H. Cook et I. Orchard, THE SHORT-TERM EFFECTS OF 5,7-DIHYDROXYTRYPTAMINE ON PERIPHERAL SEROTONIN STORES IN RHODNIUS-PROLIXUS AND THEIR LONG-TERM RECOVERY, Insect biochemistry and molecular biology, 23(8), 1993, pp. 895-904
The serotonin neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) appears to
affect invertebrate systems differently from vertebrate ones. The basi
s for, toxicity in vertebrates appears to involve the intraneuronal ac
tions of monoamine oxidase (MAO) upon.the toxin. In insects, MAO is no
t present in appreciable amounts. In this study, we demonstrate that i
n vitro 5,7-DHT competitively inhibits the uptake of [H-3]serotonin by
serotonergic neurohaemal areas. The apparent K(M) increases from 4.9
x 10(-7) to 1.7 x 10(-6) M. This neurotoxin also causes a significant
release of previously accumulated [H-3]serotonin in nominally Ca2+-fre
e saline. While 5,7-DHT does not affect the uptake of [H-3]tryptophan,
it reduces the subsequent synthesis of [H-3]serotonin. In vivo, the t
issues appear to have recovered 2 weeks after toxin treatment, as dete
rmined by immunohistochemistry. At 24 h, 1 week and 2 weeks after inje
ction, the tissues are able to take up and release [H-3]serotonin norm
ally. 1 and 2 weeks after injection, insects ingest a normal-sized blo
od meal, a behaviour acutely disrupted by 5,7-DHT treatment. The resul
ts of this and other invertebrate studies suggest that 5,7-DHT does no
t destroy serotonergic neurons, as it does in vertebrates. 5,7-DHT may
be a more useful tool to study the functions of serotonin in inverteb
rates as one may transiently affect serotonin stores.