Introduction

2-Bromopropane (2BP) was introduced in to the semiconductor and other industries as a replacement for ozonedepleting chlorofluorocarbons. In 1995, Korean workers

exposed to 2BP in an electronics factory suffered severe

reproductive and hematopoietic disorders1). Male workers developed oligozoospermia or azoospermia, and

females developed amenorrhea, while pancytopenia was

observed in both sexes, though the frequency of

hematopoietic disorders was lower than that of reproductive disorders. Therefore, the effects on reproductive

function were considered to be the most serious toxic

effect of 2BP in humans. The reproductive toxicity of

2BP has been confirmed by animal experiments. Sperm

counts are reduced in male rats injected with 2BP or

exposed to 2BP gas2). Exposure to 2BP disturbs the

estrous cycle and elicits a decrease in the number of ovulated ova in female mice and rats3–5). The reproductive

and hematopoietic toxicity of 2BP has led to a decrease

in its use and its replacement with 1-bromopropane (1BP).

However, the results of animal experiments indicate that

1BP is toxic to the peripheral nerves6, 7). The grip

strength of all four limbs of male Wistar rats decreased

following exposure to 800 ppm of 1BP for 8 h per day

for 8 wk. Maximum motor nerve conduction velocity

decreased and distal latency increased in the tail nerve at

800 ppm. Histopathological changes were evident in

Industrial Health 2008, 46, 348–359 Original Article

Alteration of Brain Levels of Neurotransmitters

and Amino Acids in Male F344 Rats Induced by

Three-week Repeated Inhalation Exposure to 

1-Bromopropane

Megumi SUDA1*, Takeshi HONMA2, Muneyuki MIYAGAWA1 and Rui-Sheng WANG1

1National Institute of Occupational Safety and Health (JNIOSH), Nagao 6–21–1, Tama-ku, Kawasaki 214-

8585, Japan 2Japan Association for Working Environment Measurement, Shiba 4–4–5, Minato-ku, Tokyo 108-8372, Japan

Received October 10, 2007 and accepted April 16, 2008

Abstract: The present study investigated the effects of 1-bromopropane (1BP) on brain neuroactive substances of rats to determine the extent of its toxicity to the central nervous system

(CNS). We measured the changes in neurotransmitters (acetylcholine, catecholamine, serotonin

and amino acids) and their metabolites or precursors in eight brain regions after inhalation exposure to 1BP at 50 to 1,000 ppm for 8 h per day for 7 d per week for 3 wk. Rats were sacrificed

at 2 h (Case 1), or at 19 h (Case 2) after the end of exposure. In Case 1, the level of 5-hydroxyindoleacetic acid (5HIAA) was lowered in some brain regions by 1BP exposure. The decrease

of 5HIAA in the frontal cortex was statistically significant at 50 ppm 1BP exposure. In Case 2,

γ-amino butyric acid (GABA) and taurine were decreased in many brain regions of exposed rats,

and a significant decrease of taurine in the midbrain occurred at 50 ppm 1BP exposure. In both

cases of 2-h and 19-h intervals from the end of exposure to sacrifice, aspartate and glutamine

levels were elevated in many brain regions, but the acetylcholine level did not change in any

brain region. Three-week repeated exposure to 1BP produced significantly changes in amino

acid contents of rat brains, particularly at 1,000 ppm.

Key words: 1-Bromopropane, Toxicity, Rat brain, Neurotransmitter, Acetylcholine, Catecholamine,

Serotonin, Amino acids

*To whom correspondence should be addressed. 
peripheral nerves and muscle fibers. However, the effects

of 1BP on the central nervous system (CNS) have been

poorly characterized. Histopathological studies showed

that 1BP had no influence on the central and peripheral

nerves in rats8), whereas some enzyme activities were

influenced by exposure to 1BP 9, 10). Electrophysiological

studies demonstrated an inhibitory restraint in hippocampal cells in 1BP-exposed rats10, 11). Our previous study,

which was performed to investigate the effects of 1BP on

CNS, showed behavioral excitation in rats following

exposure to 1BP12). The present study was undertaken to

determine the extent of CNS toxicity of 1BP by investigating the changes in neuroactive molecules in the brain.

We measured the neurotransmitters (acetylcholine, catecholamine, serotonin, and amino acids) and their metabolites or precursors in rat brains after inhalation exposure

to 1BP for 8 h per day for 7 d per week for 3 wk.

In the reports cited above, animal exposure to 1BP was

performed at 200 ppm or higher levels. However, in the

workplace, reported levels of human occupational exposure were at 60–261 ppm13) or 41.3–143 ppm14). In our

study, the level of 50 ppm was adopted to mimic the

reported human exposures to 1BP. 

Materials and Methods

Animals

Male 8-wk-old F344 rats obtained from Charles River

Japan Inc. were acclimatized in stainless steel wire net

cages in groups of five per cage for at least 5 wk with a

light/dark cycle of 12 h: 12 h (lights on at 8:00 h). The

temperature and humidity in the breeding and exposure

rooms were maintained at 23 ± 1 ̊C and 55 ± 5%, respectively. Food (CE-2, Japan Clea Inc.) and water were

accessible ad libitum. 

Experimental design and chemicals

After acclimatization, the rats were grouped such that

mean body weight did not differ among the groups. The

rats inhaled vaporized 1BP (99%, Sigma-Aldrich Japan)

in stainless steel chambers (Sibata Scientific Technology

Ltd., Japan) as described previously5, 12). The exposure

concentrations of 1BP, 50, 200, and 1,000 ppm (251,

1,006, and 5,028 mg/m3, respectively), were monitored

using a gas chromatograph (Shimadzu GC-7A, Japan)

every 20 min and adjusted with flowmeters to a constant

target value ± 5% throughout the exposure. Control rats

were exposed to clean air. We set up two cases for exposure-sacrifice intervals. In Case 1, rats were exposed to

1BP for 8 h every day for 7 d per week for 3 wk between

0:00 and 8:00 h, and were sacrificed at 2 h after the end

of exposure. In Case 2, the exposure took place between

10:00 and 18:00 h, and the interval between the end of

exposure and the sacrifice was 19 h. We chose 2 h as

the exposure-sacrifice interval in Case 1 so that the results

of Case 1 in the present study could be compared with

those of our previous study concerning 1BP toxicity12).

The interval of 19 h from the end of exposure to sacrifice in Case 2 was selected in order to observe the timecourse changes of 1BP effects. Exposure concentrations

up to 1,000 ppm in the present study were chosen because

we exposed rats to 1,000 ppm of 1BP and 2BP at maximum for 3 wk in our previous investigations performed

to elucidate reproductive and CNS toxicity12). In Cases

1 and 2, all experimental conditions were the same except

the exposure time, dark period in Case 1 and light period in Case 2, and the intervals from the end of exposure

to sacrifice. 

The experiments were conducted under the

“Institutional Guidelines for Animal Care and Use” of the

National Institute of Occupational Safety and Health,

Japan (Kawasaki).

Extraction of brain substances

Rats were sacrificed by microwave exposure (4.7 KW,

1.5 s) focused on the head (Microwave applicator,

Muromachi Kikai Co., Tokyo)15). Exposure to microwaves

rapidly increases the brain temperature and prevents rapid

postmortem changes of brain substances. The brains were

dissected into eight brain regions as described by

Glowinski and Iversen16): the frontal cortex, occipital cortex, hippocampus, striatum, midbrain, hypothalamus,

medulla oblongata, and cerebellum.

All brain samples were stored at –80 ̊C until analysis

and dissolved in 0.2 N HClO4 containing 1 mM EDTA

and 5 mM Na2S2O5 before disruption using a PotterElvehjem homogenizer. The homogenate was centrifuged

at 12,000 × g for 25 min at 4 ̊C, and the supernatant was

used for analysis17, 18). 

Analysis of acetylcholine, choline, and amino acids

Supernatants were divided into two portions (Portions

A & B). Portion A was neutralized with potassium acetate

and the supernatant was obtained after centrifugation.

This supernatant was analyzed by HPLC to quantitate the

acetylcholine (ACh) and amino acid contents. 

ACh was measured following a procedure previously

described19) except for the HPLC pump, EP-300 (Eicom,

Japan), and electrochemical detector, ECD-300 (Eicom). 

Amino acids in the supernatant of neutralized portion

A were separated by high performance liquid chromatography using an ion exchange column (ion exchange resin

#2619-F, 4 mm I.D. × 150 mm, Hitachi Co., Japan).

Amino acid components were eluted by a gradient elution method, and were changed to fluorescent derivatives

with o-phthalaldehyde. The fluorescence intensity was

1-BROMOPROPANE AND BRAIN NEUROTRANSMITTERS IN MALE RATS 349
measured using a fluorescence detector (F-1080, Hitachi).

Mobile phases comprised 0.2 M lithium citrate buffer, at

pH 3 and pH 7. The flow rate in the ion exchange column was 0.4 ml/min. The column temperature was maintained at 37 ̊C in a column oven. The detection wavelengths used were 340 nm for excitation and 450 nm for

emission. 

Analysis of monoamines and their metabolites

In Case 1 (sacrifice at 2 h after exposure), Portion B

was applied to activated alumina to adsorb norepinephrine (NE), dopamine (DA), and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC). These amines and the

metabolite were desorbed from alumina (Portion B1).

Serotonin (5HT), and 5-hydroxyindoleacetic acid

(5HIAA) remained in the eluate. The supernatant containing 5HT and 5HIAA was obtained by centrifugation

(Portion B2). Each portion was passed through a filter

of 0.45 μm pore size before performing HPLC.

Monoamines and metabolites were assayed following a

procedure previously described19, 20). 

In Case 2 (sacrifice at 19 h after exposure), Portion B

was injected directly to HPLC equipped with a

CoulArray® detector (ESA Inc., U.S.A.) after passing

through a filter of 0.45 μm pore size for analysis of NE,

3-methoxy-4-hydroxyphenylglycol (MHPG), DA,

DOPAC, homovanillic acid (HVA), 5HT, and 5HIAA.

Monoamines and metabolites were separated by reverse

phase ion pair chromatography (MCM Column, 4.6mm

I.D. × 150mm, MC Medical, Inc., Japan) using a mobile

phase comprised of 0.1 M phosphate-0.05 M citrate buffer,

pH 3.0. This buffer contained sodium 1-heptanesulfonate,

EDTA · Na2 · H2O, acetonitrile and methanol. The column temperature was maintained at 23 ̊C in an oven, and

the flow rate was 1.1 ml/min. The voltages for

CoulArray® detection were 100, 200, 300 and 400 mV.

Statistics

Means ± SD of each group were calculated from

monoamine or metabolite contents of each brain area

(nmoles/g tissue) in each rat. Ratios for metabolite/

monoamine (MHPG/NE, DOPAC/DA, HVA/DA,

5HIAA/5HT) were obtained in each rat and the mean values of these ratios were calculated in each group.

Metabolite/monoamine ratios are widely used as markers

of turnover of NE, DA and 5HT in cerebral neurons. Free

amino acid contents of the brain areas (μmoles/g tissue)

were obtained and the mean values were calculated in

each group. The statistical significance of differences

between the control and exposed groups was examined

by Dunnett’s multiple t-test using statistics software

(SPSS Japan Inc.). Differences between groups at p<0.05

were considered significant. 

Results

Effects of 1BP on the brain substances in Case 1:

Figure 1 shows the levels of ACh, DA, DOPAC, and

DOPAC/DA ratio in the eight brain regions of the male

rats at 2 h after the end of 3 wk inhalation exposure to

1BP. Brain contents of DA in the striatum at 50 ppm

and DOPAC in the hippocampus at 1,000 ppm were significantly less than control values. Levels of NE, 5HT,

5HIAA, and the 5HIAA/5HT ratio are shown in Fig. 2.

In the frontal cortex, the levels of 5HIAA in 1BP-treated

groups were lowered and the differences from the control

were significant at 50 and 1,000 ppm. In the striatum,

the levels of 5HIAA were lowered in 1BP-treated groups

in a dose-dependent manner, with statistical significance

at 200 and 1,000 ppm 1BP exposure. 

Figure 3 shows the levels of amino acids in three brain

regions of rats at 2 h after the end of 3 wk inhalation

exposure to 1BP. The sample volume was sufficient to

quantitate amino acids only in three brain regions, because

the measurement of ACh was given priority in sample

Portion A. In the rat group exposed to 1,000 ppm 1BP,

levels of aspartate and glutamine were higher than those

of the control with statistical significance (p<0.01). Such

increases in these two amino acids were not observed at

50 and 200 ppm 1BP exposure. The levels of γ-amino

butyric acid (GABA) and taurine (an amino acid containing sulfur) in the 1,000 ppm 1BP exposure group were

lower than the control group, but the difference was only

statistically significant for GABA in the hippocampus. 

Effects of 1BP on the brain substances in Case 2:

Figure 4 shows the levels of ACh, DA, DOPAC, and

HVA, and the ratios of DOPAC/DA and HVA/DA in the

eight brain regions of the rats at 19 h after the end of 3

wk inhalation exposure to 1BP. The levels of NE,

MHPG, 5HT, and 5HIAA, and the ratios of MHPG/NE

and 5HIAA/5HT are given in Fig. 5. In the 1BP-exposed

groups, the HVA level and the HVA/DA ratio in the striatum and the NE level in the hypothalamus decreased dosedependently, and differences from the control for the two

substances were significant at 1,000 ppm. The MHPG

level and the MHPG/NE ratio in the occipital cortex at

1,000 ppm 1BP exposure were significantly lower than

those of the control. Levels of 5HT in the occipital cortex and 5HIAA in the medulla oblongata were significantly higher than those of the control. 

Figure 6 shows the levels of amino acids in the eight

brain regions of the rats at 19 h after the end of 3 wk

inhalation exposure to 1BP. In the group exposed to 1BP

at 1,000 ppm, the levels of aspartate were significantly

higher than the control in the occipital cortex, hippocampus, striatum, hypothalamus, and cerebellum. Also, the

350 M SUDA et al.

Industrial Health 2008, 46, 348–359
levels of glutamine were significantly higher than the control in all brain regions except the medulla oblongata. The

midbrain contents of glutamate were significantly reduced

in the 50 and 200 ppm 1BP exposure groups, however,

the decreases were small in degree and not dose-dependent. The levels of GABA in the 1,000 ppm 1BP exposure group were significantly lower than the control in

the frontal and occipital cortex, and hippocampus. In the

1,000 ppm 1BP exposure group, the level of taurine was

significantly lower than the control in all brain regions

except the frontal cortex, the levels of taurine were also

lowered by 1BP exposure at 50 ppm. 

Table 1 shows the levels of free amino acids other than

those shown in Fig. 6 in Case 2. The increases in cystathionine, serine, threonine, and β-alanine were significant in many brain regions, particularly at exposure to

1,000 ppm 1BP.

Discussion

In both Cases 1 and 2, 1BP exposure elicited no effect

on ACh contents in any of the eight brain regions. NE

content in the hypothalamus, a brain region rich in NE,

was decreased and the MHPG level and MHPG/NE ratio

was lowered in the occipital cortex in Case 2. These

results suggest that 1BP exposure lowers activity in NE

neurons within some brain regions. 

Regarding DA and its metabolite, significant differ1-BROMOPROPANE AND BRAIN NEUROTRANSMITTERS IN MALE RATS 351

Fig. 1. Effects of 1BP exposure on brain levels of ACh, DA and DOPAC, and the DOPAC/DA ratio in male rats at 2 h after the end of

3 wk inhalation exposure. 

The amounts of amines and metabolites are expressed in nmoles/g tissue. Results are shown as means ± SD (n=4–5). 

*:p<0.05 by Dunnett’s multiple t-test.
ences from control values were decreases in striatal DA

at 50 ppm 1BP exposure and hippocampal DOPAC at

1,000 ppm 1BP exposure in Case 1. The DOPAC/DA

ratio tended lower, dose-dependently, although no statistical significance was found. In Case 2, HVA content

and HVA/DA ratio in the striatum were significantly

lower than the control at 1,000 ppm 1BP exposure. 1BP

exposure probably lowered the activity of DA neurons,

particularly in the striatum, a DA-rich brain region. 

Effects of 1BP exposure on 5HT and its metabolite,

5HIAA, were complicated. In Case 1, 5HIAA contents

of the frontal cortex and the striatum were reduced in 1BP

exposure groups. On the other hand, 5HT in the occipital cortex and 5HIAA in the medulla oblongata increased

in Case 2. These differences may be due to the time of

1BP exposure. In Case 1 rats received exposure in the

dark period, while in Case 2 they were exposed to 1BP

in the light period. It is well-known that 5HT neurons

are deeply involved in sleep and circadian rhythm21), and

the situation of 5HT neurons in the dark period is quite

different from that in the light period. 1BP exposure in

the dark period seemed to lower the activity of 5HT neurons, while 1BP exposure in the light period seemed to

enhance it. 

In Case 1, GABA in the hippocampus decreased with

statistical significance at high 1BP exposure. In Case 2,

GABA contents decreased slightly but significantly in the

frontal and occipital cortex and hippocampus. Fueta et

352 M SUDA et al.

Industrial Health 2008, 46, 348–359

Fig. 2. Effects of 1BP exposure on brain levels of NE, 5HT and 5HIAA, and the 5HIAA/5HT ratio in male rats at 2 h after the end of

3 wk inhalation exposure. 

See legend for Fig. 1. *:p<0.05, **:p<0.01 by Dunnett’s multiple t-test. 
al. reported the dysfunction of feedback inhibition in the

rat hippocampus following exposure to 1BP11, 22, 23). It

is thought that paired-pulse inhibition of the postsynaptic

membrane is caused by decrease of GABA release due to

low storage levels of GABA. The finding of Fueta et al.

is compatible with our results, because GABA was

decreased in the hippocampus in both Cases 1 and 2 of

our 1BP exposure.

In both Cases 1 and 2, aspartate and glutamine

increased and taurine decreased in almost all brain

regions. Glutamine is not a neurotransmitter, but it is a

precursor and a metabolite of glutamate, an excitatory

neurotransmitter. In our previous studies24–27), the inhalation exposure of rats to toluene, xylene, trichloroethylene,

tetrachloroethylene, and methyl bromide increased brain

glutamine. Exposure to many kinds of chemicals seems

to increase brain glutamine. Glutamine is synthesized

from ammonia and glutamate by glutamine synthetase.

Because ammonia is toxic to the nervous system, glutamine may have increased as a result of detoxification in

the brain after chemical exposure. Aspartate is known as

one of excitatory neurotransmitters28, 29), an increase in

locomotor activity was observed in rats exposed to

1BP12). Such behavioral changes may be related to the

increase in cerebral aspartate observed in this study.

The level of glutamate, another excitatory amino acid

was not affected by 1BP in almost all brain regions in

Case 2. The midbrain content of glutamate was reduced

significantly at 50 and 200 ppm 1BP exposure by the

Dunnett’s multiple t-test, however, the changes occurred

only in one brain region and were not dose-dependent,

and no statistical significance in these changes were indicated by the Kruskal-Wallis test. This suggests that the

changes in glutamate may not be significant. 

1-BROMOPROPANE AND BRAIN NEUROTRANSMITTERS IN MALE RATS 353

Fig. 3. Effects of 1BP exposure on brain levels of amino acids in male rats at 2 h after the end of 3 wk inhalation exposure. 

The amounts of amino acids are expressed in μmoles/g tissue. Results are shown as means ± SD (n=5, except the control group for hippocampal GABA, n=4.). **: p<0.01 by Dunnett’s multiple t-test.
354 M SUDA et al

.

Industrial Health 2008, 46, 348–359 Fig. 4. Effects of 1BP exposure on brain levels of ACh, DA, DOPAC and HVA, and DOPAC/DA and HVA/DA ratios in male rats at 19 h after the end of 3 wk inhalation exposure. See legend for Fig. 1. Results are shown as means ± SD (n=3–5). *: p<0.05 by Dunnett’s multiple t-test.
1-BROMOPROPANE AND BRAIN NEUROTRANSMITTERS IN MALE RATS 355 Fig. 5. Effects of 1BP exposure on brain levels of NE, MHPG, 5HT, and 5HIAA, and MHPG/NE and 5HIAA/5HT ratios in male rats at 19 h after the end of 3 wk inhalation exposure. See legend for Fig. 1. Results are shown as means ± SD (n=3–5). *: p<0.05, **: p<0.01 by Dunnett’s multiple t-test. 
356 M SUDA et al

.

Industrial Health 2008, 46, 348–359 Fig. 6. Effects of 1BP exposure on brain levels of amino acids in male rats at 19 h after the end of 3 wk inhalation exposure. See legend for Fig. 3. Results are shown as means ± SD (n=5). *: p<0.05, **: p<0.01 by Dunnett’s multiple t-test.
1-BROMOPROPANE AND BRAIN NEUROTRANSMITTERS IN MALE RATS 357 Table 1. Effects of 1BP exposure on the brain contents of major free amino acids in male rats at 19 h after the end of 3 wk inhalation exposure Tyrosine Methionine Cystathionine Serine Threonine Alanine

β -Alanine

Frontal 

cortex

Control 0.0900 ± 0.0116 0.0276 ± 0.0027 0.0260 ± 0.0016 1.028 ± 0.039 0.428 ± 0.024 0.499 ± 0.046 0.0577 ± 0.0029

50ppm 0.0940 ± 0.0109 0.0267 ± 0.0010 0.0273 ± 0.0033 1.054 ± 0.053 0.421 ± 0.006 0.506 ± 0.028 0.0583 ± 0.0023

200ppm 0.0979 ± 0.0111 0.0343 ± 0.0097 0.0263 ± 0.0022 1.042 ± 0.043 0.417 ± 0.015 0.591 ± 0.163 0.0561 ± 0.0040

1,000ppm 0.0903 ± 0.0115 0.0304 ± 0.0074 0.0416 ± 0.0050 1.178 ± 0.066** 0.606 ± 0.012** 0.457 ± 0.044 0.0797 ± 0.0077**

Occipital

cortex

Control 0.0788 ± 0.0049 0.0375 ± 0.0030 0.0405 ± 0.0038 1.010 ± 0.037 0.390 ± 0.008 0.509 ± 0.089 0.0501 ± 0.0029

50ppm 0.0776 ± 0.0105 0.0313 ± 0.0035 0.0386 ± 0.0008 0.989 ± 0.047 0.368 ± 0.033 0.475 ± 0.054 0.0509 ± 0.0041

200ppm 0.0853 ± 0.0206 0.0342 ± 0.0125 0.0357 ± 0.0015* 0.997 ± 0.025 0.376 ± 0.040 0.559 ± 0.187 0.0516 ± 0.0080

1,000ppm 0.0739 ± 0.0089 0.0350 ± 0.0043 0.0512 ± 0.0017** 1.170 ± 0.055** 0.519 ± 0.023** 0.451 ± 0.007 0.0692 ± 0.0100**

Hippocampus Control 0.0735 ± 0.0084 0.0260 ± 0.0058 0.0352 ± 0.0057 0.948 ± 0.022 0.394 ± 0.017 0.581 ± 0.094 0.0442 ± 0.0024

50ppm 0.0761 ± 0.0103 0.0227 ± 0.0029 0.0294 ± 0.0034 0.966 ± 0.029 0.400 ± 0.020 0.581 ± 0.063 0.0439 ± 0.0011

200ppm 0.0661 ± 0.0103 0.0246 ± 0.0067 0.0287 ± 0.0054 0.882 ± 0.138 0.360 ± 0.037 0.561 ± 0.033 0.0400 ± 0.0073

1,000ppm 0.0687 ± 0.0108 0.0230 ± 0.0045 0.0392 ± 0.0026 1.031 ± 0.054 0.509 ± 0.025** 0.540 ± 0.046 0.0601 ± 0.0070**

Striatum Control 0.0866 ± 0.0113 0.0401 ± 0.0044 0.0636 ± 0.0064 1.006 ± 0.043 0.475 ± 0.025 0.481 ± 0.057 0.0664 ± 0.0040

50ppm 0.0983 ± 0.0154 0.0338 ± 0.0021 0.0566 ± 0.0065 1.009 ± 0.025 0.467 ± 0.027 0.462 ± 0.062 0.0693 ± 0.0063

200ppm 0.0921 ± 0.0184 0.0437 ± 0.0084 0.0667 ± 0.0069 1.010 ± 0.066 0.460 ± 0.034 0.513 ± 0.173 0.0649 ± 0.0093

1,000ppm 0.0872 ± 0.0128 0.0338 ± 0.0060 0.0756 ± 0.0123 1.083 ± 0.103 0.591 ± 0.071** 0.391 ± 0.061 0.1024 ± 0.0175**

Midbrain Control 0.0827 ± 0.0114 0.0366 ± 0.0044 0.0653 ± 0.0096 0.577 ± 0.089 0.428 ± 0.035 0.355 ± 0.113 0.0843 ± 0.0092

50ppm 0.0856 ± 0.0133 0.0341 ± 0.0087 0.0621 ± 0.0062 0.458 ± 0.054* 0.361 ± 0.052* 0.310 ± 0.115 0.0775 ± 0.0058

200ppm 0.0861 ± 0.0227 0.0341 ± 0.0145 0.0612 ± 0.0047 0.467 ± 0.021* 0.350 ± 0.030* 0.350 ± 0.218 0.0803 ± 0.0069

1,000ppm 0.0703 ± 0.0053 0.0266 ± 0.0034 0.0788 ± 0.0071* 0.647 ± 0.066 0.486 ± 0.042 0.263 ± 0.041 0.1240 ± 0.0130**

Hypothalamus Control 0.0746 ± 0.0118 0.0402 ± 0.0068 0.0788 ± 0.0261 0.492 ± 0.022 0.367 ± 0.029 0.342 ± 0.050 0.0887 ± 0.0048

50ppm 0.0757 ± 0.0058 0.0276 ± 0.0028 0.0473 ± 0.0056* 0.464 ± 0.026 0.338 ± 0.036 0.299 ± 0.057 0.0832 ± 0.0058

200ppm 0.0866 ± 0.0250 0.0428 ± 0.0148 0.0714 ± 0.0209 0.508 ± 0.054 0.338 ± 0.038 0.417 ± 0.205 0.0857 ± 0.0066

1,000ppm 0.0704 ± 0.0096 0.0253 ± 0.0016* 0.0588 ± 0.0080 0.628 ± 0.047** 0.430 ± 0.042* 0.274 ± 0.038 0.1294 ± 0.0135**

Medulla

-oblongata

Control 0.0759 ± 0.0239 0.0343 ± 0.0095 0.1171 ± 0.0310 0.350 ± 0.097 0.380 ± 0.112 0.326 ± 0.132 0.0463 ± 0.0097

50ppm 0.0658 ± 0.0106 0.0292 ± 0.0038 0.1018 ± 0.0170 0.296 ± 0.036 0.315 ± 0.035 0.277 ± 0.051 0.0406 ± 0.0067

200ppm 0.0786 ± 0.0197 0.0336 ± 0.0125 0.1083 ± 0.0111 0.344 ± 0.074 0.356 ± 0.082 0.335 ± 0.175 0.0508 ± 0.0069

1,000ppm 0.0629 ± 0.0058 0.0290 ± 0.0040 0.1359 ± 0.0139 0.457 ± 0.059 0.440 ± 0.046 0.237 ± 0.028 0.0652 ± 0.0090**

Cerebellum Control 0.0719 ± 0.0071 0.0260 ± 0.0081 0.3355 ± 0.0225 0.488 ± 0.024 0.369 ± 0.026 0.380 ± 0.138 0.0326 ± 0.0015

50ppm 0.0733 ± 0.0083 0.0218 ± 0.0051 0.3307 ± 0.0267 0.475 ± 0.023 0.349 ± 0.021 0.371 ± 0.123 0.0327 ± 0.0009

200ppm 0.0727 ± 0.0186 0.0245 ± 0.0063 0.3145 ± 0.0340 0.476 ± 0.022 0.340 ± 0.029 0.398 ± 0.228 0.0329 ± 0.0012

1,000ppm 0.0585 ± 0.0062 0.0226 ± 0.0031 0.4334 ± 0.0291** 0.694 ± 0.042** 0.464 ± 0.018** 0.248 ± 0.008 0.0461 ± 0.0056**

The amounts of amino acids are expressed in 

μmoles/g tissue. Results are shown as means ± SD (n=5). *: p<0.05, **: p<0.01 by Dunnett’s multiple t-test.
The brain level of taurine was lowered significantly in

almost all brain regions at 1,000 ppm 1BP exposure in

Case 2. The decrease in taurine was observed in the hippocampus and midbrain at 200 ppm and lower concentrations of 1BP exposure. According to Wang et al., creatine kinase activity was decreased dose-dependently by

exposure to 1BP at 200 ppm or higher30). As an index

for detecting the influence of 1BP on the nervous system,

the level of taurine is understood to be almost equal to

or higher than that of creatine kinase activity in sensitivity. Among free amino acids in the rat brain, taurine

belongs to the group in which the brain content levels are

very high. Taurine is involved in many functions such

as detoxification, cholesterol metabolism, and neuromodulation31). It is very likely that taurine is a large source

for transamination32). At present, it is difficult to state

which function of taurine was affected by 1BP exposure.

As shown in Table 1, significant changes were observed

in some amino acids, particularly at 1,000 ppm 1BP exposure. Almost all the amino acids in Table 1 are involved

in amino acid transamination33–35). Widespread changes

of these amino acids induced by 1BP exposure may have

led to the changes in transamination in the brain.

Alternatively, the changes in transamination may have

produced the changes in amino acids contents. 

In contrast to biogenic amines like DA, 5HT, etc., the

metabolism of amino acids is complex, and amino acid

contents are considered to be constant. Contrary to our

expectation, this study elucidated that the amino acid contents of the rat brain are changeable, but it is not clear

whether the widespread changes in amino acids are specific to 1BP exposure. It seems at least that the increase

in glutamine in the brain is a common effect of exposure

to many chemicals. Further studies are necessary to elucidate the mechanism of 1BP influence on brain substances. 

Acknowledgements

We appreciate the considerable contribution of Yusuke

Tsujimura, Jun Sato, and Junko Kuwahara. 

The present study was conducted as a part of a research

project at JNIOSH on “Development of biological indicators and health management under circumstances of low

exposure level of hazardous factors” (P17-02).

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1-BROMOPROPANE AND BRAIN NEUROTRANSMITTERS IN MALE RATS 359