Nanomolar Bifenthrin Alters Synchronous Ca²⁺Oscillations and Cortical Neuron Development Independent of Sodium Channel Activity

Abstract

Bifenthrin, a relatively stable type I pyrethroid that causes tremors and impairs motor activity in rodents, is broadly used. We investigated whether nanomolar bifenthrin alters synchronous Ca 21 oscillations (SCOs) necessary for activity-dependent dendritic development. Primary mouse cortical neurons were cultured 8 or 9 days in vitro (DIV), loaded with the Ca 21 indicator Fluo-4, and imaged using a Fluorescence Imaging Plate Reader Tetra. Acute exposure to bifenthrin rapidly increased the frequency of SCOs by 2.7-fold (EC 50 5 58 nM) and decreased SCO amplitude by 36%. Changes in SCO properties were independent of modifications in voltage-gated sodium channels since 100 nM bifenthrin had no effect on the whole-cell Na 1 current, nor did it influence neuronal resting membrane potential. The L-type Ca 21 channel blocker nifedipine failed to ameliorate bifenthrin-triggered SCO activity. By contrast, the metabotropic glutamate receptor (mGluR)5 antagonist MPEP [2-methyl-6-(phenylethynyl)pyridine] normalized bifenthrin-triggered increase in SCO frequency without altering baseline SCO activity, indicating that bifenthrin amplifies mGluR5 signaling independent of Na 1 channel modification. Competitive [AP-5; (2)-2-amino-5-phosphonopentanoic acid] and noncompetitive (dizocilpine,10R)- (1)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate]) N-methyl-D-aspartate antagonists partially decreased both basal and bifenthrin-triggered SCO frequency increase. Bifenthrin-modified SCO rapidly enhanced the phosphorylation of cAMP response element-binding protein (CREB). Subacute (48 hours) exposure to bifenthrin commencing 2 DIV-enhanced neurite outgrowth and persistently increased SCO frequency and reduced SCO amplitude. Bifenthrin-stimulated neurite outgrowth and CREB phosphorylation were dependent on mGluR5 activity since MPEP normalized both responses. Collectively these data identify a new mechanism by which bifenthrin potently alters Ca 21 dynamics and Ca 21-dependent signaling in cortical neurons that have long term impacts on activity driven neuronal plasticity.

Developmental neurotoxicity of succeeding generations of insecticides

“…In this regard, in addition to the decreased glutamate and calcium levels identified after postnatal exposures (Carloni and others 2012; Carloni and others 2013), in cultures of neonatal hippocampal neurons, the activity of glutamatergic neuronal networks and the spontaneous release of glutamate in synapses are decreased (Meyer and others 2008) and, recently, a NMDA receptor-mediated mechanism was suggested to play a role in PIs neurotoxic actions during development. Cao and collaborators (Cao and others 2014) demonstrated that, in primary cultures of neonatal cortical neurons, bifenthrin, at concentrations well below those that delay sodium channel inactivation and affect sodium current, alters spontaneous synchronized calcium oscillations that are essential for normal neuronal development (Dolmetsch and others 1998; Wayman and others 2006) and increases phosphorylated CREB and activity-dependent dendritic growth. These effects are partially suppressed by NMDA receptors antagonists (Cao and others 2014).…”

Effect of repeated oral administration of bifenthrin antioxidant status and acetylcholinesterase activity in brain of rats

“…It is one of the most potent commercialized pyrethroids to date, with an oral lethal dose-50 (LD 50 ) values of 53 mg/kg in female rats and 70 mg/kg in male rats (Cao et al 2014). Pyrethroids slow the closing of sodium channel gates, following an initial influx of sodium during the depolarizing phase of an action potential, which results in a prolonged sodium tail current (Dubey, Khan, and Raina 2013;Yang and Li 2015).…”

Rapid Throughput Analysis Demonstrates that Chemicals with Distinct Seizurogenic Mechanisms Differentially Alter Ca2+ Dynamics in Networks Formed by Hippocampal Neurons in Culture

“…These recent data suggest that excitotoxic chemicals that promote seizures by engaging distinct biochemical targets might be resolved by how they differentially influence neuronal Ca 21 dynamics and SCO. Importantly, acute alterations in SCO patterns could provide valuable leads to identify downstream signaling mechanisms that affect longterm changes in neuronal development and neuropathology (Cao et al, 2014b).…”

“…Importantly, this approach is capable of high throughput discovery of anticonvulsants. The method also lends itself for studies of developmental neurotoxicants (Cao et al, 2014b) and those that promote neurodegeneration.…”