Department of Human Health
Science, Tokyo Metropolitan University,
Japan
-Kita
I, Kubota N, Yanagita S, Motoki C
Intracerebroventricular administration of
corticotropin-releasing factor antagonist
attenuates arousal response accompanied by
yawning behavior in rats. Neurosci.Letter
2008;433(3):205-208
-Kita
I, Yoshida Y, Nishino S. An activation of
parvocellular oxytocinergic neurons in the
paraventricular nucleus in oxytocin-induced
yawning and penile erection. Neurosci Res.
2006;54(4):269-275
-Kita I,
Sato-Suzuki et al.Yawning responses induced
by local hypoxia in the paraventricular nucleus
of the rat.Behavioural Brain Research
2000;117(1-2):119-126
-Kubota
N, Amemiya S, Motoki C, Otsuka T, Nishijima T,
Kita I. Corticotropin-releasing factor
antagonist reduces activation of noradrenalin
and serotonin neurons in the locus coeruleus and
dorsal raphe in the arousal response accompanied
by yawning behavior in rats. Neurosci Res.
2012;72(4):316-323
-Kubota
N, Amemiya S, Yanagita S, Kita I. Neural
pathways from the central nucleus of the
amygdala to the paraventricular nucleus of the
hypothalamus are involved in induction of
yawning behavior due to emotional stress in
rats. Behav Brain Res. 2022 Sep 1:114091.
-Sato-Suzuki I,
Kita I, Oguri M, Arita H Stereotyped yawning
responses induced by electrical and chemical
stimulation of paraventricular nucleus of the
rat Journal of Neurophysiology,
1998;80(5)2765-2775
-Seki Y, Y
Nakatani, et al Light induces cortical
activation and yawning in rat Behav Brain Res
2003;140(1-2):65-73
-Seki Y,
Sato-Suzuki I, et al Yawning/cortical
activation induced by microinjection of
histamine into the paraventricular nucleus of
the rat. Behav Brain Res.
2002;134(1-2):75-82.
Yawning behavior is characterized by mouth
opening accompanied by deep inspiration, as well
as arousal response, and is often observed not
only in states of boredom or drowsiness, but
also in stressful emotional situations in humans
and animals. These phenomena suggest that
yawning response may be an emotional behavior,
possibly through activation of the central
nucleus of amygdala (CeA), which is a critical
region for emotional responses.
However, the involvement of the CeA in
triggering yawning remains unknown. Here, we
investigated whether neuronal activation of the
CeA by microinjection of L-glutamate into the
CeA is able to induce stereotyped yawning
responses in anesthetized, spontaneously
breathing rats. In addition, we assessed the
effects of the CeA stimulation on the activation
of oxytocin (OT) and CRF
(corticotropin-releasing factor) neurons in the
paraventricular nucleus of the hypothalamus
(PVN), which is responsible for induction of
yawning, using c-Fos immunohistochemistry.
Microinjection of L-glutamate into the CeA
causes an initial depressor response in the
blood pressure and an arousal shift on the
electrocorticogram followed by a single
inspiration, which is the same as the typical
pattern of the stereotyped yawning response
induced by the PVN stimulation. In addition, the
CeA stimulation activated the neuronal
activities of both OT and CRF neurons in the
PVN, as well as yawning responses.
These results indicate that activation of
the CeA is involved in the induction of yawning
response, suggesting that yawning is an
emotional behavior.
Le bâillement se caractérise
par une large ouverture de la bouche
accompagnée d'une inspiration profonde et
par une stimulation de la vigilance. On
l'observe souvent non seulement dans des
états d'ennui ou de somnolence, mais
également dans des situations
émotionnelles stressantes chez l'homme et
les animaux. Ces phénomènes
suggèrent que le bâillement peut
être un comportement émotionnel,
possiblement par l'activation du noyau central
de l'amygdale (CeA), une région critique
pour les réponses émotionnelles.
Cependant, l'implication de la CeA dans le
déclenchement du bâillement reste
inconnue.
Ici, les auteurs ont examiné si
l'activation neuronale du CeA par microinjection
de L-glutamate dans le CeA est capable d'induire
des bâillements
stéréotypés chez des rats
anesthésiés et respirant
spontanément. De plus, ils ont
évalué les effets de la
stimulation du CeA sur l'activation des neurones
ocytocinocynergiques (OT) et CRF (facteur de
libération de la corticotropine) dans le
noyau paraventriculaire de l'hypothalamus (PVN),
responsable de l'induction du bâillement,
à l'aide de Immunohistochimie de Fos. La
microinjection de L-glutamate dans la CeA
provoque une réponse dépressive
initiale de la pression artérielle et un
décalage de l'excitation sur
l'électrocorticogramme, suivis d'une
seule inspiration, ce qui correspond au
schéma typique d'un bâillement
stéréotypée induite par la
stimulation PVN. En outre, la stimulation su CeA
a activé les activités neuronales
des neurones OT et CRF dans le PVN, ainsi que
des bâillements. Ces résultats
indiquent que l'activation du CeA est
impliquée dans l'induction du
bâillement, suggérant que
bâiller est un comportement
émotionnel.
1. Introduction
Yawning behavior is primarily characterized
by mouth opening accompanied by deep
inspiration, stretching of the trunk, and
autonomic responses, as well as arousal
response. Many studies have indicated that the
paraventricular nucleus of the hypothalamus
(PVN) is critical for the occurrence of yawning
behavior [2,27]. Indeed, our previous
studies have demonstrated that electrical and/or
chemical stimulation of the PVN can evoke a
stereotyped yawning response, i.e., an initial
depressor response and an arousal shift on
electrocorticogram (ECoG) followed by a single
large inspiration with mouth opening, in
anesthetized, spontaneously breathing rats
[17,35]. In addition, we have reported
that an increase in the frequency of spontaneous
yawns accompanied by an arousal shift on ECoG
was observed after micro-injections of
L-glutamate into the PVN [18,35].
Furthermore, it has been indicated that
activation of oxytocin (OT) and
corticotropin-releasing factor (CRF) neurons in
the PVN, each of which sends descending axons to
the lower brainstem involved in either arousal,
respiratory, cardiovascular, or other autonomic
functions, mediates the induction of yawning
accompanied by arousal response
[1,2,18&endash;20]. Recently, we
reported that emotional stress evoked by
classical fear conditioning induces yawning
behavior accompanied by activation of both OT
and CRF neurons in the PVN, as well as the
central nucleus of the amygdala (CeA) in freely
moving rats [21]. The CeA, which is part
of the amygdaloid complex, is known to be
essential for the expression of emotional
responses, including behavioral, autonomic and
hormonal responses during stressful situations
[23,25]. Furthermore, neuroanatomical
studies have shown that the CeA directly
innervates parvocellular regions in the PVN,
which contains OT and CRF neurons
[6,13,15]. Therefore, it is possible
that activation of the CeA may mediate the
induction of yawning behavior via activation of
OT and CRF neurons in the PVN. However, the
involvement of the CeA in triggering yawning
remains unknown.
In the present study, we investigated
whether neuronal activation in the CeA by
microinjection of L-glutamate into the CeA
induces stereo- typed yawning responses in
anesthetized, spontaneously breathing rats, and
compared those responses with stereotyped
yawning responses by microinjection of
L-glutamate into the PVN. In addition, we
assessed L-glutamate into the CeA (about 10
times for 60 min) to evaluate frequency of
spontaneous yawns as repeated stimuli-response
and activity of OT and CRF neurons in the PVN
during yawning responses using c- Fos
immunohistochemistry.
2.4. Determination of yawning
response
We determined yawning response according to
our previous studies [15,28]. Briefly,
we defined a typical response pattern
characterized by an initial depressor response
and an arousal shift in ECoG followed by a
single large inspiration in anesthetized and
spontaneously breathing rats as a yawning
response. In experimental observation, the
latency of a single large inspiration from the
onset of microinjection of L-glutamate into
either the CeA or PVN was measured. In addition,
we counted the number of both yawning responses
and microinjections, and calculated the
occurrence rate of yawning responses induced by
micro-injection of L-glutamate into either the
CeA or PVN (number of induced yawning/number of
microinjections).
4. Discussion
The present study physiologically
demonstrated that neuronal activation of the CeA
could induce stereotyped yawning responses.
Microinjection of L-glutamate into the CeA
caused an initial depressor response and an
arousal shift on the ECoG followed by a single
large inspiration in anesthetized, spontaneously
breathing rats. This response pattern was almost
the same as the typical pattern of stereotyped
yawning response induced by the PVN stimulation.
In addition, siginificant increases in neuronal
activities of both OT and CRF neurons in the PVN
were observed during the yawning responses
induced by chemical stimulation of the CeA.
Therefore, this study suggests that the CeA has
the potential to induce stereotyped yawning via
activation of
the OT and CRF neurons in the PVN.
Previous studies have indicated that yawning
response is reproductively evoked by electrical
or chemical stimulation of the medial
parvocellular subdivision of the PVN
[2,27,28,35]. Sato-Suzuki et al.
[35] first reported that yawning
response induced by the PVN stimulation is
typically characterized by a single large
inspiration with mouth opening that occurred
after the depressor response and the arousal
response, which is the stereotyped yawning
response. In the present study, microinjection
of L-glutamate into the CeA caused an initial
depressor response and an arousal shift on the
ECoG followed by a single large inspiration.
These physiological responses by the CeA
stimulation were qualitatively the same as the
stereotyped yawning response induced by the PVN
stimulation. Therefore, the CeA appears to be
involved in the induction of the stereotyped
yawning responses.
Although the neuronal mechanism involved in
the induction of stereotyped yawning response by
the CeA stimulation is unknown, previous studies
have indicated that the OT and CRF neurons in
the PVN are responsible for induction of the
stereotyped yawning responses
[1,2,18&endash;20]. Our
immunohistochemistry data indicated activation
of both OT and CRF neurons in the parvocellular
subdivision of the PVN after microinjections of
L-glutamate into the CeA, which induced
stereotyped yawning responses. Thus, these data
suggest that the CeA stimulation induces yawning
responses via activation of OT and CRF neurons
in the PVN. The possibility that the CeA may
mediate activation of OT and CRF neurons in the
PVN in induction of stereotyped yawning
responses is supported by neuroanatomical
evidence. Neuroanatomical studies have reported
that the CeA neurons directly innervate the
caudal lateral and medial parvocellular regions
of the PVN [6,13,15], suggesting a
possibility that the direct pathway from the CeA
to the PVN may be involved in induction of
stereotyped yawning responses. But we also
consider another possibility that induction of
stereotyped yawning responses might be mediated
by indirect pathways from the CeA to the PVN via
mesolimbic brain regions, including the ventral
tegmental area (VTA) and bed nucleus of the
stria terminals (BNST). The mesolimbic brain
regions such as the VTA and BNST are
anatomically connected with the CeA and PVN
[8&endash;11] and have been reported to
be involved in induction of yawning behavior by
neuropharmacological studies
[26,33,34,37], supporting the
possibility for indirect pathways from the CeA
to the PVN via the mesolimbic brain regions.
Thus, it is possible that neuronal activation of
the CeA directly or indirectly evoked activation
of OT and CRF neurons in the parvocellular
subdivision of the PVN, thereby inducing
stereotyped yawning responses. However, our
c-Fos immunoreactive data is correlative.
Therefore, the neuronal pathway underlying
yawning induced by neuronal activation of the
CeA should be investigated using pharmacological
and lesion studies in the near future.
The present study showed that chemical
stimulation of the CeA could induce a
stereotyped yawning response. However, it is
noticed that the stereotyped yawning response
induced by the CeA stimulation had a long
latency when compared with that by the PVN
stimulation. Furthermore, the occurrence rate of
the stereotyped yawning responses by the CeA
stimulation was lower than that by the PVN
stimulation. The reasons why the CeA stimulation
induced stereotyped yawning responses with
delayed respiratory responses and low occurrence
rate are unknown. Previous studies have
demonstrated that neuronal structure in the
medial parvocellular subdivision of the PVN is
responsible for triggering the stereotyped
yawning response [17&endash;19]. In the
present study, we stimulated the CeA, which may
not be the responsible region for triggering
stereotyped yawning responses. We assume that
the CeA is involved in the induction of the
stereotyped yawning responses via neuronal
activation of the PVN, and that the neuronal
projections from the CeA to the PVN might be the
key to understanding these delayed respiratory
responses and low occurrence of the stereotyped
yawning responses by the CeA stimulation. In
addition, we cannot rule out the possibility
that these delayed respiratory responses and low
occurrence of the stereotyped yawning responses
by the CeA stimulation may depend on brain state
(i.e., neural activity induced by anesthesia),
that is a limitation of anesthesia
research.
What is the biological significance of
yawning induced by neuronal activation of the
CeA? Yawning is often observed not only in a
state of boredom or drowsiness, but also in
stressful emotional situations in humans and
other animals. This suggests that yawning might
be a behavior toward emotional stress. Clinical
reports have shown that yawning is frequently
observed in patients with anxiety and depression
disorders, hysteria, and motion sickness
[7,38]. Ethologists and psychologists
have reported that primates commonly yawn when
neigh- boring individuals display anxiety-like
and sexual jealousy behaviors, which is
indicative of yawning via emotional contagion
[3,4]. In laboratory studies, it has
reported that injection of anxiogenic compounds
induce yawning behavior while anxiolytic drugs
reduce frequency of yawning behavior in primates
[12,22,24], and that auditory fear
conditioning induce yawning behavior in rodents
[21,29]. We have recently reported that
emotional stress evoked by contextual fear
conditioning induces yawning behavior, which is
accompanied by neuronal activation of CeA as
well as the PVN [21]. Furthermore, the
CeA is known to be particularly essential for
integration of emotional responses, and the PVN
is primarily involved in behavioral, autonomic,
and hormonal responses to stress. Most studies
have reported that neuronal activation of the
CeA connecting to the PVN is involved in
secretion of stress hormones, activation of the
autonomic nervous system, and expression of
fear- and anxiety-like behaviors (see review
[15],). Therefore, our findings suggest
that yawning is one of these emotional
behaviors. This suggestion may be supported by
the involvements of not only neurotransmitters
OT and CRF but also dopamine in expression of
yawning behavior [1,2,18&endash;20,33],
because OT, CRF, and dopamine are well known to
modulate emotion processing including
motivation/reward, adapt action, arousal, and
stress response [5,14,16,32].
In summary, we observed that
microinjection of L-glutamate into the CeA
produced a stereotyped yawning response, i.e.,
fall in blood pressure and ECoG arousal
preceding a large inspiration, in anesthetized
and spontaneously breathing rats. Furthermore,
activation of OT and CRF neurons in the PVN,
which is responsible for induction of the
stereotyped yawning response, were observed
during yawning responses induced by the CeA
stimulation. These results suggest that the CeA
modulates induction of yawning via neuronal
activation of the PVN and that yawning might be
an emotional behavior.
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