|Friday, April 13th|
1:40 PM - 2:00 PM
Neural interactions involving the synaptic release of the neurotransmitter acetylcholine onto inhibitory interneurons are essential for regulating normal brain function but are implicated to be dysfunctional in many disease states, including Alzheimer’s disease (AD), Autism Spectrum Disorders (ASD), and epilepsy. Clarifying the relationship between cholinergic inputs and GABAergic inhibition functioning may be central to understanding the driving forces of neurological dysfunction. By elucidating cholinergic targeting of specific interneuron populations, we can gain insight into a variety of neurodegenerative disease states that impact connectivity between specific populations of cholinergic and GABAergic interneurons. In our study, transgenic mouse lines that express fluorescent protein labeling in interneuron subtypes were utilized, focusing on GABAergic cells expressing somatostatin(SOM) and parvalbumin (PV). Hippocampal brain slices were counterstained with the vesicular acetylcholine transporter (vAChT) antibody, which enables visualization of acetylcholine release sites. After immunostaining, slices were imaged on a confocal microscope. Image processing involved deconvolution, which corrected for light distortion and blurring, and quantitation of bouton numbers, bouton surface area, cell surface area, overall cholinergic bouton density, and cell layer. Consistent with targeting of cholinergic fibers to a subset of interneurons, our findings demonstrate that the level of cholinergic innervation on hippocampal GABAergic interneuron subtypes is heterogenous, depending on both cell type and cell location within the hippocampus. Because both SOM and PV hippocampal cell types are selectively reduced in human cases and mouse models of AD, we predict that GABAergic interneuron populations that are the most heavily innervated by cholinergic synapses will be selectively vulnerable in disease states.
2:00 PM - 2:20 PM
Although it is well known that the neurotransmitter acetylcholine (ACh) is crucial in the central nervous system, the roles of its specific receptors are less clear. Within the brain, the most important type of receptor is the muscarinic acetylcholine receptor (mAChR), which exists as one of five subtypes. Distinguishing the unique role of each subtype could lead to the development of more effective treatments for central nervous system disorders such as Alzheimer?s disease. One subtype, the M1 mAChR, is of particular interest because it is linked to cognitive functions and has been shown to be dysfunctional in disease states. Recent evidence suggests these receptors are prevalent in the hippocampus on parvalbumin (PV)-positive interneurons. Although various genetically-modified mouse strains have been developed to study the effects of removing specific receptor subtypes, the line I worked with is unique in that M1 mAChRs have been removed only from PV cells. As part of a comprehensive study on the role of M1 mAChRs, I compared the performance of mice lacking the receptors to those with intact receptors in a behavioral cognitive test called the Morris water maze (MWM). The MWM consisted of a tank of water in which the mice were required to find and remember the location of a hidden platform. In addition to the MWM, supplementary tests are being conducted to examine M1 mAChRs on PV cells, which will lead to a better understanding of the role of M1 receptors in hippocampus-dependent cognition and its associated diseases.
David Hess-Homeier, University of Montana - Missoula
2:20 PM - 2:40 PM
Sporadic mutations in methyl-CpG-binding protein 2 (MeCP2) cause Rett Syndrome a severe, neurodevelopmental disorder characterized by loss of motor and language skills, unusual stereotyped movements, autistic features, anxiety, and an increase in aggression. Duplication of the MeCP2 gene in males results in multiple symptoms including mental retardation, autistic behaviors, stereotyped hand movements and anxiety-related behaviors. Although MeCP2 protein is found at high levels in essentially all cells in the nervous system, changes in neuronal or glial (support) cell MeCP2 expression may be responsible for the disease phenotypes. The heightened anxiety or aggression seen in people with MeCP2 disorders suggests neurons regulating moods such as serotonin, dopamine, or noradrenaline neurons may be involved. Using the UAS-Gal4 binary expression system we are able to express MeCP2 in both Drosophila octopamine neurons (the invertebrate equivalent of noradrenaline) and astrocytes (glial cells) separately. I am examining the effects of MeCP2 on the function of octopamine neurons in aggressive behavior. In Drosophila, aggression is a robust innate behavior comprised of reproducible, easily identifiable behavioral patterns. Two male flies of the same genotype are placed in a fight chamber, to compete for territory and food. After the fight, aggression is quantified by scoring the latency to aggression (time to first encounter), number of lunges (the predominant aggressive behavior), and percentage of trials that exhibit aggressive behavior. Because interactions between glia and neurons are essential for many critical brain functions, we propose that MeCP2 activity in astroctyes causes gene expression changes that change the function of neighboring neurons. I have observed increased latency to aggression and decreased lunges in flies expressing MeCP2 in OA neurons and in flies expressing MeCP2 in astrocytes. My results may be extrapolated to human beings via conserved cellular mechanisms.
Anton T. Gabrielson, University of Montana - Missoula
2:40 PM - 3:00 PM
The developmental stage at which sugar pine (Pinus lambertiana) cones become surface fuels may influence behavior of surface fires in Sierra Nevada mixed-conifer forests. This study investigates how sugar pine cones of different sizes and conditions may differ in terms of mean biomass, burning characteristics, and relative contribution to surface fuel loads. A six-category classification was developed to describe cones of different lengths and developmental stages, or condition classes. Field sampling was conducted at the Yosemite Forest Dynamics Plot (YFDP), a 25.6 hectare mapped study area in Yosemite National Park. We randomly placed 90, 9 m2 sub-plots within the YFDP and counted the number of cones per condition class in each sub-plot. Cones were returned to the laboratory, where the mean biomass and burning characteristics by condition class were determined. Sugar pine cones represent 601 kg per hectare of surface fuels in YFDP. Mean cone biomass, flame length, burn time, and mass loss differed significantly between cone condition classes (one-way ANOVA, P25 cm long) accounted for 56% of biomass per hectare. Burning characteristics were most extreme for recently-deposited mature cones: flame lengths for mature cones had a mean of 110 cm, while flame lengths for juvenile cones had a mean of 18 cm. Forest managers can use the cone classification presented here to improve accuracy of surface fuel estimates.