Dopamine agonist-induced yawning in rats: a dopamine D3 receptor mediated behavior
Collins G et al
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6 mars 2003
Hormones and Behavior
Testosterone potentiation of the effectiveness of ACTH on the induction of the strech-yawning syndrome in male Guinea Pigs
J Rodriguez-Sierra, E Terasawa, D Goldfoot, D De Wield
Wisconsin regional primate research center, University of Wisconsin


Several cases of mutually potentiating behavioral effects of peptide and steroid hormones have been suggested in recent years. These include possible interactions of luteinizing hormone-releasing hormone (LHRH) and estradiol for the display of lordosis, of ACTH and testosterone for facilitation of certain measures of sexual arousal, and of interactions between several pituitary hormones and adrenal steroids for phenomena related to agonism and to avoidance learning. The underlying neural processes through which these potentiating effects act remain to be discovered.
The display of a combined stretching and yawning pattern (SYS) has been demonstrated previously in many laboratory species following intracranial administration of ACTH.
Gispen, Wiegant, Greven, and DeWied, (1975) demonstrated that the display of SYS in response to ACTH was independent of the adrenals, gonads, and pituitary gland, and therefore probably represents a direct central effect. It has also been shown, however, that androgens (TP and dihydrotestosterone propionate, DHTP) elicited yawning in several species. However, in cases of androgen potentiated yawning, stretching was not usually seen. In the present study, the separate and combined actions of ACTH and testosterone propionate (TP) were examined for their influences on a simple stretching and yawning pattern (SYS) in the castrated male guinea pig. Attempts were made to distinguish -yawns from "stretch-yawns"and from "stretches", analyzing each of these three patterns as separate behaviors. In addition, other patterns of behavior reported to be elicited following intracranial treatment with ACTH in other species, e.g., self-grooming, penile erections, and wet-dog shaking were also recorded when they occurred. The purpose of the study was therefore to determine similarities and differences of response of the guinea pig to intracranial ACTH in comparison to those reported for other species, and to determine whether testosterone treatment interacted in these processes.
Results :
Experiment 1 revealed that intracranial administration of ACTH into the male guinea pig resulted in a dose-related increase in frequency of SYS. The lowest dosage of ACTH used (0.08 jug) was not different from the saline vehicle condition, but all other doses showed clear effects, with 0.4 µg being intermediate in effect and 2.0 µg giving the maximal response. The highest dose employed (8.0 µg) did not further enhance the response, and was in fact (nonsignificantly) less effective than the 2.0 µg treatment.
The simultaneous administration of TP in this experiment restilied in an augmented mean SYS at every dosage level employed, although the overall effect of TP + ACTI failed to be significantly different from the oil + ACTH treatment. In both treatment conditions, and at each dose level, no significant augmentation of grooming, shaking, scratching, or penile erections was found.
Experiment 2 analyzed the question of TP-ACTH interactions, and demonstrated that TP treatment itself, without the concomitant administration of ACTH only minimally influenced stretch-vawning patterns. Figure 3 shows that a mean increase in stretch-yawns occurred, but that this difference was not statistically significant. TP did induce a clear augmentation of yawns not accompanied by stretches however, it had no measurable influence on the frequency of stretches.

ACTH augmented stretch-yawns when given by itself, but had no influence on yawns or on stretches when these behaviors were displayed singly. The behavior patterns obtained with ACTH were therefore distinct from those displayed in response to the TP treatment: ACTH stimulated stretch-yawns, and TP stimulated yawns. Neither hormone stimulated stretching by itself.

When ACTH and TP were given simultaneously, no augmentation of stretching by itself was seen, and no augmentation of yawning beyond that obtained with TP-alone occurred. Stretch-yawning was considerably potentiated with the combined treatment, however, and was significantly more frequently expressed than in the TP-alone or ACTH-alone conditions. However, as in experiment 1, no significant changes in the frequencies of any other behavior measured in this study were found following treatment with ACTH with TP, or with the combined steroid and peptide treatment.

Discussion :

The present experiment clearly showed that ACTH is effective in inducing the SYS in male guinea pig as it does in a number of other mammalian species. Sex steroids are not necessary for the action of peptide hormones; ACTH induced SYS in orchidectomized males and ovariectomized females. However, testosterone potentiates the effectiveness of ACTH. This is in disagreement with a report by Bertolini and Baraldi (1976) who found no apparent differences in the incidence of SYS in androgen-injected rats compared to castrated animals after ACTH administration. This discrepancy might be due to either species differences or differences in their protocol from our experimental treatments: the rats were given androgen for only 4 days and the dose of ACTH used induced a maximal response in their animals. The present study used a different species, a relatively low dose of ACTH, a long period of androgen stimulation, and extended time observations in order to detect any facilitatory effects of testosterone on the action of ACTH.

The duration of androgen administration seems to be an important factor. In our first experiment we did not detect an androgen effect, but did so in the second experiment. The only factor that changed was that the animals continued to receive androgen for 2 additional weeks.

It is clear from the present experiment that yawning and SYS are functionally distinct behaviors, since testosterone itself is effective in inducing yawning but not SYS behavior, while ACTH is effective in inducing SYS but not yawning behavior. Thus, separate underlying neuroendocrine mechanisms may be involved in these two behaviors. On the other hand, it is premature to conclude that our resuits represent a -synergistic- effect of the two hormones as opposed to an "additive" effect. Although TP by itself did not result in a significant increase in stretch-yawning, there was indeed a nonsignificant trend in that direction. Further studies which vary both TP and ACTH doses will be necessary before a definitive answer to that question can be given. The significance of these results for an elucidation of peptide-steroid interactions ai the neural level therefore remains to be tested. However, it is possible from these results that steroids could act on brain loci as well as on the pituitary to modulate the central effect of peptidergic neurons.

Other steroids have been shown to enhance the effectiveness of peptidergic neurons for behavioral systems: e.g., estrogen pretreatment is required in order to induce female sexual behavior with LHRH in rats. Those findings, taken together with the results of the present study, suggest that testosterone might alter the sensitivity of hypothalamo-limbic-midbrain circuits to ACTH, resulting in a combined influence of these two hormones of the mediation of SYS

« It is ironic that testosterone "the male sex hormone," is more closely associated with the yawning rate than with the mounting or intromitting rates » Charles Phoenix
Sexual steroids exert several effects on both central dopaminergic and oxytocinergic systems by acting either at the genomic or membrane level  
credit photo : "Asif A. Ghazanfar and Aristides Arrenberg"
Max Planck Institute for Biological Cybernetics
Tuebingen; Germany.
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