The Journal of comparative neurology
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Comparative Study
Differential rostral projections of caudal brainstem neurons receiving trigeminal input after masseter inflammation.
To understand the functional significance of orofacial injury-induced neuronal activation, this study examined the rostral projection of caudal brainstem neurons that were activated by masseteric inflammation. Rats were injected with a retrograde tracer, Fluorogold, into the nucleus submedius of the thalamus (Sm), parabrachial nucleus (PB), lateral hypothalamus (LH), or medial ventroposterior thalamic nucleus (VPM) 7 days before injection of an inflammatory agent, complete Freund's adjuvant (CFA), into the masseter muscle. Rats were perfused at 2 hours after inflammation, and brainstem tissues were processed for Fos-Fluorogold double immunocytochemistry. ⋯ These findings emphasize the importance of the trigeminal Vi/Vc transition zone in response to orofacial deep tissue injury. Furthermore, the results differentiate the ventral and dorsal portions of the Vi/Vc transition zone, in that the Sm received projection mainly from activated neurons in the ventral Vi/Vc. The activation of Vi/Vc neurons and associated ascending pathways may facilitate somatoautonomic and somatovisceral integration and descending pain modulation after orofacial deep tissue injury.
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Mice exhibit a unique wound healing response following spinal cord injury in which the lesion site fills in with a connective tissue matrix. Previous studies have revealed that axons grow into this matrix, but the source of the axons remained unknown. The present study assesses whether any of these axons were the result of long tract regeneration. ⋯ Rubrospinal and reticulospinal tract axons also did not grow into the lesion site. 5-HT-positive axons extended to the edge of the lesion, and a few axons followed astrocyte processes into the margins of the lesion site. In contrast to the other pathways, BDA-labeled ascending sensory axons did extend into and arborized extensively within the connective tissue matrix, although the subgroup of ascending axons that are positive for CGRP did not. These results indicate that the connective tissue matrix is permissive for regeneration of some classes of ascending sensory axons but not for other axonal systems.
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The urethrogenital (UG) reflex is a spinal sexual reflex that consists of autonomic and somatic nerve activity and vaginal, uterine, and anal sphincter contractions. The UG reflex is under tonic descending inhibition by neurons in the region of the nucleus paragigantocellularis (nPGi). The location of spinal neurons activated by the UG reflex was examined in the female rat using the immediate early gene, c-fos. ⋯ Spinal interneurons involved in the UG reflex were found close to the preganglionic neurons and in the dorsal horn and intermediate and medial gray of T12-S1. NPGi inputs were found primarily on the autonomic efferents and interneurons in the medial and intermediate gray. These studies demonstrate multisegmental spinal circuits activated with the UG reflex and demonstrate that the descending inhibition from the nPGi is by means of preganglionic and somatic efferents and spinal interneurons closely associated with the efferent output.
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Dermatomes and the associated central projection fields were studied with the application of fluorescent neurotracer, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), to 21 reference points on rat trunk and hindlimb skin. Segmental distribution and rostrocaudal central level of dorsal root ganglion (DRG) neurons innervating reference points were examined and DiI-induced fluorescent areas were mapped in the horizontal plane through lamina II of the dorsal horn. Segmental levels of DRG neurons innervating reference points were generally identical to the level determined using dye-extravasation methods. ⋯ Afferents from reference points located on the ventral median line of the hindlimb projected to two separate fields: one on the medial margin of spinal cord segments L2-L5 and the other on the medial half of spinal cord segment L5. From the distribution of central projection fields of reference points, central projection fields of dermatomes were revealed as even in shape and located within corresponding spinal cord segments. The arrangement of peripheral and central fields of dermatomes and body surface regions suggests that peripheral and central projection fields of cutaneous afferent fibers are reshaped from the common prototypical pattern that exhibits an orderly and evenly sequenced arrangement.
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Here we examine whether a permanent reduction in the noradrenergic (NA) innervation of the spinal cord leads to a chronic decreased nociceptive threshold. NA denervation of rats was achieved by intrathecal injection of dopamine beta-hydroxylase antibodies conjugated to the toxin saporin. A subset of animals also underwent unilateral L5 spinal nerve ligature to induce sustained neuropathic pain behavior. ⋯ Finally, in the spinal cord of toxin-treated rats, immunoreactivity for substance P was decreased, whereas that of its receptor (NK1) was increased. These animals exhibited antinociception to a low dose of an NK1 receptor antagonist. Our results suggest that NA contributes only modestly to determining the nociceptive threshold and that its antinociceptive effects are closely linked to opioidergic and tachykinergic neurotransmission.