Blockade of the central generator of locomotor rhythm by noncompetitive NMDA receptor antagonists in Drosophila larvae

Abstract

The noncompetitive antagonists of the vertebrate N-methyl-D-aspartate (NMDA) receptor dizocilpine (MK 801) and phencyclidine (PCP), delivered in food, were found to induce a marked and reversible inhibition of locomotor activity in Drosophila melanogaster larvae. To determine the site of action of these antagonists, we used an in vitro preparation of the Drosophila third-instar larva, preserving the central nervous system and segmental nerves with their connections to muscle fibers of the body wall. Intracellular recordings were made from ventral muscle fibers 6 and 7 in the abdominal segments. In most larvae, long-lasting (>1 h) spontaneous rhythmic motor activities were recorded in the absence of pharmacological activation. After sectioning of the connections between the brain and abdominal ganglia, the rhythm disappeared, but it could be partially restored by perfusing the muscarinic agonist oxotremorine, indicating that the activity was generated in the ventral nerve cord. MK 801 and PCP rapidly and efficiently inhibited the locomotor rhythm in a dose-dependent manner, the rhythm being totally blocked in 2 min with doses over 0.1 mg/mL. In contrast, more hydrophilic competitive NMDA antagonists had no effect on the motor rhythm in this preparation. MK 801 did not affect neuromuscular glutamatergic transmission at similar doses, as demonstrated by monitoring the responses elicited by electrical stimulation of the motor nerve or pressure applied glutamate. The presence of oxotremorine did not prevent the blocking effect of MK 801. These results show that MK 801 and PCP specifically inhibit centrally generated rhythmic activity in Drosophila, and suggest a possible role for NMDA-like receptors in locomotor rhythm control in the insect CNS.

DrosophilaGlial Glutamate Transporter Eaat1 Is Regulated by Fringe-Mediated Notch Signaling and Is Essential for Larval Locomotion

“…As noted above, AMPA-like receptors have already been implicated since KaiRIA (brec) mutants are paralyzed and have reduced SRC frequency (Featherstone et al, 2005). In addition, noncompetitive NMDA receptor antagonists have also been shown to inhibit rhythmic locomotor activity in larvae (Cattaert and Birman, 2001), but the role of these NMDA-like receptors in CNS motor circuitry remains to be tested by genetic means. The metabotropic glutamate receptor mGluRA is unlikely to be involved since null mutants are viable and have only mild defects of synaptic plasticity and morphology at neuromuscular syn- apses (Parmentier et al, 1996;Ramaekers et al, 2001;Bogdanik et al, 2004;Devaud et al, 2008).…”

Synaptic Vesicles: Test for a Role in Presynaptic Calcium Regulation

“…We found that glutamate receptors become sufficiently desensitized, at millimolar concentrations of LGA (Ն5 mM), to allow 80 Hz stimulation of the nerve without muscle contraction (0.5 or 2 mM [Ca 2ϩ ] o ). Stimulation trains of 80 pulses at 80 Hz were chosen to test the Ca 2ϩ handling properties of MN terminals during activity because this paradigm resembles MN activity during fictive locomotion (Cattaert and Birman, 2001;Barclay et al, 2002). We examined the amplitude of OGB-1 fluorescence transients evoked during 10 Hz stimulation in shi MN terminals in the presence of 7 mM LGA and found no difference (paired t test; p ϭ 0.78) relative to the amplitude of transients in its absence (⌬F/F R of 28.2 Ϯ 8.5% with and 29.3 Ϯ 6.3% without; n ϭ 5).…”

Peripheral multidendritic sensory neurons are necessary for rhythmic locomotion behavior in Drosophila larvae

“…Larval crawling, used for travel across various types of terrain, is accomplished by repeated peristaltic wave-like strides (8) and involves molecules mediating neuronal signaling (9)(10)(11)(12). Whereas one study suggests that embryonic assembly of CPG for larval locomotion does not require sensory inputs, the same study reports that interference with the sensory function during embryogenesis severely disrupts the actual patterns of locomotion (13).…”