Toxicological Sciences, Vol 48, 100-106, Copyright © 1999 by Society of Toxicology
L Schmued, W Slikker, P Clausing and J Bowyer
d-Fenfluramine is a potent serotonin (5-HT) reuptake inhibitor/releaser
and, until its recent recall, was prescribed as an anoretic agent. This
study demonstrates that 10 mg/kg d-fenfluramine i.p., when administered to
rats in a warm (27 degrees C) environment, produces neuronal degeneration
within select brain regions. Degeneration was detected and localized using
a recently developed fluorescent marker of neuronal degeneration,
Fluoro-Jade. The most extensive cortical damage was in the anterior
cingulate region. In the medial thalamus, degeneration was frequently seen
within the intralaminar nuclei, and somewhat less frequently observed
within the paraventricular nucleus, the mediodorsal nucleus, and the
gelatinosis nucleus. Cerebellar damage occurred primarily in medial
Purkinje cells and occasionally in granule cells or basket cells.
Degeneration was not observed in either saline-injected control animals or
in rats given even higher doses of 25 mg/kg d- fenfluramine but kept in a
cooler environment (23 degrees C). The degeneration was clearly most
prominent in animals with body temperatures of 41 degrees to 42 degrees C,
but this degeneration was not seen in animals given saline that became
extremely hyperthermic in a 37 degrees C environment. Behavioral signs such
as tremors, myoclonus, rigidity, and splayed legs were seen in all animals
with extensive neurodegeneration. The areas damaged by d-fenfluramine, when
hyperthermia occurs, could play a role in the expression of the serotonin
syndrome. Elevated extracellular 5-HT levels alone are probably not
sufficient for neurotoxicity, and additional factors such as hyperthermia,
regional specificity of 5-HT receptor subtypes, blood flow, and/or neuronal
networks may be involved.
ARTICLES
d-Fenfluramine produces neuronal degeneration in localized regions of the cortex, thalamus, and cerebellum of the rat
Division of Neurotoxicology, National Center for Toxicological Research, Jefferson, Arkansas 72079, USA.
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