Elsevier

Neuroscience

Volume 82, Issue 1, 25 September 1997, Pages 241-254
Neuroscience

Oxytocinergic and serotonergic innervation of identified lumbosacral nuclei controlling penile erection in the male rat

https://doi.org/10.1016/S0306-4522(97)00290-XGet rights and content

Abstract

Penile erection is due to activation of proerectile neurons located in the sacral parasympathetic nucleus of the L6–S1 spinal cord in the rat. Contraction of the ischiocavernosus and bulbospongiosus striated muscles, controlled by motoneurons located in the ventral horn of the L5–L6 spinal cord, reinforces penile erection. Physiological and pharmacological arguments have been provided for a role of oxytocin and serotonin in the spinal regulation of penile erection. Immunohistochemistry of oxytocinergic and serotonergic fibres was performed at the lumbosacral level of the male rat spinal cord, and combined with retrograde tracing from the pelvic nerve or from the ischiocavernosus and bulbospongiosus muscles using wheat germ agglutinin–horseradish peroxidase. Sacral preganglionic neurons retrogradely labelled from the pelvic nerve formed a homogeneous population, predominant at the L6 level. Motoneurons retrogradely labelled from the ischiocavernosus and bulbospongiosus muscles were observed in the medial part of the dorsolateral and in the dorsomedial nuclei. Fibres immunoreactive for oxytocin were mainly distributed in the superficial layers of the dorsal horn, the dorsal gray commissure and the sacral parasympathetic nucleus. Some of these fibres were apposed to retrogradely-labelled sacral preganglionic neurons and at the ultrastructural level, some synapses were evidenced. Fibres immunoreactive for serotonin were largely and densely distributed in the dorsal horn, the dorsal gray commissure, the sacral parasympathetic nucleus and the ventral horn. Some serotonergic fibres occurred in close apposition with retrogradely-labelled sacral preganglionic neurons and motoneurons, and synapses were demonstrated at the ultrastructural level.

This study provides morphological support for a role of oxytocin and serotonin on sacral preganglionic neurons innervating pelvic organs and motoneurons innervating the ischiocavernosus and bulbospongiosus muscles.

Section snippets

Experimental procedures

The experiments were performed on 20 adult male Sprague–Dawley rats weighing 300–400 g (Charles River, Saint Aubin-les-Elbeuf, France). Animals were anaesthetized with ketamine intraperitoneally injected (150 mg/kg). In 17 rats, the left pelvic nerve was exposed through a suprapubic midline incision, and under the control of an operating microscope, cut, and its central end immersed in 1 μL of a solution of wheatgerm agglutinin–horseradish peroxidase (WGA–HRP, 25% in sterile water) for 60 min. Then

Retrograde labelling from the pelvic nerve

Neurons labelled by retrograde transport of WGA–HRP from the pelvic nerve were found in the L6 and S1 segments of the ipsilateral spinal cord and absent in the L5 segment. From a rough estimate, their number appeared to be greater in the L6 than in the S1 spinal cord. In the transverse plane labelled neurons were located in the intermediolateral column (i.e. the sacral parasympathetic nucleus, SPN) (Fig. 1A). In the longitudinal plane, labelled neurons formed a continuous band in the L6 and S1

Retrograde labelling of autonomic and somatic motoneurons in the spinal cord

Using retrograde labelling and immunocytochemistry, we showed that synapses occur between oxytocin- or 5-HT-immunoreactive fibres and identified lumbosacral autonomic and somatic motoneurons. At the ultrastructural level, the use of specific antibodies and the labelling of the same structures in several consecutive sections confirms that oxytocin and 5-HT labellings are not artifactual. Retrograde labelling from the pelvic nerve of neurons located in the intermediolateral cell column of the

Acknowledgements

The authors thank Dr K. E. McKenna for revising the manuscript.

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