Figure 7. Serotonergic modulation of DA1 is governed by the network of serotonergic neurons and not the CSDn exclusively.
(A) Optogenetic stimulation of all 5-HT neurons suppresses DA1 odor responses in saline (red) but not methysergide (black). (B) PSTH showing DA1 spiking response to cVA before (magenta) and during (green) Trh stimulation in saline. Odor pulse is 500 ms for B,E, and H. (C) Summary statistics of data in A. Stimulation in saline conditions reduced DA1 odor responses, n = 7 p=0.014, paired t-test. Methysergide blocked the suppression seen in normal saline n = 8, p=0.413. (D) The CSDn is killed by the expression of a temperature-sensitive variant of diphthera toxin. The expected location of the CSDn is illustrated with yellow, dashed circles. The remaining 5-HT circuit remains intact. 5-HT positive soma are indicated with white arrows. Note the 5-HT fiber innervation of the subesophageal ganglion (SOG) and the ellipsoid body (EB). (E) PSTH's of DA1 responses to the odor cVA in flies without CSDns. Responses in normal saline are shown in black and in the presence of methysergide in red. (F) Summary of DA1 responses from E. p=0.037, n = 5, paired t-test. (G) As in D, but with expression mediated by the Trh promoter to target dipthera toxin in all 5-HT neurons. The imaging gain was elevated until a signal in the 5-HT channel was discerned giving rise to a visible background level. Note the lack of clear dense green labeled neurons. Staining in the AL, the SOG, and the EB is largely absent. (H) Odor responses of flies with killed 5-HT systems. Colors and scales bars are the same as those in E. (I) A summary of DA1 responses from brains with ablated serotonergic systems, n = 6, paired t-test. p=0.172.