摘要:

The sonic motor nucleus (SMN) of the oyster toadfish Opsanus tau, a single midline structure in the occipital spinal cord and caudal medulla, contains large electrically-coupled motoneurons. Although interpretation is complicated by multiyear growth in soma size, neurons in males may be either large (L) or small (S), whereas females have exclusively S neurons. Golgi stains have allowed separation of five neuron variants (rostral, dorsal, stellate, ventral and caudal) which differ in location, soma shape and size, and direction and pattern of dendritic branching. All variants are present in L and S males and in females, and retrograde transport of horseradish peroxidase indicates that all variants are motoneurons. The SMN is organized into three horizontal layers with rostral and dorsal neurons forming a rostrocaudally arrayed network across the dorsal-dorsolateral surface. Stellate cells are found in the middle layer, and ventral cells with laterally directed dendrites that exit the SMN line the inferior surface. Caudal neurons with caudally directed exiting dendrites are arranged in parallel rows in the caudal fifth of the SMN. We suggest that variant differences in dendritic orientation relate to different patterns of innervation by multiple afferents to the SMN and function to maximize contacts between neurons as a means of facilitating synchronization within the nucleus. Sexual dimorphism has been demonstrated to a minor degree: all variants have larger somas in L fish than S fish, but no difference has been found in primary dendrite diameter. Larger somas would potentially support the greater amount of sound production by nesting males who produce a mating boatwhistle call. Equivalent dendrite diameter in females, who are just as likely as males to grunt, an agonistic call, suggests that female Opsanus have a well developed sonic circuitry compared to Porichthys, another toadfish in which females are typically silent.

ISSN:0006-8977    

DOI:10.1159/000113545

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The visual cortex of one of the smallest macropod marsupials, a wallaby, the quokka Setonix brachyurus, was examined at maturity and during development from postnatal day 1 to 150 in Nissl-stained or Golgi-stained sections. Injections of horseradish peroxidase into the primary visual centres in adults identified cortical neurons projecting to these regions. The pattern of cell generation was determined by tritiated thymidine/autoradiography. The adult visual cortex was composed of the usual six layers of cells with dendritic morphologies similar to those seen in eutherian (placental) mammals. The margin of Layer 6 overlapped slightly with the white matter, and pyramidal cells projecting to subcortical regions were located at all depths of Layer 6. Cortical development was similar to that of eutherian mammals, with the formation of transient cellular layers below the developing cortical plate. Autoradiographic studies confirmed that the cortical plate was composed of two layers: a compact zone of densely packed cells located pial to a striated layer containing more loosely packed cells. Postnatal cell generation of Layers 6–2took place from postnatal day 3 to day 85, with Layer 4 neurons, the main target of incoming visual axons, being generated around postnatal day 40. Cells located at maturity in the white matter, mostly of glial morphology, were generated from postnatal day 40. A subplate zone containing early differentiating cells was not evident, and postnatal 3H-thymidine labelling did not identify a population of early generated neurons below the cortical plate. In the tammar wallaby Macropus eugenii, the majority of target neurons for incoming geniculate axons are generated about 20 days after the first axons enter directly into the cortical plate without a waiting period in a subplate. Geniculate axons in the wallabies have a relatively longer 'wait' for their target neurons than do those in cats or monkeys. Therefore, if geniculate axons in marsupials make temporary synapses, while they wait for their target neurons to be generated, their temporary connections must, unlike those in cats or monkeys, be with cells already in the cortical plate.

ISSN:0006-8977    

DOI:10.1159/000113546

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

An interconnected series of brain nuclei controls song learning and behavior in male zebra finches (Poephila guttata). This study examined the distribution of fibers, terminals, and somata immunoreactive for two neuropeptides, methionine-enkephalin (ENK) and vasoactive intestinal polypeptide (VIP), in song-control nuclei of adult males. In addition, the broad pattern of major regions of labeling throughout the forebrain and midbrain was determined. The telencephalic song-control nuclei MAN (magnocellular nucleus of the anterior neostriatum), Area X of the striatum, HVC (higher vocal center), and RA (robust nucleus of the archistriatum) contained abundant ENK immunoreactivity, including labeled fibers and somata. In addition, intensely labeled fibers and terminals were seen in the thalamic nucleus DLM (medial portion of the dorsolateral nucleus of the anterior thalamus). High levels of VIP immunoreactivity were also seen in MAN, HVC, and RA, but this label consisted of fiber and terminals only. Area X and surrounding striatum contained extremely sparsely distributed VIP-Iabeled processes. Somata positive for VIP were not seen throughout cortical regions such as the neostriatum and hyperstriatum but were abundant in the lateral striatum (paleostriatum augmentatum, PA) and may contribute to a dense field of terminal labeling seen in the globus pallidus. The apparent presence of a robust VIP-positive striato-pallidal projection is not typical of major basal ganglia pathways in vertebrates, raising the possibility that passerine birds have diverged from the typical amniote pattern.

ISSN:0006-8977    

DOI:10.1159/000113547

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

An interconnected series of brain nuclei controls song learning and behavior in male zebra finches (Poephila guttata). This study examined the distribution of fibers, terminals, and somata immunoreactive for two neuropeptides, methionine-enkephalin (ENK) and vasoactive intestinal polypeptide (VIP), in song-control nuclei of adult males. In addition, the broad pattern of major regions of labeling throughout the forebrain and midbrain was determined. The telencephalic song-control nuclei MAN (magnocellular nucleus of the anterior neostriatum), Area X of the striatum, HVC (higher vocal center), and RA (robust nucleus of the archistriatum) contained abundant ENK immunoreactivity, including labeled fibers and somata. In addition, intensely labeled fibers and terminals were seen in the thalamic nucleus DLM (medial portion of the dorsolateral nucleus of the anterior thalamus). High levels of VIP immunoreactivity were also seen in MAN, HVC, and RA, but this label consisted of fiber and terminals only. Area X and surrounding striatum contained extremely sparsely distributed VIP-Iabeled processes. Somata positive for VIP were not seen throughout cortical regions such as the neostriatum and hyperstriatum but were abundant in the lateral striatum (paleostriatum augmentatum, PA) and may contribute to a dense field of terminal labeling seen in the globus pallidus. The apparent presence of a robust VIP-positive striato-pallidal projection is not typical of major basal ganglia pathways in vertebrates, raising the possibility that passerine birds have diverged from the typical amniote pattern.

ISSN:0006-8977    

DOI:10.1159/000316258

出版商:S. Karger AG    

年代:1995

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000113548

出版商:S. Karger AG    

年代:1995

数据来源: Karger