Neural network modeling of the hippocampal formation spatial signals and their possible role in navigation: a modular approach

Cells throughout the hippocampal formation show striking spatial firing correlates as a rat navigates through space. These cells are thought to play a critical role in orchestrating the navigational abilities of the animals, since damage to the hippocampal formation causes spatial learning deficits. Here, we present a theoretical framework aimed at explaining how the different spatial signals are generated, as well as how they may help guide navigational behavior. Earlier work from our laboratory has presented a simple model for how the location-related signals exhibited by hippocampal place cells could be generated, based on convergent sensory information. Here, the results of this work are combined with two more recent models, to provide a more comprehensive theoretical framework. Specifically, we present 1) A neural network model of head direction cells, based on the idea that the directional signals are generated using a path integration mechanism. Cells which combine directional and angular head velocity information project onto the head direction cells, to "update" the current directional signal. This model reproduces the basic phenomenon of direction-specific firing, as well as the anticipatory nature of this firing, reported for some head direction cells. 2) A network simulation of how the hippocampal spatial signals could be used to orchestrate instrumental learning. Here, place and directional signals converge onto motor cells, each of which are thus driven to fire to specific combinations of location and directional heading. Each active motor cell generates a small leftward or rightward "step" of the simulated animal. When the simulated goal is encountered, recently active synapses are strengthened, so that goal-directed trajectories are "stamped in". We have found these models useful in helping to clarify our thinking about the proposed theoretical principles, as well as in generating testable predictions.

Health care 2015: flight of the butterfly

Projecting out to the year 2015 sounds presumptuous. Who can predict that far ahead? Perhaps no one can. Social and organizational arrangements come slowly. It takes five years or so to implement simple concepts, sometimes decades for more radical changes. Once you have the ideas in tangible form, it can take another five years to get it working right. Early adopters bring others into the movement and, over 15-25 years, new directions dominate. It takes at least a generation of new practitioners to take on the new values and methods so what is likely to dominate in 2015 is beginning to be taken somewhat seriously as the successor movement to our current fad with externally imposed managed care. Put another way, entire generations of people will resist new ideas, making implementation unlikely until their control fades and a new generation takes the helm. The exciting challenge for the observer is to address the issue of where health is and should be going. Both are difficult challenges. Agreeing on what is important and what is not represents a competitive challenge. How do we perceive the world? Surely our value sets will color what we see. Who is not predisposed to select a future where they fit and their pet theories are likely to become reality. For these and other reasons, it is probably easier to agree on what we would like to see happen in the future than on what is happening. Unfortunately, unless we see the world as it is, we are less likely to be able to shift it in a direction we would like to see.

Direct three-dimensional image transmission through single-mode fibers with monochromatic light

Direct three-dimensional image transmission through one single-mode or multimode fiber is demonstrated. Image transmission is carried out with a grating interferometer under monochromatic, spatially incoherent illumination.

Power and new economic relationships

We are going through a transformation of our health services from a community and patient focus fueled by fee-for-service and cost-plus reimbursement. This transformation, called managed care, is shifting power away from professionals and communities into both new and old organizations financed by Wall Street. Even traditional community organizations are driven by Wall Street-dictated financial ratios that represent scoreboards to determine who gets capital for growth and development. Times are changing, organizations are changing, and still more change is ahead.

High-voltage galvanic stimulation on wound healing in guinea pigs: longer-term effects

The purpose of this investigation was to determine the effects of high-voltage stimulation (HVS) on wound tensile strength properties and wound closure (histology). Eighteen mature guinea pigs with full-thickness incisions were treated with HVS for 45 minutes daily for 2 weeks; 9 animals were studied after the 14 days of treatment and the remaining 9 were studied 2 weeks later. Five animals (10 wounds) served as controls at each time period. After 2 or 4 weeks, treated and untreated skin was harvested, tested to failure, and prepared for histological examination. Two-week-treated and control wounds had comparable values for peak force to failure, elongation, and energy absorbed to failure. Epithelialization was more advanced in treated animals at 14 days (p < .05). There was a trend (p = .068) toward stronger wounds in 4-week-treated animals (maximum load to failure), but not differences were observed between controls and treated groups for elongation or energy absorbed to failure. Dermal healing appeared to be more advanced in treated animals at 30 days. Although peak force to failure was almost 500g higher for treated guinea pigs after 2 weeks of treatment and more than 700g higher than controls after 4 weeks, mean data were highly variable, so the hypothesis that HVS augments wound strength could not be accepted. It is difficult, however, not to assign clinical significance to the findings.

A new in-vitro model to investigate antibiotic penetration of the intervertebral disc

We have studied the ability of a range of antibiotics to penetrate intervertebral disc tissue in vitro, using a mouse disc model. Equilibrium concentrations of antibiotics incorporated into the entire disc were determined by bioassay using a microbial growth-inhibition method. Uptake was significantly higher with positively-charged aminoglycosides compared with negatively-charged penicillins and cephalosporins. Uncharged ciprofloxacin showed an intermediate degree of uptake. Our results support the hypothesis that electrostatic interaction between charged antibiotics and negatively-charged glycosaminoglycans in the disc is an important factor in antibiotic penetration, and may explain their differential uptake.

A new in-vitro model to investigate antibiotic penetration of the intervertebral disc

We have studied the ability of a range of antibiotics to penetrate intervertebral disc tissue in vitro, using a mouse disc model. Equilibrium concentrations of antibiotics incorporated into the entire disc were determined by bioassay using a microbial growth-inhibition method. Uptake was significantly higher with positively-charged aminoglycosides compared with negatively-charged penicillins and cephalosporins. Uncharged ciprofloxacin showed an intermediate degree of uptake. Our results support the hypothesis that electrostatic interaction between charged antibiotics and negatively-charged glycosaminoglycans in the disc is an important factor in antibiotic penetration, and may explain their differential uptake.

The relationship of strength to function in the older adult

Reduced lower extremity strength has been associated with reduction in gait speed, balance, stair-climbing ability, and getting up from a seated position. The relationship of lower extremity strength and the ability to accomplish selected functional activities was examined in 16 healthy but frail older adults ranging in age from 75 to 88 years (mean = 80.9 years). The following measures were obtained for each subject: preferred gait speed under laboratory and free walking conditions, 5 timed chair stand-ups, and time to complete an obstacle course. Strength measures of the hip extensors, hip abductors, knee extensors, planter flexors, and dorsiflexor muscle groups were obtained using a hand-held dynamometer. The relationship between the time to complete the functional activities and each of the strength variables was determined using Pearson product moment correlations. In addition, performance was examined in relation to various combinations of strength measures (e.g., hip and knee extension). Weak, nonsignificant hip, knee and ankle strength/functional activity relationships were found for all of the variables examined. When hip extension, knee extension, and ankle plantar flexion strength values were combined and normalized to body weight, a significant strength-to-functional activity relationship was found for 14" chair stand-ups (r = .636, p < .01). When values for quadriceps strength and gait speed for 35 adults ranging in age from 60-72 years were compared to those for 75-88 year olds, marked differences emerged. A more significant relationship between knee extension force and gait speed was observed for the younger adults (r = .528 vs r = .353).(ABSTRACT TRUNCATED AT 250 WORDS)

Coprescribing of nonsteroidal anti-inflammatory drugs and cytoprotective and antiulcer drugs in Nova Scotia's senior population

Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently prescribed for the elderly and are commonly prescribed with cytoprotective or antiulcer drugs to prevent or treat gastrointestinal side effects. The objective of this study was to examine the utilization and drug costs of NSAIDs, and to examine coprescription of cytoprotective and antiulcer drugs with NSAIDs in the Nova Scotia population aged 65 years and older. The study used data from the Nova Scotia Seniors Pharmacare program database, which contains data on claims for all filled prescriptions to persons 65 years of age and older. We examined claims for the period April 1, 1993, to March 31, 1994. Aspirin accounted for the largest percentage of the total days supply of NSAIDs (25.2%), followed by diclofenac (18.8%) and naproxen (12.9%). Diclofenac accounted for the largest share of expenditures for NSAIDs (27.6%). Overall, 17.1% of the total days supply of NSAIDs were coprescribed with a cytoprotective or antiulcer drug. Histamine2 blockers accounted for most coprescribed days supply (83.6%) followed by sucralfate (8.1%), misoprostol (4.5%), and omeprazole (2.3%). The appropriateness and cost-effectiveness of these coprescriptions must be examined.

Differential activation of peroxisome proliferator-activated receptors by eicosanoids

Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that regulate gene transcription in response to peroxisome proliferators and fatty acids. PPARs also play an important role in the regulation of adipocyte differentiation. It is unclear, however, what naturally occurring compounds activate each of the PPAR subtypes. To address this issue, a screening assay was established using heterologous fusions of the bacterial tetracycline repressor to several members of the peroxisome proliferator-activated receptor (PPAR) family. This assay was employed to compare the activation of PPAR family members by known PPAR activators including peroxisome proliferators and fatty acids. Interestingly, the activation of PPARs by fatty acids was partially inhibited by the cyclooxygenase inhibitor indomethacin, which prevents prostaglandin synthesis. Indeed, prostaglandins PGA1 and 2, PGD1 and 2, and PGJ2-activated PPARs, while a number of other prostaglandins had no effect. We also screened a variety of hydroxyeicosatetraenoic acids (HETEs) for the ability to activate PPARs. 8(S)-HETE, but not other (S)-HETEs, was a strong activator of PPAR alpha. Remarkably, PPAR activation by 8(S)-HETE was stereoselective. In addition, 8(S)-HETE was able to induce differentiation of 3T3-L1 preadipocytes. These results indicate that PPARs are differentially activated by naturally occurring eicosanoids and related molecules.

Polarity-specific activities of retinoic acid receptors determined by a co-repressor

Retinoic acid receptors (RARs) and retinoid-X receptors (RXRs) activate or repress transcription by binding as heterodimers to DNA-response elements that generally consist of two direct repeat half-sites of consensus sequence AGGTCA. On response elements consisting of direct repeats spaced by five base pairs (DR + 5 elements), RAR/RXR heterodimers activate transcription in response to RAR-specific ligands, such as all-trans-retinoic acid (RA). In contrast, on elements consisting of direct repeats spaced by one base pair (DR + 1 elements), RAR/RXR heterodimers exhibit little or no response to activating ligands and repress RXR-dependent transcription. Here we show that ligand-dependent transactivation by RAR on DR + 5 elements requires the dissociation of a new nuclear receptor co-repressor, N-CoR, and recruitment of the putative co-activators p140 and p160. Surprisingly, on DR + 1 elements, N-CoR remains associated with RAR/RXR heterodimers even in the presence of RAR ligands, resulting in constitutive repression. These observations indicate that DNA-response elements can allosterically regulate RAR-co-repressor interactions to determine positive or negative regulation of gene expression.

Quinazoline thymidylate synthase inhibitors: methods for assessing the contribution of polyglutamation to their in vitro activity

Many quinazoline thymidylate synthase (TS) inhibitors undergo intracellular metabolism to polyglutamate forms which can significantly alter their activity and pharmacodynamics through improved TS inhibition and drug retention. When a series of quinazolines was tested for inhibitory activity towards TS (IC50 0.001-2 microM) and the growth of L1210 cells (IC50 0.005-10 microM), no direct correlation was observed. However, a very good correlation was apparent if a L1210 variant cell line (L1210: RD1694) was used. This line is deficient in its ability to form antifolate polyglutamates. A number of other intact cell methods have also been developed which estimate the contribution that intracellular polyglutamation makes to a compound's activity. These assays were validated using a series of quinazoline-based TS inhibitors with well-defined activity for TS, folypolyglutamate synthetase (FPGS) and the reduced-folate cell membrane carrier (RFC). Short-exposure growth-inhibition assays or the measurement of TS activity in situ after various incubation times, followed by different lengths of time in drug-free medium, can indicate both the speed and extent of appearance of retentive forms (usually polyglutamates). Continuous-exposure growth-inhibition assays, in the presence of leucovorin (LV), are also useful, since only the growth-inhibitory potency of polyglutamated analogues is significantly decreased by LV. Highly polyglutamated compounds, e.g. ZD1694, are virtually inactive in the presence of a high concentration of LV. It is proposed that these methods, when considered together, provide a greater degree of information concerning the rate and extent of polyglutamation of a particular compound than isolated FPGS assays alone.

Quinazoline-based thymidylate synthase inhibitors: relationship between structural modifications and polyglutamation

Quinazoline-based analogues of folic acid are a group of thymidylate synthase (TS) inhibitors that display a wide spectrum of activity for cultured tumour cells, partly due to their differential ability to form polyglutamate metabolites that are (i) more potent TS inhibitors and (ii) not readily effluxed from cells. The rate of cell membrane transport and folylpolyglutamate synthetase substrate activity influence compound polyglutamation. A series of intact-cell assays has been used to determine how specific modifications of 2-desamino-2-methyl-N10-propargyl-5,8-dideazafolate (ICI 198583) affect compound polyglutamation. Those containing the 'classical' glutamate structure were usually, but not always, well polyglutamated intracellularly. Replacement of N10 propargyl with smaller aliphatic substituents, particularly when combined with replacement of the benzene ring with thiophene or thiazole heterocycles, was beneficial for antitumour activity through polyglutamate formation. Fluorination of the benzene, particularly if a F was adjacent to the 'bridge region' (3'F or 2',5'diF), also gave compounds with a high dependence on polyglutamation for activity. Those analogues with 2-CH2OH or NH2 substituents were poor substrates for the reduced-folate cell membrane carrier which can account for their reduced polyglutamation rate and hence growth-inhibitory activity. A large decrease or prevention of polyglutamation was achieved by the introduction of CH3, CH2CH3, Br or C1 on C7. The concomitant enhancement in TS inhibition by these modifications gave compounds active under continuous-exposure cell culture conditions. Some ICI 198583 analogues had the glutamate moiety replaced with unnatural amino acids or dipeptides. Only the L-gamma-L-glu analogue (a polyglutamate metabolite of ICI 198583) gave activity entirely attributable to polyglutamate formation.

Nine suicide pacts. A clinical study of a consecutive series 1974-93

BACKGROUND

Suicide pacts are rarely discussed in the medical literature. We report here the medical and social aspects of a consecutive series of double or pact suicides.

METHOD

Coroners' records were examined for 722 consecutive suicides. Data were extracted from them and from medical and psychiatric records.

RESULTS

Nine pacts (2.5% of suicides) were located: 11 of the 18 people appeared to have been mentally ill at the time of death and three more had a history of mental illness. Five had a significant medical history (three cancer).

CONCLUSIONS

Mental disorder is common in those who enter suicide pacts (mainly depression, with alcohol dependence rare). Motivations for suicide appear to be relief of mental disorder and pain.

Dietary sodium intake modulates systemic but not forearm norepinephrine release

INTRODUCTION

Sodium intake has profound effects on systemic and renal sympathetic activity, but its effects on sympathetic activity in skeletal muscle vascular beds, a site at which local regulatory mechanisms could alter vascular tone directly, are unclear.

METHODS

To determine the effect of dietary sodium intake on basal and isoproterenol-stimulated systemic and forearm norepinephrine kinetics, we studied seven healthy male volunteers twice, 4 weeks apart, while they were receiving a low-sodium (10 mmol sodium/24 hours) diet and a high-sodium diet (250 mmol sodium/24 hours). Forearm blood flow, measured by plethysmography, and systemic and forearm norepinephrine spillover, measured by radioisotope dilution, were determined before and after intra-arterial infusion of 60 and 400 ng/min isoproterenol.

RESULTS

Baseline (before isoproterenol) systemic norepinephrine spillover was higher when subjects received the low-sodium diet (448.1 +/- 55.7 ng/min) compared with the high-sodium diet (269.7 +/- 42.7 ng/min; p < 0.05). In contrast, sodium intake did not affect local forearm norepinephrine spillover, either at baseline (low-sodium diet, 2.05 +/- 0.48 ng/min versus high-sodium diet, 2.63 +/- 0.79 ng/min; p = 0.50) or after stimulation with isoproterenol in doses of 60 ng/min (low-sodium diet, 8.84 +/- 2.2 ng/min versus high-sodium diet, 6.1 +/- 1.9 ng/min; p = 0.38) or 400 ng/min (low-sodium diet, 16.4 +/- 4.5 ng/min versus high-sodium diet, 16.7 +/- 2.5 ng/min; p = 0.93).

CONCLUSIONS

Under conditions of low sodium intake, systemic norepinephrine spillover was increased but forearm norepinephrine spillover was not, suggesting that alteration in sodium intake may produce a differential effect on norepinephrine spillover in different tissues but that decreased local sympathetic activity in skeletal muscle is not the likely mechanism by which a low-sodium diet may lower blood pressure or attenuate stress-induced pressor responses.

Cyclophosphamide in combination with sargramostim for treatment of recurrent medulloblastoma

Thirteen patients with recurrent medulloblastoma were treated with cyclophosphamide in association with Sargramostim. Cyclophosphamide was given at doses ranging between 1.0-2.5 g/m2 daily for two doses. Sargramostim was given at a fixed dose of 250 micrograms/m2 subcutaneously twice a day beginning 24 hours after the second cyclophosphamide dose and continuing through the leukocyte nadir until the ANC was more than 1,000 cells/microliters for two consecutive days. A total of 33 courses were given with toxicity consisting of grade 4 neutropenia in all courses and grade 3-4 thrombocytopenia in 10 of 13 patients. There were no deaths related to infection or bleeding. Four patients were taken off study because of prolonged myelosuppression. Three of these patients were at the 2.5 g/m2 level, and of these three, two developed lung toxicity (grades 2 and 4, respectively). One patient developed an allergic reaction following the first injection of Sargramostim and was also taken off study. Of 10 evaluable patients, there were 9 PR and 1 SD. We conclude that cyclophosphamide at a dose of 2.0 g/m2/day x 2 days q 4 weeks in association with Sargramostim demonstrates marked activity with acceptable toxicity in patients with recurrent medulloblastoma.

Epilepsy and children's social and psychological adjustment

This research investigates the effects of epilepsy on the social and psychological adjustment of the children studied in the National Health Interview Survey of 1988. Analyses examine the effect of epilepsy on four measures of adjustment--home behavior problems, school behavior problems, depressed mood, and impulsiveness. For each outcome, we address five questions: (1) Do children with currently active epilepsy have poorer adjustment than children with inactive epilepsy? (2) Do children with epilepsy fare worse than other children? (3) Do demographic background and family structure moderate the apparent effects of epilepsy? (4) Do family processes mediate the apparent effects of epilepsy? and (5) Do cooccurring conditions produce the apparent effects of epilepsy? Generally, we find that: (1) Children with active and inactive epilepsy fare about equally; (2) Children with any history of epilepsy fare worse than children without epilepsy; (3) Demographic and family background moderate only a small part of epilepsy's effect; and (4) A combination of family processes and cooccurring conditions appears to produce epilepsy's apparent effects.

Lack of association between angiotensinogen polymorphism (M235T) and cerebrovascular disease and carotid atheroma

Genetic influences in cerebrovascular disease (CVD) may act either independently or by predisposing to, or modulating, the effect of risk factors such as hypertension. Factors involved in the pathogenesis of atherosclerosis, thrombosis and vasoconstriction are important in CVD. The angiotensinogen gene has recently been linked with essential hypertension in affected sibships and a particular polymorphism in exon 2 of the angiotensinogen gene, a threonine to methionine substitution at position 235 (M235T), has been associated with pre-eclampsia and hypertension. In this study we examined the relation of M235T polymorphism to cerebrovascular disease and carotid atheroma in 100 consecutive Caucasian patients with internal carotid artery territory ischaemia (TIA or stroke), presenting to a carotid ultrasound service. Forty five age-matched controls (mostly patients' spouses) were also studied. Hypertension was defined as current treatment with anti-hypertensive agents, or SBP > 160 mm Hg or DBP > 95 mm Hg. Twelve of 100 cases (12%) and eight of 45 controls (12%) were homozygous for the T235 allele. T:M allele ratios were 0.34:0.66 in cases and 0.34:0.66 in controls. There was no relation between the polymorphism and either internal carotid stenosis or common carotid artery intima-media thickness. In the cases, mean percentage internal carotid artery stenosis was TT 18.3 (SD 18.7)%, MT 38.0 (27.1)% and MM 36.8 (30.2)%. Mean intima-media thickness was TT 0.87 (0.18) mm, MT 0.95 (0.34) mm and MM 0.88 (0.23) mm. There was no relation between the polymorphism and hypertension (TT 11 of 100 cases, six of 45 controls).(ABSTRACT TRUNCATED AT 250 WORDS)