June 2023

Medical Mass Spectrometry Vol. 7 No. 1

Research Paper

Studies on the analysis of 1,2,3,4-tetrahydroisoquinoline (TIQ) and1-methyl-1,2,3,4-tetrahydroisoquinoline (1-MeTIQ) in biologicalsamples using liquid chromatography-tandem mass spectrometry
1,2,4

Kazuo Igarashi*, Masayuki Ohta1, Toyofumi Nakanishi3,
2

4

Yasuhiro Kakiuchi , Philippe Bissel , Neal Castagnoli, Jr.

4

1

Department of Research Development, Association of Medicinal Analysis,522‒417, 5‒1 Koyochonaka, Higashinada-ku, Kobe, Hyogo 658‒0032, Japan2
Department of Forensic Medicine, Kindai University Faculty of Medicine,2‒377 Ohnohigashi, Osakasayama, Osaka 589‒8511, Japan
3
Faculty of Medical Sciences, Shubun University,
6 Nikko-cho, Ichinomiya, Aichi 491‒0938, Japan
4
Department of Chemistry, Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061‒0212, USA
Abstract

A speciﬁc and sensitive method for the analysis of 1,2,3,4-tetrahydroisoquinoline (TIQ) and 1-methyl-1,2,3,4-tet-rahydroisoquinoline (1-MeTIQ) as endogenous amines obtained from biological samples is described. These compounds,
processed by a combination of solvent and solid-phase extraction (SPE), have been analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The levels of TIQ and 1-MeTIQ in biological samples were determined with the aidof the deuterated internal standard (IS) 1-MeTIQ-d4 using multiple reaction monitoring (MRM, product ions m/z 90.9 of m/z

133.8 for TIQ, m/z 130.8 of m/z 147.8 for 1-MeTIQ and m/z 133.8 of m/z 151.8 for 1-MeTIQ-d4). The chromatographic sepa-

ration was conducted on a reversed phase 5CN-MS column (150×2.0 mm, i.d.) using a mobile phase comprised of methanol

and 5 mM ammonium formate (90 : 10, v/v) at a ﬂow rate of 0.2 mL/min. The calibration curves for TIQ and 1-MeTIQ using
2
1-MeTIQ-d4 were linear (r ＞0.99) in the selected concentration range for each compound. The lower limits of detection ofeach compound were 0.10 ng/mL for TIQ and 0.01 ng/mL for 1-MeTIQ. The good recoveries for TIQ (＞93.2%) and 1-MeTIQ(＞94.1%) in this assay precluded the need to concentrate samples prior to analysis. TIQ and 1-MeTIQ contents in mousebrains following intraperitoneal administration of haloperidol (HP) were measured, and TIQ content did not diﬀer signiﬁcantly
from those in control group, but 1-MeTIQ content decreased signiﬁcantly. This result agrees well previous ﬁndings in humanparkinsonism and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse brain.
Key words: TIQ and 1-MeTIQ in biological samples, Haloperidol (HP), Deuterated internal standard, 1-MeTIQ-d4, Solid-phase
Extraction (SPE), LC-MS/MS

Introduction* Corresponding author

The endogenous amines 1,2,3,4-tetrahydroisoquinoline[TIQ (1)], 1-methyl-1,2,3,4-tetrahydroisoquinoline [1-MeTIQ

Kazuo Igarashi

Department of Research Development, Association of Medicinal Analysis, 522‒417, 5‒1 Koyochonaka, Higashinada-ku,(2)] and 1-benzyl-1,2,3,4-tetrahydroisoquinoline [1-BnTIQ(3)] are structurally related to the Parkinsonian inducing
agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine [MPTP

Kobe, Hyogo 658‒0032, Japan
Tel/Fax: ＋81‒78‒855‒8315(4)]. These compounds have been detected in the brains of1‒5)
and could be related to the pathorodents and humans

E-mail: kigarashi1868@hotmail.com
Received: January 21, 2023. Accepted: April 4, 2023.
Epub May 9, 2023.

genesis of Parkinsonʼs disease (PD). TIQ and 1-BnTIQ have

DOI: 10.24508/mms.2023.06.010

been reported to be neurotoxic

6‒14)

80

in rodent and primate

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Medical Mass Spectrometry Vol. 7 No. 1

Fig. 1.

Chemical structures discussed in the text.

1＝TIQ, 2＝1-MeTIQ, 2-d4＝1-MeTIQ-d4 (I.S.), 3＝1-BnTIQ, 4＝MPTP

models of PD. Although the TIQ levels in the brains ofride was oﬀered by Dr. S Ohta (Graduate School of Bio-

individuals with PD were not signiﬁcantly diﬀerent fromthose in control brains, the levels of 1-MeTIQ were signiﬁ-

medical Sciences, Hiroshima University, Japan). The
hydrochloride salt of the IS 1-MeTIQ-d4 (2-d4) was synthe-

cantly lower in PD brains than in control brains . Further15)
more, the 1-MeTIQ level tended to decrease with age . In

sized in our laboratory by the procedures described previ19,20)®
. The cartridge, OASIS HLB (60 mg) for solidously

contrast, the 1-BnTIQ levels tend to increase in the cerebro5)
spinal ﬂuid of PD patients . Moreover, the 1-MeTIQ level

phase extraction was purchased from Waters Co. (Milford,

3,4)
was signiﬁcantly lower in the brains of MPTP- or halo-

analytical purity from commercial sources.

peridol (HP, a neuroleptic agent with structural similarities
16)
to MPTP) -treated mice . Interestingly, MPTP- or TIQ-

Preparation of standard solutions

3)

MA, USA). All other chemicals and reagents were of

Calibration curves for TIQ and 1-MeTIQ were preparedinduced bradykinesia was completely prevented by pre3)
treatment with 1-MeTIQ . Therefore, measurements of thelevels of these endogenous amines in the brain could proveas follows: Stock solutions (1 μg/mL) of each compound
were prepared in methanol. Prior to analysis, the stock solu-

of value in understanding the pathogenesis of PD.

tion of 1-MeTIQ was diluted with 0.4 M perchloric acid

A highly speciﬁc and sensitive assay is required for the(containing 0.1% w/v EDTA and 0.1% w/v ascorbic acid)estimation of these compounds that are present in only
trace levels in the brain. A gas chromatography-mass spec-to give ﬁnal concentrations of 0.02, 0.1, 0.5, 1.0, 5.0 andtrometry (GC-MS) method has been reported for the detec1‒5,16‒18). However,tion of TIQ, 1-MeTIQ and 1-BnTIQ

were added to the 0.4 M perchloric acid solution in order to

GC-MS analysis is complicated by the need to form deriva-

the extraction procedure as reported previously . For TIQ

tives with the required GC properties. In this paper, we
report a method for the detection of TIQ and 1-MeTIQ

the ﬁnal concentrations were 0.2, 1.0, 2.0, 3.0, 6.0 and

10.0 ng/mL in the spiked samples. EDTA and ascorbic acidprotect against auto oxidation of the test compounds during2)

10.0 ng/mL. The ﬁnal volume in all cases was 3 mL. Eachstandard was subjected to the same ʻwork-upʼ procedureusing liquid chromatography-electrospray ionization/tandem mass spectrometry (LC-MS/MS) and a combination ofdescribed below for the sample analyses.

solvent and solid-phase extraction (SPE). The solid-phasestep has allowed us to avoid evaporation of the solvent that

Sample collection

16)

Biological samples

we know from earlier work

leads to signiﬁcant losses of

the analytes. This assay has been applied successfully to thedetermination of TIQ and 1-MeTIQ levels in the biologicalthe Guideline for Animal Experimentation of Department of

All animal experiments were conducted in accordance withsamples (brain and liver) obtained from rat and mice. In
addition, we examined the change of TIQ and 1-MeTIQ

research development, Association of medicinal analysis.
Male ddY mice weighing 28‒30 g (6 weeks old) and malelevels in brain tissue of HP-treated mice with this assay.

Wistar rats weighing 230‒250 g (9 weeks old) (SLC, Shizuoka, Japan) were euthanized by cervical dislocation. The

Materials and Methods

brain and liver were quickly removed. The brain and liver

Chemicals and reagentswere weighed and added to the equivalent of two volumes of

TIQ hydrochloride was purchased from Wako Pure

0.4 M perchloric acid solution (containing 0.1% w/v EDTA

Chemical Industries (Osaka, Japan). 1-MeTIQ hydrochlo-

and 0.1% w/v ascorbic acid). The tissues were homogenized,
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The reversed phase column used for chromatographic sepa®
ration was COSMOSIL 5CN-MS column (2.0 mm I.D.,

and the homogenates were centrifuged at 12,000 g for 30 min
at 4°
C and then the supernatant was separated. All of thesesamples subsequently were processed as described below.
Moreover, male ddY mice weighing 28‒30 g (6 weeks

150 mm length, Nacalai Tesque, Inc., Kyoto, Japan). Theold) were injected with 4 mg/kg of haloperidol (HP, 20%
v/v Tween 20 in saline solution) intraperitoneally for four

(90 : 10, v/v)] was delivered in isocratic mode at a ﬂow rateof 0.2 mL/min. Ionization conditions for LC-MS/MS weredays. The mice were euthanized by cervical dislocation at

as follows: capillary voltage, 3.0 kV; source temperature,

24 h after the last injection and the brain was quickly
removed. The brain was weighed and added to the equiva-

150°
C; desolvation temperature, 400°
C; cone voltage, 15 V;
collision energy, 30 eV for TIQ, 16 eV for 1-MeTIQ and IS.

lent of two volumes of 0.4 M perchloric acid solution

Argon was used as the collision gas.

mobile phase [methanol and 5 mM ammonium formate(containing 0.1% w/v EDTA and 0.1% w/v ascorbic acid).
The tissues were homogenized, and the homogenates were

Results and Discussion

centrifuged at 12,000 g for 30 min at 4°
C and then the

ESI mass spectra

The ESI mass spectra of TIQ, 1-MeTIQ and deuterated
1-MeTIQ-d4 (IS) were shown in Fig. 2. TIQ, 1-MeTIQ andsupernatant was separated. The following operations were
performed as described below.

＋

IS showed the calculated MH values at m/z 133.8, 147.8

Sample preparation for LC-MS/MS analyses

and 151.8, respectively. These ions were the only dominant

Solvent extraction of TIQ and 1-MeTIQ

species present.

To a sample (3 mL) of each preparation obtained as

At the ﬁrst, selected ion monitoring (SIM) using thesedescribed above was added 1 mL of 28% v/v ammoniumhydroxide solution and 30 μL of the IS solution (1-MeTIQ-d4,ions was examined for quantitative analysis of TIQ and
1-MeTIQ. However, SIM of m/z 147.8 for 1-MeTIQ dis-

1 μg/mL in 0.1 M HCl). The resulting mixtures wereplayed some interfering background peaks. Consequently,

extracted twice with 5 mL of dichloromethane. After thewe examined the technique of multiple reaction monitoring(MRM) using the characteristic product ions from the par-centrifugation, 8 mL of the organic phase was added to
8 mL of 0.4 M perchloric acid solution (containing 0.1%

ent ions. Fig. 3 showed the product ion spectra (PIS) of
TIQ (m/z 133.8), 1-MeTIQ (m/z 147.8) and 1-MeTIQ-d4

w/v EDTA and 0.1% w/v ascorbic acid). The mixture was(m/z 151.8). The PIS of 1-MeTIQ and 1-MeTIQ-d4 at 16 V

shaken for ﬁve min and, after separation of the supernatant;the aqueous phase was processed by solid-phase extraction.

of collision energy gave the base peaks at m/z 130.8 andSolid-phase extraction (SPE)133.8, respectively. The corresponding spectrum of TIQ,
however, was more complicated with a number of rela-

SPE was conducted using Waters OASIS®

HLB

tively intense ions appearing in the spectrum including an

extraction cartridge (60 mg) that had been preconditioned
with methanol (5 mL) followed by water (5 mL). A 6 mL ali-

ion at m/z 90.9, corresponding to a benzyl carbocation orquot of each sample to be analyzed was loaded onto an

Scheme 1 presents our interpretation of the fragmentation pattern observed in the PIS of 1-MeTIQ (2). The basetropylium ion.

HLB extraction cartridge that then was washed with 6 mLof water. The analyte was subsequently eluted with 0.01%

peak in the spectrum appears at m/z 131. The proposed
pathway leading to this ion proceeds via the N-protonatedformic acid in methanol (2 mL). This solution then was＋

species 2H (m/z 148) that fragments to the benzylic carbo-

transferred to an autosampler vial and 20 μL was injected
into the LC-MS/MS system.

＋

cation i . Proton migration to the amino group leads to the＋
N-protonated aminylethylstyryl species ii that undergoes a＋Instrumentation and chromatographic conditions

further transformation to the tetralinyl cation iii (m/z 131)

LC-MS/MS was performed using a triple quadrupole tandem mass spectrometer (LCMS-8030, Shimadzu Corp.,with ammonia as the neutral loss species.
The corresponding PIS for 1-MeTIQ-d4 (2-d4) are shown

Kyoto, Japan) equipped with electrospray ionization (ESI).
The HPLC system consisted of a Shimadzu LC-30AD

in Scheme 2. Consistent with the pathway proposed for
1-MeTIQ (2), the base peak in this spectrum appears at
m/z 134. The sequences 2-d4 → 2H -d4 (m/z 152) → i-d4 →＋pump equipped with a Shimadzu Sil-30AC auto sampler.
82＋

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Medical Mass Spectrometry Vol. 7 No. 1

LC-ESI mass spectra of TIQ, 1-MeTIQ and 1-MeTIQ-d4 (I.S.).

Fig. 2.

ii -d4 → iii -d3 (m/z 134) are completely analogous to the＋＋(m/z 91).

corresponding sequences [2 → 2H (m/z 148) → i → ii →＋iii (m/z 131)] for 1-MeTIQ (2) shown in Scheme 1.
＋＋＋

The ions that were selected for the MRM studies were
the base peaks m/z 130.8 for 1-MeTIQ and m/z 133.8 for

The PIS of TIQ (1) (Fig. 3, top panel) at collision dissoci-the I.S. In the case of TIQ, we elected to monitor m/z 90.9

ation energy of 30 V is more complicated than the PIS of
1-MeTIQ (2) and 1-Me-TIQ-d4 (2-d4) that were obtained atsince this intense ion appeared in a region of the spectrum
that was relatively free of other fragment ions.

collision dissociation energy of 16 V. This probably is a

MRM chromatograms

consequence of the higher collision dissociation energy
required to fragment TIQ (1). It may be reasonable to sus-

Fig. 4 shows the MRM chromatograms of TIQ (0.20 ng/mL), 1-MeTIQ (0.02 ng/mL) and IS (5.0 ng/mL) of standard

pect that the absence of stabilization of the initially formed＋＋carbocation fragments (ii and ii -d4) by the 1-methyl groupsolutions and of extracts obtained from rat brain using these

may account for the diﬀerences in energy requirement.
Scheme 3 attempts to rationalize the fragmentation path-characteristic product ions. Similar chromatograms were

way of TIQ (1). As with the 1-methyl analogs, initial pro＋
tonation occurs on nitrogen to give 1H (m/z 134). Frag-

not display any interfering contaminants although the peaks
observed in the MRM chromatograms did not achieve base-mentation of 1Hline resolution. This was not a problem since each analyte

obtained with the other matrices. The chromatograms did＋

gives the unstable primary benzylic
carbocation iv that is converted to the more stable imin＋＋
ium ion v via a hydride migration. Fragment ion v rear-

intensity at m/z 133.8 for the IS was below the limits ofranges to the cycloheptatrienyl species vi that will lose thedetection in all tissue extracts that had not been spiked withneutral vinylamine leading to the tropylium fragment vii

the IS.

＋＋

has a unique MH value. It should be noted that the ion

＋

＋

83

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Medical Mass Spectrometry Vol. 7 No. 1

Fig. 3.

PIS (LC-MS/MS) of TIQ, 1-MeTIQ and 1-MeTIQ-d4 (I.S.).

Scheme 1.

Proposed fragmentation pathway for the PIS of 1-MeTIQ (2) observed at a collision energy of 16 V.

Scheme 2.

Proposed PIS fragmentation pathway of 1-MeTIQ-d4 (2-d4) observed at a collision energy of 16 V.

1-MeTIQ to the samples. As a result, good linearity wasobserved over the concentration ranges examined (0.2‒

Method validation
Calibration curves for TIQ (product ion m/z 90.9) and
1-MeTIQ (product ion m/z 130.8) were generated with stan-2

10.0 ng/mL, y＝0.1598x＋0.0733, r ＝0.9912 for TIQ and20.02‒10.0 ng/mL, y＝0.1656x＋0.0024, r ＝0.9998 fordard solutions containing varying concentrations of both

1-MeTIQ). The calibration curves for each compoundshowed little intra-day and inter-day variability in slopes

analytes. The data were obtained by plotting peak area
ratios (analyte/IS) vs. the added amounts of TIQ and84

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Medical Mass Spectrometry Vol. 7 No. 1

Scheme 3.

Fig. 4.

Proposed PIS fragmentation pathway of TIQ (1) observed at a collision energy of 30 V.

Typical MRM chromatograms (LC-MS/MS) of (a) solutions of standards (0.2 ng/mL for TIQ, 0.02 ng/mL for
1-MeTIQ and 5.0 ng/mL for I.S.) and (b) rat brain sample (7.22 ng/g of tissue for TIQ and 2.15 ng/g of tissue for
1-MeTIQ).

and intercepts [coeﬃcient of variation (C.V.), ＜6%, n＝5].

As shown in Table 1, the recoveries of TIQ at 1.0 ng/mL (n＝5)

The lower limits of detection were approximately 0.10 ng/
mL for TIQ and 0.01 ng/mL for 1-MeTIQ (S/N＝3).

in rat brain and liver homogenate samples were 92.1±5.6%,93.2±6.0%, respectively. The recoveries of 1-MeTIQ at

The recovery experiments of TIQ and 1-MeTIQ were
undertaken using the rat brain and liver homogenate sam-

0.5 ng/mL (n＝5) in rat brain and liver homogenate samples

ples. A constant amount of TIQ and 1-MeTIQ standard

From these results, it was suggested that the good recoveries for TIQ and 1-MeTIQ in this assay precluded the needwere 96.3±8.1% and 94.1±8.8%, respectively.

solutions were added to the centrifugation supernatants
obtained from each tissue homogenate (the spiked concen-

to concentrate samples prior to analysis. This advantage

trations of TIQ and 1-MeTIQ were 1.0 and 0.5 ng/mL,
respectively), and the TIQ and 1-MeTIQ concentrations

avoided the sample loss (up to 40% for TIQ and 55% for
1-MeTIQ) that accompanied evaporation of the organic

were determined in the same manner as described above.

required in the GC-MS assay for these compounds .
16)85

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Table 1.

Medical Mass Spectrometry Vol. 7 No. 1

Recoveries (%) of TIQ and 1-MeTIQ fromspiked samples of rat tissue homogenates
Spiked(ng/mL)

Concentration (ng/mL)
Intact*Measured**

Recovery
(%)

1.00

1.29

2.21±0.16

92.1±5.6

0.50

0.12

0.60±0.11

96.3±8.1

1.00

1.02

1.95±0.1393.2±6.0

0.50

0.09

0.56±0.12

94.1±8.8

Liver
TIQ
1-MeTIQ

TIQ(ng/g of tissue)

1-MeTIQ(ng/g of tissue)

Rat Brain

6.74±0.91

3.24±0.63

Mouse Brain

4.83±0.85

2.08±0.32

Rat Liver7.31±1.52

2.72±0.15

Mouse Liver

5.22±1.19

1.61±0.18

SampleBrain
TIQ
1-MeTIQ

The levels of TIQ and 1-MeTIQ in biologicalsamples obtained from rats and mice

Table 3.

The data are mean values±S.D., n＝10 (the number of animals pergroup).

*Mean measured concentration (n＝5). **Mean values±S.D., n＝5(the number of animals per group). The homogenate supernatants
were used as described in methods.

Table 2.

Intra- and inter-day precisions of TIQ and
1-MeTIQ contents in rat tissues by LC-MS/MS
assay

CompoundConc.
(ng/g of tissue)

Intra-day
CV (%)

Inter-day
CV (%)

TIQ

Brain

6.33

4.6

7.3

Liver

6.91

3.8

7.8

1-MeTIQ

Brain

3.12

5.8

8.6

Liver

2.64

6.1

9.1

The data showed the intra-day and inter-day variability of ﬁve
measurements.

Fig. 5.

TIQ and 1-MeTIQ contents in control andHP-treated mouse brains.
HP was dosed intraperitoneally at 4 mg/kg for 4 days.
*Signiﬁcantly diﬀerent from the corresponding control(P＜0.01, Studentʼs t-test).

Moreover, we conﬁrmed the intra-day and inter-day variability in TIQ and 1-MeTIQ levels in rat brain and rat liver
samples (Table 2). The C.V. value in intra-day (n＝5) for TIQ

shown in Fig. 5. Whereas the levels of TIQ and 1-MeTIQ inbrain were 4.83±0.88 and 2.08±0.32 ng/g of tissue in con-

was about 4.6% in rat brain, 3.8% in rat liver, respectively.
For 1-MeTIQ, the C.V. value (n＝5) was about 5.8% in rat

trol mice, respectively, those in HP-treated mice werebrain, 6.1% in rat liver, respectively. The C.V. value in inter-4.67±0.85 and 0.44±0.09 ng/g of brain tissue, respectively.

day (n＝5) for TIQ was about 7.3% in rat brain, 7.8% in rat
liver, respectively. For 1-MeTIQ, the C.V. value (n＝5) was

1-MeTIQ level was observed in the HP-treated mouse brain

A signiﬁcant decrease in the endogenous amine,

about 8.6% in rat brain, 9.1% in rat liver, respectively.
The levels of TIQ and 1-MeTIQ in biological samples

in comparison with that in control brain. However, there
was no diﬀerence in the endogenous TIQ level between
control and HP-treated mice. This result agrees well withobtained from rats and mice were shown in Table 3. TIQ
and 1-MeTIQ levels in brain and liver obtained from rats

the previous ﬁnding of MPTP-treated mice . We also havebeen very interested in these results because 1-MeTIQ con4)

ranged from 6.74 to 7.31 and 2.72 to 3.24 ng/g of tissue on
average, respectively. TIQ and 1-MeTIQ levels in brain and3)tent was reduced in parkinsonian brains . As far as the
structures of TIQ and 1-MeTIQ are concerned, the diﬀer-

liver obtained from mice ranged from 4.83 to 5.22 and 1.61

ence is whether or not they have a methyl group. TIQ has
21,22), while 1-MeTIQ has the
been reported to be neurotoxic

to 2.08 ng/g of tissue on average, respectively.
In addition, this method was applied to the determinationof the endogenous amines, TIQ and 1-MeTIQ contents in

23‒27)

opposite eﬀect and is reported to be neuroprotective. It

is possible that HP and MPTP may inhibit the enzymatic
formation of 1-MeTIQ in brain from 2-phenylethylamine

the brain after drug administration. The levels of TIQ and
1-MeTIQ in haloperidol (HP)-treated mouse brain were86

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Medical Mass Spectrometry Vol. 7 No. 1

and acetaldehyde. If this endogenous amine 1-MeTIQ plays
an important role in the development of exogenous com-

References
1) Niwa T, Takeda N, Kaneda N, Hashizume Y, Nagatsu T:

pound-induced parkinsonism, 1-MeTIQ may be a lead compound for anti-parkinsonism drugs.

Presence of tetrahydroisoquinoline and 2-methyl-tetrahy-

Next, it will be interesting to know whether these endog-

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1-methyl-tetrahydroisoquinoline as novel endogenous

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droquinoline in parkinsonian and normal human brains.

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kidney tissues but also in blood and urine samples . Moreover, TIQ and 1-MeTIQ are known to be present naturally

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28)

line are present in the human brain relation to parkinsonʼs

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4) Tasaki Y, Makino Y, Ohta S, Hirobe M: 1-Methyl-

0.9 ng/g) contents in Japanese tea, white wine and cocoa forreference. TIQ (209.5±8.4 ng/g) and 1-MeTIQ (58.4±0.9 ng/g)

1,2,3,4-tetrahydroisoquinoline, decreasing in 1-methyl-

contents in Japanese tea were much higher than white wine
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cocoa (88.3±2.5 ng/g for TIQ, 5.75±0.50 ng/g for 1-MeTIQ)
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larly, it is thought that large amounts of TIQ and 1-MeTIQ

inducing agent: A novel endogenous amine in mouse brain

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Conclusions

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The levels of the endogenous amines TIQ and 1-MeTIQ
were determined by LC-ESI/MS/MS in biological samples

tary alcohol intake of tetrahydroisoquinolines or a beta-

by a combination of solvent and solid-phase extractions.
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Pharmacol Biochem Behav 7: 381‒392, 1977.

carboline infused chronically in the ventricle of the rat.
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mice were measured, and TIQ contents did not diﬀer signiﬁcantly from those in the control group, but 1-MeTIQ

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synthesis by tetrahydroisoquinoline. Neurosci Lett 86:
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