Fast excitatory postsynaptic currents in neurons of the rabbit pelvic plexus

Cholinergic EPSCs and their potentiation by bradykinin in single paratracheal ganglion neurons attached with presynaptic boutons

We have found that bradykinin (BK) potentiates the nicotine-induced currents in airway paratracheal/parabronchial ganglia (PTG) neurons. In this study, we investigated if BK affects the cholinergic synaptic transmission in rat PTG neurons attached with synaptic buttons. Excitatory postsynaptic currents (EPSCs) were recorded in acutely dissociated PTG neurons attached with presynaptic boutons. EPSC frequency was increased in the high-K(+) external solution without affecting their amplitude. Activation and deactivation kinetics also did not change in the high-K(+) solution. Cd(2+) inhibited the EPSC frequency at 10(-7) M and also amplitude at higher concentrations without changing the kinetics. Mecamylamine inhibited both the amplitude and frequency of EPSCs and reduced the activation and deactivation kinetics. 10(-8) M BK potentiated the EPSC amplitude to 1.37 ± 0.19 times of preapplication control. In addition, its frequency was increased to 2.04 ± 0.41 times. BK did not affect the activation and deactivation kinetics. The effects of BK were mimicked by [Hyp(3)]-BK, a B2 kinin receptor agonist, whereas HOE 140, a B2 kinin receptor antagonist, abolished the effects of BK. In conclusion, BK potentiates the cholinergic synaptic transmission via B2 kinin receptors in the PTG. Since predominant control of airway function is thought to be exerted by cholinergic nerves arising from the PTG, the present findings might underlie at least partly the inflammatory pathological conditions of the lower airway.

Plasticity of pelvic autonomic ganglia and urogenital innervation

Pelvic ganglia contain a mixture of sympathetic and parasympathetic neurons and provide most of the motor innervation of the urogenital organs. They show a remarkable sensitivity to androgens and estrogens, which impacts on their development into sexually dimorphic structures and provide an array of mechanisms by which plasticity of these neurons can occur during puberty and adulthood. The structure of pelvic ganglia varies widely among species, ranging from rodents, which have a pair of large ganglia, to humans, in whom pelvic ganglion neurons are distributed in a large, complex plexus. This plexus is frequently injured during pelvic surgical procedures, yet strategies for its repair have yet to be developed. Advances in this area will come from a better understanding of the effects of injury on the cellular signaling process in pelvic neurons and also the role of neurotrophic factors during development, maintenance, and repair of these axons.

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

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 microM capsaicin applied to the artery and ganglia, or ganglionic application of 1 microM hyoscine, 30-100 microM suramin or 10 microM CNQX. Dilatations were reduced slightly by ganglionic application of NK1 and NK3 receptor antagonists (SR140333, SR142801; 1 microM), but were reduced significantly by bathing the ganglia in 0.5 mM Ca2+ and 10 mM Mg2+. 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 microM) 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.