Progesterone Withdrawal-Evoked Plasticity of Neural Function in the Female Periaqueductal Grey
Matter
Figure 3
Cartoon to depict changes in receptor expression in the PAG at different stages of the oestrous cycle. receptors are expressed mainly by
GABAergic interneurones where they are extrasynaptically located and mediate
tonic currents. The excitability of output neurons from the PAG is limited by
spontaneous activity in GABAergic interneurones. (a) When expression of receptors is low during proestrus
(Pro), oestrus (O), and early dioestrus (ED), high levels of activity in the
interneurone population limit the excitability of the output neurons. (b) When
progesterone levels fall during late dioestrus (LD), increased expression of receptors
leads to an increase in tonic current carried by GABAergic cells, thus limiting
their on-going activity. The output neurones therefore become intrinsically
more excitable, and their threshold for activation is lowered. The figure is adapted from [38].
