Journal of Neuroscience, Vol 6, 3682-3691, Copyright © 1986 by Society for Neuroscience
Perturbed pattern of catecholamine-containing neurons in mutant Drosophila deficient in the enzyme dopa decarboxylase
V Budnik, L Martin-Morris and K White
We have initiated a study of catecholamine-containing neurons in Drosophila
melanogaster because of the potential, with this organism, to perturb
catecholamine metabolism using genetic tools. The major objectives of this
study were (1) to define the pattern of catecholamine-containing neurons
and (2) to determine the effect of the absence of dopa decarboxylase (DDC)
enzyme activity on the catecholamine-containing neurons. We chose to
analyze the catecholamine- containing neurons in the ventral ganglion of
the larval CNS. To define the catecholamine-containing neurons, CNSs were
dissected and reacted with glyoxylic acid. The catecholamine
histofluorescence (CF) neuronal pattern (normal-CF neurons) in the
wild-type ventral ganglion is stereotypic. In the mutant ventral ganglia,
in the absence of DDC enzyme activity, most normal-CF neurons still exhibit
CF, probably indicating the presence of accumulated L-dopa. Interestingly,
in the mutant CNSs, additional novel neuronal subsets also exhibit CF.
Analysis of CNSs from early developmental stages revealed that the novel-CF
neurons become fluorogenic earlier than the normal-CF neurons in the mutant
CNS. To determine whether neuronal subsets, in addition to the normal-CF,
neurons are able to sequester catecholamines, CNSs from wild-type larvae
were incubated in exogenous catecholamine (L-dopa or dopamine). Incubations
in L-dopa or dopamine revealed normally nonfluorogenic neurons that are
able to take up the amine and become fluorogenic. Among the neurons able to
sequester L-dopa or dopamine are subsets that are similar to the novel-CF
neurons in the mutant CNS. This similarity is best characterized by a major
novel-CF neuronal cluster in the subesophageal-thoracic region. These
results suggest that in the absence of DDC activity, subsets of normally
nonfluorogenic neurons capable of sequestering L-dopa or dopamine
accumulate the fluorogenic catecholamine. Hypotheses that might explain the
mode of accumulation of the catecholamine within the novel-CF neurons are
considered.