Effects of deet on insect and mammalian neuronal preparations. a) The Histogram illustrates the excitatory postsynaptic potential (EPSP) amplitudes (% of control) versus time (min) after exposure to 1 μM of deet in absence (blue bars) and in the presence of atropine (red bars) in P. americana central nervous system. Application of deet without atropine (blue bars) induced a biphasic effect on EPSP amplitudes. Within the first 3 min, application of deet induced a significant increase of EPSP amplitude which reflected an elevation of acetylcholine (ACh) concentration in the synaptic cleft (see text for details). After 3 min, a significant EPSP depression was observed, suggesting a regulation of ACh concentration in the synaptic cleft through an activation of presynaptic muscarinic receptors. Pre-treatment for 10 min with atropine 1 μM (red bars) clearly reversed the EPSP depression observed with deet 1 μM, confirming the participation of the muscarinic receptors in the negative feedback of ACh release following deet exposure. Data are means ± S.E.M. b) and c) Typical examples of cockroach composite (b) and unitary (c) EPSP following deet application. Experiments were done in the presence of atropine (1 μm) to prevent an action of presynaptic muscarinic receptors. Note the increase of unitary EPSP frequency and amplitude (c) following deet application (0.5 μM) in the synapses. d) Effect of deet on the time course of full size endplate potentials (EPPs) recorded in a mouse hemidiaphragm preparation bathed with a standard Krebs-Ringer solution supplemented with 1.6 μM μ-conotoxin GIIIB to selectively block sodium channels in muscle fibres. The EPPs recorded under control conditions (trace 1), and after the addition of 500 μM deet to the medium (trace 2); note the prolongation of the decay phase of EPPs in the presence of deet, with little change in the amplitude and time to peak; the mean decay-time constant were 11.1 ± 0.7 and 3.8 ± 0.08 ms for deet-treated and controls, respectively (n = 6, P < 0.001).