摘要:

AbstractThe postnatal development of the projection from the ventral cochlear nucleus to the principal nuclei in the superior olivary complex in gerbil (Meriones unguiculatus) was studied in an age‐graded series of pups ranging from 0 to 18 days old. Small crystals of 1, 1′‐dioctadecyl3, 3, 3′, 3′‐tetramethylindocarbocyanine perchlorate (DiI) were inserted into the ventral cochlear nucleus of aldehyde‐fixed brains, and the labeled projections were examined with epifluorescence microscopy. Selected sections were photooxidized in a solution of diaminobenzidine and subsequently processed for electron microscopy to examine the development of labeled synapses in the target nuclei. Horseradish peroxidase was injected into the ventral cochlear nucleus of adult gerbils to assess the form and persistence of projections observed in the neonatal animals. In addition, electrophysiological responses to acoustic stimuli of single units in the adult auditory brainstem were analyzed to confirm the functionality of the novel projection from the ventral cochlear nucleus to the contralateral lateral superior olive.By the day of birth (PO), developing axons from the ventral cochlear nucleus have already established highly ordered pathways to the three primary nuclei of the superior olivary complex: the ipsilateral lateral superior olive, the contralateral medial nucleus of the trapezoid body, and at the lateral and medial dendrites of the ipsilateral and contralateral medial superior olive, respectively. Developing axons from the ventral cochlear nucleus that innervated the contralateral medial nucleus of the trapezoid body lacked the terminal morphology characteristic of the calyx of Held, but began to adopt a more characteristic form on P5. The mature calyx appeared around P14–16. Exuberant developmental projections to topographically inappropriate areas of the superior olivary complex were not observed at the postnatal ages studied.In addition to the projections of the ventral cochlear nucleus to the superior olivary complex described in other species, we observed the development and maintenance of a major direct projection from the ventral cochlear nucleus to the contralateral lateral superior olive. On PO, ventral cochlear nucleus axons decussate in the dorsal trapezoid body, form a plexus at the dorsal edge of the contralateral medial superior olive, and enter the ventrolateral limb of the contralateral lateral superior olive. Over the next 2 weeks, fascicles of fibers form on the hilar and ventral aspects of the ventrolateral limb. Fibers arising from these fascicles form converging, but nonoverlapping, arborizations within the ventrolateral limb at right angles to the curvature of the nucleus. The medial region was devoid of labeled axons. The direct innervation of the contralateral lateral superior olive was confirmed in the adult gerbil with anterograde horseradish peroxidase histochemistry and by the recording of excitatory responses in the innervated region to acoustic stimulation of the contralateral ear. © 1995

ISSN:0092-7317    

DOI:10.1002/cne.903530302

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe ability of an animal to localize a sound in space requires the precise innervation of the superior olivary complex by the ventral cochlear nuclei on each side of the lower brainstem. This precise pattern of innervation could require an immutable recognition of appropriate targets by afferent processes arising from these nuclei. This possibility was investigated by destroying one cochlea of gerbil pups (Meriones unguiculatus) on the second postnatal day and assessing the projections from the ventral cochlear nucleus (VCN) on the unablated side to the superior olivary complex during the subsequent 2 weeks and after the animals had reached maturity. A crystal of 1, l′‐dioctadecyl‐3, 3, 3′, 3′‐tetramethylindocarbocyanine perchlorate (DiI) was inserted into VCN on the unablated side in animals ranging in age from 3 to 14 days. To assess the permanence of any altered pattern of innervation, horseradish peroxidase was injected into VCN on the unablated side in adult, neonatally ablated animals. Finally, electrophysiological responses to acoustic stimuli delivered to the ear on the unablated side were recorded in the superior olivary complex of adult animals to assess whether altered innervation patterns were functional. Normative data were derived from our accompanying study of the development of VCN projections to the superior olivary complex in normal gerbils (Kil et al., this issue).Whereas VCN normally projects to the lateral aspect of the ipsilateral medial superior olive and to the medial aspect of the contralateral medial superior olive in control animals, in experimental animals VCN on the unablated side projects to both sides of these nuclei. Whereas in the gerbil, VCN normally projects only to the hilar area and to the ventrolateral limb of the contralateral lateral superior olive, in experimental animals VCN on the unablated side projects throughout this nucleus. This induced projection is specific in that the efferents to each limb of the contralateral nucleus are linked to the normal projection to the homotopic region of the ipsilateral nucleus. Whereas VCN innervates the contralateral medial nucleus of the trapezoid body in control animals, in experimental animals VCN on the unablated side provides calyces of Held in the ipsilateral nucleus as well.The induced projections to these three major subnuclei of the superior olivary complex first appear within 24 hours of the cochlear ablation and continue to develop over at least the subsequent 11 days. Thus, prior to the day when the cochlea becomes functional, VCN has established specific ectopic projections to loci normally innervated by VCN on the ablated side. All induced ectopic projections observed in neonatal animals were also present in neonatally ablated adult animals, indicating their permanence. As in the case of the normal projections from VCN to these subnuclei, all labeled synapses contained round vesicles and formed asymmetric synaptic junctional complexes with dendrites and somata in these target nuclei. Electrophysiological responses of single units in the ipsilateral medial nucleus of the trapezoid body demonstrated that the induced calyces of Held in this structure are quite functional in adult animals. © 1995 Wil

ISSN:0092-7317    

DOI:10.1002/cne.903530303

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

年代:1995

数据来源: WILEY

摘要:

AbstractTo investigate monoaminergic synaptic mechanisms in taste buds, we examined taste buds of mice, rats, rabbits, and mudpuppies for the presence of the neurotransmitter candidate, serotonin. Immunocytochemistry revealed serotonin‐like immunostaining in cells in mammalian taste buds and Merkel‐like basal cells in taste buds of mudpuppies. In untreated mudpuppies and in mammals injected with the precursor to serotonin, L‐tryptophan, certain taste cells showed serotonin‐like immunoreactivity, although in mammalian taste buds the immunostaining was relatively weak. After pretreating mammals with 5‐hydroxytryptophan (5‐HTP), the intermediate precursor between L‐tryptophan and serotonin, several taste cells showed strong immunoreactivity for serotonin. These findings indicate that mammalian taste cells normally contain serotonin and that taste cells can take up 5‐HTP and convert it to serotonin. Immunocytochemistry on wholemount preparations demonstrated that serotonergic cells of mudpuppies (i.e., Merkel‐like basal cells) were disposed in a ring at the periphery of taste buds. Similarly, serotonergic cells in mammalian taste buds tended to be located at the periphery of taste buds. Based on the position of serotonergic cells in the taste bud and on recent physiological studies on the actions of serotonin in taste buds, we postulate that serotonin functions as a neuromodulator or neurotransmitter in vertebrate taste buds. © 19

ISSN:0092-7317    

DOI:10.1002/cne.903530304

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe olfactory bulb receives a dense serotonergic input and appears to require serotonergic input in early olfactory associational learning. However, it is not known which cell types receive the serotonergic input or whether the cells express markers for the input throughout life. These issues need resolution in order for the mechanisms of serotonergic interactions to be better understood. The mRNA for the 5‐HT2Areceptor was localized in the olfactory bulb of postnatal day 1, 2, 14 and 9‐month‐old Sprague‐Dawley rats as well as in the bulb of adult (6 months) and aged (22‐30 month) Fisher 344 rats by in situ hybridization using an35S‐labelled 5‐HT2Aspecific oligonucleotide probe mixture. In all animals, hybridization was observed in mitral cells which are the major output cells of the main olfactory bulb. Tufted cells, located in the external plexiform layer and juxtaglomerular region, were readily observed in adult and aged animals and were also observed, albeit not as readily, in neonate pups. Quantitative analysis of the silver grain density over cells confirmed qualitative observations and showed that mitral and tufted cells were labelled in the neonate as well as in adult and aged animals. Labelled cells were also numerous in the external division of the anterior olfactory nucleus in all animals. 5‐HT2Areceptor mRNA could not be detected either qualitatively or quantitatively by in situ hybridization in the accessory olfactory bulb, nor could it be observed in the olfactory epithelium. The results suggest that the output cells of the main olfactory bulb receive serotonergic input via 5‐HT2Areceptors and that the serotonergic input onto these cells could influence olfactory functioning at all postnatal ages. © 19

ISSN:0092-7317    

DOI:10.1002/cne.903530305

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn order to examine whether the entorhinal‐hippocampal‐entorhinal circuit is reciprocal and topographic, the connections between the subiculum, the CA1 field, and the entorhinal cortex were studied with the carbocyanine dye (Dil), which moves in both retrograde and anterograde directions. We investigated the organization of reciprocal connections revealed by injections of Dil in the entorhinal cortex along the rhinal sulcus. Anterograde fluorescent labeling showed the same pattern reported in previous studies of the dorsal hippocampus. When the injection site of DiI extended into the deep layers (IV–VI) of the same cortical column, the anterograde labeling of the perforant path was accompanied by retrograde labeling of the subicular neurons and the CA1 neurons. The distribution of labeled cells overlapped the distribution of labeled fibers, and the distribution of labeled cells paralleled that of the labeled fibers in the CA1 field. DiI injection into the medial entorhinal cortex revealed fewer retrogradely labeled subicular neurons than injection into the lateral entorhinal cortex, whereas the number of labeled CA1 neurons was not dependent on the injection site. The number of labeled CA1 neurons was always several times greater than the number of subicular neurons. Thus, the amount of information conveyed by the CA1 projection might be higher than that conveyed by the subicular projection. These results indicate that the entorhinal cortex, CA1, and the subiculum are connected reciprocally and topographically. We believe that the framework of the major hippocampal circuit proposed in previous studies should be reconsidered. We propose that the CA1 projection, rather than the subicular projection, is the main projection that feeds back information from the hippocampus to the entorhinal cortex. © 1995 Wiley‐L

ISSN:0092-7317    

DOI:10.1002/cne.903530306

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

年代:1995

数据来源: WILEY

摘要:

AbstractVagal motor neurons in the rat dorsal motor nucleus of the vagus (DMN) are known to receive direct synaptic input from enkephalin‐containing terminals. We examined (1) whether the vagal motor neurons within the nucleus ambiguus (NA) also received monosynaptic input from enkephalin‐immunoreactive terminals and (2), if so, whether their ultrastructural relations differed from those in the DMN. In both regions, terminals containing Leu5‐enkephalinlike immunoreactivity (LE‐LI) were examined in relation to motor neurons identified by retrograde transport of wheat germ‐agglutinated horseradish peroxidase (WGA‐HRP) applied to the cut end of the cervical vagus nerve in single sections of the medulla oblongata of adult rats. By light microscopy, the most significant overlap between varicose processes with LE‐LI and WGA‐HRP‐containing neurons was seen in the rostral compact portion of the NA and the DMN at the level of the obex. Thus, only these regions were examined by electron microscopy. The most distinguishing ultrastructural feature of WGA‐HRP‐labeled neurons in the NA compared to the DMN was their higher incidence of nonsynaptic appositions with other neurons. In both the NA and the DMN, terminals with LE‐LI formed primarily symmetric synapses on smaller (presumably distal) dendrites; many of these dendrites, as well as most target perikarya, contained WGA‐HRP. Additionally, in the compact portion of the NA compared to the DMN (1) multiple LE‐labeled terminals more frequently contacted single perikarya or dendrites and (2) single terminals with LE‐LI more commonly showed two contacts or active zones and contained more abundant LE‐immunoreactive large (80–100 nm) densecore vesicles (dcvs). In contrast to small (40–50 nm), clear vesicles, which were usually aggregated near active zones, the immunoreactive dcvs were usually located near glial processes distal to these zones. These results indicate that enkephalin immunoreactivity is intensely localized to dcvs within terminals that may have direct inhibitory (symmetric synapses) actions on vagal motor neurons in both the compact portion of the NA and the DMN. Moreover, because numbers of dcvs and active zones have been equated with synaptic strength, our findings suggest enhanced potencies of enkephalin‐immunoreactive terminals in the compact portion of the NA. Our findings support a prominent role for enkephalin in the coordinated activity of esophageal motor neurons located in the compact port

ISSN:0092-7317    

DOI:10.1002/cne.903530307

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe distribution of myomodulin‐like immunoreactivity is described for the brain and retrocerebral complex of an insect, the locust,Schistocerca gregaria. The locust brain contains 70–100 neuronal cell bodies and numerous neuropilar processes exhibiting myomodulin‐like immunoreactivity. The most marked feature of the staining is a group of lateral tritocerebral neurones that form a highly immunoreactive tract that gives rise to a complex neuropile of stained processes in the dorsal tritocerebrum. This tract continues dorsally and bifurcates into a major branch that exits the brain via nervi corpora cardiaca 1 (NCC1) to innervate the corpora cardiaca and the corpora allata. A minor branch, consisting of several individual axons, combines with immunoreactive processes from the ventral nerve cord and generates a complex immunoreactive neuropile in the anterior and posterior regions of the protocerebrum. Immunoreactive processes are also found in the structured neuropile of the central body complex. Immunoreactive cell bodies are also found in the antennal lobes, in the lateral margins of the protocerebrum, in the optic lobes, and in a few cells in the pars intercerebralis.The results suggest that myomodulin‐like neuropeptides may play roles as central neurotransmitters or neuromodulators in insects as well as being released into the circulation as neurohormones or acting as releasing agents for neurohormones in neurohaemal areas. They also further strengthen the idea that myomodulins, which were first identified in molluscs, may represent another interphyletic family of neuropeptides. © 1995 Wiley

ISSN:0092-7317    

DOI:10.1002/cne.903530308

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

年代:1995

数据来源: WILEY

摘要:

AbstractTo examine quantitatively the pathway from the internal segment of the globus pallidus to the primary motor cortex through the thalamus, we compared the distribution of thalamocortical neurons projecting to the motor cortex with the distribution of afferent terminal fields from the pallidum in the ventrolateral nuclear group of the thalamus in four Japanese monkeys by using the anterograde and retrograde double‐labeling method. In each monkey, different fluorescent retrograde tracers (Fast Blue and Diamidino Yellow) were injected separately into the distal and proximal forelimb areas of the primary motor cortex after physiological mapping with intracortical microstimulation. In the same individual monkeys, an anterograde tracer, wheatgerm agglutinin conjugated to horseradish peroxidase, was injected into the internal segment of the globus pallidus after the forelimb part was identified physiologically.A small group of projection neurons to the distal and proximal representations of the motor cortex were found in the terminal fields from the pallidum, but a majority of the projection neurons were distributed outside the terminal area in the thalamus. These results confirm the existence of the pathway from the pallidum through the thalamus to the primary motor cortex, but also indicate that the primary motor cortex receives its major thalamic inputs from outside of the pallidal projection area, and that the pallidum sends its major outputs to nonprimary motor areas through the thalamus. © 1995 Wiley‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903530309

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe input from serotonin‐containing nerve fibres to rabbit sympathetic preganglionic neurons projecting to either the superior cervical ganglion or the adrenal medulla was investigated by combining retrograde tracing with the B subunit of cholera toxin and immunocytochemistry for serotonin. There were pronounced rostrocaudal variations in the density of serotonin fibres in the rabbit intermediolateral cell column from T1 to L4; maximum numbers of fibres were found in T3‐6 and L3–4 and minimum numbers in T1 and T10–12. By light microscopy, retrogradely labelled sympathetic preganglionic neurons projecting to the superior cervical ganglion or the adrenal medulla received variable densities of close appositions from serotonin‐immunoreactive fibres. Some neurons from each population received many close appositions, whereas others received moderate numbers or few appositions. Appositions occurred on the cell bodies, dendrites, and occasionally axons of sympathetic preganglionic neurons. Rare neurons in both groups of retrogradely labelled cells received no appositions from serotonin‐containing nerve fibres. At the ultrastructural level, synapses were found between serotonin‐positive boutons and sympathetic preganglionic neurons projecting either to the superior cervical ganglion or to the adrenal medulla. These results indicate that, through direct synaptic contacts, serotonin‐immunoreactive, presumably bulbospinal, nerve fibres affect the activity of the vast majority of sympathetic preganglionic neurons that send axons either to the superior cervical ganglion or to the adrenal medulla. This serotonin input may be sympathoexcitatory and could mediate increases in sympathetic nerve activity and in the release of catecholamines from the adrenal medulla. © 1995

ISSN:0092-7317    

DOI:10.1002/cne.903530310

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

年代:1995

数据来源: WILEY

摘要:

AbstractImmunohistochemistry was used to survey the distribution of glutamic acid decarboxylase (GAD), the synthesizing enzyme for gamma‐aminobutyric acid (GABA), throughout the visual system of the frogRana pipiens. GAD‐like immunoreactivity (GAD‐LI) was assessed in the retina, in primary retinorecipient targets, and in thalamic nuclear groups postsynaptic to primary retinal terminal zones. Within the retina, the inner plexiform layer displayed intense GAD‐LI, but immunoreactivity was absent in the ganglion cell layer (GCL). Putative amacrine, bipolar, and horizontal cell somata were also labeled.Centrally, GAD‐LI was observed in all primary visual nuclei. Dense, GAD‐like immunoreactive punctate structures (puncta), presumably terminals, were observed in the pretectal nucleus lentiformis mesencephali, posterior thalamic neuropil, and uncinate neuropil. GADlike immunoreactive puncta were noted in several laminae of the optic tectum, with the highest concentrations located within the 9th and 8th laminae. Moderate numbers of GAD‐like immunoreactive puncta were found in the mesencephalic nucleus of the basal optic root, and two thalamic neuropils—corpus geniculatum and neuropil of Bellonci. The ventrolateral area, posterocentral nucleus, and posterolateral nucleus all contained sparse amounts of GAD‐LI.These observations suggest that GABA plays an important physiological role in all central visual areas ofRana pipiens. © 19

ISSN:0092-7317    

DOI:10.1002/cne.903530311

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

年代:1995

数据来源: WILEY