Assessing the effects of three dental impression materials on the isolated sciatic nerve of rat and frog

Endocrine disruptors also function as nervous disruptors and can be renamed endocrine and nervous disruptors (ENDs)

Endocrine disruption (ED) and endocrine disruptors (EDs) emerged as scientific concepts in 1995, after numerous chemical pollutants were found to be responsible for reproductive dysfunction. The World Health Organization established in the United Nations Environment Programme a list of materials, plasticizers, pesticides, and various pollutants synthesized from petrochemistry that impact not only reproduction, but also hormonal functions, directly or indirectly. Cells communicate via either chemical or electrical signals transmitted within the endocrine or nervous systems. To investigate whether hormone disruptors may also interfere directly or indirectly with the development or functioning of the nervous system through either a neuroendocrine or a more general mechanism, we examined the scientific literature to ascertain the effects of EDs on the nervous system, specifically in the categories of neurotoxicity, cognition, and behaviour. To date, we demonstrated that all of the 177 EDs identified internationally by WHO are known to have an impact on the nervous system. Furthermore, the precise mechanisms underlying this neurodisruption have also been established. It was previously believed that EDs primarily function via the thyroid. However, this study presents substantial evidence that approximately 80 % of EDs operate via other mechanisms. It thus outlines a novel concept: EDs are also neurodisruptors (NDs) and can be collectively termed endocrine and nervous disruptors (ENDs). Most of ENDs are derived from petroleum residues, and their various mechanisms of action are similar to those of "spam" in electronic communications technologies. Therefore, ENDs can be considered as an instance of spam in a biological context.

Assessing the axonal translocation of CeO2 and SiO2 nanoparticles in the sciatic nerve fibers of the frog: an ex vivo electrophysiological study

The axonal translocation of two commonly used nanoparticles in medicine, namely CeO₂ and SiO₂, is investigated. The study was conducted on frog sciatic nerve fibers in an ex vivo preparation. Nanoparticles were applied at the proximal end of the excised nerve. A nerve stimulation protocol was followed for over 35 hours. Nerve vitality curve comparison between control and exposed nerves showed that CeO₂ has no neurotoxic effect at the concentrations tested. After exposure, specimens were fixed and then screen scanned every 1 mm along their length for nanoparticle presence by means of Fourier transform infrared microscopy. We demonstrated that both nanoparticles translocate within the nerve by formation of narrow bands in the Fourier transform infrared spectrum. For the CeO₂, we also demonstrated that the translocation depends on both axonal integrity and electrical activity. The speed of translocation for the two species was estimated in the range of 0.45–0.58 mm/h, close to slow axonal transportation rate. Transmission electron microscopy provided direct evidence for the presence of SiO₂ in the treated nerves.

Differential effects of lacosamide, phenytoin and topiramate on peripheral nerve excitability: An ex vivo electrophysiological study

BACKGROUND

Antiepileptic drugs (AEDs) are mainly used to control cortical hyperexcitability. Some of them (e.g. phenytoin (PHT) and topiramate (TPM)) have also effects on the peripheral nervous system (PNS). Lacosamide (LCM) is a novel AED that stabilizes hyperexcitable neuronal membranes by selectively enhancing the slow inactivation of voltage-gated sodium channels (VGSCs). Although the mechanism of action of LCM is fairly well understood, there are no in vitro data available regarding any possible PNS effects of LCM.

OBJECTIVE

To investigate, in vitro, the effects of LCM on peripheral nerve excitability in comparison with PHT and TPM, two AEDs that act, in part, by stabilizing the fast inactivation state of VGSCs.

METHODS

Experiments were conducted on the isolated sciatic nerve of the adult rat using standard electrophysiological methods. The effects of LCM on the amplitude and latency of the evoked compound action potential (CAP) during a 48h period of drug exposure were recorded and compared with the effects of PHT and TPM.

RESULTS

LCM produced inhibitory effects on CAP at concentrations significantly higher than the therapeutic levels (>25μg/ml). At these concentrations (62.57-125.15μg/ml), an acute and immediate increment of the latency and decrement of the amplitude of the CAP were observed. In contrast to LCM, PHT caused an acute decrement in the amplitude as well as an increment in the latency of the CAP even at subtherapeutic levels (5μg/ml). With regard to TPM, the amplitude of the CAP was not affected at the supratherapeutic concentrations but at the therapeutic concentration of 33.94μg/ml a reduced decrement of the CAP amplitude compared to the controls was observed.

CONCLUSIONS

LCM, PHT and TPM exert differential effects on peripheral nerve excitability. PHT inhibited the sciatic nerve CAP even at subtherapeutic levels whereas LCM was safe within the therapeutic concentration range. TPM did not affect the CAP amplitude even at high supratherapeutic concentrations whereas in the therapeutic range a neuroprotective effect was observed. Possible underlying mechanisms and the clinical implications of these findings are discussed.

The effects of oxaliplatin, an anticancer drug, on potassium channels of the peripheral myelinated nerve fibres of the adult rat

Oxaliplatin is a novel chemotherapeutic agent which is effective against advanced colorectal cancer, but at the same time causes severe neuropathy in the peripheral nerve fibres, affecting mainly the voltage-gated sodium (Na(+)) channels (VGNaCs), according to literature. In this study the effects of oxaliplatin on the peripheral myelinated nerve fibres (PMNFs) were investigated in vitro using the isolated sciatic nerve of the adult rat. The advantage of this nerve-preparation was that stable in amplitude evoked compound action potentials (CAP) were recorded for over 1000min. Incubation of the sciatic nerve fibres in 25, 100 and 500microM oxaliplatin, for 300-700min caused dramatic distortion of the waveform of the CAP, namely broadening the repolarization phase, repetitive firing and afterhyperpolarization (AHP), related to the malfunction of voltage-gated potassium (K(+)) channels (VGKCs). At a concentration of 5microM, oxaliplatin caused broadening of the repolarization phase of the CAP only, while the no observed effect concentration was estimated to be 1microM. These findings are indicative of severe effects of oxaliplatin on the VGKCs. In contrast, the amplitude and the rise-time of the depolarization of the CAP did not change significantly, a clear indication that the VGNaCs of the particular nerve preparation were not affected by oxaliplatin. The effects of oxaliplatin on the PMNFs were similar to those of 4-aminopyridine (4-AP), a classical antagonist of VGKCs. These similarities in the pattern of action between oxaliplatin and 4-AP combined with the fact that the effects of oxaliplatin were more pronounced and developed at lower concentrations suggest that oxaliplatin acts as a potent VGKCs antagonist.

In vitro assessment of the effects of cadmium and zinc on mammalian nerve fibres

Zinc and cadmium are environmental contaminants that have a wide range of effects on the nervous system, but zinc is also considered to be an important metal in the human body. In this study the effect of CdCl(2) and ZnCl(2), at concentrations of 50,150, 250 and 500 microM, on the nerve fibres of the sciatic nerve of the rat isolated in a three-chamber recording bath were studied. At the same concentrations, CdCl(2) and ZnCl(2) were found to have almost the same inhibitory effect on the compound action potential (CAP) of the nerve fibres. Their concentration-effect curves almost overlap and there was no significant difference in their EC(50) which for CdCl(2) is 250.1+/-18 microM (n=5) and for ZnCl(2) is 282.2+/-25 microM (n=5) correspondingly (P>0.05). The no-observed-effect concentration (NOEC) was estimated to be 50-100 microM for both metals. The identical inhibitory effect of both metals on the sciatic nerve fibres indicates a common mode of action which is related to their potential to generate reactive oxygen species (ROS).