Generation of the complex spike in cerebellar Purkinje cells.

Each neuron of the nervous system is a machine specialised to appropriately transform its synaptic inputs into a pattern of spiking output. This is achieved through the combination of specialisations in synaptic properties and location, passive cell geometry and placement of particular active ion channels. The challenge presented to the neuroscientist is to, within each cell type, identify such specialisations in input distribution and resulting active events, and assess their relative importance in the generation of action potential output patterns. The Purkinje cell, in particular its response to climbing fibre (CF) input, is an excellent setting in which to attempt to meet this challenge. The Purkinje cell receives a single, easily isolated CF axon, which makes hundreds of synapses across the cell's highly branched, active dendritic tree, resulting in the generation of prominent dendritic calcium spikes and a distinctive, reproducible burst of fast action potentials (the complex spike) at the soma. In this thesis I have separated out the importance of the size of this input, its location and the active dendritic spikes it triggers in the generation of the complex spike. I have found that, to a large extent, the complex spike pattern is determined by the size of the CF input alone. I have characterised the complex spike (its number of spikes, their timing, height and reliability) at both constant physiological frequency and across a range of paired- pulse depression causing intervals. By alternating between whole cell current and voltage clamp in the same cell, I have recorded both the complex spikes and EPSCs generated at certain paired pulse intervals. In this way I have been able to construct the EPSC - complex spike 'input - output' relationship. This demonstrated that there is a straightforward linear transformation between the EPSC input amplitude and the number and timing of spikes in the complex spike. This applies across cells, explaining a large amount of the inter-cell variability in complex spike pattern. Input location and dendritic spikes have surprisingly little influence over the Purkinje cell complex spike. I found that complex spikes generated by dendritically distributed CF input can be reproduced by using conductance clamp to inject CF-like synaptic conductance at the soma. Both CF input and somatic EPSG injection produced complex spike waveforms that can only be easily explained by a model in which spikelets are initiated at a distant site and variably propagated to the soma. By using simultaneous somatic and dendritic recording I have demonstrated that this distant site initiation site is not in the dendrites. Somatic EPSG injection reproduced complex spikes independently of dendritic spikes, and extra dendritic spikes triggered by CF stimulation were associated with only 0.24 0.09 extra somatic spikelets in the complex spike. Rather, I have found that dendritic spikes, generated reliably by the dendritic location of CF inputs, have a role in regulating the post-complex spike pause. An extra dendritic spike generates a 3.4 0.7 mV deeper AHP and a 52 11 % longer pause before spontaneous spiking resumed. In this way, I have identified specialisations that encode the size, and thus timing, of CF inputs in the complex spike burst, whilst allowing the dendritic excitation of Purkinje cells (which is strongly associated synaptic and intrinsic plasticity) to be simultaneously encoded in the post-complex spike pause. This may reflect the complex spike's proposed dual role in both controlling ongoing movement and correcting for motor errors

Believing in Belonging: An Ethnography of Young People's Constructions of Belief

Evidence from a three-year case study suggests that how young people discuss their beliefs reflect where they define and locate legitimate sites of power, meaning and authority. For many young people today, religion is an insufficient source and mode of belief and belonging. The findings discussed here suggest an orientation to family, friends and other social relationships as legitimate and sufficient sites for locating belief, authority and transcendence. I argue that the young people studied do not holds beliefs to be ‘true’, in that they are propositional creed-like statements. Young people have shifted the meaning of belief to describe affective relationships in which they feel they belong to. Such a shift necessitates a relocation of the transcendent to the everyday and social. That shift is particularly evident as young people discuss how they continue their relationships with the deceased loved ones

FBI-1 Can Stimulate HIV-1 Tat Activity and Is Targeted to a Novel Subnuclear Domain that Includes the Tat-P-TEFb—containing Nuclear Speckles

FBI-1 is a cellular POZ-domain–containing protein that binds to the HIV-1 LTR and associates with the HIV-1 transactivator protein Tat. Here we show that elevated levels of FBI-1 specifically stimulate Tat activity and that this effect is dependent on the same domain of FBI-1 that mediates Tat-FBI-1 association in vivo. FBI-1 also partially colocalizes with Tat and Tat's cellular cofactor, P-TEFb (Cdk9 and cyclin T1), at the splicing-factor–rich nuclear speckle domain. Further, a less-soluble population of FBI-1 distributes in a novel peripheral-speckle pattern of localization as well as in other nuclear regions. This distribution pattern is dependent on the FBI-1 DNA binding domain, on the presence of cellular DNA, and on active transcription. Taken together, these results suggest that FBI-1 is a cellular factor that preferentially associates with active chromatin and that can specifically stimulate Tat-activated HIV-1 transcription