Fig. 6. Effects of serotonin on light-induced responses of medulla bilateral
neurons (MBNs) recorded from the separated proximal optic stalk. (A,B) Average
intensity—response curves showing the effect of serotonin (10 pmol) on
MBN photo-responsiveness during the day (A) and the night (B). The number of
spikes induced by a light pulse is plotted against the corresponding light
intensities. Filled and open circles indicate values either before (filled
circles) or after injection (open circles). The effect of serotonin was
greater during the night than during the day. (C) Dose—response curve
showing the ability of serotonin to suppress light-evoked MBN activity during
the day (open squares) and night (filled squares). Note that the sensitivity
of MBN to serotonin was always significantly greater during the night than the
day (c, P<0.01, t-test). Values are means ± S.E.M.
of 5-8 preparations. a and b indicate a significant difference
(P<0.01, t-test) compared with Ringer-injected control
values for day and night, respectively.
