ISSN:0006-8977    

DOI:10.1159/000115298

出版商:S. Karger AG    

年代:1990

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000115299

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Three distinct opioid precursors have been identified in the central nervous system of mammals: proopiomelanocortin (POMC), proenkephalin, and prodynorphin. These precursors are derived from separate genes, synthesized in distinct neurons, and yield unique sets of opioid end products. This review will discuss the general mechanisms involved in the biosynthesis of neuropeptide precursors and consider the roles of posttranscriptional and posttranslational processing mechanisms in the generation of multiple sets of end products from a single gene. In addition, techniques that can be used for isolating and characterizing neuropeptide genes, mRNAs, and end products will be reviewed. These introductory comments will serve as the framework for a discussion of the phylogeny of the opioid precursors in the major groups of non-mammalian vertebrates.

ISSN:0006-8977    

DOI:10.1159/000115300

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Three distinct opioid precursors have been identified in the central nervous system of mammals: proopiomelanocortin (POMC), proenkephalin, and prodynorphin. These precursors are derived from separate genes, synthesized in distinct neurons, and yield unique sets of opioid end products. This review will discuss the general mechanisms involved in the biosynthesis of neuropeptide precursors and consider the roles of posttranscriptional and posttranslational processing mechanisms in the generation of multiple sets of end products from a single gene. In addition, techniques that can be used for isolating and characterizing neuropeptide genes, mRNAs, and end products will be reviewed. These introductory comments will serve as the framework for a discussion of the phylogeny of the opioid precursors in the major groups of non-mammalian vertebrates.

ISSN:0006-8977    

DOI:10.1159/000316079

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The use of histochemical methods, including enzyme histochemical, inmunohistochemical and pathway tracing methods, as tools for testing hypotheses about the mechanism of neural evolution is reviewed. Many hypotheses have been proposed to explain aspects of neural evolution, including the occurrence of encephalization, quantitative changes in homologous cell populations, changes in the alignment, orientation and parcellation of neuronal populations into cytoarchitectonic units, and the appearance of new neuronal phenotypes. It is argued here that neural evolution must be viewed as a set of coordinated changes in neural circuits, rather than as a set of discrete events. For illustrative purposes the present discussion focuses on the use of histochemical methods in testings hypotheses about neural evolution in the basal ganglia system of amniotes. Three problem areas are considered: the bases for (1) differences in the alignment and organization of catecholaminergic and noncatecholaminergic neurons into cytoarchitectonic fields within the substantia nigra; (2) differences in the relative size and neurotransmitter organization of the caudal nigral cell groups and (3) differences in the organization of pallidal efferent systems, including the organization of pallidal-pretectal and pallidal-thalamic projection systems. Furthermore, the role of comparative data in framing hypotheses concerning the adaptive significance of such changes is also considered.

ISSN:0006-8977    

DOI:10.1159/000115301

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The history of biology reveals numerous interpretations of the relationship between ontogeny and phylogeny, among them Garstang's critical realization that phylogeny can only be the history of changes in an ancestral ontogeny. One extrapolation of Garstang's conclusion is that the study of phylogeny should involve comparisons of ontogenies, in order to allow a reconstruction of the sequence of changes that led to the present variation in these ontogenies as well as the mechanisms underlying these changes. It is suggested that this can be done by recognizing homologous developmental stages among various ontogenies and subjecting these stages to a cladistic analysis. Some of the problems involving such analysis are explored in the course of examining the phylogeny of pharyngeal pouch ontogenies as a model system. It is concluded that sequences of ontogenetic stages are conserved (von Baerian recapitulation) but that terminal (Haeckelian recapitulation) and nonterminal alterations in the ancestral ontogeny are frequent. Both terminal and nonterminal alterations occur with approximately equal frequency in the case of pharyngeal pouches, but non-terminal deletion is rare to nonexistent. Examination of two additional morphological cases in which ontogeny has been utilized to infer phylogenetic changes – ontogenetic parcellation of neural systems and craniate head organization – reveals a number of problems from the point of view of a cladistical analysis of ontogenesis. Ontogenetic parcellation is essentially a recasting of Haeckel's biogenetic law and is rejected on the grounds that ontogenies do not parallel phylogenies, and only primitive and derived characters, not organisms, can be recognized. It is argued that the phylogenetic significance of transient neural characters can be determined only within a cladistical context and that insufficient ontogenetic data presently exist to evaluate most characters. Finally, the history of current models of craniate head organization is traced, and this information, along with that from more recent developmental studies, necessitates rejection of the Goodrich and Jarvik-Bjerring models. A new model is presented that purports to incorporate current ideas of somitomere and neuromere distribution, but it is deemed inadequate because, like previous models, it is based on information gleaned primarily from the ontogeny of a single species, whereas the model sought is a model of the ontogeny of ancestral craniates. To arrive at such a model, we must generate a morphotype, based on shared primitive features of cephalic ontogenies of all craniate radiations, which involves a cladistic analysis of these ontogenies.

ISSN:0006-8977    

DOI:10.1159/000115302

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Populations of animals differentiate by speciation. How speciation takes place, for long a puzzle for evolutionary biologists, should be regarded as a research opportunity for neuroethologists and comparative behaviorists. It is now clear that behavior may play an important part in the process of speciation. The existence of sexually dimorphic anatomy and behavior in many animals has provided a rich subject for investigation by comparative neurobiologists and behaviorists, who emphasize analysis of proximate mechanisms that generate dimorphism in phenotype. However, sexual dimorphisms also figure prominently in the theory of sexual selection. Sexual selection is viewed as a primary behavioral mechanism in the process of speciation. Some examples of 'explosive' speciation are presented, and the putative role that sexual selection plays in these cases is reviewed. A consideration of any evolutionary selective process must include genetics, and I will briefly summarize studies that indicate that even complex behavioral systems such as sexual selection, which sociobiologists refer to as a 'strategy', can have a relatively simple genetic basis.

ISSN:0006-8977    

DOI:10.1159/000115303

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Over the past two decades, neuroethologists have been unravelling the neural circuitry underlying some of the specialized capabilities animals use to obtain and process sensory information. Explicitly comparative studies of these systems can now be carried out to ask questions about the processes of evolutionary change in neural systems. In some cases, it can be seen how relatively minor modifications of neural networks may significantly expand the efficacy of sensory processing. Other comparative studies might ask whether expanding the number of steps involved in neural computation, or the area devoted to the representation of a particular sub-modality, constrains neural architecture in predictable ways.

ISSN:0006-8977    

DOI:10.1159/000115304

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The interrelationship of brain and body sizes has been the subject of investigations for over a hundred years. These studies have demonstrated that variation in brain weights is much smaller than that in body weights; consequently, scaling studies are ones of negative allometry. Furthermore, the variability in brain weight is greater when comparisons are between species rather than among individuals of the same species, and the degree of variability in brain size differs among orders. The largest shifts in brain sizes relative to changes in body weights are found when comparing different ontogenetic stages. Debate continues as to the importance of metabolism in determining the interrelationship of brain-body weights for interpreting differences in relative brain size. Although past advances in the study of brain-body size associations have come by increasing the size of the data bases and by improved statistical analyses, the recent utilization of transgenic animals may provide new insights into the mechanism of this association.

ISSN:0006-8977    

DOI:10.1159/000115305

出版商:S. Karger AG    

年代:1990

数据来源: Karger