Identification of neural cells activated by mating stimulus in the periaqueductal gray in female rats.

Shunji Yamada,Mitsuhiro Kawata

doi:10.3389/fnins.2014.00421

Shunji Yamada, Mitsuhiro Kawata

Open Access

https://doi.org/10.3389/fnins.2014.00421

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Abstract

Induction of lordosis as typical female sexual behavior in rodents is dependent on a mount stimulus from males and blood levels of estrogen. Periaqueductal gray (PAG) efferent neurons have been suggested to be important for lordosis behavior; however, the neurochemical basis remains to be understood. In this study, we neuroanatomically examined (1) whether PAG neurons activated by mating stimulus project to the medullary reticular formation (MRF), which is also a required area for lordosis; and (2) whether these neurons are glutamatergic. Mating stimulus significantly increased the number of cFos-immunoreactive (ir) neurons in the PAG, particularly in its lateral region. Half of cFos-ir neurons in the lateral PAG were positive for a retrograde tracer (FluoroGold; FG) injected into the MRF. cFos-ir neurons also colocalized with mRNA of vesicular glutamate transporter 2 (vGLUT2), a molecular marker for glutamatergic neurons. Using retrograde tracing and in situ hybridization in conjunction with fluorescent microscopy, we also found FG and vGLUT2 mRNA double-positive neurons in the lateral PAG. These results suggest that glutamatergic neurons in the lateral PAG project to the MRF and are involved in lordosis behavior in female rats.

Highlights

Lordosis is a typical sexual behavior of a female rodent and is induced by a male mount stimulus under proestrus levels of estrogen
PROJECTION OF MATING-STIMULATED cFos-EXPRESSING NEURONS IN THE LATERAL periaqueductal gray (PAG) To investigate whether cFos-expressing lateral PAG neurons induced by a mating stimulus project to the medullary reticular formation (MRF), FG was injected into the MRF of female rats prior to mating stimulus
The results of the study show that (1) a mating stimulus activates neurons in the lateral PAG, (2) 50% of lateral PAG neurons activated by the mating stimulus project to the reticular formation (RF), (3) 56% of these neurons are glutamatergic, and (4) there are glutamatergic neurons projecting to the RF

Summary

Introduction

Lordosis is a typical sexual behavior of a female rodent and is induced by a male mount stimulus under proestrus levels of estrogen. When PRV was injected into the lumbar epaxial muscles, which produce a lordosis posture in female rats, the PRV was sequentially labeled in the MRF, PAG, and ventromedial nucleus of the hypothalamus (VMH). The VMH is the main site of action of estrogen for inducing lordosis (Rubin and Barfield, 1983) and estrogen receptor-expressing neurons in this nucleus project to the PAG (Calizo and FlanaganCato, 2003). The PAG and MRF are important relay areas that reflexively change a male mount stimulus into an output for lordosis posture (Pfaff, 1980)

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