Muscarinic Receptors Types 1 and 2 in the Preoptic-Anterior Hypothalamic Areas Regulate Ovulation Unequally in the Rat Oestrous Cycle.

Yadira L López-Ramírez,Isabel Arrieta-Cruz,Luciano Mendoza-Garcés,Angélica Flores,María Esther Cruz,Roger Gutiérrez-Juárez,Kayro López-Ramírez,Raúl A Librado-Osorio,Roberto Domínguez

doi:10.1155/2017/4357080

Yadira L López-Ramírez, Isabel Arrieta-Cruz + Show 7 more

Open Access

https://doi.org/10.1155/2017/4357080

Copy DOI

Abstract

Muscarinic receptors types 1 (m1AChR) and 2 (m2AChR) in the preoptic and anterior hypothalamus areas (POA-AHA) were counted, and the effects of blocking these receptors on spontaneous ovulation were analysed throughout the rat oestrous cycle. Rats in each phase of the oestrous cycle were assigned to the following experiments: (1) an immunohistochemical study of the number of cells expressing m1AChR or m2AChR in the POA-AHA and (2) analysis of the effects of the unilateral blockade of the m1AChR (pirenzepine, PZP) or m2AChR (methoctramine, MTC) on either side of the POA-AHA on the ovulation rate. The number of m2AChR-immunoreactive cells was significantly higher at 09:00 h on each day of the oestrous cycle in the POA-AHA region, while no changes in the expression profile of m1AChR protein were observed. The ovulation rate in rats treated with PZP on the oestrous day was lower than that in the vehicle group. Animals treated on dioestrous-1 with PZP or MTC had a higher ovulation rate than those in the vehicle group. In contrast, on dioestrous-2, the MTC treatment decreased the ovulation rate. These results suggest that m1AChR or m2AChR in the POA-AHA could participate in the regulation of spontaneous ovulation in rats.

Highlights

Acetylcholine (ACh) is the natural ligand of the muscarinic cholinergic membrane receptor, which belongs to the superfamily of G protein-coupled receptors
A unilateral implant of atropine in the preoptic and anterior hypothalamus areas (POA-AHA) modifies ovarian follicular growth in an asymmetric manner [13]. These results suggest that depending on the day of the oestrous cycle and the side of the preoptic area (POA)-AHA involved, the ACh binding to mAChR plays a stimulatory role in gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) preovulatory secretion and in the tonic secretion of follicle-stimulating hormone (FSH)
No significant changes were observed in the number of m1AChR or m2AChR positive cells between the left and right sides of the POA-AHA region at 9:00, 13:00, or 17:00 h on each day of the oestrous cycle

Summary

Introduction

Acetylcholine (ACh) is the natural ligand of the muscarinic cholinergic membrane receptor (mAChR), which belongs to the superfamily of G protein-coupled receptors. There are five subtypes of mAChRs (m1 to m5). M1AChRs and m2AChRs have been detected in several brain areas; the highest proportion of m1AChR was found in the hippocampus, while the cerebellum and hypothalamus were the regions with the highest m2AChR expression [1]. Everett et al and Markee and Hunter [2, 3] analysed the effects of blocking the muscarinic system with atropine sulfate, revealing that the cholinergic system plays a role in regulating the secretion of ovulating hormones in rats and rabbits. The injection of atropine in the 3rd ventricle blocked the surge of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by the pituitary gland in rats on the day of proestrous [6]

Methods

Results

Conclusion