I. Satosuzuki et al., STEREOTYPED YAWNING RESPONSES INDUCED BY ELECTRICAL AND CHEMICAL-STIMULATION OF PARAVENTRICULAR NUCLEUS OF THE RAT, Journal of neurophysiology, 80(5), 1998, pp. 2765-2775
Yawning was evoked by electrical or chemical stimulation in the parave
ntricular nucleus (PVN) of anesthetized, spontaneously breathing rats.
To evaluate physiological aspects of yawning, we monitored polygraphi
c measures as follows; a coordinated motor pattern of yawning was asse
ssed by monitoring breathing [intercostal electromyogram (EMG)], mouth
opening (digastric EMG), and stretching of the trunk (back EMG). We a
lso recorded blood pressure (BP), heart rate, and the electrocorticogr
am (ECoG) to evaluate autonomic function and arousal responses during
yawning. A stereotyped yawning response was reproducibly evoked by ele
ctrical stimulation or microinjection of L-glutamate or NOC-7, a nitri
c oxide (NO)-releasing compound, into the PVN. The stereotyped yawning
response consisted of two sequential events, an initial response repr
esented a depressor response and an arousal shift in the ECoG to lower
voltage and faster rhythms. These initial changes were followed by a
yawning behavior characterized by a single large inspiration with mout
h opening and stretching of the trunk. A similar sequence of events oc
curred during spontaneous yawning; a fall in BP and ECoG arousal prece
ded a yawning behavior. An increase in the frequency of spontaneous ya
wns was also observed after microinjection of L-glutamate or NOC-7 int
o the PVN. Intravenous administration of N-G-monomethyl-L-arginine, an
inhibitor of nitric oxide synthase (NOS), prevented the stereotyped y
awning response evoked by chemical stimulation of the PVN. Histologica
l examination revealed that effective sites for the yawning responses
were located in the medial part of the rostral PVN, the site of parvoc
ellular and magnocellular neurons. NADPH-diaphorase histochemistry sho
wed the existence of NOS-containing cells in yawning-evoked sites of t
he PVN. In summary, the sequential events of yawning may be generated
by NOS-containing parvocellular neurons in the medial part of the rost
ral PVN projecting to the lower brain stem.