Effects of neonatal infraorbital lesions upon central trigeminal primary afferent projections in rat and hamster

Transganglionic and anterograde horseradish peroxidase transport was used to evaluate the central projections of undamaged trigeminal (V) nerve branches in adult rats and hamsters subjected to transection of the infraorbital nerve and to cauterization of the vibrissae follicles at birth. In rats, deafferented regions of the V brainstem nuclear complex did not receive abnormal projections from undamaged mandibular sensory afferents. Undamaged ophthalmic-maxillary fibers also failed to terminate heavily in the region deafferented by the neonatal infraorbital lesions. In the hamster, on the other hand, neonatal infraorbital nerve lesions were associated with statistically significant increases in mandibular terminal fields in the principalis, subnucleus interpolaris, and subnucleus caudalis. Tracing experiments were also carried out in neonatal rats and hamsters to determine whether the above-described differences in the response to infraorbital nerve damage reflected a difference in the maturity of the V primary afferent projections to the brainstem at the time of our neonatal lesions. In neonatal rats, the infraorbital and mandibular projections to the V brainstem nuclear complex were quite adultlike, both in their pattern and in the extent of their overlap, which was minimal. Overlap between mandibular and infraorbital terminal fields was also minimal in the newborn hamsters.     

Infraorbital nerve blockade from birth does not disrupt central trigeminal pattern formation in the rat.

We tested the hypothesis that patterned primary afferent impulse activity during early postnatal periods is necessary for central trigeminal pattern formation. Newborn rats had their whiskers trimmed daily and new slices of slow release polymer containing the sodium channel blocker, tetrodotoxin, were placed under the infraorbital nerve every 8 h for up to 9 days. Electrophysiological recordings indicated that trigeminal ganglion cells were unresponsive to peripheral stimuli and chronically silenced. Trigeminal ganglion cell numbers were unaffected by nerve blockade. Cytochrome oxidase staining patterns in the trigeminal brainstem complex, thalamus, and barrel cortex were normal on postnatal day 1, 3, 5, 7, or 9 (n = 4 each). Whisker-related patches were of normal sizes and staining densities. Similar negative results were obtained in 9 rats in which whiskers were trimmed daily and the long-acting local anesthetic bupivacaine was injected into the whisker pad at 2.5- to 4-h intervals from birth to sacrifice on postnatal day 5-9. Cytochrome oxidase staining patterns and patch properties again did not differ from normal. Thus, trigeminal pattern formation occurs even when the entire infraorbital nerve is silenced from birth.     

Long-term effects of neonatal axoplasmic transport attenuation on the organization of the rat's trigeminal system

The current study examined the long-term effects of infraorbital nerve (ION) axoplasmic transport attenuation with vinblastine on the organization of trigeminal (V) primary afferents and central vibrissae-related patterns. Retrograde tracing and single unit recording were used to evaluate the innervation of vibrissae follicles in adult (P > 60) rats that sustained application of vinblastine to the ION at birth. Single units recorded from vinblastine-treated animals yielded responses to deflection of a single vibrissa, and a significantly (P < 0.001) higher percentage of these cells (85.7%) showed rapidly adapting responses compared with normal rats (42.2%). Retrograde tracing revealed a qualitatively and normal distribution of V ganglion cells innervating A-row and E-row vibrissae follicles in vinblastine-treated rats. Transganglionic tracing with horseradish peroxidase (HRP) demonstrated a qualitatively and quantitatively normal somatotopic organization of vibrissae follicle input to V nucleus principalis (PrV) and V subnucleus interpolaris (SpI) in the vinblastine-treated animals. Despite the nearly normal mapping of V ganglion cell axons onto the vibrissae follicles and brainstem, staining for either cytochrome oxidase (CO) or parvalbumin failed to reveal vibrissae-related patterns in PrV, SpI, or the magnocellular portion of V subnucleus caudalis in these animals. Labelling of thalamocortical afferents with HRP and staining for CO also failed to reveal a cortical vibrissae-related pattern in the vinblastine-treated rats. The present results indicate that although transient attenuation of axoplasmic transport with vinblastine has limited effects on the peripheral and central projections of surviving V primary afferents, it permanently disrupts the normal development and maintenance of central vibrissae-related patterns. J. Comp. Neurol. 381:219-229, 1997. © 1997 Wiley-Liss, Inc.     

Preventing regeneration of infraorbital axons does not alter the ganglionic or transganglionic consequences of neonatal transection of this trigeminal branch

Retrograde and transganglionic tracing with a combination of horseradish peroxidase (HRP) and wheatgerm agglutinin (WGA)-conjugated HRP (WGA-HRP) was employed to determine whether transection of the infraorbital (IO) nerve on the day of birth and prevention of regeneration by retransecting it at weekly intervals until the time of a terminal anatomical experiment had effects upon ganglion cell survival and innervation of the brainstem by this trigeminal (V) branch that differed from those which followed a single transection of the same nerve on the day of birth without any attempt to prevent peripheral regeneration of the cut axons. Counts of labelled ganglion cells and examination of the brainstem labelling produced by application of HRP and WGA-HRP to the IO nerve proximal to the point of transection(s) at 6 weeks of age demonstrated no differential effects of preventing regeneration of the cut nerve. In animals subjected to a single transection of the nerve (n = 9), we counted an average of 5001.2 (S.D. = 1286.9) labelled ganglion cells and these had an average diameter of 22.7 micron (S.D. = 6.3). In the rats (n = 9) that sustained multiple nerve cuts, the average number of labelled ganglion cells was 4447.8 (S.D. = 1060.9). The mean diameter for these primary afferent neurons was 21.5 micron (S.D. = 6.6). Neither of these values were significantly different from those from the rats subjected to a single nerve cut. The cell counts from both of these groups were significantly lower than those obtained after application of HRP and WGA-HRP to the IO nerve in normal rats (n = 3, X = 12,553.3, S.D. = 1454.8), but the average cell diameter in the normals (X = 23.2, S.D. = 6.6) was not significantly greater than that in the nerve-damaged animals. The pattern of brainstem labelling observed in the rats subjected to multiple nerve cuts was the same as that in the rats which sustained a single transection of the IO nerve on the day of birth. Very little terminal labelling was observed in nucleus principalis, subnucleus oralis, subnucleus interpolaris or the magnocellular portion of caudalis. There was, however, very heavy labelling in laminae I and II of the latter nucleus.     

Postnatal NGF administration causes adult hyperalgesia and overreactivity to social stimuli but does not reverse capsaicin induced hypoalgesia

The present longitudinal analysis was aimed at assessing (i) the effects of developmental capsaicin (CAPS) administration on nociceptive responsivity and on the response of adult mice to social stimuli; (ii) the action of NGF on the ontogeny of the same nociceptive response and social stimuli; (iii) whether capsaicine treatment could be reversed by subsequent treatment with NGF. CD-1 mouse pups were treated with either capsaicin (50 mg/kg, SC) or vehicle on postnatal days (PNDs) 5 and 8. Every other day from PND 9 to PND 21 the same pups received a daily injection of NGF (0.75 mg/kg, SC). During both the prepuberal stage (PNDs 14, 21, and 28) and adulthood, mice were repeatedly tested in a hot-plate apparatus (52 ± 0.1°C for 1 min). At adulthood they also underwent an aggressive behaviour test. NGF-treated mice showed a shorter latency to hindlimb licking response in the hot plate compared to both controls and NGF-CAPS groups. CAPS-treated subjects showed a long-lasting hypoalgesia at both prepuberal and adult stages that was not modified by subsequent NGF treatment. Finally, NGF-treated mice were more aggressive that both controls and CAPS-NGF animals.     

Normal development and effects of neonatal infraorbital nerve damage upon the innervation of the trigeminal brainstem complex by primary afferent fibers containing calcitonin gene-related peptide.

Immunocytochemistry was used to study the normal development and response to infraorbital nerve (ION) damage of the innervation of the trigeminal (V) brainstem complex by axons recognized by an antibody directed against calcitonin gene-related peptide (CGRP). CGRP-like immunoreactivity (CGRPLI) was present in axons that occupied the outer V spinal tract (TrV) at all levels of the V brainstem complex. Almost no fibers terminated within V nucleus principalis (PrV), but there was dense CGRPLI in the supratrigeminal nucleus. There was also very little CGRPLI within rostral V subnucleus oralis (SpO). However, in the caudal one-half of the nucleus, a dense elongated patch of immunoreactivity was consistently present just medial to TrV. Only occasional CGRP-positive axons could be seen within V subnucleus interpolaris (SpI), but the paratrigeminal nucleus contained dense immunoreactivity. Trigeminal subnucleus caudalis (SpC) also contained CGRPLI that was very dense in lamina I and the outer portion of lamina II. Scattered terminals were also present in layers III and IV and dense terminal clusters were in lamina V. CGRP-immunoreactive neurons were present in the V ganglion by embryonic (E-) day 16 and immunoreactive axons could be seen in the V brainstem complex on E-17. At birth, CGRP-positive axons in the V brainstem complex had achieved a distribution very similar to that in adult rats. The major difference between the patterns of labelling in neonates and adults was the presence of relatively large numbers of CGRP-positive fibers in ventral PrV and SpO of the former animals. The disappearance of these fibers was completed by the middle of the third postnatal week. Transection of the ION on the day of birth had little effect upon CGRP in SpO, SpI, and SpC, but it did result in an increase in CGRP-positive fibers in PrV ipsilateral to the damaged nerve. When considered together with previous findings, these results suggest that CGRP-positive axons express this peptide well after they have entered the V brainstem complex and that the central terminal field of these fibers is not substantially altered by a manipulation which results in the death of nearly 60% of all V primary afferent neurons.     

Retinal ganglion cell response to nerve growth factor in the regenerating and intact visual system of the goldfishCarassius auratus

Light and electron microscopic observations indicated that 1 μg NGF injected into the goldfish eye at the time of optic nerve crush initiated significant retinal ganglion cell body, nuclear and nucleolar hypertrophy when compared to controls at 7 days post-axotomy (7 DPA). In addition, the ultrastructural morphometric values for NGF-treated retinal ganglion cells at 7 DPA were not significantly different from the normal hypertrophy found in 14 DPA controls. Therefore, it appears that NGF treatment caused an acceleration of the normal cell body response to axotomy by about a week. These responses were found to be specific for the NGF molecule and dose-dependent over a 100–1000 ng NGF concentration range.In contrast to the lesioned state, NGF treatment had no significant influence on intact, non-lesioned retinal ganglion cell morphology as measured by morphometric analysis. These results strongly indicate that the responsiveness of the goldfish retinal ganglion cells to NGF is initiated by the axotomy.Eyes treated with NGF in the same manner that elicited the dramatic retinal ganglion cell morphological changes at 7 DPA could also be shown to significantly increase neurite outgrowth from retinal explants cultured at the same post-operative period (i.e. 7 DPA).     

Effects of Neonatal Attenuation of Axoplasmic Flow or Transection of the Rat''s Infraorbital Nerve on the Morphology of Individual Trigeminal Primary Afferent Terminals in the Brainstem

Attenuation of axoplasmic transport in the infraorbital nerve (ION), or transection of this trigeminal (V) branch at birth, results in degradation of the central cellular aggregates related to the mystacial vibrissae. However, blockade of axoplasmic transport does not result in the nearly 90% loss of ION ganglion cells that follows neonatal transection of this nerve. The present study was undertaken to further characterize the response of individual ION axons to attenuation of axoplasmic transport and to compare these effects to the changes observed following nerve transection. Neurobiotin injections were made into the V ganglion on postnatal day (P-) 6 in normal rats and animals that had vinblastine applied to the ION or received transection of the ION on P-0. Individual labeled fibers in the portions of V nucleus principalis (PrV) and subnucleus interpolaris (SpI) innervated by the ION were drawn from single sections with the aid of a computer. Morphological analysis of fibers drawn in SpI indicated no significant differences between axons from normal and vinblastine-treated animals. The fibers drawn from rats that sustained ION transection had significantly more branch points (P < 0.05) than those from either normal or vinblastine-treated animals. In PrV, fibers drawn from vinblastine-treated rats had a slightly, but significantly, larger total process length and cross-sectional area than those from the normal animals (P < 0.05). There were no other significant differences among the three groups of axons. These results support the conclusion that application of vinblastine to the developing ION does not dramatically alter the morphologic patterning of the central arbors of its axons.     

Effect of Neonatal Axoplasmic Transport Attenuation in the Infraorbital Nerve on Vibrissae-related Patterns in the Rat's Brainstem, Thalamus and Cortex

This study evaluated the effects of neonatal attenuation of axoplasmic transport in the infraorbital nerve (ION) on the organization of vibrissae-related patterns in the rat's CNS. Application of colchicine- or vinblastine impregnated implants to the ION from birth until postnatal day (P)6 to P10 resulted in a 92.4% reduction in the number of trigeminal (V) ganglion cells labelled by application of horseradish peroxidase to the vibrissa pad and a 44.8% decrease in the number of Nissl-stained ganglion cells in the ophthalamic-maxillary portion of the V ganglion. These implants also decreased the number of myelinated fibres in the ION. In normal rats killed on P6-10, there was an average of 10 273±1259 myelinated axons in the nerve. In the animals with colchicine- or vinblastine-treated implants, this value was 3891±1965. The highest axon count in an experimental animal was 9859. In all animals, axoplasmic transport attenuation resulted in the disappearance of normal vibrissae-related cytochrome oxidase patterns in the brainstem, thalamus and primary somatosensory cortex. Axoplasmic transport attenuation did not result in the disappearance of vibrissae-related ordering of V primary afferent terminal arbors, as demonstrated by anterograde labelling with neurobiotin. These results suggest that some factor conveyed from the periphery of the V ganglion and perhaps on to the brainstem is necessary for the maintenance of vibrissae-related patterns in the thalamus and cortex.     

Neonatal primary neuronal death induced by capsaicin and axotomy involves an apoptotic mechanism

To clarify the mechanism of capsaicin-induced primary neuronal cell death, newborn and adult rats were given a subcutaneous injection of capsaicin (50 mg/kg). Neonatal capsaicin injection induced neuronal apoptosis in the trigeminal ganglion. Apoptotic neurons had peripheral stacks of long parallel endoplasmic reticulum that are characteristic to primary neurons of the B-type, and exhibited nucleoplasmic condensation, nuclear shrinkage and cytoplasmic fragmentation. Light microscopically, apoptotic neurons exhibited a sign of DNA fragmentation as revealed by a nick end labelling method. The proportion of apoptotic cells was quite low during the first 12 h after capsaicin injection (<1%), rapidly increase to 10.44% by 24 h, and decreased to 0.29% by 48 h. Normal and vehicle control levels of apoptosis were <1%. Nerve growth factor (NGF, 0.5 mg/kg) simultaneously administered with capsaicin reduced the incidence of apoptosis by about 35% at 24 h post-injection. Neonatal transection of the infraorbital nerve induced neuronal apoptosis similar to that produced by the neonatal capsaicin in the maxillary division of the trigeminal ganglion. Unlike capsaicin, however, the neurotomy-induced apoptosis was seen in neurons of both the A- and B-types. Neither the capsaicin injection nor the neurotomy induced apoptosis in adult rats, though mitochondrial swelling similar to that seen at 0.5 h after neonatal capsaicin was observed after capsaicin injection in adults. The results indicate that the capsaicin-induced and nerve injury-induced primary neuronal damages in newborn rats share a common final pathway, apoptosis.     

Cell death organizes the postnatal development of the trigeminal innervation of the cerebral vasculature

In the adult trigeminal ganglion single cell bodies that innervate the middle cerebral artery (MCA) are different from but situated near to one or more cell bodies that innervate the forehead (O'Connor and Van der Kooy, submitted). Multiple fluorescent retrograde axonal tracing in postnatal day 3-90 rats was employed to describe the development of this adult pattern of trigeminal projections. We found that close to 90% of the cells that innervate the MCA at postnatal day 5 (PND 5) are eliminated by PND 90. Less than 20% of the ganglion cells innervating the forehead die over the same postnatal period. Subpopulations of cells in the ganglion were observed to have a maximal rate of death during different postnatal periods. First, 15-20% of the cells throughout the ophthalmic division die between PND 5 and PND 10. Second, a small population of cells that had early projections to the contralateral MCA die out completely by PND 22. Third, cells with a projection only to the MCA die primarily between PND 10 and PND 54. Fourth, during the first postnatal week there are many cells that project to both the MCA and the forehead; however, 90% of this population dies by PND 90. This elimination is observed latest in the postnatal period, with these cells exhibiting their greatest rate of cell death between PND 22 and PND 90. Thus, cell death is the primary postnatal mechanism that produces this organization in the ophthalmic division of the trigeminal ganglion and retraction of axonal collaterals is a minor mechanism. We suggest that the latest period of death in cells with divergent artery and forehead projections as well as the ultimate persistence of some artery projecting cells beyond PND 90, may be due to the larger peripheral fields of innervation of these trigeminal ganglion cells.     

Are genetically hypertensive rats deficient in nerve growth factor?

We have shown previously that sympathetic ganglia from genetically hypertensive Otago Wistar (GH) rats contain fewer neurons than those of normotensive animals and are heavily innervated by substance P-containing axons. In adult GH rats treated over days 1-7 of postnatal life with 10 micrograms/rat/day of nerve growth factor (NGF) s.c., ganglion cell numbers were similar to those of normotensive rats. By contrast, NGF treatment of neonatal normotensive animals did not affect ganglion cell numbers. In NGF-treated GH animals, the numbers of substance P-positive axons were substantially reduced relative to age-matched controls. We conclude that the abnormalities seen in ganglia of GH rats may involve a perinatal deficiency of a nerve growth factor.     

Development and plasticity in hamster trigeminal primary afferent projections

At birth (gestational day 16), the hamster infraorbital nerve projects to the appropriate portion of the brainstem, though the projection lacks adult-like internal organization (patchiness). Infraorbital nerve damage at this time does not produce appreciable transganglionic atrophy in the central projections of the infraorbital nerve, but it does result in a failure to develop normal infraorbital primary afferent patches. Such damage also produces a more widespread central projection of spared mandibular afferents into regions occupied by 'regenerate' infraorbital terminals (J. Comp. Neurol., 235 (1985) 129-143). In the present study, transganglionic transport techniques were again used to show that, by postnatal day 5 (gestational day 21), rostrocaudally continuous aggregates of horseradish peroxidase-labelled infraorbital terminals are visible throughout the trigeminal brainstem nuclear complex. This aggregation pattern is nearly adult-like and isomorphic with the distribution of the mystacial vibrissae on the face. A similar infraorbital lesion performed on postnatal day 5, however, markedly decreased the density of the adult central projection of the infraorbital nerve to subnuclei principalis, oralis, interpolaris, and the magnocellular laminae of caudalis. The projection to superficial laminae of caudalis and the cervical dorsal horn was maintained. A postnatal-day-5 infraorbital lesion also failed to produce a more widespread central projection from spared mandibular primary afferents. These data suggest a relationship between the postnatal maturity of trigeminal primary afferents and the response of damaged and undamaged trigeminal afferents to infraorbital nerve transection in hamster. The similarity in the central primary afferent response to lesions at equivalent gestational times (postnatal days 5 and 0, respectively) in hamster and rat, suggests that this plasticity gradient may be a general characteristic of mammalian trigeminal primary afferents.     

Rat retinal ganglion cells upregulate the pro-apoptotic BH3-only protein Bim after optic nerve transection

Increased expression of Bim, a pro-apoptotic member of the Bcl-2 family, has been shown to be critical for neuronal apoptosis. To study the involvement of Bim in injury-induced cell death in retina, Bim expression was studied in normal rat retina and in retina after optic nerve transection using quantitative RT-PCR and immunohistochemistry. As a complement to this, the apoptotic regulators Bax, Bcl-2, caspase-3 and phosphorylated c-jun were studied. The relative levels of Bim mRNA in retina were significantly higher 4 days after optic nerve transection and below normal levels at 14 days after transection. A parallel increase in the number of Bim-immunoreactive cells in the retinal ganglion cell layer could be seen. Bim-immunoreactivity localized to retrogradely True Blue-labeled retinal ganglion cells. The relative mRNA levels for both Bax and Bcl-2 were higher at 4 days after transection when compared to normal. Immunoreactivity for Bax, Bcl-2 as well as for caspase-3 and phosphorylated c-jun, indicative of cell death, localized to True Blue-identified retinal ganglion cells 4 days after injury. Bcl-2 immunoreactivity was also seen on other cells, most likely Müller glia cells. In addition, optic nerve transection caused an increase in Bim, Bax, and Bcl-2 mRNA levels in optic nerve and superior colliculus. Our results suggest that Bim is involved in injury-induced retinal ganglion cell death and indicate that the increase in Bim and Bax expression promote cell death of axotomized retinal ganglion cells whereas the elevation in Bcl-2 in retina may contribute to the control of the extent of apoptosis after the optic nerve transection.     

Nerve growth factor rapidly stimulates arachidonate metabolism in PC12 cells: potential involvement in nerve fiber growth

Homogenates prepared from pheochromocytoma (PC12) cells that are extending nerve fibers in response to nerve growth factor (NGF) have an increased capacity to metabolize exogenous arachidonate compared with homogenates prepared from cells untreated with NGF. These changes are not a consequence of cell attachment, since they are also seen in NGF-treated PC12 cells grown in suspension and are not found in attached cells grown in the absence of NGF. This NGF-stimulated increase in arachidonate metabolic capacity occurs rapidly and before the extension of nerve fibers. In contrast to NGF, epidermal growth factor does not alter the metabolism of exogenous arachidonate by PC12 cells. Radioimmunoassay of medium from PC12 cultures indicates that intact cells produce and release increased amounts of prostaglandin (PGE) in response to NGF. Drugs that inhibit arachidonate liberation from membrane phospholipids (mepacrine or 4-bromphenacyl bromide) block NGF-stimulated nerve fiber growth by PC12 cells. Selective inhibitors of cyclooxygenase metabolism of arachidonate (indomethacin and aspirin) fail to block growth, but inhibitors of lipoxygenase metabolism (baicalein, BW755, and eicosatetraynoic acid) are potent blockers. In cultures of dorsal root ganglion neurons, inhibitors of arachidonate release (mepacrine, 4-bromphenacyl bromide) or its subsequent metabolism by lipoxygenases (nordihydroquaiaretic acid, eicosatetraynoic acid) also prevent the early morphological events of nerve fiber growth. Our data suggest that NGF rapidly and specifically increases the capacity of PC12 cells to synthesize arachidonate metabolites, and that arachidonate metabolism may be important in nerve fiber growth by both PC12 cells and dorsal root ganglion neurons.     

Stimulation and maintenance by nerve growth factor of phenylethanolamine-N-methyltransferase in superior cervical ganglia of adult rats

Treatment of newborn rats with nerve growth factor (NGF) results in a striking increase in phenylethanolamine-N-methyltransferase (PNMT) in the superior cervical ganglia. Between one and three weeks of age there is normally a 10-fold decrease in PNMT activity in ganglia of infant rats. NGF treatment maintains the PNMT in ganglia at levels 10-fold greater than in untreated controls, but the levels of enzyme in the ganglion show the same magnitude of decrease with age. Epinephrine levels are markedly increased in ganglia of NGF-treated rats younger than one week of age, but at older ages the levels of the catecholamine are only slightly greater than the controls. Dexamethasone is less effective than NGF in increasing the levels of PNMT in ganglia of infant rats and, unlike NGF, becomes ineffective by 44 days of age. These results suggest that there may be two types of PNMT-containing cells in ganglia of newborn rats.     

Anatomical consequences of neonatal infraorbital nerve transection upon the trigeminal ganglion and vibrissa follicle nerves in the adult rat

A large body of experimental literature has demonstrated that neonatal infraorbital nerve damage in rodents produces anatomical and/or functional alterations of the normal whisker representation in central trigeminal structures. Less is known about the organization of primary afferent components of the trigeminal system following this manipulation. Such information provides an important basis for interpreting the central changes observed following damage of infraorbital nerve fibers at birth. We have therefore examined the composition and order of peripheral innervation in the pathway from the trigeminal ganglion to the vibrissa follicles in adult rats subjected to unilateral neonatal infraorbital nerve transection. Electron microscopy was used to determine the number and diameter of myelinated and unmyelinated fibers in vibrissa follicle nerves of these animals. Wheat germ agglutinin-horseradish peroxidase and fluorescent retrograde tracers were employed to examine the number and diameter, as well as the topographic organization and branching, of ganglion cells innervating the vibrissae in these rats. The data presented below indicate that neonatal infraorbital nerve transection has the following consequences within the adult trigeminal nerve and ganglion: 1) an alteration of the gross morphology of vibrissal nerves, 2) a significant reduction in the average number (85.4%) and diameter (32.6%) of myelinated, but not unmyelinated, follicle nerve axons, 3) a significant decrease in the average number (36.8%) of trigeminal ganglion cells innervating vibrissa follicles, 4) no significant change in the distribution of ganglion cell diameters, 5) an increase in peripheral branching (1.8-fold) of these ganglion cell axons, and 6) an alteration of somatotopic order within the trigeminal ganglion. Taken together, these data indicate that neonatal infraorbital nerve transection produces a profound reorganization of the primary afferent component of the trigeminal neuraxis.     

Developmental relationships between trigeminal ganglia and trigeminal motoneurons in chick embryos. III. Ganglion perikarya direct motor axon growth in the periphery

The previous study in this series demonstrated that the ingrowth of the central axons of the trigeminal (V) ganglion is prerequisite to V motor axon outgrowth and somatic translocation. In the present experiment we determined whether further interactions with V ganglion cell bodies were required by V motoneurons after the V ganglion innervates the brainstem. Soon after the ganglion axons had penetrated the brainstem they were severed, and a barrier, either permeable or impermeable, was placed between the ganglion cell bodies and the metencephalon. V motor axons grew along aberrant pathways to circumvent the impermeable barriers, many rerouting to reach the V ganglion. Only those V motor nerves which contacted the V ganglion distal to the barrier reached their target musculature in the mandible. The pattern of migration of V motoneurons was normal regardless of the V motor nerve trajectory, but the cell bodies of those axons which did not reach a muscle were not fully differentiated. When permeable barriers (Millipore filters) were implanted, the nerves followed two types of trajectories. If the pore size of the filter was small (0.45 and 0.025 microns), the V motor nerves grew identically to those observed in embryos in which impermeable barriers had been implanted. If the pore size of the filter was large (8.0 and 0.08 microns), the V motor nerve grew along its normal path directly to the barrier. Small axonal bundles from these nerves frequently grew into the filter toward the distal V ganglion. These results indicate that V motor axons preferentially grow to the V ganglion perikarya after exiting from the brainstem. Contact with the V ganglion always results in V motor nerve growth to the mandible while growth of the V motor axons to aberrant target sites only occurs when the axons fail to contact the V ganglion cells distal to the barrier.     

Nerve growth factor stimulates growth of cortical pyramidal neurons in young adult rats

The cytoarchitectonics of pyramidal neurons in the cerebral cortex of non-lesioned rats can be re-modeled by i.c.v. infusions of nerve growth factor (NGF). 4 months after the application of NGF, the pyramidal neurons in layers III and V of the motor cortex and layer V of the anterior cingulate cortex were analyzed and compared with pyramidal neurons from vehicle-treated rats. NGF-treated brains showed: (1) significant increase in dendritic branching in the basilar fields of the layer V, but not layer III, neurons; and (2) a significant increase in spine density in the terminal, but not proximal, dendritic branches. These findings indicated that, besides its known effects on forebrain cholinergic neurons, NGF produces a very generalized synaptic re-modeling involving the cells responsible for the major output of the cerebral cortex in the intact adult brain. © 1979 Elsevier Science B.V. All rights reserved.     

Chronic nerve growth factor treatment of normotensive rats.

The objectives of this study were to examine the effects of chronic nerve growth factor (NGF) administration on vascular innervation and blood pressure in neonatal rats. Newborn Wistar-Kyoto (WKY) rats bred from normotensive parents were chronically treated with NGF for 8 weeks. Littermate controls received saline. Sympathetic ganglia of treated animals were greatly enlarged and in the superior cervical ganglion neuronal numbers were increased 200% and nuclear areas by 46%. The catecholamine contents of several sympathetically innervated tissues were determined biochemically and found to be significantly elevated in mesenteric arteries, aorta, ileum, adrenal and salivary glands from treated compared to control animals. The catecholamine concentrations were similar to, or exceeded those of the spontaneously hypertensive rat. Histochemically, an aberrant nerve supply was evident occupying a greater volume of the adventitia of the caudal artery and mesenteric arteries. In addition, nerve fibres could be seen penetrating the vessel wall to emerge within the lumen of mesenteric blood vessels. Analysis of the smooth muscle wall of the caudal artery revealed that a small but significantly hyperplastic response had been induced. Systolic blood pressures of NGF-treated and control animals were taken at one week intervals from 5 to 8 weeks of age utilizing the tail cuff method. The blood pressure of treated animals were within the normotensive range. It is concluded that chronic NGF treatment leads to changes in vascular innervation and muscle thickness that are similar to those seen in hypertensive animals. Furthermore, the results suggest the elevated levels of NGF seen in peripheral tissues of the spontaneously hypertensive rat are likely to be responsible for the hyperinnervation and resulting hyperplastic responses within vascular tissues, but not exclusively responsible for the elevated blood pressure.