Multiple cholinergic signaling pathways in pituitary gonadotrophs

Area of Science:

• Neuroendocrinology
• Molecular Pharmacology
• Cell Biology

Background:

• Acetylcholine (ACh) is a known paracrine factor in the anterior pituitary.
• Receptors mediating ACh actions and their specific cell types were previously unidentified.

Purpose of the Study:

• To identify cholinergic receptors in pituitary gonadotrophs.
• To elucidate the functional roles of these receptors in regulating gonadotroph function.

Main Methods:

• RT-PCR to detect nicotinic and muscarinic receptor subunit mRNA expression.
• Double immunostaining for protein localization.
• Electrophysiology (patch-clamp) to assess ion channel activity and Ca(2+) influx.
• Measurement of cAMP production and luteinizing hormone (LH) release.

Main Results:

• Multiple nicotinic (β2, β1, α9, α4) and muscarinic (M4, M3) receptor subunits were expressed in pituitary cells and LβT2 gonadotrophs.
• GnRH treatment altered α9 and α4 nicotinic subunit expression.
• Functional nicotinic channels and M3 receptor-mediated Ca(2+) mobilization were observed.
• ACh acting via M4 receptors inhibited cAMP production and GnRH-induced LH release.

Conclusions:

• Gonadotrophs express diverse cholinergic receptors, including nicotinic and muscarinic subtypes.
• ACh exerts inhibitory control over gonadotroph secretion primarily through M4 receptor-mediated cAMP down-regulation.
• Nicotinic receptor expression in vitro may compensate for reduced GnRH stimulation.