A Conditional Density Estimation Partition Model Using Logistic Gaussian Processes.

Conditional density estimation (density regression) estimates the distribution of a response variable y conditional on covariates x. Utilizing a partition model framework, a conditional density estimation method is proposed using logistic Gaussian processes. The partition is created using a Voronoi tessellation and is learned from the data using a reversible jump Markov chain Monte Carlo algorithm. The Markov chain Monte Carlo algorithm is made possible through a Laplace approximation on the latent variables of the logistic Gaussian process model. This approximation marginalizes the parameters in each partition element, allowing an efficient search of the posterior distribution of the tessellation. The method has desirable consistency properties. In simulation and applications, the model successfully estimates the partition structure and conditional distribution of y.

Noninvasive evaluation of portal hypertension: emerging tools and techniques.

Portal hypertension is the main cause of complications in patients with cirrhosis. However, evaluating the development and progression of portal hypertension represents a challenge for clinicians. There has been considerable focus on the potential role of noninvasive markers of portal hypertension that could be used to stratify patients with respect to the stage of portal hypertension and to monitor disease progression or treatment response in a longitudinal manner without having to undertake repeated invasive assessment. The pathogenesis of portal hypertension is increasingly understood and emerging knowledge of the vascular processes that underpin portal hypertension has paved the way for exploring novel biomarkers of vascular injury, angiogenesis, and endothelial dysfunction. In this paper we focus on the pathogenesis of portal hypertension and potential non-invasive biomarkers with particular emphasis on serum analytes.

Modified amino acids and peptides as substrates for the intestinal peptide transporter PepT1.

The binding affinities of a number of amino-acid and peptide derivatives by the mammalian intestinal peptide transporter PepT1 were investigated, using the Xenopus laevis expression system. A series of blocked amino acids, namely N-acetyl-Phe (Ac-Phe), phe-amide (Phe-NH2), N-acetyl-Phe-amide (Ac-Phe-NH2) and the parent compound Phe, was compared for efficacy in inhibiting the uptake of the peptide [3H]-D-Phe-L-Gln. In an equivalent set of experiments, the blocked peptides Ac-Phe-Tyr, Phe-Tyr-NH2 and Ac-Phe-Tyr-NH2 were compared with the parent compound Phe-Tyr. Comparing amino acids and derivatives, only Ac-Phe was an effective inhibitor of peptide uptake (Ki = 1.81+/- 0.37 mM). Ac-Phe-NH2 had a very weak interaction with PepT1 (Ki = 16.8+/-5.64 mM); neither Phe nor Phe-NH2 interacted with PepT1 with measurable affinity. With the dipeptide and derivatives, unsurprisingly the highest affinity interaction was with Phe-Tyr (Ki = 0.10+/-0.04 mM). The blocked C-terminal peptide Phe-Tyr-NH2 also interacted with PepT1 with a relatively high affinity (Ki = 0.94+/-0.38 mM). Both Ac-Phe-Tyr and Ac-Phe-Tyr-NH2 interacted weakly with PepT1 (Ki = 8.41+/-0.11 and 9.97+/-4.01 mM, respectively). The results suggest that the N-terminus is the primary binding site for both dipeptides and tripeptides. Additional experiments with four stereoisomers of Ala-Ala-Ala support this conclusion, and lead us to propose that a histidine residue is involved in binding the C-terminus of dipeptides. In addition, a substrate binding model for PepT1 is proposed.

Immunocytochemistry of oculomotor afferents in the squirrel monkey (Saimiri sciureus).

Attempts were made to co-define afferents of the oculomotor nuclear complex (OMC) and their putative neurotransmitters in the squirrel monkey. Wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) and wheat germ agglutinin conjugated to enzymatically inactive HRP and coupled to colloidal gold (WGAapoHRP-AU) were used as retrograde tracers in combination with immunocytochemical methods. Primarily unilateral injections were made into portions of the OMC. Stabilized tetramethylbenzidine (TMB) and silver enhanced sections were immunoreacted with antisera for choline acetyltransferase (ChAT), glutamate (GLU), aspartate (ASP), aminobutyric acid (GABA), serotonin (5-HT) and cholecystokinin (CCK). Moderate numbers of ChAT-IR neurons in caudal regions of the medial vestibular nuclei (MVN) projected to the OMC. Tracer labeled ChAT-IR cells in the MVN projected ipsilaterally to the ventral nucleus (medial rectus subdivision) of the OMC and bilaterally with contralateral dominance to other OMC subdivisions. Cholinergic neurons in the dorsal paragigantocellular reticular nucleus (DPG) projected bilaterally to each half of the OMC. Cells of the DPG, considered to contain inhibitory burst neurons impinging upon the contralateral abducens nucleus, were shown to project to virtually all subdivision of the OMC. Abducens motor neurons were ChAT-IR, but abducens internuclear neurons were not. Cells in caudal parts of the nucleus prepositus (NPP) projecting to the ipsilateral ventral nucleus of the OMC were not ChAT-positive; ChAT-IR cells in rostral NPP did not project to the OMC. Unilateral OMC injections labeled cells ipsilaterally in the RiMLF, contralaterally in the pretectal olivary nucleus, the interstitial nucleus of Cajal and the infracerebellar nucleus and bilaterally in the superior vestibular nucleus, none of which were ChAT-IR. A small number of cells in the locus ceruleus projected ipsilaterally to the OMC. Although large numbers of vestibular neurons were GLU-IR and ASP-IR, only a few tracer labeled ASP-IR neurons in the contralateral MVN projected to the OMC. No other GLU- or ASP-positive neurons were immunoreactive for GABA, 5-HT or CCK, but cells of the lateral vestibular nucleus were surrounded by CCK-IR fibers and terminals.