Effect of a Novel, Orally Active Matrix Metalloproteinase-2 and -9 Inhibitor in Spinal and Trigeminal Rat Models of Neuropathic Pain.

AIMS: To study the effects of a novel matrix metalloproteinase-2 (MMP-2) and MMP-9 inhibitor, AQU-118, on mechanical allodynia in the spinal nerve ligation (SNL) model of neuropathic pain and the chronic constriction injury of the infraorbital nerve (CCI-IoN) model of neuropathic orofacial pain. METHODS: Five groups of SNL rats were given daily oral doses of AQU-118 (5, 10, 20 mg/kg), gabapentin (100 mg/kg), or vehicle (0.5% methylcellulose) and then paw withdrawal threshold was measured with von Frey filaments (VF). Three groups of CCI-IoN rats were given daily oral doses of either AQU-118 (40 mg/kg), gabapentin (100 mg/kg), or vehicle (0.5% methylcellulose) and then mechanical allodynia was measured with facial VF and non-reflex-based orofacial stimulation test (OFST) assay. Naïve rats were also tested for the effect of AQU-118 (40 mg/kg) on basal sensitivity to mechanical stimulation/locomotive activity. RESULTS: Mechanical allodynia in SNL rats was attenuated by gabapentin (100 mg/kg) and AQU-118 (in a dose-dependent manner). Mechanical allodynia in CCI-IoN rats was also attenuated (in an equipotent manner) by both AQU-118 (40 mg/ kg) and gabapentin (100 mg/kg) as measured by both facial VF and OFST assay. Upon cessation of either AQU-118 or gabapentin, VF-related responses in both models and OFST assay times reverted to levels observed in vehicle-treated rats. No statistically significant change was observed in locomotive activity/paw withdrawal threshold by AQU-118 (40 mg/kg) in naïve rats. CONCLUSION: The results demonstrated that oral AQU-118 attenuates mechanical allodynia in both neuropathic pain models and with efficacies that mirror gabapentin at the 40 mg/kg dose used in the CCI-IoN model but without effect on basal sensitivity to mechanical stimulation/locomotive activity. These findings support a possible role for MMP-2/-9 in the etiology of neuropathic pain and also suggest that inhibition strategies represent a viable treatment option.

Report of seizure following intraoperative monitoring of transcranial motor evoked potentials.

BACKGROUND: Transcranial motor evoked potentials are used to detect iatrogenic injury to the corticospinal tracts and vascular territory of the anterior spinal artery. Tongue and lip lacerations are the most common complication of this modality. Theoretical complications include cardiac arrhythmia and seizure although there are no published reports of either. CASE REPORT: We report a case of postoperative seizure following motor evoked potential testing in a patient without a seizure history. Although anecdotal reports exist, ours is the first known published report of seizure following transcranial electrical stimulation. CONCLUSION: The intent of this novel report is to encourage the use of anesthetic regimens that raise seizure threshold, decrease stimulation threshold, and increase the specificity of motor evoked potentials. Providers should be prepared to treat intraoperative or perioperative seizure activity when the monitoring protocol includes transcranial motor evoked potentials.

Intraoperative monitoring may prevent neurologic injury in non-myelopathic patients undergoing ACDF.

The efficacy of spinal cord monitoring for patients undergoing anterior cervical discectomy and fusion (ACDF) as indicated for radiculopathy without myelopathy is debated in the literature. The reported rate of complications is low for this procedure. Previous studies have shown both improvements in outcome as well as no change in monitored vs. unmonitored patients. We report two cases where intraoperative spinal cord monitoring using somatosensory and transcranial motor evoked potentials detected impending iatrogenic injury to the spinal cord. In both cases, changes in the electrophysiological data prompted intervention and prevented a permanent neurological deficit. Based on these observations we recommend spinal cord monitoring using sensory and motor evoked potentials to prevent new deficits in non-myelopathic patients undergoing ACDF surgery.

Detection and prevention of impending brachial plexus injury secondary to arm positioning using ulnar nerve somatosensory evoked potentials during transaxillary approach for thyroid lobectomy.

Robotic assisted surgery is becoming widely used for procedures such as radical prostatectomy. The use of robotic assisted surgery to perform partial and complete thyroidectomies using a transaxillary approach is being investigated in patient populations who wish to avoid a conspicuous cervical scar. Patient positioning for this approach as well as retraction during exposure has the potential to result in postoperative brachial plexopathy similar to what is seen in other types of surgery. We report the use of ulnar nerve somatosensory evoked potentials (SSEPs) to detect and prevent positional related neuropathy in the first pediatric patient in the world to undergo this procedure. We conclude that upper extremity SSEPs should be routinely performed during robotic assisted thyroidectomy.

Comparison of the predictive validity of the mirror chamber and elevated plus maze tests in mice.

The mirror chamber (MC) is a putative test of anxiety-like behavior in mice, and is increasingly popular. Nonetheless, it is unclear whether the observed behaviors rely on the presence of mirrored panels. If so, it is unclear whether the behaviors are sensitive to clinically effective anxiolytics, and how the test compares to the elevated plus maze (EPM) in terms of predictive validity. The present studies assessed anxiety-like behaviors in different mouse strains in the MC using mirrored and non-mirrored panels, under variable lighting conditions. We also assessed the pharmacological validity of the MC and EPM tests, and the locomotor properties of active test compounds. Seven mouse strains exhibited different levels of anxiety-like behaviors in the MC, and differential sensitivity to panel and light conditions. DBA/2J mice appeared most sensitive to the mirrored, versus black or white, panels and were therefore used in pharmacological MC studies. The mGlu5 receptor antagonist MPEP significantly decreased anxiety-like behaviors, similar to an intermediate dose of the benzodiazepine diazepam. The benzodiazepines chlordiazepoxide and alprazolam and the 5HT(1A) partial agonist buspirone had no effects on anxiety-like behaviors in the MC. None of the MC effects of active test compounds were attributable to non-specific/locomotor effects. The antidepressants fluoxetine and venlafaxine increased anxiety-like behaviors in the MC. By contrast, the anxiolytic-like effects of chlordiazepoxide, diazepam and MPEP were revealed in the EPM in C57Bl6/J mice. In conclusion, the EPM test exhibits superior predictive validity compared to the MC test, despite the sensitivity of the MC to mouse strain differences.

A report of two cases of lip and tongue bite injury associated with transcranial motor evoked potentials.

Transcranial electric motor evoked potentials (TCeMEPs) are routinely used intraoperatively to detect and prevent iatrogenic injury to the spinal cord, specifically the corticospinal tract. Complications related to TCeMEP testing include the potential for seizure induction, cardiac arrhythmia, scalp burns, infection, and tongue or lip laceration. Among this list of potential complications, tongue and lip lacerations are the most common and most directly attributable to transcranial stimulation. The technique of low voltage stimulation and the correct placement of oral bite blocks is successful in preventing patient bite injuries. We report two cases of patient bite injuries following TCeMEPs and discuss potential mechanisms of injury and prevention.

Isolation of adult rhesus neural stem and progenitor cells and differentiation into immature oligodendrocytes.

Neural stem and progenitor cells (NSPCs) have been isolated from several regions of the brain from mice, rats, and humans. These cells possess the characteristics of self-renewal and differentiation along all major neural lineages. Herein, the first isolation of NSPCs from the adult rhesus macaque brain and characterization of these cells based on their gene and protein expression profile, self-renewal, and ability to differentiate along an oligodendrocyte lineage are described. Flow cytometric analysis revealed that this cell population is CD90(+)/CD164(+)/CD34(-) and, therefore, resembles a nonhematopoietic stem cell population. Similar to other mesenchymal and neural stem cell populations, rhesus NSPCs cells express stemness-related genes, including the transcription factors Oct-4, Rex-1, and Sox-2 and the gene encoding for the intermediate filament protein nestin. The co-expression of the neural and glial markers MAP2ab, GFAP, NF-L, and NeuroD was also observed at both the mRNA and protein levels. When rhesus NSPCs were induced to differentiate with a cocktail of retinoic acid and the neurotrophins (NGF, BDNF, and NT-3), they underwent morphologic changes including taking on an oligodendrocyte precursor morphology. Along with these phenotypic changes, a decrease in MAP2ab expression and new expression of the oligodendrocyte precursor protein O4 were observed. Taken together, these results demonstrate the existence of a stem and progenitor cell-like population in the nonhuman primate brain, which may have the potential to generate oligodendroglia for use in the development of cellular therapies for demyelinating diseases.

Excitatory and inhibitory local circuit input to the rat dorsal motor nucleus of the vagus originating from the nucleus tractus solitarius.

The nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus nerve (DMV) constitute sensory and motor nuclei of the dorsal vagal complex, respectively. We used whole-cell patch-clamp recordings from DMV neurons in rat brain slices and three methods of stimulation (electrical, glutamate microdrop, glutamate photostimulation) to test the hypothesis that convergent excitatory and inhibitory inputs to DMV neurons originate from intact neurons in multiple NTS areas. Electrical stimulation of the NTS resulted in evoked excitatory and inhibitory postsynaptic currents (eEPSCs and eIPSCs) in DMV neurons. Stimulation of the dorsal NTS with glutamate microdrops, which selectively stimulates the soma and dendrites of intact neurons, resulted in 31% of DMV neurons receiving eEPSCs, 44% receiving eIPSCs, and 6% receiving convergent excitatory and inhibitory inputs. Glutamate photostimulation allowed selective activation of intact neurons in multiple, discrete areas of the NTS and resulted in 36% of DMV neurons receiving eEPSCs, 65% receiving eIPSCs and 20% receiving both inputs. Data obtained by stimulation of multiple NTS areas support the hypothesis that there are anatomically convergent inputs to DMV neurons originating from intact neurons within the NTS. These data support the hypothesis that there is transfer of convergent information from the NTS to the DMV, implying that significant sensory-motor processing occurs within the brainstem.

Recurrent excitation in the dentate gyrus of a murine model of temporal lobe epilepsy.

Similar to rats, systemic pilocarpine injection causes status epilepticus (SE) and the eventual development of spontaneous seizures and mossy fiber sprouting in C57BL/6 and CD1 mice, but the physiological correlates of these events have not been identified in mice. Population responses in granule cells of the dentate gyrus were examined in transverse slices of the ventral hippocampus from pilocarpine-treated and untreated mice. In Mg(2+)-free bathing medium containing bicuculline, conditions designed to increase excitability in the slices, electrical stimulation of the hilus resulted in a single population spike in granule cells from control mice and pilocarpine-treated mice that did not experience SE. In SE survivors, similar stimulation resulted in a population spike followed, at a variable latency, by negative DC shifts and repetitive afterdischarges of 3-60 s duration, which were blocked by ionotropic glutamate receptor antagonists. Focal glutamate photostimulation of the granule cell layer at sites distant from the recording pipette resulted in population responses of 1-30 s duration in slices from SE survivors but not other groups. These data support the hypothesis that SE-induced mossy fiber sprouting and synaptic reorganization are relevant characteristics of seizure development in these murine strains, resembling rat models of human temporal lobe epilepsy.

Selective enhancement of synaptic inhibition by hypocretin (orexin) in rat vagal motor neurons: implications for autonomic regulation.

The hypocretins (orexins) are hypothalamic neuropeptides implicated in feeding, arousal, and autonomic regulation. These studies were designed to determine the actions of hypocretin peptides on synaptic transmission in the dorsal motor nucleus of the vagus nerve (DMV). Whole-cell patch-clamp recordings were made from DMV neurons in transverse slices of rat brainstem. Some of the neurons were identified as gastric-related by retrograde labeling after inoculation of the stomach wall with pseudorabies virus 152, a viral label that reports enhanced green fluorescent protein. Consistent with previous findings, hypocretins caused an inward current (6-68 pA) in most neurons at holding potentials near rest. In addition, the frequency of spontaneous IPSCs was increased in a concentration-related manner (up to 477%), with little change in EPSCs. This effect was preserved in the presence of tetrodotoxin, suggesting a presynaptic site of action. Hypocretins increased the amplitude of IPSCs evoked by electrical stimulation of the nucleus tractus solitarius (NTS) but not evoked EPSCs. Hypocretin-induced increases in the frequency of IPSCs evoked by photoactivation of caged glutamate within the NTS were also observed. Identical effects of the peptides were observed in identified gastric-related and unlabeled DMV neurons. In contrast to some previous studies, which have reported primarily excitatory actions of the hypocretins in many regions of the CNS, these data support a role for hypocretin in preferentially enhancing synaptic inhibition, including inhibitory inputs arising from neurons in the NTS. These findings indicate that the hypocretins can modulate and coordinate visceral autonomic output by acting directly on central vagal circuits.

Mechanism linking NMDA receptor activation to modulation of voltage-gated sodium current in distal retina.

In this study, we investigated the mechanism that links activation of N-methyl-D-aspartate (NMDA) receptors to inhibition of voltage-gated sodium channels in isolated catfish cone horizontal cells. NMDA channels were activated in voltage-clamped cells incubated in low-calcium saline or dialyzed with the calcium chelator BAPTA to determine that calcium influx through NMDA channels is required for sodium channel modulation. To determine whether calcium influx through NMDA channels triggers calcium-induced calcium release (CICR), cells were loaded with the calcium-sensitive dye calcium green 2 and changes in relative fluorescence were measured in response to NMDA. Responses were compared with measurements obtained when caffeine depleted stores. Voltage-clamp studies demonstrated that CICR modulated sodium channels in a manner similar to that of NMDA. Blocking NMDA receptors with AP-7, blocking CICR with ruthenium red, depleting stores with caffeine, or dialyzing cells with calmodulin antagonists W-5 or peptide 290-309 all prevented sodium channel modulation. These results support the hypothesis that NMDA modulation of voltage-gated sodium channels in horizontal cells requires CICR and activation of a calmodulin-dependent signaling pathway.

Expanded niche for white sharks.

Until the advent of electronic tagging technology, the inherent difficulty of studying swift and powerful marine animals made ecological information about sharks of the family Lamnidae difficult to obtain. Here we report the tracking of movements of white sharks by using pop-up satellite archival tags, which reveal that their migratory movements, depth and ambient thermal ranges are wider than was previously thought.