ISSN:0006-8977    

DOI:10.1159/000114153

出版商:S. Karger AG    

年代:1993

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000114154

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

The diversity in vertebrate reproductive patterns provides natural experiments that yield new insights into behavioral endocrinology. Discussed here is the generality of the concept of an organizing sex during sexual differentiation. In its present form the Organizational Concept emphasizes hormonally induced organization of the male phenotype, with the female phenotype being the neutral or default condition. Does this concept extend to vertebrates lacking genotypic sex determining mechanisms? The answer appears to be No. In species with temperature-dependent sex determination, each embryo has an equal probability of developing into either a male or a female; there is no heritable genetic predisposition for sex determination. In species with behavior-dependent sex determination, sex-change occurs during adulthood as a result of perceived alterations in the social environment. In parthenogenetic species, only female individuals exist, yet they display both male-like and female-like 'sexual' behaviors. In contrast to the contemporary view of the Organizational Concept, let us assume that the male pattern is derived and imposed upon the ancestral female pattern. If this perspective is taken, several avenues of study are identified: (i) the importance of sexual similarities; (ii) extending the principle of complementarity of sexual behaviors to the brain; (iii) temperature modulation of sexual differentiation, and (iv) the role of the brain in sex determination.

ISSN:0006-8977    

DOI:10.1159/000114155

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

The neuropeptide gonadotropin-releasing hormone (GnRH, LHRH) serves as both a hormone and a neurotransmitter, and it has multiple actions on reproductive physiology and behavior. At least seven different molecular forms of GnRH have evolved, and nearly all vertebrates studied express at least two different forms of GnRH: chicken GnRH II, and a second form that varies across classes. The GnRH cell bodies span a broad region of the forebrain and midbrain, and processes project to virtually every region of the CNS, to the vasculature, and to the cerebrospinal fluid. Comparative evidence supports the model that gnathostomic vertebrates possess two principle GnRH systems, with different embryonic and, probably, evolutionary origins, expressing different molecular forms of GnRH and projecting to different targets. The terminal nerve-septo-preoptic system serves as the principle regulator of gonadotropin release in most vertebrates. Neurons originate in the embryonic olfactory placode and migrate centrally during development, and it is proposed that ontogeny of the TN-septo-preoptic system reflects its evolutionary origins as a peripheral endocrine organ associated with the olfactory system. The second GnRH system, which arises from non-placodal precursors, comprises cell bodies in periventricular regions of the posterior diencephalon and/or midbrain. Although much less is known about the posterior GnRH system, evidence suggests that these cells served as the ancestral brain GnRH system and are the cellular locus of the chicken GnRH peptide. The GnRH system of lampreys does not appear to be homologous to either the TN-septo-preoptic or posterior GnRH system, and it is suggested that GnRH in agnathans represents a third evolutionary event.

ISSN:0006-8977    

DOI:10.1159/000114156

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

The neuropeptide gonadotropin-releasing hormone (GnRH, LHRH) serves as both a hormone and a neurotransmitter, and it has multiple actions on reproductive physiology and behavior. At least seven different molecular forms of GnRH have evolved, and nearly all vertebrates studied express at least two different forms of GnRH: chicken GnRH II, and a second form that varies across classes. The GnRH cell bodies span a broad region of the forebrain and midbrain, and processes project to virtually every region of the CNS, to the vasculature, and to the cerebrospinal fluid. Comparative evidence supports the model that gnathostomic vertebrates possess two principle GnRH systems, with different embryonic and, probably, evolutionary origins, expressing different molecular forms of GnRH and projecting to different targets. The terminal nerve-septo-preoptic system serves as the principle regulator of gonadotropin release in most vertebrates. Neurons originate in the embryonic olfactory placode and migrate centrally during development, and it is proposed that ontogeny of the TN-septo-preoptic system reflects its evolutionary origins as a peripheral endocrine organ associated with the olfactory system. The second GnRH system, which arises from non-placodal precursors, comprises cell bodies in periventricular regions of the posterior diencephalon and/or midbrain. Although much less is known about the posterior GnRH system, evidence suggests that these cells served as the ancestral brain GnRH system and are the cellular locus of the chicken GnRH peptide. The GnRH system of lampreys does not appear to be homologous to either the TN-septo-preoptic or posterior GnRH system, and it is suggested that GnRH in agnathans represents a third evolutionary event.

ISSN:0006-8977    

DOI:10.1159/000316219

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

In rats and other mammals, sex differences in the brain and behavior result from differential secretions of gonadal steroid hormones during early critical periods of neural development. We review the experimental results that support current ideas about the mechanisms of sexual differentiation in mammals, and then apply the same experimental analysis to the study of sexual differentiation of the neural song circuit in the zebra finch (Poephila guttata), a passerine song bird. Administration of estrogen to young female zebra finches causes the female to develop a more masculine song system and to sing as an adult. This estrogenic masculinization is similar to that found for copulatory behavior in mammals. However, striking differences emerge in other aspects of the sexual differentiation process. Experiments that use endocrine agents to block the masculine development in genetic males have so far failed. Moreover, the brain of zebra finches has an unusually high expression of aromatase (estrogen synthetase) in the telencephalon, and estrogen synthesized in the brain from androgen is released into the general circulation. These results suggest that the brain is the primary source of estrogen in the body. If so, then a further understanding of sexual differentiation requires more information on the factors that regulate the cerebral synthesis of estrogen.

ISSN:0006-8977    

DOI:10.1159/000114157

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

Weakly electric fish generate electric organ discharges (EODs) that are species-specific and often sexually-dimorphic. The waveform or frequency of an EOD can be altered by treating a fish with sex steroid hormones. The EOD is controlled by a few discrete nuclei in the brainstem and spinal cord and a muscle-derived electric organ. The organizational simplicity and steroid-sensitivity of the electromotor system make it a premier system for investigating how sex steroids modulate behavior, neural circuitry, and ion channels. In addition, the diversity of EOD patterns in the many species of electric fish provide a wealth of material in which to examine the evolution of sexual dimorphisms in the nervous system.

ISSN:0006-8977    

DOI:10.1159/000114158

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

The secretion of gonadotropin releasing hormone (GnRH), and hence sex steroids, is influenced by social signals produced by conspecifics and by environmental cues such as day length. The sensory systems processing these varied signals must therefore connect with the GnRH control centers in the preoptic area and hypothalamus. Forebrain pathways in frogs provide a model for how vertebrates accomplish this. Auditory information, which can transmit the features of the vocal communication signals used by frogs during reproductive social behavior, reaches both the preoptic area and ventral hypothalamus via thalamic and midbrain nuclei. An examination of these auditory pathways suggests that there are subtle differences in their anatomical, physiological, and histochemical characteristics. The suprachiasmatic nucleus, which is important for controlling circadian rhythms in vertebrates, also projects to both the preoptic area and ventral hypothalamus, providing information about environmental characteristics in parallel with the information about social signals. This pattern of connections suggests that the two major GnRH control centers in amphibian brains receive independent, parallel information about the social and environmental cues influencing reproduction.

ISSN:0006-8977    

DOI:10.1159/000114159

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

Most amphibians, reptiles and mammals possess a well defined dual olfactory system comprised of separate neural pathways that regulate different olfactory functions. One pathway originates in the nasal cavity and gives rise to what is commonly referred to as the main olfactory system. The other pathway originates in the vomeronasal organ (VNO) and gives rise to the accessory olfactory system. Functionally, the main olfactory system is thought to subserve olfactory-mediated tasks such as feeding and grooming, while the accessory olfactory system is believed to be primarily involved in mediating behavioral and physiological responses to sex pheromones. Traditionally, it has been difficult to address whether teleosts possess any components of the vomeronasal system, since they generally do not meet the criteria used to identify vomeronasal systems in other vertebrates. Previous conclusions that the nasal epithelia of fish is olfactory and not vomeronasal in nature are based on observations that teleosts lack a separate VNO-like chemosensory structure and an anatomically distinct accessory olfactory bulb. However, because sex pheromones have been identified in the goldfish, it is now possible to compare the neural substrates that regulate pheromone-induced responses in teleosts to those that mediate similar responses in other vertebrates. The olfactory system in goldfish is particularly well suited for such comparisons, because it comprises anatomical and functional subdivisions that resemble those associated with the main and accessory olfactory systems in tetrapods. The olfactory pathways that mediate endocrine and behavioral responses to sex pheromones in goldfish are described and then compared to the main and accessory olfactory systems of tetrapods. In making these comparisons, a number of similarities become apparent. First, the olfactory pathways that regulate responses to sex pheromones in goldfish are different from those that serve a more general olfactory function. Second, these functional differences appear to be subserved by separate and anatomically distinct olfactory tract projections to the brain. Third, the lateral olfactory tracts and their central projections in goldfish appear to serve a function analogous to that of the main olfactory system, while the medial olfactory tracts and their central projections comprise a pathway remarkably similar to the vomeronasal-accessory olfactory system. These findings suggest that teleosts may possess functional correlates of tetrapod vomeronasal systems, but in a form that has yet to be recognized. If so, medial olfactory tract projections in goldfish may be evolutionarily conserved and expressed in tetrapods as the vomeronasal system, or the medial olfactory tract projections may be new pathways that have evolved to serve the same function.

ISSN:0006-8977    

DOI:10.1159/000114166

出版商:S. Karger AG    

年代:1993

数据来源: Karger

摘要:

Most amphibians, reptiles and mammals possess a well defined dual olfactory system comprised of separate neural pathways that regulate different olfactory functions. One pathway originates in the nasal cavity and gives rise to what is commonly referred to as the main olfactory system. The other pathway originates in the vomeronasal organ (VNO) and gives rise to the accessory olfactory system. Functionally, the main olfactory system is thought to subserve olfactory-mediated tasks such as feeding and grooming, while the accessory olfactory system is believed to be primarily involved in mediating behavioral and physiological responses to sex pheromones. Traditionally, it has been difficult to address whether teleosts possess any components of the vomeronasal system, since they generally do not meet the criteria used to identify vomeronasal systems in other vertebrates. Previous conclusions that the nasal epithelia of fish is olfactory and not vomeronasal in nature are based on observations that teleosts lack a separate VNO-like chemosensory structure and an anatomically distinct accessory olfactory bulb. However, because sex pheromones have been identified in the goldfish, it is now possible to compare the neural substrates that regulate pheromone-induced responses in teleosts to those that mediate similar responses in other vertebrates. The olfactory system in goldfish is particularly well suited for such comparisons, because it comprises anatomical and functional subdivisions that resemble those associated with the main and accessory olfactory systems in tetrapods. The olfactory pathways that mediate endocrine and behavioral responses to sex pheromones in goldfish are described and then compared to the main and accessory olfactory systems of tetrapods. In making these comparisons, a number of similarities become apparent. First, the olfactory pathways that regulate responses to sex pheromones in goldfish are different from those that serve a more general olfactory function. Second, these functional differences appear to be subserved by separate and anatomically distinct olfactory tract projections to the brain. Third, the lateral olfactory tracts and their central projections in goldfish appear to serve a function analogous to that of the main olfactory system, while the medial olfactory tracts and their central projections comprise a pathway remarkably similar to the vomeronasal-accessory olfactory system. These findings suggest that teleosts may possess functional correlates of tetrapod vomeronasal systems, but in a form that has yet to be recognized. If so, medial olfactory tract projections in goldfish may be evolutionarily conserved and expressed in tetrapods as the vomeronasal system, or the medial olfactory tract projections may be new pathways that have evolved to serve the same function.

ISSN:0006-8977    

DOI:10.1159/000316220

出版商:S. Karger AG    

年代:1993

数据来源: Karger