Arch Pharm Res Vol 33, No 2, 301-308, 2010
DOI 10.1007/s12272-010-0216-3
301
Increases in Serotonergic Neuronal Activity Following Intra-
cerebroventricular Administration of AF64A in Rats
Sun-Hee Park and Dong Koo Lim
College of Pharmacy and the Institute for Drug Development, Chonnam National University, Kwangju 500-757, Korea
(Received July 2, 2009/Revised December 7, 2009/Accepted December 10, 2009)
Changes in the serotonergic nervous system after the intracerebroventricular (i.c.v.) admini-
stration of ethylcholine aziridinium (AF64A, 3 nmol/each ventricle) were studied in rats. Two
weeks after the infusion of AF64A, the levels of 5-HT and 5-HIAA in microdialysed cerebrospi-
nal fluid (CSF), the levels of total 5-HT and 5-HIAA, the density of serotonin uptake sites and
the activities of tryptophan hydroxylase (TPH) and monoamine oxidase (MAO) in various
brain regions were determined. After AF64A administration, the concentrations of 5-HT in
lateral ventricle were increased and the levels of 5-HIAA were decreased. However, the hip-
pocampal levels of total 5-HT were decreased without changes in the levels of 5-HIAA and the
hippocampal turnover rates of 5-HT increased. Also, the density of uptake sites of serotonin
([
3
H]citalopram binding sites) was decreased in the various brain. The activities of TPH were
increased in striatum and frontal cortex and the activity of MAO was also increased in stria-
tum. These results indicate that AF64A induces an increase in serotonergic neuronal activity
and decreased densities of 5-HT uptake sites which may affect the change in the other para-
meters of serotonergic neuronal activities. Furthermore, these results suggest that the impaired
cholinergic neuronal activity induces the alteration in the serotonergic nervous activities.
Key words:
5-HT, 5-HIAA, Serotonin uptake sites, Tryptophan hydroxylase, Monoamine oxidase
INTRODUCTION
The fundamental pathophysiology of Alzheimer's
disease (AD) remains poorly understood, the patholo-
gic manifestations of AD are loss of neurons and
neuronal connections in the brain (Larson et al., 1992)
and the degeneration of subcortical ascending systems
with neuronal losses in multiple neuronal systems
(Jellinger, 1997). Furthermore, neurochemical studies
on biopsied and autopsied brain from patients with
senile dementia have demonstrated large reductions
in the activity of the presynaptic marker enzyme
choline O-acetyltransferase (ChAT) in the cortex and
hippocampus (Cassidy et al., 1994). The loss of ChAT
activity is reported to correlate significantly with the
severity of the illness (Cassidy et al., 1994). The
cholinergic presynaptic receptors are also reduced in
number in parallel with reductions in ChAT activity
(Mash et al., 1985). These changes were shown in
dementia patients as well as in animals after chemical
lesions induced by neurotoxins, such as cholinotoxin
and ibotenic acid (Hanin et al., 1992; Mash et al.,
1985).
Ethylcholine aziridinium ion (AF64A) is known to
be a selective, irreversible neurotoxin. The infusion of
AF64A into either the hippocampus or lateral ventri-
cle induced defects of cholinergic nervous system, such
as choline uptake, reduction of ChAT and AChE acti-
vities, reduction of ACh release and the destruction of
the presynaptic terminals in cholinergic pathways
(Fisher et al., 1982; Bessho et al., 2008). The AF64A-
treated animals have been reported to have impaired
motivation, learning and memory (Chrobak et al.,
1988; Lim et al., 2001). This toxin has been proposed
as a tool in the development of animal models of
Alzheimer's disease and senile dementia of the
Alzheimer type (Hanin et al., 1992). Although AF64A
is suggested to be a useful tool for studying synaptic
circuitries and the functional role of brain cholinergic
Correspondence to: Dong Koo Lim, College of Pharmacy, Chon-
nam National University, Kwangju 500-757, Korea
Tel: 82-62-530-2928, Fax: 82-62-530-2949
E-mail: dklim@chonnam.ac.kr