Electrophysiological and pharmacological studies on neurons in the spinal cord of the albino rat

Green, Kevin Andrew (1981) Electrophysiological and pharmacological studies on neurons in the spinal cord of the albino rat. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Intra- and extracellular recording techniques have been used on the spinal cord of anaesthetized rats. The subject of investigation was (1) the synaptic activity evoked in the spinal cord following stimulation of the motor cortex, (2) what transmitters might be involved ? (3) is the pyramidal tract the only pathway responsible for the synaptic action in the cord ? The cortical surface was electrically stimulated and the field potentials and synaptic actions in the lumbar spinal segments were monitored. Fast and slow components to the field responses were observed and the latencies of synaptic actions in single units showed a bimodal distribution. This along with the different positions of the evoked cells and the field potential maxima suggested that the fast component of the responses was not conducted by fibres of the pyramidal tract in the dorsal columns. The threshold for evoking the fast wave was lower than that which was necessary for evoking the slower wave. Injection of alcohol into the dorsal columns was found to preferentially eliminate the slow field potential recorded caudally to its point of injection. Frequency potentiation of the slow wave was seen when increasing the stimulation frequency up to 10Hz but the fast component was reduced at frequencies of stimulation above 1Hz. It is suggested that the slow component is consistent with what would be expected for activity mediated by the pyramidal tract whereas the fast component may be mainly indirect via an extrapyramidal pathway. Long-duration inhibitory effects were observed in the cord dorsal horn following cortical stimulation and these appeared to have more than one component, probably pre- and postsynaptic inhibitory effects were involved. Drugs were iontophoresed onto intra- and extracellularly recorded neurons with the object of investigating synaptic transmission from the pyramidal tract fibres. Some success was achieved with possible antagonists DL-aL-aminoadipate, glutamate diethylester and atropine. Atropine reduced the synaptic excitation of three cellls evoked with long latencies from the cortex, the possibility of involvement of a cholinergic neuron is discussed. An initial study done on neurons of the land snail Helix asperse for the purpose of learning techniques of iontophoresis and intracellular recording found no evidence to support a specific reversible block off chloride channels by copper ions. At concentrations of 10 M copper ions had toxic effects, depolarizing cells and increasing membrane conductance. These effects were largely reversible over a long period of washing although chloride mediated H-responses were still greatly reduced.

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