D. Ceri Davies

Cognitive correlates of Aβ deposition in male and female mice bearing amyloid precursor protein and presenilin-1 mutant transgenes

Several transgenic mouse models of Alzheimers disease (AD) have been developed that exhibit beta-amyloid (Abeta) neuropathology and behavioural deficits. However, not all studies have investigated the relationship between the development of cognitive impairment and neuropathology. Therefore, temporal changes in cognition were investigated in male and female double-mutant APPswexPS1.M146V (TASTPM) transgenic mice using an object recognition test and correlated with the development of cerebral Abeta neuropathology. Both male and female TASTPM mice exhibited similar significant cognitive impairment at 6, 8 and 10 months of age in the object recognition test, compared to wild-type littermates. There was no such cognitive impairment at 3 or 4 months of age. Quantitative immunohistochemistry using a battery of Abeta antibodies demonstrated that cerebral Abeta deposition was first apparent in 3-month-old mice, and it increased with age. The early appearance of cerebral Abeta deposits in the double-transgenic TASTPM mice supports the evidence that mutations in the PS1 gene accelerate Abeta deposition. The cerebral Abeta load was greater in female than in male TASTPM mice at all ages investigated. In the electron microscope, mature Abeta plaques comprising a fibrillar core surrounded by degenerating neurites and reactive glia were first observed in the cortex of TASTPM mice at 6 months of age, the same age at which cognitive impairment became apparent. These results suggest that the cognitive impairment in TASTPM mice is related to the disruption of neural connectivity and not simply Abeta deposition, which first occurs 3 months earlier.

Deficits of neuronal density in CA1 and synaptic density in the dentate gyrus, CA3 and CA1, in a mouse model of Down syndrome

Ts65Dn mice are partially trisomic for the distal region of MMU16, which is homologous with the obligate segment of HSA21 triplicated in Down syndrome (DS). Ts65Dn mice are impaired in learning tasks that require an intact hippocampus. In order to investigate the neural basis of these deficits in this mouse model of Down syndrome, quantitative light and electron microscopy were used to compare the volume densities of neurons and synapses in the hippocampus of adult Ts65Dn (n=4) and diploid mice (n=4). Neuron density was significantly lower in the CA1 of Ts65Dn compared to diploid mice (p<0.01). Total synapse density was significantly lower in the dentate gyrus (DG; p<0.001), CA3 (p<0.05) and CA1 (p<0.001) of Ts65Dn compared to diploid mice. The synapse-to-neuron ratio was significantly lower in the DG (p<0.001), CA3 (p<0.01) and CA1 (p<0.001) of Ts65Dn compared to diploid mice. When the data were broken down by synapse type, asymmetric synapse density was found to be significantly lower in the DG (p<0.001), CA3 (p<0.05) and CA1 (p<0.001) of Ts65Dn compared to diploid mice, while such a difference in symmetric synapse density was only present in the DG (p<0.01). The asymmetric synapse-to-neuron ratio was significantly lower in the DG (p<0.001), CA3 (p<0.01) and CA1 (p<0.001) of Ts65Dn compared to diploid mice, but there were no such significant differences in symmetric synapse-to-neuron ratios. These results suggest that impaired synaptic connectivity in the hippocampus of Ts65Dn mice underlies, at least in part, their cognitive impairment.

AQP4 gene deletion in mice does not alter blood-brain barrier integrity or brain morphology.

The glial cell water channel aquaporin-4 (AQP4) plays an important role in brain edema, astrocyte migration, and neuronal excitability. Zhou et al. [Zhou J, Kong H, Hua X, Xiao M, Ding J, Hu G (2008) Altered blood-brain barrier integrity in adult aquaporin-4 knockout mice. Neuroreport 19:1-5] recently reported that AQP4 deletion significantly altered blood-brain barrier integrity and glial fibrillary acidic protein (GFAP) immunoreactivity in their AQP4 null mice. Here we describe a detailed characterization of baseline brain properties in our AQP4 null mice, including gross appearance, neuronal, astrocyte and oligodendrocyte characteristics, and blood-brain barrier integrity. Gross anatomical measurements included estimates of brain and ventricle size. Neurons, astrocytes and oligodendrocytes were assessed using the neuronal nuclear marker NeuN, the astrocyte marker GFAP, and the myelin stain Luxol Fast Blue. The blood-brain barrier was studied by electron microscopy and the horseradish peroxidase extravasation technique. There were no differences in brain and ventricle sizes between wild type and AQP4 null mice, nor were there differences in the cerebral cortical density of NeuN positive nuclei, perimicrovessel and glia limitans GFAP immunoreactivity, or the thickness and myelination of the corpus callosum. The ultrastructure of microvessels in the frontal cortex and caudate nucleus of wild type vs. AQP4 null mice was indistinguishable, with features including intact endothelial tight junctions, absence of perimicrovessel astrocyte foot process edema, and absence of horseradish peroxidase extravasation. In contrast to the report by Zhou et al. (2008), our data show that AQP4 deletion in mice does not produce major structural abnormalities in the brain.

L‐ornithine and phenylacetate synergistically produce sustained reduction in ammonia and brain water in cirrhotic rats

Treatment of hyperammonemia and hepatic encephalopathy in cirrhosis is an unmet clinical need. The aims of this study were to determine whether L‐ornithine and phenylacetate/phenylbutyrate (administered as the pro‐drug phenylbutyrate) (OP) combined are synergistic and produce sustained reduction in ammonia by L‐ornithine acting as a substrate for glutamine synthesis, thereby detoxifying ammonia, and the phenylacetate excreting the ornithine‐derived glutamine as phenylacetylglutamine in the urine. Sprague‐Dawley rats were studied 4 weeks after bile duct ligation (BDL) or sham operation. Study 1: Three hours before termination, an internal carotid sampling catheter was inserted, and intraperitoneal saline (placebo), OP, phenylbutyrate, or L‐ornithine were administered after randomization. BDL was associated with significantly higher arterial ammonia and brain water and lower brain myoinositol (P < 0.01, respectively), compared with sham‐operated controls, which was significantly improved in the OP‐treated animals; arterial ammonia (P < 0.001), brain water (P < 0.05), brain myoinositol (P < 0.001), and urinary phenylacetylglutamine (P < 0.01). Individually, L‐ornithine or phenylbutyrate were similar to the BDL group. In study 2, BDL rats were randomized to saline or OP administered intraperitoneally for 6 hours or 3, 5, or 10 days and were sacrificed between 4.5 and 5 weeks. The results showed that the administration of OP was associated with sustained reduction in arterial ammonia (P < 0.01) and brain water (P < 0.01) and markedly increased arterial glutamine (P < 0.01) and urinary excretion of phenylacetylglutamine (P < 0.01) in each of the OP treated groups. Conclusion: The results of this study provide proof of the concept that L‐ornithine and phenylbutyrate/phenylacetate act synergistically to produce sustained improvement in arterial ammonia, its brain metabolism, and brain water in cirrhotic rats. (HEPATOLOGY 2009.)

Distribution of CGRP‐like immunoreactivity in the chick and quail brain

Calcitonin gene‐related peptide (CGRP)‐containing neurones have been implicated in the transmission of visceral sensory information to the cortex and in the control of arterial blood pressure in mammals. However, little is known about its function in other vertebrates. As a first step toward investigating the function of CGRP in birds, its distribution was studied in the domestic chick and quail brain by means of immunocytochemistry, by using antibodies against rat CGRP. The distribution of CGRP immunoreactivity in the chick and quail central nervous system was found to be similar. CGRP‐immunoreactive (CGRPi) perikarya were not present in the telencephalon. In the diencephalon, CGRPi perikarya were present mainly in the shell of the thalamic nucleus ovoidalis, the nucleus semilunaris paraovoidalis, the nucleus dorsolateralis posterior thalami, and in the hypothalamic nucleus of the ansa lenticularis. In the brainstem, CGRPi perikarya were present in the nucleus mesencephalicus nervi trigemini, the nucleus tegmenti ventralis, the locus coeruleus, the nucleus linearis caudalis and in the parabrachial region. In addition CGRPi perikarya were found in the motor nuclei of the III, IV, V, VI, VII, IX, X, and XII cranial nerves. The telencephalon contained CGRPi fibres within the paleostriatal complex (mainly in the ventral paleostriatum), parts of the neostriatum and ventral hyperstriatum, parts of the archistriatum, and the septum. In the diencephalon, the densest plexus of CGRPi fibres was observed in the dorsal reticular thalamus. A less dense CGRPi innervation was present in some dorsal thalamic nuclei and in the medial and periventricular hypothalamus. The pretectum and midbrain tegmentum also contained CGRPi fibres, whereas the optic tectum was virtually devoid of immunolabelling. Scattered CGRPi fibres were observed in the central grey and neighbouring pontine areas. Some of the sensory fibres of the trigeminal, vagal, glossopharyngeal, and spinal nerves were also CGRPi. The results of comparative studies indicate that the presence of CGRP in some thalamo‐telencephalic projections is a primitive feature of the forebrain of amniotes. Therefore, the brain areas giving rise to and receiving such a projection in different vertebrates, are likely to be homologous. J. Comp. Neurol. 421:515–532, 2000.

Distribution of corticotropin-releasing factor-immunoreactive neurons in the central nervous system of the domestic chicken and Japanese quail

In birds, as in mammals, corticotropin‐releasing factor (CRF) is present in a number of extrahypothalamic brain regions, indicating that CRF may play a role in physiological and behavioral responses other than the control of adrenocorticotropin hormone release by the pituitary. To provide a foundation for investigation of the roles of CRF in the control of avian behavior, the distribution of CRF immunoreactivity was determined throughout the central nervous system of the domestic chicken (Gallus domesticus) and Japanese quail (Coturnix japonica). The distribution of CRF‐immunoreactive (‐ir) perikarya and fibers in the chicken and quail brain was found to be more extensive than previously reported, notably in the telencephalon. Numerous CRF‐ir perikarya and fibers were present in the hyperstriatum, hippocampus, neostriatum, lobus parolfactorius, and archistriatum, as well as in the nucleus taeniae, nucleus accumbens, and bed nucleus of the stria terminalis, which exhibited the strongest immunolabeling in the telencephalon. The presence of dense populations of CRF‐ir perikarya in the medial lobus parolfactorius, nucleus of the stria terminalis, and paleostriatum ventrale, apparently giving rise to CRF‐ir projections to the mesencephalic reticular formation, the parabrachial/pericerulear region, and the dorsal vagal complex, suggests that these telencephalic areas may constitute part of the avian “central extended amygdala.” These results have important implications for understanding the role of extrahypothalamic CRF systems in emotional responses in birds. J. Comp. Neurol. 469:559–580, 2004.

Role of aquaporin-4 in the development of brain oedema in liver failure

BACKGROUND & AIMS Liver failure is associated with progressive cytotoxic brain oedema (astrocyte swelling), which underlies hepatic encephalopathy (HE). Ammonia and superimposed inflammation are key synergistic factors in HE, but the mechanism(s) involved remain unknown. We aimed to determine whether aquaporin-4 (AQP4), an astrocyte endfeet bi-directional water channel, is associated with the brain oedema of HE. METHOD Rats (n=60) received sham-operation (sham), 5 days hyperammonaemia-inducing diet (HD), galactosamine (GALN) induced acute liver failure (ALF), 4 weeks bile duct-ligation (BDL) induced cirrhosis, or caecal ligation and puncture (CLP), a 24h model of bacterial peritonitis. Rats from every group (except CLP) were randomised to receive intraperitoneal injections of lipopolysaccharide (LPS; 1mg/kg) or saline, prior to termination 3h later. Brain water, AQP4 protein expression (western blot) and AQP4 localisation by immunogold electron microscopy were investigated. RESULTS Significant hyperammonaemia was observed in saline-injected BDL (p<0.05), GALN (p<0.01), and HD (p<0.01), compared to sham rats. LPS injection did not affect arterial ammonia or plasma biochemistry in any of the treatment groups. Increased brain water was observed in saline-injected GALN (p<0.05), HD (p<0.01), and CLP (p<0.001) compared to sham rats. Brain water was numerically increased in BDL rats, but this failed to reach significance (p=0.09). LPS treatment further increased oedema significantly in all treatment groups (p<0.05, respectively). AQP4 expression was significantly increased in saline-injected BDL (p<0.05), but not other treatment groups, compared to sham rats. Membrane polarisation was maintained in BDL rats. CONCLUSION The results suggest that AQP4 is not directly associated with the development of brain oedema in liver failure, hyperammonaemia, or sepsis. In cirrhosis, there is increased AQP4 protein expression, but membrane polarisation, is maintained, possibly in a compensatory attempt to limit severe brain oedema.

Specialist anatomy: Is the structure of teaching adequate?

BACKGROUND A knowledge and understanding of specialist anatomy, which includes radiological, laparoscopic, endoscopic and endovascular anatomy is essential for interpretation of imaging and development of procedural skills. METHODS AND MATERIALS Medical students, specialist trainees and specialists from the London (England, UK) area were surveyed to investigate individual experiences and recommendations for: (1) timing of the introduction of specialist anatomy teaching, and (2) pedagogical methods used. Opinions relating to radiological, laparoscopic, endoscopic and endovascular anatomy were collected. Non-parametric tests were used to investigate differences in recommendations between specialist trainees and specialists. RESULTS Two hundred and twenty-eight (53%) individuals responded to the survey. Imaging was most commonly used to learn radiological anatomy (94.5%). Procedural observation was most commonly used to learn laparoscopic (89.0%), endoscopic (87.3%) and endovascular anatomy (66.2%). Imaging was the most recommended method to learn radiological anatomy (92.1%). Procedural observation was the most recommended method for learning laparoscopic (80.0%), endoscopic (81.2%) and endovascular anatomy (42.5%). Specialist trainees and specialists recommended introduction of specialist anatomy during undergraduate training. CONCLUSION Although the methods for specialist anatomy learning are in practice, there is no consensus on timing and structure within the anatomy curriculum. Recommendations from trainees and specialists should be considered so that the existing curriculum can be refined to maximise learning outcomes.

Determination of biometric measures to evaluate patient suitability for transoral robotic surgery.

Transoral robotic surgery (TORS) represents a novel treatment for oropharyngeal cancer and obstructive sleep apnea. Appropriate patient selection is crucial. The purpose of this study was to investigate whether anatomic biometric measures are useful to determine the feasibility of performing TORS.

Adrenergic agents modify cerebral edema and microvessel ultrastructure in porcine sepsis.

Objective:To investigate the effects of adrenergic agents on the cerebral response to sepsis. Design:Prospective, randomized, controlled, experimental animal study. Setting:Medical school research laboratories. Subjects:Twenty-eight middle white pigs (25–30 kg). Interventions:Pigs were anesthetized, mechanically ventilated, and randomly assigned to one of the following groups: cecal peritonitis (n = 5), cecal peritonitis with dopexamine (n = 5), cecal peritonitis with dopexamine and the &bgr;2-adrenergic receptor antagonist ICI 118,551 (n = 4), cecal peritonitis with methoxamine (n = 5), cecal peritonitis with dopexamine and methoxamine (n = 4), and sham-operated (n = 5). Sham-operated pigs were killed after laparotomy, and pigs with cecal peritonitis were killed 8 hrs after its induction. Samples of frontal cerebral cortex were taken immediately after death, processed for light and electron microscopy, and then subjected to morphometric analysis. Measurements and Main Results:There was significantly more (p < .0005) cerebral perimicrovessel edema in pigs with cecal peritonitis (80.2 &mgr;m2 ± 5.3 sem) than in sham-operated pigs (26.2 &mgr;m2 ± 2.7 sem) and significantly less (p < .0005) perimicrovessel edema in dopexamine-treated pigs with cecal peritonitis (39.8 &mgr;m2 ± 5.5 sem) than in pigs with cecal peritonitis alone (80.2 &mgr;m2 ± 5.3 sem). There was no significant difference between the amount of perimicrovessel edema in pigs with cecal peritonitis treated with dopexamine plus ICI118,551 and pigs with cecal peritonitis alone. The mean cerebral microvessel endothelial cell cross-sectional area in methoxamine-treated pigs with cecal peritonitis (26.3 &mgr;m2 ± 2.6 sem) was significantly greater than that in pigs with cecal peritonitis alone (16.3 &mgr;m2 ± 2.1 sem, p = .008) or in sham-operated pigs (12.3 &mgr;m2 ± 1.3 sem, p = .0005). Conclusions:Dopexamine protects against cerebral edema formation in sepsis by stimulation of &bgr;2-adrenergic receptors, whereas the &agr;1 adrenoceptor agonist methoxamine induces cerebral microvessel endothelial cell swelling.