Bone fracture at the acute stage of stroke exacerbates stroke injury by increasing neuroinflammation. We hypothesize that activation of α‐7 nicotinic acetylcholine receptor (α‐7 nAchR) attenuates neuroinflammation and oxidative stress, and reduces brain injury in mice with bone fracture and stroke. Permanent middle cerebral artery occlusion (pMCAO) was performed in C57BL/6J mice followed by tibia fracture 1 day later. Mice were treated with 0.8 mg/kg PHA 568487 (PHA, α‐7 nAchR‐specific agonist), 6 mg/kg methyllycaconitine (α‐7 nAchR antagonist), or saline 1 and 2 days after pMCAO. Behavior was tested 3 days after pMCAO. Neuronal injury, CD68⁺, M1 (pro‐inflammatory) and M2 (anti‐inflammatory) microglia/macrophages, phosphorylated p65 component of nuclear factor kappa b in microglia/macrophages, oxidative and anti‐oxidant gene expression were quantified. Compared to saline‐treated mice, PHA‐treated mice performed better in behavioral tests, had fewer apoptotic neurons (NeuN⁺TUNEL⁺), fewer CD68⁺ and M1 macrophages, and more M2 macrophages. PHA increased anti‐oxidant gene expression and decreased oxidative stress and phosphorylation of nuclear factor kappa b p65. Methyllycaconitine had the opposite effects. Our data indicate that α‐7 nAchR agonist treatment reduces neuroinflammation and oxidative stress, which are associated with reduced brain injury in mice with ischemic stroke plus tibia fracture. image Bone fracture at the acute stage of stroke exacerbates neuroinflammation, oxidative stress, and brain injury, and our study has shown that the α‐7 nAchR agonist, PHA (PHA 568487), attenuates neuroinflammation, oxidative stress, and brain injury in mice with stroke and bone fracture. Hence, PHA could provide an opportunity to develop a new strategy to reduce brain injury in patients suffering from stroke and bone fracture.

Prolonged blockade of AMPA-type glutamate receptors in hippocampal neuron cultures leads to homeostatic enhancements of pre- and postsynaptic function that appear correlated at individual synapses, suggesting some form of transsynaptic coordination. The respective modifications are important for overall synaptic strength but their interrelationship, dynamics, and molecular underpinnings are unclear. Here we demonstrate that adaptation begins postsynaptically but is ultimately communicated to presynaptic terminals and expressed as an accelerated turnover of synaptic vesicles. Critical postsynaptic modifications occur over hours, but enable retrograde communication within minutes once AMPA receptor (AMPAR) blockade is removed, causing elevation of both spontaneous and evoked vesicle fusion. The retrograde signaling does not require spiking activity and can be interrupted by NBQX, philanthotoxin, postsynaptic BAPTA, or external sequestration of BDNF, consistent with the acute release of retrograde messenger, triggered by postsynaptic Ca ²⁺ elevation via Ca ²⁺ -permeable AMPARs.

Prolonged AMPA-receptor blockade in hippocampal neuron cultures leads to both an increased expression of GluA1 postsynaptically and an increase in vesicle pool size and turnover rate presynaptically, adaptive changes that extend beyond simple synaptic scaling. As a molecular correlate, expression of the β Ca(2+)/CaM-dependent kinase type II (βCaMKII) is increased in response to synaptic inactivity. Here we set out to clarify the role of βCaMKII in the various manifestations of adaptation. Knockdown of βCaMKII by lentiviral-mediated expression of shRNA prevented the synaptic inactivity-induced increase in GluA1, as did treatment with the CaM kinase inhibitor KN-93, but not the inactive analog KN-92. These results demonstrate that, spurred by AMPA-receptor blockade, up-regulation of βCaMKII promotes increased GluA1 expression. Indeed, transfection of βCaMKII, but not a kinase-dead mutant, increased GluA1 expression on dendrites and elevated vesicle turnover (Syt-Ab uptake), mimicking the effect of synaptic inactivity on both sides of the synapse. In cells with elevated βCaMKII, relief of synaptic-activity blockade uncovered an increase in the frequency of miniature excitatory postsynaptic currents that could be rapidly and fully suppressed by PhTx blockade of GluA1 receptors. This increased mini frequency involved a genuine presynaptic enhancement, not merely an increased abundance of synapses. This finding suggests that Ca(2+) flux through GluA1 receptors may trigger the acute release of a retrograde messenger. Taken together, our results indicate that synaptic inactivity-induced increases in βCaMKII expression set in motion a series of events that culminate in coordinated pre- and postsynaptic adaptations in synaptic transmission.