Both oral and caudal parts of the spinal trigeminal nucleus project to the somatosensory thalamus in the rat

Abstract

Recent evidence has been accumulated that not only spinal trigeminal nucleus caudalis (Sp5C) neurons but also spinal trigeminal nucleus oralis (Sp5O) neurons respond to noxious stimuli. It is unknown, however, whether Sp5O neurons project to supratrigeminal structures implicated in the sensory processing of orofacial nociceptive information. This study used retrograde tracing with Fluorogold in rats to investigate and compare the projections from the Sp5O and Sp5C to two major thalamic nuclei that relay ascending somatosensory information to the primary somatic sensory cortex: the ventroposteromedial thalamic nucleus (VPM) and the posterior thalamic nuclear group (Po). Results not only confirmed the existence of contralateral projections from the Sp5C to the VPM and Po, with retrogradely labelled neurons displaying a specific distribution in laminae I, III and V, they also showed consistent and similar numbers of retrogradely labelled cell bodies in the contralateral Sp5O. In addition, a topographic distribution of VPM projections from Sp5C and Sp5O was found: neurons in the dorsomedial parts of Sp5O and Sp5C projected to the medial VPM, neurons in the ventrolateral Sp5O and Sp5C projected to the lateral VPM, and neurons in intermediate parts of Sp5O and Sp5C projected to the intermediate VPM. All together, these data suggest that not only the Sp5C, but also the Sp5O relay somatosensory orofacial information from the brainstem to the thalamus. Furthermore, trigemino-VPM pathways conserve the somatotopic distribution of primary afferents found in each subnucleus. These results thus improve our understanding of trigeminal somatosensory processing and help to direct future electrophysiological investigations.

Differential activation of the human trigeminal nuclear complex by noxious and non‐noxious orofacial stimulation

“…These results are also supported by anatomical tract tracing studies which show that small-diameter primary afferents from deep and superficial facial structures synapse in laminae I, II and V of SpVc [Hayashi, 1985] and electrophysiological investigations that report SpVc excitation during deep and superficial orofacial noxious stimulation [Amano et al, 1986;Bolton et al, 2005;Imbe et al, 2001]. It appears that the SpVc plays a multidimensional role in the processing of orofacial pain: SpVc projects directly to the ventroposterior medial thalamic nucleus (VPM), which projects to the primary somatosensory cortex [De Chazeron et al, 2004;Guy et al, 2005], and is thought to process the sensory discriminative aspects of pain. The SpVc also projects to the lateral column of the midbrain periaqueductal gray matter, a region critical for the expression of flight/fight reactions to noxious stimuli [Bandler et al, 2000].…”

“…Unlike SpVc, which receives only direct primary afferent input, it has been reported that SpVo receives both direct primary, and second-order nociceptive inputs from neurons originating in SpVc [Dallel et al, 1998;Greenwood and Sessle, 1976;Hu et al, 1992;Voisin et al, 2002]. Like SpVc, SpVo projects directly to VPM in the thalamus and therefore is likely to play a role in the sensory discriminative aspects of orofacial pain [De Chazeron et al, 2004;Guy et al, 2005].…”

The Role of the Trigeminal Sensory Nuclear Complex in the Pathophysiology of Craniocervical Dystonia

“…Neurons of the spinal trigeminal nucleus project caudally to mid and lower cervical motor neurons innervating neck muscles (Devoize et al, 2010), and, in cats, projections have been traced caudally as far as the T6 segment (Matsushita et al, 1981). Rostrally, the spinal trigeminal nucleus projects to the thalamus (Guy et al, 2005), the superior colliculus, and the cerebellum via the inferior olive (Huerta et al, 1983;Xue et al, 2008). This organization supports the TSNC as a key structure in a large neural network modulating activity in motoneurons supplying muscles of the neck and face, and, therefore, should be considered in network models for dystonia.…”

Distribution of PDE8A in the nervous system of the Sprague-Dawley rat

“…From the neurons in the caudal trigeminal nucleus, pain impulses are projected to the thalamus via the spinothalamic system (Guy et al, 2005). Possibly indicating a role for PDE8 in trigeminal cAMP signaling, the present study shows PDE8A immunoreactivity in the dura, the neurons of the trigeminal ganglion and the caudal trigeminal nucleus.…”