Epidemiology-driven neurodevelopmental animal models of schizophrenia

While laccase of Cryptococcus neoformans is implicated in the virulence of the organism, our recent studies showing absence of melanin in the infected mouse brain has led us to a search for alternative roles for laccase in cryptococcosis. We investigated the role of laccase in protection of C. neoformans against murine alveolar macrophage (AM)-mediated antifungal activity by using a pair of congenic laccase-positive (2E-TUC) and laccase-deficient (2E-TU) strains. The laccase-positive cells with laccase derepression were more resistant to the antifungal activity of AM than a laccase-deficient strain ([28.9 ± 1.2]% versus [40.2 ± 2.6]% killing). Addition of l-dopa to Cryptococcus to produce melanin in a laccase-positive strain resulted in a slight increase in protection of C. neoformans from the antifungal activity of macrophages ([25.4 ± 3.4]% versus [28.9 ± 1.2]% killing). Recombinant cryptococcal laccase exhibited iron oxidase activity in converting Fe(II) to Fe(III). Moreover, recombinant laccase inhibited killing of C. neoformans by hydroxyl radicals catalyzed by iron in a cell-free system. Addition of the hydroxyl radical scavenger mannitol or dimethyl sulfoxide to AMs prior to the introduction of cryptococcal cells decreased killing of both strains and reduced the difference in susceptibility between the laccase-positive and laccase-deficient strains. Furthermore, laccase-mediated protection from AM killing was inhibited by the addition of Fe(II), presumably by overcoming the effects of the iron oxidase activity of cryptococcal laccase. These results suggest that the iron oxidase activity of laccase may protect C. neoformans from macrophages by oxidation of phagosomal iron to Fe(III) with a resultant decrease in hydroxyl radical formation.

https://iai.asm.org/content/iai/67/11/6034.full.pdf

Laccase protects Cryptococcus neoformans from antifungal activity of alveolar macrophages.

Dynamics of fetal circulatory responses to hypoxia and asphyxia.

The study concerned the role of the carotid sinus nerves in the effects of acute asphyxia on the fetal circulation. Fetal sheep (n = 12) were instrumented at approximately 130 days' gestation for placement of fetal vascular catheters and an occluder around the maternal descending aorta below the renal arteries. In 7 fetuses the carotid sinus nerves were cut. On the third post-operative day, asphyxia was produced by occluding the maternal aorta for 2 min and fetal blood flows were determined by the radio-labelled microsphere technique. In control, there were no differences between intact and denervated fetuses in blood gases, cardiovascular variables or blood flows, with the exception of lower blood flows to the cerebrum, caudate nucleus, kidney, skeletal muscle and scalp in the denervated group (P < 0.01). Fetal heart rate, cardiac output, stroke volume and the rate-pressure product were similar in asphyxia, with the exception that mean arterial pressure was lower in denervated fetuses after 2 min of asphyxia. Noradrenaline and adrenaline concentrations peaked at 2 min, then declined, the increase being smaller (P < 0.01) in denervated fetuses. Regional blood flows were similar in the two groups. Vascular resistance was lower in the placenta and abdominal aorta at 2 min in denervated fetuses. There were few differences in organ blood flows between intact and denervated fetuses, and the differences in flow in normoxia for the kidney, skeletal muscle and scalp (but not cerebrum, caudate nucleus and hippocampus) disappeared in asphyxia. This study confirms that section of the carotid sinus nerves has little effect on arterial blood pressure and fetal heart rate in normoxia but produces small differences in the responses to acute severe asphyxia, e.g. in arterial blood pressure and catecholamines, giving evidence for the operation of chemoreflexes. The lower blood flow to cerebrum, caudate nucleus, kidney, skeletal muscle and scalp in denervated fetuses in normoxia suggests a tonic vasodilatation, part of the drive for which comes from carotid chemo- or baroreceptors.

Circulatory responses to acute asphyxia in intact and chemodenervated fetal sheep near term.

1
The neuroendocrine system of the lungs has no clear function. However, previous studies of one of its products, somatostatin, have implicated it in lung liquid removal at birth. The present study extends this concept by investigating the effects of dopamine, a major product of this system, on lung liquid reabsorption.

2
The effects of dopamine on fetal lung liquid production and reabsorption were tested on in vitro lungs from fetal guinea-pigs of 60 ± 2 days of gestation (term = 67 days). Dopamine was placed in the outer bathing saline during the middle hour of 3 h incubations. Fluid movements across the pulmonary epithelium were monitored by a dye dilution method, and changes in rates over 1 h intervals were tested for significance by analysis of variance and regression analysis.

3
Dopamine was able to reduce fluid production or cause reabsorption (based on 42 preparations). Control preparations and those given 10−8m dopamine showed no significant changes; those given higher concentrations showed significant reductions in production or reabsorption (P < 0.025 to P < 0.0005), according to dose (42.6 ± 10.8 % reduction at 10−7m; 75.4 ± 5.9 % reduction at 10−6m; 92.1 ± 7.0 % reduction at 10−5m and 121.4 ± 12.8 % (reabsorption) at 10−4m dopamine). The linear log dose-response curve (r= 0.99) showed a theoretical threshold at 1.7 × 10−9m dopamine.

4
Effects were mediated through specific dopamine receptors (based on 78 preparations). Dopamine at 10−6m was tested together with each of three dopamine receptor antagonists at 10−5m. The general dopamine receptor antagonist haloperidol and the more specific D2 receptor blocker domperidone both abolished responses, but the D1 receptor antagonist SCH 23390 was without effect. This suggested that D2 dopamine receptors mediated the responses, and that responses were not due to conversion of dopamine to adrenaline or noradrenaline.

5
There was no evidence that responses involved amiloride-sensitive Na+ transport (based on 54 preparations). Apical amiloride at 10−6, 10−5 or 10−4m, and the more specific Na+ channel blocker benzamil (10−5m), had no effect on responses to dopamine, in contrast to their effects on responses to adrenaline in sheep.

6
It is suggested that internal release of dopamine by the neuroendocrine system of the lungs may influence lung liquid reabsorption at birth. This system, which also produces somatostatin, another agent active on lung liquid production, is maximally developed and activated at birth; it is also deficient in hyaline membrane disease.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-7793.1998.283by.x

The effect of dopamine on lung liquid production by in vitro lungs from fetal guinea-pigs

To examine the responses of the sympatho-adrenal system to reduced oxygen supply we studied plasma and tissue concentrations of catecholamines during normoxemia, hypoxemia, and asphyxia in 22 fetal guinea pigs near term. Fetal blood was obtained by cardiopuncture in utero under ketamine/xylazine-anesthesia. Catecholamines were determined in plasma and tissue of 15 organs and 14 brain parts by HPLC-ECD. During normoxemia (SO2 54 +/- 4 (SE) %, pH 7.36 +/- 0.02, n = 5) plasma catecholamine levels were low (norepinephrine 447 +/- 53, epinephrine 42 +/- 12, dopamine 44 +/- 6 pg/ml). During hypoxemia (SO2 27 +/- 3%, pH 7.32 +/- 0.01, n = 6) and asphyxia (SO2 24 +/- 2%, pH 7.23 +/- 0.02, n = 11) tissue catecholamine concentrations changed with changing blood gases and with increasing plasma catecholamines. Norepinephrine concentrations increased in both skin and lung and decreased in liver, pancreas, and scalp; those of epinephrine increased in the heart, lung liver, and scalp and decreased in the adrenal. There were only minor changes in brain catecholamine concentrations except for a 50% reduction in dopamine in the caudate nucleus. Concentrations of dopamine catabolite 3,4-dihydroxyphenylacetic acid decreased in many brain parts, suggesting that cerebral catecholamine metabolism was affected by hypoxemia and asphyxia. We conclude that the sympatho-adrenal system of fetal guinea pigs near term is mature and that its stimulation by reduced fetal oxygen supply leads to changes in both plasma and tissue catecholamine concentrations.

Catecholamine concentrations in plasma and organs of the fetal guinea pig during normoxemia, hypoxemia, and asphyxia.

During intra-uterine hypoxia and asphyxia the centralization of the fetal circulation improves fetal survival. Together with simultaneous metabolic changes, supplies of both oxygen and substrates to the essential organs are maintained (Eisner et al. 1969; Cohn et al. 1974; Jones 1977; Peeters et al. 1979; Sheldon et al. 1979; Reuss et al. 1982; Jensen et al. 1985, 1987a; Jensen and Lang, this volume).

Distribution of Catecholamines in Central and Peripheral Organs of the Fetal Guinea Pig During Normoxaemia, Hypoxaemia, and Asphyxia

Fetal guinea pigs are frequently used for perinatal investigations, but little is known about the function of their sympathetic nervous system during hypoxemia and asphyxia. To examine the responses of the sympathetic nervous system to oxygen deficiency, we studied plasma and tissue concentration of catecholamines during normoxemia, hypoxemia, and asphyxia in 22 fetal guinea pigs near term (Jelinek and Jensen 1991). Fetal blood was obtained by cardiopuncture in utero under ketamine/xylazine anesthesia of the dam. Catecholamines were determined in plasma and tissue of 15 organs and 14 brain parts by high-performance liquid chromatography with electrochemical detection.

J. Jelinek

Papers

Catecholamine concentrations in plasma and organs of the fetal guinea pig during normoxemia, hypoxemia, and asphyxia.

Distribution of Catecholamines in Central and Peripheral Organs of the Fetal Guinea Pig During Normoxaemia, Hypoxaemia, and Asphyxia

Plasma and Tissue Concentrations of Catecholamines During Normoxemia, Hypoxemia, and Asphyxia in Fetal Guinea Pigs Near Term

Regional brain blood flow and oxygen supply in guinea pig fetuses near term.