The Journal of Neuroscience, October 15, 2000, 20(20):7716-7721
Serotonin Depletion In Vivo Inhibits the Branching of
Olfactory Projection Neurons in the Lobster Deutocerebrum
Jeremy M.
Sullivan,
Jeanne L.
Benton, and
Barbara S.
Beltz
Department of Biological Sciences, Wellesley College, Wellesley,
Massachusetts 02481
Serotonin depletion during embryogenesis has been shown previously
to retard the growth of the olfactory and accessory lobes of the
lobster deutocerebrum (Benton et al., 1997). The present study was
undertaken to determine whether morphological changes in the
interneurons innervating these lobes contribute to this growth
retardation. We examined the effects of in vivo
serotonin depletion using 5,7-dihydroxytryptamine (5,7-DHT) on the
morphology of the olfactory projection neurons, one of two major
classes of interneurons that innervate both lobes. Intracellular dye
fills of olfactory projection neurons in normal embryos showed that each neuron extensively innervates either the olfactory or accessory lobe before projecting to neuropil regions in the protocerebrum. In
embryos injected with 5,7-DHT, however, the deutocerebral arbors of
13.5% of the olfactory projection neurons examined were either markedly reduced compared with normal neurons or absent. Affected neurons also exhibited a number of additional aberrant morphological features suggesting that these neurons represent cells that were affected during their initial morphogenesis. Olfactory projection neurons with aberrant morphologies were also encountered, although less
frequently (7.5% of the neurons examined), in control (sham-injected) embryos indicating that the sham injections can affect the development of the brain. This observation provides insights into the nature of
effects seen in control embryos in previous experiments (Benton et al.,
1997). The results of the present study indicate that in
vivo serotonin depletion inhibits the branching of olfactory projection neurons and suggest, therefore, that one of the functions of
serotonin during normal development is to promote the ingrowth of these
neurons into the deutocerebral neuropils.
Key words:
serotonin; development; lobster; Homarus
americanus; olfaction; olfactory projection neuron; deutocerebrum; 5,7-dihydroxytryptamine
Copyright © 2000 Society for Neuroscience 0270-6474/00/20207716-06$05.00/0