Electrical and chemical synaptic transmission in sympathetic preganglionic neurones, in vitro
The main aim of the experiments described in this thesis was to examine electrical and chemical synaptic transmission in sympathetic preganglionic neurones (SPNs). The experimental approach used was the whole-cell patch clamp recording technique from SPNs in spinal cord slices from neonate rats. The SPNs were labelled with intracellular non-cytotoxic dyes to allow visualisation of the SPN morphology and to investigate putative sites of contact between the neurones. Characteristic electrophysiological and morphological properties were used to identify all SPNs included in this study. In addition, a dendritic plexus in the IML region was described for the first time, which may form an important area of integration of synaptic and/or neurohormonal information for SPNs. Simultaneous whole-cell recordings from pairs of electronically coupled SPNs were used to directly demonstrate electrotonic coupling between SPNs. The fundamental properties of the electronic junctions were examined including the possibility of functionally rectifying junctions between SPNs. Putative dendrodendritic points of contact were suggested as sites for the intercellular junctions between SPNs. Membrane potential oscillations, which are a 'hallmark' of electronic coupling in SPNs, were directly demonstrated to represent the electrotonic transmission of action potentials and associated afterhyperpolarisations (AHPs) from neighbouring coupled cells. Further support of a role for electronic coupling between SPNs was provided by the gap junction blocker, carbenoxolone, which was shown to block electrotonic coupling between SPNs.