摘要:

The substance N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) is a neurotoxin with selective and long-lasting effects on the noradrenergic (NA) neurons of mammalian brains. The present study examines the effects of this toxin on the noradrenergic system of the goldfish brain. Single doses (50 mg/kg body weight) of DSP-4 reduce the immunoreactivity of the NA synthesizing enzyme dopamine-β-hydroxylase (DBH), as revealed by immunohistochemistry 7 and 12 days after toxin administration. The depletion involves the DBH-positive fibres and spares the DBH-positive cell bodies. Dopamine-β-hydroxylase immunoreactivity, 40 days after toxin administration, showed a complete recovery. Ultrastructural investigations confirmed that DSP-4 toxicity affects only nervous fibres and terminals, sparing cell bodies. Administration of DSP-4 also produced a marked decrease of noradrenaline (NA) levels in the goldfish brain, seven days later, while dopamine (DA) and serotonin (5-HT) levels were unaffected by toxin injection. The reduction of NA levels induced by DSP-4 was prevented by the concomitant administration of the NA uptake inhibitor desipramine. Noradrenaline levels measured 40 days after toxin administration show that DSP-4 toxicity was completely reversed. The results suggest a pronounced plasticity of the noradrenergic system in the goldfish brain.

ISSN:0006-8977    

DOI:10.1159/000113242

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Current perspectives on brain evolution relate brain size variability to two main parameters: a scaling factor that corresponds to overall body size and an ecological factor associated with behavioral capacity. I suggest in this paper that in evolution body weight and ecological conditions have different effects on brain structure, resulting in distinct differences in neural architecture, even if both factors may produce brain size increases. There are two postulated modalities of brain growth, one passive that lags behind increases in body size, and one active that relates to selection of specific behavioral abilities and hence increased processing capacity. These two modes of growth differ in three main aspects: (i) cellular and connectional rearrangements are modest in passive brain growth while they are conspicuous in active growth, corresponding to increases in processing capacity; (ii) passive brain growth follows a rather conservative allometric rule between brain components, while active growth usually affects only a few brain parts, thereby producing much steeper allometric relations between these parts and sometimes also in brain/body relations; and (iii) passive growth may either affect early periods of ontogenic brain development or produce a generalized increase in cell proliferation in later periods. On the other hand, active growth is restricted to relatively late developmental periods. Finally, an evolutionary scenario for the active mode is proposed where phylogenetic selection of an increased number of cells in particular brain regions occurs in order to facilitate neural reorganization and to increase the specificity of connections. This view emphasizes the role of connectional modifications in increasing brain capacity and contrasts with current ideas of a unitary process of phylogenetic brain growth, where a larger brain size per se produces better processing capacity, regardless of the causal factor behind it.

ISSN:0006-8977    

DOI:10.1159/000113243

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Current perspectives on brain evolution relate brain size variability to two main parameters: a scaling factor that corresponds to overall body size and an ecological factor associated with behavioral capacity. I suggest in this paper that in evolution body weight and ecological conditions have different effects on brain structure, resulting in distinct differences in neural architecture, even if both factors may produce brain size increases. There are two postulated modalities of brain growth, one passive that lags behind increases in body size, and one active that relates to selection of specific behavioral abilities and hence increased processing capacity. These two modes of growth differ in three main aspects: (i) cellular and connectional rearrangements are modest in passive brain growth while they are conspicuous in active growth, corresponding to increases in processing capacity; (ii) passive brain growth follows a rather conservative allometric rule between brain components, while active growth usually affects only a few brain parts, thereby producing much steeper allometric relations between these parts and sometimes also in brain/body relations; and (iii) passive growth may either affect early periods of ontogenic brain development or produce a generalized increase in cell proliferation in later periods. On the other hand, active growth is restricted to relatively late developmental periods. Finally, an evolutionary scenario for the active mode is proposed where phylogenetic selection of an increased number of cells in particular brain regions occurs in order to facilitate neural reorganization and to increase the specificity of connections. This view emphasizes the role of connectional modifications in increasing brain capacity and contrasts with current ideas of a unitary process of phylogenetic brain growth, where a larger brain size per se produces better processing capacity, regardless of the causal factor behind it.

ISSN:0006-8977    

DOI:10.1159/000316275

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Studies in our laboratory have revealed a robust, transient expression of cholecystokinin binding sites in the facial motor nucleus during development in the Brazilian opossum, Monodelphis domestica. To investigate the ubiquity of this phenomenon, we have performed receptor autoradiography on the hindbrains of embryonic and neonatal rat pups. Cholecystokinin binding sites are present at very low levels in the embryonic day-16 rat hindbrain, but binding sites are abundant prior to birth. The greatest increase in labelled nuclei occurs prior to 5 days of postnatal age. Binding levels are heavy in the nucleus of the solitary tract, medial vestibular nucleus, posterior dorsal tegmental nucleus, area postrema, and caudal spinal trigeminal nucleus by 30 days postnatal. Both A-type and B-type receptors are present in the neonatal brainstem, although most labelled areas appear to be B-type. A-type binding sites are present in the ventral cochlear nucleus, the nucleus of the solitary tract, the dorsal motor nucleus of the vagus, the area postrema, the spinal nucleus of the trigeminal, and the cuneate and gracile nuclei by 5 days postnatal. As reported for the Brazilian opossum, cholecystokinin binding sites are expressed in the facial motor nucleus of neonatal rats and are transient. In this study of the brainstem in laboratory rats, a transient expression is also observed in the rubrospinal tract, parvocellular reticular nucleus, raphe obscurus, cuneate and gracile nuclei, and the ventral median fissure of the spinal cord. As vasopressin binding sites and estrogen receptors have also been shown to be expressed transiently in the laboratory rat facial motor nucleus, the physiological and developmental significance of transient binding site expression remains to be elucidated.

ISSN:0006-8977    

DOI:10.1159/000113244

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The distributions of mitochondria and synapses in two areas of harbour porpoise cerebral cortex were examined by quantitative electron microscopy of sections stained for cytochrome oxidase. The distribution of cytochrome oxidase-positive and total mitochondria in the visual cortex of the lateral gyrus and in the auditory cortex of the temporal operculum was related closely to that of total cytochrome oxidase staining seen by light microscopy in the relevant areas. There were two peaks of mitochondrial numerical density in visual cortex: in layer III and the upper part of layer I. Mitochondrial distribution was more uniform in temporal cortex, where the numbers of mitochondria in layers VI, V and lower I were similar to those in visual cortex, but fewer were present in layers III, II and upper I. The laminar distribution of axodendritic synapses in both cortices was relatively uniform, and there was not such a large difference between the two areas. As large numbers of mitochondria have been described in the layers of cat visual cortex showing dark staining for cytochrome oxidase and receiving thalamic afferent input, we regard our data as suggestive of the existence of two main thalamorecipient zones in cetacean cortex: one in layer III and the other in upper layer I.

ISSN:0006-8977    

DOI:10.1159/000113245

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

To investigate the evolution of the neural organization of gonadotropin-releasing hormone (GnRH), we have examined GnRH-immunoreactivity in two brachiopterygian fishes (Polypterus palmas and Calamoichthys calabaricus). Distal regions of the terminal nerve (TN) within the medial olfactory nerve contained clusters of GnRH-immunoreactive (ir) perikarya (<10 μm). More proximal, isolated GnRH-ir neurons were present among TN fascicles as they penetrated the ventral forebrain, and a few ir neurons were observed accompanying GnRH-ir fibers in the rostromedial telencephalon. GnRH-ir neurons were not observed in the preoptic area or ventral hypothalamus. In contrast, a small group of GnRH-ir neurons was localized in the periventricular nucleus of the posterior tuberculum. GnRH-ir fibers were present in widespread areas of the brain, including the olfactory bulb, telencephalon, optic nerve, hypothalamus, thalamus, habenula, optic tectum, tegmentum, pituitary and spinal cord. To further characterize projections of TN neurons, we utilized antiserum to FMRF-amide, a small peptide produced by TN cells in other vertebrates. Perikarya that were FMRF-amide-ir within the TN were similar in distribution to GnRH-TN neurons, and the distribution of FMRF-amide-ir fibers overlapped those of GnRH-ir fibers, thus providing a useful marker for identifying TN projections. An additional population of FMRF-amide-ir neurons was present in the periventricular hypothalamus. Our results suggest that in the polypteriformes, GnRH and FMRF-amide neurons of the TN are similar to those observed in other vertebrates; however, the paucity of GnRH cells in the basal forebrain may be unique to primitive actinopterygians and elasmobranchs, and may result from the lack of migration of GnRH neurons into the forebrain, a phenomenon that likely occurs in all other vertebrate classes. Finally, the identification of GnRH-ir neurons in the posterior tuberculum is consistent with similar, and perhaps homologous, GnRH neurons present in nearly all other vertebrate classes.

ISSN:0006-8977    

DOI:10.1159/000113246

出版商:S. Karger AG    

年代:1996

数据来源: Karger