Post‐stimulus potentiation of transmission in pelvic ganglia enhances sympathetic dilatation of guinea‐pig uterine artery in vitro

Abstract

Vasodilatation produced by stimulation of preganglionic neurones in lumbar and sacral pathways to pelvic ganglia was studied using an in vitro preparation of guinea-pig uterine artery and associated nerves in a partitioned bath allowing selective drug application to the ganglia or artery. Arterial diameter was monitored using real time video imaging. Vasodilatations produced by hypogastric nerve stimulation (HN; 300 pulses, 10 Hz) were significantly larger and longer in duration than with pelvic nerve stimulation (N = 18). Stimulation of ipsilateral lumbar splanchnic nerves or ipsilateral third lumbar ventral roots also produced prolonged vasodilatations. Blockade of ganglionic nicotinic receptors (0.1-1 mM hexamethonium) delayed the onset and sometimes reduced the peak amplitude of dilatations, but slow dilatations persisted in 16 of 18 preparations. These dilatations were not reduced further by 3 µM capsaicin applied to the artery and ganglia, or ganglionic application of 1 µM hyoscine, 30-100 µM suramin or 10 µM CNQX. Dilatations were reduced slightly by ganglionic application of NK1 and NK3 receptor antagonists (SR140333, SR142801; 1 µM), but were reduced significantly by bathing the ganglia in 0.5 mM Ca 2+ and 10 mM Mg 2+ . Intracellular recordings of paracervical ganglion neurones revealed fast excitatory postsynaptic potentials (EPSPs) in all neurones on HN stimulation (300 pulses, 10 Hz), and slow EPSPs (3-12 mV amplitude) in 25 of 37 neurones. Post-stimulus action potential discharge associated with slow EPSPs occurred in 16 of 37 neurones (firing rate 9.4 ± 1.5 Hz). Hexamethonium (0.1-1 mM) abolished fast EPSPs. Hexamethonium and hyoscine (1 µM) did not reduce slow EPSPs and associated post-stimulus firing in identified vasodilator neurones (with VIP immunoreactivity) or non-vasodilator paracervical neurones. These results demonstrate a predominantly sympathetic origin of autonomic pathways producing pelvic vasodilatation in females. Non-cholinergic mediators of slow transmission in pelvic ganglia produce prolonged firing of postganglionic neurones and long-lasting dilatations of the uterine artery. This mechanism would facilitate maintenance of pelvic vasodilatation on stimulation of preganglionic neurones during sexual activity.

Novel spinal pathways identified by neuronal c-Fos expression after urethrogenital reflex activation in female guinea pigs

“…The responses to the UGR activation in female animals resemble those seen during sexual activity, including significant increases in pelvic blood flow and rhythmic contractions of the vagina and uterus (Bohlen et al, 1982a(Bohlen et al, , 1982bSipski, 2001). Afferent input arises from the pudendal nerves and the visceral responses themselves are produced by activation of autonomic pathways comprising 5 spinal preganglionic neurons, the hypogastric and pelvic nerves, with final motor neurons in the paracervical (anterior pelvic) ganglia (Morris and Gibbins, 1987;Keast, 1999;Jobling et al, 2003;Morris et al, 2005a;Wiedey, 2008). In guinea pigs, pudendal nerves project from sacral spinal cord mainly at S2 segment, hypogastric from rostral lumbar (eg.…”

“…To date, the contributions of these neurons to pathways activated by the UGR reflex are not known. Building on our previous studies in guinea pigs (which confirm and extend observations made in other species, such as rats) (Jobling et al, 2003;Morris et al, 2005a;Yuan et al, 2011;Vilimas et al, 2011), we have adapted the UGR model for female guinea-pigs. We used c-Fos immunohistochemistry to identify neurons that are activated by UGR in animals with intact spinal cord, and in animals following lesions of the spinal cord at different levels.…”

“…Two aspects of our data predict that these spinal pathways are related to pain perception: (1) c-Fos expression in superficial dorsal horn neurons is up-regulated almost exclusively by nociceptive inputs (Coggeshall, 2005); and (2) many of these c-Fos expressing neurons were found to be surrounded by CGRP-immunoreactive fibres, which are known to be primarily nocicieptive (Morris et al, 2005b). The complexity of the pathways is further demonstrated by the presence of three sensory-autonomic pathways regulating pelvic organs activity: (1) pudendal nerve inputs to sacral spinal cord with outputs via the pelvic nerve; (2) pudendal nerve inputs to sacral spinal cord with ascending pathways to lumbar outputs via lumbar splanchnic and hypogastric nerves; and (3) hypogastric nerve inputs to lumbar spinal cord with outputs via lumbar splanchnic and hypogastric nerves (Dail et al, 1985;Jobling et al, 2003;Morris and Gibbins,1987;Morris et al, 2005a;Papka and Traurig, 1993;Sato et al, 1996;Traurig and Papka, 1993;Wiedey et al, 2008;Yuan et al, 2011). In addition, there is a significant degree of intra-spinal modulation within both ascending and descending pathways .…”

“…Many of these pelvic neurons in guinea pigs also receive descending central inputs from lumbar levels (L3) in addition to inputs from the sacral spinal cord (Jobling et al, 2003;Morris et al, 2005a;Yuan et al, 2011). However, outputs of the lumbar pathways to pelvic vasodilator and uterine motor neurons appear to be inhibited by spinal neurons acting via GABA A receptors .…”

“…Indeed, many vasodilator neurons in guinea-pig paracervical ganglia receive their dominant preganglionic input from mid-lumbar (L3) spinal cord, often with convergent sacral spinal inputs (Jobling et al, 2003;Morris et al, 2005a).…”