Fig. 5. Effects of serotonin on the spontaneous activity recorded from the separated proximal optic stalk. (A) Application of serotonin into the optic lobe suppressed the spontaneous activity in a dose-dependent manner during both day (open squares) and night (filled squares). a and b indicate a significant difference (P<0.05, t-test) compared with the Ringer-injected control for day and night, respectively. Values are means ± S.E.M. of 5-8 preparations. (B) Serotonin (10 pmol) injected into the optic lobe significantly suppressed the spontaneous firing rate, which was further reduced when the contralateral optic stalk was severed. When the contralateral optic lobe was removed, the spontaneous activity was significantly reduced, and this value was increased only slightly when serotonin was injected into the protocerebral lobe after the removal of the optic lobe. Values are means ± S.E.M. of 5 preparations, given as percentage of the value before treatments (untreated). ^*P<0.01, t-test.