The Effects of Dopamine and Serotonin on Yawning Behavior in the Rat Model of Social Isolation

A sample of 80 Male rats (21-day post weaning) were chosen, and were put for 6 weeks in separate cages with black plastic buffers. Eight rats were put in one group of 8 rats in a single cage (the control group) and the rest were put in individual cages: one male rat in each cage. In group 1 or the control group (social conditions) 8 rats were put in one cage. They received saline carrier and their yawning behavior was recorded for 60 minutes. Group 2 (n=8; in separate cages) (social isolation conditions) received no treatment with serotonin and dopamine agonist and antagonist and were kept in separate cages with one rat in each cage. Their yawning behavior was also recorded for 60 minutes. Group 3 (n=8; in separate cages) included the rats that received Apomorphine (dopamine agonist) at a dose of 0.08 mg/kg via subcutaneous injection (SC), and their yawning behavior was recorded for 60 minutes. Rats in group 4 (n=8; in separate cages) received serotonin agonist (m-CPP) at a dose of 0.5 mg/kg via subcutaneous injection, and their yawning behavior was recorded for 60 minutes. Group 5 (n=8; in separate cages) included rats that received Serotonin Antagonist (Mianserin) at a dose of 0.2 mg/kg via subcutaneous injection, and their yawning behavior was recorded for 60 minutes. Group 6 (n=8; in separate cages) included rats receiving dopamine antagonist (haloperidol) at a dose of 0.1 mg/kg via Intraperitoneal (IP) injection, and their yawning behavior was recorded for 60 minutes. Group 7 (n=8; in separate cages) included rats receiving Serotonin antagonist (Mianserin) at a dose of 0.2 mg/kg via subcutaneous injection 15 minutes before injection of apomorphine (dopamine agonist) and their yawning behavior was recorded for 60 minutes. Rats in group 8 (n=8; in separate cages) received dopamine antagonist (haloperidol) at a dose of 0.1 mg/kg via intraperitoneal injection (IP) 15 minutes before the injection of serotonin agonist (m-ccp), and their yawning behavior was recorded for 60 minutes. Rats in group 9 (n=8; in separate cages) received Apomorphine (dopamine agonist) at a dose of 0.08 mg/kg and Serotonin agonist (m-CPP) injected subcutaneously (SC) at a dose of 0.5 mg/kg and their yawning behavior was recorded for 60 minutes. Group 10 (n=8; in separate cages) included rats that received dopamine antagonists (haloperidol) at 0.1 mg/kg via intraperitoneal injection (IP) and antagonist serotonin (Mianserin) at 0.2 mg/kg injected subcutaneously and their yawning belabor was recorded for 60 minutes. Dopamine agonist (apomorphine) and serotonin antagonist (Mianserin) induce yawning in the social conditions and injection of haloperidol (dopamine antagonist) before serotonin agonist (m-ccp) reduces yawning in social conditions. Yawning is different in social conditions and social isolation conditions. Using Meta-Chlorophenylpiperazineserotonin (serotonin agonist), Mianserin (serotonin antagonist), apomorphine (dopamine agonist), haloperidol (dopamine antagonist) the role of serotonin and dopamine in yawning, fear, erection etc. can be investigated as a model for human studies.

Stereotyped Yawning Responses Induced by Electrical and Chemical Stimulation of Paraventricular Nucleus of the Rat

Sato-Suzuki, Ikuko, Ichiro Kita, Mitsugu Oguri, and Hideho Arita. Stereotyped yawning responses induced by electrical and chemical stimulation of paraventricular nucleus of the rat. J. Neurophysiol. 80: 2765–2775, 1998. Yawning was evoked by electrical or chemical stimulation in the paraventricular nucleus (PVN) of anesthetized, spontaneously breathing rats. To evaluate physiological aspects of yawning, we monitored polygraphic measures as follows; a coordinated motor pattern of yawning was assessed by monitoring breathing [intercostal electromyogram (EMG)], mouth opening (digastric EMG), and stretching of the trunk (back EMG). We also recorded blood pressure (BP), heart rate, and the electrocorticogram (ECoG) to evaluate autonomic function and arousal responses during yawning. A stereotyped yawning response was reproducibly evoked by electrical stimulation or microinjection of l-glutamate or NOC-7, a nitric oxide (NO)-releasing compound, into the PVN. The stereotyped yawning response consisted of two sequential events, an initial response represented 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 mouth opening and stretching of the trunk. A similar sequence of events occurred during spontaneous yawning; a fall in BP and ECoG arousal preceded a yawning behavior. An increase in the frequency of spontaneous yawns was also observed after microinjection of l-glutamate or NOC-7 into the PVN. Intravenous administration of NG-monomethyl-l-arginine, an inhibitor of nitric oxide synthase (NOS), prevented the stereotyped yawning response evoked by chemical stimulation of the PVN. Histological examination revealed that effective sites for the yawning responses were located in the medial part of the rostral PVN, the site of parvocellular and magnocellular neurons. NADPH-diaphorase histochemistry showed the existence of NOS-containing cells in yawning-evoked sites of the PVN. In summary, the sequential events of yawning may be generated by NOS-containing parvocellular neurons in the medial part of the rostral PVN projecting to the lower brain stem.