Q: After I position a worm in the ScreenChip, should I start recording right away or wait a while?
Mechanical stimulation can temporarily reduce pumping frequency in C. elegans (1). Positioning a worm in the ScreenChip between the recording electrodes applies gentle pressure to the worm’s body, which might likewise influence pumping. We investigated this possibility below.
A: Our data suggest that you should wait 20 s before starting an EPG recording.
Adult day-1 C. elegans were recorded for 2 min in ScreenChips, in M9 with 10 mM serotonin. Mean pump frequency of each worm was calculated in 1-second bins, these data were normalized to the same worm’s pump frequency between 90 and 120 s, then averaged across all worms. t = 0 was the time at which the experimenter removed their hand from the vacuum button (indicated by a noise artifact in the recordings), after a worm was successfully positioned.
The graph below shows normalized pump frequency [mean (line) ± S.E.M. (shading); n = 41 worms] for these recordings.
We found that pump frequency gradually increased over the first 20 s of recording before reaching a steady level. There was also greater variability in pump frequency during this period. The cause of the slower pumping at the start of recordings is currently unknown, but gradual adaptation to body wall pressure is an obvious possibility. Based on these findings, we recommended that experimenters wait at least 20 s before starting EPG recordings, to allow pumping frequency to stabilize.
(1) Keane J and Avery L (2003) Mechanosensory inputs influence Caenorhabditis elegans pharyngeal activity via Ivermectin sensitivity genes. Genetics May;164(1):153-62.