Biomedical subjects
J Grigull
Publications and source records attributed to J Grigull.
Clustering of pedigrees using marker allele frequencies: impact on linkage analysis.
Ethnicity may form the basis for locus heterogeneity at certain susceptibility loci for complex diseases. Classification of pedigrees into ethnic groups is usually based upon self-report, but this may not be sensitive or specific. We investigated whether it is possible to cluster families from an admixed population using pedigree-specific marker allele frequencies. We used 323 autosomal microsatellite markers from 216 pedigrees who described themselves as either Caucasian or African American. First, we compared the stated ethnicity of pedigrees with clusters using pedigree-specific marker allele frequencies as input for a self-organizing map, a type of neural network. Using data from different chromosomes, nine pedigrees which were self-reported as African American were clustered with the Caucasian pedigrees. Removal of these nine pedigrees from the African American group did not markedly affect linkage results. We then proceeded to determine whether there was further heterogeneity between pedigrees using 1 x 3 nodes. Forty-four pedigrees were clustered in a group intermediate to the African American or Caucasian clusters. This group was composed of 36 and 8 pedigrees that described themselves as African American and Caucasian, respectively. Linkage analysis was performed in this group and results compared with the groups based upon self-reported ethnicity. Linkage to a region on chromosome 3 was observed in this intermediate group, which was more significant than any of the results obtained when pedigrees were grouped using self-reported ethnicity. Use of marker data may assist in clustering pedigrees with similar, ethnic backgrounds and may increase the power for genetic linkage studies.
The three-dimensional vestibulo-ocular reflex during prolonged microgravity.
Single-case, longitudinal studies of the three-dimensional vestibulo-ocular response (VOR) were conducted with two spaceflight subjects over a 180-day mission. For reference, a control study was performed in the laboratory with 13 healthy volunteers. Horizontal, vertical and torsional VOR was measured during active yaw, pitch and roll oscillations of the head, performed during visual fixation of real and imaginary targets. The control group was tested in the head-upright position, and in the gravity-neutral, onside and supine positions. Binocular eye movements were recorded throughout using videooculography, yielding eye position in Fick co-ordinates. Eye velocity was calculated using quaternion algebra. Head angular velocities were measured by a head-mounted rate sensor. Eye/head velocity gain and phase were evaluated for the horizontal, vertical and torsional VOR. The inclination of Listing's plane was also calculated for each test session. Control group gain for horizontal and vertical VOR was distributed closely around unity during real-target fixation, and reduced by 30-50% during imaginary-target trials. Phase was near zero throughout. During head pitch in the onside position, vertical VOR gain did not change significantly. Analysis of up/down asymmetry indicated that vertical VOR gain for downward head movement was significantly higher than for upward head movement. Average torsional VOR gain with real-target fixation was significantly higher than with imaginary-target fixation. No difference in phase was found. In contrast to vertical VOR gain, torsional VOR gain was significantly lower in the gravity-neutral supine position. Spaceflight subjects showed no notable modification of horizontal or vertical VOR gain or phase during real-target fixation over the course of the mission. However, the up/down asymmetry of vertical VOR gain was inverted in microgravity. Torsional VOR gain was clearly reduced in microgravity, with some recovery in the later phase. After landing, there was a dip in gain during the first 24 h, with subsequent recovery to near baseline over the 13-day period tested. Listing's plane appeared to remain stable throughout the mission. The findings reflect various functions of the otolith responses. The reduced torsional VOR gain in microgravity is attributed to the absence of the gravity-dependent, dynamic stimulation to the otoliths (primarily utricles). On the other hand, the reversal of vertical VOR up/down gain asymmetry in microgravity is attributed to the off-loading of the constant 1-g bias (primarily to the saccules) on Earth. The observed increase in torsional VOR gain from the 1st to the 6th month in microgravity demonstrates the existence of longer-term adaptive processes than have previously been considered. Likely factors are the adaptive reweighting of neck-proprioceptive afferents and/or enhancement of efference copy.
Novel bursting patterns emerging from model inhibitory networks with synaptic depression.
Studies show that short-term synaptic plasticity plays important roles in neural coding and the normal operation of the synapse. Basket cells in the hippocampus demonstrate this plasticity in the form of synaptic depression, and recent in vivo work indicates that basket cell activities contribute significantly to hippocampal output associated with different behavioural states. Thus it is essential to understand the generation and synchronization of patterns produced by basket cell networks with depression. We study two-cell model inhibitory networks with depression and obtain alternating bursting patterns and synchronous activity occurring between bursts. We describe mechanisms for how these patterns emerge by performing several simulations in the plane of different depression time constants, tauD. Such patterns might contribute significantly to various population activities observed in the hippocampus.