Acetylcholine regulation of GnRH neuronal activity: A circuit in the medial septum

Abstract

In vertebrates, gonadotropin-releasing hormone (GnRH)-secreting neurons control fertility by regulating gonadotrophs in the anterior pituitary. While it is known that acetylcholine (ACh) influences GnRH secretion, whether the effect is direct or indirect, and the specific ACh receptor (AChR) subtype(s) involved remain unclear. Here, we determined 1) whether ACh can modulate GnRH cellular activity and 2) a source of ACh afferents contacting GnRH neurons. Calcium imaging was used to assay GnRH neuronal activity. With GABAergic and glutamatergic transmission blocked, subtype-specific AChR agonists and antagonists were applied to identify direct regulation of GnRH neurons. ACh and nicotine caused a rise in calcium that declined gradually back to baseline after 5-6 min. This response was mimicked by an alpha3-specific agonist. In contrast, muscarine inhibited GnRH calcium oscillations, and blocking M2 and M4 together prevented this inhibition. Labeling for choline acetyltransferase (ChAT) and GnRH revealed ChAT fibers contacting GnRH neurons, primarily in the medial septum (MS), and in greater number in females than males. ChAT positive cells in the MS are known to express p75NGFRs. Labeling for p75NGFR, ChAT and GnRH indicated that ChAT fibers contacting GnRH cells originate from cholinergic cells within these same rostral areas. Together, these results indicate that cholinergic cells in septal areas can directly regulate GnRH neurons.

Cholinergic control of GnRH neuron physiology and luteinizing hormone secretion: involvement of ACh/GABA co-transmission

“…The carbachol-triggered decrease in the frequency of mPSCs after the inward current was blocked by atropine indicates the involvement of mAChRs in this process. Previous reports have also shown mAChR-dependent ion currents in goldfish (Kawai et al, 2013) and embryonic mouse GnRH neurons (Shostak et al, 2023).…”

“…Our work also revealed the subunit compositions of nAChRs; the presence of α3β4, α4β2 and α7 receptors was confirmed in GnRH neurons, of which the α3β4 and the α4β2 were localized in the same GnRH neuron. The hypothalamic presence of functional α4β2 and α7 receptors has previously been demonstrated with the major role of α7 (Huang et al, 2011) and the expression of α3 subunit shown in embryonic GnRH neurons (Shostak et al, 2023). Interestingly, the α4, α7, β2 and β4 subunits were not found in these embryonic neurons, indicating different nAChR signaling in adult versus embryonic GnRH neurons.…”

“…Retrograde viral labeling of cholinergic neurons wired to GnRH neurons revealed that the cholinergic afferents of the GnRH neurons arise exclusively from the MS and DBB. MS has also been claimed recently as the main source of cholinergic neuronal inputs to GnRH neurons (Shostak et al, 2023).…”

“…Since the electric activity of GnRH neurons and GnRH release correlate (Ordög et al, 1997; Zhang et al, 2007; Pielecka-Fortuna et al, 2008), the result suggests that cholinergic drugs likely induce GnRH release. Similarly, ACh first activated embryonic GnRH neurons and increased their intracellular Ca 2+ concentration, followed by subsequent 5-minute-long decline (Shostak et al, 2023). In our hands, however, the first phase of the recordings was characterized by a fast transient increase followed by a slow, prolonged rise in the firing rate.…”

“…Transcriptome profiling of rodent GnRH neurons and GT1-7 cells has confirmed the expression of certain nicotinic and muscarinic receptors (Todman et al, 2005; Varju et al, 2009; Arai et al, 2017), supporting the view of a direct action of cholinergic drugs upon GnRH neurons. It has been shown recently that murine GnRH neurons grown in nasal explants receive regulatory acetylcholine neurotransmission (Shostak et al, 2023). Although these findings unequivocally imply that the central cholinergic system is capable of modulating GnRH neurons, the molecular, cellular, and physiological features of this regulatory channel are largely unidentified in adult mice.…”