Responses of rat pallidum cells to cortex stimulation and effects of altered dopaminergic activity

The aim of the study was to investigate the influences of dopamine on oligosynaptic corticopallidal neurotransmission. Different cortical areas were electrically stimulated and the responses in the pallidum were recorded by single-cell electrophysiology. Out of 377 pallidal neurons, 192 (51%) responded to stimulation of at least one of the cortical areas investigated. Convergence between frontal cortex and at least one of the other cortical areas was seen in 59 of 110 (54%) pallidal neurons responding to frontal cortex stimulation. Nearly three-quarters (73%) of all responsive pallidal neurons showed a short latency reduction of activity following the stimulus, the rest responded with pure activation or an activation-depression sequence. The dopaminergic influences on this corticopallidal impulse transmission were assessed by the systemic administration of the dopamine receptor-blocking neuroleptics, haloperidol and fluphenazine, as well as by conditioning electrical stimulation of the substantia nigra. Neuroleptic administration augmented the responses to cortical stimulation in 12 of 34 pallidal neurons. Stimulation of the substantia nigra diminished the responses in 24 and augmented them in 6 of 63 of the tested neurons. We propose from the present results, and in agreement with data from conceptually different studies done by others, that dopaminergic influences reduce the flow of information from the cortex to the pallidum. This may constitute a focussing mechanism by which only information form the strongest cortical inputs would pass to the pallidum while less prominent activity would be lost.