Ventromedial Nucleus of the Hypothalamus
VMH is critical for hormone-mediated lordosis behavior
- bilateral lesions of VMH can reduce or eliminate lordosis
estrogen and progesterone act at the VMH to activate female sex behavior
- if OVX an adult female rat, lordosis behavior will not be shown
- if you give estrogen for 2 days followed by a single injection of progesterone, lordosis behavior will be shown 4 hours later
- if you implant estrogen capsules within the VMH and administer progesterone systemically, lordosis behavior will be shown (estrogen acts specifically within VMH to stimulate lordosis; this is also true for progesterone)
mechanism: (genomic)
- increases in estrogen lead to increases in ER within lateral VMH
- estrogen binds to ER induce expression of PR (genomic mechanism)
- rising progesterone levels then bind to PR induce the expression of other proteins that serve to activate lordosis (genomic mechanism)
- know that protein systhesis is critical to facilitation of lordosis--1) administration of a protein synthesis inhibitor inhibits lordosis, and 2) time-frame for effects to be seen takes 3-4 hours
- neurons within VMH project to PAG: changes in synthesis of proteins in VMH neurons leads to an increased state of excitability of neurons within the PAG that control motoneurons within brainstem and spinal cord