Intracranial abnormalities in infants treated with extracorporeal membrane oxygenation: imaging with US and CT

Findings at neuroimaging in 100 consecutive infants treated with extracorporeal membrane oxygenation (ECMO) are presented. Imaging in these infants consisted of pretreatment cranial ultrasonography (US), daily US studies while on ECMO, and follow-up cranial computed tomography (CT) after treatment. There were findings of abnormalities in 43 patients. Thirty had intracranial bleeding, often of unusual extent and distribution. Thirteen additional infants had nonhemorrhagic abnormalities alone. Bleeding considered to be major was seen in 12% of infants. Large parenchymal hemorrhages and infarcts, cerebellar hemorrhages, and diffuse edema were the most significant abnormalities, with a 50% mortality (eight of 16 patients). No lateralization was noted with respect to distribution of bleeding sites or areas of nonhemorrhagic abnormalities. US was a sensitive but imperfect screening tool for intracranial abnormalities. Abnormalities missed with US included peripheral and small parenchymal lesions, subarachnoid hemorrhage, cerebral atrophy, and sagittal sinus thrombosis.     

Monosynaptic excitation of dorsal medullary respiratory neurons by slowly adapting pulmonary stretch receptors

The discharges of individual slowly adapting pulmonary stretch receptors (PSRs) and single respiratory neurons of the dorsal respiratory group (DRG) within the ventrolateral subnucleus of the solitary tract were recorded simultaneously in anesthetized, paralyzed, artificially ventilated cats. DRG neurons were classified as P-cell, I-alpha, or I-beta, based on the alteration in activity during respiratory cycles when lung inflation was withheld compared to activity when the lungs were inflated in phase with central inspiratory drive. In some cases, vagal stimulation was also used to classify respiratory neurons. Synaptic input of PSRs onto DRG neurons was examined by the construction of cross-correlograms for the simultaneously recorded discharge of individual PSRs (reference events) and individual DRG neurons (correlated events). Monosynaptic excitatory connections were demonstrated by peaks in 26% of the cross-correlograms of PSR and P-cell pairs and 20% of the cross-correlograms of PSR and I-beta neuron pairs. The ratio of the peak number of occurrences to the background number of occurrences (k value) was comparable for P-cells and I-beta neurons: 2.96 +/- 2.09 and 1.62 +/- 0.36 (mean +/- SD), respectively. P-cells and I-beta neurons also had similar short latencies for the peak of increased probability of discharge: 2.74 +/- 0.53 and 2.57 +/- 0.63 ms, respectively. No evidence was obtained demonstrating synaptic connectivity between PSRs and I-alpha neurons. Interpretations of this negative result are discussed.     

Waterloo Vision and Mobility Study: Normal gait characteristics during dark and light adaptation in individuals with age-related maculopathy

The purpose of this study was to evaluate the gait responses of individuals with low vision compared to those of normal-visioned individuals when their vision is challenged by extreme levels of light. Twenty subjects with age-related maculopathy (ARM) and 20 subjects with normal vision first walked along a flat, unobstructed path immediately after the ambient light level was changed from low (5 lux) to high (2500 lux). The procedure was repeated after the light was reduced from the high to the low level. Muscle activity, temporal and kinematic variables, and ground reaction forces were used to detect gait characteristics because of ambient light level changes. Data suggested that ARM subjects walked slower and with more caution than normal subjects but that these differences were not related to ambient light level. Head angle, an estimate of gaze direction, was lower for ARM subjects during high light, but the gaze direction for both groups was low during low light. Among these ARM subjects, extreme levels of ambient light did not affect gait; subjects made adaptations that were reasonable to encourage safe ambulation, despite the direction of light change. Normal-visioned individuals in this study experienced more difficulty in low light than high light situations.     

Losartan, nonpeptide angiotensin II-type 1 (AT1) receptor antagonist, attenuates pressor and sympathoexcitatory responses evoked by angiotensin II andL-glutamate in rostral ventrolateral medulla

We investigated the effect of losartan, a nonpeptide angiotensin II (Ang II)-type 1 (AT₁) receptor antagonist, on the responses evoked by Ang II andL-glutamate (L-Glu) in the rostral ventrolateral medulla (RVLM). Adult spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were anesthetized with halothane and artificially ventilated. Responses of mean arterial pressure (MAP), heart rate (HR) and splanchnic sympathetic nerve activity (SNA) to microinjection of Ang II (100 pmol) orL-Glu (2 nmol) into the RVLM were examined following microinjection of losartan (10 pmol–10 nmol). Ang II increased MAP (16 ± 1mmHg in SHR and16 ± 1mmHg in WKY) and SNA (9 ± 1%and10 ± 1%, respectively), which were significantly (P < 0.01) attenuated by pretreatment with losartan (100 pmol − 10 nmol) in both strains. In addition, the pressor and sympathoexcitatory responses evoked byL-Glu were attenuated by losartan in a dose-dependent manner. The increases of MAP evoked byL-Glu (53 ± 6mmHg in SHR and39 ± 3mmHg in WKY) were suppressed to 5 ± 3mmHg(P < 0.01) and 4 ± 2mmHg (P < 0.01), respectively, in the presence of 10 nmol of losartan. The increase of SNA was also markedly inhibited by higher doses of losartan. The cardiovascular responses evoked byL-Glu, however, were not attenuated by pretreatment with either 1 nmol of [Sar¹, Thr⁸]-Ang II or 10 nmol of potassium acetate, suggesting that the effect of losartan onL-Glu response may not be attributed to the blockade of Ang II receptor or to the high concentration of potassium. These results indicate that the AT₁ receptor is responsible, in part, for the vasomotor action of Ang II in the RVLM and losartan has an inhibitory effect on pressor and sympathoexcitatory responses evoked byL-Glu by mechanisms other than those mediated by Ang II receptors.     

Effects of nicotine on bacterial toxins associated with cot death

Toxins produced by staphylococci and enterobacteria isolated from the nasopharynx of cases of sudden infant death syndrome (SIDS) have a lethal effect when injected into chick embryos. If the toxins are progressively diluted the lethal effect disappears, but certain combinations of toxins show synergy so that if sublethal doses are mixed a highly lethal effect is produced. In this paper it is shown that nicotine at very low concentrations (less than that produced in man by 0.05 cigarettes) potentiates the lethal action of certain SIDS associated bacterial toxins and markedly potentiates the lethal action of synergistic combinations of bacterial toxins. These results could explain, at least in part, why parental smoking increases the risk of SIDS. They also provide further support for the common bacterial toxin hypothesis of cot death.