Trh^c01440 mutants exhibit an increase in neuronal arborization and varicosity number, compared to wild-type.

Trh^c01440 mutant second instar larvae that are directly exposed to 10[-6]M 5-HT from 16 hours after egg laying to hatching, exhibit feeding behaviour that is indistinguishable from parental control flies, and a decrease in the complexity of serotonergic gut fibers projecting to the proventriculus. Hypersensitivity to 5-HTP is also rescued.

Larval feeding (measured by the number of mouth hook contractions in a yeast solution) is significantly affected by the decrease in neuronal 5-HT in Trh^c01440 mutants. This is unlikely to be due to aberrant motor control because body wall contractions (measured on an agar substrate) are unaffected. Heart rate in Trh^c01440 mutant white prepupae is significantly reduced relative to controls.

Trh^c01440 mutants display an unusually strong aversion to the odorant nonanol, while showing a strong attraction to the odorant heptanol (as do controls).

Female adult motor behaviour is significantly depressed by the decrease in neuronal 5-HT in Trh^c01440 mutants. Adult feeding behaviour is significantly decreased compared to controls, in both males and females.

Embryonic survival of Trh^c01440 is enhanced relative to controls. The number of eclosing animals is decreased in Trh^c01440 mutants compared to controls, suggesting that Trh activity is critical, but no vital, during the larval and/or pupal stages. Adult survival does not require Trh activity for either female or male flies.