Tooth pulp input to the shell region of nucleus ventralis posteromedialis of the cat thalamus

Abstract

A population of neurons in the somatosensory part of the nucleus ventralis posteromedialis (VPM proper) that responded to electrical stimulation of the tooth pulp were studied in cats under urethan-chloralose anesthesia. Two classes of units responsive to electrical stimulation of the contralateral canine tooth pulp were identified. One class was responsive only to tooth pulp stimulation and these units were designated as tooth pulp specific (TPS) units. The other class of units responded to mechanical stimulation of the contralateral trigeminal integument in addition to tooth pulp stimulation. Their receptive field characteristics identified them as wide dynamic range (WDR) units responsive to tooth pulp stimulation. Both classes of units were located in the shell region of the caudal VPM proper; TPS units were coexistent with trigeminal nociceptive specific (NS) units and were found in the dorsomedial as well as ventromedial parts of the NS zone. WDR units responsive to electrical stimulation of the tooth pulp were located in the dorsomedial as well as ventromedial parts of WDR zone, a narrow band, approximately 300 micron wide, just in front of the NS zone. Tooth pulp units in the dorsomedial shell region of the VPM proper responded to the maxillary canine tooth pulp, whereas those in the ventromedial shell region responded to the mandibular canine tooth pulp. Some tooth pulp units in these two regions were responsive to stimulation of both maxillary and mandibular canine teeth. Both TPS and WDR units were antidromically excited by electrical stimulation of the SI area of the somatosensory cortex. Cooling the dorsolateral surface of the caudal medulla oblongata reversibly blocked tooth pulp evoked responses of TPS and WDR units. Trigeminal tractotomy just above the level of the obex irreversibly abolished tooth pulp-evoked responses of TPS and WDR units. These findings suggested that TPS neurons in the marginal layer of the trigeminal subnucleus caudalis and WDR neurons in the lateral part of the subnucleus reticularis dorsalis relay afferent impulses derived from the tooth pulp to the shell region of the VPM proper.

Stimulation of cranial vessels excites nociceptive neurones in several thalamic nuclei of the cat

“…In recent years evidence has accumulated to suggest that nociceptive neurones in the cat are located in a ~176 region surrounding the main tactile core of the ventrobasal complex. This appears to be true for VPL (Kniffki and Mizumura 1983;Honda et al 1983;Yokota et al 1988) and VPM, where the shell region region contains nociceptive neurones responding to stimulation of facial skin (Yokota andMatsumoto 1983a, 1983b;Yokota et al 1985) and tooth pulp (Rydenhag and Roos 1986;Yokota et al 1986). …”

“…If this trigeminal cerebrovascular innervation is involved in nociception and hence in the pathogenesis of headache, then it would be expected that neurones could be similarly activated in the thalamus, probably in areas known to respond to noxious stimulation of other orofacial structures. Numerous electrophysiological studies (for a review see AlbeFessard et al 1985) have revealed trigeminal nociceptive thalamic neurones, including some with input from the teeth, in several nuclear groups: in the intralaminar group of nuclei (Dong et al 1978;Yokota et al 1985;Rydenhag and Roos 1986;Yokota 1988), the posterior group (POm) (Woda et al 1975;Matsumoto et al 1988) and the ventroposteromedial nucleus (VPM) (Yokota andMatsumoto 1983a, 1983b;Yokota et al 1985;Rydenhag and Roos 1986;Yokota et al 1986). Recently two other areas have been increasingly implicated in trigeminal nociception, the ventral periphery of VPM (VPMvp) and nucleus submedius (Craig and Burton 1981;Craig 1987;Dostrovsky et al 1987).…”

Acute and Chronic Craniofacial Pain: Brainstem Mechanisms of Nociceptive Transmission and Neuroplasticity, and Their Clinical Correlates

“…Indeed, lesions specifically of rostral components of the VBSNC or injection into them of analgesic chemicals such as morphine may disrupt some pain behavior, as well as jaw-opening reflex activity, as mentioned in Section III, and there is evidence that caudalis lesions may not completely eliminate all behavioral responses evoked by noxious orofacial stimuli (Graham et al, 1988;Dallel et al, 1989;Duale et al, 1996; and see Sessle, 1987). Also, while it has been reported that caudalis disruption can abolish tooth-pulp-evoked responses in the ventrobasal thalamus (Yokota et a!., 1986), other studies have shown, in contrast, that caudalis lesions are relatively ineffective in affecting thalamic neuronal activity evoked by noxious stimuli applied to intra-oral or peri-oral tissues (Dallel et al, 1988;Raboisson et al, 1989 Despite these findings, the relative contributions of the subnuclei interpolaris and oralis vis-a-vis the subnucleus caudalis are less apparent. The role of nterpolaris is in fact still an enigma.…”

Immunocytochemistry of enkephalin and serotonin distribution in restricted zones of the rostral trigeminal spinal subnuclei: Comparisons with subnucleus caudalis

“…A technique comparable to that employed by was used to label relay cells by retrograde transport of horseradish peroxidase (HRP) following injection of enzyme into the portion of the ventral posteromedial thalamic nucleus (VPM) showing maximal evoked response t o stimulation of the maxillary and mandibular canine tooth pulps. The use of this electrophysiological approach was to ensure that the greatest concentration of HRP would be deposited in the medial VPM, an important site of termination of oral and perioral trigeminothalamic relay cells (Albe-Fessard et al, Yokota et al, 1986). It is, of course, not possible strictly to identify which of the relay cells labeled by the injection would be carrying nociceptive transmissions.…”