Baroreceptor-mediated activation of sympathetic nerve activity to salivary glands.
ABSTRACT Salivary gland function is regulated by both the sympathetic and parasympathetic nervous systems. Previously we showed that the basal sympathetic outflow to the salivary glands (SNA(SG)) was higher in hypertensive compared to normotensive rats and that diabetes reduced SNA(SG) discharge at both strains. In the present study we sought to investigate how SNA(SG) might be modulated by acute changes in the arterial pressure and whether baroreceptors play a functional role upon this modulation. To this end, we measured blood pressure and SNA(SG) discharge in Wistar-Kyoto rats (WKY-intact) and in WKY submitted to sinoaortic denervation (WKY-SAD). We made the following three major observations: (i) in WKY-intact rats, baroreceptor loading in response to intravenous infusion of the phenylephrine evoked an increase in SNA(SG) spike frequency (81%, p<0.01) accompanying the increase mean arterial pressure (ΔMAP: +77±14mmHg); (ii) baroreceptor unloading with sodium nitroprusside infusion elicited a decrease in SNA(SG) spike frequency (17%, p<0.01) in parallel with the fall in arterial blood pressure (ΔMAP: -30±3mmHg) in WKY-intact rats; iii) in the WKY-SAD rats, phenylephrine-evoked rises in the arterial pressure (ΔMAP: +56±6mmHg) failed to produce significant changes in the SNA(SG) spike frequency. Taken together, these data show that SNA(SG) increases in parallel with pharmacological-induced pressor response in a baroreceptor dependent way in anaesthetised rats. Considering the key role of SNA(SG) in salivary secretion, this mechanism, which differs from the classic cardiac baroreflex feedback loop, strongly suggests that baroreceptor signalling plays a decisive role in the regulation of salivary gland function.
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ABSTRACT: In the salivary reflex, not only secretory cells are activated, but also myo-epithelial cells are contracted to support these cells and promote the flow of saliva, and blood vessels dilate to meet the increased demands of the tissues. The various effector cells often receive nerves from both parts of the autonomic system, and interactions may occur when the nerves act on the same type of effector, or on different types of effectors. While in an experiment electrical stimulation of the sympathetic trunk may decrease a parasympathetic salivary flow by causing marked vasoconstriction, this does not occur in the salivary reflex, since the vasoconstrictors do not take part. On the contrary, the normal sympathetic vasoconstrictor tone of the resting gland is easily overcome by activity in parasympathetic vasodilator nerves when secretion starts. Pronounced synergism can be demonstrated between sympathetic and parasympathetic secretory nerves. In dogs, for instance, in which sympathetic secretion is beta-adrenoceptor-mediated, this is marked in the case of fluid secretion. In rats and rabbits, in which beta-receptors elicit secretion of amylase, the potentiating interaction among the nerves is striking when amylase secretion is considered. Even the random release of acetylcholine from the post-ganglionic parasympathetic axons, by itself insufficient to evoke secretion, can increase the sympathetic effects. Motor nerves interact with secretory nerves by causing myo-epithelial contraction, mechanically promoting secretion. Interactions between the nerves in their long-term regulatory function on the sensitivity of the acinar secretory and myo-epithelial cells can also be demonstrated.Journal of Dental Research 03/1987; 66(2):509-17. · 4.14 Impact Factor
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ABSTRACT: Sympathetic neurones supplying the submandibular salivary gland innervate blood vessels, secretory and myoepithelial cells. Here we examined whether these functionally different sympathetic neurones show distinct reflex response patterns. In anaesthetized rats, single unit activity was recorded from postganglionic axons projecting to the gland. Neurones were tested for their responses to stimulation of baroreceptors, cutaneous nociceptors and cold receptors and to gustatory stimuli applied to the tongue. Respiratory modulation was also analysed. Only a few postganglionic neurones identified electrically (5-10%) were spontaneously active. They were excited by noxious and cold stimuli, inhibited by baroreceptor stimulation and exhibited respiratory modulation. None of the units responded to gustatory stimuli. Thus, in anaesthetized rats spontaneously active sympathetic neurones supplying the submandibular gland behave like vasoconstrictor neurones. Sympathetic neurones with other functions are probably silent.Neuroscience Letters 09/1996; 214(2-3):143-6. · 2.06 Impact Factor
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ABSTRACT: 1. The influence of sympathetic and parasympathetic nerve stimulations on salivary secretion of immunoglobulin A (IgA) was studied in the submandibular glands of anaesthetized rats by stimulating the nerve supplies with bipolar electrodes. 2. Although the flow of saliva from sympathetically stimulated glands was only 23% of that from parasympathetically stimulated glands the output of IgA was over 2-fold greater. This difference was attributable to influences of the nerves on IgA secretion through the epithelial cell polymeric immunoglobulin receptor-mediated pathway, as Western blotting with specific antibodies to IgA and secretory component revealed that secretory IgA (SIgA) dominated in all saliva samples. 3. Study of saliva secreted in sequential periods of nerve stimulation or following rest pauses suggested that SIgA secretion occurred in the absence of stimulation but this was upregulated 2.6- and 6-fold by parasympathetic and sympathetic nerve stimulations, respectively, compared with the calculated unstimulated rate. 4. The IgA content of extensively stimulated glands was 77% of levels in unstimulated contralateral control glands despite a secretion into saliva equivalent to almost 90% of the glandular IgA content. The IgA may be synthesized and secreted by glandular plasma cells at a rate which exceeds demand and/or such synthesis may be upregulated by nerve impulses. 5. The results indicate that salivary secretion of SIgA is upregulated by nerve impulses and that sympathetic nerves induce a greater effect than parasympathetic nerves.The Journal of Physiology 11/1998; 512 ( Pt 2):567-73. · 4.54 Impact Factor
Baroreceptor-mediated activation of sympathetic nerve activity to salivary glands
Robinson Sabino-Silvaa,⁎,1, Alexandre Ceronia, Tadachika Koganezawab, Lisete C. Michelinia,
Ubiratan F. Machadoa, Vagner R. Antunesa,⁎
aDepartment of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil
bDepartment of Physiology, Institute of Basic Medical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Japan
H I G H L I G H T S
► Sympathetic outflow to salivary glands (SNASG) is controlled by baroreceptor activation.
► SNASG increases in parallel with rise in arterial blood pressure.
► Pressure-induced sympathoexcitation could control blood flow to salivary glands.
a b s t r a c ta r t i c l ei n f o
Received 26 June 2012
Received in revised form 8 August 2012
Accepted 24 September 2012
Available online 28 September 2012
Salivary gland function is regulated by both the sympathetic and parasympathetic nervous systems. Previously
we showed that the basal sympathetic outflow to the salivary glands (SNASG) was higher in hypertensive
compared to normotensive rats and that diabetes reduced SNASGdischarge at both strains. In the present
study we sought to investigate how SNASGmight be modulated by acute changes in the arterial pressure
and whether baroreceptors play a functional role upon this modulation. To this end, we measured blood
pressure and SNASGdischarge in Wistar–Kyoto rats (WKY-intact) and in WKY submitted to sinoaortic denerva-
tion (WKY-SAD). We made the following three major observations: (i) in WKY-intact rats, baroreceptor loading
in response to intravenous infusion of the phenylephrine evoked an increase in SNASGspike frequency (81%,
pb0.01) accompanying the increase mean arterial pressure (ΔMAP: +77±14 mmHg); (ii) baroreceptor
unloading with sodium nitroprusside infusion elicited a decrease in SNASGspike frequency (17%, pb0.01)
in parallel with the fall in arterial blood pressure (ΔMAP: −30±3 mmHg) in WKY-intact rats; iii) in the
WKY-SAD rats, phenylephrine-evoked rises in the arterial pressure (ΔMAP: +56±6 mmHg) failed to produce
significant changes in the SNASGspike frequency. Taken together, these data show that SNASGincreases in
parallel with pharmacological-induced pressor response in a baroreceptor dependent way in anaesthetised rats.
Considering the key role of SNASGin salivary secretion, this mechanism, which differs from the classic cardiac
baroreflex feedback loop, strongly suggests that baroreceptor signalling plays a decisive role in the regulation
of salivary gland function.
© 2012 Elsevier Inc. All rights reserved.
Salivary gland function is highly controlled by the autonomic
nervous system (bothsympathetic and theparasympathetic branches),
with nerve fibres innervating secretory, myoepithelial and vascular
cells [1,2]. Parasympathetic stimulation results in the production of a
copious secretion of fluid that is relative poor in protein . The
salivary glands are target organs for postganglionic sympathetic axons
arising from ganglion cells of the superior cervical ganglion [SGC, 3].
Sympathetic nerve activation to the salivary glands (SNASG), either by
pulsed electrical stimulation of the efferent pathways , or by applica-
tion of adrenergic agonists  results in a relatively low flow of saliva
rich in protein . Saliva contains a variety of proteins, glycoproteins
and mucins, which in turn have distinct functions in the oral cavity, in-
cluding lubrification, antimicrobial activity, digestion, calcium phosphate
homeostasis and enamel remineralization . On the other hand, contin-
uous electrical stimulation of this sympathetic branch leads to an in-
tense vasoconstriction with great impairment of the blood flow and
reduced saliva secretion [8–10]. This physiological phenomenon has
been misinterpreted as a direct effect of neurotransmitter released
sequently affecting saliva secretion .
flow to organs throughout the body, including the salivary glands. This
control is accomplished by negative feedback systems incorporating
Physiology & Behavior 107 (2012) 390–396
⁎ Corresponding authors at: Department of Physiology and Biophysics, Institute of
Biomedical Sciences, University of Sao Paulo, Av. Prof. Lineu Prestes, 1524, 05505–900,
Sao Paulo (SP), Brazil. Tel.: +55 11 30917765; fax: +55 11 30917285.
E-mail addresses: email@example.com (R. Sabino-Silva), firstname.lastname@example.org
1Present address: Institute of Biological Sciences and Health, Federal University of
Alagoas (UFAL), Maceio, Brazil.
0031-9384/$ – see front matter © 2012 Elsevier Inc. All rights reserved.
Contents lists available at SciVerse ScienceDirect
Physiology & Behavior
journal homepage: www.elsevier.com/locate/phb
pressure sensors (i.e., baroreceptors) that sense the arterial blood
pressure. The arterial baroreceptor reflex is a key buffer of acute in-
creases in blood pressure . Rapid adjustments of cardiovascular func-
tion, essential for the maintenance of body homeostasis, are mediated by
the autonomic nervous system and depend on neural reflexes primarily
integrated within the brainstem (see review, Dampney, 1994 ).
With respect to the regulation of regional vascular resistance and
blood flow by the arterial baroreceptors, previous studies have docu-
mented that stimulation of aortic depressor nerve in anaesthetised rats
elicits a heterogeneous control of blood flow amongst different vascular
beds, such as renal, mesenteric and hindquarter . It has been demon-
strated that transient increases in arterial pressure induces an increase in
sympathetic axons arising from the SCG, suggesting a protective role of
baroreceptor to regulate sympathetic nerve activity (SNA) and blood
flow at the brain level .
Recently, we investigated the sympathetic outflow to salivary gland
of normotensive and hypertensive rats and showed that the autonomic
nervous system is fundamental for controlling the sodium-glucose
cotransporter 1 (SGLT1) through a protein kinase A (PKA)-mediated
to Pavlov's experiments when he described the existence of uncondi-
tioned reflex (i.e. a stimulus–response connection that required no
learning) by presenting a dog with a bowl of food and the measuring
such as physical and sexual activity, stress, food and liquid intake and
others, where the changes in salivation and fluctuation in the blood
pressure is controlled by influence of the autonomic nervous system. In
this study we wanted to unravel the physiological mechanism regulating
sympathetic nerve outflow to salivary glands during arterial pressure
changes. Here we show that modulation of the sympathetic outflow to
the salivary glands is baroreceptor dependent.
2. Research design and methods
All experimental procedures were performed in accordance with
the Ethical Principles in Animal Research of the Brazilian College of
Animal Experimentation and were approved by the Ethical Committee
for Animal Research of the Institute of Biomedical Sciences, of the
University of Sao Paulo (Protocol #97/2007).
2.1. In vivo anaesthetised rat studies
Three-month-old male Wistar–Kyoto (WKY) rats weighing
280–310 g were individually caged and allowed free access to water
and standard rodent chow diet (Nuvilab CR-1, Nuvital, Curitiba, Brazil)
and kept at a constant temperature of 22–23 °C, relative humidity of
50–60% and controlled circadian cycle (12/12 h light/dark).
2.2. Surgical procedures for hemodynamic measurements
Rats were deeply anaesthetised with halothane (5% in O2inspired
air) for all surgical procedures. The depth of anaesthesia was checked
by a flexor reflex to a paw pinch. A tracheotomy was performed by a
middle incision on the ventral surface of the neck, where a catheter
spontaneously. Subsequently, three saline-filled polyethylene catheters
(PE-10 connected to PE-50, Biocorp Australia, Huntingdale, Victoria, Aus-
tralia) were implanted in the following blood vessels: one into the left
in each femoral vein (right and left) for infusion of urethane
(750 mg kg−1, i.v) and phenylephrine (PHE, 10 μg kg−1, i.v) or sodium
nitroprusside(SNP,30 μg kg−1,i.v),accordingtotheprotocolforloading
or unloading of the baroreceptors, respectively. Rectal temperature was
measured by a thermometer and maintained between 36.5 °C and
37 °C by using a heating blanket. The venous catheter was also used for
injection of hexamethonium (30 mg kg−1, i.v) to block the sympathetic
ganglion activity and determining the background noise of the SNASG.
Arterial blood pressure and heart rate was monitored via the catheter
placed in the femoral artery connected to the digital recording system
(P23Db Transducer, 3400 Recorder; Gould, USA). All analyses were
performed off-line in Spike2 software (CED, Cambridge Electronic
Design, Cambridge, UK).
2.3. Surgical procedures for sympathetic nerve activity to salivary glands
halothane was replaced by urethane (750 mg kg−1) injected intrave-
nously. Afterward, the left common carotid, vagus nerve, left superior
cervical ganglion, external carotid and the cervical postganglionic sym-
fibres at C1 spinal level for subsequent nerve activity monitoring (see
Fig. 1). In a previous study of our laboratory  we performed a
multifibres recording of the sympathetic nerve activity to salivary
gland in normotensive and hypertensive rats (SHR). We could certify
that the biopotentials recorded from the postganglionic nerve were in-
deed projecting to salivary gland, since the same postganglionic nerve
branch was stimulated (50 Hz, 5 V, in bursts of 1 s every 10s), instead
of recorded, and the salivary glands were removed for protein analysis.
At one handwe foundanincreasein thePKAactivity andSGLT1expres-
sion at the salivary gland level ipsilateral to the electric stimulated sym-
pathetic nerve branch. On the other hand, in the contralateral non-
together, these results clearly show that the postganglionic nerve
2.4. Surgical procedures for sinoaortic denervation (SAD)
In a separate group of rats bilateral sinoaortic denervation (SAD)
was performed 3 days before the onset of experiments for sympathetic
nerve recordings. The surgical procedure for SAD carried out in this
study was previously described by Ceroni et al. 2009 , where
the entire cervical sympathetic trunk is preserved allowing us to record
by Krieger, 1964 , where the sympathetic trunk was entirely
Briefly, rats were anaesthetised with a mixture of ketamine
(80 mg kg−1, i.p.; Fort Dodge, IA, USA), and xylazine (12 mg kg−1,
i.p.; Fort Worth, TX, USA). After exposure of the neurovascular trunk
in the neck, the common carotid arteries, vagus and sympathetic
nerves were gentle dissected to allow the identification of aortic de-
pressor fibres (either travelling as a separate branch or together with
tire cervical sympathetic trunk. A third contingent of aortic baroreceptor
fibres travelling with the inferior laryngeal nerve was interrupted by
was exposed for isolation and resection of the sinus and carotid body
nerves. The skin was sutured with cotton thread. Rats were treated
with ketoprofen (Biofen 1%, Biofarm, Jaboticabal, Brazil, 2 mg kg−1
and penicillin (Pentabiotico Veterinario, Fontoura Wyeth, Brazil,
24,000 i.u. kg−1) given subcutaneously and allowed to recover for
R. Sabino-Silva et al. / Physiology & Behavior 107 (2012) 390–396
2.5. Data acquisition and analyses
Resting values of the SNASG, arterial blood pressure and heart rate
were recorded simultaneously for 30 min. The raw SNASGsignal was
amplified (10 K of gain; AN502 Differential Amplifier, Tektronix,
Beaverton,OR, USA) and filtered (band pass filter 0.1–3.0 KHz). Further
processing was performed using a data acquisition system assembled
on a microcomputer equipped with an analog-to-digital converter
on a computer running Spike 2 software (Cambridge Electronic Design,
Cambridge, UK) with custom-written scripts for off-line analyses. Basal
time constant). For SNASGfrequency (Hz) analysis, we performed spike
counting (we determined the upper margin of the nerve activity after
ganglionic blockade (threshold value) by means of a cursor. Action po-
tentials exceeding the threshold were counted and averaged every 30 s
in each animal. To determine the amplitude (μV) of the SNASGthe area
under the curve per second was evaluated 30 s (basal) before and 30 s
after the drug administration (PHE or SNP). In order to correlate the
changes in the SNASGinduced by arterial pressure rise, we evaluated
the peak and the valley of MAP elicited by administration of the PHE
or SNP, respectively, for 30 s before (basal) and 30 s after each drug in-
fusion. To standardize the data across animals, SNASGchanges were
expressed as a percentage (%) of amplitude (μV) and frequency (Hz)
from basal value averaged over 30 s before each drug administration,
after background noise, determined by intravenous injection of hexa-
methonium,wasremoved (for details seeSabino-Silva et al. 2010 ).
2.6. Experimental protocol design
Postganglionic sympathetic nerve activity and hemodynamic
measurements were monitored simultaneously in all experiments in
Recording of the post-ganglionic
fibres to salivary glands
Fig. 1. Schematic diagram showing the anatomy of the sympathetic nerve supply to salivary glands and baroreceptors afferents. Post-ganglionic sympathetic nerve fibres arising
from the superior cervical ganglion (SCG) and projecting to salivary glands along with the external carotid artery where the bipolar platinum electrode was placed for monitoring
the sympathetic nerve activity. Aortic depressor, superior laryngeal and vagus nerves are depicted side by side. Thescissors represent how the sinoaortic baroreceptor denervation
was performed bilaterally. Note that sinoaortic denervation does not compromise the postganglionic fibres projecting to salivary gland territory where the sympathetic activity was
R. Sabino-Silva et al. / Physiology & Behavior 107 (2012) 390–396
two different groups of rats: i) control (WKY-intact), and, ii) 3-days bi-
lateral sinoaortic denervated (WKY-SAD). Baroreceptor reflex wastest-
ed by pharmacological manipulation of the arterial pressure with acute
infusions either of PHE (10 μg kg−1, i.v) or SNP (30 μg kg−1, i.v) using
an infusionpump (Ati-Orion Sage Model 361, Boston, MA, USA). PHEor
SNP was infused with a 1-mL syringe connected to the venous catheter
and mounted on an infusion pump at a flow rate of 0.1 ml min−1,
which was switched on-off for a short period of time (5–10s), eliciting
arterial pressure changes in the range of around 40–50 mmHg. At
least 10–15 min were allowed between pressor (PHE) and depressor
(SNP) tests for blood pressure to return to baseline levels. At the end
of the experiment each animal received an intravenous bolus injection
of hexamethonium (30 mg kg−1, i.v) and the remaining sympathetic
nerve activity (background noise) was subtracted from SNASGsignal
during data analysis. Animals were euthanized at the end of the exper-
iment with an overdose of sodium pentobarbital (150 mg kg−1, i.v).
2.7. Statistical analysis
All data passed the test for normality and are presented as mean±
SEM. Changes in mean arterial pressure (MAP) and in the amplitude
or spike frequency of the sympathetic nerve activity to the salivary
glands (SNASG) were compared before and after baroreceptor loading
and/or unloading in the same animal from each of the respective
groups and analysed by a paired student's t-test (GraphPad Prism
version 4.0 for Windows, GraphPad Software, San Diego, CA, USA).
Linear regression was performed in both groups (WKY-intact and
WKY-SAD) by correlating percentage change in the SNASG spike
frequency (Hz) against changes in the MAP (mmHg). Differences
wereconsideredsignificantatpb0.05,and“n”is thenumberof animals
used in each group.
3.1. SNASGincreases in parallel with increases in arterial pressure
phenylephrine (PHE) or saline (vehicle volume control). Notably, the
increase in the arterial pressure is associated with simultaneous in-
crease in the SNASGand bradycardic response (typical for baroreceptor
reflex activation). Saline injection failed to produce any change in the
arterial pressure and SNASG.
Fig. 3 summarizes the data and shows a significant PHE-induced
increase in the MAP (156±8 mmHg) when compared to the baseline
values (78±9 mmHg, pb0.01, n=5, panel A). In parallel, an increase
in SNASGamplitude (63%) and spike frequency (81%, pb0.01, n=5;
panels B and C, respectively) was observed. Fig. 3, panel D, also shows a
significant fall in the MAP in NPS-infused rats (55±2 mmHg) when
compared to the baseline (85±1 mmHg, n=5, pb0.01). A significant
decrease in SNASGamplitude (11%, pb0.05) and spike frequency (17%,
pb0.01) was concurrently observed (Fig. 3, panels E and F).
Fig. 2. Intravenous injections of phenylephrine increases sympathetic nerve activity to salivary glands (SNASG) of the WKY-intact rats. Typical neurograms of the post-ganglionic
SNASGafter intravenous injection of the phenylephrine (i.v) in Wistar-Kyoto rats (WKY). Panels from top to bottom are; histogram of events s−1, integrated (∫ SNASG) and raw
sympathetic nerve signal (SNASG), heart rate (HR) and pulsatile arterial pressure (PP) obtained during basal condition, phenylephrine-induced pressor response and saline (vehicle
control) intravenous injection (arrows).
R. Sabino-Silva et al. / Physiology & Behavior 107 (2012) 390–396
Wealsoplotted thecorrelation betweenpercentages of change in the
SNASGover the entire range of MAP increases induced by intravenous
PHE infusion (Fig. 4). WKY-intact group showed a positive correlation
of the SNASGincreasing linearly with MAP increments (Yintact=ax+b;
slope: 0.752±0.04 Hz/mmHg). However, no change SNASG was
observed during MAP increases in the WKY-SAD group (YSAD=ax+b;
slope: 0.007±0.01 Hz/mmHg).
3.2. SNASGdoes not change with increases in arterial pressure in sinoaortic
Fig. 5A shows typical traces of the SNASG(histogram, integrated
and raw signal), heart rate (HR) and pulsatile arterial pressure (PP)
of one rat representative of the WKY-SAD group. In contrast to
WKY-intact group, SNASGwas not affected by PHE infusion in the
WKY-SAD group. Of note, the PHE-induced increasing in the blood
pressure was not accompanied by a reflex bradycardia, which confirms
complete baroreceptor denervation. Quantitative data (Fig. 5, panel B)
confirmed PHE-induced MAP increase (from 63±2 to 119±4 mmHg;
n=5, pb0.001), but no significant changes in either the amplitude
or spike frequency of the SNASG(panels C and D) respectively were
observed. There is no difference of the basal spike frequency of the
SNASGof the WKY-intact when compared to WKY-SAD (data no
In the present study, we report in anaesthetised rats the first direct
evidence that increased sympathetic nerve activity to salivary glands
(SNASG) during blood pressure increases is mediated by baroreceptor
afferents, revealing a potentially important role of baroreceptors in
the control of sympathetic outflow to salivary glands.
The arterialbaroreflex hasbeen extensively investigated sinceits first
description . It is well known that sympathetic outflow to different
organs and vascular beds are negatively modulated by baroreceptor
activation, that is, pressure increases accompanied by a reduction
in SNA. Cassaglia et al. 2008  provided the first experimental
evidence of increased activity of cerebral sympathetic nerve from supe-
rior cervical ganglion during blood pressure rises in lambs, suggesting
that sympathetic nerves to the cerebral circulation may act to protect
the brain during transient pressure increase, instead of contributing to
reflex restoration of the arterial pressure. In a previous study, by
monitoring the sympathetic outflowprojecting to the salivary glands
in diabetic hypertensive and normotensive rats, we were able to
show that the basal SNASGwas increased by hypertension and reduced
bydiabetes, whichcorroborate thefindings ofAnderson et al. 1995
, where the authors reported a dose–response increase in salivary
protein content during graded stimulation of SNASG.
The present set of data confirmed that SNASGis positively modulated
by baroreceptor activation, leading to sympathoexcitation. In a group of
sinoaortic-denervated animals increases in the arterial pressure failed to
produce changes in the SNASGsuggesting an essential role of barorecep-
tors in the control of sympathetic outflow to the salivary glands. Impor-
tantly, we are certain that the postganglionic sympathetic nerve being
monitored in the present study innervates the salivary glands, since
Hz (% )
M A P (m m H g )
A B C
D E F
Fig. 3. Sympathetic nerve activity to salivary glands (SNASG) is modulated by arterial baroreceptors loading (phenylephrine, i.v) and unloading (sodium nitroprusside, i.v) in
WKY-intact rats. A. Increasing in the mean arterial pressure (MAP) and percentage increase in the amplitude (B) and spike frequency (C) of SNASGbefore (Basal, 100%) and
after intravenous injection of phenylephrine (PHE). Lowering MAP (D) and percentage decrease in the amplitude (E) and spike frequency (F) of SNASGbefore (Basal, 100%) and
after intravenous injection of sodium nitroprusside (SNP). * pb0.05; **pb0.01 different from the basal, n=5.
% of SNA SG
Fig. 4. Correlation between SNASGand blood pressure increases in intact and baro-
denervated WKY rats. Linear regression performed in WKY-intact and WKY-SAD groups
by correlating percentage of normalized changes of the SNASGfrequency (Hz) against in-
creasing in the MAP (mmHg, n=5).
R. Sabino-Silva et al. / Physiology & Behavior 107 (2012) 390–396
wehave previouslyshown thatstimulationthe same postganglion-
ic nerve branch increases PKA activity and SGLT1 expression in the sali-
vary gland ipsilateral to the sympathetic nerve branch stimulated.
We have also previously shown that sympathetic innervation of the
salivary glands is important in termsof normal function . More pre-
cisely, we showed that propranolol (a non-selective β-adrenoceptor
blocker) attenuated the effects of sympathetic nerve stimulation on
SGLT1 expression compared with glands of rats not injected with pro-
surrounding the cell, which represents the SGLT1 translocation into
the plasma membrane, clearly correlated with the sympathetic nerve
It has also been argued that alpha-adrenoreceptors, present on
pre-ganglionic sympathetic neurones [20,21], canalso mediate increased
SNASG during phenylephrine-induced hypertension. However, in
sinoaortic denervated rats, administration of a vasoconstrictor, to in-
crease MAP, failed to elicit sympathoexcitation, excluding the possibili-
ty of a direct effect of phenylephrine on neurones and confirming that
the increase in the SNASGis dependent upon baroreceptor activation.
Studies conducted by Bartsch et al., 1996  using single-unit
recordings of sympathetic postganglionic axons projecting to the
submandibular gland in anaesthetized and vagotomized rats, showed
a differential regulation during distinct reflex response patterns of
these fibres, since they were excited by noxious and cold stimuli and
B C D
Fig. 5. Sympathetic nerve activity to the salivary gland (SNASG) is not affected by pressure manipulation after sinoaortic denervation in WKY rats (WKY-SAD). Typical neurograms of
the post-ganglionic SNASGafter intravenous injection of the phenylephrine (i.v) in WKY-SAD rats (A). Panels from top to bottom are; histogram of events s−1, integrated (∫ SNASG)
and raw sympathetic nerve signal (SNASG), heart rate (HR) and pulsatile arterial pressure (PP) obtained during basal condition and after phenylephrine-induced pressor response
(arrow). Intravenous phenylephrine (PHE) injection increased mean arterial pressure (B) but did not affect SNASGamplitude (C) or spike frequency (D). **pb0.01 different from the
R. Sabino-Silva et al. / Physiology & Behavior 107 (2012) 390–396
inhibited by baroreceptor stimulation. From this the authors concluded
that spontaneously active sympathetic neurones supplying the subman-
dibular gland behave like vasoconstrictors. These results are opposed to
ours, although the reasons for this discrepancy were not apparent, it
ganglionic sympathetic activity to submandibular, sublingual or parotid
glands in non-vagotomised animals.
Another important difference between our data and those reported
by Bartsch et al., 1996 , is the type of anaesthetic used. Bartsch and
colleagues 1996  performed part of their studies in animals
anaesthetised with pentobarbital sodium and they concluded that
other postganglionic sympathetic neurones (apart from those with va-
soconstrictor function) are likely to belong to the group of silent
neurones. It has been established that secretomotor neurones are con-
trolled by central mechanisms which are clearly distinct from those
controlling vasoconstrictor neurones [22,23,2]. Therefore, secretomotor
neurones would probably exhibit reflex patterns distinct from those in
vasoconstrictor neurones. However, anaesthesia may prevent sympa-
thetic secretomotor neurones from being active, and, in our study, as
the animals were anaesthetised with urethane we suggest that both
vasoconstrictors and secremotors neurones would be active, which
could produce a different pattern of discharge in the postganglionic
nerve during baroreceptor activation.
Taken together, ourdata show, in anaesthetised rats, that SNASG in-
and depressor responses, respectively, in a baroreceptor-dependent
ulating salivary gland function.
4.1. Perspectives and physiological significance
Theobservationthat sympathetic nerveactivity tothe salivaryglands
increases in parallel with blood pressure rises would indicate an impor-
tant baroreceptor-mediated behavioral response which might be impor-
tant for adaptive behaviours to various physiological, such as physical
exercises and sexual activity, and psychological challenges such as fight
The integration in the CNS that promotes neuronal modulation on
the sympathetic post-ganglionic fibers to salivary glands is still un-
known. We supposed that the neural mechanism by which the barore-
ceptor activation leads to increase in the sympathetic outflow to the
salivary gland territory would involve a direct excitation transmitted
totherostralventrolateralmedullapresympathetic neuronsvia specific
excitatory glutamatergic synapses from nucleus of the solitary tract.
However, this issue still awaits further investigation.
None. For all the authors there are no potential conflicts of interest.
This research was supported by Sao Paulo Foundation State for
Research (FAPESP): #07/50554-1 and #07/04085-0. Sabino-Silva
R was a recipient of a FAPESP fellowship #09/16502-0. We thank
Dr. Song T. Yao for helpful suggestions and language editing.
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