Origins and Neurochemical Characteristics of Porcine Intervertebral Disc Sympathetic Innervation: a Preliminary Report

Abstract

Intervertebral disc diseases (IVDDs) form a group of a vertebral column disorders affecting a large number of people worldwide. It is estimated that approximately 30% of individuals at the age of 35 and approximately 90% of individuals at the age of 60 and above will have some form of disc-affecting pathological changes leading to disc herniation, prolapse and degeneration as well as discogenic pain. Here, we aimed to establish the origins and neurochemical characteristics of porcine intervertebral disc sympathetic innervation involved in pain signalling in IVDD patients. Pigs were given an injection of the Ominipaque contrast agent and Fast Blue (FB) retrograde tracer into the L4-L5 intervertebral disc and euthanized at 2, 1, and 3 months post injection. Following euthanasia, bilateral sympathetic chain ganglia (SChG) Th13 to C1 were collected. The presence, distribution and neurochemical characteristics of retrogradely labelled SChG neurons were examined. The majority (88.8%) of all FB+ cells were found in the L3-L5 SChG. Most FB+ neurons stained for dopamine beta hydroxylase (DBH); one-third to one-quarter stained for somatostatin (SOM), neuropeptide Y (NPY) or leu-enkephalin (LENK); and only a few stained for galanin (GAL). Compared with the control, the greatest decline in neurochemical immunostaining was observed 2 weeks post injection, and the lowest decline was noticed 1 month post injection. Our study, for the first time, provides insight into the complex patterns of intervertebral disc sympathetic innervation and suggests that the best time for neurochemical balance restoration therapy would be 1 month post-injury, when the neuronal concentration of all studied substances is close to the initial physiological level, thus providing favourable conditions for successful recovery.

Identification of neuropeptide Y in superior cervical ganglion neurons that project to the oesophagus – A combined immunohistochemical labelling and retrograde tracing study in pigs

“…The present study confirms the results of previous studies in which NPY was observed in neurons located within the SCG as an important neuronal factor taking part in the regulation of blood pressure, circadian rhythms and vasoconstriction. The results of previous studies show that NPY is especially important within the autonomic nervous system and the presence of this substance has been described in approximately two-thirds of neurons located in the sympathetic ganglia (Barczewska et al, 2017). The observations made in the present study indicate, for the first time, that NPY is also present in a relatively high percentage of neuronal cells supplying the oesophagus.…”

Adrenoceptor Expression during Intervertebral Disc Degeneration

“…First, we analyzed human tissue homogenates prepared from IVDs with different degrees of degeneration and observed that apart from α1D-and β3-AR, all other AR subtypes were expressed at any stage of degeneration, suggesting that IVD tissue is able to respond to adrenergic stimulation at any time point. This would make sense given the fact that both healthy and degenerating IVD are innervated by sympathetic nerve fibers [17]. The fact that many AR subtypes were detected at the mRNA level is not surprising, because a similar AR expression pattern was described for human articular chondrocytes [24], which exhibit multiple phenotypic similarities to IVD cells [25].…”

“…The expanded type II collagen positive AF area is a clear sign of IVD degeneration. The cells there exhibit a more chondrocytic phenotype and produce enhanced amounts of type II collagen [17]. The increased type XII collagen expression in the AF might also indicate that resident cells try to respond to overloading and ongoing catabolic processes by enhanced matrix synthesis as an attempt to repair the tissue.…”

“…Recently, nerve fiber ingrowth into the IVD during degeneration was observed, however, these studies focused only on sensory nerves [14], on AR expression in dorsal root ganglia [15], or on pain mechanisms [14,16]. The only study on sympathetic nerve fibers in the IVD was performed recently by Barczewska et al, showing that sympathetic nerve fibers are present in lumbar IVDs with pathological changes [17]. At present, still no data exists investigating the expression of ARs in the IVD, which represents a prerequisite for sympathetic neurotransmitter action.…”

Repetitive in vivo manual loading of the spine elicits cellular responses in porcine annuli fibrosi

“…With respect to discogenic pain, the noteworthy decrease in the expression of galanin receptor 3, which binds the nociception-inhibiting neuropeptide galanin [28,29] and reportedly has anti-inflammatory activity [30]. These findings provoke speculation that mechanical load might somehow be involved in intervertebral disc neuroinflammation and nociception, which receives some support with the detection of inflammatory pathways in WGCNA analysis.…”