Effects of cobalt and bicuculline on focal microstimulation of rat pallidal neurons in vivo
Abstract
Deep brain stimulation (DBS) administered in the basal ganglia is an effective therapy for movement disorders; however, the mechanism(s) of action remain poorly understood. Because high-frequency electrical stimulation (HFS) preferentially activates fibers, one hypothesis of DBS action is that local release of transmitters from axon terminals underlies the inhibitory effects on spontaneous spiking observed in human intraoperative recordings. We hypothesize that blocking presynaptic release of transmitters will reduce any stimulation-induced effect and blocking of postsynaptic GABA receptors will reduce the inhibitory effect of HFS. We recorded neuronal responses after short HFS trains (2-37 microA, 0.5 seconds, 300 Hz) delivered through the recording electrode or via an adjacent electrode in 42 single globus pallidus (GP) units of anesthetized rats before and after injection of the synaptic blockers cobalt chloride (100 mM) and bicuculline methiodide (2 microg/microL). Responses to HFS trains were mainly transient ( approximately 350 milliseconds) inhibition of firing, but a late response ( approximately 1-2 seconds) and rebound burst were also found. Excitation was observed in 4 of 43 neurons studied. Neurons with transient in...Continue Reading
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