Genotype-dependent effect of ACTH1-24 on grooming and yawning in two inbred strains of rats

Yawning and Penile Erection Frequencies Are Resilient to Maternal Care Manipulation in the High-Yawning Subline of Sprague-Dawley Rats

Yawning is a stereotyped behavioral pattern characterized by wide opening of the mouth associated with deep inspiration followed by short expiration. All vertebrate species yawn, but with low frequencies. We obtained two sublines of Sprague–Dawley (SD) rats by a strict inbreeding process: one with a high-yawning frequency (HY) of 20 yawns/h, which is one order of magnitude higher with respect to the low-yawning frequency (LY) subline, with 2 yawns/h. Outbred SD rats had a yawning frequency of 1 yawn/h. HY dams had a different organization of maternal care with respect to that displayed by LY and SD dams because HY dams constructed lower quality nests and had more re-retrieving and atypical retrieving. The aim of this study was to analyze the changes in maternal care using in- and cross-fostering between the sublines and SD dams and to measure spontaneous and dopaminergic-induced yawning, penile erections, grooming and scratching bouts. We also measured the expression of dopamine D₂ receptors in the striatum using Western blot analysis. Our results showed that HY male rats reared by SD or LY dams did not significantly differ in yawning frequencies with respect to HY male rats reared by mothers of their own phenotype. Maternal care did not differ between sublines and SD dams independent of the litter they reared. However, LY rats reared by HY dams showed a significant increase in the number of spontaneous penile erections. Importantly, in-fostered HY male rats had the highest number of yawns induced by systemic administration of (−)-quinpirole supporting that higher maternal care display can influence the frequency of dopaminergic-induced yawning. In fact HY male rats in all conditions yawned more than did LY and SD male rats independent of the dam that raised them supporting a strong influence of genetic background. However SD male rats raised by LY dams showed significantly increased the dopamine D₂ receptor expression. In conclusion, maternal care and the environmental nest conditions during the lactation period did not change the phenotypic characteristics of the yawning sublines supporting that their genetic background is fundamental for the expression of spontaneous or dopaminergic-induced yawning.

Thermal imaging reveals sizable shifts in facial temperature surrounding yawning in budgerigars (Melopsittacus undulatus)

Accumulating comparative and interdisciplinary research supports a brain cooling function to yawning. In particular, previous research has shown significant decreases in both brain and skull temperature following yawning in mammals. In a recent study using a thermal imaging camera, significant reductions in both the cornea and concha temperature were observed following yawns in the high-yawning subline of Sprague-Dawley rats. Here, we performed a similar experiment to investigate shifts in facial temperature surrounding yawning in an avian species with more typical yawning patterns: budgerigars (Melopsittacus undulatus). In particular, we took maximal surface temperature recordings from the face (cere or eye) from 13 birds over a one-hour period to track changes before and after yawns. Similar to previous findings in high-yawning rats, we identified significant cooling (-0.36°C) of the face 10-20 seconds following yawning in budgerigars. Consistent with the hypothesis that yawns serve a thermoregulatory function, facial temperatures were slightly elevated just prior to yawning and then decreased significantly below baseline levels immediately thereafter. Similarly, birds that yawned during the trials had consistently higher facial temperatures compared to those that did not yawn. Moreover, yawn latency and overall yawn frequency were strongly correlated with the highest facial temperature recorded from each bird across trials. These results provide convergent evidence in support of a brain cooling function to yawning, and further validate the use of thermal imaging to monitor changes in skull temperature surrounding yawning events.

Yawning reduces facial temperature in the high-yawning subline of Sprague-Dawley rats

BACKGROUND

Yawning is a stereotyped behavior that enhances blood flow to the skull, and the resulting counterflow has been hypothesized as a mechanism for brain cooling. Studies have shown that yawns are strongly associated with physiological and pathological conditions that increase brain temperature, and that they are followed by equivalent decreases in brain temperature. However, measured reductions in cranial or facial temperatures following yawning have yet to be reported, to our knowledge. To accomplish this, we used a subline of Sprague-Dawley rats that yawn at a much greater rate (20 yawns/h) than do outbred Sprague-Dawley rats (2 yawns/h).

RESULTS

Using an infrared camera, we effectively evaluated thermal changes in the cornea and concha of these rats before, during, and after yawns. The maximum temperature in both regions significantly decreased 10 s following yawns (concha: -0.3 °C, cornea: -0.4 °C), with a return to basal temperatures after 20 s.

CONCLUSIONS

This study is the first clear demonstration of yawning-induced thermal cooling on the surface of the face, providing convergent evidence that this behavior plays a functional role in thermoregulation. As other studies have demonstrated that yawning is capable of reducing cortical brain temperature, our current data support the idea that yawning functions as a thermoregulator, affecting all structures within the head.

Comparative analysis of maternal care in the high-yawning (HY) and low-yawning (LY) sublines from Sprague-Dawley rats

High- and low-yawning rats (HY and LY) were selectively bred as a function of their spontaneous yawning frequency with the LY subline about 2 yawns/hr and the HY 20 yawns/hr. The HY rats have more grooming bouts and travel longer distances in an open field. HY dams spent less time in the nest, retrieved their pups faster, and show a longer latency to licking and mouthing the pups than the LY or outbred Sprague-Dawley (SD) animals. The percentage of HY dams that had atypical retrieving was higher, with a lower nest quality, and produced offspring whose weights were lower than those from the LY subline. We also showed that the pregnant HY dams have fewer pups and the percentage that had lost at least three pups during lactation was higher than the SD and LY dams. In conclusion, HY dams are motivated to take care of their pups, but the "fine tuning" of maternal care is disturbed.

Increased nocturnal secretion of ACTH and cortisol in obsessive compulsive disorder

Information on the function of the hypothalamic-pituitary-adrenal (HPA) axis, the main mammalian system of stress response, in obsessive compulsive disorder (OCD) is inconsistent. In this study, nine inpatients with a DSM-IV diagnosis of OCD without comorbid major depression (Yale-Brown Obsessive Compulsive Scale [Y-BOCS] score >15; HAMD-21 total score 16) and nine healthy matched controls were included. Blood of patients (seven males; 31.8 +/- 9.3 years, Y-BOCS: 27.3 +/- 4.3, HAMD-21: 13.3 +/-1.9) and controls (seven males, 31.6 +/- 9.1 years) was drawn every 20 min between 23:00 and 7:00 h during sleep using a long catheter for later ACTH and cortisol analysis. Secretion patterns of cortisol and ACTH were similar in both groups, in OCD, however, at a higher level. Area under the curve plasma concentrations of both ACTH (p<0.05) and cortisol (p<0.005) were significantly greater in patients with OCD (ACTH: 674.3 +/- 57.4; cortisol: 2148.4 +/-271.7) than in controls (ACTH: 460.2 +/- 61.0; cortisol: 1191.2 +/- 124.1). In conclusion, our findings suggest that the activity of the HPA axis in patients with OCD is increased compared to healthy controls.

Enhanced binding of dopamine D1receptors in caudate-putamen subregions in High-Yawning Sprague-Dawley rats

Previous reports have shown that the inbred High-Yawning (HY) and Low-Yawning (LY) rats differ in several behavioral characteristics related to mesolimbic and nigrostriatal dopamine (DA) function. To determine if differential expression of DA receptors or DA transporter may mediate the behavioral differences in these two sublines of the Sprague-Dawley rat, we performed a quantitative autoradiography study of the DA D1-like, D2-like, and DA-transporter binding in the basal ganglia and nucleus accumbens. The results show that levels of the D1 binding in the caudate-putamen of the HY rat were higher than in the LY animals, whereas no significant differences in the DA D2 receptors and DA transporter were noted in these sublines. These data suggest that the differences in DA receptors in D1 binding in HY rats may in part have contributed to the behavioral differences related to DA functions such as grooming and penile erection. Our findings are consistent with previous reports showing a decrease in the behavioral responses after systemic administration of DA agonist in LY compared to HY rats.