mystery of yawning
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Yawning: its cycle, its role
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Fetal yawning assessed by 3D and 4D sonography
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La parakinésie brachiale oscitante
Yawning: its cycle, its role
Warum gähnen wir ?
 
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal
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Prog. Neuro-Psychopharmocol Biol Psy
1984;8(4-6):743-746

Timing of yawns induced by a small dose of apomorphine and its alteration by naloxone
 
Henry Szechtman
Department of Neurosciences, University Hamilton, Ontario, Canada

Chat-logomini

 
Abstract
 
1. The report examines the temporal sequence of yawns induced by apomorphine and whether the opiate antagonist, naloxone, affects it.
 
2. Before administering apomorphine (0.075 mg/kg) or saline, rats (n=8) were pretreated with naloxone (1 mg/kg) or saline. Each subject received all 4 possible treatments (saline-saline, saline-apomorphine, naloxone-saline, and naloxone-apomorphine) in random order.
 
3. Results indicate that yawning induced by apomorphine seems to come in fits; that is, there is a series of yawns spaced closely together and followed by a period of quiescence before the start of another cluster of yawns.
 
4. Naloxone reduced the number of apomorphine-induced yawns, and the occurrence of very short inter-yawn intervals.
 
5. It is suggested that the timing of yawns may provide useful information regarding some pathologies and that opiates may potentiate the action of dopaminergic systems.
 
 
 
Introduction
 
During the course of a study on the interaction of dopaminergic and opiate systems (Szechtman, submitted), I observed that after an injection of apomorphine, yawning in rats appears to come in clusters; that is, a series of yawns with short inter-yawn intervals, a period of quiescence, and then another fit of yawns. While the induction of yawning by low doses of apomorphine is well known (Dubuc et al., 1982; Holmgren and Urba-Holmgren, 1980; Lal et al., 1979; Mogilnicka and Klimek, 1977; Nickolson and Berendsen, 1980; Serra et al., 1983; Yamada and Furukawa, 1980), the temporal characteristics of this response have not been documented. The purpose of this preliminary report is to draw attention to the seemingly non-random nature of the timing of yawns. In addition to apomorphine-induced yawning, data are presented showing that pretreatment with naloxone alters their timing, reducing the occurrence of very short inter-yawn intervals.
 
 
Methods
 
Animals Subjects used in this study were 8 male Sprague Dawley rats (440-550 g), housed 2 per cage in a colony with lights on from 0700 to 1900 hr. They were well habituated to testing environment and drug injections because of an earlier study (Szechtman, 1983) in which they experienced 7 injections of apomorphine (0.15 - 1.25 mg/kg) in the same apparatus as used presently.
 
Drugs. Naloxone hydrochloride was dissolved in saline (I mg/ml) and apomorphine hydrochloride in saline (2.5 mg/mi) plus 0.1% ascorbic acid. Naloxone was injected intraperitoneally and apatorphire was injected subcutaneously under the scruff of the neck.
 
Apparatus. Each rat was tested in a low plastic done, 9 an high and 27 cm in dianter, which rested on a glass floor. A mirror, inclined 45° to it, permitted a bottcsi view of the rat's behaviour which was recorded continuously on a video cassette recorder interfaced with a time-code generator.
 
Experimental Procedure Twenty minutes before the start of testing, the subject was put into a holding bowl for adaptation. Five minutes before testing, it was injected with naloxone (1 mg/kg) or saline. immediately before being transferred to the testing apparatus, it received an injection of apomorphine (0.075 mg/kg) or saline. Each rat received all 4 possible treatments (saline-saline, saline-apanorphine, nsloxone-saline, and naloxone-apomorphine) in random order. Tests were 30 minutes in duration, conducted during light-on hours and spaced 2-3 days apart. The tine of occurrence of each yawn was noted during playback of video records.
 
Statistical Analysis The frequency distributions of inter-yawn intervals following treatments with saline-apomorphine and naloxone-apomorphine were compared using the Kolmogorov-Snirnov two-sample test (Siegel, 1956)
 
Prog. Neuro-Psychopharmocol Biol Psy 1984;8(4-6):743-746
szechtman
 
Results
 
Figure 1 presents the record of yawns exhibited by each rat following treatments with saline-saline, saline-apomorphine, naloxone-saline, and naloxone-apomorphine (there was no yawning following injection of rmloxone-saline). Inspection of this figure suggests that yawning occurs in clusters; that is, several successive yawns with short inter-yawn intervals are followed by a relatively long inter-yawn interval and another grouping of yawns with short intervals between them. While this report does not provide a forcal analysis of the data, the figure does convey a clear impression of such clusterings.
 
The distribution of inter-yawn intervals for the two most effective treatments, that is, saline-apomorphine, and naloxomo-apomorphine, is shown in Figure 2. It can be seen that yawns may be spaced as close as 5 sec, of each other, especially after treatment with saline-apomorphine. Pretreatment with naloxone, reduced not only the total member of yawns during the 30 min. test (p < .01; see Szechtman, submitted, for details) but also the relative member of short inter-yawn intervals. The latter observation is supported by the Kolmogorov-Smirnov test which was used to compare the frequency distributions of inter-yawn intervals following treatments with apomorphine and naloxone plus apomorphine. It indicated a significant (p < .05) D vadslue at the lower ends of the distributions.
 
Prog. Neuro-Psychopharmocol Biol Psy 1984;8(4-6):743-746
szechtman
Discussion
 
There is a popular saying that "one yawn brings seven". Indeed, although he did not provide any data, Barbizet (1958) wrote that in humans "...a yawn is rarely isolated. It usually occurs in fits of two or three. The intensity of the yawn often increases, and each yawn is separated by a few regular breaths. Sometimes, the yawn will be repeated, irregularly, during several minutes." This report provides empirical support for this statement by showing that in rats after an injection of apomorphine, yawns seem to come in clusters. Furthermore, pretreatment with naloxone seem to alter the timing of yawns within a cluster, especially the occurrence of very short inter-yawn intervals. Because yawning is often associated with certain pathologies (reviewed by Barbizet, 1958; Heusner, 1946; Lehmann, 1979), the alteration in timing of yawns may prove useful as a differential indicator of some of these disease states.
 
The fact that yawns come in fits suggests elements of positive feedback in the circuits mediating this response. The finding that the opiate antagonist, naloxone, reduces the very short inter-yawn intervals, suggests that endogenous opiates may be released during apomorphine-induced yawning and potentiate the action of dopaminergic system in this response.