S. Vanhatalo et S. Soinila, SEROTONIN IS NOT SYNTHESIZED, BUT SPECIFICALLY TRANSPORTED, IN THE NEURONS OF THE HYPOTHALAMIC DORSOMEDIAL NUCLEUS, European journal of neuroscience, 10(5), 1998, pp. 1930-1935
A small group of neurons in the hypothalamic dorsomedial nucleus (DMN)
have been reported to contain serotonin after pharmacological treatme
nts enhancing brain serotonin levels. This study aimed at elucidating
whether these neurons are able to synthesize serotonin de novo, and wh
ether they possess a specific serotonin transport mechanism. Serotonin
content in these neurons was raised by administration of L-tryptophan
and pargyline. Double immunostaining for serotonin and tryptophan hyd
roxylase (TpOH), the serotonin synthesizing enzyme, revealed that none
of the serotonin-containing neuronal somata expressed TpOH. Intracere
broventricular colchicine treatment did not result in TpOH-IR in these
neurons. Fluoxetine, a specific serotonin transport inhibitor, preven
ted the accumulation of serotonin in these neurons. The present result
s thus indicate that the serotonin-containing DMN neurons are not able
to synthesize serotonin. Instead, they take up exogenous serotonin vi
a a specific serotonin transport mechanism. As serotonin and DMN are a
ssociated with various physiological functions, such as regulation of
food intake and modulation of fear and anxiety, the mechanisms reveale
d in the present study may participate in these clinically important b
rain functions.