摘要:

AbstractNatural and induced cell degeneration were studied in the mesencephalic parabigeminal nucleus of postnatally developing rats. Natural cell death in the normal parabigeminal nucleus had already started at birth, was maximal at 3 days, and proceeded with a declining rate until postnatal days 8–10 in the dorsal, middle, and ventral divisions that compose the nucleus. The number of neurons declined by approximately one‐third between birth and postnatal day 15. A unilateral lesion of the superior colliculus made at birth modified this pattern. In the deafferented ipsilateral middle division, the rate of cell death was above normal from day 1 to day 10, and the number of neurons at day 15 was 60% less than in unoperated controls. In the contralateral middle division, in which at least some of the neurons were axotomized by the lesion, the rate of cell death increased at days 1–2 and decreased below normal at days 3–5. Induced changes in the number of neurons were consistent with this pattern, and at day 15 the number was similar to the control value. In the ipsilateral dorsal and ventral divisions, which suffered simultaneous axotmy and deafferentation, the rate of cell death increased in 2 peaks at days 1–2 and 4–6, and the numbers of neurons dropped to negligible values at day 15. The frequency curves of degenerating cells were poor predictors of the absolute changes in neuron numbers, and evidence was found of continued postnatal migration of neurons into the developing parabigeminal nucleus. This study indicated that retrograde and anterograde degeneration cotemporal with natural cell death in the developing parabigeminal nucleus proceed with distinct time courses and interact when induced simultaneously. The nucleus regulates through a reduction in the rate of cell death after an early depletion of neurons caused by axotomy, as long as the tectal input remains intact. The results support the hypothesis that the afferent supply, as well as the integrity of axons, have major roles in the control of neuronal survival in the devel

ISSN:0092-7317    

DOI:10.1002/cne.902660202

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractSerotoninergic fibers have been reported in both the abducens and facial nuclei of the cat. Furthermore, serotoninergic dorsal raphe and oculomotor internuclear neurons occupy similar locations in the periaqueductal gray overlying the oculomotor and trochlear motor nuclei. To resolve the issue of whether these two populations of neurons overlap, serotoninergic fibers were assayed in the abducens and facial nucleus; then the morphologies and distributions of identified serotoninergic neurons and oculomotor internuclear neurons were determined.Both the abducens and facial nuclei contained varicosities labelled with antibody to serotonin, but a much higher density of immunoreactive fibers was present in the latter, especially in its medial aspect. Distinct synaptic profiles labelled with antibodies to serotonin were observed in both nuclei. In both cases, terminal profiles contained numerous small, predominantly spheroidal, synaptic vesicles as well as a few, large, dense‐core vesicles. These profiles made synaptic contacts onto dendritic and, in the facial nucleus, somatic profiles that occasionally displayed asymmetric, postsynaptic, membrane densifications.Following injection of horseradish peroxidase into either the abducens or facial nuclei, double‐label immunohistochemical techniques demonstrated that the serotoninergic and oculomotor internuclear neurons form two distinct cell populations. The immunoreactive serotoninergic cells were distributed within the dorsal raphe nucleus, predominantly caudal to the retrogradely labelled oculomotor internuclear neurons. The latter were located in the oculomotor nucleus along its dorsal border and in the adjacent supraoculomotor area.Intracellular injection of horseradish peroxidase revealed that oculomotor internuclear neurons have multipolar somata with up to ten long, tapering dendrites that bifurcate approximately five times. Their dendritic fields were generally contained within the nucleus and adjacent supraoculomotor area. In contrast, putative serotoninergic neurons were often spindle‐shaped and exhibited far fewer primary dendrites. Many of these long, narrow, sparsely branched dendrites crossed the midline and extended to the surface of the cerebral aqueduct. In the vicinity of the aqueduct they branched repeatedly to form a dendritic thicket. The axons of the intracellularly stained serotoninergic neurons emerged either from the somata or the end of a process with dendritic morphology, and in some cases they produced axon collaterals within the periaqueductal gray.Thus the oculomotor internuclear and serotoninergic populations differ in both distribution and morphology. Although the definitive origin of the serotoninergic input to either the abducens or facial nucleus could not be established, this study suggests that neither the oculomotor internuclear nor the dorsal raphe neurons provide the serotoninergic terminal observed in the abducens and facial nuclei. The relationship of the morphology of these cell populations to their putative functions and the relationship of serotoninergic synaptic ultrastructure to the role of serotonin in motor nuclei is discussed in the light of recent physiological observa

ISSN:0092-7317    

DOI:10.1002/cne.902660203

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe distribution of retinohypothalamic projections and the organization of the suprachiasmatic region of the hypothalamus was investigated in the house sparrow (Passer domesticus). Retinohypothalamic projections (RHT) were studied by two anterograde tracing methods, and hypothalamic organization was investigated immunohistochemically with antisera against a number of substances known to be present in the mammalian suprachiasmatic nucleus (SCN): bombesin (BBS), glutamic acid decarboxylase (GAD), 5‐hydroxytryptamine (5HT), neuropeptide Y (NPY), neurotensin (NT), somatostatin (SS), substance P (SP), vasoactive intestinal polypeptide (VIP), and arginine vasopressin (AVP). Observations from these experiments were analysed within the framework of a cytoarchitectural study using Nissl‐stained material.From this study, we have identified an area in the anterior hypothalamus which we believe is an avian homologue of the mammalian SCN. This area contains a nucleus located in close apposition to the optic chiasm between the dorsal supraoptic decussation (DSD) and the ventral lateral geniculate body (GLv) for much of its rostrocaudal extent. The central portion of this nucleus contains neurons that exhibit GAD‐ and BBS‐like immunoreactivity and is the terminal field for the RHT. For this reason, we term this nucleus the visual SCN. It also contains axon plexuses exhibiting 5HT‐like, SP‐like, and NPY‐like immunoreactivity and is bordered ventrally by AVP‐like, SP‐like, and NT‐like immunoreactive cells and medially by VIP‐like and SS‐like immunoreactive cells. Although it is not established that these cell groups together compose a single suprachiasmatic nucleus, the organization in the avian brain of a nuclear complex with a retinorecipient area surrounded by nonvisual components would be very similar to th

ISSN:0092-7317    

DOI:10.1002/cne.902660204

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractLight microscopical degeneration and ultrastructural alterations in the rat spinal dorsal horn were studied following either cutting of the sciatic nerve or rhizotomy at L4 and L5; survival time for both procedures was 3 weeks. Fink‐Heimer silver methods showed minimal degeneration of afferent central processes after sciatic section, and limited ultrastructural changes were present. Both rhizotomy and nerve section resulted in degenerating terminals. Most were swollen and electron lucent, with loss of vesicles; some electron‐dense terminals were present, particularly after rhizotomy. Both procedures also produced significant degeneration of postsynaptic dendrites and soma, evidenced by either increases in electron density, or loss of organelles and cavitation, or accumulation of osmiophilic floccular material. Glial processes frequently were expanded and extended to engulf single degenerating terminals and dendrites, or terminal‐dendrite units; in other cases glial tongues separated terminals from their postsynaptic dendrite. Glial processes often wrapped around degenerating profiles or groups of profiles in several layers, sometimes forming complex labyrinths. These results confirm past descriptions of pre‐ and postsynaptic changes resulting from peripheral nerve section, but newly reveal that dendritic destruction and increased glial activity are also significant following rhizotomy. Documentation of these changes is relevant for studies of reorganization following nerve and spinal cord damage, as well as providing an ultrastructural basis for evaluation of effects of neurotoxins that affect primary afferents, as described in a companio

ISSN:0092-7317    

DOI:10.1002/cne.902660205

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractStudies of deafferentation and regeneration, as well as studies requiring several tracing techniques, would benefit from availability of a substance that would selectively lesion the central components of a single peripheral nerve. Pronase, a combination of proteolytic enzymes, was tested for this purpose.Three weeks following microinjection of Pronase (5–25 mg) into the rat sciatic nerve, many ganglia cells in the L3‐L5 ganglia were degenerated. Degeneration of primary afferents also was evident in the dorsal horn, as detected by silver Fink‐Heimer methods. Patterns of terminal fields coincided with those mapped in normal rats for the sciatic nerve by using HRP transport.Ultrastructural changes were similar to those seen at 3 weeks following sciatic nerve section or rhizotomy, as described in our companion paper. However, degenerative changes following Pronase injection of the sciatic nerve were quantitatively greater than those following sciatic nerve section alone. Degenerating terminals were either electron lucent and swollen, electron dense, or filamentous with loss of vesicles. Postsynaptic dendrites, and occasionally somata, also showed signs of degeneration. Some became electron dense, others accumulated osmiophilic floccular material, but most became electron lucent and developed large membrane‐bound cavities. Glial processes expanded around degenerating elements, wrapping around both terminals and dendrites. Glial sheets covered denervated dendritic and somatic spines, separating them from their terminals. Labyrinth formations of glial sheaths around debris were also found. Pronase appears to mimic the effects of mechanical destruction of primary afferents, but when compared to rhizotomy, is selective for the afferents of a single nerve, and, when compared to nerve section, produces a greater effect. Further, the substance is relatively safe for investigators compared to other toxins such a

ISSN:0092-7317    

DOI:10.1002/cne.902660206

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractFollowing optic nerve crush in various species of frog, a proportion of the retinal ganglion cells re‐establishes functional contact with the optic tectum. However, as much as 50% of the retinal ganglion cells die during this process. The determinants of an individual ganglion cell's fate have not been established. In this study ofRana pipiens, cell survival after optic nerve crush was compared with that after nerve cut followed by stump separation, a procedure that considerably delayed entry of optic axons to the brain. It was also ascertained, in the case of delayed ingrowth, whether application of nerve growth factor immediately after lesion influenced the cell death process.This study confirmed that retinal ganglion cell death is a relatively late event in regeneration, because in several animals‐where anterograde HRP labeling demonstrated regenerating axons within the tectum, no cell death had occurred. There was no statistically significant difference in cell death at 75 days after lesion between animals receiving nerve crush and those receiving nerve cut with stump separation, even though most crush animals had regenerated a complete visual projection, whereas most nerve cut animals had not. The application of NGF did not influence the level of cell death at 75 days after lesion.These results suggest that contact of optic axons with the optic tract or tectum is not necessary for retinal ganglion cell death to occur. However, this does not necessarily mean that contact with the brain is not involved with cell death during regeneration following nerve crush because it is possible that the mechanisms of cell death are different when axons are prevented from regenerating. Further investigations are therefore required to establish the reasons for this cell de

ISSN:0092-7317    

DOI:10.1002/cne.902660207

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractSubstance P‐like immunoreactive (SP‐LI) neurons were identified within the inner nuclear layer and ganglion cell layer of the chick retina. The SP‐LI cells in the inner nuclear layer consisted of several subtypes of neurons, differing in soma size and dendritic arborization. In the ganglion cell layer a population of moderately labelled SP‐LI neurons was also present. About 6–9 m̈m in diameter and spaced 50–80 m̈m apart, they formed a regular array across the entire retina, with a density of about 400 cells/mm2in the superior temporal retina, declining to less than 100 cells/mm2in the peripheral retina. The total number of SP‐LI cells in the ganglion cell layer was approximately 75,000. Individual axons could be followed toward the optic nerve head. Lesions near the optic nerve head resulted in axotomy of ganglion cells within a limited portion of the retina. Two days postaxotomy there were numerous SP‐LI swellings in the proximal segments of axotomized axons. SP‐LI neurons in the axotomized zone were larger, more numerous, and showed increased staining of their processes. Fourteen days following a retinal lesion, there was depletion of all SP‐LI cells in the ganglion cell layer within the axotomized zone, but the SP‐LI neurons in the inner nuclear layer were not noticeably affected.Following a localized injection of rhodamine‐coupled latex beads into the optic tectum, a population of retinal ganglion cells (RGCs) in the contra‐lateral retina was retrogradely labelled. Many of these cells also exhibited SP‐like immunoreactivity.Examination of the optic tectum indicated the presence of SP‐LI fibres in laminae 2–13 (nomenclature of Cajal:Histologie du Systems Nerveux.Vol. 2. Paris: Maloine, '11), with immunoreactive terminal regions present mainly in laminae 2–4, 7, and 9–13. SP‐LI cell bodies were found predominantly in laminae 10–12 and 13. Fourteen days following a retinal lesion, SP‐LI processes and terminals were depleted from laminae 2 and 3. Immunoreactive cells and processes in the remaining laminae of the optic tectum were not noticeably altered.The present report confirms the existence of SP‐LI retinal ganglion cells in the chick retina and demonstrates their contribution to lamina sp

ISSN:0092-7317    

DOI:10.1002/cne.902660208

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThis study examines the time of origin of cells in the external granular layer (EGL) in the frog cerebellum during early stages of development. Premetamorphic bullfrog tadpoles were given multiple intraperitoneal injections of3H‐thymidine (10 m̈Ci/g body weight per injection) at developmental stages ranging from 4 weeks to 1 year and were killed at either 6 or 12 months of age. Autoradiograms were analyzed to determine the time when cells of the EGL were generated by an examination of the labeling pattern in the neuroepithelial cap where EGL cells were presumably formed and in the EGL into which they migrated.The developmental stage of the cerebellum in the 6‐month‐old tadpole was essentially the same as that of the 12‐month‐old animal except for an increased size in the older tadpole. The cerebellum in both age groups contained a distinct neuroepithelial cap and an EGL, which was somewhat better formed in the 12‐month‐old tadpole. Some heavily labeled cells were found in the neuroepithelial caps of 6‐month‐old tadpoles from injection times of 6 weeks to 6 months. In the cerebella of 12‐month‐old tadpoles, however, heavily labeled cells were found in the neuroepithelial cap only with the injection time of 12 months; with injection times from 7 to 11 months, the cells were labeled lightly. Labeled EGL cells were found in the cerebella of 6‐month‐old tadpoles from an injection time of 6 weeks on; with injection times from 10 weeks to 6 months some EGL cells contained heavy amounts of label. In the cerebella of 12‐month‐old tadpoles, labeling of EGL cells was not detectable with injection times of 7–9 months; they contained light to medium labeling with injection times of 10 and 11 months and heavy labeling when injected at 12 months. These results indicate that EGL cells are generated continuously in premetamorphic tadpoles from the age of 6 weeks to 12 months. Furthermore, these results suggest that the rate of EGL cell formation is faster during the second half‐year of

ISSN:0092-7317    

DOI:10.1002/cne.902660209

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractHistochemical mapping of AChE‐positive neuroblasts in sectioned and whole‐mounted preparations of the chick embryo mesencephalon and prosencephalon allows a correlation of early neural tube morphogenesis (segmentation, longitudinal compartmentation) with the heterochronic pattern of neurogenesis. One significant finding is that the initial appearance of neuroblasts in the forebrain does not follow neuromeric segmentation, but evolves in parallel with it. Early neuroblasts appear as separate, distinct groups within specific matrix territories at the center of the transverse neuromeric segments. Neighbouring segments display different spatiotemporal patterns of neurogenesis. Overall gradients of differentiation in the rostrocaudal and ventrodorsal directions are absent, whereas a clear‐cut segment‐related, mosaic pattern becomes evident. Notwithstanding this, gross regularities of heterochrony in the neurogenetic behavior of the different segments lead to a definition of elemental longitudinal compartments of the forebrain and mesencephalon (floor, paramedian, basal, and alar regions) on the basis of precocious differentiation of the basal region and retarded differentiation of the paramedian and alar

ISSN:0092-7317    

DOI:10.1002/cne.902660210

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractGABAergic neurons have been identified in the piriform cortex of the opossum at light and electron microscopic levels by immunocytochemical localization of GABA and the GABA‐synthesizing enzyme glutamic acid decarboxylase and by autoradiographic visualization of high‐affinity3H‐GABA uptake. Four major neuron populations have been distinguished on the basis of soma size, shape, and segregation at specific depths and locations: large horizontal cells in layer Ia of the anterior piriform cortex, small globular cells with thin dendrites concentrated in layers Ib and II of the posterior piriform cortex, and multipolar and fusiform cells concentrated in the deep part of layer III in anterior and posterior parts of the piriform cortex and the subjacent endopiriform nucleus. All four populations were well visualized with both antisera, but the large layer Ia horizontal cells displayed only very light3H‐GABA uptake, thus suggesting a lack of local axon collaterals or lack of high‐affinity GABA uptake sites. The large, ultrastructurally distinctive somata of layer Ia horizontal cells receive a very small number of symmetrical synapses; the thin, axonlike dendrites of small globular cells are exclusively postsynaptic and receive large numbers of both symmetrical and asymmetrical synapses, in contrast to somata which receive a small number of both types; and the deep multipolar and fusiform cells receive a highly variable number of symmetrical and asymmetrical synapses on somata and proximal dendrites.Labeled puncta of axon terminal dimensions were found in large numbers in the neuropil surrounding pyramidal cell somata in layer II and in the endopiriform nucleus. Moderately large numbers of labeled puncta were found in layer I at the depth of pyramidal cell apical dendrites with greater numbers in layer Ia at the depth of distal apical segments than in layer Ib.High‐affinity GABA uptake was demonstrated in the termination zone of the projection from the anterior olfactory nucleus to the anterior piriform cortex. Cell bodies of origin of this projection displayed heavy retrograde labeling with3H‐GABA. Matching neuropil and cellular labeling was demonstrated with the GABA‐BSA antiserum but not with the GAD antiserum, thus suggesting that GABA is normally present in these cells but is taken up from the neuropil rather than synthesized. No comparable high‐affinity GABA uptake was demonstrated in the association fiber systems that originate in the piriform cortex.The functional significance of the present results is discussed with respect to: feedback and feedforward inhibitory circuits, a possible role of the GABAergic neurons distinguished in generation of a slow inhibitory process mediated by GABABreceptors in addition to the well‐known fast inhibitory process mediated by GABAAreceptors, autoregulation of excitability level by inhibitory processes vs. participation in integrative processes, and the role of inhibitory processes in epileptogenesis. Special features of the piriform cortex that make it well suited as a model for analysis of inhibitory processes in cerebral c

ISSN:0092-7317    

DOI:10.1002/cne.902660211

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY