Dental Pulp Neurons in the Subnucleus Reticularis Ventralis of the Cat

Abstract

In order to understand their functional significance, the response characteristics were studied of dental pulp neurons within the subnucleus reticularis ventralis (SRV) of the caudal medulla oblongata in the cat. Furthermore, we attempted to identify neurons relaying to the SRV and projecting the area of dental pulp neurons of the SRV.
Experiments were carried out on cats anesthetized with urethane and chloralose. Single unit activities were recorded from the SRV using glass capillary microelectrodes filled with 2% pontamine sky blue in 0.5M sodium acetate.
The neurons usually responded to bilateral dental pulp afferents, and were located within the dorsolateral part of the SRV. They were usually excited by mechanical stimulation of the ipsi- or bilateral cornea. In addition, they responded to noxious mechanical stimulation of the ipsi- or bilateral pinna, face and/or tongue. Some of the neurons were also activated by tapping the nose. Units having receptive fields similar to these neurons were found in lamina VII of the first cervical cord and in the intralaminar nuclei. About half of the neurons tested were antidromically activated by electrical stimulation of the nucleus centralis lateralis. It was also found that a significant proportion of the neurons was antidromically activated by electrical stimulation of the mesencephalic reticular formation.
The spinal trigeminal tract was cut at the level of the obex in order to interrupt trigeminal primary afferent input to the trigeminal subnucleus caudalis and its nearby bulbar lateral reticular formation. After a tractotomy, dental pulp neurons were found in the SRV. Neurons antidromically excited by electrical stimulation of the SRV were found within the nucleus reticularis parvocellularis.
These results suggest that dental pulp neurons relay trigeminal nociceptive inputs directly or indirectly via the mesencephalic reticular formation to the intralaminar nuclei and that neurons relaying trigeminal nociceptive input onto the SRV are located within the rostral to the obex.