Neuropeptide action in sympathetic ganglia. Evidence for distinct functions in intact and axotomized ganglia

Changes in the Neurochemical Coding of the Anterior Pelvic Ganglion Neurons Supplying the Male Pig Urinary Bladder Trigone after One-Sided Axotomy of Their Nerve Fibers

The present study investigated the effect of unilateral axotomy of urinary bladder trigone (UBT)-projecting nerve fibers from the right anterior pelvic ganglion (APG) on changes in the chemical coding of their neuronal bodies. The study was performed using male pigs with immunohistochemistry and quantitative real-time PCR (qPCR). The animals were divided into a control (C), a morphological (MG) or a molecular biology group (MBG). APG neurons supplying UBT were revealed using the retrograde tracing technique with Fast Blue (FB). Unilateral axotomy resulted in an over 50% decrease in the number of FB+ neurons in both APG ganglia. Immunohistochemistry revealed significant changes in the chemical coding of FB+ cells only in the right ganglion: decreased expression of dopamine-B-hydroxylase (DBH)/tyrosine hydroxylase (TH) and up-regulation of the vesicular acetylcholine transporter (VAChT)/choline acetyltransferase (ChAT), galanin (GAL), vasoactive intestinal polypeptide (VIP) and brain nitric oxide synthase (bNOS). The qPCR results partly corresponded with immunofluorescence findings. In the APGs, genes for VAChT and ChAT, TH and DBH, VIP, and NOS were distinctly down-regulated, while the expression of GAL was up-regulated. Such data may be the basis for further studies concerning the plasticity of these ganglia under experimental or pathological conditions.

PACAP signaling in stress: insights from the chromaffin cell

Pituitary adenylate cyclase-activating polypeptide (PACAP) was first identified in hypothalamus, based on its ability to elevate cyclic AMP in the anterior pituitary. PACAP has been identified as the adrenomedullary neurotransmitter in stress through a combination of ex vivo, in vivo, and in cellula experiments over the past two decades. PACAP causes catecholamine secretion, and activation of catecholamine biosynthetic enzymes, during episodes of stress in mammals. Features of PACAP signaling allowing stress transduction at the splanchnicoadrenomedullary synapse have yielded insights into the contrasting roles of acetylcholine's and PACAP's actions as first messengers at the chromaffin cell, via differential release at low and high rates of splanchnic nerve firing, and differential signaling pathway engagement leading to catecholamine secretion and chromaffin cell gene transcription. Secretion stimulated by PACAP, via calcium influx independent of action potential generation, is under active investigation in several laboratories both at the chromaffin cell and within autonomic ganglia of both the parasympathetic and sympathetic nervous systems. PACAP is a neurotransmitter important in stress transduction in the central nervous system as well, and is found at stress-transduction nuclei in brain including the paraventricular nucleus of hypothalamus, the amygdala and extended amygdalar nuclei, and the prefrontal cortex. The current status of PACAP as a master regulator of stress signaling in the nervous system derives fundamentally from the establishment of its role as the splanchnicoadrenomedullary transmitter in stress. Experimental elucidation of PACAP action at this synapse remains at the forefront of understanding PACAP's role in stress signaling throughout the nervous system.

Axotomy-induced changes in the chemical coding pattern of colon projecting calbindin-positive neurons in the inferior mesenteric ganglia of the pig

The present study examines the response of colon-projecting neurons localized in the inferior mesenteric ganglia (IMG) to axotomy in the pig animal model. In all animals (n = 8), a median laparotomy was performed under anesthesia and the retrograde tracer Fast Blue was injected into the descending colon wall. In experimental animals (n = 4), the descending colon was exposed and the bilateral caudal colonic nerves were identified and severed. All animals were euthanized and the inferior mesenteric ganglia were harvested and processed for double-labeling immunofluorescence for calbindin-D28k (CB) in combination with either tyrosine hydroxylase (TH), neuropeptide Y (NPY), somatostatin (SOM), vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), Leu-enkephalin (LENK), substance P, vesicular acetylcholine transporter, or galanin. Immunohistochemistry revealed significant changes in the chemical coding pattern of injured inferior mesenteric ganglion neurons. In control animals, Fast Blue-positive neurons were immunoreactive to TH, NPY, SOM, VIP, NOS, LENK, and CB. In the experimental group, the numbers of TH-, NPY-, and SOM-expressing neurons were reduced, whereas the number of neurons immunoreactive to LENK was increased. Our data indicate that the colon-projecting neurons of the porcine IMG react to the axotomy in a similar, but not an identical manner in a comparison to other species, especially rodents. Further studies are needed to elucidate the detailed factors/mechanisms involved in the response to nerve injury.

Axotomy induced changes in neuronal plasticity of sympathetic chain ganglia (SChG) neurons supplying descending colon in the pig

Sympathetic neurons are capable of extensive regeneration following axonal injury. To investigate the response to axotomy of colon-projecting neurons (CPN) localized in the porcine sympathetic chain ganglia (SChG), the retrograde Fast Blue (FB) tracer, axonal transection and double immunohistochemistry methods were applied. The CPN were localized exclusively in the lumbar SChG and displayed a predominantly catecholaminergic [i.e. Tyrosine Hydroxylase (TH)/Dopamine β Hydroxylase (DβH)] and Neuropeptide Y (NPY) positive phenotype under physiological conditions. Axotomy led to a significant decrease in TH/DβH production and a simultaneous increase in the neuropeptides Galanin (GAL) and Somatostatin (SOM), but not NPY or Vasoactive Intestinal Peptide (VIP) expression in retrogradely traced perikarya. Furthermore, the decrease in density of TH-/DβH-, VIP-, Leu(5)-Enkephalin (LENK)-, Choline Acetyltransferase (ChAT)-immunoreactive (-IR) nerve fibers occurred after axotomy. These data suggest a species-specific response to axonal damage of the CPN localized in porcine SChG. Since the SChG neurons supervise the vasculature of gut both in physiological and pathological conditions, and since pig is a more accurate animal model of human gut than a rodent (Swindle et al., 1992), these data may contribute to the understanding of the pathology of several gut illnesses, like Crohn Disease and Irritable Bowel Syndrome which commonly affect western populations.

A standardized surgical technique for rat superior cervical ganglionectomy

Superior cervical ganglionectomy (SCGx) is a valuable microsurgical model to study the role of the sympathetic nervous system in a vast array of physiological and pathological processes, including homeostatic regulation, circadian biology and the dynamics of neuronal dysfunction and recovery after injury. Despite having several experimental applications in the rat, a thorough description of a standardized procedure has never been published. Here, we provide a brief review of the principal features and experimental uses of the SCGx, the surgical anatomy of the neck and sympathetic cervical chain, and a step-by-step description of how to consistently remove the superior cervical ganglia through the omohyoid muscle or the carotid triangle. Furthermore, we suggest procedures and precautions to be taken during and after surgery to optimize results and describe tools to validate surgical success. We expect that the following standardized and optimized protocol will allow researchers to organize knowledge into a cohesive framework in those areas where the SCGx is applied.

Potent pro-inflammatory actions of leukemia inhibitory factor in the spinal cord of the adult mouse

Injury in the peripheral or central nervous systems causes a significant rise in the levels of the pleiotropic cytokine leukemia inhibitory factor (LIF). This increase influences cell survival, reactive gliosis and inflammatory responses. Since prior work has focused primarily on peripheral nerve and brain, little is known about the role of LIF in the spinal cord injury response. We address this issue by examining the effects of injury in the LIF knockout (KO) mouse, as well as using an adenoviral vector to over-express LIF in the spinal cord of adult mice. We find that LIF over-expression results in a dramatic rise in cell proliferation, primarily in microglia/macrophages. Astrocytes are not stimulated to proliferate but are activated by the elevated LIF. LIF over-expression also causes the development of severe hindlimb motor dysfunction, an effect mediated by the enhanced activation of microglia/macrophages, as inhibiting microglial activation with minocycline attenuates these motor deficits. Conversely, proliferation is significantly diminished and the microglial/macrophage response to spinal cord injury is much less in the LIF KO compared to wild type (WT). Thus, LIF is a potent pro-inflammatory factor in the adult spinal cord and represents a potential target for the manipulation of inflammatory reactions after spinal cord injury.

Vasoactive intestinal peptide and nitric oxide promote survival of adult rat myenteric neurons in culture

Several motility disorders originate in the enteric nervous system (ENS). Our knowledge of factors governing survival of the ENS is poor. Changes in the expression of vasoactive intestinal peptide (VIP) and nitric oxide synthase (NOS) in enteric neurons occur after neuronal injury and in intestinal adaptation. The aim of this study was to evaluate whether VIP and nitric oxide (NO) influence survival of cultured, dissociated myenteric neurons. Neuronal survival was evaluated after 0, 4, and 8 days in culture. Influence of VIP and NO on neuronal survival was examined after culturing in the presence of VIP, NO donor, VIP antiserum, or NOS inhibitor. A marked loss of neurons was noted during culturing. VIP and NO significantly promoted neuronal survival. Corroborating this was the finding of an enhanced neuronal cell loss when cultures were grown in the presence of VIP antiserum or NOS inhibitor.

Pituitary adenylate cyclase-activating polypeptide and vasoactive intestinal peptide inhibit dendritic growth in cultured sympathetic neurons

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are related neuropeptides that are released by the preganglionic sympathetic axons. These peptides have previously been implicated in the regulation of sympathetic neurotransmitter metabolism and cell survival in postganglionic sympathetic neurons. In this study we consider the possibility that PACAP and VIP also affect the morphological development of these neurons. Postganglionic rat sympathetic neurons formed extensive dendritic arbors after exposure to bone morphogenetic protein-7 (BMP-7) in vitro. PACAP and VIP reduced BMP-7-induced dendritic growth by approximately 70-90%, and this suppression was maintained for 3 weeks. However, neither PACAP nor VIP affected axonal growth or cell survival. The actions of PACAP and VIP appear to be mediated by PAC1 receptors because their effects were suppressed by an antagonist that binds to PAC1 and VPAC2 receptors (PACAP6-38), but not by an antagonist that binds to the VPAC1 and VPAC2 receptors. Moreover, exposure to PACAP and VIP caused phosphorylation and nuclear translocation of cAMP response element-binding protein, and agents that increase the intracellular concentration of cAMP mimicked the PACAP-induced inhibition of dendritic growth. These data suggest that peptides released by preganglionic nerves modulate dendritic growth in sympathetic neurons by a cAMP-dependent mechanism.