Organization of trigeminothalamic tracts and other thalamic afferent systems of the brainstem in the rat: Presence of gelatinosa neurons with thalamic connections

Abstract

Thalamic projections from trigeminal and certain other nuclei of the brainstem of the rat have been investigated using the technique of retrograde transport of horseradish peroxidase (HRP). The pattern of trigeminothalamic projections is very specifically related to the individual subnuclei of the complex. The Main Sensory Nucleus (MSN) provides profuse cross connections to the ventrobasal thalamus (VB); these arise exclusively from medium and small-sized neurons, but never from the large cells. In addition to these crossed connections, a small ipsilateral dorsal trigeminothalamic tract arises from the dorsal third of the most rostral part of the MSN; this is the only ipsilateral connection to VB found in the trigeminal complex. Subnucleus Oralis has no projections to the thalamus; it is suggested that it may be concerned primarily with reflex activation of the facial nucleus, with which it is co-extensive in the rostro-caudal axis. Subnucleus Interpolaris has a well-defined crossed projection of moderate size which arises from the large, medium and some of the small neurons. Subnucleus Caudalis has a sparse output to the thalamus and differs in its projections from rostral to caudal. At the most rostral level, all layers (marginal, transitional gelatinosa and magnocellularis) contain neurons which project to the thalamus; particularly conspicuous in this respect are the marginal neurons, most of which are strongly labelled. The presence of gelatinosa neurons projecting to the thalamus emphasizes a point made in earlier reports, that these neurons do not form an homogeneous population. At caudal levels, the marginal neurons are the major source of thalamic projections, while connections to the thalamus form deeper lying neurons are infrequent. With a single exception, the medullary reticular nuclei contained no neurons with thalamic connections; a small number of reticulo-thalamic neurons were found in the ventral pontine area. Marked labelling of the medial cuneate nucleus and moderate labelling of the gracilis and lateral cuneate nuclei occurred contralaterally to the injection site. A small numebr of medial cuneate and gracile neurons project to the ipsilateral thalamus. Projections from the solitary nucleus were always ipsialteral. The boundaries of individual subnuclei of the lateral sensory trigeminal complex in the rat have been redefined on the basis of cytological criteria; these are in good accord with the corresponding thalamic projection patterns.

Organisation of reciprocal connections between trigeminal and vestibular nuclei in the rat

“…Injections of neuronal tracers, wheat germ agglutinin-horseradish peroxidase (WGA-HRP), biocytin, or biotylinated dextran amine (BDA, 10,000 MW, lysine-fixable) were made into the 5P, into one of the subdivisions of the 5Sp, or into the VN following stereotaxic coordinates of Paxinos and Watson (1986). The terminology for the trigeminal nuclei subdivisions follows that proposed by Fukushima and Kerr (1979) and Hayashi (1985). The subdivisions of the VN identified in cats by Brodal and Pompeiano (1957a, b) recognised four main nuclei: the superior (SVN), the lateral (LVN) subdivided into a dorsal and a ventral part, the medial (MVN), and the inferior (IVN) and smaller groups f, l, x, y, and z.…”

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

“…Nonetheless, all three components of the spinal tract nucleus also contain thalamicprojecting LTM neurons and so, along with the main sensory nucleus, likely contribute to our appreciation of fine touch. It is clear, from early anatomical investigations based on the distribution of degenerative neural endings in the thalamus following brainstem lesions, as well as from more recent anatomical studies using anterograde and/or retrograde tracers, that there are substantial projections to the thalamus from the subnucleus caudalis and caudal interpolaris (Fukushima and Kerr, 1979;Bruce et at., 1987;Magnusson et at., 1987;Kemplay and Webster, 1989;DiFiglia and Aronin, 1990;Yoshida et al, 1991;Luo and Dessem, 1995;and see Sessle, 1987;Craig and Dostrovsky, 1997). These include projections to the ventrobasal thalamus and thalamic nucleus submedius.…”

Trigeminal projections to hypoglossal and facial motor nuclei in the rat

“…The terminology for the trigeminal nuclei subdivisions follows that of Fukushima and Kerr (1979). The 5c is further subdivided cytoarchitecturally into laminae that resemble laminae of the spinal cord.…”