Effect of heat stress on 7-day-old chick diencephalic BDNF gene expression and blood corticostrone level

Temperature is a critical variable in health and disease. Thermal stressors such as heat stress elicit neuroendocrine responses including activation of the HPA axis .Heat stress is a challenge for animal and human society. It has been shown that brain monoaminergic system is changed during acute and chronic heat stress condition. Commercial and domestic poultry are very susceptible animals to the heat stress. High environmental temperature led to heat stress condition and had negative effect on physiological performance. One effect of heat stress is changed molecular and cellular mechanisms. These changes in diencephalon, as an awaking center (thalamus) and autonomic mechanisms center (hypothalamus), have profound physiological performance results. However the goal of experiment was to investigate effect of heat stress on diencephalic BDNF gene expression and blood corticostrone level.

In this experiment, 20 seven-day-old male chicks divided in 1- heat stress group (10 chicks) and 2- control group (10 chicks in normal temperature condition). Heat stress induced by 39 C◦ and continued to 5 hours. Control group temperature was 30 C◦. At the end of 5 hours duration, chicks was anesthetized with Isofluran gas and killed. Blood gathered from jugular vein. Brain dissected and diencephalon was frozen in liquid nitrogen immediately. Blood corticosterone level was measured by ELIZA method, BDNF gene expression assayed by quantitative real time PCR technique with the SYBR green method.

In this experiment, heat stress significantly reduced diencephalic BDNF gene expression. However, corticosterone level significantly elevated in heat stress exposed chicks. It would be able to say that there is a relation between BDNF gene expression and blood corticosterone concentration.

These results showed changes in BDNF gene expression during heat stress condition is associated to blood corticosterone level elevation. Taken together, the results showed that a significant relationship between Hypothalamus-Hypophysis- Adernal cortex activity during acute heat stress condition and diencephalic BDNF gene expression as a neuroprotective agent of brain.