摘要:

AbstractAlthough the connections of the auditory brainstem nuclei are well described in adult mammals, almost nothing is known concerning how and when these connections develop. The purpose of the present study was to describe the development of the efferent projections of the cochlear nucleus (CN), the first central relay station in the ascending auditory pathway of mammals. We used two tracers in rats aged between embryonic day 15 (E15) and postnatal day 14 (P14; birth in the rat is at E22 = P0). The carbocyanine dye DiI was applied into the CN in aldehyde‐fixed tissue. The second tracer, biocytin, was applied into the ventral acoustic stria in an in vitro slice preparation.The ontogeny of the efferent projections from the CN could be divided into three periods. The first period (E15–E17) is characterized by axonal outgrowth. Axons traverse nuclei in the superior olivary complex and the lateral lemniscus and finally grow up into the inferior colliculus, but axon collaterals do not from during this period. The second period (E18–P5) is marked by pronounced collateral branching of CN fibers in auditory brainstem nuclei. Collateralisation in the contralateral inferior colliculus starts shortly before that in the ipsilateral superior olivary complex. The remaining auditory nuclei become successively innervated, as indicated by collaterals found in them. During the third period (P5–P14) terminal structures mature further, as shown by the morphological changes of the calyces of Held in the medial nucleus of the trapezoid body.In conclusion, our results show that the efferent connections from the cochlear nucleus form over a period of almost two weeks and are laid down without forming aberrant internuclear connections. On a nuclear level, an adult‐like projection pattern is already achieved one week prior to the onset of physiological hearing. © 1993 Wiley

ISSN:0092-7317    

DOI:10.1002/cne.903280202

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe goal of this study was to determine whether processes of neurons in the mesencephalic nucleus of the trigeminal nerve (Mes V) of chick embryos arrive in their peripheral target prior to the period of developmental cell death, and to determine whether neurons with early target contact survive to a greater extent than neurons with processes that reach their peripheral target later. The arrival of Mes V nerve fibers in the masticatory muscles was determined by injecting the fluorescent tracer DiI, and the position of labeled and unlabeled neurons was mapped in subdivisions of the Mes V nucleus. Developmental changes in the numerical configuration of Mes V subdivisions were studied in DiI‐labeled as well as Nissl‐stained material. The expression of law‐affinity (p75) neurotrophin receptors was investigated throughout development of the Mes V nucleus with in situ hybridization to assess whether and how levels of expression of this trophic receptor may relate to target innervation and cell death. The extent of cell death was evaluated by counting pyknotic nuclei.Processes of Mes V neurons invade their peripheral target between 5 and 7 days of incubation (E5–7). At E7–12, between 800 and 1,400 labeled Mes V neurons were distributed throughout the two main subdivisions of the Mes V nucleus, the tectal commissure and the optic tectum. Only few Mes V neurons were labeled in the posterior commissure or outside the brain. Cell counts in Nissl‐stained material from E7–13 revealed that the numbers of Mes V neurons in the optic tectum decreased to about 40–60%, and in the tectal commissure to 20–25%, whereas Mes V neurons in the posterior commissure disappeared almost entirely. Few Mes V neurons remained in the leptomeninges at E8–10, but a considerable number was found outside the midbrain at E11, indicating ongoing migration of some Mes V neurons. Neurotrophin receptors were differentially expressed in the Mes V nucleus: Before and after the period of cell death, 90–100% of Mes V neurons expressed neurotrophin receptors, whereas during, and immediately preceding the period of developmental cell death (E9–E13), merely 70% of Mes V neurons expressed this receptor. These findings are consistent with the hypothesis that early target contact may provide an advantage for the survival of Mes V neurons and that competition for trophic factors may occur in the peripheral target of this nucleus prior to the period of cell death.

ISSN:0092-7317    

DOI:10.1002/cne.903280203

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe hypothalamic and basal forebrain sites of synthesis of preprogalanin mRNA were identified in three adult monkeys (Macaca fascicularis) by in situ hybridisation performed with a radiolabelled cRNA probe transcribed from human preprogalanin cDNA. With stringent hybridisation conditions, the cRNA probe was hybridised to free‐floating sections containing structures contiguous with the rostral hypothalamus through to the caudal limit of the hypothalamus as defined by the mammillary bodies. Specific hybridisation of the preprogalanin cRNA probe occurred throughout the hypothalamus but was particularly intense in the arcuate, paraventricular (parvicellular and magnocellular portions), and dorsomedial nuclei. Moderate hybridisation was found in the periventricular nucleus and scattered hybridisation in the medial preoptic nucleus. The medial preoptic area and the anterior and lateral hypothalmic areas showed moderate to intense hybridisation in scattered cells. A few cells in the tuberal portion and dorsal cap of the anterior portion of the supraoptic nucleus were labelled. Isolated cells were also labelled in the zona incerta. There was little labelling in the dorsal hypothalamic area but moderate labelling in the posterior hypothalamic area. Structures contiguous with the rostral hypothalamus including the diagonal band of Broca, bed nucleus of stria terminalis, substantia innominata, and basal nucleus of Meynert showed intense hybridisation. These data indicate a widespread distribution of preprogalanin mRNA in the monkey hypothalamus. A comparison with the previously reported distribution of preprogalanin mRNA in the rat, as well as with the distribution of galanin‐like immunoreactivity in the rat and human, suggests some important species differences. Of particular interest were differences in the supraoptic, suprachiasmatic, and dorsomedial nuclei. The intense hybridisation throughout the paraventricular nucleus and in the rostral arcuate nucleus suggests that galanin may play a role in the regulation of both posterior and anterior pituitary function. © 1993 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903280204

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

年代:1993

数据来源: WILEY

摘要:

AbstractWholemount antibody labeling techniques and horseradish peroxidase backfilling were used to analyze the pattern of neuronal differentiation in the embryonicXenopuscentral nervous system between stages 22 and 35/36. In the spinal cord, the first neurons to differentiate are the Rohon‐Beard neurons; they are followed by ventral neurons with descending axons (descending interneurons, motoneurons) and lateral interneurons with commissural axons. The somata and axons of these primary neurons form dorsal, ventral, and lateral columns, respectively; the ventral and lateral columns uninterruptedly continue forward into the brainstem. The distribution and projection patterns of spinal neurons were analyzed quantitatively. Rohon‐Beard neurons, commissural interneurons, and primary motoneurons vary in number from segment to segment. Thus, these neurons are not distributed in a segmental pattern. In each segment, neurons of a given type project axons whose length varies over a wide range. The numerical distribution of length of axons formed by a population of neurons of a given type was calculated and expressed as the projection profile of these neurons. For each type of neuron and spinal segment, the projection profile is different. Furthermore, the projection profiles change in a systematic way along the spinal cord. For example, the fraction of Rohon‐Beard neurons with long ascending axons steadily increases if one moves towards caudal spinal levels. The findings suggest that suprasegmental cues with a graded distribution along the spinal cord determine the number and projection profile of a particular cell type in a given segment. © 1993 Wiley‐L

ISSN:0092-7317    

DOI:10.1002/cne.903280205

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe innervation of the inner conical body of the vibrissal follicle‐sinus complex of the rat was examined by high‐voltage and conventional transmission electron microscopy of serial and semi‐serial sections. The inner conical body is innervated by axons supplied almost exclusively by several superficial vibrissal nerves that arise from the infraorbital branch of the trigeminal nerve and converge upon the neck of the follicle‐sinus complex. Each superficial vibrissal nerve contains a few Aδ myelinated axons and several bundles of 20–30 unmyelinated axons. These axons enter the inner conical body and distribute circumferentially within 7–10 ring‐like arrays that encircle the vibrissal follicle and are stacked through the superficial‐to‐deep extent of the inner conical body. Each ring consists of 1 or 2 myelinated axons and several small bundles of 2–15 unmyelinated axons enclosed in sheaves of parallel collagen fibrils. Myelinated axons provide exclusively lanceolate endings that may arise at the termination of the axon or at nodes of Ranvier. Within the small bundles, unmyelinated axons individually terminate in succession as abrupt cytoplasmic swellings referred to as cytoplasmic blebs, which contain mitochondria or clusters of clear or dense‐core vesicles. Because of their affiliation with collagen fibrils and the proximity of myelinated axons, the blebbed endings may have been misinterpreted as Ruffini endings in previous studies. Their structure, distribution, and origin from unmyelinated axons suggest that the blebbed endings may constitute a unique array of low‐threshold C‐mechanorecepto

ISSN:0092-7317    

DOI:10.1002/cne.903280206

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe purpose of the present study was to determine the relationship between the duration of a spinal neuron's neurogenic period and the length of its axon or level of projection. Spinal segment L1 was chosen for examination and neurons were divided into four projection groups: (1) supraspinal projection (SSp), (2) long ascending propriospinal (LAPr), (3) short ascending propriospinal (SAPr), and (4) descending propriospinal (DPr). To determine the duration of the neurogenic period for each group,3H‐thymidine was administered to fetal rats during the proliferative period for spinal neuroblasts on one of embryonic (E) days E13 through E16. Between 50 and 100 days after birth neurons in each group were labeled with the retrograde fluorescent tracer Fluoro‐Gold. To demonstrate nerve cells with SSp projections, spinal cords were hemisected at spinal segment C3 in one group of animals and Fluoro‐Gold was applied to the sectioned surface of the cord. Three additional sets of animals were used to label nerve cells with LAPr, SAPr, and DPr projections by injecting Fluoro‐Gold into the gray matter at spinal segments C6, T12, and L5, respectively. Neurons labeled with both Fluoro‐Gold and3H‐thymidine and neurons labeled with Fluoro‐Gold alone in each animal in each group were counted and the data statistically analyzed. Results showed that within each spinal lamina neurons with different projections were generated, i.e., completed cell division, at significantly different rates. Neurons with the longest axons, those with SSP projections, were generated first. These were followed by those with LAPr projections, and finally those with SAPr and DPr projections. In most laminae there was no significant difference between the neurogenic periods of rostrally projecting short propriospinal (SAPr) neurons versus caudally projecting short propriospinal (DPr) neurons. It was concluded that the duration of the neurogenic period for a given group of neurons within each spinal lamina is inversely related to the distance between the nerve cell and its projection site regardless of the direction of its projection. © 1993 W

ISSN:0092-7317    

DOI:10.1002/cne.903280207

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe inferior olive is divided into several subnuclei that receive specific sensory information. The caudal dorsal cap of the medial accessory subdivision of the inferior olive receives horizontal optokinetic information from the nucleus of the optic tract. The immediately subjacent b̃‐nucleus receives vertical vestibular information mediated by a GABAergic pathway originating from the ipsilateral descending and medial vestibular nuclei. None of the transmitters to the dorsal cap have been identified.Using choline acetyltransferase (ChAT) immunohistochemistry, we have identified a cholinergic pathway that terminates exclusively in the dorsal cap of rats and monkeys. No other division of the inferior olive received a significant cholinergic innervation. In the rabbit, immunostaining for ChAT reveals a weaker and more diffuse cholinergic innervation of both the dorsal cap and the subjacent b̃‐nucleus.In rats and rabbits we injected iontophoretically the orthograde tracerPhaseolus vulgarisleucoagglutinin (PHA‐L) into the medial and descending vestibular nuclei (MVN, DVN) as well as the nucleus prepositus hypoglossi (NPH) in order to trace the possible origin of the cholinergic projection. PHA‐L injections into the NPH and medial aspect of the MVN labeled terminals within the contralateral dorsal cap. PHA‐L injections in the central and lateral aspects of the MVN as well as the DVN labeled the ipsilateral b̃‐nucleus.Pressure injections of wheat germ agglutinin‐horseradish peroxidase (WGA‐HRP) in the caudal dorsal cap of the rabbit inferior olive demonstrated a predominantly contralateral projection to the dorsal cap from the lateral aspect of the NPH. However, pressure injections of HRP into the caudal dorsal cap combined with ChAT immunohistochemistry in the rabbit demonstrated that most of the neurons of the NPH that projected to the dorsal cap were not cholinergic, and that most of the ChAT‐positive neurons within the NPH occupied a more ventral location than the neurons within the NPH that were retrogradely labeled from the HRP injection into the contralateral dorsal cap.In the rat, we made lesions in the MVN, DVN and NPH by injection of ibotenic acid (0.3–0.5 m̈l), in an attempt to deplete the dorsal cap of the inferior olive of its cholinergic input. Lesions confined to the NPH and medial aspect of the MVN of the rat caused a loss of ChAT staining in the contralateral dorsal cap. Lesions placed more laterally within the MVN or DVN failed to deplete ChAT‐positive terminals in the contralateral or ipsilateral dorsal caps.The dorsal cap of the rat and monkey receives a discrete cholinergic projection. In the rat, this projection originates from the contralateral NPH. In the rabbit, the caudal inferior olive receives a weak cholinergic projection. The dorsal cap receives a projection from the contralateral NPH. However, this projection is mediated by a non‐cholinergic transmit

ISSN:0092-7317    

DOI:10.1002/cne.903280208

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

年代:1993

数据来源: WILEY

摘要:

AbstractA study has been made of the nonpyramidal, local circuit neurons in developing and mature macaque monkey prefrontal cortex with Golgi and immunocytochemical techniques. The area chosen for study is located between the cingulate gyrus and the ventral bank of the principal sulcus, and contains areas 9 and 46 as described by Walker (J. Comp. Neurol.73:59–86, '40). In Golgi studies, the unique axonal features of impregnated neurons made possible the identification of thirteen separate classes of local circuit neurons. Five of these cell types, in their general characteristics, resembled classes identified in human prefrontal cortex, as well as in other cortical areas of macaque monkeys and other species. Measurements of the scale of axon arbors and dendritic fields of the Golgi‐stained local circuit neurons also suggested particular spatial relationships of certain classes to the scale of intrinsic lattice connections made by the axons of pyramidal neurons in the same region. Similarities in morphology between cells described in human prefrontal cortex and neuron varieties described in this study indicate that this region of monkey prefrontal cortex may serve as a useful model for neuron populations in human prefrontal cortex.Sufficient morphological detail was present in immunocytochemical studies to suggest one or more identifying biochemical characteristics for seven of the thirteen classes of local circuit neurons. The calcium binding proteins, parvalbumin, calbindin D‐28K, and calretinin, were found in chandelier and wide arbor neurons, neurogliaform cells, and double bouquet neurons, respectively. In addition, cholecystokinin immunoreactivity was present in medium arbor neurons and in narrow arbor cells connecting layers 2 and 4. Somatostatin 281–12immunoreactivity was detected in beaded axon neurons in layers 5 and 6. This biochemical characterization of local circuit neurons, although incomplete, confirms the separate identity of at least some of the varieties distinguished by Golgi morphology, and allows a start to be made on studies examining changes in their functional state. The general inhibitory nature of these interneurons suggests that they are likely to play a crucial role in determining patterns of neural activation in the prefrontal cortex. © 1993 Wiley

ISSN:0092-7317    

DOI:10.1002/cne.903280209

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

年代:1993

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.903280201

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

年代:1993

数据来源: WILEY