Task-Dependent Differences in Operant Behaviors of Rats With Acute Exposure to High Ambient Temperature: A Potential Role of Hippocampal Dopamine Reuptake Transporters

Effects of heat stress on the feeding preference of yellow-feathered broilers and its possible mechanism

Heat stress is the most critical factor affecting animal feeding in summer. This experiment was conducted to investigate the effects of heat stress on the feeding preference of yellow-feathered broilers and its possible mechanism. As a result, the preference of yellow-feathered broilers for Tenebrio molitor was significantly decreased, and the fear response and serum corticosterone of broilers were significantly increased when the ambient temperatures are 35 °C (P < 0.05). In the central nervous system, consistent with the change in feeding preference, decreased dopamine in the nucleus accumbens (NAc) and increased mRNA levels of MAO-B in the ventral tegmental area (VTA) and NAc were found in yellow-feathered broilers (P < 0.05). In addition, we found significantly increased mRNA levels of corticotropin-releasing hormone receptor 1, corticotropin-releasing hormone receptor 2 and glucocorticoid receptor in the VTA and NAc of female broilers (P < 0.05). However, no similar change was found in male broilers. On the other hand, the serum levels of insulin and glucagon-like peptide-1 were increased only in male broilers (P < 0.05). Accordingly, the mRNA levels of insulin receptor and glucagon-like peptide-1 receptor in the VTA and the phosphorylation of mTOR and PI3K were increased only in male broilers (P < 0.05). In summary, the preference of yellow-feathered broilers for Tenebrio molitor feed decreased under heat stress conditions, and hedonic feeding behavior was significantly inhibited. However, the mechanism by which heat stress affects hedonic feeding behavior may contain gender differences. The insulin signaling pathway may participate in the regulation of heat stress on the male broiler reward system, while stress hormone-related receptors in the midbrain may play an important role in the effect of heat stress on the reward system of female broilers.

Micronuclei and nuclear buds in amniotic tissue of rats treated with cyclophosphamide

Fetal development can be altered by DNA damage caused by maternal exposure to chemical, physical, or biological agents during gestation. One method of assessing genotoxicity is to detect micronuclei (MNs) and/or nuclear abnormalities. This can be performed in vivo and requires only frequently dividing tissues, such as amniotic tissue (AT), which is in contact with the fetal environment and is composed of very thin layers of cells. This study evaluated the presence of MNs, nucleoplasmic bridges, and nuclear buds (NBs) in the fetal AT following maternal exposure to cyclophosphamide (CP) during pregnancy. Pregnant Wistar rats were divided into a negative control group and an experimental group that was orally administered CP (10 mg/kg). Daily blood smears were obtained from pregnant rats on days 14-19 of gestation. The rats were dissected, and fetal ATs were obtained on the 19th day of gestation. The MN and NB frequencies in AT cells were analyzed using a fluorescence microscope (100 ×). Micronucleated erythrocytes in the peripheral blood of the control rats were also assessed. Micronucleated polychromatic erythrocyte frequencies were significantly higher than those in the controls. Polychromatic erythrocyte frequencies were lower in CP-treated rats than in controls at 48-120 h. Fetuses in the CP-treated group also showed a significant increase in MNs and NBs in AT cells. In conclusion, AT could be used for analyzing MNs and NBs in rats following maternal exposure to a genotoxic agent and as a viable alternative for analyzing the integrity of fetal DNA during gestation.

Arcuate proopiomelanocortin is part of a novel neural connection for short-term low-degree of high ambient temperature effects on food intake

High ambient temperature (HTa) is an important environmental factor influencing food intake (FI). We previously demonstrated that low-degree HTa exposure decreased FI earlier than activated physiological responses, and this effect was related to the median preoptic nucleus (MnPO) and arcuate nucleus (Arc) connection. The present study refines the condition of low-degree HTa exposure and focuses on the mechanism of Arc neural activation. We demonstrated in the first experiment that with the usual ambient temperature (Ta) at 23 °C, the low degree HTa condition is at a 7 °C temperature difference and with 90 min exposure. Rats exposed to this short-term low-degree HTa had significantly lower 1-h FI than those exposed to control Ta (CTa) without differences in rectal temperature and hematocrit. Under nonfeeding conditions, HTa could enhance c-Fos at the Arc without the activation of proopiomelanocortin (POMC) neurons. Under feeding conditions, HTa could enhance both c-Fos and POMC at Arc. In addition, the number of c-Fos and POMC colocalizations in the HTa group was higher than that in the CTa group. Finally, intracerebral preinfusion with a subthreshold dose of the melanocortin antagonist SHU9119 reversed the effect of low-degree HTa exposure on FI. Therefore, we conclude that the effect of short-term low-degree HTa exposure on FI in rats is mediated in part by activation of POMC neurons at the Arc. The results partially support the hypothesis that Arc is a crucial hypothalamic nucleus for the effect of low-degree HTa exposure on FI.

Effect of short- and long-term heat exposure on brain monoamines and emotional behavior in mice and rats

Heat exposure affects several physiological, neuronal, and emotional functions. Notably, monoaminergic neurotransmitters in the brain such as noradrenaline, dopamine, and serotonin, which regulate several basic physiological functions, such as thermoregulation, food intake, and energy balance, are affected by heat exposure and heat acclimation. Furthermore, cognition and emotional states are also affected by heat exposure and changes in brain monoamine levels. Short-term heat exposure has been reported to increase anxiety in some behavioral tests. In contrast, there is a possibility that long-term heat exposure decreases anxiety due to heat acclimation. These changes might be due to adaptation of the core body temperature and/or brain monoamine levels by heat exposure. In this review, we first outline the changes in brain monoamine levels and thereafter focus on changes in emotional behavior due to heat exposure and heat acclimation. Finally, we describe the relationships between emotional behavior and brain monoamine levels during heat acclimation.