摘要:

AbstractThe developmental remodeling of thalamic projections to frontal and prefrontal cortical fields was investigated in the rat by using a double retrograde tracing technique. Bilateral cortical injections of fluorescent tracers were made either in neonatal (first or second postnatal day) or in adult animals. In neonates, the cell populations retrogradely labeled from each cortical injection overlapped in a medial thalamic region that included the midline nuclei and the medial part of the mediodorsal nucleus, ventral medial nucleus, and nucleus gelatinosus. In adults, the overlap region was confined within the boundaries of the midline nuclei. Quantitative analysis showed that this overlap area was three times as wide in neonates as in adults. The neurons located in this region projected unilaterally both in neonatal and adult animals; bilaterally projecting cells were virtually absent.In neonates, a second set of contralaterally projecting neurons was found in more lateral thalamic regions. This population consisted of cell clusters in the dorsal part of the central lateral nucleus and in the lateral part of the ventral medial nucleus; scattered cells were also observed throughout other nuclei. This second cell population was represented in part by neurons bifurcating bilaterally. In adult animals, neurons projecting contralaterally were observed only occasionally in the lateral thalamus.The present results demonstrate that the bilaterality of thalamocortical projections undergoes a reduction during postnatal development. The mechanisms underlying this remodeling and the possible functional role of the transient‐crossed thalamocortical system are discusse

ISSN:0092-7317    

DOI:10.1002/cne.902810102

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe role of endogenous opioid systems (endogenous opioids and opioid receptors) in neuronal development was examined in 10‐ and 21‐day‐old rats by utilizing an opioid antagonist (naltrexone) paradigm. Throughout the first 3 weeks of life, Sprague‐Dawley rats were given daily subcutaneous injections of either 50 mg/kg naltrexone, a dosage that invoked a complete (24 hours/day) receptor blockade, or 1 mg/kg naltrexone, a dosage which intermittently blocked (4–6 hours/day) opioid receptors and exacerbated opioid action; animals injected with sterile water served as controls. Pyramidal cells from the frontoparietal cortex (layer III) and hippocampal field CA1, and cerebellar Purkinje cells, were impregnated by using the Golgi‐Kopsch method; total and mean dendrite segment length, branch frequency, and spine concentration were analyzed morphometrically. Perturbations of endogenous opioid systems caused region‐dependent alterations in dendrite complexity and/or spine concentration in all brain areas. Continuous opioid receptor blockade resulted in dramatic increases in dendrite and/or spine elaboration compared to controls at 10 days in all brain regions; however, these increases were only evident in the hippocampus at 21 days. With intermittent blockade, dendrite and/or spine growth were often subnormal, being predominant at day 21. Our results indicate that endogenous opioid systems are critical regulators of neuronal differentiation, and they control growth through an inhibitory mechanism. Considering previous findings demonstrating that neurobehavioral ontogeny is dependent on endogenous opioid‐opioid receptor interactions, the present results suggest an opioid‐dependent, structure‐function relationship between neuronal and be

ISSN:0092-7317    

DOI:10.1002/cne.902810103

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe immunocytochemical distribution of authentic proenkephalin‐containing perikarya and nerve fibers in the brain ofRana esculentawas determined with antisera directed toward different epitopes of preproenkephalin. The pattern of proenkephalinlike immunoreactivity was similar with antisera directed toward [Met5]‐enkephalin, [Met5]‐enkephalin‐Arg6, [Met5]‐enkephalin‐Arg6‐Phe7, [Leu5]‐enkephalin, and metorphamide; however, the intensity of the labelling varied depending on the target antigen.Proenkephalin‐containing perikarya were located in all major subdivisions of the brain except the metencephalon. In the telencephalon, immunoreactive perikarya were detected in the dorsal, medial, and lateral pallium; the medial septal nucleus; the dorsal and ventral striatum; and the amygdala. In the diencephalon, immunoreactive perikarya were detected in the preoptic nucleus, in the dorsal and ventral caudal hypothalamus, and in an area that appeared to be homologous to the paraventricular nucleus. In the mesencephalon, numerous immunoreactive perikarya were detected in layer 6 of the optic tectum and a few scattered perikarya were detected in layer 4 of the optic tectum. Immunoreactive perikarya also occurred in the laminar nucleus of the torus semicircularis. In the rhombencephalon, immunoreactive perikarya were detected in the obex region and the nucleus of the solitary tract. Immunoreactive fibers of varying density were observed in all major subdivisions of the brain with the densest accumulations of fibers occurring in the dorsal pallium, the lateral and medial forebrain bundles, the amygdala, the periventricular hypothalamus, the superficial region of the caudolateral brainstem, and in a tract that appeared to be homologous to the tractus solitarius.The extensive system of proenkephalin‐containing perikarya and nerve fibers in the brain of an amphibian showed many similarities to the distribution of proenkephalin‐containing perikarya and nerve fibers previously described

ISSN:0092-7317    

DOI:10.1002/cne.902810104

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe hippocampus is especially vulnerable to ischemic damage. Neurons in the CA3c region and dentate hilus demonstrate fast progressive damage while CA1 pyramidal cells demonstrate delayed neuronal damage. The delayed CA1 pyramidal cell loss could be caused by postischemic neuronal hyperactivity if hippocampal interneurons are lost after ischemia. Therefore we have counted the L‐glutamic acid decarboxylase (GAD)‐immunoreactive neurons in the hippocampus from control rats and rats surviving 4 or 11 days after 20 minutes of cerebral ischemia. All rats were injected intraventricularly with colchicine before they were killed.The hippocampal cell counts showed an increase in GAD‐immunoreactive somata visualized on the fourth postischemic day. Eleven days after ischemia, the number of GAD‐immunoreactive neurons visualized in the hippocampus CA1 and CA3c region decreased. GAD‐immunoreactive baskets were visualized in the pyramidal cell layer and the granule cell layer in controls and 4 days after ischemia, but not in the CA1 and CA3c pyramidal cell layer 11 days after ischemia.We suggest the number of GAD‐immunoreactive neurons visualized on the fourth postischemic day increases because somatal GAD accumulation increases and, therefore, ischemia may enhance GAD production. Our previous counts of CA1 interneurons 21 days after ischemia in toluidine‐stained semithin sections demonstrated no interneuron loss. Therefore we suggest that the decreased number of CA1 and CA3c GAD‐immunoreactive neurons visualized 11 days after ischemia is related to a decreased GAD production. It is possible at this stage after ischemia that the interneurons have decreased their GAD production because they have lost their input and/or target cells.We conclude that our counts of GAD‐immunoreactive neurons visualized after ischemia express changes in the content of somatal GAD rather than the actual number of GAD‐immunoreactive somata. Finally, we conclude that the delayed loss of CA1 pyramidal cells seen 4 days after ischemia is not preceded by loss of hippocampal GAD‐i

ISSN:0092-7317    

DOI:10.1002/cne.902810105

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe origins of the descending spinal pathways in sea lampreys (Petromyzon marinus), silver lampreys (Ichthyomyzon unicuspis), and Pacific hagfish (Eptatretus stouti) were identified by the retrograde transport of horseradish peroxidase (HRP) placed in the rostral spinal cord. In lampreys, the majority of HRP‐labeled cells were located along the length of the brainstem reticular formation in the inferior, middle, and superior reticular nuclei of the medulla, mesencephalic tegmentum, and nucleus of the medial longitudinal fasciculus. Labeled reticular cells included the Mauthner and Müller cells. Horseradishperoxidase‐filled cells were also present in the descending trigeminal tract, intermediate and posterior octavomotor nuclei, and a diencephalic cell group, the nucleus of the posterior tubercle. As in lampreys, the reticular formation of the Pacific hagfish was the largest source of descending afferents to the spinal cord. Labeled cells were found in the dorsolateral and ventromedial reticular nuclei, the dorsal tegmentum at the juncture of the medulla and midbrain, and the nucleus of the medial longitudinal fasciculus. Additional medullary cells projecting to the cord were located in the perivagal nucleus, the central gray, and the anterior and posterior magnocellular octavolateralis nuclei. The existence of reticulospinal and possible vestibulo‐, trigemino‐, and solitary spinal projections in lampreys and hagfishes and the wide distribution of these pathways in jawed vertebrates suggest that they evolved in the common ancestor of gnathostomes and both groups of jawless fishes. However, descending spinal pathways from the cerebellum, red nucleus, and telencephalon appear to be gnathostome ch

ISSN:0092-7317    

DOI:10.1002/cne.902810106

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

年代:1989

数据来源: WILEY

摘要:

AbstractEfferent and afferent connections of the dorsal and ventral respiratory groups in the medulla of the cat were mapped by axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase. Injections of wheat germ agglutinin‐horseradish peroxidase into the dorsal respiratory group and the three principal subdivisions of the ventral respiratory group (caudal, rostral, and Bötzinger Complex) revealed extensive interconnections between these regions and with a limited number of other brainstem neuron populations. Major neuron populations with efferent projections to the regions of the dorsal and ventral respiratory groups include the parabrachial nuclear complex (medial parabrachial, lateral parabrachial, and Kölliker‐Fuse nuclei), subregions of the lateral paragigantocellular reticular nucleus, subregions of the lateral and magnocellular tegmental fields, inferior central and postpyramidal nuclei of the raphe, and sensory trigeminal nuclei. A previously unidentified neuron population with extensive efferent projections to the dorsal and ventral respiratory groups was found near the ventral surface of the rostral medulla; we refer to this group as the retrotrapezoid nucleus. The results suggest that the dorsal and ventral respiratory groups form an extensively interconnected neuronal system receiving convergent inputs from the same brainstem nuclear groups, consistent with the hypothesis that the dorsal and ventral groups are primarily sites for integration of sensory and premotor respiratory drive inputs. Neuron populations in the rostral ventrolateral medulla with projections to both the dorsal and ventral respiratory groups, particularly the retrotrapezoid nucleus and neighboring subregions of the lateral paragigantocellular reticular nucleus, are candidate sites for participation in respiratory rhythmogenesis or other critical functions of the brainstem respiratory control system such as intracranial chemorece

ISSN:0092-7317    

DOI:10.1002/cne.902810107

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe frontal lobe connections of different architectonic areas of the superior temporal sulcus (STS) in the rhesus monkey were investigated with the aid of both anterograde and retrograde tracing techniques. The proisocortical area in the rostralmost STS connects with proisocortical regions on the ventral and medial surfaces of the frontal lobe. The frontal lobe projections of polymodal cortex (area TPO) in the upper bank of the STS are organized according to the rostral‐to‐caudal topography of the sulcus. Rostral TPO interconnects with ventral (areas 13, 12, 11, and 14), medial (areas 24, 32, 14, and 9), and lateral (areas 10, 12, and 46) sectors of the frontal lobe. The midportion of polymodal cortex projects to, and receives fibers from, rostral subdivisions of lateral prefrontal cortex, viz. dorsal area 46, areas 9 and 10, whereas the caudal segment of TPO has reciprocal connections with caudal subdivisions (areas 46, 8, and 6) of the lateral frontal lobe.Visual‐related zones (areas TEa and TEm) in the rostral lower bank of the STS have connectional relationships with orbitofrontal areas 11 and 12 and lateral frontal areas 46 and 8. A presumed somatic sensory‐related area in the rostral depth of the STS (area IPa) projects to orbital (areas 11 and 14) and lateral (areas 46, 10, and 12) sectors of the front

ISSN:0092-7317    

DOI:10.1002/cne.902810108

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

年代:1989

数据来源: WILEY

摘要:

AbstractSerotonin‐containing neurons in the brain of the weak‐electric fishGnathonemus petersii(mormyridae, teleostei) were studied with the aid of immunohistochemical labeling. Study of the central serotoninergic innervation was focused on the structures subserving the command of the electric organ and the first central relay of the electrosensory system.In the midline raphe nuclei, serotoninergic neurons formed a column that stretched from the ventral caudal medulla to the dorsal midbrain, ending caudal to the cerebellar peduncle. In the dorsal tegmentum, serotoninergic neurons were found bilaterally at the anterior margin of the decussation of the lateral lemniscus. Labeled neurons were also present bilaterally immediately anterior to the cerebellar peduncle and also in the pretectal region. In the hypothalamus, many serotoninergic neurons were in contact with the ventricular wall, and a few were present in the preoptic area. This distribution of serotoninergic cell bodies showed many similarities to that in other fish and higher vertebrates but lacked the lateral spread of the serotoninergic raphe system found in the midbrain tegmentum in mammals.Labeled fibers were found in both the preelectromotor medullary relay nucleus and the electromotor command nucleus. These serotoninergic projections were traced to the posterior raphe. Serotoninergic fibers also formed a dense network in the cortex and in the nucleus of the electrosensory lobe, both of which receive primary input from electroreceptors.These results suggest that serotonin may have a role in the modulation of the intrinsic, rhythmic electromotor command and in the gating of electrosensory in

ISSN:0092-7317    

DOI:10.1002/cne.902810109

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

年代:1989

数据来源: WILEY

摘要:

AbstractIn the chicken cochlea, the structural features of the cilia bundles of individual hair cells vary systematically along the length of the sensory epithelium. As a first approach to understanding the developmental mechanisms that underlie this precise arrangement of structurally distinct hair cells, the spatiotemporal pattern of the terminal mitoses of their precursor cells was investigated by administering3H‐thymidine, a radioactive precursor to DNA. This demonstrated that the first hair cells were produced during the sixth day of incubation and formed a longitudinal band that extended along most of the length of the sensory epithelium. The epithelium grew further through appositional addition of hair cells at the edges of this first band of cells, and the hair cell addition process expanded into the surrounding areas during the next 3 days. By the ninth day of incubation all the hair cells in the sensory epithelium except for those at the peripheral edges in the distal (apex) portion had been produced through terminal mitoses. Our results have demonstrated that hair cells that have similar stereocilia phenotypes do not all leave the mitotic cycle at the same tim

ISSN:0092-7317    

DOI:10.1002/cne.902810110

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe synaptic organization of the rat interpeduncular nucleus is highly ordered in the normal adult. By 90 days of age, 90% of crest synapses in its intermediate subnuclei are formed by two cholinergic endings, one from each medial habenula. Stereological calculation of the number of crest synapses per intermediate subnucleus, based on total samples of crest synapses in 3–4 sections through the subnucleus, allows comparisons of afferent pairing among ages without interference by other developmental changes. Between 21 and 90 days of age, the total number of crest synapses per intermediate subnucleus increases tenfold (p ≤ 10−8), from 90,000 at 21 days of age, through 130,000 at 28 days, 440,000 at 45 days, to 1,000,000 at 90 days. The volume of the intermediate subnucleus increases fivefold during the same interval.Electron microscopic degeneration was used to estimate the pairing of left and right habenula afferents at crest synapses at the same ages. Through 21 days of age, only one‐third of crest synapses are formed with pairing of one left and one right medial habenula afferent, whereas two‐third have both afferent endings arising from the same medial habenula. At 28 days of age left‐right pairing has increased to 43%, and at 45 days of age 53%, or 240,000, are so paired. The number of same‐side paired crest synapses at 45 days, 210,000, is 3.5 times the number so paired at 21 days (p = .003). This indicates continuedformationof considerable numbers of crest synapses with this transient mode of pairing as late as 45 days of age. Since the number with same‐side pairing in the adult, 100,000, is half the number at 45 days (p ≤ 10−8),remodelingof afferent pairing must continue to be an important process in the development of interpeduncular nucleus throughout the period of synaptogenesis. Conversely, the data are inconsistent with the principal alternative, a marked change in synapse formation after 21 days of age such that newly forming crest synapses are initially left‐right paired.The remodeling may involve any of several modes of synapse elimination and/or altered pairing. It appears to be similar to remodeling observed in a number of other systems, although these have rarely addressed connectivity at the level of individual synapses. Since the cellular and molecular mechanisms of remodeling in general remain to be discovered, a system where these processes can be experimentally approached in terms of their level of action at individual synaptic sites ma

ISSN:0092-7317    

DOI:10.1002/cne.902810111

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

年代:1989

数据来源: WILEY