Browsing by Subject "whisker-to-barrel system"

Sensory systems display a topographical organization, and in the murine somatosensory system there is oneto-one correspondence between individual whiskers and individual cortical columns called barrels. Functional connectivity in the whisker-to-barrel system is formed prenatally and refined after birth, guided by both spontaneous and whisker-evoked activity. GABAergic connectivity emerges already prenatally and includes transient circuits, but the exact role of GABAergic signalling in early development is elusive. The neuronal, major chloride extruder, potassium-chloride cotransporter (KCC2) is heavily upregulated in the cortex during the first two postnatal weeks resulting in the emergence of hyperpolarizing inhibition. However, in cortical interneurons (INs) KCC2 expression can be detected already at the time of birth. The role of this early interneuronal KCC2 expression is unclear. The aim of this thesis was to study the role of KCC2 in the network activity of cortical INs during the perinatal period. Transgenic mice with conditional inactivation of Kcc2 gene, and expression of the calcium indicator GCaMP6f in GAD2+ neurons (INs) were used to image cortical Ca2+ activity. Transcranial widefield Ca2+ imaging in awake head-fixed mice was performed at the day of birth (P0) and showed that spontaneous, but not evoked, activity was significantly reduced in the knock-out animals. Moreover, immunostaining for the activity-induced transcription factor Egr1 showed that thalamic network activity was significantly decreased in the knock-out and heterozygous animals, suggesting involvement of subcortical areas in the decreased cortical activity. Additional experiments are needed to elucidate the role of other mechanisms contributing to the observed change in activity.