Structure-function relationships in rat medullary and cervical dorsal horns. I. Trigeminal primary afferents

Abstract

Intracellular recording and horseradish peroxidase (HRP) labeling were used to examine structure-function relationships in the medullary dorsal horn (MDH) and rostral cervical dorsal horn. In Nembutal-anesthetized rats, 78 trigeminal (V) primary afferent fibers were physiologically characterized and injected with HRP. Axons were sufficiently well stained to reconstruct all of their collaterals in the MDH. Many also extended into the cervical dorsal horn. Except for four axons, which responded best to noxious stimuli, all responded at short (mean = 0.50 ms) latencies to V ganglion shocks and to innocuous stimulation. Forty-five of our recovered fibers were associated with facial vibrissae and responded in either a rapidly adapting, slowly adapting type I, slowly adapting type IIa, or slowly adapting type IIb fashion. The adequate stimuli consisted of either slow deflection, high-velocity deflection, or a noxious pinch of the vibrissa follicle. The collaterals of all of the above-described mystacial vibrissa primary afferents proceeded directly to their region of arborization in a plane perpendicular to the lateral border of the medulla to collectively form a largely continuous, circumscribed terminal column. This longitudinally oriented column of terminal and en passant boutons angled from lamina V rostrally to lamina III caudally. In the magnocellular laminae of the MDH, all mystacial vibrissa primary afferents gave rise to similarly shaped arbors, regardless of their functional classification. While morphological variability was observed both within and between individual axons, variance between functional classes was no greater than that within a class. Moreover, number of collaterals, number of boutons, or bouton size did not distinguish functional classes. Nonmystacial vibrissa afferent arbors, with more caudal peripheral fields, had their primary arbor focus in C1 and C2 dorsal horn. These arbors had relatively little rostrocaudal overlap with mystacial vibrissa afferents, though they exhibited the same lamina V-to-III shift as they descended through the cervical cord. Unlike mystacial vibrissa afferents in the MDH, their collaterals followed a tortuous course and often occupied laminae II-V in one transverse section. The relative location of each vibrissa afferent's terminal field could be predicted by the particular vibrissa innervated. Dorsal vibrissae afferents had ventrolateral terminations and ventral vibrissae afferents terminated dorsomedially. Rostral vibrissae were represented in the rostral MDH, whereas caudal vibrissae were represented in the caudal MDH and rostral cervical dorsal horn.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional development of the vibrissae somatosensory system of the rat: (14C) 2-deoxyglucose metabolic mapping study

“…These observations show the correspondence between the periphery and Sp5I and Sp5O, as suggested by prior anatomical and electrophysiological studies (Nord, 1967(Nord, , 1968Belford and Killackey, 1980;Hayashi, 1980;Arvidsson, 1982;Bates and Killackey;Jacquin et al, 1986Jacquin et al, , 1988Dallel et al, 1990;Jacquin and Rhoades, 1990). In neonatal subjects, the foci of 2DG uptake corresponded well to that of the adult rat (Gonzalez and Sharp, 1985).…”

“…In some instances, there was a slight expansion of 2DG uptake into regions outside the vibrissa representation zone, i.e., the substantia gelatinosa and the lamina V. This could be mediated by laminae III/IV caudalis neurons, some of which have dendritic trees extending into the superficial laminae (Gobel, 1979;Sharp et al, 1988). The uptake extending into the deeper lamina V may also be due to the presence of some low-threshold mechanoreceptive neurons at the border of the laminae IV and V, which could be activated by whisker stimulation (Hu et al, 1981;Jacquin al et al, 1986).…”

Activation of trigeminal intranuclear pathway in rats with temporomandibular joint inflammation

“…It has been reported that trigeminal nociceptive information is sent to the nucleus caudalis of the trigeminal spinal nucleus and upper cervical cord (1)(2)(3). Following peripheral inflammation, Fos studies have revealed that two peaks of Fos protein-like immunoreactive cells (Fos protein-LI cells) are expressed; one in the transition zone between the trigeminal spinal nucleus interpolaris and caudalis (Vi/Vc zone), and one in the caudal laminated region between the caudalis and upper cervical dorsal horn (Vc/C 1,2 zone) (4).…”

Ultrastructural observations of synaptic connections of vibrissa afferent terminals in cat principal sensory nucleus and morphometry of related synaptic elements

“…These findings have provided a general picture of the termination pattern of vibrissa afferents but have not clarified the characteristics of the central terminations from functionally different afferent fibers. Studies using the intra-axonal staining technique have revealed that the morphologies of central terminations from low-threshold mechanoreceptive vibrissa afferents differ between FA and SA types within each trigeminal nucleus (Shigenaga et al, 1990;Miyoshi et al, 1994) and between different nuclei (Jacquin et al, 1986a(Jacquin et al, ,b, 1988(Jacquin et al, , 1989Shigenaga et al, 1990;Miyoshi et al, 1994). These results suggest that the characteristics of the morphology of primary afferent terminations are well correlated, with a morphologic segregation within the cytoarchitectonically different zones of the trigeminal sensory nuclei, and that sensory information from functionally distinct fibers is processed in a characteristic manner in the individual nuclei.…”