In Vivo Electrophysiology of Peptidergic Neurons in Deep Layers of the Lumbar Spinal Cord after Optogenetic Stimulation of Hypothalamic Paraventricular Oxytocin Neurons in Rats.

Daisuke Uta,Takumi Oti,Tatsuya Sakamoto,Hirotaka Sakamoto

doi:10.3390/ijms22073400

Abstract

The spinal ejaculation generator (SEG) is located in the central gray (lamina X) of the rat lumbar spinal cord and plays a pivotal role in the ejaculatory reflex. We recently reported that SEG neurons express the oxytocin receptor and are activated by oxytocin projections from the paraventricular nucleus of hypothalamus (PVH). However, it is unknown whether the SEG responds to oxytocin in vivo. In this study, we analyzed the characteristics of the brain–spinal cord neural circuit that controls male sexual function using a newly developed in vivo electrophysiological technique. Optogenetic stimulation of the PVH of rats expressing channel rhodopsin under the oxytocin receptor promoter increased the spontaneous firing of most lamina X SEG neurons. This is the first demonstration of the in vivo electrical response from the deeper (lamina X) neurons in the spinal cord. Furthermore, we succeeded in the in vivo whole-cell recordings of lamina X neurons. In vivo whole-cell recordings may reveal the features of lamina X SEG neurons, including differences in neurotransmitters and response to stimulation. Taken together, these results suggest that in vivo electrophysiological stimulation can elucidate the neurophysiological response of a variety of spinal neurons during male sexual behavior.

Highlights

In the rodent spinal cord, there are several spinal centers that regulate the male sexual function
We examined in vivo extracellular recordings from lamina X oxytocin-responsive neurons in the upper lumbar spinal cord (L3–L4 level) after superfusion of oxytocin or optogenetic stimulation of the Paraventricular Nucleus of the Hypothalamus (PVH) of Oxtr promoter-human heparin-binding epidermal growth factor-like growth factor-channel rhodopsin (ChR2)-EYFP BAC (Oxtr-ChR2-EYFP) transgenic rats (Figure 4a)
We showed that activation of oxytocin neurons in the hypothalamus increases spontaneous firing of lamina X neurons in the lumbar spinal cord in vivo

Summary

Introduction

In the rodent spinal cord, there are several spinal centers that regulate the male sexual function. GRP neurons project their axons to the sacral autonomic nucleus and to the somatic spinal nucleus in the lower lumbar and the upper sacral spinal cord (L5–L6 and S1 level), which innervates bulbocavernosus and ischiocavernosus striated muscles attached to the base of the penis [7,8]. We have recently reported that hypothalamic oxytocin neurons project to the upper lumbar spinal cord (L3–L4 level) and are male-biased [9]. These axonal projections activate the SEG/GRP neurons, which express the oxytocin receptors (OXTR), and influence penile reflexes, such as erection and ejaculation [9]

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