Table 2.

Summary of the alterations of autophagic activities in the spinal cord after nerve injury in different models of rats and mice.

Reference	Animal Models	Western Blot Findings	IHC Findings	Effects of Therapeutic Agents
Increased autophagic activities in the spinal cord neurons, decreased autophagic activities in the spinal cord microglia and astrocytes after nerve injury, and autophagy acts as a pain suppressor.
Berliocchi et al., 2011 [30], 2015 [31]	Mice with chronic constriction injury (CCI), spared nerve injury (SNI), and spinal nerve ligation (SNL).	LC3-II and p62 increased in the mice with spinal nerve ligation (SNL) on day 7 after nerve injury. LC3-II increased in the mice with spared nerve injury (SNI) on day 14 after nerve injury. Beclin-1 increased in the mice with chronic constriction injury (CCI) on day 14 after nerve injury.	Autophagic proteins (p62) were co-stained with NeuN in the spinal cord.	Intrathecal chloroquine (can inhibit autophagic flux and block the late stage of autophagy) enhanced pain behavior.
Chen et al., 2018 [32]	Rats with chronic constriction injury (CCI).	LC3-II and Beclin-1 increased from day 1 to day 7 (peak at day 3) after nerve injury. p62 decreased from day 1 to day 7 after nerve injury.	Nil.	Intraperitoneal rapamycin before chronic constriction injury suppressed pain behavior, upregulated LC3-II/Beclin-1 expressions, and suppressed astrocyte activation in the spinal cord. 3-MA showed the opposite effect.
Liu et al., 2020 [33]	Rats received streptozotocin (STZ) injection (diabetic rats).	p-PI3K, p-AKT, and p-mTOR decreased, but LC3-II and Beclin1 increased 3 weeks after STZ injection.	Nil.	Intravenous PI3K inhibitor (LY294002) suppressed pain behavior and increased LC3-II expressions in the spinal cord of diabetic rats.
Jin et al., 2018 [35]	Rats with chronic constriction injury (CCI).	LC3-II/I ratio and p62 increased on day 9 after nerve injury. (The authors suggested that increased LC3-II indicated that autophagic flux was blocked in the late stage of autophagy and concluded that autophagic activities in the spinal cord decreased after nerve injury.)	Autophagic proteins (LC3) were co-stained with GFAP in the spinal cord.	Subcutaneously (s.c.) Koumine treatment suppressed pain behavior, upregulated autophagic activities, and downregulated proinflammatory cytokine expressions in the spinal cord of rats with CCI. Intrathecal chloroquine (autophagy inhibitor) blocked the effects of Koumine.
Wang et al., 2020 [36]	Rats with spared nerve injury (SNI).	LC3-II decreased but triggering receptor expressed on myeloid cells 2 (TREM2), p62, and proinflammatory cytokine increased on day 7 after nerve injury.	Nil.	Intrathecal resveratrol treatment (suppressed TREM2 expressions) suppressed pain behavior, suppressed proinflammatory cytokine, and increased LC3-II expressions in the spinal cord. 3-MA (autophagy suppressor) reduced the analgesic effects of resveratrol.
Hu et al., 2021 [37]	Rats with spared nerve injury (SNI).	LC3-II decreased, but Beclin-1 and p62 increased from day 7 to day 14 after nerve injury.	Nil.	Intravenous rapamycin treatment decreased pain behavior, increased LC3-II expressions and autophagosome number in the spinal cord, and suppressed C- and A-fiber-evoked field potentials from day 7 to day 14 after nerve injury.
Shi et al., 2013 [34]	Rats with spinal nerve ligation (SNL).	LC3-II/LC3-1 ratio of the primary microglia culture isolated from rats with SNL decreased from day 2 to day 14 after nerve injury. P62 of the primary microglia culture isolated from rats with SNL increased from day 5 to day 14 after nerve injury.	Autophagic proteins (LC3-II) were co-stained with Iba1 in primary microglia culture.	Intrathecal administration of microRNA-195 inhibitor reduced the pain behavior of rats with SNL and increased the LC3-II/LC3-I ratio in the spinal dorsal horn.
Li et al., 2021 [38]	Mice with spinal nerve ligation (SNL).	LC3-II/LC3-I ratio and Atg5 expressions decreased, but SQSTM1/p62 (autophagy receptor) increased from day 7 to day 28 after nerve injury.	SQSTM1 was mainly co-stained with GFAP rather than NeuN. Electron microscopic studies showed the number of autophagosomes decreased, mainly in the astrocyte of mice with SNL.	Intrathecal rapamycin treatment on day 7 to day 9 after nerve injury suppressed pain behavior on day 10 and day 14 after nerve injury and increased LC3-II/LC3-I ratio in the spinal cord. 3-MA showed the opposite effects.
Increased autophagic activities in the spinal cord neurons and microglia after nerve injury, and autophagy acts as a pain enhancer.
Cai et al., 2020 [42]	Rats with chronic constriction injury (CCI).	LC3-II, circular RNAs-7 (ciRS-7), and proinflammatory cytokines (IL-6, IL-12, TNF-α) levels increased from day 7 to day 20 after nerve injury.	Nil.	Intrathecal si-ciRS-7 treatment suppressed pain behaviors and decreased autophagic proteins (LC3-II) and proinflammatory cytokines (IL-12, TNF-α) expressions.
Zhang et al., 2013 [39]	Rats with spinal nerve ligation (SNL).	Nil.	Autophagic proteins (LC3 and Beclin-1) were co-stained with NeuN and Calretinin (a marker of GABAergic interneurons) in the spinal dorsal horn and increased on day 14 after nerve injury.	Intrathecal 3-MA 3 days after SNL decreased pain behavior from day 7 to day 10 after nerve injury.
Ma et al., 2016 [40]	Rats with spinal nerve ligation (SNL).	LC3-II of the primary microglia culture isolated from the rats that received SNL increased on day 10 after nerve injury.	Nil.	Intrathecal administration of modified citrus pectin (a kind of anti-inflammatory protein) suppressed pain behavior of rats with SNL, and rapamycin reversed those effects.
Weijia Chen et al., 2017 [41]	Rats with spinal nerve ligation (SNL).	LC3-II of the primary microglia culture isolated from the rats with SNL increased but p62 levels decreased on day 10 after nerve injury.	Autophagic proteins (LC3) were co-stained with Iba-1 (microglia marker) in the spinal cord.	Intrathecal TLR-3 agonist enhanced pain behavior of rats with SNL and increased autophagy and proinflammatory cytokines (IL-1β and TNF-α) expressions in the dorsal horn of rats with SNL. Intrathecal 3-MA administration reversed previous findings.