Browsing by Subject "Purkinje cells"
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Item Developmental difference in the expression of neuronal damage following simulated hypoxia with cerebellar Purkinje cells(Texas Tech University, 1998-12) Barenberg, Paul DavidMorphological changes leading to neuronal cell death following a hypoxic insult in the brain are unclear. Cerebellar Purkinje cells (PCs) have been shown to exhibit selective vulnerability to hypoxia. In previous studies, PCs, in adult rats exposed to hypoxia, have shown a necrotic morphology, characterized by swelling of the cells, loss of membrane integrity, and lysis. In contrast, morphological changes in neonatal PCs following hypoxic injury consisted of cytoplasmic darkening and microvacuolization. This change, known previously as coagulative necrosis, has since been referred to as "dark cell degeneration" (DCD). The intent of the present study was to identify and characterize the mode of toxicity in 9-day-old and 21-day-old rat cerebellar Purkinje cells following hypoxic injury. Subsequent studies were designed to determine whether h5^oxic-induced DCD in PCs from 9-day-old rats represented an apoptotic event. Sagittal cerebellar slice preparation was used in the hypoxic model. Treated slices were submerged in Acsf and exposed to 30' of hypoxia (95% N2, 5% CO2) followed by 60' and 120' reoxygenation periods. The handling control slices were submerged in Acsf and exposed to an oxygenated environment (95% O2, 5% CO2) followed by reoxygenation periods. A Toluidine blue stain at the light microscopic level was used to characterize the morphological differences in the younger and older PCs. To identify whether DCD occurring in 9-day-old rat PCs is related to apoptosis, the following analyses were performed: DNA fragmentation using gel electrophoresis and in situ DNA labeling (TUNEL) and chromatin condensation observed with Hoechst nuclear stain. Purkinje cells stained with Toluidine blue exhibited 67%(±8) DCD and 10% (±2) necrosis in the 9-day-old rats compared to 70%(±12) necrosis and 30%(±5) DCD in the 21-day-old rats. PCs from 9-day-old rat slices displayed shrunken, rounded appearance with darkened nuclei and vacuolated cytoplasm, all morphological characteristics of apoptosis. In addition to morphological similarities to apoptosis, PCs from the 9-day-old rat showed with Hoechst staining, chromatin clumping. Using DNA gel electrophoresis, hypoxic-treated cerebellar slices exhibited DNA laddering upon the formation of oligonucleosomal-sized fragments of DNA (180-200bp) TUNEL assay which provides cellular specificity of the apoptotic activity in the cerebellar slice showed limited staining in the nucleus of the PCs of the treated slice. From the present findings, brain maturity influences the morphological phenotype of neurodegeneration of the Purkinje cells in response to a hypoxic insult. Based upon the lack of TUNEL staining in the PC nuclei, the hypoxic-induced DCD in PCs does not appear to resemble a classic type of apoptosis.Item Electrophysiological analysis of cerebellar serotonergic mechanisms in thiamine deficiency(Texas Tech University, 1983-08) Lee, Rong-shengNot availableItem Electrophysiological and pharmacological characterization of the serotonergic system on cerebellar purkinje cells(Texas Tech University, 1984-08) Lee, MunhyangIt has been shown that serotonergic fibers distribute widely in the cerebellum. The objectives of these experiments were to evaluate the effects of serotonin on cerebellar Purkinje cells and the influence of this substance upon the glutaminergic system within the cerebellum. This study consisted of four interrelated investigations. The first evaluated the responses of Purkinje cells to iontophoretically applied serotonin alone and in combination with various serotonin antagonists. It was observed that serotonin elicited one of three different effects on Purkinje cells: inhibition, excitation, or biphasic action consisting of inhibition followed by excitation. Excitatory effects of serotonin were antagonized or attenuated by iontophoretic application of the serotonin antagonist methysergide, whereas inhibitory effects were attenuated by the application of spiperone and ketanserin. These data suggest tentatively an involvement of different receptor sites for the inhibitory and excitatory effects of serotonin on Purkinje cells. The second set of experiments were conducted to investigate the actions of the cationic inhibitors of synaptic transmission, cobalt and manganese, and thereby determine whether presynaptic mechanisms were involved in the effects of serotonin. Excitations and inhibitions mediated by serotonin were not altered significantly in the presence of these ions. These data suggest that serotonin-mediated inhibitions and excitations may occur postsynaptically. Evaluation of the effect of serotonin on Purkinje cells after treatment with 5,7-dihydroxytryptamine (5,7-DHT) was the third part of this study. Serotonin applied microiontophoretically elicited the same effects on Purkinje cells in both treated and untreated animals: inhibition, excitation, or a biphasic effect. The spontaneous firing rates of the Purkinje cells were, however, shifted to lower frequencies after treatment with 5,7-DHT. In addition, the rate dependency of the activity of serotonin disappeared in animals treated with 5, 7-DHT. These results indicate that serotonin influences the spontaneous firing rate of Purkinje cells tonically in the normal state. The last part of this study was to evaluate the interaction of serotonin with the glutaminergic system that is known to exist in the cerebellum. Microiontophoretically applied serotonin inhibited the glutamate-induced excitation of Purkinje cells consistently. In conclusion, the present study suggests that the intrinsic serotonergic system exerts a tonic influence on the spontaneous firing rates of Purkinje cells. Secondly, microiontophoretically applied serotonin affects Purkinje cell firing directly and modulates glutamate-induced excitations of Purkinje cells.Item Excitatory amino acids in the cerebellum(Texas Tech University, 1993-08) Netzeband, Jeffrey GlenIn recent years, it has been shown diat the class of excitatory amino acid transmitters is very important for neurotransmission throughout the nervous system. Glutamate and aspartate are the most common endogenous transmitters of this class, but it is now known that they exert their actions through a multitude of receptor subtypes. Furthermore, modifications of excitatory amino acid transmission are believed to underlie many forms of sensory and motor learning in the brain, whereas perturbations of these systems underlie many neuropathologies. Since the cerebellum is involved with motor coordination and the cerebellar Purkinje cell forms a crucial link in the formation of motor learning, a thorough understanding of excitatory amino acid neurotransmission would be desirable. Extracellular recording techniques were coupled with microiontophoretic application of drugs to test the effectiveness of several endogenously and exogenously occurring excitatory amino acids in exciting cerebellar Purkinje cells in the anesthetized rat. Also, further characterization of N-methyl-D-aspartate (NMDA)-mediated responses was done as some studies have suggested that Purkinje cells do not have NMDA receptors. Results from these studies indicate that agents from all classes of excitatory amino acids are enable of exciting Purkinje cells and that NMDA-induced excitations are mediated through the classically defined NMDA receptor. Additionally, serotonin was shown to depress responses elicited by some but not all of the excitatory amino acids. These results suggest that all classes of excitatory amino acids are important for neurotransmission within the cerebellum and that serotonin may selectively modulate some of these pathways, thus affecting motor learning and coordination.Item Ionic contributions to the oscillatory firing activity of rat cerebellar Purkinje cells(Texas Tech University, 1993-05) Chang, Whasook SeoIntrinsic rhythmic firing patterns of neurons are believed to be mediated by sequential activation of a set of membrane ionic conductances. One of the most significant properties of oscillatory neurons in general is the presence of a negative slope resistance (NSR) region in the steadystate, whole cell voltage clconp current-voltage relationship (I-V curve). Although it has been emphasized that rhythmic activity may form a basis for an intrinsic functional context of the cerebellum, ionic conductances involved in oscillatory activity in cerebellar Purkinje cells (PCs) have yet to be fully determined. The major objective of this dissertation was to investigate the contribution of various conductances such as sodium (iNa)/ calcium (Ica)/ cationic inward (Ih)/ ^^d calcium-activated potassium (iR/ca))oscillatory activity of PCs.