Trace Amine-Associated Receptor 1 Modulates Dopaminergic
Lothar Lindemann, Claas Aiko Meyer, Karine Jeanneau, Amyaouch Bradaia,
Laurence Ozmen, Horst Bluethmann, Bernhard Bettler, Joseph G. Wettstein, Edilio Borroni,
Jean-Luc Moreau, and Marius C. Hoener
Pharmaceuticals Division, Central Nervous System Research (L.L., K.J., L.O., J.G.W., E.B., J.-L.M., M.C.H.) and Roche Center
for Medical Genomics (C.A.M., H.B.), F. Hoffmann-La Roche Ltd., Basel, Switzerland; and Department of Biomedicine, Institute
of Physiology, Pharmacenter, University of Basel, Basel, Switzerland (A.B., B.B.)
Received October 9, 2007; accepted December 13, 2007
The recent identification of the trace amine-associated receptor
(TAAR)1 provides an opportunity to dissociate the effects of
trace amines on the dopamine transporter from receptor-me-
diated effects. To separate both effects on a physiological level,
a Taar1 knockout mouse line was generated. Taar1 knockout
mice display increased sensitivity to amphetamine as revealed
by enhanced amphetamine-triggered increases in locomotor
activity and augmented striatal release of dopamine compared
with wild-type animals. Under baseline conditions, locomotion
and extracellular striatal dopamine levels were similar between
Taar1 knockout and wild-type mice. Electrophysiological re-
cordings revealed an elevated spontaneous firing rate of dopa-
minergic neurons in the ventral tegmental area of Taar1 knock-
outmice. The endogenous
specifically decreased the spike frequency of these neurons in
wild-type but not in Taar1 knockout mice, consistent with the
prominent expression of Taar1 in the ventral tegmental area.
Taken together, the data reveal TAAR1 as regulator of dopa-
Trace amines such as p-tyramine, ?-phenylethylamine, oc-
topamine, and tryptamine are endogenous amine compounds
related to the classic neurotransmitters dopamine, serotonin,
and noradrenaline by structure, metabolism, and tissue dis-
tribution (Philips, 1984). However, trace amines are found in
the mammalian brain at concentrations approximately 1000-
fold lower than catecholamines (Berry, 2004). Trace amines
have been postulated to function as cotransmitters in classi-
cal neurotransmitter systems (Saavedra and Axelrod, 1976),
as neurotransmitters in their own right (Sabelli et al., 1978)
or as neuromodulators of catecholamines (for review, see
(Borowsky et al., 2001; Bunzow et al., 2001) and detailed
characterization of the trace amine-associated receptor
(TAAR) family in various species (Lindemann and Hoener,
2005; Lindemann et al., 2005) provided the basis to further
elucidate the interplay between trace amines and cat-
echolamines and to understand the physiological roles of
trace amines at the molecular level. The TAAR family con-
sists of three subgroups (TAAR1–4, TAAR5, and TAAR6–9)
and is phylogenetically and functionally distinct from other G
protein-coupled receptor families and from invertebrate oc-
topamine or tyramine receptors (Lindemann and Hoener,
2005). With the exception of TAAR1 and TAAR4, none of the
other TAARs are sensitive to one of the classical trace amines
p-tyramine, ?-phenylethylamine, octopamine, and tryptamine
(Borowsky et al., 2001; Lindemann et al., 2005; Liberles and
Buck, 2006). All TAARs except TAAR1 were recently de-
tected in mouse olfactory sensory neurons, and mouse
TAAR5, TAAR7, and TAAR3 have been shown to be activated
by small-molecular-weight volatile amines, suggesting a po-
tential role of TAARs as odorant receptors in rodents
(Liberles and Buck, 2006). However, the endogenous ligands
have not yet been identified for TAARs other than TAAR1
This work was supported by F. Hoffmann-La Roche Ltd. and the Swiss
Science Foundation Grant 3100-067100.01 (to B.B.).
Article, publication date, and citation information can be found at
S The online version of this article (available at http://jpet.aspetjournals.org)
contains supplemental material.
ABBREVIATIONS: TAAR, trace amine-associated receptor; kb, kilobase(s); PCR, polymerase chain reaction; NLS, nuclear localization signal; ES,
embryonic stem; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; RT, reverse transcription; PBS, phosphate-buffered saline; DOPAC,
3,4-dihydroxyphenylacetic acid; 5-HIAA, 5-hydroxyindoleacetic acid; HPLC, high-performance liquid chromatography; GBR 12935, 1-[2-(diphe-
THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS
Copyright © 2008 by The American Society for Pharmacology and Experimental Therapeutics
JPET 324:948–956, 2008
Vol. 324, No. 3
Printed in U.S.A.
Supplemental material to this article can be found at:
at ASPET Journals on December 27, 2015
and TAAR4. Taar1 is encoded by a single exon in all species
analyzed, couples to the G protein G?s, and it responds to
p-tyramine and ?-phenylethylamine, with an EC50between
0.2 and 1.4 ?M and with much lower sensitivity also to
octopamine and tryptamine (Borowsky et al., 2001; Linde-
mann et al., 2005). In humans, all Taar genes are located in
a narrow region of approximately 109 kb in the locus 6q23.1
(Lindemann et al., 2005), which has been genetically linked
to schizophrenia and bipolar disorder (Cao et al., 1997; Ci-
chon et al., 2001; Vladimirov et al., 2007).
The interest in trace amines and their target receptors is
fueled by their proposed link to highly prevalent psychiatric
disorders, most notably depression and schizophrenia (for
reviews, see Branchek and Blackburn, 2003; Lindemann and
Hoener, 2005). It has been reported that trace amines exhibit
some amphetamine-like properties through inhibition of the
dopamine transporter (Parker and Cubeddu, 1988; Berry,
2004; Sotnikova et al., 2004), but little is known about the
effects of trace amines mediated directly by activation or
inhibition of TAAR1. The Taar1 knockout mouse line allows
to dissociate the specific contributions of dopamine trans-
porter and of TAAR1 to the physiological effects of trace
Materials and Methods
All animal experiments performed at F. Hoffmann-La Roche Ltd.
(Basel, Switzerland) were performed in compliance with Swiss Fed-
eral and Cantonal laws on animal research and approved by the
cantonal veterinary office.
Two 4.7- and 1.7-kb genomic fragments located 5? and 3? from the
Taar1 coding sequence were amplified from C57BL/6 genomic DNA
by PCR with the oligonucleotides F3 and R1 and with the oligonu-
cleotides F4 and R2, respectively (Fig. 1). The targeting vector was
assembled from these genomic fragments, a LacZ coding sequence
fused to a nuclear localization sequence (NLS; Kalderon et al., 1984),
a PgK-NeoR(Galceran et al., 2000), and a diphtheria toxin cassette
(Gabernet et al., 2005). The targeting vector was linearized with
SacII and electroporated into C57BL/6 embryonic stem (ES) cells,
and G-418 (Geneticin; Invitrogen, Paisley, UK)-resistant ES cell
clones were selected as described previously (Gabernet et al., 2005).
An ES cell clone carrying a homologous recombination event was
Fig. 1. Generation of Taar1 knockout mice. a, strategy for the targeted deletion of the Taar1 gene in mouse ES cells. The Taar1 coding sequence was
replaced by a cDNA encoding for LacZ linked to a NLS sequence. The NLSLacZ cDNA was fused in frame with the endogenous Taar1 start codon.
S, SacI; E, EcoRV; and N, NsiI. The homologous recombination was confirmed by PCR on genomic DNA derived from Taar1?/?and Taar1?/?animals
(b–e; PCR 1–4). b, PCR 1, PCR amplification of the whole Taar1 wild-type and the targeted Taar1 locus using oligonucleotides located 5? and 3? to
the genomic fragments comprised in the targeting vector. The generated PCR fragments had the expected sizes (10.7 kb for wild-type allele and 13
kb for the targeted allele, respectively) and DNA sequence (data not shown). c, PCR 2, PCR using oligonucleotides surrounding the single Taar1 coding
exon produced PCR fragments of correct sizes (2.7 kb for the wild-type allele and 5.1 kb for the targeted allele) and DNA sequence (data not shown).
d, PCR 3, PCR amplification using oligonucleotides within the LacZ coding sequence and 5? of the genomic arms comprised in the targeting vector
resulted in a fragment of the expected size (7.3 kb) and DNA sequence (data not shown) only in the targeted allele. e, PCR 4, PCR amplification using
oligonucleotides within the NeoRcoding sequence and 3? of the genomic arms comprised in the targeting vector resulted in a fragment of the expected
size (2.9 kb) and DNA sequence (data not shown) only in the targeted allele (Taar1?/?). f–h, analysis of whole brain cDNA from Taar1?/?and Taar1?/?
animals for the presence of Gapdh (f), Taar1 (g), and LacZ (h) transcripts. Taar1 transcripts were detected only in Taar1?/?cDNA, and LacZ
transcripts were found only in Taar1?/?cDNA. i, standard genotyping PCR with genomic DNA derived from Taar1?/?, Taar1?/?, and Taar1?/?
animals of the F2 generation.
TAAR1 Modulates Dopaminergic Activity
at ASPET Journals on December 27, 2015
identified by PCR (data not shown), and it was used to generate
chimeras according to standard protocols (Joyner, 1999). The recom-
binant allele was maintained in a pure C57BL/6 background
(Charles River Laboratories, Les Oncins, France) in a specific-patho-
gen-free facility with a 12:12-h day/night cycle and ad libitum access
to food and water.
The correct homologous recombination was further confirmed by
PCR amplification of fragments PCR 1 to 3 (Fig. 1) from genomic
DNA derived from tail biopsies of Taar1?/?animals and subsequent
DNA sequence analysis (for details regarding PCR conditions and
oligonucleotide sequences, see Supplemental Material). Standard
genotyping was performed by PCR using oligonucleotides detecting
the disrupted- and the intact Taar1 coding sequence, respectively
(for details regarding PCR conditions and oligonucleotide sequences,
see Supplemental Material).
The purity of the C57BL/6 genetic background of the knockout
mouse line was confirmed by microsatellite analysis of Taar1?/?
animals of the F1 generation using a total of 37 markers (for details
regarding the panel of microsatellite markers and oligonucleotides
used in the microsatellite analysis, see Supplemental Material).
Genomic DNA of six individual animals was analyzed along with
samples of C57BL/6, DBA/2, and 129/SV mice (The Jackson Labora-
tory, Bar Harbor, ME).
Whole brain cDNA of 2-week-old and adult Taar1?/?and
Taar1?/?mice was analyzed for the presence of transcripts encoding
glyceraldehyde-3-phosphate dehydrogenase (Gapdh), Taar1, and
NLSLacZ by means of RT-PCR. Whole brain cDNAs were prepared
essentially as described by Lindemann et al. (2005), and PCR was
performed using the following oligonucleotides for the individual
transcripts (for oligonucleotide sequences, see Supplemental Mate-
rial): GAPDH, GAPDHU and GAPDHD (452-bp PCR fragment);
NLSLacZ, LacZ U1, and LacZ D1 (631-bp PCR fragment); and
TAAR1, mTAAR U1, and mTAAR D1 (936-bp PCR fragment).
Drugs were purchased from Sigma Chemie (Buchs, Switzerland)
at the highest purity available, and d-amphetamine was synthesized
by F. Hoffmann-La Roche Ltd. Drugs were dissolved in 0.9% NaCl,
and they were administered i.p. before the behavioral testing or the
collection of microdialysis samples, as indicated for the individual
experiments. In each experiment, drugs were administered following
a pseudorandomized design over one to several treatment cycles,
with a minimum period of 10 to 14 days between two cycles.
Histochemistry on Tissue Sections
Adult mice were transcardially perfused under terminal isoflu-
rane anesthesia consecutively with phosphate-buffered saline (PBS)
and fixative [2% (w/v) paraformaldehyde and 0.2% (w/v) glutaralde-
hyde in PBS]. Brains were postfixed for 4 h in fixative at 4°C,
immersed overnight in 0.5 M sucrose in PBS at 4°C, embedded in
OCT compound (Medite Medizintechnik, Nunningen, Switzerland)
in Peel-A-Way tissue embedding molds (Polysciences, Warrington,
PA), and frozen on liquid nitrogen. Tissue sections were cut on a
cryostat (Leica Microsystems AG, Glattbrugg, Switzerland) at 10 to
50 ?m, thaw-mounted on gelatin-coated glass slides (Fisher Scien-
tific, Wohlen, Switzerland), air-dried at room temperature for 4 h,
and processed immediately for LacZ staining.
For LacZ staining, tissue sections were washed five times for 10
min in PBS and then incubated for 16 to 24 h in LacZ-staining
solution [1 mg/ml 5-bromo-4-chloro-3-indolyl-?-D-galactopyranoside,
5 mM K3Fe(CN)6, 5 mM K4Fe(CN)6, and 2 mM MgCl2in PBS] at
37°C. The staining was stopped by washing the tissue sections five
times for 10 min at room temperature in PBS. Tissue sections were
dehydrated through an ascending ethanol series, equilibrated to
xylene, coverslipped with DePex (Serva, Heidelberg, Germany), and
analyzed on an Axioplan I microscope equipped with an Axiocam
digital camera system (Carl Zeiss AG, Feldbach, Switzerland).
Locomotor Activity. A computerized Digiscan 16 Animal Activ-
ity Monitoring System (Omnitech Electronics, Columbus, OH) was
used to quantify spontaneous locomotor activity. Data were obtained
simultaneously from eight Digiscan activity chambers placed in a
soundproof room with a 12:12-h day/night cycle. All tests were per-
formed during the light phase (6:00 AM–6:00 PM). Each activity
monitor consisted of a Plexiglas box (20 ? 20 ? 30.5 cm) with
sawdust bedding on the floor surrounded by invisible horizontal and
vertical infrared sensor beams. The cages were connected to a Digi-
scan Analyzer linked to a PC constantly collecting the beam status
information. With this system, different behavioral parameters
could be measured, such as horizontal and vertical activity, total
distance traveled, and stereotypies. The mice were tested via a
pseudo-Latin squares design with at least a 10-day interval between
two consecutive test sessions. Animals were habituated for 30 min.
Vehicle (saline 0.9%) or d-amphetamine (1 and 2.5 mg/kg i.p.) was
then administered to wild-type (n ? 24) and Taar1 knockout (n ? 24)
mice. Locomotor activity was recorded during 30-min habituation
and 90 min after treatment starting immediately after the mice were
placed in the test compartment.
Mice were additionally assessed for body temperature, body
weight, grip strength, and general motor coordination (rotarod test;
for protocols and data regarding this additional behavioral testing,
see Supplemental Material).
Statistics. Behavioral observations were recorded as mean val-
ues ? S.E.M., and they were analyzed with an unpaired t-test.
Locomotor activity data (total distance) were analyzed with a two-
factor (genotype and dose) analysis of variance with repeated mea-
sures. Comparisons of dose effects in each genotype were undertaken
with a repeated measures analysis of variance, followed in signifi-
cant cases by paired t-tests. A P value of 0.05 was accepted as
In Vivo Microdialysis Assessment of Extracellular
Biogenic Amine Neurotransmitter Levels
Four-month-old male mice were used for these experiments.
Surgery and Implantation of the Microdialysis Probe.
Forty-five minutes before anesthesia, mice received s.c. injections of
0.075 mg/kg buprenorphine. Mice were subsequently anesthetized
with isoflurane and placed in a stereotaxic device equipped with dual
manipulator arms and an anesthetic mask. Anesthesia was main-
tained with 0.8 to 1.2% isoflurane (v/v; support gas oxygen/air, 2:1).
The head was shaved, and the skin was cut along the midline to
expose the skull. A small bore hole was made in the skull to allow the
stereotaxical insertion of the microdialysis probe (a vertical probe
carrying a 2-mm polyacrylonitrile dialysis membrane; Brains On-
line, Groningen, The Netherlands) in the striatum (coordinates: A,
0.9 mm; L, ?1.8 mm; and V, ?4.6 mm). The probe was fixed using
binary dental cement. Once the cement was firm, the wound was
closed with silk thread for suture (Silkam; B. Braun Melsungen AG,
Melsungen, Germany), the animal was removed from the stereotaxic
instrument and returned to its cage. At the end of the surgery as well
as 24 h later, mice were treated with meloxicam 1 mg/kg s.c. The
body weight of an animal was measured before the surgery and in
the following days to monitor its recovery from surgery.
Microdialysis Experiments. All microdialysis experiments
were carried out 3 to 4 days after surgery in awake, freely moving
mice. On the day of the experiment, the inlet of the implanted
dialysis probe was connected to a microperfusion pump (CMA/Micro-
dialysis, Solna, Sweden), and the outlet was connected to a fraction
collector. The microdialysis probe was then perfused with Ringer’s
solution (147 mM NaCl, 3 mM KCl, 1.2 mM CaCl2, and 1.2 mM
MgCl2) at a constant flow rate of 1.5 ?l/min, and dialysates were
collected in 15-min aliquots in plastic vials containing 37.5 ?l of 0.02
M acetic acid. Four samples of dialysates were collected before phar-
macological treatment to determine the baseline levels of biogenic
Lindemann et al.
at ASPET Journals on December 27, 2015
amines and their metabolites. Mice were then treated intraperitone-
ally with 2.5 mg/kg d-amphetamine, and dialysate samples were
collected for further 2.5 h. Dialysate samples were stored frozen at
?80°C until analysis.
Analysis of Microdialysate. Dialysate samples were analyzed
at Brains On-Line for monoamines and their metabolites. The con-
centrations of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC),
serotonin, 5-hydroxyindoleacetic acid (5-HIAA), and noradrenaline
were measured by means of an HPLC equipped with an electrochem-
ical detector essentially as described in van der Vegt et al. (2003).
Concentrations of norepinephrine, dopamine, and serotonin were
determined within the same samples by HPLC separation and elec-
trochemical detection. Samples were split into two aliquots; one
aliquot was used for the simultaneous analysis of norepinephrine
and dopamine, the other was used for the analysis of serotonin.
Norepinephrine and Dopamine. Aliquots (20 ?l) were injected
onto the HPLC column by a refrigerated microsampler system, con-
sisting of a syringe pump (model 402; Gilson, Villier Le Bel, France),
a multicolumn injector (model 233 XL; Gilson), and a temperature
regulator (model 832; Gilson). Chromatographic separation was per-
formed on a reversed-phase 150- ? 2.1-mm (3-?m) C18 Thermo BDS
Hypersil column (Thermo Electron Corporation, Waltham, MA). The
mobile phase (isocratic) consisted of a sodium acetate buffer (4.1 g/l
Na acetate) with 2.5% (v/v) methanol, 150 mg/l Titriplex (EDTA), 150
mg/l 1-octanesulfonic acid, and 150 mg/l tetramethylammonium
chloride (pH 4.1, adjusted with glacial acetic acid). The mobile phase
was run through the system at a flow rate of 0.35 ml/min by an
HPLC pump (model LC-10AD vp; Shimadzu, Kyoto, Japan).
Norepinephrine and dopamine were detected electrochemically
using a potentiostate (model Intro; Antec Leyden, Zoeterwoude, The
Netherlands) fitted with a glassy carbon electrode set at ?500 mV
versus silver/silver chloride (Antec Leyden). Data were analyzed by
Chromatography Data System (class-vp; Shimadzu) software. Con-
centrations of monoamines were quantified by an external standard
Serotonin. Aliquots of dialysate (20 ?l) were injected onto the
HPLC column as described for norepinephrine and dopamine. Chro-
matographic separation was performed on a reversed-phase 100- ?
2-mm (3-?m) C18 ODS Hypersil column (Phenomenex, Torrance,
CA). The mobile phase (isocratic) consisted of a sodium acetate buffer
(4.1 g/l Na acetate) with 4.5% (v/v) methanol, 500 mg/l Titriplex
(EDTA), 50 mg/l 1-heptanesulfonic acid, and 30 ?l/l tetraethylam-
monium (pH 4.74 adjusted with glacial acetic acid). The mobile phase
was run through the system at a flow rate of 0.4 ml/min by an HPLC
pump (model LC-10AD vp; Shimadzu). Serotonin was detected elec-
trochemically using the same method as described for norepineph-
rine and dopamine.
Slice Electrophysiology in the Ventral Tegmental Area
Horizontal slices (250 ?m in thickness cut with a VT1000 vi-
bratome; Leica, Wetzlar, Germany) of the midbrain were prepared
from Taar1 knockout and littermate wild-type mice. Slices were
cooled in artificial cerebrospinal fluid containing 119 mM NaCl, 2.5
mM KCl, 1.3 mM MgCl2, 2.5 mM CaCl2, 1.0 mM NaH2PO4, 26.2 mM
NaHCO3, and 11 mM glucose). Slices were continuously bubbled
with a mixture of 95% O2and 5% CO2and transferred after 1 h to the
recording chamber superfused with artificial cerebrospinal fluid (1.5
ml/min) at 32 to 34°C. The ventral tegmental area was identified as
the region medial to the medial terminal nucleus of the accessory
optical tract. Visualized whole-cell current-clamp recording tech-
niques were used to measure the spontaneous firing rate and holding
currents of neurons. All cells used for the statistical analysis dis-
played a stable firing activity for at least 30 min. The internal
solution contained 140 mM potassium gluconate, 4 mM NaCl, 2 mM
MgCl2, 1.1 mM EGTA, 5 mM HEPES, 2 mM Na2ATP, 5 mM sodium
creatine phosphate, and 0.6 mM Na2GTP; the pH was adjusted to 7.3
with KOH. Data were obtained with an Axopatch 200B (Molecular
Devices, Sunnyvale, CA), filtered at 2 kHz and digitized at 10 kHz,
and acquired and analyzed with pClamp9 (Molecular Devices). Val-
ues are expressed as mean ? S.E.M. For statistical comparisons the
Kolmogorov-Smirnov test was used. The level of significance was set
at P ? 0.05.
Generation of Taar1 Knockout Mice. To address the
physiological role of TAAR1 in vivo, a targeted mouse mutant
[B6-Taar1tm1(NLSLacZ)Blt, subsequently designated Taar1?]
was generated in which the entire Taar1 coding sequence
was replaced by a reporter gene consisting of LacZ fused to
an NLS (Fig. 1a). In the targeted allele, LacZ is expressed
from the endogenous Taar1 promoter, thus providing a sen-
sitive means to study TAAR1 tissue distribution. Homolo-
gous recombination in embryonic stem cells (data not shown)
and homozygous mutants were diagnosed by PCR and se-
quence analysis of PCR-derived DNA fragments spanning
the entire targeted and wild-type single exon-encoded Taar1
gene locus (Fig. 1, b–e). The gene replacement was further
confirmed by means of RT-PCR on cDNA prepared from
whole brains of 2-week-old and adult homozygous knockout
mice (Taar1?/?) and wild-type siblings (Taar1?/?). As ex-
pected, transcripts encoding TAAR1 were detected only in
wild-type but not in Taar1 knockout brain cDNA. In contrast,
LacZ transcripts were amplified from Taar1 knockout but
not from wild-type brain cDNA (Fig. 1, f–i).
To ensure a pure genetic background critical for behavioral
analysis, the Taar1 knockout mouse line was generated us-
ing C57BL/6-derived ES cells, and it was subsequently main-
tained on a pure C57BL/6 background. The purity of the
genetic background was confirmed by analyzing genomic
DNA derived from the targeted ES clones and Taar1?/?
animals at the F1 generation, respectively, with a panel of
microsatellite markers (data not shown; for the selection of
microsatellite markers and oligonucleotide sequences, see
TAAR1 Is Expressed in Dopaminergic and Serotoner-
gic Systems. The TAAR1 expression pattern in the central
nervous system was analyzed, making use of the LacZ reporter
that was inserted into the Taar1 gene in frame with the endog-
enous start codon. Owing to the low Taar1 expression levels in
mouse brain as revealed by our RT-PCR experiments (see
above) and by previous reports (Borowsky et al., 2001; Bunzow
et al., 2001), an NLS-tagged version of the LacZ reporter was
chosen to improve sensitivity. Staining of serial brain sections
of adult Taar1 knockout and wild-type brains revealed a dis-
crete and specific labeling of nuclei mainly in dopaminergic and
serotonergic brain areas; specifically in the hypothalamus and
preoptic area (Fig. 2a, box i; and b), ventral tegmental area (Fig.
2a, box ii; and c), amygdala (Fig. 2a, box ii; and d), dorsal raphe
2a, box iv; and f), and in the parahippocampal region (rhinal
cortices) and subiculum (Fig. 2g, arrows and arrowheads, re-
spectively). In contrast to previous reports suggesting Taar1
mRNA localization in additional brain areas such as the olfac-
tory bulb and cerebellar Purkinje cells (Borowsky et al., 2001),
no LacZ expression was observed in these regions. However, it
cannot be ruled out that the LacZ reporter might leave brain
areas with particularly low Taar1 expression unrecognized due
to the potentially lower sensitivity of the reporter compared
with in situ hybridization. No LacZ staining was detected in
TAAR1 Modulates Dopaminergic Activity
at ASPET Journals on December 27, 2015
Taar1?/?brain sections, and no obvious morphological alter-
ations were found in Taar1?/?compared with Taar1?/?brains
(data not shown).
Physical and Behavioral Properties of Taar1 Knock-
out Mice. The general health, physical state, and sensory
functions of Taar1 knockout mice was examined according to
a modified version of standard procedures used for behav-
ioral phenotyping of genetically modified mice (Irwin, 1968;
Hatcher et al., 2001). The comparison of all three genotypes
(Taar1?/?, Taar?/?, and Taar1?/?) did not reveal any signif-
icant differences regarding their general state of health, their
viability, fertility, life span, and nest building behavior (data
not shown) and their body weight and body temperature (see
Supplemental Fig. S1). Regarding general motor functions
and behavior, no differences between genotypes were ob-
served when analyzing dexterity and motor coordination (see
Supplemental Fig. S1), and there was no statistically signif-
icant difference in spontaneous locomotor activity, although
Taar1?/?mice showed a trend to be slightly more active
during the first 30 to 45 min of each recording session
Taar1 Knockout Mice Display Elevated Sensitivity
to Amphetamine. The effect of d-amphetamine on the loco-
motor function of Taar1?/?and Taar1?/?littermates was
compared (Fig. 3). A dose of 1 mg/kg d-amphetamine caused
a significant increase in locomotor activity in Taar1?/?ani-
mals (P ? 0.05), but not in wild-type siblings, whereas no
difference was observed in vehicle-treated animals (Fig. 3a).
A higher dose of d-amphetamine (2.5 mg/kg i.p.) significantly
increased locomotor activity also in wild-type animals (P ?
0.05), but the effect was substantially stronger in Taar1?/?
animals than in wild-type littermates (P ? 0.05) (Fig. 3b).
Fig. 2. Expression profile of TAAR1 in the mouse central nervous system, as revealed by the LacZ reporter. Note that the staining was confined to
the cell bodies due to the nuclear localization signal fused to the LacZ coding sequence. a, parasagittal brain section from the medial part of the brain
with labeling of cell bodies in the hypothalamus and preoptic areas (i), the amygdala and the ventral tegmental area (ii), the dorsal raphe nucleus (iii),
and the nucleus of the solitary tract (iv). Note that staining in the area of the rhinal cortices, subiculum, spinal trigeminal nucleus, and medullary
reticular nucleus was not apparent at this parasagittal level. b, coronal section from a mid-rostral brain region with labeling in the hypothalamus and
preoptic areas, including periventricular hypothalamus nucleus, bed nucleus of the stria terminalis (medial division), A14 dopamine cells, anterior
commissural nucleus, medial preoptic area, and medial and anterodorsal preoptic nuclei. c, coronal section from a mid-rostral brain region revealing
TAAR1 expression in the ventral tegmental area. d, coronal section from a mid-ventral brain region with staining in the area of the amygdala including
basolateral and medial amygdaloid nuclei, and amygdalopiriform transition area. e, coronal section taken at a rostral level revealing staining in the
dorsal raphe nucleus. f, coronal section from a far-rostral brain region with labeling in the nucleus of the solitary tract (solid arrow), the spinal
trigeminal nucleus (caudal part, open arrows), and the medullary reticular nucleus (arrowheads). g, coronal section taken from a mid-rostral brain
region with staining in the area of the parahippocampal region (rhinal cortices, arrows) and the subiculum (arrowheads).
Lindemann et al.
at ASPET Journals on December 27, 2015
The behavioral differences in response to d-amphetamine
between Taar1?/?and wild-type animals were further ana-
lyzed by means of in vivo microdialysis in the striatum. The
effect of d-amphetamine (2.5 mg/kg i.p.) on the extracellular
levels of catecholamines in the striatum reached its maxi-
mum after 30 min in both genotypes, with peak levels of
dopamine and norepinephrine in Taar1?/?mice 11- and 4.9-
fold higher compared with baseline values, respectively (Fig.
4, a and c). The increased dopamine and norepinephrine
releases were approximately 2.3-fold higher in Taar1?/?
mice compared with wild-type siblings. No significant differ-
ences in basal levels of dopamine and norepinephrine were
detected (Table 1).
The levels of the dopamine metabolite DOPAC were de-
creased in Taar1?/?compared with Taar1?/?mice 45 min
after d-amphetamine administration (Table 1) and returned
close to basal levels after 135 min (Fig. 4b). There were no
significant differences in the basal DOPAC levels between
Taar1?/?and Taar1?/?mice (Table 1). Serotonin levels re-
mained unchanged after d-amphetamine application in wild-
type animals (Table 1), but they increased by 2.5-fold com-
pared with basal levels 30 min after administration in
Taar1?/?mice (Fig. 4d). No significant differences were
observed before as well as after d-amphetamine administra-
tion for the serotonin metabolite 5-HIAA in Taar1?/?and
Taar1?/?mice (Table 1).
The increased dopamine levels in Taar1?/?mice could derive
from increased expression of the dopamine transporter. This
can be excluded as radioligand binding with the dopamine
transporter-specific radioligand [3H]GBR 12935 on brain sec-
tions of Taar1?/?and Taar1?/?mice did not reveal significant
differences in the expression levels in both genotypes (data not
TAAR1 Activity Decreases the Spontaneous Firing
Rate of Dopaminergic Neurons in the Ventral Tegmen-
tal Area. The differences in dopaminergic neurotransmis-
sion between Taar1?/?and Taar1?/?littermates (?1.5–2
months of age) were further investigated by electrophysiolog-
Fig. 3. Locomotor activity of Taar1?/?and Taar1?/?mice after a single
application of 1 mg/kg d-amphetamine i.p. (n ? 24) (a) and 2.5 mg/kg
d-amphetamine i.p. (n ? 24) (b). The increase in locomotor activity
triggered by the amphetamine challenge was significantly higher in
Taar1?/?mice compared with their wild-type littermates (filled symbols,
straight lines), whereas there were no significant differences between
genotypes in vehicle-treated animals (open symbols, dashed lines). $, P ?
0.05 versus Taar1?/?/d-amphetamine group; §, P ? 0.05 versus Taar1?/?/
vehicle group; and ?, P ? 0.05 versus Taar1?/?/vehicle group.
Fig. 4. Increased amphetamine-trig-
gered transmitter release in the stria-
tum in absence of TAAR1 revealed by
in vivo microdialysis. Extracellular lev-
els of dopamine, DOPAC, noradrena-
line, and serotonin in the striatum of
gle application of d-amphetamine (2.5
mg/kg i.p.; n ? 7–8) as revealed by in
vivo microdialysis. Dialysates of the
same animals were analyzed for all four
compounds. a and b, the amphetamine-
triggered increase in the extracellular
dopamine levels was 2.3-fold as big
in the striatum of Taar1?/?mice as in
their Taar1?/?littermates, whereas
there was only a marginal decrease in
the levels of the dopamine catabolite
DOPAC in both Taar1?/?and Taar1?/?
animals in response to amphetamine,
with no significant differences between
the genotypes. c, increase in the level of
noradrenalin in response to the am-
phetamine challenge was 2.4-fold as big
as in wild-type animals. d, 2.5-fold in-
crease in the serotonin level triggered
by amphetamine was observed only
in Taar1?/?mice, but not in their
Taar1?/?littermates. ?, P ? 0.05 com-
pared with Taar1?/?mice.
TAAR1 Modulates Dopaminergic Activity
at ASPET Journals on December 27, 2015
ical recordings in dopaminergic neurons in the ventral teg-
mental area. Dopaminergic neurons were identified by their
large hyperpolarization-activated cation currents (Vacher et
al., 2006). The mean spike frequency recorded under current-
clamp conditions in Taar1?/?(n ? 22) and in Taar1?/?mice
(n ? 25) was 2.3 ? 0.8 and 17.2 ? 1.2 Hz (P ? 0.0001; Fig.
5a), respectively, thereby revealing a significantly higher
firing rate in Taar1?/?neurons compared with wild-type
neurons. The data suggest that in wild-type mice TAAR1
tonically decreases the firing rate of dopaminergic neurons.
It was further observed that the resting membrane potential
in dopaminergic neurons in Taar1?/?mice (?33.5 ? 0.5 mV;
n ? 26) was depolarized compared with Taar1?/?animals
(?47.8 ? 0.7 mV; n ? 22). The depolarized resting membrane
potential in Taar1?/?mice could be either cause or conse-
quence of the increased firing rate. Next, it was tested
whether application of the TAAR1 agonist p-tyramine de-
creases the spontaneous firing rate of dopaminergic neurons
in the ventral tegmental area of wild-type mice. Bath appli-
cation of 10 ?M p-tyramine caused a significant decrease in
the spike frequency in Taar1?/?(control, F ? 2.1 ? 0.3 Hz;
p-tyramine, F ? 0.63 ? 0.04 Hz; n ? 19, P ? 0.0001) but not
in the Taar1?/?mice [control, F ? 16.73 ? 1.15 Hz;
p-tyramine, F ? 16.57 ? 1.35 Hz; n ? 15; P ? 0.05 (Fig. 5b)].
A hyperpolarization of the resting membrane potential from
?46.2 ? 0.6 to ?55.6 ? 1.2 mV (n ? 19) after p-tyramine
application in wild-type but not in Taar1?/?littermates was
also observed. Both the decrease in spike frequency and the
hyperpolarization after application of p-tyramine have been
reported previously for wild-type dopaminergic neurons in
the ventral tegmental area (Geracitano et al., 2004). To-
gether with the depolarization recorded in Taar1?/?mice,
this finding suggests that TAAR1 is either constitutively
active or tonically activated by an endogenous ligand. These
observations provide evidence that TAAR1 negatively modu-
lates the spontaneous firing of dopaminergic neurons in the
ventral tegmental area.
The Taar1 knockout mouse mutant reported here is based
on a pure C57BL/6 genetic background with a complete de-
letion of the Taar1 coding sequence. In the mouse mutant,
the NLSLacZ cDNA is expressed from the endogenous Taar1
locus, thus providing a reporter for the TAAR1 tissue distri-
The Taar1 knockout displays a hypersensitivity toward the
psychostimulant d-amphetamine as revealed by behavioral
and neurochemical observations. The hyperlocomotion in-
duced by a single amphetamine challenge was substantially
stronger in Taar1?/?animals compared with wild-type sib-
lings with maximum levels reached at 45 min after injection
(Fig. 3). In vivo microdialysis revealed that the amphet-
amine-triggered release of dopamine, norepinephrine, and
serotonin reached approximately 2.5-fold higher levels in the
Taar1?/?than in the Taar1?/?animals, with a maximum at
30 min after amphetamine application (Fig. 4, a–d). For
these findings, any strong bias originating from a potential
baseline phenotype of the knockout can be excluded. The
physical, neurological, and behavioral phenotypes (see Sup-
plemental Fig. S1) including basal locomotor activity (Fig. 3)
and the baseline extracellular concentrations of all neuro-
transmitters studied (Fig. 4, a, c, and d) are indistinguishable
between Taar1?/?and Taar1?/?animals. The effects of am-
phetamine on locomotor activity and extracellular dopamine
and norepinephrine levels in Taar1?/?and Taar1?/?mice
seen here are comparable to observations reported by Wolin-
sky et al. (2007) with another TAAR1 knockout mouse line.
Extracellular levels of catecholamines in the striatum of Taar1 knockout and wild-type littermates
Basal levels are the average of four samples taken per animal before amphetamine application. Peak levels were taken 30 min after 2.5 mg/kg d-amphetamine i.p. injection.
Seven to eight animals per genotype were used.
Basal Level 30? Amphetamine Basal Level 30? Amphetamine
2.23 ? 0.65
0.30 ? 0.12
0.23 ? 0.04
132 ? 44
124 ? 19
8.99 ? 2.75
0.49 ? 0.13
0.23 ? 0.04
95 ? 23
114 ? 22
2.27 ? 0.68
0.38 ? 0.18
0.36 ? 0.12
148 ? 36
119 ? 18
23.6 ? 8.0
1.52 ? 0.81
0.99 ? 0.39
133 ? 29
110 ? 17
Fig. 5. Electrophysiological analysis of dopaminergic neurons in the
ventral tegmental area of Taar1 knockout and wild-type littermate mice.
a, spontaneous firing rate of dopaminergic neurons was significantly
lower in the wild-type (left) than in the Taar1?/?mice (right). Cumulative
probability histogram of spike intervals in the wild-type (blue trace) and
Taar1 knockout mice (red trace). In the Taar1?/?mice, the distribution of
interevent intervals was significantly shifted to the left, indicating an
increase in the spontaneous spike frequency. b, TAAR1 agonist p-tyra-
mine at 10 ?M decreased the firing rate of dopaminergic neurons in the
wild-type but not in the Taar1 knockout littermate mice, as shown by the
shift in the cumulative probability histogram of interevent intervals in
the wild-type (left) but not in the Taar1 knockout mice (right).
Lindemann et al.
at ASPET Journals on December 27, 2015
However, whereas for our Taar1 knockout mouse line the
locomotor activity responses were significantly different be-
tween Taar1?/?and Taar1?/?littermates using 1.0 and 2.5
mg/kg d-amphetamine in several experiments, Wolinsky et
al. (2007) observed significantly different amphetamine re-
sponses only for a dose of 1 mg/kg, but not for 2.5 mg/kg. This
discrepancy could be due to the different genetic background
of the two Taar1 knockout mouse lines: whereas the Taar1
knockout described here comprises a congenic C57BL/6 back-
ground, the Taar1 knockout reported by Wolinsky et al.
(2007) comprises a mixed 129/Sv ? C57BL/6 genetic back-
ground. The effects seen with amphetamine are most likely
composed of two elements. First, amphetamine triggers the
release of dopamine and norepinephrine from synaptic vesi-
cles (King and Ellinwood, 1992), which in turn produces
elevated locomotor activity. Second, a modulation of catechol-
amine neurotransmission through
TAAR1 by trace amines has been suggested (Berry, 2004;
Geracitano et al., 2004), consistent with Taar1 expression in
brain areas with predominantly dopaminergic and serotoner-
gic neurotransmission (Fig. 2) (Borowsky et al., 2001). The
latter mechanism is further supported by the different firing
pattern observed in dopaminergic neurons of Taar1?/?and
Taar1?/?animals (Fig. 5).
The application of p-tyramine causes a significant decrease
in the firing rate and a concomitant hyperpolarization of the
membrane potential in wild-type but not in Taar1?/?dopa-
minergic neurons, which is well in line with reports from
Geracitano et al. (2004). In contrast, in the Taar1?/?mice the
spontaneous firing rate of dopaminergic neurons is 8.6-fold
higher, and the resting membrane potential is depolarized
compared with Taar1?/?mice (Fig. 5). This suggests that
TAAR1 is tonically active under physiological conditions, ei-
ther due to the presence of an ambient ligand or because of
constitutive receptor activity. It has been proposed that trace
amines stimulate, in an amphetamine-like manner, a trans-
porter-mediated efflux of dopamine from the dendrites of
dopaminergic neurons (Raiteri et al., 1978). The increased
spontaneous firing rate observed in Taar1?/?dopaminergic
neurons does not measurably increase basal levels of extra-
cellular dopamine in the striatum, as shown in our microdi-
alysis experiments (Fig. 4). It is conceivable that in Taar1?/?
mice, the increased firing rate and the associated increase in
dopamine release is offset by the reduced release of dopamine
due to lack of TAAR1 activity. It has been proposed that
TAAR1 activity causes an indirect activation of D2dopamine
autoreceptors by increasing the efflux of newly synthesized
dopamine (Geracitano et al., 2004). This could explain the
hyperpolarization observed after p-tyramine application, be-
cause D2autoreceptors are positively coupled to G protein-
coupled inwardly rectifying potassium channels (Kir3) that
hyperpolarize the membrane (Schmitz et al., 2003). One pos-
sible mechanism underlying a TAAR1-mediated activation of
D2receptors could involve a formation of heterodimers of
TAAR1 with D2receptors. Such a positive modulation of D2
dopamine receptors through formation of heterodimers has
been reported for the somatostatin receptor 5 (Rocheville et
al., 2000). However, it is equally possible that TAAR1 causes
a hyperpolarization by a direct coupling to K?channels via
G??, as described for a variety of other G protein-coupled
receptors (Mark and Herlitze, 2000). It is noteworthy that
dopaminergic neurons in the ventral tegmental area also
receive excitatory input from glutamatergic afferents origi-
nating in the prefrontal cortex and inhibitory input from
local GABAergic neurons (Yamaguchi et al., 2007). Alterna-
tively, tonically active TAAR1 might elicit a net inhibitory
effect on D2receptors in wild-type animals (Wolinsky et al.,
2007); the absence of TAAR1 in the knockout mice would
consequently result in a D2disinhibition, which in turn
would be reflected in the observed supersensitivity to psycho-
stimulants such as amphetamine. TAAR1 may by any of the
discussed mechanisms modulate the neurotransmitter re-
lease at glutamatergic or GABAergic terminals, respectively,
and thereby control the firing rate and the resting membrane
potential of dopaminergic neurons.
Dopaminergic neurons projecting to the striatum originate
from the substantia nigra and ventral tegmental area in the
midbrain area where dopamine is produced. According to the
LacZ signals, TAAR1-positive cell bodies are indeed located
in the ventral tegmental area (Fig. 2, a and c) and the
amygdala (Fig. 2, a and d), confirming an anatomical overlap
between TAAR1 and dopaminergic brain structures. The
ventral tegmental area plays important roles in the context
of drug addiction and withdrawal (Aston-Jones and Harris,
2004), and the amygdala is essential for attention, memory,
emotions, and fear (Nathan et al., 2004; Yaniv et al., 2004).
TAAR1 is also expressed in the bed nucleus of the stria
terminalis (Walker et al., 2003; Fig. 2, a and b), an area de-
scribed to modulate responses to aversive or threatening stim-
uli, and in the dorsal raphe nucleus (Fig. 2, a and e), a seroto-
nergic brain area highly relevant for stress, depression, drug
addiction, anxiety, and fear (Deakin, 2003; Abrams et al., 2004).
Staining was furthermore detected in parahippocampal regions
essential role in memory processes (Eichenbaum, 2000; de Cur-
tis and Pare, 2004), and in the medial preoptic area that is
Taar1 has been almost exclusively detected in brain areas as-
sociated with mood, attention, memory, fear, and addiction,
which is in agreement with the proposed roles of trace amines
in the context of conditions involving emotional and behavioral
dysfunctions (Lindemann and Hoener, 2005).
In summary, a close interaction between TAAR1 and the
dopaminergic system has been demonstrated. TAAR1, ei-
ther constitutively active or stimulated by agonists nega-
tively modulates the firing rate of dopaminergic neurons
and the release of dopamine in response to the psycho-
We thank A. J. Sleight for stimulating discussions, A. Albientz and
P. Glaentzlin for technical assistance, and T. Cremers (Brains On-
line) for determination of neurotransmitter levels in microdialysis
Abrams JK, Johnson PL, Hollis JH, and Lowry CA (2004) Anatomic and functional
topography of the dorsal raphe nucleus. Ann N Y Acad Sci 1018:46–57.
Aston-Jones G and Harris GC (2004) Brain substrates for increased drug seeking
during protracted withdrawal. Neuropharmacology 47:167–179.
Berry MD (2004) Mammalian central nervous system trace amines. Pharmacologic
amphetamines, physiologic neuromodulators. J Neurochem 90:257–271.
Borowsky B, Adham N, Jones KA, Raddatz R, Artymyshyn R, Ogozalek KL, Durkin
MM, Lakhlani PP, Bonini JA, Pathirana S, et al. (2001) Trace amines: identifica-
tion of a family of mammalian G protein-coupled receptors. Proc Natl Acad Sci
U S A 98:8966–8971.
Branchek TA and Blackburn TP (2003) Trace amine receptors as targets for novel
therapeutics: legend, myth and fact. Curr Opin Pharmacol 3:90–97.
TAAR1 Modulates Dopaminergic Activity
at ASPET Journals on December 27, 2015
Bunzow JR, Sonders MS, Arttamangkul S, Harrison LM, Zhang G, Quigley DI, Download full-text
Darland T, Suchland KL, Pasumamula S, Kennedy JL, et al. (2001) Amphetamine,
3,4-methylenedioxymethamphetamine, lysergic acid diethylamide, and metabo-
lites of the catecholamine neurotransmitters are agonists of a rat trace amine
receptor. Mol Pharmacol 60:1181–1188.
Cao Q, Martinez M, Zhang J, Sanders AR, Badner JA, Cravchik A, Markey CJ,
Beshah E, Guroff JJ, Maxwell ME, et al. (1997) Suggestive evidence for a schizo-
phrenia susceptibility locus on chromosome 6q and a confirmation in an indepen-
dent series of pedigrees. Genomics 43:1–8.
Cichon S, Schumacher J, Muller DJ, Hurter M, Windemuth C, Strauch K, Hemmer
S, Schulze TG, Schmidt-Wolf G, Albus M, et al. (2001) A genome screen for genes
predisposing to bipolar affective disorder detects a new susceptibility locus on 8q.
Hum Mol Genet 10:2933–2944.
de Curtis M and Pare D (2004) The rhinal cortices: a wall of inhibition between the
neocortex and the hippocampus. Prog Neurobiol 74:101–110.
Deakin JF (2003) Depression and antisocial personality disorder: two contrasting
disorders of 5HT function. J Neural Transm Suppl 64:79–93.
Eichenbaum H (2000) A cortical-hippocampal system for declarative memory. Nat
Rev Neurosci 1:41–50.
Gabernet L, Pauly-Evers M, Schwerdel C, Lentz M, Bluethmann H, Vogt K, Alberati
D, Mohler H, and Boison D (2005) Enhancement of the NMDA receptor function by
reduction of glycine transporter-1 expression. Neurosci Lett 373:79–84.
Galceran J, Miyashita-Lin EM, Devaney E, Rubenstein JL, and Grosschedl R (2000)
Hippocampus development and generation of dentate gyrus granule cells is regu-
lated by LEF1. Development 127:469–482.
Geracitano R, Federici M, Prisco S, Bernardi G, and Mercuri NB (2004) Inhibitory
effects of trace amines on rat midbrain dopaminergic neurons. Neuropharmacology
Hatcher JP, Jones DN, Rogers DC, Hatcher PD, Reavill C, Hagan JJ, and Hunter AJ
(2001) Development of SHIRPA to characterise the phenotype of gene-targeted
mice. Behav Brain Res 125:43–47.
Irwin S (1968) Comprehensive observational assessment: Ia. A systematic, quanti-
tative procedure for assessing the behavioral and physiologic state of the mouse.
Joyner AL (1999) Gene Targeting, 2nd ed. The Practical Approach Series, Oxford
University Press, New York.
Kalderon D, Roberts BL, Richardson WD, and Smith AE (1984) A short amino acid
sequence able to specify nuclear location. Cell 39:499–509.
King GR and Ellinwood EH (1992) Amphetamines and other stimulants, in Sub-
stance Abuse: A Comprehensive Textbook (Lowinson JH, Ruiz P, Millman RB, and
Langrod JG eds). Lippincott Williams & Wilkins, Baltimore, MD.
Liberles SD and Buck LB (2006) A second class of chemosensory receptors in the
olfactory epithelium. Nature 442:645–650.
Lindemann L, Ebeling M, Kratochwil NA, Bunzow JR, Grandy DK, and Hoener MC
(2005) Trace amine-associated receptors form structurally and functionally dis-
tinct subfamilies of novel G protein-coupled receptors. Genomics 85:372–385.
Lindemann L and Hoener MC (2005) A renaissance in trace amines inspired by a
novel GPCR family. Trends Pharmacol Sci 26:274–281.
Mark MD and Herlitze S (2000) G-protein mediated gating of inward-rectifier K?
channels. Eur J Biochem 267:5830–5836.
McGinty D, Gong H, Suntsova N, Alam MN, Methippara M, Guzman-Marin R, and
Szymusiak R (2004) Sleep-promoting functions of the hypothalamic median pre-
optic nucleus: inhibition of arousal systems. Arch Ital Biol 142:501–509.
Nathan SV, Griffith QK, McReynolds JR, Hahn EL, and Roozendaal B (2004)
Basolateral amygdala interacts with other brain regions in regulating glucocorti-
coid effects on different memory functions. Ann N Y Acad Sci 1032:179–182.
Parker EM and Cubeddu LX (1988) Comparative effects of amphetamine, phenyl-
ethylamine and related drugs on dopamine efflux, dopamine uptake and mazindol
binding. J Pharmacol Exp Ther 245:199–210.
Philips SR (1984) Analysis of trace amines: endogenous levels and the effects of
various drugs on tissue concentrations in the rat, in Neurobiology of the Trace
Amines: Analytical, Physiological, Pharmacological, Behavioral, and Clinical As-
pects (Boulton AA, Baker GB, Dewhurst WG and Sandler M eds), Humana Press,
Raiteri M, Cerrito F, Cervoni AM, Del Carmine R, Ribera MT, and Levi G (1978)
Studies on dopamine uptake and release in synaptosomes. Adv Biochem Psycho-
Rocheville M, Lange DC, Kumar U, Patel SC, Patel RC, and Patel YC (2000)
Receptors for dopamine and somatostatin: formation of hetero-oligomers with
enhanced functional activity. Science 288:154–157.
Saavedra JM and Axelrod J (1976) Octopamine as a putative neurotransmitter. Adv
Biochem Psychopharmacol 15:95–110.
Sabelli HC, Borison RL, Diamond BI, Havdala HS, and Narasimhachari N (1978)
Phenylethylamine and brain function. Biochem Pharmacol 27:1707–1711.
Schmitz Y, Benoit-Marand M, Gonon F, and Sulzer D (2003) Presynaptic regulation
of dopaminergic neurotransmission. J Neurochem 87:273–289.
Sotnikova TD, Budygin EA, Jones SR, Dykstra LA, Caron MG, and Gainetdinov RR
(2004) Dopamine transporter-dependent and -independent actions of trace amine
beta-phenylethylamine. J Neurochem 91:362–373.
Vacher CM, Gassmann M, Desrayaud S, Challet E, Bradaia A, Hoyer D, Waldmeier
P, Kaupmann K, Pevet P, and Bettler B (2006) Hyperdopaminergia and altered
locomotor activity in GABAB1-deficient mice. J Neurochem 97:979–991.
van der Vegt BJ, Lieuwes N, Cremers TI, de Boer SF, and Koolhaas JM (2003)
Cerebrospinal fluid monoamine and metabolite concentrations and aggression in
rats. Horm Behav 44:199–208.
Vladimirov V, Thiselton DL, Kuo P-H, McClay J, Fanous A, Wormley B, Vittum J,
Ribble R, Moher B, van den Oord E, et al. (2007) A region of 35 kb containing the
trace amine associated receptor 6 (TAAR6) gene is associated with schizophrenia
in the Irish study of high-density schizophrenia families. Mol Psychiatry 12:842–
Walker DL, Toufexis DJ, and Davis M (2003) Role of the bed nucleus of the stria
terminalis versus the amygdala in fear, stress, and anxiety. Eur J Pharmacol
Wolinsky TD, Swanson CJ, Smith KE, Zhong H, Borowsky B, Seeman P, Branchek
T, and Gerald CP (2007) The trace amine 1 receptor knockout mouse: an animal
model with relevance to schizophrenia. Genes Brain Behav 6:628–639.
Yamaguchi T, Sheen W, and Morales M (2007) Glutamatergic neurons are present in
the rat ventral tegmental area. Eur J Neurosci 25:106–118.
Yaniv D, Desmedt A, Jaffard R, and Richter-Levin G (2004) The amygdala and
appraisal processes: stimulus and response complexity as an organizing factor.
Brain Res Rev 44:179–186.
Address correspondence to: Dr. Marius C. Hoener, Pharmaceuticals Divi-
sion, Central Nervous System Research, Department PRDNP5 CH, Bldg.
70/331, F. Hoffmann-La Roche Ltd., CH-4070 Basel, Switzerland. E-mail:
Lindemann et al.
at ASPET Journals on December 27, 2015