The aim of this project was to develop an in vitro hemisected adult hamster spinal cord preparation in order to study the dorsal root reflex (DRR) and primary afferent depolarization (PAD). Techniques were developed to isolate the hamster spinal cord with its lumbar dorsal roots intact. The dorsal horn was shown to be electrophysiologically viable. The Dim and dorsal horn potential (DEP) were recorded on stimulation of the dorsal roots. Spontaneous potentials were also observed. The relationship between the DRR and DEP was examined by comparison of the spread of these potentials between lumbar dorsal segments and the effect of conditioning stimuli on the amplitude of the various potentials. The constituents of the artificial csf could be manipulated, or drugs perfused over the spinal cord dissolved in the csf. The DRR and Dfff were demonstrated to be of synaptic origin. The GABA antagonist bicuculline also antagonised these potentials, while pentabarbital potentiated the DEP. These observations are consistent with the mediation of this potential by OABA. Observations were also made on the effect of strychnine and tubocurarine. No effect was observed on the extracellular potentials when excitatory or inhibitory amino acids were perfused over the spinal cord, with the exception of the glutamate analogues n-methyl-D-aspartate and kainate. Spontaneous activity was inhibited by acetylcholine and potentiated by 4-amino-pyridine. Techniques were extended from the observation of extracellular field potentials to extracellular recordings from single primary afferent units. Single unit DRRs were observed in some fibres. Those fibres which possessed a reflex action potential had a faster conduction velocity. Intra-axonal recordings were achieved from primary afferent fibres of 2 - 8µ diameter, for up to 2 hours. Spontaneous and evoked PAD was observed in 17 of the 31 fibres penetrated. The mean membrane potential was -69.7 ± 1.25mV (± SEM) with action potential amplitude of 83 t 2mV, PAD amplitude was 2.6 ± 0.3mV and of 190 t 14ms duration. The PAD was synaptically generated and bicuculline sensitive, with a reversal potential of -53mV. The fibres were depolarized by GABA. Spontaneous and evoked reflex action potentials were observed to arise on the rising phase of PAD. The extracellular and intra-axonal observations are consistent with the theory that PAD is generated presynaptically by a GABA mediated synaptic mechanism.