María J. Azanza

Steady magnetic fields mimic the effect of caffeine on neurons.

We have observed that steady magnetic fields (SMF) of 1160 and 2600 gauss (G) mimic the inhibitory and excitatory actions of caffeine on neurons. We had observed that isolated mollusc neurons exposed to SMF were either inhibited or excited by mechanisms that appear Ca2+-dependent. Our results with caffeine corroborate that changes in Ca2+ kinetics underlie the electrophysiological membrane changes observed in neurons exposed to SMF.

Synaptic neurone activity under applied 50 Hz alternating magnetic fields.

The effect of 50 Hz alternating magnetic fields of 10-150 Gauss (1-15 mT) intensity on neurone synaptic activity for glutamate and acetylcholine has been studied. The applied 50 Hz alternating magnetic field does not modify the synaptic activity induced by glutamate or acetylcholine on neurones. It has been observed that both caffeine and glutamate induce similar effects, either stimulation or inhibition, on different neurone types. It is shown that applied 50 Hz alternating magnetic fields mimic the synaptic effect of glutamate. A mimic effect has also been observed between the induced effect by applying 50 Hz alternating magnetic field on neurones and the one induced by caffeine and glutamate on the same neurone. The application of Ringer solutions with different concentrations of Ca2+/K+ ions suggest that Ca2+ ions are involved in the elicited responses to either caffeine, glutamate or 50 Hz magnetic fields. Our conclusion is that the observed mimic induced effects for 50 Hz alternating magnetic fields, caffeine and glutamate on neurones corroborate that Ca2+ ions are the cytosolic effectors of the applied 50 Hz alternating magnetic fields interaction with neurone plasma membrane.

Immunohistochemical and ultrastructural characteristics of interstitial cells of Cajal in the rabbit duodenum. Presence of a single cilium.

Santiago Ramón y Cajal discovered a new type of cell related to the myenteric plexus and also to the smooth muscle cells of the circular muscle layer of the intestine. Based on their morphology, relationships and staining characteristics, he considered these cells as primitive neurons. One century later, despite major improvements in cell biology, the interstitial cells of Cajal (ICCs) are still controversial for many researchers. The aim of study was to perform an immunohistochemical and ultrastructural characterization of the ICCs in the rabbit duo‐denum. We have found interstitial cells that are positive for c‐Kit, CD34 and nestin and are also positive for Ki67 protein, tightly associated with somatic cell proliferation. By means of electron microscopy, we describe ICCs around enteric ganglia. They present triangular or spindle forms and a very voluminous nucleus with scarce per‐inuclear chromatin surrounded by a thin perinuclear cytoplasm that expands with long cytoplasmic processes. ICC processes penetrate among the smooth muscle cells and couple with the processes of other ICCs located in the connective tissue of the circular muscle layer and establish a three‐dimensional network. Intercellular con‐tacts by means of gap‐like junctions are frequent. ICCs also establish gap‐like junctions with smooth muscle cells. We also observe a population of interstitial cells of stellate morphology in the connective tissue that sur‐rounds the muscle bundles in the circular muscle layer, usually close to nervous trunks. These cells establish different types of contacts with the muscle cells around them. In addition, the presence of a single cilium show‐ing a structure 9 + 0 in an ICC is demonstrated for the first time. In conclusion, we report positive staining c‐kit, CD34, nestin and Ki 67. ICCs fulfilled the usual transmission electron microscopy (TEM) criteria. A new ultrastructural characteristic of at least some ICCs is demonstrated: the presence of a single cilium. Some populations of ICCs in the rabbit duodenum present certain immunohistochemical and ultrastructural characteristics that often are present in progenitor cells.

Model for the effect of static magnetic fields on isolated neurons

Abstract A model which explains the effect of static magnetic fields on isolated neurons through Ca 2+ liberation from their binding sites at cell membrane, by a combined effect of lipid membrane molecules cooperative superdiamagnetism and electrostatic repulsion (Coulomb explosion) of Ca 2+ at both sides of the membrane, is developed.

ELF-magnetic field induced effects on the bioelectric activity of single neurone cells

Abstract The membrane bioelectric activity recorded from single neurones is dramatically modified under applied extremely low frequency magnetic fields (ELF-MF) of 50 Hz and 1–15 mT peak intensity. In ≌27% of the neurones studied a firing rhythm is generated for ≌7 mT, which resembles synchronous oscillations activity. The possibility that ELF-MF could generate neuronal networks synchrony firing does exist as an explanatory physical model shows.

Isolated neuron amplitude spike decrease under static magnetic fields

Abstract Isolated Helix aspersa neurons under strong enough static magnetic fields B (0.07–0.7 T) show a decrease of the spike depolarization voltage of the form ∼exp(αB2), with α dependent on neuron parameters. A tentative model is proposed which explains such behaviour through a deactivation of Na+K+-ATP-ase pumps due to protein superdiamagnetic rotation. Values for the cluster and protein in cluster numbers are estimated.

Measurement of the red blood cell membrane magnetic susceptibility

Abstract Accurate magnetic measurements, at ⋍ 300 K and at magnetic fields up to 5 T have been performed, using superconducting quantum interference device magnetometry, in dried powders of human red blood cell membranes (RBC) fragments. The measured susceptibility is χ = −(4.59 ± 0.15) × 10−7 emu/g Oe, being field independent. We have developed a model to calculate the magnetization induced on aggregates of clusters of diamagnetically correlated anisotropic phospholipid molecules (superdiamagnetism) and concluded that χ is directly related, in the form Δχ = 2χ, to the anisotropy of the bilayer diamagnetic susceptibility, expressed as Δχ ≡ χ - χ⊥, where χ| and χ⊥ are the susceptibilities parallel and perpendicular to the longer molecular axis respectively. The value obtained for Δχ is then − (9.18 ± 0.30) × 10−7 emu/g Oe. Comparison between Δχ and the model-calculated magnetization for the correlated superdiamagnetic molecular clusters of RBC and likely Helix aspersa neuron membranes, gives an upper bound of NC ≈ 5 × 106 phospholipids.

Study of neuron survival on polypyrrole‐embedded single‐walled carbon nanotube substrates for long‐term growth conditions

Cultures of primary embryonic rat brain hippocampus neurons with supporting glia cells were carried out on different substrates containing polypyrrole (PPy) and/or single-walled carbon nanotubes (SWCNTs). Neuron adhesion, neurites and dendrites branching elongation, and development of neuron networks on substrates were followed by phase-contrast optical microscopy and quantified to state cell survival and proliferation. Suspensions of as-grown and purified SWCNTs were sprayed on a glass coverslips and PPy/SWCNTs were deposited by potentiodynamic electrochemical deposition. Cell neurotoxicity revealed by neuron death was very high for purified SWCNTs substrates in good agreement with [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT) test showing lower viability on SWCNTs containing substrates compared with PPy-substrates and control samples probably due to the metal content and the carboxylic groups introduced during the purification. It is interesting to highlight that neurons grown on PPy-substrates adhere developing neurites and branching dendrites earlier even than on control cultures. On subsequent days the neurons are able to adapt to nanotube substrates developing neuron networks for 14-day cultures with similar patterns of complexity for control, PPy and PPy/SWCNT substrates. PPy/SWCNT substrates show a lower impedance value at frequencies under 1 Hz. We have come to the conclusion that glia cells and PPy added to the culture medium and substrates respectively, improve in some degree nanotube biocompatibility, cell adhesion and hence cell viability.

EVIDENCE OF SYNCHRONIZATION OF NEURONAL ACTIVITY OF MOLLUSCAN BRAIN GANGLIA INDUCED BY ALTERNATING 50 Hz APPLIED MAGNETIC FIELD

Experimental evidence for the appearance of synchronized bioelectric activity in neurons under applied extremely low frequency (ELF) magnetic fields is shown. We have studied the synchronizing process by recording the intracellular bioelectric activity from pairs of neurons randomly chosen from the brain ganglia of the snail Helix aspersa. The recordings were made in real time under exposure to sinusoidal low frequency (50 Hz) weak (B0=1–15 mT) magnetic fields. Synchronization was observed in 27% of the pairs tested. A linear dependence of the firing frequency f with the energy density of the applied magnetic field (i.e., f∝B02) was presented. The ability of low frequency sinusoidal weak magnetic fields to promote “magnetic synchronization” is exciting and opens new avenues for induced electromagnetic field bioeffects.

SNAIL NEURON BIOELECTRIC ACTIVITY INDUCED UNDER STATIC OR SINUSOIDAL MAGNETIC FIELDS REPRODUCES MAMMAL NEURON RESPONSES UNDER TRANSCRANIAL MAGNETIC STIMULATION

We have applied static (SMF) or alternating magnetic fields (AMF) to snail (Helix aspersa) single-unit neurons, in the range of those applied in magnetic stimulation (MS)/transcranial magnetic stimulation (TMS). From the experiments we have performed during the past 10 years, we have collected a blind selection of neurons and their responses to either SMF or AMF. Blind selection means that we do not know the nature of neurons. We do not know whether they are sensitive, motor, secretory, pacemaker, or inter-neurons. We have seen that the behavior of single-unit neurons under SMF/AMF exposure (SMF range: 3 mT–0.7 T; AMF range: 1–15 mT) fits well with the electrophysiologic activity described for mammals and human whole brain under MS/TMS (pulsed magnetic field range: 0.3 mT–2.4 T). The neuron experiments shown here have been aleatorily selected from a collection of about 200 neurons studied. Our results could explain some of the effects described induced in mammal neurons under MS/TMS for clinical purposes.