Effects of Acute Intracerebroventricular Microinfusions of Bupropion on Background Spike Activity of Locus Coeruleus Neurons in Rats
Considering that noradrenergic (NAE) neurons of the locus coeruleus (LC) play significant roles in the formation of biological rhythms, pain, addictions, and mood disorders, we tested the effects of acute intracerebroventricular microinfusions of bupropion, an inhibitor of NA reuptake used in cli...
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Інститут фізіології ім. О.О. Богомольця НАН України
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irk-123456789-1483042019-02-18T01:25:11Z Effects of Acute Intracerebroventricular Microinfusions of Bupropion on Background Spike Activity of Locus Coeruleus Neurons in Rats Pakdel, F.G. Amirabadi, S. Naderi, S. Osalou, M.A. Cankurt, U. Jahanbani, M. Shahabi, P. Considering that noradrenergic (NAE) neurons of the locus coeruleus (LC) play significant roles in the formation of biological rhythms, pain, addictions, and mood disorders, we tested the effects of acute intracerebroventricular microinfusions of bupropion, an inhibitor of NA reuptake used in clinics as an antidepressant, on background spike activity on LC neurons in chloral-hydrate anesthetized rats. Ten microliters of the solutions containing 0.001, 0.01, 0.1, 1.0, or 10.0 µmol bupropion were infused during 3 min; spike activity of single LC neurons identified according to the known characteristics was recorded extracellularly by glass microelectrodes. Microinfusions of 0.01 to 10.0 µmol bupropion suppressed background spiking of the above neurons in a dose-dependent manner. The normalized mean intensities and durations of inhibition were 17.3, 19.4, 26.3, and 41.1% and 1.4, 7.1, 12.4, and 18.3 min, respectively. The smallest dose (0.001 µmol) was ineffective. It is assumed that bupropion increases the NA level in proximity to NAE LC neurons. The actions of bupropion on other cerebral neuromodulatory systems need further examination. Inhibition of LC neuronal activity by bupropion can help to explain some acute, chronic, and side effects of this agent used in clinics for correction of mood disorders. Враховуючи, що норадренергічні (НАЕ) нейрони блакитної плями (locus coeruleus – LC) відіграють істотну роль у формуванні біологічних ритмів, болю, фармакологічних залежностей та розладів настрою, ми тестували впливи гострих інтрацеребровентрикулярних мікроінфузій антидепресанта бупропіону на фонову активність нейронів LC у щурів. Уводили 10 мкл (тривалість інфузій 3 хв) розчинів, що вміщували різні дози (0.001, 0.01, 0.1, 1.0 або 10.0 мкмоль) бупропіону – інгібітора зворотного захоплення норадреналіну, що використовується в клініці як антидепресант. Імпульсну активність поодиноких нейронів LC відводили позаклітинно скляними мікроелектродами. Мікроінфузії 0.01–10.0 мкмоль бупропіону дозозалежно пригнічували фонову імпульсацію цих нейронів. Середня нормована інтенсивність та тривалість гальмування складали в даних випадках 17.3, 19.4, 26.3 і 41.1 % та 1.4, 7.1, 12.4 і 18.3 хв відповідно. Найменша доза бупропіону (0.001 мкмоль) була неефективною. Вважається, що бупропіон зумовлює підвищення рівнів цього катехоламіну в зоні розташування НАЕ-нейронів LC. Взаємодія бупропіону з іншими центральними нейромодуляторними системами потребує подальшого вивчення. Факт гальмування нейронної імпульсної активності в LC під впливом бупропіону може сприяти інтерпретації особливостей гострих та хронічних впливів цього агента та його побічних ефектів при застосуванні в клініці для корекції розладів настрою. 2014 Article Effects of Acute Intracerebroventricular Microinfusions of Bupropion on Background Spike Activity of Locus Coeruleus Neurons in Rats / F.G. Pakdel, S. Amirabadi, S. Naderi, M.A. Osalou, U. Cankurt, M. Jahanbani, P. Shahabi // Нейрофизиология. — 2014. — Т. 46, № 4. — С. 352-358. — Бібліогр.: 37 назв. — англ. 0028-2561 http://dspace.nbuv.gov.ua/handle/123456789/148304 611.815 + 577.175.5 en Нейрофизиология Інститут фізіології ім. О.О. Богомольця НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| description |
Considering that noradrenergic (NAE) neurons of the locus coeruleus (LC) play significant
roles in the formation of biological rhythms, pain, addictions, and mood disorders, we tested
the effects of acute intracerebroventricular microinfusions of bupropion, an inhibitor of NA
reuptake used in clinics as an antidepressant, on background spike activity on LC neurons in
chloral-hydrate anesthetized rats. Ten microliters of the solutions containing 0.001, 0.01, 0.1,
1.0, or 10.0 µmol bupropion were infused during 3 min; spike activity of single LC neurons
identified according to the known characteristics was recorded extracellularly by glass microelectrodes. Microinfusions of 0.01 to 10.0 µmol bupropion suppressed background spiking of the above neurons in a dose-dependent manner. The normalized mean intensities and
durations of inhibition were 17.3, 19.4, 26.3, and 41.1% and 1.4, 7.1, 12.4, and 18.3 min,
respectively. The smallest dose (0.001 µmol) was ineffective. It is assumed that bupropion
increases the NA level in proximity to NAE LC neurons. The actions of bupropion on other
cerebral neuromodulatory systems need further examination. Inhibition of LC neuronal activity by bupropion can help to explain some acute, chronic, and side effects of this agent used
in clinics for correction of mood disorders. |
| format |
Article |
| author |
Pakdel, F.G. Amirabadi, S. Naderi, S. Osalou, M.A. Cankurt, U. Jahanbani, M. Shahabi, P. |
| spellingShingle |
Pakdel, F.G. Amirabadi, S. Naderi, S. Osalou, M.A. Cankurt, U. Jahanbani, M. Shahabi, P. Effects of Acute Intracerebroventricular Microinfusions of Bupropion on Background Spike Activity of Locus Coeruleus Neurons in Rats Нейрофизиология |
| author_facet |
Pakdel, F.G. Amirabadi, S. Naderi, S. Osalou, M.A. Cankurt, U. Jahanbani, M. Shahabi, P. |
| author_sort |
Pakdel, F.G. |
| title |
Effects of Acute Intracerebroventricular Microinfusions of Bupropion on Background Spike Activity of Locus Coeruleus Neurons in Rats |
| title_short |
Effects of Acute Intracerebroventricular Microinfusions of Bupropion on Background Spike Activity of Locus Coeruleus Neurons in Rats |
| title_full |
Effects of Acute Intracerebroventricular Microinfusions of Bupropion on Background Spike Activity of Locus Coeruleus Neurons in Rats |
| title_fullStr |
Effects of Acute Intracerebroventricular Microinfusions of Bupropion on Background Spike Activity of Locus Coeruleus Neurons in Rats |
| title_full_unstemmed |
Effects of Acute Intracerebroventricular Microinfusions of Bupropion on Background Spike Activity of Locus Coeruleus Neurons in Rats |
| title_sort |
effects of acute intracerebroventricular microinfusions of bupropion on background spike activity of locus coeruleus neurons in rats |
| publisher |
Інститут фізіології ім. О.О. Богомольця НАН України |
| publishDate |
2014 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/148304 |
| citation_txt |
Effects of Acute Intracerebroventricular Microinfusions of Bupropion on Background Spike Activity of Locus Coeruleus Neurons in Rats / F.G. Pakdel, S. Amirabadi, S. Naderi, M.A. Osalou, U. Cankurt, M. Jahanbani, P. Shahabi // Нейрофизиология. — 2014. — Т. 46, № 4. — С. 352-358. — Бібліогр.: 37 назв. — англ. |
| series |
Нейрофизиология |
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NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2014.—T. 46, № 4352
UDC 611.815 + 577.175.5
F. G. PAKDEL,1,2 S. AMIRABADI,2 S. NADERI,3 M. A. OSALOU,3 U. CANKURT,4 M. JAHANBANI,5 and P. SHAHABI6
EFFECTS OF ACUTE INTRACEREBROVENTRICULAR MICROINFUSIONS OF
BUPROPION ON BACKGROUND SPIKE ACTIVITY OF LOCUS COERULEUS
NEURONS IN RATS
Received 5.12.2013
Considering that noradrenergic (NAE) neurons of the locus coeruleus (LC) play significant
roles in the formation of biological rhythms, pain, addictions, and mood disorders, we tested
the effects of acute intracerebroventricular microinfusions of bupropion, an inhibitor of NA
reuptake used in clinics as an antidepressant, on background spike activity on LC neurons in
chloral-hydrate anesthetized rats. Ten microliters of the solutions containing 0.001, 0.01, 0.1,
1.0, or 10.0 µmol bupropion were infused during 3 min; spike activity of single LC neurons
identified according to the known characteristics was recorded extracellularly by glass mi-
croelectrodes. Microinfusions of 0.01 to 10.0 µmol bupropion suppressed background spik-
ing of the above neurons in a dose-dependent manner. The normalized mean intensities and
durations of inhibition were 17.3, 19.4, 26.3, and 41.1% and 1.4, 7.1, 12.4, and 18.3 min,
respectively. The smallest dose (0.001 µmol) was ineffective. It is assumed that bupropion
increases the NA level in proximity to NAE LC neurons. The actions of bupropion on other
cerebral neuromodulatory systems need further examination. Inhibition of LC neuronal activ-
ity by bupropion can help to explain some acute, chronic, and side effects of this agent used
in clinics for correction of mood disorders.
KEYWORDS: locus coeruleus neurons, background impulse activity, firing rate,
bupropion, intracerebroventricular microinfusions.
1 Neurophysiology Research Center, Urmia University of Medical Sciences,
Urmia, Iran.
2 Department of Physiology, Faculty of Medicine, Urmia University of
Medical Sciences, Urmia, Iran.
3 Danesh Pey Hadi Co., Faculty of Medicine, Urmia University of Medical
Sciences, Urmia, Iran.
4 Department of Histology & Embryology, School of Medicine, Dokuz EyluL
University (DEU), Izmir, Turkey.
5 Biology Department, Payame Noor University, Teheran, Iran.
6 Tabriz Neuroscience Research Center, Tabriz Medical Science University,
Tabriz, Iran.
Correspondence should be addressed to: F. G. Pakdel (e-mail: info@fgpakdel.
com, fgpakdell@umsu.ac.ir, fgpakdell@yahoo.com)
INTRODUCTION
The noradrenergic (NAE) neurons of the locus
coeruleus (LC) play essential roles in the control
of important biological phenomena such as sleep,
cardiovascular control, depression, etc. [1]. The
monoamine hypothesis of depression genesis was
proposed in 1965; as was assumed, monoamines,
noradrenaline (NA) in particular, are likely to be
the key elements in the etiology and progression of
depression. This hypothesis motivated researchers to
elucidate the roles of monoamine neurotransmitters,
serotonin (5-hydroxytryptamine, 5-HT), noradrenaline
(NA), and dopamine (DA), in the pathogenesis of
depression. Further development of the catecholamine
hypothesis proposed that depression may be related
simply to a deficiency of catecholamines, mostly of
NA [2]. However, both elevations and reductions in the
level of NA or its metabolites have been demonstrated
in the cerebrospinal fluid (CSF), plasma, and urine of
depressed patients, and this made controversial the
respective statements on the involvement of NA in the
initiation of depression [3].
According to the monoamine hypothesis on the
etiology of depression, the LC plays a major role in the
respective disorders [4]; the deficiency of monoamines
in the brain regions is the major factor for the
development of depression, and most antidepressant
drugs increase the synaptic availability of monoamines
[5-7]. However, convincing evidence of a primary
role of dysfunction of the specific monoamine brain
systems in patients with major depressive disorders
has not been found [5].
Although the main effects of antidepressants were
NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2014.—T. 46, № 4 353
EFFECTS OF ACUTE INTRACEREBROVENTRICULAR MICROINFUSIONS
thought to be reflected in the activation of LC neurons,
studies of LC neuronal activity revealed a paradoxical
evidence of both decreased density of neurons
and increased tyrosine hydroxylase activity [8, 9].
Chronic administration of some antidepressants can
decrease background and burst evoked firing of LC
neurons [10, 11]. Recently, West et al. reported that
an antidepressant, paroxetine, increased LC neuronal
activity in young rats [12]; thus, it was shown that the
effect of some antidepressants on LC neuronal activity
may be unique.
As was reported, acute systemic administration of
bupropion in rats inhibited LC-NAE neuronal activity.
This inhibition appeared unrelated to a direct action of
bupropion on LC-NAE neurons or to its modulatory
action on other neurotransmitters in the brain regions.
Metabolites of bupropion can alter neuronal activity of
the above neurons [13]. Desipramine, an NA reuptake
blocker, was found to inhibit LC neuronal activity,
but the nature of such inhibitory effects exerted by its
metabolites or itself was not convincingly interpreted
[14]. In our recent study, we assumed that bupropion
may increase the activity in the ventral tegmental area
indirectly via inhibition of GABAergic neurons [15].
We assume that inhibition of LC neuronal activity
by bupropion is provided by the direct action of
bupropion on NA receptors localized on the dendrites
and/or soma of LC-NAE neurons. This study was
designed to test the effects of intracerebroventricular
(ICV) acute microinfusions of bupropion on impulse
neuronal activity in the LC and to evaluate the direct/
indirect nature of the effect of this agent.
METHODS
Healthy male Wistar rats (Pasteur Institute, Iran; body
mass 250–280 g) were used. Animals were housed
three in a cage at a 12 h light/dark cycle (7:00 a.m. to
7:00 p.m.) and controlled temperature (22 ± 2°C) with
food and water ad libitum. Animals were divided into
seven groups: control, sham, and five groups microin-
fused with solutions containing different amounts of
bupropion (n = 6 to 12 rats in each group). The rats
were anesthetized with chloral hydrate (400 mg/kg,
i.p.; the booster dose was about 10-15% of the initial
dose) and secured in a stereotaxic instrument (Stoelt-
ing, USA). The body temperature was monitored con-
tinuously and maintained at ~37°C throughout the
experiment. The bregma and interaural stereotaxic co-
ordinates were measured for each rat, and the location
of the opening for LC recording was determined ac-
cording to the rat stereotaxic brain atlas [16].
Single unit spike activity was recorded from LC
neurons as described previously [17]. Briefly, after an-
esthesia and opening of the skull, a glass microelec-
trode (in vitro impedance 3-6 MΩ) filled with a 2%
solution of Pontamine Sky Blue in 0.5 M sodium acet-
ate was inserted in the brain into the region of LC lo-
calization (Bregma –9.84, ML 1.35, and DV 6.8 mm
with respect to the bregma zero-zero plane) until sin-
gle neuronal activity could be clearly detected. For all
neuronal recordings, the criteria described earlier [18-
21] were taken into account. These criteria were the
following; (i) long-lasting positive-negative waveform
with a notch, (ii) biphasic excitation-inhibition re-
sponses to contralateral hind paw pinch, and (iii) regu-
lar background activity with a relatively low firing rate
(0.5-5.0 sec–1). The units satisfying the mentioned cri-
teria were recorded in the case of stable amplitude and
firing rate. The recorded activity was filtered (band-
pass 300-3000 Hz), amplified, digitized, and addressed
to a PC computer (Electromodule 3111 data acquisi-
tion system, Http://www.sciencebeam.com/). Digitized
data were displayed on an oscilloscope using Neuro-
Comet software (Http://www.sciencebeam.com). This
software was also used for window discrimination of
spikes and analysis of the activity. Peri-stimulus time
histograms (PSTHs) for single units were plotted with
1-msec-long bins. Sensitization or desensitization of
the recorded units was tested by contralateral hind paw
compression. All units with no respective shifts were
included in the analysis. Frequency graphs were also
plotted for estimation of the firing rate stability.
The PSTHs extracted on-line or off-line were
checked again by a blind-control person. Samples of
spiking used for plotting PSTHs and current frequen-
cy graphs were 5 min long. In each record, the spiking
stability was estimated within a 5-min-long interval,
and a subsequent 10-min-long interval was used for
baseline estimation. Forty-min-long recordings were
used for assessing possible effects of infusions of ar-
tificial cerebrospinal fluid (ACSF) or the drug (bupro-
pion), with cut-off on the 60th min.
For bupropion infusion, a 30-gauge stainless steel
needle was connected to a 10 µl Hamilton syringe by a
polyethylene tube. The needle was stereotaxically in-
serted into the right lateral ventricle. The drug vehicle
(ACSF) or solutions containing different amounts of
bupropion were injected by a microsyringe pump. The
volumes of all injections were 10 µl, and the duration
of infusion was 3 min. Concentrations of bupropion
NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2014.—T. 46, № 4354
F. G. PAKDEL, S. AMIRABADI, S. NADERI et al.
in the solutions used for microinfusions were 0.0001,
0.001, 0.01, 0.1, and 1.0 M; thus, the amounts of in-
fused bupropion, considering the volume of infusions
(10 µl), were 0.001, 0.01, 0.1, 1.0, and 10.0 µmol, re-
spectively.
After the experiments, all animals were deeply anes-
thetized and perfused with 10% phosphate-buffered
formalin solution. The brains were removed and fixed
in the perfusion solution. Coronal 40-µm-thick sec-
tions were prepared on a microtome and stained by
Fast Cresyl Violet. The trajectory path and location of
the infusion cannula tip were verified under a light mi-
croscope. The rats with unsuccessful injections were
excluded from the analysis.
Drugs, chemicals, and equipment used in our study
included bupropion, formalin, Pontamine Sky Blue,
Fast Cresyl Violet, chloral hydrate (Sigma-Aldrich,
USA), sodium acetate and sodium chloride (Merck,
Germany), polyethylene microtubes (A-M system,
USA), and Hamilton microsyringes (Hamilton Bona-
duz AG, Switzerland).
Numerical data of the firing rate of single units were
analyzed using one-way analysis of variance (ANOVA).
Analysis of the effect of different doses of the drug
was carried out using ANOVA and the Tukey’s post-
hoc test. P < 0.05 indicated the least statistical signifi-
cance in intergroup comparisons. Numerical data are
shown below as means ± s.d.
RESULTS
An example of the typical LC neuronal spike is shown
in Fig. 1 A; the upper and lower levels of window dis-
crimination are also seen. The absolute amplitude of
the extracellularly recorded single unit spikes varied
between 40 and 250 µV. A brief pinch of the contralat-
eral paw served as the test for verifying that the neu-
ron belongs to the LC nucleus. The paw pinch elicited
a burst of activity in single units in chloral hydrate-
anesthetized rats; such bursts were accompanied by a
period of after-inhibition (Fig. 1 B). A greater pressure
could elicit a more significant increase in the burst fir-
ing rate with no sensitization.
Figure 2A is a typical graph for the firing rate of
an LC neuron in an anesthetized rat of the control
group. The neuron firing rate was, in this case, 1.88 ±
± 0.05 sec–1. As can be seen, variations of the firing
rate of background activity are minimum; the station-
arity of this activity is a typical feature of LC NAE
neurons. For testing of the microinfusion volume ef-
fect on LC neuronal activity, the drug vehicle (ACSF)
was microinjected in the sham group (10 µl/3 min).
Figure 2B shows a typical example of the neuronal fir-
ing rate observed under such conditions. In this sam-
ple, the mean firing rate within the pre-microinfusion
period (minutes 1 to 10) was 1.90 ± 0.04 sec–1, while
that within the post-microinfusion interval (minutes
14 to 45) was 1.87 ± 0.04 sec–1. Analysis of the firing
rates within the pre- and post-microinfusion of ACSF
showed that there was no statistically significant dif-
ference between these values (t-test, P = 0.31). Thus,
microinjections of 10 µl of ASCF exerted negligible
effects on background firing of LC neurons.
In the control group (n = 8), 24 LC neurons were re-
corded, and 26 units were recorded in the sham group
(n = 7). The average firing rate of control-group neu-
rons was 2.54 ± 1.11sec–1, while that in the sham group
was 2.65 ± 1.26 sec–1. In all records, there was no sig-
nificant difference between the pre-microinfusion and
1 msec
50 µV
A
B
F i g. 1. Pattern of spike activity recorded from locus coeruleus (LC) neurons. A) Waveform of a typical extracellularly recorded single unit
spike of an LC neuron. A notch on the ascending spike limb is seen; limits for window discrimination by NeuroComet software are shown.
B) Typical response of an LC neuron to a brief pinch of the contralateral paw. Background firing of this neuron was low-frequency and
regular. The sensory-evoked response was followed by a silence period (post-stimulus inhibition).
Р и с. 1. Патерн імпульсної активності, що відводиться від нейронів блакитної плями (LC).
NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2014.—T. 46, № 4 355
EFFECTS OF ACUTE INTRACEREBROVENTRICULAR MICROINFUSIONS
post-microinfusion periods.
Figure 3 shows the effects of different ICV-infused
bupropion doses (0.001, 0.01, 0.1, 1.0, and 10.0 µmol)
on the background firing rate of five LC neurons. It
is obvious that bupropion-induced effects are clearly
dose-dependent. Doses of 0.01 to 10.0 µmol provided
noticeable inhibition of LC activity, while there was
no significant inhibitory effect of the lowest bupropion
dose (0.001 µmol).
The significant dependence of the intensity of bu-
propion-induced suppression of background impulse
activity generated by LC NAE neurons and the time
course of this inhibition are more clearly visible on a
graph of normalized changes in this activity for the en-
tire examined group. The effects of infusions of 0.001,
0.01, 0.1, 1.0, and 10.0 µmol bupropion were exam-
ined on 22, 28, 23, 29, and 34 LC neurons, respec-
tively. The mean normalized intensities of decreases in
the rate of background firing were 1.41 ± 0.12, 7.14 ±
± 4.85, 12.40 ± 3.11, and 18.30 ± 5.45% for the doses
of infused bupropion of 0.01, 0.1, 1.0, and 10.0 µmol,
respectively (Fig. 4, 2-5). In all cases, the firing rates
of LC neurons within the pre-microinfusion period
were taken as 100%. The maxima of bupropion-evoked
inhibition of spiking were also shifted with increase
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F i g. 2. Frequency graphs of background activity generated by locus
coeruleus (LC) neurons. A) Graph illustrating a stationary pattern
of background spiking of an LC neuron. B) Graph illustrating the
absence of a significant effect of intracerebroventricular infusion of
the vehicle (ASCF) on background activity of an LC neuron. The
moment of beginning (arrow) and duration of infusion are shown
above the graph and on the abscissa, respectively.
Р и с. 2. Графіки частоти фонової активності, генерованої
нейронами блакитної плями (LC).
F i g. 3. Effects of different doses of ICV-microinfused bupropion
(0.001, 0.01, 0.1, 1.0, and 10.0 µmol, 1-5, respectively) on
background firing of five LC neurons (1-5). The time of infusion is
indicated on the abscissa.
Р и с. 3. Впливи внутрішньошлуночкових мікроінфузій
різних доз бупропіону (0.001, 0.01, 0.1, 1.0 або 10 мкмоль, 1–5
відповідно; 10 мкл/3 хв) на фонові розряди п’яти нейронів LC
(1–5).
Fig. 4. Averaged normalized bupropion-induced changes, %, in
the firing rate of the examined LC neurons. The mean firing rates
within the pre-infusion period were taken in each case as 100%.
Other indications are similar to those in Fig. 3.
Р и с. 4. Усереднені по групі нормовані зміни (%) частоти
розряду досліджених нейронів LC, викликані інфузіями
бупропіону
in the dose of the infused drug, and the total duration
of inhibition increased (Fig. 4). The duration of sup-
pression of impulsation was calculated by repeated-
measure ANOVA for determination of the differences
between points. The averaged durations of such sup-
pression at the above-mentioned bupropion doses were
1.41 ± 1.20, 7.14 ± 4.85, 12.40 ± 3.11, and 18.00 ±
± 4.45 min, respectively. These data are summarized
in the diagrams of Fig. 5. The smallest infused bupro-
pion dose (0.001 µmol) provided no significant effect
on LC neuronal firing rate (P = 0.23).
DISCUSSION
Our electrophysiological data demonstrated that
min
min
NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2014.—T. 46, № 4356
F. G. PAKDEL, S. AMIRABADI, S. NADERI et al.
acute ICV microinfusions of bupropion, an NA
reuptake inhibitor frequently qualified as an atypical
antidepressant, are capable of significantly suppressing
background neuronal activities of single LC neurons
in a clear dose-dependent manner. No dramatic
sensitization or desensitization in the influence of
bupropion on LC neurons was observed, and this agent
could inhibit the above background neuronal activity
for a few minutes.
Hypotheses on the mechanisms by which
antidepressants, such as bupropion, can produce
inhibition of LC neuronal activity are controversial.
The main suggested mechanism for inhibition of LC
neurons by antidepressants is the involvement of
NA reuptake blocking in the vicinity of the dendritic
tree and/or soma of these neurons. Blocking of this
reuptake process by bupropion is consistent with a
strong inhibitory action on LC firing that is exerted via
stimulation of somatodendritic alpha-2 NA receptors
localized on LC neurons. The elevated NA level in
close proximity to somatodendritic synapses results in
more intense binding of NA to alpha-2 receptors and
provides hyperpolarization of LC neurons. This effect
can be mimicked by clonidine (an alpha 2-adrenoceptor
agonist) [22-24]. Not only NA reuptake inhibitors,
but also other inhibitors influencing biogenic amines,
in particular 5-HT reuptake inhibitors, can suppress
spiking of LC neurons. The respective findings
revealed that serotonergic receptors are localized on
the LC cell bodies, and the action of 5-HT within
the regions adjacent to these receptors inhibits LC
activation [25]. Therefore, any agent that can increase
the NA concentration in the synaptic environment
can inhibit LC impulse activity. Monoamine oxidase
(MAO) inhibitors can also suppress spiking of LC
neurons by increasing the NA level [26].
Observations made in our study on the inhibitory
action of acute ICV infusions of bupropion are
consistent with what other investigators found after
administration of antidepressant drugs [27-29]. There
were reports, however, that chronic administrations
of some antidepressants did not decrease background
or sensory-evoked LC neuronal activity due to
manifestations of tolerance under conditions of chronic
action of these drugs [28, 30, 31]. It should be taken
into account that tolerance could not significantly
develop in our experiments where acute action of
bupropion was tested.
The involvement of NA receptors of LC neurons in
the pathogenesis of major depression (MD) has been
studied in post mortem cases. Based on the data of
many researches, an abnormal state of the central
NAE system was proposed to play an important
role in the pathophysiology of this disease. Alpha-2
adrenoreceptors throughout the LC were found
to be significantly elevated in patients suffering
from MD compared to the matched control subjects
[32]. Increased levels of tyrosine hydroxylase and
decreased levels of the NA transporter (NAT) imply
NA deficiency in the LC related to MD. The NAT is a
membrane protein responsible for termination of the
action of synaptic NA and is a site of action for many
drugs used to treat MD [33].
The mechanism of reduction of the LC neuronal
firing rate due to acute ICV infusions of bupropion is
not fully understood. There is well-known evidence
that the effect of bupropion (a rapid and significant
drop in the firing rate of LC cells) is antagonized
by yohimbine and piperoxane (alpha-2 adrenergic
antagonists), implying that there is ultimately
activation of alpha-2 receptors in the rat brain [34].
An indirect mechanism of bupropion for suppression
of LC firing does not completely explain the effect
of this drug on LC neurons because inhibition of NA
uptake can be demonstrated in vivo only at tenfold-
higher doses [35]. At the same time, our findings on
the action of bupropion are consistent with what other
researchers reported after acute administration of
antidepressant drugs [27-29, 36, 37].
0 10.0 1.0 0.1 0.01 μmol
10
20
30
40
50
60
% min
Fig. 5. Dose dependence of the effects of ICV microinfusions of
bupropion on the duration (filled columns, min) and maximum
inhibition (open columns, %) of LC background spike neuronal
activity. The duration of inhibition of the activity was calculated
by repeated-measure ANOVA for determination of the differences
between points. The maximum inhibition was estimated as the
average in the experimental groups. The mean firing rates within
the pre-infusion period was assumed as 100%. Asterisks, crosses,
and diagonal crosses indicate cases with P < 0.05 in comparison to
groups treated with 10.0, 1.0, and 0.1 µmol, respectively. ANOVA
with post-hoc Tukey’s protected t-test was used.
Р и с. 5. Дозозалежність характеристик гальмування (тривалості,
хв, та максимальної інтенсивності гальмування, %), фонової
імпульсної активності (чорні та білі стовпчики відповідно) під
впливом мікроінфузій бупропіону.
NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2014.—T. 46, № 4 357
EFFECTS OF ACUTE INTRACEREBROVENTRICULAR MICROINFUSIONS
The acute antidepressant effect of bupropion is more
closely associated with its action on the firing rate
of NAE LC neurons than with its effect on midbrain
mesolimbic dompaminergic neurons. These results
confirm previous findings [10, 11, 38].
Thus, we found that ICV microinfusions of the
atypical antidepressant bupropion inhibit background
impulse activity of LC-NAE neurons in chloral
hydrate-anesthetized rats in a dose-dependent manner.
A detailed understanding of the pharmacological
properties of bupropion should help to establish
the true efficacy of its action on NA uptake.
Potent interactions of bupropion with cholinergic,
histaminergic, serotonergic, and dopaminergic
systems in the brain should be examined for adequate
interpretation of the effects of this drug. At the same
time, our data add some information helping to explain
acute, chronic, and side effects of bupropion used in
clinics for correction of mood disorders.
Acknowledgment. This work was supported by grant No.
1029 to F. G. Pakdel by the Research Council of the Urmia
University of Medical Sciences, Urmia, Iran. The authors are
grateful to the Danesh Pey Hadi Company, a knowledge-based
company of the Faculty of medicine, Urmia University of
Medical Sciences for the support of the research.
All procedures and experiments were in accordance with
the guidelines for the Care and Use of Experimental Animals
outlined by the Laboratory Animal Center of the Urmia
University of Medical Sciences and with the National Institutes
of Health (NIH) Guide for Care and Use of Laboratory Animals.
These procedures were approved by the Urmia Medical Science
Research Ethics Committee (UMSREC) for biomedical
researches.
The authors of this paper, F. G. Pakdel, S. Amirabadi,
S. Naderi, M. A. Osalou, U. Cankurt, M. Jahanbani, and
P. Shahabi, confirm that they have no conflict of interest.
Ф. Г. Пакдел1,2, С. Амірабаді 2, С. Надері3, М. А. Осалоу3,
У. Канкурт4, М. Джаханбані5, П. Шахабі6,
ВПЛИВИ ГОСТРИХ ІНТРАЦЕРЕБРОВЕНТРИКУЛЯРНИХ
МІКРОІНФУЗІЙ БУПРОПІОНУ НА ФОНОВУ
ІМПУЛЬСНУ АКТИВНІСТЬ НЕЙРОНІВ БЛАКИТНОЇ
ПЛЯМИ У ЩУРІВ
1 Нейрофізіологічний дослідницький центр Урмійського
університету медичних наук (Іран).
2 Медичний факультет Урмійського університету медичних
наук (Іран).
3 Компанія Данеш Пей Хаді, Медичний факультет
Урмійського університету медичних наук (Іран).
4 Медичний факультет Університету Докуз Єйлул, Ізмір
(Туреччина).
5 Біологічний факультет Університету Пайаме Нуур, Теге-
ран (Іран).
6 Дослідницький центр нейронаук Табризького
університету медичних наук (Іран).
Резюме
Враховуючи, що норадренергічні (НАЕ) нейрони бла-
китної плями (locus coeruleus – LC) відіграють істотну
роль у формуванні біологічних ритмів, болю, фармако-
логічних залежностей та розладів настрою, ми тестували
впливи гострих інтрацеребровентрикулярних мікроінфу-
зій антидепресанта бупропіону на фонову активність не-
йронів LC у щурів. Уводили 10 мкл (тривалість інфузій
3 хв) розчинів, що вміщували різні дози (0.001, 0.01, 0.1,
1.0 або 10.0 мкмоль) бупропіону – інгібітора зворотно-
го захоплення норадреналіну, що використовується в клі-
ніці як антидепресант. Імпульсну активність поодиноких
нейронів LC відводили позаклітинно скляними мікроелек-
тродами. Мікроінфузії 0.01–10.0 мкмоль бупропіону дозоза-
лежно пригнічували фонову імпульсацію цих нейронів. Се-
редня нормована інтенсивність та тривалість гальмування
складали в даних випадках 17.3, 19.4, 26.3 і 41.1 % та 1.4,
7.1, 12.4 і 18.3 хв відповідно. Найменша доза бупропіону
(0.001 мкмоль) була неефективною. Вважається, що бупро-
піон зумовлює підвищення рівнів цього катехоламіну в зоні
розташування НАЕ-нейронів LC. Взаємодія бупропіону з
іншими центральними нейромодуляторними системами по-
требує подальшого вивчення. Факт гальмування нейронної
імпульсної активності в LC під впливом бупропіону може
сприяти інтерпретації особливостей гострих та хронічних
впливів цього агента та його побічних ефектів при застосу-
ванні в клініці для корекції розладів настрою.
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