IL-1ra alleviates inflammatory hyperalgesia through preventing phosphorylation of NMDA receptor NR-1 subunit in rats

Abstract

Although it has been shown that pro-inflammatory cytokines such as interleukin-1beta (IL-1beta) facilitate perception of noxious inputs at the spinal level, the mechanisms have not been understood. This study determined the cell type that produces IL-1beta, the co-localization of IL-1 receptor type I (IL-1RI) and Fos and NR1 in the spinal cord, and the effects of IL-1 receptor antagonist (IL-1ra) on NR1 phosphorylation and hyperalgesia in a rat model of inflammatory pain. Phosphorylation of NR1, an essential subunit of the NMDA receptor (NMDAR), is known to modulate NMDAR activity and facilitate pain. Hyperalgesia was induced by injecting complete Freund's adjuvant (CFA, 0.08ml, 40microg Mycobacterium tuberculosis) into one hind paw of each rat. Paw withdrawal latency (PWL) was tested before CFA (-48h) for baseline and 2 and 24h after CFA to assess hyperalgesia. IL-1ra was given (i.t.) 24h before CFA to block the action of basal IL-1beta and 2h prior to each of two PWL tests to block CFA-induced IL-1beta. Spinal cords were removed for double immunostaining of IL-1beta/neuronal marker and IL-1beta/glial cell markers, IL-1RI/Fos and IL-1RI/NR1, and for Western blot to measure NR1 phosphorylation. The data showed that: (1) astrocytes produce IL-1beta, (2) IL-1RI is localized in Fos- and NR1-immunoreactive neurons within the spinal dorsal horn, and (3) IL-1ra at 0.01mg/rat significantly increased PWL (P<0.05) and inhibited NR1 phosphorylation compared to saline control. The results suggest that spinal IL-1beta is produced by astrocytes and enhances NR1 phosphorylation to facilitate inflammatory pain.

Endogenous Interleukin-1β in Neuropathic Rats Enhances Glutamate Release from the Primary Afferents in the Spinal Dorsal Horn through Coupling with Presynaptic N-Methyl-d-aspartic Acid Receptors*

“…Surprisingly, only a handful of studies directly address the impacts created by these cytokines on spinal glutamatergic synaptic activities. In a rat model of inflammatory pain induced by injecting complete Freund's adjuvant, IL-1␤ produced by activated astrocytes increased phosphorylation of NMDA receptors in the spinal dorsal horn (62). In another model of inflammatory pain induced by carrageenan, it was demonstrated that elevated levels of TNF␣ in the spinal dorsal horn increase AMPA receptor activities by enhancing trafficking of AMPA receptors from the cytosol to the membrane (63).…”

Neuroplasticity of ascending and descending pathways after somatosensory system injury: reviewing knowledge to identify neuropathic pain therapeutic targets

“…This process is because of most of the inflammatory mediators released by reactive microglia interacting with membrane receptors of nociceptive second-order projection neurons in the dorsal horn of the spinal cord, causing hyperexcitability and sensitization among them. [47][48][49][50] It is important to mention that traumatic spinal cord injury also induces spinal microglial cell reactivation, which leads to an increase of inflammatory mediators and hyperexcitability in spinal nociceptive projection neurons. 18 After microglial cell reactivation is produced by an injury in the nociceptive somatosensory system, a long-standing reactivation of spinal astrocytes occurs (4150 days post-injury), inducing hypertrophy within (increase in vimentin and GFAP glial fibrillary acidic cytoskeleton proteins) and a release of inflammatory mediators that contribute to hyperexcitability and sensitization of nociceptive neurons in the dorsal horn of the spinal cord.…”

“…18 After microglial cell reactivation is produced by an injury in the nociceptive somatosensory system, a long-standing reactivation of spinal astrocytes occurs (4150 days post-injury), inducing hypertrophy within (increase in vimentin and GFAP glial fibrillary acidic cytoskeleton proteins) and a release of inflammatory mediators that contribute to hyperexcitability and sensitization of nociceptive neurons in the dorsal horn of the spinal cord. [47][48][49][50][51] On the other hand, neuropathic pain is also promoted by spinal cord injury. It is well known that spinal cord injury causes the astrocyte and microglial cell reactivation and the generation and release of several soluble factors such as cytokines (IL1, IL6 and TNF-alpha), chemokines (CCL2) and prostaglandins (PGE2) that interact with nociceptive projection neurons and afferent primary nerve fibers at the dorsal horn of spinal cord segments located rostral and caudal to the lesion site, causing hyperexcitability of these nociceptive neurons and pain neurotransmission in the dorsal horn.…”

Electroacupuncture Inhibits Spinal Interleukin-17A to Alleviate Inflammatory Pain in a Rat Model

“…These cells produces a number of algesic substances such as the proinflammatory cytokines interleukin 1 beta (IL-1β), tumor necrosis factor alpha (TNF-α), and IL-6 to promote spinal transmission and processing of noxious signals [1,2]. It is reported that IL-1β is up-regulated in spinal astrocytes to increase NMDA NR1 phosphorylation, an essential subunit of the N-methyl Daspartate receptor (NMDAR), which in turn promote pain in an inflammatory pain rat model [3][4][5][6] . IL-17A, recently found in astrocytes of patients with multiple sclerosis [7], increase in concentration in the spinal cord of rats with nerve injury [8].…”