Membrane-contaminant interaction found by 3D force field calculations.

Enthalpies of contaminant transfer from water to a 1,2-Dilauroyl-DL-phosphatidyl ethanolamine (DLPE) membrane were calculated in order to study the suitability of 3D force fields for the calculation of membrane-water partitioning constants (Kmw) and as potential descriptors for bio-concentration. A 3D DLPE membrane model was built in a MM+ force field using AM1 atomic charges. 3,5-Dichlorobiphenyl (PCB14), 4,4'-dichlorobiphenyl (PCB15), 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)-ethane (PPDDT or p,p'-DDT) and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) were inserted into apolar and polar sites and their interaction energies with the membrane were calculated by geometrical optimization (GO). Energies of hydratation were subtracted from membrane-contaminant interactions of selected sites. The resulting values for the enthalpies of transfer from water to the membrane were 4.7, -2.3, 11.5 and -9.2 kcal/mol for PCB14, PCB15, PPDDT and atrazine, respectively. In contrast to PCB15, the value of PCB14 compared favorably with the experimental values of similar membranes. PCB14, PCB15 and PPDDT had their lowest energies in the apolar sites of the membrane, whereas atrazine tended to accumulate in the polar membrane-bulk water boundary site. Potential advantages and limitations of the approach were discussed.

Electrophysiological assessment of maturation of regenerating motor nerve fibres in infants with brachial plexus palsy.

Age-related changes ('maturation') of the distal latency (L) and conduction velocity (CV) along the axilla-to-wrist segment have been analysed in the regenerating median and ulnar nerves of 24 children with brachial plexus palsy and have been compared with developmental changes in healthy nerves. Results show that maturation of L and CV is more rapid after regeneration than during normal development. Up to three years of age, when L and CV in regenerating nerves reached their maximum maturity, CV values were within normal limits for both nerves in about half of the cases, indicating good regeneration ability in newborns. No specific differences were found between L and CV in the time taken to reach full maturation in the same and in different regenerating nerves, which is contrary to normally developing nerves. The results also demonstrate that the maturation process of regenerating nerves does not lead to the attainment of different specific L values characteristic of normally developing median and ulnar nerves, but to uniform non-specific values close to the mean between them. This was explained by the lack of specific afferent inflow to developing motor neurons (the result of a sensory fibre lesion), which causes the non-specific development of motor units.

Progressive peripheral neuron degeneration in ataxia-telangiectasia: an electrophysiological study in children.

Electrophysiological examinations were performed on 32 children aged three to 17 years who had typical clinical manifestations of ataxia-telangiectasia (AT). EMG findings demonstrated neurogenic lesions, more pronounced in the distal leg muscles of older children where they resembled the picture characteristic of motor neuron disease. Electrophysiological and nerve conduction results showed that generalised, progressive, sensory nervous system degeneration, with neurogenic amyotrophy affecting the distal part of the lower limbs, is an established feature of this disease and can be considered one of the diagnostic characteristics of AT. This allows the syndrome to be classified as an hereditary spinocerebellar degeneration.

Changes in somatosensory evoked potentials during kindling: analogy to learning modifications.

Cortical somatosensory evoked potential (SSEP) changes were studied during kindling of the right pericruciate cortex and in the right hippocampus in 7 cats. The test electric stimuli were delivered to left and right anterior paw. The ipsi- and contralateral SSEPs were averaged before kindling and about every 35th day during kindling. Paroxysmal epileptic discharges developed in all cats. The main consistent changes in all the SSEPs involved components N2-P3-N3, i.e., those with latencies of 90--330 msec. Specifically we noted (1) a gradual decrease in the duration and latency of the N3 component (2) an increase in the slope of the P3-N3 component and (3) a decrease in the duration and latency of the p3 component. These changes were present in both hemispheres, ipsi- and contralateral to both right and left paw stimulation, though favoring the contralateral responses. The changes started to develop before the appearance of spontaneous epileptic activity and seem to be independent of the epileptogenic effect of kindling. Thus, during kindling two types of neuronal function modification seem to take place: epileptogenic and nonepileptogenic. The nonepileptogenic nature of kindling is discussed from the point of view that some forms of learning and kindling are based on similar neurophysiological processes, which lead to permanent neuronal bioelectrical changes. These plastic changes underlie the development of such processes as memory and epilepsy. The difference between these two processes may be in the disturbance of spatiotemporal distribution of coherence in neuronal ensembles.

Carpal tunnel syndrome in children with mucopolysaccharidoses: needs for surgical tendons and median nerve release.

This report analyzes the clinical and electrophysiological results of the carpal tunnel release operation in mentally retarded children with mucopolysaccharidoses and discusses the needs for early surgical intervention.