Chronic stress in Lizards: Studies on the Behavior and Benzodiazepine Receptors in Liolaemus koslowskyi and Cnemidophorus tergolaevigatus

The Presence of a Shelter in an Open Field Test Has Differential Effects on the Behavior and Stress Response of Two Mouse Species

The open field test (OFT) is frequently used in research to assess anxiety-like behavior and locomotor activity. Its simple design can lead to the misconception that it is a standardized procedure comparable between laboratories. However, some modifications in the setup can cause changes in behavior. Different species might also react differently to the modifications introduced. There is thus need for a better understanding of the impact of modifications and their value for the species in question. Here, we tested two closely related mouse species, Mus musculus and Mus spretus, in an OFT with and without the presence of a shelter. We assessed mouse exploratory behavior through the analysis of multiple behavioral traits, and stress response through the measurement of circulating cortisol levels. Both species had elevated cortisol levels during the OFT in contrast to control animals which were not exposed to the OFT. While the presence of a shelter in the OFT increased the exploratory behavior in both mouse species, M. spretus, but not M. musculus, showed a reduction in cortisol levels. Also, other measured behaviors show a rather proactive coping strategy of the commensal M. musculus in contrast to a reactive strategy of the non-commensal M. spretus. Our study revealed a strong species-specific influence of the OFT design on the resulting behavior and stress levels of mice, illustrating the importance of OFT designs to account for the characteristics of the species under study. The addition of a shelter might be considered to improve experimental results by promoting animal welfare.

Effects of blood extraction and ecophysiological experiments on stress in adult males of Liolaemus attenboroughi

Stress during laboratory experiments can affect the outcomes of ecophysiological studies. The serum corticosterone concentration (CORT), the leukocyte profile, heterophil/lymphocyte ratio (H/L), and the presence of blood endoparasites were analyzed as a proxy of stress and immunological state in adult males of the lizard Liolaemus attenboroughi, endemic to Patagonia, Argentina. The results of the ecophysiological variables (preferred temperature, running speed, locomotor endurance, and body condition index, BCI) were analyzed in relation to stress indicators obtained from blood samples taken at three different times: at capture, and on the third and seventh days in the laboratory. Males at capture showed a high percentage of lymphocytes and heterophils and a low of basophils, monocytes, and eosinophils. Haemogregorina-type endoparasites have been recorded in the genus Liolaemus for the first time. The proportion of infected males remained stable during captivity; however, these males showed higher CORT levels, increased percentages of basophils, and decreased percentages of lymphocytes. There was a significant increment in CORT and H/L, and a decrease in BCI during laboratory experiments, compared with baseline values at capture. The performance was not related to the CORT or the repeated blood sampling. The BCI decreased, possibly due to energy reserve mobilization caused by acute stress. This study shows that blood extraction and ecophysiological experiments over 7 days have a minor effect on the stress indicators used.

Constitutive gene expression differs in three brain regions important for cognition in neophobic and non-neophobic house sparrows (Passer domesticus)

Neophobia (aversion to new objects, food, and environments) is a personality trait that affects the ability of wildlife to adapt to new challenges and opportunities. Despite the ubiquity and importance of this trait, the molecular mechanisms underlying repeatable individual differences in neophobia in wild animals are poorly understood. We evaluated wild-caught house sparrows (Passer domesticus) for neophobia in the lab using novel object tests. We then selected a subset of neophobic and non-neophobic individuals (n = 3 of each, all females) and extracted RNA from four brain regions involved in learning, memory, threat perception, and executive function: striatum, caudal dorsomedial hippocampus, medial ventral arcopallium, and caudolateral nidopallium (NCL). Our analysis of differentially expressed genes (DEGs) used 11,889 gene regions annotated in the house sparrow reference genome for which we had an average of 25.7 million mapped reads/sample. PERMANOVA identified significant effects of brain region, phenotype (neophobic vs. non-neophobic), and a brain region by phenotype interaction. Comparing neophobic and non-neophobic birds revealed constitutive differences in DEGs in three of the four brain regions examined: hippocampus (12% of the transcriptome significantly differentially expressed), striatum (4%) and NCL (3%). DEGs included important known neuroendocrine mediators of learning, memory, executive function, and anxiety behavior, including serotonin receptor 5A, dopamine receptors 1, 2 and 5 (downregulated in neophobic birds), and estrogen receptor beta (upregulated in neophobic birds). These results suggest that some of the behavioral differences between phenotypes may be due to underlying gene expression differences in the brain. The large number of DEGs in neophobic and non-neophobic birds also implies that there are major differences in neural function between the two phenotypes that could affect a wide variety of behavioral traits beyond neophobia.