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. 2017 Jul 27;24(4):191–200. doi: 10.1159/000477604

Nerve Injury Increases the Expression of Alpha-2/Delta-1 Subunit of L-Type Calcium Channel in Sensory Neurons of Rat Spinal and Trigeminal Nerves

Daisuke Tachiya 1,*, Tadasu Sato 1, Hiroyuki Ichikawa 1
PMCID: PMC5969352  PMID: 29849442

Abstract

By immunohistochemistry, an effect of nerve injury on distribution of alpha-2/delta-1 subunit of L-type calcium channel was investigated in rat's 4th and 5th lumbar dorsal root ganglia (DRGs), trigeminal ganglion (TG), and mesencephalic trigeminal nucleus (Mes5). The immunoreactivity was expressed by 52.2% of DRG neurons and 31.4% of TG neurons in intact animals. These neurons mostly had small-to-medium-sized cell bodies. In the DRG and TG, alpha-2/delta-1 subunit-positive neurons were lightly or moderately stained. However, the number of alpha-2/delta-1 subunit-immunoreactive (-IR) neurons dramatically increased in the ipsilateral DRG at 3-28 days after sciatic nerve transection (75.3-79.5%) and in the ipsilateral TG at 7 days after infraorbital nerve transection (66.3%). The IR density of alpha-2/delta-1 subunit in DRG and TG neurons was also elevated by the transection. In the injured DRG and TG, many sensory neurons with small-to-medium-sized cell bodies were strongly stained. Some large DRG and TG neurons showing strong staining intensity also appeared after the treatment. In the intact Mes5, sensory neurons were mostly devoid of alpha-2/delta-1 subunit-immunoreactivity (0.4%). However, alpha-2/delta-1-IR sensory neurons on the ipsilateral side of the Mes5 dramatically increased at 7 days after masseteric nerve transection (31.3%). A double immunofluorescence method also demonstrated that c-Jun activating transcription factor 3 (ATF3)-positive DRG (98.3-99.9%) and Mes5 (81.8%) neurons mostly co-expressed alpha-2/delta-1 subunit after the nerve injuries. However, alpha-2/delta-1 subunit immunoreactivity was relatively infrequent among ATF3-immunonegative DRG neurons (51.6-74.1%) and Mes5 neurons (<1%). The present study indicates that the nerve injury increases the protein level of alpha-2/delta-1 subunit among several types of axotomized sensory neurons in the spinal and trigeminal nervous systems.

Keywords: Dorsal root ganglion, L-type calcium channel complex, Alpha-2/delta-1 subunit, Nerve injury, Rat, Immunohistochemistry

Introduction

The alpha-2/delta-1 subunit is a high-molecular polypeptide subunit of the L-type voltage-dependent calcium channel complex. This subunit is located in muscle and neuronal cells, and plays a role in intracellular calcium release [1,2]. Previous studies have demonstrated the presence and distribution of this subunit in the sensory ganglion of spinal nerves [3,4]. In the dorsal root ganglion (DRG), alpha-2/delta-1 subunit is localized to small-to-medium-sized neurons [4]. Large DRG neurons are mostly free from the protein or mRNA. In the spinal cord, alpha-2/delta-1 subunit-containing nerve terminals are abundant in the superficial laminae of the dorsal horn, a projection site of nociceptive afferents in the DRG. Thus, alpha-2/delta-1 subunit-containing small- and medium-sized DRG neurons transmit nociceptive information to the superficial dorsal horn [5,6,7].

Sensory neurons innervating oral and craniofacial structures are located in the trigeminal ganglion (TG) and mesencephalic trigeminal nucleus (Mes5). In the TG, small- and medium-sized neurons project their central terminals to superficial laminae of the spinal trigeminal nucleus, and are thought to transduce nociceptive information [8,9,10]. Large TG neurons transmit mechanoreceptive information to the brainstem, whereas Mes5 neurons participate in proprioceptive information [10,11,12]. In a previous immunohistochemical study, alpha-2/delta-1 subunit-containing terminals are dense in the brainstem spinal trigeminal nucleus [4]. Such terminals are sparse in other portions of brainstem trigeminal sensory nuclei. However, the distribution of the subunit has never been reported in sensory neurons of the trigeminal system.

Peripheral nerve injuries have several effects on sensory neurons in the DRG and TG. Transection of sciatic and infraorbital nerves results in increase of DRG and TG neurons, which express c-Jun activating transcription factor 3 (ATF3), a marker for injured neurons [13,14,15]. By Western blotting analysis, sciatic nerve chronic constriction injury, spinal nerve transection, and ligation elevated the alpha-2/delta-1 subunit protein level in the DRG and spinal cord [6,7]. It is suggested that increase of this subunit is associated with neuropathic pain in the animal models. In addition, in situ hybridization histochemical study has demonstrated that partial sciatic nerve ligation increases alpha-2/delta-1 subunit mRNA level in small and large DRG neurons [16]. However, ATF3-positive neurons are infrequent after the partial ligation of the sciatic nerve compared to sciatic nerve transection [13]-[15]. And, it is unclear whether alpha-2/delta-1 subunit is expressed by injured or uninjured DRG neurons with small or large cell bodies. In the TG, a previous study using Western blots has demonstrated that chronic constriction of the infraorbital nerve increases in the protein level of alpha-2/delta-1 subunit [17]. However, little is known about the effect of nerve transection on the expression of the subunit in TG neurons or Mes5 neurons.

To know changes of alpha-2/delta-1 subunit in injured DRG, TG, and Mes5 may facilitate understanding the function of the subunit in the spinal and trigeminal sensory system.

In this study, we examine the change of alpha-2/delta-1 subunit-immunoreactivity in the rat DRG, TG, and Mes5 after transection of sciatic, infraorbital, and masseteric nerves. Double immunofluorescence study for alpha-2/delta-1 subunit and ATF3 was also performed to know their co-expression in axotomized DRG and Mes5 neurons.

Materials and Methods

Specimens

A total of 44 male Wistar rats (180-250 g) were used in this study. Transection of the unilateral sciatic, infraorbital, and masseteric nerves was performed on 24 animals under deep anesthesia by i.p. injection with pentobarbital sodium (64.8 mg/kg). The left nerves were exposed through incision of the skin and subcutaneous layer and transected using microscissors with the transected proximal stump ligated using 4-0 silk (Sofsilk®, USA) to inhibit spontaneous reconnection and regeneration. Control groups comprised intact animals (n = 8) and sham-operated animals (n = 12) in which the left nerves were exposed without nerve injury.

At various survival periods after transection of sciatic (1, 3, 7, and 28 days), infraorbital (7 days), and masseteric (7days) nerves, the rats were deeply anesthetized by isoflurane inhalation to the level at which respiration was markedly suppressed and perfused through the left ventricle with saline for 20-40 s for exsanguination followed by Zamboni fixative (n = 4 at each post-injury interval) [18]. Left 4th and 5th lumbar DRGs, TGs, and brainstems containing the Mes5 were dissected and further fixed in the same fixative overnight at 4°C. The materials were cryoprotected by immersing until sunken in 0.02 M phosphate-buffered saline containing 20% sucrose (pH 7.4), and serially frozen-sectioned at 8 μm thickness. Complete series of sections were divided into 10 subsets for the DRG and 20 subsets for the TG and Mes5. Every 10 and 20th sections of the DRG, and the TG and Mes5, respectively, were stained for alpha-2/delta-1 subunit or both alpha-2/delta-1 subunit and ATF3.

The experiments were carried out under the control of the Animal Research Control Committee in accordance with the Guidelines for Care and Use of Laboratory Animals in Tohoku University, and the Japanese Government Notification on Feeding and Safekeeping of Animals (No. 6). All efforts were made to minimize the number of animals used and the intensity of their suffering.

Immunohistochemistry

For demonstrating distributional changes of alpha-2/delta-1 subunit, the sections were incubated with mouse monoclonal antibody against rabbit alpha-2/delta-1 subunit (1:1,000, abcam, United Kingdom) for 24 h at room temperature, biotinylated rabbit anti-mouse immunoglobulin G (IgG) (Vector Laboratories, USA) and avidin-biotin-horseradish peroxidase complex (Vector Laboratories). Following nickel ammonium sulfate-intensified diaminobenzidine reaction, the sections were dehydrated in a graded series of alcohols, cleared in lemosol, and cover-slipped with Softmount (Wako Pure Chemical Industries, Ltd., Japan).

For simultaneous visualization of ATF3 and alpha-2/delta-1 subunit, a double immunofluorescence method was used. Sections of the DRG and Mes5 were incubated for 24 h at room temperature with a mixture of rabbit antiserum against human ATF3 (1:1,000, Peninsula, USA) and mouse monoclonal alpha-2/delta-1 subunit antibody (1:100). The sections were then treated with a mixture of fluorescein isothiocyanate-conjugated donkey anti-rabbit IgG (1:100; Jackson ImmunoResearch Labs, USA) and lissamine rhodamine Red™-X-conjugated donkey anti-mouse IgG (1:300, Jackson ImmunoResearch Labs) for 2 h at room temperature. Specificities of antibodies used in this study have been described elsewhere [4,19]. For negative controls, in addition, primary antibodies were omitted from the immunohistochemical procedures. No staining was observed in the control.

Morphometric Analysis

For morphometric analysis of alpha-2/delta-1 subunit-containing neurons, 3 sections of the DRG and TG were randomly selected in each animal. The microscopic image of these sections was captured with a digital camera (DS-Ri1, Nikon, Japan), and stored into a computer (Z400 Workstation, Hewlett-Packard, Japan). The average proportion of such neurons was recorded for each animal. For cell size analysis of alpha-2/delta-1 subunit-containing DRG and TG neurons, the cross-sectional area of positive and negative cell bodies that contained the nucleolus was measured to avoid examination of cell body peripheries. The outline of each neuronal cell body was drawn with a computer mouse (Hewlett-Packard) on the image of microscopic fields. The pixel number within outlines was converted into the area of neuronal cell bodies by Lumina Vision program software (Mitani Corporation, Japan). Optical densities of alpha-2/delta-1 subunit-positive DRG and TG neurons and background (negative neurons) were also measured by the same software. The density of positive neurons in the ipsilateral DRG and TG was divided by the background density. The quotient was recorded for each positive neuron and will be hereafter referred to as the immunoreactive (IR) density. Data for the IR density were obtained from 3 sections of each DRG and TG from 16 animals at 7 days after nerve transection or sham operation. Data about 4 and 5th lumbar DRGs were combined in intact, sham-operated, and sciatic nerve-transected animals.

Results

Effect of Nerve Transection on Alpha-2/Delta-1 Subunit

Sensory neurons expressed alpha-2/delta-1 subunit immunoreactivity in the DRG (52.2 ± 5.3%; Fig. 1a, d) and TG (31.4 ± 1.4%) of intact animals. The IR products were localized to the cytoplasm and cytoplasmic membrane of these neurons. Proportions of alpha-2/delta-1 subunit-IR neurons were similar in intact and sham-operated DRGs (mean proportion ± SD = 50.2 ± 4.3%, n = 4) and TGs (33.1 ± 5.9%, n = 4). However, sciatic nerve transection increased the number of alpha-2/delta-1 subunit-IR neurons in the ipsilateral DRG (Fig. 1b-d). In the injured DRG, the means ± SD of the percentage proportion of alpha-2/delta-1 subunit-IR neurons at 1, 3, 7, and 28 days were 66.0 ± 6.9, 78.0 ± 3.0, 79.5 ± 12.1, and 75.3 ± 2.4% respectively. Data were obtained from 4 animals at each stage. Transection of the infraorbital nerve also increased the proportion of alpha-2/delta-1 subunit-IR neurons in the ipsilateral TG (66.3 ± 9.7%, n = 4). The difference between intact and sham-operated animals, and animals with sciatic and infraorbital nerve transection was statistically significant (Tukey's test, p < 0.05; Fig. 1d).

Fig. 1.

Fig. 1

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Microphotographs for alpha-2/delta-1 subunit in the intact DRG (a) and the DRG at 3 days (b) and 28 days (c) after sciatic nerve transection. Sciatic nerve transection greatly increases the number of alpha-2/delta-1 subunit-IR neurons (b, c) compared to intact animals (a). d A line graph showing proportions of alpha-2/delta-1 subunit-IR neurons in the intact DRG (0 days) and the DRG at 1, 3, 7, and 28 days after the transection. The difference between intact animals and animals at 3, 7, and 28 days after the nerve injury was statistically significant (Tukey's test, p < 0.05). Bar = 400 μm (a). a-c are at the same magnification.

Cell size analysis demonstrated that more than half of small neurons (<600 μm2) were IR for alpha-2/delta-1 subunit in the ipsilateral DRG (78.0%, 828/1,062) and TG (55.8%, 206/369) at 7 days after the sham operation (Fig. 2a, c, 3a, c). Half (441/753) and one third (212/633) of medium-sized (600-800 μm2) DRG and TG neurons, respectively, contained alpha-2/delta-1 subunit immunoreactivity. Approximately 10% of large neurons (>1,200 μm2) expressed the immunoreactivity in the DRG (136/936) and TG (25/288; Fig. 2c, 3c). The cell size distribution of alpha-2/delta-1 subunit-IR neurons appeared to be similar in sham-operated and intact DRGs and TGs. However, sciatic and infraorbital nerve transection dramatically increased the number of alpha-2/delta-1 subunit-IR neurons with medium-sized to large cell bodies in the ipsilateral DRG and TG, respectively (Fig. 2b, 3b). At 7 days after the nerve injuries, small DRG and TG neurons mostly showed 2/delta-1 subunit-immunoreactivity (DRG, 92.2%, 1305/1416; TG, 89.3%, 394/441). More than 70% of medium-sized neurons expressed alpha-2/delta-1 subunit-immunoreactivity in the DRG (991/1206) and TG (688/946). Large DRG (64%; 686/1078) and TG neurons (39.9%; 250/626) contained the immunoreactivity (Fig. 2d, 3d).

Fig. 2.

Fig. 2

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Microphotographs for alpha-2/delta-1 subunit in the DRG at 7 days after sham operation (a) and sciatic nerve transection (b). Sciatic nerve transection causes an increase in the number and IR density of alpha-2/delta-1 subunit-positive DRG neurons (b) compared to sham operation (a). Bar = 200 μm (a). a, b are at the same magnification. c, d Histograms showing cell size spectra of alpha-2/delta-1 subunit-IR and immunonegative neurons in sham-operated C and injured D DRGs. Data for sham operation and sciatic nerve transection were obtained from 2745 and 3698 DRG neurons, respectively. e, f Point graphs showing correlation between the cell size and IR density of alpha-2/delta-1 subunit-positive neurons in sham-operated E and injured (f) DRGs. Data for sham operation and sciatic nerve transection were obtained from 1398 and 2957 alpha-2/delta-1 subunit-positive neurons, respectively.

Fig. 3.

Fig. 3

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Microphotographs for alpha-2/delta-1 subunit in the TG at 7 days after sham operation (a) and infraorbital nerve transection (b). Infraorbital nerve transection causes an increase in the number and IR density of alpha-2/delta-1 subunit-positive TG neurons (b) compared to sham operation (a). Bar = 200 μm (a). a, b are at the same magnification. c, d indicate histograms showing cell size spectra of alpha-2/delta-1 subunit-IR and immunonegative neurons in sham-operated (c) and injured (d) TGs. Data for sham operation and infraorbital nerve transection were obtained from 1290 and 2013 TG neurons, respectively. e, f indicate point graphs showing correlation between the cell size and IR density of alpha-2/delta-1 subunit-positive neurons in sham-operated (e) and injured (f) TGs. Data for sham operation and infraorbital nerve transection were obtained from 443 and 1,332 alpha-2/delta-1 subunit-positive neurons, respectively.

By densitometric analysis, most of alpha-2/delta-1 subunit-IR neurons were weakly (the IR density <1.25) or moderately (the IR density = 1.25-1.5) stained in the ipsilateral DRG and TG of sham-operated animals (Fig. 2e, 3e). The staining pattern was similar in sham-operated and intact DRGs and TGs. However, the nerve injuries increased the IR density in the ipsilateral DRG and TG (Fig. 2b, 3b). As a result, strong immunoreaction (the IR density >1.5) was detected in medium-sized to large DRG neurons after sciatic nerve transection. And many sensory neurons with medium-sized cell bodies were strongly stained in infraorbital nerve-transected TG (Table 1, 2).

Table 1.

IR density of alpha-2/delta-1-positive DRG neurons after sciatic nerve transection

n Staining intensity
weak, % moderate, % strong, %
Sham operation
 Small 828 47.6 50.4 2.0
 Medium-sized 441 82.5 17.5 0
 Large 136 99.3 0.7 0
Sciatic nerve transection
 Small 1,305 20 40.1 39.9
 Medium-sized 991 36.1 33.1 30.8
 Large 686, 44.2 32.5 23.3
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The number within each parenthesis indicates the raw number of positive DRG neurons analyzed for each cell size category. The data were obtained from 4 sham-operated and 4 transected animals.

Table 2.

IR density of alpha-2/delta-1-positive TG neurons after ION transection

n Staining intensity
weak, % moderate, % strong, %
Sham operation
 Small 206 46.1 31.1 22.8
 medium-sized 212 55.2 41.5 3.3
 Large 25 96 4 0
ION transection
 Small 394 31.7 29.2 39.1
 Medium-sized 688) 48.0 27.6 24.4
 Large 250 73.2 23.6 3.2
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The number within each parenthesis indicates the raw number of positive TG neurons analyzed for each cell size category. The data were obtained from 4 sham-operated and 4 transected animals.

Sensory neurons were mostly devoid of alpha-2/delta-1 subunit-immunoreactivity in intact (0.4 ± 0.4%, n = 4) and sham-operated (0%, n = 4) Mes5s (Fig. 4a). However, alpha-2/delta-1-IR Mes5 neurons dramatically increased on the ipsilateral side to masseteric nerve transection; 31.3 ± 9.1% (n = 4) of Mes5 neurons were IR for the subunit after the injury (Fig. 4b). These neurons were scattered throughout the Mes5, and showed weak or moderate staining intensity. The difference between intact and sham-operated Mes5s, and Mes5s with masseteric nerve transection was statistically significant (Tukey's test, p < 0.05).

Fig. 4.

Fig. 4

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Microphotographs for alpha-2/delta-1 subunit in the Mes5 at 7 days after sham operation (a) and masseteric nerve transection (b). In sham-operated animals, almost all Mes5 neurons lack alpha-2/delta-1 subunit-immunoreactivity (a). However, many alpha-2/delta-1 subunit-IR neurons appear in the Mes5 on the side ipsilateral to masseteric nerve transection (b). Bar = 200 μm (a). a, b are at the same magnification.

Co-Expression of Alpha-2/Delta-1 Subunit and ATF3

ATF3-IR neurons were very rare in the DRG and Mes5 of intact and sham-operated animals. On the ipsilateral and contralateral side to sham operations, only 3.5 ± 2.6% (n = 4) and 1.9 ± 1.8% (n = 4) of sensory neurons were IR for ATF3 (Fig. 5a-c, g-i). However, nerve injuries dramatically increased the number of ATF3-IR neurons in the ipsilateral DRG and Ms5 (Fig. 5d). In the DRG, numerous sensory neurons expressed ATF3-immunoreacitivity at 1 day (mean ± SD 51.4 ± 10.8%, n = 4), 3 days, (37.5 ± 7.4%, n = 4), 7 days (64.5 ± 5.5%, n = 4), and 28 days (50.6 ± 10.1%, n = 4) after sciatic nerve transection. On the ipsilateral side of the Mes5, 37.5 ± 14.6% of sensory neurons expressed ATF3-immunoreactivity at 7 days after masseteric nerve transection (Fig. 5j). The double immunofluorescence method revealed co-expression of alpha-2/delta-1 subunit and ATF3 in the injured DRG and Mes5 (Fig. 5a-f). At 1 day after sciatic nerve transection, half (mean ± SD, 57.0 ± 5.0%) of ATF3-IR DRG neurons showed alpha-2/delta-1 subunit immunoreactivity. However, virtually all ATF3-IR DRG neurons were IR for alpha-2/delta-1 subunit at 3-28 days (3 days, 98.3 ± 1.5%; 7 days, 97.2 ± 1.0%; 28 days 99.9 ± 0.2%) after the nerve injury. And 46.5 ± 11.5, 44.3 ± 9.6, 74.4 ± 5.1, and 60.8 ± 10.7% of alpha-2/delta-1 subunit-IR DRG neurons contained ATF3-immunoreactivity at 1, 3, 7, and 28 days, respectively, after sciatic nerve transection (Fig. 5d-f). In contrast, more than half of ATF3-immunonegative DRG neurons contained alpha-2/delta-1 subunit immunoreactivity (1 day, 69.7 ± 5.1%; 3 days, 74.1 ± 7.6%; 7 days, 51.6 ± 4.4%; 28 days, 64.7 ± 8.0%). At 7days after masseteric nerve transection, 81.8 ± 16.4% (n = 4) of ATF3-IR neurons co-expressed alpha-2/delta-1 subunit-immunoreactivity on the ipsilateral side of the Mes5 (Fig. 5j-l). Almost all of alpha-2/delta-1 subunit-IR Mes5 neurons were IR for ATF3 (98.9 ± 2.3%, n = 4). Less than 1% (0.9 ± 1.8%, n = 4) of ATF3-immunonegative Mes5 neurons expressed alpha-2/delta-1 subunit-immunoreactivity.

Fig. 5.

Fig. 5

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Microphotographs for ATF3 (a, d, g, j) alpha-2/delta-1 subunit (b, e, h, k) and both (c, f, i, l) in the DRG (a-f) and Mes5 (g-l) at 7 days after sham operation (a-c), (g-i), and nerve injuries (d-f), (j-l). a-c, d-f, g-i, and j-l show the same fields of view, respectively. Co-expression of ATF3 and alpha-2/delta-1 subunit is very rare in the DRG (a-c) and Mes5 (g-i) of sham-operated animals. However, sciatic and masseteric nerve transection induces their co-expression in DRG (d-f) and Mes5 (arrows in j-l), respectively. Bar = 100 μm (a) and 50 μm (g). a-f and g-l are at the same magnifications.

Discussion

Primary sensory neurons are classified into several types on the basis of their cell sizes and peripheral distributions by immunohistochemistry [20,21,22,23,24,25,26,27,28]. In the DRG and TG, small- and medium-sized nociceptors have unmyelinated or finely myelinated axons, and terminate as free nerve endings in their peripheral receptive fields [20,21,23,26,27,29]. Large mechanoreceptors in these ganglia have thick myelinated axons and corpuscular endings in the skin and oral mucosa [22,24,25,28,30,31]. Large proprioceptors in the DRG innervate muscle spindles in the spinal nervous system. In the trigeminal nervous system, proprioceptors in the Mes5 innervate masseteric muscles and periodontal ligaments. In this study, small-to-medium-sized neurons in the intact DRG and TG contained alpha-2/delta-1 subunit-immunoreactivity [3,4]. Therefore, alpha-2/delta-1 subunit is probably expressed by nociceptive afferents in the spinal and trigeminal nervous systems. In intact animals, however, the subunit was infrequent among large DRG and TG neurons, and Mes5 neurons. It is likely that spinal and trigeminal mechanoreceptors and proprioceptors are mostly devoid of alpha-2/delta-1 subunit.

Transection of sciatic and infraorbital nerves increased the number of alpha-2/delta-1 subunit-containing DRG and TG neurons in all cell size categories. In addition, many alpha-2/delta-1 subunit-containing neurons appeared in the Mes5 after masseteric nerve transection. The present densitometric analysis also demonstrated that sciatic and infraorbital nerve transection increased the number of small- and medium-sized DRG and TG neurons, which were strongly stained. The staining intensity in large DRG and TG neurons was also elevated by the nerve transection. These findings suggest that the nerve injuries increase the synthesis capacity of alpha-2/delta-1 subunit in various types of spinal and trigeminal sensory neurons. In addition, ATF3-IR DRG and Mes5 neurons mostly co-expressed alpha-2/delta-1 subunit immunoreactivity after sciatic and masseteric nerve transection. The alpha-2/delta-1 subunit-immunoreactivity was relatively infrequent among ATF3-immunonegative neurons in the injured DRG. In the injured Mes5, ATF3-immunonegative neurons were mostly devoid of alpha-2/delta-1 subunit-immunoreactivity. It is likely that the expression of alpha-2/delta-1 subunit is elevated in injured sensory neurons but not uninjured sensory neurons after transection of spinal and trigeminal nerves.

The alpha-2/denta-1 subunit was localized to the cytoplasm and cytoplasmic membrane of DRG, TG, and Mes5 neurons with or without nerve injury. In the cytoplasmic membrane, this subunit is associated with calcium channel trafficking and calcium channel function [32]. In addition, this subunit can bind to the extracellular matrix proteins of the thrombospondin family and is necessary for synapse formation induced by thrombospondin [33,34]. The alpha-2/denta-1 subunit in the cytoplasm of axotomized neurons may accelerate synaptogenesis for neuronal regeneration and plasticity. It is possible that alpha-2/denta-1 subunit has both extracellular and intracellular functions in several types of injured sensory neurons in the spinal and trigeminal nervous systems.

Disclosure Statement

The authors do not have any conflicts of interest to disclose.

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