A four-year curriculum in professional ethics and law for dental students

The four-year sequence of ethics courses at the School of Dentistry, University of Detroit Mercy is described in this article. A course blending lectures and small group discussion is taught each year, focusing on the issues facing students relevant to the students' stage of professional development. The sequence concludes with an Ethics Round in which students present a personal patient-based ethics case.

Synthesis of novel derivatives of 1,4,7-triazacyclononane

[structure: see text]. The coordination environment of 1,4,7-triazacyclononane can be adapted, through sequential functionalization of two secondary amines, to generate ligands applicable in biomimetic studies. Two "amino acids" and an amino derivative have been prepared from 1,4,7-triazatricyclo[5.2.1.0(4,10)]decane. This synthon allows efficient attachment of one functional group to the macrocyclic ring, forming a monoamidinium salt. Hydrolysis generates a formyl derivative, which was further functionalized at the secondary amine and hydrolyzed in strong acid to generate ligands 1-3.

Pharmacokinetics of nelfinavir in human immunodeficiency virus-infected infants

BACKGROUND

Nelfinavir dosed at approximately 20 to 30 mg/kg three times a day (TID) in older children provides exposure similar to 750 mg TID in adults. However, the pharmacokinetics (PK) of nelfinavir in infants who are < 2 years of age is not well-described. The objective of this study was to determine the pharmacokinetics of nelfinavir in infants < 2 years of age.

METHODS

Nelfinavir concentrations were evaluated in 22 HIV-infected infants between 15 days and 2 years of age receiving nelfinavir as part of Pediatric ACTG Study 356. Nelfinavir therapy was initiated at approximately 25 mg/kg TID (n = 18) or approximately 55 mg/kg twice a day (n = 4) and given in combination with nevirapine, stavudine and lamivudine. PK samples were obtained predose and 1.5 and 4 h postdose at approximately 6-month intervals. Eight infants (all < or = 3 months of age) also had intensive PK samples collected at Week 1.

RESULTS

The median apparent clearance in the infants with intensive pharmacokinetic sampling was 2.7 liters/h/kg (range, 1.8 to > or = 10) and was similar between twice a day and TID dosing cohorts. Overall nelfinavir concentrations at all collection times were lower in these infants than previously reported in older pediatric patients.

CONCLUSIONS

Nelfinavir concentrations in infants are highly variable and lower than those seen in adult or older pediatric populations receiving labeled dosing. Therefore it is necessary to further evaluate nelfinavir safety, effectiveness and pharmacokinetics at higher doses than used among other pediatric populations.

The application of decision analysis to the surgical treatment of early osteoarthritis of the wrist

Osteoarthritis of the wrist is a complication of a number of common traumatic conditions. Arthrodesis of the radiocarpal joint, proximal row carpectomy and excision of the scaphoid, combined with midcarpal arthrodesis, have all been reported as surgical options. There have been no randomised studies comparing these procedures, and the feasibility of conducting this type of trial is limited. We used decision analysis to compare the three surgical techniques. The variables for the model used were based principally on data from the literature. Extensive sensitivity analyses were carried out to test the impact of the values given to these variables on the outcome of the model. The model indicated that the preferred treatment is proximal row carpectomy. Decision analysis allows a comparison between alternative treatments, when evidence from a randomised trial is lacking or unobtainable. The decision-analysis model may also provide insight into aspects of a problem which would be difficult, or impossible, to evaluate by a cohort study.

The application of decision analysis to the surgical treatment of early osteoarthritis of the wrist

Osteoarthritis of the wrist is a complication of a number of common traumatic conditions. Arthrodesis of the radiocarpal joint, proximal row carpectomy and excision of the scaphoid, combined with midcarpal arthrodesis, have all been reported as surgical options. There have been no randomised studies comparing these procedures, and the feasibility of conducting this type of trial is limited.

We used decision analysis to compare the three surgical techniques. The variables for the model used were based principally on data from the literature. Extensive sensitivity analyses were carried out to test the impact of the values given to these variables on the outcome of the model. The model indicated that the preferred treatment is proximal row carpectomy.

Decision analysis allows a comparison between alternative treatments, when evidence from a randomised trial is lacking or unobtainable. The decision-analysis model may also provide insight into aspects of a problem which would be difficult, or impossible, to evaluate by a cohort study.

A computational model of dendrite elongation and branching based on MAP2 phosphorylation

We introduce a new computational model of dendritic development in neurons. In contrast to previous models, our model explicitly includes cellular mechanisms involved in dendritic development. It is based on recent experimental data which indicates that the phosphorylation state of microtubule-associated protein 2 (MAP2) may play a key role in controlling dendritic elongation and branching (Audesirk et al., 1997). Dephosphorylated MAP2 favours elongation by promoting microtubule polymerization and bundling, whilst branching is more likely to occur when MAP2 is phosphorylated and microtubules are spaced apart. In the model, the rate of elongation and branching is directly determined by the ratio of phosphorylated to dephosphorylated MAP2. This is regulated by calmodulin-dependent protein kinase II (CaMKII) and calcineurin, which are both dependent on the intracellular calcium concentration. Results from computer simulations of the model suggest that the wide variety of branching patterns observed among different cell types may be generated by the same underlying mechanisms and that elongation and branching are not necessarily independent processes. The model predicts how the branching pattern will change following manipulations with calcium, CaMKII and MAP2 phosphorylation.

A new pentaplex PCR system for forensic casework analysis

In 1998 the Federal Criminal Police Office of Germany (BKA) established a central genetic database of offenders and suspects to facilitate comparisons with biological samples from future criminal offences. The five obligatory short tandem repeat (STR) loci in this database (TH01, SE33, vWA, FGA and D21S11) were co-amplified in a new PCR pentaplex analysing system together with the sex-specific locus amelogenin. Due to overlapping fragment sizes, amplification products were fluorescent dye-labelled with different colours, separated by electrophoresis and detected directly using the ABI PRISM 310 Genetic Analyzer. Reproducible and reliable results were obtained from as low as 125 pg template DNA, indicating high specificity and sensitivity of the assay. Environmental studies and enzymatic digest with DNase I revealed an excellent stability of the pentaplex system with typeable results even in cases of partially degraded DNA. Complete and reproducible DNA typing was possible in blood-stain mixtures with the minor component as low as 10%. Mean stutter peak intensities were analysed for all loci and ranged from 2.7 +/- 0.8% (TH01) to 10.6 +/- 1.6% (vWA) of the main signal intensity. Allele frequencies were determined in a North Bavarian population sample (n = 121). The combination of five systems resulted in a mean exclusion chance of 99.86% and a power of discrimination of 99.999996%. No deviation from Hardy-Weinberg equilibrium could be found.

Syntheses, crystal structures, magnetic properties, and EPR spectra of tetranuclear copper(II) complexes featuring pairs of "roof-shaped" Cu2X2 dimers with hydroxide, methoxide, and azide bridges

Hydroxo- and methoxo-bridged tetranuclear copper(II) complexes of the tetramacrocyclic ligand 1,2,4,5-tetrakis(1,4,7-triazacyclonon-1-ylmethyl)benzene (Ldur), have been prepared from [Cu4Ldur(H2O)8](ClO4)8.9H2O (1). Addition of base to an aqueous solution of 1 gave [Cu4Ldur(mu2-OH)4](ClO4)4 (2). Diffusion of MeOH into a DMF solution of 2 produces [Cu4Ldur(mu2-OMe)4](ClO4)4.HClO4.2/3MeOH (3), a complex which hydrolyzes on exposure to moisture regenerating 2. The structurally related azido-bridged complex, [Cu4Ldur(mu2-N3)4](PF6)4.4H2O.6CH3CN (4), was produced by reaction of Ldur with 4 molar equiv of Cu(OAc)2.H2O and NaN3 in the presence of excess KPF6. Compounds 2-4 crystallize in the triclinic space group P1 (No. 2) with a = 10.248(1) A, b = 12.130(2) A, c = 14.353(2) A, alpha = 82.23(1) degrees, beta = 80.79(1) degrees, gamma = 65.71(1) degrees, and Z = 1 for 2, a = 10.2985(4) A, b = 12.1182(4) A, c = 13.9705(3) A, alpha = 89.978(2) degrees, beta = 82.038(2) degrees, gamma = 65.095(2) degrees, and Z = 1 for 3, and a = 12.059(2) A, b = 12.554(2) A, c = 14.051(2) A, alpha = 91.85(1) degrees, beta = 98.22(1) degrees, gamma = 105.62(1) degrees, and Z = 1 for 4. The complexes feature pairs of isolated dibridged copper(II) dimers with "roof-shaped" Cu2(mu2-X)2 cores (X = OH-, OMe-, N3-), as indicated by the dihedral angle between the two CuX2 planes (159 degrees for 2, 161 degrees for 3, and 153 degrees for 4). This leads to Cu.Cu distances of 2.940(4) A for 2, 2.962(1) A for 3, and 3.006(5) A for 4. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -27 cm(-1)) for the hydroxo-bridged copper(II) centers in 2 and very strong antiferromagnetic coupling (J = -269 cm(-1)) for the methoxo-bridged copper(II) centers in 3. Pairs of copper(II) centers in 4 display the strongest ferromagnetic interaction (J = 94 cm(-1)) reported thus far for bis(mu2-1,1-azido)-bridged dicopper units. Spectral measurements on a neat powdered sample of 4 at 33.9 GHz or 90 Ghz confirm the spin-triplet ground state for the azido-bridged copper(II) pairs.

Recombinant CD4-IgG2 in human immunodeficiency virus type 1-infected children: phase 1/2 study. The Pediatric AIDS Clinical Trials Group Protocol 351 Study Team

The use of recombinant CD4-IgG2 in pediatric human immunodeficiency virus type 1 (HIV-1) infection was evaluated by single and multidose intravenous infusions in 18 children in a phase 1/2 study. The study drug was well tolerated, and dose proportionality was observed in terms of area under time-concentration curve and peak serum concentration. Acute decreases of >0.7 log(10) copies/mL in serum HIV-1 RNA concentration were seen in 4 of the 6 children treated with 4 weekly 10 mg/kg doses. At 14 days after treatment, 3 children had sustained reductions in serum HIV-1 RNA; the other children had rebounded to baseline levels or above. By 28 days after therapy, the peak HIV-1 cellular infectious units was reduced in all 6 children, including the 2 who had experienced an earlier transient increase in values. Thus, recombinant CD4-IgG2 treatment of HIV-1-infected children appears to be well tolerated and capable of reducing HIV-1 burden.

Periodic limb movements in sleep: state-dependent excitability of the spinal flexor reflex

OBJECTIVE

To test the hypothesis that periodic limb movements (PLMs) are related to spinal flexor reflexes (FRs), the authors compared the state-dependent changes in FR excitability in 10 patients with restless legs syndrome (RLS) and PLMs with those from matched controls.

BACKGROUND

PLM is a disorder of motor control during sleep, frequently occurring in RLS. Clinically, PLMs resemble spinal FRs.

METHODS

FRs were obtained by electrically stimulating the medial plantar nerve and recording from antagonist leg and thigh muscles bilaterally.

RESULTS

Compared with controls, patients had significantly increased spinal cord excitability, as indicated by lower threshold and greater spatial spread of the FR, which was more prominent during sleep. Multiple late responses were seen during sleep in all patients and in some controls at higher threshold. The most prominent of these responses had a very long duration and a latency range of 250 to 800 msec, and because of its close temporal relationship to the FR stimulus, the authors considered it was a late, high-threshold component of the FR (FR3). The authors also found a similarity between the pattern of muscle recruitment and spatial spread of late components of the FR and those of spontaneous PLMs.

CONCLUSIONS

The results support the hypothesis that PLMs in RLS and FRs share common spinal mechanisms and suggest that PLMs may result from enhanced spinal cord excitability in RLS patients. Because dopaminergic mechanisms are involved in spinal FR control, the results are consistent with the current view that RLS is a disorder of dopaminergic function.

Coordination chemistry of a novel tetramacrocyclic ligand derived from 1,4,7-triazacyclononane: synthesis, structure, and properties of nickel(II) and copper(II) complexes

A new polynucleating ligand, 1,2,4,5-tetrakis(1,4,7-triazacyclonon-1-ylmethyl)benzene (Ldur), has been prepared and characterized as its dodecahydrobromide salt. Addition of base to an aqueous solution of this salt and 4 molar equivalents (m.e.) of a Ni(II) salt produces a mixture of bi- and trinuclear complexes, which can be separated by cation-exchange chromatography (CEC) and crystallized as [Ni2Ldur](ClO4)(4).2H2O (1) and [Ni3Ldur(H2O)6](ClO4)(6).9H2O (2). The "full capacity" tetranuclear complex, [Ni4Ldur(H2O)12](ClO4)(8).8H2O (3), is obtained by slow addition of Ldur to a refluxing aqueous solution of excess Ni2+ ions, followed by CEC purification. Treatment of Ldur with 4 m.e. of a copper(II) salt produces exclusively the tetranuclear complex, [Cu4Ldur(H2O)8](ClO4)(8).9H2O (4), while reaction with only 2 m.e. of Cu2+ ions yields the binuclear complex, [Cu2Ldur](ClO4)(4).4H2O (5). The X-ray structures of complexes 1,2,4, and [Cu2Ldur](ClO4)(4).3H2O (5') have been determined; all are monoclinic, P2(1)/c: for 1, a = 9.497(3) A, b = 13.665(5) A, c = 19.355(6) A, beta = 100.57(2) degrees, V = 2469(1) A3, and Z = 2; for 2, a = 22.883(7) A, b = 15.131(6) A, c = 20.298(8) A, beta = 97.20(3) degrees, V = 6973(4) A3, and Z = 4; for 4, a = 16.713(7) A, b = 16.714(6) A, c = 14.775(11) A, beta = 108.24(5) degrees, V = 3920(4) A3, and Z = 2; and for 5', a = 9.5705(1) A, b = 13.0646(1) A, c = 20.1298(2) A, beta = 103.1618(8) degrees, V = 2450.81(4) A3, and Z = 2. The metal centers in 1 and 5' lie in distorted octahedral environments, each facially coordinated by two of the triamine rings of Ldur, the cation in each case being centrosymmetric. In 2, one of the nickel(II) centers is similarly sandwiched by two triamine rings, while the other two nickel(II) centers are each coordinated by a single triamine ring from the ligand, with their distorted octahedral coordination spheres each being completed by three water molecules. In 4, the four triamine rings of Ldur bind to separate copper(II) centers, with two water molecules occupying the remaining two sites of the distorted square pyramidal (SP) coordination spheres, the cation again being centrosymmetric.

Purification and characterization of human Syk produced using a baculovirus expression system

The cytoplasmic tyrosine kinase p72syk (Syk) plays an essential role in signaling via a variety of immune and nonimmune cell receptors. Syk is activated in response to the engagement of the appropriate cell surface receptors and can phosphorylate downstream targets and recruit additional SH2-domain-containing proteins. In order to study the characteristics of Syk in vitro, we have overexpressed untagged, full-length human Syk in a recombinant baculovirus expression system. The enzyme was purified to 95% purity using a novel two-step affinity chromatography process using reactive yellow and phosphotyrosine columns. Yields of 3-10 mg purified Syk were obtained from 1 liter of infected insect cells. Western blotting, internal protein sequencing, and the specific tyrosine phosphorylation of a Syk peptide substrate indicated authenticity of the purified protein. The enzymatic properties of Syk were in good agreement with published data for the human enzyme, as the apparent K(m) of Syk for ATP was 10 microM and the peptide substrate was 3 microM. The recombinant protein also showed similar biochemical characteristics to the native protein isolated from B-cells such as autophosphorylation. Proteolytic cleavage of purified recombinant Syk was used to generate the kinase domain by micro-calpain. We therefore describe an efficient expression system and purification methodology to produce biologically active human Syk.

Combination therapy with efavirenz, nelfinavir, and nucleoside reverse-transcriptase inhibitors in children infected with human immunodeficiency virus type 1. Pediatric AIDS Clinical Trials Group 382 Team

BACKGROUND

Consistent long-term viral suppression has been difficult to achieve in children with human immunodeficiency virus type 1 (HIV-1) infection. We tested the safety and antiviral efficacy of a novel combination consisting of efavirenz, nelfinavir, and one or more nucleoside reverse-transcriptase inhibitors in 57 children previously treated with only nucleoside reverse-transcriptase inhibitors.

METHODS

The children were monitored for 48 weeks after the initiation of therapy. We assessed plasma concentrations of efavirenz and nelfinavir, plasma HIV-1 RNA levels, and lymphocyte subpopulations.

RESULTS

At base line, the 57 HIV-1-infected children (age range, 3.8 to 16.8 years) had a median of 699 CD4 cells per cubic millimeter and 10,000 copies of HIV-1 RNA per milliliter of plasma. The most common treatment-related effects of at least moderate severity were rash (in 30 percent of children), diarrhea (in 18 percent), neutropenia (in 12 percent), and biochemical abnormalities (in 12 percent). Serious side effects were uncommon. The mean values for the area under the curve for efavirenz and nelfinavir corresponded to expected values. In an intention-to-treat analysis, 76 percent of children had plasma HIV-1 RNA levels of less than 400 copies per milliliter after 48 weeks of therapy and 63 percent had levels of less than 50 copies per milliliter. A high plasma HIV-1 RNA level at base line significantly decreased the likelihood that plasma levels of HIV-1 RNA would become undetectable during treatment.

CONCLUSIONS

In HIV-1-infected children who were previously treated with nucleoside reverse-transcriptase inhibitors, the combination of efavirenz, nelfinavir, and nucleoside reverse-transcriptase inhibitors was generally well tolerated and had a potent and sustained antiviral effect.

Sorting feeder cattle with a system that integrates ultrasound backfat and marbling estimates with a model that maximizes feedlot profitability in value-based marketing

Studies were conducted to evaluate a feeder cattle sorting system for tracking future carcass merit. The Kansas State University (KSU) sorting system combines initial body weight, ultrasound backfat thickness and marbling score with economic data to project the number of days on feed that will maximize profitability. The KSU sorting system was applied, 3 to 4 mo before slaughter, on 4101 yearling steers at two large feedlots located in southern Alberta. In Feedlot 1, steers averaging 408.7 kg (SD = 45.2 kg) were randomly assigned to two treatment groups: sorted by weight (control; n = 856) and sorted by the KSU sorting system (n = 849). In Feedlot 2, steers averaging 494.4 kg (SD = 42.3 kg) were randomly assigned to two treatment groups: not sorted (control; n = 798) and sorted by the KSU sorting system (n = 1598). Whole pens were marketed when the majority of steers in the pen approached the carcass weight and grade characteristics required for optimal return. The KSU sorted steers gained 0.12 kg d−1 faster at Feedlot 1 (P = 0.043) and 0.05 kg d−1 faster at Feedlot 2 (P = 0.036) than control steers. Feed intake, feed efficiency, death loss, warm carcass weight, backfat thickness, l. dorsi area, marbling score and lean meat yield were similar between sorting systems regardless of feedlot. The KSU sorting system reduced dark cutting (B4) carcasses to zero (0.0% KSU vs. 1.3% Control; P = 0.005) and increased AAA quality grade carcasses by 40.8% (31.4% KSU vs. 22.3% Control; P = 0.001) in Feedlot 1. In Feedlot 2, the KSU sorting system reduced over-fat carcasses (Y3) by 47.4% (10.2% KSU vs. 19.4% Control; P = 0.001) and increased AA carcasses by 14.7% (52.3% KSU vs. 45.6% Control; P = 0.003). These changes resulted in the KSU sorted steers being more profitable than control steers by $27.67 head−1 in Feedlot 1 and $15.22 head−1 in Feedlot 2. The increased net return was primarily due to improved weight gains and a more desirable distribution of carcass yield and quality grades. Key words: Ultrasound, carcass uniformity, steers

Osteonecrosis of the base of the second metacarpal: a case report

Osteonecrosis of the metacarpal is rare. Previously reported cases have only involved the metacarpal heads, with the long finger being the most commonly affected. We present a patient with avascular necrosis involving the base of the second metacarpal.

Using amino-cerv after cervical LEEP

OBJECTIVE

To evaluate the ability of Amino-Cerv to promote healing of the cervix following loop electrical excision procedure (LEEP) of the cervix for cervical intraepithelial neoplasia.

STUDY DESIGN

A randomized study was conducted on 48 women in a private office setting. Patients were divided into two groups, to use or not use Amino-Cerv intravaginally for two weeks after the procedure. Statistical analysis of the findings were performed using the chi 2 test.

RESULTS

Twenty of 24 (83%) of women using Amino-Cerv had completely healed tissue at four weeks, whereas 12 of 24 (50%) in the untreated group had healed tissue at four weeks. Findings were not statistically significant at two weeks but were statistically significant (P < .005, power = .55) at four weeks after the procedure.

CONCLUSION

Amino-Cerv after LEEP of the cervix promotes healing.

Physiologic events initiating REM sleep in patients with the postpolio syndrome

BACKGROUND

We previously studied the occurrence of muscle tone reduction (MTR), sawtooth waves (STW), and REM in sleep, and found a stereotypical sequence of these events in normal subjects. Patients with the postpolio syndrome may have involvement of the reticular formation in the brainstem, an area known to mediate initiation of REM sleep. We hypothesized that such brainstem pathology might affect the stereotyped sequence of events initiating REM sleep.

METHODS

We measured the latencies to the onsets of the first MTR, the first STW, and the first REM in 13 patients with postpolio syndrome, 7 of whom had bulbar involvement. All latencies were calculated from the last body movement before the onset of REM sleep.

RESULTS

Using analysis of variance, we found highly significant differences among the overall mean latencies of the three types of onset (MTR, STW, REM) and also between the mean latencies of the two subgroups of patients (bulbar, nonbulbar). Although the latencies for the entire group were longer than those of the normal volunteers, the differences were not significant. However, when the bulbar and nonbulbar groups were compared, analysis of variance showed significantly longer latencies for the bulbar group than for the nonbulbar group (p < 0.0001). The values for the nonbulbar patients closely resembled those for the normal controls. Although the latencies differed, the slopes of the regressions of REM on STW, STW on MTR, and REM on MTR resembled each other closely (p = 0.924).

CONCLUSION

Prolongation of these latencies may be due to prolonged recruitment time for neurons in the pontine tegmentum, following damage from polio. This may be a sensitive marker of a brainstem lesion, and may also represent a type of sleep pathology not previously explored.

Molecular characterization of Escherichia coli FtsE and FtsX

The genes ftsE and ftsX are organized in one operon together with ftsY. FtsY codes for the receptor of the signal recognition particle (SRP) that functions in targeting a subset of inner membrane proteins. We have found no indications for a structural relationship between FtsE/X and FtsY. Evidence is presented that FtsE and FtsX form a complex in the inner membrane that bears the characteristics of an ATP-binding cassette (ABC)-type transporter. FtsE is a hydrophilic nucleotide-binding protein that has a tendency to dimerize and associates with the inner membrane through an interaction with the integral membrane protein FtsX. An FtsE null mutant showed filamentous growth and appeared viable on high salt medium only, indicating a role for FtsE in cell division and/or salt transport.

The effects of spectacle wear in infancy on eye growth and refractive error in the marmoset (Callithrix jacchus)

We made a comprehensive study, involving observations on 45 marmosets, of the effects on ocular growth and refraction of wearing spectacles from the ages of 4-8 weeks. This period was within the period early in life when the eye grows rapidly and refraction changes from hyperopia to its adult value of modest myopia. In one series of experiments we studied the effect of lenses of powers -8, -4, +4 and +8D fitted monocularly. In another series of experiments we studied the effect of lenses of equal and opposite powers fitted binocularly, with the two eyes alternately occluded, so as to give an incentive to use both eyes, and in particular to accommodate, for at least part of each day, through the negative lens. The vitreous chamber of eyes that wore negative lenses of -4D or -8D, combined with alternate occlusion, elongated more rapidly than that of the fellow eye (negative lens eye-positive lens eye, 0.21 +/- 0.03 mm (S.E.M.), P < 0.01 and 0.25 +/- 0.06 mm, P < 0.05, respectively) and became relatively more myopic (2.8 +/- 0.26D, P < 0.01 and 2.4 +/- 0.61D, P < 0.05 respectively). Eyes that wore -4D lenses monocularly elongated more rapidly and became myopic than fellow eyes. Eyes that wore +4D or +8D lenses were less strongly affected: animals that wore +8D lenses monocularly (without alternate occlusion) developed a slight relative hyperopia (0.99 +/- 0.21D, P < 0.01), with the more hyperopic eyes also slightly shorter (0.09 +/- 0.05 mm) than their fellow eyes, but eyes wearing +4D lenses were not significantly different from their fellow eyes. Animals that wore -8D lenses monocularly (without alternate occlusion) developed a slight relative hyperopia after three weeks of lens-wear (0.85 +/- 0.26D, P < 0.05). These were the only eyes that responded in a non-compensatory direction to the optical challenge of spectacle wear, and we interpret this effect as one due to visual deprivation. After the removal of lenses, the degree of anisometropia slowly diminished in those groups of animals in which it had been induced, but in the three groups in which the largest effects had been produced by lens-wear the overall mean anisometropia (0.68 +/- 0.24D, P < 0.01) and vitreous chamber depth (VCD) discrepancy (0.09 +/- 0.03 mm, P < 0.01) were still significant at the end of the experiments, when the animals were 273 days old. The reduction of anisometropia in these groups was associated with an increase in the rate of elongation of the vitreous chamber in the eyes that had previously grown normally i.e. the less myopic eyes grew more rapidly than their fellow eyes: in the seven weeks following lens-wear these eyes became more myopic and longer than normal eyes (refraction P < 0.001; VCD P < 0.001). Control experiments showed that occlusion of one eye for 50% of the day had no effect on eye growth and refraction, and therefore that alternate occlusion itself had no effect.

Normal development of refractive state and ocular component dimensions in the marmoset (Callithrix jacchus)

Refractive state and ocular dimensions were studied longitudinally in nine normal marmosets. Animals were anaesthetised and examined (with some exceptions) at 4, 6, 7, 8, 10, 15, 24 and 39 weeks of age. Cycloplegic retinoscopy showed that hyperopia early in life rapidly diminished. Refraction corrected for the artefact of retinoscopy stabilised by 8 weeks of age, but at a slightly myopic value, rather than at emmetropia. The ocular components continued to change throughout the period studied. Corneal radius, measured by photokeratometry, increased slightly during development. Anterior segment depth and vitreous chamber depth (VCD), measured by A-scan ultrasonography, increased throughout development while lens thickness initially increased and then decreased. Data from the eyes of these normal animals were compared with that from the contralateral eyes of animals which received short periods of monocular deprivation early in life (Troilo, D., & Judge S.J. (1993). Ocular development and visual deprivation myopia in the common marmoset (Callithrix jacchus jacchus). Vision Research, 33, 1311-24); eyes which viewed through no lens or a plano lens (Graham, B. & Judge, S.J. (1999)). The effects of spectacle wear in infancy on eye growth and refractive error in the marmoset (Callithrix jacchus). Vision Research, 39, 189-206), and eyes of normal animals in another colony. There were no significant differences between the first two groups and the normal animals in our colony while age-matched animals from the other colony were slightly but significantly less myopic than our animals.

Probabilistic synaptic transmission in the associative net

The associative net model of heteroassociative memory with binary-valued synapses has been extended to include recent experimental data indicating that in the hippocampus, one form of synaptic modification is a change in the probability of synaptic transmission. Pattern pairs are stored in the net by a version of the Hebbian learning rule that changes the probability of transmission at synapses where the presynaptic and post-synaptic units are simultaneously active from a low, base value to a high, modified value. Numerical calculations of the expected recall response of this stochastic associative net have been used to assess the performance for different values of the base and modified probabilities. If there is a cost incurred with generating the difference between these probabilities, then a difference of about 0. 4 is optimal. This corresponds to the magnitude of change seen experimentally. Performance can be greatly enhanced by using multiple cue presentations during recall.