Figure 1.
Chemical structures of the pharmacological agents used in this study.
Table 1.
Toxicity values of DEET to three mosquito strains and the housefly.
Table 2.
AChE inhibition data expressed as mean (n = 3) IC50 values.
Figure 2.
Neurophysiological recordings from the CNS of third instar larvae of M. domestica A) Nerve discharges before and after DEET, toluene, and lidocaine treatment across different CNS preparations, as indicated.
Initial firing frequencies in spikes/second (Hz) for each experiment are given to the left of each trace. B) Concentration-response curves for DEET, toluene, and lidocaine on CNS nerve discharge of M. domestica larvae from replicated recordings (n = 4–5 preparations per curve, with each concentration replicated 4 times), as shown in A. Data points represent mean percentage increase of baseline firing rate, and error bars represent SEM of drug concentrations replicated at least 3 times. When error bars are absent, it is because they are smaller than the size of the symbol.
Figure 3.
Effect of phentolamine on the activity of DEET (A), octopamine (B), propoxur (C) and 4-AP (D) on discharge rates of housefly larvae CNS preparations (n = 3–5 preparations per curve, with each concentration replicated 3–5 times).
Data points represent mean percentage increase of baseline firing rate, and error bars represent SEM of drug concentrations replicated at least 3 times. When error bars are absent, it is because they are smaller than the size of the symbol. Data points at each concentration for drug alone were compared to drug + phentolamine, and statistical significance (t-test, P<0.05) is indicated by an asterisk.
Figure 4.
Effects of DEET on octopaminergic systems in firefly and Sf21 cells.
A) Dose-dependent action of DEET, CDM, and propoxur on the light organ of the firefly, Photinus pyralis. See text for explanation. B) Activation of an octopamine receptor in Sf21 cells shown by internal calcium fluorescence. Bars represent means of normalized fluorescence with error bars denoting SEM, replicated across individual plates of cells (n = 3). Statistics for each column were determined by a paired t-test against matched control raw fluorescent values, where an asterisk represents statistical significance at P<0.05. For labels, OA = octopamine and PA = phentolamine. All compounds were applied at 100 µM.
Figure 5.
Recordings of the electrically-evoked EPSPs at the neuromuscular junction in M. domestica larvae after exposure to DEET (n = 11), lidocaine (n = 8), toluene (n = 8), and propoxur (n = 5).
In the DEET and lidocaine traces, the remaining transients after block of the EPSP are stimulus artifacts, which are also reflected by any negative excursions from baseline in all traces (artifact amplitudes were truncated from the recordings for clarity of display).
Figure 6.
Block of neonatal rat cortical sodium and potassium channels by DEET and related compounds.
A) Inward sodium currents activated by a 15 msec pulse to 0 mV from a holding potential of −80 mV. Control is the peak inward sodium current before treatment. Increasing DEET concentrations blocked the current, each trace taken after 1 min incubation in drug, and there was little change thereafter. Each trace is matched in form to treatment: thick line, Control; thin line, Washout; dashed line, 100 µM DEET; dotted line, 300 µM DEET; and dotted/dashed line, 1 mM DEET. B) Concentration-response curves generated from peak sodium currents as shown in A, replicated across different cells treated with DEET (n = 3), toluene (n = 6), or lidocaine (n = 4). Symbols are mean percentage of control current amplitude, with each concentration of blocker replicated 3–6 times. Error bars represent SEM of currents. C) Typical outward currents activated by a 500 msec pulse to +60 mV from a holding potential of −80 mV, and displayed concentration-dependent block by DEET. D) Typical current-voltage relationships and DEET inhibition of potassium currents in rat cortical neurons. Currents were evoked by stepping the membrane voltage between −100 and +100 mV in 20 mV increments from a holding potential of −80 mV. Amplitude of the sustained current was calculated at 200 msec. E) Concentration-response curves for DEET-mediated inhibition of rat neuronal potassium channels from recordings as shown in C, using responses at +60 mV. Symbols are mean percentage of control current amplitude, and error bars represent SEM of currents replicated across different cells (n≥3).