Bethanechol-induced increase in hypothalamic estrogen receptor binding in female rats is related to capacity for estrogen-dependent reproductive behavior

Neuroactive agents associated with different neurotransmitter systems can modulate the number of hypothalamic estrogen binding sites. It has been demonstrated previously that the muscarinic cholinergic agonist, bethanechol, administered 30 min prior to in vitro estrogen receptor assays increases the concentration of hypothalamic estrogen binding sites by 30-35% in female rats. Bethanechol was without effect on male hypothalamic preparations. In order to investigate further this sex difference and in an attempt to determine a relationship between the modulation of estrogen binding sites and a sexually differentiated function, bethanechol was given to female rats rendered either anovulatory and capable of displaying lordosis or anovulatory and behaviorally insensitive to estrogen. The results showed that bethanechol significantly increased the number of estrogen binding sites in females capable of displaying lordosis but not in females which did not show this estrogen-dependent behavior. It is possible that the capacity for drug-induced modulation of estrogen binding sites could be related functionally to the ability to display lordosis behavior.