Browsing by Author "Pousi, Suvi Päivikki"

Neurotrophic factors are essential for the development of the central nervous system. By signalling through Trk receptors, they have multiple effects on for example the survival of neurons, growth of axons and dendrites and stability of synapses. BDNF, which signals through TrkB receptor, is a neurotrophic factor with an important role in the formation and stabilization of glutamatergic synapses. It is also known to be released in an activity dependent manner. The mechanisms by which BDNF and TrkB signalling regulate synaptic transmission depend on the type and developmental stage of the synapse, and they are not well known. The electrical activity of immature networks consists of intrinsic activity with intermittent bursts of synchronous activity, which is believed to fine tune the synaptic connectivity through Hebbian plasticity mechanisms, which are stabilized by homeostatic mechanisms. Homeostatic regulation can be especially important during the development of the neural network while the glutamatergic transmisson is very labile. Little is known of the signalling routes that participate in the homeostatic plasticity during the development of the neural network. The aim of the thesis was to investigate how the long-term inhibition of TrkB signalling affects the glutamatergic transmission and the homeostatic regulation in area CA3 of neonatal hippocampus by using gene manipulated TrkBF616A mouse strain. The TrkB receptors in the TrkBF616A strain are modified so that they can be blocked with a kinase inhibitor (1NMPP1). In part of the work C57BL/6 -mice were used as control. In addition to the acute measurements the hippocampal slices were incubated in control conditions and with inhibitory drugs (TTX and 1NMPP1) for 15 to 20 hours, after which miniature excitatory postsynaptic currents (mEPSCs) were recorded with whole-cell patch clamp from area CA3 pyramidal cells. The research shows that continuous TrkB signalling is essential for the maintenance of AMPA receptor mediated synaptic transmission in CA3 area of neonatal hippocampus in TrkBF616A mice. Long-term inhibition of TrkB signalling decreases the amplitude of mEPSCs. TrkB-signalling seems to be needed also for the homeostatic response caused by network activity deprivation. The results also indicate that the inhibition of TrkB signalling increases the frequency of mEPSCs, possibly by a homeostatic mechanism. However, the results also show that the TrkBF616A mice strain might differ from wild type mice and the kinase inhibitor 1NMPP1 might have non-specific effects that are not currently known, so more extensive research on the matter is still needed to confirm the results.