinder model. The multicompartmental model is more appropriate for exploring synaptic signaling and transient events in CA1 pyramidal neurons. 6. There was significant attenuation of synaptic potential, current, and charge as they spread from the dendritic tree to the soma. Charge suffered the least and voltage suffered the most attenuation. Attenuation depended weakly on Rm and strongly on synaptic location. Delay of time to peak was more distorted for voltage than for current and was more affected by Rm. 7. Adequate space clamp is not possible for most of the synapses on these cells. Application of a somatic voltage clamp had no significant effect on voltage transients in the subsynaptic membrane. 8. The possible existence of steep voltage gradients within the dendritic tree is consistent with the idea that there can be some degree of local processing and that different regions of the neuron may function semiautonomously. These spatial gradients are potentially relevant to synaptic plasticity in the hippocampus, and they also suggest caution in interpreting some neurophysiological results.

A biliary-cutaneous fistula occurring as a late complication of laparoscopic cholecystectomy is described. The fistula was associated with retained gallstone fragments following intra-operative spillage and attempted retrieval. The fate of intra-peritoneal gallstones is reviewed and preventative measures discussed.

Amygdala stimulation was shown to enhance the trisynaptic (fast, R1) component of the electromyogram recorded in the rat orbicularis oculi (oo) muscle, which is responsible for the active force generating eyelid closure. The eyeblink was elicited via direct electrical stimulation of the supraorbital branch of the trigeminal nerve. Possible mechanisms responsible for the effect of amygdala stimulation on the eyeblink reflex were evaluated by measuring the amount of R1 enhancement as a function of the interstimulus interval (ISI) between the onset of amygdala and trigeminal nerve stimulation. Amygdala stimulation produced significant R1 enhancement at ISIs that imply short-latency excitation of the eyeblink circuit by way of a fast-acting neurotransmitter.

Quinazolines bearing a secondary 4-(arylamino) substituent demonstrate an SAR for inhibition of the gastric (H+/K+)-ATPase different from the previously described 3-acylquinolines, suggesting that, although these compounds are also K(+)-competitive, they probably bind to the enzyme in a different orientation. Compounds bearing a tertiary 4-(arylamino) substituent, however, in particular 4-(N-methylarylamino), appear to possess an SAR quite similar to the 3-acylquinolines. We show that this arises from the effect of the N-methylation, which is to orientate the 4-(arylamino) substituent syn to C5, analogous to the 3-acylquinolines. Compounds possessing both a 4-(N-methylarylamino) substituent and a 2-(arylamino) substituent proved to be very potent, K(+)-competitive inhibitors of K(+)-stimulated ATPase activity with Ki values down to 12 nM. Some compounds also proved to be effective inhibitors of stimulated acid secretion in both the rat and dog when dosed intravenously. However, although a number of these demonstrated activity after oral administration in the dog, the level and variability precluded further evaluation.

3-Acyl-4-(arylamino)quinolines were previously identified as gastric (H+/K+)-ATPase inhibitors, and clinical efficacy has been demonstrated for compound 3 (SK&F 96067). In the present study the further structure-activity relationship of this series is developed. Only a limited range of substituents are tolerated on the N-aryl ring or the 6- and 7-positions of the quinoline, and although hydroxylated derivatives were identified possessing markedly greater affinity for the enzyme, none of these proved to have adequate potency after oral dosing. In contrast, the 8-position of the quinoline ring proved suitable for a wide variety of substituents, allowing modification of physicochemical properties while retaining primary activity. This led to the identification of compound 4 (SK&F 97574), which combines good oral potency with a somewhat longer duration of action than 3 (though much shorter than covalent inhibitors such as omeprazole). This compound was selected for further development and evaluation in man.

Confocal laser scanning microscopy (CLSM) was used to visualize presynaptic elements of mossy-fiber synapses in living rat hippocampal slices. Mossy fiber (mf) axons and their boutons were labeled in transverse hippocampal slices by injecting one of three fluorescent dyes (diI, diA, or fast diI) into stratum granulosum of the dentate gyrus and/or stratum lucidum of CA3. Three-dimensional (3D) images of the mf boutons were obtained from serial optical sections in stratum lucidum. The 3D data were used to quantify and characterize the size and shape of the boutons based on their volumes (V) and surface areas (A), and the latter were compared with conventional 2D analyses. Various geometric models were fitted to the V-A relationship, one of which provided a reasonable approximation to the data. The results demonstrate that this approach is useful for quantifying and characterizing the size and shape of mf expansions and raise the possibility of detecting and analyzing in real time activity-dependent modifications in presynaptic structure.

Changes in the intracellular Ca2+ concentration ([Ca2+]i) within CA1 hippocampal pyramidal neurons were imaged using confocal laser scanning microscopy in conjunction with Ca(2+)-sensitive fluorescent indicators. The imaging was performed in thick hippocampal brain slices while simultaneously measuring or controlling electrical activity with sharp microelectrodes or whole-cell patch-clamp electrodes. The combination of imaging and electrophysiology was essential for interpreting the changes in [Ca2+]i. We compared the increases in [Ca2+]i produced by either of two methods--direct depolarization of the cell via the somatic electrode or high-frequency stimulations of synaptic inputs. The increases in [Ca2+]i in the soma and proximal dendrites caused by both methods were of comparable magnitude and they always decayed within seconds in healthy cells. However, the spatial patterns of distal Ca2+ increases were different. Separate sets of synaptic inputs to the same cell resulted in different spatial patterns of [Ca2+]i transients. We isolated and observed what appeared to be a voltage-independent component of the synaptically mediated [Ca2+]i transients. This work demonstrates that the combination of neurophysiology and simultaneous confocal microscopy is well suited for visualizing and analyzing [Ca2+]i changes within highly localized regions of neurons in thick brain slices. The approach should allow further analysis of the relative contribution of voltage- and agonist-dependent influences on [Ca2+]i within neurons throughout the CNS and it raises the possibility of routinely relating subcellular [Ca2+]i changes to structural and functional modifications.

1. We investigated the effects of metabotropic glutamate (mGlu) receptor activation on intracellular Ca2+ concentration ([Ca2+]i) in the soma and dendrites of hippocampal CA1 pyramidal neurons. Changes in [Ca2+]i were measured using confocal imaging simultaneously with whole-cell recording techniques. Differences in [Ca2+]i were visualized as changes in the fluorescence of the Ca(2+)-sensitive dye Fluo-3. 2. Brief application of the specific mGlu receptor agonist (1S,3R)-ACPD to either the apical or basal dendrites produced initially localized increases in [Ca2+]i that subsequently propagated as waves throughout much of the neuron. These Ca2+ waves, which propagated at approximately 40 microns/s, were shown not to reflect intracellular Ca2+ diffusion or extracellular diffusion of ACPD and were always accompanied by small outward membrane currents. 3. Repetitive application of ACPD failed to trigger further Ca2+ release. We found that a threshold level of voltage-gated Ca2+ entry during trains of action potentials was needed to prime further mGlu-stimulated Ca2+ release. In contrast, the passage of time alone did not cause the mGlu-release system to reactivate--restoration of ACPD-stimulated Ca2+ release. The spike-mediated Ca2+ signal was unaffected by mGlu-stimulated depletion of intracellular stores. 4. These experiments demonstrate that specific mGlu receptor activation can mobilize Ca2+ in dendrites of CA1 neurons and trigger waves of Ca(2+)-induced Ca(2+)-release throughout the cell. A use-dependent relationship between voltage-gated Ca2+ entry during trains of action potentials and mGlu-stimulated Ca2+ release is suggested.

1. The quantal mechanism underlying the expression of long-term potentiation (LTP) was studied in the mossy-fiber (mf) synapses of the rat hippocampus. Whole-cell recordings were used to measure the excitatory postsynaptic currents (EPSCs) before and after LTP induction in brain slices maintained at 31 +/- 1 degrees C. 2. Evoked EPSCs were recorded from 473 CA3 pyramidal neurons. The mf synapses were stimulated using paired pulses (40-ms interpulse interval) repeated every 2-10 s. At least 400 pairs of mf responses were obtained before and during the expression of LTP, which was produced by high-frequency (100 Hz) mf stimulation. Sufficiently stationary data were obtained from five neurons that exhibited LTP and that also satisfied strict criteria and procedures that are necessary for eliciting and identifying unitary mf responses. 3. Three independent lines of evidence implicated a presynaptic component to the mechanism underlying mf LTP. The first was based on a graphical version of the classical method of variance. The graphical variance (GV) method was evaluated by clamping the cell at two different holding potentials during paired-pulse facilitation (PPF). The results indicated that the GV method can distinguish changes in mean quantal content m and mean quantal size q in rat mf synapses. The same analysis, when applied to PPF before and after LTP induction, indicated that both result from an increase in m. 4. The second line of evidence was based on the classical method of failures. Consistent with the inference that mf LTP is due to an increase in m, there was a statistically significant reduction in the number of quantal release failures.(ABSTRACT TRUNCATED AT 250 WORDS)

The induction of long-term potentiation (LTP) is generally assumed to be triggered by Ca2+ entry into dendritic spines via NMDA receptor-gated channels. A previous computational model proposed that spines serve several functions in this process. First, they compartmentalize and amplify increase in [Ca2+]i. Second, they augment the nonlinear relationship between synaptic strength and the probability or magnitude of LTP induction. Third, they isolate the metabolic machinery responsible for LTP induction from increases in [Ca2+]i produced by voltage-gated Ca2+ channels in the dendritic shaft. Here we examine this last prediction of the model using methods that combine confocal microscopy with simultaneous neurophysiological recordings in hippocampal brain slices. Either of two Ca(2+)-sensitive dyes were injected into CA1 pyramidal neurons. Direct depolarization of the neurons via the somatic electrode produced clear increases in Ca2+ signals within the dendritic spines, a result that was not predicted by the previous spine model. Our new spine model suggests that some of this signal could theoretically result from Ca(2+)-bound dye diffusing from the dendritic shaft into the spine. Dye diffusion alone cannot, however, explain the numerous cases in which the Ca2+ signal in the spine was considerably larger than that in the adjacent dendritic shaft. The latter observations raise the possibility of voltage-gated Ca2+ entry directly into the spine or else perhaps via Ca(2+)-dependent Ca2+ release. The new spine model accommodates these observations as well as several other recent experimental results.

We have characterised the Ca2+ channel blocking properties of a new non-peptide Ca2+ channel antagonist, SB 201823-A, in cultures of rat sensory neurones. The IC50 for SB 201823-A against total Ca2+ current in sensory neurones was 4.9 microM. SB 201823-A showed little selectivity for sub-types of neuronal Ca2+ channel but was selective for Ca2+ channels over Na+ and K+ channels. Efficacy against other types of cation channel such as agonist gated channels was not assessed. SB 201823-A was neuroprotective in vivo when administered post-ischaemia in one focal and one global model of neuronal ischaemia. In the rat photothrombotic focal lesion model, SB 201823-A administered i.p. 10 min post-ischaemia resulted in a dramatic reduction in lesion volume. In the gerbil bilateral carotid artery occlusion global model, SB 201823-A dosed i.p. 30 min post-occlusion resulted in both histological and functional improvements when compared to vehicle treated animals. These data suggest that such novel neuronal Ca2+ channel antagonists may have potential in ameliorating both the pathological and functional consequences of stroke in man.

Much of the current interest in the hippocampus concerns a rapid and persistent form of synaptic plasticity, called long-term potentiation (LTP), that is a candidate substrate for some of the mnemonic functions of this structure. There are at least two kinds of LTP in the hippocampus. One form is found at the synapse between the mossy fibers of the granule cells and the pyramidal neurons of the CA3 region. Attempts to examine the mechanism underlying this form of LTP have yielded contradictory conclusions. The authors show how the complex circuitry of the dentate gyrus and adjacent hippocampus may have caused the contradictions. To overcome problems introduced by the circuitry, a specific set of procedures and criteria for evoking and identifying mossy fiber responses is proposed. Use of these or similar procedures and criteria will improve the design and interpretation of experiments on mossy fiber LTP and allow more informative comparisons among species and brain regions and across laboratories.

The synchronous performance of aortic and gastrointestinal surgery may hold an increased risk of aortic graft infection. The experience of one surgeon who performed 32 such synchronous operations over a period of 11 years is reviewed. No graft infection occurred and it is concluded that such combined operations may be safer to perform than staged surgery in elderly patients.

Previously, gastric (H+/K+)-ATPase inhibitors such as 2 have been prepared as analogues of 1a on the presumption that the 3-carbethoxy substituent plays a key role in establishing the orientation of the 4-arylamino group. In this paper we explore further the contribution made to activity by the quinoline 3-substituent. We show that, for compounds bearing such a substituent, only a particular combination of properties provides high activity, both in vitro and as inhibitors of gastric acid secretion in vivo. The ability of the substituent to affect activity by restricting rotation about the Cquin-N bond through a combination of both a pi-electron withdrawal and hydrogen bonding is supported by the current study. However, high activity is only achieved if the effect of this group on the quinoline pK(a) is kept to a minimum. 3-Acyl substituents provide an optimum combination of electronic properties. From this series, compound 17c (SK&F 96067) was shown to be a potent inhibitor of histamine-stimulated gastric acid secretion after oral dosing in the Heidenhain pouch dog and was selected for further development and evaluation in man.

In this study we compared the results of measurement of duodenogastric reflux using 24-hour intragastric pH monitoring and nasogastric aspiration with analysis of bile acid and alpha amylase concentrations. Eight patients were studied at least 5 months after biliary and/or gastric surgery. The correlation coefficient of pH and bile acid concentration was 0.36 (p less than 0.001) and of pH and amylase concentration was 0.48 (p less than 0.001). If a pH greater than 4.0 was taken to indicate duodenogastric reflux this had a sensitivity of 84% compared with either high bile acid or amylase concentration. Bile acid concentration has been the "standard" method of measuring duodenogastric reflux. pH monitoring is relatively simple to perform, causes little patient distress, and can measure episodes of duodenogastric reflux over a continuous 24-hour period.

Further work on compounds 1 has identified the 4-position as a site where substantial modifications are tolerated, leading to analogues which are more potent and less toxic than those described previously. The best compound in the series is 13a (SK&F 96356), which is a potent inhibitor of gastric acid secretion in both the pentagastrin-stimulated rat and the histamine-stimulated dog. This compound shows reversible, K(+)-competitive binding to the enzyme. Because of its fluorescent properties, it is also proving useful in vitro as a probe of the structure and function of the (H+/K+)-ATPase.

A modified technique for the recovery of larvae from pasture is described involving two centrifugations of pasture washings in a solution of potassium iodide. On average, the technique recovered 96% of larvae and was simple to perform. At three sites in South Australia (rainfall 550-330 mm year-1), the numbers of larvae present on pasture each month using this technique was compared with results obtained using one or four tracer sheep. The general pattern of larval availability was similar using the two methods, but discrepancies were noted. In some instances, particularly when numbers of larvae were low, pasture sampling underestimated the numbers of larvae available to sheep; in other situations, when the numbers of larvae were high, tracer sheep probably underestimated the number being ingested. Increasing the numbers of tracer sheep from one to four did not appreciably increase the correspondence between the two methods.

We present a biophysical model of electrical and Ca(2+) dynamics following activation of N-methyl-D-aspartate (NMDA) receptors located on a dendritic spine. The model accounts for much of the phenomenology of the induction of long-term potentiation at a Hebbian synapse in hippocampal region CA1. Computer simulations suggested four important functions of spines in this Ca(2+)-dependent synaptic modification: (i) compartmentalizing transient changes in [Ca(2+)] to just those synapses that satisfy the conjunctive requirement for synaptic modification; (ii) isolating the spine head from changes in the [Ca(2+)] at the dendritic shaft; (iii) amplifying the concentration changes at those synapses; and (iv) increasing the voltage dependence of the processes underlying long term potentiation induction. This proposed role of spines in the regulation of Ca(2+) dynamics contrasts with traditional approaches to spine function that have stressed electronic properties. This model can be used to explore the computational implications of Hebbian synapses.

The 4-(arylamino)quinoline 4, previously described as an antiulcer compound, is shown to be an inhibitor of the gastric (H+/K+)-ATPase. It is postulated that 1-arylpyrrolo[3,2-c]quinolines 6 act as conformationally restrained analogues of 4. A series of derivatives of 6 has been prepared and shown to be potent inhibitors of the target enzyme in vitro. Substitution in the ortho position of the aryl ring is important for activity. Unsaturation in the 5-membered ring makes little difference, but introduction of heteroatoms into the same ring markedly reduces activity. In more detailed kinetic experiments, 15c and 4 both show reversible, K(+)-competitive binding to the enzyme, with submicromolar Ki values. The compounds appear to act at the lumenal face of the enzyme and to require protonation for activity. Several compounds in the series are shown to be potent inhibitors of pentagastrin-stimulated acid secretion in the rat.

The manner in which the circuitry of the amygdala computes its suspected mnemonic functions has been a mystery, partly because the cytoarchitectual complexity of this nuclear group has impeded the necessary cellular analysis. Here we report in vitro methods and results that may help elucidate cellular learning mechanisms in amygdala neurons. The amygdala brain slice preparation was combined with the single-electrode clamp (SEC) technique for intracellular analysis of membrane properties and synaptic responses. With respect to the active and passive membrane properties, we found considerable diversity among the population of cells that were sampled in the lateral and basolateral nuclei (n = 85). Synaptic inputs to these neurons were studied by stimulating the external capsule (EC), which was shown to produce a complex response that typically consisted of an excitatory followed by an inhibitory component. Based on several criteria, the excitatory component appeared to reflect a monosynaptic connection from the EC. One immediate goal was to discover whether the excitatory component displays the phenomenon of long-term potentiation (LTP)--a persistent increase in synaptic strength that can be induced by brief periods of the appropriate synaptic stimulation. Indeed, we found that high-frequency (100 Hz) stimulation of the EC induced LTP in 80% of the cells from which suitable recordings were obtained (n = 20). This finding of LTP in the amygdala is significant in regard to current efforts to explore linkages between this use-dependent form of synaptic plasticity and rapid kinds of associative learning.

We have examined the evolution of the concept of a Hebbian synaptic modification and have suggested a contemporary definition. The biophysical mechanism demonstrated in vitro to control the induction of one type of hippocampal LTP has been shown to satisfy our definition of a Hebbian synaptic modification. Whether this biophysical mechanism is involved in the organization of behavior in the manner that Hebb originally envisioned remains to be seen. We have also summarized several modification algorithms that have been explored in theoretical studies of learning in adaptive networks. These algorithms also satisfied our definition of a Hebbian modification, but their relationships to known neurobiology require further exploration. By reviewing the biophysical mechanisms and formal algorithms together, we have exposed obvious similarities and differences. Such comparisons may help bridge the gap between computational theory and knowledge of the neurobiology of use-dependent synaptic change. Current models of LTP reveal that the activity-modification relationships are extremely sensitive to the biophysical/molecular details. The activity-modification relationships obviously can have a major influence on adaptive neurodynamics at the network level. As more accurate representations of the biological complexity and diversity are introduced into adaptive network simulations, we expect to gain new insights into the classes of computation that particular networks are capable of performing.

Three years after the start of an experiment to assess the merits of thiabendazole (TBZ) treatment of trichostrongylid parasites in weaner sheep, field isolates of Ostertagia spp and Trichostrongylus spp were made from weaner sheep treated under one of three treatment schemes. Treatment frequencies were "nil", "planned" (5 or 6/year) and "regular" (every 3 weeks). In addition an isolate was taken from a group of "tracer" sheep drenched with TBZ every 10 days. Resistance to TBZ was assessed using an in vitro egg hatch assay, pre- and post-treatment faecal egg counts and a controlled anthelmintic efficiency test. Pre- and post-treatment egg counts revealed the presence of TBZ-resistance in field isolates of mixed species. Egg hatch assays indicated a level of resistance for Ostertagia spp which was proportional to the frequency of TBZ treatment. The "planned", "regular" and "tracer" strains of Ostertagia spp had resistance ratios for eggs of 4, 13 and 15 respectively when compared to the "nil" strain. In the anthelmintic efficiency assay treatment with 44 mg kg-1 and 88 mg kg-1 of TBZ removed 82 and 96% respectively of the total Ostertagia burden (adults and larvae) from the "nil" strain and 30 and 75% respectively from the "planned" strain. The same dose rates against the "regular" and "tracer" strains and additional rates of 132 or 176 mg kg-1 against the "tracer" strain failed to reduce the Ostertagia burden significantly. Intestinal Trichostrongylus spp from all isolates were fully susceptible to TBZ at 44 mg kg-1. Levamisole at 7.0 mg kg-1 was highly effective (99% reduction) against the "tracer" strain of Ostertagia.

We describe a light-guidance system that uses intersecting helium-neon laser beams to provide precise guidance for biopsy approaches from any direction (including compound angles) during CT-guided biopsy of the chest and abdomen. Interactive software provides visualization of the proposed path, indicates the segment of that path that will pass through each section, and displays the settings for the apparatus.

This study examines the effect of excision of the submandibular salivary glands, the main source of epidermal growth factor (EGF), and the role of gender on the healing of acetic acid-induced gastric ulcers in rats. In male rats excision of the submandibular glands delayed ulcer healing. At 15 and 25 days the unhealed ulcer areas were significantly larger in the sialoadenectomy group than in control animals, and fewer completely healed ulcers were seen in this group at 25 days. Ulcer healing in female rats was slower. At day 25 ulcers were healed in 12% of female rats with intact salivary glands, compared with 68% in males. Female rats also showed larger unhealed ulcer areas after sialoadenectomy than controls. We conclude that removal of the main source of EGF in the gastrointestinal tract is associated with a delay in healing of gastric ulcers. The significant difference in healing observed between female and male rats may be influenced by the known androgenic regulation of EGF production in the salivary glands.

An electrophysiological stimulation paradigm similar to one that produces Pavlovian conditioning was applied to synaptic inputs to pyramidal neurons of hippocampal brain slices. Persistent synaptic enhancement was induced in one of two weak synaptic inputs by pairing high-frequency electrical stimulation of the weak input with stimulation of a third, stronger input to the same region. Forward (temporally overlapping) but not backward (temporally separate) pairings caused this enhancement. Thus hippocampal synapses in vitro can undergo the conditional and selective type of associative modification that could provide the substrate for some of the mnemonic functions in which the hippocampus is thought to participate.

Long-term synaptic potentiation (LTP) is a leading candidate for a synaptic mechanism of rapid learning in mammals. LTP is a persistent increase in synaptic efficacy that can be quickly induced. The biophysical process that controls one type of LTP is formally similar to a synaptic memory mechanism postulated decades ago by the psychologist Donald Hebb. A key aspect of the modification process involves the N-methyl-D-aspartate (NMDA) receptor-ionophore complex. This ionophore allows calcium influx only if the endogenous ligand glutamate binds to the NMDA receptor and if the voltage across the associated channel is also sufficiently depolarized to relieve a magnesium block. According to one popular hypothesis, the resulting increase in the intracellular calcium concentration activates protein kinases that enhance the postsynaptic conductance. Further biophysical and molecular understanding of the modification process should facilitate detailed explorations of the mnemonic functions of LTP.

Interactions between two excitatory monosynaptic inputs to hippocampal neurons of the CA1 region were examined in the in vitro slice. By adjusting the strengths of the electrical stimuli delivered to the two input pathways, one was made to generate a weak and the other a strong synaptic response. Simultaneous tetanic stimulation of both input pathways resulted in a subsequent long-term enhanced synaptic efficacy in the weak input under conditions in which the same tetanic stimulation of either input alone failed to have this effect. This form of long-term synaptic potentiation (LTP), known as associative LTP, was shown in some cases to last hours without decrement. The plastic changes were localized within the CA1 region and appear to reside in the pre- or postsynaptic elements of the monosynaptic excitatory input to the pyramidal neurons. The increased synaptic efficacy could not be accounted for by any of several measured postsynaptic passive membrane properties.

Previous studies using cholescintigraphy and measurement of bile salts in gastric juice have demonstrated that duodenogastric reflux is increased after cholecystectomy, a factor that may contribute to postoperative complaints in some patients. We studied 24-hour continuous gastric pH in healthy subjects, patients with cholelithiasis, and patients who had undergone cholecystectomy. Cholecystectomy decreased the percentage of time that gastric pH is below 2 and increased the time it is above 4 and 6. Furthermore, there was a greater increase in the more alkaline pH values in patients who were symptomatic than in those who were asymptomatic. The results demonstrated that cholecystectomy is associated with an alkaline shift in the 24-hour gastric pH profile that is most marked in symptomatic patients. This suggests that gastric alkaline episodes may be related to some postcholecystectomy symptoms.

Chloramphenicol combined with cefotaxime, moxalactam, cefoperazone, aztreonam, or imipenem was tested in vitro against clinical isolates of Klebsiella pneumoniae. By time-kill cultures (killing curves), chloramphenicol interfered with activity of all five beta-lactams. When chloramphenicol was added before the beta-lactams, the action of cefotaxime, moxalactam, or cefoperazone against all isolates was antagonized at all times tested. The action of aztreonam was antagonized against four of six isolates. With imipenem, antagonism occurred against half of the isolates at some time during 24 h when chloramphenicol was added simultaneously, provided that a sufficient inoculum of K. pneumoniae was employed. Generally, less antagonism resulted when chloramphenicol was added after the cephalosporins. Interference of bactericidal activity of three new cephalosporins by chloramphenicol has potential clinical relevance to the therapy of gram-negative bacillary meningitis. The lesser antagonism of aztreonam and imipenem by chloramphenicol is of uncertain clinical relevance but indicates that this in vitro phenomenon may apply to a wide range of beta-lactam antibiotics.

Oxmetidine is a potent and specific antagonist of the histamine H2-receptor. Oxmetidine is also cytotoxic to isolated rat hepatocytes through inhibition of mitochondrial oxidative phosphorylation. The purpose of this investigation was to test a variety of H2-receptor antagonists that are structural analogs of oxmetidine in an attempt to identify a critical structural component or a physicochemical property of the molecule which may be responsible for cytotoxicity. Six histamine receptor H2-antagonists were tested. The minimum drug concentrations that caused 100% cell death (leakage of intracellular lactate dehydrogenase and loss of intracellular potassium) ranged from 0.87 to 22.50 mM for the analogs tested. At toxic concentrations, two of the least potent analogs, SK&F 92909 and SK&F 9205A both caused a rapid decrease in hepatocyte O2 consumption and ATP content which occurred before any evidence of cell injury. The potency of these molecules as cytotoxicants to isolated hepatocytes did not correlate with their potency as histamine H2-receptor antagonists whereas there was a significant correlation between increasing potency and increasing octanol/water partition coefficients. These data suggest that lipid solubility may be a key factor in the cytotoxicity of this class of drugs to isolated rat hepatocytes.

The contributions of black Americans to early American culture have still not been fully explored or given the attention deserved. A case in point is the significant contributions African slaves made to 18th-century American folk medicine. A review of the events incident to the smallpox epidemic in Boston in 1721 will illustrate the degree to which some reputable men of science depended on the testimony and experience of Africans in dealing with a particularly dread disease.