A radioautographic technique was developed by which it was possible to visua1iz.e y-aminobutyric acid frABA) that was bound to isolated abdominal stretch receptors of the crayfish during brief incubation in a suitable salt solution containing yABASH of high specific activity. The binding, which takes place even at 0 to 4", was enhanced at room temperature. The pattern of labeling was found to be consistent with a greater degree of focalization than elsewhere at the axodendritic endings between branches of the inhibitory axon and the dendrites of the sensory neuron. Neither thym~dine-3H nor Dt,-leucine-3H showed a simitar pattern. The characteristic binding of rAI3A by the stretch receptors was disrupted by distilled water, formalin, or by employing a Na+-free saline.

The kinetics of an electromagnetic field EMF target pathway are used to estimate frequency windows for EMF bioeffects. Ionrligand binding is characterized via first order kinetics from which a specific electrical impedance can be derived. The resistancercapacitance properties of the binding pathway impedance, determined by the kinetics of the rate-determining step, define the frequency range over which the target pathway is most sensitive to external EMF. Applied signals may thus be configured such that their spectral content closely matches that of the target, using evaluation of the signal to thermal noise ratio to optimize waveform parameters. Ž. Using the approach proposed in this study, a pulsed radio frequency PRF waveform, currently employed clinically for soft tissue repair, was retuned by modulation of burst duration, producing significant bioeffects at substantially reduced signal amplitude. Application is made to Ca 2q rCalmodulin-dependent myosin phosphorylation, for which the binding time constants may be estimated from reported kinetics, neurite outgrowth from embryonic chick dorsal root explants and bone repair in a fracture model. The results showed that the retuned signal produced increased phosphorylation rates, neurite outgrowth and biomechanical strength that were indistinguishable from those produced by the clinical signal, but with a tenfold reduction in peak signal amplitude, f 800-fold reduction in average amplitude and f 10 6-fold reduction in average power.

This study presents new information concerning the electrochemical conditions of tantium electrodes in a culture system which has heen used to deliver direct curr$nt to peripheral neme ganglia. Current and potential measurements of both cathode and anode have shown that this system is well-defined and reproducible, and that the potential of the anode when it is tantalum drives the potential of either the platinum or tantalum cathode. Voltammetric mevurements have shown that the working potential of the cathode during the discharge of a 1.4 V battery is associated with an electrochemical process involving oxygen or. hydrogen peroxide. Some hypotheses concerning the electrical and electrochemical behavior of the system have been addressed.

Few studies are available that relate conductivity and temperature in solutions commonly used in tissue culture media. The purpose of this paper is to provide equations relating conductivity and temperature (in the range 20 "C-40 "C) for five solutions: 0.9% saline, MEM (Minimum Essential Media), horse serum, MEM with 1 % horse serum, and MEM with 10% horse serum.

Regeneration of the sciatic nerve was studied in rats pretreated in a pulsed electromagnetic field (PEMF). The rats were exposed between a pair of Helmholtz coils at a pulse repetition rate of 2 pps at a field density of 60 or 300 pT. The PEMF treatment was then discontinued. After an interval of recovery, regeneration of the sciatic nerve was initiated by a crush lesion. Regeneration of sensory fibers was measured by the "pinch test" after an additional 3-6 days. A variety of PEMF pretreatments including 4 h /day for 1-4 days or exposure for 15 midday during 2 days resulted in an increased regeneration distance, measured 3 days after the crush lesion. This effect could be demonstrated even after a 14-day recovery period. In contrast, pretreatment for 4 hlday for 2 days at 60 pT did not affect the regeneration distance. The results showed that PEMF pretreatment conditioned the rat sciatic nerve in a manner similar to that which occurs after a crush lesion, which indicates that PEMF affects the neuronal cell body. However, the mechanism of this effect remains obscure. 0 1993 Wiley-l.is.;. Inc.

Previous studies in our laboratory showed that neurite outgrowth in vitro and nerve regeneration in vivo were stimulated by 2 Hz, 0.3 mT (3 G) pulsed electromagnetic ®elds (PEMF). To learn more about the effects of PEMF on nerve cells, we exposed PC6 cells, a standard neuronal-like cell model, to the same pulsed electromagnetic ®elds for 2 h/day for 2 days and asked whether two different cell processes, proliferation and differentiation, were affected. The cells were also treated with a differentiating agent, nerve growth factor (NGF), to further de®ne any interactive effects. We found that proliferation was unaffected by either PEMF or NGF alone or in combination. Differentiation, expressed as neurite outgrowth, was strongly upregulated with NGF, but this NGF response was signi®cantly depressed in cells treated with PEMF. Bioelectromagnetics 22:267±271, 2001.

It is an honor and privilege to introduce to you this year's d'Arsonval Award recipient, Dr. Nancy Wertheimer. Dr. Wertheimer has been a member of the Bioelectromagnetics Society for many years and has been recognized by colleagues on an international scale as the person who was most instrumental in pointing out the potential health hazards of power lines and environmental electromagnetic ®elds. Nancy and her long-time associate Ed Leeper published the ®rst report of an association between residential electrical wiring con®guration and childhood leukemia. Dr. Wertheimer was born in New Haven, Connecticut and attended the University of Michigan where she received her B.S. degree in psychology and biology. She received her M.A. and her Ph.D. in experimental psychology from Harvard and Radcliffe. Her postgraduate studies were in biochemistry at the University of Colorado and in Epidemiology at the University of Minnesota. She obtained an academic position in the Department of Preventive Medicine,

Interactions between the hormone melatonin at pharmacological concentrations (10 À3 M) and 2 Hz, 0.3 mT pulsed electromagnetic ®elds (PEMF) on the proliferation and invasion of human breast cancer cells were studied in vitro. Three types of human breast cancer cells were used in this study: MDA-MB-435, MDA-MB-231, and MCF-7. Results showed that cellular growth of MDA-MB-231 cells, which were reported to be lowly metastatic, and MCF-7 cells, which were reported to be nonmetastatic, were both signi®cantly reduced by melatonin regardless of the presence of the ®eld. Results also showed that MDA-MB-435 and MDA-MB-231 cells were invasive, with MDA-MB-231 cells being more invasive than the MDA-MB-435 cells for both unexposed and experimental-PEMF groups. In addition, invasion studies showed that MCF-7 cells were not invasive and that melatonin did not have any effects on the invasion of these cells, with or without the PEMF. It is also suggested that since metastasis requires growth and invasion into tissue, anti-invasion agents can be used in conjunction with melatonin to prevent formation of secondary metastases. The overall studies suggest that PEMF at 2 Hz, 0.3 mT does not in¯uence cancer metastasis; while having clinical merit in the healing of soft tissue injury, this ®eld has shown no in¯uence on cancer cells as 60 Hz power line ®elds have. Bioelectromagnetics 22:178±184, 2001.

We have previously shown that neurite outgrowth from 6-day chick embryo dorsal root ganglia (DRG) in vitro was stimulated when nerve growth factor (NGF) and pulsed magnetic fields (PMF) are used in combination. 392 DRGs were studied in a field excited by a commercial PMF generator. We have now analyzed an additional 416 DRGs exposed to very similar PMFs produced by an arbitrary wavefrom generator and power amplifier. We reproduced our previous findings that combination of NGF and bursts of asymmetric, 220 ps-wide, 4.0 mT-peak pulses induced significantly (p<O.OS) greater outgrowth than NGF alone, that fields without NGF do not significantly alter outgrowth, and that, unlike NGF alone, 4.0 mT fields and NGF can induce asymmetric outgrowth. The asymmetry does not seem to have a preferred orientation with respect to the induced electric field. Analysis of the data for the entire 808 DRGs confirms these findings. Importantly, we find similar results for pulse bursts repeated at 15 or 25 Hz. 01996 Wiley-Liss, Inc.

We suggest an experimental comparison of two directions for applying the time-varying magnetic fields which have been found to speed spontaneous regeneration of injured peripheral nerves and in attempts to repair spinal cord injuries. Time-varying magnetic fields induce currents in a plane perpendicular to the magnetic field direction. The lower conductivity of the spinal cord's sheath (dura matter) or of the myelin sheath of peripheral nerves would seem to confine the induced electric fields and currents to the spinal cord or nerve itself. The proposed comparison could allow choosing between two possible modes of action of the fields: (1) Magnetically-induced electric fields or currents may be encouraging ion flow or otherwise helping enzyme, channel or other interactions at the cell membrane, as is thought to be the case in field stimulation of healing in bone. This mechanism should be independent of field direction. (2) Work in developing organisms and with fields applied to nerve cells in vitro has shown that neurite growth is guided parallel to both endogenous and external electric fields. This mechanism would be effective when induced electric fields are parallel, but not when they are perpendicular to the nerve. Any experimental test should seek to produce as close as possible to the same induced current intensity with both field directions. Possible confounding factors, as well as breakdowns in the assumptions of the simple model presented here, would have to be considered. This proposal was motivated by a recent report in which the authors listed a changed field direction as one of several possible reasons for an unsuccessful experiment. Bioelectromagnetics 28:488-492, 2007.

Electromagnetic fields (EMFs) have been demonstrated to enhance mammalian peripheral nerve regeneration in vitro and in vivo. Using an EMF signal shown to enhance neurite outgrowth in vitro, we tested this field in vivo using three different amplitudes. The rat sciatic nerve was crushed. Whole body exposure was performed for 4 h/day for 5 days in a 96-turn solenoid coil controlled by a signal generator and power amplifier. The induced electric field at the target tissue consisted of a bipolar rectangular pulse, having 1 and 0.3 ms durations in each polarity, respectively. Pulse repetition rate was 2 per second. By varying the current, the coils produced fields consisting of sham (no current) and peak magnetic fields of 0.03 mT, 0.3 mT, and 3 mT, corresponding to peak induced electric fields of 1, 10, and 100 mV/cm, respectively, at the tissue target. Walking function was assessed over 43 days using video recording and measurement of the 1-5 toe-spread, using an imaging program. Comparing injured to uninjured hind limbs, mean responses were evaluated using a linear mixed statistical model. There was no difference found in recovery of the toe-spread function between any EMF treatments compared to sham.

The effects of pulsed electromagnetic fields (PEMF) on rat sciatic nerve regeneration after a crush lesion were determined. The rats were placed between a pair of Helmholtz coils and exposed to PEMF of frequency 2 Hz and magnetic flux density of 0.3 mT. A 4 h/day treatment for 3-6 days increased the rate of nerve regeneration by 22%. This stimulatory effect was independent of the orientation of the coils. Exposure times of 1 h/day-10 h/day were equally effective in stimulating nerve regeneration. Rats exposed to PEMF for 4 h/day for 7 days before crush, followed by 3 days after crush without PEMF, also showed significantly increased regeneration. This pre-exposure 'conditioning' effect suggests that PEMF influences regeneration indirectly.

Segments of 2-, 4-, 6-and 8-day neural tube, or of 15-day peripheral nerve were implanted longitudinally into limb stumps of 4-day chick embryos whose right-wing buds were amputated at the future elbow region. Stumps of amputated limbs (ALs) implanted with 7day heart or without implant served as controls. Effects of progressively older neural tube implants (NTIs) upon ALs and host spinal cord neurons were analyzed by area measurements of the peripheral limb field (PLF) and NTI and by cell counts of the host lateral motor column (LMC). Nine days postamputation, 2-and 4-day NTIs contained many neurons and induced epimorphic regeneration in more than one-fourth of the embryos. Six-day NTIs contained few neurons and induced only tissue regeneration. Eight-day NTIs and peripheral nerve containing only non-neuronal cells were as ineffective as controls in stimulating regeneration, although peripheral nerve did cause a significant increase in the peripheral field. The NTIs of all ages and implants of peripheral nerve were equally effective in protecting LMC neurons from amputation-induced cell death in the host spinal cord. The results may indicate that neurons of the implant induce limb regeneration and non-neuronal cells of the implant protect against LMC neuronal death.

The right wingbuds of stage 23-25 chick embryos were amputated at the future elbow region and a segment of 2-day neural tube was implanted longitudinally into the limb stump of experimental embryos to induce limb regeneration. Control embryos had no implant in the amputated limb stump. To analyze effects of the neural tube implant (NTI) upon the host nervous system, quantitative determinations were made of the peripheral limb field (PLF), dorsal root ganglia (DRG) and spinal cord lateral motor column (LMC) of the amputated side for comparison with similar determinations of the unamputated side in all embryos. The PLF was estimated by determining the area of the skeletal elements of the amputated and unamputated limb of each embryo. The size of the DRG was estimated by determining the sectional-profile area of a pair of ganglia; the LMC was determined by counting the neurons on both sides of a single spinal cord segment. The PLF was less on the amputated than on the unamputated side but was significantly greater in amputated limbs that received a NTI. The size of the DRG was positively correlated with the size of the PLF in all groups, indicating the DRG was not directly affected by the NTI but did respond to target structures. The number of neurons in the LMC was not positively correlated with the PLF and was not reduced by limb amputation in embryos with a NTI. The data suggest that the NTI may have protected host spinal cord cells from the induced-cell death expected to follow limb amputation; perhaps the implant produces a neuronal survival factor.

y-Aminobutyric acid and the enzyme which forms it from Lglutamic acid, glutamic decarboxylase, occur uniquely in the central nervous system of various vertebrate species. In all species studied to date (mouse, chick, bullfrog, and rabbit) there has been found to be a progressive increase in the content of y-aminobutyric acid in the whole brain or in specific areas of brain during development (l-3). This acid was first barely detectable in extracts of whole brain of the chick embryo on the fourth day of incubation, increasing in quantity with the age of the embryo (2). The application of new and sensitive analytical techniques for y-aminobutryic acid (4)) glutamic decarboxylase (5)) and y-aminobutyric acid-cr-keto glutarate transaminase (6) has made it feasible to determine the time course of increase of these variables in a single brain structure, the optic lobe, in the chick during embryonic development and after hatching. This structure was chosen for study because preliminary survey had shown it to have a high level of y-aminobutyric acid and because it furnishes early in development a well defined, relatively large structure which is known to be of considerable functional importance in the activity of the avian central nervous system. EXPERIMENTAL PROCEDURE y-Aminobutyric Acid and Related Enzymes in Chick Optic Lobe Vol. 236, No. 2 y-Aminobutyric Acid and Related Enzymes in Chick Optic Lobe Vol. 236, No. 2