摘要:

AbstractThe ontogeny of intersegmental (propriospinal) projections was studied in the chick embryo spinal cord between embryonic day 2.5 and day 6. Our goals were (1) to determine the earliest projections of intersegmental interneurons between specific spinal regions and to establish the cell types involved; and (2) to follow the ontogeny of these projections during the early formative stages of spinal cord development. Studies were carried out in vitro by using an isolated spinal cord/brainstem preparation. Horseradish peroxidase injections were made either uni‐ or bilaterally at various levels of the spinal cord along the rostrocaudal axis of the embryo. HRP histochemistry was done on Vibratome sections with diaminobenzidine as the chromogen.Following unilateral injections at day 2.5, labelled commissural interneurons were found contralaterally and were confined to the injected segment. Subsequently, labelled cells were found progressively further away from the injected segment. By day 4.5 reciprocal projections extended between lumbar and brachial regions. Interneurons with intersegmental axonal projections were often undifferentiated, consisting of primitive unipolar or bipolar cells with little, if any, dendritic development. In some cases migrating interneurons could be retrogradely labelled from two or three segments away from the location of their translocating cell body. Anterograde Golgi‐like labelling of early undifferentiated cells revealed growing axons, axonal terminals, and growth cones. Five or six reasonably distinct classes of intersegmental interneurons were identified based on their location, axonal projections, and morphology of dendritic arbors. These appeared to be segmentally and bilaterally arranged along the rostrocaudal axis of the spinal cord. The axons of some of these types of interneurons exhibited preferences in their longitudinal projections within the ventral and ventrolateral marginal zone at the very onset of pathway formation. From the present observations it can be concluded that intersegmental connectivity precedes the development of ascending and descending supraspinal, as well as primary afferent connections in the chick embryo spinal c

ISSN:0092-7317    

DOI:10.1002/cne.902750202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractUltrastructural changes occurring in the dorsal motor nucleus of the vagus of the guinea pig after nerve transection were investigated. Two neuronal populations could be distinguished. Large neurons corresponding to the vagal motoneurons showed chromatolysis. They were found to develop complex changes in cell surface, which appeared either as a folding up and formation of flaplike processes or as invagination of adjacent neuronal or glial elements. Large processes often covered part of the plasmalemma and formed stacks of several neuronal lamellae. Smaller processes were mostly seen to extend into the neuropil, where they intermingled and adopted a budlike shape. These changes occurred in the cell somata within the first week after axotomy. The dendrites were affected after a short delay. The changes persisted for several months in most of the neurons, including the ones that showed signs of recovery from chromatolysis. The newly formed cellular extensions had a growth‐cone‐like internal structure, containing numerous smooth‐surfaced vesicles or cisternae, a feltwork of filamentous material, dense‐cored vesicles, and occasionally free polyribosomes. These surface changes did not occur in the second neuronal cell type of this nucleus, which had a smaller perikaryon characterized by a scanty cytoplasm. These cells did not show a retrograde degeneration and thus are probably interneurons. Acetylcholinesterase was used as a cytochemical marker of neuronal membranes. Surprisingly, the vagal motoneurons did not show a loss of enzymatic activity after nerve transection. Rather, a redistribution seemed to occur with intensified staining of the plasmalemma. The newly formed processes were consistently found to be acetylcholinesterase positive. It is suggested that the morphological changes observed correspond to an asyetunobserved growth process in the adult central nervous system, which involves perikarya and dendrites of regenerating guinea pig vagal moto

ISSN:0092-7317    

DOI:10.1002/cne.902750203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe anterior intermediate sensory neuropile (aISN) is a prominent neuropile in the ventral nerve cord of locusts and bushcrickets. Previous studies have shown that it receives its main sensory input from auditory receptors. In this paper we examine the structural and physiological relationship between tympanal receptor terminations and the dendrites of sound‐sensitive interneurones in the homologous neuropile of locusts and bushcrickets.Each individual receptor fibre of the bushcricket terminates in a some what different target area of the neuropile. The ordering is with respect to the characteristic frequency of the fibres (tonotopic) in the anterior‐posterior and dorsoventral axis. In the locust, representatives of the four tympanal receptor groups branch in different areas of the aISN. Most of the dorsal neuropilar region, and the anterior ventral region, do not receive input from tympanal receptors.The dendrites of identified sound‐sensitive interneurones were examined in the context of this afferent projection. Local interneurones as well as intersegmental interneurones in bushcrickets have dendritic branches in the whole aISN or part of it and thus overlap with at least some receptors. By recording intracellularly from their main neurites, short‐latency synaptic potentials were found in response to receptor spikes indicating monosynaptic input. The tuning of these neurones could be predicted by their dendritic morphology. In contrast, in the locust only local and bisegmental neurones are monosynaptically connected with tympanal receptors, but not the studied intersegmental neurones. This is consistent with the finding that most or all branches of intersegmental neurones lie in the dorsal area of neuropile where no receptors terminate. Anatomical and physiological evidence is presented for identified local neurones providing the excitatory and inhibitory synaptic input for such intersegmental neurones.The difference in the basic wiring diagram in the homologous neuropile of the two orthopteran groups is discussed with respect to the possible different roles that sound plays in their be

ISSN:0092-7317    

DOI:10.1002/cne.902750204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe nucleus basalis (NB) of the human brain is a large, complex, and highly differentiated structure. Many of its neurons are magnocellular, hyperchromic, isodendritic, acetylcholinesterase‐rich, and choline‐acetyltransferase‐positive. Concurrent histochemical and immunological staining demonstrated that all choline‐acetyltransferase‐positive NB neurons in the human brain also contain acetylcholinesterase enzyme activity. Only a small minority of acetylcholinesterase‐rich magnocellular cell bodies in the NB failed to show choline acetyltransferase immunoreactivity. Sections that were counterstained for Nissl substance showed that 80‐90% of all magnocellular neurons in the NB were choline‐acetyltransferase‐positive and therefore cholinergic. These characteristics, which are very similar to those of the NB in the monkey brain, justified the designation of these cholinergic neurons in the human brain as the Ch4 (or NB‐Ch4) complex. On morphological grounds, the compact parts of the human NB‐Ch4 complex were divided into distinct sectors which appeared to show a greater level of differentiation than in the monkey brain. In addition to the compact sectors, interstitial elements of NB‐Ch4 were embedded within adjacent fiber bundles.The putative cortical projections from NB‐Ch4 were identified in the form of acetylcholinesterase‐rich fibers. These fibers formed a dense plexus in all cortical regions but also displayed laminar and regional variations. Limbic and paralimbic areas had higher concentrations of these fibers than the immediately adjacent neocortical association areas. Alzheimer's disease was associated with a marked depletion of cortical acetylcholinesterase. Two cases of Alzheimer's disease with relatively selective NB‐Ch4 cell loss supported the hypothesis that the corticopetal cholinergic pathways in the human brain may have a topographical organization simila

ISSN:0092-7317    

DOI:10.1002/cne.902750205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe pattern of acetylcholinesterase activity in the tree shrew (Tupaia belangeri) lateral geniculate nucleus (LGN) undergoes a number of striking changes during postnatal development. The adult tree shrew LGN is made up of six cellular layers divided by relatively cell‐free interlaminar zones. At birth, however, the nucleus appears unlaminated when processed with conventional Nissl‐staining techniques. The cellular lamination appears during the first postnatal week. The eyes open much later, typically at the end of the third week after birth.In the adult tree shrew, acetylcholinesterase (AChE) activity is found throughout the nucleus (both within and between the six cellular layers). In most sections examined, reaction product is slightly more intense in the lateral cell layers (4, 5, and 6).This is in sharp contrast to the pattern at birth (postnatal day zero, or P0). The detectable AChE activity at this age is apparently found in inchoate layers 1‐2 and 4‐5. Within these pairs, areas innervated by the ipsilateral eye (i.e., incipient layers 1 and 5) appear to contain more reaction product. From P0 to P4, the density of AChE activity increases in layers 1‐2 and 4‐5 and becomes detectable in the barely evident layers 3 and (usually) 6 at this age. By the middle of the second postnatal week, after laminae are clearly apparent with a Nissl stain, AChE activity has increased and is mainly associated with each cellular layer in the nucleus. During the third week after birth this pattern undergoes a radical shift. The most intense AChE activity is now in the interlaminar zones. Finally, as the adult pattern emerges, AChE activity increases in the cellular layers and all areas of the nucleus exhibit relatively high levels of AChE activity.Superimposed on this changing laminar pattern of AChE activity are changes related to the retinotopic map within the nucleus. Portions of the LGN representing central vision develop their characteristic pattern of activity several days ahead of the regions representing more peripheral visual field locations.AChE activity is also found transiently in the optic tract near the LGN during the first 3 postnatal weeks. Two (possibly three) groups of AChE‐carrying fibers can be traced from the optic chiasm to their apparent sites of termination (or origin) in the parabigeminal nucleus, ventral lateral geniculate nucleus, and dorsal LGN. The activity present in the optic tract disappears shortly after eye opening.These results suggest that AChE and/or its associated neurotransmitter, acetylcholine, may play a role in the sequential development of connections and lamination in the LGN. The observed shifting pattern of AChE activity is consistent with a morphogenetic role for the enzyme, as suggested by others. However, it may also simply reflect the establishment and neurochemical maturation of cholinergic synapses during developme

ISSN:0092-7317    

DOI:10.1002/cne.902750206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe hippocampi of two 1‐year‐old female baboons (Papio anubis) were used for a combined Golgi/electron microscope (EM) study of characteristic cell types in the hippocampus proper and fascia dentata. Results were compared with previous Golgi/EM studies of hippocampal neurons in small laboratory animals.Cell bodies ofpyramidal neurons in CA1were more loosely distributed than known from studies on the rat or guinea pig. Numerous basal and horizontal dendrites originating from the perikaryon filled in the space between neighboring cell bodies. Apical stem dendrites were varying in length, depending on the position of the parent cell body in outer or inner portions of the pyramidal layer. Dendrites were densely covered with spines which in the EM showed very complex synaptic contacts.In contrast to our observations in rats and guinea pigs,CA3 pyramidal cellsin the monkey hippocampus exhibited numerous large spines orexcrescencesnot only on apical dendrites but also on basal dendrites running through stratum oriens. These excrescences appeared to be more complex than in small rodents. They often branched, protruding deeply into presynaptic mossy fiber boutons, and formed multiple asymmetric synaptic contacts.Granule cellsof the monkey fascia dentata, in contrast to those of the rodent, occasionally had basal dendrites extending into the hilar region. In the EM, granule cells either with or without basal dendrites exhibited fine structural characteristics that were very similar to those described in Golgi/EM studies of granule cells in the rat fascia dentata.Of the various types ofnonpyramidal neuronsthe horizontal cells in stratum oriens with dendrites parallel to the alveus were analyzed. As seen in rats, these cells exhibited large amounts of rough endoplasmic reticulum, indentations of the nuclear membrane, and nuclear inclusions. Numerous terminals formed synaptic contacts on dendritic shafts. In contrast to rodents, numerous spines arose from dendrites and cell bodies of these neurons. In the EM, often single spines were found to establish synaptic contacts with several presynaptic boutons.In summary, our correlated light and EM study of four characteristic cell types, which are present in both nonprimates and primates, demonstrates a much more complex dendritic pattern and synaptic organization of these neurons in primates than in commonly studied small laboratory anim

ISSN:0092-7317    

DOI:10.1002/cne.902750207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe short– and long–term effects of ricin injections into nerves have been evaluated with light microscopy in the dorsal root ganglia, spinal cord, and peripheral nerves in rats and cats. Dorsal root ganglion cells initially exhibited chromatolysis, followed by gliosis and cell death. These changes were associated with Fink‐Heimer degeneration in the somatotopically appropriate region of the dorsalhorn. There were no signs of chromatolysis in dorsal horn neurons in ricin‐injected animals, but chromatolytic motoneurons were observed. Ricin produced acute necrosis of injected nerves and dissolution of axoplasm. At long survival times (4 weeks) some apparently regenerating axons were seen in the injection sites of rats. Cell counts indicated that a substantial percentage of dorsal root ganglion neurons associated with the injected nerves were killed, but the presence of regenerating axons suggested that some cells survived the ricin treatment. Although the lesion may not always be complete, even with maximum sublethal doses, this method appears to be useful for specifically destroying afferent fibers associated with a particular nerve without transynaptic destruction of dorsal horn

ISSN:0092-7317    

DOI:10.1002/cne.902750208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractA new deafferentation technique, the application of ricin to peripheral nerves, was used to test for collateral sprouting of undamaged primary afferent fibers within the adult mammalian spinal cord dorsal horn. The right sciatic nerves in rats were injected with ricin 14 to 57 days prior to bilateral labelling of dorsal rootlets with horseradish peroxidase. To equate the number of surviving dorsal root fibers on the two sides, the left sciatic nerves were injected 5 days prior to labelling. In each animal, horseradish peroxidase was applied to a bilateral pair of lumbar or low thoracic dorsal rootlets 18 hours prior to sacrifice to test for sprouting by labelling primary afferent fibers and terminals in the right (experimental) and left (control) dorsal horns.Although there is overlap of degenerated and intact primary afferent fields in this preparation, a postulated precondition for sprouting (Murray and Goldberger:J. Neurosci. 6: 3205‐3217, '86), we found no evidence for sprouting of undamaged, myelinated afferent fibers in the experimental dorsal horns. The pattern of labelling was symmetrical in all animals, and the density of labelling was not consistently greater on the experimental side. These results support the conclusions of Rodin et al. (J. Comp. Neurol. 215: 187‐198, '83) and Rodin and Kruger (Somatosens. Res. 2: 171‐192, '84), who also found no sprouting in the rat's dorsal horn after surgical deafferentation, and do not support the assertion that the difference between the results of those studies and earlier studies in cats was due to a lack of overlap of degenerated and intact dorsal roots in th

ISSN:0092-7317    

DOI:10.1002/cne.902750209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractIn order to visualize the relative abundance of each of three potentially inhibitory neurotransmitters in the nuclei of the brainstem auditory pathway, receptor sites for glycine, GABA‐A, and muscarinic acetylcholine (ACh) have been localized in the cat's brainstem auditory system. Conventional autoradiographic receptor‐binding procedures were used and the distributions of the receptors were inferred from the respective distributions of tritiated strychnine, muscimol, and quinuclidinyl benzilate (QNB) binding sites.The results show that glycine may be the major inhibitory neurotransmitter in the auditory system as it ascends to the midbrain in that relatively high levels of strychnine binding are present in every major nucleus of the system. In contrast, high levels of muscimol binding of high‐affinity GABA‐A receptors are confined mostly to the dorsal cochlear nucleus, the dorsal nucleus of the lateral lemniscus, and the central and cortical regions of the inferior colliculus, while high levels of QNB binding of muscarinic ACh receptors are seen only in the central and cortical regions of the inferior col

ISSN:0092-7317    

DOI:10.1002/cne.902750210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902750201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY