Oligodendrocyte Progenitor Cell Proliferation and Fate after White Matter Stroke in Juvenile and Adult Mice.

The incidence of stroke in children is 2.4 per 100,000 person-years and results in long-term motor and cognitive disability. In ischemic stroke, white matter (WM) is frequently injured, but is relatively understudied compared to grey matter injury. Previous research suggests that the cellular response to WM ischemic injury is different at different ages. Little is known about whether WM repair mechanisms differ in children and adults. We utilized a model of focal ischemic WM injury to determine the oligodendrocyte (OL) response to focal WM ischemic injury in juvenile and adult mice. Methods: Juvenile (21-25 days of age) versus adult (2-3 months of age) mice underwent stereotaxic injection of the potent vasoconstrictor N5-(1-iminoethyhl)-L-ornithine (L-NIO) into the lateral corpus callosum (CC). Animals were sacrificed on postoperative day 3 (acute) or 21 (chronic). Cell birth-dating was performed acutely after WM stroke with 5-ethynyl-2-deoxyuridine (EdU) injected intraperitoneally. Immunohistochemistry was performed, as well as stereology, to measure injury volume. The acute oligodendrocyte progenitor cell (OPC) proliferation and the chronic OL cell fate were determined with immunohistochemistry. Compound action potentials were measured in the CC at acute and chronic time points. Results: Acutely WM injury volume was smaller in juveniles. There was significantly greater OPC proliferation in juvenile animals (acute) compared to adults, but newly born OLs did not survive and mature into myelinating cells at chronic time points. In addition, juveniles did not have improved histological or functional recovery when compared to adults. Protecting newly born OPCs is a potential therapeutic target in children with ischemic stroke.

Nalbuphine Reduces Opioid-Associated Urinary Retention in Pediatric Patients.

OBJECTIVES: To evaluate the effect of nalbuphine administration on urine output in critically ill children with opioid-associated urinary retention. DESIGN: Institutional review board approved, single center, retrospective medical chart review. SETTING: Large medical-surgical PICU within a free-standing, tertiary care children's hospital. PATIENTS: Patients admitted to the PICU between October 1, 2014, and February 29, 2016, who received IV nalbuphine after meeting criteria for opioid-associated oliguria (defined as urine output below 1 mL/kg/hr and received at least one dose of opioid therapy within the preceding 12 hr). INTERVENTIONS: None. MEASUREMENT AND MAIN RESULTS: Seventeen patients who received 21 doses of nalbuphine were analyzed. The median age and weight of patients were 6 years (interquartile range, 3-11.5 yr) and 18 kg (interquartile range, 12-35 kg), respectively. Two distinct dosing strategies became evident, specifically 0.05 mg/kg (n = 11 doses) and 0.1 mg/kg (n = 10 doses). Urine output increased significantly from baseline (median, 0 mL/kg/hr; interquartile range, 0-0.53 mL/kg/hr) to 6 hours post nalbuphine administration (median, 1.48 mL/kg/hr; interquartile range, 0-2 mL/kg/hr; p = 0.0002). Patients who received 0.1 mg/kg/dose had a greater urine output response compared with those who received 0.05 mg/kg/dose. Five patients (29%) had a catheter inserted into their bladder after administration of nalbuphine. Pain scores (grouped 6 hr before and after nalbuphine administration and single pain scores documented immediately before and after nalbuphine administration) were unchanged. CONCLUSIONS: Nalbuphine administration, at a dose of 0.1 mg/kg, improved urine output in a cohort of children with opioid-associated urinary retention. Pain control did not appear influenced by the provision of nalbuphine. Additional studies are needed to determine the influence of nalbuphine on urinary catheter insertion rates and catheter-associated urinary tract infections.

Methylnaltrexone in the Management of Opioid-Associated Urinary Retention in Children.

OBJECTIVE: To evaluate the association between methylnaltrexone and urine output (UOP) in critically ill children with opioid-associated urinary retention. METHODS: This retrospective study included patients admitted to the pediatric intensive care unit between December 1, 2019, and November 30, 2020, who received methylnaltrexone for opioid-associated oliguria (spontaneous UOP below 1 mL/kg/hr and at least 1 dose of an opioid within the preceding 6 hours). RESULTS: Twenty-five patients (median age = 5.5 years, IQR 1.7-16.4; median weight = 19 kg, IQR 9-45) were included. Mean methylnaltrexone dose was 0.15 ± 0.006 mg/kg. A statistically significant increase in UOP from baseline to 6 hours following methylnaltrexone was observed (p = 0.001), but not all patients responded. Fourteen patients (56%) had no UOP following methylnaltrexone administration, while 11 (44%) demonstrated a robust increase (median = 0 mL/kg/hr at baseline [IQR 0-0] to 1.96 mL/kg/hr [IQR 1.08-2.22; p = 0.001]) within 6 hours following methylnaltrexone administration. Younger patients responded better than older patients (responder age = 2.5 years [IQR 0.8-7]) versus 11.4 years [IQR 1.75-17.5] for non-responders) (p = 0.04). Both intravenous (IV) and subcutaneous (SQ) routes were associated with an increase in UOP (IV, p = 0.04; SQ, p = 0.02). The effect persisted for up to 24 hours after administration. Sixty-four percent of patients required urinary catheter placement. Pain scores (averaged 6 hours before and after methylnaltrexone) remained unchanged (p = 0.44). CONCLUSIONS: Methylnaltrexone may increase spontaneous UOP in some children with opioid-associated urinary retention, but urinary catheterization rates remain high.

BDNF promoter-mediated beta-galactosidase expression in the olfactory epithelium and bulb.

The neurotrophin brain-derived neurotrophic factor (BDNF) has been implicated in the generation and differentiation of new olfactory sensory neurons (OSNs) and in the regulation of branching of OSN axons in their target glomeruli. However, previous reports of BDNF mRNA and protein expression in olfactory epithelium and olfactory bulb (OB) have been inconsistent, raising questions on the proposed roles for BDNF. Here, we report on beta-galactosidase (beta-gal) expression in adult gene-targeted mice where the BDNF promoter drives expression of the Escherichia coli lacZ gene (BDNF(lacZneo) mice). We find that beta-gal is expressed in a small subset of OSNs with axons that reach the olfactory nerve layers throughout the OB. In the OB, we find expression of beta-gal in gamma-aminobutyric acidergic but not dopaminergic periglomerular cells and external tufted cells and in interneurons located in the mitral cell layer. Our results are inconsistent with the regulation of generation and differentiation of new OSNs elicited by the release of BDNF from horizontal basal cells. The results are consistent with a role for BDNF in competitive branching of OSN axons within the glomeruli of the OB.

Endogenous Sex Steroids Dampen Neuroinflammation and Improve Outcome of Traumatic Brain Injury in Mice.

The role of biological sex in short-term and long-term outcome after traumatic brain injury (TBI) remains controversial. The observation that exogenous female sex steroids (progesterone and estrogen) reduce brain injury coupled with a small number of clinical studies showing smaller injury in women suggest that sex steroids may play a role in outcome from TBI. We used the controlled cortical impact (CCI) model of TBI in mice to test the hypothesis that after CCI, female mice would demonstrate less injury than male mice, related to the protective role of endogenous steroids. Indeed, adult females exhibit histological protection (3.7 ± 0.5 mm3) compared to adult male mice (6.8 ± 0.6 mm3), and females that lacked sex steroids (ovex) showed increased injury compared to intact females. Consistent with histology, sensorimotor deficits measured as reduced contralateral limb use were most pronounced in male mice (31.9 ± 6.9% reduced limb use) compared to a 12.7 ± 3.8% reduction in female mice. Ovex mice exhibited behavioral deficits similar to males (31.5 ± 3.9% reduced limb use). Ovex females demonstrated increased microglial activation relative to intact females in both the peri-injury cortex and the reticular thalamic nucleus. Ovex females also demonstrated increased astrogliosis in comparison to both females and males in the peri-injury cortex. These data indicate that female sex steroids reduce brain sensitivity to TBI and that reduced acute neuroinflammation may contribute to the relative protection observed in females.

Carotid artery blood flow decreases after rapid head rotation in piglets.

Modification of cerebral perfusion pressure and cerebral blood flow (CBF) are crucial components of the therapies designed to reduce secondary damage after traumatic brain injury (TBI). Previously we documented a robust decrease in CBF after rapid sagittal head rotation in our well-validated animal model of diffuse TBI. Mechanisms responsible for this immediate (<10 min) and sustained (∼24 h) reduction in CBF have not been explored. Because the carotid arteries are a major source of CBF, we hypothesized that blood flow through the carotid arteries (Q) and vessel diameter (D) would decrease after rapid nonimpact head rotation without cervical spine injury. Four-week-old (toddler) female piglets underwent rapid (<20 msec) sagittal head rotation without impact, previously shown to produce diffuse TBI with reductions in CBF. Ultrasonographic images of the bilateral carotid arteries were recorded at baseline (pre-injury), as well as immediately after head rotation and 15, 30, 45, and 60 min after injury. Diameter (D) and waveform velocity (V) were used to calculate blood flow (Q) through the carotid arteries using the equation Q=(0.25)πD(2)V. D, V, and Q were normalized to the pre-injury baseline values to obtain a relative change after injury in right and left carotid arteries. Three-way analysis of variance and post-hoc Tukey-Kramer analyses were used to assess statistical significance of injury, time, and side. The relative change in carotid artery diameter and flow was significantly decreased in injured animals in comparison with uninjured sham controls (p<0.0001 and p=0.0093, respectively) and did not vary with side (p>0.39). The average carotid blood velocity did not differ between sham and injured animals (p=0.91). These data suggest that a reduction in global CBF after rapid sagittal head rotation may be partially mediated by a reduction in carotid artery flow, via vasoconstriction.

Olfactory discrimination varies in mice with different levels of α7-nicotinic acetylcholine receptor expression.

Previous studies have shown that schizophrenics have decreased expression of α7-nicotinic acetylcholine (α7) receptors in the hippocampus and other brain regions, paranoid delusions, disorganized speech, deficits in auditory gating (i.e., inability to inhibit neuronal responses to repetitive auditory stimuli), and difficulties in odor discrimination and detection. Here we use mice with decreased α7 expression that also show a deficit in auditory gating to determine if these mice have similar deficits in olfaction. In the adult mouse olfactory bulb (OB), α7 expression localizes in the glomerular layer; however, the functional role of α7 is unknown. We show that inbred mouse strains (i.e., C3H and C57) with varying α7 expressions (e.g., α7 wild-type [α7+/+], α7 heterozygous knock-out [α7+/-] and α7 homozygous knock-out mice [α7-/-]) significantly differ in odor discrimination and detection of chemically-related odorant pairs. Using [(125)I] α-bungarotoxin (α-BGT) autoradiography, α7 expression was measured in the OB. As previously demonstrated, α-BGT binding was localized to the glomerular layer. Significantly more expression of α7 was observed in C57 α7+/+ mice compared to C3H α7+/+ mice. Furthermore, C57 α7+/+ mice were able to detect a significantly lower concentration of an odor in a mixture compared to C3H α7+/+ mice. Both C57 and C3H α7+/+ mice discriminated between chemically-related odorants sooner than α7+/- or α7-/- mice. These data suggest that α7-nicotinic-receptors contribute strongly to olfactory discrimination and detection in mice and may be one of the mechanisms producing olfactory dysfunction in schizophrenics.

Evaluation of the validity of a maximum likelihood adaptive staircase procedure for measurement of olfactory detection threshold in mice.

Threshold is defined as the stimulus intensity necessary for a subject to reach a specified percent correct on a detection test. MLPEST (maximum likelihood parameter estimation by sequential testing) is a method that is able to determine threshold accurately and more rapidly than many other methods. Originally developed for human auditory and visual tasks, it has been adapted for human olfactory and gustatory tests. In order to utilize this technique for olfactory testing in mice, we have adapted MLPEST methodology for use with computerized olfactometry as a tool to estimate odor detection thresholds. Here we present Monte Carlo simulations and operant conditioning data that demonstrate the potential utility of this technique in mice, we explore the ramifications of altering MLPEST test parameters on performance, and we discuss the advantages and disadvantages of using MLPEST compared to other methods for the estimation of thresholds in rodents. Using MLPEST, we find that olfactory detection thresholds in mice deficient for the cyclic nucleotide-gated channel subunit A2 are similar to those of wild-type animals for odorants the knockout animals are able to detect.