Differential galanin upregulation in dorsal root ganglia and spinal cord after graded single ligature nerve constriction of the rat sciatic nerve

https://doi.org/10.1016/j.jchemneu.2007.07.001Get rights and content

Abstract

Single ligature nerve constriction (SLNC) is a newly developed animal model for the study of neuropathic pain. SLNC of the rat sciatic nerve induces pain-related behaviors, as well as changes in the expression of neuropeptide tyrosine and the Y1 receptor in lumbar dorsal root ganglia (DRGs) and spinal cord. In the present study, we have analyzed the expression of another neuropeptide, galanin, in lumbar DRGs and spinal cord after different degrees of constriction of the rat sciatic nerve. The nerve was ligated and reduced to 10–30, 40–80 or 90% of its original diameter (light, medium or strong SLNCs). At different times after injury (7, 14, 30, 60 days), lumbar 4 and 5 DRGs and the corresponding levels of the spinal cord were dissected out and processed for galanin-immunohistochemistry. In DRGs, SLNC induced a gradual increase in the number of galanin-immunoreactive (IR) neurons, in direct correlation with the degree of constriction. Thus, after light SLNC, a modest upregulation of galanin was observed, mainly in small-sized neurons. However, following medium or strong SLNCs, there was a more drastic increase in the number of galanin-IR neurons, involving also medium and large-sized cells. The highest numbers of galanin-IR neurons were detected 14 days after injury. In the dorsal horn of the spinal cord, medium and strong SLNCs induced a marked ipsilateral increase in galanin-like immunoreactivity in laminae I–II. These results show that galanin expression in DRGs and spinal cord is differentially regulated by different degrees of nerve constriction and further support its modulatory role on neuropathic pain.

Introduction

Single ligature nerve constriction (SLNC) is a newly developed animal model for the study of neuropathic pain (Brumovsky et al., 2004) based on the widely used chronic constriction injury (CCI) model (Bennett and Xie, 1988). However, whereas CCI is achieved with four loose ligatures around the sciatic nerve, SLNC only requires a single ligature. It also has the advantage of permitting different degrees of controlled constriction of the nerve, resulting in three main levels of injury: light, medium or strong, with a reduction of 10–30, 40–80 or 90% of the original diameter of the nerve, respectively. Using this model, it has already been shown that the development of neuropathic pain-related behaviors is dependent on the degree of constriction (Brumovsky et al., 2004). Moreover, intensity-graded SLNCs of the sciatic nerve also induce changes of different magnitude in the expression of neuropeptide tyrosine (NPY) and one of its associated receptors, the Y1 receptor, in primary afferent neurons (Brumovsky et al., 2004).

Galanin, another neuropeptide expressed at low levels by dorsal root ganglion (DRG) neurons (Skofitsch and Jacobowitz, 1985), has also been reported to undergo a strong upregulation after different types of sciatic nerve lesions, such as axotomy, partial nerve transaction (PNT), crush and CCI (Hökfelt et al., 1987, Villar et al., 1989, Nahin et al., 1994, Ma and Bisby, 1997, Zhang et al., 1998, Shi et al., 1999). However, there is no information on galanin expression in primary afferent neurons after graded constrictions of the rat sciatic nerve.

Both pro- and anti-nociceptive effects have been attributed to galanin, probably related to the activation of different receptors (Liu et al., 2001). In fact, three galanin receptors have been cloned so far: GalR1, -R2 and -R3 (Branchek et al., 2000). In normal conditions, both GalR1 and -R2 have been detected in DRGs (see Kerekes et al., 2003) and spinal cord (see Waters and Krause, 2000, Brumovsky et al., 2006).

Since the exact role of galanin in pain processing is not yet fully understood, it seemed relevant to study its expression after sciatic nerve injury, with a different experimental model to the ones used before. For this purpose, we induced different degrees of controlled constriction of the rat sciatic nerve using SLNC, and analyzed galanin-like immunoreactivity (LI) in the lumbar DRGs and the dorsal horn of the spinal cord.

Section snippets

Nerve injury model

Young adult Sprague–Dawley male rats (200–300 g, Fucal, Buenos Aires, Argentina) were anesthetized with chloral hydrate (350 mg/kg, i.p.) and their sciatic nerve was exposed at the mid-thigh level and dissected free from the surrounding tissue. The nerve was then wrapped with a thin square strip (5 mm) of polyethylene and constricted to varying degrees with a tie around the strip using 3.0 silk suture (Barbour Threads, Lisburn, Ireland). In this way, the diameter of the nerve was reduced 10–30%

DRGs

In control ganglia, galanin-LI was restricted to small-sized neurons and could be observed only in 2.3 ± 0.3% of total DRG neurons (Fig. 1, Fig. 2). In contralateral ganglia, no changes in galanin expression could be detected, independently of the degree of constriction and the evaluated survival time (Fig. 1, Fig. 2). SLNC of the sciatic nerve induced a gradual increase in the number of galanin-IR primary afferent neurons, paralleling the degree of constriction, in all the evaluated survival

Discussion

The present results show that the extent of galanin upregulation observed in lumbar DRGs and spinal cord of rats subjected to a sciatic nerve SLNC, is dependent on the degree of the constriction. Thus, a small but still significant increase in the number of galanin-IR neuronal profiles, mostly of small size, was observed after light SLNC. However, following medium or strong SLNCs, there was a more drastic increase in the number of neurons expressing galanin, involving also medium and

Acknowledgements

This work was supported by Austral University, PICTO-CRUP 30930 and Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET). We are grateful to Silvina Ruffolo, Germán Ruffolo and Guillermo Gastón for their skilful technical assistance.

References (33)

Cited by (26)

  • Investigating the potential of GalR2 as a drug target for neuropathic pain

    2023, Neuropeptides
    Citation Excerpt :

    Interestingly, expression was no longer limited to small diameter neurons, with GalR2 expression seen in neurons of all sizes and approximately 35% of the total observed neuronal cells (Chen et al., 2018). The numbers of DRG neurons expressing Galanin in a rat model of sciatic nerve ligation was also observed to proportionally increase with the degree of ligation (Coronel et al., 2008). Galanin was initially detected in small c-fibre neurons, but upon increased severity of injury, its expression was also observed in medium and large neurons.

  • Effects of trigeminal nerve injury on the expression of galanin and its receptors in the rat trigeminal ganglion

    2020, Neuropeptides
    Citation Excerpt :

    In the brain and spinal cord of rats, GAL is expressed in various types of neurons and nerve fiber terminals and associated with modulation of action potentials (Bai et al. 2018; Ch'ng et al. 1985; Simpson et al. 1999; Yue et al. 2011). In the dorsal root ganglion (DRG) and trigeminal ganglion (TG) of rats, GAL is mainly expressed by small sensory neurons that can propagate nociceptive signals (Coronel et al. 2008; Deguchi et al. 2006). Previous studies have reported GAL is involved in the neuropathic pain caused by nerve injury with excitatory and inhibitory effects (Lang et al. 2015).

  • Spinal neuropeptide expression and neuropathic behavior in the acute and chronic phases after spinal cord injury: Effects of progesterone administration

    2017, Peptides
    Citation Excerpt :

    As already mentioned, it has long been known that injury to peripheral nerves induces considerable changes in the expression of galanin, NPY and their associated receptors in primary afferent neurons [8,10,15,9]. Concerning the peptides, their upregulated synthesis in DRG neurons results in increased axonal transport and enhanced like-immunoreactivity in afferent nerve endings in the dorsal horn [36,37]. In contrast, most evidence suggests that galanin and NPY expression levels remain unaffected in spinal cord neurons after peripheral nerve injury [8,10], with the exception of upregulated galanin mRNA levels in the rat dorsal horn after sciatic nerve crush [38].

  • A Mechanistic Approach to the Development of Gene Therapy for Chronic Pain

    2016, International Review of Cell and Molecular Biology
View all citing articles on Scopus
View full text