A Thesis Submitted to the Faculty of Graduate Studies in Partial Fulfilment of the Requirements for the Degree of Master of Science Department of Neuroscience

An investigation was conducted into the activation mode of layer V pyramidal neurons of the motor cortex in response to intracortical microstimulation (ICMS) used to derive motor maps. An experimental preparation that combines ICMS and patch clamp single-cell electrophysiology was used. Bath application of glutamate (AMPA and NMDA) and GABA A receptor antagonists caused a significant reduction in spiking responses, suggesting a mainly synaptic mode of activation. These findings validate this preparation termed slice-ICMS in further examinations of neurotransmitter systems in motor map expression. In a second study, an investigation into the role of the cannabinoid receptor 1 in the excitability of motor cortex layer V pyramidal neurons was conducted. Endocannabinoids (eCBs) are ubiquitous retrograde messengers that inhibit neurotransmitter release in the central nervous system. CB1 receptor activation decreased excitability in layer V pyramidal neurons measured as a decrease in spiking responses to ICMS. This effect was compromised when rats were repeatedly stressed, suggesting downregulation of the CB1 receptor with stress in the motor cortex.