Medialis dorsalis thalamic unitary response to tooth pulp stimulation and its conditioning by brainstem and limbic activation

In nembutalized cats tooth pulp stimulation (TPS) was effective in exciting 18% of medialis dorsalis (MD) thalamic units. Facilitation of spontaneous MD unitary discharge followed high frequency stimulation of the lateral amygdala (25%), dorsal hippocampus (22%), mesencephalic reticular formation (20%) and septal nuclei (17%). Conditioning high-frequency stimulation of limbic and reticular structures, strongly facilitated the MD unitary responses to TPS. None of the thalamic neurons involved in nociception seems to project to the cerebral cortex. The conditioning effect on MD response of limbic and reticular stimulation suggests that these central structures may be involved in the modulation of the nociceptive input.