The influence of pulsed magnetic fields (PMFs) on nonsynaptic potentials recorded from the central and peripheral nervous systems in vitro

Abstract

The influence of pulsed magnetic fields (PMFs) on nonsynaptic potentials recorded from the central and peripheral nervous system in vitro has been investigated. The population spikes (PSs) recorded from hippocampal slices during antidromic stimulation and compound action potentials (CAPs) recorded from the segments of the sciatic nerve were used as indicators of neuronal activity. The potentials recorded from both preparations were significantly and permanently enhanced following PMF (0.16 Hz, 15 mT) exposure. The increase in the antidromic PS occurred even in the presence of potassium channel blocker tetraethylammonium (TEA) and was accompanied by multiple spiking. Among all frequencies of PMF tested (0.5, 0.16, 0.07, 0.03, 0.0 Hz), the frequency of 0.5 Hz was the most effective in enhancement of potential amplitude. The influence of PMF on the amplitude of two CAPs evoked by the pair of electrical stimuli applied in rapid succession has also been evaluated. In control conditions the potential triggered by the second stimuli was slightly smaller expressing the phenomenon of short-term depression (STD). Although PMF exposure amplified the amplitude of both potentials, the increase in the size of the first potential was significantly greater increasing further the magnitude of STD. The blocking of potassium channels reversed STD into facilitation. One of the possible mechanisms involved in PMF action could be the modification of the axonal threshold, which was significantly reduced following exposure to PMF.

Pulsed magnetic stimulation modifies amplitude of action potentials in vitro via ionic channels‐dependent mechanism

“…As reported by us previously [Ahmed, 2008b; Ahmed and Wieraszko, ] and confirmed in these studies, exposure of segments of the sciatic nerve to PMFs of a very specific pattern amplified the amplitude of the action potential (Fig. ).…”

“…While upper part of the picture shows continuous changes in amplitude of CAP, lower part depicts shapes of the potential before (a), and after (b) application of PMFs. B : Average results of 10 experiments; BL, baseline; PMFs, PMFs exposed preparations; * P = 0.005; (All results depicted in this figure are presented according to Ahmed and Wieraszko [] modified). All results in this and all subsequent figures are expressed as means ± SD.…”

“…Previous investigations revealed that magnetic fields modulated neuronal activity recorded from brain slices [Wieraszko, ; Wieraszko et al, ; Ahmed and Wieraszko, ; Tokay et al, ; Varro et al, ; Balassa et al, ], and fragments of sciatic nerve [Ahmed and Wieraszko, ]. PMF‐induced amplification of nerve cell activity in hippocampal slices, expressed as an increase in the amplitude of evoked potentials [Wieraszko, ], was correlated to rise in concentration of 3'‐5'‐cyclic adenosine monophosphate (cAMP) [Hogan and Wieraszko, ], and with enhancement of release and uptake of the neurotransmitter, glutamate [Wieraszko ; Wieraszko et al, ; Wieraszko and Ahmed, ].…”

In vitro Magnetic Stimulation: A Simple Stimulation Device to Deliver Defined Low Intensity Electromagnetic Fields

“…Focally targeted LI-rTMS in animal models has required technical advances to generate new coils; such as implantable sub-millimeter-coils that activate local neurons and downstream circuits (Bonmassar et al, 2012; Park et al, 2013) and small non-invasive external coils for examining cell and circuit effects (Rodger et al, 2012; Makowiecki et al, 2014). Stimulation devices have also been created specifically for in vitro studies (Roth and Basser, 1990; Maccabee et al, 1993; Ahmed and Wieraszko, 2009, 2015; Basham et al, 2009; RamRakhyani et al, 2013). However, like human coils (Post et al, 1999; Rotem and Moses, 2008; Stock et al, 2012; Vlachos et al, 2012; Ma et al, 2013; Lenz et al, 2016) they cannot be applied for repeated stimulation sessions within an incubator and thus any observed effects of stimulation cannot be separated from environmental confounders.…”

“…In addition, the efficiency of electric field induction depends on the relative sizes of coil and target (Weissman et al, 1992; Deng et al, 2013), thus the electric fields induced by human coils in small in vitro targets are different to those generated in the human brain, so that information obtained cannot be directly translated back to the clinic. In low-intensity stimulation (LI-rMS) studies, solenoids (Di Loreto et al, 2009; Varro et al, 2009) or coils made “in house” have been applied to one-off experiments on cultured neurons/slices (Ahmed and Wieraszko, 2009; Rotem et al, 2014) or isolated nerves (Maccabee et al, 1993; Basham et al, 2009; RamRakhyani et al, 2013; Ahmed and Wieraszko, 2015) that do not permit on-going stimulation sessions to model treatment-based protocols. Moreover, given that NIBS acts on complex neural circuits, stimulation parameters should ideally be assessed in culture models which retain some neural circuitry: e.g., organotypic hippocampal (Hausmann et al, 2001; Hogan and Wieraszko, 2004; Vlachos et al, 2012; Lenz et al, 2016) and cortico-striatal slices, hindbrain explants (Chedotal et al, 1997; Letellier et al, 2009) or microfluidic circuit cultures (Szelechowski et al, 2014).…”