This study highlights the possible pathological role of MMP-12 in the context of ischemic stroke. Male rats were subjected to a two-hour middle cerebral artery occlusion (MCAO) procedure. MMP-12 shRNA expressing plasmid formulation was administered to these rats twenty-four hours after reperfusion. The results showed a predominant upregulation of MMP-12 (approximately 47, 58, 143, and 265 folds on days 1, 3, 5, 7 post-ischemia, respectively) in MCAO subjected rats. MMP-12 expression was localized to neurons, oligodendrocytes and microglia, but not astrocytes. Transcriptional inactivation of MMP-12 significantly reduced the infarct size. The percent infarct size was reduced from 62.87 ± 4.13 to 34.67 ± 5.39 after MMP-12 knockdown compared to untreated MCAO subjected rats. Expression of myelin basic protein was increased, and activity of MMP-9 was reduced in ischemic rat brains after MMP-12 knockdown. Furthermore, a significant reduction in the extent of apoptosis was noticed after MMP-12 knockdown. TNFα expression in the ipsilateral regions of MCAO-subjected rats was reduced after MMP-12 knockdown in addition to the reduced protein expression of apoptotic molecules that are downstream to TNFα signaling. Specific knockdown of MMP-12 after focal cerebral ischemia offers neuroprotection that could be mediated via reduced MMP-9 activation and myelin degradation as well as inhibition of apoptosis.
Excitatory neuromodulators such as serotonin (5‐HT) and Substance P are synthesized in and released from raphe 5‐HT neurons and increase the excitability of neurons within the brainstem nuclei responsible for controlling breathing. These neuromodulators have also been shown to increase the excitability of respiratory chemoreceptors, including the CO2‐sensitive Phox2b‐expressing (Phox2b+) neurons in the retrotrapezoid nucleus (RTN). However, the importance of this raphe‐derived neuromodulation of the RTN for the hypoxic and hypercapnic ventilatory chemoreflexes has not been tested in vivo. We hypothesize that unilateral ablation of serotonergic terminals within the RTN will attenuate the ventilatory chemoreflexes in vivo. To test this hypothesis, 8 week‐old female Sprague‐Dawley rats received stereotaxic injections of 5,7‐Dihydroxytryptamine (5,7‐DHT; 2 mg/ml, 2 μl vol.) unilaterally targeting the RTN to selectively lesion axon terminals from serotonergic neurons under anesthesia. Desipramine (30mg/kg, intraperitoneal) was administered 30 min prior to toxin injection to prevent axon terminal lesions of other aminergic neurons and limit the off‐target effects of 5,7‐DHT. Breathing was measured in room air, hypercapnia (7% CO2 challenge), and hypoxia (12% O2 challenge) before the lesions and then 3, 5, 7, 10, and 14 days after injection. Three days after injection, we observed a 41% decrease in the ventilatory response to hypercapnia and a 45% decrease in the ventilatory response to hypoxia, driven by a decrease in breathing frequency in both cases (N=4). However, the reduced chemoreflexes normalized over the two weeks after injection. There was no consistent effect following sham injection (N=2) of saline (2 μl vol.). These preliminary data suggest that the serotonergic terminals surrounding the RTN play a vital role in facilitating both hypercapnic and hypoxic ventilatory chemoreflexes in vivo, and support our overall hypothesis that raphe‐derived excitatory neuromodulation of the RTN is essential for ventilatory chemoreflexes in vivo.Support or Funding InformationThis work was supported by NIH HL122358.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
Brain chemoreceptors play a vital role in regulating blood gas homeostasis in response to acute changes in CO2 and/or pH. Serotonergic (5‐HT) neurons, which also produce and release other neuromodulatory peptides, have properties consistent with being central respiratory chemoreceptors. In addition, recent in vitro studies have highlighted important contributions of G‐protein‐coupled 5‐HT receptors (5‐HT2 and/or 5‐HT7 receptors) to the chemosensitivity of additional putative central respiratory chemoreceptors within the retrotrapezoid nucleus (RTN) marked by the expression of Phox2b. However, the importance of raphe‐derived neuromodulation of the RTN on eupneic breathing as well as hypoxic and hypercapnic ventilatory chemoreflexes in vivo is unclear. Here we hypothesized that unilateral ablation of serotonergic terminals within the RTN cause a time‐dependent attenuation of ventilatory chemoreflexes in vivo. To test this hypothesis, 8‐week‐old Sprague‐Dawley rats received unilateral stereotaxic injections of the 5‐HT pre‐synaptic terminal toxin 5,7‐Dihydroxytryptamine (5,7‐DHT; 2 mg/ml, 2 µl vol.) with or without fluorescent microbeads (for injection site localization) targeted to the RTN after pretreatment with desipramine (30mg/kg; IP) to limit off‐target effects on other aminergic neurons/terminals. A control group received an equal volume injection of vehicle in the RTN. Breathing was measured via whole body plethysmography while exposed to room air, hypercapnia (7% CO2 challenge), or hypoxia (12% O2 challenge) 2‐3 days (d) before and 3, 5, 7, 10, and 14d post‐injection. Preliminary data showed that RTN‐targeted injections reduced ventilatory chemoreflexes 3, 5, and 7d post‐injection with slightly greater effects in the 5,7‐DHT injected group. Ventilatory chemoreflexes returned to control levels by 14d post‐injection. To confirm the lesion site within the RTN and determine the extent of 5‐HT‐specific lesioning, we have also begun to quantify 5‐HT using immunofluorescent staining. However, additional preliminary data showed no differences in 5‐HT when comparing 5,7‐DHT and control groups. Although these studies are ongoing, our data suggest that unilateral RTN‐targeted 5‐HT terminal lesions reduce ventilatory chemoreflexes.
Excitatory neuromodulators such as serotonin (5‐HT) and Substance P are synthesized in and released from raphe 5‐HT neurons and increase the excitability of neurons within the brainstem nuclei responsible for controlling breathing. These neuromodulators have also been shown to increase the excitability of respiratory chemoreceptors, including the CO2‐sensitive Phox2b‐expressing (Phox2b+) neurons in the retrotrapezoid nucleus (RTN). However, the importance of this raphe‐derived neuromodulation of the RTN for the hypoxic and hypercapnic ventilatory chemoreflexes has not been tested in vivo. We hypothesize that unilateral ablation of serotonergic terminals within the RTN will attenuate the ventilatory chemoreflexes in vivo. To test this hypothesis, 8 week‐old female Sprague‐Dawley rats received stereotaxic injections of 5,7‐Dihydroxytryptamine (5,7‐DHT; 2 mg/ml, 2 μl vol.) unilaterally targeting the RTN to selectively lesion axon terminals from serotonergic neurons under anesthesia. Desipramine (30mg/kg, intraperitoneal) was administered 30 min prior to toxin injection to prevent axon terminal lesions of other aminergic neurons and limit the off‐target effects of 5,7‐DHT. Breathing was measured in room air, hypercapnia (7% CO2 challenge), and hypoxia (12% O2 challenge) before the lesions and then 3, 5, 7, 10, and 14 days after injection. Three days after injection, we observed a 41% decrease in the ventilatory response to hypercapnia and a 45% decrease in the ventilatory response to hypoxia, driven by a decrease in breathing frequency in both cases (N=4). However, the reduced chemoreflexes normalized over the two weeks after injection. There was no consistent effect following sham injection (N=2) of saline (2 μl vol.). These preliminary data suggest that the serotonergic terminals surrounding the RTN play a vital role in facilitating both hypercapnic and hypoxic ventilatory chemoreflexes in vivo, and support our overall hypothesis that raphe‐derived excitatory neuromodulation of the RTN is essential for ventilatory chemoreflexes in vivo. Support or Funding Information This work was supported by NIH HL122358. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.