Fig. 9

Functional pictogram of the GnRH pulse generator, hot flushes and neurotransmitters. a individuals with functional ovaries such as premenopausal women or intact rodents; (b) oestrogen-deficient such as postmenopausal women or ovariectomized rodents. In the presence of functional ovaries a cocktail of stimulatory and inhibitory neurotransmitters in the hypothalamus [such as serotonin, norepinephrine (NE), dopamine (DA) and γ-aminobutyric acid (GABA)] causes regular, phasic and synchronous activation of GnRH-producing neurons, which results in normal pulsatile release of GnRH into the portal vessels connecting the hypothalamus with the anterior pituitary gland. This pulsatile pattern is important for the normal sensitivity of GnRH receptors of LH and FSH producing cells and therefore for normal reproductive health. The absence of ovarian steroids causes a dysbalance of neurotransmitters and the GnRH neurons are overstimulated, thus resulting in high GnRH pulses and consequently high LH and FSH levels in the serum. Under these conditions the dysregulated neurotransmitters spill over to temperature and heart regulating neurons, thus producing hot flushes and tachycardia