Trigeminal Nociceptive Neurons in the Intralaminar Nuclei of the Cat Thalamus

Abstract

In order to understand the functional significance of trigeminal nociceptive neurons in the intralaminar nuclei, their response characteristics were studied in the cat. Furthermore, we attempted to identify neurons relaying trigeminal nociceptive input to the intralaminar nuclei.
Experiments were carried out on cats anesthetized with urethane and chloralose. Single unit activities were recorded from the thalamus using glass capillary microelectrodes filled with 2% pontamine sky blue in 1M sodium acetate.
Trigeminal nociceptive neurons were found in the nuclei centralis lateralis, centralis medialis and parafascicularis of the intralaminar nuclei. They were excited by mechanical stimulation of the contra- or bilateral cornea at a strength above the human corneal pain threshold. Furthermore, they were frequently excited by noxious mechanical stimulation of the contra- or bilateral pinna, face and/or tongue. Tapping the nose dorsum and/or electrical stimulation of the canine dental pulp had excitatory effects in some trigeminal nociceptive neurons. These receptive field characteristics were similar to those of trigeminal nociceptive neurons in the caudal medulla oblongata. In addition, most of them were activated by noxious stimulation of the spinal nerve territory and by visceral sympathetic afferent nerves. Following electrical stimulation of the contralateral nucleus centralis lateralis, a majority of trigeminal nociceptive neurons in the dorsolateral part of the subnucleus reticularis ventralis of the caudal medulla oblongata were antidromically activated, suggesting that these nociceptive neurons relay trigeminal nociceptive input to the nucleus centralis lateralis.