Linear relationship between the maintenance of hippocampal long-term potentiation and retention of an associative memory.

The hypothesis that the maintenance or decay of an associative memory trace after an extended retention interval is a function of the residual strength of the synapses originally strengthened during learning was examined in a classical conditioning paradigm in which high-frequency stimulation of a hippocampal input--the medial perforant path--served as a conditioned stimulus. Rats received perforant path stimulus-foot shock pairings while engaged in a previously acquired food-motivated lever-pressing task. Conditioned suppression of lever pressing was the behavioral measure of learning and retention of the association. Stimulus trains to the perforant path at an intensity above the threshold for eliciting a population spike induced long-term potentiation of synaptic transmission in the dentate gyrus. Synaptic potentials recorded extracellularly in the dentate gyrus were subsequently monitored for 31 days to examine quantitatively the decay of synaptic potentiation, a period after which retention of the learned association was assessed. All rats learned the association to a similar extent and displayed equivalent amounts of long-term potentiation by the end of conditioning. A slowly decaying function of synaptic potentiation was observed in remembering rats, i.e., rats with high retention performance after the 31-day learning-to-retention interval, while forgetting was associated with a rapid decay of long-term potentiation. Behavioral performance at the long-term memory test was linearly correlated with the amplitude of long-term potentiation maintained just prior to the retention test. The results favor the hypothesis that long-term associative memory depends, at least in part, on the maintenance of elevated synaptic strengths in the pathway activated during learning and suggest a role for the lasting component of long-term potentiation in the maintenance of memory.     

Curietherapy using a ruthenium and iridium disk in the treatment of choroid melanoma

Following the experience of the German authors, the treatment of choroidal melanoma with ruthenium 106 disk was introduced in Lyon. Between 1983 and 1988, 127 patients were treated. Results are analysed on a group of 84 patients followed 18 months and more. In 72 cases a reduction of thickness was noted. It was complete in 33 cases. Enucleation was performed in 10 patients due to no response or regrowth. In 3 cases the tumor was sterilized. Five patients died of metastases, and 73 are alive, 3 of them with liver metastases. An afterloading iridium template disk was used in 8 patients. 4 of them with a tumor thickness between 6.5 and 8 mm had a good response. Edema of the fovea was observed in 21% of cases, while cataracts were very unusual with Ru 106. An enucleation was performed in 6 patients because of a complication. A useful vision may be preserved in 60% of cases. The scleral tolerance dose is close to 1,500 Gy. These results are in agreement with those of the literature and are considered to be satisfactory for tumors not exceeding 5 to 6 mm in thickness. If the tumor is located close to the fovea or the papilla, and/or if the thickness is 8 mm or more, proton beam could be a good alternative.     

Infant feeding until the age of 4 months old in Seine-Maritime

This study reports infant feeding practices during the first 4 months of life. A representative sample of 10% of the births in the Seine-Maritime department formed the subject of a questionnaire cohort study carried on at home by public health institution for infants specialized nurses. Among 1,407 interviewed mothers, 52% had been thinking about their future child feeding before birth, essentially with their circles, especially their husbands. The type of feeding had been chosen before pregnancy in 64.3% of cases. Earlier choices resulted more often in breast-feeding. 46.2% of mothers tried to breast-feed their children, however 17% among them discontinued when back home. Carrying out breast-feeding (median duration 10 weeks) delayed the feeding diversification and was associated with a lower frequency of health difficulties in children.     

Does retention of the ovaries improve long-term survival after hysterectomy? A gynecological oncological perspective.

Ovarian cancer is, in most cases, a lethal disease as it is virtually impossible to diagnose at an early stage and almost impossible to treat successfully when detected at an advanced stage. In postmenopausal women, there is no prevention for ovarian cancer but oophorectomy. Therefore, from the gynecological oncological perspective, where benign gynecological pathology requires surgery in postmenopausal women, oophorectomy should be the preferred option.     

Biological and physical properties of autogenous vascularized fibular grafts in dogs

The biological and biomechanical properties of normal fibulae, fibulae that had had a sham operation, and both vascularized and non-vascularized autogenous grafts were studied in dogs at three months after the operation. The study was designed to quantify and correlate changes in these properties in orthotopic, stably fixed, weight-bearing grafts and to provide a baseline for additional studies of allografts. The grafts were eight centimeters long and internally fixed. The mechanical properties of the grafts were studied by torsional testing. Metabolic turnover of the grafts was evaluated by preoperative labeling of the dogs with 3H-tetracycline for resorption of bone mineral and with 3H-proline for turnover of collagen. Cortical bone area and porosity were measured. Postoperative formation of bone was evaluated by sequential labeling with fluorochrome. The vascularized grafts resembled the fibulae that had had a sham operation and those that had not had an operation with regard to the total number of osteons and the remodeling process, as measured both morphometrically and metabolically. The vascularized grafts were stronger and stiffer than the non-vascularized grafts and were not different from the bones that had had a sham operation. In contrast, the non-vascularized grafts were smaller, weaker, less stiff, and more porotic, had fewer osteons, and demonstrated increased turnover and resorption compared with the vascularized grafts, the bones that had had a sham operation, and the bones that had not been operated on.     

Modifications of the hydrophilicity of heterocyclic methacrylate copolymers for protein release

A series of copolymers comprising ethyl methacrylate (EM) and tetrahydrofurfuryl methacrylate (THFMA) gelled with either THFMA monomer or hydroxyethyl methacrylate (HEMA) monomer have been developed. In this paper, we examine the water uptake characteristics of the polymer systems and address the possibility of increasing the hydrophilicity of the systems by changing the ratios of the copolymers. We have investigated whether protein release from the polymers is related to the composition of the polymer systems. More protein was released from the polymers gelled with the more hydrophilic monomer (HEMA) than with THFMA. This was consistent with the calculated diffusion coefficients, which were 10 times greater for the polymers gelled with HEMA than those gelled with THFMA. Interestingly, the water uptake and protein release profiles were not dependent on the ratio of EM and THFMA in the copolymers. This is probably due to the conflicting roles of THFMA in the copolymer; it is both the more hydrophilic component as well as a cross-linking agent. In addition, it would appear that the structural and surface topography of these polymers had more significant effects on protein release than copolymer composition.     

Torsional loads in the early postoperative period following total hip replacement

Torques generated in one subject during the early postoperative period were measured with a telemeterized total hip component. The patient was examined during gait, stair ascent, rising from a chair, and single-limb stance. The torques were plotted against both the resultant joint contact force and the force component directed along the stem axis. During gait, the maximum torque was 35 Nm, recorded at a walking velocity of 1.7 m/sec. The peak torques during stair ascent and during rising from a seated position were found to be 23 and 15 Nm, respectively. The maximum value for torque measured in this study was 37 Nm during one attempt at single-limb stance. Comparison of plots for torque versus stem-axis component for the four activities shows that the torque increased more rapidly for chair exits than for gait up to resultant contact force values of as much as 1,000 N. For stair ascent, the same was true to values of 1,400 N. Within any given activity, the relationship between stem torque and resultant or stem-axis force showed considerable variability. These results indicate that experiments evaluating the stability of femoral components in total hip arthroplasty should incorporate a component directed along the stem axis, as well as a component normal to the plane of the prosthesis. The results also suggest that theoretical stress analysis models should consider the broad variability in the orientation of the joint force at the hip.