摘要:

AbstractThe synaptic organization of the mediodorsal thalamic nucleus (MD) in the rat was studied with the electron microscope, and correlated with the termination of afferent fibers labeled with wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP). Presynaptic axon terminals were classified into four categories in MD on the basis of the size, synaptic vesicle morphology, and synaptic membrane specializations: (1) small axon terminals with round synaptic vesicles (SR), which made asymmetrical synaptic contacts predominantly with small dendritic shafts; (2) large axon terminals with round vesicles (LR), which established asymmetrical synaptic junctions mainly with large dendritic shafts; (3) small to medium axon terminals with pleomorphic vesicles (SMP), which formed symmetrical synaptic contacts with somata and small‐diameter dendrites; (4) large axon terminals with pleomorphic vesicles (LP), which made symmetrical synaptic contacts with large dendritic shafts. Synaptic glomeruli were also identified in MD that contained either LR or LP terminals as the central presynaptic components. No presynaptic dendrites were identified.In order to identify terminals arising from different sources, injections of WGA‐HRP were made into cortical and subcortical structures known to project to MD, including the prefrontal cortex, piriform cortex, amygdala, ventral pallidum and thalamic reticular nucleus. Axons from the amygdala formed LR terminals, while those from the prefrontal and insular cortex ended exclusively in SR terminals. Fibers labeled from tie piriform cortex formed both LR and SR endings. Based on their morphology, all of these are presumed to be excitatory. In contrast, the axons from the ventral pallidum ended as LP terminals, and those from the thalamic reticular nucleus formed SMP terminals. Both are presumed to be inhibitory. At least some terminals from these sources have also been identified as GABAergic, based on double labeling with anterogradely transported WGA‐HRP and glutamic acid decarboxylase (GAD) immunocytoch

ISSN:0092-7317    

DOI:10.1002/cne.903030402

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

年代:1991

数据来源: WILEY

摘要:

AbstractDuring growth of the axolotl, motor neurons, and muscle fibres are added to the motor system. By double labelling neurons with tritiated thymidine and retrogradely transported HRP, we show that some motor neurons are born at postembryonic stages. Further analysis of motor neurons with the aid of HRP reveals this population of newly, born cells relatively frequently in small (5–7 cm long) axolotls, but only rarely in large (7–13 cm long) axolotls. Evidence is presented that suggests that these immature cells are in the process of migrating from close to the ependyma out to the ventral horn. HRP transport also reveals growth cones of advancing axons within spinal nerves in animals up to 6 cm in length. Cell counts by light and electron microscopic methods show that muscle fibres are generated throughout larval life in the iliotibialis, a typical limb muscle. This analysis provides data consistent with the notion that new muscle fibres are added from a localised growth zone situated at the superficial edge of the muscle. These results are discussed in terms of the correlation between continuous growth of the motor system and the ability of the axolotl to functionally repair lesions to the peripheral nervous sys

ISSN:0092-7317    

DOI:10.1002/cne.903030403

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe characteristics of motor units in the iliotibialis posterior muscle of the axolotl hindlimb are described. Tension recording and intracellular electrophysiological methods demonstrate that the physiological properties of the population of motor units are continuously distributed rather than grouped into a series of discrete types. Overlap between motor units occurs and this is positively correlated with motor unit size but negatively correlated with differences in time to peak tension. Immunocytochemical staining with antimyosin antibodies combined with histochemical demonstration of actomyosin ATPase activity revealed at least four types of muscle fibre which were distributed asymmetrically within iliotibialis posterior. The results are discussed in terms of the continuous growth of the muscle and the interactions between muscle and nerve in the formation of the axolotl motor system.

ISSN:0092-7317    

DOI:10.1002/cne.903030404

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe prefrontal cortex (PFC) projections to the basal forebrain cholinergic cell groups in the medial septum (MS), vertical and horizontal limbs of the diagonal band of Broca (VDB and HDB), and the magnocellular basal nucleus (MBN) in the rat were investigated by anterograde transport ofPhaseolus vulgarisleuco‐agglutinin (PHA‐L) combined with acetylcholinesterase (AChE) histochemistry or choline acetyltransferase (ChAT) immunocytochemistry. The experiments revealed rich PHA‐L‐labeled projections to discrete parts of the basal forebrain cholinergic system (BFChS) essentially originating from all prefrontal areas investigated. The PFC afferents to the BFChS display a topographic organization, such that medial prefrontal areas project to the MS, VDB, and the medial part of the HDB, whereas the orbital and agranular insular areas predominantly innervate the HDB and MBN, respectively. Since the recurrent BFChS projection to the prefrontal cortex is arranged according to a similar topography, the relationship between the BFChS and the prefrontal cortex is characterized by reciprocal connections. Furthermore, tracer injections in the PFC resulted in anterograde labeling of numerous “en passant” and terminal boutons apposing perikarya and proximal dendrites of neurons in the basal forebrain, which were stained for the cholinergic marker enzymes. These results indicate that prefrontal cortical afferents make direct synaptic contacts upon the cholinergic neurons in the basal forebrain, although further analysis at the electron microscopic level will be needed to provide conclusi

ISSN:0092-7317    

DOI:10.1002/cne.903030405

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

年代:1991

数据来源: WILEY

摘要:

AbstractComparative analyses were made of the immunohistochemical and biochemical distributions of three prosomatostatin‐derived peptides (PSDP) in human, perfused monkey, and unperfused monkey neocortex. The PSDP we examined were the tetradecapeptide somatostatin 14 (SS14); the N‐terminal extension of this peptide, somatostatin 28 (SS28); and somatostatin 281–12(SS281–12). In immunohistochemical experiments, numerous SS28‐immunoreactive perikarya were located in both superficial and deep layers of perfused monkey cortex, but none were present in the cerebral cortex from unperfused monkey or autopsied human brains. In contrast, the number of SS281–12‐immunoreactive neurons was five times greater in the superficial cortical layers of unperfused monkey than of perfused monkey brain. Moreover, unperfused monkey and human cortex contained notably more SS14‐immunoreactive processes than perfused monkey cortex. These data suggested that SS28 may have been converted into SS14 and SS281–12in unperfused tissue during the post‐mortem interval. This hypothesis was examined biochemically by measuring the levels of immunoreactivity of SS14, SS28, and SS281–12in samples of unperfused monkey cortex frozen at different time intervals after removal from the brain. Samples frozen 10 minutes or longer after removal contained only 10–20% the level of SS28 immunoreactivity measured in samples frozen immediately or 1 minute after removal. The levels of SS14 and SS281–12immunoreactivity did not demonstrate such reductions, and may instead have increased at early time points.To further characterize post‐mortem effects on PSDP and to explore for species differences, we performed a detailed comparison of the regional, laminar, and cellular distribution of SS281–12immunoreactivity under the three conditions. A progressive loss of immunoreactivity, particularly in radial fibers, was found at increasing post‐mortem intervals in unperfused monkey neocortex, indicating that differences in density and distribution of immunoreactive fibers between human and perfused monkey may result from post‐mortem peptide degradation in unperfused tissue. In contrast, the larger size of SS281–12‐immunoreaetive white matter neurons in humans as compared to monkeys appeared partially due to a post‐mortem effect but also reflected a species difference. In addition, the density of white matter neurons was found to be significantly greater in human than in perfused or unperfused monkey.These data indicate that any study of human autopsy material must be assessed in light of possible post‐mortem effects. Although studies of perfused monkey cortex may yield data that more accurately reflect the normal distribution of PSDP in neocortex, one cannot rely exclusively upon these data as a predictor of the distribution of PSDP in human neocortex because species differences exist. Thus, evaluation of the role of chemically identified neural systems in human neocortex may be more effectively made if studies of human autopsy material are augmented by comparisons to both

ISSN:0092-7317    

DOI:10.1002/cne.903030406

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

年代:1991

数据来源: WILEY

摘要:

AbstractEarly postnatal lesions of the primary somatosensory cortex alter the vibrissa‐related cytochrome oxidase (CO) pattern in nucleus principlis (PrV) of the rat's trigeminal (V) brainstem complex (Erzurumlu and Ebner, '88:Dev. Brain Res.44:302–308). At present, the reason for this change is not clear. It may be that the corticotrigeminal projection is necessary for the maintenance of vibrissa‐related patterns in PrV. However, it is also possible that the loss of the normal pattern of CO activity reflects a change in the organization of brainstem cells resulting from transneuronal retrograde degeneration. In order to address this question, we made lesions of either the primary somatosensory cortex (S‐I) or ventrobasal thalamus (VB) in newborn rats and directly assayed distributions of V primary afferents by transganglionic transport of horseradish peroxidase and V‐thalamic neurons by retrograde transport of either fluorogold or true blue. Neonatal cortical and thalamic lesions produced no qualitative change in the distribution of primary afferent terminals in either PrV or V subnucleus interpolaris (SpI) beyond that which could be attributed to shrinkage of the brainstem resulting from retrograde degeneration. Most importantly, the “patchy” pattern of terminations observed in normal rats remained apparent in the brain‐damaged animals. The normal distribution of V‐thalamic neurons in PrV wasdisrupted by both cortical and thalamic lesions. These cells are normally patterned in a way that matches the distribution of primary afferent terminals and thus that of the mystacial vibrissae. This was not the case in the neonatally brain‐damaged rats. Taken together, these results are consistent with the conclusion that neonatal cortical and thalamic lesions disrupt the normal CO pattern in PrV primarily because of their effects upon the patterning of brainstem cells. The present findings demonstrate further that clustering of primary afferents does not require a normal complement of p

ISSN:0092-7317    

DOI:10.1002/cne.903030407

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn this study we used serial section electron microscopy and three‐dimensional reconstructions to examine four midget ganglion cells of the human retina. The four cells were located in the parafoveal retina 2.5 mm or 8° from the foveal center. Both typea(with dendritic trees in distal inner plexiform layer) and typeb(with dendritic trees in proximal inner plexiform layer) midget ganglion cells have been studied. These culls have dendritic trees of 7–9 μm diameter, and their complete dendritic trees in the neuropil of the inner plexiform layer can be analyzed, as well as the bipolar cell axon terminals having synaptic input, by a study of 100–150 serial ultrathin sections. Typeamidget ganglion cells appear to be in a one‐to‐one relationship with fiat midget bipolar cell axon terminals ending in distal inner plexiform layer. Typebmidget ganglion cells are in a one‐to‐one synaptic relationship with invaginating midget bipolar cell axon terminals in proximal inner plexiform layer. The midget bipolar cells primarily involved with the midget ganglion cells do not contact other ganglion cell dendrites. In other words, midget bipolar cells appear to be in exclusive contact with single midget ganglion cells in the human retina.The midget ganglion cells receive most of their input from their associated midget bipolar cells in the form of ribbon synapses at dyads or monads (55–81 ribbons total), although ribbonless synapses are seen occasionally. In all four midget ganglion cells reconstructed, one or two other bipolar cell axon terminals, presumed to be from wide‐field bipolar types, provide 1–3 ribbon synapses each. The number of amacrine synapses upon a midget ganglion cell's dendritic tree is approximately equal to the number of bipolar ribbon inputs (43%–56% bipolar ribbons: 44%–57% amacrine synapses).We assume from our knowledge of response characteristics of ganglion cells in other mammalian retinas (Nelson et al., '78:J. Neurophysiol.41:427–483), that the typeamidget ganglion cell and its exclusive connectivity with a flat midget bipolar cell forms a single cone connected OFF‐center pathway, whereas the typebmidget ganglion cell with its exclusive connectivity to an invaginating midget bipolar cell forms a single cone connected ON‐center pathway,

ISSN:0092-7317    

DOI:10.1002/cne.903030408

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe expression of mRNAs encoding different β subunits (β1, β2and β3) of the gamma‐aminobutyric acidA(GABAA) receptor in the rat brain was investigated by in situ hybridization histochemistry. Transcripts of each subunit showed region‐specific localization. Some areas contained all three β subunit mRNAs, while other areas showed marked differences in the location and level of expression of each subunit mRNA. The regions with strong to very strong labeling by the β3probe were as follows: the olfactory bulb, the cortex, the caudate‐putamen, the accumbens nucleus, the hypothalamus, the amygdala, the hippocampal formation, and some areas of the brainstem and spinal cord. Weak to moderate labeling was detected in the thalamus, superior and inferior colliculus, and many areas of the brainstem. The regions with strong to very strong labeling by the β2probe were as follows: the olfactory bulb, the ventral pallidum, the globus pallidus, the nucleus of the diagonal band, the preoptic magnocellular nucleus, the thalamus, the subthalamic nucleus, the substantia nigra, and the cerebellum. Weak to moderate labeling was detected in the regions that showed strong expression of β3subunit mRNA. Expression of β1subunit mRNA was only weak to moderate compared to that of the β2and β3subunit mRNAs. The regions with moderate labeling by the β1probe were the following: the cortex, the claustrum, the bed nucleus of the stria terminale, some nuclei of thalamus and amygdala, the hypothalamus, the hippocampal formation, the subiculum, the cerebellum, and several areas of the brainstem and spinal cord. Thus, our findings showed that the β subunit mRNAs of the GABAAreceptor were differentially expressed in the rat brain, perhaps indicating the existence of different subtypes of the GABAAreceptor in diffe

ISSN:0092-7317    

DOI:10.1002/cne.903030409

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

年代:1991

数据来源: WILEY

摘要:

AbstractTwo largely separate populations of neuropeptide‐containing striatonigral projection neurons have been distinguished in pigeons, one population whose neurons contain substance P (SP) and dynorphin (DYN) and a second population whose neurons contain enkephalin (ENK) (Reiner, '86a; Anderson and Reiner, 90a). In the present study, we investigated the abundance of these two types of neurons relative to all striatonigral projection neurons by combining retrograde labeling by the fluorescent dye fluorogold with immunofluorescence labeling for SP and ENK.Pigeons received large intranigral injections of fluorogold to retrogradely label the striatonigral projection neurons, and several days later they were treated with colchicine (32 hours before transcardial perfusion). Adjacent series of sections through the basal ganglia were labeled for SP and ENK using immunofluorescence techniques. The tissue was examined using fluorescence microscopy and the percentages of retrogradely labeled neurons containing either SP or ENK were quantified. We found that 85–95% of the fluorogold‐labeled striatonigral neurons were SP+, whereas only 1–4% were ENK+.Thus the majority of striatonigral projection neurons in pigeons appear to contain SP, whereas a small percentage contain ENK. Only a small percentage of striatonigral neurons did not contain either. Since striatal projection neurons also contain GABA (Reiner, '86b), the present results suggest that a high percentage of striatonigral projection neurons coexpress SP, DYN and GABA, whereas a small fraction coexpress ENK and GABA. The available data are consistent with the conclusion that this is true in reptilian and mammalian species

ISSN:0092-7317    

DOI:10.1002/cne.903030410

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

年代:1991

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.903030401

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

年代:1991

数据来源: WILEY