Upregulation of presynaptic proteins and protein kinases associated with enhanced glutamate release from axonal terminals (synaptosomes) of the medial prefrontal cortex in rats with neuropathic pain

Abstract

Although nerve injury-induced long-term postsynaptic changes have been investigated, less is known regarding the molecular mechanisms within presynaptic axonal terminals. We investigated the molecular changes in presynaptic nerve terminals underlying chronic pain-induced plastic changes in the medial prefrontal cortex (mPFC). After neuropathic pain was induced by spared nerve injury (SNI) in rats, we assessed the release of the excitatory neurotransmitter glutamate by using in vitro synaptosomal preparations from the mPFC. We also measured the levels of synaptic proteins and protein kinases in synaptosomes using Western blotting. The results showed that unilateral long-term SNI augmented depolarization-evoked glutamate release from synaptosomes of the bilateral mPFC. This result was confirmed by a rapid destaining rate of FM1-43 dye in SNI-operated rats. Unilateral long-term nerve injury also significantly increased synaptic proteins (including synaptophysin, synaptotagmin, synaptobrevin, syntaxin, and 25-kDa synaptosome-associated protein) in synaptosomal fractions from the bilateral mPFC, and ultrastructure images demonstrated increased synaptic vesicular profiles in synaptosomes from SNI animals. Chronic pain upregulated the phosphorylation of endogenous protein kinases, including extracellular signal-regulated kinases 1 and 2 (ERK1/2) and Ca(2+)/calmodulin-dependent kinase II (CaMKII), and synapsin I, the primary presynaptic target of ERK1/2 and CaMKII. Both presynaptic proteins and protein kinases were upregulated after SNI in a time-dependent manner. These results indicate that the long-term neuropathic pain-induced enhancement of glutamate release in the mPFC is linked to increased synaptic vesicle proteins and the activation of the ERK1/2- and CaMKII-synapsin signaling cascade in presynaptic axonal terminals.

Intra-nucleus accumbens administration of the calcium/calmodulin-dependent protein kinase II inhibitor AIP induced antinociception in rats with mononeuropathy

“…Studies reported that CaMKII is involved in the pain modulation in the brain [3,8,14]. Using CaMKII RNA-specific interfering RNA to treat visceral hypersensitive rats reduced the visceromotor response to graded colorectal distension.…”

“…Accumulating evidences suggest that CaMKII plays a key role in modulation at different levels of the central nervous system in many types of pain, especially in inflammatory pain, neuropathologic pain, cancer pain, visceral pain and postoperative pain [4,5,8,10,11,14,15,22]. Changes in the expression and activity of CaMKII are accompanied with increases in CaMKII inhibition and pain related behavior; using CaMKII inhibitors, silencing CaMKII gene expression, or delivery of CaMKII antagonist antennapedia-CaMKIINtide, attenuate pain related symptoms and produce analgesic effects in acute and chronic pain.…”

Brain Neuroplastic Changes Accompany Anxiety and Memory Deficits in a Model of Complex Regional Pain Syndrome

“…These data are in agreement with previous findings showing that decreased levels of synaptophysin are accompanied by impairment in cognitive function and memory 84 and vice versa. 85 In contrast, some brain regions (such as the prefrontal cortex) display increased levels of synaptic proteins, 86 including synaptophysin, 87 following chronic painful conditions.…”

Modulation of pain, nociception, and analgesia by the brain reward center

“…The dysfunction of these channels is driven by alterations in the activity of the protein kinase A/cAMP pathway under chronic pain states, thus contributing to the hyperexcitability and persistent firing of pyramidal neurons, which likely affect the perception of pain-like and mood-related symptoms. Neuropathic pain induced by the spared nerve injury model also leads to changes in synaptic proteins involved in mPFC plasticity (Hung et al, 2014). Specifically, spared nerve injury leads to an increase in synaptotagmin, synaptobrevin, and synaptophysin, and promoted time-dependent phosphorylation of extracellular regulated kinases 1 and 2 and CaMKII, as well as an increase in glutamate release.…”