Development of the brain stem in the rat. IV. Thymidine-radiographic study of the time of orgin of neurons in the pontine region

Groups of pregnant rats ware injected with two successive daily doses of ³H-thymidine form gestational day 12 and 13 (E12 + 13) until the day before parturition (E21 + 22) in order to label in their embryos the proliferating precursors of neurons. At 60 days of age the proportion of neurons generated (or no longer labeled) on specific embryonic days was determined quantitatively in 14 nuclei of the pontine region. Peak production time of neurons of the trigeminal mesencephalic nucleus was on day E11 or earlier, with a small proportion generated on day E12. Peak production time of the trigeminal motor neurons was on day E12, with a small proportion produced earlier. Neurons of the principal sensory nucleus were generated between days E13 and E16, with a peak on day E14; the late-produced neurons tended to belong to a class of intermediate and large cells. The bulk of the neurons of the supratrigeminal and infratrigeminal nuclei arose on day E15 and E16. Neurons of the locus coeruleus are produced mostly on day E12, with about 20% of the cells arising on day E13. The bulk of the neurons of the dorsal tegmental nucleus (Gudden's) are produced between days E13 and E15, whereas most of the neurons of the deep (ventral) tegmental nucleus are produced on day E15. A dorsal-to-caudal gradient was also obtained between the dorsal and vental nuclei of the lateral lemniscus, the neurons of the former being generated between days E12 and E15; the latter, between days E13 and E17. The neurons of both the pars lateralis and the pars medialis of the parabrachial nucleus were produced simultaneously between days E13 and E15, with a peak on day E13. the heterogeneous collection of neurons of the pontine paramedial reticular formation was produced from day E11 (or earlier) until day E15. Finally, the neurons of the raphe pontis parvicellularis were generated at an even rate between days E13 and E15, whereas the bulk of the neurons of the raphe pontis magnocellularis were produced on days E15 and E16. On the basis of datings obtained for 9 subdivisions of the entire brain stem trigeminal complex, hypotheses were offered of the cytogenetic components of the system. The sequence of neuron production in the dorsal and deep tegmental nuclei was related to their connections with divisions of the mammillary and habenular nuclei on a “first come-first serve” basis.     

Primary sensory ganglion cells projecting to the principal trigeminal nucleus in the mallard, Anas platyrhynchos

The trigeminal and glossopharyngeal ganglia of the adult mallard were studied following HRP injections into the principal trigeminal nucleus (PrV). The PrV consists of the principal trigeminal nucleus proper (prV) and the principal glossopharyngeal nucleus (prIX). After an injection into the prV, the labeled cells were found in the ipsilateral trigeminal ganglion. After an injection into the prIX, labeled cells were found in the ipsilateral distal glossopharyngeal ganglion, but not in the proximal ganglion of the IX and X cranial nerve (pGIX + X). In Nissl preparations, two types of ganglion cells in the trigeminal ganglion, pGIX + X, and distal ganglion of N IX could be distinguished: larger light cells and smaller dark cells. We could not determine whether the HRP-labeled cells belonged to both types or to one of them; but because all the labeled cells were over 20 microns, we concluded that the smallest cells (10-19 microns) in the trigeminal ganglion and distal ganglion of N IX did not project to the PrV. The labeling of the cells in the distal ganglion of N IX (average 34.5 microns) was uniformly moderate. In the trigeminal ganglion there were two types of labeled cells: heavily labeled cells (average 29.1 microns) and moderately labeled cells (average 35.1 l microns). These two types of labeling (moderate and heavy) may reflect two types of primary sensory neurons: cells with ascending, nonbifurcating axons, and cells with bifurcating axons. We speculate that the former are proprioceptive neurons and the latter tactile neurons. Labeled bifurcating axons in the sensory trigeminal complex gave off collaterals to all parts of the descending trigeminal nucleus except to the caudalmost laminated spinal part.     

Effects of nerve growth factor on sensory neurons in the chick embryo: a stereological study

Chicken embryos on days 6-13 of incubation received injections of purified beta NGF (80 micrograms/day) for 3 or 4 days and were then killed. Sensory ganglia were fixed and taken for embedding and sectioning. A stereological method based on unfolding of cell-diameter frequencies was used to determine the number of neurons of different size in the spinal, trigeminal and nodose ganglia. The total volume of the ganglia was also determined. NGF induced increases in diameter of the neural crest-derived dorsomedial (DM) neurons in spinal and trigeminal ganglia. Injected NGF did not influence ventrolateral (VL) neurons of neural crest origin in the spinal ganglia nor the ventrolateral neurons of placodal origin in the trigeminal ganglion. The volumes of spinal and trigeminal ganglia increased by 50 and 100%, respectively. The volume of the nodose ganglion and the total number and size of the placodal nodose neurons were unaffected by NGF. The results demonstrate a clear difference in the response to NGF in vivo between smaller and larger sensory neurons.     

Trigeminal ganglion cell processes are spatially ordered prior to the differentiation of the vibrissa pad.

The rodent trigeminal system is characterized by the punctate organization of its afferents and neurons that replicate the distribution of mystacial vibrissae and sinus hairs on the snout. We have examined the development of topographic equivalence between the sensory periphery on the snout and the brainstem trigeminal nuclei in rats. Lipophilic tracers Dil (1,1'-dioctodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) and DiA [4-(4-dihexadecylaminostyryl)-N-methylpyridinium iodide] were used to label trigeminal ganglion cells and their processes differentially from discrete regions of the presumptive vibrissa field in fixed embryos. Our results show that trigeminal ganglion cell processes are spatially ordered as they reach their peripheral and central targets on embryonic day 12 (E12). Peripheral processes of dorsomedially situated ganglion cells course dorsally toward the presumptive vibrissa field, and those of ventrolaterally situated ganglion cells project ventrally. On E13, the central processes of dorsomedially situated ganglion cells enter the brainstem medially whereas those of ventrolaterally situated ganglion cells enter laterally. This spatial order of trigeminal ganglion cell processes precedes the emergence of vibrissa rows in the periphery and the differentiation of brainstem trigeminal nuclei. Thus, the subsequent transfer of the vibrissa-related pattern to the brainstem trigeminal nuclei occurs along a preexisting, spatially aligned bridge formed by the trigeminal ganglion cells.     

Genesis of neurons in the retinal ganglion cell layer of the monkey.

We have analyzed the genesis of various neuronal classes and subclasses in the ganglion cell layer of the primate retina. Neurons were classified according to their size and the time of their origin was determined by pulse labeling with 3H-thymidine administered to female monkeys 38 to 70 days pregnant. All offspring were sacrificed postnatally, and their retinas processed for autoradiography. The somata of cells in the retinal ganglion cell layer generated on embryonic day (E) 38 ranged from 9 to 14 microns in diameter. Between E40 and E56, the minimum soma diameter remained around 8-9 microns, while the maximum gradually increased to 22 microns. As a consequence, the means of the distributions of labeled cells also increased with age, from 11.8 microns diameter for cells generated on E38 to 14.6 microns diameter at E56. Over this period the percentage of labeled cells in the 10.5-16.5 microns and greater than 16.5 microns diameter range gradually increased. The proportion of the labeled cells in the less than 10.5 microns diameter range decreased from E38 to E45, but subsequently increased rapidly. At the end of neurogenesis in the retinal ganglion cell layer, around E70, most labeled cells were considerably smaller (7-9 microns) than those generated earlier. Our results indicate that within the ganglion cell layer of the macaque, neurons of small caliber are generated first, followed successively by medium sized cells. Large, putative P alpha cells are generated late. The production between E56 and E70 of cells with the smallest somata suggests that the last-generated neurons in the ganglion cell layer are predominantly displaced amacrine cells. Within the same sector of retina, different classes of neurons in the ganglion cell layer of the rhesus monkey appear to have a sequential schedule of production.     

Developing neuronal populations of the cat retinal ganglion cell layer

An improved flat-mount procedure demonstrates that the developing ganglion cell layer of the cat retina contains two morphologically distinct populations of presumed neurons at all ages between embryonic day 36 (E36) and adulthood. One population resembles the adult "classical neurons" composing the ganglion cells and bar-cells of Hughes, while the remaining cells, which are smaller and possess much less Nissl substance, presumably correspond to precursors of the adult microneurons. Although the total neuron population of the retinal ganglion cell layer remains quite constant at all studied ages, its component subpopulations alter significantly during prenatal development; some 50% of classical neurons disappear before birth and the microneuron population doubles during the same period. An obvious centroperipheral gradient exists for classical neurons by stage E47, but the microneuron density gradient only becomes apparent at birth. A 2:1 centroperipheral ratio for the total neuron population is also apparent at E47. Centroperipheral neuronal density gradients continue to increase during postnatal growth. Loss of classical neurons during prenatal life as a result of cell death or transformation into microneurons, has been postulated as a mechanism for determining neuron density gradients. Cell death does occur in the ganglion cell population but it is not yet established whether microneurons of the ganglion cell layer originate from ganglion cell transformation or migrate as a differentiated class from the ventricular layer. However, it can be concluded that not all microneurons originate from ganglion cell transformation, because the total loss of classical neurons is less than the increase in microneuron numbers during development. The population magnitudes of both neuronal classes in the ganglion cell layer stabilise after birth. However, it is during the postnatal period that the adult cruciate density topography is achieved by both populations. It is concluded that differential areal growth is the prime mechanism for postnatal cell redistribution.     

Development of the brain stem in the rat. V. Thymidine-radiographic study of the time of origin of neurons in the midbrain tegmentum

Groups of pregnant rats were injected with two successive daily doses of ³H-thymidine from gestational day E12 and 13 (E12 + 13) until the day before parturition (E21 + 22) in order to label in their embryos the proliferating precursors of neurons. At 60 days of age the proportion of neurons generated (no longer labeled) on specific embryonic days was determined quantitatively in 18 regions of the midbrain tegmentum. The neurons of the oculomotor and trochlear nuclei are generated concurrently on days E12 and E13. There was a mirror image cytogenetic gradient in these nuclei and this was interpreted as the dispersal of neurons derived from a common neuroepithelial source to the medial longitudinal fasciculus. Neurons in three other components of the tegmental visual system are produced in rapid succession after the motor nuclei. In the nucleus of Darkschewitsch peak production time was on days E12 and E13, extending to day E15; in the Edinger-Westphal nucleus the time span was the same but with a pronounced peak on day E13; finally, the neurons of the parabigeminal nucleus were produced between days E13 and E15 with a peak on day E14. The neurons of the periaqueductal gray were generated between days E13 and 17 with a pronounced ventral-to-lateral and lateral-to-dorsal gradient. In the red nucleus the neurons were produced on days E13 and E14 with a caudal-to-rostral gradient: the cells of the magnocellular division preceding slightly but significantly the cells of the parvocellular division. The neurons of the interpeduncular nucleus originated between days E13 and E15; the peak in its ventral portion was on day E13, in its dorsal portion on days E14 and E15. A ventral-to-dorsal gradient was seen also in both the dorsal and the median raphe nuclei in which neuron production occurred between days E13 and E15. The neurons of the pars compacta and pars reticulata of the substantia nigra were both produced between days E13 and E15 with a modified lateral-to-medial gradient. This gradient extended to the ventral tegmental area where neurons of the pars medialis were produced between days E14 and E16. With the exception of the central gray, neuron production was rapid and relatively early in the structures situated ventral to the midbrain tectum. A comparison of the cytogenetic gradients in the raphe nuclei of the lower and upper medulla, the pontine region, and the midbrain suggests that they originate from at least three separate neuroepithelial sources.     

Autoradiographic study of histogenesis in the mouse olfactory bulb. I. Time of origin of neurons and neuroglia

Time of origin (final cell division) of neurons and neuroglia of the mouse olfactory and accessory olfactory formations was determined by autoradiography. Animals were injected with thymidine-H³ at various developmental stages and killed at or near maturity. In the olfactory formation mitral cells (the largest neurons) arise first, mainly over the three day period from the eleventh day of gestation (E11) to E13, tufted cells chiefly from E13 to E18, and granule cells (the smallest neurons) mainly from E18 to postnatal day 20. Most of the smaller and more superficial peripheral tufted cells arise later than the deeper and larger middle and internal tufted cells. All three types of granule cells have a time of origin extending well into postnatal life, with internal granule cells arising over a longer and later period than periglomerular cells or granule cells of the mitral cell layer. Neuroglial precursors undergo final cell division chiefly between E17 and P10. In the phylogenetically less evolved accessory olfactory formation, mitral cells originate earlier than their homologues in the olfactory formation; mitral cells principally from E10 to E12 and granule cells chiefly from E12 to E18. The results support the concept that some germinal layers of the central nervous system are programmed to produce a succession of cell types, larger cells before smaller ones.     

Infrared sensory neurons in the trigeminal ganglia of crotaline snakes: transganglionic HRP transport

Trigeminal neurons were labeled by inserting HRP into holes cut in the pit receptor membranes of a crotaline snake, Agkistrodon blomhoffi brevicaudus. Neurons were labeled in the ophthalmic ganglion and the maxillary division of the maxillo-mandibular ganglion, and the HRP was further transported across the ganglia and through the lateral descending trigeminal tract (dlv) to label axon terminals exclusively in the dlv nucleus (DLV). In 6 successful preparations, 7.1-19.3% of totals of 5568-5986 cells in the maxillary division of the ganglion were labeled, but none at all were labeled in the mandibular division. Only a few or none at all were labeled in the ophthalmic ganglion. Cells in the two ganglia ranged in size from 10 to 55 micrometers, but large cells (greater than or equal to 40 micrometers) were scarce (4.9% of the total population). All HRP-labeled neurons fell in the median range of 20-39 micrometers. We concluded that these ganglion cells were infrared neurons, and were therefore the origin of the A delta fibers in the pit membrane. There were no HRP-labeled neurons above or below this range, in spite of the fact that smaller cells (less than or equal to 19 micrometers) made up 35.8% of the total population. In normal Nissl preparations we found both light- and dark-staining cells, but the size range of neither corresponded to the size range of infrared neurons.     

Glial cell activation and altered metabolic profile in the spinal-trigeminal axis in a rat model of multiple sclerosis associated with the development of trigeminal sensitization

Trigeminal neuralgia is often an early symptom of multiple sclerosis (MS), and it generally does not correlate with the severity of the disease. Thus, whether it is triggered simply by demyelination in specific central nervous system areas is currently questioned. Our aims were to monitor the development of spontaneous trigeminal pain in an animal model of MS, and to analyze: i) glial cells, namely astrocytes and microglia in the central nervous system and satellite glial cells in the trigeminal ganglion, and ii) metabolic changes in the trigeminal system. The subcutaneous injection of recombinant MOG_1-125 protein fragment to Dark Agouti male rats led to the development of relapsing-remitting EAE, with a first peak after 13 days, a remission stage from day 16 and a second peak from day 21. Interestingly, orofacial allodynia developed from day 1 post injection, i.e. well before the onset of EAE, and worsened over time, irrespective of the disease phase. Activation of glial cells both in the trigeminal ganglia and in the brainstem, with no signs of demyelination in the latter tissue, was observed along with metabolic alterations in the trigeminal ganglion. Our data show, for the first time, the spontaneous development of trigeminal sensitization before the onset of relapsing-remitting EAE in rats. Additionally, pain is maintained elevated during all stages of the disease, suggesting the existence of parallel mechanisms controlling motor symptoms and orofacial pain, likely involving glial cell activation and metabolic alterations which can contribute to trigger the sensitization of sensory neurons.     

Embryonic development of the chick primary trigeminal sensory-motor complex

The objective of this study is to define the development of all components in the chick embryonic trigeminal primary sensory-motor complex, from their first appearance through the formation of central and peripheral axonal projections up to stage 34 (8 days of incubation). This was accomplished by two labeling procedures: application of the monoclonal antibody HNK-1, which binds to the precursors of all these components except the placode-derived neurons, and application of HRP to axons cut immediately distal to the trigeminal ganglion. Single immunopositive motor neuron precursors are present at stage 12. These accumulate in the transient medial motor column, whose neurons initiate axon outgrowth by stage 13–14, concomitant with the onset of translocation of their somata to form the definitive trigeminal lateral motor column (LMC). Intiially these translocating somata accumulate on the medial margin of the LMC. Beginning on incubation day 5, axons growing from newly formed motor neurons pass beside the lateral margin of the LMC, and the nuclei of these cells subsequently follow this pathway. These events follow a rostral-to-caudal sequence, and this phase of motor nucleus formation is complete by day 8. The lateral translocation of some caudally located nuclei is arrested beginning on day 5. This cessation, which proceeds rostrally, demarcates neurons that form the dorsal motor nucleus of the trigeminal complex. Sensory neurite formation is intiated in ophthalmic placode-derived cells at stage 14.5, one stage later by maxillomandibular neurons, and from mesencephalic V cells at stage 15. Neural crest cells do not initiate axon formation until at least day 4 to 5. Following application of HRP distal to the condensing ganglion at stage 16, labeled ophthalmic nerve projections appear in contact with the wall of the hindbrain centrally and overlying the optic vesicle peripherally. Fibers forming the descending tract elongate rapidly, reaching the level of the VIIth nerve root (200 m?m caudal to the trigeminal root) by stage 18 and the cervical cord by stage 22. Labeled terminal arborizations of descending trigeminal afferents are first visible at stage 22 and are evident along the entire descending and proximal ascending tracts by stage 27. Later-developing descending axons grow in close association with existing trigeminal fibers, though a few growth cones are consistently evident superficial to the other fibers. No projections different from those reported in adult birds are seen, nor are there any contralateral afferent projections. Peripheral axons from neurons in the mesencephalic trigeminal nucleus emerge from the trigeminal ganglion beginning at stage 21. These cells are labeled only when tracer is applied to the mandibular nerve.     

A quantitative comparison between the ganglion cell populations and axonal outflows of the visual streak and periphery of the rabbit retina

A vertical density profile of the ganglion cells 2 mm temporal of the optic nerve head in the rabbit retina has been produced by counting somata in the cresyl-violet-stained, ganglion cell layer of a flat-mounted retina. Somata classified as ganglion cells were characterized by obvious Nissl staining in an extensive cytoplasm and typically had diameters greater than 9 μm. The accuracy of the profile, and thus of the classification criteria, has been substantiated by electron micrographic determination of the numbers of ganglion cell axons arising within local regions of known area on the same retina This study indicates that Vaney and Hughes' estimate ('76) of 547,100 presumed ganglion cells in the rabbit retina should be changed to 373,500 ganglion cells. The latter value is within the statistical error of their optic nerve count of 394,000 fibers The mean diameter of ganglion cells 6 mm from the visual streak in the inferior periphery (density: 550 cells/mm²) was 28% greater than that of cells on the peak of the streak (density: 5,400 cells/mm²), although the form of the ganglion cell diameter distribution did not change markedly with eccentricity. The increase in the mean size of ganglion cells in the periphery appeared to be approximately matched by an increase in the size of their axons. Larger axons became myelinated farther from the edge of the myelinated band than did smaller axons Within the ganglion cell layer there was another population of cells which were quite distinct from the obvious neuroglia: Their nuclei were similar to those of the larger ganglion cells and many appeared to have Nissl granules within their limited cytoplasm. About half of this heterogeneous population was classified as “coronate cells,” which were characterized by the partial nuclear encapsulation of their eccentric cytoplasm.     

Cell body responses to axonal injury: traumatic axotomy versus toxic neuropathy

To compare the evolution of cell body responses to two different types of axonal injuries--sciatic nerve crush (axotomy) and chronic 2,5-hexanedione-induced neuropathy--we studied rat lumbar dorsal root ganglion neurons with light microscopy and morphometry. Compared with control neurons, axotomized cells showed early (1 day) increases in the frequencies of two responses, nuclear eccentricity and Nissl body displacement, and later (4 day) increases in average satellite cell nuclei and decreases in perikaryal diameters. In toxin-induced axonal degeneration, there were similar patterns of defined alterations, although the evolution progressed over weeks and the response magnitudes were smaller. We conclude that the two experimental conditions show basic morphologic similarities, implying cell body reorganization in toxic axonopathy may be a response to axonal dysfunction or degeneration.     

Development of substance P-immunoreactive neurons in cranial sensory ganglia of the rat

Substance P-like immunoreactivity has been observed in fetal and adult cranial sensory ganglia. It first appears at day 16 of gestation in sensory neurons of trigeminal, superior-jugular, petrous and nodose ganglia, as well as in the autonomic myenteric plexus, and at day 17 in cervical dorsal root ganglion cells. Substance P immunoreactivity can be visualized much earlier (day 12) in the central nervous system. The ganglionic immunoreactivity subsequently increases during fetal life but drops at birth. The reactive material is first diffuse, then slowly becomes granular, and is mostly concentrated in coarse perinuclear inclusions in adult sensory neurons. Most substance P-positive neurons in trigeminal and superior-jugular ganglia are small, but medium-sized and large positive neurons are also observed in the trigeminal, petrous and nodose ganglia.Our observations give a precise picture of the development of substance P immunoreactivity in sensory neurons and are in general agreement with previous reports on some fetal and adult rat sensory ganglia. They indicate that in the rat, maturation of peripheral substance P-containing sensory neurons is slower than that of central substance P neurons or equivalent sensory neurons in other species. The examination of fetal material allows the observation of numerous immunoreactive sensory neurons which cannot be visualized after birth. We hypothesize a possible different embryonic origin (neural crest or placodal) for small nociceptive and larger substance P-containing neurons in rat cranial sensory ganglia.     

Generation patterns of immunocytochemically identified cholinergic neurons at autonomic levels of the rat spinal cord.

The time at which a neuron is "born" appears to have significant consequences for the cell's subsequent differentiation. As part of a continuing investigation of cholinergic neuronal development, we have combined ChAT immunocytochemistry and [3H]thymidine autoradiography to determine the generation patterns of somatic and autonomic motor neurons at upper thoracic (T1-3), upper lumbar (L1-3), and lumbosacral (L6-S1) levels of the rat spinal cord. Additionally, the generation patterns of two subsets of cholinergic interneurons (partition cells and central canal cluster cells) were compared with those of somatic and autonomic motor neurons. Embryonic day 11 (E11) was the first day of cholinergic neuronal generation at each of the three spinal levels studied, and it also was the peak generation day for somatic and autonomic neurons in the upper thoracic spinal cord. The peak generation of homologous neurons at upper lumbar and lumbosacral spinal levels occurred at E12 and E13, respectively. Somatic and autonomic motor neurons were generated synchronously, and their production at each rostrocaudal level was virtually completed within a 2-day period. Cholinergic interneurons were generated 1 or 2 days later than motor neurons at the same rostrocaudal level. In summary, the birthdays of all spinal cholinergic neurons studied followed the general rostrocaudal spatiotemporal gradient of spinal neurogenesis. In addition, the generation of cholinergic interneurons also followed the general ventrodorsal gradient. In contrast, however, autonomic motor neurons disobeyed the rule of a ventral-to-dorsal progression of spinal neuronal generation, thus adding another example in which autonomic motor neurons display unusual developmental patterns.     

Peripheral target regulation of dendritic geometry in the rat superior cervical ganglion

Dendritic arborizations of neurons in the adult rat superior cervical ganglion were measured in control ganglia and in ganglia innervating peripheral targets that were relatively larger or smaller than normal. The relative size of the target--the submandibular gland in these experiments--was manipulated during development by changing the ratio between the amount of target tissue and the number of innervating ganglion cells. Thus, ligating the submandibular salivary duct reduced the size of the gland, whereas partially denervating the gland produced a relatively larger target by making a smaller number of ganglion cells innervate a gland of normal size. Neurons innervating targets that were smaller than normal had significantly smaller dendritic arborizations and cell bodies than control cells. Conversely, neurons projecting to relatively larger than normal targets had larger dendritic arborizations and cell bodies, and more primary dendritic branches. Such cells were also innervated by a larger than normal number of preganglionic inputs. A similar change in dendritic geometry was observed when relative target size was increased after cutting the cervical sympathetic trunk, showing that target regulation of dendritic geometry is not dependent on ganglion cell activity or the presence of presynaptic innervation. Dendrites in the superior cervical ganglion normally grow in parallel with body size throughout life (Purves et al., 1986a; Voyvodic, 1987a). The present results imply that an important aspect of dendritic growth is an ongoing responsiveness of ganglion cells to feedback signals arising from the peripheral targets they innervate.     

Effects of nerve growth factor on autonomic neurons in the chick embryo: A stereological study

Quantitative effects of nerve growth factor (NGF) on the sympathetic, Remak and ciliary ganglia in chicken embryos were investigated. Purified mouse beta NGF was injected (80 micrograms per day for three or four consecutive days) into the yolk sac at different stages (starting on days 6, 8, 10 and 13) of embryonic development. Ganglia were taken for fixation and embedding one day after the last NGF injection. The number of neurons belonging to the different size classes was determined by a computer aided stereological method based on unfolding of cell diameter frequencies. The volume of sympathetic ganglia was increased at all stages with a maximum of 8-fold occurring on day 10. The ganglion of Remak showed a 3-fold volume increase up to embryonic days 10 and 12. Ciliary ganglia did not exhibit any differences in volume or neuron size between the controls and the embryos injected with NGF. The number of neurons was increased in younger sympathetic and Remak ganglia in response to NGF, as was the recruitment of neurons to the larger size classes.     

Cooperation and competition during development: neonatal lesioning of the superior cervical ganglion induces cell death of trigeminal neurons innervating the cerebral blood vessels but prevents the loss of axon collaterals from the neurons that survive

In the adult rodent trigeminal ganglion there is a period of postnatal cell death in the population of cells with axons innervating the middle cerebral artery (O'Connor and van der Kooy, 1986b). The superior cervical ganglion (SCG) also has a projection to the middle cerebral artery (MCA; Mayberg et al., 1984; Cowen et al., 1986, 1987; present report). We hypothesized that the trigeminal ganglion cells innervating the MCA may be competing with the superior cervical projection for target area or for a target factor for survival, and thus the removal of the superior cervical projection at birth (sympathectomy) may promote the survival of some of the trigeminal-artery innervating cells that normally would die. Multiple fluorescent retrograde tracing was employed to analyze the postnatal development of the trigeminal projection to the MCA in sympathectomized and sibling control rats. We found that the SCG projection to the MCA exhibits a period of postnatal cell death. The trigeminal ganglion projection exhibits axon degeneration as well as postnatal cell death. Postnatal day 0 (P0) lesioning of the SCG did not prevent cell death or axon loss in the trigeminal projection to the cerebral artery. In fact, increased cell death of the trigeminal-artery projecting neurons was observed in the lesioned animals when compared to nonlesioned sibling controls. By P55, we found that 80% of these trigeminal neurons had died in lesioned animals, compared with 50% in controls. In both control and sympathectomized rats, close to 90% of the trigeminal neurons innervating the artery in the neonate can no longer be retrogradely labeled from the MCA by tracer applications at P25-90. Thus, although the presence of an intact SCG may protect some trigeminal-artery projecting neurons from cell death, it does not prevent axon retraction and does not permit a larger absolute number of trigeminal axons to innervate the arteries in the adult. Thus, separate mechanisms are responsible for the survival of perikarya versus the retraction of their axons from the MCA. Surprisingly, in the neonatally sympathectomized rats almost 20% of those trigeminal cells that maintained a projection to the MCA at P90 also had a projection to the forehead. In contrast, less than 3% of the artery innervating trigeminal cells in the P90 control rats had an axon collateral to the forehead.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cell growth in the lateral geniculate nucleus of kittens following the opening or closing of one eye.

Closing one eye of kittens at 23 days after birth resulted in paler Nissl staining of the deprived cells in the lateral geniculate nucleus (LGN) that was detectable two days later. Differences between the two sides of the brain in mean cell area increased to a peak in binocular lamina A at 4--6 days after eyelid suture, and then fell to a trough at eight days before rising progressively to a higher level at 31 days. In lamina A1 the peak and trough were later. Opening one eye of kittens after 23 days of binocular closure from birth resulted in more intense Nissl staining of the stimulated cells in the LGN that was detectable four days later. The stimulated cells grew faster than the cells connected to the eye that remained closed, and this differential growth reached a peak at 17 days in binocular lamina A and at 21 days in lamina A1 before falling to a trough at 26--31 days. These results are compared with the time course of anabolic changes that have been measured in other neurons during stimulation. The coefficient of variation of cell size was computed and found to be slightly decreased for deprived cells and increased for stimulated cells. This suggests that larger cells changes their sizes proportionately more than smaller cells. The cells were measured in fronzen sections without shrinkage, and the areas are at least 25% larger than those reported previously after paraffin or celloidin embedding.