Release of classical transmitters and nitric oxide in the rat olfactory bulb, evoked by vaginocervical stimulation and potassium, varies with the oestrus cycle.

In vivo microdialysis was used to investigate the effects of ovariectomy and the oestrus cycle on vaginocervical stimulation-evoked classical transmitter and nitric oxide release in the olfactory bulb of anaesthetized (urethane) and conscious rats. During pro-oestrus/oestrus, vaginocervical stimulation (1 or 10 min) significantly increased concentrations of glutamate, aspartate, GABA, noradrenaline, dopamine and nitric oxide (citrulline) but failed to do so in met-oestrus/di-oestrus or following ovariectomy. Potassium chloride-evoked GABA, noradrenaline and nitric oxide release in the olfactory bulb was also significantly enhanced during pro-oestrus/oestrus. The effects of vaginocervical stimulation on olfactory bulb transmitter release during pro-oestrus/oestrus were significantly reduced by pelvic or vagus nerve section. Basal concentrations of classical transmitters and nitric oxide in the olfactory bulb did not vary across the oestrus cycle although noradrenaline and dopamine levels were reduced following ovariectomy. These results confirm our previous electrophysiological data showing that the olfactory bulb mitral cells are only excited by vaginocervical stimulation during pro-oestrus/oestrus. They also suggest that sex hormones acting primarily at the level of the olfactory bulb dramatically enhance the ability of vaginocervical stimulation to evoke release of both classical transmitters and nitric oxide in this region. Such alterations in neurochemical release in the olfactory bulb may be important for mediating plasticity changes underlying olfactory recognition of mates or offspring.