The effect of stress on the expression of GnRH and GnRH receptor genes in the discrete regions of the hypothalamus and pituitary of anestrous ewes

Abstract

Using the Reverse Transcription-Polymerase Chain Reaction (RT-PCR) technique, the gonadotropin releasing-hormone (GnRH) mRNA and GnRH receptor (GnRH-R) mRNA were analyzed in the preoptic area (POA), anterior (AH) and ventromedial (VM) hypothalamus, stalk/median eminence (SME) and anterior pituitary gland (AP) of anestrous ewes subjected to short or prolonged footshock stimulation. No GnRH gene expression was detected in the SME and AP. The comparable levels of GnRH mRNA were found in the POA, AH and VM in control ewes. Short and prolonged footshock stimulation significantly increased GnRH mRNA in all analyzed tissue. The highest responses in GnRH mRNA to the short stress occurred in the POA whereas to the prolonged stress in the POA and VM. In non-stressed ewes the GnRH-R mRNA were detected in tissue continuum throughout the POA, AH, VM, SME and AP. The highest concentration of GnRH-R mRNA was detected in the SME. Short as well as prolonged stress stimuli caused an increase in GnRH-R mRNA levels in all analyzed tissue. The highest responses in GnRH-R mRNA expression were found in the VM. In spite of profound up-regulation of GnRH mRNA and GnRH-R mRNA under the short and prolonged stress conditions, the increase of luteinizing hormone (LH) secretion was noted only during acute stress. It is suggested that the increase of expression of GnRH and GnRH-R genes in anestrous ewes are not directly related to GnRH level and GnRH-R activity.