Axon and ganglion cell injury in rabbits after percutaneous trigeminal balloon compression.

New Zealand white rabbits were used to determine whether the changes in the Vth cranial nerve sensory root after compression were associated with the loss of a specific subclass of Vth cranial nerve ganglion cells, the disappearance of a distinct subset of primary afferent terminals in Vth cranial nerve nucleus caudalis, and/or injury to a specific axonal fiber type. There was no significant difference in the size of surviving ganglion cells after Vth cranial nerve compression, as measured 2 to 3 months after injury (P > 0.5, n = 4). Densitometric analysis of the nerves of rabbits that survived > 2 months after compression showed no significant difference in the immunoreactivity of substance P and calcitonin gene-reactive protein between compressed and control sides (P > 0.1, n = 4). Fink-Heimer staining of the Vth cranial nerve subnucleus caudalis revealed that transganglionic degeneration was most dense in the deeper layers, which are the sites of termination of large myelinated fibers. Ultrastructural evaluation of the type of myelinated axons injured by Vth cranial nerve compression in rabbits killed 7, 14, 37, and 270 days after injury was studied, and morphometric analysis was performed. The frequency distribution of axon diameters was significantly different for injured and control areas. The injured areas had higher ratios of small (< 3-microns diameter) to large-diameter axons compared to control distribution. These data indicate that balloon compression results in loss of fibers from the Vth cranial nerve sensory root and extensive transganglionic degeneration in the Vth cranial nerve brain stem complex. Cell size measurements and immunocytochemical data suggest that there is no specific loss of small ganglion cells or fine-caliber primary afferents. These experiments suggest that balloon compression relieves trigeminal pain by injuring the myelinated axons involved in the sensory trigger to the pain.

Patterning of local intracortical projections within the vibrissae representation of rat primary somatosensory cortex.

Anterograde and retrograde tracing with biotinylated dextran amine and Phaseolus vulgaris leukoagglutinin was used to assess projection patterns within the vibrissae representation of the rat's primary somatosensory cortex (S-I). Large and small injections of either tracer into the center of the vibrissae representation yielded dense anterograde and retrograde labelling throughout much of the tangential extent of the vibrissae representation within S-I. In all layers, the pattern and extent of retrograde and anterograde label was in rough congruence. The organization of this labelling varied across cortical layers. In layers II and III, labelled fibers extended away from injection sites in all directions and yielded a uniform pattern, which decreased in density with increasing distance from the tracer injection. There was a tendency for labelling to be more extensive along the representation of the row of vibrissae follicles that included the injection site than across rows. There was also a tendency for anterograde labelling to be more extensive in the direction of the representation of follicles more rostral on the face than that injected. In lamina IV, both labelled fibers and cells were restricted for the most part to the septa regions between the barrels. However, a small number of retrogradely labelled neurons were also located in the barrels (approximately one-ninth of the number found in the septa). The pattern observed in laminae II-III was repeated in layers V and VI. In these laminae, there was no evidence of a pattern of intracortical connections related to the vibrissae representation in overlying lamina IV.

Long-term age-related consequences of forelimb damage upon expression of primary afferent phenotypes in the cervical dorsal horn.

Rats that sustained forelimb removal on either embryonic day 16 (E-16) or the day of birth (P-0), or transection of the brachial plexus in adulthood, had sections through the cervical dorsal horn stained for galanin, calcitonin gene-related peptide (CGRP), or the plant lectin Bandieria simplicifolia-I (BS-I) 35-50 days after these lesions. The results of these experiments demonstrated age-related differences in the effects of peripheral nerve damage upon the distributions of each of these three primary afferent markers in the dorsal horn. Damage to the brachial plexus in adulthood caused a significant increase in the density of galanin immunoreactivity in the medial portion of layers I and II and the appearance of galanin immunoreactivity in layers III and IV of the cervical dorsal horn. Such lesions resulted in significant reductions in the density of CGRP immunoreactivity in layers I and II and of BS-I binding in lamina II. Forelimb removal on the day of birth resulted in no significant change in the density of galanin immunoreactivity in layers I and II, but in the appearance of galanin-immunoreactive fibers in layers III-V. Neonatal forelimb removal resulted in no significant change in the density of CGRP immunoreactivity in layers I and II, but in a significant reduction in the density of BS-I binding in the medial portion of lamina II. Removal of the forelimb on E-16 caused a significant increase in the density of galanin immunoreactivity in layers III-V, but had no significant effect on the density or distribution of either CGRP immunoreactivity or BS-I binding in the cervical dorsal horn. These results suggest that peripheral nerve damage at all ages may cause an up-regulation of galanin in a wider distribution of ganglion cell types than was previously thought to be the case, and that there are different sensitive periods for lesion-induced, long-term changes in the innervation of the dorsal horn by CGRP- and BS-I-positive primary afferent axons.

Evidence for survival of the central arbors of trigeminal primary afferents after peripheral neonatal axotomy: experiments with galanin immunocytochemistry and Di-I labelling.

Studies employing axoplasmic transport techniques have suggested that the central arbors of vibrissae-related primary afferents are rapidly and permanently lost from the trigeminal (V) brainstem complex after transection of the intraorbital nerve (ION). The present study reexamined this issue using immunocytochemistry for galanin (GAL) and anterograde labelling with Di-I to evaluate V brainstem organization in rats that sustained damage to the ION or individual vibrissae follicles in infancy or adulthood. After adult nerve damage, GAL-positive fibers are increased in layers I and II of V subnucleus caudalis (SpC). This was apparent by 3 days after the lesion. In rats that sustained nerve damage at birth (P0), GAL immunoreactivity (IR) appeared throughout the V brainstem complex and had a patchy distribution similar to that of vibrissae-related V primary afferents in normal rats. Increased GAL-IR in rostral portions of the V brainstem complex was observed in rats that sustained ION damage as late as P14. Additional experiments in which nerve damage was followed by destruction of the V ganglion demonstrated that this GAL-IR was contained in primary afferents. Damage to single vibrissa follicles or to a row of follicles produced a single patch or row of GAL-IR terminals in the somatotopically appropriate portion of the ipsilateral V brainstem complex. Di-I labelling in neonatally nerve-damaged rats demonstrated that primary afferent axons filled the central territory normally innervated by this nerve and that their terminal distribution was patchy. These results suggest that the V ganglion cells that survive neonatal axotomy may retain somatotopically organized projections to the V brainstem complex for at least a limited postnatal period.

Lesion-induced changes in the central terminal distribution of galanin-immunoreactive axons in the dorsal column nuclei.

Rats that sustained forelimb removal on either embryonic day (E) 16, on the day of birth (P-0), or transection of the brachial plexus in adulthood had brainstem sections stained for galanin, calcitonin gene-related peptide (CGRP), or substance P (SP) at various intervals after these lesions were made. In normal adult rats, only a few galanin-immunoreactive fibers are present in the cuneate nucleus and most are located in its caudal portion. CGRP-positive axons are also sparse in the cuneate and are distributed mainly in the periphery of the nucleus. SP-positive axons are seen throughout the cuneate nucleus. In rats that sustained forelimb removals at birth or transection of the brachial plexus in adulthood, dense galanin immunoreactivity was present throughout the cuneate nucleus at all rostrocaudal levels on the side of the brainstem ipsilateral to the lesion. The changes after lesions that were made in the adult animals were apparent within 1 week, the earliest time analyzed. Increases in galanin immunoreactivity in the cuneate of animals that sustained forelimb removals on P-0 were first visible on P-2. Neither forelimb removal at birth nor brachial plexus lesions in adulthood had any qualitative effect upon the distribution or density of CGRP- or SP-immunoreactivity in the cuneate nucleus. Removal of a forelimb on E-16 did not increase the density of galanin-immunoreactive fibers in the cuneate nucleus. Such lesions also failed to produce any appreciable change in the density of either CGRP- or SP-positive fibers in the cuneate nucleus. The present data raise the possibility that large caliber, non-peptidergic primary afferent axons which innervate the cuneate nucleus may express galanin after damage at birth or in adulthood.

Galanin immunoreactivity reveals a vibrissae-related primary afferent pattern in perinatal rats after neonatal infraorbital nerve transection.

Immunocytochemistry was used to demonstrate the distribution of galanin immunoreactivity in the trigeminal (V) brainstem complex of normal rats and rats that sustained neonatal transection of the infraorbital nerve (ION, the V branch that supplies the mystacial vibrissae). In normal adult and perinatal (postnatal day [P-] 7) rats, there is very little galanin immunoreactivity in the rostral part of the V brainstem complex. However, there is dense immunoreactivity for this peptide in layers I and II of V subnucleus caudalis (SpC). There was a marked upregulation of galanin immunoreactivity at all levels of the V brainstem complex of P-7 rats that sustained ION transection on P-0. In V subnucleus interpolaris and the magnocellular part of SpC, this immunoreactivity occurred in clusters which had a pattern resembling that of the mystacial vibrissae. In animals examined at 30 days or more after ION transection, there were a few more galanin-immunoreactive fibers on the deafferented side of the brainstem than on the intact side, but there was no evidence of a vibrissae-related pattern. Our interpretation of these results is that galanin immunocytochemistry reveals a vibrissae-related pattern in the central arbors of axotomized primary afferents for at least 1 week after they have been disconnected from the periphery.