Reduced and misexpression of 5-HT₂ receptors alters development, behavior and CNS activity in Drosophila melanogaster

The misexpression as well as a knock down of the 5-HT_2dro receptor produces slower body movements in larvae and altered development. When 1 st instar larvae are raised with altered expression levels a high degree of death occurred. Exposure of the CNS to 5-HT in control larva increases motor unit excitability; however, when the 5-HT_2dro expression is decreased the relative sensitivity to exogenously applied 5-HT is enhanced. This is likely a function of reduced basal CNS activity in this line. No change was observed for the strain with an over-expression compared to controls. Evoked sensory-CNS-motor circuits as well as spontaneous motor neuronal activity are also reduced. Like CNS activity, Heart Rate (HR) in larva is sensitive to 5-HT. When the 1 st instar to early 3rd instar were chronically reduced or misexpressed in the 5-HT receptor no alteration to 5-HT sensitivity on HR occurred, although the initial HR was lower in both strains as compared to wild type. Thus, a normal expression of the 5-HT_2dro is required for development and CNS responsiveness to 5-HT, but this receptor subtype might not function in acute responsiveness of the heart to 5-HT, although the receptor has some effect on basal heart rate.